6,000 research outputs found
Hexagonal spiral growth in the absence of a substrate
Experiments on the formation of spiraling hexagons (350 - 1000 nm in width)
from a solution of nanoparticles are presented. Transmission electron
microscopy images of the reaction products of chemically synthesized cadmium
nanocrystals indicate that the birth of the hexagons proceeds without
assistance from static screw or edge dislocatons, that is, they spiral without
constraints provided by an underlying substrate. Instead, the apparent growth
mechanism relies on what we believe is a dynamical dislocation identified as a
dense aggregate of small nanocrystals that straddles the spiraling hexagon at
the crystal surface. This nanocrystal bundle, which we term the "feeder", also
appears to release nanocrystals into the spiral during the growth process.Comment: 4 pages, 5 figure
Solvable Examples of Drift and Diffusion of Ions in Non-uniform Electric Fields
The drift and diffusion of a cloud of ions in a fluid are distorted by an
inhomogeneous electric field. If the electric field carries the center of the
distribution in a straight line and the field configuration is suitably
symmetric, the distortion can be calculated analytically. We examine the
specific examples of fields with cylindrical and spherical symmetry in detail
assuming the ion distributions to be of a generally Gaussian form. The effects
of differing diffusion coefficients in the transverse and longitudinal
directions are included
Azimuthal Correlation in Lepton-Hadron Scattering via Charged Weak-Current Processes
We consider the azimuthal correlation of the final-state particles in charged
weak-current processes. This correlation provides a test of perturbative
quantum chromodynamics. The azimuthal asymmetry is large in the semi-inclusive
processes in which we identify a final-state hadron, say, a charged pion
compared to that in the inclusive processes in which we do not identify
final-state particles and use only the calorimetric information. In
semi-inclusive processes the azimuthal asymmetry is more conspicuous when the
incident lepton is an antineutrino or a positron than when the incident lepton
is a neutrino or an electron. We analyze all the possible charged weak-current
processes and study the quantitative aspects of each process. We also compare
this result to the ep scattering with a photon exchange.Comment: 25 pages, 2 Postscript figures, uses RevTeX, fixes.st
Flavor changing interactions mediated by scalars at the weak scale
The quark and lepton mass matrices possess approximate flavor symmetries.
Several results follow if the interactions of new scalars possess these
approximate symmetries. Present experimental bounds allow these exotic scalars
to have a weak scale mass. The Glashow-Weinberg criterion is rendered
unnecessary. Finally, rare leptonic B meson decays provide powerful probes of
these scalars, especially if they are leptoquarks.Comment: 13 pages, report LBL-3234
Calibration of liquid argon and neon detectors with
We report results from tests of Kr, as a calibration
source in liquid argon and liquid neon. Kr atoms are
produced in the decay of Rb, and a clear Kr
scintillation peak at 41.5 keV appears in both liquids when filling our
detector through a piece of zeolite coated with Rb. Based on this
scintillation peak, we observe 6.0 photoelectrons/keV in liquid argon with a
resolution of 6% (/E) and 3.0 photoelectrons/keV in liquid neon with a
resolution of 19% (/E). The observed peak intensity subsequently decays
with the Kr half-life after stopping the fill, and we
find evidence that the spatial location of Kr atoms in
the chamber can be resolved. Kr will be a useful
calibration source for liquid argon and neon dark matter and solar neutrino
detectors.Comment: 7 pages, 12 figure
A 83Krm Source for Use in Low-background Liquid Xenon Time Projection Chambers
We report the testing of a charcoal-based Kr-83m source for use in
calibrating a low background two-phase liquid xenon detector. Kr-83m atoms
produced through the decay of Rb-83 are introduced into a xenon detector by
flowing xenon gas past the Rb-83 source. 9.4 keV and 32.1 keV transitions from
decaying 83Krm nuclei are detected through liquid xenon scintillation and
ionization. The characteristics of the Kr-83m source are analyzed and shown to
be appropriate for a low background liquid xenon detector. Introduction of
Kr-83m allows for quick, periodic calibration of low background noble liquid
detectors at low energy.Comment: Updated to version submitted to JINS
Phase Segregation Dynamics in Particle Systems with Long Range Interactions I: Macroscopic Limits
We present and discuss the derivation of a nonlinear non-local
integro-differential equation for the macroscopic time evolution of the
conserved order parameter of a binary alloy undergoing phase segregation. Our
model is a d-dimensional lattice gas evolving via Kawasaki exchange dynamics,
i.e. a (Poisson) nearest-neighbor exchange process, reversible with respect to
the Gibbs measure for a Hamiltonian which includes both short range (local) and
long range (nonlocal) interactions. A rigorous derivation is presented in the
case in which there is no local interaction. In a subsequent paper (part II),
we discuss the phase segregation phenomena in the model. In particular we argue
that the phase boundary evolutions, arising as sharp interface limits of the
family of equations derived in this paper, are the same as the ones obtained
from the corresponding limits for the Cahn-Hilliard equation.Comment: amstex with macros (included in the file), tex twice, 20 page
Calculation of the interfacial free energy of a binary hard-sphere fluid at a planar hard wall
This is the publisher's version, also available electronically from http://scitation.aip.org/content/aip/journal/jcp/140/2/10.1063/1.4858433Using molecular-dynamics simulation and Gibbs-Cahn Integration, we calculate the interfacial free energy γ of a binary hard-sphere fluid mixture at a structureless, planar hard wall. The calculation is performed as a function of packing fraction (density) for several values of the diameter ratio α = σ2/σ1, where σ1 and σ2 are the diameters of the two particle types in the mixture. Our results are compared to those obtained from the bulk version of the White Bear Mark II (WBII) classical density-functional theory, which is a modification of the Fundamental-Measure Theory of Rosenfeld. The WBII bulk theory is shown to be in very good agreement with the simulation results, with significant deviation only at the very highest packing fractions
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