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Adelphi, MD, United States

The University of Maryland University College is an American public university located in the unincorporated community of Adelphi in Prince George's County, Maryland in the United States. It is known primarily for its distance learning classes and programs, but UMUC also offers classes on campus at its Academic Center in Largo, and at satellite campuses across the Baltimore-Washington Metropolitan Area, throughout Maryland, as well as in Europe, the Middle East, and Asia. UMUC serves over 90,000 students worldwide and is one of the largest distance learning institutions in the world. UMUC is open to all applicants with a 100 percent acceptance rate for undergraduate programs. The university offers 120 academic programs in instructor-led and online classes, including bachelor, masters, and doctoral degrees as well as undergraduate and graduate certificates. UMUC is a member of the University System of Maryland, which includes eleven separate public universities in Maryland. Wikipedia.


Liu X.-J.,University of Maryland University College
Physical Review Letters | Year: 2012

We study the charge character of the Andreev bound states (ABSs) in one-dimensional topological superconductors with spatial inversion symmetry (SIS) breaking. Despite the absence of the SIS, we show a hidden symmetry for the Bogoliubov-de Gennes equations around Fermi points in addition to the particle-hole symmetry. This hidden symmetry protects that the charge of the ABSs is solely dependent on the corresponding Fermi velocities. On the other hand, if the SIS is present, the ABSs are charge neutral, similar to Majorana fermions. We also propose that the charge of the ABSs can be experimentally measured in the tunneling transport spectroscopy from the resonant differential tunneling conductance. © 2012 American Physical Society.


Ptuskin V.,Russian Academy of Sciences | Zirakashvili V.,Russian Academy of Sciences | Seo E.-S.,University of Maryland University College
Astrophysical Journal | Year: 2010

The spectra of high-energy protons and nuclei accelerated by supernova remnant (SNR) shocks are calculated, taking into account magnetic field amplification and Alfvénic drift both upstream and downstream of the shock for different types of SNRs during their evolution. The maximum energy of accelerated particles may reach 5×1018 eV for Fe ions in Type IIb SNRs. The calculated energy spectrum of cosmic rays after propagation through the Galaxy is in good agreement with the spectrum measured at the Earth. © 2010. The American Astronomical Society. All rights reserved.


Cooper E.D.,University of Maryland University College
Current Biology | Year: 2014

Few facts in biology are more certain than offspring inheriting genetic material from their parents, but not all genes are acquired this way. A new report documents the horizontal transfer of a potentially adaptive gene between distantly related plants. © 2014 Elsevier Ltd.


Veeraragavan A.,Massachusetts Institute of Technology | Cadou C.P.,University of Maryland University College
Combustion and Flame | Year: 2011

An analytical model for flame stabilization in meso-scale channels is developed by solving the two-dimensional partial differential equations associated with heat transport in the gas and structure and species transport in the gas. It improves on previous models by eliminating the need to assume values for the Nusselt numbers in the pre and post-flame regions. The effects of heat loss to the environment, wall thermal conductivity, and wall geometry on the burning velocity and extinction are explored. Extinction limits and fast and slow burning modes are identified but their dependence on structure thermal conductivity and heat losses differ from previous quasi one-dimensional analyses. Heat recirculation from the post-flame to the pre-flame is shown to be the primary mechanism for flame stabilization and burning rate enhancement in micro-channels. Combustor design parameters like the wall thickness ratio, thermal conductivity ratio, and heat loss to the environment each influence the flame speed through their influence on the total heat recirculation. These findings are used to propose a simple methodology for preliminary micro-combustor design. © 2011 The Combustion Institute.


Margetis D.,University of Maryland University College
Multiscale Modeling and Simulation | Year: 2012

We study stationary quantum fluctuations around a mean field limit in trapped, dilute atomic gases of repulsively interacting bosons at zero temperature. Our goal is to describe quantum-mechanically the lowest macroscopic many-body bound state consistent with a microscopic Hamiltonian that accounts for inhomogeneous particle scattering processes. In the mean field limit, the wave function of the condensate (macroscopic quantum state) satisfies a defocusing cubic nonlinear Schrödinger-type equation, the Gross-Pitaevskii equation. We include consequences of pair excitation, i.e., the scattering of particles in pairs from the condensate to other states, proposed in [T. T. Wu, J. Math. Phys., 2 (1961), pp. 105-123]. Our derivations rely on an uncontrolled yet physically motivated assumption for the many-body wave function. By relaxing mathematical rigor, from a particle Hamiltonian with a spatially varying interaction strength we derive via heuristics an integro-partial differential equation for the pair collision kernel, K, under a stationary condensate wave function, φ. For a scattering length with periodic microstructure of subscale ε, we formally describe via classical homogenization the lowest many-body bound state in terms of φ and K up to second order in ε. If the external potential is slowly varying, we solve the homogenized equations via boundary layer theory. As an application, we describe the partial depletion of the condensate. © 2012 Society for Industrial and Applied Mathematics.


McGaugh S.S.,University of Maryland University College
Astronomical Journal | Year: 2012

The baryonic Tully-Fisher relation (BTFR) is an empirical relation between baryonic mass and rotation velocity in disk galaxies. It provides tests of galaxy formation models in ΛCDM and of alternative theories like modified Newtonian dynamics (MOND). Observations of gas-rich galaxies provide a measure of the slope and normalization of the BTFR that is more accurate (if less precise) than that provided by star-dominated spirals, as their masses are insensitive to the details of stellar population modeling. Recent independent data for such galaxies are consistent with M b = AV 4 f with A = 47 6 M km -4 s 4. This is equivalent to MOND with a 0 = 1.3 0.3 s -2. The scatter in the data is consistent with being due entirely to observational uncertainties. It is unclear why the physics of galaxy formation in ΛCDM happens to pick out the relation predicted by MOND. We introduce a feedback efficacy parameter to relate halo properties to those of the galaxies they host. correlates with star formation rate and gas fraction in the sense that galaxies that have experienced the least star formation have been most impacted by feedback. © 2012. The American Astronomical Society. All rights reserved.


Hultman N.E.,University of Maryland University College
Wiley Interdisciplinary Reviews: Climate Change | Year: 2011

Despite a history of problems, nuclear power is being discussed as a potentially useful and appropriate electricity source for both developed and developing countries. For example, expanding nuclear power's share of electricity portfolios could reduce, relative to a fossil-intensive baseline, greenhouse gas emissions that lead to climate change. Moreover, nuclear power has long been advocated as a route to energy security and indeed, for many of the nuclear nations, it could decrease dependence on oil imports under certain technological scenarios, such as an increased use of plug-in hybrid vehicles. The nuclear industry argues that a new generation of reactors, representing a refinement of existing technology, will enable this expansion. Because of these new motivations, some advocates have applied the term 'nuclear renaissance' to the possibility of a rapid expansion of nuclear power to satisfy a projected growing global electricity demand, while simultaneously reducing greenhouse gas emissions. This article outlines the primary challenges that this unique energy source presents for such a renaissance. Like other technologies, nuclear is situated in a social and political-economic matrix that influences its evolution. After reviewing the basic aspects of the technology, I discuss the history of the existing nuclear fleet, then address the prospects for advanced and next-generation nuclear technologies. I review the economics of nuclear power as it is currently deployed and the potential changes to these economics under potential future development. In examining future scenarios, I explore the effects of national and international policies on nuclear energy. © 2011 John Wiley & Sons, Ltd.


Anderson M.L.,Franklin And Marshall College | Anderson M.L.,University of Maryland University College
Behavioral and Brain Sciences | Year: 2010

Abstract An emerging class of theories concerning the functional structure of the brain takes the reuse of neural circuitry for various cognitive purposes to be a central organizational principle. According to these theories, it is quite common for neural circuits established for one purpose to be exapted (exploited, recycled, redeployed) during evolution or normal development, and be put to different uses, often without losing their original functions. Neural reuse theories thus differ from the usual understanding of the role of neural plasticity (which is, after all, a kind of reuse) in brain organization along the following lines: According to neural reuse, circuits can continue to acquire new uses after an initial or original function is established; the acquisition of new uses need not involve unusual circumstances such as injury or loss of established function; and the acquisition of a new use need not involve (much) local change to circuit structure (e.g., it might involve only the establishment of functional connections to new neural partners). Thus, neural reuse theories offer a distinct perspective on several topics of general interest, such as: the evolution and development of the brain, including (for instance) the evolutionary-developmental pathway supporting primate tool use and human language; the degree of modularity in brain organization; the degree of localization of cognitive function; and the cortical parcellation problem and the prospects (and proper methods to employ) for function to structure mapping. The idea also has some practical implications in the areas of rehabilitative medicine and machine interface design. © 2010 Cambridge University Press.


Highton R.,University of Maryland University College
Molecular Phylogenetics and Evolution | Year: 2014

A study of DNA sequence variation in the plethodontid salamander Batrachoseps attenuatus by Martínez-Solano et al. (2007) revealed more species than acknowledged by the authors. They sequenced 677 base pairs of the cytochrome-b mitochondrial gene in 178 individuals from 123 populations of the currently recognized species B. attenuatus from throughout most of its known range in southwestern Oregon and northern and central California. Their data show that the common ancestor of the species diverged into five clades during the late Miocene Epoch, an estimated 9.2-5.5. mya, with subsequent divergences producing at least 39 living lineages that replace each other geographically. These groups have been diverging independently from each other throughout the Pleistocene Epoch and many of them have probably reached the species level of divergence. © 2013 Elsevier Inc.


Kapit E.,University of Oxford | Hafezi M.,University of Maryland University College | Simon S.H.,University of Oxford
Physical Review X | Year: 2014

Recent progress in nanoscale quantum optics and superconducting qubits has made the creation of strongly correlated, and even topologically ordered, states of photons a real possibility. Many of these states are gapped and exhibit anyon excitations, which could be used for a robust form of quantum information processing. However, while numerous qubit array proposals exist to engineer the Hamiltonian for these systems, the question of how to stabilize the many-body ground state of these photonic quantum simulators against photon losses remains largely unanswered. We here propose a simple mechanism that achieves this goal for Abelian and non-Abelian fractional quantum Hall states of light. Our construction uses a uniform two-photon drive field to couple the qubits of the primary lattice with an auxiliary "shadow" lattice, composed of qubits with a much faster loss rate than the qubits of the primary quantum simulator itself. This coupling causes hole states created by photon losses to be rapidly refilled, and the system's manybody gap prevents further photons from being added once the strongly correlated ground state is reached. The fractional quantum Hall state (with a small, transient population of quasihole excitations) is thus the most stable state of the system, and all other configurations will relax toward it over time. The physics described here could be implemented in a circuit QED architecture, and the device parameters needed for our scheme to succeed are in reach of current technology.We also propose a simple six-qubit device, which could easily be built in the near future, that can act as a proof of principle for our scheme.


Jenkins C.N.,Institute Pesquisas Ecologicas | Van Houtan K.S.,National Oceanic and Atmospheric Administration | Van Houtan K.S.,Duke University | Pimm S.L.,Duke University | Sexton J.O.,University of Maryland University College
Proceedings of the National Academy of Sciences of the United States of America | Year: 2015

Because habitat loss is the main cause of extinction, where and how much society chooses to protect is vital for saving species. The United States is well positioned economically and politically to pursue habitat conservation should it be a societal goal. We assessed the US protected area portfolio with respect to biodiversity in the country. New synthesis maps for terrestrial vertebrates, freshwater fish, and trees permit comparison with protected areas to identify priorities for future conservation investment. Although the total area protected is substantial, its geographic configuration is nearly the opposite of patterns of endemism within the country. Most protected lands are in the West, whereas the vulnerable species are largely in the Southeast. Private land protections are significant, but they are not concentrated where the priorities are. To adequately protect the nation's unique biodiversity, we recommend specific areas deserving additional protection, some of them including public lands, but many others requiring private investment. © 2015, National Academy of Sciences. All rights reserved.


Colombini M.,University of Maryland University College
Biochimica et Biophysica Acta - Bioenergetics | Year: 2010

A key, decision-making step in apoptosis is the release of proteins from the mitochondrial intermembrane space. Ceramide can self-assemble in the mitochondrial outer membrane to form large stable channels capable of releasing said proteins. Ceramide levels measured in mitochondria early in apoptosis are sufficient to form ceramide channels in the outer membrane. The channels are in dynamic equilibrium with non-conducting forms of ceramide in the membrane. This equilibrium can be strongly influenced by other sphingolipids and Bcl-2 family proteins. The properties of ceramide channels formed in a defined system, planar phospholipid membranes, demonstrate that proteins are not required for channel formation. In addition, experiments in the defined system reveal structural information. The results indicated that the channels are barrel-like structures whose staves are ceramide columns that span the membrane. Ceramide channels are good candidates for the protein release pathway that initiates the execution phase of apoptosis. © 2010 Elsevier B.V.


Hyeon C.,Korea Institute for Advanced Study | Thirumalai D.,University of Maryland University College
Nature Communications | Year: 2011

The distances over which biological molecules and their complexes can function range from a few nanometres, in the case of folded structures, to millimetres, for example, during chromosome organization. Describing phenomena that cover such diverse length, and also time, scales requires models that capture the underlying physics for the particular length scale of interest. Theoretical ideas, in particular, concepts from polymer physics, have guided the development of coarse-grained models to study folding of DNA, RNA and proteins. More recently, such models and their variants have been applied to the functions of biological nanomachines. Simulations using coarse-grained models are now poised to address a wide range of problems in biology. © 2011 Macmillan Publishers Limited. All rights reserved.


Nurmis J.,University of Maryland University College
Wiley Interdisciplinary Reviews: Climate Change | Year: 2016

During the last decade (2005–2015), artists from all over the world have taken on climate change as the subject matter of their work. Encouraged by activists (most notably Bill McKibben), artists have appropriated climate change as a social problem and decided that they too, alongside journalists, scientists, and activists, were called upon to engage with this issue. Dozens of noteworthy exhibitions, most notably in Boulder (2007), London and Copenhagen (2009), Paris (2012), New York (2013), Boston (2014), and Melbourne (2015), have placed climate change art on the map as a new and timely genre, displaying relevant artworks both alongside climate negotiations and in dedicated gallery spaces such as the Barbican in London. I argue that much progress has been made in appropriating climate change art as an essentially artistic, rather than propagandistic or activist practice. Although caught in the net of many criticisms, climate change art plays a crucial role in allowing the public to rethink the role of human beings’ everyday activities in irrevocably altering the climate system. In effect, climate change art makes the Anthropocene a cultural reality. However, the review points out a strong artistic trend toward the imagery of apocalyptic sublime, which results in art that may be poignant, but falls out of step with the self-professed motivations of artists and curators alike. WIREs Clim Change 2016, 7:501–516. doi: 10.1002/wcc.400. For further resources related to this article, please visit the WIREs website. © 2016 Wiley Periodicals, Inc.


Coasne B.,Charles Gerhardt Institute | Fourkas J.T.,University of Maryland University College
Journal of Physical Chemistry C | Year: 2011

The structure and dynamics of benzene confined at 293 K in silica nanopores of different diameters (D = 2.0 nm and D = 3.6 nm) are investigated by means of grand canonical Monte Carlo and molecular dynamics simulations. In order to account in a realistic way for the interactions between benzene and the silica surface, we consider a recent model that accounts for the π-electrons of the aromatic cycle in the benzene molecule. Confined benzene exhibits significant layering and orientational ordering in the vicinity of the silica surface (up to two adsorbed layers) and tends to recover its bulk properties in the pore center. Using suitable order parameters, we show that benzene molecules close to the pore surface tend to have their ring lying flat on the silica surface (and hence perpendicular to the pore axis). Such a preferential parallel orientation with respect to the silica surface suggests that a proper description of the π-electrons of the benzene aromatic ring and its specific Coulombic interaction with the partial charges carried by the silica atoms is crucial. The dynamics of benzene confined in the silica nanopores is always slower than in the bulk. Both the translational and rotational dynamics of confined benzene can be described as a bulklike contribution in the pore center that depends on the pore size and a surface contribution that is nearly insensitive to the pore size. These simulation results are discussed in the light of available experimental data on the structure and dynamics of benzene confined in nanoporous silicas. © 2011 American Chemical Society.


Mohapatra R.N.,University of Maryland University College
AIP Conference Proceedings | Year: 2012

I review a recent work on gauged flavor with left-right symmetry, where all masses and all Yukawa couplings owe their origin to spontaneous flavor symmetry breaking. This is suggested as a precursor to a full understanding of flavor of quarks and leptons. An essential ingredient of this approach is the existence of heavy vector-like fermions, which is the home of flavor, which subsequently gets transmitted to the familiar quarks and leptons via the seesaw mechanism. I then discuss implications of extending this idea to include supersymmetry and finally speculate on a possible grand unified model based on the gauge group SU(5)L×SU(5)R which provides a group theoretic origin for the vector-like fermions. © 2012 American Institute of Physics.


Liang B.,Changsha University of Science and Technology | Liu Y.,Changsha University of Science and Technology | Xu Y.,University of Maryland University College
Journal of Power Sources | Year: 2014

Silicon (Si)-based materials have the highest capacity among the investigated anode materials and have been recognized as one of the most promising materials for lithium-ion batteries. However, it is still a significant challenge to obtain good performance for practical applications due to the huge volume change during the electrochemical process. To date, the most successful strategy is to introduce other components into Si to form composite or alloy materials. In this review, the recent progress in Si-based materials utilized in lithium-ion batteries is reviewed in terms of composite systems, nano-structure designs, material synthesis methods, and electrochemical performances. The merits and disadvantages of different Si-based materials, the understanding of the mechanisms behind the performance enhancement as well as the challenges faced in Si anodes are also discussed. We are trying to present a full scope of the Si-based materials, and help understand and design future structures of Si anodes in lithium-ion batteries. © 2014 Elsevier B.V. All rights reserved.


O'Brochta D.A.,University of Maryland University College
G3 (Bethesda, Md.) | Year: 2012

Transposon-based forward and reverse genetic technologies will contribute greatly to ongoing efforts to study mosquito functional genomics. A piggyBac transposon-based enhancer-trap system was developed that functions efficiently in the human malaria vector, Anopheles stephensi. The system consists of six transgenic lines of Anopheles stephensi, each with a single piggyBac-Gal4 element in a unique genomic location; six lines with a single piggyBac-UAStdTomato element; and two lines, each with a single Minos element containing the piggyBac-transposase gene under the regulatory control of the hsp70 promoter from Drosophila melanogaster. Enhancer detection depended upon the efficient remobilization of piggyBac-Gal4 transposons, which contain the yeast transcription factor gene Gal4 under the regulatory control of a basal promoter. Gal4 expression was detected through the expression of the fluorescent protein gene tdTomato under the regulatory control of a promoter with Gal4-binding UAS elements. From five genetic screens for larval- and adult-specific enhancers, 314 progeny were recovered from 24,250 total progeny (1.3%) with unique patterns of tdTomato expression arising from the influence of an enhancer. The frequency of piggyBac remobilization and enhancer detection was 2.5- to 3-fold higher in female germ lines compared with male germ lines. A small collection of enhancer-trap lines are described in which Gal4 expression occurred in adult female salivary glands, midgut, and fat body, either singly or in combination. These three tissues play critical roles during the infection of Anopheles stephensi by malaria-causing Plasmodium parasites. This system and the lines generated using it will be valuable resources to ongoing mosquito functional genomics efforts.


Stearns F.W.,University of Maryland University College
Genetics | Year: 2010

Pleiotropy is defined as the phenomenon in which a single locus affects two or more distinct phenotypic traits. The term was formally introduced into the literature by the German geneticist Ludwig Plate in 1910, 100 years ago. Pleiotropy has had an important influence on the fields of physiological and medical genetics as well as on evolutionary biology. Different approaches to the study of pleiotropy have led to incongruence in the way that it is perceived and discussed among researchers in these fields. Furthermore, our understanding of the term has changed quite a bit since 1910, particularly in light of modern molecular data. This review traces the history of the term " pleiotropy" and reevaluates its current place in the field of genetics. Copyright © 2010 by the Genetics Society of America.


Torrens P.M.,University of Maryland University College
Annals of GIS | Year: 2015

Virtual geographic environments (VGEs) have long enjoyed significant synergy with geosimulation as a visual medium for model results, but more could be done to fashion two-way harmony between them, with the potential benefit that geosimulation could usefully serve as a process engine for VGEs and as a unifying scaffold for connecting VGEs to other systems. In this article, I argue for three promising bridges between geosimulation and VGEs. First, geosimulation could be relied upon in introducing synthetic human characters in VGEs to augment the significant physical detail that VGEs currently provide with ambient behavioural processes. Second, building blocks of geosimulation, based around polyspatial automata, could help to resolve long-standing requirements for common data and process models for VGEs. Finally, slipstreaming of geographic information across geosimulation and VGE scaffolds could be useful in reconciling diverse and many-model processes, with disparate form and scales, in a cohesive pipeline. Together, these three variations can facilitate the exchange of diverse model objects, processes, and information between geosimulation and VGEs, greatly expanding their interoperability and explorative reach. I demonstrate the usefulness of these developments with example scenarios that focus on urban mobilities, urban complexity, and urban failures in both ordinary and extraordinary scenarios. Applications to urban phenomena, in particular, may have particular value as we approach new vantages on cities supported by big data, big awareness, and immersive media that greatly expand the volume, breadth, and depth of questioning that our VGEs may be called on to support. © 2015 Paul Torrens.


Baz A.M.,University of Maryland University College
Journal of Vibration and Acoustics, Transactions of the ASME | Year: 2010

Extensive efforts are being exerted to develop various types of acoustic metamaterials to effectively control the flow of acoustical energy through these materials. However, all these efforts are focused on passive metamaterials with fixed material properties. In this paper, the emphasis is placed on the development of a class of one-dimensional acoustic metamaterials with tunable effective densities in an attempt to enable the adaptation to varying external environment. More importantly, the active metamaterials can be tailored to have increasing or decreasing variation of the material properties along and across the material volume. With such unique capabilities, physically realizable acoustic cloaks can be achieved and objects treated with these active metamaterials can become acoustically invisible. The theoretical analysis of this class of active acoustic metamaterials is presented and the theoretical predictions are determined for an array of fluid cavities separated by piezoelectric boundaries. These boundaries control the stiffness of the individual cavity and in turn its dynamical density. Various control strategies are considered to achieve different spectral and spatial control of the density of this class of acoustic metamaterials. A natural extension of this work is to include active control capabilities to tailor the bulk modulus distribution of the metamaterial in order to build practical configurations of acoustic cloaks. Copyright © 2010 by ASME.


Kishek R.A.,University of Maryland University College
Physical Review Letters | Year: 2012

The multipactor is a vacuum discharge based on a secondary electron emission. A novel resonant form is proposed that combines one- and two-surface impacts within a single period, provided the total transit time is an odd number of rf half-periods and the product of secondary yields exceeds unity. For low fD products, the simplest such mode is shown to significantly increase the upper electric field boundary of the multipacting region and lead to overlap of higher-order bands. The results agree nicely with 3D particle-in-cell code simulations. Practical implications of the findings are discussed. © 2012 American Physical Society.


Nelson R.H.,University of Maryland University College
Forest Policy and Economics | Year: 2013

Traditionally, forestry professionals in the United States have believed that forest management is a scientific discipline that should be undertaken by value-neutral experts. This understanding originated in the progressive era, typically dated from 1890 to 1920, as part of a wider progressive belief in the "scientific management" of American society. The U.S. Forest Service was created in 1905 to advance this mission, including on the national forests directly managed by the Forest Service itself. In the last few decades of the twentieth century, however, such core tenets of professional forestry came under increasing challenge from the environmental movement. Instead of seeing a forest as a "natural resource" to be used to advance the economic progress of American society, environmentalists now saw forests as having an "intrinsic value" independent of human welfare. By the early twenty-first century, reflecting such new thinking in American society, the old idea of "multiple-use management" of the national forests (and other natural systems) had lost out to "ecosystem management." This article finds that this shift in forest management philosophy reflected new (secular) religious directions in American society, as the progressive "gospel of efficiency" increasingly lost out to a new environmental "gospel of naturalness.". © 2013 Published by Elsevier B.V.


Malkov M.A.,University of California at San Diego | Diamond P.H.,University of California at San Diego | Sagdeev R.Z.,University of Maryland University College
Physical Review Letters | Year: 2012

The much-anticipated proof of cosmic ray (CR) acceleration in supernova remnants must hinge on the full consistency of acceleration theory with the observations; direct proof is impossible because of CR-orbit scrambling. Recent observations indicate deviations between helium and proton CR rigidity spectra inconsistent with the theory. By considering an initial (injection) phase of the diffusive shock acceleration, where elemental similarity does not apply, we demonstrate that the spectral difference is, in fact, a unique signature of the acceleration mechanism. Collisionless shocks inject more He2 + when they are stronger and so produce harder He2 + spectra. The injection bias is due to Alfvén waves driven by the more abundant protons, so the He2 + ions are harder to trap by these waves. By fitting the p/He ratio to the PAMELA data, we bolster the diffusive shock acceleration case for resolving the century-old mystery of CR origin. © 2012 American Physical Society.


Kirkpatrick T.R.,University of Maryland University College | Belitz D.,University of Oregon
Physical Review Letters | Year: 2012

We develop a theory for a generic instability of a Fermi liquid in dimension d>1 against the formation of a Luttinger-liquid-like state. The density of states at the Fermi level is the order parameter for the ensuing quantum phase transition, which is driven by the effective interaction strength. A scaling theory in conjunction with an effective field theory for clean electrons is used to obtain the critical behavior of observables. In the Fermi-liquid phase the order-parameter susceptibility, which is measurable by tunneling, is predicted to diverge for 1


Almeida M.,University of Maryland University College
ISME Journal | Year: 2016

The Human Microbiome Project (HMP) identified the 16S rRNA gene sequences of 'most wanted' taxa—prevalent in the healthy human microbiota but distant from previously known sequences. Since 2012, few of the corresponding genomes have been isolated and sequenced, and only through advanced isolation techniques. We demonstrate that the genomes of the most wanted taxa can be identified computationally through their correlation in abundance across multiple public metagenomic data sets. We link over 200 most wanted sequences with nearly complete genome sequences, including half of the taxa identified as high-priority targets by the HMP. The genomes we identify have strong similarity to genomes reconstructed through expensive isolation techniques, and provide a more complete functional characterization of these organisms than can be extrapolated from their 16S rRNA gene. We also provide insights into the function of organisms for which 16S rRNA gene signatures were recently reported to be associated with health and host genetic factors.The ISME Journal advance online publication, 4 March 2016; doi:10.1038/ismej.2016.35. © 2016 International Society for Microbial Ecology


Carruthers P.,University of Maryland University College
Consciousness and Cognition | Year: 2015

This paper argues that our awareness of the mental states of other agents is often perceptual in character. It draws partly on recent experimental findings concerning perception of animacy and intentionality. But it also emphasizes the unencapsulated nature of perception generally, and argues that concepts (including mental-state concepts) can be bound into the contents of conscious perception. One of the main arguments used in support of this conclusion draws on recent work concerning the nature and contents of working memory. © 2015 Elsevier Inc.


Ranganathan M.,Indian Institute of Technology Kanpur | Weeks J.D.,University of Maryland University College
Physical Review Letters | Year: 2013

We extend the terrace-step-kink model of crystal growth to impure solutions where the impurities act as barriers to step motion. The effects of supersaturation, step curvature, step repulsions, and impurities on step motion are treated in a unified free energy framework. The model reproduces several features seen in experiments on growth of potassium dihydrogen phosphate crystals, wherein a dead zone at low supersaturations and a recovery of crystal growth by motion of large coherent step bunches at larger supersaturations are observed. We identify a key feature of solution growth that leads to these effects. © 2013 American Physical Society.


Ball G.F.,University of Maryland University College
Philosophical Transactions of the Royal Society B: Biological Sciences | Year: 2016

The song-control system, a neural circuit that controls the learning and production of birdsong, provided the first example in vertebrates of prominent macro-morphological sex differences in the brain. Forebrain nuclei HVC, robust nucleus of the arcopallium (RA) and area X all exhibit prominent male-biased sex differences in volume in zebra finches and canaries. Subsequent studies compared species that exhibited different degrees of a sex difference in song behaviour and revealed an overall positive correlation between male biases in song behaviour and male biases in the volume of the song nuclei. However, several exceptions have been described in which male biases in HVC and RA are observed even though song behaviour is equal or even female-biased. Other phenotypic measures exhibit lability in both sexes. In the duetting plain-tailed wren (Pheugopedius euophrys), males and females have auditory cells in the song system that are tuned to the joint song the two sexes produce rather than just male or female components. These findings suggest that there may be constraints on the adaptive response of the song system to ecological conditions as assessed by nucleus volume but that other critical variables regulating song can respond so that each sex can modify its song behaviour as needed. © 2016 The Author(s) Published by the Royal Society. All rights reserved.


Shaya E.J.,University of Maryland University College | Tully R.B.,University of Hawaii at Manoa
Monthly Notices of the Royal Astronomical Society | Year: 2013

The confinement of most satellite galaxies in the Local Group to thin planes presents a challenge to the theory of hierarchical galaxy clustering. The Pan-Andromeda Archaeological Survey (PAndAS) collaboration has identified a particularly thin configuration with kinematic coherence among companions of M31 and there have been long-standing claims that the dwarf companions to the MilkyWay lie in a plane roughly orthogonal to the disc of our galaxy. This discussion investigates the possible origins of four Local Group planes: the plane similar, but not identical to that identified by the PAndAS collaboration, an adjacent slightly tilted plane and two planes in the vicinity of the Milky Way: one with very nearby galaxies and the other with more distant ones. Plausible orbits are found by using a combination of Numerical Action methods and a backward in time integration procedure. This investigation assumes that the companion galaxies formed at an early time in accordance with the standard cosmological model. For M31, M33, IC10 and Leo I, solutions are found that are consistent with measurements of their proper motions. For galaxies in planes, there must be commonalities in their proper motions, and this constraint greatly limits the number of physically plausible solutions. Key to the formation of the planar structures has been the evacuation of the Local Void and consequent build-up of the Local Sheet, a wall of this void.Most of the M31 companion galaxies were born in early-forming filamentary or sheet-like substrata that chased M31 out of the void. M31 is a moving target because of its attraction towards the Milky Way, and the result has been alignments stretched towards our galaxy. In the case of the configuration around the Milky Way, it appears that our galaxy was in a three-way competition for companions with M31 and Centaurus A. Only those within a modest band fell our way. The Milky Way's attraction towards the Virgo Cluster resulted in alignment along the MilkyWay-Virgo Cluster line. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Sadegh Zadeh K.,University of Maryland University College
Journal of Computational Physics | Year: 2011

Numerical solutions of flow equation in fluid content-based form or in fluid pressure head-based form are often tradeoffs between speed, accuracy, and convenience. The fluid-content based form can be solved quite rapidly with low CPU time and perfect mass balance. However, it cannot be used in saturated regions (as diffusivity function becomes infinite) and strictly becomes invalid in composite, layered, and real heterogeneous porous materials, due to singularity and discontinuity in fluid content profile. This formulation also gives misleading impression that gradient in fluid content causes the flow of fluid in porous materials, where in reality gravity and fluid pressure potential gradient produce the motion. The pressure head-based form, on the other hand, is more flexible but due to its highly nonlinear nature is much more time-consuming and produces poor global mass balance for dry initial conditions. Very fine spatial and temporal discretizations are needed to maintain mass balance property for these scenarios. The mixed form of the flow equation partially solves these issues as it maintains acceptable mass balance and is applicable to layered, heterogeneous, and composite fractured foundations. However, it is only applicable in unsaturated zones. In this study, a switching algorithm was proposed and implemented in which the mass conservative mixed form and the pressure head-based form were, respectively, used in the unsaturated and saturated zones of an initial-boundary value flow problem involving a variably saturated porous medium. The algorithm showed excellent agreement with a reference solution, obtained on a very fine spatiotemporal mesh. The simulator was then calibrated with several real-world large-scale experimental datasets. In all cases, the proposed algorithm exhibited close agreements with the experimental time-space series. The algorithm poses excellent mass balance property and can easily be used in both saturated and unsaturated regions without special treatment of fluid content discontinuities in heterogeneous and layered porous media. The proposed algorithm can also be extended to simulate multiphase and multidimensional flow problems. © 2010 Elsevier Inc.


