The University of Maine is a public research university located in Orono, Maine, United States. The university was established in 1865 as a land grant college and is referred to as the flagship university of the University of Maine System. Having an enrollment of over 11,000 students, UMaine is the largest university in the state and is the only institution in Maine classified as a research university by the Carnegie Classification of Institutions of Higher Education. The University of Maine's athletic teams are nicknamed the Black Bears, and sport blue and white uniforms. Wikipedia.
Astumian R.D.,University of Maine, United States
Annual Review of Biophysics | Year: 2011
Proteins and other macromolecules can act as molecular machines that convert energy from one form to another through cycles of conformational transitions. In a macroscopically fluctuating environment or at the single-molecule level, the probability for a molecule to be in any state j fluctuates, and the probability current from any other state i to state j is given as the sum of a steady-state current and a pumped current, Iij=I ssij+FijdPj/dt, where Fij is the fraction of the fluctuating current into and out of state j coming directly from state i, and dPj/dt is the rate of change of the probability for the molecule to be in state j. If the fluctuations arise from an equilibrium source, microscopic reversibility guarantees that the time average of the pumped current is zero. If, however, the fluctuations arise due to the action of a nonequilibrium source, the time average of the pumped current is not in general zero and can be opposite in sign to the steady-state current. The pumped current provides a mechanism by which fluctuations, whether generated externally or arising from an internal nonequilibrium chemical reaction, can do electrical, mechanical, or chemical work on a system by coupling into the equilibrium conformational transitions of a protein. In this review I examine work elaborating the mechanism of stochastic pumping and also discuss a thermodynamically consistent approach for modeling the effects of dynamic disorder on enzymes and other proteins. © 2011 by Annual Reviews. All rights reserved.
Borkum J.M.,University of Maine, United States
Headache | Year: 2016
Background Blau theorized that migraine triggers are exposures that in higher amounts would damage the brain. The recent discovery that the TRPA1 ion channel transduces oxidative stress and triggers neurogenic inflammation suggests that oxidative stress may be the common denominator underlying migraine triggers. Objective The aim of this review is to present and discuss the available literature on the capacity of common migraine triggers to generate oxidative stress in the brain. Methods A Medline search was conducted crossing the terms "oxidative stress" and "brain" with "alcohol," "dehydration," "water deprivation," "monosodium glutamate," "aspartame," "tyramine," "phenylethylamine," "dietary nitrates," "nitrosamines," "noise," "weather," "air pollutants," "hypoglycemia," "hypoxia," "infection," "estrogen," "circadian," "sleep deprivation," "information processing," "psychosocial stress," or "nitroglycerin and tolerance." "Flavonoids" was crossed with "prooxidant." The reference lists of the resulting articles were examined for further relevant studies. The focus was on empirical studies, in vitro and of animals, of individual triggers, indicating whether and/or by what mechanism they can generate oxidative stress. Results In all cases except pericranial pain, common migraine triggers are capable of generating oxidative stress. Depending on the trigger, mechanisms include a high rate of energy production by the mitochondria, toxicity or altered membrane properties of the mitochondria, calcium overload and excitotoxicity, neuroinflammation and activation of microglia, and activation of neuronal nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. For some triggers, oxidants also arise as a byproduct of monoamine oxidase or cytochrome P450 processing, or from uncoupling of nitric oxide synthase. Conclusions Oxidative stress is a plausible unifying principle behind the types of migraine triggers encountered in clinical practice. The possible implications for prevention and for understanding the nature of the migraine attack are discussed. © 2015 American Headache Society.
