706 research outputs found
Magnetic Monopoles in Field Theory and Cosmology
The existence of magnetic monopoles is predicted by many theories of particle
physics beyond the Standard Model. However, in spite of extensive searches,
there is no experimental or observational sign of them. I review the role of
magnetic monopoles in quantum field theory and discuss their implications for
particle physics and cosmology. I also highlight their differences and
similarities with monopoles found in frustrated magnetic systems, and discuss
how experiments carried out in these systems could help us understand the
physics of fundamental monopoles.Comment: 15 pages, no figures. Based on a talk given at the discussion meeting
"Emergent magnetic monopoles in frustrated magnetic systems" at the Kavli
Royal Society International Centre, 17-18 October 2011. To be published in
Philosophical Transactions of the Royal Society
Saltatory drift in a randomly driven two-wave potential
Dynamics of a classical particle in a one-dimensional, randomly driven
potential is analysed both analytically and numerically. The potential
considered here is composed of two identical spatially-periodic saw-tooth-like
components, one of which is externally driven by a random force. We show that
under certain conditions the particle may travel against the averaged external
force performing a saltatory unidirectional drift with a constant velocity.
Such a behavior persists also in situations when the external force averages
out to zero. We demonstrate that the physics behind this phenomenon stems from
a particular behavior of fluctuations in random force: upon reaching a certain
level, random fluctuations exercise a locking function creating points of
irreversibility which the particle can not overpass. Repeated (randomly) in
each cycle, this results in a saltatory unidirectional drift. This mechanism
resembles the work of an escapement-type device in watches. Considering the
overdamped limit, we propose simple analytical estimates for the particle's
terminal velocity.Comment: 14 pages, 6 figures; appearing in Journal of Physics: Condensed
Matter, special issue on Molecular Motors and Frictio
A model for luminescence of localized state ensemble
A distribution function for localized carriers,
, is proposed by solving a
rate equation, in which, electrical carriers' generation, thermal escape,
recapture and radiative recombination are taken into account. Based on this
distribution function, a model is developed for luminescence from localized
state ensemble with a Gaussian-type density of states. The model reproduces
quantitatively all the anomalous temperature behaviors of localized state
luminescence. It reduces to the well-known band-tail and luminescence quenching
models under certain approximations.Comment: 14 pages, 4 figure
Infrared phonon dynamics of multiferroic BiFeO3 single crystal
We discuss the first infrared reflectivity measurement on a BiFeO3 single
crystal between 5 K and room temperature. The 9 predicted ab-plane E phonon
modes are fully and unambiguously determined. The frequencies of the 4 A1
c-axis phonons are found. These results settle issues between theory and data
on ceramics. Our findings show that the softening of the lowest frequency E
mode is responsible for the temperature dependence of the dielectric constant,
indicating that the ferroelectric transition in BiFeO3 is soft-mode driven.Comment: 5 pages (figures included
Demonstration of a controllable three-dimensional Brownian motor in symmetric potentials
We demonstrate a Brownian motor, based on cold atoms in optical lattices,
where isotropic random fluctuations are rectified in order to induce controlled
atomic motion in arbitrary directions. In contrast to earlier demonstrations of
ratchet effects, our Brownian motor operates in potentials that are spatially
and temporally symmetric, but where spatiotemporal symmetry is broken by a
phase shift between the potentials and asymmetric transfer rates between them.
