1,502 research outputs found
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Effect of geometrical constraint condition on the formation of nanoscale twins in the Ni-based metallic glass composite
We investigated the effect of geometrically constrained stress-strain conditions on the formation of nanotwins in -brass phase reinforced Ni59Zr20 Ti16 Si2 Sn3 metallic glass (MG) matrix deformed under macroscopic uniaxial compression. The specific geometrically constrained conditions in the samples lead to a deviation from a simple uniaxial state to a multi-axial stress state, for which nanocrystallization in the MG matrix together with nanoscale twinning of the brass reinforcement is observed in localized regions during plastic flow. The nanocrystals in the MG matrix and the appearance of the twinned structure in the reinforcements indicate that the strain energy is highly confined and the local stress reaches a very high level upon yielding. Both the effective distribution of reinforcements on the strain enhancement of composite and the effects of the complicated stress states on the development of nanotwins in the second-phase brass particles are discussed
Experimental Entanglement Concentration and Universal Bell-state Synthesizer
We report a novel Bell-state synthesizer in which an interferometric
entanglement concentration scheme is used. An initially mixed polarization
state from type-II spontaneous parametric down-conversion becomes entangled
after the interferometric entanglement concentrator. This Bell-state
synthesizer is universal in the sense that the output polarization state is not
affected by spectral filtering, crystal thickness, and, most importantly, the
choice of pump source. It is also robust against environmental disturbance and
a more general state, partially mixedpartially entangled state, can be
readily generated as well.Comment: Minor update (Newer data
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Feasibility study and design concept for an orbiting ice-penetrating radar sounder to characterize in three-dimensions the Europan ice mantle down to (and including) any ice/ocean interface
This report presents a radar sounding model based on the range of current working hypotheses for the nature of Europa's icy shell.Institute for Geophysic
Maxwell's field coupled nonminimally to quadratic torsion: Induced axion field and birefringence of the vacuum
We consider a possible (parity conserving) interaction between the
electromagnetic field and a torsion field of spacetime. For
generic elementary torsion, gauge invariant coupling terms of lowest order fall
into two classes that are both nonminimal and {\it quadratic} in torsion. These
two classes are displayed explicitly. The first class of the type
yields (undesirable) modifications of the Maxwell equations. The second class
of the type doesn't touch the Maxwell equations but rather
modifies the constitutive tensor of spacetime. Such a modification can be
completely described in the framework of metricfree electrodynamics. We
recognize three physical effects generated by the torsion: (i) An axion field
that induces an {\em optical activity} into spacetime, (ii) a modification of
the light cone structure that yields {\em birefringence} of the vacuum, and
(iii) a torsion dependence of the {\em velocity of light.} We study these
effects in the background of a Friedmann universe with torsion. {\it File
tor17.tex, 02 August 2003}Comment: 6 page
Support for regulation versus compliance: Face masks during COVID-19
Objectives: Wearing masks could still be one of the few non-pharmaceutical interventions for controlling the pandemic. There are people who wear them and people who don't, but this framing is overly simplistic. We aim to chart the contradictions in attitudes and behavior regarding mask wearing and describe the messaging challenge that these generate. Study design: Our data come from a survey administered to a nationally representative sample of 2000 respondents from the YouGov panel of US households in AugustâSeptember 2020. Methods: Respondents were asked whether they wear a facemask when they go outside their home since the COVID-19 epidemic began and whether they support or oppose your municipal government passing mask wearing regulation. We also collected respondentsâ demographic and economic characteristics, knowledge regarding the facts of COVID-19 and political ideology. Results: A substantial majority of Americans (60%) both favor a masking requirement and are themselves wearing masks, while 13% oppose a mask mandate and do not wear masks. In contrast, 17% of Americans oppose a mask mandate but are currently wearing one, while 10% do not wear a mask but favor a mask mandate. These two groups are distinctively different from one another and the other groups in their socioeconomic characteristics, risk perception and political beliefs. Conclusions: Our study offers a better understanding of the mismatch between mask wearing behavior and attitude toward the mask mandate, which will help the public health authorities to devise policies regarding mask wearing as an effective intervention to manage the pandemic
Exact-exchange density-functional theory for quasi-two-dimensional electron gases
A simple exact-exchange density-functional method for a quasi-two-dimensional
electron gas with variable density is presented. An analytical expression for
the exact-exchange potential with only one occupied subband is provided,
without approximations. When more subbands are occupied the exact-exchange
potential is obtained numerically. The theory shows that, in contradiction with
LDA, the exact-exchange potential exhibits discontinuities and the system
suffers a zero-temperature first-order transition each time a subband is
occupied. Results suggesting that the translational symmetry might be
spontaneously broken at zero temperature are presented. An extension of the
theory to finite temperatures allows to describe a drop in the intersubband
spacing in good quantitative agreement with recent experiments.Comment: 14 pages, 3 figure
The Mersey Estuary : sediment geochemistry
This report describes a study of the geochemistry of
the Mersey estuary carried out between April 2000 and
December 2002. The study was the first in a new programme
of surveys of the geochemistry of major British estuaries
aimed at enhancing our knowledge and understanding of the
distribution of contaminants in estuarine sediments.
