867 research outputs found
A prospective randomized trial comparing sequential ganciclovir-high dose acyclovir to high dose acyclovir for prevention of cytomegalovirus disease in adult liver transplant recipients
Cytomegalovirus disease is an important cause of morbidity following liver transplantation. To date there has not been an effective prophylaxis for CMV disease after liver transplantation. One hundred forty-three patients were randomized to receive either high dose oral acyclovir (800 mg 4 times a day) alone for 3 months after transplantation (acyclovir group) or intravenous ganciclovir (5 mg/kg twice a day) for 14 days followed by high dose oral acyclovir to complete a 3-month regimen (ganciclovir group). Of 139 patients available for evaluation, 43 of 71 (61%) patients from the acyclovir group developed CMV infection compared with 16 of 68 (24%) from the ganciclovir group (relative risk, 3.69; 95% confidence interval, 2.07-6.56; PcO.OOOOl). Of those randomized, CMV disease was seen in 20 (28%) of the acyclovir group compared with 6 (9%) of the ganciclovir group (relative risk, 5.11; 95% confidence interval, 2.05-12.75; P=0.0001). The median time to onset of CMV infection was 45 days in the acyclovir group compared with 78 days in the ganciclovir group (P=0.004). The median time to onset of CMV disease was 40 days in the acyclovir group compared with 78 days in the ganciclovir patients (P=0.02). With respect to primary CMV infection, there was no difference in the rates in the 2 groups, but tissue invasive disease and recurrent CMV disease were less frequent in the ganciclovir group. It is concluded that a course of 2 weeks of ganciclovir immediately after transplantation followed by high dose oral acyclovir for 10 weeks is superior to a 12-week course of high dose oral acyclovir alone for prevention of both CMV infection and CMV disease after liver transplantation. However, the lack of significant effect in seronegative recipients who received grafts from seropositive donors suggests that other strategies are needed to prevent CMV infection in this high risk population. © 1994 by Williams & Wilkins
Neutrinos with Mixing in Twisting Magnetic Fields
Transitions in a system of neutrinos with vacuum mixing and magnetic moments,
propagating in matter and transverse magnetic field, are considered. It is
shown that in the realistic case of magnetic field direction varying along the
neutrino path qualitatively new phenomena become possible: permutation of
neutrino conversion resonances, appearance of resonances in the
neutrino-antineutrino () transition
channels, neutrino-antineutrino resonant conversion, large amplitude
oscillations, merging of different
resonances (triple resonances). Possible phenomenological implications of these
effects are briefly discussed.Comment: LaTeX, 35 pages, 4 figures (not included but available upon request).
In memoriam of Ya.A. Smorodinsky. SISSA-170/92/E
Three-generation study of neutrino spin-flavor conversion in supernova and implication for neutrino magnetic moment
We investigate resonant spin-flavor (RSF) conversions of supernova neutrinos
which are induced by the interaction of neutrino magnetic moment and supernova
magnetic fields. From the formulation which includes all three-flavor neutrinos
and anti-neutrinos, we give a new crossing diagram that includes not only
ordinary MSW resonance but also magnetically-induced RSF effect. With the
diagram, it is found that four conversions occur in supernova, two are induced
by the RSF effect and two by the pure MSW. We also numerically calculate
neutrino conversions in supernova matter, using neutrino mixing parameters
inferred from recent experimental results and a realistic supernova progenitor
model. The results indicate that until 0.5 seconds after core bounce, the
RSF-induced transition occurs
efficiently (adiabatic resonance), when \mu_\nu \agt 10^{-12} \mu_B
(B_0 / 5 \times 10^{9} \mathrm G)^{-1}, where is the strength of the
magnetic field at the surface of iron core. We also evaluate the energy
spectrum as a function of at the SuperKamiokande detector and the
Sudbury Neutrino Observatory using the calculated conversion probabilities, and
find that the spectral deformation might have possibility to provide useful
information on neutrino magnetic moment as well as magnetic field strength in
supernovae.Comment: 35 pages, 13 figure
Quantum-mechanical model for particles carrying electric charge and magnetic flux in two dimensions
We propose a simple quantum mechanical equation for particles in two
dimensions, each particle carrying electric charge and magnetic flux. Such
particles appear in (2+1)-dimensional Chern-Simons field theories as charged
vortex soliton solutions, where the ratio of charge to flux is a constant
independent of the specific solution. As an approximation, the charge-flux
interaction is described here by the Aharonov-Bohm potential, and the
charge-charge interaction by the Coulomb one. The equation for two particles,
one with charge and flux () and the other with () where
is a pure number is studied in detail. The bound state problem is solved
exactly for arbitrary and when . The scattering problem is
exactly solved in parabolic coordinates in special cases when takes integers or half integers. In both cases the cross sections obtained
are rather different from that for pure Coulomb scattering.Comment: 12 pages, REVTeX, no figur
K-shell photoionization of ground-state Li-like boron ions [B]: Experiment and Theory
Absolute cross sections for the K-shell photoionization of ground-state
Li-like boron [B(1s2s S)] ions were measured by employing the
ion-photon merged-beams technique at the Advanced Light Source synchrotron
radiation facility. The energy ranges 197.5--200.5 eV, 201.9--202.1 eV of the
[1s(2s\,2p)P]P and [1s(2s\,2p)P] P
resonances, respectively, were investigated using resolving powers of up to
17\,600. The energy range of the experiments was extended to about 238.2 eV
yielding energies of the most prominent
[1s(2\,n)]P resonances with an absolute accuracy
of the order of 130 ppm. The natural linewidths of the [1s(2s\,2p)P]
P and [1s(2s\,2p)P] P resonances were measured
to be meV and meV, respectively, which compare
