31,715 research outputs found
Investigation of line-of-sight propagation in dense atmosphere, phase 3, part 1
The investigation of microwave absorption in the 1 to 10 GHz frequency band by the Jovian atmosphere has continued, and an estimate of the strength of signal fading at these frequencies due to layers of turbulence in Jupiter's atmosphere is given. The microwave absorption due to gaseous ammonia is estimated both in terms of a power loss in dB/km, and in total power loss in dB for slant-path communication with a probe at altitudes down to pressures of several tens of atmospheres. The graphs indicate a frequency-squared scaling of the absorption, and appreciable losses at altitudes where the pressure is several atmospheres. An estimate of turbulence strength is given. This may turn out to be quite crude considering the absence of any relevant data. A planetary scaling law which appears to hold reasonably well for Earth to Venus, is extrapolated to Jupiter. No reasonable modifications of the estimate can alter the conclusion that direct-path fading is negligible for pressure regimes up to 20 atm
Nominal Wage Rigidities in Mexico: Evidence from Social Security Records
This paper analyses the existence and extent of downward nominal wage rigidities in the Mexican labor market using data from the administrative records of the Mexican Social Security Institute (IMSS). This longitudinal, firm-level dataset allows us to track workers employed with the same firm, observe their wage profiles and calculate the nominal-wage changes they experience over time. Based on the estimated density functions of nominal wage changes and other moments of the distribution, we are able to calculate several standard tests of nominal wage rigidity that have been proposed in the literature. Furthermore, we extend these tests to take into account the presence of minimum wage laws that may affect the distribution of nominal wage changes. The densities and tests calculated using these date are similar to those obtained using administrative data from other countries, and constitute a significant improvement over the measures of nominal wage rigidities obtained from household survey data. We find considerably more wage rigidity than previous estimates obtained for Mexico using data from the National Urban Employment Survey suggest. Furthermore, we find evidence that the extent of nominal wage rigidities has been falling over time. We also document the importance of minimum wages in the Mexican labor market, as evidenced by the large fraction of minimum wage earners and the widespread indexation of wage changes to the minimum wage increases.
Lattice formulation of (2,2) supersymmetric gauge theories with matter fields
We construct lattice actions for a variety of (2,2) supersymmetric gauge
theories in two dimensions with matter fields interacting via a superpotential.Comment: 13 pages, 2 figures. Appendix added, references updated, typos fixe
Periodic orbit effects on conductance peak heights in a chaotic quantum dot
We study the effects of short-time classical dynamics on the distribution of
Coulomb blockade peak heights in a chaotic quantum dot. The location of one or
both leads relative to the short unstable orbits, as well as relative to the
symmetry lines, can have large effects on the moments and on the head and tail
of the conductance distribution. We study these effects analytically as a
function of the stability exponent of the orbits involved, and also numerically
using the stadium billiard as a model. The predicted behavior is robust,
depending only on the short-time behavior of the many-body quantum system, and
consequently insensitive to moderate-sized perturbations.Comment: 14 pages, including 6 figure
An alternative to the plasma emission model: Particle-In-Cell, self-consistent electromagnetic wave emission simulations of solar type III radio bursts
1.5D PIC, relativistic, fully electromagnetic (EM) simulations are used to
model EM wave emission generation in the context of solar type III radio
bursts. The model studies generation of EM waves by a super-thermal, hot beam
of electrons injected into a plasma thread that contains uniform longitudinal
magnetic field and a parabolic density gradient. In effect, a single magnetic
line connecting Sun to earth is considered, for which several cases are
studied. (i) We find that the physical system without a beam is stable and only
low amplitude level EM drift waves (noise) are excited. (ii) The beam injection
direction is controlled by setting either longitudinal or oblique electron
initial drift speed, i.e. by setting the beam pitch angle. In the case of zero
pitch angle, the beam excites only electrostatic, standing waves, oscillating
at plasma frequency, in the beam injection spatial location, and only low level
