Determination of the mobility profile in GaAs-MESFETs

A process for measuring charge carrier mobility for gallium-arsenide metal semiconductor field effect transistors is described in an attempt to optimize the relationship between this factor and production. The measuring procedure allows an actual determination of local mobility in the channel. The physical basis for the process and features of the measuring room are outlined. The measuring technique is described and recommendations are made for setting measuring parameters

Toy model for molecular motors

A hopping model for molecular motors is presented consisting of a state with asymmetric hopping rates with period 2 and a state with uniform hopping rates. State changes lead to a stationary unidirectional current of a particle. The current is explicitly calculated as a function of the rate of state changes, including also an external bias field. The Einstein relation between the linear mobility of the particle and its diffusion coefficient is investigated. The power input into the system is derived, as well as the power output resulting from the work performed against the bias field. The efficiency of this model is found to be rather small.Comment: 11 pages Latex, 7 postscript figures, to be published in Physica

Nonequilibrium Fluctuations, Travelling Waves, and Instabilities in Active Membranes

The stability of a flexible fluid membrane containing a distribution of mobile, active proteins (e.g. proton pumps) is shown to depend on the structure and functional asymmetry of the proteins. A stable active membrane is in a nonequilibrium steady state with height fluctuations whose statistical properties are governed by the protein activity. Disturbances are predicted to travel as waves at sufficiently long wavelength, with speed set by the normal velocity of the pumps. The unstable case involves a spontaneous, pump-driven undulation of the membrane, with clumping of the proteins in regions of high activity.Comment: 4 two-column pages, two .eps figures included, revtex, uses eps

Assessing the Educational Environment of a Flipped Physical Therapy Course: Utilization of the Dundee Ready Education Environment Measure (DREEM)

Purpose: Using valid and reliable measures to assess curricula within health professions programs has gained significant attention in recent years. The educational environment is considered a key domain for student success. The primary aim of this study was to measure the educational environment following the addition of a flipped classroom model within a physical therapy course as measured by the Dundee Ready Education Environment Measure. Methods: A first year doctorate of physical therapy course, “Physical Agents”, was redesigned to include a flipped classroom model, incorporating 24 videos that students reviewed independently, prior to hands-on laboratory learning. Following the conclusion of the course, students (n=57) completed the Dundee Ready Education Environment Measure, a valid and reliable survey designed to measure the educational environment within health profession programs. The Dundee Ready Education Environment Measure contains 50 items, rated from 0 to 4 (5-point Likert scale, “0” strongly disagree to “4” strongly agree), assessing five domains: students’ perceptions of learning; perceptions of teachers; academic self-perception; perceptions of atmosphere; and social self-perception. Descriptive statistics included mean global score (out of 200, 151 to 200 being an excellent environment) mean domain scores, and mean item scores. Cumulative grade point average between students in the flipped classroom model (n=58) and those who previously received a traditional teaching model (n=59) for the course were also compared. Student’s t-test was utilized with significance accepted at p\u3c0.05. Results: The mean global score (168 ± 13.3), indicated that the flipped classroom model fostered an excellent educational environment. Additionally, all mean domain scores, including students’ perceptions of learning (41.3 ± 3.9), perceptions of teachers (39.2 ± 2.9), academic self-perception (25.1 ± 2.5) perception of atmosphere (40.1 ± 4.1) and social self-perception (22.1 ± 2.9) fell into the highest rank of each subscale. Individual item analysis demonstrated 26 items (52%) were identified as especially strong areas, five items (10%) were identified as areas that could be improved, and no individual items were identified as requiring particular concern or immediate attention. Further, no significant differences were seen in cumulative course grade point average between the flipped classroom model (3.74 ± 0.44) and the traditional teaching model (3.71 ± 0.46). Conclusions: The flipped classroom model, utilizing an online learning environment, fostered an excellent educational environment for the physical therapy Physical Agents class. No difference in course grade point average between the flipped classroom model and previous traditional teaching model was seen. Further investigations examining performance on didactic and psychomotor activities within the flipped classroom model are recommended

