27,924 research outputs found
Peeling and Sliding in Nucleosome Repositioning
We investigate the mechanisms of histone sliding and detachment with a
stochastic model that couples thermally-induced, passive histone sliding with
active motor-driven histone unwrapping. Analysis of a passive loop or twist
defect-mediated histone sliding mechanism shows that diffusional sliding is
enhanced as larger portions of the DNA is peeled off the histone. The mean
times to histone detachment and the mean distance traveled by the motor complex
prior to histone detachment are computed as functions of the intrinsic speed of
the motor. Fast motors preferentially induce detachment over sliding. However,
for a fixed motor speed, increasing the histone-DNA affinity (and thereby
decreasing the passive sliding rate) increases the mean distance traveled by
the motor.Comment: 5 pp, 4 fig
The effects of ground hydrology on climate sensitivity to solar constant variations
The effects of two different evaporation parameterizations on the climate sensitivity to solar constant variations are investigated by using a zonally averaged climate model. The model is based on a two-level quasi-geostrophic zonally averaged annual mean model. One of the evaporation parameterizations tested is a nonlinear formulation with the Bowen ratio determined by the predicted vertical temperature and humidity gradients near the earth's surface. The other is the linear formulation with the Bowen ratio essentially determined by the prescribed linear coefficient
Chapman-Enskog expansion about nonequilibrium states: the sheared granular fluid
The Chapman-Enskog method of solution of kinetic equations, such as the
Boltzmann equation, is based on an expansion in gradients of the deviations fo
the hydrodynamic fields from a uniform reference state (e.g., local
equilibrium). This paper presents an extension of the method so as to allow for
expansions about \emph{arbitrary}, far-from equilibrium reference states. The
primary result is a set of hydrodynamic equations for studying variations from
the arbitrary reference state which, unlike the usual Navier-Stokes
hydrodynamics, does not restrict the reference state in any way. The method is
illustrated by application to a sheared granular gas which cannot be studied
using the usual Navier-Stokes hydrodynamics.Comment: 23 pages, no figures. Submited to PRE Replaced to correct misc.
errors Replaced to correct misc. errors, make notation more consistant,
extend discussio
Temporal Dynamics of Photon Pairs Generated by an Atomic Ensemble
The time dependence of nonclassical correlations is investigated for two
fields (1,2) generated by an ensemble of cold Cesium atoms via the protocol of
Duan et al. [Nature Vol. 414, p. 413 (2001)]. The correlation function R(t1,t2)
for the ratio of cross to auto-correlations for the (1,2) fields at times
(t1,t2) is found to have a maximum value Rmax=292(+-)57, which significantly
violates the Cauchy-Schwarz inequality R<=1 for classical fields. Decoherence
of quantum correlations is observed over 175 ns, and is described by our model,
as is a new scheme to mitigate this effect.Comment: 5 pages, 5 figure
Heralded Entanglement between Atomic Ensembles: Preparation, Decoherence, and Scaling
Heralded entanglement between collective excitations in two atomic ensembles
is probabilistically generated, stored, and converted to single photon fields.
By way of the concurrence, quantitative characterizations are reported for the
scaling behavior of entanglement with excitation probability and for the
temporal dynamics of various correlations resulting in the decay of
entanglement. A lower bound of the concurrence for the collective atomic state
of 0.9\pm 0.3 is inferred. The decay of entanglement as a function of storage
time is also observed, and related to the local dynamics.Comment: 4 page
Flow field predictions for a slab delta wing at incidence
Theoretical results are presented for the structure of the hypersonic flow field of a blunt slab delta wing at moderately high angle of attack. Special attention is devoted to the interaction between the boundary layer and the inviscid entropy layer. The results are compared with experimental data. The three-dimensional inviscid flow is computed numerically by a marching finite difference method. Attention is concentrated on the windward side of the delta wing, where detailed comparisons are made with the data for shock shape and surface pressure distributions. Surface streamlines are generated, and used in the boundary layer analysis. The three-dimensional laminar boundary layer is computed numerically using a specially-developed technique based on small cross-flow in streamline coordinates. In the rear sections of the wing the boundary layer decreases drastically in the spanwise direction, so that it is still submerged in the entropy layer at the centerline, but surpasses it near the leading edge. Predicted heat transfer distributions are compared with experimental data
Magnetically-induced reconstructions of the ground state in a few-electron Si quantum dot
We report unexpected fluctuations in the positions of Coulomb blockade peaks
at high magnetic fields in a small Si quantum dot. The fluctuations have a
distinctive saw-tooth pattern: as a function of magnetic field, linear shifts
of peak positions are compensated by abrupt jumps in the opposite direction.
The linear shifts have large slopes, suggesting formation of the ground state
with a non-zero angular momentum. The value of the momentum is found to be well
defined, despite the absence of the rotational symmetry in the dot.Comment: 5 pages, 4 figures, accepted to PR
- …