Zero temperature phase diagram of the square-shoulder system

Particles that interact via a square-shoulder potential, consisting of an impenetrable hard core with an adjacent, repulsive, step-like corona, are able to self-organize in a surprisingly rich variety of rather unconventional ordered structures. Using optimization strategies that are based on ideas of genetic algorithms we encounter, as we systematically increase the pressure, the following archetypes of aggregates: low-symmetry cluster and columnar phases, followed by lamellar particle arrangements, until at high pressure values compact, high-symmetry lattices emerge. These structures are characterized in the NPT ensemble as configurations of minimum Gibbs free energy. Based on simple considerations, i.e., basically minimizing the number of overlapping coronae while maximizing at the same time the density, the sequence of emerging structures can easily be understood.Comment: Submitted to J. Chem. Phy

Unraveling quantum dissipation in the frequency domain

We present a quantum Monte Carlo method for solving the evolution of an open quantum system. In our approach, the density operator evolution is unraveled in the frequency domain. Significant advantages of this approach arise when the frequency of each dissipative event conveys information about the state of the system.Comment: 4 pages, 4 Postscript figures, uses RevTe

Magnetic Fields in Star-Forming Molecular Clouds I. The First Polarimetry of OMC-3 in Orion A

The first polarimetric images of the OMC-3 region of the Orion A filamentary molecular cloud are presented. Using the JCMT, we have detected polarized thermal emission at 850 microns from dust along a 6' length of the dense filament. The polarization pattern is highly ordered and is aligned with the filament throughout most of the region. The plane-of-sky magnetic field direction is perpendicular to the measured polarization. The mean percentage polarization is 4.2% with a 1 sigma dispersion of 1%. This region is part of the integral-shaped filament, and active star formation is ongoing along its length. The protostellar outflow directions do not appear to be consistently correlated with the direction of the plane-of-sky field or the filament structure itself. Depolarization toward the filament center, previously detected in many other star-forming cores and protostars, is also evident in our data. (abstract abridged)Comment: 9 pages plus 2 figures (1 colour); accepted for publication in the March 10, 2000 issue (vol. 531 #2) of The Astrophysical Journa

An Updated Ultraviolet Calibration for the Swift/UVOT

We present an updated calibration of the Swift/UVOT broadband ultraviolet (uvw1, uvm2, and uvw2) filters. The new calibration accounts for the ~1% per year decline in the UVOT sensitivity observed in all filters, and makes use of additional calibration sources with a wider range of colours and with HST spectrophotometry. In this paper we present the new effective area curves and instrumental photometric zeropoints and compare with the previous calibration.Comment: 4 pages, 3 figures, 2 tables. Presented at GRB 2010 symposium, Annapolis, November 2010 to be published in American Institute of Physics Conference Serie

Millimeter wave satellite concepts, volume 1

The identification of technologies necessary for development of millimeter spectrum communication satellites was examined from a system point of view. Development of methodology based on the technical requirements of potential services that might be assigned to millimeter wave bands for identifying the viable and appropriate technologies for future NASA millimeter research and development programs, and testing of this methodology with selected user applications and services were the goals of the program. The entire communications network, both ground and space subsystems was studied. Cost, weight, and performance models for the subsystems, conceptual design for point-to-point and broadcast communications satellites, and analytic relationships between subsystem parameters and an overall link performance are discussed along with baseline conceptual systems, sensitivity studies, model adjustment analyses, identification of critical technologies and their risks, and brief research and development program scenarios for the technologies judged to be moderate or extensive risks. Identification of technologies for millimeter satellite communication systems, and assessment of the relative risks of these technologies, was accomplished through subsystem modeling and link optimization for both point-to-point and broadcast applications

HST/STIS Imaging of the Host Galaxy of GRB980425/SN1998bw

We present HST/STIS observations of ESO 184-G82, the host galaxy of the gamma-ray burst GRB 980425 associated with the peculiar Type Ic supernova SN1998bw. ESO 184-G82 is found to be an actively star forming SBc sub-luminous galaxy. We detect an object consistent with being a point source within the astrometric uncertainty of 0.018 arcseconds of the position of the supernova. The object is located inside a star-forming region and is at least one magnitude brighter than expected for the supernova based on a simple radioactive decay model. This implies either a significant flattening of the light curve or a contribution from an underlying star cluster.Comment: 12 pages, 2 figures, AASTeX v5.02 accepted for publication in ApJ Letter

Enhanced winnings in a mixed-ability population playing a minority game

We study a mixed population of adaptive agents with small and large memories, competing in a minority game. If the agents are sufficiently adaptive, we find that the average winnings per agent can exceed that obtainable in the corresponding pure populations. In contrast to the pure population, the average success rate of the large-memory agents can be greater than 50 percent. The present results are not reproduced if the agents are fed a random history, thereby demonstrating the importance of memory in this system.Comment: 9 pages Latex + 2 figure

Evolutionary quantum cosmology in a gauge-fixed picture

We study the classical and quantum models of a flat Friedmann-Robertson-Walker (FRW) space-time, coupled to a perfect fluid, in the context of the consensus and a gauge-fixed Lagrangian frameworks. It is shown that, either in the usual or in the gauge-fixed actions, the evolution of the universe based on the classical cosmology represents a late time power law expansion, coming from a big-bang singularity in which the scale factor goes to zero for the standard matter, and tending towards a big-rip singularity in which the scale factor diverges for the phantom fluid. We then employ the familiar canonical quantization procedure in the given cosmological setting to find the cosmological wave functions in the corresponding minisuperspace. Using a gauge-fixed (reduced) Lagrangian, we show that, it may lead to a Schr\"{o}dinger equation for the quantum-mechanical description of the model under consideration, the eigenfunctions of which can be used to construct the time dependent wave function of the universe. We use the resulting wave function in order to investigate the possibility of the avoidance of classical singularities due to quantum effects by means of the many-worlds and ontological interpretation of quantum cosmology.Comment: 15 pages, 10 figures, typos corrected, Refs. adde

A microscopic quantum dynamics approach to the dilute condensed Bose gas

We derive quantum evolution equations for the dynamics of dilute condensed Bose gases. The approach contains, at different orders of approximation, for cases close to equilibrium, the Gross Pitaevskii equation and the first order Hartree Fock Bogoliubov theory. The proposed approach is also suited for the description of the dynamics of condensed gases which are far away from equilibrium. As an example the scattering of two Bose condensates is discussed.Comment: 8 pages, submitted to Phys. Rev.

Interacting classical and quantum ensembles

A consistent description of interactions between classical and quantum systems is relevant to quantum measurement theory, and to calculations in quantum chemistry and quantum gravity. A solution is offered here to this longstanding problem, based on a universally-applicable formalism for ensembles on configuration space. This approach overcomes difficulties arising in previous attempts, and in particular allows for backreaction on the classical ensemble, conservation of probability and energy, and the correct classical equations of motion in the limit of no interaction. Applications include automatic decoherence for quantum ensembles interacting with classical measurement apparatuses; a generalisation of coherent states to hybrid harmonic oscillators; and an equation for describing the interaction of quantum matter fields with classical gravity, that implies the radius of a Robertson-Walker universe with a quantum massive scalar field can be sharply defined only for particular `quantized' values.Comment: 31 pages, minor clarifications and one Ref. added, to appear in PR