7,025 research outputs found
Current reversals in a rocking ratchet: dynamical vs symmetry-breaking mechanisms
Directed transport in ratchets is determined by symmetry-breaking in a system
out of equilibrium. A hallmark of rocking ratchets is current reversals: an
increase in the rocking force changes the direction of the current. In this
work for a bi-harmonically driven spatially symmetric rocking ratchet we show
that a class of current reversal is precisely determined by symmetry-breaking,
thus creating a link between dynamical and symmetry-breaking mechanisms
Simulation of Beam-Beam Effects and Tevatron Experience
Effects of electromagnetic interactions of colliding bunches in the Tevatron
had a variety of manifestations in beam dynamics presenting vast opportunities
for development of simulation models and tools. In this paper the computer code
for simulation of weak-strong beam-beam effects in hadron colliders is
described. We report the collider operational experience relevant to beam-beam
interactions, explain major effects limiting the collider performance and
compare results of observations and measurements with simulations.Comment: 23 pages, 17 figure
Classical and relativistic dynamics of supersolids: variational principle
We present a phenomenological Lagrangian and Poisson brackets for obtaining
nondissipative hydrodynamic theory of supersolids. A Lagrangian is constructed
on the basis of unification of the principles of non-equilibrium thermodynamics
and classical field theory. The Poisson brackets, governing the dynamics of
supersolids, are uniquely determined by the invariance requirement of the
kinematic part of the found Lagrangian. The generalization of Lagrangian is
discussed to include the dynamics of vortices. The obtained equations of motion
do not account for any dynamic symmetry associated with Galilean or Lorentz
invariance. They can be reduced to the original Andreev-Lifshitz equations if
to require Galilean invariance. We also present a relativistic-invariant
supersolid hydrodynamics, which might be useful in astrophysical applications.Comment: 22 pages, changed title and content, added reference
On the Fourier transform of the characteristic functions of domains with -smooth boundary
We consider domains with -smooth boundary and
study the following question: when the Fourier transform of the
characteristic function belongs to ?Comment: added two references; added footnotes on pages 6 and 1
Realistic Tunneling States for the Magnetic Effects in Non-Metallic Real Glasses
The discovery of magnetic and compositional effects in the low temperature
properties of multi-component glasses has prompted the need to extend the
standard two-level systems (2LSs) tunneling model. A possible extension
\cite{Jug2004} assumes that a subset of tunneling quasi-particles is moving in
a three-welled potential (TWP) associated with the ubiquitous inhomogeneities
of the disordered atomic structure of the glass. We show that within an
alternative, cellular description of the intermediate-range atomic structure of
glasses the tunneling TWP can be fully justified. We then review how the
experimentally discovered magnetic effects can be explained within the approach
where only localized atomistic tunneling 2LSs and quasi-particles tunneling in
TWPs are allowed. We discuss the origin of the magnetic effects in the heat
capacity, dielectric constant (real and imaginary parts), polarization echo and
SQUID magnetization in several glassy systems. We conclude by commenting on a
strategy to reveal the mentioned tunneling states (2LSs and TWPs) by means of
atomistic computer simulations and discuss the microscopic nature of the
tunneling states in the context of the potential energy landscape of
glass-forming systems.Comment: 48 pages, 27 figures; mini-review for the Proceedings of the XIV
International Workshop on Complex Systems (Fai della Paganella, Trento, March
2015) (submitted to Phil.Mag.). arXiv admin note: text overlap with
arXiv:cond-mat/0210221 by other author
Neutron-Electron EDM Correlations in Supersymmetry and Prospects for EDM Searches
Motivated by recent progress in experimental techniques of electric dipole
moment (EDM) measurements, we study correlations between the neutron and
electron EDMs in common supersymmetric models. These include minimal
supergravity (mSUGRA) with small CP phases, mSUGRA with a heavy SUSY spectrum,
the decoupling scenario and split SUSY. In most cases, the electron and neutron
EDMs are found to be observable in the next round of EDM experiments. They
exhibit certain correlation patterns. For example, if d_n ~ 10^{-27} e cm is
found, d_e is predicted to lie in the range 10^{-28}-10^{-29} e cm.Comment: 16 pages,12 figures. To appear in JHEP. A note on stability of the
correlations added in Conclusions; refs. and footnotes adde
Commensurate structural modulation in the charge- and orbitally-ordered phase of the quadruple perovskite (NaMn)MnO
By means of synchrotron x-ray and electron diffraction, we studied the
structural changes at the charge order transition =176 K in the
mixed-valence quadruple perovskite (NaMn)MnO. Below we
find satellite peaks indicating a commensurate structural modulation with the
same propagation vector q =(1/2,0,-1/2) of the CE magnetic order that appears
at low temperature, similarly to the case of simple perovskites like
LaCaMnO. In the present case, the modulated structure
together with the observation of a large entropy change at gives
evidence of a rare case of full Mn/Mn charge and orbital order
consistent with the Goodenough-Kanamori model.Comment: Accepted for publication in Phys. Rev. B Rapid Communication
ALTICORE: an initiative for coastal altimetry
ALTICORE (value-added ALTImetry for COastal REgions) is an international initiative whose main objective is to encourage the operational use of altimetry over coastal areas, by improving the quality and availability of coastal altimetry data. The ALTICORE proposal has recently been submitted for funding to the INTAS scheme (www.intas.be) by a consortium of partners from Italy, France, UK, Russia and Azerbaijan. ALTICORE is also meant as a contribution to the ongoing International Altimeter Service effort.