Ashworth S.,University of Maine, United States
PloS one | Year: 2010
Podocytes are highly specialized epithelial cells on the visceral side of the glomerulus. Their interdigitating primary and secondary foot processes contain an actin based contractile apparatus that can adjust to changes in the glomerular perfusion pressure. Thus, the dynamic regulation of actin bundles in the foot processes is critical for maintenance of a well functioning glomerular filtration barrier. Since the actin binding protein, cofilin-1, plays a significant role in the regulation of actin dynamics, we examined its role in podocytes to determine the impact of cofilin-1 dysfunction on glomerular filtration. We evaluated zebrafish pronephros function by dextran clearance and structure by TEM in cofilin-1 morphant and mutant zebrafish and we found that cofilin-1 deficiency led to foot process effacement and proteinuria. In vitro studies in murine and human podocytes revealed that PMA stimulation induced activation of cofilin-1, whereas treatment with TGF-β resulted in cofilin-1 inactivation. Silencing of cofilin-1 led to an accumulation of F-actin fibers and significantly decreased podocyte migration ability. When we analyzed normal and diseased murine and human glomerular tissues to determine cofilin-1 localization and activity in podocytes, we found that in normal kidney tissues unphosphorylated, active cofilin-1 was distributed throughout the cell. However, in glomerular diseases that affect podocytes, cofilin-1 was inactivated by phosphorylation and observed in the nucleus. Based on these in vitro and in vivo studies we concluded cofilin-1 is an essential regulator for actin filament recycling that is required for the dynamic nature of podocyte foot processes. Therefore, we describe a novel pathomechanism of proteinuria development.
Ruthven D.M.,University of Maine, United States
Microporous and Mesoporous Materials | Year: 2012
The extensive kinetic data accumulated, over many years, from a series of experimental studies of the kinetics of adsorption/desorption of a wide range of different sorbates in type A zeolites are reviewed and analyzed in an attempt to develop a coherent understanding of the behavior of these systems. Kinetic data for large laboratory synthesized crystals and small commercial crystals, measured under similar conditions, have been studied in detail. In well dehydrated crystals the sorption rates are generally controlled by intracrystalline diffusion but exposure to traces of water leads to the development of surface resistance and a pronounced reduction in the sorption rate. Zeolite samples of different origin show widely different sorption rates but the diffusional activation energies (for a given sorbate) are essentially constant. The differences between the different samples appear to be due mainly to differences in the cation distribution caused by differences in the initial dehydration procedure. The ideal cation distribution (in 5A) in which all window sites are unoccupied is realized only in very carefully dehydrated samples in which the water was removed slowly at gradually increasing temperature under a high vacuum. In the small commercial 5A crystals many of the windows are blocked, even though all the cations could theoretically be accommodated in the 6-ring sites. This is probably due to cation hydration reactions which are likely to occur when the dehydration conditions are not carefully controlled. © 2012 Elsevier Inc. All rights reserved.
Astumian R.D.,University of Maine, United States
Biophysical Journal | Year: 2015
A simple model for a chemically driven molecular walker shows that the elastic energy stored by the molecule and released during the conformational change known as the power-stroke (i.e., the free-energy difference between the pre- and post-power-stroke states) is irrelevant for determining the directionality, stopping force, and efficiency of the motor. Further, the apportionment of the dependence on the externally applied force between the forward and reverse rate constants of the power-stroke (or indeed among all rate constants) is irrelevant for determining the directionality, stopping force, and efficiency of the motor. Arguments based on the principle of microscopic reversibility demonstrate that this result is general for all chemically driven molecular machines, and even more broadly that the relative energies of the states of the motor have no role in determining the directionality, stopping force, or optimal efficiency of the machine. Instead, the directionality, stopping force, and optimal efficiency are determined solely by the relative heights of the energy barriers between the states. Molecular recognition - the ability of a molecular machine to discriminate between substrate and product depending on the state of the machine - is far more important for determining the intrinsic directionality and thermodynamics of chemo-mechanical coupling than are the details of the internal mechanical conformational motions of the machine. In contrast to the conclusions for chemical driving, a power-stroke is very important for the directionality and efficiency of light-driven molecular machines and for molecular machines driven by external modulation of thermodynamic parameters. © 2015 Biophysical Society.
