Nuclear radiation problems, unmanned thermionic reactor ion propulsion spacecraft

A nuclear thermionic reactor as the electric power source for an electric propulsion spacecraft introduces a nuclear radiation environment that affects the spacecraft configuration, the use and location of electrical insulators and the science experiments. The spacecraft is conceptually configured to minimize the nuclear shield weight by: (1) a large length to diameter spacecraft; (2) eliminating piping penetrations through the shield; and (3) using the mercury propellant as gamma shield. Since the alumina material is damaged by the high nuclear radiation environment in the reactor it is desirable to locate the alumina insulator outside the reflector or develop a more radiation resistant insulator

Database of Molecular Masers and Variable Stars

We present the database of maser sources in H2O, OH and SiO lines that can be used to identify and study variable stars at evolved stages. Detecting the maser emission in H2O, OH and SiO molecules toward infrared-excess objects is one of the methods of identification long-period variables (LPVs, including Miras and Semi-Regular), because these stars exhibit maser activity in their circumstellar shells. Our sample contains 1803 known LPV objects. 46% of these stars (832 objects) manifest maser emission in the line of at least one molecule: H2O, OH or SiO. We use the database of circumstellar masers in order to search for long-periodic variables which are not included in the General Catalogue of Variable Stars (GCVS). Our database contains 4806 objects (3866 objects without associations in GCVS catalog) with maser detection in at least one molecule. Therefore it is possible to use the database in order to locate and study the large sample of long-period variable stars. Entry to the database at http://maserdb.netComment: Accepted for publication in RA

A Sedimentological Study of Modern and Ancient Lacustrine Environments at Michael Bay, Lake Huron

Modern and ancient environments associated with Lakes Algoma and Huron were studied according to attributes of stratigraphy, sediment texture, parameters, sediment size distribution, bedforms, and primary sedimentary structures. Results from a computation of wave refraction diagrams and from an examination of the wave climate characteristics indicate that the modern embayment is low energy. A sediment texture comparison between modern and ancient environments indicates that higher energy pervailed in the ancient environment relative to the present day environment. The cobble and gravel sediments as well as an extensive belt of foredunes preserved in the ancient environment are evidence of this high energy. Sediment textural parameters of mean, standard deviation, skewness, and kurtosis were combined in bivariate plots to test their reliability for discriminating between environments. Results from four combinations of those parameters were not totally favourable. Only a plot of standard deviation versus skewness proved useful. Component populations are useful discriminators of depositional environments. Inferred environments of beach, fluvial, and dune as well as modern lacustrine sediments could be identified by the characteristics of their component population curves. Moreover, characteristic curves that represent various subenvironments for the modern near shore zone are evident. These have been assimilated into a grain size distribution facies indicator. Provision of a facies model for a barred-lacustrine bayhead was made possible by an examination of preserved bedforms and primary sedimentary structures. High energy bedforms of parallel laminae and massive bedding are always preserved to low energy ripple cross-laminae. The sequence of ripple cross-laminae that forms in response to increasing energy as as follows: symmetrical, assymetrical, oscillatory, and combined flow. An examination of such preserved features yields information that can be used to decipher flow directions, energy gradients, and flow characteristics within specific subenvironments

A Sedimentological Study of Modern and Ancient Lacustrine Environments at Michael Bay, Lake Huron

