1,149 research outputs found
A Stepwise Planned Approach to the Solution of Hilbert's Sixth Problem. III : Measurements and von Neumann Projection/Collapse Rule
Supmech, the universal mechanics developed in the previous two papers,
accommodates both quantum and classical mechanics as subdisciplines (a brief
outline is included for completeness); this feature facilitates, in a supmech
based treatment of quantum measurements, an unambiguous treatment of the
apparatus as a quantum system approximated well by a classical one. Taking
explicitly into consideration the fact that observations on the apparatus are
made when it has `settled down after the measurement interaction' and are
restricted to macroscopically distinguishable pointer readings, the unwanted
superpositions of (system + apparatus) states are shown to be suppressed; this
provides a genuinely physics based justification for the (traditionally
\emph{postulated}) von Neumann projection/collapse rule. The decoherence
mechanism brought into play by the stated observational constraints is free
from the objections against the traditional decoherence program.Comment: 29 pages; one section and two references added; results unchange
Relativistic Tunneling Through Two Successive Barriers
We study the relativistic quantum mechanical problem of a Dirac particle
tunneling through two successive electrostatic barriers. Our aim is to study
the emergence of the so-called \emph{Generalized Hartman Effect}, an effect
observed in the context of nonrelativistic tunneling as well as in its
electromagnetic counterparts, and which is often associated with the
possibility of superluminal velocities in the tunneling process. We discuss the
behavior of both the phase (or group) tunneling time and the dwell time, and
show that in the limit of opaque barriers the relativistic theory also allows
the emergence of the Generalized Hartman Effect. We compare our results with
the nonrelativistic ones and discuss their interpretation.Comment: 7 pages, 3 figures. Revised version, with a new appendix added.
Slightly changes in the styles and captions of Figures 1 and 2. To appear in
Physical Review
Predicting speech fluency and naming abilities in aphasic patients
There is a need to identify biomarkers that predict degree of chronic speech fluency/language impairment and potential for improvement after stroke. We previously showed that the Arcuate Fasciculus lesion load (AF-LL), a combined variable of lesion site and size, predicted speech fluency in patients with chronic aphasia. In the current study, we compared lesion loads of such a structural map (i.e., AF-LL) with those of a functional map [i.e., the functional gray matter lesion load (fGM-LL)] in their ability to predict speech fluency and naming performance in a large group of patients. The fGM map was constructed from functional brain images acquired during an overt speaking task in a group of healthy elderly controls. The AF map was reconstructed from high-resolution diffusion tensor images also from a group of healthy elderly controls. In addition to these two canonical maps, a combined AF-fGM map was derived from summing fGM and AF maps. Each canonical map was overlaid with individual lesion masks of 50 chronic aphasic patients with varying degrees of impairment in speech production and fluency to calculate a functional and structural lesion load value for each patient, and to regress these values with measures of speech fluency and naming. We found that both AF-LL and fGM-LL independently predicted speech fluency and naming ability; however, AF lesion load explained most of the variance for both measures. The combined AF-fGM lesion load did not have a higher predictability than either AF-LL or fGM-LL alone. Clustering and classification methods confirmed that AF lesion load was best at stratifying patients into severe and non-severe outcome groups with 96% accuracy for speech fluency and 90% accuracy for naming. An AF-LL of greater than 4 cc was the critical threshold that determined poor fluency and naming outcomes, and constitutes the severe outcome group. Thus, surrogate markers of impairments have the potential to predict outcomes and can be used as a stratifier in experimental studies
Search for via the transition at LHCb and factory
It is interesting to study the characteristics of the whole family of
which contains two different heavy flavors. LHC and the proposed factory
provide an opportunity because a large database on the family will be
achieved. and its excited states can be identified via their decay modes.