Alaei S.,University of Maryland University College
Proceedings - Annual IEEE Symposium on Foundations of Computer Science, FOCS | Year: 2011

For Bayesian combinatorial auctions, we present a general framework for approximately reducing the mechanism design problem for multiple buyers to the mechanism design problem for each individual buyer. Our framework can be applied to any setting which roughly satisfies the following assumptions: (i) The buyer's types must be distributed independently (not necessarily identically). (ii) The objective function must be linearly separable over the set of buyers (iii) The supply constraints must be the only constraints involving more than one buyer. Our framework is general in the sense that it makes no explicit assumption about any of the following: (i) The buyer's valuations (e.g., sub modular, additive, etc). (ii) The distribution of types for each buyer. (iii) The other constraints involving individual buyers (e.g., budget constraints, etc). We present two generic n-buyer mechanisms that use 1-buyer mechanisms as black boxes. Assuming that we have an α-approximate 1-buyer mechanism for each buyer and assuming that no buyer ever needs more than 1/k of all copies of each item for some integer k ≥ 1, then our generic n-buyer mechanisms are γ k·α-approximation of the optimaln-buyer mechanism, in which γ k is a constant which is at least 1 - 1/√k+3. Observe that γ k is at least 1/2 (for k=1) and approaches 1 as k increases. As a byproduct of our construction, we improve a generalization of prophet inequalities. Furthermore, as applications of our main theorem, we improve several results from the literature. © 2011 IEEE.


Galitski V.,University of Maryland University College
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2011

We propose a Lie-algebraic duality approach to analyze nonequilibrium evolution of closed dynamical systems and thermodynamics of interacting quantum lattice models (formulated in terms of Hubbard-Stratonovich dynamical systems). The first part of the paper utilizes a geometric Hilbert-space-invariant formulation of unitary time evolution, where a quantum Hamiltonian is viewed as a trajectory in an abstract Lie algebra, while the sought-after evolution operator is a trajectory in a dynamic group, generated by the algebra via exponentiation. The evolution operator is uniquely determined by the time-dependent dual generators that satisfy a system of differential equations, dubbed here dual Schrödinger-Bloch equations, which represent a viable alternative to the conventional Schrödinger formulation. These dual Schrödinger-Bloch equations are derived and analyzed on a number of specific examples. It is shown that deterministic dynamics of a closed classical dynamical system occurs as action of a symmetry group on a classical manifold and is driven by the same dual generators as in the corresponding quantum problem. This represents quantum-to-classical correspondence. In the second part of the paper, we further extend the Lie-algebraic approach to a wide class of interacting many-particle lattice models. A generalized Hubbard-Stratonovich transform is proposed and it is used to show that the thermodynamic partition function of a generic many-body quantum lattice model can be expressed in terms of traces of single-particle evolution operators governed by the dynamic Hubbard-Stratonovich fields. The corresponding Hubbard-Stratonovich dynamical systems are generally nonunitary, which yields a number of notable complications, including breakdown of the global exponential representation. Finally, we derive Hubbard-Stratonovich dynamical systems for the Bose-Hubbard model and a quantum spin model and use the Lie-algebraic approach to obtain new nonperturbative dual descriptions of these theories. © 2011 American Physical Society.


Fan X.,University of Michigan | White I.M.,University of Maryland University College
Nature Photonics | Year: 2011

Optofluidics - the synergistic integration of photonics and microfluidics - is a new analytical field that provides a number of unique characteristics for enhancing the sensing performance and simplifying the design of microsystems. This Review describes various optofluidic architectures developed over the past five years, emphasizes the mechanisms by which optofluidics enhances biological/chemical analytic capabilities, including sensing and the precise control of biological micro- and nanoparticles, and also highlights new research directions to which the field of optofluidics may lead. © 2011 Macmillan Publishers Limited. All rights reserved.


Atulasimha J.,Virginia Commonwealth University | Flatau A.B.,University of Maryland University College
Smart Materials and Structures | Year: 2011

A unique combination of low hysteresis, moderate magnetostriction at low magnetic fields, good tensile strength, machinability and recent progress in commercially viable methods of processing iron-gallium alloys make them well poised for actuator and sensing applications. This review starts with a brief historical note on the early developments of magnetostrictive materials and moves to the recent work on FeGa alloys and their useful properties. This is followed by sections addressing the challenges specific to the characterization and processing of FeGa alloys and the state of the art in modeling their actuation and sensing behavior. © 2011 IOP Publishing Ltd.


Kirkpatrick T.R.,University of Maryland University College | Belitz D.,University of Oregon
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

An earlier theory of the quantum phase transition in metallic ferromagnets is revisited and generalized in three ways. It is shown that the mechanism that leads to a fluctuation-induced first-order transition in metallic ferromagnets with a low Curie temperature is valid, (1) irrespective of whether the magnetic moments are supplied by the conduction electrons or by electrons in another band, (2) for ferromagnets in the XY and Ising universality classes as well as for Heisenberg ferromagnets, and (3) for any systems with a nonzero homogeneous magnetization, such as ferrimagnets or canted ferromagnets. This vastly expands the class of materials for which a first-order transition at low temperatures is expected, and it explains why strongly anisotropic ferromagnets, such as UGe 2, display a first-order transition as well as Heisenberg magnets. © 2012 American Physical Society.


Ding C.,University of Maryland University College
Land Use Policy | Year: 2013

Beijing has a unique spatial pattern that is characterized by an inverted U-shape building height curve and geometrically developed transportation network (rings of highways and axial roads). The inverted U-shape curve of building heights is mainly the outcome of building height restrictions in inner city for historical preservation. This paper estimates the economic costs of the building height restrictions by using land development data. Through comparing land development without building height restrictions and simulations, we show that the economic costs are substantial. The impacts of the building height restrictions include land price decrease by up to 60%, housing output decrease by up to 70%, and land investment decrease by 85%. To accommodate the loss of housing output, the city edge has to expand, causing urban sprawl (given all other things equal). In order to offset building space reduction, housing prices rise by 20% and the city edge expands by 12%. Finally, induced travel costs resulting from urban sprawl and low density caused by building height restrictions may not be trivial. © 2012.


Jacobson T.,University of Maryland University College | Sotiriou T.P.,University of Cambridge
Physical Review Letters | Year: 2010

It has recently been pointed out that particles falling freely from rest at infinity outside a Kerr black hole can in principle collide with an arbitrarily high center of mass energy in the limiting case of maximal black hole spin. Here we aim to elucidate the mechanism for this fascinating result, and to point out its practical limitations, which imply that ultraenergetic collisions cannot occur near black holes in nature. © 2010 The American Physical Society.


Chronis-Tuscano A.,University of Maryland University College | Stein M.A.,University of Illinois at Chicago
CNS Drugs | Year: 2012

Given the high heritability of the disorder, attention-deficit hyperactivity disorder (ADHD) is common among parents of children with ADHD. Parental ADHD is associated with maladaptive parenting, negative parent-child interaction patterns and a diminished response to behavioural parent training. We describe our previous research demonstrating that stimulant medications for mothers with ADHD are associated with reductions in maternal ADHD symptoms. Although limited beneficial effects on self-reported parenting were also found in our study, the impact of ADHD medications on functional outcomes related to parenting and family interactions may not be sufficient for many families. Many questions remain with regard to how best to treat multiplex ADHD families in which a parent and child have ADHD. In particular, future studies are needed: (1) to evaluate how best to sequence pharmacotherapy, psychosocial treatment for adult ADHD and behavioural parenting interventions; (2) to determine the best approach to maintaining treatment effects over the long term for both parents and children; and (3) to identify individual predictors of treatment response. © 2012 Springer International Publishing AG. All rights reserved.


Ho H.T.,University of Maryland University College | Gopalan R.,ATandT Labs Research
International Journal of Computer Vision | Year: 2014

Many classification algorithms see a reduction in performance when tested on data with properties different from that used for training. This problem arises very naturally in face recognition where images corresponding to the source domain (gallery, training data) and the target domain (probe, testing data) are acquired under varying degree of factors such as illumination, expression, blur and alignment. In this paper, we account for the domain shift by deriving a latent subspace or domain, which jointly characterizes the multifactor variations using appropriate image formation models for each factor. We formulate the latent domain as a product of Grassmann manifolds based on the underlying geometry of the tensor space, and perform recognition across domain shift using statistics consistent with the tensor geometry. More specifically, given a face image from the source or target domain, we first synthesize multiple images of that subject under different illuminations, blur conditions and 2D perturbations to form a tensor representation of the face. The orthogonal matrices obtained from the decomposition of this tensor, where each matrix corresponds to a factor variation, are used to characterize the subject as a point on a product of Grassmann manifolds. For cases with only one image per subject in the source domain, the identity of target domain faces is estimated using the geodesic distance on product manifolds. When multiple images per subject are available, an extension of kernel discriminant analysis is developed using a novel kernel based on the projection metric on product spaces. Furthermore, a probabilistic approach to the problem of classifying image sets on product manifolds is introduced. We demonstrate the effectiveness of our approach through comprehensive evaluations on constrained and unconstrained face datasets, including still images and videos. © 2014 Springer Science+Business Media New York.


Mishra A.N.,Georgia State University | Agarwal R.,University of Maryland University College
Information Systems Research | Year: 2010

The process by which organizations incorporate technological innovations into existing routines and use them on a regular basis persists as a central concern in the literature. Although we now have a fairly robust understanding of the drivers of innovation adoption, the use of innovations is less understood. In this paper, we draw on two streams of literature, managerial and organizational sensemaking, and organizational capabilities that have hitherto been used independently, to investigate organizational use of information technology (IT)-based innovations. Building on and extending prior work, we posit that organizational capabilities serve as complements to managers' technological frames related to an innovation. We focus on the use of an important technological innovation-business-to-business (B2B) electronic markets for procurement. We examine interactions between three technological frames-benefits frame, threat frame, and adjustment frame, and two organizational capabilities-technological opportunism and technological sophistication, and their relationship with the use of B2B electronic markets in firms. We test our research model using survey data collected from 292 firms. Results largely support the proposed conceptualization and shed new light on the key factors associated with firms' use of B2B electronic markets. Theoretical and practical implications of the findings are discussed. © 2010 INFORMS.


Tyagi H.,University of Maryland University College
IEEE Journal on Selected Areas in Communications | Year: 2013

A set of terminals observe correlated data and seek to compute functions of the data using interactive public communication. At the same time, it is required that the value of a private function of the data remains concealed from an eavesdropper observing this communication. In general, the private function and the functions computed by the nodes can be all different. We show that a class of functions are securely computable if and only if the conditional entropy of data given the value of private function is greater than the least rate of interactive communication required for a related multiterminal source-coding task. A single-letter formula is provided for this rate in special cases. © 1983-2012 IEEE.


Ceccagnoli M.,Georgia Institute of Technology | Forman C.,Georgia Institute of Technology | Huang P.,University of Maryland University College | Wu D.J.,Georgia Institute of Technology
MIS Quarterly: Management Information Systems | Year: 2012

It has been argued that platform technology owners cocreate business value with other firms in their platform ecosystems by encouraging complementary invention and exploiting indirect network effects. In this study, we examine whether participation in an ecosystem partnership improves the business performance of small independent software vendors (ISVs) in the enterprise software industry and how appropriability mechanisms influence the benefits of partnership. By analyzing the partnering activities and performance indicators of a sample of 1,210 small ISVs over the period 1996-2004, we find that joining a major platform owner's platform ecosystem is associated with an increase in sales and a greater likelihood of issuing an initial public offering (IPO). In addition, we show that these impacts are greater when ISVs have greater intellectual property rights or stronger downstream capabilities. This research highlights the value of interoperability between software products, and stresses that value cocreation and appropriation are not mutually exclusive strategies in interfirm collaboration.


Lin Z.,Adobe Systems | Davis L.S.,University of Maryland University College
IEEE Transactions on Pattern Analysis and Machine Intelligence | Year: 2010

We propose a shape-based, hierarchical part-template matching approach to simultaneous human detection and segmentation combining local part-based and global shape-template-based schemes. The approach relies on the key idea of matching a part-template tree to images hierarchically to detect humans and estimate their poses. For learning a generic human detector, a pose-adaptive feature computation scheme is developed based on a tree matching approach. Instead of traditional concatenation-style image location-based feature encoding, we extract features adaptively in the context of human poses and train a kernel-SVM classifier to separate human/nonhuman patterns. Specifically, the features are collected in the local context of poses by tracing around the estimated shape boundaries. We also introduce an approach to multiple occluded human detection and segmentation based on an iterative occlusion compensation scheme. The output of our learned generic human detector can be used as an initial set of human hypotheses for the iterative optimization. We evaluate our approaches on three public pedestrian data sets (INRIA, MIT-CBCL, and USC-B) and two crowded sequences from Caviar Benchmark and Munich Airport data sets. © 2010 IEEE.


Gopal A.,University of Maryland University College | Koka B.R.,Rice University
MIS Quarterly: Management Information Systems | Year: 2012

In this paper, the interacting effect of formal contracts and relational governance on vendor profitability and quality in the software outsourcing industry are examined. We focus on a critical manifestation of relational governance-The presence of relational flexibility in the exchange relationship-and argue that the enacted observation of relational flexibility is driven by perceptions of exchange hazards. In a departure from extant literature, however, we propose that the benefits accruing from it are asymmetric and depend on how the exchange risks are apportioned by the formal contract. Formally, we hypothesize that relational flexibility provides greater benefits to an exchange partner that faces the greater proportion of risk in a project, induced through the contract. In addition, we hypothesize that these benefits manifest on the performance dimensions that are of importance to the risk-exposed partner. We test our hypotheses on 105 software projects completed by a software outsourcing vendor for multiple clients. The results show that relational flexibility positively affects profitability in only fixed price contracts, where the vendor faces greater risk, while positively affecting quality only in time and materials contracts, where the client is at greater risk. We thus provide evidence for the asymmetric benefits from relational governance, thereby arguing for a more contingent and limited view of the value of relational governance, based on risk-exposure, rather than the more expansive view prevalent in the literature contending that relational governance provides benefits for all parties to an exchange. We conclude with a discussion of the research and managerial implications of our findings.


Gopal A.,University of Maryland University College | Gosain S.,CA Capital
Information Systems Research | Year: 2010

Past research has studied how the selection and use of control portfolios in software projects is based on environmental and task characteristics. However, little research has examined the consequences of control mode choices on project performance. This paper reports on a study that addresses this issue in the context of outsourced software projects. In addition, we propose that boundary-spanning activities between the vendor and the client enable knowledge sharing across organizational and knowledge domain boundaries. This is expected to lead to facilitation of control through specific incentives and performance norms that are suited to client needs as well as the vendor context. Therefore, we argue that boundary spanning between the vendor and client moderates the relationship between formal controls instituted by the vendor on the development team and project performance. We also hypothesize the effect of collaboration as a clan control on project performance. We examine project performance in terms of software quality and project efficiency. The research model is empirically tested in the Indian software industry setting on a sample of 96 projects. The results suggest that formal and informal control modes have a significant impact on software project outcomes, but need to be finely tuned and directed toward appropriate objectives. In addition, boundary-spanning activities significantly improve the effectiveness of formal controls. Finally, we find that collaborative culture has provided mixed benefits by enhancing quality but reducing efficiency. © 2010 INFORMS.


Vitak J.,University of Maryland University College
Journal of Broadcasting and Electronic Media | Year: 2012

A large body of research argues that self-presentation strategies vary based on audience. But what happens when the technical features of Web sites enable-or even require-users to make personal disclosures to multiple audiences at once, as is often the case on social network sites (SNSs)? Do users apply a lowest common denominator approach, only making disclosures that are appropriate for all audience members? Do they employ technological tools to disaggregate audiences? When considering the resources that can be harnessed from SNS interactions, researchers suggest users need to engage with their network in order to reap benefits. The present study presents a model including network composition, disclosures, privacy-based strategies, and social capital. Results indicate that (1) audience size and diversity impacts disclosures and use of advanced privacy settings, (2) privacy concerns and privacy settings impact disclosures in varying ways; and (3) audience and disclosure characteristics predict bridging social capital. © 2012 Copyright Taylor and Francis Group, LLC.


Appelbaum I.,University of Maryland University College
Applied Physics Letters | Year: 2013

I address the measurement of density of states within and beyond the superconducting gap in tunnel-coupled finite-size nanostructures using a capacitive method. Third-harmonic generation is used to yield the full differential conductance spectrum without destruction of the low dimensionality otherwise induced by intimate ohmic coupling to an electrode. The method is particularly relevant to attempts to discern the presence of the fragile Majorana fermion quasiparticle at the end of spin-orbit-coupled nanowires in appropriate magnetic field conditions by their signature mid-gap density of states. © 2013 AIP Publishing LLC.


Strohmayer T.,NASA | Mahmoodifar S.,University of Maryland University College
Astrophysical Journal | Year: 2014

We present results of targeted searches for signatures of non-radial oscillation modes (such as r- and g-modes) in neutron stars using RXTE data from several accreting millisecond X-ray pulsars (AMXPs). We search for potentially coherent signals in the neutron star rest frame by first removing the phase delays associated with the star's binary motion and computing fast Fourier transform power spectra of continuous light curves with up to 230 time bins. We search a range of frequencies in which both r- and g-modes are theoretically expected to reside. Using data from the discovery outburst of the 435 Hz pulsar XTE J1751-305 we find a single candidate, coherent oscillation with a frequency of 0.5727597 × νspin = 249.332609 Hz, and a fractional Fourier amplitude of 7.46 × 10-4. We estimate the significance of this feature at the 1.6 × 10-3 level, slightly better than a 3σ detection. Based on the observed frequency we argue that possible mode identifications include rotationally modified g-modes associated with either a helium-rich surface layer or a density discontinuity due to electron captures on hydrogen in the accreted ocean. In the latter case the presence of sufficient hydrogen in this ultracompact system with a likely helium-rich donor would present an interesting puzzle. Alternatively, the frequency could be identified with that of an inertial mode or a core r-mode modified by the presence of a solid crust; however, the r-mode amplitude required to account for the observed modulation amplitude would induce a large spin-down rate inconsistent with the observed pulse timing measurements. For the AMXPs XTE J1814-338 and NGC 6440 X-2 we do not find any candidate oscillation signals, and we place upper limits on the fractional Fourier amplitude of any coherent oscillations in our frequency search range of 7.8 × 10 -4 and 5.6 × 10-3, respectively. We briefly discuss the prospects and sensitivity for similar searches with future, larger X-ray collecting area missions. © 2014. The American Astronomical Society. All rights reserved.


Shmueli G.,University of Maryland University College | Koppius O.R.,Erasmus University Rotterdam
MIS Quarterly: Management Information Systems | Year: 2011

This research essay highlights the need to integrate predictive analytics into information systems research and shows several concrete ways in which this goal can be accomplished. Predictive analytics include empirical methods (statistical and other) that generate data predictions as well as methods for assessing predictive power. Predictive analytics not only assist in creating practically useful models, they also play an important role alongside explanatory modeling in theory building and theory testing. We describe six roles for predictive analytics: new theory generation, measurement development, comparison of competing theories, improvement of existing models, relevance assessment, and assessment of the predictability of empirical phenomena. Despite the importance of predictive analytics, we find that they are rare in the empirical IS literature. Extant IS literature relies nearly exclusively on explanatory statistical modeling, where statistical inference is used to test and evaluate the explanatory power of underlying causal models, and predictive power is assumed to follow automatically from the explanatory model. However, explanatory power does not imply predictive power and thus predictive analytics are necessary for assessing predictive power and for building empirical models that predict well. To show that predictive analytics and explanatory statistical modeling are fundamentally disparate, we show that they are different in each step of the modeling process. These differences translate into different final models, so that a pure explanatory statistical model is best tuned for testing causal hypotheses and a pure predictive model is best in terms of predictive power. We convert a well-known explanatory paper on TAM to a predictive context to illustrate these differences and show how predictive analytics can add theoretical and practical value to IS research.


Polisensky E.,U.S. Navy | Ricotti M.,University of Maryland University College | Ricotti M.,University of Paris Pantheon Sorbonne
Monthly Notices of the Royal Astronomical Society | Year: 2014

We investigate the claim that the largest subhaloes in high-resolution dissipationless cold dark matter (CDM) simulations of the Milky Way are dynamically inconsistent with observations of its most luminous satellites.We find that the inconsistency is largely attributable to the large values of s8 and ns adopted in the discrepant simulations, producing satellites that form too early and therefore are too dense. We find the tension between observations and simulations adopting parameters consistent with WMAP9 is greatly diminished, making the satellites a sensitive test of CDM. We find the Via Lactea II halo to be atypical for haloes in a WMAP3 cosmology, a discrepancy that we attribute to its earlier formation epoch than the mean for its mass. We also explore warm dark matter (WDM) cosmologies for 1-4 keV thermal relics. In 1 keV cosmologies, subhaloes have circular velocities at kpc scales ~60 per cent lower than their CDM counterparts, but are reduced by only 10 per cent in 4 keV cosmologies. Since relic masses < 2-3 keV are ruled out by constraints from the number of Milky Way satellites and Lyman a forest,WDM has a minor effect in reducing the densities of massive satellites. Given the uncertainties on the mass and formation epoch of the Milky Way, the need for reducing the satellite densities with baryonic effects or WDM is alleviated. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Roedig C.,Johns Hopkins University | Krolik J.H.,Johns Hopkins University | Miller M.C.,University of Maryland University College
Astrophysical Journal | Year: 2014

Observations indicate that most massive galaxies contain a supermassive black hole, and theoretical studies suggest that when such galaxies have a major merger, the central black holes will form a binary and eventually coalesce. Here we discuss two spectral signatures of such binaries that may help distinguish them from ordinary active galactic nuclei. These signatures are expected when the mass ratio between the holes is not extreme and the system is fed by a circumbinary disk. One such signature is a notch in the thermal continuum that has been predicted by other authors; we point out that it should be accompanied by a spectral revival at shorter wavelengths and also discuss its dependence on binary properties such as mass, mass ratio, and separation. In particular, we note that the wavelength λ n at which the notch occurs depends on these three parameters in such a way as to make the number of systems displaying these notches ; longer wavelength searches are therefore strongly favored. A second signature, first discussed here, is hard X-ray emission with a Wien-like spectrum at a characteristic temperature 100 keV produced by Compton cooling of the shock generated when streams from the circumbinary disk hit the accretion disks around the individual black holes. We investigate the observability of both signatures. The hard X-ray signal may be particularly valuable as it can provide an indicator of black hole merger a few decades in advance of the event. © 2014. The American Astronomical Society. All rights reserved.


Armstrong R.W.,University of Maryland University College
Symmetry | Year: 2014

Several materials science type research topics are described in which advantageous use of crystal symmetry considerations has been helpful in ferreting the essential elements of dislocation behavior in determining material properties or for characterizing crystal/polycrystalline structural relationships; for example: (1) the mechanical strengthening produced by a symmetrical bicrystal grain boundary; (2) cleavage crack formation at the intersection within a crystal of symmetrical dislocation pile-ups; (3) symmetry aspects of anisotropic crystal indentation hardness measurements; (4) X-ray diffraction topography imaging of dislocation strains and subgrain boundary misorientations; and (5) point and space group aspects of twinning. Several applications are described in relation to the strengthening of grain boundaries in nanopolycrystals and of multiply-oriented crystal grains in polysilicon photovoltaic solar cell materials. A number of crystallographic aspects of the different topics are illustrated with a stereographic method of presentation. © 2014 by the author; licensee MDPI, Basel, Switzerland.


Tugarinov V.,University of Maryland University College
Progress in nuclear magnetic resonance spectroscopy | Year: 2014

A description of the utility of deuteration in protein NMR is provided with an emphasis on quantitative evaluation of the effects of deuteration on a number of NMR parameters of proteins: (1) chemical shifts, (2) scalar coupling constants, (3) relaxation properties (R1 and R2 rates) of nuclei directly attached to one or more deuterons as well as protons of methyl groups in a highly deuterated environment, (4) scalar relaxation of 15N and 13C nuclei in 15N-D and 13C-D spin systems as a measure of hydrogen bonding strength, and (5) NOE-based applications of deuteration in NMR studies of protein structure. The discussion is restricted to the 'indirect' use of deuterium in the sense that the description of NMR parameters and properties of the nuclei affected by nearby deuterons (15N, 13C, 1H) is provided rather than those of deuterium itself. Copyright © 2013 Elsevier B.V. All rights reserved.


Reynolds C.S.,University of Maryland University College
Space Science Reviews | Year: 2014

I review the current status of X-ray reflection (a.k.a. broad iron line) based black hole spin measurements. This is a powerful technique that allows us to measure robust black hole spins across the mass range, from the stellar-mass black holes in X-ray binaries to the supermassive black holes in active galactic nuclei. After describing the basic assumptions of this approach, I lay out the detailed methodology focusing on “best practices” that have been found necessary to obtain robust results. Reflecting my own biases, this review is slanted towards a discussion of supermassive black hole (SMBH) spin in active galactic nuclei (AGN). Pulling together all of the available XMM-Newton and Suzaku results from the literature that satisfy objective quality control criteria, it is clear that a large fraction of SMBHs are rapidly-spinning, although there are tentative hints of a more slowly spinning population at high (M>5×107 M⊙) and low (M<2×106 M⊙) mass. I also engage in a brief review of the spins of stellar-mass black holes in X-ray binaries. In general, reflection-based and continuum-fitting based spin measures are in agreement, although there remain two objects (GRO J1655–40 and 4U 1543–475) for which that is not true. I end this review by discussing the exciting frontier of relativistic reverberation, particularly the discovery of broad iron line reverberation in XMM-Newton data for the Seyfert galaxies NGC 4151, NGC 7314 and MCG–5-23-16. As well as confirming the basic paradigm of relativistic disk reflection, this detection of reverberation demonstrates that future large-area X-ray observatories such as LOFT will make tremendous progress in studies of strong gravity using relativistic reverberation in AGN. © 2013, Springer Science+Business Media Dordrecht.


Munday J.N.,University of Maryland University College
Journal of Applied Physics | Year: 2012

The limiting efficiency of photovoltaic energy conversion was determined by Shockley and Queisser using the theory of detailed balance, which described the balance between absorption and emission of photons. However, when a material is placed on top of a solar cell that modifies the transmission of photons (e.g., a photonic crystal), both the absorption and emission of photons are modified. Here, we show how the addition of a photonic structure can lead to an effective modification of the energy bandgap of the material and can subsequently change its maximum theoretical efficiency. We consider the effect of non-ideal photonic structures and the effect of non-radiative recombination within the cell and find that, with realistic materials, efficiency gains of several percent can be achieved with the addition of photonic structures. © 2012 American Institute of Physics.


McKenzie H.C.,University of Maryland University College
Veterinary Clinics of North America - Equine Practice | Year: 2011

Hyperlipidemia is the presence of elevated lipid concentrations in the blood and is associated with periods of negative energy balance and physiologic stress. In increased concentrations, circulating lipids typically occur in the triglyceride form, which may interfere with numerous normal physiologic functions, particularly by reducing insulin sensitivity. Although the hyperlipidemia risk is greatest in ponies, miniature horses, and donkeys, all equids are at risk if they are in a situation involving negative energy balance. The sedentary lifestyle of many modern horses and the frequent feeding of high-carbohydrate diets contribute substantially to the risk of excessive fat mobilization and the development of hyperlipidemias. © 2011 Elsevier Inc.


Jeffery W.R.,Eugene Bell Center for Regenerative Biology and Tissue Engineering | Jeffery W.R.,University of Maryland University College
Genesis | Year: 2015

Summary: This year marks the 125th anniversary of the beginning of regeneration research in the ascidian Ciona intestinalis. A brief note was published in 1891, reporting the regeneration of the Ciona neural complex and siphons. This launched an active period of Ciona regeneration research culminating in the demonstration of partial body regeneration: the ability of proximal body parts to regenerate distal ones, but not vice versa. In a process resembling regeneration, wounds in the siphon tube were discovered to result in the formation of an ectopic siphon. Ciona regeneration research then lapsed into a period of relative inactivity after the purported demonstration of the inheritance of acquired characters using siphon regeneration as a model. Around the turn of the present century, Ciona regeneration research experienced a new blossoming. The current studies established the morphological and physiological integrity of the regeneration process and its resemblance to ontogeny. They also determined some of the cell types responsible for tissue and organ replacement and their sources in the body. Finally, they showed that regenerative capacity is reduced with age. Many other aspects of regeneration now can be studied at the mechanistic level because of the extensive molecular tools available in Ciona. genesis 53:48-65, 2015. © 2014 Wiley Periodicals, Inc.


Wigginton K.R.,University of Maryland University College | Kohn T.,Ecole Polytechnique Federale de Lausanne
Current Opinion in Virology | Year: 2012

Drinking waters are treated for enteric virus via a number of disinfection techniques including chemical oxidants, irradiation, and heat, however the inactivation mechanisms during disinfection remain elusive. Owing to the fact that a number of significant waterborne virus strains are not readily culturable in vitro at this time (e.g. norovirus, hepatitis A), the susceptibility of these viruses to disinfection is largely unknown. An in-depth understanding of the mechanisms involved in virus inactivation would aid in predicting the susceptibility of non-culturable virus strains to disinfection and would foster the development of improved disinfection methods. Recent technological advances in virology research have provided a wealth of information on enteric virus compositions, structures, and biological functions. This knowledge will allow for physical/chemical descriptions of virus inactivation and thus further our understanding of virus disinfection to the most basic mechanistic level. © 2011 Elsevier B.V. All rights reserved.


