1,563 research outputs found
Charge Transport in Polymer Ion Conductors: a Monte Carlo Study
Diffusion of ions through a fluctuating polymeric host is studied both by
Monte Carlo simulation of the complete system dynamics and by dynamic bond
percolation (DBP) theory. Comparison of both methods suggests a multiscale-like
approach for calculating the diffusion coefficients of the ion
Dynamic percolation theory for particle diffusion in a polymer network
Tracer-diffusion of small molecules through dense systems of chain polymers
is studied within an athermal lattice model, where hard core interactions are
taken into account by means of the site exclusion principle. An approximate
mapping of this problem onto dynamic percolation theory is proposed. This
method is shown to yield quantitative results for the tracer correlation factor
of the molecules as a function of density and chain length provided the
non-Poisson character of temporal renewals in the disorder configurations is
properly taken into account
Research in the Economics of Forestry
The study of economics won’t keep you out of the breadline; but at least you’ll know why you’re there. So it is with forest economics: It won\u27t alone solve our forestry needs, but at least it helps us mightily to understand them. And used in conjunction with the other sciences and arts of forestry, economics research helps us not only to understand, but also to solve, the needs of forestry for contributing the utmost to the wellbeing of the world, the community, and the individual enterprise
Quality of a Which-Way Detector
We introduce a measure Q of the "quality" of a quantum which-way detector,
which characterizes its intrinsic ability to extract which-way information in
an asymmetric two-way interferometer. The "quality" Q allows one to separate
the contribution to the distinguishability of the ways arising from the quantum
properties of the detector from the contribution stemming from a-priori
which-way knowledge available to the experimenter, which can be quantified by a
predictability parameter P. We provide an inequality relating these two sources
of which-way information to the value of the fringe visibility displayed by the
interferometer. We show that this inequality is an expression of duality,
allowing one to trace the loss of coherence to the two reservoirs of which-way
information represented by Q and P. Finally, we illustrate the formalism with
the use of a quantum logic gate: the Symmetric Quanton-Detecton System (SQDS).
The SQDS can be regarded as two qubits trying to acquire which way information
about each other. The SQDS will provide an illustrating example of the
reciprocal effects induced by duality between system and which-way detector.Comment: 10 pages, 5 figure
Lattice QCD with mixed actions
We discuss some of the implications of simulating QCD when the action used
for the sea quarks is different from that used for the valence quarks. We
present exploratory results for the hadron mass spectrum and pseudoscalar meson
decay constants using improved staggered sea quarks and HYP-smeared overlap
valence quarks. We propose a method for matching the valence quark mass to the
sea quark mass and demonstrate it on UKQCD clover data in the simpler case
where the sea and valence actions are the same.Comment: 15 pages, 10 figures some minor modification to text and figures.
Accepted for publicatio
The Complexity of Mean Flow Time Scheduling Problems with Release Times
We study the problem of preemptive scheduling n jobs with given release times
on m identical parallel machines. The objective is to minimize the average flow
time. We show that when all jobs have equal processing times then the problem
can be solved in polynomial time using linear programming. Our algorithm can
also be applied to the open-shop problem with release times and unit processing
times. For the general case (when processing times are arbitrary), we show that
the problem is unary NP-hard.Comment: Subsumes and replaces cs.DS/0412094 and "Complexity of mean flow time
scheduling problems with release dates" by P.B, S.
X-Ray Detection of Transient Magnetic Moments Induced by a Spin Current in Cu
We have used a MHz lock-in x-ray spectro-microscopy technique to directly
detect changes of magnetic moments in Cu due to spin injection from an adjacent
Co layer. The elemental and chemical specificity of x-rays allows us to
distinguish two spin current induced effects. We detect the creation of
transient magnetic moments of on Cu atoms
within the bulk of the 28 nm thick Cu film due to spin-accumulation. The moment
value is compared to predictions by Mott's two current model. We also observe
that the hybridization induced existing magnetic moments on Cu interface atoms
are transiently increased by about 10% or .
This reveals the dominance of spin-torque alignment over Joule heat induced
disorder of the interfacial Cu moments during current flow
Microscopic chaos from Brownian motion?
A recent experiment on Brownian motion has been interpreted to exhibit direct
evidence for microscopic chaos. In this note we demonstrate that virtually
identical results can be obtained numerically using a manifestly
microscopically nonchaotic system.Comment: 3 pages, 1 figure, Comment on P. Gaspard et al, Nature vol 394, 865
(1998); rewritten in a more popular styl
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