94,816 research outputs found
Nuclear Magnetic Resonance Implementation of a Quantum Clock Synchronization Algorithm
The quantum clock synchronization algorithm proposed by I. L. Chuang (Phys.
Rev. Lett, 85, 2006(2000)) has been implemented in a three qubit nuclear
magnetic resonance quantum system. The effective-pure state is prepared by the
spatial averaging approach. The time difference between two separated clocks
can be determined by reading out directly through the NMR spectra.Comment: 13 pages, 5 figure
Phenomenological Analysis of and Elastic Scattering Data in the Impact Parameter Space
We use an almost model-independent analytical parameterization for and
elastic scattering data to analyze the eikonal, profile, and
inelastic overlap functions in the impact parameter space. Error propagation in
the fit parameters allows estimations of uncertainty regions, improving the
geometrical description of the hadron-hadron interaction. Several predictions
are shown and, in particular, the prediction for inelastic overlap
function at TeV shows the saturation of the Froissart-Martin
bound at LHC energies.Comment: 15 pages, 16 figure
Calculating potentials of mean force and diffusion coefficients from nonequilibirum processes without Jarzynski's equality
In general, the direct application of the Jarzynski equality (JE) to
reconstruct potentials of mean force (PMFs) from a small number of
nonequilibrium unidirectional steered molecular dynamics (SMD) paths is
hindered by the lack of sampling of extremely rare paths with negative
dissipative work. Such trajectories, that transiently violate the second law,
are crucial for the validity of JE. As a solution to this daunting problem, we
propose a simple and efficient method, referred to as the FR method, for
calculating simultaneously both the PMF U(z) and the corresponding diffusion
coefficient D(z) along a reaction coordinate z for a classical many particle
system by employing a small number of fast SMD pullings in both forward (F) and
time reverse (R) directions, without invoking JE. By employing Crook's
transient fluctuation theorem (that is more general than JE) and the stiff
spring approximation, we show that: (i) the mean dissipative work W_d in the F
and R pullings are equal, (ii) both U(z) and W_d can be expressed in terms of
the easily calculable mean work of the F and R processes, and (iii) D(z) can be
expressed in terms of the slope of W_d. To test its viability, the FR method is
applied to determine U(z) and D(z) of single-file water molecules in
single-walled carbon nanotubes (SWNTs). The obtained U(z) is found to be in
very good agreement with the results from other PMF calculation methods, e.g.,
umbrella sampling. Finally, U(z) and D(z) are used as input in a stochastic
model, based on the Fokker-Planck equation, for describing water transport
through SWNTs on a mesoscopic time scale that in general is inaccessible to MD
simulations.Comment: ReVTeX4, 13 pages, 6 EPS figures, Submitted to Journal of Chemical
Physic
The Chandra Detection of Galactic Center X-ray Features G359.89-0.08 and G359.54+0.18
We report on the detection of two elongated X-ray features G359.89-0.08 and
G359.54+0.18 in the Galactic center (GC) region using the Chandra X-ray
Observatory. G359.89-0.08 is an elongated X-ray feature located 2\arcmin
in projection south of the center of the Galaxy, SgrA. This X-ray feature
source is partially coincident with a slightly curved (``wisp''-like)
non-thermal radio source. The X-ray spectrum of G359.89-0.08 can be best
characterized as non-thermal, with a photon index of 2. The morphological and
spectral characteristics of the X-ray and radio emission associated with
G359.89-0.08 are best interpreted as the synchrotron emission from a
ram-pressure confined pulsar wind nebula. G359.54+0.18 is one of the most
prominent radio non-thermal filaments (NTFs) in the GC region, located
30\arcmin in projection from SgrA. A narrow (10\arcsec)
filament of X-ray emission appears to arise from one of the two strands that
comprise the radio NTF. Although the photon statistics are poor for this
source, the X-ray emission is also likely to be non-thermal in nature. Several
models for the production of X-ray emission in G359.54+0.18 are discussed.Comment: 19 pages with 6 figures included, accepted by A
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