Time filter

Source Type

Blacksburg, VA, United States

Virginia Polytechnic Institute and State University, popularly known as Virginia Tech, is a public land-grant university with a main campus in Blacksburg, Virginia, educational facilities in six regions statewide, and a study-abroad site in Switzerland. The commonwealth's third-largest university and a leading research institution, Virginia Tech offers 225 undergraduate and graduate degree programs to some 31,000 students and manages a research portfolio of $454 million. The university fulfills its land-grant mission of transforming knowledge to practice through technological leadership and by fueling economic growth and job creation locally, regionally, and across Virginia.The Virginia Tech Board of Visitors serves as the university's governing body. The board comprises 13 members who are appointed by the governor of Virginia. Serving as ex-officio, non-voting representatives are the president of the state Board of Agriculture and Consumer Services; the presidents of the university's faculty senate and staff senate; and an undergraduate student and a graduate student selected through a competitive review process. Wikipedia.

Hoffman B.M.,Northwestern University | Lukoyanov D.,Northwestern University | Yang Z.-Y.,Utah State University | Dean D.R.,Virginia Polytechnic Institute and State University | Seefeldt L.C.,Utah State University
Chemical Reviews | Year: 2014

Nitrogen fixation has a profound agronomic, economic, and ecological impact owing to the fact that the availability of fixed nitrogen represents the factor that most frequently limits agricultural production throughout the world. The trapping and characterization of five nitrogenase catalytic intermediates, which correspond to three of the five stages involved in binding and reduction of nitrogen most especially the Janus intermediate, E4, and including the nitrogenous intermediate states have identified the 'prompt-alternating (P-A)'. Until now, the data indicating that some H2 must be evolved during N2 reduction has been viewed as being much more compelling than the data indicating an obligatory evolution of one H2 for every N 2 reduced. The test reaction highlighted the role of N2 as cocatalyst in reductions catalyzed by nitrogenase that would not occur in the absence of N2.

Magallon S.,National Autonomous University of Mexico | Hilu K.W.,Virginia Polytechnic Institute and State University | Quandt D.,University of Bonn
American Journal of Botany | Year: 2013

Premise of the study: Land plants play an essential role in the evolution of terrestrial life. Their time of origin and diversification is fundamental to understanding the evolution of life on land. We investigated the timing and the rate of molecular evolution of land plants, evaluating the effects of different types of molecular data, including temporal information from fossils, and using different molecular clock methods. Methods: Ages and absolute rates were estimated independently with two substitutionally different data sets: a highly conserved 4-gene data set and matK, a fast-evolving gene. The vascular plant backbone and the crown nodes of all major lineages were calibrated with fossil-derived ages. Dates and absolute rates were estimated while including or excluding the calibrations and using two relaxed clocks that differ in their implementation of temporal autocorrelation. Key results: Land plants diverged from streptophyte alga 912 (870-962) million years ago (Mya) but diversified into living lineages 475 (471-480) Mya. Ages estimated for all major land-plant lineages agree with their fossil record, except for angiosperms. Different genes estimated very similar ages and correlated absolute rates across the tree. Excluding calibrations resulted in the greatest age differences. Different relaxed clocks provided similar ages, but different and uncorrelated absolute rates. Conclusions: Whole-genome rate accelerations or decelerations may underlie the similar ages and correlated absolute rates estimated with different genes. We suggest that pronounced substitution rate changes around the angiosperm crown node may represent a challenge for relaxed clocks to model adequately. © 2013 Botanical Society of America.

Kraak V.I.,Virginia Polytechnic Institute and State University | Story M.,Duke University
Obesity Reviews | Year: 2015

Reducing the extent and persuasive power of marketing unhealthy foods to children worldwide are important obesity prevention goals. Research is limited to understand how brand mascots and cartoon media characters influence children's diet. We conducted a systematic review of five electronic databases (2000-2014) to identify experimental studies that measured how food companies' mascots and entertainment companies' media characters influence up to 12 diet-related cognitive, behavioural and health outcomes for children under 12 years. Eleven studies met the inclusion criteria. Studies used 21 unique popular media characters, but no brand mascots. Results suggest that cartoon media character branding can positively increase children's fruit or vegetable intake compared with no character branding. However, familiar media character branding is a more powerful influence on children's food preferences, choices and intake, especially for energy-dense and nutrient-poor foods (e.g. cookies, candy or chocolate) compared with fruits or vegetables. Future research should use a theoretically grounded conceptual model and larger and more diverse samples across settings to produce stronger findings for mediating and moderating factors. Future research can be used to inform the deliberations of policymakers, practitioners and advocates regarding how media character marketing should be used to support healthy food environments for children. © 2014 The Authors.

Fritz M.S.,Virginia Polytechnic Institute and State University
Prevention Science | Year: 2014

Mediation analysis is often used to investigate mechanisms of change in prevention research. Results finding mediation are strengthened when longitudinal data are used because of the need for temporal precedence. Current longitudinal mediation models have focused mainly on linear change, but many variables in prevention change nonlinearly across time. The most common solution to nonlinearity is to add a quadratic term to the linear model, but this can lead to the use of the quadratic function to explain all nonlinearity, regardless of theory and the characteristics of the variables in the model. The current study describes the problems that arise when quadratic functions are used to describe all nonlinearity and how the use of nonlinear functions, such as exponential decay, address many of these problems. In addition, nonlinear models provide several advantages over polynomial models including usefulness of parameters, parsimony, and generalizability. The effects of using nonlinear functions for mediation analysis are then discussed and a nonlinear growth curve model for mediation is presented. An empirical example using data from a randomized intervention study is then provided to illustrate the estimation and interpretation of the model. Implications, limitations, and future directions are also discussed. © 2013, Society for Prevention Research.

Bisset K.R.,Virginia Polytechnic Institute and State University
BMC genomics | Year: 2012

Many important biological problems can be modeled as contagion diffusion processes over interaction networks. This article shows how the EpiSimdemics interaction-based simulation system can be applied to the general contagion diffusion problem. Two specific problems, computational epidemiology and human immune system modeling, are given as examples. We then show how the graphics processing unit (GPU) within each compute node of a cluster can effectively be used to speed-up the execution of these types of problems. We show that a single GPU can accelerate the EpiSimdemics computation kernel by a factor of 6 and the entire application by a factor of 3.3, compared to the execution time on a single core. When 8 CPU cores and 2 GPU devices are utilized, the speed-up of the computational kernel increases to 9.5. When combined with effective techniques for inter-node communication, excellent scalability can be achieved without significant loss of accuracy in the results. We show that interaction-based simulation systems can be used to model disparate and highly relevant problems in biology. We also show that offloading some of the work to GPUs in distributed interaction-based simulations can be an effective way to achieve increased intra-node efficiency.

Barney J.N.,Virginia Polytechnic Institute and State University
Invasive Plant Science and Management | Year: 2014

The United States is charging toward the largest expansion of agriculture in 10,000 years with vast acreages of primarily exotic perennial grasses planted for bioenergy that possess many traits that may confer invasiveness. Cautious integration of these crops into the bioeconomy must be accompanied by development of best management practices and regulation to mitigate the risk of invasion posed by this emerging industry. Here I review the current status of United States policy drivers for bioenergy, the status of federal and state regulation related to invasion mitigation, and survey the scant quantitative literature attempting to quantify the invasive potential of bioenergy crops. A wealth of weed risk assessments are available on exotic bioenergy crops, and generally show a high risk of invasion, but should only be a first-step in quantifying the risk of invasion. The most information exists for sterile giant miscanthus, with preliminary empirical studies and demographic models suggesting a relatively low risk of invasion. However, most important bioenergy crops are poorly studied in the context of invasion risk, which is not simply confined to the production field; but also occurs in crop selection, harvest and transport, and feedstock storage. Thus, I propose a nested-feedback risk assessment (NFRA) that considers the entire bioenergy supply chain and includes the broad components of weed risk assessment, species distribution models, and quantitative empirical studies. New information from the NFRA is continuously fed back into other components to further refine the risk assessment; for example, empirical dispersal kernels are utilized in landscape-level species distribution models, which inform habitat invasibility studies. Importantly, the NFRA results in a relative invasion risk to known species (e.g., is giant reed a higher or lower invasion risk than johnsongrass). This information is used to design robust mitigation plans that include record keeping, regular scouting and reporting, prudent harvest and transport practices that consider species biology, and eradication protocols as an ultimate precaution. Finally, a socio-political balance must be struck (i.e., a cost-benefit analysis) among our energy choices that consider the broader implications, which includes the risk of future invasions. Nomenclature: Giant miscanthus, Miscanthus × giganteus J. M. Greef and Deuter ex Hodk. and Renvoize, giant reed, Arundo donax L., Johnsongrass, Sorghum halepense (L.) Pers.

Xu X.,Harvard University | Culligan P.J.,Columbia University | Taylor J.E.,Virginia Polytechnic Institute and State University
Applied Energy | Year: 2014

Existing strategies for residential energy savings through physical renovation or motivating occupant energy conservation behavior can be costly and/or have transitory effects. Focusing on multi-family dwellings, an important subset of the urban residential sector, we propose an Energy Saving Alignment Strategy (ESAS) that has advantageous cost-effectiveness and a long-lasting influence. By aligning the distribution of residents' thermostat preferences with the indoor temperature, ESAS aims to maximize thermal comfort and, accordingly, energy savings in multi-family buildings where indoor temperatures vary between apartments as a function of apartment orientation and floor level. Using a case study of a 1084-apartment public housing complex in New York, we classify both occupants' thermostat preferences and apartments' operative temperatures into five groups, and optimize energy efficiency by assigning each group of occupants to the group of apartments that best aligns with their thermostat preference. We test ESAS in eight cities representing all four U.S. census regions and six climate zones. Simulation results reveal 2.1-42.0% in energy savings compared to random apartment assignments depending on geographic location, with the highest energy reductions occurring in cities with mild climates, where the range of occupant thermostat preferences coincides with the natural indoor temperature range. We conclude by providing suggested guidelines on how ESAS might work in practice, and recommendations for extending ESAS research. © 2014 Elsevier Ltd.

Johri A.,Virginia Polytechnic Institute and State University
Proceedings of the ACM Conference on Computer Supported Cooperative Work, CSCW | Year: 2011

Email has been the primary communication medium in organizations for decades and despite studies that demonstrate its obvious disadvantages, the prevailing thinking is that email is irreplaceable. In this paper I challenge that view through a field study of a distributed firm that is highly successful in developing and delivering products without regular use of email in the workplace. Group blogging and IRC were the primary tools used and they allowed improved coordination and knowledge sharing compared to email. This paper contributes to scant literature in CSCW on firm-level technology use. Copyright 2011 ACM.

Bian K.,Peking University | Park J.-M.J.,Virginia Polytechnic Institute and State University
IEEE Transactions on Mobile Computing | Year: 2013

In decentralized cognitive radio (CR) networks, establishing a link between a pair of communicating nodes requires that the radios 'rendezvous in a common channel such a channel is called a rendezvous channel-to exchange control information. When unlicensed (secondary) users opportunistically share spectrum with licensed (primary or incumbent) users, a given rendezvous channel may become unavailable due to the appearance of licensed user signals. Ideally, every node pair should be able to rendezvous in every available channel (i.e., maximize the rendezvous diversity) so that the possibility of rendezvous failures is minimized. Channel hopping (CH) protocols have been proposed previously for establishing pairwise rendezvous. Some of them enable pairwise rendezvous over all channels but require global clock synchronization, which may be very difficult to achieve in decentralized networks. Maximizing the pairwise rendezvous diversity in decentralized CR networks is a very challenging problem. In this paper, we present a systematic approach for designing CH protocols that maximize the rendezvous diversity of any node pair in decentralized CR networks. The resulting protocols are resistant to rendezvous failures caused by the appearance of primary user (PU) signals and do not require clock synchronization. The proposed approach, called asynchronous channel hopping (ACH), has two noteworthy features: 1) any pair of CH nodes are able to rendezvous on every channel so that the rendezvous process is robust to disruptions caused by the appearance of PU signals; and 2) an upper bounded time-to-rendezvous (TTR) is guaranteed between the two nodes even if their clocks are asynchronous. We propose two optimal ACH designs that maximize the rendezvous diversity between any pair of nodes and show their rendezvous performance via analytical and simulation results. © 2002-2012 IEEE.

Sultan C.,Virginia Polytechnic Institute and State University
Mechanical Systems and Signal Processing | Year: 2013

Linear system design for accurate decoupling approximation is examined using the peak to peak gain of the error system. The design problem consists in finding values of system parameters to ensure that this gain is small. For this purpose a computationally inexpensive upper bound on the peak to peak gain, namely the star norm, is minimized using a stochastic method. Examples of the methodology's application to tensegrity structures design are presented. Connections between the accuracy of the approximation, the damping matrix, and the natural frequencies of the system are examined, as well as decoupling in the context of open and closed loop control. © 2012 Elsevier Ltd.

Sharma P.,Virginia Polytechnic Institute and State University
Integrative biology : quantitative biosciences from nano to macro | Year: 2013

Investigating the mechanistic influence of the tumor microenvironment on cancer cell migration and membrane blebbing is crucial in the understanding and eventual arrest of cancer metastasis. In this study, we investigate the effect of suspended and aligned nanofibers on the glioma cytoskeleton, cell shape, migration and plasma membrane blebbing dynamics using a non-electrospinning fiber-manufacturing platform. Cells attached in repeatable shapes of spindle on single fibers, rectangular on two parallel fibers and polygonal on intersecting fibers. Structural stiffness (N m(-1)) of aligned and suspended nanofibers (average diameter: 400 nm, length: 4, 6, and 10 mm) was found to significantly alter the migration speed with higher migration on lower stiffness fibers. For cells attached to fibers and exhibiting blebbing, an increase in cellular spread area resulted in both reduced bleb count and bleb size with an overall increase in cell migration speed. Blebs no longer appeared past a critical cellular spread area of approximately 1400 μm(2). Our results highlighting the influence of the mechanistic environment on the invasion dynamics of glioma cells add to the understanding of how biophysical components influence glioma cell migration and blebbing dynamics.

Starr M.,American University of Washington | Dominiak L.,Federal Reserve Board | Aizcorbe A.,Virginia Polytechnic Institute and State University
Health Affairs | Year: 2014

Researchers have disagreed about factors driving up health care spending since the 1980s. One camp, led by Kenneth Thorpe, identifies rising numbers of people being treated for chronic diseases as a major factor. Charles Roehrig and David Rousseau reach the opposite conclusion: that three-quarters of growth in average spending reflects the rising costs of treating given diseases. We reexamined sources of spending growth using data from four nationally representative surveys. We found that rising costs of treatment accounted for 70 percent of growth in real average health care spending from 1980 to 2006. The contribution of shares of the population treated for given diseases increased in 1997-2006, but even then it accounted for only one-third of spending growth. We highlight the fact that Thorpe's inclusion of population growth as part of disease prevalence explains the appreciable difference in results. An important policy implication is that programs to better manage chronic diseases may only modestly reduce average spending growth. © 2014 Project HOPE.

Clements J.R.,Virginia Polytechnic Institute and State University
Journal of Foot and Ankle Surgery | Year: 2012

Surgical treatment for traumatic dislocation of the talus is a challenging procedure that is often associated with complications. Application of allograft cellular bone matrix with viable mesenchymal stem and osteoprogenitor cells can eliminate the need for autograft and may increase fusion rates in procedures such as tibiocalcaneal arthrodesis. This report describes the treatment of an adult man who presented with a right ankle fracture and subtalar joint dislocation after a motor vehicle accident. After initial treatment with open reduction and internal fixation, the patient developed avascular necrosis of the talus and septic arthritis of the tibiotalar and subtalar joints. After treatment of the infection, the patient was ultimately treated with multistage talectomy and tibiocalcaneal arthrodesis augmented with a cellular bone allograft. Approximately 3 months after the final operation, plain radiographs and computed tomography confirmed solid fusion at the arthrodesis interface. The patient's recovery was uneventful thereafter, and amputation was avoided. This case, which presented additional challenges because of the large defect created by the infection, suggests that use of an allograft cellular bone matrix has the potential to replicate the bone-healing properties of autograft without the constraints and morbidity associated with autograft harvesting. © 2012 American College of Foot and Ankle Surgeons.

Meng X.-J.,Virginia Polytechnic Institute and State University
Virus Research | Year: 2011

Hepatitis E virus (HEV) is an important but extremely understudied pathogen. The mechanisms of HEV replication and pathogenesis are poorly understood, and a vaccine against HEV is not yet available. HEV is classified in the family Hepeviridae consisting of at least four recognized major genotypes. Genotypes 1 and 2 HEV are restricted to humans and associated with epidemics in developing countries, whereas genotypes 3 and 4 HEV are zoonotic and responsible for sporadic cases worldwide. The identification and characterization of a number of animal strains of HEV from pigs, chickens, rabbits, rats, mongoose, deer, and possibly cattle and sheep have significantly broadened the host range and diversity of HEV. The demonstrated ability of cross-species infection by some animal strains of HEV raises public health concerns for zoonotic HEV infection. Pigs are a recognized reservoir for HEV, and pig handlers are at increased risk of zoonotic HEV infection. Sporadic cases of hepatitis E have been definitively linked to the consumption of raw or undercooked animal meats such as pig livers, sausages, and deer meats. In addition, since large amounts of viruses excreted in feces, animal manure land application and runoffs can contaminate irrigation and drinking water with concomitant contamination of produce or shellfish. HEV RNA of swine origin has been detected in swine manure, sewage water and oysters, and consumption of contaminated shellfish has also been implicated in sporadic cases of hepatitis E. Therefore, the animal strains of HEV pose not only a zoonotic risk but also food and environmental safety concerns. © 2011 Elsevier B.V.

Kaestle C.E.,Virginia Polytechnic Institute and State University
Prevention Science | Year: 2012

Engaging in trading sex is associated with many co-occurring problems, including elevated risk for sexually transmitted infections. Various dimensions of social support from parents, schools, and mentors may be protective against sex trading and may ameliorate the impact of risk factors. This study analyzes data from respondents to Waves I and III of the National Longitudinal Study of Adolescent Health (Add Health) who had not participated in sex trading for money or drugs in Wave I so that risk and protective factors for first initiations of selling or buying sex could be examined longitudinally. About 2% of the study sample began selling sex and about 2% began buying sex between Wave I and Wave III. The respondent's sex, race/ethnicity, history of sexual abuse, shoplifting, marijuana use, and experiences of homelessness or running away were significant predictors of trading sex (p < 0.05). Being happy at school was associated with lower selling of sex, and feeling part of school was associated with lower buying of sex even after controlling for demographics and risk factors (p < 0.05). Results indicate a need for early intervention for youth who experience sexual abuse or running away. Elements of school connectedness have a protective effect on selling and buying sex. Promoting school connectedness may advance public health goals. © 2012 Society for Prevention Research.

Goodman M.L.,Virginia Polytechnic Institute and State University
Astrophysical Journal | Year: 2011

A magnetohydrodynamic model that includes a complete electrical conductivity tensor is used to estimate conditions for photospherically driven, linear, non-plane Alfvénic oscillations extending from the photosphere to the lower corona to drive a chromospheric heating rate due to Pedersen current dissipation that is comparable to the observed net chromospheric radiative loss of 107ergcm-2 s-1. The heating rates due to electron current dissipation in the photosphere and corona are also computed. The wave amplitudes are computed self-consistently as functions of an inhomogeneous background (BG) atmosphere. The effects of the conductivity tensor are resolved numerically using a resolution of 3.33 m. The oscillations drive a chromospheric heating flux F Ch 107-10 8ergcm-2 s-1 at frequencies ν 10 2-103mHz for BG magnetic field strengths B ≳ 700G and magnetic field perturbation amplitudes 0.01-0.1 B. The total resistive heating flux increases with ν. Most heating occurs in the photosphere. Thermalization of Poynting flux in the photosphere due to electron current dissipation regulates the Poynting flux into the chromosphere, limiting F Ch. F Ch initially increases with ν, reaches a maximum, and then decreases with increasing ν due to increasing electron current dissipation in the photosphere. The resolution needed to resolve the oscillations increases from 10 m in the photosphere to 10km in the upper chromosphere and is ν-1/2. Estimates suggest that these oscillations are normal modes of photospheric flux tubes with diameters 10-20km, excited by magnetic reconnection in current sheets with thicknesses 0.1km. © 2011. The American Astronomical Society. All rights reserved..

Asryan L.V.,Virginia Polytechnic Institute and State University | Suris R.A.,RAS Ioffe Physical - Technical Institute
Applied Physics Letters | Year: 2010

We derive a closed-form expression for the upper limit for the modulation bandwidth of a semiconductor quantum dot (QD) laser. The highest possible bandwidth increases directly with overlap integral of the electron and hole wave functions in a QD, number of QD-layers, and surface density of QDs in a layer, and is inversely proportional to the inhomogeneous line broadening caused by the QD-size dispersion. At 10% QD-size fluctuations and 100% overlap, the upper limit for the modulation bandwidth in a single QD-layer laser can be as high as 60 GHz. © 2010 American Institute of Physics.

Shi C.,Shanghai JiaoTong University | Parker R.G.,Virginia Polytechnic Institute and State University
Journal of Sound and Vibration | Year: 2013

This work studies the symmetry breaking effects on the vibration mode structure of centrifugal pendulum vibration absorber (CPVA) systems when multiple groups of absorbers are used. An absorber group is a set of equally spaced, identical absorbers. Absorbers within a group are cyclically symmetric while the entire system is asymmetric because the groups have no pre-defined relative angular spacing. One rotational and two translational degrees of freedom for the rotor and a single arclength degree of freedom for each absorber are considered in the planar model. The well-defined structure of the vibration modes is obtained by analytical and numerical investigations of the associated eigenvalue problem. This vibration mode structure is similar to that for CPVA systems with equally spaced, identical absorbers. Thus, the disrupted symmetry from multiple absorber groups does not destroy the vibration mode structure resulting from the cyclic symmetry within each group. The critical speeds and flutter instability of the system are investigated. © 2013 Elsevier B.V. All rights reserved.

Rahman S.,Texas A&M University | Grasley Z.,Virginia Polytechnic Institute and State University
Cement and Concrete Research | Year: 2014

A poromechanical composite model is developed to predict time-dependent stress and strain fields in freezing concrete containing aggregates with undesirable combinations of geometry and constitutive properties. Sensitivity of the stress fields to the aggregate and matrix constitutive parameters is assessed to inform improved concrete design. The model trends presented in this paper are in agreement with experimental results from literature. The model indicates that for both air-entrained and non-air-entrained concrete, destructive tensile stress may be triggered at the aggregate-matrix boundary, with the severity enhanced by the Mandel-Cryer effect. It is determined that high-porosity, low-permeability aggregates are most vulnerable to D-cracking. © 2013 Elsevier Ltd.

Falkinham J.O.,Virginia Polytechnic Institute and State University
Clinics in Chest Medicine | Year: 2015

Nontuberculous mycobacteria (NTM) include over 150 species. The source for human infection is the environment. NTM are normal inhabitants of soil and drinking water. NTM grow and persist in many buildings. They are not contaminants of drinking water, but members of the natural drinking water microbial population. Infection occurs because humans share the same habitats. Because the ecology, antibiotic susceptibility, and virulence of individual species differs, identifying NTM isolates to species is important. Treatment requires multiple antibiotics. NTM patients are innately sensitive to NTM infection, resulting in reinfection. Knowledge of the sources of NTM can reduce exposure to environmental NTM. © 2015 Elsevier Inc.

Tsang P.W.M.,City University of Hong Kong | Poon T.-C.,Virginia Polytechnic Institute and State University | Poon T.-C.,CAS Shanghai Institute of Optics and fine Mechanics
Optics Express | Year: 2013

We report a novel and fast method for converting a digital, complex Fresnel hologram into a phase-only hologram. Briefly, the pixels in the complex hologram are scanned sequentially in a row by row manner. The odd and even rows are scanned from opposite directions, constituting to a bidirectional error diffusion process. The magnitude of each visited pixel is forced to be a constant value, while preserving the exact phase value. The resulting error is diffused to the neighboring pixels that have not been visited before. The resulting novel phase-only hologram is called the bidirectional error diffusion (BERD) hologram. The reconstructed image from the BERD hologram exhibits high fidelity as compared with those obtained with the original complex hologram. ©2013 Optical Society of America.

Van Dyke M.,Virginia Polytechnic Institute and State University
Acta Biomaterialia | Year: 2013

Natural extracellular matrix (ECM) proteins possess critical biological characteristics that provide a platform for cellular adhesion and activation of highly regulated signaling pathways. However, ECM-based biomaterials can have several limitations, including poor mechanical properties and risk of immunogenicity. Synthetic biomaterials alleviate the risks associated with natural biomaterials but often lack the robust biological activity necessary to direct cell function beyond initial adhesion. A thorough understanding of receptor-mediated cellular adhesion to the ECM and subsequent signaling activation has facilitated development of techniques that functionalize inert biomaterials to provide a biologically active surface. Here we review a range of approaches used to modify biomaterial surfaces for optimal receptor-mediated cell interactions, as well as provide insights into specific mechanisms of downstream signaling activation. In addition to a brief overview of integrin receptor-mediated cell function, so-called "biomimetic" techniques reviewed here include (i) surface modification of biomaterials with bioadhesive ECM macromolecules or specific binding motifs, (ii) nanoscale patterning of the materials and (iii) the use of "natural-like" biomaterials. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Curthoys I.S.,University of Sydney | Grant J.W.,Virginia Polytechnic Institute and State University
Experimental Brain Research | Year: 2015

The mechanism by which vestibular neural phase locking occurs and how it relates to classical otolith mechanics is unclear. Here, we put forward the hypothesis that sound and vibration both cause fluid pressure waves in the inner ear and that it is these pressure waves which displace the hair bundles on vestibular receptor hair cells and result in activation of type I receptor hair cells and phase locking of the action potentials in the irregular vestibular afferents, which synapse on type I receptors. This idea has been suggested since the early neural recordings and recent results give it greater credibility. © 2014, Springer-Verlag Berlin Heidelberg.

Pasupathy R.,Virginia Polytechnic Institute and State University
Operations Research | Year: 2010

The stochastic root-finding problem is that of finding a zero of a vector-valued function known only through a stochastic simulation. The simulation-optimization problem is that of locating a real-valued function's minimum, again with only a stochastic simulation that generates function estimates. Retrospective approximation (RA) is a sample-path technique for solving such problems, where the solution to the underlying problem is approached via solutions to a sequence of approximate deterministic problems, each of which is generated using a specified sample size, and solved to a specified error tolerance. Our primary focus, in this paper, is providing guidance on choosing the sequence of sample sizes and error tolerances in RA algorithms. We first present an overview of the conditions that guarantee the correct convergence of RA's iterates. Then we characterize a class of error-tolerance and sample-size sequences that are superior to others in a certain precisely defined sense. We also identify and recommend members of this class and provide a numerical example illustrating the key results. © 2010 INFORMS.

Garner H.R.,Virginia Polytechnic Institute and State University
Urologic Oncology: Seminars and Original Investigations | Year: 2011

About 3,000 new citations that are highly similar to citations in previously published manuscripts that appear each year in the biomedical literature (Medline) alone. This underscores the importance for the opportunity for editors and reviewers to have detection system to identify highly similar text in submitted manuscripts so that they can then review them for novelty. New software-based services, both commercial and free, provide this capability. The availability of such tools provides both a way to intercept suspect manuscripts and serve as a deterrent. Unfortunately, the capabilities of these services vary considerably, mainly as a consequence of the availability and completeness of the literature bases to which new queries are compared. Most of the commercial software has been designed for detection of plagiarism in high school and college papers; however, there is at least 1 fee-based service (CrossRef) and 1 free service (etblast.org), which are designed to target the needs of the biomedical publication industry. Information on these various services, examples of the type of operability and output, and things that need to be considered by publishers, editors, and reviewers before selecting and using these services is provided. © 2011 Elsevier Inc.

Burkhart H.E.,Virginia Polytechnic Institute and State University
Forest Ecology and Management | Year: 2013

Quantification of site occupancy or stand density is essential for modeling forest stand mortality, growth and yield. A variety of measures of stand density have been proposed. Diverse tree and stand attributes have been employed, but direct comparisons of the effectiveness of various measures for estimating number of trees for fully stocked stands and for predicting growth for stands at different stages of development are not possible due to the varying forms of the measures.Maximum size-density relationships are a widely-used type of stand density measure. Reineke's stand density index (SDI), which is based on number of stems per unit area and quadratic mean stem diameter, is the most commonly-applied stand density measure of this type. In the study reported here, stand density indices were developed by employing the structure of Reineke's index but using the stand attributes of mean stem volume and mean stand height, as well as mean stem diameter. When estimating number of trees and periodic volume growth per unit area using data from sample plots in planted stands of loblolly pine, the SDI based on mean diameter performed best with mean stem volume being second best and mean stand height third. © 2012 Elsevier B.V.

Johri A.,Virginia Polytechnic Institute and State University
Engineering Studies | Year: 2012

An understanding of newcomer participation is important both from the perspective of engineering organizations and to prepare future engineers but we know little about how newcomers to engineering practices traverse their trajectory of participation. Prior work on newcomers has addressed socialization processes but has overlooked the sociomaterial nature of engineering practices and its consequences for newcomer participation. In this paper, I present an in-depth case study of a newcomer navigating his early days in an industrial research and development laboratory. I identify 'demoing', or the use of prototypes to communicate research outcomes, as a highly valued practice at the studied firm and trace a newcomer's participation from entry until his first demo, which signaled significant progress toward full participation. I argue that as engineers move from being novices toward fuller participation, they need to become sociomaterial experts - both socially adept and proficient at using materiality in conjunction with each other. © 2012 Copyright Taylor and Francis Group, LLC.

Junker R.R.,University of Salzburg | Tholl D.,Virginia Polytechnic Institute and State University
Journal of Chemical Ecology | Year: 2013

Microorganisms colonize the surfaces of plant roots, leaves, and flowers known as the rhizosphere, phyllosphere, and anthosphere. These spheres differ largely in a number of factors that may determine the ability of microbes to establish themselves and to grow in these habitats. In this article, we focus on volatile organic compounds (VOCs) emitted by plants, and we discuss their effects on microbial colonizers, with an emphasis on bacteria. We present examples of how growth-inhibiting properties and mechanisms of VOCs such as terpenoids, benzenoid compounds, aliphatics, and sulfur containing compounds prevent bacterial colonization at different spheres, in antagonism with their role as carbon-sources that support the growth of different bacterial taxa. The notion that VOCs represent important factors that define bacterial niches is further supported by results for representatives of two bacterial genera that occupy strongly diverging niches based on scent emissions of different plant species and organs. Bacteria are known to either positively or negatively affect plant fitness and to interfere with plant-animal interactions. Thus, bacteria and other microbes may select for VOCs, enabling plants to control microbial colonizers on their surfaces, thereby promoting the growth of mutualists and preventing the establishment of detrimental microbes. © 2013 Springer Science+Business Media New York.

Mostaghimi S.,Virginia Polytechnic Institute and State University
Water, Air, and Soil Pollution | Year: 2011

Limited data on microbial partitioning between the freely suspended and particulate attached phases during transport along overland flow pathways have resulted in high uncertainty in bacterial fate and transport models and the application of these models to watershed management plans. The objectives of this study were to examine differences in attachment between E. coli and enterococci in runoff from plots with highly and sparsely vegetated grassland; investigate relations between flow regime, total suspended solids, and E. coli and enterococci attachment; and identify the particle size categories to which the attached cells were associated. Two rainfall simulations were conducted on large field plots 3 m wide by 18.3 m long with highly and both highly and sparsely vegetated covers and treated with standard cowpats. Results from the first experiment representing pasture with highly vegetated cover indicate that the majority of E. coli and enterococci are transported from the fresh manure source in the unattached state with only 4.8% of E. coli and 13% of enterococci associated with particles. The second experiment which compared partitioning in runoff from both highly and sparsely vegetated covers found lower bacterial attachment rates: the average E. coli percent attached was 0.06% from plots with highly vegetated cover and 2.8% from plots with sparsely vegetated cover while the corresponding values for enterococci were 0.98% and 1.23%, respectively. The findings from this study provide the first set of data on bacterial partitioning in overland flow from large field plots, and results may be helpful for parameterizing water quality models and designing conservation practices. © 2010 Springer Science+Business Media B.V.

