Path Integral Monte Carlo Simulations Of Positronium Annihilation: From Micropores To Mesopores

Path integral Monte Carlo (PIMC) can reproduce the results of simple analytical calculations in which a single quantum particle is used to represent positronium within an idealized spherical pore. Our calculations improve on this approach by explicitly treating the positronium as a two-particle e(-), e(+) system interacting via the Coulomb interaction. We study the lifetime and the internal contact density, kappa, which controls the self-annihilation behavior for positronium in model spherical pores as a function of temperature and pore size. We compare the results with both PIMC and analytical calculations for a single-particle model

Shrinking binary and planetary orbits by Kozai cycles with tidal friction

At least two arguments suggest that the orbits of a large fraction of binary stars and extrasolar planets shrank by 1-2 orders of magnitude after formation: (i) the physical radius of a star shrinks by a large factor from birth to the main sequence, yet many main-sequence stars have companions orbiting only a few stellar radii away, and (ii) in current theories of planet formation, the region within ~0.1 AU of a protostar is too hot and rarefied for a Jupiter-mass planet to form, yet many "hot Jupiters" are observed at such distances. We investigate orbital shrinkage by the combined effects of secular perturbations from a distant companion star (Kozai oscillations) and tidal friction. We integrate the relevant equations of motion to predict the distribution of orbital elements produced by this process. Binary stars with orbital periods of 0.1 to 10 days, with a median of ~2 d, are produced from binaries with much longer periods (10 d to 10^5 d), consistent with observations indicating that most or all short-period binaries have distant companions (tertiaries). We also make two new testable predictions: (1) For periods between 3 and 10 d, the distribution of the mutual inclination between the inner binary and the tertiary orbit should peak strongly near 40 deg and 140 deg. (2) Extrasolar planets whose host stars have a distant binary companion may also undergo this process, in which case the orbit of the resulting hot Jupiter will typically be misaligned with the equator of its host star.Comment: Submitted to ApJ; 18 pages, 10 figure

Interacting Binaries with Eccentric Orbits. III. Orbital Evolution due to Direct Impact and Self-Accretion

The rapid circularization and synchronization of the stellar components in an eccentric binary system at the onset of Roche lobe overflow (RLO) is a fundamental assumption common to all binary stellar evolution and population synthesis codes, even though the validity of this assumption is questionable both theoretically and observationally. Here we calculate the evolution of the orbital elements of an eccentric binary through the direct three-body integration of a massive particle ejected through the inner Lagrangian point of the donor star at periastron. The trajectory of this particle leads to three possible outcomes: direct accretion (DA) onto the companion star within a single orbit, self-accretion (SA) back onto the donor star within a single orbit, or a quasi-periodic orbit around the companion star. We calculate the secular evolution of the binary orbit in the first two cases and conclude that DA can increase or decrease the orbital semi-major axis and eccentricity, while SA always decreases the orbital both orbital elements. In cases where mass overflow contributes to circularizing the orbit, circularization can set in on timescales as short as a few per cent of the mass transfer timescale. In cases where mass overflow increases the eccentricity, the orbital evolution is governed by competition between mass overflow and tidal torques. In the absence of tidal torques, mass overflow resulting in DI can lead to substantially subsynchronously rotating donor stars. Contrary to common assumptions, DI furthermore does not always provide a strong sink of orbital angular momentum in close mass-transferring binaries; in fact we instead find that a significant part can be returned to the orbit during the particle orbit. The formulation presented here can be combined with stellar and binary evolution codes to generate a better picture of the evolution of eccentric, RLO binary star systems.Comment: 15 pages, 10 figures, Accepted for publication in Ap

The Written Description Requirement

It is now well accepted that this provision of the 1952 Patent Act (Patent Act) includes a written description requirement that is separate and distinct from the enablement requirement. Thus, a specification may enable one of ordinary skill to make or use a claimed invention, but still not adequately describe the invention in a way that the public knows that the inventor was in possession of the claimed invention at the time of filing the application. For example, a patent specification that discloses various patterns of eight wooden shingles, does not necessarily provide written description for a claim amendment that recites “at least six shingles,” even though the specification would enable one so inclined to construct a panel of at least six wooden shingles. However, it was not entirely clear from the language of the Patent Act itself that there was a written description requirement separate and distinct from the enablement requirement. The well-accepted understanding that these are separate and distinct requirements flows from judicial decisions, and not the text of the Patent Act itself

Thermal conductivity measurements of proton-heated warm dense aluminum.

Thermal conductivity is one of the most crucial physical properties of matter when it comes to understanding heat transport, hydrodynamic evolution, and energy balance in systems ranging from astrophysical objects to fusion plasmas. In the warm dense matter regime, experimental data are very scarce so that many theoretical models remain untested. Here we present the first thermal conductivity measurements of aluminum at 0.5-2.7 g/cc and 2-10 eV, using a recently developed platform of differential heating. A temperature gradient is induced in a Au/Al dual-layer target by proton heating, and subsequent heat flow from the hotter Au to the Al rear surface is detected by two simultaneous time-resolved diagnostics. A systematic data set allows for constraining both thermal conductivity and equation-of-state models. Simulations using Purgatorio model or Sesame S27314 for Al thermal conductivity and LEOS for Au/Al release equation-of-state show good agreement with data after 15 ps. Discrepancy still exists at early time 0-15 ps, likely due to non-equilibrium conditions

A Two-Chain Path Integral Model Of Positronium

We have used a path integral Monte Carlo technique to simulate positronium (Ps) in a cavity. The primitive propagator is used, with a pair of interacting chains representing the positron and electron. We calculate the energy and radial distribution function for Ps enclosed in a hard, spherical cavity, and the polarizability of the model Ps in the presence of an electrostatic field. We find that the positron distribution near the hard wall differs significantly from that for a single particle in a hard cavity. This leads to systematic deviations from predictions of free-volume models which treat Ps as an effective, single particle. A virial-type estimator is used to calculate the kinetic energy of the particle in the presence of hard walls. This estimator is found to be superior to a kinetic-type estimator given the interaction potentials, cavity sizes, and chain lengths considered in the current study. (C) 2000 American Institute of Physics. [S0021-9606(00)50447-4]