27,624 research outputs found
Chromomagnetic instability in dense quark matter
The results for the Debye and Meissner screening masses of the gluons and the
photon in the case of neutral and beta-equilibrated dense two-flavor quark
matter are presented. In the limits of the normal phase and the ideal
two-flavor color superconducting phase, the screening masses coincide with the
known results. Most interestingly, we find that the Meissner screening masses
squared can be negative, indicating a plasma-type chromomagnetic instability in
dense quark matter.Comment: 5 pages and 2 figures. To appear in Phys. Rev. D; version slightly
shortened on request of editor
The gapless 2SC phase
Recent results on the gapless 2SC phase are reviewed. These include: the
thermal stability under the constraint of the local charge neutrality
condition, the properties at zero and nonzero temperatures, and the color
screening properties.Comment: To appear in the proceedings of 6th Conference on Strong and
Electroweak Matter 2004 (SEWM04), Helsinki, Finland, 16-19 Jun 2004. Typos
correcte
Threshold Regression for Survival Analysis: Modeling Event Times by a Stochastic Process Reaching a Boundary
Many researchers have investigated first hitting times as models for survival
data. First hitting times arise naturally in many types of stochastic
processes, ranging from Wiener processes to Markov chains. In a survival
context, the state of the underlying process represents the strength of an item
or the health of an individual. The item fails or the individual experiences a
clinical endpoint when the process reaches an adverse threshold state for the
first time. The time scale can be calendar time or some other operational
measure of degradation or disease progression. In many applications, the
process is latent (i.e., unobservable). Threshold regression refers to
first-hitting-time models with regression structures that accommodate covariate
data. The parameters of the process, threshold state and time scale may depend
on the covariates. This paper reviews aspects of this topic and discusses
fruitful avenues for future research.Comment: Published at http://dx.doi.org/10.1214/088342306000000330 in the
Statistical Science (http://www.imstat.org/sts/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Replica study of pinned bubble crystals
In higher Landau levels (), the ground state of the two-dimensional
electron gas in a strong perpendicular magnetic field evolves from a Wigner
crystal for small filling of the partially filled Landau level, into a
succession of bubble states with increasing number of guiding centers per
bubble as increases, to a modulated stripe state near . In
this work, we compute the frequency-dependent longitudinal conductivity of the Wigner and bubble crystal states in the presence
of disorder. We apply an elastic theory to the crystal states which is
characterized by a shear and a bulk modulus. We obtain both moduli from the
microscopic time-dependent Hartree-Fock approximation. We then use the replica
and Gaussian variational methods to handle the effects of disorder. Within the
semiclassical approximation we get the dynamical conductivity as well as the
pinning frequency as functions of the Landau level filling factor and compare
our results with recent microwave experiments.Comment: 19 pages and 6 eps figure
Specialty Crops and the 2007 Farm Bill: The Potential Role of Farm Savings Accounts
This paper discusses the findings of a research project that examined the potential benefits of establishing farm savings accounts for specialty crop growers1. The primary goal of the project was to determine whether farm savings accounts would provide specialty crop growers with a useful tool for managing financial risk. The project examined how various farm savings account proposals ultimately impacted the benefits that specialty crop growers would receive from the accounts.Agricultural Finance, Crop Production/Industries,
The Paradox of Risk Balancing: Do Risk-reducing Policies Lead to More Risk for Farmers?
The study presents stochastic optimal control/dynamic programming (SOC/DP) to derive the optimal debt level and consumption in farm models concerning two sources of uncertainty: the return on assets and interest rate. The SOC/DP analytic framework is used to analyze the impacts of risk-reducing farm policies on farmâs financial and risk adjustments. The results show the violations of the risk-balancing concept, which theorizes that risk-reducing farm policies may lead to increases in financial leverage, total risk, and the expected returns. Also, this study examines the extent to which the estimates of the optimal debt level are biased when interest rate risk is ignored.Stochastic Optimal Control/Dynamic Programming, Financial Leverage, Uncertainty, Risk Balancing, Agricultural and Food Policy, Risk and Uncertainty,
Vacuum Interpretation for Supergravity M-Branes
A non-local classical duality between the three-block truncated 11D
supergravity and the 8D vacuum gravity with two commuting Killing symmetries is
established. The supergravity four-form field is generated via an inverse
dualisation of the corresponding Killing two-forms in six dimensions. 11D
supersymmetry condition is shown to be equivalent to existence of covariantly
constant spinors in eight dimensions. Thus any solution to the vacuum Einstein
equations in eight dimensions depending on six coordinates and admitting
Killing spinors have supersymmetric 11D-supergravity counterparts. Using this
duality we derive some new brane solutions to 11D-supergravity including 1/4
supersymmetric intersecting M-branes with a NUT parameter and a dyon solution
joining the M2 and M5-branes intersecting at a point.Comment: 4 pages, latex, no figure
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