Reames D.V.,University of Maryland University College
Solar Physics | Year: 2010

We investigate the topology of magnetic clouds using energetic particles from a variety of sources outside the clouds as probes to remotely sense the interconnections of the magnetic field. We find that only a small percentage of field lines in magnetic clouds are truly closed directly to the Sun, so as to exclude particles from an external source. Field lines that are open to the outer heliosphere must be mixed with closed field lines on a fine spatial scale in the clouds to explain the simultaneous observation of anomalous cosmic rays from the outer heliosphere and of counter-streaming suprathermal electrons from the corona. The results of this paper show that, given sufficient time, particles accelerated at shock waves outside magnetic clouds have access to the interior and to a wide region of solar longitude in interplanetary space surrounding the clouds. © 2010 Springer Science+Business Media B.V.


Deffayet C.,CNRS Astroparticle and Cosmology Lab | Jacobson T.,University of Maryland University College
Classical and Quantum Gravity | Year: 2012

We discuss the structure of horizons in spacetimes with two metrics, with applications to the Vainshtein mechanism and other examples. We show, without using the field equations, that if the two metrics are static, spherically symmetric, nonsingular and diagonal in a common coordinate system, then a Killing horizon for one must also be a Killing horizon for the other. We then generalize this result to the axisymmetric case. We also show that the surface gravities must agree if the bifurcation surface in one spacetime lies smoothly in the interior of the spacetime of the other metric. These results imply for example that the Vainshtein mechanism of nonlinear massive gravity theories cannot work to recover black holes if the dynamical metric and the non-dynamical flat metric are both diagonal. They also explain the global structure of some known solutions of bigravity theories with one diagonal and one non-diagonal metric, in which the bifurcation surface of the Killing field lies in the interior of one spacetime and on the conformal boundary of the other. © 2012 IOP Publishing Ltd.


Smolyaninov I.I.,University of Maryland University College | Narimanov E.E.,Purdue University
Physical Review Letters | Year: 2010

We demonstrate that the extraordinary waves in indefinite metamaterials experience an ( - ++) effective metric signature. During a metric signature change transition in such a metamaterial, a Minkowski space-time is created together with a large number of particles populating the space-time. Such metamaterial models provide a tabletop realization of metric signature change events suggested to occur in Bose-Einstein condensates and quantum gravity theories. © 2010 The American Physical Society.


Kirkpatrick T.R.,University of Maryland University College | Belitz D.,University of Oregon
Physical Review Letters | Year: 2010

It is shown that columnar fluctuations, in conjunction with weak quenched disorder, lead to a T3/2 temperature dependence of the electrical resistivity. This is proposed as an explanation of the observed non-Fermi-liquid behavior in the helimagnet MnSi, with one possible realization of the columnar fluctuations provided by Skyrmion lines that have independently been proposed to be present in this material. © 2010 The American Physical Society.


Levin M.,University of Maryland University College | Gu Z.-C.,University of California at Santa Barbara
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

We construct a two-dimensional (2D) quantum spin model that realizes an Ising paramagnet with gapless edge modes protected by Ising symmetry. This model provides an example of a "symmetry-protected topological phase." We describe a simple physical construction that distinguishes this system from a conventional paramagnet: We couple the system to a Z 2 gauge field and then show that the π-flux excitations have different braiding statistics from that of a usual paramagnet. In addition, we show that these braiding statistics directly imply the existence of protected edge modes. Finally, we analyze a particular microscopic model for the edge and derive a field theoretic description of the low energy excitations. We believe that the braiding statistics approach outlined in this paper can be generalized to a large class of symmetry-protected topological phases. © 2012 American Physical Society.


Rupke D.S.N.,Rhodes College | Veilleux S.,University of Maryland University College
Astrophysical Journal Letters | Year: 2011

The quasi-stellar object (QSO)/merger Mrk 231 is arguably the nearest and best laboratory for studying QSO feedback. It hosts several outflows, including broad-line winds, radio jets, and a poorly understood kpc-scale outflow. In this Letter, we present integral field spectroscopy from the Gemini telescope that represents the first unambiguous detection of a wide-angle, kiloparsec-scale outflow from a powerful QSO. Using neutral gas absorption, we show that the nuclear region hosts an outflow with blueshifted velocities reaching 1100kms-1, extending 2-3kpc from the nucleus in all directions in the plane of the sky. A radio jet impacts the outflow north of the nucleus, accelerating it to even higher velocities (up to 1400kms-1). Finally, 3.5 kpc south of the nucleus, star formation is simultaneously powering an outflow that reaches more modest velocities of only 570kms-1. Blueshifted ionized gas is also detected around the nucleus at lower velocities and smaller scales. The mass and energy flux from the outflow are ≳2.5 times the star formation rate and ≳0.7% of the active galactic nucleus luminosity, consistent with negative feedback models of QSOs. © 2011. The American Astronomical Society. All rights reserved.


Anderson C.M.,NASA | Samuelson R.E.,University of Maryland University College
Icarus | Year: 2011

Vertical distributions and spectral characteristics of Titan's photochemical aerosol and stratospheric ices are determined between 20 and 560cm-1 (500-18μm) from the Cassini Composite Infrared Spectrometer (CIRS). Results are obtained for latitudes of 15°N, 15°S, and 58°S, where accurate temperature profiles can be independently determined. In addition, estimates of aerosol and ice abundances at 62°N relative to those at 15°S are derived. Aerosol abundances are comparable at the two latitudes, but stratospheric ices are ∼3 times more abundant at 62°N than at 15°S. Generally, nitrile ice clouds (probably HCN and HC3N), as inferred from a composite emission feature at ∼160cm-1, appear to be located over a narrow altitude range in the stratosphere centered at ∼90km. Although most abundant at high northern latitudes, these nitrile ice clouds extend down through low latitudes and into mid southern latitudes, at least as far as 58°S. There is some evidence of a second ice cloud layer at ∼60km altitude at 58°S associated with an emission feature at ∼80cm-1. We speculate that the identify of this cloud may be due to C2H6 ice, which in the vapor phase is the most abundant hydrocarbon (next to CH4) in the stratosphere of Titan. Unlike the highly restricted range of altitudes (50-100km) associated with organic condensate clouds, Titan's photochemical aerosol appears to be well-mixed from the surface to the top of the stratosphere near an altitude of 300km, and the spectral shape does not appear to change between 15°N and 58°S latitude. The ratio of aerosol-to-gas scale heights range from 1.3-2.4 at about 160km to 1.1-1.4 at 300km, although there is considerable variability with latitude. The aerosol exhibits a very broad emission feature peaking at ∼140cm-1. Due to its extreme breadth and low wavenumber, we speculate that this feature may be caused by low-energy vibrations of two-dimensional lattice structures of large molecules. Examples of such molecules include polycyclic aromatic hydrocarbons (PAHs) and nitrogenated aromatics. Finally, volume extinction coefficients NχE derived from 15°S CIRS data at a wavelength of λ=62.5μm are compared with those derived from the 10°S Huygens Descent Imager/Spectral Radiometer (DISR) data at 1.583μm. This comparison yields volume extinction coefficient ratios NχE(1.583μm)/NχE(62.5μm) of roughly 70 and 20, respectively, for Titan's aerosol and stratospheric ices. The inferred particle cross-section ratios χE(1.583μm)/χE(62.5μm) appear to be consistent with sub-micron size aerosol particles, and effective radii of only a few microns for stratospheric ice cloud particles. © 2011.


Cheng M.,University of Maryland University College
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

We study the superconducting proximity effect on the helical edge states of time-reversal-symmetric fractional topological insulators (FTI). The Cooper pairing of physical electrons results in many-particle condensation of the fractionalized excitations on the edge. We find localized zero-energy modes emerge at interfaces between superconducting regions and magnetically insulating regions, which are responsible for the topological degeneracy of the ground states. By mapping the low-energy effective Hamiltonian to the quantum chiral Potts model, we determine the operator algebra of the zero modes and show that they exhibit nontrivial braiding properties. We then demonstrate that the Josephson current in the junction between superconductors mediated by the edge states of the FTI exhibit fractional Josephson effect with period as multiples of 4π. © 2012 American Physical Society.


Yang J.,University of Wisconsin - Madison | Ulukus S.,University of Maryland University College
IEEE Transactions on Communications | Year: 2012

We consider the optimal packet scheduling problem in a single-user energy harvesting wireless communication system. In this system, both the data packets and the harvested energy are modeled to arrive at the source node randomly. Our goal is to adaptively change the transmission rate according to the traffic load and available energy, such that the time by which all packets are delivered is minimized. Under a deterministic system setting, we assume that the energy harvesting times and harvested energy amounts are known before the transmission starts. For the data traffic arrivals, we consider two different scenarios. In the first scenario, we assume that all bits have arrived and are ready at the transmitter before the transmission starts. In the second scenario, we consider the case where packets arrive during the transmissions, with known arrival times and sizes. We develop optimal off-line scheduling policies which minimize the time by which all packets are delivered to the destination, under causality constraints on both data and energy arrivals. © 2012 IEEE.


Chopra N.,University of Maryland University College
IEEE Transactions on Automatic Control | Year: 2012

In this technical note, we study output synchronization of networked multiagent systems. The agents, modeled as nonlinear systems with relative degree one, exchange information over a network described by an interagent communication graph. Inspired by the results of Igarashi , we extend our earlier results on output synchronization to include the case of strongly connected graphs. We first demonstrate output synchronization for input-output passive systems communicating over strongly connected graphs and include the practical case of constant time delays in communication. It is well known (Byrnes ) that weakly minimum phase systems with relative degree one are feedback equivalent to a passive system with a positive definite storage function. We exploit this feedback equivalence to develop control laws for output synchronization of such systems, exchanging outputs on strongly connected graphs, and in the presence of communication delays. A numerical example is also presented to illustrate the proposed results. © 2012 IEEE.


Simpson J.T.,Ontario Cancer Institute | Pop M.,University of Maryland University College
Annual Review of Genomics and Human Genetics | Year: 2015

The current genomic revolution was made possible by joint advances in genome sequencing technologies and computational approaches for analyzing sequence data. The close interaction between biologists and computational scientists is perhaps most apparent in the development of approaches for sequencing entire genomes, a feat that would not be possible without sophisticated computational tools called genome assemblers (short for genome sequence assemblers). Here, we survey the key developments in algorithms for assembling genome sequences since the development of the first DNA sequencing methods more than 35 years ago. Copyright © 2015 by Annual Reviews. All rights reserved.


A'Hearn M.F.,University of Maryland University College
Annual Review of Astronomy and Astrophysics | Year: 2011

Recent results, many but not all from flybys of comets by spacecraft, particularly the results from Deep Impact, have dramatically improved our understanding of the physical properties of cometary nuclei. Characteristic features are modest size (R<20 km), high porosity, low strength, and heterogeneity. There is also evidence that can be interpreted as showing the original cometesimals in a cometary nucleus and suggesting radial migration of macroscopic cometesimals during the aggregation of nuclei, which in turn aggregated into the cores of the giant planets. © 2011 by Annual Reviews. All rights reserved.


Colombini M.,University of Maryland University College
Biochimica et Biophysica Acta - Molecular Cell Research | Year: 2016

The voltage dependent anion-selective channel, VDAC, is the major permeability pathway by which molecules and ion cross the mitochondrial outer membrane. This pathway has evolved to optimize the flow of these substances and to control this flow by a gating process that is influenced by a variety of factors including transmembrane voltage. The permeation pathway formed through the membrane by VDAC is complex. Small ion flow is primarily influenced by the charged surface of the inner walls of the channel. Channel closure changes this landscape resulting in a change from a channel that favors anions to one that favors cations. Molecular ions interact more intimately with the inner walls of the channel and are selected by their 3-dimensional structure, not merely by their size and charge. Molecular ions typically found in cells are greatly favored over those that are not. For these larger structures the channel may form a low-energy translocation path that complements the structure of the permeant. © 2016 Elsevier B.V.


Levin M.,University of Maryland University College
Physical Review X | Year: 2013

We discuss the question of when a gapped two-dimensional electron system without any symmetry has a protected gapless edge mode. While it is well known that systems with a nonzero thermal Hall conductance, KH ≠ 0, support such modes, here we show that robust modes can also occur when KH = 0-if the system has quasiparticles with fractional statistics. We show that some types of fractional statistics are compatible with a gapped edge, while others are fundamentally incompatible. More generally, we give a criterion for when an electron system with Abelian statistics and KH = 0 can support a gapped edge: We show that a gapped edge is possible if and only if there exists a subset of quasiparticle typesMsuch that (1) all the quasiparticles inMhave trivial mutual statistics, and (2) every quasiparticle that is not in M has nontrivial mutual statistics with at least one quasiparticle in M. We derive this criterion using three different approaches: a microscopic analysis of the edge, a general argument based on braiding statistics, and finally a conformal field theory approach that uses constraints from modular invariance. We also discuss the analogous result for two-dimensional boson systems. © Published by the American Physical Society.


Belov G.A.,University of Maryland University College | Sztul E.,University of Alabama at Birmingham
Journal of virology | Year: 2014

Viruses are obligatory intracellular parasites and utilize host elements to support key viral processes, including penetration of the plasma membrane, initiation of infection, replication, and suppression of the host's antiviral defenses. In this review, we focus on picornaviruses, a family of positive-strand RNA viruses, and discuss the mechanisms by which these viruses hijack the cellular machinery to form and operate membranous replication complexes. Studies aimed at revealing factors required for the establishment of viral replication structures identified several cellular-membrane-remodeling proteins and led to the development of models in which the virus used a preexisting cellular-membrane-shaping pathway "as is" for generating its replication organelles. However, as more data accumulate, this view is being increasingly questioned, and it is becoming clearer that viruses may utilize cellular factors in ways that are distinct from the normal functions of these proteins in uninfected cells. In addition, the proteincentric view is being supplemented by important new studies showing a previously unappreciated deep remodeling of lipid homeostasis, including extreme changes to phospholipid biosynthesis and cholesterol trafficking. The data on viral modifications of lipid biosynthetic pathways are still rudimentary, but it appears once again that the viruses may rewire existing pathways to generate novel functions. Despite remarkable progress, our understanding of how a handful of viral proteins can completely overrun the multilayered, complex mechanisms that control the membrane organization of a eukaryotic cell remains very limited. Copyright © 2014, American Society for Microbiology. All Rights Reserved.


Villarreal A.,University of Maryland University College
Demography | Year: 2014

The rate of Mexico-U.S. migration has declined precipitously in recent years. From 25 migrants per thousand in 2005, the annual international migration rate for Mexican men dropped to 7 per thousand by 2012. If sustained, this low migration rate is likely to have a profound effect on the ethnic and national-origin composition of the U.S. population. This study examines the origins of the migration decline using a nationally representative panel survey of Mexican households. The results support an explanation that attributes a large part of the decline to lower labor demand for Mexican immigrants in the United States. Decreases in labor demand in industrial sectors that employ a large percentage of Mexican-born workers, such as construction, are found to be strongly associated with lower rates of migration for Mexican men. Second, changes in migrant selectivity are also consistent with an economic explanation for the decline in international migration. The largest declines in migration occurred precisely among the demographic groups most affected by the Great Recession: namely, economically active young men with low education. Results from the statistical analysis also show that the reduction in labor demand in key sectors of the U.S. economy resulted in a more positive educational selectivity of young migrants. © 2014, Population Association of America.


Kuchner M.J.,NASA | Stark C.C.,University of Maryland University College
Astronomical Journal | Year: 2010

We modeled the three-dimensional structure of the Kuiper Belt (KB) dust cloud at four different dust production rates, incorporating both planet-dust interactions and grain-grain collisions using the collisional grooming algorithm. Simulated images of a model with a face-on optical depth of -10 -4 primarily show an azimufhally symmetric ring at 40-47 AU in submillimeter and infrared wavelengths; this ring is associated with the cold classical KB. For models with lower optical depths (10-6 and 10 -7), synthetic infrared images show that the ring widens and a gap opens in the ring at the location of Neptune; this feature is caused by trapping of dust grains in Neptune's mean motion resonances. At low optical depths, a secondary ring also appears associated with the hole cleared in the center of the disk by Saturn. Our simulations, which incorporate 25 different grain sizes, illustrate that grain-grain collisions are important in sculpting today's KB dust, and probably other aspects of the solar system dust complex; collisions erase all signs of azimuthal asymmetry from the submillimeter image of the disk at every dust level we considered. The model images switch from being dominated by resonantly trapped small grains ("transport dominated") to being dominated by the birth ring ("collision dominated") when the optical depth reaches a critical value of τ - v/c, where v is the local Keplerian speed. © 2010. The American Astronomical Society. All rights reserved.


Gupta V.,University of Notre Dame | Martins N.C.,University of Maryland University College
IEEE Transactions on Automatic Control | Year: 2010

Consider a discrete-time networked control system, in which the controller has direct access to noisy measurements of the output of the plant. However, information flows from the controller to the actuator via a channel that features Bernoulli erasure events. If an erasure occurs, the channel outputs an erasure symbol; otherwise, it transmits a real finite-dimensional vector. We determine necessary and sufficient conditions for the stabilizability of an unstable linear time-invariant finite-dimensional plant. Given a minimal state-space representation for the plant, the necessary and sufficient conditions for stabilizability are expressed in terms of the probability of erasure at the channel and of the spectral radius of the one-step state transition matrix. There are two main results in the technical note. The first result shows that if the actuator has processing capabilities, then the necessary and sufficient conditions for stabilizability remain unchanged with or without acknowledgements from the actuator to the controller. The second result shows that the stabilizability conditions are identical for two types of actuators: (Type I) Processing at the actuator has access to the plant's model; © 2009 IEEE.


Babu K.S.,Oklahoma State University | Mohapatra R.N.,University of Maryland University College
Physical Review Letters | Year: 2012

We show that grand unified theories based on SO(10) generate quite naturally baryon number violating dimension seven operators that violate B-L, and lead to novel nucleon decay modes such as n→e -K +, e -π + and p→νπ +. We find that in two-step breaking schemes of nonsupersymmetric SO(10), the partial lifetimes for these modes can be within reach of experiments. The interactions responsible for these decay modes also provide a new way to understand the origin of matter in the Universe via the decays of grand unified theory (GUT) scale scalar bosons of SO(10). Their (B-L)-violating nature guarantees that the GUT scale induced baryon asymmetry is not washed out by the electroweak sphaleron interactions. In minimal SO(10) models this asymmetry is closely tied to the masses of quarks, leptons and the neutrinos. © 2012 American Physical Society.


Nicholson A.N.,University of Maryland University College
Physical Review Letters | Year: 2012

The ground state energies of universal N-body clusters tied to Efimov trimers, for N even, are shown to be encapsulated in the statistical distribution of two particles interacting with a background auxiliary field at large Euclidean time when the interaction is tuned to the unitary point. Numerical evidence that this distribution is log normal is presented, allowing one to predict the ground state energies of the N-body system. © 2012 American Physical Society.


Cohen T.D.,University of Maryland University College
Physical Review Letters | Year: 2012

It is shown that at sufficiently large N c for incident momenta which are much larger than the QCD scale, the total nucleon-nucleon cross section is independent of incident momentum and given by σtotal= 2π log2(N c)/(mπ2). This result is valid in the extreme large N c regime of log (N c)1 and has corrections of relative order log (log (N c))/log (N c). A possible connection of this result to the Froissart-Martin bound is discussed. © 2012 American Physical Society.


Powell S.,University of Maryland University College
Physical Review Letters | Year: 2012

Certain frustrated systems, including spin ice and dimer models, exhibit a Coulomb phase at low temperatures, with power-law correlations and fractionalized monopole excitations. Transitions out of this phase, at which the effective gauge theory becomes confining, provide examples of unconventional criticality. This Letter studies the behavior at nonzero monopole density near such transitions, using scaling theory to arrive at universal expressions for the crossover phenomena. For a particular transition in spin ice, quantitative predictions are made by mapping to the XY model and confirmed using Monte Carlo simulations. © 2012 American Physical Society.


Wang K.,Beijing Normal University | Dickinson R.E.,University of Texas at Austin | Liang S.,University of Maryland University College
Journal of Climate | Year: 2012

Pan evaporation (EP), an index of atmospheric evaporative demand, has been widely reported to have weakened in the past decades. However, its interpretation remains controversial because EP observations are not globally available and observations of one of its key controls, surface incident solar radiation Rs, are even less available. Using global-distributed Rs from both direct measurements (available through the Global Energy Balance Archive) and derived from sunshine duration, the authors calculated the potential evaporation from 1982 to 2008 from approximately 1300 stations. The findings herein show that the contribution of water vapor pressure deficit (VPD) to monthly variability of EP is much larger than that of other controlling factors, of Rs, wind speed (WS), and air temperature Ta. The trend of the aerodynamic component of EP, which includes contributions of VPD, WS, and Taa, accounted for 86% of the long-term trend of EP. The aerodynamic component was then calculated from 4250 globally distributed stations and showed a negligible averaged trend from 1973 to 2008 because the reduction in WS canceled out the impact of the elevated VPD. The long-term trend of WS dominates the long-term trend of the aerodynamic component of EP at the 4250 stations. Atmospheric evaporative demand increased in most arid and semiarid areas, indicating a decrease in water availability in those areas. © 2012 American Meteorological Society.


Galloway G.E.,University of Maryland University College
Journal of the American Water Resources Association | Year: 2011

In January 2010, hydrologists, climatologists, engineers, and scientists met in Boulder, Colorado, to discuss the report of the death of hydrologic stationarity and the implications this might have on water resources planning and operations in the United States and abroad. For decades planners have relied on design guidance from the Interagency Advisory Committee on Water Data Bulletin 17B that was based upon the concept of stationarity. After 21/2days of discussion it became clear that the assembled community had yet to reach an agreement on whether or not to replace the assumption of stationarity with an assumption of nonstationarity or something else. Hydrologists were skeptical that data gathered to this point in the 21st Century point to any significant change in river parameters. Climatologists, on the other hand, point to climate change and the predicted shift away from current conditions to a more turbulent flood and drought filled future. Both groups are challenged to provide immediate guidance to those individuals in and outside the water community who today must commit funds and efforts on projects that will require the best estimates of future conditions. The workshop surfaced many approaches to dealing with these challenges. While there is good reason to support additional study of the death of stationarity, its implications, and new approaches, there is also a great need to provide those in the field the information they require now to plan, design, and operate today's projects. © 2011 American Water Resources Association.


Baldwin A.H.,University of Maryland University College
Estuaries and Coasts | Year: 2013

To test species composition and biomass responses to excess nutrients, herbaceous plants of tidal freshwater and oligohaline wetlands in a Chesapeake Bay subestuary were fertilized with nitrogen (N), phosphorus (P), both N and P (N + P), or not fertilized (Control) for 4 years. In marshes, the N treatment increased abundance measures of perennials but decreased those of annuals while the P treatment increased annuals and decreased perennials. In swamps, however, perennials increased in response to P. Total herbaceous aboveground biomass production was not limited by N, P, or N + P in marshes or swamps. These findings suggest that annual species are more susceptible than perennials to P limitation, possibly due to lack of a large perenniating root organ and lower susceptibility to mycorrhizal inoculation. Furthermore, eutrophication effects are likely to vary between swamp and marsh habitats and depend on whether the dominant nutrient supplied is nitrogen or phosphorus. © 2011 Coastal and Estuarine Research Federation.


Sarbach O.,Universidad Michoacana de San Nicolas de Hidalgo | Tiglio M.,University of Maryland University College
Living Reviews in Relativity | Year: 2012

Many evolution problems in physics are described by partial differential equations on an infinite domain; therefore, one is interested in the solutions to such problems for a given initial dataset. A prominent example is the binary black-hole problem within Einstein's theory of gravitation, in which one computes the gravitational radiation emitted from the inspiral of the two black holes, merger and ringdown. Powerful mathematical tools can be used to establish qualitative statements about the solutions, such as their existence, uniqueness, continuous dependence on the initial data, or their asymptotic behavior over large time scales. However, one is often interested in computing the solution itself, and unless the partial differential equation is very simple, or the initial data possesses a high degree of symmetry, this computation requires approximation by numerical discretization. When solving such discrete problems on a machine, one is faced with a finite limit to computational resources, which leads to the replacement of the infinite continuum domain with a finite computer grid. This, in turn, leads to a discrete initial-boundary value problem. The hope is to recover, with high accuracy, the exact solution in the limit where the grid spacing converges to zero with the boundary being pushed to infinity. The goal of this article is to review some of the theory necessary to understand the continuum and discrete initial boundary-value problems arising from hyperbolic partial differential equations and to discuss its applications to numerical relativity; in particular, we present wellposed initial and initial-boundary value formulations of Einstein's equations, and we discuss multi-domain high-order finite difference and spectral methods to solve them.


Armstrong R.W.,University of Maryland University College
Materials Transactions | Year: 2014

Pioneering research results reported in the early 1950's by E. O. Hall and N. J. Petch on iron and steel materials have led to an expanded description of the grain size dependence of the complete stressstrain behavior of a wider range of materials and including assessments of other mechanical properties such as the ductile to brittle transition behavior and the hardness of materials, particularly, of nanocrystalline materials. The dislocation pile-up model that was presented originally for the inverse square root of grain diameter dependence of material strength has endured. Most recently, the pile-up model description has been more definitely associated with the Griffith theory of achieving a critical stress concentration at the tip of a crack; and, the Hall-Petch analysis has been connected to the macro-scale description of the fracture mechanics stress intensity parameter. These topics and other 60 years of Hall-Petch type researches are tracked over time in the present report while giving special emphasis to current order-of-magnitude strength improvements that are reported for metals with nanopolycrystalline grain diameters. © 2013 The Japan Institute of Metals and Materials.


Reggia J.A.,University of Maryland University College
Neural Networks | Year: 2013

Efforts to create computational models of consciousness have accelerated over the last two decades, creating a field that has become known as artificial consciousness. There have been two main motivations for this controversial work: to develop a better scientific understanding of the nature of human/animal consciousness and to produce machines that genuinely exhibit conscious awareness. This review begins by briefly explaining some of the concepts and terminology used by investigators working on machine consciousness, and summarizes key neurobiological correlates of human consciousness that are particularly relevant to past computational studies. Models of consciousness developed over the last twenty years are then surveyed. These models are largely found to fall into five categories based on the fundamental issue that their developers have selected as being most central to consciousness: a global workspace, information integration, an internal self-model, higher-level representations, or attention mechanisms. For each of these five categories, an overview of past work is given, a representative example is presented in some detail to illustrate the approach, and comments are provided on the contributions and limitations of the methodology. Three conclusions are offered about the state of the field based on this review: (1) computational modeling has become an effective and accepted methodology for the scientific study of consciousness, (2) existing computational models have successfully captured a number of neurobiological, cognitive, and behavioral correlates of conscious information processing as machine simulations, and (3) no existing approach to artificial consciousness has presented a compelling demonstration of phenomenal machine consciousness, or even clear evidence that artificial phenomenal consciousness will eventually be possible. The paper concludes by discussing the importance of continuing work in this area, considering the ethical issues it raises, and making predictions concerning future developments. © 2013 Elsevier Ltd.


Mi B.,University of Maryland University College | Elimelech M.,Yale University
Desalination | Year: 2013

This study investigated the silica scaling and cleaning behavior in forward osmosis (FO) and how it compared with that in reverse osmosis (RO). The comparison between FO and RO modes shows that, under the hydrodynamic conditions tested, the flux decline rates under silica scaling are very similar in the two modes, but the flux recovery is close to 100% in the FO mode while it is only around 80% in the RO mode. Cellulose acetate (CA) and polyamide (PA) membranes were used to study the effects of membrane materials on silica scaling and cleaning. It is found that the flux decline rates for both membranes are similar, but the flux recovery of the CA membrane is 30-40% higher than that of the PA membrane. AFM force measurements indicate that membrane surface roughness increases the adhesion force between the PA membrane and a silica gel layer, significantly decreasing the cleaning efficiency of the PA membrane. Results from dynamic light scattering and energy-dispersive X-ray spectroscopy indicate that silica scaling is initiated as monosilicic acid deposits on the membrane surface, followed by polymerization/condensation that forms an amorphous silica gel layer at the interface between the membrane and silica particles. © 2012 Elsevier B.V..


Porter L.C.,University of Maryland University College
Journal of Health and Social Behavior | Year: 2014

This study investigates the link between incarceration and health behavior among a sample of young adults from the National Longitudinal Study of Adolescent Health (N = 1,670). The association is analyzed using propensity score methods and a strategic comparison group: respondents who have been convicted of crimes, but not incarcerated. Findings suggest that former inmates consume more fast food and have a higher likelihood of smoking than do similarly situated peers. These associations operate partly through increased financial strife and decreased social standing. Given the role of health behavior in predicting future health outcomes, poor health behavior may be a salient force driving health and mortality risk among the formerly incarcerated population. © American Sociological Association 2014.


Isaacs L.,University of Maryland University College
Accounts of Chemical Research | Year: 2014

ConspectusThis Account focuses on stimuli responsive systems that function in aqueous solution using examples drawn from the work of the Isaacs group using cucurbit[n]uril (CB[n]) molecular containers as key recognition elements. Our entry into the area of stimuli responsive systems began with the preparation of glycoluril derived molecular clips that efficiently distinguish between self and nonself by H-bonds and π-π interactions even within complex mixtures and therefore undergo self-sorting. We concluded that the selectivity of a wide variety of H-bonded supramolecular assemblies was higher than previously appreciated and that self-sorting is not exceptional behavior. This lead us to examine self-sorting within the context of CB[n] host-guest chemistry in water.We discovered that CB[n] homologues (CB[7] and CB[8]) display remarkably high binding affinity (Ka up to 1017 M-1) and selectivity toward their guests, which renders CB[n]s prime components for the construction of stimuli responsive host-guest systems. The CB[7] ·adamantaneammonium ion complex, which is particularly privileged (K a = 4.2 × 1012 M-1), was introduced by us as a stimulus to trigger constitutional changes in multicomponent self-sorting systems. For example, we describe how the free energy associated with the formation of host-guest complexes of CB[n]-type receptors can drive conformational changes of included guests like triazene-arylene foldamers and cationic calix[4]arenes, as well as induced conformational changes (e.g., ammonium guest size dependent homotropic allostery, metal ion triggered folding, and heterochiral dimerization) of the hosts themselves.Many guests display large pKa shifts within their CB[n]-guest complexes, which we used to promote pH controlled guest swapping and thermal trans-to-cis isomerization of azobenzene derivatives. We also used the high affinity and selectivity of CB[7] toward its guests to outcompete an enzyme (bovine carbonic anhydrase) for a two-faced inhibitor, which allowed stimuli responsive regulation of enzymatic activity. These results prompted us to examine the use of CB[n]-type receptors in both in vitro and in vivo biological systems. We demonstrated that adamantaneammonium ion can be used to intracellularly sequester CB[7] from gold nanoparticles passivated with hexanediammonium ion·CB[7] complexes and thereby trigger cytotoxicity. CB[7] derivatives bearing a biotin targeting group enhance the cytotoxicity of encapsulated oxaliplatin toward L1210FR cells. Finally, acyclic CB[n]-type receptors function as solubilizing excipients for insoluble drugs for drug delivery purposes and as a broad spectrum reversal agent for the neuromuscular blocking agents rocuronium, vecuronium, and cis-atracurium in rats. The work highlights the great potential for integration of CB[n]-type receptors with biological systems. © 2014 American Chemical Society.