Jia T.,SiRF | Buehrer R.M.,Virginia Polytechnic Institute and State University
IEEE Transactions on Mobile Computing | Year: 2011

In this work, we propose a set-theoretic approach to collaborative position location for wireless networks. The proposed method borrows the concept from the parallel projection method (PPM), originally developed for signal recovery with inconsistent convex feasibility sets, modifies and extends the technique to an iterative and distributed numerical algorithm to estimate node locations, based on incomplete and noisy internode distance estimates. We demonstrate that in the case of noncollaborative position location, the proposed method is analytically equivalent to the parallel implementation of Kaczmarz Algorithm that is guaranteed to converge to a local minimizer and thus a stationary point. For collaborative position location, the proposed iterative PPM is computationally much more efficient than existing methods such as SDP and MDS-MAP, while achieving comparable or better localization accuracy and robustness to non-line-of-sight (NLOS) bias. Finally, our proposed method can be implemented in a parallel and distributed fashion, and is scalable for large network deployment. © 2011 IEEE.

Sewall K.B.,Virginia Polytechnic Institute and State University
Integrative and Comparative Biology | Year: 2015

Cognition and communication both can be essential for effectively navigating the social environment and thus, social dynamics could select for enhanced abilities for communication and superior cognition. Additionally, social experience can influence both the ability to communicate effectively and performance in cognitive tasks within an individual's lifetime, consistent with phenotypic plasticity in these traits. Historically, research in animal cognition and animal communication has often addressed these traits independently, despite potential commonalities in social function and underlying mechanisms of the brain. Integrating research on animal communication and cognition will provide a more comprehensive understanding of how the social environment may shape behavior and specializations of the brain for sociality through both evolutionary and developmental processes. This selective review of research on the impacts of social dynamics on cognition and communication in animals aims to highlight areas for future research at both the ultimate and proximate levels. In particular, additional work on the effects of the social environment on cognitive performance over an individual's lifetime, and comparative studies of specialized abilities for communication, should be pursued. © 2015 The Author 2015. Published by Oxford University Press on behalf of the Society for Integrative and Comparative Biology. All rights reserved. For permissions please email: journals.permissions@oup.com.

Kingston D.G.I.,Virginia Polytechnic Institute and State University | Snyder J.P.,Emory University
Accounts of Chemical Research | Year: 2014

ConspectusPaclitaxel (PTX), introduced into the clinic in 1991, has revealed itself as an effective antimicrotubule drug for treatment of a range of otherwise intractable cancers. Along with docetaxel (DTX) and in combination with other agents such as cisplatin, it has proven to be a first-line therapy. Unfortunately, PTX and DTX carry severe liabilities such as debilitating side effects, rapid onset of resistance, and rather complex molecular structures offering substantial challenges to ease of synthetic manipulation. Consequently, the past 15 years has witnessed many efforts to synthesize and test highly modified analogs based on intuitive structural similarity relationships with the PTX molecular skeleton, as well as efforts to mimic the conformational profile of the ligand observed in the macromolecular tubulin-PTX complex.Highly successful improvements in potency, up to 50-fold increases in IC50, have been achieved by constructing bridges between distal centers in PTX that imitate the conformer of the electron crystallographic binding pose. Much less successful have been numerous attempts to truncate PTX by replacing the baccatin core with simpler moieties to achieve PTX-like potencies and applying a wide range of flexible synthesis-based chemistries. Reported efforts, characterized by a fascinating array of baccatin substitutes, have failed to surpass the bioactivities of PTX in both microtubule disassembly assays and cytotoxicity measurements against a range of cell types. Most of the structures retain the main elements of the PTX C13 side chain, while seeking a smaller rigid bicycle as a baccatin replacement adorned with substituents to mimic the C2 benzoyl moiety and the oxetane ring.We surmise that past studies have been handicapped by solubility and membrane permeability issues, but primarily by the existence of an expansive taxane binding pocket and the discrepancy in molecular size between PTX and the pruned analogs. A number of these molecules offer molecular volumes 50-60% that of PTX, fewer contacts with the tubulin protein, severe mismatches with the PTX pharmacophore, lessened capacity to dispel binding site waters contributing to δGbind, and unanticipated binding poses. The latter is a critical drawback if molecular designs of simpler PTX structures are based on a perceived or known PTX binding conformation. We conclude that design and synthesis of a highly cytotoxic tubulin-Assembly agent based on the paclitaxel pharmacophore remains an unsolved challenge, but one that can be overcome by focus on the architecture of the taxane binding site independent of the effective, but not unique, hand-in-glove match represented by the PTX-tubulin complex. © 2014 American Chemical Society.

Spinello D.,University of Ottawa | Stilwell D.J.,Virginia Polytechnic Institute and State University
IEEE Transactions on Automatic Control | Year: 2010

We consider the problem of estimating the state of a system when measurement noise is a function of the system's state. We propose generalizations of the extended Kalman filter and the iterated extended Kalman filter that can be utilized when the state estimate distribution is approximately Gaussian. The state estimate is computed by an iterative root-searching method that maximizes a maximum likelihood function. The new filter allows for the consistent treatment of a class of control problem involving nonlinear estimation from measurements with state-dependent noise. The effectiveness of the estimation algorithm is illustrated for a control problem with a mobile bearing-only sensor. © 2006 IEEE.

Ellingson S.W.,Virginia Polytechnic Institute and State University
IEEE Vehicular Technology Conference | Year: 2015

Frequency-agile cognitive radio is a potential solution to the problem of inefficient use of radio spectrum in the 30-300 MHz (VHF) range. This is especially attractive if networks based on this technology can operate in spectrum left unused by existing users, as opposed to being allocated new spectrum through refarming. This paper presents a preliminary survey of this band in a large U.S. city, with the goal of quantifying spectral occupancy and thereby gaining some insight into the feasibility of this approach. A comparable measurement of the 25-90 MHz band in a rural environment is also presented, for comparison. In the urban measurement, it is found that sufficient spectrum is probably available: for example, it is estimated that approximately 80% of the 30-60 MHz band is essentially free of signals to within about 7 dB of the environmental noise limit at 30 kHz spectral resolution. However, these measurements are limited in duration, spatial sampling, temporal density, and spectral resolution. Requirements for a more comprehensive measurement campaign are proposed. © 2005 IEEE.

The preservation of a homomorphic sex-determining chromosome in some organisms without transformation into a heteromorphic sex chromosome is a long-standing enigma in evolutionary biology. A dominant sex-determining locus (or M-locus) in an undifferentiated homomorphic chromosome confers the male phenotype in the yellow fever mosquito Aedes aegypti. Genetic evidence suggests that the M-locus is in a nonrecombining region. However, the molecular nature of the M-locus has not been characterized. Using a recently developed approach based on Illumina sequencing of male and female genomic DNA, we identified a novel gene, myo-sex, that is present almost exclusively in the male genome but can sporadically be found in the female genome due to recombination. For simplicity, we define sequences that are primarily found in the male genome as male-biased. Fluorescence in situ hybridization (FISH) on A. aegypti chromosomes demonstrated that the myo-sex probe localized to region 1q21, the established location of the M-locus. Myo-sex is a duplicated myosin heavy chain gene that is highly expressed in the pupa and adult male. Myo-sex shares 83% nucleotide identity and 97% amino acid identity with its closest autosomal paralog, consistent with ancient duplication followed by strong purifying selection. Compared with males, myo-sex is expressed at very low levels in the females that acquired it, indicating that myo-sex may be sexually antagonistic. This study establishes a framework to discover male-biased sequences within a homomorphic sex-determining chromosome and offers new insights into the evolutionary forces that have impeded the expansion of the nonrecombining M-locus in A. aegypti.

Huber P.,Virginia Polytechnic Institute and State University
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2010

We discuss the possibility to use a high energy neutrino beam from a muon storage ring to provide one way communication with a submerged submarine. Neutrino interactions produce muons which can be detected either, directly when they pass through the submarine or by their emission of Cerenkov light in sea water, which, in turn, can be exploited with sensitive photo detectors. Due to the very high neutrino flux from a muon storage ring, it is sufficient to mount either detection system directly onto the hull of the submersible. The achievable data transfer rates compare favorable with existing technologies and do allow for a communication at the usual speed and depth of submarines. © 2010 Elsevier B.V.

Jung S.,Virginia Polytechnic Institute and State University
Physics of Fluids | Year: 2010

Caenorhabditis elegans (C. elegans) is a nematode that often swims in saturated soil in nature. We investigated the locomotive behavior of C. elegans swimming in a fluid with particles of various sizes and found that the nematode swims a greater distance per undulation than it does in a fluid without particles. The Strouhal number (a ratio of lateral to forward velocity) of C. elegans significantly decreases in a saturated particulate medium (0.50±0.13) in comparison to a fluid without particles (1.6±0.27). This result was unexpected due to the generally low performance of a body moving in a high drag medium. In our model, a saturated granular system is approximated as a porous medium where only the hydrodynamic forces on the body are considered. Combining these assumptions with resistive force theory, we find that a porous medium provides more asymmetric drag on a slender body, and consequently that C. elegans locomotes with a greater distance per undulation. © 2010 American Institute of Physics.

Kohl P.,Imperial College London | Gourdie R.G.,Virginia Polytechnic Institute and State University
Journal of Molecular and Cellular Cardiology | Year: 2014

Heterocellular electrotonic coupling between cardiac myocytes and non-excitable connective tissue cells has been a long-established and well-researched fact in vitro. Whether or not such coupling exists in vivo has been a matter of considerable debate. This paper reviews the development of experimental insight and conceptual views on this topic, describes evidence in favour of and against the presence of such coupling in native myocardium, and identifies directions for further study needed to resolve the riddle, perhaps less so in terms of principal presence which has been demonstrated, but undoubtedly in terms of extent, regulation, patho-physiological context, and actual relevance of cardiac myocyte-non-myocyte coupling in vivo. This article is part of a Special Issue entitled "Myocyte-Fibroblast Signalling in Myocardium.". © 2013 The Authors.

Goodman M.L.,Virginia Polytechnic Institute and State University
Astrophysical Journal | Year: 2014

A magnetohydrodynamic model is used to determine conditions under which the Lorentz force accelerates plasma to type 2 spicule speeds in the chromosphere. The model generalizes a previous model to include a more realistic pre-spicule state, and the vertical viscous force. Two cases of acceleration under upper chromospheric conditions are considered. The magnetic field strength for these cases is ≤12.5 and 25 G. Plasma is accelerated to terminal vertical speeds of 66 and 78 km s-1 in 100 s, compared with 124 and 397 km s -1 for the case of zero viscosity. The flows are localized within horizontal diameters ∼80 and 50 km. The total thermal energy generated by viscous dissipation is 10 times larger than that due to Joule dissipation, but the magnitude of the total cooling due to rarefaction is ≳ this energy. Compressive heating dominates during the early phase of acceleration. The maximum energy injected into the corona by type 2 spicules, defined as the energy flux in the upper chromosphere, may largely balance total coronal energy losses in quiet regions, possibly also in coronal holes, but not in active regions. It is proposed that magnetic flux emergence in intergranular regions drives type 2 spicules. © 2014. The American Astronomical Society. All rights reserved.

Akers R.M.,Virginia Polytechnic Institute and State University | Nickerson S.C.,University of Georgia
Journal of Mammary Gland Biology and Neoplasia | Year: 2011

It is a given in biology that structure and function go hand-in-hand. At the level of the mammary alveoli, copious milk production depends on the proliferation of mammary epithelial cells and the biochemical and structural differentiation of these cells after parturition. For example, data from quantitative structural studies demonstrate that differences in milk production between beef and dairy cows correspond with a relative failure of alveolar cell differentiation in cattle not specifically selected for milk yield. It is likely, but not proven, that production differences within or between dairy breeds are also determined by differences in the capacity of alveolar cells to differentiate or to maintain an adequate state of differentiation. These observations strongly support the belief that insults from mastitis that lead to losses in mammary function are directly related to disruption of alveolar cell integrity, sloughing of cells, induced apoptosis, and increased appearance of poorly-differentiated cells. Ironically, reduced milk production in cases of subclinical mastitis, is also associated with increases in milk somatic cell count. Thus the elevated neutrophil migration evoked to fight inflammation can inadvertently rendered alveolar epithelial cells non-secretory. A challenge to future researchers will be to devise mastitis treatments and therapies that prevent and/or repair damage to alveolar structure and maximize subsequent secretory cell differentiation. © Springer Science+Business Media, LLC 2011.

Choi V.,Virginia Polytechnic Institute and State University
Quantum Information and Computation | Year: 2011

One of the most important questions in studying quantum computation is: whether a quantum computer can solve NP-complete problems more eficiently than a classical computer? In 2000, Farhi, et al. (Science, 292(5516):472-476, 2001) proposed the adiabatic quantum optimization (AQO), a paradigm that directly attacks NP-hard optimization problems. How powerful is AQO? Early on, van Dam and Vazirani claimed that AQO failed (i.e. would take exponential time) for a family of 3SAT instances they constructed. More recently, Altshuler, et al. (Proc Natl Acad Sci USA, 107(28): 12446-12450, 2010) claimed that AQO failed also for random instances of the NP-complete Exact Cover problem. In this paper, we make clear that all these negative results are only for a specific AQO algorithm. We do so by demonstrating difierent AQO algorithms for the same problem for which their arguments no longer hold. Whether AQO fails or succeeds for solving the NP-complete problems (either the worst case or the average case) requires further investigation. Our AQO algorithms for Exact Cover and 3SAT are based on the polynomial reductions to the NP-complete Maximum-weight Independent Set (MIS) problem. © Rinton Press.

Lu K.,Virginia Polytechnic Institute and State University
Electrochimica Acta | Year: 2012

This study addresses focused ion beam (FIB) patterning guidance effect on the nanopore development during the subsequent anodization on uneven surfaces. Different shape, uneven features are first created on aluminum surfaces. After that, hexagonally arranged nanoconcaves with different inter-concave distances are patterned across the surfaces. The pore development in different anodization electrolytes as well as with different interpore distances and feature surface curvatures are studied. The results show that FIB guided anodization can produce ordered nanopore arrays on various uneven surfaces. In the nanopore depth direction, pores grow perpendicularly to the tangential direction of the surface, which leads to pore splitting or termination based on the surface curvature. © 2011 Elsevier Ltd. All rights reserved.

Becker M.H.,Virginia Polytechnic Institute and State University | Harris R.N.,James Madison University
PLoS ONE | Year: 2010

Chytridiomycosis, caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), is an infectious disease that causes population declines of many amphibians. Cutaneous bacteria isolated from redback salamanders, Plethodon cinereus, and mountain yellow-legged frogs, Rana muscosa, inhibit the growth of Bd in vitro. In this study, the bacterial community present on the skin of P. cinereus individuals was investigated to determine if it provides protection to salamanders from the lethal and sub-lethal effects of chytridiomycosis. When the cutaneous bacterial community was reduced prior to Bd exposure, salamanders experienced a significantly greater decrease in body mass, which is a symptom of the disease, when compared to infected individuals with a normal bacterial community. In addition, a greater proportion of infected individuals with a reduced bacterial community experienced limb-lifting, a behavior seen only in infected individuals. Overall, these results demonstrate that the cutaneous bacterial community of P. cinereus provides protection to the salamander from Bd and that alteration of this community can change disease resistance. Therefore, symbiotic microbes associated with this species appear to be an important component of its innate skin defenses. © 2010 Becker, Harris.

Li S.-R.,Yangzhou University | Batra R.C.,Virginia Polytechnic Institute and State University
Composite Structures | Year: 2013

Analytical relations between the critical buckling load of a functionally graded material (FGM) Timoshenko beam and that of the corresponding homogeneous Euler-Bernoulli beam subjected to axial compressive load have been derived for clamped-clamped (C-C), simply supported-simply supported (S-S) and clamped-free (C-F) edges. However, no such relation is found for clamped-simply supported (C-S) beams. For C-S beams, the transcendental equation has been derived to find the critical buckling load for the FGM Timoshenko beam which is similar to that for a homogeneous Euler-Bernoulli beam. For the FGM beams Young's modulus, E, and Poisson's ratio, ν, are assumed to vary through the thickness. The significance of this work is that for the C-C, S-S and C-F FGM Timoshenko beams, the critical buckling load can be easily found from that of the corresponding homogeneous Euler-Bernoulli beam and two constants whose values depend upon the through-the-thickness variations of E and ν. For the C-S FGM Timoshenko beam the transcendental equation for the determination of the critical buckling load is similar to that for the corresponding homogeneous Euler-Bernoulli beam. © 2012 Elsevier Ltd.

Galloway D.L.,U.S. Geological Survey | Burbey T.J.,Virginia Polytechnic Institute and State University
Hydrogeology Journal | Year: 2011

The extraction of groundwater can generate land subsidence by causing the compaction of susceptible aquifer systems, typically unconsolidated alluvial or basin-fill aquifer systems comprising aquifers and aquitards. Various ground-based and remotely sensed methods are used to measure and map subsidence. Many areas of subsidence caused by groundwater pumping have been identified and monitored, and corrective measures to slow or halt subsidence have been devised. Two principal means are used to mitigate subsidence caused by groundwater withdrawal-reduction of groundwater withdrawal, and artificial recharge. Analysis and simulation of aquifer-system compaction follow from the basic relations between head, stress, compressibility, and groundwater flow and are addressed primarily using two approaches-one based on conventional groundwater flow theory and one based on linear poroelasticity theory. Research and development to improve the assessment and analysis of aquifer-system compaction, the accompanying subsidence and potential ground ruptures are needed in the topic areas of the hydromechanical behavior of aquitards, the role of horizontal deformation, the application of differential synthetic aperture radar interferometry, and the regional-scale simulation of coupled groundwater flow and aquifer-system deformation to support resource management and hazard mitigation measures. © 2011 Springer-Verlag (outside the USA).

Baird T.D.,Virginia Polytechnic Institute and State University
Population and Environment | Year: 2015

Throughout developing countries, major world religions are spreading into areas important for biodiversity conservation, and little is know about the potential effects of this expansion. This paper examines the effect of religious ideals on mechanisms that underlie changes in population growth, economic development, and land conversion within a polygamous, agro-pastoral society near Tarangire National Park in northern Tanzania where Christianity is spreading rapidly. Mixed qualitative and quantitative methods of data collection and analysis are used to (1) identify primary Christian ideals and church messages within local communities regarding family planning, development, and land use; and (2) estimate the association between church membership and household measures of family size, school enrollment, and land use controlling for other factors. Findings indicate that the effects of church messages and membership may be consistent with conversation goals to limit population growth, promote local development, and encourage certain land uses over others. © 2014, Springer Science+Business Media New York.

Kaestle C.E.,Virginia Polytechnic Institute and State University
Journal of Adolescent Health | Year: 2015

Purpose To determine (1) how reports of the ages of first cigarette smoked and daily smoking onset change from adolescence through emerging adulthood and into young adulthood and (2) what predicts reporting inconsistencies and recanting for both smoking milestones. Methods Multinomial logistic regression models compared relative risks of the following: (1) consistent reporting of milestone age (reference group); (2) recanting at either subsequent wave; or (3) inconsistent reporting of age in at least one subsequent wave, using data from Waves I, III, and IV of the National Longitudinal Study of Adolescent to Adult Health. Results Instability and forward telescoping between adolescence and emerging adulthood leveled off by young adulthood. For smoking first cigarette, those who started younger had more inconsistencies and recanting than those who started later, as did African-American, Latino, and Asian respondents compared with non-Latino white respondents. Native American respondents also had higher relative risks of recanting, as did those with low parental education. Males were more inconsistent than females. Depression, same-sex attractions or relationships, and family structure were not associated with reporting stability. Binge drinking, marijuana, and other illegal drugs were associated with lower levels of recanting. For age of daily smoking, starting older versus younger, sex, race, ethnicity, and use of marijuana were significant predictors of report stability. Conclusions Stage of life may influence forward telescoping in smoking self-reports. Stability of reports of adolescent smoking by emerging and young adults in the United States appears biased by age of onset, sex, race, and other substance use. © 2015 Society for Adolescent Health and Medicine.

Santos W.L.,Virginia Polytechnic Institute and State University | Lynch K.R.,University of Virginia
ACS Chemical Biology | Year: 2015

The transfer of the gamma phosphate from ATP to sphingosine (Sph) to generate a small signaling molecule, sphingosine 1-phosphate (S1P), is catalyzed by sphingosine kinases (SphK), which exist as two isoforms, SphK1 and SphK2. SphK is a key regulator of S1P and the S1P:Sph/ceramide ratio. Increases in S1P levels have been linked to diseases including sickle cell disease, cancer, and fibrosis. Therefore, SphKs are potential targets for drug discovery. However, the current chemical biology toolkit needed to validate these enzymes as drug targets is inadequate. With this review, we survey in vivo active SphK inhibitors and highlight the need for developing more potent and selective inhibitors. © 2014 American Chemical Society.

Cary S.C.,University of Waikato | Cary S.C.,University of Delaware | McDonald I.R.,University of Waikato | Barrett J.E.,Virginia Polytechnic Institute and State University | Cowan D.A.,University of the Western Cape
Nature Reviews Microbiology | Year: 2010

The arid soils of the Antarctic Dry Valleys constitute some of the oldest, coldest, driest and most oligotrophic soils on Earth. Early studies suggested that the Dry Valley soils contained, at best, very low levels of viable microbiota. However, recent applications of molecular methods have revealed a dramatically contrasting picture a very wide diversity of microbial taxa, many of which are uncultured and taxonomically unique, and a community that seems to be structured solely by abiotic processes. Here we review our understanding of these extreme Antarctic terrestrial microbial communities, with particular emphasis on the factors that are involved in their development, distribution and maintenance in these cold desert environments. © 2010 Macmillan Publishers Limited. All rights reserved.

Falkinham J.O.,Virginia Polytechnic Institute and State University
Future Microbiology | Year: 2010

Nontuberculous mycobacteria (NTM) are environmental opportunistic pathogens of humans and animals. They are found in a wide variety of habitats to which humans are exposed, including drinking water distribution systems and household water and plumbing. In that regard, they are distinct from their obligate pathogenic relatives, the members of the Mycobacterium tuberculosis complex. Owing to the presence of NTM in the human environment, human activities have had direct impacts on their ecology and thereby their epidemiology. NTM are oligotrophic, able to grow at low organic matter concentrations and over a wide range of temperatures, and even at low oxygen concentrations. Thus, NTM are normal inhabitants of natural waters and drinking waters. Discovery of the presence of NTM-polluted soils is not surprising in light of the ability of NTM to degrade a variety of hydrocarbon pollutants. A major human activity selecting for the growth and predominance of mycobacteria in habitats is disinfection. In comparison to other bacteria, NTM are disinfectant, heavy metal and antibiotic resistant. Therefore, the use of any antimicrobial agent selects for mycobacteria. Use of disinfectant in drinking water treatment selects for mycobacteria that can grow and come to proliferate in drinking water distribution systems in the absence of disinfectant-sensitive competing microorganisms. NTM selection may also occur as a consequence of antibiotics in drinking water sources. © 2010 Future Medicine Ltd.

Weiss C.J.,Virginia Polytechnic Institute and State University
Geochemistry, Geophysics, Geosystems | Year: 2010

Long-period, global-scale electromagnetic induction data have long been recognized as containing potentially useful information for constraining our understanding of the dynamics and physiochemical state of Earth's deep interior. A key component to realizing the potential of this data set is the ability to compute the induction response of a fully 3-D Earth mantle in global spherical geometries. In this contribution a novel finite difference method is described which preserves many algorithmic advantages of staggered grid discretizations in Cartesian computational electromagnetics but is generalized for the sphere by introducing a hybrid, tensor product mesh consisting of concentrically nested, triangulated, spherical shells topologically connected node-for-node in the radial direction. Such a discretization allows for a flexible distribution of mesh nodes in the lateral sense and avoids the problems associated with excessive node density near the poles which results from conformally mapping the standard Cartesian mesh. Modified finite difference templates for spherical geometries are derived and presented, as is a comparison with integral equation solutions for a simple double-hemisphere test model. As a first step toward applying the algorithm for mantle induction studies, results of a conservative, thermally activated mantle heterogeneity model confirm that mantle structure remains observable in the presence of the strongly conductive ocean and may manifest important, diagnostic signatures in the orientation of the horizontal component of induced magnetic field. Copyright 2010 by the American Geophysical Union.

ElGawady M.A.,Washington State University | Dawood H.M.,Virginia Polytechnic Institute and State University
Engineering Structures | Year: 2012

Precast segmental construction technique is an excellent candidate for economic rapid bridge construction in highly congested urban environments and environmentally sensitive regions. This paper presents three dimensional nonlinear finite element models using ABAQUS{minus 45 degree rule}Standard for evaluating the behavior of segmental precast post-tensioned piers under lateral loads. The piers were constructed by stacking precast concrete filled fiber reinforced polymer tube segments one on top of the other and then connecting the assembly structurally with vertical post-tensioning tendons passing through ducts located in the precast segments. A stress-strain relationship for confined concrete was used to model the concrete. The post-tensioning tendons were modeled with beam elements. The model was able to predict the backbone curves for two piers subjected to cyclic loads. A parametric study indicated that increasing the applied post-tensioning force increases nominal strength. Finally, the model showed that the pier aspect ratio, cross sectional diameter size, pier size, and confinement have significant effects on the performance of the investigated piers. © 2012 Elsevier Ltd.

Yue P.,Virginia Polytechnic Institute and State University | Feng J.J.,University of British Columbia
Physics of Fluids | Year: 2011

The Cahn-Hilliard model uses diffusion between fluid components to regularize the stress singularity at a moving contact line. In addition, it represents the dynamics of the near-wall layer by the relaxation of a wall energy. The first part of the paper elucidates the role of the wall relaxation in a flowing system, with two main results. First, we show that wall energy relaxation produces a dynamic contact angle that deviates from the static one, and derive an analytical formula for the deviation. Second, we demonstrate that wall relaxation competes with Cahn-Hilliard diffusion in defining the apparent contact angle, the former tending to "rotate" the interface at the contact line while the latter to "bend" it in the bulk. Thus, varying the two in coordination may compensate each other to produce the same macroscopic solution that is insensitive to the microscopic dynamics of the contact line. The second part of the paper exploits this competition to develop a computational strategy for simulating realistic flows with microscopic slip length at a reduced cost. This consists in computing a moving contact line with a diffusion length larger than the real slip length, but using the wall relaxation to correct the solution to that corresponding to the small slip length. We derive an analytical criterion for the required amount of wall relaxation, and validate it by numerical results on dynamic wetting in capillary tubes and drop spreading. © 2011 American Institute of Physics.

Hudait M.K.,Virginia Polytechnic Institute and State University
ECS Transactions | Year: 2012

Shrinking feature sizes of CMOS transistor has enabled increase in transistor densities and this rising number of transistors increases the power consumption in ICs. Thus, the computing power is primarily constrained by power consumption and high-speed operation. Beyond sub 22 nm technology node, high mobility III-V materials and new device architectures have the potential to provide higher switching speeds and to operate at lower voltage <0.5V than Si FETs. Heterogeneous integration of such high mobility materials with quantum well field effect transistor architecture configuration have recently emerged a promising transistor option for ultra-high speed and low voltage operation. This paper reviews the recent development of the heterogeneous integration of high indium InGaAs quantum well FETs on Si and provide a technological solution for making nanoscale transistors, various integration scheme and solve the physics issues of the origin of defects and dislocations to InGaAs quantum well transistors. As a result, InGaAs quantum well FETs are poised to achieve higher drive current, low-off-state leakage, higher I ON/I OFF ratio, higher f T, controlled short channel effect and thus have a potential for future high-speed and ultra-low-power electronics. ©The Electrochemical Society.

Meng X.-J.,Virginia Polytechnic Institute and State University
Annual Review of Animal Biosciences | Year: 2013

Porcine circovirus type 2 (PCV2) is the primary causative agent of porcine circovirus-associated disease (PCVAD). The virus preferentially targets the lymphoid tissues, which leads to lymphoid depletion and immunosuppression in pigs. The disease is exacerbated by immunostimulation or concurrent infections with other pathogens. PCV2 resides in certain immune cells, such as macrophage and dendritic cells, and modulates their functions. Upregulation of IL-10 and proinflammatory cytokines in infected pigs may contribute to pathogenesis. Pig genetics influence host susceptibility to PCV2, but the viral genetic determinants for virulence remain unknown. PCV2 DNA and proteins interact with various cellular genes that control immune responses to regulate virus replication and pathogenesis. Both neutralizing antibodies and cell-mediated immunity are important immunological correlates of protection. Despite the availability of effective vaccines, variant strains of PCV2 continue to emerge. Although tremendous progress has been made toward understanding PCV2 pathogenesis and immune interactions, many important questions remain. © 2013 by Annual Reviews.

Al-Haik M.,Virginia Polytechnic Institute and State University
Journal of Computational and Theoretical Nanoscience | Year: 2014

In this study molecular dynamics simulations were conducted to model ternary mixture based on asphaltene and two different resin systems found in the Venezuelan crude. These simulations were carried out particularly to elucidate the effect of different thermal environments ranging from ?25 to 60-C on the physical and mechanical properties of the three component model asphalteneresins system. The transition from ?25-C to 60-C yielded a 21% reduction in density and almost 94% in shear modulus, indicating a solid to non-Newtonian fluid glass transition in between these two extremes. While the results obtained should be considered qualitatively due to the simplified molecular structures and the averaging taking place throughout the MD steps, they could provide guidelines for changing the components of the asphaltene mix toward improving the properties under different thermal regimes; for example to prevent asphalt cracking at cold weather. Copyright © 2014 American Scientific Publishers.

Kingston D.G.I.,Virginia Polytechnic Institute and State University
Journal of Natural Products | Year: 2011

Natural products continue to provide a diverse and unique source of bioactive lead compounds for drug discovery, but maintaining their continued eminence as source compounds is challenging in the face of the changing face of the pharmaceutical industry and the changing nature of biodiversity prospecting brought about by the Convention on Biological Diversity. This review provides an overview of some of these challenges and suggests ways in which they can be addressed so that natural products research can remain a viable and productive route to drug discovery. Results from International Cooperative Biodiversity Groups (ICBGs) working in Madagascar, Panama, and Suriname are used as examples of what can be achieved when biodiversity conservation is linked to drug discovery. © 2010 The American Chemical Society and American Society of Pharmacognosy.

Priya S.,Virginia Polytechnic Institute and State University
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control | Year: 2010

Vibration energy harvesting has gained tremendous attention in the past decade and continues to grow rapidly. There are various transduction mechanisms for converting the vibration energy into electrical energy, out of which the piezoelectric mechanism has been shown to provide advantages at the micro-to-meso scale. In the past few years, several studies have tried to address the question of which piezoelectric composition is better for energy harvesting; however, discussion on this subject continues. The intent of this letter is to provide an answer for this question through a simple criterion which can be used in routine material evaluation. © 2010 IEEE.

Davis F.M.,Virginia Polytechnic Institute and State University
Annals of biomedical engineering | Year: 2012

A novel constitutive model that describes stress relaxation in transversely isotropic soft collagenous tissues such as ligaments and tendons is presented. The model is formulated within the nonlinear integral representation framework proposed by Pipkin and Rogers (J. Mech. Phys. Solids. 16:59-72, 1968). It represents a departure from existing models in biomechanics since it describes not only the strain dependent stress relaxation behavior of collagenous tissues but also their finite strains and transverse isotropy. Axial stress-stretch data and stress relaxation data at different axial stretches are collected on rat tail tendon fascicles in order to compute the model parameters. Toward this end, the rat tail tendon fascicles are assumed to be incompressible and undergo an isochoric axisymmetric deformation. A comparison with the experimental data proves that, unlike the quasi-linear viscoelastic model (Fung, Biomechanics: Mechanics of Living Tissues. Springer, New York, 1993) the constitutive law can capture the observed nonlinearities in the stress relaxation response of rat tail tendon fascicles.

Taylor L.T.,Virginia Polytechnic Institute and State University
Journal of Chromatography A | Year: 2012

The use of additives to dramatically extend the range of solute polarity amenable to CO2 based supercritical fluid chromatography (pcSFC) was predicted over 20 years ago. At that time additives were predicted to have multiple functions such as enhancement of mobile phase solvating power, ion suppression, and ion pairing. The adsorption of mobile phase components on the stationary phase causing a modification of its surface was predicted, but the implications for separations were not defined. Reports published in the late 1980s showed that while water could not function as a primary modifier due to it poor solubility in carbon dioxide, its use as an additive was more promising. The past decade has seen very little published work concerning water and pcSFC. Now reports are beginning to appear that demonstrate enhanced selectivity with water, and application of the technology to polypeptide salts, drug molecules, and nucleobases. This review attempts to bridge the past with the present. As evidenced by the studies described in this review, water may offer much potential as an additive in that it could (a) enhance the solvating power of the mobile phase, (b) introduce HILIC-like analyte partitioning, (c) simplify preparative purifications, and (d) offer a more mass spectrometrically compatible interface. © 2012 Elsevier B.V.

