50,146 research outputs found
Limiting dynamics for spherical models of spin glasses at high temperature
We analyze the coupled non-linear integro-differential equations whose
solutions is the thermodynamical limit of the empirical correlation and
response functions in the Langevin dynamics for spherical p-spin disordered
mean-field models. We provide a mathematically rigorous derivation of their FDT
solution (for the high temperature regime) and of certain key properties of
this solution, which are in agreement with earlier derivations based on
physical grounds
Interplay between localization and absorption in disordered waveguides
This work presents results of ab-initio simulations of continuous wave
transport in disordered absorbing waveguides. Wave interference effects cause
deviations from diffusive picture of wave transport and make the diffusion
coefficient position- and absorption-dependent. As a consequence, the true
limit of a zero diffusion coefficient is never reached in an absorbing random
medium of infinite size, instead, the diffusion coefficient saturates at some
finite constant value. Transition to this absorption-limited diffusion exhibits
a universality which can be captured within the framework of the
self-consistent theory (SCT) of localization. The results of this work (i)
justify use of SCT in analyses of experiments in localized regime, provided
that absorption is not weak; (ii) open the possibility of diffusive description
of wave transport in the saturation regime even when localization effects are
strong.Comment: 10 pages, 3 figure
Ram Pressure Stripping of Spiral Galaxies in Clusters
We use 3-dimensional SPH/N-BODY simulations to study ram pressure stripping
of gas from spiral galaxies orbiting in clusters. We find that the analytic
expectation of Gunn & Gott (1972) relating the gravitational restoring force
provided by the disk to the ram pressure force, provides a good approximation
to the radius that gas will be stripped from a galaxy. However, at small radii
it is also important to consider the potential provided by the bulge component.
A spiral galaxy passing through the core of a rich cluster such as Coma, will
have its gaseous disk truncated to kpc, thus losing of its
diffuse gas mass. The timescale for this to occur is a fraction of a crossing
time years. Galaxies orbiting within poorer clusters, or inclined
to the direction of motion through the intra-cluster medium will lose
significantly less gas. We conclude that ram-pressure alone is insufficient to
account for the rapid and widespread truncation of star-formation observed in
cluster galaxies, or the morphological transformation of Sab's to S0's that is
necessary to explain the Butcher-Oemler effect.Comment: 8 pages, 7 figures, to be published in MNRAS. Levels added/corrected
on figures 3, 4 and
Re-visit of HST FUV observations of hot-Jupiter system HD 209458: No Si III detection and the need for COS transit observations
The discovery of OI atoms and CII ions in the upper atmosphere of HD 209458b,
made with the Hubble Space Telescope Imaging Spectrograph (STIS) using the
G140L grating, showed that these heavy species fill an area comparable to the
planet's Roche lobe. The derived ~10% transit absorption depths require
super-thermal processes and/or supersolar abundances. From subsequent Cosmic
Origins Spectrograph (COS) observations, CII absorption was reported with
tentative velocity signatures, and absorption by SiIII ions was also claimed in
disagreement with a negative STIS G140L detection. Here, we revisit the COS
dataset showing a severe limitation in the published results from having
contrasted the in-transit spectrum against a stellar spectrum averaged from
separate observations, at planetary phases 0.27, 0.72, and 0.49. We find
variable stellar SiIII and CII emissions that were significantly depressed not
only during transit but also at phase 0.27 compared to phases 0.72 and 0.49.
Their respective off-transit 7.5 and 3.1% flux variations are large compared to
their reported 8.2+/-1.4% and 7.8+/-1.3% transit absorptions. Significant
variations also appear in the stellar line shapes, questioning reported
velocity signatures. We furthermore present archive STIS G140M transit data
consistent with no SiIII absorption, with a negative result of 1.7+/-18.7
including ~15% variability. Silicon may still be present at lower ionization
states, in parallel with the recent detection of extended magnesium, as MgI
atoms. In this frame, the firm detection of OI and CII implying solar or
supersolar abundances contradicts the recent inference of potential x20-125
subsolar metallicity for HD 209458b.Comment: Accepted for publication in Ap
Geoengineering: Whiter skies?
One proposed side effect of geoengineering with stratospheric sulfate aerosols is sky whitening during the day and afterglows near sunset, as is seen after large volcanic eruptions. Sulfate aerosols in the stratosphere would increase diffuse light received at the surface, but with a non-uniform spectral distribution. We use a radiative transfer model to calculate spectral irradiance for idealized size distributions of sulfate aerosols. A 2% reduction in total irradiance, approximately enough to offset anthropogenic warming for a doubling of CO_2 concentrations, brightens the sky (increase in diffuse light) by 3 to 5 times, depending on the aerosol size distribution. The relative increase is less when optically thin cirrus clouds are included in our simulations. Particles with small radii have little influence on the shape of the spectra. Particles of radius ∼0.5 μm preferentially increase diffuse irradiance in red wavelengths, whereas large particles (∼0.9 μm) preferentially increase diffuse irradiance in blue wavelengths. Spectra show little change in dominant wavelength, indicating little change in sky hue, but all particle size distributions produce an increase in white light relative to clear sky conditions. Diffuse sky spectra in our simulations of geoengineering with stratospheric aerosols are similar to those of average conditions in urban areas today
Georgia Water: "A Public Resource Or A Commodity" What Are The Real Policy Questions?
In this paper we first address the question as to the strength of Georgia's commitment to protect public interests in the state's water resources as such commitments are expressed in existing laws. Comparing legislative declarations of state policy in Georgia with those in 36 other Eastern States, we find that none of the states have expressions of this commitment that would reasonably be regarded as more strongly stated than Georgia law. In conclusion, we find that Georgia water law currently recognizes the public's dependence on the state's water resources and its commitment to policies and programs that assure that water is used prudently for the maximum benefit of the people. Adding "public resource" language to the law would not substantively strengthen these existing policy declarations.Attention is then turned to the "water as a commodity" issue. We argue here that the "water as a commodity" issues is at best poorly framed. In our view debate in Georgia should center on alternatives for resolving the reallocation issue; it should focus on the question as to how Georgia is to strike a balance between private, competing use of water and public, non-competing uses of water (e.g., instream flows), and how this balance is to be adjusted over time in response to changes in social, environmental, and climatic conditions. When market mechanisms are considered as one of the means to achieve reallocation, evaluation of their effectiveness is dependent on a particular set of market institutions. Thus, being "for" or "against" markets makes no more sense that being "for" or "against" water use permits -- everything depends on the provisions and protections of specific laws and proposals. Working Paper # 2002-00
Gross loan flows
Changes in net lending hide the much larger and more variable gross lending flows. We present a series of stylized facts about gross loan flows and how they vary over time, bank size, and the business cycle. We look at both the intensive (increases and decreases) and extensive (entry and exits) margins. We compare these results with the output from a simple stochastic search model.Bank loans ; Business cycles
- …