3,735 research outputs found
Robustly Unstable Eigenmodes of the Magnetoshearing Instability in Accretion Disk
The stability of nonaxisymmetric perturbations in differentially rotating
astrophysical accretion disks is analyzed by fully incorporating the properties
of shear flows. We verify the presence of discrete unstable eigenmodes with
complex and pure imaginary eigenvalues, without any artificial disk edge
boundaries, unlike Ogilvie & Pringle(1996)'s claim. By developing the
mathematical theory of a non-self-adjoint system, we investigate the nonlocal
behavior of eigenmodes in the vicinity of Alfven singularities at
omega_D=omega_A, where omega_D is the Doppler-shifted wave frequency and
omega_A=k_// v_A is the Alfven frequency. The structure of the spectrum of
discrete eigenmodes is discussed and the magnetic field and wavenumber
dependence of the growth rate are obtained. Exponentially growing modes are
present even in a region where the local dispersion relation theory claims to
have stable eigenvalues. The velocity field created by an eigenmode is
obtained, which explains the anomalous angular momentum transport in the
nonlinear stage of this stability.Comment: 11pages, 11figures, to be published in ApJ. For associated eps files,
see http://dino.ph.utexas.edu/~knoguchi
Human Tâcell lymphotrophic virus in solidâorgan transplant recipients: Guidelines from the American society of transplantation infectious diseases community of practice
These updated guidelines from the Infectious Diseases Community of Practice of the American Society of Transplantation review the diagnosis, prevention, and management of Human Tâcell lymphotrophic virus 1 (HTLV)â1 in the preâ and postâtransplant period. HTLVâ1 is an oncogenic human retrovirus rare in North America but endemic in the Caribbean and parts of Africa, South America, Asia, and Oceania. While most infected persons do not develop disease, <5% will develop adult Tâcell leukemia/lymphoma or neurological disease. No proven antiviral treatment for established HTLVâ1 infection is available. The effect of immunosuppression on the development of HTLVâ1âassociated disease in asymptomatically infected recipients is not well characterized, and HTLVâ1âinfected individuals should be counseled that immunosuppression may increase the risk of developing HTLVâ1âassociated disease and they should be monitored postâtransplant for HTLVâ1âassociated disease. Currently approved screening assays do not distinguish between HTLVâ1 and HTLVâ2, and routine screening of deceased donors without risk factors in low seroprevalence areas is likely to result in significant organ wastage and is not recommended. Targeted screening of donors with risk factors for HTLVâ1 infection and of living donors (as time is available to perform confirmatory tests) is reasonable.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/151899/1/ctr13575.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151899/2/ctr13575_am.pd
Tilted-Cone Induced Cusps and Nonmonotonic Structures in Dynamical Polarization Function of Massless Dirac Fermions
The polarization function of electrons with the tilted Dirac cone found in
organic conductors is studied using the tilted Weyl equation. The dynamical
property is explored based on the analytical treatment of the particle-hole
excitation. It is shown that the polarization function as the function of both
the frequency and the momentum exhibits cusps and nonmonotonic structures. The
polarization function depends not only on the magnitude but also the direction
of the external momentum. These properties are characteristic of the tilted
Dirac cone, and are contrast to the isotropic case of grapheme. Further, the
results are applied to calculate the optical conductivity, the plasma frequency
and the screening of Coulomb interaction, which are also strongly influenced by
the tilted cone.Comment: 28 pages, 12 figures, to be published in Journal of the Physical
Society of Japan Vol. 79 (2010) No. 1
Aperiodic quantum oscillations of particle-hole asymmetric Dirac cones
We report experimental measurements and theoretical analysis of Shubnikov-de
Haas (SdH) oscillations in a Dirac cone system: the a-(BEDT-TTF)2I3 organic
metal under hydrostatic pressure. The measured SdH oscillations reveal
anomalies at high magnetic fields B where the 1/B oscillations periodicity is
lost above 7 T. We interpret these unusual results within a theoretical model
that takes into account intrinsic distortions of the a-(BEDT-TTF)2I3 Dirac
cones such as a parabolic particle-hole asymmetric correction. Others possible
causes, such as a cone tilting or a Zeeman effect, are carefully ruled out. The
observations are consistent among a-(BEDT-TTF)2I3 samples with different Fermi
levels
Muon Acceleration in Cosmic-ray Sources
Many models of ultra-high energy cosmic-ray production involve acceleration
in linear accelerators located in Gamma-Ray Bursts magnetars, or other sources.