Khunjar W.O.,Virginia Polytechnic Institute and State University | Love N.G.,University of Michigan
Chemosphere | Year: 2011

The sorption of carbamazepine (CBZ), iopromide (IOP), trimethoprim (TMP) and 17α-ethinylestradiol (EE2) was evaluated using four biomass types (pure ammonia oxidizing bacterial culture, two heterotrophic enrichment cultures with varying levels of oxygenase activity, and a full-scale nitrifying activated sludge (NAS) culture). CBZ and IOP did not sorb to the four biomass types. EE2 did not sorb to the pure culture but sorbed significantly to the heterotrophic cultures and NAS. TMP sorbed to the heterotrophic cultures and NAS, and was not evaluated for the pure culture. Three floc characteristics (hydrophobicity, median particle size, organic matter content) correlated moderately well with the EE2 organic matter sorption coefficient (KOM,EE2). Zeta potential did not correlate well with KOM,EE2 but did with KOM,TMP, indicating that TMP sorption is more influenced by electrostatic factors than EE2. Once divalent cation-linked exocellular polymeric substances (EPS) were removed from flocs, EE2 and TMP sorption to the non-EPS (cellular) fraction decreased by approximately 50%. The correlation between KOM,EE2 for the non-EPS cellular fraction deteriorated while the correlation between KOM,TMP improved. EE2 seemed to sorb more strongly to EPS protein whereas TMP sorbed equally to polysaccharide and protein EPS. Attempts to develop predictive models were not successful. Pharmaceuticals that sorbed to biomass samples underwent biodegradation whereas those that did not sorb were not biodegraded, suggesting a relationship between sorption and pharmaceutical biotransformation. © 2010 Elsevier Ltd.

Hitt N.P.,U.S. Geological Survey | Angermeier P.L.,Virginia Polytechnic Institute and State University
Journal of the North American Benthological Society | Year: 2011

If organisms move beyond the boundaries of local sampling units, regional metacommunity dynamics could undermine the ability of bioassessment studies to characterize local environmental quality. We tested the prediction that fish dispersal influences local fish community structure and bioassessment metrics as a function of site position within stream networks. We evaluated fish community data from the US Environmental Protection Agency's Regional Environmental Monitoring and Assessment Program in West Virginia, USA, to compare the influences of stream network position, ecoregion, basin, and stream size on local fish community composition. We assigned sites to 1 of 3 stream network positions: 1) main channels (MC, n = 12) encompassed streams with upstream catchment areas >200 km2, 2) mainstem tributaries (MT, n = 43) flowed into MC-sized confluences within 15 fluvial km, 3) headwater tributaries (HT, n = 31) lacked such riverine confluences within 15 fluvial km. MT and HT sites had similar upstream catchment sizes and landuse gradients, but species richness was greater in MT sites than HT sites, whereas MT and MC sites were not different in this regard. Three bioassessment metrics were greater in MT sites than HT sites (intolerant species richness, cyprinid species richness, benthic species richness), but a multimetric index of biotic integrity did not differ among stream network positions. Ordinations revealed that fish community composition was organized primarily by zoogeographic basin (Monongahela River basin, New River basin, Ohio River basin), ecoregion (Central Appalachian Plateau, Western Appalachian Plateau, Ridge and Valley), and stream size. Riverine specialists were more abundant in MT than HT sites and were more abundant in basins connected to the Ohio River than in basins isolated from the Ohio River by a large waterfall (New River). Our results suggest that contemporary dispersal among streams influences fish community composition over small spatial scales (101 km), historical dispersal constrained by zoogeographic barriers influences community structure over larger areas (10 2 km), and contemporary dispersal by fishes influences certain metrics commonly used in bioassessment programs. © 2011 The North American Benthological Society.

Kiran E.,Virginia Polytechnic Institute and State University
Journal of Supercritical Fluids | Year: 2012

This paper reports on the miscibility and foaming of a bioabsorbable polymer, poly(p-dioxanone) in CO 2 + acetone mixtures at high pressures. Liquid-liquid miscibility pressures have been determined in acetone for polymer concentrations in the range from 1 to 15 wt% over a temperature range from 70 to 170°C. Phase boundaries were also determined for 5, 7.5 and 10 wt% solutions in CO 2 (11 wt%) + acetone (89 wt%); and for 7.5 wt% polymer solutions in CO 2 (25 wt%) + acetone (75 wt%) fluid mixture. The solutions in both acetone and in acetone + CO 2 mixtures were found to display UCST type behavior. In solvent mixtures, miscibility pressures show a marked increase with increased carbon dioxide content. At 150°C, for the 7.5 wt% polymer solution, the miscibility pressures increased from about 25 MPa in pure acetone to 40 MPa in 10 wt% CO 2 mixture and to about 65 MPa in 25 wt% CO 2 containing mixture. Foaming experiments were carried out in a specially designed mold with porous plates in pure carbon dioxide and also in mixtures containing acetone at low addition levels (<1 wt%) at temperatures between 80 and 100°C and at pressures between 20 and 45 MPa. Foams with relatively large and distinctly interconnected pores with pore diameters in the range from 20 to 100 μm were generated if pressures were greater than 20 MPa and the temperatures were less than 92°C. Larger pores and interconnectivity were favored when foaming was carried out from mixtures containing acetone. © 2011 Elsevier B.V.

Becker M.H.,Virginia Polytechnic Institute and State University
EcoHealth | Year: 2011

Populations of native Panamanian golden frogs (Atelopus zeteki) have collapsed due to a recent chytridiomycosis epidemic. Reintroduction efforts from captive assurance colonies are unlikely to be successful without the development of methods to control chytridiomycosis in the wild. In an effort to develop a protective treatment regimen, we treated golden frogs with Janthinobacterium lividum, a skin bacterium that has been used to experimentally prevent chytridiomycosis in North American amphibians. Although J. lividum appeared to colonize A. zeteki skin temporarily, it did not prevent or delay mortality in A. zeteki exposed to Batrachochytrium dendrobatidis, the causative agent of chytridiomycosis. After introduction of J. lividum, average bacterial cell counts reached a peak of 1.7 × 10(6) cells per frog ~2 weeks after treatment but declined steadily after that. When J. lividum numbers declined to ~2.8 × 10(5) cells per frog, B. dendrobatidis infection intensity increased to greater than 13,000 zoospore equivalents per frog. At this point, frogs began to die of chytridiomycosis. Future research will concentrate on isolating and testing antifungal bacterial species from Panama that may be more compatible with Atelopus skin.

Dove P.M.,Virginia Polytechnic Institute and State University
Elements | Year: 2010

The ability of organisms to synthesize skeletons and functional biomineral structures is one of the most remarkable events in the timeline of mineral evolution. The relatively abrupt rise of such forms in the fossil record marks the beginning of a new type of chemistry whereby biology develops a playbook of mineralization processes whose strategies scientists are only beginning to decipher. The fi rst outlines of an impressive picture are emerging, in which the biochemical machinery and sequence of instructions that pass forward to subsequent generations are being defi ned. Yet, skeletons are anything but static in the transfer. The fossil record shows the dynamic responses of skeletal structures to shifts in environmental conditions over geologic time.

Seefeldt L.C.,Utah State University | Hoffman B.M.,Northwestern University | Dean D.R.,Virginia Polytechnic Institute and State University
Current Opinion in Chemical Biology | Year: 2012

Nitrogenase is a two-component enzyme that catalyzes the nucleotide-dependent reduction of N 2 to 2NH 3. This process involves three redox-active metal-containing cofactors including a [4Fe-4S] cluster, an eight-iron P cluster and a seven-iron plus molybdenum FeMo-cofactor, the site of substrate reduction. A deficit-spending model for electron transfer has recently been proposed that incorporates protein conformational gating that favors uni-directional electron transfer among the metalloclusters for the activation of the substrate-binding site. Also reviewed is a proposal that each of the metal clusters cycles through only two redox states of the metal-sulfur core as the system accumulates the multiple electrons required for substrate binding and reduction. In particular, it was suggested that as FeMo-cofactor acquires the four electrons necessary for optimal binding of N 2, each successive pair of electrons is stored as an Fe-H --Fe bridging hydride, with the FeMo-cofactor metal-ion core retaining its resting redox state. We here broaden the discussion of stable intermediates that might form when FeMo-cofactor receives an odd number of electrons. © 2012 Elsevier Ltd.

Kearns G.,Virginia Polytechnic Institute and State University
Transactions of the Institute of British Geographers | Year: 2010

Halford Mackinder's work is drawn upon repeatedly by those who would promote imperialism. Mackinder argued that geography could find a new relevance after the Age of Explorations by serving instead the cause of the New Imperialism. Mackinder's geography was not only a science of empire, it was also a way of promoting the cause of Empire. In the face of the revival of Mackinder's work allied with the promotion of an American Empire, we can turn to those among Mackinder's contemporaries who challenged the use of geography to serve Empire. From the scholarship of these dissidents we can sketch ways to challenge the claims that force is the most important dimension of international relations, that the world divides naturally into mutually hostile camps, and that there are some uses of force that are sanctioned by the promotion of democracy. © 2010 The Author. Journal compilation © Royal Geographical Society (with The Institute of British Geographers) 2010.

Farhood M.,Virginia Polytechnic Institute and State University
IEEE Transactions on Automatic Control | Year: 2012

The paper presents a parameter-dependent Lyapunov approach for the control of nonstationary linear-parameter varying systems. The work is motivated by the challenges encountered in controlling nonlinear systems about pre-specified aggressive trajectories, specifically ones which eventually settle into periodic orbits. The control design method uses the $\ell 2-induced norm performance measure, and the analysis and synthesis results are given in terms of parameterized linear matrix inequalities. Two fast and easy-to-implement algorithms for online controller construction are also provided. © 2006 IEEE.

Peschiera G.,Columbia University | Taylor J.E.,Virginia Polytechnic Institute and State University
Energy and Buildings | Year: 2012

There is a growing need to reduce building energy consumption to limit greenhouse gas emissions and lessen the strain on our electricity grids. Researchers have shown that people are more likely to implement conservation practices in response to energy consumption feedback the more socially proximal the norm provided in that feedback. It has also been shown that sharing individual room-level electricity usage information with peers is more effective in inducing consumption reduction than exposure to generic norms. Designers of energy use feedback systems are leveraging social networks to encourage energy-efficient behavior. Yet, despite growing interest in the role of peer networks to induce energy savings, we know little about how properties of peer networks, such as a given user's position in a peer network, impact consumption behavior. In a 22-room study group where building residents shared room-level electricity consumption information among peer groups in the same building, we tested the correlation of network degree and Eigenvector centrality with percent change in consumption relative to non-participants. This result shows that energy use feedback is more effective in promoting the implementation of energy saving practices as more peers share energy usage information through the feedback system. This finding underscores the importance of exploring and exploiting linkages between social structure and energy conservation. © 2012 Elsevier B.V. All rights reserved.

Mcclure S.M.,Stanford University | Bickel W.K.,Virginia Polytechnic Institute and State University
Annals of the New York Academy of Sciences | Year: 2014

Dual-systems theories explain lapses in self-control in terms of a conflict between automatic and deliberative modes of behavioral control. Numerous studies have now tested whether the brain areas that control behavior are organized in a manner consistent with dual-systems models. Brain regions directly associated with the mesolimbic dopamine system, the nucleus accumbens and ventromedial prefrontal cortex in particular, capture some of the features assumed by automatic processing. Regions in the lateral prefrontal cortex are more closely linked to deliberative processing and the exertion of self-control in the suppression of impulses. While identifying these regions crudely supports dual-systems theories, important modifications to what constitutes automatic and deliberative behavioral control are also suggested. Experiments have identified various means by which automatic processes may be sculpted. Additional work decomposes deliberative processes into component functions such as generalized working memory, reappraisal of emotional stimuli, and prospection. The importance of deconstructing dual-systems models into specific cognitive processes is clear for understanding and treating addiction. We discuss intervention possibilities suggested by recent research, and focus in particular on cognitive training approaches to bolster deliberative control processes that may aid quit attempts. © 2014 New York Academy of Sciences.

Renardy M.,Virginia Polytechnic Institute and State University
Journal of Mathematical Fluid Mechanics | Year: 2011

We consider the hydrostatic Euler equations in a strip bounded by two free surfaces. We show that the initial value problem is well-posed only if the horizontal velocity is uniform in every cross section of the strip. © 2009 Birkhäuser Verlag Basel/Switzerland.

Liu J.,Ohio State University | Shroff N.B.,Ohio State University | Sherali H.D.,Virginia Polytechnic Institute and State University
IEEE Journal on Selected Areas in Communications | Year: 2012

Cooperative networking is known to have significant potential in increasing network capacity and transmission reliability. Although there have been extensive studies on applying cooperative networking in multi-hop ad hoc networks, most works are limited to the basic three-node relay scheme and single-antenna systems. These two limitations are interconnected and both are due to a limited theoretical understanding of the optimal power allocation structure in MIMO cooperative networks (MIMO-CN). In this paper, we study the structural properties of the optimal power allocation in MIMO-CN with per-node power constraints. More specifically, we show that the optimal power allocations at the source and each relay follow a matching structure in MIMO-CN. This result generalizes the power allocation result under the basic three-node setting to the multi-relay setting, for which the optimal power allocation structure has been heretofore unknown. We further quantify the performance gain due to cooperative relay and establish a connection between cooperative relay and pure relay. Finally, based on these structural insights, we reduce the MIMO-CN rate maximization problem to an equivalent scalar formulation. We then propose a global optimization method to solve this simplified and equivalent problem. © 2006 IEEE.

Baidas M.W.,Kuwait University | MacKenzie A.B.,Virginia Polytechnic Institute and State University
IEEE Transactions on Wireless Communications | Year: 2012

In this paper, power allocation for multi-source multi-relay cooperative wireless networks is considered. An ascending-clock auction algorithm is proposed to efficiently allocate cooperative relay power among multiple source nodes in a distributed fashion. In particular, each source node reports its optimal power demand to each relay node based on the relays' announced prices. It is proven that the proposed auction algorithm enforces truthful power demands and converges in a finite number of time-steps to the unique Walrasian Equilibrium allocation that maximizes the sum of utilities. Numerical results are presented to supplement the theoretical analysis and demonstrate the efficiency of the proposed distributed relay power allocation algorithm. © 2012 IEEE.

Balci O.,Virginia Polytechnic Institute and State University
Simulation | Year: 2012

Conducting large-scale complex modeling and simulation (M&S) projects continues to pose significant challenges for M&S engineers, project managers, and sponsoring organizations. This paper presents a M&S life cycle to alleviate the challenges. The M&S life cycle describes a framework for organization of the processes, work products, quality assurance activities, and project management activities required to develop, use, maintain, and reuse a M&S application from birth to retirement. It provides guidance to a M&S developer (engineer), manager, organization, and community of interest. The M&S life cycle specifies the work products to be created by executing the corresponding processes, together with the integrated verification, validation, and quality assurance activities. The M&S life cycle is critically needed to modularize and structure a M&S application development, and to provide valuable guidance for conducting a M&S project successfully. © 2012 The Society for Modeling and Simulation International.

Brenseke B.,Virginia Polytechnic Institute and State University
Journal of pregnancy | Year: 2013

Chronic diseases such as type 2 diabetes and cardiovascular disease are the leading cause of death and disability worldwide. Although the metabolic syndrome has been defined in various ways, the ultimate importance of recognizing this combination of disorders is that it helps identify individuals at high risk for both type 2 diabetes and cardiovascular disease. Evidence from observational and experimental studies links adverse exposures in early life, particularly relating to nutrition, to chronic disease susceptibility in adulthood. Such studies provide the foundation and framework for the relatively new field of developmental origins of health and disease (DOHaD). Although great strides have been made in identifying the putative concepts and mechanisms relating specific exposures in early life to the risk of developing chronic diseases in adulthood, a complete picture remains obscure. To date, the main focus of the field has been on perinatal undernutrition and specific nutrient deficiencies; however, the current global health crisis of overweight and obesity demands that perinatal overnutrition and specific nutrient excesses be examined. This paper assembles current thoughts on the concepts and mechanisms behind the DOHaD as they relate to maternal nutrition, and highlights specific contributions made by macro- and micronutrients.

Kolivras K.N.,Virginia Polytechnic Institute and State University
Climate Research | Year: 2010

Climate variability brought about by the El Niño-Southern Oscillation has been linked to outbreaks of infectious diseases, such as hantavirus pulmonary syndrome, cholera, and malaria. Additionally, climate change affects the distribution of diseases, causing some regions to become more or less favorable for the transmission of certain pathogens. Mosquitoes in particular are sensitive to climate change, and mosquito-borne diseases may become more common at higher latitudes and elevations under warmer conditions. This study examined the potential changes in dengue risk in Hawaii, USA, in response to climate variability and change using GIS. Dengue, transmitted by mosquitoes of the genus Aedes, is considered to be an emerging disease and almost half of the world's population is at risk of infection. Previous research has identified mosquito habitat and potential dengue risk areas in Hawaii based on average climate conditions, and this study incorporated notions of climate variability and change to that model and determined the population at risk under different scenarios. Dengue risk areas generally contract during El Niño-induced droughts and expand as a result of increased precipitation received during La Niña events. Future climate scenarios predict warmer temperatures and wetter summers in Hawaii over the next 25 yr, which will cause an expansion of mosquito habitat and potential dengue risk areas. The results of this study contribute to the overall understanding of climate-dengue relationships and will aid public health officials in efforts to determine where to concentrate resources for mosquito and dengue surveillance, given certain current or forecast climate conditions. © Inter-Research 2010.

Hitt N.P.,U.S. Geological Survey | Roberts J.H.,Virginia Polytechnic Institute and State University
Oikos | Year: 2012

Spatial variation in extinction and colonization is expected to influence community composition over time. In stream fish communities, local species richness (alpha diversity) and species turnover (beta diversity) are thought to be regulated by high extinction rates in headwater streams and high colonization rates in downstream areas. We evaluated the spatiotemporal structure of fish communities in streams originally surveyed by Burton and Odum 1945 (Ecology 26: 182-194) in Virginia, USA and explored the effects of species traits on extinction and colonization dynamics. We documented dramatic changes in fish community structure at both the site and stream scales. Of the 34 fish species observed, 20 (59%) were present in both time periods, but 11 (32%) colonized the study area and three (9%) were extirpated over time. Within streams, alpha diversity increased in two of three streams but beta diversity decreased dramatically in all streams due to fish community homogenization caused by colonization of common species and extirpation of rare species. Among streams, however, fish communities differentiated over time. Regression trees indicated that reproductive life-history traits such as spawning mound construction, associations with mound-building species, and high fecundity were important predictors of species persistence or colonization. Conversely, native fishes not associated with mound-building exhibited the highest rates of extirpation from streams. Our results demonstrate that stream fish colonization and extinction dynamics exhibit hierarchical spatial structure and suggest that mound-building fishes serve as keystone species for colonization of headwater streams. © 2011 The Authors. Oikos © 2012 Nordic Society Oikos.

Zobel C.W.,Virginia Polytechnic Institute and State University
Decision Support Systems | Year: 2011

Two of the primary measures that characterize the concept of disaster resilience are the initial impact of a disaster event and the subsequent time to recovery. This paper presents a new analytic approach to representing the relationship between these two characteristics by extending a multi-dimensional approach for predicting resilience into a technique for fitting the resilience function to the preferences and priorities of a given decision maker. This allows for a more accurate representation of the perceived value of different resilience scenarios to that individual, and thus makes the concept more relevant in the context of strategic decision making. © 2010 Elsevier B.V. All rights reserved.

Chapman M.C.,Virginia Polytechnic Institute and State University
Bulletin of the Seismological Society of America | Year: 2013

The 23 August 2011 Mw 5.7 Virginia earthquake was studied using local and teleseismic recordings. The earthquake was a shallow reverse rupture in the central Virginia seismic zone. The epicenter was at 37.905° N, 77.975° W, with focal depth 8.0 km. A few local stations recorded both the mainshock and several of the larger aftershocks. This allowed location of the mainshock epicenter relative to the accurate locations of aftershocks recorded by a temporary local deployment of stations. The aftershocks define a planar zone oriented in agreement with the mainshock focal mechanism nodal plane. The mainshock focal depth was determined by comparing teleseismic waveforms with synthetics. Local and teleseismic recordings show evidence of a complex rupture, and were used to locate two large subevents relative to a small initial subevent. The initial slip episode had moment of roughly 2.5 × 1016 N·m, and was followed 0.75 s later by a subevent with a moment of approximately 2.3 × 1017 N·m that amounted to approximately 60% of the total moment release. A third subevent with moment approximately 1.2 × 1017 N·m occurred 1.57 s after rupture initiation. The mainshock rupture occurred at the base of the early aftershock zone. Rupture initiated near the southwestern corner of the aftershock zone and proceeded to the northeast along strike and up-dip. The three subevents may have involved a small fault area: the estimated distance between the initial and final subevent is only 2.0 km. However, the total rise time of the earthquake was comparatively large. The estimated distance between the subevents and the origin time difference between subevents suggests a slow rupture velocity of 1.3-1.7 km=s. This was a consequence of the rupture being comprised of two short-duration energetic slip events that were well separated in time along with a small, possibly low stress-drop, initiation event.

Platini T.,Virginia Polytechnic Institute and State University
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2011

Motivated by the classification of nonequilibrium steady states suggested by R. K. P. Zia and B. Schmittmann, in J. Stat. Mech.1742-546810.1088/1742-5468/ 2007/07/P07012 (2007) P07012, we propose to measure the violation of the detailed balance criterion by the p norm (||K*||p) of the matrix formed by the probability currents. Its asymptotic analysis, for the totally asymmetric simple exclusion process, motivates the definition of a "distance" from equilibrium K* obtained for p=1. In addition, we show that the latter quantity and the average activity * are both related to the probability distribution of the entropy production. Finally, considering the open asymmetric simple exclusion process and open zero-range process, we show that the current of particles gives an exact measure of the violation of detailed balance. © 2011 American Physical Society.

Falconier M.K.,Virginia Polytechnic Institute and State University
Journal of Marital and Family Therapy | Year: 2015

The accumulated knowledge about the negative impact of financial strain on couple's relationship functioning and the magnitude of the latest economic downturn have brought together the fields of financial counseling and couples' therapy. This article describes the development of a new interdisciplinary program that aims at helping couples under financial strain improve their financial management, communication, and dyadic coping skills. The article also reports the results from its initial pilot-testing with data collected from 18 financially distressed couples before and after participation in the program and 3 months later. Results from repeated measures ANOVAs suggest that the program may help reduce both partners' financial strain and the male negative communication and improve both partners' financial management skills and strategies to cope together with financial strain, and the male relationship satisfaction. These findings together with the high satisfaction reported by participants regarding the structure and content of the sessions and homework suggest that this program may be a promising approach to help couples experiencing financial strain. Gender differences, clinical implications, and possibilities for further research are also discussed. © 2014 American Association for Marriage and Family Therapy.

Pruden A.,Virginia Polytechnic Institute and State University
Environmental Science and Technology | Year: 2014

Global initiatives are underway to advance the sustainability of urban water infrastructure through measures such as water reuse. However, there are growing concerns that wastewater effluents are enriched in antibiotics, antibiotic resistant bacteria, and antibiotic resistance genes, and thus could serve as a contributing factor to growing rates of antibiotic resistance in human infections. Evidence for the role of the water environment as a source and pathway for the spread of antimicrobial resistance is examined and key knowledge gaps are identified with respect to implications for sustainable water systems. Efforts on the part of engineers along with investment in research in epidemiology, risk assessment, water treatment and water delivery could advance current and future sustainable water strategies and help avoid unintended consequences. © 2013 American Chemical Society.

Das K.,Texas A&M University | Batra R.C.,Virginia Polytechnic Institute and State University
Journal of Fluids and Structures | Year: 2011

The local water slamming refers to the impact of a part of a ship hull on stationary water for a short duration during which high local pressures occur on the hull. We simulate slamming impact of rigid and deformable hull bottom panels by using the coupled Lagrangian and Eulerian formulation included in the commercial software LS-DYNA. We use the Lagrangian formulation to describe plane-strain deformations of the hull panel and consider geometric nonlinearities. The Eulerian formulation is used to analyze deformations of the water. Deformations of the hull panel and of the water are coupled through the hydrodynamic pressure exerted by water on the hull, and the velocity of particles on the hull wetted surface affecting deformations of the water. The continuity of surface tractions and the inter-penetrability of water into the hull are satisfied by using a penalty method. The computer code is verified by showing that the computed pressure distributions for water slamming on rigid panels agree well with those reported in the literature. The pressure distributions computed for deformable panels are found to differ from those obtained by using a plate theory and Wagner's slamming impact theory. We have also delineated jet flows near the edges of the wetted hull, and studied delamination induced in a sandwich composite panel due to the hydroelastic pressure. © 2011 Elsevier Ltd.

Wells K.J.,Virginia Polytechnic Institute and State University
Antipode | Year: 2015

In 1978 the local government in the District of Columbia approved a measure to tax up to 70% of the profits made on residential speculation. The tax was the first of its kind in the USA. But, it was quickly overturned and deemed by supporters and opponents a failure. Based on 10 months of archival research and interviews in Washington, DC, this paper examines how property rights became a narrative barrier that tax supporters could not overcome. By narrative barrier, I mean the set of rules that shaped how speculation was discussed. Tax supporters did not publicly convey a counter-hegemonic vision of how tenure security and economic wealth could be achieved for black residents through means other than private ownership and real estate investment. This paper contributes to understandings of housing markets, housing crises, and intersections between housing justice and property rights. © 2015 Antipode Foundation Ltd.

Farkas D.,Virginia Polytechnic Institute and State University
Current Opinion in Solid State and Materials Science | Year: 2013

This paper reviews recent results in the simulation of the mechanical response of metallic microstructures at the atomic level. The role of the grain boundary network in deformation process is the concentration of this paper as studied by virtual tensile and nanoindentation tests. The grain boundary network is found to contribute to plastic deformation through the process of dislocation nucleation, absorption and transmission, as well as grain boundary accommodation mechanisms such as grain boundary sliding and migration. The microstructural grain boundary network is also critical to the nucleation and propagation of cracks. The challenges and opportunities in this area are discussed. © 2013 Elsevier Ltd. All rights reserved.

Obilade T.T.,Virginia Polytechnic Institute and State University
International Archives of Medicine | Year: 2015

Globally, persons with diseases like leprosy, tuberculosis, H1N1, SARS or HIV/AIDS have been stigmatized. The ongoing Ebola virus disease (EVD) outbreak in West Africa has been the longest outbreak in the history of the disease and the first outbreak to ever occur in West Africa. The strain of Ebolavirus in West Africa is one of the most virulent strains of the Filoviridae family and case fatalities can be as high as 90%. Treatment of EVD is mainly supportive and societal attributes contribute to stigmatization of the disease and ultimately the spread of the disease. The method used in this study was a search in major databases including PUBMED and Google Scholar. The search phrase used in PUBMED was Ebola stigma. In Google Scholar, the search phrases used included Ebola stigma, EVD, perception of disease, culture and disease. The study also included a review of current events and data from the World Health Organization (WHO) and Centers for Disease Control and Prevention (CDC). In this review, an overview of filoviral hemorrhagic fevers was discussed. The cultural beliefs on the causes of diseases and the stigmatization of infectious diseases in history were examined. In addition, the virulence between severe acute respiratory syndrome (SARS) and EVD were compared. Specifically, it examined Ebola stigmatization and identified societal attributes responsible for the stigma and the implications for controlling the spread. It also points to ways to reduce EVD stigmatization as a way of controlling the spread of EVD. While there is a lot of ongoing research for the cure and control of EVD, little attention is being paid to the role of stigmatization in the control of the disease. Fear is the driving force of EVD stigmatization because EVD is a virulent, fast killing disease that has no cure. Powerlessness is another driving force in stigmatization. The sensationalism in news reporting and the mistrust of the government are factors playing on fear and rumor. Counselling should be provided to the community before survivors of EVD return home. Survivors of EVD should be counselled before going home. The government should set up a task force on stigmatization and make efforts to regain the trust of the people. Memorials for those that died from EVD should be erected in each of the districts affected. Schools should not be closed for long periods and should only be closed if there is recourse to distance education. Faith based organizations can also use the methods for distance education as a means to encourage their followers. © Under License of Creative Commons Attribution 3.0 License.

Sharpe E.,Virginia Polytechnic Institute and State University
Fortschritte der Physik | Year: 2015

It was recently argued that quantum field theories possess one-form and higher-form symmetries, labelled 'generalized global symmetries.' In this paper, we describe how those higher-form symmetries can be understood mathematically as special cases of more general 2-groups and higher groups, and discuss examples of quantum field theories admitting actions of more general higher groups than merely one-form and higher-form symmetries. We discuss analogues of topological defects for some of these higher symmetry groups, relating some of them to ordinary topological defects. We also discuss topological defects in cases in which the moduli 'space' (technically, a stack) admits an action of a higher symmetry group. Finally, we outline a proposal for how certain anomalies might potentially be understood as describing a transmutation of an ordinary group symmetry of the classical theory into a 2-group or higher group symmetry of the quantum theory, which we link to WZW models and bosonization. It was recently argued that quantum field theories possess one-form and higher-form symmetries, labelled 'generalized global symmetries.' In this paper, we describe how those higher-form symmetries can be understood mathematically as special cases of more general 2-groups and higher groups, and discuss examples of quantum field theories admitting actions of more general higher groups than merely one-form and higher-form symmetries. We discuss analogues of topological defects for some of these higher symmetry groups, relating some of them to ordinary topological defects. We also discuss topological defects in cases in which the moduli 'space' (technically, a stack) admits an action of a higher symmetry group. Finally, we outline a proposal for how certain anomalies might potentially be understood as describing a transmutation of an ordinary group symmetry of the classical theory into a 2-group or higher group symmetry of the quantum theory, which we link to WZW models and bosonization. © 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim. All rights reserved.

Plaut R.H.,Virginia Polytechnic Institute and State University
International Journal of Solids and Structures | Year: 2015

Arches and beams buckled upward are analyzed. The structure is pushed downward from above at a specific location along the span until snap-through occurs and the structure jumps to an inverted equilibrium shape. Each beam or arch is modeled as an inextensible elastica. Critical displacements are computed for buckled beams with both ends pinned, both ends clamped, or one end clamped and the other end pinned. Circular arches with pinned ends are also investigated. The ends are immovable. The critical displacement is obtained directly from a theoretical equilibrium shape of the initial unloaded structure. Numerical results are presented for four height-to-span ratios of the initial structure, showing the critical displacement for any application point along the span. At the onset of snap-through, the imposed displacement is at or below the horizontal chord connecting the ends. © 2015 Elsevier Ltd.

Buehler R.,Virginia Polytechnic Institute and State University
Transportation Research Part D: Transport and Environment | Year: 2012

This article examines the role of bicycle parking, cyclist showers, free car parking and transit benefits as determinants of cycling to work. The analysis is based on commute data of workers in the Washington, DC area. Results of rare events logistic regressions indicate that bicycle parking and cyclist showers are related to higher levels of bicycle commuting-even when controlling for other explanatory variables. The odds for cycling to work are greater for employees with access to both cyclist showers and bike parking at work compared to those with just bike parking, but no showers at work. Free car parking at work is associated with 70% smaller odds for bike commuting. Employer provided transit commuter benefits appear to be unrelated to bike commuting. Regression coefficients for control variables have expected signs, but not all are statistically significant. © 2012 Elsevier Ltd.

Fukao T.,Virginia Polytechnic Institute and State University | Xiong L.,Huazhong Agricultural University
Current Opinion in Plant Biology | Year: 2013

Both high and low extremes in precipitation increasingly impact agricultural productivity and sustainability as a consequence of global climate change. Elucidation of the genetic basis underlying stress tolerance facilitates development of new rice varieties with enhanced tolerance. Submergence tolerance is conferred by a single master regulator that orchestrates various acclimation responses, whereas drought tolerance is regulated by a number of small-effect loci that are largely influenced by genetic background and environment. Detailed molecular studies have uncovered the functional importance of genes and signaling components which coordinate various morphological and physiological responses to submergence and drought, providing new insight into understanding the complex regulatory mechanisms of stress tolerance in rice. © 2013 Elsevier Ltd.

Cramer M.S.,Virginia Polytechnic Institute and State University
Physics of Fluids | Year: 2012

We estimate the bulk viscosity of a selection of well known ideal gases. A relatively simple formula is combined with published values of rotational and vibrational relaxation times. It is shown that the bulk viscosity can take on a wide variety of numerical values and variations with temperature. Several fluids, including common diatomic gases, are seen to have bulk viscosities which are hundreds or thousands of times larger than their shear viscosities. We have also provided new estimates for the bulk viscosity of water vapor in the range 380-1000 K. We conjecture that the variation of bulk viscosity with temperature will have a local maximum for most fluids. The Lambert-Salter correlation is used to argue that the vibrational contribution to the bulk viscosities of a sequence of fluids having a similar number of hydrogen atoms at a fixed temperature will increase with the characteristic temperature of the lowest vibrational mode. © 2012 American Institute of Physics.