Modern and ancient environments associated with Lakes Algoma and Huron were studied according to attributes of stratigraphy, sediment texture, parameters, sediment size distribution, bedforms, and primary sedimentary structures. Results from a computation of wave refraction diagrams and from an examination of the wave climate characteristics indicate that the modern embayment is low energy. A sediment texture comparison between modern and ancient environments indicates that higher energy pervailed in the ancient environment relative to the present day environment. The cobble and gravel sediments as well as an extensive belt of foredunes preserved in the ancient environment are evidence of this high energy. Sediment textural parameters of mean, standard deviation, skewness, and kurtosis were combined in bivariate plots to test their reliability for discriminating between environments. Results from four combinations of those parameters were not totally favourable. Only a plot of standard deviation versus skewness proved useful. Component populations are useful discriminators of depositional environments. Inferred environments of beach, fluvial, and dune as well as modern lacustrine sediments could be identified by the characteristics of their component population curves. Moreover, characteristic curves that represent various subenvironments for the modern near shore zone are evident. These have been assimilated into a grain size distribution facies indicator. Provision of a facies model for a barred-lacustrine bayhead was made possible by an examination of preserved bedforms and primary sedimentary structures. High energy bedforms of parallel laminae and massive bedding are always preserved to low energy ripple cross-laminae. The sequence of ripple cross-laminae that forms in response to increasing energy as as follows: symmetrical, assymetrical, oscillatory, and combined flow. An examination of such preserved features yields information that can be used to decipher flow directions, energy gradients, and flow characteristics within specific subenvironments

Prolific pair production with high-power lasers

Prolific electron-positron pair production is possible at laser intensities approaching 10^{24} W/cm^2 at a wavelength of 1 micron. An analysis of electron trajectories and interactions at the nodes (B=0) of two counter-propagating, circularly polarised laser beams shows that a cascade of gamma-rays and pairs develops. The geometry is generalised qualitatively to linear polarisation and laser beams incident on a solid target.Comment: 4 pages, 1 figure, minor revisions, accepted for publication in Physical Review Letter

Identification of Very Red Counterparts of SiO Maser and OH/IR Objects in the GLIMPSE Survey

Using the 3.6/4.5/5.8/8.0 micron images with 1.2 arcsec pixel resolution from the Spitzer/GLIMPSE survey, we investigated 23 masing and 18 very red objects that were not identified in the 2MASS survey. Counterparts for all selected objects were found in the GLIMPSE images. Color indices in these IR bands suggest the presence of a high-extinction layer of more than a few tenths of a solar mass in front of the central star. Furthermore, radio observations in the SiO and H2O maser lines found characteristic maser-line spectra of the embedded objects, e.g., the SiO J=1-0 line intensity in the v=2 state stronger than that of the v=1 state, or very widespread H2O maser emission spectra. This indicates that these objects are actually enshrouded by very thick circumstellar matter, some of which cannot be ascribed to the AGB wind of the central star. Individually interesting objects are discussed, including two newly found water fountains and an SiO source with nebulosity.Comment: High resolution figures available at ftp://ftp.nro.nao.ac.jp/nroreport/no653.pdf.gz. ApJ No. 655 no.1 issue in pres

Physisorption of Nucleobases on Graphene

We report the results of our first-principles investigation on the interaction of the nucleobases adenine (A), cytosine (C), guanine (G), thymine (T), and uracil (U) with graphene, carried out within the density functional theory framework, with additional calculations utilizing Hartree--Fock plus second-order Moeller-Plesset perturbation theory. The calculated binding energy of the nucleobases shows the following hierarchy: G > T ~ C ~ A > U, with the equilibrium configuration being very similar for all five of them. Our results clearly demonstrate that the nucleobases exhibit significantly different interaction strengths when physisorbed on graphene. The stabilizing factor in the interaction between the base molecule and graphene sheet is dominated by the molecular polarizability that allows a weakly attractive dispersion force to be induced between them. The present study represents a significant step towards a first-principles understanding of how the base sequence of DNA can affect its interaction with carbon nanotubes, as observed experimentally.Comment: 7 pages, 3 figure

Separation of colour degree of freedom from dynamics in a soliton cellular automaton

We present an algorithm to reduce the coloured box-ball system, a one dimensional integrable cellular automaton described by motions of several colour (kind) of balls, into a simpler monochrome system. This algorithm extracts the colour degree of freedom of the automaton as a word which turns out to be a conserved quantity of this dynamical system. It is based on the theory of crystal basis and in particular on the tensor products of sl_n crystals of symmetric and anti-symmetric tensor representations.Comment: 19 page

Fast Neutron Response Of A 6Li^{6}Li-loaded Liquid Scintillator

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