Baker R.H.,American Museum of Natural History | Wilkinson G.S.,University of Maryland University College
PLoS Genetics | Year: 2010

Chromosomal location has a significant effect on the evolutionary dynamics of genes involved in sexual dimorphism, impacting both the pattern of sex-specific gene expression and the rate of duplication and protein evolution for these genes. For nearly all non-model organisms, however, knowledge of chromosomal gene content is minimal and difficult to obtain on a genomic scale. In this study, we utilized Comparative Genomic Hybridization (CGH), using probes designed from EST sequence, to identify genes located on the X chromosome of four species in the stalk-eyed fly genus Teleopsis. Analysis of log2 ratio values of female-to-male hybridization intensities from the CGH microarrays for over 3,400 genes reveals a strongly bimodal distribution that clearly differentiates autosomal from X-linked genes for all four species. Genotyping of 33 and linkage mapping of 28 of these genes in Teleopsis dalmanni indicate the CGH results correctly identified chromosomal location in all cases. Syntenic comparison with Drosophila indicates that 90% of the X-linked genes in Teleopsis are homologous to genes located on chromosome 2L in Drosophila melanogaster, suggesting the formation of a nearly complete neo-X chromosome from Muller element B in the dipteran lineage leading to Teleopsis. Analysis of gene movement both relative to Drosophila and within Teleopsis indicates that gene movement is significantly associated with 1) rates of protein evolution, 2) the pattern of gene duplication, and 3) the evolution of eyespan sexual dimorphism. Overall, this study reveals that diopsids are a critical group for understanding the evolution of sex chromosomes within Diptera. In addition, we demonstrate that CGH is a useful technique for identifying chromosomal sex-linkage and should be applicable to other organisms with EST or partial genomic information. © 2010 Baker, Wilkinson.


Seo E.S.,University of Maryland University College
Astroparticle Physics | Year: 2012

Direct measurements of cosmic rays with balloon-borne detectors are used for understanding cosmic ray origin, acceleration and propagation, as well as exploring the supernova acceleration limit and searching for exotic sources such as dark matter. The energy reach of direct measurements is currently limited to ∼1015 eV by the detector size and exposure time, but incident particles are identified element-by-element with excellent charge resolution. A challenge of balloon-borne experiments is that the detectors must be large enough to collect adequate statistics, yet stay within the weight limit available for balloon flight. Innovative approaches now promise high quality measurements over an energy range that was not previously possible. Recent results and their implications are reviewed. The outlook of existing and future experiments is also discussed. © 2012 Elsevier B.V. All rights reserved.


Carter G.G.,University of Maryland University College
Proceedings. Biological sciences / The Royal Society | Year: 2013

Common vampire bats often regurgitate food to roost-mates that fail to feed. The original explanation for this costly helping behaviour invoked both direct and indirect fitness benefits. Several authors have since suggested that food sharing is maintained solely by indirect fitness because non-kin food sharing could have resulted from kin recognition errors, indiscriminate altruism within groups, or harassment. To test these alternatives, we examined predictors of food-sharing decisions under controlled conditions of mixed relatedness and equal familiarity. Over a 2 year period, we individually fasted 20 vampire bats (Desmodus rotundus) and induced food sharing on 48 days. Surprisingly, donors initiated food sharing more often than recipients, which is inconsistent with harassment. Food received was the best predictor of food given across dyads, and 8.5 times more important than relatedness. Sixty-four per cent of sharing dyads were unrelated, approaching the 67 per cent expected if nepotism was absent. Consistent with social bonding, the food-sharing network was consistent and correlated with mutual allogrooming. Together with past work, these findings support the hypothesis that food sharing in vampire bats provides mutual direct fitness benefits, and is not explained solely by kin selection or harassment.


Fan J.,University of Maryland University College
Nature Photonics | Year: 2016

A hallmark feature of topological physics is the presence of one-way propagating chiral modes at the system boundary. The chirality of edge modes is a consequence of the topological character of the bulk. For example, in a non-interacting quantum Hall model, edge modes manifest as mid-gap states between two topologically distinct bulk bands. The bulk–boundary correspondence dictates that the number of chiral edge modes, a topological invariant called the winding number, is completely determined by the bulk topological invariant, the Chern number. Here, for the first time, we measure the winding number in a 2D photonic system. By inserting a unit flux quantum at the edge, we show that the edge spectrum resonances shift by the winding number. This experiment provides a new approach for unambiguous measurement of topological invariants, independent of the microscopic details, and could possibly be extended to probe strongly correlated topological orders. © 2016 Nature Publishing Group


Deroche M.L.,University of Maryland University College
The Journal of the Acoustical Society of America | Year: 2012

Two experiments investigated the ability of 17 school-aged children to process purely temporal and spectro-temporal cues that signal changes in pitch. Percentage correct was measured for the discrimination of sinusoidal amplitude modulation rate (AMR) of broadband noise in experiment 1 and for the discrimination of fundamental frequency (F0) of broadband sine-phase harmonic complexes in experiment 2. The reference AMR was 100 Hz as was the reference F0. A child-friendly interface helped listeners to remain attentive to the task. Data were fitted using a maximum-likelihood technique that extracted threshold, slope, and lapse rate. All thresholds were subsequently standardized to a common d' value equal to 0.77. There were relatively large individual differences across listeners: eight had relatively adult-like thresholds in both tasks and nine had higher thresholds. However, these individual differences did not vary systematically with age, over the span of 6-16 yr. Thresholds were correlated across the two tasks and were about nine times finer for F0 discrimination than for AMR discrimination as has been previously observed in adults.


Gao G.G.,University of Maryland University College
Journal of medical Internet research | Year: 2012

Americans increasingly post and consult online physician rankings, yet we know little about this new phenomenon of public physician quality reporting. Physicians worry these rankings will become an outlet for disgruntled patients. To describe trends in patients' online ratings over time, across specialties, to identify what physician characteristics influence online ratings, and to examine how the value of ratings reflects physician quality. We used data from RateMDs.com, which included over 386,000 national ratings from 2005 to 2010 and provided insight into the evolution of patients' online ratings. We obtained physician demographic data from the US Department of Health and Human Services' Area Resource File. Finally, we matched patients' ratings with physician-level data from the Virginia Medical Board and examined the probability of being rated and resultant rating levels. We estimate that 1 in 6 practicing US physicians received an online review by January 2010. Obstetrician/gynecologists were twice as likely to be rated (P < .001) as other physicians. Online reviews were generally quite positive (mean 3.93 on a scale of 1 to 5). Based on the Virginia physician population, long-time graduates were more likely to be rated, while physicians who graduated in recent years received higher average ratings (P < .001). Patients gave slightly higher ratings to board-certified physicians (P = .04), those who graduated from highly rated medical schools (P = .002), and those without malpractice claims (P = .1). Online physician rating is rapidly growing in popularity and becoming commonplace with no evidence that they are dominated by disgruntled patients. There exist statistically significant correlations between the value of ratings and physician experience, board certification, education, and malpractice claims, suggesting a positive correlation between online ratings and physician quality. However, the magnitude is small. The average number of ratings per physician is still low, and most rating variation reflects evaluations of punctuality and staff. Understanding whether they truly reflect better care and how they are used will be critically important. ©Guodong Gordon Gao, Jeffrey S McCullough, Ritu Agarwal, Ashish K Jha.


Gnaupel-Herold T.,University of Maryland University College | Gnaupel-Herold T.,U.S. National Institute of Standards and Technology
Journal of Applied Crystallography | Year: 2012

A program is introduced that calculates diffraction elastic constants for the Reuss, modified Voigt, Hill, Kröner and inverse Kröner models. For materials with preferred orientation it uses the orientation distribution function (ODF) to calculate the anisotropic stress factors. The ODF is read in text format as output from the freely available texture programs popLA and MTEX. The software also calculates the orientation-dependent mixing ratios of intensities of overlapped reflections, anisotropic bulk constants, and stress from lattice strain and vice versa. © 2012 International Union of Crystallography Printed in Singapore-all rights reserved.


Chin E.R.,University of Maryland University College
Exercise and Sport Sciences Reviews | Year: 2010

Intracellular calcium (Ca) plays an important role in regulating muscle force production, metabolism, and muscle gene expression. It is hypothesized that the precise pattern of Ca oscillations, determined by the Ca channels activated and the contributing Ca pools, controls the coupling between neural activation, force production, cellular energetics, and gene expression. The physiological and cellular coordination between these events will be discussed. Copyright © 2010 by the American College of Sports Medicine.


Colwell R.R.,University of Maryland University College
Current Topics in Microbiology and Immunology | Year: 2013

One Health approaches have tended to focus on closer collaboration among veterinarians and medical professionals, but remain unclear about how ecological approaches could be applied or how they might benefit public health and disease control. In this chapter, we review ecological concepts, and discuss their relevance to health, with an emphasis on emerging infectious diseases (EIDs). Despite the fact that most EIDs originate in wildlife, few studies account for the population, community, or ecosystem ecology of the host, reservoir, or vector. The dimensions of ecological approaches to public health that we propose in this chapter are, in essence, networks of population dynamics, community structure, and ecosystem matrices incorporating concepts of complexity, resilience, and biogeochemical processes. © Springer-Verlag Berlin Heidelberg 2013.


Rowe M.L.,University of Maryland University College
Child Development | Year: 2012

Quantity and quality of caregiver input was examined longitudinally a sample of 50 parent-child dyads to determine which aspects of input contribute most to children's vocabulary skill across early development. Measures of input gleaned from parent-child interactions at child ages 18, 30, and 42months were examined relation to children's vocabulary skill on a standardized measure 1year later (e.g., 30, 42, and 54months). Results show that controlling for socioeconomic status, input quantity, and children's previous vocabulary skill; using a diverse and sophisticated vocabulary with toddlers; and using decontextualized language (e.g., narrative) with preschoolers explains additional variation later vocabulary ability. The differential effects of various aspects of the communicative environment at several points early vocabulary development are discussed. © 2012 The Authors. Child Development © 2012 Society for Research Child Development, Inc.


Yoon P.H.,University of Maryland University College | Yoon P.H.,Kyung Hee University
Geophysical Research Letters | Year: 2011

A recent observation shows that large-amplitude whistler waves propagating obliquely with respect to the ambient magnetic field may be responsible for energizing the radiation belt electrons to relativistic energies (MeV) within a time scale as short as a fraction of a second. Test-particle simulations available in the literature invariably adopt simple model wave forms for the oblique whistlers, such that rigorous analysis of these waves have not been performed to this date. The present Letter solves fully nonlinear cold electron fluid equation for obliquely propagating large-amplitude whistlers. Relativistic test particle simulation is then performed over these exact wave solutions, and it is shown that a population of initially low energy electrons can be accelerated tocal O 10 MeV energies, within a few seconds time scale. Copyright 2011 by the American Geophysical Union.


Cameron M.K.,University of Maryland University College
Journal of Computational Physics | Year: 2013

We propose an approach for finding dominant reactive channels and calculating percentages of reactive flux through each channel in chemical systems driven by a deterministic potential force and a small thermal noise. We assume that the temperature is low enough so that the reactive flux focuses around a finite number of paths connecting the reactant and the product states. These paths can be found in a systematic way by solving a Hamilton-Jacobi equation for the so called MaxFlux functional. We argue that the name "MaxFlux" is misleading: it should be called the resistivity functional instead. Once the network of transition paths is found, one can define an equivalent electric circuit and find the currents through each of its wires. These currents give estimates of the reactive flux along the corresponding transition paths. We test our approach on the problem of finding transition paths in the Alanine-Dipeptide with two dihedral angles where the reactive current can be computed exactly. The percentages of the reactive flux through each reactive channel given by our approach turn out to be in remarkable agreement with the exact ones. We apply this approach to the problem of finding escape paths of a CO molecule from a Myoglobin protein. We find a collection of exit locations and establish percentages of the reactive flux through each of them. © 2013 Elsevier Inc.


Pearlin L.I.,University of Maryland University College
Journals of Gerontology - Series B Psychological Sciences and Social Sciences | Year: 2010

This paper compares the meanings and applications of concepts relevant to both the life course and the stress process frameworks. Some of these concepts bear the same labels but serve quite different scholarly agendas. Other concepts have different labels but have closely related applications. The purpose of this kind of comparative analysis is to help both fields clarify the conceptual tools needed to advance their scholarly goals.


Brown M.,University of Maryland University College
Gondwana Research | Year: 2010

The modern plate tectonics regime is characterized by a duality of thermal environments, one representing the subduction zone and the other representing the arc-backarc or orogenic hinterland. This duality is the hallmark of one-sided (asymmetric) subduction, and the characteristic imprint of one-sided subduction in the geological record is predicted to be the broadly contemporaneous occurrence of two contrasting types of metamorphic belt, one of high dT/dP type and the other low dT/dP type. The broadly contemporaneous occurrence of granulite and ultrahigh-temperature metamorphism with eclogite-high-pressure granulite metamorphism in the geological record since the Neoarchean Era is evidence of dual thermal environments and indicates that subduction has operated on Earth since that time. Classic 'paired' metamorphic belts in which an inboard high dT/dP metamorphic belt is juxtaposed against an outboard low dT/dP metamorphic belt along a tectonic contact-such as the Ryoke and Sanbagawa belts in Japan-are found in Phanerozoic accretionary orogens of the circum-Pacific. Generally, they appear to result from juxtaposition of terranes with different metamorphic facies series that may or may not be exactly contemporaneous and that may or may not be far-traveled. This is a consequence of the difference between globally-continuous subduction, generating a low-to-intermediate dT/dP environment in the subduction zone and a high dT/dP environment in the arc-backarc system, and metamorphic imprints in the geological record that represent discrete 'events' due to changes in plate kinematics or subduction boundary dynamics, or as a result of collision of ridges, arcs or continents with the upper plate at the trench. The concept of 'paired' metamorphic belts may be generalized and extended more widely than in the original proposition to subduction-to-collision orogenic systems in addition to accretionary orogenic systems. In this wider application, the term "paired metamorphic belts" may be used for "penecontemporaneous belts of contrasting type of metamorphism that record different apparent thermal gradients, one warmer and the other colder, juxtaposed by plate tectonics processes" (Brown, 2009). This extends the original concept of Miyashiro (1961) beyond the simple pairing of high dT/dP and low dT/dP metamorphic belts in circum-Pacific accretionary orogens, and makes it more useful in the context of our better understanding of the relationship between thermal regimes and tectonic settings. This is particularly useful in subduction-to-collision orogenic systems, where the suture and lower plate materials will register the imprint of low-to-intermediate dT/dP and the upper plate will register penecontemporaneous high dT/dP metamorphism commonly manifested at shallow crustal levels by the occurrence of granites in the rock record. © 2009 Elsevier B.V. All rights reserved.


Adomaitis R.A.,University of Maryland University College
Journal of Crystal Growth | Year: 2010

A multiscale model of atomic layer deposition (ALD) inside a nanoporous material is developed in this paper. The overall model couples a lattice Monte Carlo simulator describing molecular-scale growth of the ALD film to a continuum description of the precursor transport within the nanopore. The multiscale simulation approach is used to study how intra-pore precursor depletion leads to nonuniform ALD films and to examine whether film properties, such as composition and surface roughness, are functions of position within the pore. © 2010 Elsevier B.V. All rights reserved.


Koenig M.A.,University of Minnesota | Woodward A.L.,University of Maryland University College
Developmental Psychology | Year: 2010

Three studies examined 24-month-olds' sensitivity to the prior accuracy of the source of information and the way in which young children modify their word learning from inaccurate sources. In Experiments 1A, 2, and 3, toddlers interacted with an accurate or inaccurate speaker who trained and tested children's comprehension of a new word-object link. In Experiment 1, children performed less systematically in response to an inaccurate than to an accurate source. In Experiments 2 and 3, after toddlers' comprehension of the new word-object links was tested by the original source, a second speaker requested the target objects. In Experiment 2, children responded randomly in response to the second speaker's requests when novel words were previously presented by an inaccurate source. In Experiment 3, toddlers responded randomly in response to both speakers in the inaccurate condition when their memory for words was taxed by a brief delay period. Taken together, these findings suggest that toddlers attend to accuracy information, that they treat inaccuracy as a feature of a particular individual, and that the word-object representations formed as a result may be fragile and short lived. Findings are discussed in terms of possible mechanisms by which children adjust their word learning from problematic speakers. © 2010 American Psychological Association.


Tartaglino-Mazzucchelli G.,University of Maryland University College
Journal of High Energy Physics | Year: 2010

We propose a new superspace formulation for N = (4, 4) conformal supergravity in two dimensions. This is based on a geometry where the structure group of the curved superspace is chosen to be SO(1,1)×SU(2) L×SU(2) R. The off-shell supergravity multiplet possesses super-Weyl transformations generated by an unconstrained real scalar superfield. The new supergravity formulation turns out to be an extension of the minimal multiplet introduced in 1988 by Gates et. al. and it allows the existence of various off-shell matter supermultiplets. Covariant twisted-II and twisted-I multiplets respectively describe the field strength of an Abelian vector multiplet and its prepotential. Moreover, we introduce covariant bi-projective superfields. These define a large class of matter multiplets coupled to 2D N = (4, 4) conformal supergravity. They are the analogue of the covariant projective superfields recently introduced for 4D and 5D matter-coupled supergravity but they differ by the fact that bi-projective superfields are defined with the use of two CP1 instead of one. We conclude by giving a manifestly locally supersymmetric and super-Weyl invariant action principle in bi-projective superspace. © SISSA 2010.


Kahn J.D.,University of Maryland University College
Biophysical Journal | Year: 2014

Investigators have constructed dsDNA molecules with several different base modifications and have characterized their bending and twisting flexibilities using atomic force microscopy, DNA ring closure, and single-molecule force spectroscopy with optical tweezers. The three methods provide persistence length measurements that agree semiquantitatively, and they show that the persistence length is surprisingly similar for all of the modified DNAs. The circular dichroism spectra of modified DNAs differ substantially. Simple explanations based on base stacking strength, polymer charge, or groove occupancy by functional groups cannot explain the results, which will guide further high-resolution theory and experiments. © 2014 Biophysical Society.


Narasimhan R.,University of Maryland University College | Stow D.,San Diego State University
Remote Sensing of Environment | Year: 2010

Monitoring the growth and distribution of Arctic tundra vegetation is important for understanding changes in early growing season conditions in Arctic ecosystems in response to a warming climate. The primary objective of this study is to examine the utility of computed Daily Moderate Resolution Imaging Spectroradiometer (MODIS) Normalized Difference Vegetation Index (NDVI) products relative to 16-day maximum value composite (MVC) datasets for observing early season green-up dynamics of Arctic tundra vegetation across the North Slope of Alaska. Greening in the Arctic typically occurs shortly after snowmelt and can potentially be captured by using satellite observations that are available on a daily basis. Daily MODIS Snow Cover products were employed to retrieve dates of complete snowmelt (DOCS) for 2003-2005 for pixels that were cloud free at the time of complete snowmelt. Given the sparseness of cloud-free observations in both space and time, early season NDVI trajectories for cloud-free pixels were derived using daily MODIS data based on two approaches: a chronosequence (temporally continuous but aspatial) and a pixel trajectory (temporally discontinuous but spatial explicit) approach. On average during the three-year period, 12.5% of the North Slope region was cloud free at the time of complete snowmelt and a majority of these cloud-free pixels (65%) were associated with the Coastal Plain province. In contrast, the Foothills region was relatively less cloudy from the time following complete snowmelt until peak greenness (56%) than the Coastal Plain province (61%). As a result, vegetation communities that lie mostly in the Foothills province such as shrub tundra and moist acidic tundra classes had more cloud-free observations available to characterize NDVI trajectories using the pixel trajectory approach. Complete snowmelt in the North Slope generally occurred between day of year (DOY) 140 and 170 over the three years with areas covered by the shrub tundra vegetation community (Foothills province) experiencing snowmelt first in all three years with mean DOCS ranging from DOY 148 in 2004 to DOY 158 in 2003. For approximately two weeks following complete snowmelt (Phase I, a period of rapid NDVI increase), the Daily NDVI derived trajectories were substantially different from the MVC NDVI trajectories. Early season integrated NDVI (ESINDVI) values computed for Phase I were 7% higher using the Daily NDVI approaches relative to those derived from the MVC MODIS data for the North Slope region. Following this initial period, until peak greenness (Phase 2, a period of gradual NDVI increase), the Daily and MVC trajectories were similar in shape and magnitude. This study demonstrates the utility of the Daily MODIS Snow product for assessing cloud cover and snowmelt patterns and Daily MODIS NDVI data for observing and detecting sharp and rapid changes in early season vegetation phenology as seen during Phase I. © 2010 Elsevier Inc. All rights reserved.


Cohen T.D.,University of Maryland University College
Journal of High Energy Physics | Year: 2010

It is shown that large Nc QCD must have a Hagedorn spectrum (i.e., a spectrum of hadron which grows exponentially with the hadrons' mass) provided that certain technical assumptions concerning the applicability of perturbation theory to a certain class of correlation functions apply. The basic argument exploits the interplay of confinement and asymptotic freedom. © SISSA 2010.


Sati H.,University of Maryland University College
Journal of Physics A: Mathematical and Theoretical | Year: 2011

M-theory can be defined on closed manifolds as well as on manifolds with boundary. As an extension, we show that manifolds with corners appear naturally in M-theory. We illustrate this with four situations: the lift to bounding 12 dimensions of M-theory on anti-de Sitter spaces, ten-dimensional heterotic string theory in relation to 12 dimensions, and the two M-branes within M-theory in the presence of a boundary. The M2-brane is taken with (or as) a boundary and the worldvolume of the M5-brane is viewed as a tubular neighborhood. We then concentrate on the (variant) of the heterotic theory as a corner and explore analytical and geometric consequences. In particular, we formulate and study the phase of the partition function in this setting and identify the corrections due to the corner(s). The analysis involves considering M-theory on disconnected manifolds and makes use of the extension of the Atiyah-Patodi-Singer index theorem to manifolds with corners and the b-calculus of Melrose. © 2011 IOP Publishing Ltd.


Rao W.-F.,Rutgers University | Wuttig M.,University of Maryland University College | Khachaturyan A.G.,Rutgers University
Physical Review Letters | Year: 2011

A new class of functional materials with giant nonhysteretic strain responses to applied fields is considered. They are decomposed two-phase systems consisting of single-domain nanoprecipitates of a low-symmetry phase. Their strain response is caused by the field-induced change of structural orientation of the domain states of these precipitates. The superresponse follows from the novel concept of structural anisotropy that is analogous to the magnetic anisotropy. Its vanishing produces a new glasslike structural state. The developed phase field theory and modeling allow us to formulate criteria for searching superresponsive two-phase nanostructured alloys. © 2011 American Physical Society.


Paoletti M.S.,Institute for Research in Electronics and Applied Physics | Lathrop D.P.,Institute for Research in Electronics and Applied Physics | Lathrop D.P.,University of Maryland University College
Physical Review Letters | Year: 2011

We present measurements of the angular momentum flux (torque) in Taylor-Couette flow of water between independently rotating cylinders for all regions of the (Ω1, Ω2) parameter space at high Reynolds numbers, where Ω1 (Ω2) is the inner (outer) cylinder angular velocity. We find that the Rossby number Ro=(Ω1-Ω2)/Ω2 fully determines the state and torque G as compared to G(Ro=∞)≡G ∞. The ratio G/G∞ is a linear function of Ro⊃-1 in four sections of the parameter space. For flows with radially increasing angular momentum, our measured torques greatly exceed those of previous experiments, but agree with the analysis of Richard and Zahn. © 2011 The American Physical Society.


McGaugh S.S.,University of Maryland University College
Physical Review Letters | Year: 2011

The current cosmological paradigm, the cold dark matter model with a cosmological constant, requires that the mass-energy of the Universe be dominated by invisible components: dark matter and dark energy. An alternative to these dark components is that the law of gravity be modified on the relevant scales. A test of these ideas is provided by the baryonic Tully-Fisher relation (BTFR), an empirical relation between the observed mass of a galaxy and its rotation velocity. Here, I report a test using gas rich galaxies for which both axes of the BTFR can be measured independently of the theories being tested and without the systematic uncertainty in stellar mass that affects the same test with star dominated spirals. The data fall precisely where predicted a priori by the modified Newtonian dynamics. The scatter in the BTFR is attributable entirely to observational uncertainty, consistent with a single effective force law. © 2011 American Physical Society.


Bederson B.B.,University of Maryland University College
Behaviour and Information Technology | Year: 2011

Zoomable user interfaces (ZUIs) have received a significant amount of attention in the 18 years since they were introduced. They have enjoyed some success, and elements of ZUIs are widely used in computers today, although the grand vision of a zoomable desktop has not materialised. This paper describes the premise and promise of ZUIs along with their challenges. It describes design guidelines, and offers a cautionary tale about research and innovation. © 2011 Taylor & Francis.


Cavanagh J.F.,University of New Mexico | Shackman A.J.,University of Maryland University College
Journal of Physiology Paris | Year: 2015

Evidence from imaging and anatomical studies suggests that the midcingulate cortex (MCC) is a dynamic hub lying at the interface of affect and cognition. In particular, this neural system appears to integrate information about conflict and punishment in order to optimize behavior in the face of action-outcome uncertainty. In a series of meta-analyses, we show how recent human electrophysiological research provides compelling evidence that frontal-midline theta signals reflecting MCC activity are moderated by anxiety and predict adaptive behavioral adjustments. These findings underscore the importance of frontal theta activity to a broad spectrum of control operations. We argue that frontal-midline theta provides a neurophysiologically plausible mechanism for optimally adjusting behavior to uncertainty, a hallmark of situations that elicit anxiety and demand cognitive control. These observations compel a new perspective on the mechanisms guiding motivated learning and behavior and provide a framework for understanding the role of the MCC in temperament and psychopathology. © 2014 Elsevier Ltd.


Ottinger M.A.,University of Maryland University College
Annals of the New York Academy of Sciences | Year: 2010

The interplay of neuroendocrine processes and gonadal function is exquisitely expressed during aging. In females, loss of ovarian function results in decreased circulating estradiol. As a result, estrogen-dependent endocrine and behavioral responses decline, including impaired cognitive function reflecting the impact of declining estrogen on the hippocampus circuits, and decreased metabolic endocrine function. Concurrently, age-related changes in neuroendocrine response also contribute to the declining reproductive function. Our session considered key mechanisms in reproductive aging including the roles of ovarian function (Finch and Holmes) and the hypothalamic median eminence (Yin and Gore) with an associated age-related cognitive decline that accompanies estrogen loss (Morrison and colleagues). Effects of smoking, obesity, and insulin resistance (Sowers and colleagues) impact the timing of the perimenopause transition in women. Animal models provide excellent insights into conserved mechanisms and key overarching events that bring about endocrine and behavioral aging. Environmental factors are key triggers in timing endocrine aging with implications for eventual disease. Session presentations will be considered in the context of the broader topic of indices and predictors of aging-related change. © 2010 New York Academy of Sciences.


Akamatsu Y.,Nagoya University | Yamamoto N.,Kyoto University | Yamamoto N.,University of Maryland University College
Physical Review Letters | Year: 2013

We study the collective modes in relativistic electromagnetic or quark-gluon plasmas with an asymmetry between left- and right-handed chiral fermions, based on the recently formulated kinetic theory with Berry curvature corrections. We find that there exists an unstable mode, signaling the presence of a plasma instability. We argue the fate of this "chiral plasma instability" including the effect of collisions, and briefly discuss its relevance in heavy ion collisions and compact stars. © 2013 American Physical Society.


Pessoa L.,University of Maryland University College
Behavioral and Brain Sciences | Year: 2012

Lindquist et al. provide a convincing case against what they call the locationist account of emotion. Their quantitative approach elegantly illustrates the shortcomings of this still-entrenched viewpoint. Here, I discuss how a network perspective will advance our understanding of structure-function mappings in general, and the relationship between emotion and cognition in the brain. © 2012 Cambridge University Press.


Chun S.H.,Samsung | La R.J.,University of Maryland University College
IEEE/ACM Transactions on Networking | Year: 2013

Recently, dynamic spectrum sharing has been gaining interest as a potential solution to scarcity of available spectrum. We investigate the problem of designing a secondary spectrum-trading market when there are multiple sellers and multiple buyers and propose a general framework for the trading market based on an auction mechanism. To this end, we first introduce a new optimal auction mechanism, called the generalized Branco's mechanism (GBM). The GBM, which is both incentive-compatible and individually rational, is used to determine the assigned frequency bands and prices for them. Second, we assume that buyers of the spectrum are selfish and model their interaction as a noncooperative game. Using this model, we prove that when the sellers employ the GBM to vend their frequency bands, they can guarantee themselves the largest expected profits by selling their frequency bands jointly. Third, based on the previous finding, we model the interaction among the sellers as a cooperative game and demonstrate that, for any fixed strategies of the buyers, the core of the cooperative game is nonempty. This suggests that there exists a way for the sellers to share the profits from the joint sale of the spectrum so that no subset of sellers will find it beneficial to vend their frequency bands separately without the remaining sellers. Finally, we propose a profit-sharing scheme that can achieve any expected profit vector in the nonempty core of the cooperative game while satisfying two desirable properties. © 1993-2012 IEEE.


Kim D.,KAIST | Lee Y.W.,KAIST | Lee S.B.,KAIST | Lee S.B.,University of Maryland University College | Han S.W.,KAIST
Angewandte Chemie - International Edition | Year: 2012

The many faces of noble metals: Through the simultaneous reduction of Au and Pd ions in the presence of octahedral Au nanocrystal (NC) seeds, hexoctahedron-like convex Au@Pd core-shell NCs, enclosed predominantly by high-index {12 5 3} facets, were synthesized under aqueous room-temperature conditions (see picture). The convex Au@Pd NCs showed much higher electrocatalytic properties toward ethanol oxidation than other types of Au@Pd NCs. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Mosleh A.,University of Maryland University College
Nuclear Engineering and Technology | Year: 2014

Probabilistic risk assessment (PRA) has been used in various technological fields to assist regulatory agencies, managerial decision makers, and systems designers in assessing and mitigating the risks inherent in these complex arrangements. Has PRA delivered on its promise? How do we gage PRA performance? Are our expectations about value of PRA realistic? Are there disparities between what we get and what we think we are getting form PRA and its various derivatives? Do current PRAs reflect the knowledge gained from actual events? How do we address potential gaps? These are some of the questions that have been raised over the years since the inception of the field more than forty years ago. This paper offers a brief assessment of PRA as a technical discipline in theory and practice, its key strengths and weaknesses, and suggestions on ways to address real and perceived shortcomings.