Harne R.L.,Virginia Polytechnic Institute and State University
Journal of the Acoustical Society of America | Year: 2012

Conversion of ambient vibrational energy into electric power has been the impetus of much modern research. The traditional analysis has focused on absolute electrical power output from the harvesting devices and efficiency defined as the convertibility of an infinite resource of vibration excitation into power. This perspective has limited extensibility when applying resonant harvesters to host resonant structures when the inertial influence of the harvester is more significant. Instead, this work pursues a fundamental understanding of the coupled dynamics of a main mass-spring-damper system to which an electromagnetic or piezoelectric mass-spring-damper is attached. The governing equations are derived, a metric of efficiency is presented, and analysis is undertaken. It is found that electromagnetic energy harvesting efficiency and maximum power output is limited by the strength of the coupling such that no split system resonances are induced for a given mass ratio. For piezoelectric harvesters, only the coupling strength and certain design requirements dictate maximum power and efficiency achievable. Since the harvesting circuitry must follow the split resonances as the piezoelectric harvesters become more massive, the optimum design of piezoelectric harvesters appears to be more involved than for electromagnetic devices. © 2012 Acoustical Society of America.

Si H.,Tennessee State University | Liu D.,Virginia Polytechnic Institute and State University
Journal of Nutritional Biochemistry | Year: 2014

Aging is well-known an inevitable process that is influenced by genetic, lifestyle and environmental factors. However, the exact mechanisms underlying the aging process are not well understood. Increasing evidence shows that aging is highly associated with chronic increase in reactive oxygen species (ROS), accumulation of a low-grade proinflammatory phenotype and reduction in age-related autophagy, suggesting that these factors may play important roles in promoting aging. Indeed, reduction of ROS and low-grade inflammation and promotion of autophagy by calorie restriction or other dietary manipulation can extend lifespan in a wide spectrum of model organisms. Interestingly, recent studies show that some food-derived small molecules, also called phytochemicals, can extend lifespan in various animal species. In this paper, we review several recently identified potential antiaging phytochemicals that have been studied in cells, animals and humans and further highlight the cellular and molecular mechanisms underlying the antiaging actions by these molecules. © 2014 Elsevier Inc.

Murray-Tuite P.,Virginia Polytechnic Institute and State University | Wolshon B.,Louisiana State University
Transportation Research Part C: Emerging Technologies | Year: 2013

This paper presents a review of highway-based evacuation modeling and simulation and its evolution over the past decade. The review includes the major components of roadway transportation planning and operations, including the current state of modeling in the forecasting of evacuation travel demand, distribution and assignment of evacuation demand to regional road networks to reach destinations, assignment of evacuees to various modes of transportation, and evaluation and testing of alternative management strategies to increase capacity of evacuation networks or manage demand. Although this discussion does not cover recent work in other modes used in evacuation such as air, rail, and pedestrian, this paper does highlight recent interdisciplinary modeling work in evacuation to help bridge the gap between the behavioral sciences and engineering and the application of emerging techniques for the verification, validation, and calibration of models. The manuscript also calls attention to special considerations and logistical difficulties, which have received limited attention to date. In addition to these concerns, the following future directions are discussed: further interdisciplinary efforts, including incorporating the medical community; using new technologies for communication of warnings and traffic condition information, data collection, and increased modeling resolution and confidence; using real-time information; and further model refinements and validation. © 2012 Elsevier Ltd.

Walker J.J.,South Dakota State University | de Beurs K.M.,University of Oklahoma | Wynne R.H.,Virginia Polytechnic Institute and State University
Remote Sensing of Environment | Year: 2014

The patchy and heterogeneous arrangement of vegetation in dryland areas complicates the extraction of phenological signals using existing remote sensing data. This study examined whether the phenological analysis of a range of dryland land cover classes would benefit from the availability of synthetic images at Landsat spatial resolution and MODIS time intervals. We assembled a series of 500. m MODIS and Landsat-5 TM datasets from April to November, 2005-2009, over a study site in central Arizona that encompasses diverse dryland vegetation classes along an elevation gradient of 2000. m. We applied the spatial and temporal adaptive reflectance fusion model (STARFM) to each MODIS image to create a time series of synthetic images at 30. m resolution. We subjected a subset of the synthetic imagery to a pixel-based regression analysis with temporally coincident Landsat images to analyze the effect of the underlying vegetation class on the accuracy of the STARFM results. To evaluate the usefulness of the increased spatial resolution compared to a MODIS product, we analyzed the variability of the date of peak greenness values of all 30. m. pixels within unmixed MODIS pixels. Finally, we examined differences in the temporal distributions of peak greenness extracted from both the Enhanced Vegetation Index (EVI) and Normalized Difference Vegetation Index (NDVI) synthetic imagery time series. Our results indicate that characteristics of the vegetation classes strongly influence STARFM algorithm performance, with Pearson correlation coefficient values ranging from 0.72 to 0.96 depending on the Landsat band and the land cover class. Responses in the near-infrared (NIR) spectrum yielded the lowest correlations, particularly for the Ponderosa Pine class. The phenological variability exhibited by each land cover class was dependent on the precipitation patterns of each growing season, but was sufficiently high to make the application of STARFM imagery at this scale uniformly beneficial. The peak greenness dates extracted from EVI and NDVI time series were temporally synchronized for the Grassland class but diverged for the classes of mixed woody and herbaceous vegetation types. © 2014 Elsevier Inc.

Falkinham J.O.,Virginia Polytechnic Institute and State University
Seminars in Respiratory and Critical Care Medicine | Year: 2013

Nontuberculous mycobacteria (NTM) are environmental, opportunistic human pathogens whose reservoirs include peat-rich potting soil and drinking water in buildings and households. In fact, humans are likely surrounded by NTM. NTM are ideally adapted for residence in drinking water distribution systems and household and building plumbing as they are disinfectant-resistant, surface adherent, and able to grow on low concentrations of organic matter. For individuals at risk for NTM infection, measures can be taken to reduce NTM exposure. These include avoiding inhalation of dusts from peat-rich potting soil and aerosols from showers, hot tubs, and humidifiers. A riskanalysis of the presence of NTM in drinking water has not been initiated because the virulence of independent isolates of even single NTM species (e.g., Mycobacterium avium) is quite broad, and virulence determinants have not been identified. © 2013 by Thieme Medical Publishers, Inc.

Friston K.J.,University College London | Stephan K.E.,University College London | Stephan K.E.,ETH Zurich | Montague R.,University College London | And 2 more authors.
The Lancet Psychiatry | Year: 2014

In this Review, we discuss advances in computational neuroscience that relate to psychiatry. We review computational psychiatry in terms of the ambitions of investigators, emerging domains of application, and future work. Our focus is on theoretical formulations of brain function that put subjective beliefs and behaviour within formal (computational) frameworks-frameworks that can be grounded in neurophysiology down to the level of synaptic mechanisms. Understanding the principles that underlie the brain's functional architecture might be essential for an informed phenotyping of psychopathology in terms of its pathophysiological underpinnings. We focus on active (Bayesian) inference and predictive coding. Specifically, we show how basic principles of neuronal computation can be used to explain psychopathology, ranging from impoverished theory of mind in autism to abnormalities of smooth pursuit eye movements in schizophrenia. © 2014 Elsevier Ltd.

Kim S.-G.,Massachusetts Institute of Technology | Priya S.,Virginia Polytechnic Institute and State University | Kanno I.,Kobe University
MRS Bulletin | Year: 2012

Piezoelectric microelectromechanical systems technology for harvesting small magnitudes of energy from ambient vibrations. This technology promises to eliminate the need for replacing chemical batteries or complex wiring in microsensors/microsystems, moving us closer toward battery-less autonomous sensors systems and networks. To achieve this goal, a fully assembled energy harvester the size of a US quarter dollar coin (diameter = 24.26 mm, thickness = 1.75 mm) should be able to robustly generate about 100 ? W of continuous power from ambient vibrations. In addition, the cost of the device should be suffi ciently low for mass scale deployment. At the present time, most of the devices reported in the literature do not meet these requirements. This article reviews the current state of the art with respect to the key challenges such as high power density and wide bandwidth of operation. This article also describes improvements in piezoelectric materials and resonator structure design, which are believed to be the solutions to these challenges. Epitaxial growth and grain texturing of piezoelectric materials is being developed to achieve much higher energy conversion effi ciency. For embedded medical systems, lead-free piezoelectric thin fi lms are being developed, and MEMS processes for these new classes of materials are being investigated. Nonlinear resonating beams for wide bandwidth resonance are also being developed to enable more robust operation of energy harvesters.© 2012 Materials Research Society.

Anderson L.B.,Virginia Polytechnic Institute and State University | Taylor W.,Massachusetts Institute of Technology
Journal of High Energy Physics | Year: 2014

Abstract: We systematically analyze a broad class of dual heterotic and F-theory models that give four-dimensional supergravity theories, and compare the geometric constraints on the two sides of the duality. Specifically, we give a complete classification of models where the heterotic theory is compactified on a smooth Calabi-Yau threefold that is elliptically fibered with a single section and carries smooth irreducible vector bundles, and the dual F-theory model has a corresponding threefold base that has the form of a ℙ1 bundle. We formulate simple conditions for the geometry on the F-theory side to support an elliptically fibered Calabi-Yau fourfold. We match these conditions with conditions for the existence of stable vector bundles on the heterotic side, and show that F-theory gives new insight into the conditions under which such bundles can be constructed. In particular, we find that many allowed F-theory models correspond to vector bundles on the heterotic side with exceptional structure groups, and determine a topological condition that is only satisfied for bundles of this type. We show that in many cases the F-theory geometry imposes a constraint on the extent to which the gauge group can be enhanced, corresponding to limits on the way in which the heterotic bundle can decompose. We explicitly construct all (4962) F-theory threefold bases for dual F-theory/heterotic constructions in the subset of models where the common twofold base surface is toric, and give both toric and non-toric examples of the general results. © 2014, The Author(s).

Goodman M.L.,Virginia Polytechnic Institute and State University | Judge P.G.,High Altitude Observatory
Astrophysical Journal | Year: 2012

An MHD model of a hydrogen plasma with flow, an energy equation, NLTE ionization and radiative cooling, and an Ohm's law with anisotropic electrical conduction and thermoelectric effects is used to self-consistently generate atmospheric layers over a 50 km height range. A subset of these solutions contains current sheets and has properties similar to those of the lower and middle chromosphere. The magnetic field profiles are found to be close to Harris sheet profiles, with maximum field strengths 25-150 G. The radiative flux FR emitted by individual sheets is 4.9 × 105-4.5 × 106ergcm-2s-1, to be compared with the observed chromospheric emission rate of 107ergcm-2s -1. Essentially all emission is from regions with thicknesses 0.5-13km containing the neutral sheet. About half of FR comes from sub-regions with thicknesses 10 times smaller. A resolution ≲ 5-130 m is needed to resolve the properties of the sheets. The sheets have total H densities 1013-1015 cm-3. The ionization fraction in the sheets is 2-20 times larger, and the temperature is 2000-3000K higher than in the surrounding plasma. The Joule heating flux FJ exceeds FR by 4%-34%, the difference being balanced in the energy equation mainly by a negative compressive heating flux. Proton Pedersen current dissipation generates 62%-77% of the positive contribution to FJ . The remainder of this contribution is due to electron current dissipation near the neutral sheet where the plasma is weakly magnetized. © 2012. The American Astronomical Society. All rights reserved..

Pitt D.,Virginia Polytechnic Institute and State University
Environment and Planning C: Government and Policy | Year: 2010

Many US municipalities are engaged in climate mitigation planning, or efforts to reduce their communities' greenhouse gas (GHG) emissions through land-use, transportation, and energy planning. However, they face a number of procedural and institutional obstacles that limit the adoption and implementation of those plans. The literature identifies some of the factors that lead municipalities to join relevant policy networks, but provides little guidance for overcoming the aforementioned obstacles and adopting policies to reduce community-wide GHG emissions. With this study I increase the understanding of climate mitigation planning by examining whether the adoption of these plans and policies is driven primarily by local demographic, economic, environmental, or political - institutional characteristics. My research is based upon a survey of 255 US municipalities. I combine the survey responses with secondary data and use multiple regression techniques to estimate the impact of fifteen demographic, political -institutional, economic, and environmental variables on the adoption of climate mitigation plans and policies. The influence of neighboring jurisdictions, the presence of staff members assigned to energy or climate planning, and the level of community environmental activism are found to have the greatest impact on climate mitigation policy adoption. These findings support the conclusion that the extent of climate mitigation planning is driven primarily by internal processes, and municipalities that are successful in this area do not fit any one profile according to their demographic, economic, or environmental characteristics. © 2010 Pion Ltd and its Licensors.

Detty J.M.,Plymouth State University | McGuire K.J.,Virginia Polytechnic Institute and State University
Water Resources Research | Year: 2010

A small research watershed in the Hubbard Brook Experimental Forest in New Hampshire was equipped with a spatially distributed instrument network designed to continuously monitor hydrometric responses in the shallow subsurface. We analyzed rainfall events during seasonal wet up from late summer through autumn to investigate the mechanisms of runoff generation and the patterns of rainfall-runoff response at the catchment outlet. Our results show that storm quick flow depths displayed a threshold relationship with two independently measured soil moisture indices: a maximum water table height index and the sum of gross precipitation and antecedent soil moisture. Quick flow depths during events with below-threshold criteria were not significantly correlated with either index, while quick flow depths during events with above-threshold criteria were strongly correlated with both indices (r≥0.98). The effective runoff contributing area (estimated by event runoff ratios) also changed significantly between above- and below-threshold conditions, as did the synchronicity between groundwater fluctuations and streamflow. Below the threshold, we inferred that catchment runoff was generated primarily in the near-stream zones, while above the threshold the contributing area likely expanded laterally onto neighboring hillslopes. Our results show that the effective saturated hydraulic conductivity appeared to increase significantly during runoff events with above-threshold conditions, possibly owing to water tables rising into highly transmissive near-surface soils. We believe the observed threshold pattern may partially be explained as a transmissivity feedback mechanism and/or preferential flows through macropore networks which allowed for a rapid expansion of the runoff contributing area onto hillslopes, resulting in increased runoff yields. © 2010 by the American Geophysical Union.

Baxter E.F.,Boston University | Caddick M.J.,Virginia Polytechnic Institute and State University
Geology | Year: 2013

The release of volatiles from subducting lithologies is a crucial triggering process for arc magmatism, seismicity, the growth and maturation of continents, and the global geological water-CO2 cycle. While models exist to predict slab volatile release from hydrous phases, it is challenging to reconstruct and test these fluid fluxes in nature. Here we show that the growth of garnet may be used as a proxy for devolatilization at blueschist to lower eclogite facies conditions in subduction zones. Using thermodynamic analysis including the effects of garnet fractionation and fluid removal, we show the proportional relationship between garnet and water production in two end-member crustal lithologies (pelitic sediment and hydrated mid-oceanic-ridge basalt [MORB]) in three representative subduction geotherms. Dehydrating minerals such as lawsonite, chlorite, amphibole, and epidote contribute to garnet growth, especially between ~1.4 and 3.0 GPa where geophysical models and observations predict dehydration. The average production ratio for altered MORB compositions is 0.52 (wt% water as fluid per vol% garnet) in cooler geotherms (Honshu [Japan] and Nicaragua) and 0.27 in hotter geotherms (Cascadia [North America]), whereas for pelite the production ratios are about half (0.24 and 0.13, respectively). Garnet growth correlates with production of 3.3-5.9 wt% water in hydrated MORB and 1.8-3.1 wt% water in pelite, representing 42%-100% of the water lost between 0.5 and 6.5 GPa from a fully saturated starting material. Garnet abundance, its pressure-temperature growth span, and its growth chronology may be used to recognize, reconstruct, and test models for progressive subduction zone dehydration. © 2013 Geological Society of America.

Goodman M.L.,Virginia Polytechnic Institute and State University
Astrophysical Journal | Year: 2012

A 2.5D, time-dependent magnetohydrodynamic model is used to test the proposition that observed type II spicule velocities can be generated by a Lorentz force under chromospheric conditions. It is found that current densities localized on observed space and time scales of type II spicules and that generate maximum magnetic field strengths ≤50 G can generate a Lorentz force that accelerates plasma to terminal velocities similar to those of type II spicules. Maximum vertical flow speeds are ∼150-460kms-1, horizontally localized within ∼2.5-10km from the vertical axis of the spicule, and comparable to slow solar wind speeds, suggesting that significant solar wind acceleration occurs in type II spicules. Horizontal speeds are ∼20 times smaller than vertical speeds. Terminal velocity is reached 100 s after acceleration begins. The increase in the mechanical and thermal energy of the plasma during acceleration is (2-3) × 1022ergs. The radial component of the Lorentz force compresses the plasma during the acceleration process by factors as large as 100. The Joule heating flux generated during this process is essentially due to proton Pedersen current dissipation and can be ∼0.1-3.7 times the heating flux of 106ergscm-2s -1 associated with middle-upper chromospheric emission. About 84%-94% of the magnetic energy that accelerates and heats the spicules is converted into bulk flow kinetic energy. © 2012. The American Astronomical Society. All rights reserved.

Fogel S.,Virginia Polytechnic Institute and State University
American Surgeon | Year: 2013

Ehlers-Danlos syndrome (EDS) is a closely related group of disorders caused by a heritable defect in collagen synthesis, which leads to marked healing difficulties. It has been estimated to occur in between one in 2500 and one in 5000 individuals but likely occurs more frequently than reported. EDS has probably been seen by all general surgeons several times over the course of a career. The purpose of this report is to describe the findings that should raise the index of suspicion, to aid in the diagnosis, and to characterize the general surgical procedures seen in patients with EDS by reviewing a single surgeon's experience in managing such patients with a review of the literature. Recommendations for treatment are given. A retrospective review of the experience of a single surgeon of 25 procedures in 15 patients with EDS is being reported. This is believed to be the largest series by one surgeon as yet reported. There was a wide variety of procedures performed, including ventral hernia repair (n = 6), inguinal hernia repair (n = 4), colectomy (n = 3), anal fistula (n = 3), and one each of an exploratory laparotomy, an appendectomy, a closure of a dehiscence, a Hickman catheter placement, an open lysis of adhesions for small bowel obstruction (SBO), a laparoscopic lysis of adhesions for SBO, an open cholecystectomy, a laparoscopic cholecystectomy, and an excision of a round ligament endometrioma. There was only one death, which was in a patient with Type IV EDS who was the first patient in this series. He presented with a spontaneous sigmoid perforation treated by Hartmann procedure and went on to develop two more colon perforations and to die of sepsis. The morbidity included only two recurrent ventral hernias, a wound dehiscence, a wound hematoma, and recurrence of the anal fistula. Although patients with EDS pose significant healing problems, successful general surgical procedures can be performed in most patients. Among other recommendations, total avoidance of colon anastomoses and colostomies in favor of total abdominal colectomy and ileostomy and routine closure of the abdominal wall with mesh or retention sutures is advocated. Making the diagnosis is the key to having successful outcomes. Further recommendations on avoiding operation and on the conduct of the operation, if needed, are given. Copyright Southeastern Surgical Congress.

Houk A.E.,Virginia Polytechnic Institute and State University
The Journal of parasitology | Year: 2013

Diarrhea caused by intestinal coccidia (Cystoisospora species) is a common problem in pet dogs and in dogs in animal shelters. Cystoisospora canis has the largest oocysts of the 4 named species of coccidia infecting dogs. The present study examined an isolate of C. canis obtained from a dog from São Paulo, SP, Brazil. Oocysts sporulated within 2 days at room temperature, and 20 sporulated oocysts were measured at 37.6 by 28.6 μm (range 35-42 by 26-31 μm). Most sporulated oocysts contained 2 sporocysts, each with 4 sporozoites, although a few (<1%) were Caryospora-like and contained 1 sporocyst with 8 sporozoites. Two experiments using a total of 11 female 6-wk-old beagles were conducted to determine the pathogenicity of oral infection with 5 × 10(4) sporulated oocysts of this isolate of C. canis. Five of the 11 dogs had natural infections with Cystoisospora ohioensis-like (n = 4) or C. canis (n = 1) species prior to the predicted patent period of 9-10 days. Ten of the dogs developed diarrhea with occasional blood, and 3 dogs were affected to the extent that clinical treatment for coccidiosis using sulfadimethoxine was recommended. Dog CRU had a natural C. canis infection and did not develop clinical disease after oral infection with C. canis oocysts. This dog had a prepatent period of 9 days and a patent period of 3 days, corresponding to experimental infection with the new isolate of C. canis. It excreted fewer C. canis oocysts than did the other dogs. The 4 dogs with natural C. ohioensis-like infection all developed clinical disease, and 1 required treatment. The prepatent period was 9-10 days, and the patent period was 10-11 days in these dogs. All 6 dogs not naturally infected with Cystoisospora developed clinical disease, and 2 required treatment. The prepatent period was 9-10 days, and the patent period was 8-12 days. The present study confirms that C. canis is a primary pathogen for young dogs. It demonstrates that prior infection with C. canis but not C. ohioensis-like coccidia confers some resistance to clinical disases and a decrease in oocyst production in dogs challenged with C. canis.

Beddoes K.,Virginia Polytechnic Institute and State University
International Journal of Engineering Education | Year: 2011

Despite decades of research on and efforts to increase the low numbers of women in engineering in many parts of the world, underrepresentation persists. This paper analyzes recent engineering education scholarship to determine what reasons are given to explain why underrepresentation is a problem, in other words, how underrepresentation is problematized. Using discourse analysis as the theoretical lens, and drawing on prior research that employed similar methods and theoretical perspectives, this paper examines an international dataset of engineering education journal articles and conference proceedings from 1995-2008. Four categories of problematizations are identified and discussed in order to advance critical reflection that could be beneficial in moving forward discussions about underrepresentation. © 2011 TEMPUS Publications.

Katz S.,Trent University | Calasanti T.,Virginia Polytechnic Institute and State University
Gerontologist | Year: 2015

"Successful aging" is one of gerontology's most successful ideas. Applied as a model, a concept, an approach, an experience, and an outcome, it has inspired researchers to create affiliated terms such as "healthy," "positive," "active," "productive," and "effective" aging. Although embraced as an optimistic approach to measuring life satisfaction and as a challenge to ageist traditions based on decline, successful aging as defined by John Rowe and Robert Kahn has also invited considerable critical responses. This article takes a critical gerontological perspective to explore such responses to the Rowe-Kahn successful aging paradigm by summarizing its empirical and methodological limitations, theoretical assumptions around ideas of individual choice and lifestyle, and inattention to intersecting issues of social inequality, health disparities, and age relations. The latter point is elaborated with an examination of income, gender, racial, ethnic, and age differences in the United States. Conclusions raise questions of social exclusion and the future of successful aging research. © 2014 The Author.

Buehler R.,Virginia Polytechnic Institute and State University | Pucher J.,Rutgers University
Transportation | Year: 2012

This article analyzes the variation in bike commuting in large American cities, with a focus on assessing the influence of bike paths and lanes, which have been the main approach to increasing cycling in the USA. To examine the role of cycling facilities, we used a newly assembled dataset on the length of bike lanes and paths in 2008 collected directly from 90 of the 100 largest U. S. cities. Pearson's correlation, bivariate quartile analysis, and two different types of regressions were used to measure the relationship between cycling levels and bikeways, as well as other explanatory and control variables. Ordinary Least Squares and Binary Logit Proportions regressions confirm that cities with a greater supply of bike paths and lanes have significantly higher bike commute rates-even when controlling for land use, climate, socioeconomic factors, gasoline prices, public transport supply, and cycling safety. Standard tests indicate that the models are a good fit, with R 2 ranging between 0. 60 and 0. 65. Computed coefficients have the expected signs for all variables in the various regression models, but not all are statistically significant. Estimated elasticities indicate that both off-street paths and on-street lanes have a similar positive association with bike commute rates in U. S. cities. Our results are consistent with previous research on the importance of separate cycling facilities and provide additional information about the potentially different role of paths vs. lanes. Our analysis also revealed that cities with safer cycling, lower auto ownership, more students, less sprawl, and higher gasoline prices had more cycling to work. By comparison, annual precipitation, the number of cold and hot days, and public transport supply were not statistically significant predictors of bike commuting in large cities. © 2011 Springer Science+Business Media, LLC.

Kornyshev A.A.,Imperial College London | Qiao R.,Virginia Polytechnic Institute and State University
Journal of Physical Chemistry C | Year: 2014

Electrical double layers are ubiquitous; they will inevitably emerge, given mobile charge carriers and an interface. They play a decisive role in well-known problems such as electrochemical reactions, electrokinetics, and colloidal stability and thus have been studied extensively since the very concept of the double layer was postulated by Helmholtz. Furthermore, the transition between different lateral arrangements of counter and co-ions during electrification of narrow pores has been observed in simulations and shown to greatly affect both the capacitance and dynamics of the double layers. These relatively new issues and developments all point to new challenges in understanding the three-dimensional (3D) structures of the double layers controlled by the electrification of surfaces. The new feature of the double layer in ionic liquids is that structural transitions can take place in the adjacent layer to the electrode, even when its ions may not be specifically adsorbed on the electrode.

Cook B.J.,Virginia Polytechnic Institute and State University
Policy Studies Journal | Year: 2010

This article investigates the potential linkage between particular policy design ideas and distinctive patterns of politics and power relations. The research examines a sequence of four cases involving the use of the cap-and-trade policy design principally to combat global climate change through the reduction of greenhouse gas emissions. Through the lens of arenas of power framework, the comparative case analysis suggests the existence of consistent linkages between particular cap-and-trade design ideas, and distinct patterns of political conflict and empowerment. The article concludes with a brief consideration of what the findings suggest about the national politics of climate change policymaking in the United States in the near term, and more important, an assessment of the implications for the further development and refinement of policy theory. © 2010 Policy Studies Organization.

Belden L.K.,Virginia Polytechnic Institute and State University | Wojdak J.M.,Radford University
Oecologia | Year: 2011

Predators can have important impacts on host-parasite dynamics. For many directly transmitted parasites, predators can reduce transmission by removing the most heavily infected individuals from the population. Less is known about how predators might influence parasite dynamics in systems where the parasite relies on vectors or multiple host species to complete their life cycles. Digenetic trematodes are parasitic flatworms with complex life cycles typically involving three host species. They are common parasites in freshwater systems containing aquatic snails, which serve as obligate first intermediate hosts, and multiple trematode species use amphibians as second intermediate hosts. We experimentally examined the impact of predatory salamanders (Ambystoma jeffersonianum) and trematode parasites (Echinostoma trivolvis and Ribeiroia ondatrae) on short-term survival of wood frog tadpoles (Rana sylvatica) in 150-L outdoor pools. Two trematode species were used in experiments because field surveys indicated the presence of both species at our primary study site. Parasites and predators both significantly reduced tadpole survival in outdoor pools; after 6 days, tadpole survival was reduced from 100% in control pools to a mean of 46% in pools containing just parasites and a mean of 49% in pools containing just predators. In pools containing both infected snails and predators, tadpole survival was further reduced to a mean of 5%, a clear risk-enhancement or synergism. These dramatic results suggest that predators may alter transmission dynamics of trematodes in natural systems, and that a complete understanding of host-parasite interactions requires studying these interactions within the ecological framework of community interactions. © 2011 Springer-Verlag.

Burbey T.J.,Virginia Polytechnic Institute and State University
Journal of Hydrology | Year: 2010

Wells tapping confined aquifer systems are known to commonly produce water-level fluctuations caused by strain-induced Earth tides. In this investigation, a straightforward methodology is presented for quantifying the specific storage and secondary porosity of a fractured fault-zone aquifer system using Earth tides. Water-level and barometric pressure head data are smoothed and then filtered to remove low frequency responses. The resulting tidal signals are used in the program BAYTAP-G to yield amplitude and phase shifts of all the major tidal groups. The resulting tidal parameters can be used to compute the time-dependent volumetric strain caused by the M2 and O1 tides. Stress-strain hysteresis loops are produced when the reduced water levels are compared to the volumetric strain induced by these tides. For amplification factors near unity (representing the ratio of pressure response to tidal loading in the fracture to water-level response in the well) the slopes of the loops represent the specific storage of the fracture. The barometric efficiency and specific storage can then be used to estimate a secondary porosity and other parameters of the aquifer system. This analysis was carried out at the Fractured Rock research Site (FRS) in the Blue Ridge Physiographic Province in Floyd County, Virginia. © 2009 Elsevier B.V. All rights reserved.

Ellingson S.W.,Virginia Polytechnic Institute and State University
IEEE Transactions on Antennas and Propagation | Year: 2011

A number of new and planned radio telescopes will consist of large arrays of low-gain antennas operating at frequencies below 300 MHz. In this frequency regime, Galactic noise can be a significant or dominant contribution to the total noise. This, combined with mutual coupling between antennas, makes it difficult to predict the sensitivity of these instruments. This paper describes a system model and procedure for estimating the system equivalent flux density (SEFD)a useful and meaningful metric of the sensitivity of a radio telescopethat accounts for these issues. The method is applied to LWA-1, the first station of the Long Wavelength Array (LWA) interferometer. LWA-1 consists of 512 bowtie-type antennas within a 110 $\times$ 100 m elliptical footprint, and is designed to operate between 10 MHz and 88 MHz using receivers having noise temperature of about 250 K. It is shown that the correlation of Galactic noise between antennas significantly desensitizes the array for beam pointings which are not close to the zenith. It is also shown that considerable improvement is possible using beamforming coefficients which are designed to optimize signal-to-noise ratio under these conditions. Mutual coupling is found to play a significant role, but does not have a consistently positive or negative influence. In particular, we demonstrate that pattern multiplication (assuming the behavior of single antennas embedded in the array is the same as those same antennas by themselves) does not generate reliable estimates of SEFD. © 2011 IEEE.

Wasko C.,Virginia Polytechnic Institute and State University
TechTrends | Year: 2013

Augmented reality (AR) enhanced learning environments have been designed to teach a variety of subjects by having learners act like professionals in the field as opposed to students in a classroom. The environments, grounded in constructivist and situated learning theories, place students in a meaningful, non-classroom environment and force them to collaborate with each other in order to solve an ill-defined problem. AR content, accessed via a mobile broadband device (MBD) such as a phone or tablet, is used to guide the learning experiences. Student participants have reported an increased interest in the settings of the experiences and have expressed a positive attitude towards this innovative form of instructional delivery. Using newly available software loaded on MBDs, teachers and/or students can design and share AR enhanced learning environments that are tied to unique places in their communities. © 2013 Association for Educational Communications and Technology.

Baral N.,Virginia Polytechnic Institute and State University
Environmental Conservation | Year: 2014

Ecotourism has been promoted to reconcile seemingly conflicting goals of tourism development and nature conservation. Given its importance, how has ecotourism fared in the Annapurna Conservation Area (ACA) and how resilient was it to the Maoist insurgency in Nepal (1996-2006)? Drawing upon more than 10 months of field research, participant observation, semi-structured surveys and content analysis of 21 annual reports, ecotourism was evaluated by organizing ACA's programmes and activities under the four major emerging themes, namely local capacity building, waste management, education and infrastructure development; the most prominent theme was local capacity building. Annual visitor numbers declined during the insurgency, but ecotourism managed to survive, mainly due to self-organization of local tourism entrepreneurs. Local tourism entrepreneurs facilitated self-organization through capacity building and diversification of livelihoods. In the aftermath of the insurgency, visitor numbers rebounded and ecotourism continued to develop and evolve; ecotourism was thus resilient to the insurgency. Building local capacity, facilitating self-organization and diversifying livelihoods can enhance the resilience of ecotourism, sustaining stability and helping to deal with uncertainty. Copyright © 2013 Foundation for Environmental Conservation.

Okumoto S.,Virginia Polytechnic Institute and State University | Jones A.,Carnegie Institution for Science | Frommer W.B.,Carnegie Institution for Science
Annual Review of Plant Biology | Year: 2012

Molecular activities are highly dynamic and can occur locally in subcellular domains or compartments. Neighboring cells in the same tissue can exist in different states. Therefore, quantitative ormation on the cellular and subcellular dynamics of ions, signaling molecules, and metabolites is critical for functional understanding of organisms. Mass spectrometry is generally used for monitoring ions and metabolites; however, its temporal and spatial resolution are limited. Fluorescent proteins have revolutionized many areas of biology-e.g., fluorescent proteins can report on gene expression or protein localization in real time-yet promoter-based reporters are often slow to report physiologically relevant changes such as calcium oscillations. Therefore, novel tools are required that can be deployed in specific cells and targeted to subcellular compartments in order to quantify target molecule dynamics directly. We require tools that can measure enzyme activities, protein dynamics, and biophysical processes (e.g., membrane potential or molecular tension) with subcellular resolution. Today, we have an extensive suite of tools at our disposal to address these challenges, including translocation sensors, fluorescence-intensity sensors, and Fodierster resonance energy transfer sensors. This review summarizes sensor design principles, provides a database of sensors for more than 70 different analytes/processes, and gives examples of applications in quantitative live cell imaging. © 2012 by Annual Reviews. All rights reserved.

