627 research outputs found
Valuation, Adverse Selection, and Market Collapses
We study a market for funding real investment where valuation—meaning investors devoting resources to acquiring information about future payoffs—creates an adverse selection problem. Unlike previous models, more valuation is associated with lower market prices and so greater returns to valuation. This strategic complementarity in the capacity to do valuation generates multiple equilibria. With multiple equilibria, the equilibrium without valuation is most efficient despite funding some unprofitable investments. Switches to valuation equilibria, valuation runs, look like credit crunches. A large investor can ensure the efficient equilibrium only if it can precommit to a price and potentially, only if subsidized
Super-diffusion in optical realizations of Anderson localization
We discuss the dynamics of particles in one dimension in potentials that are
random both in space and in time. The results are applied to recent optics
experiments on Anderson localization, in which the transverse spreading of a
beam is suppressed by random fluctuations in the refractive index. If the
refractive index fluctuates along the direction of the paraxial propagation of
the beam, the localization is destroyed. We analyze this broken localization,
in terms of the spectral decomposition of the potential. When the potential has
a discrete spectrum, the spread is controlled by the overlap of Chirikov
resonances in phase space. As the number of Fourier components is increased,
the resonances merge into a continuum, which is described by a Fokker-Planck
equation. We express the diffusion coefficient in terms of the spectral
intensity of the potential. For a general class of potentials that are commonly
used in optics, the solutions of the Fokker-Planck equation exhibit anomalous
diffusion in phase space, implying that when Anderson localization is broken by
temporal fluctuations of the potential, the result is transport at a rate
similar to a ballistic one or even faster. For a class of potentials which
arise in some existing realizations of Anderson localization atypical behavior
is found.Comment: 11 pages, 2 figure
Decay of Quantum Accelerator Modes
Experimentally observable Quantum Accelerator Modes are used as a test case
for the study of some general aspects of quantum decay from classical stable
islands immersed in a chaotic sea. The modes are shown to correspond to
metastable states, analogous to the Wannier-Stark resonances. Different regimes
of tunneling, marked by different quantitative dependence of the lifetimes on
1/hbar, are identified, depending on the resolution of KAM substructures that
is achieved on the scale of hbar. The theory of Resonance Assisted Tunneling
introduced by Brodier, Schlagheck, and Ullmo [9], is revisited, and found to
well describe decay whenever applicable.Comment: 16 pages, 11 encapsulated postscript figures (figures with a better
resolution are available upon request to the authors); added reference for
section
Do Gamma-Ray Burst Sources Repeat?
The demonstration of repeated gamma-ray bursts from an individual source
would severely constrain burst source models. Recent reports (Quashnock and
Lamb 1993; Wang and Lingenfelter 1993) of evidence for repetition in the first
BATSE burst catalog have generated renewed interest in this issue. Here, we
analyze the angular distribution of 585 bursts of the second BATSE catalog
(Meegan et al. 1994). We search for evidence of burst recurrence using the
nearest and farthest neighbor statistic and the two-point angular correlation
function. We find the data to be consistent with the hypothesis that burst
sources do not repeat; however, a repeater fraction of up to about 20% of the
observed bursts cannot be excluded.Comment: ApJ Letters, in press, 13 pages, including three embedded figures.
uuencoded Unix-compressed PostScrip
State laws on tobacco control – United States, 1998
Problem/Condition: State laws addressing tobacco use, the leading preventable cause of death in the United States, are summarized. Laws address smoke-free indoor air, minors’ access to tobacco products, advertising of tobacco products, and excise taxes on tobacco products.
Reporting Period Covered: Legislation effective through December 31, 1998. Description of System: CDC identified laws addressing tobacco control by using an on-line legal research database. CDC’s findings were verified with the National Cancer Institute’s State Cancer Legislative Database.
