162,236 research outputs found
An example of optimal field cut in lattice gauge perturbation theory
We discuss the weak coupling expansion of a one plaquette SU(2) lattice gauge
theory. We show that the conventional perturbative series for the partition
function has a zero radius of convergence and is asymptotic. The average
plaquette is discontinuous at g^2=0. However, the fact that SU(2) is compact
provides a perturbative sum that converges toward the correct answer for
positive g^2. This alternate methods amounts to introducing a specific coupling
dependent field cut, that turns the coefficients into g-dependent quantities.
Generalizing to an arbitrary field cut, we obtain a regular power series with a
finite radius of convergence. At any order in the modified perturbative
procedure, and for a given coupling, it is possible to find at least one (and
sometimes two) values of the field cut that provide the exact answer. This
optimal field cut can be determined approximately using the strong coupling
expansion. This allows us to interpolate accurately between the weak and strong
coupling regions. We discuss the extension of the method to lattice gauge
theory on a D-dimensional cubic lattice.Comment: 9 pages, 11 figs., uses revtex4, modified presentatio
Towards First-principles Electrochemistry
Chemisorbed molecules at a fuel cell electrode are a very sensitive probe of
the surrounding electrochemical environment, and one that can be accurately
monitored with different spectroscopic techniques. We develop a comprehensive
electrochemical model to study molecular chemisorption at either constant
charge or fixed applied voltage, and calculate from first principles the
voltage dependence of vibrational frequencies -- the vibrational Stark effect
-- for CO adsorbed on close-packed platinum electrodes. The predicted
vibrational Stark slopes are found to be in very good agreement with
experimental electrochemical spectroscopy data, thereby resolving previous
controversies in the quantitative interpretation of in-situ experiments and
elucidating the relation between canonical and grand-canonicaldescriptions of
vibrational surface phenomena.Comment: 10 pages, 2 figure
Rate of Convergence in Nonlinear Hartree Dynamics with Factorized Initial Data
The mean field dynamics of an -particle weekly interacting Boson system
can be described by the nonlinear Hartree equation. In this paper, we present
estimates on the 1/N rate of convergence of many-body Schr\"{o}dinger dynamics
to the one-body nonlinear Hartree dynamics with factorized initial data with
two-body interaction potential in .Comment: AMS LaTex, 21 page
Current dependent fluctuations in a BiSrCuO thin film
The current dependence of the excess conductivity is measured up to for a BiSrCuO thin film, as a function of doping. It
is found to be anomalously sensitive to the transport current and to behave as
a universal function of in the whole doping range. We discuss these
results in the perspective of a granular superconductor with a gapless-like
behavior
Mechanical and electrochemical properties of multiple-layer diode laser cladding of 316L stainless steel
In the present investigation, a detailed mechanical and electrochemical properties of multiple-layer laser clad 316L stainless steel (from the powders produced by gas atomized route) has been carried out. Multiple-layer laser cladding of 316L stainless steel has been conducted using a diode laser. The mechanical property (rmcrohardness) of the fabricated product has been evaluated using a microhardness testing machine and correlated with the process parameters. The electrochemical property, mainly pitting corrosion resistance of the fabricated layer corresponding to maximum microhardness (in a 3.56% NaCl solution) has been evaluated using standard potentiodynamic polarization testing. The microhardness of the laser assisted fabricated layers was found to vary from 170 to 278 VHN, increased with decrease in applied power density and increase in scan speed and was higher than that of conventionally processed 316L (155 VHN). The superior microhardness value is attributed to grain refinement associated with laser melting and rapid solidification. The critical potential to pit formation (E-PP1) was measured to be 550 mV saturated calomel electrode (SCE) and superior to the conventionally processed 316L stainless steel (445 mV (SCE)). (c) 2005 Elsevier B.V. All rights reserved
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