456 research outputs found
Effect of anisotropy on the field induced quantum critical properties of the three dimensional s=1/2 Heisenberg model
The field induced quantum critical properties of the three dimensional
spin-1/2 anisotropic antiferromagnetic Heisenberg model has been studied. We
have investigated the quantum phase transition between the spiral order and
field induced ferromagnetic order by means of Bose-Einstein condensation of
magnons in terms of a bosonic representation. The effect of in-plane anisotropy
on the critical properties has been studied via the bosonic model by Green's
function approach. We have found an analytic expression for the gap exponent in
addition to numerical results for the critical magnetic field in terms of
anisotropy parameter. The in-plane anisotropy breaks the U(1) symmetry
explicitly which changes the universal behavior by a drastic change on the gap
exponent. Moreover, the critical magnetic field depends strongly on the
in-plane anisotropies. The divergence of the transverse structure factor at the
antiferromagnetic wave vector confirms the onset of the magnetic order which
scales with the negative value of gap exponent as the magnetic field approaches
the critical one. The transverse staggered magnetization as an order parameter
vanishes with exponent when the magnetic field reaches its critical
value in low field region.Comment: 9 pages and 2 figure
An experimental investigation of the independent effect of suction and degree of saturation on very small-strain stiffness of unsaturated sand
The paper presents an experimental investigation of very small strain stiffness of unsaturated sand. A triaxial test apparatus was equipped with bender elements and compression discs in order to assess the stiffness at very small strains by measuring the velocity of propagation of shear and compression waves through an unsaturated sample. The negative water column method was adopted to apply suction at the base of the sample. The experiments were designed to investigate the independent effect of suction and degree of saturation on the wave propagation velocities. This was achieved by testing the sand sample on both the drying and wetting path
A continuous model for microtubule dynamics with catastrophe, rescue and nucleation processes
Microtubules are a major component of the cytoskeleton distinguished by
highly dynamic behavior both in vitro and in vivo. We propose a general
mathematical model that accounts for the growth, catastrophe, rescue and
nucleation processes in the polymerization of microtubules from tubulin dimers.
Our model is an extension of various mathematical models developed earlier
formulated in order to capture and unify the various aspects of tubulin
polymerization including the dynamic instability, growth of microtubules to
saturation, time-localized periods of nucleation and depolymerization as well
as synchronized oscillations exhibited by microtubules under various
experimental conditions. Our model, while attempting to use a minimal number of
adjustable parameters, covers a broad range of behaviors and has predictive
features discussed in the paper. We have analyzed the resultant behaviors of
the microtubules changing each of the parameter values at a time and observing
the emergence of various dynamical regimes.Comment: 25 pages, 12 figure
A first principle (3+1) dimensional model for microtubule polymerization
In this paper we propose a microscopic model to study the polymerization of
microtubules (MTs). Starting from fundamental reactions during MT's assembly
and disassembly processes, we systematically derive a nonlinear system of
equations that determines the dynamics of microtubules in 3D. %coexistence with
tubulin dimers in a solution. We found that the dynamics of a MT is
mathematically expressed via a cubic-quintic nonlinear Schrodinger (NLS)
equation. Interestingly, the generic 3D solution of the NLS equation exhibits
linear growing and shortening in time as well as temporal fluctuations about a
mean value which are qualitatively similar to the dynamic instability of MTs
observed experimentally. By solving equations numerically, we have found
spatio-temporal patterns consistent with experimental observations.Comment: 12 pages, 2 figures. Accepted in Physics Letters
An experimental investigation of the independent effect of suction and degree of saturation on very small-strain stiffness of unsaturated sand
The paper presents an experimental investigation of very small strain stiffness of unsaturated sand. A triaxial test apparatus was equipped with bender elements and compression discs in order to assess the stiffness at very small strains by measuring the velocity of propagation of shear and compression waves through an unsaturated sample. The negative water column method was adopted to apply suction at the base of the sample. The experiments were designed to investigate the independent effect of suction and degree of saturation on the wave propagation velocities. This was achieved by testing the sand sample on both the drying and wetting path
Model of ionic currents through microtubule nanopores and the lumen
It has been suggested that microtubules and other cytoskeletal filaments may
act as electrical transmission lines. An electrical circuit model of the
microtubule is constructed incorporating features of its cylindrical structure
with nanopores in its walls. This model is used to study how ionic conductance
along the lumen is affected by flux through the nanopores when an external
potential is applied across its two ends. Based on the results of Brownian
dynamics simulations, the nanopores were found to have asymmetric inner and
outer conductances, manifested as nonlinear IV curves. Our simulations indicate
that a combination of this asymmetry and an internal voltage source arising
from the motion of the C-terminal tails causes a net current to be pumped
across the microtubule wall and propagate down the microtubule through the
lumen. This effect is demonstrated to enhance and add directly to the
longitudinal current through the lumen resulting from an external voltage
source, and could be significant in amplifying low-intensity endogenous
currents within the cellular environment or as a nano-bioelectronic device.Comment: 43 pages, 6 figures, revised versio
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