1,528 research outputs found
Mechano-transduction: from molecules to tissues.
External forces play complex roles in cell organization, fate, and homeostasis. Changes in these forces, or how cells respond to them, can result in abnormal embryonic development and diseases in adults. How cells sense and respond to these mechanical stimuli requires an understanding of the biophysical principles that underlie changes in protein conformation and result in alterations in the organization and function of cells and tissues. Here, we discuss mechano-transduction as it applies to protein conformation, cellular organization, and multi-cell (tissue) function
Structure formation in binary colloids
A theoretical study of the structure formation observed very recently [Phys.
Rev. Lett. 90, 128303 (2003)] in binary colloids is presented. In our model
solely the dipole-dipole interaction of the particles is considered,
electrohidrodynamic effects are excluded. Based on molecular dynamics
simulations and analytic calculations we show that the total concentration of
the particles, the relative concentration and the relative dipole moment of the
components determine the structure of the colloid. At low concentrations the
kinetic aggregation of particles results in fractal structures which show a
crossover behavior when increasing the concentration. At high concentration
various lattice structures are obtained in a good agreement with experiments.Comment: revtex, 4 pages, figures available from authors due to size problem
Crystal Structure of the Hexamerization Domain of N-ethylmaleimide–Sensitive Fusion Protein
AbstractN-ethylmaleimide–sensitive fusion protein (NSF) is a cytosolic ATPase required for many intracellular vesicle fusion reactions. NSF consists of an amino-terminal region that interacts with other components of the vesicle trafficking machinery, followed by two homologous ATP-binding cassettes, designated D1 and D2, that possess essential ATPase and hexamerization activities, respectively. The crystal structure of D2 bound to Mg2PLUSPUSSIGN-AMPPNP has been determined at 1.75 Å resolution. The structure consists of a nucleotide-binding and a helical domain, and it is unexpectedly similar to the first two domains of the clamp-loading subunit δ′ of E. coli DNA polymerase III. The structure suggests several regions responsible for coupling of ATP hydrolysis to structural changes in full-length NSF
Generalized Drude model: Unification of ballistic and diffusive electron transport
For electron transport in parallel-plane semiconducting structures, a model
is developed that unifies ballistic and diffusive transport and thus
generalizes the Drude model. The unified model is valid for arbitrary magnitude
of the mean free path and arbitrary shape of the conduction band edge profile.
Universal formulas are obtained for the current-voltage characteristic in the
nondegenerate case and for the zero-bias conductance in the degenerate case,
which describe in a transparent manner the interplay of ballistic and diffusive
transport. The semiclassical approach is adopted, but quantum corrections
allowing for tunneling are included. Examples are considered, in particular the
case of chains of grains in polycrystalline or microcrystalline semiconductors
with grain size comparable to, or smaller than, the mean free path. Substantial
deviations of the results of the unified model from those of the ballistic
thermionic-emission model and of the drift-diffusion model are found. The
formulation of the model is one-dimensional, but it is argued that its results
should not differ substantially from those of a fully three-dimensional
treatment.Comment: 14 pages, 5 figures, REVTEX file, to appear in J. Phys.: Condens.
Matte
Ewald methods for inverse power-law interactions in tridimensional and quasi-two dimensional systems
In this paper, we derive the Ewald method for inverse power-law interactions
in quasi-two dimensional systems. The derivation is done by using two different
analytical methods. The first uses the Parry's limit, that considers the Ewald
methods for quasi-two dimensional systems as a limit of the Ewald methods for
tridimensional systems, the second uses Poisson-Jacobi identities for lattice
sums. Taking into account the equivalence of both derivations, we obtain a new
analytical Fourier transform intregral involving incomplete gamma function.
Energies of the generalized restrictive primitive model of electrolytes
(-RPM) and of the generalized one component plasma model (-OCP) are
given for the tridimensional, quasi-two dimensional and monolayers systems. Few
numerical results, using Monte-Carlo simulations, for -RPM and -OCP
monolayers systems are reported.Comment: to be published in Journal of Physics A: Mathematical and Theoretical
(19 pages, 2 figures and 3 tables
Magnetization of ferrofluids with dipolar interactions - a Born--Mayer expansion
For ferrofluids that are described by a system of hard spheres interacting
via dipolar forces we evaluate the magnetization as a function of the internal
magnetic field with a Born--Mayer technique and an expansion in the dipolar
coupling strength. Two different approximations are presented for the
magnetization considering different contributions to a series expansion in
terms of the volume fraction of the particles and the dipolar coupling
strength.Comment: 19 pages, 11 figures submitted to PR
Signatures of electron correlations in the transport properties of quantum dots
The transition matrix elements between the correlated and
electron states of a quantum dot are calculated by numerical diagonalization.
They are the central ingredient for the linear and non--linear transport
properties which we compute using a rate equation. The experimentally observed
variations in the heights of the linear conductance peaks can be explained. The
knowledge of the matrix elements as well as the stationary populations of the
states allows to assign the features observed in the non--linear transport
spectroscopy to certain transition and contains valuable information about the
correlated electron states.Comment: 4 pages (revtex,27kB) + 3 figures in one file ziped and uuencoded
(postscript,33kB), to appear in Phys.Rev.B as Rapid Communicatio
Anomalous Kondo-effect in Quantum Dot at non-zero bias
We present measurements on the Kondo-effect in a small quantum dot connected
strongly to one lead and weakly to the other. The conductance of the dot
reveals an offset of the Kondo resonance at zero magnetic field. While the
resonance persists in the negative bias regime, it is suppressed in the
opposite direction. This demonstrates the pinning of the Kondo resonance to the
Fermi levels of the left and right lead. As an outlook we exploit the spin
blockade effect to gain information about the spin state of the quantum dot in
the Kondo regime.Comment: submitted to PRL; revised version: 2 figures change
[Ni(cod)<sub>2</sub>][Al(OR<sup>F</sup>)<sub>4</sub>], a source for naked nickel(I) chemistry
Experimental Evidence for Coulomb Charging Effects in an Open Quantum Dot at Zero Magnetic Field
We have measured the low-temperature transport properties of an open quantum
dot formed in a clean one-dimensional channel. For the first time, at zero
magnetic field, continuous and periodic oscillations superimposed upon
ballistic conductance steps are observed when the conductance through the dot
exceeds . We ascribe the observed conductance oscillations to
evidence for Coulomb charging effects in an open dot. This is supported by the
evolution of the oscillating features for as a function of both
temperature and barrier transparency. Our results strongly suggest that at zero
magnetic field, current theoretical and experimental understanding of Coulomb
charging effects overlooks charging in the presence of fully transmitted 1D
channels.Comment: To appear in Phys. Rev. Lett. 81 (Oct 19 issue
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