Okumoto S.,Virginia Polytechnic Institute and State University
Plant Journal | Year: 2012

Quantitative imaging in live cells is a powerful method for monitoring the dynamics of biomolecules at an excellent spatio-temporal resolution. Such an approach, initially limited to a small number of substrates for which specific dyes were available, has become possible for a large number of biomolecules due to the development of genetically encoded, protein-based sensors. These sensors, which can be introduced into live cells through a transgenic approach, offer the benefits of quantitative imaging, with an extra advantage of non-invasiveness. In the past decade there has been a drastic expansion in the number of biomolecules for which genetically encoded sensors are available, and the functional properties of existing sensors are being improved at a dramatic pace. A number of technical improvements have now made the application of genetically encoded sensors in plants rather straightforward, and some of the sensors such as calcium indicator proteins have become standard analytical tools in many plant laboratories. The use of a handful of probes has already revealed an amazing specificity of cellular biomolecule dynamics in plants, which leads us to believe that there are many more discoveries to be made using genetically encoded sensors. In this short review, we will summarize the progress made in the past 15 years in the development in genetically encoded sensors, and highlight significant discoveries made in plant biology. © 2012 The Author. The Plant Journal © 2012 Blackwell Publishing Ltd.

Gillaspy G.E.,Virginia Polytechnic Institute and State University
New Phytologist | Year: 2011

The simple polyol, myo-inositol, is used as a building block of a cellular language that plays various roles in signal transduction. This review describes the terminology used to denote myo-inositol-containing molecules, with an emphasis on how phosphate and fatty acids are added to create second messengers used in signaling. Work in model systems has delineated the genes and enzymes required for synthesis and metabolism of many myo-inositol-containing molecules, with genetic mutants and measurement of second messengers playing key roles in developing our understanding. There is increasing evidence that molecules such as myo- inositol(1,4,5)trisphosphate and phosphatidylinositol(4,5)bisphosphate are synthesized in response to various signals plants encounter. In particular, the controversial role of myo-inositol(1,4,5)trisphosphate is addressed, accompanied by a discussion of the multiple enzymes that act to regulate this molecule. We are also beginning to understand new connections of myo-inositol signaling in plants. These recent discoveries include the novel roles of inositol phosphates in binding to plant hormone receptors and that of phosphatidylinositol(3)phosphate binding to pathogen effectors. © 2011 The Author. New Phytologist © 2011 New Phytologist Trust.

Notter D.R.,Virginia Polytechnic Institute and State University
Animal Reproduction Science | Year: 2012

Sheep and goats are produced in a wide range of production systems and climatic conditions and possess great genetic diversity in reproductive potentials. Mean litter sizes range from near 1 to 3 or more, and patterns of seasonal reproduction are often strongly synchronised to local conditions. Thus, optimisation, rather than maximisation, of reproductive potentials is required, and optimum reproductive rates are often well below those which could be achieved. However, changing employment patterns, increasing urbanisation, and emergence of new markets provide corresponding opportunities for sustainable intensification of small ruminant production, potentially requiring enhancements in reproductive potentials. Heritabilities for most reproductive traits are less than those for many other traits, usually ranging from 0.05 to 0.15, and opportunities for within-breed selection are therefore limited. Substantial changes in litter size or major changes in seasonal breeding patterns are thus best achieved by crossing of divergent breeds to rapidly reset genetic potentials for these traits, followed by within-breed selection to optimise reproductive potentials. Various mutations influencing ovulation rate and litter size in sheep provide additional opportunities to rapidly adjust genetic potentials, but require careful breeding management. Comparable major genes have not yet been found in goats or for traits associated with breeding season. © 2012 Elsevier B.V.

Rubiales D.,CSIC - Institute for Sustainable Agriculture | Monica F.-A.,Virginia Polytechnic Institute and State University
Agronomy for Sustainable Development | Year: 2012

Parasitic weeds decrease severely the production of major grain and forage legumes. The most economically damaging weeds for temperate legumes are broomrapes, in particular Orobanche crenata. Broomrape species such as Orobanche foetida, Orobanche minor, and Phelipanche aegyptiaca can also induce high local damage. Other parasitic weeds such as Striga gesnerioides and Alectra vogelii decrease yield of legume crops throughout semi-arid areas of sub-Saharan Africa. Dodders such as Cuscuta campestris can be damaging for some crops. Here, we review methods to control parasitic weeds. Preventing the movement of weed seeds into uninfested areas is a crucial component of control. Once a field is infested with parasitic weeds, controlling its seed production is very difficult. The only effective way to cope with parasitic weeds is to apply an integrated approach. Seedbank demise can be achieved by fumigation and solarization. However, this method is not economically feasible for low-value and low-input legume crops. A number of cultural practices including delayed sowing, hand weeding, no-tillage, nitrogen fertilization, intercropping, or rotations can contribute to seed bank demise. Other strategies such as suicidal germination, activation of systemic acquired resistance, biocontrol or target site herbicide resistance are promising solutions that are being explored but are not yet ready for direct application. The only methods currently available to farmers are the use of resistant varieties and chemical control, although both have their limitations. Chemical control with systemic herbicides such as glyphosate or imidazolinones at low rates is possible. Advances in modeling and the availability of new technologies allow the development of precision agriculture or sitespecific farming. The most economical and environmentally friendly control option is the use of resistant crop varieties; however, breeding for resistance is a difficult task considering the scarce and complex nature of resistance in most crops. These strategies for parasitic weed management in legume crops will be presented and critically discussed. © INRA and Springer Science+Business Media B.V. 2011.

Cameron K.W.,Virginia Polytechnic Institute and State University
Computer | Year: 2013

For many enhanced computing designs, the energy efficiency is counterintuitive and should be viewed more critically. © 1970-2012 IEEE.

Weiss C.J.,Virginia Polytechnic Institute and State University
Computers and Geosciences | Year: 2013

An essential element for computational hypothesis testing, data inversion and experiment design for electromagnetic geophysics is a robust forward solver, capable of easily and quickly evaluating the electromagnetic response of arbitrary geologic structure. The usefulness of such a solver hinges on the balance among competing desires like ease of use, speed of forward calculation, scalability to large problems or compute clusters, parsimonious use of memory access, accuracy and by necessity, the ability to faithfully accommodate a broad range of geologic scenarios over extremes in length scale and frequency content. This is indeed a tall order. The present study addresses recent progress toward the development of a forward solver with these properties. Based on the Lorenz-gauged Helmholtz decomposition, a new finite volume solution over Cartesian model domains endowed with complex-valued electrical properties is shown to be stable over the frequency range 10-2-1010Hz and range 10-3-105m in length scale. Benchmark examples are drawn from magnetotellurics, exploration geophysics, geotechnical mapping and laboratory-scale analysis, showing excellent agreement with reference analytic solutions. Computational efficiency is achieved through use of a matrix-free implementation of the quasi-minimum-residual (QMR) iterative solver, which eliminates explicit storage of finite volume matrix elements in favor of "on the fly" computation as needed by the iterative Krylov sequence. Further efficiency is achieved through sparse coupling matrices between the vector and scalar potentials whose non-zero elements arise only in those parts of the model domain where the conductivity gradient is non-zero. Multi-thread parallelization in the QMR solver through OpenMP pragmas is used to reduce the computational cost of its most expensive step: the single matrix-vector product at each iteration. High-level MPI communicators farm independent processes to available compute nodes for simultaneous computation of multi-frequency or multi-transmitter responses. © 2013 Elsevier Ltd.

Viehland D.D.,Virginia Polytechnic Institute and State University | Salje E.K.H.,University of Cambridge
Advances in Physics | Year: 2014

Domain boundaries typically constitute only a minute fraction of the total volume of a crystal. However, a special (but not unusual) situation can occur in which the domain boundary energy becomes very small. Specifically, the domain size is miniaturized to near-atomic scales and the domain boundary density becomes extremely high. In such cases, the properties of the crystal become dominated by a combination of both the domains and the domain boundaries. This phenomenon differs from most ferromagnetic or ferroelectric materials wherein the motion of the domain boundaries dominates the response. As reported herein, novel emergent phenomena that differ from the properties of either the domains or the domain boundaries may be expected. In this article, we focus on one specific state found in ferroic materials -namely, the adaptive ferroic state. This state can be found, for example, in tweed-like structures in morphotropic phase boundary piezoelectric crystals, ferromagnetic shape memory alloys, and pre-martensitic states. In these materials, the properties of the twin boundaries represent the principal contributors to the functionality of a given system. In fact, further investigations of domain boundary-dominated phenomena could result in novel potential for tailoring functional properties for a desired outcome. It should also be noted that new properties can be designed into twin boundaries that are not the properties of the domains. In this paper, adaptive structures and functional twin boundaries are reviewed, and examples of various observed functionalities (e.g. superconductivity, polarity, and ferroelectricity) and corresponding twin boundary structures are provided. In addition, this review confirms that various theoretically predicted, structurally bridging low-symmetry phases do, in fact, exist. Moreover, the values of the lattice constants of the adaptive state are adjustable parameters that are determined by combinations of cubic, rhombohedral/tetragonal phases, and geometrical invariant conditions. Finally, we show that, in such cases, macroscopic properties are controlled by the unique functionality of the twin walls. Looking forward, domain boundary-dominated phenomena offer an important approach for enhancing the properties of the bulk, and to unique local properties where the "twin is the device". We encourage the community to rethink their approaches to materials by design that have treated the structure as homogeneous and to consider the alternative paradigm where the local structure is different from the apparent average symmetry. © 2014 Taylor & Francis.

Pfeiffer D.G.,Virginia Polytechnic Institute and State University
Florida Entomologist | Year: 2013

An invasive pest of South American origin, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), a devastating pest of tomato (Solanum lycopersicum L.), is reported for the first time in Senegal in 2012. It was first reported in Spain in 2006 and since then it has spread to most of Europe and Mediterranean region. Its occurrence in Senegal is a serious concern as it is likely to spread from there to the rest of West and Central Africa in the near future.

Baccouch M.,University of Nebraska at Omaha | Adjerid S.,Virginia Polytechnic Institute and State University
Computer Methods in Applied Mechanics and Engineering | Year: 2011

We extend the error analysis of Adjerid and Baccouch [1,2] for the discontinuous Galerkin discretization error to variable-coefficient linear hyperbolic problems as well as nonlinear hyperbolic problems on unstructured meshes. We further extend this analysis to transient hyperbolic problems and prove that the local superconvergence results presented in [1] still hold for both steady and transient variable-coefficient linear and nonlinear problems. This local error analysis allows us to construct asymptotically correct a posteriori error estimates by solving local hyperbolic problems with no boundary conditions on each element of general unstructured meshes. We illustrate the superconvergence and the efficiency of our a posteriori error estimates by showing computational results for several linear and nonlinear numerical examples. © 2010 Elsevier B.V.

Woodall W.H.,Virginia Polytechnic Institute and State University | Montgomery D.C.,Arizona State University
Journal of Quality Technology | Year: 2014

The purpose of this paper is to provide an overview and our perspective of recent research and applications of statistical process monitoring. The focus is on work done over the past decade or so. We review briefly a number of important areas, including health-related monitoring, spatiotemporal surveillance, profile monitoring, use of autocorrelated data, the effect of estimation error, and high-dimensional monitoring, among others. We briefly discuss the choice of performance metrics. We provide references and offer some directions for further research.

Cho Y.,Konkuk University | Lai J.-S.,Virginia Polytechnic Institute and State University
IEEE Transactions on Vehicular Technology | Year: 2013

This paper presents the design and control of a high-efficiency multiphase dc-dc converter for a truck auxiliary power unit (APU) fed by a fuel-cell stack. The power-stage design methodology and the operation of the designed power stage used to achieve high efficiency are described in detail. To operate the designed converter as a truck APU, the mode transfer control scheme, where smooth transitions of the voltage and current control modes are necessary, is proposed, and the current controller design procedure is described. A 5-kW four-phase dc-dc converter prototype is built with the proposed power-stage configuration, and the proposed control strategy is applied to control the dc-dc converter. The efficiency of the converter is more than 99.5% at near 10% load and above 98% from 10% to 100% load range. Simulations and experimental results are provided to verify the feasibilities of dc-dc converter operation and the proposed control strategy in the truck APU application. © 2003 IEEE.

Allen B.L.,Virginia Polytechnic Institute and State University
Science Technology and Human Values | Year: 2013

Through exploring multiple contemporary conceptions of justice, this article illustrates that justice matters when considering outcomes in nongovernmental organization (NGO) assistance. In environmental justice (EJ) scholarship, the term justice has been underproblematized, assuming a tacit understanding of the concept as fairness or equitable distribution of environmental harms. Using the rebuilding of two heavily damaged poor and minority neighborhoods in post-Katrina New Orleans as case studies, this article makes evident the different conceptualizations of justice embedded within the strategies and techniques of NGOs and community organizations. Examining both practices and outcomes, I argue that the definition of justice that NGOs implicitly or explicitly adopt in their strategies and technologies of assistance can lead to very different results in postdisaster neighborhood revitalization. For science and technology studies, conceptions of justice can help articulate a more critical social science that opens up the descriptive/normative divide. This is important in thinking about equitable social change and allied policy-as it applies not only to NGO assistance but also to other science and technology issues that intersect with marginalized communities as well. © The Author(s) 2013.

Hall K.D.,U.S. National Institute of Diabetes and Digestive and Kidney Diseases | Hammond R.A.,Brookings Institution | Rahmandad H.,Virginia Polytechnic Institute and State University
American Journal of Public Health | Year: 2014

Obesity is associatedwith a prolonged imbalance between energy intake and expenditure, both ofwhich are regulated by multiple feedback processes within and across individuals. These processes constitute 3 hierarchical control systems-homeostatic, hedonic, and cognitive-with extensive interaction among them. Understanding complex eating behavior requires consideration of all 3 systems and their interactions. Existing models of these processes are widely scattered, with relatively few attempts to integrate across mechanisms. We briefly review available empirical evidence and dynamicmodels, discussing challenges and potential for better integration. We conclude that developing richer models of dynamic interplay among systems should be a priority in the future study of obesity and that systems science modeling offers the potential to aid in this goal.

Rimstidt J.D.,Virginia Polytechnic Institute and State University
Applied Geochemistry | Year: 2015

An established engineering model is used to identify conditions where diffusion controls the dissolution of quartz and forsterite in packed beds. The model shows that diffusion control is favored at low advection flux, large grain size, high temperature, and high pH (if the reaction consumes H+). Quartz dissolution is chemical reaction controlled for most geochemically reasonable combinations of temperature, grain size, and flow rate. On the other hand, forsterite dissolution rates can be diffusion controlled for typical advection fluxes, grain sizes, temperatures, and pH's. The apparent activation energy for diffusion-controlled reactions in a packed bed is much higher than the <~20kJ/mol value that is often used to identify diffusion controlled reactions. The models are quite general and can be adapted to deal with other mineral dissolution and precipitation reactions. © 2015 Elsevier Ltd.

Renardy M.,Virginia Polytechnic Institute and State University
Archive for Rational Mechanics and Analysis | Year: 2010

We derive rigorous criteria for the linear stability of viscoelastic flows under periodic boundary conditions. The results are based on recent work of R. Shvydkoy (Commun Math Phys 265:507-545, 2006). © 2010 Springer-Verlag.

Kou Z.,Wayne State University | VandeVord P.J.,Virginia Polytechnic Institute and State University | VandeVord P.J.,Salem Medical Center
GLIA | Year: 2014

An improved understanding and characterization of glial activation and its relationship with white matter injury will likely serve as a novel treatment target to curb post injury inflammation and promote axonal remyelination after brain trauma. Traumatic brain injury (TBI) is a significant public healthcare burden and a leading cause of death and disability in the United States. Particularly, traumatic white matter (WM) injury or traumatic axonal injury has been reported as being associated with patients' poor outcomes. However, there is very limited data reporting the importance of glial activation after TBI and its interaction with WM injury. This article presents a systematic review of traumatic WM injury and the associated glial activation, from basic science to clinical diagnosis and prognosis, from advanced neuroimaging perspective. It concludes that there is a disconnection between WM injury research and the essential role of glia which serve to restore a healthy environment for axonal regeneration following WM injury. Particularly, there is a significant lack of non-invasive means to characterize the complex pathophysiology of WM injury and glial activation in both animal models and in humans. An improved understanding and characterization of the relationship between glia and WM injury will likely serve as a novel treatment target to curb post injury inflammation and promote axonal remyelination. © 2014 Wiley Periodicals, Inc.

Freidel L.,Perimeter Institute for Theoretical Physics | Leigh R.G.,Urbana University | Minic D.,Virginia Polytechnic Institute and State University
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2014

After many years, the deep nature of spacetime in string theory remains an enigma. In this Letter we incorporate the concept of Born reciprocity in order to provide a new point of view on string theory in which spacetime is a derived dynamical concept. This viewpoint may be thought of as a dynamical chiral phase space formulation of string theory, in which Born reciprocity is implemented as a choice of a Lagrangian submanifold of the phase space, and amounts to a generalization of T-duality. In this approach the fundamental symmetry of string theory contains phase space diffeomorphism invariance and the underlying string geometry should be understood in terms of dynamical bi-Lagrangian manifolds and an apparently new geometric structure, somewhat reminiscent of para-quaternionic geometry, which we call Born geometry. © 2014 Elsevier B.V.

Sultan C.,Virginia Polytechnic Institute and State University
Mechanical Systems and Signal Processing | Year: 2010

The design of vector second-order linear systems for accurate proportional damping approximation is addressed. For this purpose an error system is defined using the difference between the generalized coordinates of the non-proportionally damped system and its proportionally damped approximation in modal space. The accuracy of the approximation is characterized using the energy gain of the error system and the design problem is formulated as selecting parameters of the non-proportionally damped system to ensure that this gain is sufficiently small. An efficient algorithm that combines linear matrix inequalities and simultaneous perturbation stochastic approximation is developed to solve the problem and examples of its application to tensegrity structures design are presented. © 2010 Elsevier Ltd. All rights reserved.

Mullins D.E.,Virginia Polytechnic Institute and State University
Annual Review of Entomology | Year: 2015

Cockroaches are a group of insects that evolved early in geological time. Because of their antiquity, they for the most part display generalized behavior and physiology and accordingly have frequently been used as model insects to examine physiological and biochemical mechanisms involved with water balance, nutrition, reproduction, genetics, and insecticide resistance. As a result, a considerable amount of information on these topics is available. However, there is much more to be learned by employing new protocols, microchemical analytical techniques, and molecular biology tools to explore many unanswered questions. © 2015 by Annual Reviews. All rights reserved.

Hernick M.,Virginia Polytechnic Institute and State University
Expert Review of Anti-Infective Therapy | Year: 2013

Actinomycetes, including Mycobacterium species, are Gram-positive bacteria that use the small molecule mycothiol (MSH) as their primary reducing agent and in the detoxification of xenobiotics. Due to these important functions, MSH is a potential target for the development of antibiotics for the treatment of tuberculosis. This review summarizes the progress to date on the viability of enzymes involved in MSH biosynthesis and MSH-dependent detoxification as drug targets, biochemical characterization of target enzymes (structure, mechanism and substrate specificity) and development of MSH biosynthesis and MSH-dependent detoxification enzyme inhibitors. In addition, the ability of MSH to influence the sensitivity of mycobacteria to existing antibiotics and potential of MSH biosynthesis and MSH-dependent detoxification enzyme inhibitors to modulate the activity of existing antibiotics are described. © 2013 Expert Reviews Ltd.

Roman M.,Virginia Polytechnic Institute and State University
Industrial Biotechnology | Year: 2015

Cellulose nanocrystals (CNCs) are a biobased nanomaterial attracting increasing interest for a range of potential applications. This article reviews the current literature on the pulmonary, oral, dermal, and cytotoxicity of CNCs. Current studies of the oral and dermal toxicity of CNCs have shown a lack of adverse health effects, whereas studies of the pulmonary and cytotoxicity have yielded discordant results. Additional studies are needed to support the general conclusion that CNCs are nontoxic on ingestion or contact with the skin and to determine whether CNCs have adverse health effects on inhalation or elicit inflammatory or oxidative stress responses at the cellular level. This review underscores the importance of careful sample characterization and exclusion of interfering factors, such as the presence of endotoxins or toxic chemical impurities, for a detailed understanding of the potential adverse health effects of CNCs by various exposure routes. © Copyright 2015, Mary Ann Liebert, Inc.

Parast M.M.,North Carolina A&T State University | Adams S.G.,Virginia Polytechnic Institute and State University
International Journal of Production Economics | Year: 2012

The purpose of this paper is to investigate the effect of corporate social responsibility and benchmarking on organizational performance in the petroleum industry. We find that top management support for quality is the main driver of practices associated with corporate social responsibility. Corporate social responsibility appears to have a significant impact on internal quality results (operational performance) but it does not have a significant effect on external quality results (firm performance). We did not find a very strong relationship between benchmarking and internal/external quality results. Our findings suggest that the implementation of corporate social responsibility in the petroleum industry is economically driven. Recommendations for managers and future research have been outlined. © 2011 Published by Elsevier B.V.

Mehta R.K.,Michigan Technological University | Agnew M.J.,Virginia Polytechnic Institute and State University
European Journal of Applied Physiology | Year: 2012

Most occupational tasks involve some level of mental/cognitive processing in addition to physical work; however, the etiology of work-related musculoskeletal disorders (WMSDs) due to these demands remains unclear. The aim of this study was to quantify the interactive effects of physical and mental workload on muscle endurance, fatigue, and recovery during intermittent work. Twelve participants, balanced by gender, performed intermittent static shoulder abductions to exhaustion at 15, 35, and 55% of individual maximal voluntary contraction (MVC), in the absence (control) and presence (concurrent) of a mental arithmetic task. Changes in muscular capacity were determined using endurance time, strength decline, electromyographic (EMG) fatigue indicators, muscle oxygenation, and heart rate measures. Muscular recovery was quantified through changes in strength and physiological responses. Mental workload was associated with shorter endurance times, specifically at 35% MVC, and greater strength decline. EMG and oxygenation measures showed similar changes during fatigue manifestation during concurrent conditions compared to the control, despite shorter endurance times. Moreover, decreased heart rate variability during concurrent demand conditions indicated increased mental stress. Although strength recovery was not influenced by mental workload, a slower heart rate recovery was observed after concurrent demand conditions. The findings from this study provide fundamental evidence that physical capacity (fatigability and recovery) is adversely affected by mental workload. Thus, it is critical to determine or evaluate occupational demands based on modified muscular capacity (due to mental workload) to reduce risk of WMSD development. © Springer-Verlag 2011.

Hunter S.R.,Cornell University | Pasupathy R.,Virginia Polytechnic Institute and State University
INFORMS Journal on Computing | Year: 2013

Consider the context of selecting an optimal system from among a finite set of competing systems, based on a "stochastic" objective function and subject to multiple "stochastic" constraints. In this context, we characterize the asymptotically optimal sample allocation that maximizes the rate at which the probability of false selection tends to zero. Since the optimal allocation is the result of a concave maximization problem, its solution is particularly easy to obtain in contexts where the underlying distributions are known or can be assumed. We provide a consistent estimator for the optimal allocation and a corresponding sequential algorithm fit for implementation. Various numerical examples demonstrate how the proposed allocation differs from competing algorithms. © 2013 INFORMS.

Holliday J.A.,Virginia Polytechnic Institute and State University
G3 (Bethesda, Md.) | Year: 2012

Climate is the primary driver of the distribution of tree species worldwide, and the potential for adaptive evolution will be an important factor determining the response of forests to anthropogenic climate change. Although association mapping has the potential to improve our understanding of the genomic underpinnings of climatically relevant traits, the utility of adaptive polymorphisms uncovered by such studies would be greatly enhanced by the development of integrated models that account for the phenotypic effects of multiple single-nucleotide polymorphisms (SNPs) and their interactions simultaneously. We previously reported the results of association mapping in the widespread conifer Sitka spruce (Picea sitchensis). In the current study we used the recursive partitioning algorithm 'Random Forest' to identify optimized combinations of SNPs to predict adaptive phenotypes. After adjusting for population structure, we were able to explain 37% and 30% of the phenotypic variation, respectively, in two locally adaptive traits--autumn budset timing and cold hardiness. For each trait, the leading five SNPs captured much of the phenotypic variation. To determine the role of epistasis in shaping these phenotypes, we also used a novel approach to quantify the strength and direction of pairwise interactions between SNPs and found such interactions to be common. Our results demonstrate the power of Random Forest to identify subsets of markers that are most important to climatic adaptation, and suggest that interactions among these loci may be widespread.

Moskal J.T.,Virginia Polytechnic Institute and State University | Capps S.G.,BENSOL
Journal of Arthroplasty | Year: 2011

Advocates for navigated (NAV) total hip arthroplasty (THA) emphasize the potential for improved component placement. We reviewed published literature to investigate the claim of increased precision of acetabular component placement in navigated THA compared to conventional (N-NAV) THA. Major medical and publishers' databases were searched, making no restrictions for study type, yet restricting results to English-language sources. Nine studies of varying methodological quality involving 1479 THA with a mean age of 59.10 years were included. There was no statistically significant difference in mean acetabular component abduction and anteversion angles between the NAV and N-NAV groups. There was a statistically significant difference in the incidence of acetabular component placement in the "safe zone," with NAV having significantly more "safe placements" than N-NAV, regardless of the chosen safe zone. In addition, NAV had significantly fewer dislocations than N-NAV. These outcomes demonstrate the possible patient benefit from navigation and resulting tighter control of component position. © 2011 Elsevier Inc.

Hoffman B.M.,Northwestern University | Lukoyanov D.,Northwestern University | Dean D.R.,Virginia Polytechnic Institute and State University | Seefeldt L.C.,Utah State University
Accounts of Chemical Research | Year: 2013

Biological nitrogen fixation, the reduction of N2 to two NH 3 molecules, supports more than half the human population. The predominant form of the enzyme nitrogenase, which catalyzes this reaction, comprises an electron-delivery Fe protein and a catalytic MoFe protein. Although nitrogenase has been studied extensively, the catalytic mechanism has remained unknown. At a minimum, a mechanism must identify and characterize each intermediate formed during catalysis and embed these intermediates within a kinetic framework that explains their dynamic interconversion. The Lowe-Thorneley (LT) model describes nitrogenase kinetics and provides rate constants for transformations among intermediates (denoted En, where n is the number of electrons (and protons), that have accumulated within the MoFe protein). Until recently, however, research on purified nitrogenase had not characterized any En state beyond E0.In this Account, we summarize the recent characterization of three freeze-trapped intermediate states formed during nitrogenase catalysis and place them within the LT kinetic scheme. First we discuss the key E4 state, which is primed for N 2 binding and reduction and which we refer to as the "Janus intermediate" because it lies halfway through the reaction cycle. This state has accumulated four reducing equivalents stored as two [Fe-H-Fe] bridging hydrides bound to the active-site iron-molybdenum cofactor ([7Fe-9S-Mo-C- homocitrate]; FeMo-co) at its resting oxidation level. The other two trapped intermediates contain reduced forms of N2. One, intermediate, designated I, has S = 1/2 FeMo-co. Electron nuclear double resonance/hyperfine sublevel correlation (ENDOR/HYSCORE) measurements indicate that I is the final catalytic state, E8, with NH3 product bound to FeMo-co at its resting redox level. The other characterized intermediate, designated H, has integer-spin FeMo-co (non-Kramers; S ≥ 2). Electron spin echo envelope modulation (ESEEM) measurements indicate that H contains the [-NH2] fragment bound to FeMo-co and therefore corresponds to E7.These assignments in the context of previous studies imply a pathway in which (i) N2 binds at E4 with liberation of H2, (ii) N2 is promptly reduced to N2H2, (iii) the two N's are reduced in two steps to form hydrazine-bound FeMo-co, and (iv) two NH3 are liberated in two further steps of reduction. This proposal identifies nitrogenase as following a "prompt-alternating (P-A)" reaction pathway and unifies the catalytic pathway with the LT kinetic framework. However, the proposal does not incorporate one of the most puzzling aspects of nitrogenase catalysis: obligatory generation of H2 upon N2 binding that apparently "wastes" two reducing equivalents and thus 25% of the total energy supplied by the hydrolysis of ATP. Because E4 stores its four accumulated reducing equivalents as two bridging hydrides, we propose an answer to this puzzle based on the organometallic chemistry of hydrides and dihydrogen. We propose that H 2 release upon N2 binding involves reductive elimination of two hydrides to yield N2 bound to doubly reduced FeMo-co. Delivery of the two available electrons and two activating protons yields cofactor-bound diazene, in agreement with the P-A scheme. This keystone completes a draft mechanism for nitrogenase that both organizes the vast body of data on which it is founded and serves as a basis for future experiments. © 2013 American Chemical Society.

Bell M.A.,Virginia Polytechnic Institute and State University
Child Development | Year: 2012

Fifty 8-month-old infants participated in a study of the interrelations among cognition, temperament, and electrophysiology. Better performance on a working memory task (assessed using a looking version of the A-not-B task) was associated with increases in frontal-parietal EEG coherence from baseline to task, as well as elevated levels of frontal-occipital coherence during both baseline and task. Enhanced performance was also associated with decreased heart period (increased heart rate) from baseline to task. Infants with better working memory performance had parents who rated them high on activity level and distress to limitations. When considered collectively, EEG coherence and heart period contributed unique variance in the prediction of high and low performance groups. Implications for the study of infant cognition are discussed. © 2011 The Author. Child Development © 2011 Society for Research in Child Development, Inc.

Tornabene F.,University of Bologna | Fantuzzi N.,University of Bologna | Viola E.,University of Bologna | Batra R.C.,Virginia Polytechnic Institute and State University
Composite Structures | Year: 2015

We investigate recovery of through-the-thickness transverse normal and shear strains and stresses in statically deformed functionally graded (FG) doubly-curved sandwich shell structures and shells of revolution using the generalized zigzag displacement field and the Carrera Unified Formulation (CUF). Three different through-the-thickness distributions of the volume fractions of constituents and two different homogenization techniques are employed to deduce the effective moduli of linear elastic isotropic materials. The system of partial differential equations for different Higher-order Shear Deformation Theories (HSDTs) is numerically solved by using the Generalized Differential Quadrature (GDQ) method. Either the face sheets or the core is assumed to be made of a FGM. The through-the-thickness stress profiles are recovered by integrating along the thickness direction the 3-dimensional (3-D) equilibrium equations written in terms of stresses. The stresses are used to find the strains by using Hooke's law. The computed displacements and the recovered through-the-thickness stresses and strains are found to compare well with those obtained by analyzing the corresponding 3-D problems with the finite element method and a commercial code. The stresses for the FG structures are found to be in-between those for the homogeneous structures made of the two constituents of the FGM. © 2014 Elsevier Ltd.

Falkinham III J.O.,Virginia Polytechnic Institute and State University
Emerging Infectious Diseases | Year: 2011

To determine whether plumbing could be a source of nontuberculous mycobacteria (NTM) infection, during 2007 2009 I isolated NTM from samples from household water systems of NTM patients. Samples from 22/37 (59%) households and 109/394 (28%) total samples yielded NTM. Seventeen (46%) of the 37 households yielded ≥1 Mycobacterium spp. isolate of the same species as that found in the patient; in 7 of those households, the patient isolate and 1 plumbing isolate exhibited the same repetitive sequence-based PCR DNA fingerprint. Households with water heater temperatures ≤ 125°C (≤50°C) were significantly more likely to harbor NTM compared with households with hot water temperatures ≥130°F (≥55°C) (p = 0.0107). Although households with water from public or private water systems serving multiple households were more likely to have NTM (19/27, 70%) compared with households with a well providing water to only 1 household (5/12, 42%), that difference was not significant (p = 0.1532).