In this work we will describe the anticipated project stages, namely: 1) improvement of the most widely distributed, 1 Hz, data by analyzing the corrective terms and providing the best solutions, including those derived from appropriate local modelling; 2) development of a set of algorithms to automate quality control and gap-filling functions for the coastal regions; 3) development of testing strategies to ensure a thorough validation of the data.
The improved products will be delivered to ALTICORE users via Grid-compliant technology; this makes it easier to integrate the local data holdings, allows access from a range of services, e.g. directly into model assimilation or GIS systems and should therefore facilitate a widespread and complete assessment of the 1Hz data performance and limitations. We will also outline the design and implementation of the Grid-compliant system for efficient access to distributed archives of data; this consists of regional data centres, each having primary responsibility for regional archives, local corrections and quality control, and operating a set of web-services allowing access to the full functionality of data extraction.
We will conclude by discussing a follow-on phase of the project; this will investigate further improvements on the processing strategy, including the use of higher frequency (10 or 20 Hz) data. Phenomena happen at smaller spatial scales near the coast, so this approach is necessary to match the required resolution. The whole project will hopefully promote the 15-year sea surface height from altimetry to the rank of operational record for the coastal areas
Numerical study of jets produced by conical wire arrays on the Magpie pulsed power generator
The aim of this work is to model the jets produced by conical wire arrays on
the MAGPIE generator, and to design and test new setups to strengthen the link
between laboratory and astrophysical jets. We performed the modelling with
direct three-dimensional magneto-hydro-dynamic numerical simulations using the
code GORGON. We applied our code to the typical MAGPIE setup and we
successfully reproduced the experiments. We found that a minimum resolution of
approximately 100 is required to retrieve the unstable character of the jet. We
investigated the effect of changing the number of wires and found that arrays
with less wires produce more unstable jets, and that this effect has magnetic
origin. Finally, we studied the behaviour of the conical array together with a
conical shield on top of it to reduce the presence of unwanted low density
plasma flows. The resulting jet is shorter and less dense.Comment: Accepted for publication in Astrophysics & Space Science. HEDLA 2010
conference procedings. Final pubblication will be available on Springe
A high-efficiency spin-resolved phototemission spectrometer combining time-of-flight spectroscopy with exchange-scattering polarimetry
We describe a spin-resolved electron spectrometer capable of uniquely
efficient and high energy resolution measurements. Spin analysis is obtained
through polarimetry based on low-energy exchange scattering from a
ferromagnetic thin-film target. This approach can achieve a similar analyzing
power (Sherman function) as state-of-the-art Mott scattering polarimeters, but
with as much as 100 times improved efficiency due to increased reflectivity.
Performance is further enhanced by integrating the polarimeter into a
time-of-flight (TOF) based energy analysis scheme with a precise and flexible
electrostatic lens system. The parallel acquisition of a range of electron
kinetic energies afforded by the TOF approach results in an order of magnitude
(or more) increase in efficiency compared to hemispherical analyzers. The lens
system additionally features a 90{\deg} bandpass filter, which by removing
unwanted parts of the photoelectron distribution allows the TOF technique to be
performed at low electron drift energy and high energy resolution within a wide
range of experimental parameters. The spectrometer is ideally suited for
high-resolution spin- and angle-resolved photoemission spectroscopy
(spin-ARPES), and initial results are shown. The TOF approach makes the
spectrometer especially ideal for time-resolved spin-ARPES experiments.Comment: 16 pages, 11 figure
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