20,276 research outputs found
Spin-Charge Decoupling and Orthofermi Quantum Statistics
Currently Gutzwiller projection technique and nested Bethe ansatz are two
main methods used to handle electronic systems in the infinity limit. We
demonstrate that these two approaches describe two distinct physical systems.
In the nested Bethe ansatz solutions, there is a decoupling between the spin
and charge degrees of freedom. Such a decoupling is absent in the Gutzwiller
projection technique. Whereas in the Gutzwiller approach, the usual
antisymmetry of space and spin coordinates is maintained, we show that the
Bethe ansatz wave function is compatible with a new form of quantum statistics,
viz., orthofermi statistics. In this statistics, the wave function is
antisymmetric in spatial coordinates alone. This feature ultimately leads to
spin-charge decoupling.Comment: 12 pages, LaTex Journal_ref: A slightly abridged version of this
paper has appeared as a brief report in Phys. Rev. B, Vol. 63, 132405 (2001
Influence of age on outcome from thrombolysis in acute stroke: a controlled comparison in patients from the Virtual International Stroke Trials Archive (VISTA)
<p><b>Background and Purpose:</b> Thrombolysis for acute ischemic stroke in patients aged >80 years is not approved in some countries due to limited trial data in the very elderly. We compared outcomes between thrombolysed and nonthrombolysed (control) patients from neuroprotection trials to assess any influence of age on response.</p>
<p><b>Method:</b>Among patients with ischemic stroke of known age, pretreatment severity (baseline National Institutes of Health Scale Score), and 90-day outcome (modified Rankin Scale score; National Institutes of Health Scale score), we compared the distribution of modified Rankin score in thrombolysed patients with control subjects by Cochran-Mantel-Haenszel test and then logistic regression after adjustment for age and baseline National Institutes of Health Scale score. We examined patients ≤80 and ≥ 81 years separately and then each age decile.</p>
<p><b>Results:</b> Rankin data were available for 5817 patients, 1585 thrombolysed and 4232 control subjects; 20.5% were aged >80 years (mean ± SD, 85.1 ± 3.4 years). Baseline severity was higher among thrombolysed than control subjects (median National Institutes of Health Scale score 14 versus 13, P<0.05). The distribution of modified Rankin Scale scores was better among thrombolysed patients (P<0.0001; OR, 1.39; 95% CI, 1.26 to 1.54). The association occurred independently with similar magnitude among young (P<0.0001; OR, 1.42; 95% CI, 1.26 to 1.59) and elderly (P=0.002; OR, 1.34; 95% CI, 1.05 to 1.70) patients. ORs were consistent across all age deciles >30 years; outcomes assessed by National Institutes of Health Scale score gave supporting significant findings, and dichotomized modified Rankin Scale score outcomes were also consistent.</p>
<p><b>Conclusions:</b> Outcome after thrombolysis for acute ischemic stroke was significantly better than in control subjects. Despite the expected poorer outcomes among elderly compared with young patients that is independent of any treatment effect, the association between thrombolysis treatment and improved outcome is maintained in the very elderly. Age alone should not be a barrier to treatment.</p>
Vector meson masses in hot nuclear matter : the effect of quantum corrections
The medium modification of vector meson masses is studied taking into account
the quantum correction effects for the hot and dense hadronic matter. In the
framework of Quantum Hadrodynamics, the quantum corrections from the baryon and
scalar meson sectors were earlier computed using a nonperturbative variational
approach through a realignment of the ground state with baryon-antibaryon and
sigma meson condensates. The effect of such corrections was seen to lead to a
softer equation of state giving rise to a lower value for the compressibility
and, an increase in the in-medium baryonic masses than would be reached when
such quantum effects are not taken into account. These quantum corrections
arising from the scalar meson sector result in an increase in the masses of the
vector mesons in the hot and dense matter, as compared to the situation when
only the vacuum polarisation effects from the baryonic sector are taken into
account.Comment: 13 pages revtex file, 6 figure
Current-Induced Spin Polarization in Gallium Nitride
Electrically generated spin polarization is probed directly in bulk GaN using
Kerr rotation spectroscopy. A series of n-type GaN epilayers are grown in the
wurtzite phase both by molecular beam epitaxy (MBE) and metalorganic chemical
vapor deposition (MOCVD) with a variety of doping densities chosen to broadly
modulate the transverse spin lifetime, T2*. The spin polarization is
characterized as a function of electrical excitation energy over a range of
temperatures. Despite weak spin-orbit interactions in GaN, a current-induced
spin polarization (CISP) is observed in the material at temperatures of up to
200 K.Comment: 16 pages, 3 figure
Peristaltic Transport of a Physiological Fluid in an Asymmetric Porous Channel in the Presence of an External Magnetic Field
The paper deals with a theoretical investigation of the peristaltic transport
of a physiological fluid in a porous asymmetric channel under the action of a
magnetic field. The stream function, pressure gradient and axial velocity are
studied by using appropriate analytical and numerical techniques. Effects of
different physical parameters such as permeability, phase difference, wave
amplitude and magnetic parameter on the velocity, pumping characteristics,
streamline pattern and trapping are investigated with particular emphasis. The
computational results are presented in graphical form. The results are found to
be in perfect agreement with those of a previous study carried out for a
non-porous channel in the absence of a magnetic field
Effects of Dirac sea polarization on hadronic properties - A chiral SU(3) approach
The effect of vacuum fluctuations on the in-medium hadronic properties is
investigated using a chiral SU(3) model in the nonlinear realization. The
effect of the baryon Dirac sea is seen to modify hadronic properties and in
contrast to a calculation in mean field approximation it is seen to give rise
to a significant drop of the vector meson masses in hot and dense matter. This
effect is taken into account through the summation of baryonic tadpole diagrams
in the relativistic Hartree approximation (RHA), where the baryon self energy
is modified due to interactions with both the non-strange and the
strange scalar fields.Comment: 25 pages including 13 figures,figure styles modified,few clarifying
sentences added in text, to appear in Phys. Rev.
- âŠ