26,476 research outputs found
The Free Energy of N=4 Super-Yang-Mills and the AdS/CFT Correspondence
We compute the high-temperature limit of the free energy for four-dimensional
N=4 supersymmetric SU(N_c) Yang-Mills theory. At weak coupling we do so for a
general ultrastatic background spacetime, and in the presence of slowly-varying
background gauge fields. Using Maldacena's conjectured duality, we calculate
the strong-coupling large-N_c expression for the special case that the
three-space has constant curvature. We compare the two results paying
particular attention to curvature corrections to the leading order expressions.Comment: 26 pages.Minor corrections to eqs.(19),(21). Results and conclusions
unchanged. References adde
The un-structured student
SQL (Structured Query Language) is intended to liberate users from the complex syntax, complex semantics and complex memory management that would be required of a procedural approach to relational database manipulation, and so allow users to concentrate on problem-solving. However, students still have problems with language features, program concepts and the legacy of their prior learning. This paper aims to assist lecturers teaching SQL.We present typical student mistakes, attempt to explain why these mistakes arise, and propose possible remedies
Equilibration rates in a strongly coupled nonconformal quark-gluon plasma
We initiate the study of equilibration rates of strongly coupled quark-gluon
plasmas in the absence of conformal symmetry. We primarily consider a
supersymmetric mass deformation within gauge theory and use
holography to compute quasinormal modes of a variety of scalar operators, as
well as the energy-momentum tensor. In each case, the lowest quasinormal
frequency, which provides an approximate upper bound on the thermalization
time, is proportional to temperature, up to a pre-factor with only a mild
temperature dependence. We find similar behaviour in other holographic plasmas,
where the model contains an additional scale beyond the temperature. Hence, our
study suggests that the thermalization time is generically set by the
temperature, irrespective of any other scales, in strongly coupled gauge
theories.Comment: 6 pages, 7 figure
sQGP as hCFT
We examine the proposal to make quantitative comparisons between the strongly
coupled quark-gluon plasma and holographic descriptions of conformal field
theory. In this note, we calculate corrections to certain transport
coefficients appearing in second-order hydrodynamics from higher curvature
terms to the dual gravity theory. We also clarify how these results might be
consistently applied in comparisons with the sQGP.Comment: 13 page
Stability of bubble nuclei through Shell-Effects
We investigate the shell structure of bubble nuclei in simple
phenomenological shell models and study their binding energy as a function of
the radii and of the number of neutron and protons using Strutinsky's method.
Shell effects come about, on the one hand, by the high degeneracy of levels
with large angular momentum and, on the other, by the big energy gaps between
states with a different number of radial nodes. Shell energies down to -40 MeV
are shown to occur for certain magic nuclei. Estimates demonstrate that the
calculated shell effects for certain magic numbers of constituents are probably
large enough to produce stability against fission, alpha-, and beta-decay. No
bubble solutions are found for mass number A < 450.Comment: 9 pages and 9 figures in the eps format include
Stratified charge rotary aircraft engine technology enablement program
The multifuel stratified charge rotary engine is discussed. A single rotor, 0.7L/40 cu in displacement, research rig engine was tested. The research rig engine was designed for operation at high speeds and pressures, combustion chamber peak pressure providing margin for speed and load excursions above the design requirement for a high is advanced aircraft engine. It is indicated that the single rotor research rig engine is capable of meeting the established design requirements of 120 kW, 8,000 RPM, 1,379 KPA BMEP. The research rig engine, when fully developed, will be a valuable tool for investigating, advanced and highly advanced technology components, and provide an understanding of the stratified charge rotary engine combustion process
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Antiferromagnetic s-d exchange coupling in GaMnAs
Measurements of coherent electron spin dynamics in
Ga(1-x)Mn(x)As/Al(0.4)Ga(0.6)As quantum wells with 0.0006% < x < 0.03% show an
antiferromagnetic (negative) exchange bewteen s-like conduction band electrons
and electrons localized in the d-shell of the Mn2+ impurities. The magnitude of
the s-d exchange parameter, N0 alpha, varies as a function of well width
indicative of a large and negative contribution due to kinetic exchange. In the
limit of no quantum confinement, N0 alpha extrapolates to -0.09 +/- 0.03 eV
indicating that antiferromagnetic s-d exchange is a bulk property of GaMnAs.
Measurements of the polarization-resolved photoluminescence show strong
discrepancy from a simple model of the exchange enhanced Zeeman splitting,
indicative of additional complexity in the exchange split valence band.Comment: 5 pages, 4 figures and one action figur
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