1,546 research outputs found
Nonequilibrium coupled Brownian phase oscillators
A model of globally coupled phase oscillators under equilibrium (driven by
Gaussian white noise) and nonequilibrium (driven by symmetric dichotomic
fluctuations) is studied. For the equilibrium system, the mean-field state
equation takes a simple form and the stability of its solution is examined in
the full space of order parameters. For the nonequilbrium system, various
asymptotic regimes are obtained in a closed analytical form. In a general case,
the corresponding master equations are solved numerically. Moreover, the
Monte-Carlo simulations of the coupled set of Langevin equations of motion is
performed. The phase diagram of the nonequilibrium system is presented. For the
long time limit, we have found four regimes. Three of them can be obtained from
the mean-field theory. One of them, the oscillating regime, cannot be predicted
by the mean-field method and has been detected in the Monte-Carlo numerical
experiments.Comment: 9 pages 8 figure
Neutron beam test of CsI crystal for dark matter search
We have studied the response of Tl-doped and Na-doped CsI crystals to nuclear
recoils and 's below 10 keV. The response of CsI crystals to nuclear
recoil was studied with mono-energetic neutrons produced by the
H(p,n)He reaction. This was compared to the response to Compton
electrons scattered by 662 keV -ray. Pulse shape discrimination between
the response to these 's and nuclear recoils was studied, and quality
factors were estimated. The quenching factors for nuclear recoils were derived
for both CsI(Na) and CsI(Tl) crystals.Comment: 21pages, 14figures, submitted to NIM
Epitaxially strained [001]-(PbTiO)(PbZrO) superlattice and PbTiO from first principles
The effect of layer-by-layer heterostructuring and epitaxial strain on
lattice instabilities and related ferroelectric properties is investigated from
first principles for the [001]-(PbTiO)(PbZrO) superlattice and
pure PbTiO on a cubic substrate. The results for the superlattice show an
enhancement of the stability of the monoclinic r-phase with respect to pure
PbTiO. Analysis of the lattice instabilities of the relaxed centrosymmetric
reference structure computed within density functional perturbation theory
suggests that this results from the presence of two unstable zone-center modes,
one confined in the PbTiO layer and one in the PbZrO layer, which
produce in-plane and normal components of the polarization, respectively. The
zero-temperature dielectric response is computed and shown to be enhanced not
only near the phase boundaries, but throughout the r-phase. Analysis of the
analogous calculation for pure PbTiO is consistent with this
interpretation, and suggests useful approaches to engineering the dielectric
properties of artificially structured perovskite oxides.Comment: 8 pages, 5 figure
High-pressure effects on structural, magnetic, and vibrational properties of van der Waals antiferromagnet MnPS₃
The crystal structure, vibrational spectra, and magnetic structure of quasi-two-dimensional layered van der Waals material MnPS3 were studied using x-ray diffraction and Raman spectroscopy at high pressures up to 28 GPa, and neutron diffraction up to 3.6 GPa, respectively. A structural phase transition between two monoclinic modifications of the same C2/m symmetry was observed, evolving gradually in the pressure range of about 1–6 GPa. The transition is accompanied by abrupt shortening of lattice parameters, significant reduction of the monoclinic distortion, and anomalies in the pressure behavior of several Raman-mode frequencies. No more structural phase transitions were revealed in the studied pressure range. The antiferromagnetic (AFM) state with a propagation vector k= (0, 0, 0) remains stable in ambient pressure and high-pressure structural phases of MnPS3 at least up to 3.6 GPa. The Néel temperature increases noticeably with a pressure coefficient of dTN/dP=6.7 K/GPa, leading to modification of the dominant first-neighbor magnetic interaction exchange parameter with a relevant coefficient dJ1/dP≈−0.6 meV/GPa. This observation is in contrast to the pressure behavior of FePS3, demonstrating modification of the AFM state from 2D-like to 3D-like at the similar pressure-induced structural phase transition. The different pressure response of the magnetic states of MnPS3 and FePS3 is analyzed in terms of competing in-plane and interplane magnetic interactions
Integrating wild and agrobiodiversity conservation