These source models require very high accelerating gradients, keV/cm,
with the minimum gradient set by the length of the source. At gradients above
1.6 keV/cm, muons produced by hadronic interactions undergo significant
acceleration before they decay. This acceleration hardens the neutrino energy
spectrum and greatly increases the high-energy neutrino flux. We rule out many
models of linear acceleration, setting strong constraints on plasma wakefield
accelerators and on models for sources like Gamma Ray Bursts and magnetars.Comment: 5 pgs. submitted for publicatio
Temperature Dependence of Spin Correlation and Charge Dynamics in the Stripe Phase of High-T_c Superconductors
We examine the temperature dependence of the electronic states in the stripe
phase of high-Tc cuprates by using the t-J model with a potential that
stabilizes vertical charge stripes. Charge and spin-correlation functions and
optical conductivity are calculated by using finite-temperature Lanczos method.
At zero temperature, the antiferromagnetic correlation between a spin in a
charge stripe and that in a spin domain adjacent to the stripe is weak, since
the charge stripe and the spin domain are almost separated. With increasing
temperature, the correlation increases and then decreases toward high
temperature. This is in contrast to other correlations that decrease
monotonically. From the examination of the charge dynamics, we find that this
anomalous temperature dependence of the correlation is the consequence of a
crossover from one-dimensional electronic states to two-dimensional ones.Comment: 7 pages in two-column format, 6 figures, to be published in Phys.
Rev.
Strong magnetic field dependence of critical current densities and vortex activation energies in an anisotropic clean MgB2 thin film
We report the influence of two-band superconductivity on the flux creep and the critical current densities of a MgB2 thin film. The small magnetic penetration depth of lambda=50 +/- 10 nm at T=4 K is related to a clean pi-band. We find a high self-field critical current density J(C), which is strongly reduced with applied magnetic field, and attribute this to suppression of the superconductivity in the pi-band. The temperature dependence of the creep rate S (T) at low magnetic field can be explained by a simple Anderson-Kim mechanism. The system shows high pinning energies at low field that are strongly suppressed by high field. (C) 2014 Elsevier Ltd. All rights reserved.X1112Ysciescopu
Magnetic phase separation in ordered alloys
We present a lattice model to study the equilibrium phase diagram of ordered
alloys with one magnetic component that exhibits a low temperature phase
separation between paramagnetic and ferromagnetic phases. The model is
constructed from the experimental facts observed in CuAlMn and it
includes coupling between configurational and magnetic degrees of freedom which
are appropriated for reproducing the low temperature miscibility gap. The
essential ingredient for the occurrence of such a coexistence region is the
development of ferromagnetic order induced by the long-range atomic order of
the magnetic component. A comparative study of both mean-field and Monte Carlo
solutions is presented. Moreover, the model may enable the study of the
structure of the ferromagnetic domains embedded in the non-magnetic matrix.
This is relevant in relation to phenomena such as magnetoresistance and
paramagnetism.Comment: 12 pages, 11 figures, accepted in Phys. Rev.
Zettawatt-Exawatt Lasers and Their Applications in Ultrastrong-Field Physics: High Energy Front
Since its birth, the laser has been extraordinarily effective in the study
and applications of laser-matter interaction at the atomic and molecular level
and in the nonlinear optics of the bound electron. In its early life, the laser
was associated with the physics of electron volts and of the chemical bond.
Over the past fifteen years, however, we have seen a surge in our ability to
produce high intensities, five to six orders of magnitude higher than was
possible before. At these intensities, particles, electrons and protons,
acquire kinetic energy in the mega-electron-volt range through interaction with
intense laser fields. This opens a new age for the laser, the age of nonlinear
relativistic optics coupling even with nuclear physics. We suggest a path to
reach an extremely high-intensity level W/cm in the coming
decade, much beyond the current and near future intensity regime W/cm, taking advantage of the megajoule laser facilities. Such a laser at
extreme high intensity could accelerate particles to frontiers of high energy,
tera-electron-volt and peta-electron-volt, and would become a tool of
fundamental physics encompassing particle physics, gravitational physics,
nonlinear field theory, ultrahigh-pressure physics, astrophysics, and
cosmology. We focus our attention on high-energy applications in particular and
the possibility of merged reinforcement of high-energy physics and ultraintense
laser.Comment: 25 pages. 1 figur
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