Untaroiu C.D.,Virginia Polytechnic Institute and State University
Computational and Mathematical Methods in Medicine | Year: 2013

The mechanical properties of brain under various loadings have been reported in the literature over the past 50 years. Step-and-hold tests have often been employed to characterize viscoelastic and nonlinear behavior of brain under high-rate shear deformation; however, the identification of brain material parameters is typically performed by neglecting the initial strain ramp and/or by assuming a uniform strain distribution in the brain samples. Using finite element (FE) simulations of shear tests, this study shows that these simplifications have a significant effect on the identified material properties in the case of cylindrical human brain specimens. Material models optimized using only the stress relaxation curve under predict the shear force during the strain ramp, mainly due to lower values of their instantaneous shear moduli. Similarly, material models optimized using an analytical approach, which assumes a uniform strain distribution, under predict peak shear forces in FE simulations. Reducing the specimen height showed to improve the model prediction, but no improvements were observed for cubic samples with heights similar to cylindrical samples. Models optimized using FE simulations show the closest response to the test data, so a FE-based optimization approach is recommended in future parameter identification studies of brain. © 2013 Costin D. Untaroiu.

Fortenberry R.C.,NASA | Crawford T.D.,Virginia Polytechnic Institute and State University | Lee T.J.,NASA
Astrophysical Journal | Year: 2013

The A 1 B1 ← X̃ 1A′ excitation into the dipole-bound state of the cyanomethyl anion (CH 2CN?) has been hypothesized as the carrier for one diffuse interstellar band. However, this particular molecular system has not been detected in the interstellar medium even though the related cyanomethyl radical and the isoelectronic ketenimine molecule have been found. In this study, we are employing the use of proven quartic force fields and secondorder vibrational perturbation theory to compute accurate spectroscopic constants and fundamental vibrational frequencies for X̃ 1A ′ CH2CN ? in order to assist in laboratory studies and astronomical observations. © 2013. The American Astronomical Society. All rights reserved. Printed in the U.S.A.

Parker R.G.,Virginia Polytechnic Institute and State University
Mechanism and Machine Theory | Year: 2014

Back-side gear tooth contact happens when anti-backlash (or scissor) gears are used, tooth wedging or tight mesh occurs, or vibration amplitudes are high enough that teeth separate and pass the backlash zone. An accurate description of the back-side gear tooth mesh stiffness is needed to study gear mechanics in such cases. This work studies the time-varying back-side mesh stiffness and its correlation with backlash by analyzing the relationship between the drive-side and back-side mesh stiffnesses. Results of this work yield the general form of the back-side mesh stiffness in terms of the known drive-side mesh stiffness for an arbitrary gear pair. The analytical results are confirmed by simulation results from gear contact analysis software that precisely tracks drive- and back-side gear tooth contact. © 2014 Elsevier Ltd.

Wang S.,University of Texas at San Antonio | Lee F.C.,Virginia Polytechnic Institute and State University
IEEE Transactions on Industrial Electronics | Year: 2010

This paper reviews and analyzes five parasitic capacitance cancellation methods. Critical parameters and constraints determining the cancellation frequency ranges are identified, and the effective frequency range for each cancellation method is derived based on these constraints. Due to these constraints, each method has specific advantages for certain applications. The cancellation techniques, which all make use of either mutual capacitance or mutual inductance, are applied to different applications based on their advantages, and the experiments are carried out to verify the analysis. © 2006 IEEE.

Gillaspy G.E.,Virginia Polytechnic Institute and State University
Advances in Experimental Medicine and Biology | Year: 2013

Work over the recent years has greatly expanded our understanding of the specific molecules involved in plant phosphoinositide signaling. Physiological approaches, combined with analytical techniques and genetic mutants have provided tools to understand how individual genes function in this pathway. Several key differences between plants and animals have become apparent. This chapter will highlight the key areas where major differences between plants and animals occur. In particular, phospholipase C and levels of phosphatidylinositol phosphates differ between plants and animals, and may influence how inositol second messengers form and function in plants. Whether inositol 1,4,5-trisphosphate and/or inositol hexakisphosphate (InsP6) function as second messengers in plants is discussed. Recent data on potential, novel roles of InsP6 in plants is considered, along with the existence of a unique InsP6 synthesis pathway. Lastly, the complexity of myo-inositol synthesis in plants is discussed in reference to synthesis of phosphoinositides and impact on plant growth and development. © 2013 Springer Science+Business Media Dordrecht.

Hanna J.A.,Virginia Polytechnic Institute and State University
International Journal of Solids and Structures | Year: 2015

I present conditions for compatibility of velocities, conservation of mass, and balance of momentum and energy across moving discontinuities in inextensible strings and sheets of uniform mass density. The balances are derived from an action with a time-dependent, non-material boundary, and reduce to matching of material boundary conditions if the discontinuity is stationary with respect to the body. I first consider a point discontinuity in a string and a line discontinuity in a sheet, in the context of classical inertial motion in three Euclidean dimensions. I briefly comment on line discontinuities terminating in point discontinuities in a sheet, discontinuous line discontinuities in a sheet, and an approach to dynamic fracture that treats a crack tip in a sheet as a time-dependent boundary point. I provide two examples of general solutions for conservative sheet motions near a line discontinuity. The approach also enables treatment of actions depending on higher derivatives of position; I thus derive balances for an elastica which are applicable to moving contact problems. © 2015 Elsevier Ltd.

Livnat A.,Virginia Polytechnic Institute and State University
Biology Direct | Year: 2013

Background: The modern evolutionary synthesis leaves unresolved some of the most fundamental, long-standing questions in evolutionary biology: What is the role of sex in evolution? How does complex adaptation evolve? How can selection operate effectively on genetic interactions? More recently, the molecular biology and genomics revolutions have raised a host of critical new questions, through empirical findings that the modern synthesis fails to explain: for example, the discovery of de novo genes; the immense constructive role of transposable elements in evolution; genetic variance and biochemical activity that go far beyond what traditional natural selection can maintain; perplexing cases of molecular parallelism; and more. Presentation of the hypothesis: Here I address these questions from a unified perspective, by means of a new mechanistic view of evolution that offers a novel connection between selection on the phenotype and genetic evolutionary change (while relying, like the traditional theory, on natural selection as the only source of feedback on the fit between an organism and its environment). I hypothesize that the mutation that is of relevance for the evolution of complex adaptation-while not Lamarckian, or "directed" to increase fitness-is not random, but is instead the outcome of a complex and continually evolving biological process that combines information from multiple loci into one. This allows selection on a fleeting combination of interacting alleles at different loci to have a hereditary effect according to the combination's fitness. Testing and implications of the hypothesis: This proposed mechanism addresses the problem of how beneficial genetic interactions can evolve under selection, and also offers an intuitive explanation for the role of sex in evolution, which focuses on sex as the generator of genetic combinations. Importantly, it also implies that genetic variation that has appeared neutral through the lens of traditional theory can actually experience selection on interactions and thus has a much greater adaptive potential than previously considered. Empirical evidence for the proposed mechanism from both molecular evolution and evolution at the organismal level is discussed, and multiple predictions are offered by which it may be tested. Reviewers: This article was reviewed by Nigel Goldenfeld (nominated by Eugene V. Koonin), Jürgen Brosius and W. Ford Doolittle. © 2013 Livnat; licensee BioMed Central Ltd.

Rimstidt J.D.,Virginia Polytechnic Institute and State University | Brantley S.L.,Pennsylvania State University | Olsen A.A.,University of Maine, United States
Geochimica et Cosmochimica Acta | Year: 2012

This paper demonstrates a method for systematic analysis of published mineral dissolution rate data using forsterite dissolution as an example. The steps of the method are: (1) identify the data sources, (2) select the data, (3) tabulate the data, (4) analyze the data to produce a model, and (5) report the results. This method allows for a combination of critical selection of data, based on expert knowledge of theoretical expectations and experimental pitfalls, and meta-analysis of the data using statistical methods.Application of this method to all currently available forsterite dissolution rates (0. <. pH. <. 14, and 0. <. T<. 150. °C) normalized to geometric surface area produced the following rate equations:. For pH. <. 5.6 and 0°. <. T<. 150. °C, based on 519 data. logrgeo=6.05(0.22)-0.46(0.02)pH-3683.0(63.6)1/T(R2=0.88)For pH. >. 5.6 and 0°. <. T<. 150. °C, based on 125 data. logrgeo=4.07(0.38)-0.256(0.023)pH-3465(139)1/T(R2=0.92)The R2 values show that ~10% of the variance in r is not explained by variation in 1/T and pH. Although the experimental error for rate measurements should be±~30%, the observed error associated with the logr values is ~0.5logunits (±300% relative error). The unexplained variance and the large error associated with the reported rates likely arises from the assumption that the rates are directly proportional to the mineral surface area (geometric or BET) when the rate is actually controlled by the concentration and relative reactivity of surface sites, which may be a function of duration of reaction. Related to these surface area terms are other likely sources of error that include composition and preparation of mineral starting material.Similar rate equations were produced from BET surface area normalized rates. Comparison of rate models based on geometric and BET normalized rates offers no support for choosing one normalization method over the other. However, practical considerations support the use of geometric surface area normalization. Comparison of Mg and Si release rates showed that they produced statistically indistinguishable dissolution rates because dissolution was stoichiometric in the experiments over the entire pH range even though the surface concentrations of Mg and Si are known to change with pH. Comparison of rates from experiments with added carbonate, either from CO2 partial pressures greater than atmospheric or added carbonate salts, showed that the existing data set is not sufficient to quantify any effect of dissolved carbonate species on forsterite dissolution rates. © 2012 Elsevier Ltd.

Spotila J.A.,Virginia Polytechnic Institute and State University
Geology | Year: 2012

Mountain peaks influence local climate, are proxies for topographic youth and exhumation, and are the most recognized features of mountain belts, yet are largely incidental to the modern conceptual framework of orogenic erosion that is focused on valley incision. Here it is shown that the three-dimensional distribution of prominent peaks is related to the confluences of major divides and thus to drainage basin structure. Divide-junction summits dominate mountain landscapes in both glacial and fluvial settings and likely result from the inherent stability of pyramidal peaks, in terms of both protection from valley erosion and greater mechanical stability relative to linear ridges. The potential stability of divide-junction peaks may make them anchor points for drainage divide networks, and thus the peaks work against the tendency of drainage divides to migrate. The influence of divide structure on peak heights also suggests that differences in headwall retreat rates may result in different frequency and relative relief of peaks in glacial versus fluvial settings. These results imply that interfluve topography and drainage divide structure offer relevant information for the understanding of landscape evolution. © 2012 Geological Society of America.

Elenes E.Y.,Virginia Polytechnic Institute and State University | Hunter S.A.,Kettering College
Journal of Bone and Joint Surgery - American Volume | Year: 2014

Background: Allograft safety is contingent on effective sterilization. However, current sterilization methods have been associated with decreased biomechanical strength and higher failure rates of soft-tissue allografts. In this study, electron beam (e-beam) sterilization was explored as an alternative sterilization method to preserve biomechanical integrity. We hypothesized that e-beam sterilization would not significantly alter the biomechanical properties of tendon allograft compared with aseptic, nonsterilized controls and gamma-irradiated grafts. Methods: Separate sets of forty fresh-frozen tibialis tendon allografts (four from each of ten donors) and forty bisected bone-patellar tendon-bone (BTB) allografts (four from each of ten donors) were randomly assigned to four study groups. One group received a 17.1 to 21.0-kGy gamma radiation dose; two other groups were sterilized with an e-beam at either a high (17.1 to 21.0-kGy) or low (9.2 to 12.2-kGy) dose. A fourth group served as nonsterilized controls. Each graft was cyclically loaded to 200 N of tension for 2000 cycles at a frequency of 2 Hz, allowed to relax for five minutes, and then tested in tension until failure at a 100%/sec strain rate. One-way analysis of variance testing was used to identify significant differences. Results: Tibialis tendons sterilized with both e-beam treatments and with gamma irradiation exhibited values for cyclic tendon elongation, maximum load, maximum displacement, stiffness, maximum stress, maximum strain, and elastic modulus that were not significantly different from those of nonsterilized controls. BTB allografts sterilized with the high e-beam dose and with gamma irradiation were not significantly different in cyclic tendon elongation, maximum load, maximum displacement, stiffness, maximum stress, maximum strain, and elastic modulus from nonsterilized controls. BTB allografts sterilized with the e-beam at the lower dose were significantly less stiff than nonsterilized controls (p = 0.014) but did not differ from controls in any other properties. The difference in stiffness likely resulted from variations in tendon size rather than the treatments, as the elastic moduli of the groups were similar. Conclusions: The biomechanical properties of tibialis and BTB allografts sterilized with use of an e-beam at a dose range of 17.1 to 21.0 kGy were not different from those of aseptic, nonsterilized controls or gamma-irradiated allografts. Clinical Relevance: E-beam sterilization can be a viable method to produce safe and biomechanically uncompromised soft-tissue allografts. Copyright © 2014 by The Journal of Bone and Joint Surgery, Incorporated.

Jarrott S.E.,Virginia Polytechnic Institute and State University
Journal of Intergenerational Relationships | Year: 2011

Intergenerational programs target diverse youth, elder and community needs with creative practices and considerable success. With the earliest nonfamilial intergenerational interventions identified in the 1960s (i.e., Foster Grandparents in 1965), intergenerational program research is relatively new compared to parallel lines of inquiry in child, youth or adult development. Recently, scholars have encouraged practitioners and researchers alike to increase their use of theory- and evidence- based practices and state of the art research techniques. The present content analysis reflects four decades of intergenerational research published in English language journals to determine if characteristics of intervention studies echo these recommendations. Program and evaluation characteristics were coded along with research results. I describe trends in participant groups, study subjects, research designs, sources of data, methods of analysis and outcomes measured. Implications for practice and research for intergenerational scholars are addressed in the context of this developing area of intervention research. © Taylor & Francis Group, LLC.

Buehler R.,Virginia Polytechnic Institute and State University
Journal of Transport Geography | Year: 2011

Germany and the USA have among the highest motorization rates in the world. Yet Germans make a four times higher share of trips by foot, bike, and public transport and drive for a 25% lower share of trips as Americans. Using two comparable national travel surveys this paper empirically investigates determinants of transport mode choice in Germany and the USA. In both countries higher population density, a greater mix of land-uses, household proximity to public transport, and fewer cars per household are associated with a lower share of trips by automobile. However, considerable differences remain: all groups of society in America are more car-dependent than Germans. Even controlling for dissimilarities in socio-economic factors and land-use, Germans are more likely to walk, cycle, and use public transport. Moreover, Americans living in dense, mixed-use areas, and close to public transport are more likely to drive than Germans living in lower density areas, with more limited mix of land-uses, and farther from public transport. Differences in transport policy that make car travel slower, more expensive, less convenient, and alternatives to the automobile more attractive in Germany may help account for the remaining differences. © 2010 Elsevier Ltd.

Kelly P.T.,University of Wisconsin - Milwaukee | He Z.,Virginia Polytechnic Institute and State University
Bioresource Technology | Year: 2014

Identifying proper application of microbial fuel cell (MFC) technology and understanding how MFCs can be effectively integrated into the existing wastewater treatment process is critical to further development of this technology. In this study, four identical MFCs were used to treat the wastes sampled from different stages of a cheese wastewater treatment process, and both treatment performance and energy balance were examined. The two MFCs treating liquid wastes achieved more than 80% removal of total chemical oxygen demand (TCOD), while the other two MFCs fed with sludge or cheese whey removed about 60% of TCOD. The MFC-2 treating the dissolved air flotation effluent generated the highest Coulombic efficiency of 27.2±3.6% and the highest power density of 3.2±0.3Wm-3, and consumed the least amount of energy of 0.11kWhm-3, indicating that MFCs may be more suitable for treating low-strength wastewater in terms of both treatment and energy performance. © 2014 Elsevier Ltd.

Kim-Spoon J.,Virginia Polytechnic Institute and State University | Cicchetti D.,University of Minnesota | Rogosch F.A.,University of Rochester
Child Development | Year: 2013

The longitudinal contributions of emotion regulation and emotion lability-negativity to internalizing symptomatology were examined in a low-income sample (171 maltreated and 151 nonmaltreated children, from age 7 to 10 years). Latent difference score models indicated that for both maltreated and nonmaltreated children, emotion regulation was a mediator between emotion lability-negativity and internalizing symptomatology, whereas emotion lability-negativity was not a mediator between emotion regulation and internalizing symptomatology. Early maltreatment was associated with high emotion lability-negativity (age 7) that contributed to poor emotion regulation (age 8), which in turn was predictive of increases in internalizing symptomatology (from age 8 to 9). The results imply important roles of emotion regulation in the development of internalizing symptomatology, especially for children with high emotion lability-negativity. © 2012 Society for Research in Child Development, Inc.

Cho J.-H.,U.S. Army | Swami A.,U.S. Army | Chen I.-R.,Virginia Polytechnic Institute and State University
IEEE Communications Surveys and Tutorials | Year: 2011

Managing trust in a distributed Mobile Ad Hoc Network (MANET) is challenging when collaboration or cooperation is critical to achieving mission and system goals such as reliability, availability, scalability, and reconfigurability. In defining and managing trust in a military MANET, we must consider the interactions between the composite cognitive, social, information and communication networks, and take into account the severe resource constraints (e.g., computing power, energy, bandwidth, time), and dynamics (e.g., topology changes, node mobility, node failure, propagation channel conditions). We seek to combine the notions of "social trust" derived from social networks with "quality-of-service (QoS) trust" derived from information and communication networks to obtain a composite trust metric. We discuss the concepts and properties of trust and derive some unique characteristics of trust in MANETs, drawing upon social notions of trust. We provide a survey of trust management schemes developed for MANETs and discuss generally accepted classifications, potential attacks, performance metrics, and trust metrics in MANETs. Finally, we discuss future research areas on trust management in MANETs based on the concept of social and cognitive networks. © 2011 IEEE.

Detty J.M.,Plymouth State University | McGuire K.J.,Virginia Polytechnic Institute and State University
Hydrological Processes | Year: 2010

Hydrologic connectivity is regarded as one of the key controls in determining catchment rainfall-run-off response and has been linked to the export of solutes from uplands to streams. We sought to identify the patterns of hydrologic connectivity within a small forested watershed by monitoring the shallow groundwater fluctuations of simple topographically defined landform sequences (footslope-backslope-shoulder). A spatially distributed instrument network was employed to continuously measure hydrometric responses of the shallow subsurface during seasonal wet-up from summer through winter in a small till mantled research catchment. We demonstrate that the spatial patterns of shallow water table extent and duration, and therefore hydrologic connectivity, had a strong seasonal signature. During the low antecedent soil moisture conditions typically associated with the growing season, water tables were patchy, discontinuous, and only the wettest near-stream footslope areas were consistently hydrologically connected with the stream network. During the dormant season, footslopes and backslopes maintained water tables that persisted between storm events and were almost continuously connected with the stream network. In the largest storm events, the typically driest landforms (shoulder slopes) established shallow transient water tables, suggesting that nearly the entire catchment was temporarily hydrologically connected with the stream network. In addition, we found significant differences (p < 0.05) in the magnitude and duration of groundwater responses to rainfall among landform groups both seasonally and during events. These results have implications for using a similarity approach in representing characteristic hydrologic responses of topographically defined watershed elements, determining hydrologic connectivity between watershed elements, as well as for understanding solute transport in catchments. Copyright © 2010 John Wiley & Sons, Ltd.

Renardy M.,Virginia Polytechnic Institute and State University
Journal of Non-Newtonian Fluid Mechanics | Year: 2010

We formulate a model which can describe fluids with a non-monotone shear stress/shear rate relationship. It is shown how yield stress fluids arise as a limiting case of such a model. Differences between critical stresses for " fast" and " slow" yielding, hysteresis phenomena and thixotropy are naturally explained by the model. © 2010 Elsevier B.V.

Johri A.,Virginia Polytechnic Institute and State University
Computers in Human Behavior | Year: 2012

One critical and to date understudied social psychological construct with significant implications for technology-mediated distributed work is impression formation. Forming useful impressions of each other is crucial for coworkers to avoid mistrust, misattribution, and conflict, and thereby, work effectively and productively. In this theoretical review paper I systematically outline how elements of distributed and virtual work - geographic dispersion, electronic dependence, heterogeneity, and dynamic structures - shape coworkers' impression of each other by influencing information and motivation, the main moderators of impression formation. I develop a model of how the impression formation process acts in technology-mediated distributed work settings, draw propositions, and identify ways to mitigate the breakdown in impression formation among distributed coworkers. Finally, I conceptualize impression accuracy in terms of descriptive, predictive, and explanatory knowledge about others and discuss how it can be increased with positive outcomes for trust, attribution, knowledge sharing, and conflict resolution. © 2012 Elsevier Ltd. All rights reserved.

Wang Y.,Virginia Polytechnic Institute and State University | Inman D.J.,University of Michigan
Journal of Intelligent Material Systems and Structures | Year: 2012

This article presents a summary of passive, semipassive, semiactive, and active control methods for schemes using harvested energy as the main source of energy to suppress vibrations via piezoelectric materials. This concept grew out of the fact that energy dissipation effects resulting from energy harvesting can cause structural damping. First, the existing equivalent electromechanical modeling methods are reviewed for vibration-based energy harvesters using piezoelectric transducers. Modeling of base excitation cantilever beam ranges from lumped to distributed parameter formulations. The commonly used electrical power conditioning circuits and their optimization are also summarized and discussed. The energy dissipation from harvesting induces structural damping, and this leads to the concept of purely passive shunt damping. This article reviews the literature on vibration control laws along the lines of purely passive, semipassive, semiactive, and active control. The classification of pervious results is built on whether external power is supplied to the piezoelectric transducers. The focus is placed on recent articles investigating semipassive and semiactive control strategies derived from synchronized switching damping. However, whether or not the harvested energy is large enough to satisfy a vibration suppression requirement has become an important topic of research but has not yet specifically been addressed in previous studies. Hence, this survey also reviews the possible control methods aiming for less control energy consumption and addresses the potential application for simultaneous vibration control and energy harvesting. © The Author(s) 2012.

Gandhi M.A.,Lockheed Martin | Mili L.,Virginia Polytechnic Institute and State University
IEEE Transactions on Signal Processing | Year: 2010

A new robust Kalman filter is proposed that detects and bounds the influence of outliers in a discrete linear system, including those generated by thick-tailed noise distributions such as impulsive noise. Besides outliers induced in the process and observation noises, we consider in this paper a new type called structural outliers. For a filter to be able to counter the effect of these outliers, observation redundancy in the system is necessary. We have therefore developed a robust filter in a batch-mode regression form to process the observations and predictions together, making it very effective in suppressing multiple outliers. A key step in this filter is a new prewhitening method that incorporates a robust multivariate estimator of location and covariance. The other main step is the use of a generalized maximum likelihood-type (GM) estimator based on Schweppe's proposal and the Huber function, which has a high statistical efficiency at the Gaussian distribution and a positive breakdown point in regression. The latter is defined as the largest fraction of contamination for which the estimator yields a finite maximum bias under contamination. This GM-estimator enables our filter to bound the influence of residual and position, where the former measures the effects of observation and innovation outliers and the latter assesses that of structural outliers. The estimator is solved via the iteratively reweighted least squares (IRLS) algorithm, in which the residuals are standardized utilizing robust weights and scale estimates. Finally, the state estimation error covariance matrix of the proposed GM-Kalman filter is derived from its influence function. Simulation results revealed that our filter compares favorably with the H ∞-filter in the presence of outliers. © 2006 IEEE.

Renardy M.,Virginia Polytechnic Institute and State University
Journal of Non-Newtonian Fluid Mechanics | Year: 2010

We consider the equations for time-dependent creeping flow of an upper convected Maxwell fluid in the limit of infinite Weissenberg number. We identify a particular class of solutions which is analogous to potential flow and discuss several examples. We also discuss more general solutions for two-dimensional flow. © 2009 Elsevier B.V. All rights reserved.

Belanger F.,Virginia Polytechnic Institute and State University | Crossler R.E.,Mississippi State University
MIS Quarterly: Management Information Systems | Year: 2011

Information privacy refers to the desire of individuals to control or have some influence over data about themselves. Advances in information technology have raised concerns about information privacy and its impacts, and have motivated Information Systems researchers to explore information privacy issues, including technical solutions to address these concerns. In this paper, we inform researchers about the current state of information privacy research in IS through a critical analysis of the IS literature that considers information privacy as a key construct. The review of the literature reveals that information privacy is a multilevel concept, but rarely studied as such. We also find that information privacy research has been heavily reliant on studentbased and USA-centric samples, which results in findings of limited generalizability. Information privacy research focuses on explaining and predicting theoretical contributions, with few studies in journal articles focusing on design and action contributions. We recommend that future research should consider different levels of analysis as well as multilevel effects of information privacy. We illustrate this with a multilevel framework for information privacy concerns. We call for research on information privacy to use a broader diversity of sampling populations, and for more design and action information privacy research to be published in journal articles that can result in IT artifacts for protection or control of information privacy.

Melville S.,Virginia Polytechnic Institute and State University | Craig L.,Simon Fraser University
Microbiology and Molecular Biology Reviews | Year: 2013

Type IV pili (T4P) are surface-exposed fibers that mediate many functions in bacteria, including locomotion, adherence to host cells, DNAuptake (competence), and protein secretion and that can act as nanowires carrying electric current. T4P are composed of a polymerized protein, pilin, and their assembly apparatuses share protein homologs with type II secretion systems in eubacteria and the flagella of archaea. T4P are found throughout Gram-negative bacterial families and have been studied most extensively in certain model Gramnegative species. Recently, it was discovered that T4P systems are also widespreadamongGram-positive species, in particular the clostridia. Since Gram-positive and Gram-negative bacteria have many differences in cell wall architecture and other features, it is remarkable how similar the T4P core proteins are between these organisms, yet there are many key and interesting differences to be found as well. In this review, we compare the two T4P systems and identify and discuss the features they have incommonand where they differ to provide a very broad-based view of T4P systems across all eubacterial species. Copyright © 2013, American Society for Microbiology. All Rights Reserved.

Sorrentino D.,Virginia Polytechnic Institute and State University | Sorrentino D.,University of Udine
Nature Reviews Gastroenterology and Hepatology | Year: 2013

Postoperative recurrence of Crohn's disease is a frequent and often severe sequela of the disease. Until a few years ago it was deemed inescapable, as all the conventional medications used to treat the disease have been proven of little benefit in preventing recurrence after surgical treatment. In the past few years, anti-TNF agents given immediately after surgery have shown a remarkable efficacy in the prevention of disease recurrence. Large, randomized, controlled trials are currently underway to confirm these findings. Anti-TNF treatment of endoscopic lesions that occur after surgery seems to be less effective than using TNF antagonists to prevent recurrence. However, although the data are limited, this treatment strategy seems to be still superior to all the other prevention strategies that are not based on anti-TNF agents. Limited data are available on long-term outcomes of patients treated with anti-TNF agents after surgery. They suggest that these medications are safe and effective after many years of treatment. In addition, these agents might prevent recurrence even at doses lower than those used in patients with Crohn's disease who have not had surgery. © 2013 Macmillan Publishers Limited. All rights reserved.

Hong Y.,Virginia Polytechnic Institute and State University
Computational Statistics and Data Analysis | Year: 2013

The Poisson binomial distribution is the distribution of the sum of independent and non-identically distributed random indicators. Each indicator follows a Bernoulli distribution and the individual probabilities of success vary. When all success probabilities are equal, the Poisson binomial distribution is a binomial distribution. The Poisson binomial distribution has many applications in different areas such as reliability, actuarial science, survey sampling, econometrics, etc. The computing of the cumulative distribution function (cdf) of the Poisson binomial distribution, however, is not straightforward. Approximation methods such as the Poisson approximation and normal approximations have been used in literature. Recursive formulae also have been used to compute the cdf in some areas. In this paper, we present a simple derivation for an exact formula with a closed-form expression for the cdf of the Poisson binomial distribution. The derivation uses the discrete Fourier transform of the characteristic function of the distribution. We develop an algorithm that efficiently implements the exact formula. Numerical studies were conducted to study the accuracy of the developed algorithm and approximation methods. We also studied the computational efficiency of different methods. The paper is concluded with a discussion on the use of different methods in practice and some suggestions for practitioners. © 2012 Elsevier B.V. All rights reserved.

Esen A.,Virginia Polytechnic Institute and State University
Cellular and Molecular Life Sciences | Year: 2010

β-Glucosidases ( are found in all domains of living organisms, where they play essential roles in the removal of nonreducing terminal glucosyl residues from saccharides and glycosides. β-Glucosidases function in glycolipid and exogenous glycoside metabolism in animals, defense, cell wall lignification, cell wall β-glucan turnover, phytohormone activation, and release of aromatic compounds in plants, and biomass conversion in microorganisms. These functions lead to many agricultural and industrial applications. β-Glucosidases have been classified into glycoside hydrolase (GH) families GH1, GH3, GH5, GH9, and GH30, based on their amino acid sequences, while other β-glucosidases remain to be classified. The GH1, GH5, and GH30 β-glucosidases fall in GH Clan A, which consists of proteins with (β/α)8-barrel structures. In contrast, the active site of GH3 enzymes comprises two domains, while GH9 enzymes have (α/α) 6 barrel structures. The mechanism by which GH1 enzymes recognize and hydrolyze substrates with different specificities remains an area of intense study. © Springer Basel AG 2010.

Johri A.,Virginia Polytechnic Institute and State University
Information and Software Technology | Year: 2011

Context: Studies on global software development have documented severe coordination and communication problems among coworkers due to geographic dispersion and consequent dependency on technology. These problems are exacerbated by increase in the complexity of work undertaken by global teams. However, despite these problems, global software development is on the rise and firms are adopting global practices across the board, raising the question: What does successful global software development look like and what can we learn from its practitioners? Objective: This study draws on practice-based studies of work to examine successful work practices of global software developers. The primary aim of this study was to understand how workers develop practices that allow them to function effectively across geographically dispersed locations. Method: An ethnographically-informed field study was conducted with data collection at two international locations of a firm. Interview, observation and archival data were collected. A total of 42 interviews and 3 weeks of observations were conducted. Results: Teams spread across different locations around the world developed work practices through sociomaterial bricolage. Two facets of technology use were necessary for the creation of these practices: multiplicity of media and relational personalization at dyadic and team levels. New practices were triggered by the need to achieve a work-life balance, which was disturbed by global development. Reflecting on my role as a researcher, I underscore the importance of understanding researchers' own frames of reference and using research practices that mirror informants' work practices. Conclusion: Software developers on global teams face unique challenges which necessitate a shift in their work practices. Successful teams are able to create practices that span locations while still being tied to location based practices. Inventive use of material and social resources is central to the creation of these practices. © 2011 Elsevier B.V. All rights reserved.

Hirsh R.F.,Virginia Polytechnic Institute and State University
Technology and Culture | Year: 2011

Despite widespread acceptance of the notion that studies of the past provide tangible benefits, academic historians usually remain reluctant to apply "lessons" from history to the realms of public and business policy. This article suggests reasons for that reluctance while also suggesting that historians of technology can make valuable contributions to the policy community. In particular, these professionals can employ tools and insights developed in their field to highlight the social contexts in which technology evolves, helping decision makers understand why specific policies may or may not accomplish stated goals. The article also suggests means by which historians can influence policy, such as through their teaching, their writing and speaking to lay ! audiences, and their direct participation in government bodies. Due to institutional disincentives for this nontraditional activity, however, historians interested in policy work should already have acquired secure, tenured positions within their academic institutions. © 2011 by the Society for the History of Technology. All rights reserved.

Barbeau W.E.,Virginia Polytechnic Institute and State University
Autoimmunity Reviews | Year: 2012

Prevention and treatment of type 1 diabetes is hampered by the fact that the key environmental trigger(s) of the disease is still unknown. Much of the data on this subject points to two possibilities, viruses and wheat gluten. Viruses appear to be involved as an etiological agent in some cases of type 1 diabetes, particularly in fulminant type 1 diabetes. Further analysis of the data suggests that viruses are not the sole trigger of type 1 diabetes in humans, and that wheat gluten may play a role in initiating the disease. Viruses may be the key environmental trigger in some cases of type 1 diabetes, and wheat gluten in others. Conceivably, some cases of type 1 diabetes might be caused by viruses and wheat gluten acting together as disease triggers. © 2012 Elsevier B.V.