This research shows that both wild biodiversity and agrobiodiversity provide multiple ecosystem services that support food production, underpin food security and human wellbeing. We consider that biodiversity conservation efforts in agricultural contexts should better integrate wild and agrobiodiversity approache
Lattice instabilities of PbZrO3/PbTiO3 [1:1] superlattices from first principles
Ab initio phonon calculations for the nonpolar reference structures of the
(001), (110), and (111) PbZrO_3/PbTiO_3 [1:1] superlattices are presented. The
unstable polar modes in the tetragonal (001) and (110) structures are confined
in either the Ti- or the Zr-centered layers and display two-mode behavior,
while in the cubic (111) case one-mode behavior is observed. Instabilities with
pure oxygen character are observed in all three structures. The implications
for the ferroelectric behavior and related properties are discussed.Comment: 12 pages, 2 figures, 7 tables, submitted to PR
Anomalous Dynamics of Forced Translocation
We consider the passage of long polymers of length N through a hole in a
membrane. If the process is slow, it is in principle possible to focus on the
dynamics of the number of monomers s on one side of the membrane, assuming that
the two segments are in equilibrium. The dynamics of s(t) in such a limit would
be diffusive, with a mean translocation time scaling as N^2 in the absence of a
force, and proportional to N when a force is applied. We demonstrate that the
assumption of equilibrium must break down for sufficiently long polymers (more
easily when forced), and provide lower bounds for the translocation time by
comparison to unimpeded motion of the polymer. These lower bounds exceed the
time scales calculated on the basis of equilibrium, and point to anomalous
(sub-diffusive) character of translocation dynamics. This is explicitly
verified by numerical simulations of the unforced translocation of a
self-avoiding polymer. Forced translocation times are shown to strongly depend
on the method by which the force is applied. In particular, pulling the polymer
by the end leads to much longer times than when a chemical potential difference
is applied across the membrane. The bounds in these cases grow as N^2 and
N^{1+\nu}, respectively, where \nu is the exponent that relates the scaling of
the radius of gyration to N. Our simulations demonstrate that the actual
translocation times scale in the same manner as the bounds, although influenced
by strong finite size effects which persist even for the longest polymers that
we considered (N=512).Comment: 13 pages, RevTeX4, 16 eps figure
Existence of superposition solutions for pulse propagation in nonlinear resonant media
Existence of self-similar, superposed pulse-train solutions of the nonlinear,
coupled Maxwell-Schr\"odinger equations, with the frequencies controlled by the
oscillator strengths of the transitions, is established. Some of these
excitations are specific to the resonant media, with energy levels in the
configurations of and and arise because of the interference
effects of cnoidal waves, as evidenced from some recently discovered identities
involving the Jacobian elliptic functions. Interestingly, these excitations
also admit a dual interpretation as single pulse-trains, with widely different
amplitudes, which can lead to substantially different field intensities and
population densities in different atomic levels.Comment: 11 Pages, 6 Figures, presentation changed and 3 figures adde
Higher Grading Conformal Affine Toda Teory and (Generalized) Sine-Gordon/Massive Thirring Duality
Some properties of the higher grading integrable generalizations of the
conformal affine Toda systems are studied. The fields associated to the
non-zero grade generators are Dirac spinors. The effective action is written in
terms of the Wess-Zumino-Novikov-Witten (WZNW) action associated to an affine
Lie algebra, and an off-critical theory is obtained as the result of the
spontaneous breakdown of the conformal symmetry. Moreover, the off-critical
theory presents a remarkable equivalence between the Noether and topological
currents of the model. Related to the off-critical model we define a real and
local Lagrangian provided some reality conditions are imposed on the fields of
the model. This real action model is expected to describe the soliton sector of
the original model, and turns out to be the master action from which we uncover
the weak-strong phases described by (generalized) massive Thirring and
sine-Gordon type models, respectively. The case of any (untwisted) affine Lie
algebra furnished with the principal gradation is studied in some detail.
The example of is presented explicitly.Comment: 28 pages, JHEP styl
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