Purifying and Reversible Physical Processes

Starting from the observation that reversible processes cannot increase the purity of any input state, we study deterministic physical processes, which map a set of states to a set of pure states. Such a process must map any state to the same pure output, if purity is demanded for the input set of all states. But otherwise, when the input set is restricted, it is possible to find non-trivial purifying processes. For the most restricted case of only two input states, we completely characterize the output of any such map. We furthermore consider maps, which combine the property of purity and reversibility on a set of states, and we derive necessary and sufficient conditions on sets, which permit such processes.Comment: 5 pages, no figures, v2: only minimal change

Physical processes in comets

When this program began in 1975 only limited photometry had been carried out on comets at any wavelength. Program goals were to observe many comets, including faint periodic comets, at a range of heliocentric distances in order to begin to understand the range of behavior among comets and in a given comet during its approach and departure from the sun. Then a study of the continuum of scattered light from dust was added. More recently the value of joint team observations in visible and infrared light has been recognized and utilized as often as possible. All 1978 to 1982 data was reanalyzed and 1983 to 1986 data analyzed in the framwork of the post-Halley paradigm, covering 25 comets in all. Four observing runs (June, July, Sept., and Jan.) with Hanner produced excellent results on Wilson, Bradfield, P/Klemola, and P/Borrelly and lesser data on other objects, including the last reported IR photometry of P/Halley. The Wilson and Halley data have been reduced

Radiative torque alignment: Essential Physical Processes

We study the physical processes that affect the alignment of grains subject to radiative torques (RATs). To describe the action of RATs, we use the analytical model (AMO) of RATs introduced in Paper I. We focus our discussion on the alignment by anisotropic radiation flux with respect to magnetic field, which defines the axis of grain Larmor precession. Such an alignment does not invoke paramagnetic dissipation (i.e. Davis-Greenstein mechanism), but, nevertheless, grains tend to be aligned with long axes perpendicular to the magnetic field. When we account for thermal fluctuations within grain material, we show that for grains, which are characterized by a triaxial ellipsoid of inertia, the zero-$J$ attractor point obtained in our earlier study develops into a low-$J$ attractor point. We study effects of stochastic gaseous bombardment and show that gaseous bombardment can drive grains from low-$J$ to high-$J$ attractor points in cases when the high-$J$ attractor points are present. As the alignment of grain axes with respect to angular momentum is higher for higher values of $J$, counter-intuitively, gaseous bombardment can increase the degree of grain alignment in respect to the magnetic field. We also study the effects of torques induced by H$_2$ formation and show that they can change the value of angular momentum at high-$J$ attractor point, but marginally affect the value of angular momentum at low-$J$ attractor points. We compare the AMO results with those obtained using the direct numerical calculations of RATs acting upon irregular grains and validate the use of the AMO for realistic situations of RAT alignment.Comment: 31 pages. MNRAS 2007, in press, typos are corrected

Physical Processes in Star-Gas Systems

First we present a recently developed 3D chemodynamical code for galaxy evolution from the K**2 collaboration. It follows the evolution of all components of a galaxy such as dark matter, stars, molecular clouds and diffuse interstellar matter (ISM). Dark matter and stars are treated as collisionless N-body systems. The ISM is numerically described by a smoothed particle hydrodynamics (SPH) approach for the diffuse (hot) gas and a sticky particle scheme for the (cool) molecular clouds. Physical processs such as star formation, stellar death or condensation and evaporation processes of clouds interacting with the ISM are described locally. An example application of the model to a star forming dwarf galaxy will be shown for comparison with other codes. Secondly we will discuss new kinds of exotic chemodynamical processes, as they occur in dense gas-star systems in galactic nuclei, such as non-standard ``drag''-force interactions, destructive and gas producing stellar collisions. Their implementation in 1D dynamical models of galactic nuclei is presented. Future prospects to generalize these to 3D are work in progress and will be discussed.Comment: 4 pages, 4 figures, "The 5th Workshop on Galactic Chemodynamics" - Swinburne University (9-11 July 2003). To be published in the Publications of the Astronomical Society of Australia in 2004 (B.K. Gibson and D. Kawata, eds.). Accepted version, minor changes relative to origina

Physical Processes in Naked Singularity Formation

Gravitational collapse is one of the most fruitful subjects in gravitational physics. It is well known that singularity formation is inevitable in complete gravitational collapse. It was conjectured that such a singularity should be hidden by horizons if it is formed from generic initial data with physically reasonable matter fields. Many possible counterexamples to this conjecture have been proposed over the past three decades, although none of them has proved to be sufficiently generic. In these examples, there appears a singularity that is not hidden by horizons. This singularity is called a `naked singularity.' The appearance of a naked singularity represents the formation of an observable high-curvature, strong-gravity region. In this paper we review examples of naked singularity formation and recent progress in research of observable physical processes - gravitational radiation and quantum particle creation - from a forming naked singularity.Comment: 76 pages, 25 figure file

Physical processes behind the alignment effect

The radio/optical alignment effect for small powerful radio galaxies has been shown to be produced by shock waves formed by the interaction of the head of the jet and/or cocoon with clouds embedded in the interstellar/intergalactic medium. We present here preliminary results of analytical and numerical solutions that have been made to account for the production of implosive shock waves induced by embedding cold clouds in the radio lobe of expanding powerful radio sources.Comment: 4 pages. To be published in Multiwavelength AGN Surveys", Cozumel, Dec 8 - 12, 200

Physical processes in planetary rings

A summary of research performed in 1990 is presented. The subject areas covered include perturbed narrow rings and the dynamics of circumplanetary dust. Progress made in the area of perturbed narrow rings includes: (1) the possible discovery of an undocumented moonlet in the environs of Saturn's F ring; and (2) the investigation of the consequences of a close satellite perturbing a narrow ring using numerical simulation. Progress made in the area of circumplanetary dust includes: (1) studies of the motion of circumplanetary dust under the action of radiation pressure and various electromagnetic processes; and (2) the initiation of a systematic explanation of the curious consequences of some of the perturbations that act on small particles