The formation and differentiation of the continental crust occurs at convergent plate margins in accretionary and collisional orogenic belts where sufficient heat is generated to achieve high-grade metamorphism and anatexis. Volumetrically significant H2O-present melting requires an influx of aqueous fluid along zones of high-strain deformation or via fracture networks, or recycling of the fluid dissolved in melt via melt migration and fluid exsolution during crystallization. In contrast, in "dry" crust, melting occurs via hydrate-breakdown melting reactions at higher temperatures than H2O-present melting; volumetrically significant melt production requires temperatures above ~800 8C. Melting wets residual grains, and anatectic crust becomes porous at a few vol.% melt. Feedback between deformation and melting creates a dynamic rheological environment; as melt volume increases to the melt connectivity transition, which varies but is around 7 vol.% (see discussion later in the text), melt may escape from the source in the first of several melt-loss events with increasing temperature. Major and accessory phase controls on melt production and melt composition for different pressure-temperature-time paths are evaluated using calculated phase equilibria for average pelite. The pristine to slightly retrogressed condition of peritectic minerals in residual crust requires significant loss of melt from the system. The consequences of melt loss are evaluated here. In residual crust, evidence of melt at the grain scale may be preserved in microstructures, whereas evidence of melt extraction pathways at outcrop scale is recorded by leucosome networks. Strain and anisotropy of permeability control the form of mesoscale melt channels with strong anisotropy promoting high-melt focusing. The sequence of structures observed in nature records a transition from storage to drainage; focused melt flow occurs by dilatant shear failure of low-melt-fraction rocks, leading to the formation of networks of channels that allow accumulation and storage of melt and that form the link for melt flow from grain boundaries to ascent conduits. Melt ascent is via ductile-to-brittle fracture; ductile fractures may propagate along foliation as sills or from dilation or shear bands as dikes. Emplacement of horizontal tabular and wedge-shaped plutons occurs around the brittle-ductile transition zone, whereas vertical lozenge-shaped plutons represent crystallization of magma in the ascent conduit. Blobby plutons form by lateral expansion in the ascent conduit localized by thermal or mechanical instabilities.


Dev P.S.B.,University of Manchester | Dev P.S.B.,TU Munich | Mohapatra R.N.,University of Maryland University College
Physical Review Letters | Year: 2015

We show that the excess events observed in a number of recent LHC resonance searches can be simultaneously explained within a nonsupersymmetric left-right inverse seesaw model for neutrino masses with WR mass around 1.9 TeV. The minimal particle content that leads to gauge coupling unification in this model predicts gR≃0.51 at the TeV scale, which is consistent with data. The extra color singlet, SU(2)-triplet fermions required for unification can be interpreted as the dark matter of the Universe. Future measurements of the ratio of same-sign to opposite-sign dilepton events can provide a way to distinguish this scenario from the canonical cases of type-I and inverse seesaw, i.e., provide a measure of the relative magnitudes of the Dirac and Majorana masses of the right-handed neutrinos in the SU(2)R doublet of the left-right symmetric model. © 2015 American Physical Society. © 2015 American Physical Society.


Kirkpatrick T.R.,University of Maryland University College | Belitz D.,University of Oregon
Physical Review Letters | Year: 2013

A quantum phase transition that was recently observed in a high-mobility silicon metal-oxide-semiconductor field-effect transistor is analyzed in terms of a scaling theory. The most striking characteristic of the transition is a divergence of the thermopower, according to an inverse linear law, as a critical value of the electron density is approached. A scaling description of this transition yields predictions about the critical behavior of other observables, e.g., the specific heat. We also explore the possibility that this transition realizes a recently predicted transition from a Fermi liquid to a non-Fermi-liquid state. © 2013 American Physical Society.


Senthil T.,Massachusetts Institute of Technology | Levin M.,University of Maryland University College
Physical Review Letters | Year: 2013

A simple physical realization of an integer quantum Hall state of interacting two dimensional bosons is provided. This is an example of a symmetry-protected topological (SPT) phase which is a generalization of the concept of topological insulators to systems of interacting bosons or fermions. Universal physical properties of the boson integer quantum Hall state are described and shown to correspond with those expected from general classifications of SPT phases. © 2013 American Physical Society.


Vishkin U.,University of Maryland University College
Communications of the ACM | Year: 2014

The current generation of general-purpose multicore hardware must be fixed to support more application domains and to allow cost-effective parallel programming. Open-ended problems and programming is characterized by the way problems may be posed and computer programs developed rather than by a particular application. Many problems whose initial understanding does not imply clear output, or sometimes even input, definitions lend themselves to irregular programming. Today's general-purpose multicore hardware does not provide sufficient support for any of these domains. Today's general-purpose multicore hardware does not provide sufficient support for any of these domains. It must be fixed to support more of them, and to allow cost-effective parallel programming. A fix will require changes both to current hardware, and to the overall ecological system comprising them, including programming practice and compilers.


Kirkpatrick T.R.,University of Maryland University College | Belitz D.,University of Oregon
Physical Review Letters | Year: 2014

We determine the preasymptotic critical behavior at the quantum ferromagnetic transition in strongly disordered metals. We find that it is given by effective power laws, in contrast to the previously analyzed asymptotic critical behavior, which is valid only in an unobservably small region. The consequences for analyzing experiments are discussed, in particular, ways to distinguish between critical behavior and Griffiths-phase effects. © 2014 American Physical Society.


Yarmola T.,University of Maryland University College
Communications in Mathematical Physics | Year: 2011

We consider steady states for a class of mechanical systems with particle-disk interactions coupled to two, possibly unequal, heat baths. We show that any steady state that satisfies some natural assumptions is ergodic and absolutely continuous with respect to a Lebesgue-type reference measure and conclude that there exists at most one absolutely continuous steady state. © 2011 Springer-Verlag.


Flores-Lopez C.A.,University of Maryland University College
PLoS neglected tropical diseases | Year: 2011

The genetic diversity of Trypanosoma cruzi, the etiological agent of Chagas disease, has been traditionally divided in two major groups, T. cruzi I and II, corresponding to discrete typing units TcI and TcII-VI under a recently proposed nomenclature. The two major groups of T. cruzi seem to differ in important biological characteristics, and are thus thought to represent a natural division relevant for epidemiological studies and development of prophylaxis. To understand the potential connection between the different manifestations of Chagas disease and variability of T. cruzi strains, it is essential to have a correct reconstruction of the evolutionary history of T. cruzi. Nucleotide sequences from 32 unlinked loci (>26 Kilobases of aligned sequence) were used to reconstruct the evolutionary history of strains representing the known genetic variability of T. cruzi. Thorough phylogenetic analyses show that the original classification of T. cruzi in two major lineages does not reflect its evolutionary history and that there is only strong evidence for one major and recent hybridization event in the history of this species. Furthermore, estimates of divergence times using Bayesian methods show that current extant lineages of T. cruzi diverged very recently, within the last 3 million years, and that the major hybridization event leading to hybrid lineages TcV and TcVI occurred less than 1 million years ago, well before the contact of T. cruzi with humans in South America. The described phylogenetic relationships among the six major genetic subdivisions of T. cruzi should serve as guidelines for targeted epidemiological and prophylaxis studies. We suggest that it is important to reconsider conclusions from previous studies that have attempted to uncover important biological differences between the two originally defined major lineages of T. cruzi especially if those conclusions were obtained from single or few strains.


Nacev A.,University of Maryland University College
International journal of nanomedicine | Year: 2011

A nanoparticle delivery system termed dynamic magnetic shift (DMS) has the potential to more effectively treat metastatic cancer by equilibrating therapeutic magnetic nanoparticles throughout tumors. To evaluate the feasibility of DMS, histological liver sections from autopsy cases of women who died from breast neoplasms were studied to measure vessel number, size, and spatial distribution in both metastatic tumors and normal tissue. Consistent with prior studies, normal tissue had a higher vascular density with a vessel-to-nuclei ratio of 0.48 ± 0.14 (n = 1000), whereas tumor tissue had a ratio of 0.13 ± 0.07 (n = 1000). For tumors, distances from cells to their nearest blood vessel were larger (average 43.8 μm, maximum 287 μm, n ≈ 5500) than normal cells (average 5.3 μm, maximum 67.8 μm, n ≈ 5500), implying that systemically delivered nanoparticles diffusing from vessels into surrounding tissue would preferentially dose healthy instead of cancerous cells. Numerical simulations of magnetically driven particle transport based on the autopsy data indicate that DMS would correct the problem by increasing nanoparticle levels in hypovascular regions of metastases to that of normal tissue, elevating the time-averaged concentration delivered to the tumor for magnetic actuation versus diffusion alone by 1.86-fold, and increasing the maximum concentration over time by 1.89-fold. Thus, DMS may prove useful in facilitating therapeutic nanoparticles to reach poorly vascularized regions of metastatic tumors that are not accessed by diffusion alone.


Link L.E.,University of Maryland University College
Ocean Engineering | Year: 2010

Hurricane Katrina created the one of the worst natural disaster in the history of the United States, resulting in over 1600 fatalities and $30B in direct economic losses in southern Louisiana. The Louisiana and Mississippi coastlines experienced the highest surge level recorded in North America and Katrina-generated waves in the Gulf of Mexico that equaled the highest previously measured by NOAA buoys. What happened in New Orleans epitomizes the risk of living below sea level in a coastal city, depending on structures that were the result of considerable compromise and piecemeal funding and construction. The Interagency Performance Evaluation Task Force was established to examine the performance of the New Orleans and southeast Louisiana hurricane protection system and provide real-time input to the repairs and rebuilding of the system. In addition to this atypical just-in-time forensic analysis, the task force examined the risk of living in New Orleans prior to and following the repairs to the hurricane protection system. Much of the forensic analysis depended on modeling and simulation of hurricane surge and waves. With virtually all measurement instruments swept away by Katrina, only models and high-water marks were available to recreate the conditions that the structures experienced during the storm. Because of the complexities of the region and the processes involved, simulation of hurricane surge and waves required many fresh ideas and new approaches and these topics, along with new concepts for future planning and design, are the focus of this special issue. Yet, the need to influence the repair and rebuilding of the damaged structures prior to the next hurricane season (roughly 9 months) dictated using existing computational tools that were ready to go. The same modeling and simulation approach was put to work to define the surge and wave hazard New Orleans faces for the future. To put this important body of work in context, this paper provides a broad overview of the entire scope of work of the task force and summarizes its principal findings. © 2009 Elsevier Ltd.


Montesi L.G.J.,University of Maryland University College
Journal of Structural Geology | Year: 2013

Lithospheric deformation on Earth is localized under both brittle and ductile deformation conditions. As high-temperature ductile rheologies are fundamentally strain-rate hardening, the formation of localized ductile shear zones must involve a structural or rheological change or a change in deformation conditions such as an increase in temperature. In this contribution, I develop a localization potential that quantifies the weakening associated with these changes. The localization potential corresponds to the increase in strain rate resulting from that change under constant stress conditions. I provide analytical expressions for the localization potential associated with a temperature increase, grain size reduction, an increase in water fugacity, melt content, or the abundance of a weak mineral phase. I show that these processes cannot localize deformation from a mantle convection scale (103 km) to a ductile shear zone scale (1 km). To achieve this, is it necessary to invoke a structural transition whereby the weak phase in a rock forms interconnected layers. This process is efficient only if one phase is much weaker than the others or if the weakest phase has a highly non-linear rheology. Micas, melt, and fine-grained aggregates - unless dry rheologies are used - have the necessary characteristics. As none of these phases is expected to be present in the dry lithosphere of Venus, this concept can explain why Venus, unlike the Earth, does not display a global network of plate boundaries. The diffuse plate boundary in the Central Indian Ocean may be as yet non-localized because serpentinization has not reached the ductile levels of the lithosphere. © 2013 Elsevier Ltd.


Fisher D.R.,University of Maryland University College
Environment and Planning C: Government and Policy | Year: 2013

In this paper, I look at how subnational policies in the United States are interacting with policy making at the federal level to address the issue of global climate change. I focus on a coordinated attempt to get the national government to fund local efforts to address climate change. Although local climate initiatives in the US were successfully translated into a national policy to support these local efforts, their implementation through hybrid arrangements that are being formed between business and local governmental actors will potentially create additional challenges to federal policy making. I introduce the notion of boomerang federalism, which builds on the extant research on federalism and vertical policy integration, to explain the process through which local efforts mobilize initiatives at the national level that, in turn, provide support for the local initiatives themselves. Reviewing the implementation process of this effort, I discuss the ways that businesses are working alongside local governments to address climate change.


Khraiwesh B.,King Abdullah University of Science and Technology | Zhu J.-K.,King Abdullah University of Science and Technology | Zhu J.-K.,Purdue University | Zhu J.,University of Maryland University College
Biochimica et Biophysica Acta - Gene Regulatory Mechanisms | Year: 2012

Small, non-coding RNAs are a distinct class of regulatory RNAs in plants and animals that control a variety of biological processes. In plants, several classes of small RNAs with specific sizes and dedicated functions have evolved through a series of pathways. The major classes of small RNAs include microRNAs (miRNAs) and small interfering RNAs (siRNAs), which differ in their biogenesis. miRNAs control the expression of cognate target genes by binding to reverse complementary sequences, resulting in cleavage or translational inhibition of the target RNAs. siRNAs have a similar structure, function, and biogenesis as miRNAs but are derived from long double-stranded RNAs and can often direct DNA methylation at target sequences. Besides their roles in growth and development and maintenance of genome integrity, small RNAs are also important components in plant stress responses. One way in which plants respond to environmental stress is by modifying their gene expression through the activity of small RNAs. Thus, understanding how small RNAs regulate gene expression will enable researchers to explore the role of small RNAs in biotic and abiotic stress responses. This review focuses on the regulatory roles of plant small RNAs in the adaptive response to stresses. This article is part of a Special Issue entitled: Plant gene regulation in response to abiotic stress. © 2011 Elsevier B.V.


Ji X.,Shanghai JiaoTong University | Ji X.,University of Maryland University College
Physical Review Letters | Year: 2013

I show that the parton physics related to correlations of quarks and gluons on the light cone can be studied through the matrix elements of frame-dependent, equal-time correlators in the large momentum limit. This observation allows practical calculations of parton properties on a Euclidean lattice. As an example, I demonstrate how to recover the leading-twist quark distribution by boosting an equal-time correlator to a large momentum. © 2013 American Physical Society.


Han B.,Pohang University of Science and Technology | Davis L.S.,University of Maryland University College
IEEE Transactions on Pattern Analysis and Machine Intelligence | Year: 2012

Background modeling and subtraction is a natural technique for object detection in videos captured by a static camera, and also a critical preprocessing step in various high-level computer vision applications. However, there have not been many studies concerning useful features and binary segmentation algorithms for this problem. We propose a pixelwise background modeling and subtraction technique using multiple features, where generative and discriminative techniques are combined for classification. In our algorithm, color, gradient, and Haar-like features are integrated to handle spatio-temporal variations for each pixel. A pixelwise generative background model is obtained for each feature efficiently and effectively by Kernel Density Approximation (KDA). Background subtraction is performed in a discriminative manner using a Support Vector Machine (SVM) over background likelihood vectors for a set of features. The proposed algorithm is robust to shadow, illumination changes, spatial variations of background. We compare the performance of the algorithm with other density-based methods using several different feature combinations and modeling techniques, both quantitatively and qualitatively. © 2012 IEEE.


Zhou Q.,University of Maryland University College | Ho T.-L.,Ohio State University
Physical Review Letters | Year: 2011

Quantum simulation is a highly ambitious program in cold atom research currently being pursued in laboratories worldwide. The goal is to use cold atoms in optical lattices to simulate models for unsolved strongly correlated systems, so as to deduce their properties directly from experimental data. An important step in this effort is to determine the temperature of the system, which is essential for deducing all thermodynamic functions. This step, however, remains difficult for lattice systems at the moment. Here, we propose a method based on a generalized fluctuation-dissipation theorem. It does not rely on numerical simulations and gives a universal thermometry scheme for quantum gas systems including mixtures and spinor gases, provided that the local density approximation is valid. © 2011 American Physical Society.


Miller M.C.,University of Maryland University College | Davies M.B.,Lund Observatory
Astrophysical Journal | Year: 2012

Massive black holes have been discovered in all closely examined galaxies with high velocity dispersion. The case is not as clear for lower-dispersion systems such as low-mass galaxies and globular clusters. Here we suggest that above a critical velocity dispersion 40kms-1, massive central black holes will form in relaxed stellar systems at any cosmic epoch. This is because above this dispersion primordial binaries cannot support the system against deep core collapse. If, as previous simulations show, the black holes formed in the cluster settle to produce a dense subcluster, then given the extremely high densities reached during core collapse the holes will merge with each other. For low velocity dispersions and hence low cluster escape speeds, mergers will typically kick out all or all but one of the holes due to three-body kicks or the asymmetric emission of gravitational radiation. If one hole remains, it will tidally disrupt stars at a high rate. If none remain, one is formed after runaway collisions between stars, and then it tidally disrupts stars at a high rate. The accretion rate after disruption is many orders of magnitude above Eddington. If, as several studies suggest, the hole can accept matter at that rate because the generated radiation is trapped and advected, then it will grow quickly and form a massive central black hole. © 2012 The American Astronomical Society. All rights reserved.


Dheeraj P.R.,University of Maryland University College | Strohmayer T.E.,NASA
Astrophysical Journal | Year: 2012

We present results of new XMM-Newton observations of the ultraluminous X-ray source (ULX) NGC5408 X-1, one of the few ULXs to show quasi-periodic oscillations (QPOs). We detect QPOs in each of four new (100ks) pointings, expanding the range of frequencies observed from 10 to 40mHz. We compare our results with the timing and spectral correlations seen in stellar-mass black hole systems, and find that the qualitative nature of the timing and spectral behavior of NGC5408 X-1 is similar to systems in the steep power-law state exhibiting Type-C QPOs. However, in order for this analogy to quantitatively hold we must only be seeing the so-called saturated portion of the QPO frequency - photon index (or disk flux) relation. Assuming this to be the case, we place a lower limit on the mass of NGC5408 X-1 of ≳ 800 M . Alternatively, the QPO frequency is largely independent of the spectral parameters, in which case a close analogy with the Type-C QPOs in stellar systems is problematic. Measurement of the source's timing properties over a wider range of energy spectral index is needed to definitively resolve this ambiguity. We searched all the available data for both a broad Fe emission line as well as high-frequency QPO analogs (0.1-1Hz), but detected neither. We place upper limits on the equivalent width of any Fe emission feature in the 6-7keV band and of the amplitude (rms) of a high-frequency QPO analog of 10eV and 4%, respectively. © 2012. The American Astronomical Society. All rights reserved..


Lin G.-D.,University of Michigan | Monroe C.,University of Maryland University College | Duan L.-M.,University of Michigan
Physical Review Letters | Year: 2011

Sharp quantum phase transitions typically require a large system with many particles. Here we show that, for a frustrated fully connected Ising spin network represented by trapped atomic ions, the competition between different spin orders leads to rich phase transitions whose sharpness scales exponentially with the number of spins. This unusual finite-size scaling behavior opens up the possibility of observing sharp quantum phase transitions in a system of just a few trapped ion spins. © 2011 American Physical Society.


Kesar A.S.,University of Maryland University College
IEEE Transactions on Antennas and Propagation | Year: 2011

A method for the detection of underground anomalies by electromagnetic (EM) shock waves is presented. Following Grischkowsky [Phys. Rev. Lett., vol. 59, pp. 16631666, 1987], an EM shock wave will develop in a dielectric medium by exciting a pulse which leaks into the dielectric bulk from a transmission line. A shock wave occurs when the group velocity in the line exceeds the phase velocity in the dielectric. This mechanism is similar to Cherenkov radiation. In this paper the transmission and reception of the EM shock wave between two identical leaky transmission lines is introduced. For underground detection, the two lines are placed in boreholes and are made in a manner in which the speed of propagation in the line is faster than the speed of propagation in the ground. The effect on the shock wave by an underground anomaly such as a dielectric or metallic pipeline located between the two boreholes is studied. The anomaly scatters the shock wave, resulting in a detectable disturbance in the received signal. The time delay of this disturbance, with respect to the time when the pulse was transmitted, is correlated with the location of the object. Numerical examples are presented by using a two-dimensional finite-difference time-domain algorithm. © 2006 IEEE.


Erlebacher J.,Johns Hopkins University | Margetis D.,University of Maryland University College
Physical Review Letters | Year: 2014

Shape fluctuations in nanoparticles strongly influence their stability. Here, we introduce a quantitative model of such shape fluctuations and apply this model to the important case of Pt-shell/transition metal-core nanoparticles. By using a Gibbs distribution for the initial shapes, we find that there is typically enough thermal energy at room temperature to excite random shape fluctuations in core-shell nanoparticles, whose amplitudes are sufficiently high that the cores of such particles are transiently exposed to the surrounding environment. If this environment is acidic and dissolves away the core, then a hollow shell containing a pinhole is formed; however, this pinhole quickly closes, leaving a hollow nanoparticle. These results favorably compare to experiment, much more so than competing models based on the room-temperature Kirkendall effect. © 2014 American Physical Society.


Cooper E.D.,University of Maryland University College
Trends in Plant Science | Year: 2014

Phylogenetic analysis is an increasingly common and valuable component of plant science. Knowledge of the phylogenetic relationships between plant groups is a prerequisite for understanding the origin and evolution of important plant features, and phylogenetic analysis of individual genes and gene families provides fundamental insights into how those genes and their functions evolved. However, despite an active research community exploring and improving phylogenetic methods, the analytical methods commonly used, and the phylogenetic results they produce, are accorded far more confidence than they warrant. In this opinion article, I emphasise that important parts of the green plant phylogeny are inconsistently resolved and I argue that the lack of consistency arises due to inadequate modelling of changes in the substitution process. © 2014 Elsevier Ltd.


Das S.,University of Maryland University College
Colloids and Surfaces A: Physicochemical and Engineering Aspects | Year: 2014

A charged soft interface is characterized by a charged polyelectrolyte layer (PEL) sandwiched between an uncharged rigid surface and an electrolyte solution. The PEL harbors or consists of a particular kind of ion (henceforth denoted as PEL ion), different from the electrolyte ions. The PEL ions remain excluded from locations outside the PEL. This gives rise to a Donnan potential (ψD) deep within the PEL, with the PEL-electrolyte interface (having an electrostatic potential, also called the surface potential, ψ0) behaving as a possible ion-selective permeable membrane. In this paper, we provide closed-form explicit analytical expressions for the interrelationship between ψD and ψ0 for both positively and negatively charged PEL with pH-dependent charge densities. We demonstrate that for a given magnitude of ψD, magnitude of ψ0 is identical for both positively and negatively charged PEL, dictated only by a parameter α, which depends on the difference between pH and pKa values for negatively charged PEL or the difference between pKb and pOH values for positively charged PEL. Most importantly, derivation of explicit form of interrelationship between ψD and ψ0, hitherto missing in the existing literature, allows us to provide substantially new insights into the relative variation of ψD and ψ0 and at the same time helps us to rectify several earlier misconceptions. Further, using this explicit relationship, it becomes possible to quantify the capacitance of a soft interface as explicit functions of α and the Donnan potential, with relevance for development of possible soft-interface-based energy storage system. © 2014 Elsevier B.V.


Reames D.V.,University of Maryland University College
Astrophysical Journal | Year: 2012

We have searched for evidence of significant shock acceleration of He ions of ∼1-10MeVamu-1 in situ at 258interplanetary traveling shock waves observed by the Wind spacecraft. We find that the probability of observing significant acceleration, and the particle intensity observed, depends strongly upon the shock speed and less strongly upon the shock compression ratio. For most of the 39 fast shocks with significant acceleration, the observed spectral index agrees with either that calculated from the shock compression ratio or with the spectral index of the upstream background, when the latter spectrum is harder, as expected from diffusive shock theory. In many events the spectra are observed to roll downward at higher energies, as expected from Ellison-Ramaty and from Lee shock-acceleration theories. The dearth of acceleration at ∼85% of the shocks is explained by (1) a low shock speed, (2) a low shock compression ratio, and (3) a low value of the shock-normal angle with the magnetic field, which may cause the energy spectra that roll downward at energies below our observational threshold. Quasi-parallel shock waves are rarely able to produce measurable acceleration at 1AU. The dependence of intensity on shock speed, seen here at local shocks, mirrors the dependence found previously for the peak intensities in large solar energetic-particle events upon speeds of the associated coronal mass ejections which drive the shocks. © 2012 The American Astronomical Society. All rights reserved.


Edelson R.,University of Maryland University College | Malkan M.,University of California at Los Angeles
Astrophysical Journal | Year: 2012

We have developed the ''S IX'' statistic to identify bright, highly likely active galactic nucleus (AGN) candidates solely on the basis of Wide-field Infrared Survey Explorer (WISE), Two Micron All-Sky Survey (2MASS), and ROSAT all-sky survey (RASS) data. This statistic was optimized with data from the preliminary WISE survey and the Sloan Digital Sky Survey, and tested with Lick 3 m Kast spectroscopy. We find that sources with S IX< 0 have a ≳95% likelihood of being an AGN (defined in this paper as a Seyfert 1, quasar, or blazar). This statistic was then applied to the full WISE/2MASS/RASS dataset, including the final WISE data release, to yield the ''W2R'' sample of 4316 sources with S IX< 0. Only 2209 of these sources are currently in the Veron-Cetty and Veron (VCV) catalog of spectroscopically confirmed AGNs, indicating that the W2R sample contains nearly 2000 new, relatively bright (J ≲ 16) AGNs. We utilize the W2R sample to quantify biases and incompleteness in the VCV catalog. We find that it is highly complete for bright (J< 14), northern AGNs, but the completeness drops below 50% for fainter, southern samples and for sources near the Galactic plane. This approach also led to the spectroscopic identification of 10 new AGNs in the Kepler field, more than doubling the number of AGNs being monitored by Kepler. The W2R sample contains better than 1 bright AGN every 10 deg2, permitting construction of AGN samples in any sufficiently large region of sky. © 2012. The American Astronomical Society. All rights reserved.


Green D.,Institute for Advanced Study | Komargodski Z.,Institute for Advanced Study | Katz A.,University of Maryland University College
Physical Review Letters | Year: 2011

We describe renormalizable supersymmetric four-dimensional theories which lead to gaugino mediation and various generalizations thereof. Even though these models are strongly coupled, we can demonstrate the parametric suppression of soft scalar masses via Seiberg duality. We show that our models have a parameter which continuously interpolates between suppressed soft scalar masses and their conventional gauge mediated contribution. The main physical effect which we utilize is the general relation between massive deformations in one frame and the Higgs mechanism in the dual frame. Some compelling and relatively unexplored phenomenological scenarios arise naturally in this framework. We offer preliminary comments on various aspects of the phenomenology and outline several of the outstanding open problems. © 2011 American Physical Society.


Gralla S.E.,University of Maryland University College
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

Previous work established a universal form for the equation of motion of small bodies in theories of a metric and other tensor fields that have second-order field equations following from a covariant Lagrangian in four spacetime dimensions. Differences in the motion of the "same" body in two different theories are entirely accounted for by differences in the body's effective mass and charges in those different theories. Previously the process of computing the mass and charges for a particular body was left implicit, to be determined in each particular theory as the need arises. I now obtain explicit expressions for the mass and charges of a body as surface integrals of the fields it generates, where the integrand is constructed from the symplectic current for the theory. This allows the entire prescription for computing the motion of a small body to be written down in a few lines, in a manner universal across bodies and theories. For simplicity I restrict to scalar and vector fields (in addition to the metric), but there is no obstacle to treating higher-rank tensor fields. I explicitly apply the prescription to work out specific equations for various body types in Einstein gravity, generalized Brans-Dicke theory (in both Jordan and Einstein frames), Einstein-Maxwell theory and the Will-Nordvedt vector-tensor theory. In the scalar-tensor case, this clarifies the origin and meaning of the "sensitivities" defined by Eardley and others, and provides explicit formulas for their evaluation. © 2013 American Physical Society.


Barnes E.,University of Maryland University College | Economou S.E.,U.S. Navy
Physical Review Letters | Year: 2011

We introduce a method for solving the problem of an externally controlled electron spin in a quantum dot interacting with host nuclei via the hyperfine interaction. Our method accounts for generalized (nonunitary) evolution effected by external controls and the environment, such as coherent lasers combined with spontaneous emission. As a concrete example, we develop the microscopic theory of the dynamics of nuclear-induced frequency focusing as first measured in Science 317, 1896 (2007)SCIEAS0036-807510.1126/science.1146850; we find that the nuclear relaxation rates are several orders of magnitude faster than those quoted in that work. © 2011 American Physical Society.


Demb J.B.,Yale University | Singer J.H.,University of Maryland University College
Visual Neuroscience | Year: 2012

Amacrine cells represent the most diverse class of retinal neuron, comprising dozens of distinct cell types. Each type exhibits a unique morphology and generates specific visual computations through its synapses with a subset of excitatory interneurons (bipolar cells), other amacrine cells, and output neurons (ganglion cells). Here, we review the intrinsic and network properties that underlie the function of the most common amacrine cell in the mammalian retina, the AII amacrine cell. The AII connects rod and cone photoreceptor pathways, forming an essential link in the circuit for rod-mediated (scotopic) vision. As such, the AII has become known as the rod amacrine cell. We, however, now understand that AII function extends to cone-mediated (photopic) vision, and AII function in scotopic and photopic conditions utilizes the same underlying circuit: AIIs are electrically coupled to each other and to the terminals of some types of ON cone bipolar cells. The direction of signal flow, however, varies with illumination. Under photopic conditions, the AII network constitutes a crossover inhibition pathway that allows ON signals to inhibit OFF ganglion cells and contributes to motion sensitivity in certain ganglion cell types. We discuss how the AII's combination of intrinsic and network properties accounts for its unique role in visual processing. © Copyright Cambridge University Press 2012.


