7,269 research outputs found
Symmetries of the ratchet current
Recent advances in nonequilibrium statistical mechanics shed new light on the
ratchet effect. The ratchet motion can thus be understood in terms of symmetry
(breaking) considerations. We introduce an additional symmetry operation
besides time-reversal, that effectively reverses the nonequilibrium driving.
That operation of field-reversal combined with time-reversal decomposes the
nonequilibrium action so to clarify under what circumstances the ratchet
current is a second order effect around equilibrium, what is the direction of
the ratchet current and what are possibly the symmetries in its fluctuations.Comment: 13 pages, heavily extended versio
Extended Weak Coupling Limit for Friedrichs Hamiltonians
We study a class of self-adjoint operators defined on the direct sum of two
Hilbert spaces: a finite dimensional one called sometimes a ``small subsystem''
and an infinite dimensional one -- a ``reservoir''. The operator, which we call
a ``Friedrichs Hamiltonian'', has a small coupling constant in front of its
off-diagonal term. It is well known that under some conditions in the weak
coupling limit the appropriately rescaled evolution in the interaction picture
converges to a contractive semigroup when restricted to the subsystem. We show
that in this model, the properly renormalized and rescaled evolution converges
on the whole space to a new unitary evolution, which is a dilation of the above
mentioned semigroup. Similar results have been studied before \cite{AFL} in
more complicated models and they are usually referred to as "stochastic Limit".Comment: changes in notation and title, minor correction
Does operational oceanography address the needs of fisheries and applied environmental scientists?
Although many oceanographic data products are now considered operational, continued dialogue between data producers and their user communities is still needed. The fisheries and environmental science communities have often been criticized for their lack of multidisciplinarity, and it is not clear whether recent developments in operational oceanographic products are addressing these needs. The International Council for the Exploration of the Sea (ICES) Working Group on Operational Oceanographic products for Fisheries and Environment (WGOOFE) identified a potential mismatch between user requirements and the perception of requirements by the providers. Through a questionnaire (98 respondents), WGOOFE identified some of these issues. Although products of physical variables were in higher demand, several biological parameters scored in the top 10 rankings. Users placed specific focus on historic time series products with monthly or annual resolution and updating on similar time scales. A significant percentage requested access to numerical data rather than graphical output. While the outcomes of this survey challenge our views of operational oceanography, several initiatives are already attempting to close the gap between user requirements and products available
Derivation of some translation-invariant Lindblad equations for a quantum Brownian particle
We study the dynamics of a Brownian quantum particle hopping on an infinite
lattice with a spin degree of freedom. This particle is coupled to free boson
gases via a translation-invariant Hamiltonian which is linear in the creation
and annihilation operators of the bosons. We derive the time evolution of the
reduced density matrix of the particle in the van Hove limit in which we also
rescale the hopping rate. This corresponds to a situation in which both the
system-bath interactions and the hopping between neighboring sites are small
and they are effective on the same time scale. The reduced evolution is given
by a translation-invariant Lindblad master equation which is derived
explicitly.Comment: 28 pages, 4 figures, minor revisio
Approach to ground state and time-independent photon bound for massless spin-boson models
It is widely believed that an atom interacting with the electromagnetic field
(with total initial energy well-below the ionization threshold) relaxes to its
ground state while its excess energy is emitted as radiation. Hence, for large
times, the state of the atom+field system should consist of the atom in its
ground state, and a few free photons that travel off to spatial infinity.
Mathematically, this picture is captured by the notion of asymptotic
completeness. Despite some recent progress on the spectral theory of such
systems, a proof of relaxation to the ground state and asymptotic completeness
was/is still missing, except in some special cases (massive photons, small
perturbations of harmonic potentials). In this paper, we partially fill this
gap by proving relaxation to an invariant state in the case where the atom is
modelled by a finite-level system. If the coupling to the field is sufficiently
infrared-regular so that the coupled system admits a ground state, then this
invariant state necessarily corresponds to the ground state. Assuming slightly
more infrared regularity, we show that the number of emitted photons remains
bounded in time. We hope that these results bring a proof of asymptotic
completeness within reach.Comment: 45 pages, published in Annales Henri Poincare. This archived version
differs from the journal version because we corrected an inconsequential
mistake in Section 3.5.1: to do this, a new paragraph was added after Lemma
3.
Prospects of searches for long-lived charged particles with MoEDAL
We study the prospects of searches for exotic long-lived particles with the
MoEDAL detector at the LHC, assuming the integrated luminosity of 30 fb
that is expected at the end of Run 3. MoEDAL incorporates nuclear track
detectors deployed a few metres away from the interaction point, which are
sensitive to any highly-ionizing particles. Hence MoEDAL is able to detect
singly- or doubly-charged particles with low velocities or , respectively, and lifetimes larger than . We
examine the MoEDAL sensitivity to various singly-charged supersymmetric
particles with long lifetimes and to several types of doubly-charged long-lived
particles with different spins and SU(2) charges. We compare the prospective
MoEDAL mass reaches to current limits from ATLAS and CMS, which involve
auxiliary analysis assumptions. MoEDAL searches for doubly-charged fermions are
particularly competitive.Comment: 19 pages, 5 figure
Global damage identification based on vibration signatures applied to masonry structures
The present paper aims at damage assessment of masonry structures in an early stage. Two replicates of historical constructions were built in virgin state, one arch with 1.5 m span and one shear wall of 1 m2. Afterwards, progressive damage was applied and sequential mo-dal identification analysis was performed in each damage stage, aiming at finding adequate relations between changes in dynamical behaviour and internal crack growth. During the dynamic tests, accelerations and strains were recorded in many points of the replicates. Comparisons between different techniques based on vibrations measurements were made to evaluate which methods are the most suitable for identifying damage in masonry con-structions
Spin structure function g_1 at low x: status and plans
A brief review of measurements and expectations concerning the spin structure
function g_1 of the nucleon at low values of the scaling variable x is given.Comment: 4 pages, 3 figures. Invited talk presented at the ``International
Workshop on the Spin Structure of the Proton and Polarized Collider
Physics'', ECT*, Trento, Italy, July 23-28, 200
- …