14,109 research outputs found
Time dependent transformations in deformation quantization
We study the action of time dependent canonical and coordinate
transformations in phase space quantum mechanics. We extend the covariant
formulation of the theory by providing a formalism that is fully invariant
under both standard and time dependent coordinate transformations. This result
considerably enlarges the set of possible phase space representations of
quantum mechanics and makes it possible to construct a causal representation
for the distributional sector of Wigner quantum mechanics.Comment: 16 pages, to appear in the J. Math. Phy
Enhancement of the Benjamin-Feir instability with dissipation
It is shown that there is an overlooked mechanism whereby some kinds of
dissipation can enhance the Benjamin-Feir instability of water waves. This
observation is new, and although it is counterintuitive, it is due to the fact
that the Benjamin-Feir instability involves the collision of modes with
opposite energy sign (relative to the carrier wave), and it is the negative
energy perturbations which are enhanced.Comment: 15 pages, 2 figures To download more papers, go to
http://www.cmla.ens-cachan.fr/~dias. Physics of Fluids (2007) to appea
Sensitivity of ATLAS to FCNC single top quark production
The anomalous production of single top quarks via flavour-changing neutral currents (FCNCs), u(c)+g -> t, is studied using the ATLAS detector at the Large Hadron Collider. Detector simulation is done using the fast simulation package ATLFAST. A number of important systematic effects have been addressed. Based on a cut-based analysis, we shows that, with 10 fb-1, ATLAS can observe such top FCNC interactions with 5 sigma significance if the anomalous coupling strengths are k_ug/Lambda=k_cg/Lambda >= 0.0120 (sys.) TeV-1, or equivalently Br(t->ug)+Br(t->cg) >= 2.64 (sys.) x 10^{-4}$. In terms of production cross section, such a discovery requires at least 13.7 pb of anomalous single top quark production. With this level of sensitivity, ATLAS will be able to test some models of new physics
Generalized Weyl-Wigner map and Vey quantum mechanics
The Weyl-Wigner map yields the entire structure of Moyal quantum mechanics
directly from the standard operator formulation. The covariant generalization
of Moyal theory, also known as Vey quantum mechanics, was presented in the
literature many years ago. However, a derivation of the formalism directly from
standard operator quantum mechanics, clarifying the relation between the two
formulations is still missing. In this paper we present a covariant
generalization of the Weyl order prescription and of the Weyl-Wigner map and
use them to derive Vey quantum mechanics directly from the standard operator
formulation. The procedure displays some interesting features: it yields all
the key ingredients and provides a more straightforward interpretation of the
Vey theory including a direct implementation of unitary operator
transformations as phase space coordinate transformations in the Vey idiom.
These features are illustrated through a simple example.Comment: 15 pages, LaTe
NATURAL CONVECTION IN HIGH ASPECT RATIO THREE-DIMENSIONAL ENCLOSURES WITH UNIFORM HEAT FLUX ON THE HEATED WALL
In this work, the laminar natural convection in high aspect ratio three-dimensional
enclosures has been numerically studied. The enclosures studied here were heated with
uniform heat flux on a vertical wall and cooled at constant temperature on the opposite
wall. The remaining walls were considered adiabatic. Fluid properties were assumed
constant except for the density change with temperature on the buoyancy term. The
governing equations were solved using the finite volumes method and the dimensionless
form of these equations has the Prandtl number and the modified Rayleigh number as
parameters. The influences of the Rayleigh number and of the cavity aspect ratio on the
Nusselt number, for a Prandtl number of 0.7, were analyzed. Results were obtained for
values of the modified Rayleigh number up to 106 and for aspect ratios ranging from 1 to
20. The results were compared with two-dimensional results available in the literature and
the variation of the average Nusselt number with the parameters studied were discussed
Phase diagram of the antiferromagnetic XY model in two dimensions in a magnetic field
The phase diagram of the quasi-two-dimensional easy-plane antiferromagnetic
model, with a magnetic field applied in the easy plane, is studied using the
self-consistent harmonic approximation. We found a linear dependence of the
transition temperature as a function of the field for large values of the
field. Our results are in agreement with experimental data for the spin-1
honeycomb compound BaNi_2V_2O_3Comment: 3 page
Photometric and proper motion study of neglected open cluster NGC 2215
Optical UBVRI photometric measurements using the Faulkes Telescope North were
taken in early 2011 and combined with 2MASS JHK and WISE infrared
photometry as well as UCAC4 proper motion data in order to estimate the main
parameters of the galactic open cluster NGC 2215 of which large uncertainty
exists in the current literature. Fitting a King model we estimate a core
radius of 1.120.04 (0.240.01pc) and a limiting radius of
0.5 (0.940.11pc) for the cluster. The results of isochrone
fits indicates an age of with a distance of
pc, a metallicity of dex and a reddening of
. A proportion of the work in this study was undertaken by
Australian and Canadian upper secondary school students involved in the Space
to Grow astronomy education project, and is the first scientific publication to
have utilized our star cluster photometry curriculum materials.Comment: 10 pages, 9 Figures, 3 Table
Tuned liquid dampers simulation for earthquake response control of buildings
This paper is focused on the study of an earthquake protection system, the Tuned Liquid Damper (TLD), which
can, if adequately designed, reduce earthquake demands on buildings. This positive effect is accomplished taking
into account the oscillation of the free surface of a fluid inside a tank (sloshing). The behaviour of an isolated
Tuned Liquid Damper, subjected to a sinusoidal excitation at its base, with different displacement amplitudes,
was studied by finite element analysis. The efficiency of the TLD in improving the seismic response of an existing building, representative of modern architecture buildings in southern European countries was also evaluated based on linear dynamic analyses
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