Li T.,University of Maryland University College
Modelling and Simulation in Materials Science and Engineering | Year: 2011

Graphene is intrinsically non-flat and corrugates randomly. Since the corrugating physics of atomically thin graphene is strongly tied to its electronics properties, randomly corrugating morphology of graphene poses a significant challenge to its application in nanoelectronic devices for which precise (digital) control is the key. Recent studies revealed that the morphology of substrate-supported graphene is regulated by the graphene-substrate interaction, thus is distinct from the random intrinsic morphology of freestanding graphene. The regulated extrinsic morphology of graphene sheds light on new pathways to fine tune the properties of graphene. To guide further research to explore these fertile opportunities, this paper reviews recent progress on modeling and experimental studies of the extrinsic morphology of graphene under a wide range of external regulation, including two-dimensional and one-dimensional substrate surface features and one-dimensional and zero-dimensional nanoscale scaffolds (e.g. nanowires and nanoparticles). © 2011 IOP Publishing Ltd.


Smolyaninov I.I.,University of Maryland University College
Physical Review Letters | Year: 2011

As demonstrated by Chernodub, vacuum in a strong magnetic field behaves as Abrikosov vortex lattice in a type-II superconductor. We investigate electromagnetic behavior of vacuum in this state and demonstrate that vacuum behaves as a hyperbolic metamaterial. If the magnetic field is constant, low frequency extraordinary photons experience this medium as a (3+1) Minkowski spacetime in which the role of time is played by the spatial z coordinate. Variations of the magnetic field curve this spacetime, and may lead to formation of "electromagnetic black holes." Since hyperbolic metamaterials behave as diffractionless "perfect lenses," and large enough magnetic fields probably existed in the early Universe, the demonstrated hyperbolic behavior of early vacuum may have imprints in the large scale structure of the present-day Universe. © 2011 American Physical Society.


Hafezi M.,University of Maryland University College
Physical Review Letters | Year: 2014

Motivated by the recent theoretical and experimental progress in implementing topological orders with photons, we analyze photonic systems with different topologies and present a scheme to probe their topological features. Specifically, we propose a scheme to modify the boundary phases to manipulate edge state dynamics. Such a scheme allows one to measure the winding number of the edge states. Furthermore, we discuss the effect of loss and disorder on the validity of our approach. © 2014 American Physical Society.


Baraldi A.,University of Maryland University College
IEEE Transactions on Geoscience and Remote Sensing | Year: 2011

Proposed in recent literature, a novel two-stage stratified hierarchical hybrid remote-sensing image understanding system (RS-IUS) architecture comprises the following: 1) a first-stage pixel-based application-independent top-down (physical-model-driven and prior-knowledge-based) preliminary classifier and 2) a second-stage battery of stratified hierarchical context-sensitive application-dependent modules for class-specific feature extraction and classification. The first-stage preliminary classifier is implemented as an operational automatic near-real-time per-pixel multisource multiresolution application-independent spectral-rule-based decision-tree classifier (SRC). To the best of the author's knowledge, SRC provides the first operational example of an automatic multisensor multiresolution Earth-observation (EO) system of systems envisaged under ongoing international research programs such as the Global Earth Observation System of Systems (GEOSS) and the Global Monitoring for the Environment and Security (GMES). For the sake of simplicity, the original SRC formulation adopts crisp (hard) membership functions unsuitable for dealing with component cover classes of mixed pixels (class mixture). In this paper, the crisp (hierarchical) SRC first stage of a two-stage hybrid RS-IUS is replaced by a fuzzy (horizontal) SRC. In operational terms, a relative comparison of the fuzzy SRC against its crisp counterpart reveals that the former features the following: 1) the same degree of automation which cannot be surpassed, i.e., they are both "fully automatic"; 2) a superior map information/knowledge representation where component cover classes of mixed pixels are modeled; 3) the same robustness to changes in the input multispectral imagery acquired across time, space, and sensors; 4) a superior maintainability/scalability/reusability guaranteed by an internal horizontal (flat) modular structure independent of hierarchy; and 5) a computation time increased by 30% in a single-process single-thread implementation. This computation overload would reduce to zero in a single-process multithread implementation. In line with theory, the conclusion of this work is that the operational qualities of the fuzzy and crisp SRCs differ, but both SRCs are suitable for the development of operational automatic near-real-time multisensor satellite-based measurement systems such as those conceived as a visionary goal by the ongoing GEOSS and GMES research initiatives. © 2011 IEEE.


Cheng M.,Microsoft | Cheng M.,University of Maryland University College | Gu Z.-C.,California Institute of Technology
Physical Review Letters | Year: 2014

It has been shown that the symmetry-protected topological (SPT) phases with finite Abelian symmetries can be described by Chern-Simons field theory. We propose a topological response theory to uniquely identify the SPT orders, which allows us to obtain a systematic scheme to classify bosonic SPT phases with any finite Abelian symmetry group. We point out that even for finite Abelian symmetry, there exist bosonic SPT phases beyond the current Chern-Simons theory framework. We also apply the theory to fermionic SPT phases with Zm symmetry and find the classification of SPT phases depends on the parity of m: for even m there are 2m classes, m out of which is intrinsically fermionic SPT phases and cannot be realized in any bosonic system. Finally we propose a classification scheme of fermionic SPT phases for any finite, Abelian symmetry. © 2014 American Physical Society.


Rossi E.,College of William and Mary | Das Sarma S.,University of Maryland University College
Physical Review Letters | Year: 2011

The inhomogenous real-space electronic structure of gapless and gapped disordered bilayer graphene is calculated in the presence of quenched charge impurities. For gapped bilayer graphene, we find that for current experimental conditions the amplitude of the fluctuations of the screened disorder potential is of the order of (or often larger than) the intrinsic gap Δ induced by the application of a perpendicular electric field. We calculate the crossover chemical potential Δcr, separating the insulating regime from a percolative regime in which less than half of the area of the bilayer graphene sample is insulating. We find that most of the current experiments are in the percolative regime with ΔcrΔ. The huge suppression of Δcr compared with Δ provides a possible explanation for the large difference between the theoretical band gap Δ and the experimentally extracted transport gap. © 2011 American Physical Society.


Hu L.,University of Maryland University College | Wu H.,Stanford University | Cui Y.,Stanford University
MRS Bulletin | Year: 2011

Metals possess the highest conductivity among all room-temperature materials; however, ultrathin metal films demonstrate decent optical transparency but poor sheet conductance due to electron scattering from the surface and grain boundaries. This article discusses engineered metal nanostructures in the form of nanogrids, nanowires, or continuous nanofibers as efficient transparent and conductive electrodes. Metal nanogrids are discussed, as they represent an excellent platform for understanding the fundamental science. Progress toward low-cost, nano-ink-based printed silver nanowire electrodes, including silver nanowire synthesis, film fabrication, wire-wire junction resistance, optoelectronic properties, and stability, are also discussed. Another important factor for low-cost application is to use earth-abundant materials. Copper-based nanowires and nanofibers are discussed in this context. Examples of device integrations of these materials are also given. Such metal nanostructure-based transparent electrodes are particularly attractive for solar cell applications. © 2011 Materials Research Society.


Hu B.L.,University of Maryland University College
International Journal of Modern Physics D | Year: 2011

Happy Birthday Mario, the philosopher, the king and the philosopher king! - This was explained in the first few slides of my talk at Mariofest. In an earlier, different occasion I had compared Mario, in his capacity of an inspiring mentor and a chief architect, in building up an eminent school of theoretical physics and astrophysics in Argentina, to my own Ph.D. advisor, the late Professor John Archibald Wheeler, in the USA. The nature of this meeting could perhaps allow me to also relate some of my past experience with Wheeler, and to pay homage to his influence on me in the same capacity as is done here by many young researchers, leaders in their own rights in different fields of physics and astrophysics, with Mario. So please forgive me if you find me delving at times into the past, referring to what I was thinking when I was a graduate student, some 40 years ago, on certain topics, some still of current interest. One of these ideas bears on the present theme of gravity in relation to thermodynamics, another on the philosophy I use for understanding it. © 2011 World Scientific Publishing Company.


Fang W.,Zhejiang University | St. Leger R.J.,University of Maryland University College
PLoS ONE | Year: 2012

The low survival of microbial pest control agents exposed to UV is the major environmental factor limiting their effectiveness. Using gene disruption we demonstrated that the insect pathogenic fungus Metarhizium robertsii uses photolyases to remove UV-induced cyclobutane pyrimidine dimers (CPD) and pyrimidine (6-4) photoproducts [(6-4)PPs] from its DNA. However, this photorepair is insufficient to fix CPD lesions and prevent the loss of viability caused by seven hours of solar radiation. Expression of a highly efficient archaeal (Halobacterium salinarum) CPD photolyase increased photorepair &30-fold in both M. robertsii and Beauveria bassiana. Consequently, transgenic strains were much more resistant to sunlight and retained virulence against the malaria vector Anopheles gambiae. In the field this will translate into much more efficient pest control over a longer time period. Conversely, our data shows that deleting native photolyase genes will strictly contain M. robertsii to areas protected from sunlight, alleviating safety concerns that transgenic hypervirulent Metarhizium spp will spread from mosquito traps or houses. The precision and malleability of the native and transgenic photolyases allows design of multiple pathogens with different strategies based on the environments in which they will be used. © 2012 Fang, St. Leger.


Reames D.V.,University of Maryland University College
Solar Physics | Year: 2014

This is a study of abundances of the elements He, C, N, O, Ne, Mg, Si, S, Ar, Ca, and Fe in solar energetic particles (SEPs) in the 2 - 15 MeV amu-1 region measured on the Wind spacecraft during 54 large SEP events occurring between November 1994 and June 2012. The origin of most of the temporal and spatial variations in abundances of the heavier elements lies in rigidity-dependent scattering during transport of the particles away from the site of acceleration at shock waves driven out from the Sun by coronal mass ejections (CMEs). Variation in the abundance of Fe is correlated with the Fe spectral index, as expected from scattering theory but not previously noted. Clustering of Fe abundances during the "reservoir" period, late in SEP events, is also newly reported. Transport-induced enhancements in one region are balanced by depletions in another, thus, averaging over these variations produces SEP abundances that are energy independent, confirms previous SEP abundances in this energy region, and provides a credible measure of element abundances in the solar corona. These SEP-determined coronal abundances differ from those in the solar photosphere by a well-known function that depends upon the first ionization potential (FIP) or ionization time of the element. © 2013 Springer Science+Business Media Dordrecht.


Nguyen D.,University of Maryland University College
Environment and Planning B: Planning and Design | Year: 2010

Sprawl opponents have blamed sprawl for weakening linkages among the residents and social capital but there is a lack of empirical evidence to support their argument. This study examines the relationship between the county sprawl index and social-capital factors from the 2000 Social Capital Community Benchmark Survey data. Using 3-level hierarchical models, this study shows that for the US, urban sprawl may support some types of social capital while negatively impacting the others. Furthermore, changing urban form via population density and street accessibility at the county level may not be ideal to improve social capital. © 2010 Pion Ltd and its Licensors.


Brown M.,University of Maryland University College
Bulletin of the Geological Society of America | Year: 2013

At low temperatures (<750 °C at moderate to high crustal pressures), the production of sufficient melt to reach the melt connectivity transition (~7 vol%), enabling melt drainage, requires an influx of aqueous fluid along structurally controlled pathways or recycling of fluid via migration of melt and exsolution during crystallization. At higher temperatures, melting occurs by fluid-absent reactions, particularly hydrate-breakdown reactions involving micas and/or amphibole in the presence of quartz and feldspar. These reactions produce 20-70 vol%, melt according to protolith composition, at temperatures up to 1000 °C. Calculated phase diagrams for pelite are used to illustrate the mineralogical controls on melt production and the consequences of different clockwise pressure-temperature (P-T) paths on melt composition. Preservation of peritectic minerals in residual granulites requires that most of the melt produced was extracted, implying a flux of melt through the suprasolidus crust, although some may be trapped during transport, as recorded by composite migmatitegranite complexes. Peritectic minerals may be entrained during melt drainage, consistent with observations from leucosomes in migmatites, and dissolution of these minerals during ascent may be important in the evolution of some crustal magmas. Since siliceous melt wets grains, suprasolidus crust may become porous at only a few volume % melt, as evidenced by microstructures in residual migmatites in which quartz or feldspar pseudomorphs form after melt films and pockets. With increasing melt volume and decreasing effective pressure, assuming the residue is able to deform and compact, the source becomes permeable at the melt connectivity transition. At this threshold, a change from distributed shear-enhanced compaction to localized dilatant shear failure enables melt segregation. The result is a highly permeable vein network that allows transfer of melt to ascent conduits at the initiation of a melt-extraction event. Melt is drained from the anatectic zone via several extraction events, consistent with evidence for incremental construction of plutons from multiple batches of magma. Buoyancy-driven magma ascent occurs via dikes in fractures or via high-permeability zones controlled by tectonic fabrics; the way in which these features relate to compaction and the generation of porosity waves is discussed. Emplacement of laccoliths (horizontal tabular intrusions) and wedge-shaped plutons occurs around the ductile-to-brittle transition zone, whereas steep tabular sheeted and blobby plutons represent back freezing of melt in the ascent conduit or lateral expansion localized by instabilities in the magma-wallrock system, respectively. © 2013 Geological Society of America.


Yoon J.-H.,University of Maryland University College | Zeng N.,The Interdisciplinary Center
Climate Dynamics | Year: 2010

Rainfall variability over the Amazon basin has often been linked to variations in Pacific sea surface temperature (SST), and in particular, to the El Niño/Southern Oscillation (ENSO). However, only a fraction of Amazon rainfall variability can be explained by ENSO. Building upon the recent work of Zeng (Environ Res Lett 3:014002, 2008), here we provide further evidence for an influence on Amazon rainfall from the tropical Atlantic Ocean. The strength of the North Atlantic influence is found to be comparable to the better-known Pacific ENSO connection. The tropical South Atlantic Ocean also shows some influence during the wet-to-dry season transition period. The Atlantic influence is through changes in the north-south divergent circulation and the movement of the ITCZ following warm SST. Therefore, it is strongest in the southern part of the Amazon basin during the Amazon's dry season (July-October). In contrast, the ENSO related teleconnection is through anomalous east-west Walker circulation with largely concentrated in the eastern (lower) Amazon. This ENSO connection is seasonally locked to boreal winter. A complication due to the influence of ENSO on Atlantic SST causes an apparent North Atlantic SST lag of Amazon rainfall. Removing ENSO from North Atlantic SST via linear regression resolves this causality problem in that the residual Atlantic variability correlates well and is in phase with the Amazon rainfall. A strong Atlantic influence during boreal summer and autumn is particularly significant in terms of the impact on the hydro-ecosystem which is most vulnerable during the dry season, as highlighted by the severe 2005 Amazon drought. Such findings have implications for both seasonal-interannual climate prediction and understanding the longer-term changes of the Amazon rainforest. © Springer-Verlag 2009.


Dolgopyat D.,University of Maryland University College | Liverani C.,University of Rome Tor Vergata
Communications in Mathematical Physics | Year: 2011

We consider a finite region of a lattice of weakly interacting geodesic flows on manifolds of negative curvature and we show that, when rescaling the interactions and the time appropriately, the energies of the flows evolve according to a nonlinear diffusion equation. This is a first step toward the derivation of macroscopic equations from a Hamiltonian microscopic dynamics in the case of weakly coupled systems. © 2011 Springer-Verlag.


Blichert-Toft J.,University Claude Bernard Lyon 1 | Puchtel I.S.,University of Maryland University College
Earth and Planetary Science Letters | Year: 2010

In this study, we present Lu-Hf isotope systematics and Lu and Hf abundances for komatiites from the lowermost part of the 2.8Ga Kostomuksha greenstone belt in the Baltic Shield and compare these, as well as available Sm-Nd isotope data, with those for the best characterized Archean komatiite systems. The Lu-Hf isotope compositions of four spatially associated differentiated lava flows from the Kostomuksha greenstone belt yield an isochron (MSWD=1.6) with an age of 2931±300Ma, which represents the first Lu-Hf isochron obtained for a suite of co-magmatic komatiite lavas. The calculated mean initial 176Hf/177Hf for the Kostomuksha komatiite samples is 0.281107±3 (2σmean), which corresponds to an initial ε176Hf of +4.9±0.1 (2σmean). Assuming that mantle differentiation occurred 10Ma after Earth's accretion at 4.558Ga, this precise initial ratio requires a time-integrated 176Lu/177Hf=0.03759±8, which is identical to the average time-integrated 176Lu/177Hf=0.0375±6 calculated for the best characterized late Archean komatiite systems. Together with the calculated average time-integrated 147Sm/144Nd=0.2091±4 for the same late Archean komatiite systems, these parameters represent our best estimate of the Lu/Hf and Sm/Nd properties in the late Archean mantle and indicate derivation of komatiite magmas from around the globe from long-term melt-depleted sources that were remarkably homogenous in terms of lithophile trace element systematics. These time-integrated ratios are identical to the respective values of 0.0375 and 0.209 calculated by Boyet and Carlson (2006) for the so-called Early Depleted Reservoir (EDR), and may indicate that the late Archean mantle was similar in composition to the putative EDR, whereas early Archean systems had higher, and Proterozoic systems lower time-integrated Lu/Hf and Sm/Nd ratios. The observed decrease in time-integrated Lu/Hf and Sm/Nd in komatiite sources over time is interpreted as strong evidence for the existence of a hidden enriched reservoir complementary to the EDR that has been gradually mixed back into the mantle over time. The overall depletion of the early mantle likely occurred very early in Earth's history as a result of either global magma ocean differentiation or extraction and subsequent long-term isolation of primordial terrestrial crust. © 2010 Elsevier B.V.


Heer J.,Stanford University | Shneiderman B.,University of Maryland University College
Communications of the ACM | Year: 2012

The increasing scale and availability of digital data provides an extraordinary resource for informing public policy, scientific discovery, business strategy, and personal lives. To enable analysts to explore large datasets involving varied data types, flexible visual analysis tools must provide appropriate controls for specifying the data and views of interest. Classic scientific visualization systems use data-flow graphs, in which the visualization process is deconstructed into a set of finer-grained operators for data import, transformation, layout, or coloring. When analyzing data with visualizations, users regularly traverse the space of views in an iterative fashion. Interactive visualizations often serve not only as data-exploration tools, but also as a means for recording, organizing, and communicating insights gained during exploration. Data-aware annotations allow a pointing intention to be reapplied to different views of the same data, enabling reuse of references across different choices of visual encodings.


Sitnov M.I.,Johns Hopkins University | Swisdak M.,University of Maryland University College
Journal of Geophysical Research: Space Physics | Year: 2011

The onset of reconnection in 2-D current sheet equilibria that include an X line separating tail-like regions with magnetized electrons is simulated with a full-particle code. The onset is driven by a finite convection electric field applied outside the current sheet. In the case of tearing stable tails with no accumulated magnetic flux, the convection electric field penetrates the sheet near the X line. In contrast, in multiscale equilibria where the X line is framed by local areas of enhanced flux, the electric field avoids the X line, directly penetrates the areas of increased flux, and ejects them downstream. The ejecta form dipolarization fronts (DFs), sharp magnetic pileups with a thickness on the order of the ion inertial length, much smaller than the mesoscales of the initial flux increase regions. The DFs move with the reconnection outflows in the direction opposite the magnetic field stretching, while behind them new X lines, distinct from the original, form. Simulations with a reduced driving field suggest that DF formation shares properties with the ion tearing instability, which is consistent with its potential destabilization in multiscale equilibria. Weak driving of equilibria with tearing stable tails first forms flux accumulation regions, which then rapidly transform into DFs, making 2-D equilibria inherently metastable. The results are compared with observations of DFs, the statistical visualization of Earth's magnetotail during substorm onset, and the bubble-blob pair formation model. Copyright 2011 by the American Geophysical Union.


Carson Smith J.,University of Maryland University College
Medicine and Science in Sports and Exercise | Year: 2013

Purpose: Despite the well-known anxiolytic effect of acute exercise, it is unknown if anxiety reductions after acute exercise conditions survive in the face of a subsequently experienced arousing emotional exposure. The purpose of this study was to compare the effects of moderate-intensity cycle ergometer exercise to a seated rest control condition on state anxiety symptoms after exposure to a variety of highly arousing pleasant and unpleasant stimuli. Methods: Thirty-seven healthy and normally physically active young adults completed two conditions on separate days: 1) 30 min of seated rest and 2) 30 min of moderate-intensity cycle ergometer exercise (RPE = 13; "somewhat hard"). After each condition, participants viewed 90 arousing pleasant, unpleasant, and neutral pictures from the International Affective Picture System for 30 min. State anxiety was measured before and 15 min after each condition, and again after exposure to the affective pictures. Results: State anxiety significantly decreased from baseline to after the exercise and seated rest conditions (P = 0.003). After the emotional picture-viewing period, state anxiety significantly increased to baseline values after the seated rest condition (P = 0.001) but remained reduced after the exercise condition. Conclusion: These findings suggest that the anxiolytic effects of acute exercise may be resistant to the potentially detrimental effects on mood after exposure to arousing emotional stimuli. © 2012 by the American College of Sports Medicine.


Walker R.J.,University of Maryland University College
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences | Year: 2014

Discovery of small enrichments in 182W/184Win some Archaean rocks, relative to modern mantle, suggests both exogeneous and endogenous modifications to highly siderophile element (HSE) and moderately siderophile element abundances in the terrestrial mantle. Collectively, these isotopic enrichments suggest the formation of chemically fractionated reservoirs in the terrestrial mantle that survived the putative Moon-forming giant impact, and also provide support for the late accretion hypothesis. The lunar mantle sources of volcanic glasses and basalts were depleted in HSEs relative to the terrestrialmantle by at least a factor of 20. The most likely explanations for the disparity between the Earth and Moon are either that the Moon received a disproportionately lower share of late accreted materials than the Earth, such as may have resulted from stochastic late accretion, or the major phase of late accretion occurred prior to the Moon-forming event, and the putative giant impact led to little drawdown of HSEs to the Earth's core. High precision determination of the 182W isotopic composition of the Moon can help to resolve this issue. © 2014 The Author(s) Published by the Royal Society.


Webber W.,University of Maryland University College
ACM Transactions on Information Systems | Year: 2013

Recall, the proportion of relevant documents retrieved, is an important measure of effectiveness in information retrieval, particularly in the legal, patent, and medical domains. Where document sets are too large for exhaustive relevance assessment, recall can be estimated by assessing a random sample of documents, but an indication of the reliability of this estimate is also required. In this article, we examine several methods for estimating two-tailed recall confidence intervals. We find that the normal approximation in current use provides poor coverage in many circumstances, even when adjusted to correct its inappropriate symmetry. Analytic and Bayesian methods based on the ratio of binomials are generally more accurate but are inaccurate on small populations. The method we recommend derives beta-binomial posteriors on retrieved and unretrieved yield, with fixed hyperparameters, and a Monte Carlo estimate of the posterior distribution of recall. We demonstrate that this method gives mean coverage at or near the nominal level, across several scenarios, while being balanced and stable. We offer advice on sampling design, including the allocation of assessments to the retrieved and unretrieved segments, and compare the proposed beta-binomial with the officially reported normal intervals for recent TREC Legal Track iterations. © 2013 ACM 1046-8188/2013/01-ART2 s15.00.


Giglio L.,University of Maryland University College | Randerson J.T.,University of California at Irvine | Van Der Werf G.R.,VU University Amsterdam
Journal of Geophysical Research: Biogeosciences | Year: 2013

We describe the fourth generation of the Global Fire Emissions Database (GFED4) burned area data set, which provides global monthly burned area at 0.25° spatial resolution from mid-1995 through the present and daily burned area for the time series extending back to August 2000. We produced the full data set by combining 500 m MODIS burned area maps with active fire data from the Tropical Rainfall Measuring Mission (TRMM) Visible and Infrared Scanner (VIRS) and the Along-Track Scanning Radiometer (ATSR) family of sensors. We found that the global annual area burned for the years 1997 through 2011 varied from 301 to 377Mha, with an average of 348Mha. We assessed the interannual variability and trends in burned area on the basis of a region-specific definition of fire years. With respect to trends, we found a gradual decrease of 1.7Mhayr - 1 (- 1.4%yr - 1) in Northern Hemisphere Africa since 2000, a gradual increase of 2.3Mhayr - 1 (+1.8%yr - 1) in Southern Hemisphere Africa also since 2000, a slight increase of 0.2Mhayr - 1 (+2.5%yr - 1) in Southeast Asia since 1997, and a rapid decrease of approximately 5.5Mhayr - 1 (- 10.7%yr - 1) from 2001 through 2011 in Australia, followed by a major upsurge in 2011 that exceeded the annual area burned in at least the previous 14 years. The net trend in global burned area from 2000 to 2012 was a modest decrease of 4.3Mhayr - 1 (- 1.2%yr - 1). We also performed a spectral analysis of the daily burned area time series and found no vestiges of the 16 day MODIS repeat cycle. Key pointsThe area of the land surface burned annually has been decreasing since 2000.This trend is in part due to a decline in burning in Northern-Hemisphere Africa.The area burned in some regions has been increasing, however. ©2013. American Geophysical Union. All Rights Reserved.


Barrett K.,University of Alaska Anchorage | Kasischke E.S.,University of Maryland University College
Remote Sensing of Environment | Year: 2013

Fire activity in the Alaskan boreal forest, though episodic at annual and intra-annual time scales, has experienced an increase over the last several decades. Increases in burned area and fire severity are not only releasing more carbon to the atmosphere, but likely shifting vegetation composition in the region towards greater deciduous dominance and a reduction in coniferous stands. While some recent studies have addressed qualitative differences between large and small fire years in the Alaskan boreal forest, the ecological effects of a greater proportion of burning occurring during large fire years and during late season fires have not yet been examined.Some characteristics of wildfires that can be detected remotely are related to fire severity and can provide new information on spatial and temporal patterns of burning. This analysis focused on boreal wildfire intensity (fire radiative power, or FRP) contained in the Moderate Resolution Imaging Spectroradiometer (MODIS) daily active fire product from 2003 to 2010. We found that differences in FRP resulted from seasonality and intra-annual variability in fire activity levels, vegetation composition, latitudinal variation, and fire spread behavior.Our studies determined two general categories of active fire detections: new detections associated with the spread of the fire front and residual pixels in areas that had already experienced front burning. Residual pixels had a lower average FRP than front pixels, but represented a high percentage of all pixels during periods of high fire activity (large fire years, late season burning, and seasonal periods of high fire activity). As a result, the FRP from periods of high fire activity was less intense than those from periods of low fire activity. Differences related to latitude were greater than expected, with higher latitudes burning later in the season and at a higher intensity than lower latitudes. Differences in vegetation type indicate that coniferous vegetation is the most fire prone, but deciduous vegetation is not particularly fire resistant, as the proportion of active fire detections in deciduous stands is roughly the same as the fraction of deciduous vegetation in the region.Qualitative differences between periods of high and low fire activity are likely to reflect important differences in fire severity. Large fire years are likely to be more severe, characterized by more late season fires and a greater proportion of residual burning. Given the potential for severe fires to effect changes in vegetation cover, the shift toward a greater proportion of area burning during large fire years may influence vegetation patterns in the region over the medium to long term. © 2012.


Goswami P.,Florida State University | Roy B.,University of Maryland University College
Physical Review B - Condensed Matter and Materials Physics | Year: 2014

We consider the competition between the conventional s-wave and the triplet Balian-Werthamer or the B-phase pairings in doped three-dimensional narrow-gap semiconductors, such as CuxBi2Se3 and Sn1-xInxTe. When the coupling constants of the two contending channels are comparable, we find a simultaneously time-reversal and parity violating p+is state at low temperatures, which provides an example of a dynamic axionic state of matter. In contradistinction to the time-reversal invariant, topological B phase, the p+is state possesses gapped Majorana fermions as surface Andreev bound states, which give rise to an anomalous surface thermal Hall effect. The anomalous gravitational and electrodynamic responses of the p+is state can be described by the θ vacuum structure, where θ≠0 or π. © 2014 American Physical Society.


Coen J.L.,U.S. National Center for Atmospheric Research | Schroeder W.,University of Maryland University College
Geophysical Research Letters | Year: 2013

Large wildfires may grow for weeks or months from ignition until extinction. Simulating events with coupled numerical weather prediction (NWP)-wildland fire models is a challenge because NWP model errors grow with time. A new simulation paradigm was tested. Coupled Atmosphere-Wildland Fire Environment model simulations of the 2012 Little Bear Fire in New Mexico were implemented for multiple days of fire growth from ignition and then used spatially refined (375 m) 12 h satellite active fire data derived from the Visible Infrared Imaging Radiometer Suite (VIIRS) to initialize a fire in progress. The simulations represented fire growth well for 12-24 h after each initialization in comparison to later satellite passes but strayed from mapped area with time. A cycling approach, in which successive VIIRS perimeters were used to initialize fire location for the next 12 h period, overcame this and can be used with cycled weather forecasts to predict even a long-lived fire's lifecycle. Key Points A coupled weather-fire model simulated 5.5 days during a wildfire Satellite fire detection defined initial fire extent and validated later times This enabled simulation of long-duration fires or ones with lulls in growth ©2013 The Authors. Geophysical Research Letters published by Wiley on behalf of the American Geophysical Union.


Cohen H.B.,University of Maryland University College
Blood | Year: 2013

Sepsis is a highly fatal disease caused by an initial hyperinflammatory response followed by a state of profound immunosuppression. Although it is well appreciated that the initial production of proinflammatory cytokines by macrophages accompanies the onset of sepsis, it remains unclear what causes the transition to an immunosuppressive state. In this study, we reveal that macrophages themselves are key regulators of this transition and that the surface enzyme CD39 plays a critical role in self-limiting the activation process. We demonstrate that Toll-like receptor (TLR)-stimulated macrophages modulate their activation state by increasing the synthesis and secretion of adenosine triphosphate (ATP). This endogenous ATP is paradoxically immunosuppressive due to its rapid catabolism into adenosine by CD39. Macrophages lacking CD39 are unable to transition to a regulatory state and consequently continue to produce inflammatory cytokines. The importance of this transition is demonstrated in a mouse model of sepsis, where small numbers of CD39-deficient macrophages were sufficient to induce lethal endotoxic shock. Thus, these data implicate CD39 as a key "molecular switch" that allows macrophages to self-limit their activation state. We propose that therapeutics targeting the release and hydrolysis of ATP by macrophages may represent new ways to treat inflammatory diseases.


Godoy O.,University of California at Santa Barbara | Kraft N.J.B.,University of Maryland University College | Levine J.M.,University of California at Santa Barbara | Levine J.M.,ETH Zurich
Ecology Letters | Year: 2014

Recent hypotheses argue that phylogenetic relatedness should predict both the niche differences that stabilise coexistence and the average fitness differences that drive competitive dominance. These still largely untested predictions complicate Darwin's hypothesis that more closely related species less easily coexist, and challenge the use of community phylogenetic patterns to infer competition. We field parameterised models of competitor dynamics with pairs of 18 California annual plant species, and then related species' niche and fitness differences to their phylogenetic distance. Stabilising niche differences were unrelated to phylogenetic distance, while species' average fitness showed phylogenetic structure. This meant that more distant relatives had greater competitive asymmetry, which should favour the coexistence of close relatives. Nonetheless, coexistence proved unrelated to phylogeny, due in part to increasing variance in fitness differences with phylogenetic distance, a previously overlooked property of such relationships. Together, these findings question the expectation that distant relatives should more readily coexist. © 2014 John Wiley & Sons Ltd/CNRS.


