604 research outputs found
Hole Transport in Impurity Band and Valence Bands Studied in Moderately Doped GaAs:Mn Single Crystals
We report on simple experiment on temperature-dependent Hall effect
measurements in GaMnAs single crystalline samples with Mn composition estimated
at 0.05-0.3 at.% which is slightly below the onset of ferromagnetism. Impurity
band transport is visible for Mn compositions of ~0.3 at.% as a clear metallic
behaviour. The results show interesting situation that the Metal-Insulator
transition in GaAs:Mn occurs within the impurity band which is separated from
the valence bands for Mn concentrations studied here. We also discuss on the
equilibrium high temperature solubility limit of Mn in GaAs, unknown precisely
in the literature.Comment: 9 pages, 2 figures, Proc. of 35th International School on the Physics
of Semiconducting Compounds, Jaszowiec 2007, Poland, to appear in Acta
Physica Polonica A (2007
Lorentz-covariant reduced spin density matrix and EPR-Bohm correlations
We show that it is possible to define a Lorentz-covariant reduced spin
density matrix for massive particles. Such a matrix allows one to calculate the
mean values of observables connected with spin measurements (average
polarizations). Moreover, it contains not only information about polarization
of the particle but also information about its average kinematical state. We
also use our formalism to calculate the correlation function in the
Einstein--Podolsky--Rosen--Bohm type experiment with massive relativistic
particles.Comment: 7 pages, 1 figur
Photon polarization and Wigner's little group
To discuss one-photon polarization states we find an explicit form of the
Wigner's little group element in the massless case for arbitrary Lorentz
transformation. As is well known, when analyzing the transformation properties
of the physical states, only the value of the phase factor is relevant. We show
that this phase factor depends only on the direction of the momentum
and does not depend on the frequency . Finally, we use
this observation to discuss the transformation properties of the linearly
polarized photons and the corresponding reduced density matrix. We find that
they transform properly under Lorentz group.Comment: Version published in Phys. Rev. A, few typos correcte
Destruction of states in quantum mechanics
A description of destruction of states on the grounds of quantum mechanics
rather than quantum field theory is proposed. Several kinds of maps called
supertraces are defined and used to describe the destruction procedure. The
introduced algorithm can be treated as a supplement to the von Neumann-Lueders
measurement. The discussed formalism may be helpful in a description of EPR
type experiments and in quantum information theory.Comment: 14 pp, 1 eps figure, LaTeX2e using iopart class. Final version, will
be published in J. Phys. A: Math. Ge
Hidden Lorentz symmetry of the Hořava–Lifshitz gravity
In this Letter it is shown that the Hořava–Lifshitz gravity theory admits Lorentz symmetry preserving preferred global time foliation of the spacetime
Einstein-Podolsky-Rosen correlations of Dirac particles - quantum field theory approach
We calculate correlation function in the Einstein--Podolsky--Rosen type of
experiment with massive relativistic Dirac particles in the framework of the
quantum field theory formalism. We perform our calculations for states which
are physically interesting and transforms covariantly under the full Lorentz
group action, i.e. for pseudoscalar and vector state.Comment: 9 pages, 2 figures. Published versio
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Concept detection in longitudinal brain MR images using multi-modal cues
Advances in medical imaging techniques and devices has resulted in increased use of imaging in monitoring disease progression in patients. However, extracting decision-enabling information from the resulting longitudinal multi-modal image sets poses a challenge. Radiologists often have to manually identify and quantify certain regions of interest in the longitudinal image sets, which bear upon the patient's condition. As the number of patients increases, the number of longitudinal multi-modal images grows, and the manual annotation and quantification of pathological concepts quickly becomes impractical. In this paper we explore how minimal annotations provided by the user at a few time points can be effectively leveraged to automatically annotate data in the entire multi-modal longitudinal image sets. In particular, we investigate the required number of annotated images per time point and across time for obtaining reasonable results for the entire image set, and what multi-modal cues can help boost the overall annotation results
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