Chen F.,University of Tennessee at Knoxville | Tholl D.,Virginia Polytechnic Institute and State University | Bohlmann J.,University of British Columbia | Pichersky E.,University of Michigan
Plant Journal | Year: 2011

Some plant terpenes such as sterols and carotenes are part of primary metabolism and found essentially in all plants. However, the majority of the terpenes found in plants are classified as 'secondary' compounds, those chemicals whose synthesis has evolved in plants as a result of selection for increased fitness via better adaptation to the local ecological niche of each species. Thousands of such terpenes have been found in the plant kingdom, but each species is capable of synthesizing only a small fraction of this total. In plants, a family of terpene synthases (TPSs) is responsible for the synthesis of the various terpene molecules from two isomeric 5-carbon precursor 'building blocks', leading to 5-carbon isoprene, 10-carbon monoterpenes, 15-carbon sesquiterpenes and 20-carbon diterpenes. The bryophyte Physcomitrella patens has a single TPS gene, copalyl synthase/kaurene synthase (CPS/KS), encoding a bifunctional enzyme producing ent-kaurene, which is a precursor of gibberellins. The genome of the lycophyte Selaginella moellendorffii contains 18 TPS genes, and the genomes of some model angiosperms and gymnosperms contain 40-152 TPS genes, not all of them functional and most of the functional ones having lost activity in either the CPS- or KS-type domains. TPS genes are generally divided into seven clades, with some plant lineages having a majority of their TPS genes in one or two clades, indicating lineage-specific expansion of specific types of genes. Evolutionary plasticity is evident in the TPS family, with closely related enzymes differing in their product profiles, subcellular localization, or the in planta substrates they use. © 2011 The Authors.

Huber P.,Virginia Polytechnic Institute and State University
Physical Review C - Nuclear Physics | Year: 2011

In this paper we study the effect of well-known higher-order corrections to the allowed β-decay spectrum on the determination of antineutrino spectra resulting from the decays of fission fragments. In particular, we try to estimate the associated theory errors and find that induced currents like weak magnetism may ultimately limit our ability to improve the current accuracy and under certain circumstance could even greatly increase the theoretical errors. We also perform a critical evaluation of the errors associated with our method to extract the antineutrino spectrum using synthetic β spectra. It turns out that a fit using only virtual β branches with a judicious choice of the effective nuclear charge provides results with a minimal bias. We apply this method to actual data for 235U, 239Pu, and 241Pu and confirm, within errors, recent results, which indicate a net 3% upward shift in energy-averaged antineutrino fluxes. However, we also find significant shape differences which can, in principle, be tested by high-statistics antineutrino data samples. © 2011 American Physical Society.

Distler J.,University of Texas at Austin | Sharpe E.,Virginia Polytechnic Institute and State University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2011

In this short article we discuss quantization of the Fayet-Iliopoulos parameter in supergravity theories. We argue that, in supergravity, the Fayet-Iliopoulos parameter determines a lift of the group action to a line bundle, and such lifts are quantized. Just as D-terms in rigid N = 1 supersymmetry are interpreted in terms of moment maps and symplectic reductions, we argue that in supergravity the quantization of the Fayet-Iliopoulos parameter has a natural understanding in terms of linearizations in geometric invariant theory quotients, the algebro-geometric version of symplectic quotients. © 2011 American Physical Society.

Moskal J.T.,Virginia Polytechnic Institute and State University
Orthopedics | Year: 2011

In general, the literature makes numerous positive claims regarding the direct anterior approach with a fracture table for total hip arthroplasty (THA), including quicker recovery and return to unassisted ambulation, along with reduced soft tissue damage, surgery time, pain, and risk of dislocation with early elimination of hip precautions. The benefits of the direct anterior approach are mostly due from muscle preservation rather than muscle splitting, which occurs with the more traditional approaches. With the use of the muscle-preserving direct anterior approach for THA, there is less muscle damage and earlier return to function, and postoperative precautions are not needed. The most significant improvements in THA have been allowing patients to be immediately weight bearing as tolerated after THA, incorporating a multimodal pain management protocol, and now using the direct anterior approach. There is a learning curve, and I strongly recommend that people attend cadaver-based learning centers as well as surgeon visitations. We must always remember the oath we took to "do no harm," especially when embarking on a new procedure such as the direct anterior approach in THA or any other new procedure or technology. My position in the debate is not whether we should embrace this technique or other new techniques, but rather how they should be introduced.

Setareh M.,Virginia Polytechnic Institute and State University
Journal of Performance of Constructed Facilities | Year: 2010

Buildings with large column-free floors or long-cantilevered structures can be susceptible to annoying vibrations due to everyday occupants' activities such as walking. Computer modeling and analytical representation of building structural properties to predict the floor response subjected to excitations due to human activities are important issues that require further studies. Vibration testing and analysis of built structures can assist in more accurate estimation of structure dynamic properties. This paper presents the results of the modal testing conducted on an office building floor and analysis of the collected vibration measurements. It compares these results with the structural response using computer analyses. It also presents a sensitivity study to assess the importance of various structural parameters on the floor dynamic response. From the results presented, it is concluded that for the structure used in this study the raised flooring and nonstructural elements acted mainly as added mass and did not contribute to the floor damping. Conclusions are also made on the importance of various structural parameters on floor response and the analysis of the modal test results. © 2010 ASCE.

Setareh M.,Virginia Polytechnic Institute and State University
Journal of Performance of Constructed Facilities | Year: 2010

People are generally very sensitive to unexpected vibrations. Very small levels of building floor movements due to activities such as walking can become annoying to occupants. Accurate prediction, evaluation, and assessment of vibrations can greatly assist engineers and architects to design cost-effective building structures without such problems. In an attempt to clarify some of the issues related to this common serviceability problem, this paper presents a study of the various parameters used for the evaluation and assessment of building vibrations. Provisions of several current standards and design guides commonly used in North America and U.K. to evaluate and assess building vibrations as related to human perception and comfort are reviewed. These provisions are then applied using the vibrations measured during a number of walking tests conducted on a large cantilevered office building floor. Based on the results of this study, it is concluded that the vibration dose value (VDV) recommended by some standards and design guides provides a consistent and reasonable method of evaluation of building floor vibrations. In addition, new relationships between VDV, peak frequency-weighted acceleration, and crest factor are established to estimate the VDV. © 2010 ASCE.

Kong L.,Virginia Polytechnic Institute and State University
International Journal of Quantum Chemistry | Year: 2011

Cumulants are usually interpreted as the connected components of density matrices, but this interpretation fails and practical problems arise when the rank n of cumulants is larger than the number of particles (N) in the system. In that case, cumulants defined in the traditional way become disconnected. To solve this problem, the definition of cumulants is extended by introducing a simple modulation factor. The modified cumulants reduce to the conventional definition, but they vanish when N < n. Using the modified definition also eliminates the error in the approximation of density matrices by low-rank cumulants, when N < n. The problem assumes a slightly different form when we work with active space-based theories, and it can be solved by a similar approach. Another problem with cumulants, due to spin coupling [Herbert, Int J Quantum Chem 2007, 107, 703], can be solved via the introduction of a similar modulation factor. A related yet more serious issue, termed as the local particle number constraint problem, is also discussed. © 2010 Wiley Periodicals, Inc.

Simons-Morton B.G.,Virginia Polytechnic Institute and State University
The Journal of adolescent health : official publication of the Society for Adolescent Medicine | Year: 2014

PURPOSE: Secondary task engagement that distracts the driver is a contributing factor to motor vehicle crashes among adults. However, the association between eye glance duration and crash risk with novice teenage drivers has not been determined.METHODS: Vehicles of 42 newly licensed teenage drivers were instrumented with cameras, accelerometers, Global Positioning System(s) (GPS), and other devices. Data were collected continuously for 18 months. Crashes and near crashes (CNCs) were identified by examining highly elevated gravitational force events. Video footage of the 6 seconds prior to each CNC and randomly sampled non-CNC road segments were coded for the duration of eye glances off the forward roadway and the presence of secondary task engagement. The likelihood (odds ratios) of CNC due to eye glance behavior was calculated by comparing the prevalence of secondary task engagement and duration of eyes off road prior to CNC with the prevalence and duration of eyes off road during non-CNC road segments.RESULTS: Crash risk increased with the duration of single longest glance during all secondary tasks (OR=3.8 for >2 s) and wireless secondary task engagement (OR=5.5 for >2 s). Single longest glance provided a more consistent estimate of crash risk than total time eyes off the forward roadway.CONCLUSIONS: Those eye glances away from the forward roadway involving secondary tasks increased the likelihood of CNC. The longer the duration of eye glance away from the road the greater the risk, regardless of type of secondary task. Education and policy discouraging secondary task engagement, particularly for prolonged periods, is warranted. Copyright © 2014 Society for Adolescent Health and Medicine. All rights reserved.

Harne R.L.,Virginia Polytechnic Institute and State University
Smart Materials and Structures | Year: 2012

Fundamental studies in vibrational energy harvesting consider the electromechanically coupled devices to be excited by uniform base vibration. Since many harvester devices are massspring systems, there is a clear opportunity to exploit the mechanical resonance in a fashion identical to tuned mass dampers to simultaneously suppress the vibration of the host structure via reactive forces while converting the absorbed vibration into electrical power. This paper presents a general analytical model for the coupled electro-elastic dynamics of a vibrating panel to which distributed energy harvesting devices are attached. One such device is described which employs a corrugated piezoelectric spring layer. The model is validated by comparison to measured elastic and electric frequency response functions. Tests on an excited panel show that the device, contributing 1% additional mass to the structure, concurrently attenuates the lowest panel mode accelerance by >20dB while generating 0.441νW for a panel drive acceleration of 3.29ms 2. Adjustment of the load resistance connected to the piezoelectric spring layer verifies the analogy between the present harvester device and an electromechanically stiffened and damped vibration absorber. The results show that maximum vibration suppression and energy harvesting objectives occur for nearly the same load resistance in the harvester circuit. © 2012 IOP Publishing Ltd.

Falkinham J.O.,Virginia Polytechnic Institute and State University
Annals of the American Thoracic Society | Year: 2013

In light of the increasing prevalence of Mycobacterium avium pulmonary disease and the challenges of treating patients with M. avium infection, consideration of measures to reduce exposure is warranted. Because M. avium inhabits water and soil, humans are surrounded by that opportunistic pathogen. Because infection has been linked to the presence of M. avium in household plumbing, increasing hot water temperature, reducing aerosol (mist) exposures in bathrooms and showers, and installing filters that prevent the passage of mycobacteria will likely reduce M. avium exposure. Granular activated carbon (charcoal) filters support the growth of M. avium and should be avoided. When gardening, avoid the inhalation of soil dusts by using a mask or wetting the soil because peat-rich potting soils have high numbers of mycobacteria. © 2013 by the American Thoracic Society.

Chou T.,University of California at Los Angeles | Mallick K.,CEA Saclay Nuclear Research Center | Zia R.K.P.,Virginia Polytechnic Institute and State University
Reports on Progress in Physics | Year: 2011

Unlike equilibrium statistical mechanics, with its well-established foundations, a similar widely accepted framework for non-equilibrium statistical mechanics (NESM) remains elusive. Here, we review some of the many recent activities on NESM, focusing on some of the fundamental issues and general aspects. Using the language of stochastic Markov processes, we emphasize general properties of the evolution of configurational probabilities, as described by master equations. Of particular interest are systems in which the dynamics violates detailed balance, since such systems serve to model a wide variety of phenomena in nature. We next review two distinct approaches for investigating such problems. One approach focuses on models sufficiently simple to allow us to find exact, analytic, non-trivial results. We provide detailed mathematical analyses of a one-dimensional continuous-time lattice gas, the totally asymmetric exclusion process. It is regarded as a paradigmatic model for NESM, much like the role the Ising model played for equilibrium statistical mechanics. It is also the starting point for the second approach, which attempts to include more realistic ingredients in order to be more applicable to systems in nature. Restricting ourselves to the area of biophysics and cellular biology, we review a number of models that are relevant for transport phenomena. Successes and limitations of these simple models are also highlighted. © 2011 IOP Publishing Ltd.

Williams J.H.,Virginia Polytechnic Institute and State University
Scandinavian Journal of Medicine and Science in Sports | Year: 2010

This investigation sought to determine if a relative age effect exists in the FIFA U17 World Cup competition. Birthdates of players competing in the most recent six competitions, from 1997 to 2007 were examined. For all competitions, the distributions of birth months were significantly different than expected with more players born in the early months of the year compared with the later months. For the entire cohort of players, 40% were born in the first quarter of the year while only 16% were born in the last 3 months. A small portion of this effect seems to be due to physical stature of the players. This relative age effect held for all FIFA-designated geographical zones except for Africa. The African region displayed a reverse relative age effect with a relatively large portion of players born in the later part of the year, particularly in December of the age appropriate year. The results of this investigation show that at the highest level of youth soccer, there is a strong bias toward inclusion of players born early in the selection year. © 2009 John Wiley & Sons A/S.

Jarrett M.A.,University of Alabama | Ollendick T.H.,Virginia Polytechnic Institute and State University
Journal of Consulting and Clinical Psychology | Year: 2012

Objective: The present study evaluated a 10-week psychosocial treatment designed specifically for children with attention-deficit/hyperactivity disorder (ADHD) and a comorbid anxiety disorder. Method: Using a nonconcurrent multiple baseline design, the authors treated 8 children ages 8-12 with ADHD, combined type, and at least 1 of 3 major anxiety disorders (separation anxiety disorder, generalized anxiety disorder, social phobia). The integrated treatment protocol involved parent management training for ADHD and family-based cognitive-behavioral therapy for anxiety. Pretreatment assessments included semistructured diagnostic interviews and other standardized measures to determine study eligibility. Children were randomized to 1 of 3 baseline control conditions (i.e., 2, 3, or 4 weeks) and subsequently treated in a university-based psychosocial treatment clinic. Weekly assessments of ADHD and anxiety disorder symptoms occurred throughout treatment and comprehensive assessments were obtained at pretreatment, 1-week posttreatment, and 6-months posttreatment. Results: Single-case results supported greater success in the treatment phase relative to the baseline phase for both ADHD and anxiety symptoms, and ADHD and anxiety symptoms appeared to change concurrently. Pre-post group analyses revealed significant and clinically meaningful improvements in ADHD and anxiety symptoms at 1-week posttreatment, but only anxiety symptoms moved into the subclinical range. At 6-months follow-up, treatment effects were maintained with new movement into the subclinical range for ADHD. Conclusions: The present study provides initial data on an integrated treatment protocol for ADHD and anxiety. Further replication and evaluation are needed. Implications of the findings are discussed. © 2012 American Psychological Association.

Yuan A.S.V.,Virginia Polytechnic Institute and State University
Journal of Youth and Adolescence | Year: 2010

This study used the National Longitudinal Study of Adolescent Health to explore gender differences in the relationship between body perceptions and behavior and changes in adolescents' psychological well-being over a one-year time period. The sample included 12,814 adolescents (51% girls) aged 11-20 comprised of 68% Non-Hispanic White, 15% African American, 12% Hispanic, and 4% Asian. Perceptions of being larger or more developed generally decreased girls' psychological well-being over time. Body perceptions and behavior did not significantly influence changes in boys' psychological well-being over time. Non-Hispanic White girls were the most influenced and Non-Hispanic White boys were the least influenced by body perceptions and behavior. Perceived relative development influenced early adolescent girls, whereas perceptions of being overweight influenced middle to late adolescent girls. Additionally, trying to lose weight influenced middle adolescent boys and girls. These results imply that body perceptions and behavior disadvantage girls' psychological well-being relative to boys during adolescence. © 2009 Springer Science+Business Media, LLC.

Jain E.,Indian Institute of Technology Kanpur | Jain E.,Virginia Polytechnic Institute and State University | Kumar A.,Indian Institute of Technology Kanpur
Nature Protocols | Year: 2013

Low cost and high efficiency make disposable bioreactors feasible for small-scale therapeutic development and initial clinical trials. We have developed a cryogel-based disposable bioreactor matrix, which has been used for production of protein therapeutics such as urokinase and monoclonal antibodies (mAbs). The protocol discusses the application of a cryogel bioreactor for mAb production. Cryogels composed of either polyacrylamide (PAAm) coupled to gelatin or semi-interpenetrating PAAm-chitosan are synthesized by free-radical polymerization at -12C. Hybridoma cells are immobilized over the cryogel bioreactor and incubated for 48 h. Medium is circulated thereafter at 0.2 ml min -1 and bioreactors can be run continuously for 60 d. The cryogel-based packed-bed bioreactor can be formulated as a monolith or as beads; it also has an efficiency four times what can be obtained using a tissue-culture flask, a high surface-to-volume ratio and effective nutrient transport. After incubation, the bioreactor setup will take about 60 min using a pre-prepared sterilized cryogel. © 2013 Nature America, Inc. All rights reserved.

Jelesko J.G.,Virginia Polytechnic Institute and State University
Frontiers in Plant Science | Year: 2012

For the past decade, our understanding of the plant purine uptake permease (PUP) transporter family was primarily oriented on purine nucleobase substrates and their tissue-specific expression patterns in Arabidopsis. However, a tobacco PUP-like homolog demonstrating nicotine uptake permease activity was recently shown to affect both nicotine metabolism and root cell growth. These new findings expand the physiological role for PUP-like transporters to include plant secondary metabolism. Molecular evolution analyses of PUP-like transporters indicate they are distinct group within an ancient super family of drug and metabolite transporters (DMTs). The PUP-like family originated during terrestrial plant evolution sometime between the bryophytes and the lycophytes. A phylogenetic analysis indicates that the PUP-like transporters were likely derived from a pre-existing nucleotide-sugar transporter family within the DMT super family. Within the lycophyte Selaginella, there are three paralogous groups of PUP-like transporters. One of the three PUP-like paralogous groups showed an extensive pattern of gene duplication and diversification within the angiosperm lineage, whereas the more ancestral PUP-like paralogous groups did not. Biochemical characterization of four closely related PUP-like paralogs together with model-based phylogenetic analyses indicate both subfunctionalization and neofunctionalization during the molecular evolution of angiosperm PUP-like transporters. These findings suggest that members of the PUP-like family of DMT transporters are likely involved in diverse primary and secondary plant metabolic pathways. © 2012 Jelesko.

Troya D.,Virginia Polytechnic Institute and State University
Theoretical Chemistry Accounts | Year: 2012

We present a classical trajectory study of the dynamics of collisions between OH radicals and fluorinated self-assembled monolayers (F-SAMs). The gas/surface interaction potential required in the simulations has been derived from high-level ab initio calculations (focal-point-CCSD(T)/aug-cc-pVQZ) of various approaches of OH to a model fluorinated alkane. The two lowest-energy doublet potential energy surfaces considered in the electronic structure calculations have been averaged to produce a pairwise analytic potential. This analytic potential has been subsequently employed to propagate classical trajectories of collisions between OH and F-SAMs at initial conditions relevant to recent experiments on related systems. The calculated rotational distributions of the inelastically scattered OH agree well with the experiment, which serves to validate the accuracy of the simulations. Investigation of the dynamics of energy transfer for different initial rotational states of OH indicates that an increase in the initial rotation of OH results in increases in both the final average OH rotational and translational energy and in a slight decrease in the amount of energy transferred to the surface. Analysis of the dynamics as a function of the desorption angle of OH from the surface shows that while there is a correlation between the final scattering angle and OH's amount of final translational energy, the amount of rotational energy in OH is largely independent of the desorption angle. The mechanism of the collisions is found to be mostly direct; in about 90% of most trajectories, OH only collides with the surface once before desorbing, which exemplifies the rigidity of fluorinated monolayer surfaces and their inability to efficiently accommodate gas species. © 2012 Springer-Verlag.

Belanger F.,Virginia Polytechnic Institute and State University | Carter L.,North Carolina A&T State University
Journal of the Association of Information Systems | Year: 2012

As information and communication technologies began to support new forms of interaction between governments and their constituents, the concept of e-government emerged as a new domain for Information Systems (IS) researchers. The past decade has seen a variety of e-government themes researched and presented by scholars in IS, public administration, and political science. In order to reflect on the history of the IS discipline, this article provides an historical assessment of electronic government research. In particular, we review highly cited e-government articles and e-government articles published in the AIS Senior Scholars' basket of journals to assess existing publication outlets, theoretical foundations, methodological approaches, sampling, and topic areas. The analysis of the literature reveals significant insights about the metamorphosis of e-government research over time, the assessment of which serves as a basis for recommendations for future research on this global phenomenon.

Weiss R.,Virginia Polytechnic Institute and State University
Marine Geology | Year: 2012

Boulders are moved differently in storm and tsunami and produce different characteristics of the boulder deposits. This contribution is motivated by two observations. One by Bourgeois and MacInnes (2010), which described that boulders were moved selectively due to different bed roughness during 15 November 2006 tsunami on the island of Matua. The second topic is motivated by the boulder lines on Ishigaki Island by Goto et al. (2010). Both topics are approached with linear wave theory and stability analysis. From both, the safety factor is derived for a spherical boulder with bed roughness and exposure as moment arms, with which we are able to quantify the influence of bed roughness on the incipient motion of boulders. For constant forces, a bed roughness of about 30% of the boulder radius will prevent boulder transport. Furthermore, the comparison between storm and tsunami waves in terms of the amplitude necessary to move boulders revealed that amplitude of storm waves is smaller than tsunami, which we ascribe to the contribution of both velocity components to lift forces. The comparison of total energy and number of waves revealed that storms have a larger total energy and a much larger number of waves, which lead us to the conclusion that tsunamis produce unorganized boulder deposits; whereas, storms are capable of organizing boulders along lines and in clusters. © 2012 Elsevier B.V.

This paper reports on the foaming of poly(ε-caprolactone-co-lactide) in carbon dioxide and carbon dioxide + acetone mixtures. Experiments were carried out in specially designed molds with porous metal surfaces and fluid circulation features to generate foams with uniform dimensions at 60, 70 and 80 °C at pressures in the range 7-28 MPa. Depending upon the conditions, foams with pores in the range from 5 to 200 μm were generated. Adding acetone to carbon dioxide improved the uniformity of the pores compared to foams formed by carbon dioxide alone. In addition, a unique high-pressure solution extrusion system was designed and used to form porous tubular constructs by piston-extrusion of a solution from a high-pressure dissolution chamber through an annular die into a second chamber maintained at controlled pressure/temperature and fluid conditions. Long uniform porous tubular constructs with 6 mm ID and 1 mm wall thickness were generated with glassy polymers like poly(methyl methacrylate) by extruding solutions composed of 50 wt% polymer + 50 wt% acetone, or 25 wt% polymer + 10% acetone + 65% carbon dioxide at 70 °C and 28 MPa. Pores were in the 50 μm range. The feasibility of forming similar tubular constructs were demonstrated with poly(ε-caprolactone-co-lactide) as well. Tubular foams of the copolymer with interconnected pores with pore sizes in the 50 μm range were generated by extrusion of the copolymer solution composed of 25 wt% polymer + 10 wt% acetone + 65 wt% carbon dioxide at 70 °C and 28 MPa. Reducing the acetone content in the solution led to a reduction of pore sizes. Comparisons with the foaming behavior of the homopolymer poly(ε-caprolactone) that were carried out in the molds with porous metal plates show that the foaming behavior of the copolymer is more akin to the foaming behavior of the caprolactone homopolymer component. © 2010 Elsevier B.V.

Mcdonald S.M.,Virginia Polytechnic Institute and State University
Wiley Interdisciplinary Reviews: RNA | Year: 2013

RNA viruses are ubiquitous in nature, infecting every known organism on the planet. These viruses can also be notorious human pathogens with significant medical and economic burdens. Central to the lifecycle of an RNA virus is the synthesis of new RNA molecules, a process that is mediated by specialized virally encoded enzymes called RNA-dependent RNA polymerases (RdRps). RdRps directly catalyze phosphodiester bond formation between nucleoside triphosphates in an RNA-templated manner. These enzymes are strikingly conserved in their structural and functional features, even among diverse RNA viruses belonging to different families. During host cell infection, the activities of viral RdRps are often regulated by viral cofactor proteins. Cofactors can modulate the type and timing of RNA synthesis by directly engaging the RdRp and/or by indirectly affecting its capacity to recognize template RNA. High-resolution structures of RdRps as apoenzymes, bound to RNA templates, in the midst of catalysis, and/or interacting with regulatory cofactor proteins, have dramatically increased our understanding of viral RNA synthetic mechanisms. Combined with elegant biochemical studies, such structures are providing a scientific platform for the rational design of antiviral agents aimed at preventing and treating RNA virus-induced diseases. © 2013 John Wiley & Sons, Ltd.

Miscibility and foaming of poly(l-lactic acid) (PLLA) in carbon dioxide + acetone mixtures have been explored over the temperature and pressure ranges from 60 to 180 °C and 14 to 61 MPa. Liquid-liquid phase boundaries were determined in a variable-volume view-cell for polymer concentrations up to 25 wt% PLLA and fluid mixtures containing 67-93 wt% CO2 over a temperature range from 60 to 180 °C. Even though not soluble in carbon dioxide at pressures tested, the polymer could be completely solubilized in mixtures of carbon dioxide and acetone at modest pressures. Foaming experiments were carried out in different modes. Free-expansions were carried out by exposure and swelling in pure carbon dioxide in a view-cell followed by depressurization. Foaming experiments were also carried out within the confinement of specially designed molds with porous metal surfaces as boundaries to direct the fluid escape path and to generate foams with controlled overall shape and dimensions. These experiments were conducted in pure carbon dioxide and also in carbon dioxide + acetone fluid mixtures over a wide range of temperatures and pressures. Foaming in carbon dioxide + acetone mixtures was limited to 1 and 4 wt% acetone cases. Microstructures were examined using an environmental scanning electron microscope (ESEM). Depending upon the conditions employed, pore diameters ranging from 5 to 400 μm were generated. At a given temperature, smaller pores were promoted when foaming was carried out by depressurization from higher pressures. At a given pressure, smaller pores were generated from expansions at lower temperatures. Foams with larger pores were produced in mixtures of carbon dioxide with acetone. © 2010 Elsevier B.V.

Angel R.J.,Virginia Polytechnic Institute and State University | Finger L.W.,Carnegie Institution of Washington
Journal of Applied Crystallography | Year: 2011

SINGLE, a program that runs under Windows operating systems, can be used to control a variety of four-circle Eulerian-cradle single-crystal diffractometers including Huber instruments equipped with Huber motor controllers, the Stoe Stadi-4 and the Siemens P4. The software can be configured, via variables set by the user, to operate any of these diffractometers with a variety of environmental devices including furnaces and diamond-anvil pressure cells. It is specifically designed to determine unit-cell parameters to a precision of 1 part in 30 000. © 2011 International Union of Crystallography Printed in Singapore-all rights reserved.

Trkman P.,University of Ljubljana | Desouza K.C.,Virginia Polytechnic Institute and State University
Journal of Strategic Information Systems | Year: 2012

In a networked environment, it is essential for organizations to share knowledge among themselves if they want to achieve the global objectives such as collaborative innovation and increased effectiveness and efficiency of operations. However, sharing knowledge is not risk-free. An organization might lose its competitive edge if it shares too much or certain key knowledge. In addition, an organization might suffer if its intellectual property is improperly handled by its business partners. While the literature has touted the value of knowledge sharing within networks, there is a conspicuous absence of studies examining the risks of sharing knowledge. To address this gap, we develop an exploratory framework that categorizes knowledge-sharing risks across multiple dimensions. Such a framework is a structured approach to knowledge risk management and complements the practice-based approach to knowledge risk management that is presented in (Marabelli and Newell, this issue). Our framework outlines the various kinds of knowledge risks that organizations are facing. We use a combination of knowledge-based and transaction cost theories to show how knowledge risk impacts knowledge transfer among entities in the network, the whole network, and the risk mitigation options. © 2011 Elsevier B.V. All rights reserved.

Reynolds Jr. M.R.,Virginia Polytechnic Institute and State University
Quality and Reliability Engineering International | Year: 2013

This article considers the Bernoulli CUSUM chart for detecting a decrease in the proportion p of nonconforming items when a continuous stream of Bernoulli observations from the process is available. The properties of the Bernoulli CUSUM chart can be obtained using a Markov chain model. However, in some cases, the number of transient states in the Markov chain may be so large that it is not feasible to work directly with the transition matrix. This article provides a solution to the equations used in defining the Markov chain so that properties of the chart can be obtained without explicitly using the transition matrix. This solution allows the practitioner to determine the control limit required to give a specified in-control performance. A simple example is used to show that using the Bernoulli CUSUM chart is a better option than the standard practice of artificially grouping the observations into samples of size n > 1 and using a Shewhart chart. Copyright © 2012 John Wiley & Sons, Ltd.

Diaz A.,La Sierra University | Wang X.,Virginia Polytechnic Institute and State University
Current Opinion in Virology | Year: 2014

With its high yield, small genome, and ability to replicate in the yeast Saccharomyces cerevisiae, Brome mosaic virus (BMV) has served as a productive model to study the general features of positive-strand RNA virus infection. BMV RNA is replicated in spherules, vesicle-like invaginations of the outer perinuclear endoplasmic reticulum membrane that remain connected to the cytoplasm via a neck-like opening. Each spherule contains the viral replicase proteins as well as genomic RNAs. Recent advances indicate that multiple interactions between the viral proteins with themselves, cellular membranes, and host factors play crucial roles in BMV-mediated spherule formation. These findings are probably applicable to other positive-strand RNA viruses and might potentially provide new targets for antiviral treatments.

Hennigan K.,Stanford University | D'Ardenne K.,Virginia Polytechnic Institute and State University | McClure S.M.,Stanford University
Journal of Neuroscience | Year: 2015

Emerging evidence implicates the midbrain dopamine system and its interactions with the lateral habenula in processing aversive information and learning to avoid negative outcomes. We examined neural responses to unexpected, aversive events using methods specialized for imaging the midbrain and habenula in humans. Robust activation to aversive relative to neutral events was observed in the habenula and two regions within the ventral midbrain: one located within the ventral tegmental area (VTA) and the other in the substantia nigra (SN). Aversive processing increased functional connectivity between the VTA and the habenula, putamen, and medial prefrontal cortex, whereas the SN exhibited a different pattern of functional connectivity. Our findings provide evidence for a network comprising the VTA and SN, the habenula, and mesocorticolimbic structures that supports processing aversive events in humans. © 2015 the authors.

Dillenbourg P.,Ecole Polytechnique Federale de Lausanne | Evans M.,Virginia Polytechnic Institute and State University
International Journal of Computer-Supported Collaborative Learning | Year: 2011

Interactive tabletops are gaining increased attention from CSCL researchers. This paper analyses the relation between this technology and teaching and learning processes. At a global level, one could argue that tabletops convey a socio-constructivist flavor: they support small teams that solve problems by exploring multiple solutions. The development of tabletop applications also witnesses the growing importance of face-to-face collaboration in CSCL and acknowledges the physicality of learning. However, this global analysis is insufficient. To analyze the educational potential of tabletops in education, we present 33 points that should be taken into consideration. These points are structured on four levels: individual user-system interaction, teamwork, classroom orchestration, and socio-cultural contexts. God lies in the details. © 2011 International Society of the Learning Sciences, Inc.; Springer Science + Business Media, LLC.

Bahel E.,Virginia Polytechnic Institute and State University
Journal of Environmental Economics and Management | Year: 2011

This paper studies the stockpiling issue for an oil importing country that is likely to suffer embargoes, the occurrence and duration of which are uncertain. I show the existence of a decreasing reserves path that the country wants to attain in order to hedge against these disruptions. Allowing the importing country to invest in R&D in order to free itself from the embargo threat, I determine the optimal effort that should be engaged in research. The incentive to develop a backstop is shown to increase with the depletion of the reserves. © 2011 Elsevier Inc.

Eatherton M.R.,Virginia Polytechnic Institute and State University | Hajjar J.F.,Northeastern University
Earthquake Spectra | Year: 2011

There has been widespread interest in the development and use of self-centering (SC)lateral resisting systems that eliminate residual drifts after large earthquakes. SC systems often include a restoring force component and a component that dissipates seismic energy. Typically, it is assumed that the criterion for self-centering is satisfied if the restoring force is proportioned to be greater than the force required to yield the energy dissipating component. A parametric SDOF study was conducted using time-history analyses on several prototype buildings to quantify the effect of varying system parameters on structural response including residual drifts. The ambient resistance of the rest of the building was considered, as well as proportioning the system with less restoring force than the yield capacity of the dissipative component. In addition, the probabilistic mechanismthat creates a propensity for reducing residual drifts in systems with little or no restoring force is explored and quantified. It was found that a restoring force that is at least one-half of the force required to yield the dissipative component will still reliablyeliminate residual drifts in a non-softening system. © 2011, Earthquake Engineering Research Institute.

Grove T.Z.,Virginia Polytechnic Institute and State University | Regan L.,Yale University
Current Opinion in Structural Biology | Year: 2012

In this review we highlight recent accomplishments in the design of materials from proteins and peptides. Examples include hydrogels made from aggregating designed β-hairpin peptides, whose physical properties respond to small changes in the amino acid composition of the peptide; materials that combine different segments of natural elastomeric proteins - such as elastin, resilin, silk fibroin whose bulk properties are dictated in unanticipated ways by their composition; and hydrogels formed by strings or arrays of protein modules, which are cross-linked by multivalent versions of their peptide ligands, and which may exhibit exquisite stimuli-responsive behavior. The suitability of the unique properties of such new materials for practical applications is also considered. © 2012 Elsevier Ltd.