Behrenfeld M.J.,Oregon State University |
Boss E.S.,University of Maine, United States
Annual Review of Marine Science | Year: 2014
Nutrient and light conditions control phytoplankton division rates in the surface ocean and, it is commonly believed, dictate when and where high concentrations, or blooms, of plankton occur. Yet after a century of investigation, rates of phytoplankton biomass accumulation show no correlation with cell division rates. Consequently, factors controlling plankton blooms remain highly controversial. In this review, we endorse the view that blooms are not governed by abiotic factors controlling cell division, but rather reflect subtle ecosystem imbalances instigated by climate forcings or food-web shifts. The annual global procession of ocean plankton blooms thus represents a report on the recent history of predator-prey interactions modulated by physical processes that, almost coincidentally, also control surface nutrient inputs. Copyright © 2014 by Annual Reviews.
Agency: Department of Health and Human Services | Branch: National Institutes of Health | Program: STTR | Phase: Phase I | Award Amount: 225.00K | Year: 2015
DESCRIPTION provided by applicant Osteoarthritis OA diagnosed in over of the US population is the primary cause of musculoskeletal lower extremity disability Although there is no cure exercise remains the core treatment to manage OA regardless of age comorbidity pain severity or disability Yet many people with this condition do not engage in regular fitness and thus may resort to invasive and risky joint replacement surgeries due to pain and decreased mobility or they may experience health decline due to sedentary lifestyles The goal of this Phase I STTR proposal is to complete the design safety and usability testing of AFARI tm for use by individuals diagnosed with lower extremity OA Created to fill an unmet need for populations who without adequate mobility support would be less likely fully unable or unwilling to participate in ambulatory exercise AFARI is a three wheeled device and provides the mechanisms to unload body weight AFARI was created to promote participation in outdoor walking jogging or running Although durable medical equipment DME such as walkers crutches and canes is available to those who need it DME is minimally functional for outdoor exercise and is often perceived as stigmatizing and inconvenient Therefore many people with lower extremity OA abandon these devices AFARI was designed to mitigate abandonment and eliminate a number of barriers to regular outdoor fitness activity by persons with lower extremity OA AFARI will allow the user to safely and successfully initiate maintain and or increase the length and intensity of their exercise programs In preliminary market research for AFARI respondents indicated that form was as important as function and ease of use if they were to adopt AFARI and the device was designed with these principles in mind Through this STTR effort several major barriers to timely commercialization of AFARI will be researched so that they can be eliminated The safety and stability of AFARI will be proven though mechanical testing and human evaluation The weight bearing monitoring system will be concurrently validated against bodily weight bearing measures An evaluation of the reduction in fall risk tested by fear of falling will be undertaken Data on usability destigmatizing design and overall desirability of AFARI will be collected and tasks will be planned to educate clinicians regarding AFARI and its benefits To accomplish the objective of this Phase I study to demonstrate the initial feasibility of AFARI for people with lower extremity OA such that we can proceed with expanded efforts in Phase II four specific aims will be met AIM Validation of the functionalit and safety of AFARI AIM Concurrent validation of the weight bearing monitoring system AIM Conducting preliminary usability testing focusing on comfort function convenience stigma reduction and design preferences and AIM Planning for clinician education about AFARI PUBLIC HEALTH RELEVANCE Although osteoarthritis diagnosed in over of the US population and a primary cause of musculoskeletal lower extremity disability has no cure exercise is an efficacious treatment to manage it regardless of age comorbidity pain severity or disability Yet many people with this condition do not engage in regular fitness due in large part to the absence of well designed adaptive mobility devices thereby placing them at risk for costly invasive painful surgeries and or further deterioration in health and fitness To meet the growing need for exercise engagement supported with mobility equipment AFARITM an aesthetically designed mobility assistive device with wireless sensor feedback that provides balance stability and weight bearing assistance to those seeking safe and effective support while participating in outdoor rehabilitation and fitness is proposed
Hughes T.,University of Maine, United States
Quaternary Science Reviews | Year: 2011