Results: Since a previous surveillance summary on state tobacco-control laws published in November 1995 (covering legislation effective through June 30, 1995), several states have enacted new restrictions or strengthened existing legislation that addresses smoke-free indoor air, minors’ access to tobacco, tobacco advertising, and tobacco taxes. Five states strengthened their smoke-free indoor air legislation. All states and Washington, D.C., continued to prohibit the sale and distribution of tobacco products to minors; however, 21 states expanded minors’ access laws by designating enforcement authorities, adding license suspension or revocation for sale to minors, or requiring signage. Since the 1995 report, eight additional states (a total of 19 states and Washington, D.C.) now ban vending machines from areas accessible to minors. Thirteen states restrict advertising of tobacco products, an increase of four states since the 1995 report. Although the number of states that tax cigarettes and smokeless tobacco did not change, 13 states increased excise taxes on cigarettes, and five states increased excise taxes on smokeless tobacco products. The average state excise tax on cigarettes is 38.9¢ per pack, an increase of 7.4¢ compared with the average tax in the 1995 report.
Interpretation: State laws addressing tobacco control vary in relation to restrictiveness, enforcement and penalties, preemptions, and exceptions.
Actions Taken: The data summarizing state tobacco-control laws are available through CDC’s State Tobacco Activities Tracking and Evaluation (STATE) System*; the laws are collected and updated every quarter. The STATE System also contains statespecific data on the prevalence of tobacco use, tobacco-related deaths, and the costs of tobacco use. Information from the STATE System is available for use by policy makers at the state and local levels to plan and implement initiatives to prevent and reduce tobacco use. In addition, CDC is using this information to assess the ongoing impact of tobacco-control programs and policies on tobacco use
Epidemiology and outcomes of candidemia in 2019 patients: data from the prospective antifungal therapy alliance registry.
BACKGROUND: Candidemia remains a major cause of morbidity and mortality in the health care setting, and the epidemiology of Candida infection is changing.
METHODS: Clinical data from patients with candidemia were extracted from the Prospective Antifungal Therapy (PATH) Alliance database, a comprehensive registry that collects information regarding invasive fungal infections. A total of 2019 patients, enrolled from 1 July 2004 through 5 March 2008, were identified. Data regarding the candidemia episode were analyzed, including the specific fungal species and patient survival at 12 weeks after diagnosis.
RESULTS: The incidence of candidemia caused by non-Candida albicans Candida species (54.4%) was higher than the incidence of candidemia caused by C. albicans (45.6%). The overall, crude 12-week mortality rate was 35.2%. Patients with Candida parapsilosis candidemia had the lowest mortality rate (23.7%; P
CONCLUSIONS: The epidemiology and choice of therapy for candidemia are rapidly changing. Additional study is warranted to differentiate host factors and differences in virulence among Candida species and to determine the best therapeutic regimen
The Fermi GBM Gamma-Ray Burst Spectral Catalog: Four Years Of Data
In this catalog we present the updated set of spectral analyses of GRBs
detected by the Fermi Gamma-Ray Burst Monitor (GBM) during its first four years
of operation. It contains two types of spectra, time-integrated spectral fits
and spectral fits at the brightest time bin, from 943 triggered GRBs. Four
different spectral models were fitted to the data, resulting in a compendium of
more than 7500 spectra. The analysis was performed similarly, but not
identically to Goldstein et al. 2012. All 487 GRBs from the first two years
have been re-fitted using the same methodology as that of the 456 GRBs in years
three and four. We describe, in detail, our procedure and criteria for the
analysis, and present the results in the form of parameter distributions both
for the observer-frame and rest-frame quantities. The data files containing the
complete results are available from the High-Energy Astrophysics Science
Archive Research Center (HEASARC).Comment: Accepted for publication in ApJ
Dynamical Characterization and Room-Temperature Control of an Optically Addressable Single Spin in Hexagonal Boron Nitride
Hexagonal boron nitride (h-BN), a wide bandgap, two-dimensional solid-state
material, hosts pure single-photon emitters that have shown signatures of
optically-addressable electronic spins. Here, we report on a single emitter in
h-BN exhibiting optically detected magnetic resonance at room temperature, and
we propose a model for its electronic structure and optical dynamics. Using
photon emission correlation spectroscopy in conjunction with time-domain
optical and microwave experiments, we establish key features of the emitter's
electronic structure. Specifically, we propose a model that includes a spinless
optical ground and excited state, a metastable spin-1/2 configuration, and an
emission modulation mechanism. Using optical and spin dynamics simulations, we
constrain and quantify transition rates in the model, and we design protocols
that optimize the signal-to-noise ratio for spin readout. This constitutes a
necessary step toward quantum control of spin states in h-BN.Comment: 14 pages, 15 figures. arXiv admin note: text overlap with
arXiv:2201.0888
- …