6,905 research outputs found
Spin polarizations and spin Hall currents in a two-dimensional electron gas with magnetic impurities
We consider a two-dimensional electron gas in the presence of Rashba
spin-orbit coupling, and study the effects of magnetic s-wave impurities and
long-range non-magnetic disorder on the spin-charge dynamics of the system. We
focus on voltage induced spin polarizations and their relation to spin Hall
currents. Our results are obtained using the quasiclassical Green function
technique, and hold in the full range of the disorder parameter .Comment: 5 pages, 2 figures. References added, minor stylistic modification
ATLAS RPC offline monitoring and data quality assessment
In this work several aspects of ATLAS RPC offline monitoring and data quality
assessment are illustrated with cosmics data selected by RPC trigger. These
correspond to trigger selection, front-end mapping, detection efficiency and
occupancy, which are studied in terms of low level quantities such as: RPC
off-line hits and standalone tracks. The tools and techniques presented are
also extended to the forthcoming LHC p-p beam collisions.Comment: Poster section at ICHEP08, Philadelphia, USA, July 2008. 3 pages,
LaTeX, 3 eps figure
Tachyons, Scalar Fields and Cosmology
We study the role that tachyon fields may play in cosmology as compared to
the well-established use of minimally coupled scalar fields. We first elaborate
on a kind of correspondence existing between tachyons and minimally coupled
scalar fields; corresponding theories give rise to the same cosmological
evolution for a particular choice of the initial conditions but not for any
other. This leads us to study a specific one-parameter family of tachyonic
models based on a perfect fluid mixed with a positive cosmological constant.
For positive values of the parameter one needs to modify Sen's action and use
the sigma process of resolution of singularities. The physics described by this
model is dramatically different and much richer than that of the corresponding
scalar field. For particular choices of the initial conditions the universe,
that does mimick for a long time a de Sitter-like expansion, ends up in a
finite time in a special type of singularity that we call a "big brake". This
singularity is characterized by an infinite deceleration.Comment: 7 figures. Enlarged discussion of the big brake cosmology.
Continuation of the model clarified. References adde
Theory of scanning gate microscopy
A systematic theory of the conductance measurements of non-invasive (weak
probe) scanning gate microscopy is presented that provides an interpretation of
what precisely is being measured. A scattering approach is used to derive
explicit expressions for the first and second order conductance changes due to
the perturbation by the tip potential in terms of the scattering states of the
unperturbed structure. In the case of a quantum point contact, the first order
correction dominates at the conductance steps and vanishes on the plateaus
where the second order term dominates. Both corrections are non-local for a
generic structure. Only in special cases, such as that of a centrally symmetric
quantum point contact in the conductance quantization regime, can the second
order correction be unambiguously related with the local current density. In
the case of an abrupt quantum point contact we are able to obtain analytic
expressions for the scattering eigenfunctions and thus evaluate the resulting
conductance corrections.Comment: 19 pages, 7 figure
The Natural Role of Mathematics in the Sciences: How Maharishi\u27s Vedic Science Answers the Question of the Unreasonable Effectiveness of Mathematics in the Sciences
Mathematicians and scientists have for a long time tried to understand why mathematics, a subjective creation of the human intellect, is so effective in the sciences, which study the objective, physical world. Satisfactory reasons have not been found because there has not been a comprehensive understanding of the relationship between the subjective and the objective aspects of life. In this paper we will see that Maharishiâs Vedic Science, by explaining the link between the subjective realm where mathematics is located and the objective world that science examines, can resolve this problem in a natural way
KLOE results at the Frascati -factory DANE
The KLOE experiment at the Frascati -factory DANE has collected
about 0.5 fb of data till the end of the year 2002. These data allow to
perform a wide physics program, ranging from the physics of charged and neutral
kaons to radiative -decays. Results are presented for the lifetime
and the semileptonic processes . From the light meson
spectroscopy program, results on the decays as well as are presented.Comment: 5 pages, 3 figures, Proceedings contribution to the 10th Int.
Symposium on "Meson-Nucleon Physics and the Structure of the Nucleon"
(MENU04), Beijing, China, Aug. 30 - Sept. 4, 200
Do supernovae favor tachyonic Big Brake instead de Sitter?
We investigate whether a tachyonic scalar field, encompassing both dark
energy and dark matter-like features will drive our universe towards a Big
Brake singularity or a de Sitter expansion. In doing this it is crucial to
establish the parameter domain of the model, which is compatible with type Ia
supernovae data. We find the 1-sigma contours and evolve the tachyonic sytem
into the future. We conclude, that both future evolutions are allowed by
observations, Big Brake becoming increasingly likely with the increase of the
positive model parameter k.Comment: 8 pages, 6 figures, to be published in the Proceedings of the
Invisible Universe International Conference, Paris, 2009, Ed. J. M. Alimi;
v2: reference
Variable Modified Chaplygin Gas and Accelerating Universe
In this letter, I have proposed a model of variable modified Chaplygin gas
and shown its role in accelerating phase of the universe. I have shown that the
equation of state of this model is valid from the radiation era to quiessence
model. The graphical representations of statefinder parameters characterize
different phase of evolution of the universe. All results presented in the
letter concerns the case .Comment: 7 Latex pages, 5 figures, revtex styl
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