162 research outputs found
A new elastic potential function for rubbery materials
A new four-parameter elastic potential function is proposed which represents data on the elastic deformation of rubbery materials with the same parameters in various deformation fields up to break
Student-Athletes with Learning Disabilities: Unique Problems, Unique Solutions
This paper explored the issues/acing student-athletes with learning disabilities and their academic counselors. Understanding the nature of learning disabilities and their effects can enhance the counselor's ability to address the complex needs of the student-athlete with a learning disability. The increasing numbers of college student-athletes who have diagnosed learning disabilities demands notice. This paper provided an explanation of the problems of diagnosis and treatment. Suggestions for academic counselors were provided, as well
Borderline Aggregation Kinetics in ``Dry'' and ``Wet'' Environments
We investigate the kinetics of constant-kernel aggregation which is augmented
by either: (a) evaporation of monomers from finite-mass clusters, or (b)
continuous cluster growth -- \ie, condensation. The rate equations for these
two processes are analyzed using both exact and asymptotic methods. In
aggregation-evaporation, if the evaporation is mass conserving, \ie, the
monomers which evaporate remain in the system and continue to be reactive, the
competition between evaporation and aggregation leads to several asymptotic
outcomes. For weak evaporation, the kinetics is similar to that of aggregation
with no evaporation, while equilibrium is quickly reached in the opposite case.
At a critical evaporation rate, the cluster mass distribution decays as
, where is the mass, while the typical cluster mass grows with
time as . In aggregation-condensation, we consider the process with a
growth rate for clusters of mass , , which is: (i) independent of ,
(ii) proportional to , and (iii) proportional to , with . In
the first case, the mass distribution attains a conventional scaling form, but
with the typical cluster mass growing as . When , the
typical mass grows exponentially in time, while the mass distribution again
scales. In the intermediate case of , scaling generally
applies, with the typical mass growing as . We also give an
exact solution for the linear growth model, , in one dimension.Comment: plain TeX, 17 pages, no figures, macro file prepende
Maxwell Model of Traffic Flows
We investigate traffic flows using the kinetic Boltzmann equations with a
Maxwell collision integral. This approach allows analytical determination of
the transient behavior and the size distributions. The relaxation of the car
and cluster velocity distributions towards steady state is characterized by a
wide range of velocity dependent relaxation scales, , with
the ratio of the passing and the collision rates. Furthermore, these
relaxation time scales decrease with the velocity, with the smallest scale
corresponding to the decay of the overall density. The steady state cluster
size distribution follows an unusual scaling form . This distribution is primarily algebraic, , for , and is exponential otherwise.Comment: revtex, 10 page
Nonlinear drift-diffusion model of gating in the fast Cl channel
The dynamics of the open or closed state region of an ion channel may be described by a probability density p(x,t) which satisfies a Fokker-Planck equation. The closed state dwell-time distribution fc(t) derived from the Fokker-Planck equation with a nonlinear diffusion coefficient D(x)âexp(âÎłx), Îł>0 and a linear ramp potential Uc(x), is in good agreement with experimental data and it may be shown analytically that if Îł is sufficiently large, fc(t)âtâ2âÎœ for intermediate times, where Îœ=UcâČâÎłââ0.3 for a fast Cl channel. The solution of a master equation which approximates the Fokker-Planck equation exhibits an oscillation superimposed on the power law trend and can account for an empirical rate-amplitude correlation that applies to several ion channels.S. R. Vaccar
MscS-like mechanosensitive channels in plants and microbes
The challenge of osmotic stress is something all living organisms must face as a result of environmental dynamics. Over the past three decades, innovative research and cooperation across disciplines have irrefutably established that cells utilize mechanically gated ion channels to release osmolytes and prevent cell lysis during hypoosmotic stress. Early electrophysiological analysis of the inner membrane of Escherichia coli identified the presence of three distinct mechanosensitive activities. The subsequent discoveries of the genes responsible for two of these activities, the mechanosensitive channels of large (MscL) and small (MscS) conductance, led to the identification of two diverse families of mechanosensitive channels. The latter of these two families, the MscS family, consists of members from bacteria, archaea, fungi, and plants. Genetic and electrophysiological analysis of these family members has provided insight into how organisms use mechanosensitive channels for osmotic regulation in response to changing environmental and developmental circumstances. Furthermore, determining the crystal structure of E. coli MscS and several homologues in several conformational states has contributed to our understanding of the gating mechanisms of these channels. Here we summarize our current knowledge of MscS homologues from all three domains of life and address their structure, proposed physiological functions, electrophysiological behaviors, and topological diversity
ATP release via anion channels
ATP serves not only as an energy source for all cell types but as an âextracellular messenger-for autocrine and paracrine signalling. It is released from the cell via several different purinergic signal efflux pathways. ATP and its Mg2+ and/or H+ salts exist in anionic forms at physiological pH and may exit cells via some anion channel if the pore physically permits this. In this review we survey experimental data providing evidence for and against the release of ATP through anion channels. CFTR has long been considered a probable pathway for ATP release in airway epithelium and other types of cells expressing this protein, although non-CFTR ATP currents have also been observed. Volume-sensitive outwardly rectifying (VSOR) chloride channels are found in virtually all cell types and can physically accommodate or even permeate ATP4- in certain experimental conditions. However, pharmacological studies are controversial and argue against the actual involvement of the VSOR channel in significant release of ATP. A large-conductance anion channel whose open probability exhibits a bell-shaped voltage dependence is also ubiquitously expressed and represents a putative pathway for ATP release. This channel, called a maxi-anion channel, has a wide nanoscopic pore suitable for nucleotide transport and possesses an ATP-binding site in the middle of the pore lumen to facilitate the passage of the nucleotide. The maxi-anion channel conducts ATP and displays a pharmacological profile similar to that of ATP release in response to osmotic, ischemic, hypoxic and salt stresses. The relation of some other channels and transporters to the regulated release of ATP is also discussed
Xenobiotic-metabolizing enzymes in the skin of rat, mouse, pig, guinea pig, man, and in human skin models
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