Ice sheets are the only components of Earth's climate system that can self-destruct. This paper presents the quantitative force balance for bottom-up modeling of ice sheets, as first presented qualitatively in this journal as a way to quantify ice-bed uncoupling leading to self-destruction of ice sheets (Hughes, 2009a). Rapid changes in sea level and climate can result if a large ice-sheet self-destructs quickly, as did the former Laurentide Ice Sheet of North America between 8100 and 7900 BP, thereby terminating the last cycle of Quaternary glaciation. Ice streams discharge up to 90 percent of ice from past and present ice sheets. A hypothesis is presented in which self-destruction of an ice sheet begins when ubiquitous ice-bed decoupling, quantified as a floating fraction of ice, proceeds along ice streams. This causes ice streams to surge and reduce thickness by some 90 percent, and height above sea level by up to 99 percent for floating ice, so the ice sheet undergoes gravitational collapse. Ice collapsing over marine embayments becomes floating ice shelves that may then disintegrate rapidly. This floods the world ocean with icebergs that reduce the ocean-to-atmosphere heat exchange, thereby triggering climate change. Calving bays migrate up low stagnating ice streams and carve out the accumulation zone of the collapsed ice sheet, which prevents its recovery, decreases Earth's albedo, and terminates the glaciation cycle. This sequence of events may coincide with a proposed life cycle of ice streams that drain the ice sheet. A first-order treatment of these life cycles is presented that depends on the longitudinal force balance along the flowbands of ice streams and gives a first approximation to ice-bed uncoupling at snapshots during gravitational collapse into ice shelves that disintegrate, thereby removing the ice sheet. The stability of the Antarctic Ice Sheet is assessed using this bottom-up approach. © 2011 Elsevier Ltd.
Vel S.S.,University of Maine, United States
Composite Structures | Year: 2010
An exact elasticity solution is presented for the free and forced vibration of functionally graded cylindrical shells. The functionally graded shells have simply supported edges and arbitrary material gradation in the radial direction. The three-dimensional linear elastodynamics equations, simplified to the case of generalized plane strain deformation in the axial direction, are solved using suitable displacement functions that identically satisfy the boundary conditions. The resulting system of coupled ordinary differential equations with variable coefficients are solved analytically using the power series method. The analytical solution is applicable to shallow as well as deep shells of arbitrary thickness. The formulation assumes that the shell is made of a cylindrically orthotropic material but it is equally applicable to the special case of isotropic materials. Results are presented for two-constituent isotropic and fiber-reinforced composite materials. The homogenized elastic stiffnesses of isotropic materials are estimated using the self-consistent scheme. In the case of fiber-reinforced materials, the effective properties are obtained using either the Mori-Tanaka or asymptotic expansion homogenization (AEH) methods. The fiber-reinforced composite material studied in the present work consists of silicon-carbide fibers embedded in titanium matrix with the fiber volume fraction and fiber orientation graded in the radial direction. The natural frequencies, mode shapes, displacements and stresses are presented for different material gradations and shell geometries. © 2010 Elsevier Ltd.
Stemmann L.,University Pierre and Marie Curie |
Boss E.,University of Maine, United States
Annual Review of Marine Science | Year: 2012
Understanding pelagic ecology and quantifying energy fluxes through the trophic web and from the surface to the deep ocean requires the ability to detect and identify all organisms and particles in situ and in a synoptic manner. An idealized sensor should observe both the very small living or dead particles such as picoplankton and detritus, respectively, and the large particles such as aggregates and meso- to macroplankton. Such an instrument would reveal an astonishing amount and diversity of living and nonliving particles present in a parcel of water. Unfortunately such sensors do not exist. However, complex interactions constrain the space, temporal, and size distributions of these objects in such ways that general rules can be inferred from the measurement of their optical properties. Recent technological developments allow for the in situ measurement of the optical properties and size distributions of particles and plankton in a way such that synoptic surveys are possible. This review deals with particle and plankton size distributions (PSDs) as well as how particles' geometry and nature affect their optical properties. Finally, we propose the integration of the PSD into size-structured mathematical models of biogeochemical fluxes. © Copyright © 2012 by Annual Reviews. All rights reserved.