Gu Z.-C.,Perimeter Institute for Theoretical Physics | Levin M.,University of Maryland University College
Physical Review B - Condensed Matter and Materials Physics | Year: 2014

We study the effect of interactions on two-dimensional fermionic symmetry-protected topological (SPT) phases using the recently proposed braiding statistics approach. We focus on a simple class of examples: superconductors with a Z2 Ising symmetry. Although these systems are classified by Z in the noninteracting limit, our results suggest that the classification collapses to Z8 in the presence of interactions - consistent with previous work that analyzed the stability of the edge. Specifically, we show that there are at least eight different types of Ising superconductors that cannot be adiabatically connected to one another, even in the presence of strong interactions. In addition, we prove that each of the seven nontrivial superconductors have protected edge modes. © 2014 American Physical Society.


Roy B.,Florida State University | Roy B.,University of Maryland University College
Physical Review B - Condensed Matter and Materials Physics | Year: 2014

A variational ground state for insulating bilayer graphene (BLG), subject to quantizing magnetic fields, is proposed. Due to the Zeeman coupling, the layer antiferromagnet (LAF) order parameter in fully gapped BLG gets projected onto the spin easy plane, and simultaneously a ferromagnet order, which can further be enhanced by exchange interaction, develops in the direction of the magnetic field. The activation gap for the ν=0 Hall state then displays a crossover from quadratic to linear scaling with the magnetic field, as it gets stronger, and I obtain excellent agreement with a number of recent experiments with realistic strengths for the ferromagnetic interaction. A component of the LAF order, parallel to the external magnetic field, gives birth to additional incompressible Hall states at filling ν=±2, whereas the remote hopping in BLG yields ν=±1 Hall states. Evolution of the LAF order in tilted magnetic fields, scaling of the gap at ν=2, the effect of external electric fields on various Hall plateaus, and different possible hierarchies of fractional quantum Hall states are highlighted. © 2014 American Physical Society.


Herrmann J.W.,University of Maryland University College
Journal of Scheduling | Year: 2011

Fair sequences are useful in a variety of applications, including manufacturing and computer systems. This paper considers the generation of cyclic fair sequences for a given set of products, each of which must be produced multiple times in each cycle. The objective is to create a sequence so that, for each product, the variability of the time between consecutive completions is minimized. Because minimizing response time variability is known to be NP-hard and the performance of existing heuristics is poor for certain classes of problems, we present an aggregation approach that combines products with the same demand, creates a sequence for the aggregated instance, and then disaggregates this solution into a feasible sequence for the original instance. Computational experiments show that using aggregation can reduce response time variability dramatically and also reduces computational effort. © 2009 Springer Science+Business Media, LLC.


Sau J.D.,University of Maryland University College | Sachdev S.,Harvard University
Physical Review B - Condensed Matter and Materials Physics | Year: 2014

It has long been known that two-dimensional metals with antiferromagnetic exchange interactions have a weak-coupling instability to the superconductivity of spin-singlet, d-wave electron pairs. We examine additional possible instabilities in the spin-singlet particle-hole channel and study their interplay with superconductivity. We perform an unrestricted Hartree-Fock-BCS analysis of bond order parameters in a single-band model on the square lattice with nearest-neighbor exchange and repulsion, while neglecting on-site interactions. The dominant particle-hole instability is found to be an incommensurate, bidirectional, bond density wave with wave vectors along the (1,1) and (1,-1) directions and an internal d-wave symmetry. The magnitude of the ordering wave vector is close to the separation between points on the Fermi surface, which intersect the antiferromagnetic Brillouin zone boundary. The temperature dependence of the superconducting and bond order parameters demonstrates their mutual competition. We also obtain the spatial dependence of the two orders in a vortex lattice induced by an applied magnetic field: "halos" of the bond order appear around the cores of the vortices. © 2014 American Physical Society.


De Keersmaecker K.,Catholic University of Leuven | Sulima S.O.,Catholic University of Leuven | Dinman J.D.,University of Maryland University College
Blood | Year: 2015

Ribosomopathies are largely congenital diseases linked to defects in ribosomal proteins or biogenesis factors. Some of these disorders are characterized by hypoproliferative phenotypes such as bone marrow failure and anemia early in life, followed by elevated cancer risks later in life. This transition from hypo- to hyperproliferation presents an intriguing paradox in the field of hematology known as "Dameshek's riddle." Recent cancer sequencing studies also revealed somatically acquired mutations and deletions in ribosomal proteins in T-cell acute lymphoblastic leukemia and solid tumors, further extending the list of ribosomopathies and strengthening the association between ribosomal defects and oncogenesis. In this perspective, we summarize and comment on recent findings in the field of ribosomopathies. We explain how ribosomopathies may provide clues to help explain Dameshek's paradox and highlight some of the open questions and challenges in the field. © 2015 by The American Society of Hematology.


Armstrong R.W.,University of Maryland University College
Materials | Year: 2011

The industrially-important WC-Co composite materials provide a useful, albeit complicated materials system for understanding the combined influences on hardness and strength properties of the constituent WC particle strengths, the particle sizes, their contiguities, and of Co binder hardness and mean free paths, and in total, the volume fraction of constituents. A connection is made here between the composite material properties, especially including the material fracture toughness, and the several materials-type considerations of: (1) related hardness stress-strain behaviors; (2) dislocation (viscoplastic) thermal activation characterizations; (3) Hall-Petch type reciprocal square root of particle or grain size dependencies; and (4) indentation and conventional fracture mechanics results. Related behaviors of MgO and Al2O3 crystal and polycrystal materials are also described for the purpose of making comparisons. © 2011 by the authors.


Akamatsu Y.,Nagoya University | Yamamoto N.,University of Maryland University College
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

Charged plasmas with chirality imbalance are unstable and tend to reduce the imbalance. This chiral plasma instability is, however, not captured in (anomalous) hydrodynamics for high-temperature non-Abelian plasmas. We derive a Langevin-type classical effective theory with anomalous parity-violating effects for non-Abelian plasmas that describes the chiral plasma instability at the magnetic scale. We show that the time scale of the instability is of order [g4Tln(1/g)]-1 at weak coupling. © 2014 American Physical Society.


Gelso C.,University of Maryland University College
Psychotherapy Research | Year: 2014

The development and empirical examination of a tripartite model of the therapeutic relationship over nearly three decades are described. The model asserts that all therapeutic relationships, to varying degrees, consist of a real relationship, a working alliance, and a transference-countertransference configuration. Research testing propositions about how each of these components is related to treatment process and outcome, and to each other, is presented. Many propositions have been supported, but some have been disconfirmed. Although the tripartite, or perhaps a quadripartite, model appears to be empirically and theoretically viable, continued research and theoretical development will serve to refine the model further. The development and testing of additional models that unpack the global concept of the therapeutic relationship would also be useful. © 2013 © 2013 Society for Psychotherapy Research.


Zolkos S.G.,Woods Hole Oceanographic Institution | Goetz S.J.,Woods Hole Oceanographic Institution | Dubayah R.,University of Maryland University College
Remote Sensing of Environment | Year: 2013

Estimating biomass of terrestrial vegetation is not only a rapidly expanding research area, but also a subject of tremendous interest for reducing carbon emissions associated with deforestation and forest degradation (REDD). The accuracy of biomass estimates, and rate of biomass change, is not only important in the context of carbon markets emerging under REDD, but also for characterizing uncertainty in estimates of carbon cycling and the global carbon budget. There is particular interest in mapping biomass so that carbon stocks and stock changes can be monitored consistently across a range of scales - from relatively small projects (tens of hectares) to national or continental scales - but also so that other benefits of forest conservation can be factored into decision making (e.g. biodiversity and habitat corridors). We conducted an analysis of reported biomass accuracy estimates from more than 70 refereed articles using different remote sensing platforms (airborne and spaceborne) and sensor types (optical, radar, and lidar), with a particular focus on lidar since those papers reported the lowest errors when used in a synergistic manner with other coincident multi-sensor measurements. We show systematic differences in accuracy between different types of lidar systems flown on different platforms but, perhaps more importantly, differences between forest types (biomes) and plot sizes used for field calibration and assessment. We discuss these findings in relation to monitoring, reporting and verification under REDD, and also in the context of more systematic assessment of factors that influence accuracy and error estimation. © 2012 Elsevier Inc.


Cameron M.K.,University of Maryland University College
Journal of Statistical Physics | Year: 2013

The large time behavior of a stochastic system with infinitesimally small noise can be described in terms of Freidlin's cycles. We show that if the system is gradient and the potential satisfies certain non-restrictive conditions, the hierarchy of cycles has a structure of a full binary tree, and each cycle is exited via the lowest saddle adjacent to it. Exploiting this property, we propose an algorithm for computing the asymptotic zero-temperature path and building a hierarchy of Freidlin's cycles associated with the transition process between two given local equilibria. This algorithm is suitable for systems with a complex potential energy landscape with numerous minima. We apply it to find the asymptotic zero-temperature path and Freidlin's cycles involved into the transition process between the two lowest minima of the Lennard-Jones cluster of 38 atoms. D. Wales's stochastic network of minima and transition states of this cluster is used as an input. © 2013 Springer Science+Business Media New York.


Malkov M.A.,University of California at San Diego | Sagdeev R.Z.,University of Maryland University College
Astrophysical Journal | Year: 2015

Cosmic rays (CR), constrained by scattering on magnetic irregularities, are believed to propagate diffusively. However, a well-known defect of diffusive approximation, whereby some of the particles propagate unrealistically fast, has directed interest toward an alternative CR transport model based on the "telegraph" equation. Though, its derivations often lack rigor and transparency leading to inconsistent results. We apply the classic Chapman-Enskog method to the CR transport problem. We show that no "telegraph" (second order time derivative) term emerges in any order of a proper asymptotic expansion with systematically eliminated short timescales. Nevertheless, this term may formally be converted from the fourth order hyper-diffusive term of the expansion. However, both the telegraph and hyperdiffusive terms may only be important for a short relaxation period associated with either strong pitch-angle anisotropy or spatial inhomogeneity of the initial CR distribution. Beyond this period the system evolves diffusively in both cases. The term conversion, that makes the telegraph and Chapman-Enskog approaches reasonably equivalent, is possible only after this relaxation period. During this period, the telegraph solution is argued to be unphysical. Unlike the hyperdiffusion correction, it is not uniformly valid and introduces implausible singular components to the solution. These dominate the solution during the relaxation period. Because they are shown not to be inherent in the underlying scattering problem, we argue that the telegraph term is involuntarily acquired in an asymptotic reduction of the problem. © 2015. The American Astronomical Society. All rights reserved.


Isaacs L.,University of Maryland University College
Israel Journal of Chemistry | Year: 2011

This article begins by describing the synthesis and recognition properties of the cucurbit[n]uril homologues CB[5], CB[6], CB[7], CB[8], and CB[10]. Subsequently, we describe the state-of-the-art in understanding the mechanism of CB[n] formation. We describe the experiments that establish that glycoluril (1H) undergoes condensation with formaldehyde by a combination of chain-growth and step-growth polymerization processes. Chain-growth processes deliver methylene bridged glycoluril oligomers 2C-8C as intermediates that may undergo macrocyclization to nor-seco-CB[n] when the oligomer is long enough (5C-8C) and subsequently form CB[n]. Step-growth processes allow oligomers to condense to give longer oligomers connected by a single CH2-bridge that undergo macrocyclization to deliver (±)-bis-nor-seco-CB[6] and bis-nor-seco-CB[10]. Lastly, we describe some of the exciting new recognition processes of the newly formed members of the CB[n] family. For example, bis-nor-seco-CB[10] undergoes homotropic allostery during ternary complex formation, (±)-bis-nor-seco-CB[6] exhibits moderately diastereoselective recognition processes (d.r. up to 88 : 12) with chiral ammonium ions in water, and norseco-CB[6] functions as an aldehyde reactive CB[n] synthon that can control the folding of alkanediammonium ions into a backfolded conformation in water. © 2011 Wiley-VCH Verlag GmbH&Co. KGaA.


Kirkpatrick T.R.,University of Maryland University College | Belitz D.,University of Oregon
Physical Review Letters | Year: 2015

The third law of thermodynamics constrains the phase diagram of systems with a first-order quantum phase transition. For a zero conjugate field, the coexistence curve has an infinite slope at T=0. If a tricritical point exists at T>0, then the associated tricritical wings are perpendicular to the T=0 plane, but not to the zero-field plane. These results are based on the third law and basic thermodynamics only, and are completely general. As an explicit example we consider the ferromagnetic quantum phase transition in clean metals, where a first-order quantum phase transition is commonly observed. © 2015 American Physical Society. © 2015 American Physical Society.


Deffner S.,University of Maryland University College
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2013

We describe a minimal model of a quantum Maxwell demon obeying Hamiltonian dynamics. The model is solved exactly, and we analyze its steady-state behavior. We find that writing information to a quantum memory induces a probability current through the demon, which is the quantum analog of the classical Maxwell demon's action. Our model offers a simple and pedagogical paradigm for investigating the thermodynamics of quantum information processing. © 2013 American Physical Society.


Bely A.E.,University of Maryland University College
Integrative and Comparative Biology | Year: 2010

The ability to regenerate lost or damaged body parts is widespread among animals and provides obvious potential benefits. It is therefore perplexing that this ability has become greatly restricted or completely lost in many lineages. Despite growing interest in the cellular and molecular basis of regeneration, our understanding of how and why regenerative abilities are lost remains rudimentary. In an effort to develop a framework for studying losses of regeneration, here I outline an approach for rigorously identifying such losses, review broad patterns of regenerative ability across animals, describe some of the clearest examples of regeneration loss, discuss some possible scenarios by which regeneration may be lost, and review recent work in annelids that is providing new insights into loss of regenerative ability. © 2010 The Author. Published by Oxford University Press on behalf of the Society for Integrative and Comparative Biology. All rights reserved.


Ries L.,University of Maryland University College | Sisk T.D.,Northern Arizona University
Oikos | Year: 2010

For decades, researchers have categorized species as "edge-loving" or "edge-avoiding", but recent studies that show inconsistencies in responses have called these labels into question and led to a sense that edge effects are idiosyncratic and difficult to understand. We suggest that species would be better categorized according to their sensitivity to edges, not the direction of observed responses because no species should be expected to show the same response to all edge types. Measures of edge sensitivity will apply widely across taxa and landscapes and allow metrics that are broadly comparable, making generalities easier to discern. Finally, while the direction of observed edge responses remains a critical (but largely understood) dynamic, most reported edge responses are neutral, so discovering when species are least likely to respond to edges will increase our understanding of edge ecology and associated fragmentation effects. We offer a case study that measures edge sensitivity of 15 butterfly species at 12 edge types. We found that sensitivity is weakly related to vulnerability to predation, but more importantly we show how our results generate new predictions about edge sensitivity that can be explored in future studies. © 2010 The Authors.


Van Nguyen H.,University of Maryland University College | Porikli F.,MItsubishi Electric
IEEE Transactions on Pattern Analysis and Machine Intelligence | Year: 2013

We introduce a novel implicit representation for 2D and 3D shapes based on Support Vector Machine (SVM) theory. Each shape is represented by an analytic decision function obtained by training SVM, with a Radial Basis Function (RBF) kernel so that the interior shape points are given higher values. This empowers support vector shape (SVS) with multifold advantages. First, the representation uses a sparse subset of feature points determined by the support vectors, which significantly improves the discriminative power against noise, fragmentation, and other artifacts that often come with the data. Second, the use of the RBF kernel provides scale, rotation, and translation invariant features, and allows any shape to be represented accurately regardless of its complexity. Finally, the decision function can be used to select reliable feature points. These features are described using gradients computed from highly consistent decision functions instead from conventional edges. Our experiments demonstrate promising results. © 1979-2012 IEEE.


Tilley D.R.,University of Maryland University College
Ecological Modelling | Year: 2011

The emergy associated with materials can amount to a large portion of the total emergy budget required to make something or operate a system. Many materials are recycled and often retain much of their high transformity properties, but emergy accounting lacks clear rules for emergy recycling. Odum offered some guidelines on emergy recycling when he proposed that earthly biogeochemical cycles were coupled to energy flows, organized hierarchically, and could be quantified by their emergy per mass. Brown built on this early guideline to introduce the concept of "emformation," which proposed that the emergy of materials (material-emergy) could be tracked separately from the emergy of energy (energy-emergy) and the emergy of information. Emergy accounting that adheres to emformation, distinguishes between the sources of emergy and provides a way to subtract recycled material-emergy from the emergy required to make something. The aim in this paper is to adapt Dynamic Emergy Accounting (DEA) to represent the emformation principle and to provide a means for modeling the cycling of emergy. To accomplish this, the mini-model EmCycClos was created with a closed material cycle coupled to energy throughput. Equations for tracking energy-emergy and material-emergy separately were included. Separate tracking required new emergy variables, henceforth called partial transformities and partial specific emergies. EmCycClos demonstrated that as a material is used to catalyze energy production that is stored, its emergy is added to the stored product along with the emergy from the energy that drove the process. The new storage has material-emergy and energy-emergy coupled together. The stored product then drives a second production function whereby the material is 100% recycled back to its first state, along with its material-emergy, and the second product leaves the system with only the energy-emergy. This resulted in more emergy on the internal pathway than on either the input or output. EmCycClos revealed that the emergy, transformity, specific emergy, energy and material of all flows and storages could reach steady state conditions similar to what would be expected from non-dynamic systems. The new emergy attributes behaved dynamically with the ability to increase or decrease in the face of transient perturbation, thus demonstrating that transformity and specific-emergy are dynamic variables. This expansion of DEA provides a mathematical basis for understanding the recycling of emergy on material loops, and thus offers insight on how to fine-tune emergy evaluations concerned with significant material budgets. © 2011 Elsevier B.V.


Nguyen H.,University of Maryland University College | Bouchard M.,Simon Fraser University
Justice Quarterly | Year: 2013

Variations in criminal performance have been much less explored than other parameters of criminal careers. We explore the factors associated with differential criminal achievement in a sample of 154 adolescent offenders involved in cannabis cultivation. Drawing from theories of earnings attainment, we examine the role of drug use, criminal social capital and criminal human capital in providing either (a) monetary, or (b) in kind (cannabis) rewards from crime. Results reveal that criminal social capital and criminal human capital are related to performance while drug use explains little of the variation. Their effects, however, differ between outcomes: young offenders who are mainly connected to adult growers tend to be paid in kind, whereas respondents connected to a majority of other young growers tend to receive money. Criminal human capital is crucial to earning money but insignificant to obtaining larger payments in cannabis. Implications for criminal career and desistance research are discussed. © 2013 Copyright Academy of Criminal Justice Sciences.


Lee H.-K.,University of Maryland University College | Lee H.-K.,Johns Hopkins University | Kirkwood A.,Johns Hopkins University
Seminars in Cell and Developmental Biology | Year: 2011

Discovery of long-term potentiation (LTP) in the dentate gyrus of the rabbit hippocampus by Bliss and Lømo opened up a whole new field to study activity-dependent long-term synaptic modifications in the brain. Since then hippocampal synapses have been a key model system to study the mechanisms of different forms of synaptic plasticity. At least for the postsynaptic forms of LTP and long-term depression (LTD), regulation of AMPA receptors (AMPARs) has emerged as a key mechanism. While many of the synaptic plasticity mechanisms uncovered in at the hippocampal synapses apply to synapses across diverse brain regions, there are differences in the mechanisms that often reveal the specific functional requirements of the brain area under study. Here we will review AMPAR regulation underlying synaptic plasticity in hippocampus and neocortex. The main focus of this review will be placed on postsynaptic forms of synaptic plasticity that impinge on the regulation of AMPARs using hippocampal CA1 and primary sensory cortices as examples. And through the comparison, we will highlight the key similarities and functional differences between the two synapses. © 2011 Elsevier Ltd.


Crivat G.,University of Maryland University College | Taraska J.W.,U.S. National Institutes of Health
Trends in Biotechnology | Year: 2012

Watching biological molecules provides clues to their function and regulation. Some of the most powerful methods of labeling proteins for imaging use genetically encoded fluorescent fusion tags. There are four standard genetic methods of covalently tagging a protein with a fluorescent probe for cellular imaging. These use (i) autofluorescent proteins, (ii) self-labeling enzymes, (iii) enzymes that catalyze the attachment of a probe to a target sequence, and (iv) biarsenical dyes that target tetracysteine motifs. Each of these techniques has advantages and disadvantages. In this review, we cover new developments in these methods and discuss practical considerations for their use in imaging proteins inside living cells. © 2011.


Corcoran A.J.,Wake forest University | Corcoran A.J.,University of Maryland University College | Conner W.E.,Wake forest University
Science | Year: 2014

Communication signals are susceptible to interference ("jamming") from conspecifics and other sources. Many active sensing animals, including bats and electric fish, alter the frequency of their emissions to avoid inadvertent jamming from conspecifics. We demonstrated that echolocating bats adaptively jam conspecifics during competitions for food. Three-dimensional flight path reconstructions and audio-video field recordings of foraging bats (Tadarida brasiliensis) revealed extended interactions in which bats emitted sinusoidal frequency-modulated ultrasonic signals that interfered with the echolocation of conspecifics attacking insect prey. Playbacks of the jamming call, but not of control sounds, caused bats to miss insect targets. This study demonstrates intraspecific food competition through active disruption of a competitor's sensing during food acquisition. © 2014, American Association for the Advancement of Science. All rights reserved.


Rakovic S.V.,University of Maryland University College | Lazar M.,TU Eindhoven
Automatica | Year: 2012

This technical communique delivers a systematic procedure for obtaining a suitable terminal cost function for model predictive control based on Minkowski cost functions. It is shown that, for any given stabilizing linear state feedback control law and associated λ-contractive proper C-set, there always exists a non-trivial scaling of the λ-contractive proper C-set such that the associated Minkowski function satisfies the standard MPC terminal cost stability inequality. © 2012 Elsevier Ltd. All rights reserved.


Oran E.S.,University of Maryland University College
Proceedings of the Combustion Institute | Year: 2015

This paper focuses on two extremes of explosions: the general class of Type Ia supernova (SNIa), which are surprisingly uniform thermonuclear explosions of white dwarf stars, and a specific gasoline vapor-cloud explosion that occurred at the Buncefield fuel depot in 2005. In both cases, recurring questions are whether an initial spark or small, local ignition could result in a detonation, and if so, how could this happen? The broader question is: What is the origin of the deflagration-to-detonation transition (DDT) in confined, partially confined, and unconfined systems? The importance of DDT to SNIa is based on the use of these objects as cosmological "standard candles" that are used for measuring distances and curvature in the universe. The importance of DDT to Buncefield is related to design and operational safety of industrial plants and fuel storage facilities. Combinations of observations, specific laboratory experiments, and selected numerical simulations have given us information and some understanding of the DDT process and its likelihood. Numerical simulation both of large- and small-scale phenomena in these reactive flows were important ingredients in the studies. The invention and discovery of numerical algorithms, including (but not limited to) monotone methods, implicit large-eddy simulation, and adaptive mesh refinement, enabled these simulations certainly as much as the increase in computer speed and memory. Unresolved issues that arose in these studies include the nonequilibrium, non-Kolmogorov properties of the turbulence and turbulent fluctuations in these flows, how these prepare the system for transitions, and how to represent the chemical reactions and energy release in the high temperatures and pressures that are near and might signal a transition.


Brown M.,University of Maryland University College
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences | Year: 2010

Volumetrically significant melt production requires crustal temperatures above approximately 800°C. At the grain scale, the former presence of melt may be inferred based on various microstructures, particularly pseudomorphs of melt pores and grain-boundary melt films. In residual migmatites and granulites, evidence of melt-extraction pathways at outcrop scale is recorded by crystallized products of melt (leucosome) and residual material from which melt has drained (melanosome). These features form networks or arrays that potentially demonstrate the temporal and spatial relations between deformation and melting. As melt volume increases at sites of initial melting, the feedback between deformation and melting creates a dynamic rheological environment owing to localization and strain-rate weakening. With increasing temperature, melt volume increases to the melt connectivity transition, in the range of 2-7 vol% melt, at which point melt may escape in the first of several melt-loss events, where each event represents a batch of melt that left the source and ascended higher in the crust. Each contributing process has characteristic length and time scales, and it is the nonlinear interactions and feedback relations among them that give rise to the dissipative structures and episodicity of melt-extraction events that are recorded as variations in the spatial and temporal patterning of the crust. Focused melt flow occurs by dilatant shear failure of low-melt fraction rocks creating melt-flow networks that allow accumulation and storage of melt, and form the link for melt flow from grain boundaries to veins allowing drainage to crustal-scale ascent conduits. Preliminary indications suggest that anatectic systems are strongly self-organized from the bottom up, becoming more ordered by decreasing the number and increasing the width of ascent conduits from the anatectic zone through the overlying subsolidus crust to the ductile-to-brittle transition zone, where the melt accumulates in plutons. © 2010 The Royal Society.


Sati H.,University of Maryland University College
International Journal of Geometric Methods in Modern Physics | Year: 2011

Studying the M-branes leads us naturally to new structures that we call Membrane-, Membranec, StringK(ℤ,3) and Fivebrane K(ℤ,4) structures, which we show can also have twisted counterparts. We study some of their basic properties, highlight analogies with structures associated with lower levels of the Whitehead tower of the orthogonal group, and demonstrate the relations to M-branes. © 2011 World Scientific Publishing Company.


El-Sherif A.A.,Alexandria University | Liu K.J.R.,University of Maryland University College
IEEE Transactions on Wireless Communications | Year: 2011

Spectrum sensing is an essential functionality of cognitive radio networks. However, the effect of errors in the spectrum sensing process on the performance of the multiple access layer of both primary and secondary networks has not gained much attention. This paper aims at bridging the gap between the study of spectrum sensing and the multiple access of cognitive radio networks. To achieve this goal we pose and answer the question how the spectrum sensing errors affects the performance of cognitive radio networks from a multiple access protocol design point of view. The negative effects of the spectrum sensing errors on the throughput of both primary and secondary networks are characterized through queuing theory analysis of both networks. To alleviate these negative effects a novel joint design of the spectrum sensing and channel access mechanisms is proposed. This design is based on the observation that, in a binary hypothesis testing problem, the value of the test statistics could be used as a confidence measure for the test outcome. Therefore, this value will be used to define different channel access probabilities for secondary users. Results reveal a significant performance improvement in the maximum stable throughput of both primary and secondary networks by virtue of the proposed technique. © 2011 IEEE.


Kraft N.J.B.,University of Maryland University College | Godoy O.,University of California at Santa Barbara | Godoy O.,CSIC - Institute of Natural Resources and Agriculture Biology of Seville | Levine J.M.,ETH Zurich
Proceedings of the National Academy of Sciences of the United States of America | Year: 2015

Understanding the processes maintaining species diversity is a central problem in ecology, with implications for the conservation and management of ecosystems. Although biologists often assume that trait differences between competitors promote diversity, empirical evidence connecting functional traits to the niche differences that stabilize species coexistence is rare. Obtaining such evidence is critical because traits also underlie the average fitness differences driving competitive exclusion, and this complicates efforts to infer community dynamics from phenotypic patterns. We coupled fieldparameterized mathematical models of competition between 102 pairs of annual plants with detailed sampling of leaf, seed, root, and whole-plant functional traits to relate phenotypic differences to stabilizing niche and average fitness differences. Single functional traits were often well correlated with average fitness differences between species, indicating that competitive dominance was associated with late phenology, deep rooting, and several other traits. In contrast, single functional traits were poorly correlated with the stabilizing niche differences that promote coexistence. Niche differences could only be described by combinations of traits, corresponding to differentiation between species in multiple ecological dimensions. In addition, several traits were associated with both fitness differences and stabilizing niche differences. These complex relationships between phenotypic differences and the dynamics of competing species argue against the simple use of single functional traits to infer community assembly processes but lay the groundwork for a theoretically justified trait-based community ecology.


Protas M.,University of California at Berkeley | Jeffery W.R.,University of Maryland University College
Wiley Interdisciplinary Reviews: Developmental Biology | Year: 2012

Cave animals are excellent models to study the general principles of evolution as well as the mechanisms of adaptation to a novel environment: the perpetual darkness of caves. In this article, two of the major model systems used to study the evolution and development (evo-devo) of cave animals are described: the teleost fish Astyanax mexicanus and the isopod crustacean Asellus aquaticus. The ways in which these animals match the major attributes expected of an evo-devo cave animal model system are described. For both species, we enumerate the regressive and constructive troglomorphic traits that have evolved during their adaptation to cave life, the developmental and genetic basis of these traits, the possible evolutionary forces responsible for them, and potential new areas in which these model systems could be used for further exploration of the evolution of cave animals. Furthermore, we compare the two model cave animals to investigate the mechanisms of troglomorphic evolution. Finally, we propose a few other cave animal systems that would be suitable for development as additional models to obtain a more comprehensive understanding of the developmental and genetic mechanisms involved in troglomorphic evolution. © 2012 Wiley Periodicals, Inc.


Komaee A.,University of Maryland University College
IEEE Transactions on Signal Processing | Year: 2011

Bayesian estimation of the arrival time of a single pulse is considered in the presence of a white noise. The employed model is a stochastic process consisted of a randomly delayed causal pulse and an additive white Gaussian noise, where the prior density of the delay is known. The history of this stochastic process is given at every point in time and the problem is to obtain the conditional expectation of an arbitrary function of the arrival time. The paper adopts a stochastic differential equation approach to develop nonlinear filters to efficiently compute this estimation. The filtering problem is resolved for a number of pulse shapes which allow for a finite-dimensional solution. These pulse shapes include step, exponential, and rectangular functions, as well as a piecewise constant function which well approximates a broad class of waveforms. The application of this filtering problem in real-time pulse arrival detection is discussed. The task of this operation is to report the event of pulse arrival as soon after occurrence as possible. The performance of nonlinear filtering is numerically verified for this application. © 2011 IEEE.


