1,542 research outputs found
Dynamic Moment Analysis of the Extracellular Electric Field of a Biologically Realistic Spiking Neuron
Based upon the membrane currents generated by an action potential in a
biologically realistic model of a pyramidal, hippocampal cell within rat CA1,
we perform a moment expansion of the extracellular field potential. We
decompose the potential into both inverse and classical moments and show that
this method is a rapid and efficient way to calculate the extracellular field
both near and far from the cell body. The action potential gives rise to a
large quadrupole moment that contributes to the extracellular field up to
distances of almost 1 cm. This method will serve as a starting point in
connecting the microscopic generation of electric fields at the level of
neurons to macroscopic observables such as the local field potential
Charge asymmetry in high-energy photoproduction in the electric field of a heavy atom
The charge asymmetry in the differential cross section of high-energy
photoproduction in the electric field of a heavy atom is obtained.
This asymmetry arises due to the Coulomb corrections to the amplitude of the
process (next-to-leading term with respect to the atomic field). The deviation
of the nuclear electric field from the Coulomb field at small distances is
crucially important for the charge asymmetry. Though the Coulomb corrections to
the total cross section are negligibly small, the charge asymmetry is
measurable for selected final states of and . We further discuss
the feasibility for experimental observation of this effect.Comment: 6 pages, 3 figure
The Nature of Superfluidity in Ultracold Fermi Gases Near Feshbach Resonances
We study the superfluid state of atomic Fermi gases using a BCS-BEC crossover
theory. Our approach emphasizes non-condensed fermion pairs which strongly
hybridize with their (Feshbach-induced) molecular boson counterparts. These
pairs lead to pseudogap effects above and non-BCS characteristics below.
We discuss how these effects influence the experimental signatures of
superfluidity.Comment: 4 pages, 3 figures, submitted to PRA Rapid Communications;
introduction rewritten, figure replace
Protein-mediated DNA Loop Formation and Breakdown in a Fluctuating Environment
Living cells provide a fluctuating, out-of-equilibrium environment in which
genes must coordinate cellular function. DNA looping, which is a common means
of regulating transcription, is very much a stochastic process; the loops arise
from the thermal motion of the DNA and other fluctuations of the cellular
environment. We present single-molecule measurements of DNA loop formation and
breakdown when an artificial fluctuating force, applied to mimic a fluctuating
cellular environment, is imposed on the DNA. We show that loop formation is
greatly enhanced in the presence of noise of only a fraction of , yet
find that hypothetical regulatory schemes that employ mechanical tension in the
DNA--as a sensitive switch to control transcription--can be surprisingly robust
due to a fortuitous cancellation of noise effects
Classical field techniques for condensates in one-dimensional rings at finite temperatures
For a condensate in a one-dimensional ring geometry, we compare the
thermodynamic properties of three conceptually different classical field
techniques: stochastic dynamics, microcanonical molecular dynamics, and the
classical field method. Starting from non-equilibrium initial conditions, all
three methods approach steady states whose distribution and correlation
functions are in excellent agreement with an exact evaluation of the partition
function in the high-temperature limit. Our study helps to establish these
various classical field techniques as powerful non-perturbative tools for
systems at finite temperatures.Comment: 7 pages, 7 figures; minor changes, one reference adde
Feshbach resonances and collapsing Bose-Einstein condensates
We investigate the quantum state of burst atoms seen in the recent Rb-85
experiments at JILA. We show that the presence of a resonance scattering state
can lead to a pairing instability generating an outflow of atoms with energy
comparable to that observed. A resonance effective field theory is used to
study this dynamical process in an inhomogeneous system with spherical
symmetry
Virtual light-by-light scattering and the g factor of a bound electron
The contribution of the light-by-light diagram to the g factor of electron
and muon bound in Coulomb field is obtained. For electron in a ground state,
our results are in good agreement with the results of other authors obtained
numerically for large Z. For relatively small Z our results have essentially
higher accuracy as compared to the previous ones. For muonic atoms, the
contribution is obtained for the first time with the high accuracy in whole
region of Z.Comment: 10 pages, 3 figures, RevTe
Corrections to deuterium hyperfine structure due to deuteron excitations
We consider the corrections to deuterium hyperfine structure originating from
the two-photon exchange between electron and deuteron, with the deuteron
excitations in the intermediate states. In particular, the motion of the two
intermediate nucleons as a whole is taken into account. The problem is solved
in the zero-range approximation. The result is in good agreement with the
experimental value of the deuterium hyperfine splitting.Comment: 7 pages, LaTe
Bose-Einstein Condensation from a Rotating Thermal Cloud: Vortex Nucleation and Lattice Formation
We develop a stochastic Gross-Pitaveskii theory suitable for the study of
Bose-Einstein condensation in a {\em rotating} dilute Bose gas. The theory is
used to model the dynamical and equilibrium properties of a rapidly rotating
Bose gas quenched through the critical point for condensation, as in the
experiment of Haljan et al. [Phys. Rev. Lett., 87, 21043 (2001)]. In contrast
to stirring a vortex-free condensate, where topological constraints require
that vortices enter from the edge of the condensate, we find that phase defects
in the initial non-condensed cloud are trapped en masse in the emerging
condensate. Bose-stimulated condensate growth proceeds into a disordered vortex
configuration. At sufficiently low temperature the vortices then order into a
regular Abrikosov lattice in thermal equilibrium with the rotating cloud. We
calculate the effect of thermal fluctuations on vortex ordering in the final
gas at different temperatures, and find that the BEC transition is accompanied
by lattice melting associated with diminishing long range correlations between
vortices across the system.Comment: 15 pages, 12 figure
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