The Brownian motor is demonstrated in three dimensions and the noise-induced
drift is controllable in our system.Comment: 5 pages, 4 figure
Напрями та шляхи вдосконалення матеріально-технічного забезпечення підприємств АПК регіону
Background The growing number of web-based psychological treatments, based on textual communication, generates a wealth of data that can contribute to knowledge of online and face-to-face treatments. We investigated whether clients language use predicted treatment outcomes and adherence in Master Your Mood (MYM), an online group course for young adults with depressive symptoms. Methods Among 234 participants from a randomised controlled trial of MYM, we tested whether their word use on course application forms predicted baseline levels of depression, anxiety and mastery, or subsequent treatment adherence. We then analysed chat session transcripts of course completers (n=67) to investigate whether word use changes predicted changes in treatment outcomes. Results Depression improvement was predicted by increasing use of 'discrepancy words' during treatment (e.g. should). At baseline, more discrepancy words predicted higher mastery level. Adherence was predicted by more words used at application, more social words and fewer discrepancy words. Limitations Many variables were included, increasing the chance of coincidental results. This risk was constrained by examining only those word categories that have been investigated in relation to depression or adherence. Conclusions This is the first study to link word use during treatment to outcomes of treatment that has proven to be effective in an RCT. The results suggest that paying attention to the length of problem articulation at application and to 'discrepancy words' may be wise, as these seem to be psychological markers. To expand knowledge of word use as psychological marker, research on web-based treatment should include text analysis. © 2014 The Authors
Thermodynamic basis of the concept of "recombination resistances"
The concept of "recombination resistance" introduced by Shockley and Read
(Phys. Rev. 87, 835 (1952)) is discussed within the framework of the
thermodynamics of irreversible processes ruled by the principle of the minimum
rate of entropy production. It is shown that the affinities of recombination
processes represent "voltages" in a thermodynamic Ohm-like law where the net
rates of recombinations represent the "currents". The quantities thus found
allow for the definition of the "dissipated power" which is to be related to
the rate of entropy production of the recombination processes dealt with.Comment: Submitted to Phys. Rev.
Influence of the lattice topography on a three-dimensional, controllable Brownian motor
We study the influence of the lattice topography and the coupling between
motion in different directions, for a three-dimensional Brownian motor based on
cold atoms in a double optical lattice. Due to controllable relative spatial
phases between the lattices, our Brownian motor can induce drifts in arbitrary
directions. Since the lattices couple the different directions, the relation
between the phase shifts and the directionality of the induced drift is non
trivial. Here is therefore this relation investigated experimentally by
systematically varying the relative spatial phase in two dimensions, while
monitoring the vertically induced drift and the temperature. A relative spatial
phase range of 2pi x 2pi is covered. We show that a drift, controllable both in
speed and direction, can be achieved, by varying the phase both parallel and
perpendicular to the direction of the measured induced drift. The experimental
results are qualitatively reproduced by numerical simulations of a simplified,
classical model of the system
The Free Will Theorem
On the basis of three physical axioms, we prove that if the choice of a
particular type of spin 1 experiment is not a function of the information
accessible to the experimenters, then its outcome is equally not a function of
the information accessible to the particles. We show that this result is
robust, and deduce that neither hidden variable theories nor mechanisms of the
GRW type for wave function collapse can be made relativistic. We also establish
the consistency of our axioms and discuss the philosophical implications.Comment: 31 pages, 6figure
Gyrokinetic Simulations Compared with Magnetic Fluctuations Diagnosed with a Faraday-Effect Radial Interferometer-Polarimeter in the DIII-D pedestal
Experimental data on electromagnetic fluctuations in DIII-D, made available
by the Faraday-effect Radial Interferometer-Polarimeter (RIP) diagnostic, is
examined in comparison with detailed gyrokinetic simulations using Gyrokinetic
Electromagnetic Numerical Experiment (GENE). The diagnostic has the unique
capability of making internal measurements of fluctuating magnetic fields
. Local linear simulations identify
microtearing modes (MTMs) over a substantial range of toroidal mode numbers
(peaking at ) with frequencies in good agreement with the experimental
data. Local nonlinear simulations reinforce this result by producing a magnetic
frequency spectrum in good agreement with that diagnosed by RIP. Simulated heat
fluxes are in the range of experimental expectations. However, magnetic
fluctuation amplitudes are substantially lower than the experimental
expectations. Possible sources of this discrepancy are discussed, notably the
fact that the diagnostics are localized at the mid-plane -- the poloidal
location where the simulations predict the fluctuation amplitudes to be
smallest. Despite some discrepancies, several connections between simulations
and experiments, combined with general criteria discriminating between
potential pedestal instabilities, strongly point to MTMs as the source of the
observed magnetic fluctuations
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