18,419 research outputs found
Modified Friedman scenario from the Wheeler-DeWitt equation
We consider the possible modification of the Friedman equation due to
operator ordering parameter entering the Wheeler-DeWitt equation.Comment: 2 pages, 1 figur
Measurement of the complex Faraday angle in thin-film metals and high temperature superconductors
A sensitive polarization modulation technique uses photoelastic modulation
and hetrodyne detection to simultaneously measure the Faraday rotation and
induced ellipticity in light transmitted by semiconducting and metallic
samples. The frequencies measured are in the mid-infrared and correspond to the
spectral lines of a CO2 laser. The measured temperature range is continuous and
extends from 35 to 330K. Measured samples include GaAs and Si substrates, gold
and copper films, and YBCO and BSCCO high temperature superconductors.Comment: 12 pages of text, 6 figures, fixed typos in formulas, added figur
Exchange induced charge inhomogeneities in rippled neutral graphene
A new mechanism that induces charge density variations in corrugated graphene
is proposed. Here it is shown how the interplay between lattice deformations
and exchange interactions can induce charge separation, i.e., puddles of
electrons and holes, for realistic deformation values of the graphene sheet.
The induced charge density lies in the range of cm,
which is compatible with recent measurements.Comment: 4 pages, two figures include
Equilibrium topology of the intermediate state in type-I superconductors of different shapes
High-resolution magneto-optical technique was used to analyze flux patterns
in the intermediate state of bulk Pb samples of various shapes - cones,
hemispheres and discs. Combined with the measurements of macroscopic
magnetization these results allowed studying the effect of bulk pinning and
geometric barrier on the equilibrium structure of the intermediate state.
Zero-bulk pinning discs and slabs show hysteretic behavior due to geometric
barrier that results in a topological hysteresis -- flux tubes on penetration
and lamellae on flux exit. (Hemi)spheres and cones do not have geometric
barrier and show no hysteresis with flux tubes dominating the intermediate
field region. It is concluded that flux tubes represent the equilibrium
topology of the intermediate state in reversible samples, whereas laminar
structure appears in samples with magnetic hysteresis (either bulk or
geometric). Real-time video is available in
http://www.cmpgroup.ameslab.gov/supermaglab/video/Pb.html
NOTE: the submitted images were severely downsampled due to Arxiv's
limitations of 1 Mb total size
Coupled mode effects on energy transfer in weakly coupled, two-temperature plasmas
The effects of collective modes on the temperature relaxation in fully ionized, weakly coupled plasmas are investigated. A coupled mode (CM) formula for the electron-ion energy transfer is derived within the random phase approximation and it is shown how it can be evaluated using standard methods. The CM rates are considerably smaller than rates based on Fermi's golden rule for some parameters and identical for others. It is shown how the CM effects are connected to the occurrence of ion acoustic modes and when they occur. Interestingly, CM effects occur also for plasmas with very high electron temperatures; a regime, where the Landau–Spitzer approach is believed to be accurate
On Urabe's criteria of isochronicity
We give a short proof of Urabe's criteria for the isochronicity of periodical
solutions of the equation . We show that apart from the
harmonic oscillator there exists a large family of isochronous potentials which
must all be non-polynomial and not symmetric (an even function of the
coordinate x).Comment: 8 page
A theoretical approach to thermal noise caused by an inhomogeneously distributed loss -- Physical insight by the advanced modal expansion
We modified the modal expansion, which is the traditional method used to
calculate thermal noise. This advanced modal expansion provides physical
insight about the discrepancy between the actual thermal noise caused by
inhomogeneously distributed loss and the traditional modal expansion. This
discrepancy comes from correlations between the thermal fluctuations of the
resonant modes. The thermal noise spectra estimated by the advanced modal
expansion are consistent with the results of measurements of thermal
fluctuations caused by inhomogeneous losses.Comment: 10 pages, 4 figure
High temperature expansion applied to fermions near Feshbach resonance
We show that, apart from a difference in scale, all of the surprising
recently observed properties of a degenerate Fermi gas near a Feshbach
resonance persist in the high temperature Boltzmann regime. In this regime, the
Feshbach resonance is unshifted. By sweeping across the resonance, a thermal
distribution of bound states (molecules) can be reversibly generated.
Throughout this process, the interaction energy is negative and continuous. We
also show that this behavior must persist at lower temperatures unless there is
a phase transition as the temperature is lowered. We rigorously demonstrate
universal behavior near the resonance.Comment: 4 pages, 4 figures (3 color, 1 BW), RevTeX4; ver4 -- updated
references, changed title -- version accepted for publication in Physical
Review Letter
Evaluation of specific heat for superfluid helium between 0 - 2.1 K based on nonlinear theory
The specific heat of liquid helium was calculated theoretically in the Landau
theory. The results deviate from experimental data in the temperature region of
1.3 - 2.1 K. Many theorists subsequently improved the results of the Landau
theory by applying temperature dependence of the elementary excitation energy.
As well known, many-body system has a total energy of Galilean covariant form.
Therefore, the total energy of liquid helium has a nonlinear form for the
number distribution function. The function form can be determined using the
excitation energy at zero temperature and the latent heat per helium atom at
zero temperature. The nonlinear form produces new temperature dependence for
the excitation energy from Bose condensate. We evaluate the specific heat using
iteration method. The calculation results of the second iteration show good
agreement with the experimental data in the temperature region of 0 - 2.1 K,
where we have only used the elementary excitation energy at 1.1 K.Comment: 6 pages, 3 figures, submitted to Journal of Physics: Conference
Serie
Unified approach to structure factors and neutrino processes in nucleon matter
We present a unified approach to neutrino processes in nucleon matter based
on Landau's theory of Fermi liquids that includes one- and
two-quasiparticle-quasihole pair states as well as mean-field effects. We show
how rates of neutrino processes involving two nucleons may be calculated in
terms of the collision integral in the Landau transport equation for
quasiparticles. Using a relaxation time approximation, we solve the transport
equation for density and spin-density fluctuations and derive a general form
for the response functions. We apply our approach to neutral-current processes
in neutron matter, where the spin response function is crucial for calculations
of neutrino elastic and inelastic scattering, neutrino-pair bremsstrahlung and
absorption from strongly-interacting nucleons. We calculate the relaxation
rates using modern nuclear interactions and including many-body contributions,
and find that rates of neutrino processes are reduced compared with estimates
based on the one-pion exchange interaction, which is used in current
simulations of core-collapse supernovae.Comment: 16 pages, 4 figures; NORDITA-2008-30; published versio
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