favourably with theoretical results of 4.40 meV and 30.53 meV determined using
an intermediate coupling R-matrix method.Comment: 6 figures and 2 table
SU(16) grandunification: breaking scales, proton decay and neutrino magnetic moment
We give a detailed renormalization group analysis for the SU(16) grandunified
group with general breaking chains in which quarks and leptons transform
separately at intermediate energies. Our analysis includes the effects of Higgs
bosons. We show that the grandunification scale could be as low as GeV and give examples where new physics could exist at relatively low
energy ( GeV). We consider proton decay in this model and show that
it is consistent with a low grandunification scale. We also discuss the
possible generation of a neutrino magnetic moment in the range of to
with a very small mass by the breaking of the embedded
SU(2) symmetry at a low energy.Comment: (16 pages in REVTEX + 6 figures not included) OITS-49
Resonant Spin-Flavor Conversion of Supernova Neutrinos and Deformation of the Electron Antineutrino Spectrum
The neutrino spin-flavor conversion of \bar\nu_e and \nu_\mu which is induced
by the interaction of the Majorana neutrino magnetic moment and magnetic fields
in the collapse-driven supernova is investigated in detail. We calculate the
conversion probability by using the latest precollapse models of Woosley and
Weaver (1995), and also those of Nomono and Hashimoto (1988), changing the
stellar mass and metallicity in order to estimate the effect of the
astrophysical uncertainties. Contour maps of the conversion probability are
given for all the models as a function of neutrino mass squared difference and
the neutrino magnetic moment times magnetic fields. It is shown that in the
solar metallicity models some observational effects are expected with \Delta
m^2 = 10^{-5}--10^{-1} [eV^2] and \mu_\nu >~ 10^{-12} (10^9 G / B_0) [\mu_B],
where B_0 is the strength of the magnetic fields at the surface of the iron
core. We also find that although the dependence on the stellar models or
stellar mass is not so large, the metallicity of precollapse stars has
considerable effects on this conversion. Such effects may be seen in a
supernova in the Large or Small Magellanic Clouds, and should be taken into
account when one considers an upper bound on \mu_\nu from the SN1987A data.Comment: 19 pages, LaTeX, using revtex. To appear in Phys. Rev. D. 16 figures
attatche
A search for periodic modulations of the solar neutrino flux in Super-Kamiokande-I
A search for periodic modulations of the solar neutrino flux was performed
using the Super-Kamiokande-I data taken from May 31st, 1996 to July 15th, 2001.
The detector's capability of measuring the exact time of events, combined with
a relatively high yield of solar neutrino events, allows a search for
short-time variations in the observed flux. We employed the Lomb test to look
for periodic modulations of the observed solar neutrino flux. The obtained
periodogram is consistent with statistical fluctuation and no significant
periodicity was found
Optically trapped bacteria pairs reveal discrete motile response to control aggregation upon cellâcell approach
Aggregation of bacteria plays a key role in the formation of many biofilms. The critical first step is cellâcell approach, and yet the ability of bacteria to control the likelihood of aggregation during this primary phase is unknown. Here, we use optical tweezers to measure the force between isolated Bacillus subtilis cells during approach. As we move the bacteria towards each other, cell motility (bacterial swimming) initiates the generation of repulsive forces at bacterial separations of ~3 ÎŒm. Moreover, the motile response displays spatial sensitivity with greater cellâcell repulsion evident as inter-bacterial distances decrease. To examine the environmental influence on the inter-bacterial forces, we perform the experiment with bacteria suspended in Tryptic Soy Broth, NaCl solution and deionised water. Our experiments demonstrate that repulsive forces are strongest in systems that inhibit biofilm formation (Tryptic Soy Broth), while attractive forces are weak and rare, even in systems where biofilms develop (NaCl solution). These results reveal that bacteria are able to control the likelihood of aggregation during the approach phase through a discretely modulated motile response. Clearly, the force-generating motility we observe during approach promotes biofilm prevention, rather than biofilm formation
Collisional kinetics of non-uniform electric field, low-pressure, direct-current discharges in H
A model of the collisional kinetics of energetic hydrogen atoms, molecules,
and ions in pure H discharges is used to predict H emission
profiles and spatial distributions of emission from the cathode regions of
low-pressure, weakly-ionized discharges for comparison with a wide variety of
experiments. Positive and negative ion energy distributions are also predicted.
The model developed for spatially uniform electric fields and current densities
less than A/m is extended to non-uniform electric fields, current
densities of A/m, and electric field to gas density ratios MTd at 0.002 to 5 Torr pressure. (1 Td = V m and 1 Torr =
133 Pa) The observed far-wing Doppler broadening and spatial distribution of
the H emission is consistent with reactions among H, H,
H, and H ions, fast H atoms, and fast H molecules, and with
reflection, excitation, and attachment to fast H atoms at surfaces. The
H excitation and H formation occur principally by collisions of
fast H, fast H, and H with H. Simplifications include using a
one-dimensional geometry, a multi-beam transport model, and the average
cathode-fall electric field. The H emission is linear with current
density over eight orders of magnitude. The calculated ion energy distributions
agree satisfactorily with experiment for H and H, but are only in
qualitative agreement for H and H. The experiments successfully modeled
range from short-gap, parallel-plane glow discharges to beam-like,
electrostatic-confinement discharges.Comment: Submitted to Plasmas Sources Science and Technology 8/18/201
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