The report first summarises the physical setting, historical
development, geology, hydrography and bathymetry of the
Mersey estuary and its catchment. Details of the sampling
and analytical programmes are then given followed by a
discussion of the sedimentology and geochemistry. The
chemistry of the water column and suspended particulate
matter have not been studied, the chief concern being with
the geochemistry of the surface and near-surface sediments
of the Mersey estuary and an examination of their likely
sources and present state of contamination
Doping dependent Irreversible Magnetic Properties of Ba(Fe1-xCox)2As2 Single Crystals
We discuss the irreversible magnetic properties of self-flux grown
Ba(Fe1-xCox)2As2 single crystals for a wide range of concentrations covering
the whole phase diagram from the underdoped to the overdoped regime, x=0.038,
0.047, 0.058, 0.071, 0.074, 0.10, 0.106 and 0.118. Samples were characterized
by a magneto-optical method and show excellent spatial uniformity of the
superconducting state. The overall behavior closely follows classical Bean
model of the critical state. The field-dependent magnetization exhibits second
peak at a temperature and doping - dependent magnetic field, Hp. The evolution
of this fishtail feature with doping is discussed. Magnetic relaxation is
time-logarithmic and unusually fast. Similar to cuprates, there is an apparent
crossover from collective elastic to plastic flux creep above Hp. At high
fields, the field dependence of the relaxation rate becomes doping independent.
We discuss our results in the framework of the weak collective pinning and show
that vortex physics in iron-based pnictide crystals is much closer to high-Tc
cuprates than to conventional s-wave (including MgB2) superconductors.Comment: for the special issue of Physica C on iron-based pnictide
superconductor
Crossover between ionic/covalent and pure ionic bonding in magnesium oxyde clusters
An empirical potential with fluctuating charges is proposed for modelling
(MgO)_n clusters in both the molecular (small n) and bulk (n->infty) regimes.
Vectorial polarization forces are explicitely taken into account in the
self-consistent determination of the charges. Our model predicts cuboid cluster
structures, in agreement with previous experimental and theoretical results.
The effective charge transferred between magnesium and oxygen smoothly
increases from 1 to 2, with an estimated crossover size above 300 MgO
molecules
Field-induced XY behavior in the S=1/2 antiferromagnet on the square lattice
Making use of the quantum Monte Carlo method based on the worm algorithm, we
study the thermodynamic behavior of the S=1/2 isotropic Heisenberg
antiferromagnet on the square lattice in a uniform magnetic field varying from
very small values up to the saturation value. The field is found to induce a
Berezinskii-Kosterlitz-Thouless transition at a finite temperature, above which
a genuine XY behavior in an extended temperature range is observed. The phase
diagram of the system is drawn, and the thermodynamic behavior of the specific
heat and of the uniform and staggered magnetization is discussed in sight of an
experimental investigation of the field-induced XY behavior.Comment: 4 pages, 4 figure
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