As suggested by experimentalists, is not easy to be
clearly measured, instead, the trajectories of and occurring in
the decay of () can be unambiguously
identified, thus the measurement seems easier and more reliable, therefore this
mode is more favorable at early running stage of LHCb and the proposed
factory. In this work, we calculate the rate of
in terms of the QCD multipole-expansion and the numerical results indicate that
the experimental measurements with the luminosity of LHC and factory are
feasible.Comment: 12 pages, 1 figures and 4 tables, acceptted by SCIENCE CHINA Physics,
Mechanics & Astronomy (Science in China Series G
Radiation of Neutron Stars Produced by Superfluid Core
We find that neutron star interior is transparent for collisionless electron
sound, the same way as it is transparent for neutrinos. In the presence of
magnetic field the electron sound is coupled with electromagnetic radiation and
form the fast magnetosonic wave. We find that electron sound is generated by
superfluid vortices in the stellar core. Thermally excited helical vortex waves
produce fast magnetosonic waves in the stellar crust which propagate toward the
surface and transform into outgoing electromagnetic radiation. The vortex
radiation has the spectral index -0.45 and can explain nonthermal radiation of
middle-aged pulsars observed in the infrared, optical and hard X-ray bands. The
radiation is produced in the stellar interior which allows direct determination
of the core temperature. Comparing the theory with available spectra
observations we find that the core temperature of the Vela pulsar is T=8*10^8K,
while the core temperature of PSR B0656+14 and Geminga exceeds 2*10^8K. This is
the first measurement of the temperature of a neutron star core. The
temperature estimate rules out equation of states incorporating Bose
condensations of pions or kaons and quark matter in these objects. Based on the
temperature estimate and cooling models we determine the critical temperature
of triplet neutron superfluidity in the Vela core Tc=(7.5\pm 1.5)*10^9K which
agrees well with recent data on behavior of nucleon interactions at high
energies. Another finding is that in the middle aged neutron stars the vortex
radiation, rather then thermal conductivity, is the main mechanism of heat
transfer from the stellar core to the surface. Electron sound opens a
perspective of direct spectroscopic study of superdense matter in the neutron
star interiors.Comment: 43 pages, 7 figures, to appear in Astrophysical Journa
Inclusive Particle Spectra at RHIC
A simulation is performed of the recently reported data from PHOBOS at
energies of 56 and 130 A GeV using the relativistic heavy ion cascade LUCIFER
which had previously given a good description of the NA49 inclusive spectra at
E=17.2 A GeV. The results compare well with these early measurements at RHIC.Comment: 4 pages, 2 figure
The magnetic dipole transitions in the binding system
The magnetic dipole transitions between the vector mesons and their
relevant pseudoscalar mesons (, , , ,
and etc, the binding states of system) of
the family are interesting. To see the `hyperfine' splitting due to
spin-spin interaction is an important topic for understanding the spin-spin
interaction and the spectrum of the the binding system. The
knowledge about the magnetic dipole transitions is also very useful for
identifying the vector boson mesons experimentally, whose masses are
just slightly above the masses of their relevant pseudoscalar mesons
accordingly. Considering the possibility to observe the vector mesons via the
transitions at factory and the potentially usages of the theoretical
estimate on the transitions, we fucus our efforts on calculating the magnetic
dipole transitions, i.e. precisely to calculate the rates for the transitions
such as decays and , and particularly
work in the Behte-Salpeter framework. In the estimate, as a typical example, we
carefully investigate the dependance of the rate
on the mass difference as well.Comment: 10 pages, 2 figures, 1 tabl
Mesons with Beauty and Charm: Spectroscopy
Applying knowledge of the interaction between heavy quarks derived from the
study of and bound states, we calculate the
spectrum of mesons. We compute transition rates for the
electromagnetic and hadronic cascades that lead from excited states to the
ground state, and briefly consider the prospects for
experimental observation of the spectrum.Comment: 32 pages + 2 uuencoded PostScript figures Fermilab-Pub-94/032-
Flavor and Spin Contents of the Nucleon in the Quark Model with Chiral Symmetry
A simple calculation in the framework of the chiral quark theory of Manohar
and Georgi yields results that can account for many of the ''failures'' of the
naive quark model: significant strange quark content in the nucleon as
indicated by the value of the -
asymmetry in the nucleon as measured by the deviation from Gottfried sum rule
and by the Drell-Yan process, as well as the various quark contributions to the
nucleon spin as measured by the deep inelastic polarized lepton-nucleon
scatterings.Comment: figure has been separated from tex file. No other changes. Preprint
CMU-HEP94-3
J/Psi Suppression in Heavy Ion Collisions at the CERN SPS
We reexamine the production of J/Psi and other charmonium states for a
variety of target-projectile choices at the SPS. For this study we use a newly
constructed cascade code LUCIFER II, which yields acceptable descriptions of
both hard and soft processes, specifically Drell-Yan and hidden charm
production, and soft energy loss and meson production, at the SPS. Glauber
calculations of other authors are redone, and compared directly to the cascade
results. The modeling of the charmonium states differs from that of earlier
workers in its unified treatment of the hidden charm meson spectrum, which is
introduced from the outset as a set of coupled states. The result is a
description of the NA38 and NA50 data in terms of a conventional hadronic
picture. The apparently anomalous suppression found in the most massive Pb+Pb
system arises from three sources: destruction in the initial nucleon-nucleon
cascade, use of coupled channels to exploit the larger breakup in the less
bound Chi and Psi' states, and comover interaction in the final low energy
phase.Comment: 36 pages (15 figures
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