EM drift wave noise is also generated. (iii) In the case of oblique beam pitch
angles, again electrostatic waves with same properties are excited. However,
now the beam also generates EM waves with the properties commensurate to type
III radio bursts. The latter is evidenced by the wavelet analysis of transverse
electric field component, which shows that as the beam moves to the regions of
lower density, frequency of the EM waves drops accordingly. (iv) When the
density gradient is removed, electron beam with an oblique pitch angle still
generates the EM radiation. However, in the latter case no frequency decrease
is seen. Within the limitations of the model, the study presents the first
attempt to produce simulated dynamical spectrum of type III radio bursts in
fully kinetic plasma model. The latter is based on 1.5D non-zero pitch angle
(non-gyrotropic) electron beam, that is an alternative to the plasma emission
classical mechanism.Comment: Physics of Plasmas, in press, May 2011 issue (final accepted version
Neutrino Oscillations as a Probe of Dark Energy
We consider a class of theories in which neutrino masses depend significantly
on environment, as a result of interactions with the dark sector. Such theories
of mass varying neutrinos (MaVaNs) were recently introduced to explain the
origin of the cosmological dark energy density and why its magnitude is
apparently coincidental with that of neutrino mass splittings. In this Letter
we argue that in such theories neutrinos can exhibit different masses in matter
and in vacuum, dramatically affecting neutrino oscillations. Both long and
short baseline experiments are essential to test for these interactions. As an
example of modifications to the standard picture, we consider simple models
which may simultaneously account for the LSND anomaly, KamLAND, K2K and studies
of solar and atmospheric neutrinos, while providing motivation to continue to
search for neutrino oscillations in short baseline experiments such as BooNE.Comment: 5 pages, 1 figure, refs added, additional data considered, minor
change in conclusions about LSN
Anomaly Cancellation in 2+1 dimensions in the presence of a domainwall mass
A Fermion in 2+1 dimensions, with a mass function which depends on one
spatial coordinate and passes through a zero ( a domain wall mass), is
considered. In this model, originally proposed by Callan and Harvey, the gauge
variation of the effective gauge action mainly consists of two terms. One comes
from the induced Chern-Simons term and the other from the chiral fermions,
bound to the 1+1 dimensional wall, and they are expected to cancel each other.
Though there exist arguments in favour of this, based on the possible forms of
the effective action valid far from the wall and some facts about theories of
chiral fermions in 1+1 dimensions, a complete calculation is lacking. In this
paper we present an explicit calculation of this cancellation at one loop valid
even close to the wall. We show that, integrating out the ``massive'' modes of
the theory does produce the Chern-Simons term, as appreciated previously. In
addition we show that it generates a term that softens the high energy
behaviour of the 1+1 dimensional effective chiral theory thereby resolving an
ambiguity present in a general 1+1 dimensional theory.Comment: 17 pages, LaTex file, CU-TP-61
Brownian Motion Model of Quantization Ambiguity and Universality in Chaotic Systems
We examine spectral equilibration of quantum chaotic spectra to universal
statistics, in the context of the Brownian motion model. Two competing time
scales, proportional and inversely proportional to the classical relaxation
time, jointly govern the equilibration process. Multiplicity of quantum systems
having the same semiclassical limit is not sufficient to obtain equilibration
of any spectral modes in two-dimensional systems, while in three-dimensional
systems equilibration for some spectral modes is possible if the classical
relaxation rate is slow. Connections are made with upper bounds on
semiclassical accuracy and with fidelity decay in the presence of a weak
perturbation.Comment: 13 pages, 6 figures, submitted to Phys Rev
Neutrino-Deuteron Scattering in Effective Field Theory at Next-to-Next-to Leading Order
We study the four channels associated with neutrino-deuteron breakup
reactions at next-to-next to leading order in effective field theory. We find
that the total cross-section is indeed converging for neutrino energies up to
20 MeV, and thus our calculations can provide constraints on theoretical
uncertainties for the Sudbury Neutrino Observatory. We stress the importance of
a direct experimental measurement to high precision in at least one channel, in
order to fix an axial two-body counterterm.Comment: 32 pages, 14 figures (eps
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