2,070 research outputs found
General relations of heavy quark-antiquark potentials induced by reparameterization invariance
A set of general relations between the spin-independent and spin-dependent
potentials of heavy quark and anti-quark interactions are derived from
reparameterization invariance in the Heavy Quark Effective Theory. It covers
the Gromes relation and includes some new interesting relations which are
useful in understanding the spin-independent and spin-dependent relativistic
corrections to the leading order nonrelativistic potential.Comment: 11 pages, TUIMP-TH-93/54, CCAST-93-3
Energy-Momentum Complex in M\o ller's Tetrad Theory of Gravitation
M\o ller's Tetrad Theory of Gravitation is examined with regard to the
energy-momentum complex. The energy-momentum complex as well as the
superpotential associated with M\o ller's theory are derived. M\o ller's field
equations are solved in the case of spherical symmetry. Two different
solutions, giving rise to the same metric, are obtained. The energy associated
with one solution is found to be twice the energy associated with the other.
Some suggestions to get out of this inconsistency are discussed at the end of
the paper.Comment: LaTeX2e with AMS-LaTeX 1.2, 13 page
Target mass number dependence of subthreshold antiproton production in proton-, deuteron- and alpha-particle-induced reactions
Data from KEK on subthreshold \bar{\mrm{p}} as well as on and
\mrm{K}^\pm production in proton-, deuteron- and -induced reactions
at energies between 2.0 and 12.0 A GeV for C, Cu and Pb targets are described
within a unified approach. We use a model which considers a nuclear reaction as
an incoherent sum over collisions of varying numbers of projectile and target
nucleons. It samples complete events and thus allows for the simultaneous
consideration of all final particles including the decay products of the
nuclear residues. The enormous enhancement of the \bar{\mrm{p}} cross
section, as well as the moderate increase of meson production in deuteron and
induced compared to proton-induced reactions, is well reproduced for
all target nuclei. In our approach, the observed enhancement near the
production threshold is mainly due to the contributions from the interactions
of few-nucleon clusters by simultaneously considering fragmentation processes
of the nuclear residues. The ability of the model to reproduce the target mass
dependence may be considered as a further proof of the validity of the cluster
concept.Comment: 9 pages, 4 figure
Quantum Walk in Position Space with Single Optically Trapped Atoms
The quantum walk is the quantum analogue of the well-known random walk, which
forms the basis for models and applications in many realms of science. Its
properties are markedly different from the classical counterpart and might lead
to extensive applications in quantum information science. In our experiment, we
implemented a quantum walk on the line with single neutral atoms by
deterministically delocalizing them over the sites of a one-dimensional
spin-dependent optical lattice. With the use of site-resolved fluorescence
imaging, the final wave function is characterized by local quantum state
tomography, and its spatial coherence is demonstrated. Our system allows the
observation of the quantum-to-classical transition and paves the way for
applications, such as quantum cellular automata.Comment: 7 pages, 4 figure
Follow-up study of sensory-motor polyneuropathy in Type 1 (insulin-dependent) diabetic subjects after simultaneous pancreas and kidney transplantation and after graft rejection
The influence of successful simultaneous pancreas and kidney transplantation on peripheral polyneuropathy was investigated in 53 patients for a mean observation period of 40.3 months. Seventeen patients were followed-up for more than 3 years. Symptoms and signs were assessed every 6 months using a standard questionnaire, neurological examination and measurement of sensory and motor nerve conduction velocities. While symptoms of polyneuropathy improved (pain, paraesthesia, cramps, restless-legs) and nerve conduction velocity increased, there was no change of clinical signs (sensation, muscle-force, tendon-reflexes). Following kidney-graft-rejection there was a slight decrease of nerve conduction verlocity during the first year, which was not statistically significant. Following pancreas-graft rejection there was no change of nerve conduction velocity during the first year. Comparing the maximum nerve conduction velocity of the patients with pancreas-graft-rejection to the nerve conduction velocities of these patients at the end of the study, there was a statistically significant decrease of 6.5 m/s.
In conclusion, we believe that strict normalization of glucose metabolism alters the progressive course of diabetic polyneuropathy. It may be stabilized or partly reversed after successful grafting even in long-term diabetic patients
New Fermions at ee Colliders: I. Production and Decay
We analyze the production in collisions of new heavy fermions
stemming from extensions of the Standard Model. We write down the most general
expression for the production of two heavy fermions and their subsequent
decays, allowing for the polarization of the ee initial state and
taking into account the final polarization of the fermions. We then discuss the
various decay modes including cascade and three body decays, and the production
mechanisms, both pair production and single production in association with
ordinary fermions.Comment: 21 pages (no figures), Preprint UdeM-LPN-TH-93-15
WormBase 2007
WormBase (www.wormbase.org) is the major publicly available database of information about Caenorhabditis elegans, an important system for basic biological and biomedical research. Derived from the initial ACeDB database of C. elegans genetic and sequence information, WormBase now includes the genomic, anatomical and functional information about C. elegans, other Caenorhabditis species and other nematodes. As such, it is a crucial resource not only for C. elegans biologists but the larger biomedical and bioinformatics communities. Coverage of core areas of C. elegans biology will allow the biomedical community to make full use of the results of intensive molecular genetic analysis and functional genomic studies of this organism. Improved search and display tools, wider cross-species comparisons and extended ontologies are some of the features that will help scientists extend their research and take advantage of other nematode species genome sequences
Class II (DR) antigenexpression on CD8+ lymphocyte subsets in acquired immune deficiency syndrome (AIDS)
Finite-size behaviour of the microcanonical specific heat
For models which exhibit a continuous phase transition in the thermodynamic
limit a numerical study of small systems reveals a non-monotonic behaviour of
the microcanonical specific heat as a function of the system size. This is in
contrast to a treatment in the canonical ensemble where the maximum of the
specific heat increases monotonically with the size of the system. A
phenomenological theory is developed which permits to describe this peculiar
behaviour of the microcanonical specific heat and allows in principle the
determination of microcanonical critical exponents.Comment: 15 pages, 7 figures, submitted to J. Phys.
Review of the k-Body Embedded Ensembles of Gaussian Random Matrices
The embedded ensembles were introduced by Mon and French as physically more
plausible stochastic models of many--body systems governed by one--and
two--body interactions than provided by standard random--matrix theory. We
review several approaches aimed at determining the spectral density, the
spectral fluctuation properties, and the ergodic properties of these ensembles:
moments methods, numerical simulations, the replica trick, the eigenvector
decomposition of the matrix of second moments and supersymmetry, the binary
correlation approximation, and the study of correlations between matrix
elements.Comment: Final version. 29 pages, 4 ps figures, uses iopart.st
- …