Beckett D.,University of Maryland University College
Methods in Molecular Biology | Year: 2012

Elucidation of mechanisms of energy transduction through macromolecules in allosteric systems requires application of a broad range of techniques and approaches. High-resolution structures of the end states in an allosteric system provide invaluable clues about allosteric mechanism. Thermodynamic and kinetic studies reveal the rules that govern the transitions between states in the system. Acquisition of detailed molecular level information about allosteric mechanism requires interrogation of the structural and dynamic properties of both intermediates and end states in the allosteric cycle. Many experimental and computational tools have been developed to probe allostery. Among these are hydrogen-deuterium exchange detected by either NMR spectroscopy or mass spectrometry. This article provides a detailed description of application of hydrogen exchange detected by mass spectrometry (HDX-MS) to investigate an allosteric system. © 2012 Springer Science+Business Media, LLC.


Ding C.,University of Maryland University College
Urban Studies | Year: 2013

'New Geographical Economy' suggests an inverted-U-shaped relationship between transport costs and regional economic concentration. By using data on Chinese prefectures, this paper examines the relationship between transport development and economic concentration, to investigate the 'point effect' and 'network effect' of transport stocks and to gauge their relative magnitudes. The paper concludes the following: the development of urban roads leads to rising GDP shares in the city-proper for both manufacturing and service industries; major regional roads have the same effect. A 'point effect' is found for both urban roads and major regional roads in GDPs. There are spillover effects for both urban roads and major regional roads. Finally, different types of transport infrastructure have different economic impacts. The policy implication is that the urban-rural economic growth gap is likely to continue to increase with urban and regional transport development during the rapid urbanisation concurrently undertaken. © 2012 Urban Studies Journal Limited.


Basar G.,University of Maryland University College | Dunne G.V.,University of Connecticut
Journal of High Energy Physics | Year: 2015

Abstract: The Nekrasov-Shatashvili limit for the low-energy behavior of N=2 and N=2* supersymmetric SU(2) gauge theories is encoded in the spectrum of the Mathieu and Lamé equations, respectively. This correspondence is usually expressed via an all-orders Bohr-Sommerfeld relation, but this neglects non-perturbative effects, the nature of which is very different in the electric, magnetic and dyonic regions. In the gauge theory dyonic region the spectral expansions are divergent, and indeed are not Borel-summable, so they are more properly described by resurgent trans-series in which perturbative and non-perturbative effects are deeply entwined. In the gauge theory electric region the spectral expansions are convergent, but nevertheless there are non-perturbative effects due to poles in the expansion coefficients, and which we associate with worldline instantons. This provides a concrete analog of a phenomenon found recently by Drukker, Mariño and Putrov in the large N expansion of the ABJM matrix model, in which non-perturbative effects are related to complex space-time instantons. In this paper we study how these very different regimes arise from an exact WKB analysis, and join smoothly through the magnetic region. This approach also leads to a simple proof of a resurgence relation found recently by Dunne and Ünsal, showing that for these spectral systems all non-perturbative effects are subtly encoded in perturbation theory, and identifies this with the Picard-Fuchs equation for the quantized elliptic curve. © 2015, The Author(s).


Abazajian K.N.,University of Maryland University College
Journal of Cosmology and Astroparticle Physics | Year: 2011

I show that the spectrum and morphology of a recent Fermi-LAT observation of the Galaxy center are consistent with a millisecond pulsar population in the nuclear Central stellar cluster of the Milky Way. The Galaxy Center gamma-ray spectrum is consistent with the spectrum of four of eight globular clusters that have been detected in the gamma-ray. A dark matter annihilation interpretation cannot be ruled out, though no unique features exist that would require this conclusion. © 2011 IOP Publishing Ltd and SISSA.


Colombini M.,University of Maryland University College | Mannella C.A.,New York State Department of Health
Biochimica et Biophysica Acta - Biomembranes | Year: 2012

VDAC is now universally accepted as the channel in the mitochondrial outer membrane responsible for metabolite flux in and out of mitochondria. Its discovery occurred over two independent lines of investigation in the 1970s and 80s. This retrospective article describes the history of VDAC's discovery and how these lines merged in a collaboration by the authors. The article was written to give the reader a sense of the role played by laboratory environment, personalities, and serendipity in the discovery of the molecular basis for the unusual permeability properties of the mitochondrial outer membrane. This article is part of a Special Issue entitled: VDAC structure, function, and regulation of mitochondrial metabolism. © 2011 Elsevier B.V. All rights reserved.


Cardiovascular disease (CVD) and CVD risk factors are highly heritable, and numerous lines of evidence indicate they have a strong genetic basis. While there is nothing known about the interactive effects of genetics and exercise training on CVD itself, there is at least some literature addressing their interactive effect on CVD risk factors. There is some evidence indicating that CVD risk factor responses to exercise training are also heritable and, thus, may have a genetic basis. While roughly 100 studies have reported significant effects of genetic variants on CVD risk factor responses to exercise training, no definitive conclusions can be generated at the present time, because of the lack of consistent and replicated results and the small sample sizes evident in most studies. There is some evidence supporting "possible" candidate genes that may affect these responses to exercise training: APO E and CETP for plasma lipoprotein-lipid profiles; eNOS, ACE, EDN1, and GNB3 for blood pressure; PPARG for type 2 diabetes phenotypes; and FTO and BAR genes for obesity-related phenotypes. However, while genotyping technologies and statistical methods are advancing rapidly, the primary limitation in this field is the need to generate what in terms of exercise intervention studies would be almost incomprehensible sample sizes. Most recent diabetes, obesity, and blood pressure genetic studies have utilized populations of 10,000 -250,000 subjects, which result in the necessary statistical power to detect the magnitude of effects that would probably be expected for the impact of an individual gene on CVD risk factor responses to exercise training. Thus at this time it is difficult to see how this field will advance in the future to the point where robust, consistent, and replicated data are available to address these issues. However, the results of recent large-scale genomewide association studies for baseline CVD risk factors may drive future hypothesis-driven exercise training intervention studies in smaller populations addressing the impact of specific genetic variants on well-defined physiological phenotypes. © 2011 the American Physiological Society.


Jacobson T.,University of Maryland University College | Jacobson T.,CNRS Paris Institute of Astrophysics
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

We show that Hořava gravity can be obtained from Einstein-aether theory in the limit that the twist coupling constant goes to infinity, while holding fixed the expansion, shear and acceleration couplings. This limit helps to clarify the relation between the two theories, and allows Hořava results to be obtained from Einstein-aether ones. The limit is illustrated with several examples, including rotating black hole equations, parametrized post-Newtonian parameters, and radiation rates from binary systems. © 2014 American Physical Society.


The DART (direct analysis in real time) ion source is a novel atmospheric pressure ionization technique that enables efficient ionization of gases, liquids and solids with high throughput. A major limit to its wider application in the analysis of gases is its poor detection sensitivity caused by open-air sampling. In this study, a confined interface between the DART ion source outlet and mass spectrometer sampling orifice was developed, where the plasma generated by the atmospheric pressure glow discharge collides and ionizes gas-phase molecules in a Tee-shaped flow tube instead of in open air. It leads to significant increase of collision reaction probability between high energy metastable molecules and analytes. The experimental results show that the ionization efficiency was increased at least by two orders of magnitude. This technique was then applied in the real time analysis of volatile organic compounds (VOCs) of Citrus Limon (lemon) and wounded Allium Cepa (onion). The confined DART ion source was proved to be a powerful tool for the studies of plant metabolomics. Copyright © 2012 John Wiley & Sons, Ltd.


Pessoa L.,University of Maryland University College
Physics of Life Reviews | Year: 2014

What is the relationship between brain and behavior? The answer to this question necessitates characterizing the mapping between structure and function. The aim of this paper is to discuss broad issues surrounding the link between structure and function in the brain that will motivate a network perspective to understanding this question. However, as others in the past, I argue that a network perspective should supplant the common strategy of understanding the brain in terms of individual regions. Whereas this perspective is needed for a fuller characterization of the mind-brain, it should not be viewed as panacea. For one, the challenges posed by the many-to-many mapping between regions and functions is not dissolved by the network perspective. Although the problem is ameliorated, one should not anticipate a one-to. one mapping when the network approach is adopted. Furthermore, decomposition of the brain network in terms of meaningful clusters of regions, such as the ones generated by community-finding algorithms, does not by itself reveal "true" subnetworks. Given the hierarchical and multi-relational relationship between regions, multiple decompositions will offer different "slices" of a broader landscape of networks within the brain. Finally, I described how the function of brain regions can be characterized in a multidimensional manner via the idea of diversity profiles. The concept can also be used to describe the way different brain regions participate in networks. © 2014 Elsevier B.V.


Chai T.,5830 University Research Court | Chai T.,University of Maryland University College | Draxler R.R.,5830 University Research Court
Geoscientific Model Development | Year: 2014

Both the root mean square error (RMSE) and the mean absolute error (MAE) are regularly employed in model evaluation studies. Willmott and Matsuura (2005) have suggested that the RMSE is not a good indicator of average model performance and might be a misleading indicator of average error, and thus the MAE would be a better metric for that purpose. While some concerns over using RMSE raised by Willmott and Matsuura (2005) and Willmott et al. (2009) are valid, the proposed avoidance of RMSE in favor of MAE is not the solution. Citing the aforementioned papers, many researchers chose MAE over RMSE to present their model evaluation statistics when presenting or adding the RMSE measures could be more beneficial. In this technical note, we demonstrate that the RMSE is not ambiguous in its meaning, contrary to what was claimed by Willmott et al. (2009). The RMSE is more appropriate to represent model performance than the MAE when the error distribution is expected to be Gaussian. In addition, we show that the RMSE satisfies the triangle inequality requirement for a distance metric, whereas Willmott et al. (2009) indicated that the sums-of-squares-based statistics do not satisfy this rule. In the end, we discussed some circumstances where using the RMSE will be more beneficial. However, we do not contend that the RMSE is superior over the MAE. Instead, a combination of metrics, including but certainly not limited to RMSEs and MAEs, are often required to assess model performance. © Author(s) 2014. CC Attribution 3.0 License.


Li Z.,University of Maryland University College
Journal of Transportation Engineering | Year: 2011

This study presents an arterial signal optimization model that can consider queue blockage among intersection lane groups under oversaturated conditions. The proposed model captures traffic dynamics with the cell transmission concept, which takes into account complex flow interactions among different lane groups. With the embedded formulations for forward wave, backward wave, and the horizontal queue, the proposed arterial signal optimization model can yield effective signal plans for both saturated and under-saturated intersections. To evaluate the performance of the proposed model, this study has conducted extensive simulation experiments with a segment of Georgia Avenue intersecting the Capital Beltway in Silver Spring, Maryland. Through comparisons with signal-timing plans from TRANSYT-7F (Release 10), the proposed model shows its promise for signal-timing optimization, particularly under congested conditions. © 2011 American Society of Civil Engineers.


Belov G.A.,University of Maryland University College
Viruses | Year: 2015

All positive strand RNA viruses of eukaryotes replicate their genomes in association with membranes. These viruses actively change cellular lipid metabolism to build replication membranes enriched in specific lipids. The ubiquitous use of membranes by positive strand RNA viruses apparently holds major evolutionary advantages; however our understanding of the mechanistic role of membranes, let alone of specific lipid components of the membrane bilayer, in the viral replication cycle is minimal. The replication complexes that can be isolated from infected cells, or reconstituted in vitro from crude cell lysates, do not allow controlled manipulation of the membrane constituents thus limiting their usefulness for understanding how exactly membranes support the replication reaction. Recent work from Peter Nagy group demonstrates that replication of a model positive strand RNA virus can be reconstituted in the in vitro reaction with liposomes of chemically defined composition and reveals an exclusive role of phosphatidylethanolamine in sustaining efficient viral RNA replication. This study opens new possibilities for investigation of membrane contribution in the replication process that may ultimately lead to development of novel broad spectrum antiviral compounds targeting the membrane-dependent elements of the replication cycle conserved among diverse groups of viruses. © 2015 by the authors; licensee MDPI, Basel, Switzerland.


Leishman G.J.,University of Maryland University College
Journal of the American Helicopter Society | Year: 2010

The development of significantly better performing helicopters and new types of rotorcraft will require that the subject of aeromechanics be mastered to a much higher level than it is now. A future goal must be to acquire a true predictive capability for problems in aeromechanics that are free of modeling contradictions. It is argued that we have reached a "dip" in the progress of furthering the capabilities of the helicopter and also in our abilities to innovate new forms of rotorcraft with sufficiently high levels of confidence and robustness in their design. This dip can be correlated to a large extent with our compromised capabilities in truly understanding the multiplicity of problems in aeromechanics, and in the inability to design-out the perceived "barrier" problems that limit, in some manner or other, the flight capabilities of all types of rotorcraft. In this context, it is postulated that such a dip coincides with a "comfort zone," where we have some factual knowledge of the physical problems but still mostly a tacit understanding and a postdictive (i.e., after the fact) modeling capability. On the other side of the dip is an improved paradigm where we have mastered the problems by having a fundamental scientific understanding and gaining a predictive capability of high confidence. Getting through the dip requires an invigorated investment in advanced rotorcraft research that will have more revolutionary outcomes if imaginative design solutions are to follow. Our overarching objective should be to make sound engineering design decisions based on validated models of aeromechanics that have verifiable predictive capabilities. To this end, it is argued that we must strive for mastery of the necessary understanding by using a much better balance of all of the tools available to us, including existing data, theory, numerical models, and the best types of new experiments that we can possibly devise, the latter which must encompass ambitious laboratory experiments, wind tunnel testing, and flight tests of new prototype vehicles. The extraordinary changes needed for advancement mean that we cannot continue to root our research in the comfort zone of only tentative or calibrated understanding, and so retaining only limited abilities to comprehend aeromechanical anomalies and resolve ever more challenging engineering crises. Finite resources will also dictate that we continue to work more efficiently to generalize both current and new knowledge of aeromechanics into much more useful forms, and to act aggressively to eliminate any efforts that are not aligned with the authentic purpose of improving the understanding of all rotorcraft and their component systems. © 2010 The American Helicopter Society.


Nagarajan N.,Genome Institute of Singapore | Pop M.,University of Maryland University College
Nature Reviews Genetics | Year: 2013

Advances in sequencing technologies and increased access to sequencing services have led to renewed interest in sequence and genome assembly. Concurrently, new applications for sequencing have emerged, including gene expression analysis, discovery of genomic variants and metagenomics, and each of these has different needs and challenges in terms of assembly. We survey the theoretical foundations that underlie modern assembly and highlight the options and practical trade-offs that need to be considered, focusing on how individual features address the needs of specific applications. We also review key software and the interplay between experimental design and efficacy of assembly. © 2013 Macmillan Publishers Limited. All rights reserved.


Smolyaninov I.I.,University of Maryland University College
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2013

Subwavelength confinement of light in nonlinear hyperbolic metamaterials due to formation of spatial solitons has attracted much recent attention because of its seemingly counterintuitive behavior. In order to achieve self-focusing in a hyperbolic wire medium, a nonlinear self-defocusing Kerr medium must be used as a dielectric host. Here we demonstrate that this behavior finds a natural explanation in terms of the analog of gravity. A wave equation describing the propagation of extraordinary light inside hyperbolic metamaterials exhibits (2+1)-dimensional Lorentz symmetry. The role of time in the corresponding effective three-dimensional Minkowski space-time is played by the spatial coordinate aligned with the optical axis of the metamaterial. Nonlinear optical Kerr effect "bends" this space-time resulting in effective gravitational force between extraordinary photons. In order for the effective gravitational constant to be positive, a negative self-defocusing Kerr medium must be used as a host. If gravitational self-interaction is strong enough, the spatial soliton may collapse into a black hole analog. © 2013 American Physical Society.


Huang J.,University of Maryland University College | Yin Z.,CAS Fujian Institute of Research on the Structure of Matter | Zheng Q.,CAS Fujian Institute of Research on the Structure of Matter
Energy and Environmental Science | Year: 2011

As an n-type inorganic semiconductor, ZnO has been widely used in organic solar cells (OSCs) and hybrid solar cells (HSCs) due to its salient characteristics such as low cost, easy synthesis, non-toxicity, high stability, and good optoelectronic properties. This article reviews the applications of ZnO in solar cells, including ZnO/organic HSCs, and OSCs with ZnO acting as electrode buffer layers or transparent electrodes. For ZnO/organic HSCs, ZnO serves as the electron acceptor material, while organic semiconductors act as electron donor materials. For the buffer layers or electrode applications, ZnO is used as an electron collection and hole blocking material where its structure plays an important role in the determination of the device performance (e.g., power conversion efficiency, lifetime, stability, etc.). Special emphasis goes to the device performance of OSCs and HSCs, which depends not only on the active materials and the device configurations, but also on the structural characteristics of the ZnO buffer layer. Finally, we briefly give an analysis on the opportunities and challenges for this promising semiconductor in OSCs and HSCs. © 2011 The Royal Society of Chemistry.


Yi R.,University of Maryland University College | Landes R.D.,University of Arkansas for Medical Sciences
Nicotine and Tobacco Research | Year: 2012

Introduction: Given the lack of consensus regarding changes in temporal and probability discounting as a function of smoking abstinence in cigarette smokers, the present study comprehensively examined possible changes in these processes following a period of acute smoking abstinence consistent with elevated withdrawal symptoms and craving. Methods: Computerized temporal and probability discounting assessments were collected from cigarette smokers following normal smoking and 24-hr smoking abstinence, with the order of normal smoking and abstinence sessions counterbalanced across participants. Other conditions included commodity (money and cigarettes), sign (gains and losses), and magnitude ($50 and $1,000). Results: Twenty four-hour smoking abstinence resulted in a reduction in expired carbon monoxide to near-zero levels and increases in withdrawal and craving. Examination of discounting parameters as a function of smoking abstinence revealed a general pattern of increase in the temporal discounting of monetary gains and losses following abstinence but not in the temporal discounting of cigarettes nor probability discounting of money or cigarettes. Pearson correlations also revealed an expected pattern of significant relationships. Conclusions: The present study is a comprehensive examination of temporal and probability discounting following smoking abstinence and reveals a generalized change in intertemporal decision making for monetary rewards. © The Author 2012. Published by Oxford University Press on behalf of the Society for Research on Nicotine and Tobacco. All rights reserved.


Levermore C.D.,University of Maryland University College | Masmoudi N.,Courant Institute of Mathematical Sciences
Archive for Rational Mechanics and Analysis | Year: 2010

We establish a Navier-Stokes-Fourier limit for solutions of the Boltzmann equation considered over any periodic spatial domain of dimension two or more. We do this for a broad class of collision kernels that relaxes the Grad small deflection cutoff condition for hard potentials and includes for the first time the case of soft potentials. Appropriately scaled families of DiPerna-Lions renormalized solutions are shown to have fluctuations that are compact. Every limit point is governed by a weak solution of a Navier-Stokes-Fourier system for all time. © 2009 Springer-Verlag.


Wall A.C.,University of Maryland University College
Classical and Quantum Gravity | Year: 2013

The generalized second law can be used to prove a singularity theorem, by generalizing the notion of a trapped surface to quantum situations. Like Penrose's original singularity theorem, it implies that spacetime is null-geodesically incomplete inside black holes, and to the past of spatially infinite Friedmann-Robertson-Walker cosmologies. If space is finite instead, the generalized second law requires that there only be a finite amount of entropy producing processes in the past, unless there is a reversal of the arrow of time. In asymptotically flat spacetime, the generalized second law also rules out traversable wormholes, negative masses, and other forms of faster-than-light travel between asymptotic regions, as well as closed timelike curves. Furthermore it is impossible to form baby universes which eventually become independent of the mother universe, or to restart inflation. Since the semiclassical approximation is used only in regions with low curvature, it is argued that the results may hold in full quantum gravity. The introduction describes the second law and its time-reverse, in ordinary and generalized thermodynamics, using either the fine-grained or the coarse-grained entropy. (The fine-grained version is used in all results except those relating to the arrow of time.) © 2013 IOP Publishing Ltd.


O'Neill S.M.,University of Maryland University College | Jones T.W.,University of Minnesota
Astrophysical Journal | Year: 2010

We report on a series of three-dimensional magnetohydrodynamic simulations of active galactic nucleus (AGN) jet propagation in realistic models of magnetized galaxy clusters. We are primarily interested in the details of energy transfer between jets and the intracluster medium (ICM) to help clarify what role such flows could have in the reheating of cluster cores. Our simulated jets feature a range of intermittency behaviors, including intermittent jets that periodically switch on and off and one model jet that shuts down completely, naturally creating a relic plume. The ICM into which these jets propagate incorporates tangled magnetic field geometries and density substructure designed to mimic some likely features of real galaxy clusters. We find that our jets are characteristically at least 60% efficient at transferring thermal energy to the ICM. Irreversible heat energy is not uniformly distributed, however, instead residing preferentially in regions very near the jet/cocoon boundaries. While intermittency affects the details of how, when, and where this energy is deposited, all of our models generically fail to heat the cluster cores uniformly. Both the detailed density structure and nominally weak magnetic fields in the ICM play interesting roles in perturbing the flows, particularly when the jets are non-steady. Still, this perturbation is never sufficient to isotropize the jet energy deposition, suggesting that some other ingredient is required for AGN jets to successfully reheat cluster cores. © 2010. The American Astronomical Society. All rights reserved.


Wolfire M.G.,University of Maryland University College | Hollenbach D.,Search for Extraterrestrial Intelligence Institute | McKee C.F.,University of California at Berkeley
Astrophysical Journal | Year: 2010

The mass of molecular gas in an interstellar cloud is often measured using line emission from low rotational levels of CO, which are sensitive to the CO mass, and then scaling to the assumed molecular hydrogen H2 mass. However, a significant H2 mass may lie outside the CO region, in the outer regions of the molecular cloud where the gas-phase carbon resides in C or C+. Here, H2 self-shields or is shielded by dust from UV photodissociation, whereas CO is photodissociated. This H2 gas is "dark" in molecular transitions because of the absence of CO and other trace molecules, and because H2 emits so weakly at temperatures 10K


Christie J.M.,University of Glasgow | Murphy A.S.,University of Maryland University College
American Journal of Botany | Year: 2013

Light is a key environmental factor that drives many aspects of plant growth and development. Phototropism, the reorientation of growth toward or away from light, represents one of these important adaptive processes. Modern studies of phototropism began with experiments conducted by Charles Darwin demonstrating that light perception at the shoot apex of grass coleoptiles induces differential elongation in the lower epidermal cells. This led to the discovery of the plant growth hormone auxin and the Cholodny- Went hypothesis attributing differential tropic bending to lateral auxin relocalization. In the past two decades, molecular-genetic analyses in the model flowering plant Arabidopsis thaliana has identifi ed the principal photoreceptors for phototropism and their mechanism of activation. In addition, several protein families of auxin transporters have been identifi ed. Despite extensive efforts, however, it still remains unclear as to how photoreceptor activation regulates lateral auxin transport to establish phototropic growth. This review aims to summarize major developments from over the last century and how these advances shape our current understanding of higher plant phototropism. Recent progress in phototropism research and the way in which this research is shedding new light on old concepts, including the Cholodny-Went hypothesis, is also highlighted. © 2013 Botanical Society of America.


Hitaj C.,University of Maryland University College
Journal of Environmental Economics and Management | Year: 2013

This paper analyzes the drivers of wind power development in the United States, focusing on government renewable energy incentives and access to the electricity grid. The effects of wind capacity, electricity transmission line coverage and grid regulation, as well as state and federal subsidies from 1998 to 2007 are estimated via random effects Tobit, Probit, and ordinary least squares instrumental variables regression. The results indicate that the federal production tax credit, state-level sales tax credit and production incentives play an important role in promoting wind power. In addition, higher wind power penetration levels can be achieved by bringing more parts of the electricity transmission grid under independent system operator regulation. This paper concludes that state and federal government policies play a significant role in wind power development both by providing financial support and by improving physical and procedural access to the electricity grid. © 2012 Elsevier Inc.


Dinman J.D.,University of Maryland University College
Wiley Interdisciplinary Reviews: RNA | Year: 2012

While ribosomes must maintain translational reading frame in order to translate primary genetic information into polypeptides, cis-acting signals located in mRNAs represent higher order information content that can be used to fine-tune gene expression. Classes of signals have been identified that direct a fraction of elongating ribosomes to shift reading frame by one base in the 5′ (-1) or 3′ (+1) direction. This is called programmed ribosomal frameshifting (PRF). Although mechanisms of PRF differ, a common feature is induction of ribosome pausing, which alters kinetic partitioning rates between in-frame and out-of-frame codons at specific 'slippery' sequences. Many viruses use PRF to ensure synthesis of the correct ratios of virus-encoded proteins required for proper viral particle assembly and maturation, thus identifying PRF as an attractive target for antiviral therapeutics. In contrast, recent studies indicate that PRF signals may primarily function as mRNA destabilizing elements in cellular mRNAs. These studies suggest that PRF may be used to fine-tune gene expression through mRNA decay pathways. The possible regulation of PRF by noncoding RNAs is also discussed. © 2012 John Wiley & Sons, Ltd.


Arnaut L.R.,Imperial College London | Gradoni G.,University of Maryland University College
IEEE Transactions on Electromagnetic Compatibility | Year: 2013

We derive a probability distribution, confidence intervals and statistics of the quality (Q) factor of an arbitrarily shaped mode-stirred reverberation chamber, based on ensemble distributions of an idealized random cavity field with assumed perfect stir efficiency. It is shown that Q exhibits a Fisher-Snedecor F-distribution whose degrees of freedom are governed by the number of simultaneously excited cavity modes per stir state. The most probable value of Q is shown to be between a fraction 2/9 and 1 of its mean value, and between a fraction 4/9 and 1 of its asymptotic mean (composite Q) value. The arithmetic mean value is found to exceed the values of most other theoretical metrics for centrality of Q. For a rectangular cavity, we retrieve the known asymptotic expression for Q in the limit of a highly overmoded regime. © 1964-2012 IEEE.


Marsat S.,University of Maryland University College | Marsat S.,NASA
Classical and Quantum Gravity | Year: 2015

We investigate cubic-in-spin effects for inspiralling compact object binaries, both in the dynamics and in the energy flux emitted in gravitational waves, at the leading post-Newtonian order. We use a Lagrangian formalism to implement finite-size effects, and extend it to cubic order in the spins, which corresponds to the octupolar order in a multipolar decomposition. This formalism allows us to derive the equation of motion, equations of precession for the spin, and stress-energy tensor of each body in covariant form, and admits a formal generalization to any multipolar order. For spin-induced multipoles, i.e.in the case where the rotation of the compact object is solely responsible for the additional multipole moments, we find a unique structure for the octupolar moment representing cubic-in-spin effects. We apply these results to compute the associated effects in the dynamics of compact binary systems, and deduce the corresponding terms in the energy loss rate due to gravitational waves. These effects enter at the third-and-a-half post-Newtonian order, and can be important for binaries involving rapidly spinning black holes. We provide simplified results for spin-aligned circular orbits, and discuss the quantitative importance of the new contributions. © 2015 IOP Publishing Ltd.


Chen Z.-L.,University of Maryland University College
Operations Research | Year: 2010

In many applications involving make-to-order or time-sensitive (e.g., perishable, seasonal) products, finished orders are often delivered to customers immediately or shortly after the production. Consequently, there is little or no finished product inventory in the supply chain such that production and outbound distribution are very intimately linked and must be scheduled jointly to achieve a desired on-time delivery performance at minimum total cost. Research on integrated scheduling models of production and outbound distribution is relatively recent but is growing very rapidly. In this paper, we provide a survey of such existing models. We present a unified model representation scheme, classify existing models into several different classes, and for each class of the models give an overview of the optimality properties, computational tractability, and solution algorithms for the various problems studied in the literature. We clarify the tractability of some open problems left in the literature and some new problems by providing intractability proofs or polynomial-time exact algorithms. We also identify several problem areas and issues for future research. © 2010 INFORMS.


Records A.R.,University of Maryland University College
Molecular Plant-Microbe Interactions | Year: 2011

Whether they live in the soil, drift in the ocean, survive in the lungs of human hosts or reside on the surfaces of leaves, all bacteria must cope with an array of environmental stressors. Bacteria have evolved an impressive suite of protein secretion systems that enable their survival in hostile environments and facilitate colonization of eukaryotic hosts. Collectively, gram-negative bacteria produce six distinct secretion systems that deliver proteins to the extracellular milieu or directly into the cytosol of host cells. The type VI secretion system (T6SS) was discovered recently and is encoded in at least one fourth of all sequenced gramnegative bacterial genomes. T6SS proteins are evolutionarily and structurally related to phage proteins, and it is likely that the T6SS apparatus is reminiscent of phage injection machinery. Most studies of T6SS function have been conducted in the context of host-pathogen interactions. However, the totality of data suggests that the T6SS is a versatile tool with roles in virulence, symbiosis, interbacterial interactions, and antipathogenesis. This review gives a brief history of T6SS discovery and an overview of the pathway's predicted structure and function. Special attention is paid to research addressing the T6SS of plant-associated bacteria, including pathogens, symbionts and plant growth-promoting rhizobacteria. © 2011 The American Phytopathological Society.


Lips K.,University of Maryland University College
Molecular Ecology | Year: 2014

For the past 17 years, scientists have been compiling a list of amphibian species susceptible to infection by the amphibian-killing chytrid fungus, Batrachochytrium dendrobatidis (Bd), all over the world, with >500 species infected on every continent except Antarctica (Olson et al.). Where Bd has been found, the impacts on amphibians has been one of two types: either Bd arrives into a naïve amphibian population followed by a mass die-off and population declines (e.g. Lips et al.), or Bd is present at some moderate prevalence, usually infecting many species but at apparently nonlethal intensities for a long time. In this issue of Molecular Ecology, Rodriguez et al. () discover that the Atlantic Coastal Forest of Brazil is home to two Bd lineages: the Global Pandemic Lineage (Bd-GPL) - the strain responsible for mass die-offs and population declines - and a lineage endemic to Brazil (Bd-Bz). Even more surprising was that both lineages have been present in this area for the past 100 years, making these the oldest records of Bd infecting amphibians. The team also described a moderate but steady prevalence of ~20% across all sampled anuran families for over 100 years, indicating that Brazil has been in an enzootic disease state for over a century. Most amphibians were infected with Bd-GPL, suggesting this lineage may be a better competitor than Bd-Bz or may be replacing the Bd-Bz lineage. Rodriguez et al. () also detected likely hybridization of the two Bd lineages, as originally described by Schloegel et al. (). © 2014 John Wiley & Sons Ltd.


Jarzynski C.,University of Maryland University College
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2013

Transitionless quantum driving achieves adiabatic evolution in a hurry, using a counterdiabatic Hamiltonian to stifle nonadiabatic transitions. Here this shortcut to adiabaticity is cast in terms of a generator of adiabatic transport. This yields a classical analog of transitionless driving, and provides a strategy for constructing quantal counterdiabatic Hamiltonians. As an application of this framework, exact classical and quantal counterdiabatic terms are obtained for a particle in a box and for even-power-law potentials in one degree of freedom. © 2013 American Physical Society.


Opher M.,Boston University | Drake J.F.,University of Maryland University College