Mechanical Instabilities of Biological Tubes

We study theoretically the shapes of biological tubes affected by various pathologies. When epithelial cells grow at an uncontrolled rate, the negative tension produced by their division provokes a buckling instability. Several shapes are investigated : varicose, enlarged, sinusoidal or sausage-like, all of which are found in pathologies of tracheal, renal tubes or arteries. The final shape depends crucially on the mechanical parameters of the tissues : Young modulus, wall-to-lumen ratio, homeostatic pressure. We argue that since tissues must be in quasistatic mechanical equilibrium, abnormal shapes convey information as to what causes the pathology. We calculate a phase diagram of tubular instabilities which could be a helpful guide for investigating the underlying genetic regulation

Merger of a bubble and a soap film

The coalescence of a drop into a fluid bath is a subject of continuing interest in fluid dynamics, owing to its dynamical complexity, its accessibility in the laboratory, and its aesthetic appeal. It has been known for some time that a drop gently placed on a static bath of the same fluid may initially combine only partially with the underlying bath, resulting in a daughter droplet of approximately half the diameter of the parent droplet. This process can then repeat, giving rise to the so-called “coalescence cascade” until the final droplet is small enough to be completely absorbed.National Science Foundation (U.S.) (Grant CMMI-1333242)MIT-France Progra

Two-Component Fluid Membranes Near Repulsive Walls: Linearized Hydrodynamics of Equilibrium and Non-equilibrium States

We study the linearized hydrodynamics of a two-component fluid membrane near a repulsive wall, via a model which incorporates curvature- concentration coupling as well as hydrodynamic interactions. This model is a simplified version of a recently proposed one [J.-B. Manneville et al. Phys. Rev. E, 64, 021908 (2001)] for non-equilibrium force-centres embedded in fluid membranes, such as light-activated bacteriorhodopsin pumps incorporated in phospholipid (EPC) bilayers. The pump/membrane system is modeled as an impermeable, two-component bilayer fluid membrane in the presence of an ambient solvent, in which one component, representing active pumps, is described in terms of force dipoles displaced with respect to the bilayer midpoint. We first discuss the case in which such pumps are rendered inactive, computing the mode structure in the bulk as well as the modification of hydrodynamic properties by the presence of a nearby wall. We then discuss the fluctuations and mode structure in steady state of active two-component membranes near a repulsive wall. We find that proximity to the wall smoothens membrane height fluctuations in the stable regime, resulting in a logarithmic scaling of the roughness even for initially tensionless membranes. This explicitly non-equilibrium result, a consequence of the incorporation of curvature-concentration coupling in our treatment, also indicates that earlier scaling arguments which obtained an increase in the roughness of active membranes near repulsive walls may need to be reevaluated.Comment: 39 page Latex file, 3 encapsulated Postscript figure

Length, Protein-Protein Interactions, and Complexity

The evolutionary reason for the increase in gene length from archaea to prokaryotes to eukaryotes observed in large scale genome sequencing efforts has been unclear. We propose here that the increasing complexity of protein-protein interactions has driven the selection of longer proteins, as longer proteins are more able to distinguish among a larger number of distinct interactions due to their greater average surface area. Annotated protein sequences available from the SWISS-PROT database were analyzed for thirteen eukaryotes, eight bacteria, and two archaea species. The number of subcellular locations to which each protein is associated is used as a measure of the number of interactions to which a protein participates. Two databases of yeast protein-protein interactions were used as another measure of the number of interactions to which each \emph{S. cerevisiae} protein participates. Protein length is shown to correlate with both number of subcellular locations to which a protein is associated and number of interactions as measured by yeast two-hybrid experiments. Protein length is also shown to correlate with the probability that the protein is encoded by an essential gene. Interestingly, average protein length and number of subcellular locations are not significantly different between all human proteins and protein targets of known, marketed drugs. Increased protein length appears to be a significant mechanism by which the increasing complexity of protein-protein interaction networks is accommodated within the natural evolution of species. Consideration of protein length may be a valuable tool in drug design, one that predicts different strategies for inhibiting interactions in aberrant and normal pathways.Comment: 13 pages, 5 figures, 2 tables, to appear in Physica

Shedding light on pilot-wave phenomena

This paper is associated with a video winner of a 2015 APS/DFD Gallery of Fluid Motion Award. The original video is available from the Gallery of Fluid Motion, http://dx.doi.org/10.1103/APS.DFD.2015.GFM.V0064National Science Foundation (U.S.) (Grant CMMI-1333242