19,656 research outputs found
Nonequilibrium work distribution of a quantum harmonic oscillator
We analytically calculate the work distribution of a quantum harmonic
oscillator with arbitrary time-dependent angular frequency. We provide detailed
expressions for the work probability density for adiabatic and nonadiabatic
processes, in the limit of low and high temperature. We further verify the
validity of the quantum Jarzynski equalityComment: 6 pages, 3 figure
The nature and evolution of Ultraluminous Infrared Galaxies: A mid-infrared spectroscopic survey
We report the first results of a low resolution mid-infrared spectroscopic
survey of an unbiased, far-infrared selected sample of 60 ultraluminous
infrared galaxies, using ISOPHOT-S on board ISO. We use the ratio of the 7.7um
`PAH' emission feature to the local continuum as a discriminator between
starburst and AGN activity. About 80% of all the ULIRGs are found to be
predominantly powered by star formation but the fraction of AGN powered objects
increases with luminosity.
Observed ratios of the PAH features in ULIRGs differ slightly from those in
lower luminosity starbursts. This can be plausibly explained by the higher
extinction and/or different physical conditions in the interstellar medium of
ULIRGs. The PAH feature-to-continuum ratio is anticorrelated with the ratio of
feature-free 5.9um continuum to the IRAS 60um continuum, confirming suggestions
that strong mid-IR continuum is a prime AGN signature. The location of
starburst-dominated ULIRGs in such a diagram is consistent with previous
ISO-SWS spectroscopy which implies significant extinction even in the
mid-infrared.
We have searched for indications that ULIRGs which are advanced mergers might
be more AGN-like, as postulated by the classical evolutionary scenario. No such
trend has been found amongst those objects for which near infrared images are
available to assess their likely merger status.Comment: aastex, 4 eps figures. Revised version, accepted by ApJ (Letters
Mid-Infrared line diagnostics of Active Galaxies -- A spectroscopic AGN survey with ISO-SWS
We present medium resolution (R approx. 1500) ISO-SWS 2.4--45 micron spectra
of a sample of 29 galaxies with active nuclei. This data set is rich in fine
structure emission lines tracing the narrow line regions and (circum-)nuclear
star formation regions, and it provides a coherent spectroscopic reference for
future extragalactic studies in the mid-infrared. We use the data set to
briefly discuss the physical conditions in the narrow line regions (density,
temperature, excitation, line profiles) and to test for possible differences
between AGN sub-types. Our main focus is on new tools for determining the
propertibes of dusty galaxies and on the AGN-starburst connection. We present
mid-IR line ratio diagrams which can be used to identify composite (starburst +
AGN) sources and to distinguish between emission excited by active nuclei and
emission from (circum-nuclear) star forming regions. For instance, line ratios
of high to low excitation lines like [O IV]25.9um/[Ne II]12.8um, that have been
used to probe for AGNs in dusty objects, can be examined in more detail and
with better statistics now. In addition, we present two-dimensional diagnostic
diagrams that are fully analogous to classical optical diagnostic diagrams, but
better suited for objects with high extinction. Finally, we discuss
correlations of mid-infrared line fluxes to the mid- and far-infrared
continuum. We compare these relations to similar relations in starburst
galaxies in order to examine the contribution of AGNs to the bolometric
luminosities of their host galaxies. The spectra are available in electronic
form from the authors.Comment: 24 pages, 23 figures, 5 tables. Accepted for A&
Nonequilibrium entropy production for open quantum systems
We consider open quantum systems weakly coupled to a heat reservoir and
driven by arbitrary time-dependent parameters. We derive exact microscopic
expressions for the nonequilibrium entropy production and entropy production
rate, valid arbitrarily far from equilibrium. By using the two-point energy
measurement statistics for system and reservoir, we further obtain a quantum
generalization of the integrated fluctuation theorem put forward by Seifert
[PRL 95, 040602 (2005)].Comment: 4 pages, 1 figur
On the succinctness of query rewriting over shallow ontologies
We investigate the succinctness problem for conjunctive query rewritings over OWL2QL ontologies of depth 1 and 2 by means of hypergraph programs computing Boolean functions. Both positive and negative results are obtained. We show that, over ontologies of depth 1, conjunctive queries have polynomial-size nonrecursive datalog rewritings; tree-shaped queries have polynomial positive existential rewritings; however, in the worst case, positive existential rewritings can be superpolynomial. Over ontologies of depth 2, positive existential and nonrecursive datalog rewritings of conjunctive queries can suffer an exponential blowup, while first-order rewritings can be superpolynomial unless NP �is included in P/poly. We also analyse rewritings of tree-shaped queries over arbitrary ontologies and note that query entailment for such queries is fixed-parameter tractable
Warranties, Durability, and Maintenance: Two Sided Moral Hazard in a Continuous-Time Model
We consider the provision of an optimal warranty in a continuous-time model with two-sided moral hazard. The optimal warranty must balance the producer’s durability incentive and the buyer’s maintenance incentive. Too little warranty protection gives the producer too much incentive to produce low durability, while too much warranty protection gives the consumer too much incentive to neglect maintenance. The derived optimal warranty is a “block warranty” that is high for an initial block of time and zero thereafter. The first-best would be available under a very high warranty for a very short time interval, except for the incentive this would create for the consumer to abuse the product to collect the warranty
Apollo experience report: Development of the extravehicular mobility unit
The development and performance history of the Apollo extravehicular mobility unit and its major subsystems is described. The three major subsystems, the pressure garment assembly, the portable life-support system, and the oxygen purge system, are defined and described in detail as is the evolutionary process that culminated in each major subsystem component. Descriptions of ground-support equipment and the qualification testing process for component hardware are also presented
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