15,719 research outputs found
Improving the Functional Control of Aged Ferroelectrics using Insights from Atomistic Modelling
We provide a fundamental insight into the microscopic mechanisms of the
ageing processes. Using large scale molecular dynamics simulations of the
prototypical ferroelectric material PbTiO3, we demonstrate that the
experimentally observed ageing phenomena can be reproduced from intrinsic
interactions of defect-dipoles related to dopant-vacancy associates, even in
the absence of extrinsic effects. We show that variation of the dopant
concentration modifies the material's hysteretic response. We identify a
universal method to reduce loss and tune the electromechanical properties of
inexpensive ceramics for efficient technologies.Comment: 6 pages, 3 figure
Realistic Expanding Source Model for Invariant One-Particle Multiplicity Distributions and Two-Particle Correlations in Relativistic Heavy-Ion Collisions
We present a realistic expanding source model with nine parameters that are
necessary and sufficient to describe the main physics occuring during
hydrodynamical freezeout of the excited hadronic matter produced in
relativistic heavy-ion collisions. As a first test of the model, we compare it
to data from central Si + Au collisions at p_lab/A = 14.6 GeV/c measured in
experiment E-802 at the AGS. An overall chi-square per degree of freedom of
1.055 is achieved for a fit to 1416 data points involving invariant pi^+, pi^-,
K^+, and K^- one-particle multiplicity distributions and pi^+ and K^+
two-particle correlations. The 99-percent-confidence region of parameter space
is identified, leading to one-dimensional error estimates on the nine fitted
parameters and other calculated physical quantities. Three of the most
important results are the freezeout temperature, longitudinal proper time, and
baryon density along the symmetry axis. For these we find values of 92.9 +/-
4.4 MeV, 8.2 +/- 2.2 fm/c, and 0.0222 + 0.0096 / - 0.0069 fm^-3, respectively.Comment: 37 pages and 12 figures. RevTeX 3.0. Submitted to Physical Review C.
Complete preprint, including device-independent (dvi), PostScript, and LaTeX
versions of the text, plus PostScript files of all figures, are available at
http://t2.lanl.gov/publications/publications.html or at
ftp://t2.lanl.gov/publications/res
Ferromagnetic Domain Structure of La0.78Ca0.22MnO3 Single Crystals
The magneto-optical technique has been employed to observe spontaneous
ferromagnetic domain structures in La0.78Ca0.22MnO3 single crystals. The
magnetic domain topology was found to be correlated with the intrinsic twin
structure of the investigated crystals. With decreasing temperature the regular
network of ferromagnetic domains undergoes significant changes resulting in
apparent rotation of the domain walls in the temperature range of 70-150 K. The
apparent rotation of the domain walls can be understood in terms of the
Jahn-Teller deformation of the orthorhombic unit cell, accompanied by
additional twinning.Comment: 7 pages, 5 figures, to be published in PR
Differences in structural and pain phenotypes in the sodium monoiodoacetate and meniscal transection models of osteoarthritis
This study was funded by Arthritis Research UK Grant number 18769.Peer reviewedPublisher PD
Superconductivity in Ca-doped graphene
Graphene, a zero-gap semimetal, can be transformed into a metallic,
semiconducting or insulating state by either physical or chemical modification.
Superconductivity is conspicuously missing among these states despite
considerable experimental efforts as well as many theoretical proposals. Here,
we report superconductivity in calcium-decorated graphene achieved by
intercalation of graphene laminates that consist of well separated and
electronically decoupled graphene crystals. In contrast to intercalated
graphite, we find that Ca is the only dopant that induces superconductivity in
graphene laminates above 1.8 K among intercalants used in our experiments such
as potassium, caesium and lithium. Ca-decorated graphene becomes
superconducting at ~ 6 K and the transition temperature is found to be strongly
dependent on the confinement of the Ca layer and the induced charge carrier
concentration. In addition to the first evidence for superconducting graphene,
our work shows a possibility of inducing and studying superconductivity in
other 2D materials using their laminates
Class of dilute granular Couette flows with uniform heat flux
In a recent paper [F. Vega Reyes et al., Phys. Rev. Lett. 104, 028001 (2010)]
we presented a preliminary description of a special class of steady Couette
flows in dilute granular gases. In all flows of this class the viscous heating
is exactly balanced by inelastic cooling. This yields a uniform heat flux and a
linear relationship between the local temperature and flow velocity. The class
(referred to as the LTu class) includes the Fourier flow of ordinary gases and
the simple shear flow of granular gases as special cases. In the present paper
we provide further support for this class of Couette flows by following four
different routes, two of them being theoretical (Grad's moment method of the
Boltzmann equation and exact solution of a kinetic model) and the other two
being computational (molecular dynamics and Monte Carlo simulations of the
Boltzmann equation). Comparison between theory and simulations shows a very
good agreement for the non-Newtonian rheological properties, even for quite
strong inelasticity, and a good agreement for the heat flux coefficients in the
case of Grad's method, the agreement being only qualitative in the case of the
kinetic model.Comment: 15 pages, 10 figures; v2: change of title plus some other minor
change
Detection of charge motion in a non-metallic silicon isolated double quantum dot
As semiconductor device dimensions are reduced to the nanometer scale,
effects of high defect density surfaces on the transport properties become
important to the extent that the metallic character that prevails in large and
highly doped structures is lost and the use of quantum dots for charge sensing
becomes complex. Here we have investigated the mechanism behind the detection
of electron motion inside an electrically isolated double quantum dot that is
capacitively coupled to a single electron transistor, both fabricated from
highly phosphorous doped silicon wafers. Despite, the absence of a direct
charge transfer between the detector and the double dot structure, an efficient
detection is obtained. In particular, unusually large Coulomb peak shifts in
gate voltage are observed. Results are explained in terms of charge
rearrangement and the presence of inelastic cotunneling via states at the
periphery of the single electron transistor dot
Kinetic Theory of a Dilute Gas System under Steady Heat Conduction
The velocity distribution function of the steady-state Boltzmann equation for
hard-core molecules in the presence of a temperature gradient has been obtained
explicitly to second order in density and the temperature gradient. Some
thermodynamical quantities are calculated from the velocity distribution
function for hard-core molecules and compared with those for Maxwell molecules
and the steady-state Bhatnagar-Gross-Krook(BGK) equation. We have found
qualitative differences between hard-core molecules and Maxwell molecules in
the thermodynamical quantities, and also confirmed that the steady-state BGK
equation belongs to the same universality class as Maxwell molecules.Comment: 36 pages, 4 figures, 5 table
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