Ullrich C.J.,Virginia Polytechnic Institute and State University
Energy Economics | Year: 2012

This paper uses high frequency spot price data from eight wholesale electricity markets in Australia, Canada, and the United States to estimate realized volatility and the frequency of price spikes. I find similar levels of realized volatility in Australia and North America, with estimates ranging from 1500% to 2700%, much greater than estimates reported previously in the literature. In hourly data, the frequency of price spikes ranges from approximately 35% to 40% in seven of eight markets. I present evidence that increasing the lag length in the calculation of bipower variation improves jump detection in electricity prices. © 2012 Elsevier B.V.

Socha J.J.,Virginia Polytechnic Institute and State University
Integrative and Comparative Biology | Year: 2011

Although many cylindrical animals swim through water, flying snakes of the genus Chrysopelea are the only limbless animals that glide through air. Despite a lack of limbs, these snakes can actively launch by jumping, maintain a stable glide path without obvious control surfaces, maneuver, and safely land without injury. Jumping takeoffs employ vertically looped kinematics that seem to be different than any other behavior in limbless vertebrates, and their presence in a closely related genus suggests that gap-crossing may have been a behavioral precursor to the evolution of gliding in snakes. Change in shape of the body by dorsoventral flattening and high-amplitude aerial undulation comprise two key features of snakes' gliding behavior. As the snake becomes airborne, the body flattens sequentially from head to vent, forming a cross-sectional shape that is roughly triangular, with a flat surface and lateral "lips" that protrude ventrally on each side of the body; these may diminish toward the vent. This shape likely provides the snake with lift coefficients that peak at high angles of attack and gentle stall characteristics. A glide trajectory is initiated with the snake falling at a steep angle. As the snake rotates in the pitch axis, it forms a wide "S" shape and begins undulating in a complex three-dimensional pattern, with the body angled upward relative to the glide path. The head moves side-to-side, sending traveling waves posteriorly toward the tail, while the body (most prominently, the posterior end) oscillates in the vertical axis. These active movements while gliding are substantially different and more dynamic than those used by any other animal glider. As the snake gains forward speed, the glide path becomes less steep, reaching minimally recorded glide angles of 13°. In general, smaller snakes appear to be more proficient gliders. Chrysopelea paradisi can also maneuver and land either on the ground or on vegetation, but these locomotor behaviors have not been studied in detail. Future work aims to understand the mechanisms of production and control of force in takeoff, gliding, and landing, and to identify the musculoskeletal adaptations that enable this unique form of locomotion. © The Author 2011. Published by Oxford University Press on behalf of the Society for Integrative and Comparative Biology. All rights reserved.

Tong Y.,University of Wisconsin - Milwaukee | He Z.,Virginia Polytechnic Institute and State University
Journal of Hazardous Materials | Year: 2013

This research aims to develop a new approach for in situ nitrate removal from groundwater by using a bioelectrochemical system (BES). The BES employs bioelectricity generated from organic compounds to drive nitrate moving from groundwater into the anode and reduces nitrate to nitrogen gas by heterotrophic denitrification. This laboratory study of a bench-scale BES demonstrated effective nitrate removal from both synthetic and actual groundwater. It was found that applying an electrical potential improved the nitrate removal and the highest nitrate removal rate of 208.2±13.3g NO3 --Nm-3d-1 was achieved at 0.8V. Although the open circuit condition (no electricity generation) still resulted in a nitrate removal rate of 158.5±4.2gm-3d-1 due to ion exchange, electricity production could inhibit ion exchange and prevent introducing other undesired ions into groundwater. The nitrate removal rate exhibited a linear relationship with the initial nitrate concentration in groundwater. The BES produced a higher current density of 33.4Am-3 and a higher total coulomb of 244.7±9.1C from the actual groundwater than the synthetic groundwater, likely because other ions in the actual groundwater promoted ion movement to assist electricity generation. Further development of this BES will need to address several key challenges in anode feeding solution, ion competition, and long-term stability. © 2013 Elsevier B.V.

Manteghi M.,Virginia Polytechnic Institute and State University
Microwave and Optical Technology Letters | Year: 2013

The electrically coupled loop antenna is presented as a dual for the existing planar inverted F antenna (PIFA).The basic drawbacks of the PIFA are low radiation efficiency and high electric field in the near zone. The dual antenna has high radiation efficiency and low electric field in the near zone that makes it a good candidate for cellphones and implanted antenna applications. The antenna is designed and simulated using HFSS and the results are compared with the measured data. Copyright © 2013 Wiley Periodicals, Inc.

Ross S.D.,Virginia Polytechnic Institute and State University
Chaos (Woodbury, N.Y.) | Year: 2010

Ridges in the state space distribution of finite-time Lyapunov exponents can be used to locate dynamical boundaries. We describe a method for obtaining dynamical boundaries using only trajectories reconstructed from time series, expanding on the current approach which requires a vector field in the phase space. We analyze problems in musculoskeletal biomechanics, considered as exemplars of a class of experimental systems that contain separatrix features. Particular focus is given to postural control and balance, considering both models and experimental data. Our success in determining the boundary between recovery and failure in human balance activities suggests this approach will provide new robust stability measures, as well as measures of fall risk, that currently are not available and may have benefits for the analysis and prevention of low back pain and falls leading to injury, both of which affect a significant portion of the population.

Rypel A.L.,Virginia Polytechnic Institute and State University
Canadian Journal of Fisheries and Aquatic Sciences | Year: 2012

Latitudinal growth compensation (i.e., countergradient growth) is increasingly suspected to be pervasive across diverse taxa. However, a major challenge limiting wider exploration of this topic lies in the difficulty of quantifying these relationships. Common garden experiments, and ideally genetics, remain the only true methods for understanding the genetic basis for compensatory growth. However, previous research suggests that comparative life-history data might produce concomitant, albeit nonconfirmatory, results on countergradient growth variations. However, there have been no evaluations of the precision of such estimates against those that are experimentally derived. I examined countergradient growth variations using comparative size-at-age data for striped bass (Morone saxatilis), a species for which experiments have already quantified countergradient growth patterns, and compared results derived from both techniques. The slope of the growth-latitude relationship for striped bass in eastern North America as measured with comparative data was virtually identical to that produced from experiments. Furthermore, comparative estimates of countergradient growth variations developed using a variety of metrics produced highly concordant results with one another. Comparative life-history data are not a replacement for experiments, but do provide valuable information on countergradient growth variations, especially for species and hypotheses not amenable to experimentation.

Tauber U.C.,Virginia Polytechnic Institute and State University | Diehl S.,University of Innsbruck | Diehl S.,Austrian Academy of Sciences
Physical Review X | Year: 2014

The universal critical behavior of the driven-dissipative nonequilibrium Bose-Einstein condensation transition is investigated employing the field-theoretical renormalization group method. Such criticality may be realized in broad ranges of driven open systems on the interface of quantum optics and many-body physics, from exciton-polariton condensates to cold atomic gases. The starting point is a noisy and dissipative Gross-Pitaevski equation corresponding to a complex-valued Landau-Ginzburg functional, which captures the near critical nonequilibrium dynamics, and generalizes model A for classical relaxational dynamics with nonconserved order parameter. We confirm and further develop the physical picture previously established by means of a functional renormalization group study of this system. Complementing this earlier numerical analysis, we analytically compute the static and dynamical critical exponents at the condensation transition to lowest nontrivial order in the dimensional ε expansion about the upper critical dimension dc = 4 and establish the emergence of a novel universal scaling exponent associated with the nonequilibrium drive.We also discuss the corresponding situation for a conserved order parameter field, i.e., (sub)diffusive model B with complex coefficients.

Lu K.,Virginia Polytechnic Institute and State University
Materials Science and Engineering R: Reports | Year: 2015

Silicon oxycarbide (SiOC)-based materials are a class of polymer-derived ceramics that enables the formation of a homogeneous structure at the molecular level starting from polymer precursors. In this system, oxygen and carbon atoms share bonds with silicon atoms in the amorphous network structure while elemental carbon, and possibly nanosized SiO2 and SiC nanodomains may co-exist. Because of the flexibility of molecular level composition and microstructure designs, the systems can be made porous with high specific surface areas by changing the precursor compositions and the ceramization conditions. In this review, two strategies of creating porous SiOCs are discussed: conventional approach of using fugitive fillers, as well as pore formation and selective removal of certain SiOC matrix compositions (such as carbon, SiO2, or SiC) at the molecular level. For the former, it includes ceramic replication of an organic template, direct foaming, and sacrificial pore formers. For the latter, it includes molecular level pore formation, molecular level species removal, and SiOC porous network creation through molecular templates. Direct pore formation can be achieved by changing processing conditions, using different precursor architectures, and using different hydrosilylation agents. For SiOC porous network creation through molecular level species removal, it includes molecular level free carbon removal, molecular level SiO2 nanocluster removal, and molecular level carbon removal from SiC (and possibly BCx for SiOBC). To understand single nanometer (<10 nm) pore formation and phase separation for selective species removal, SiOC nanostructure models and composition descriptions after the pyrolysis are explained. © 2015 Elsevier B.V. All rights reserved.

Although ambient temperature has diverse effects on disease dynamics, few studies have examined how temperature alters pathogen transmission by changing host physiology or behaviour. Here, we test whether reducing ambient temperature alters host foraging, pathology and the potential for fomite transmission of the bacterial pathogen Mycoplasma gallisepticum (MG), which causes seasonal outbreaks of severe conjunctivitis in house finches (Haemorhous mexicanus). We housed finches at temperatures within or below the thermoneutral zone to manipulate food intake by altering energetic requirements of thermoregulation. We predicted that pathogen deposition on bird feeders would increase with temperature-driven increases in food intake and with conjunctival pathology. As expected, housing birds below the thermoneutral zone increased food consumption. Despite this difference, pathogen deposition on feeders did not vary across temperature treatments. However, pathogen deposition increased with conjunctival pathology, independently of temperature and pathogen load, suggesting that MG could enhance its transmission by increasing virulence. Our results suggest that in this system, host physiological responses are more important for transmission potential than temperature-dependent alterations in feeding. Understanding such behavioural and physiological contributions to disease transmission is critical to linking individual responses to climate with population-level disease dynamics.

Hanauer D.A.,University of Michigan | Ramakrishnan N.,Virginia Polytechnic Institute and State University
Journal of the American Medical Informatics Association | Year: 2013

Objective We describe an approach for modeling temporal relationships in a large scale association analysis of electronic health record data. The addition of temporal information can inform hypothesis generation and help to explain the relationships. We applied this approach on a dataset containing 41.2 million timestamped International Classification of Diseases, Ninth Revision (ICD-9) codes from 1.6 million patients. Methods We performed two independent analyses including a pairwise association analysis using a Χ2 test and a temporal analysis using a binomial test. Data were visualized using network diagrams and reviewed for clinical significance. Results We found nearly 400 000 highly associated pairs of ICD-9 codes with varying numbers of strong temporal associations ranging from ≥1 day to ≥10 years apart. Most of the findings were not considered clinically novel, although some, such as an association between Helicobacter pylori infection and diabetes, have recently been reported in the literature. The temporal analysis in our large cohort, however, revealed that diabetes usually preceded the diagnoses of H pylori, raising questions about possible cause and effect. Discussion Such analyses have significant limitations, some of which are due to known problems with ICD-9 codes and others to potentially incomplete data even at a health system level. Nevertheless, large scale association analyses with temporal modeling can help provide a mechanism for novel discovery in support of hypothesis generation. Conclusions Temporal relationships can provide an additional layer of meaning in identifying and interpreting clinical associations.

Meng X.-J.,Virginia Polytechnic Institute and State University
Seminars in Liver Disease | Year: 2013

Hepatitis E is an important disease in many developing countries of Asia and Africa with large explosive outbreaks and is also endemic with sporadic or cluster cases of hepatitis in many industrialized countries. The causative agent, hepatitis E virus (HEV), is currently classified in the family Hepeviridae. Thus far, four putative genera of HEV representing mammalian, avian, and fish species have been identified and characterized worldwide. Within the mammalian HEV that infects humans, genotypes 1 and 2 are associated with epidemics and restricted to humans, whereas genotypes 3 and 4 are zoonotic and associated with sporadic and cluster cases of hepatitis E. As a fecal-orally transmitted disease, waterborne transmission is still an important route of HEV transmission especially for large outbreaks associated with genotypes 1 and 2. However, genetic identification of numerous animal strains of HEV and the demonstrated ability of cross-species infection by these animal strains have significantly broadened the host range and diversity of HEV and raised public health concerns for zoonosis and food safety associated with genotypes 3 and 4 HEV infection. Pigs and likely other animal species serve as reservoirs for HEV. Direct contact with infected pigs and other animals and consumption of contaminated animal meat and meat products pose risks for HEV infection. In this article, the current understanding of the zoonotic and foodborne transmissions of HEV as well as strategies to prevent zoonosis and ensure food safety is discussed. Copyright © 2013 by Thieme Medical Publishers, Inc.

Cameron K.W.,Virginia Polytechnic Institute and State University
Computer | Year: 2010

Green IT techniques can significantly reduce an organization's and ultimately a country's carbon footprint. A survey has indicated that PCs operate on as little as 110 W for thin clients to as much as 450 W for heavy-duty machines. Typical 1-U or 2-U servers with two or four CPUs will operate at between 250 and 450 W depending on configuration and load. Reducing the energy consumption of a 10,000-machine deployment of 150-W systems in California would save a lot of money due to high energy costs, but the carbon emissions impact would be equivalent to removing only 10 automobiles annually from the road. Besides the savings from reduced energy use, moderate deployments of 1,000 machines or more would reduce carbon emissions by hundreds of tons. Businesses that reduce IT power usage could reap secondary benefits from trading credits with a cap-and-trade system in place. With proper monitoring and tracking technology, businesses could generate thousands to hundreds of thousands of dollars from the sales of carbon credits on the open market.

Cameron K.W.,Virginia Polytechnic Institute and State University
Computer | Year: 2010

Realizing energy-proportional computing will require rethinking traditional performance-driven design. © 2010 IEEE.

Recent work has demonstrated that 4-hydroxybenzoic acid is the in vivo precursor to the 1-(4-aminophenyl)-1-deoxy-d-ribitol (APDR) moiety present in the C1 carrier coenzyme methanopterin present in the methanogenic archaea. For this transformation to occur, the hydroxyl group of the 4-hydroxybenzoic acid must be replaced with an amino group at some point in the biosynthetic pathway. Using stable isotopically labeled precursors and liquid chromatography with electrospray-ionization mass spectroscopy, the first step of this transformation in Methanocaldococcus jannaschii occurs by the reaction of 4-hydroxybenzoic acid with phosphoribosyl pyrophosphate (PRPP) to form 4-(β-d-ribofuranosyl)hydroxybenzene 5′-phosphate (β-RAH-P). The β-RAH-P then condenses with l-aspartate in the presence of ATP to form 4-(β-d-ribofuranosyl)-N-succinylaminobenzene 5′-phosphate (β-RFSA-P). Elimination of fumarate from β-RFSA-P produces 4-(β-d-ribofuranosyl)aminobenzene 5′-phosphate (β-RFA-P), the known precursor to the APDR moiety of methanopterin [White, R. H. (1996) Biochemistry 35, 3447-3456]. This work represents the first biochemical example of the conversion of a phenol to an aniline. © 2011 American Chemical Society.

Baird T.D.,Virginia Polytechnic Institute and State University | Leslie P.W.,University of North Carolina at Chapel Hill
Global Environmental Change | Year: 2013

Recent studies have identified poverty reduction near parks and protected areas, findings that challenge an extensive literature on the social burdens associated with protected areas. These studies move the discussion on the social dynamics of conservation forward, however, they do not offer insight into the underlying mechanisms that shape household-level outcomes such as income and wealth. By focusing on protected areas as centers of uncertainty, upheaval, and disturbance, this study examines the character and incidence of livelihood diversification within communities near Tarangire National Park in northern Tanzania compared to communities far from the park. Livelihood diversification is well understood as a coping and/or risk mitigation strategy pursued in response to various types of shocks, and uncertainty more generally. This study draws on mixed methodologies to construct multivariate statistical models to estimate the effect of proximity to the park on measures of livelihood diversification. The results indicate that proximity to park is strongly correlated with livelihood diversification, suggesting that households near the park are adapting to opportunities and constraints and may be seeking to reduce variance in income and wealth in response to disturbances and uncertainty associated with the park. © 2013 Elsevier Ltd.

Philen M.,Virginia Polytechnic Institute and State University
Journal of Intelligent Material Systems and Structures | Year: 2012

Variable stiffness f2mc are investigated for vibration isolation through analysis and experiments. The f2mc are novel structures that have been shown to achieve significant changes in stiffness through simple valve control. The objective of this research is to develop analysis tools to investigate the f2mc variable modulus system for semi-active vibration isolation and to validate the results through experiments. A non-linear analytical model of an isolation mount based on the f2mc tube with a proportional valve is developed. Analysis results indicate that the f2mc-based isolation mount is effective for reducing the force transmitted to the foundation and that the transmissibility ratio can be tuned via proportional valve control. Experimental results agree with analysis results and validate semi-active vibration isolation using a proportional valve. © The Author(s) 2011.

Augmented or enhanced hearing protection devices (HPDs), as contrasted with conventional HPDs, which attenuate noise strictly through static, passive means, have proliferated in the past decade. These advancements in HPDs are generally delineated into passive (non-powered) and active (powered electronic) designs. While passive augmentations are reviewed in a parallel paper elsewhere in this issue, 1 active augmentations include various analog and digital circuits for achieving electronic phase cancellation of noise; electronic modulated sound transmission circuits, which amplify a passband of ambient sound and transmit it through the HPD (ceasing to amplify at a predetermined noise level); and tactical communications and protection systems (TCAPS), which may include any of the aforementioned electronic elements plus microphone/receiver communications elements. The intended benefits of electronic augmented HPDs, some of which are realized in practice and others not, include more natural hearing for the user, improved speech communications and signal detection, reduced noise-induced annoyance, improved military tactics, stealth and gunfire protection, and provision of protection that is somewhat tailored for the user's needs, noise exposure, and/or job requirements. This paper provides a technical overview of active augmented HPDs that were available or have been prototyped circa early-2010. In some cases, no empirical research on the augmentations and their performance was available in the research literature; in these cases, this review relied on patents, corporate literature, and/or the author's experience. For other technologies, a limited amount of empirical, operational performance research was available and it is covered herein. Finally, in view that at the juncture of this article the United States (U.S.) Environmental Protection Agency (EPA) was in the process of promulgating a comprehensive new federal law to govern the testing and labeling of hearing protectors of various types, those elements of the proposed law pertaining to specific augmentation technologies are mentioned herein, 2 along with that proposed law's cited ANSI standards, as well as ISO standards that address hearing protector attenuation testing.

Augmentations or enhancements to conventional HPDs, that is, those which attenuate noise strictly through static, passive means, are generally delineated into passive (non-electronic) and active (powered electronic) designs. While powered electronic augmentations are reviewed in Casali 1 (a parallel paper elsewhere in this issue), passive augmentations are represented by mechanical networks to achieve flat-by-frequency attenuation; level-dependent leakage pathways that house acoustically-variable occluders to yield minimal attenuation during quiet periods but sharply increasing attenuation upon intense noise bursts (such as gunfire); quarter-wave resonance ducts to bolster attenuation of specific frequencies; selectable cartridges or valves that enable passive attenuation to be adjusted for specific exposure needs; and dynamically adjustable-fit devices that provide adjustment features to enable personalized fit to the user as well as some degree of attenuation control. Intended benefits of passive augmented HPDs (akin to those of active devices as well) include (1) more natural hearing for the user, (2) improved speech communications and signal detection, (3) reduced noise-induced annoyance, (4) improved military tactics, stealth maintenance and gunfire protection, and (5) provision of protection that is tailored for the user's needs, noise exposure, and/or job requirements. This paper provides a technical overview of passive augmented HPDs that were available or have been prototyped circa early-2010. In cases where no empirical research results on the passive augmentations and their performance were available in the research literature, this review relied on patents, corporate literature, and/or the author's experience. For certain augmentations, a limited amount of empirical, operational performance research was available and it is covered herein. Finally, in view that at the juncture of this article the United States (U.S.) Environmental Protection Agency (EPA) was in the process of promulgating a comprehensive new federal law to govern the testing and labeling of hearing protectors of various types, those elements of the proposed law that pertain only to specific passive augmentation technologies are mentioned herein, 2 along with references to relevant standards on hearing protector attenuation testing.

The Internet is a trusted source of health information for growing majorities of Web users. The promise of online health interventions will be realized with the development of purely online theory-based programs for Web users that are evaluated for program effectiveness and the application of behavior change theory within the online environment. Little is known, however, about the demographic, behavioral, or psychosocial characteristics of Web-health users who represent potential participants in online health promotion research. Nor do we understand how Web users' psychosocial characteristics relate to their health behavior-information essential to the development of effective, theory-based online behavior change interventions. This study examines the demographic, behavioral, and psychosocial characteristics of Web-health users recruited for an online social cognitive theory (SCT)-based nutrition, physical activity, and weight gain prevention intervention, the Web-based Guide to Health (WB-GTH). Directed to the WB-GTH site by advertisements through online social and professional networks and through print and online media, participants were screened, consented, and assessed with demographic, physical activity, psychosocial, and food frequency questionnaires online (taking a total of about 1.25 hours); they also kept a 7-day log of daily steps and minutes walked. From 4700 visits to the site, 963 Web users consented to enroll in the study: 83% (803) were female, participants' mean age was 44.4 years (SD 11.03 years), 91% (873) were white, and 61% (589) were college graduates; participants' median annual household income was approximately US $85,000. Participants' daily step counts were in the low-active range (mean 6485.78, SD 2352.54) and overall dietary levels were poor (total fat g/day, mean 77.79, SD 41.96; percent kcal from fat, mean 36.51, SD 5.92; fiber g/day, mean 17.74, SD 7.35; and fruit and vegetable servings/day, mean 4.03, SD 2.33). The Web-health users had good self-efficacy and outcome expectations for health behavior change; however, they perceived little social support for making these changes and engaged in few self-regulatory behaviors. Consistent with SCT, theoretical models provided good fit to Web-users' data (root mean square error of the approximation [RMSEA] < .05). Perceived social support and use of self-regulatory behaviors were strong predictors of physical activity and nutrition behavior. Web users' self-efficacy was also a good predictor of healthier levels of physical activity and dietary fat but not of fiber, fruits, and vegetables. Social support and self-efficacy indirectly predicted behavior through self-regulation, and social support had indirect effects through self-efficacy. Results suggest Web-health users visiting and ultimately participating in online health interventions may likely be middle-aged, well-educated, upper middle class women whose detrimental health behaviors put them at risk of obesity, heart disease, some cancers, and diabetes. The success of Internet physical activity and nutrition interventions may depend on the extent to which they lead users to develop self-efficacy for behavior change, but perhaps as important, the extent to which these interventions help them garner social-support for making changes. Success of these interventions may also depend on the extent to which they provide a platform for setting goals, planning, tracking, and providing feedback on targeted behaviors.

Kennelly P.J.,Virginia Polytechnic Institute and State University
Journal of Biological Chemistry | Year: 2014

The third domain of life, the Archaea (formerly Archaebacteria), is populated by a physiologically diverse set of microorganisms, many of which reside at the ecological extremes of our global environment. Although ostensibly prokaryotic in morphology, the Archaea share much closer evolutionary ties with the Eukarya than with the superficially more similar Bacteria. Initial genomic, proteomic, and biochemical analyses have revealed the presence of "eukaryotic" protein kinases and phosphatases and an intriguing set of serine-, threonine-, and tyrosine-phosphorylated proteins in the Archaea that may offer new insights into this important regulatory mechanism. © 2014 by The American Society for Biochemistry and Molecular Biology, Inc.

Marshall J.D.,Auburn University | Charney F.A.,Virginia Polytechnic Institute and State University
Earthquake Engineering and Structural Dynamics | Year: 2012

The concept of the hybrid passive control system is studied analytically by investigating the seismic response of steel frame structures. Hybrid control systems consist of two different passive elements combined into a single device or system. The hybrid systems investigated in this research consist of a rate-dependent damping device paired with a rate-independent energy dissipation element. The innovative configurations exploit individual element strengths and offset their weaknesses through multiphased behavior. A nine-story, five-bay steel moment-frame was used for the analysis. Six different seismic resisting systems were analyzed and compared. The conventional systems included a special moment-resisting frame (SMRF) and a dual SMRF-buckling-restrained brace (BRB) system. The final four configurations are hybrid passive systems. The different hybrid configurations utilize a BRB and either a high-damping rubber damper or viscous fluid damper. The analyses were run in the form of an incremental dynamic analysis. Several damage measures were calculated, including maximum roof drift, base shear, and total roof acceleration. The results demonstrate the capability of hybrid passive control systems to improve structural response compared with conventional lateral systems and to be effective for performance-based seismic design. Each hybrid configuration improved some aspect of structural response with some providing benefits for multiple damage measures. The multiphased nature provides improved response for frequent and severe seismic events. © 2011 John Wiley & Sons, Ltd.

Plaut R.H.,Virginia Polytechnic Institute and State University | Stephens T.C.,TenCate Geosynthetics
Geotextiles and Geomembranes | Year: 2012

Geotextile tubes are often used to dewater contaminated or other material. Slurry is pumped into the tube, some of it permeates out through the fabric, and some or all of the particles in the remaining slurry consolidate at the bottom of the tube. This process is often repeated a number of times until the consolidated material (fill) takes up most of the volume in the tube. Interface friction between the fill and the tube may cause a significant increase in the maximum tension in the tube, and may induce failure by tearing. In the analysis of this system here, the tube is assumed to be long and a cross section is analyzed. The tube material is assumed to be inextensible with no bending stiffness, the tube weight is neglected, the foundation is rigid and horizontal, the slurry is modeled as a liquid, and friction acts between the fill and the tube. The relevant parameters are the tube circumference and height, the specific (unit) weights of the slurry and the fill, the height of the fill, and the coefficient of friction. The equations are derived and solved numerically, and the effects of the parameters on the tube behavior are investigated. Friction has a negligible effect on the cross-sectional area. However, the maximum tension, occurring at the top of the tube, increases as the coefficient of friction increases, and can be significantly greater than the value predicted by standard procedures that neglect friction. © 2012 Elsevier Ltd.

Scharf B.E.,Virginia Polytechnic Institute and State University
Current Opinion in Microbiology | Year: 2010

Since the discovery of protein phosphorylation in bacterial nitrogen assimilation and chemotaxis more than 30 years ago, many biochemical techniques for the analysis of two-component signal transduction systems have been developed. Over time the experimental conditions to follow the flow of phosphate groups from histidine kinases to the cognate response regulators in vitro have been fine tuned. Several approaches were applied to circumvent the instability of the phosphorylated form of response regulator proteins to analyze the structures of their activated forms. Recently, a FRET (fluorescence resonance energy transfer) assay was developed to monitor interactions of chemotaxis proteins in vivo. The availability of bacterial genome sequence databases has facilitated the identification of two-component systems and enabled prediction of interacting kinase-response regulators pairs.

Remillieux M.C.,Virginia Polytechnic Institute and State University
Applied Acoustics | Year: 2012

This paper presents the formulation and experimental validation of a numerical tool that can predict: (1) the external pressure loading due to impulsive sound generated by an outdoor point source and (2) the resulting fully coupled vibro-acoustic response at low frequencies of a two-dimensional building component (e.g. wood-framed wall with windows) backed by a rigid rectangular cavity. The model allows for the building component to have arbitrary geometry and boundary conditions. Assuming linear-acoustic propagation and acoustically rigid surfaces, the external pressure loading is computed with a three-dimensional numerical model, in the time domain, by combining the image-source method for the reflected field (specular reflections) with an extension of the Biot-Tolstoy-Medwin (BTM) method for the diffracted field. The fully coupled vibro-acoustic response of the fluid-structure system is computed in the time-domain using a modal-decomposition approach. The natural frequencies and mode shapes of the structure are computed with a finite-element model based on shell theory. Acoustic natural frequencies and mode shapes of the cavity are computed analytically assuming hard-wall boundary conditions. The experimental validation of the numerical model is also presented. Experiments were conducted on wood-framed walls without and with a window using a speaker to generate N-waves and load the walls structurally. It is found that numerical simulations are in good agreement with experimental data for these two cases. © 2012 Elsevier Ltd. All rights reserved.

Johri A.,Virginia Polytechnic Institute and State University
ALT-J: Research in Learning Technology | Year: 2011

Although the use of digital information technologies in education has become commonplace, there are few, if any, central guiding frameworks or theories that explicate the relationship between technology and learning practices. In this paper, I argue that such a theoretical framework can assist scholars and practitioners alike by working as a conduit to study and design learning technologies. Towards this goal, I propose socio-materiality as a key theoretical construct with valuable insights and implications for the field of learning technology. Sociomateriality helps balance the disproportionate attention given to either the social implications of technology use or the material aspects of technology design. Furthermore, I forward 'socio-material bricolage' as a useful analytical framework to examine and design technology-infused learning environments. I illustrate the value of the framework by applying it to three case studies of formal and informal technology-based learning. © 2011 Association for Learning Technology.

Tholl D.,Virginia Polytechnic Institute and State University
Advances in Biochemical Engineering/Biotechnology | Year: 2015

Terpenoids (isoprenoids) represent the largest and most diverse class of chemicals among the myriad compounds produced by plants. Plants employ terpenoid metabolites for a variety of basic functions in growth and development but use the majority of terpenoids for more specialized chemical interactions and protection in the abiotic and biotic environment. Traditionally, plant-based terpenoids have been used by humans in the food, pharmaceutical, and chemical industries, and more recently have been exploited in the development of biofuel products. Genomic resources and emerging tools in synthetic biology facilitate the metabolic engineering of high-value terpenoid products in plants and microbes. Moreover, the ecological importance of terpenoids has gained increased attention to develop strategies for sustainable pest control and abiotic stress protection. Together, these efforts require a continuous growth in knowledge of the complex metabolic and molecular regulatory networks in terpenoid biosynthesis. This chapter gives an overview and highlights recent advances in our understanding of the organization, regulation, and diversification of core and specialized terpenoid metabolic pathways, and addresses the most important functions of volatile and nonvolatile terpenoid specialized metabolites in plants. © Springer International Publishing Switzerland 2015

Xing J.,Virginia Polytechnic Institute and State University
Journal of Physics A: Mathematical and Theoretical | Year: 2010

Theoretical studies of nonequilibrium systems are complicated by the lack of a general framework. In this work we first show that a transformation recently introduced by Ao (2004 J. Phys. A: Math. Gen. 37 L25) is related to previous works of Graham (1977 Z. Phys. B 26 397) and Eyink et al (1996 J. Stat. Phys. 83 385), which can also be viewed as the generalized application of the Helmholtz theorem in vector calculus. We then show that systems described by ordinary stochastic differential equations with white noise can be mapped to thermostated Hamiltonian systems. A steady-state of a dissipative system corresponds to the equilibrium state of the corresponding Hamiltonian system. These results provide a solid theoretical ground for corresponding studies on nonequilibrium dynamics, especially on nonequilibrium steady state. Mapping permits the application of established techniques and results for Hamiltonian systems to dissipative non-Hamiltonian systems, those for thermodynamic equilibrium states to nonequilibrium steady states. We discuss several implications of this work. © 2010 IOP Publishing Ltd.

Zia R.K.P.,Virginia Polytechnic Institute and State University
Journal of Statistical Physics | Year: 2010

When Lenz proposed a simple model for phase transitions in magnetism, he couldn't have imagined that the "Ising model" was to become a jewel in field of equilibrium statistical mechanics. Its role spans the spectrum, from a good pedagogical example to a universality class in critical phenomena. A quarter century ago, Katz, Lebowitz and Spohn found a similar treasure. By introducing a seemingly trivial modification to the Ising lattice gas, they took it into the vast realms of non-equilibrium statistical mechanics. An abundant variety of unexpected behavior emerged and caught many of us by surprise. We present a brief review of some of the new insights garnered and some of the outstanding puzzles, as well as speculate on the model's role in the future of non-equilibrium statistical physics. © Springer Science+Business Media, LLC 2009.

Lekien F.,Free University of Colombia | Ross S.D.,Virginia Polytechnic Institute and State University
Chaos | Year: 2010

We generalize the concepts of finite-time Lyapunov exponent (FTLE) and Lagrangian coherent structures to arbitrary Riemannian manifolds. The methods are illustrated for convection cells on cylinders and Möbius strips, as well as for the splitting of the Antarctic polar vortex in the spherical stratosphere and a related point vortex model. We modify the FTLE computational method and accommodate unstructured meshes of triangles