64,271 research outputs found
Chemical structure matching using correlation matrix memories
This paper describes the application of the Relaxation By Elimination (RBE) method to matching the 3D structure of molecules in chemical databases within the frame work of binary correlation matrix memories. The paper illustrates that, when combined with distributed representations, the method maps well onto these networks, allowing high performance implementation in parallel systems. It outlines the motivation, the neural architecture, the RBE method and presents some results of matching small molecules against a database of 100,000 models
Tangential discontinuities in the solar wind
Tangential discontinuities in solar wind derived from Mariner 5 plasma and magnetic field dat
Titanium and advanced composite structures for a supersonic cruise arrow wing configuration
Structural design studies were made, based on current technology and on an estimate of technology to be available in the mid 1980's, to assess the relative merits of structural concepts and materials for an advanced arrow wing configuration cruising at Mach 2.7. Preliminary studies were made to insure compliance of the configuration with general design criteria, integrate the propulsion system with the airframe, and define an efficient structural arrangement. Material and concept selection, detailed structural analysis, structural design and airplane mass analysis were completed based on current technology. Based on estimated future technology, structural sizing for strength and a preliminary assessment of the flutter of a strength designed composite structure were completed. An advanced computerized structural design system was used, in conjunction with a relatively complex finite element model, for detailed analysis and sizing of structural members
X-ray Signatures of Circumnuclear Gas in AGN
X-ray spectra of AGN are complex. X-ray absorption and emission features
trace gas covering a wide range of column densities and ionization states. High
resolution spectra show the absorbing gas to be outflowing, perhaps in the form
of an accretion disk wind. The absorbing complex shapes the form of the X-ray
spectrum while X-ray reverberation and absorption changes explain the spectral
and timing behaviour of AGN. We discuss recent progress, highlighting some new
results and reviewing the implications that can be drawn from the data.Comment: Proceedings of the conference "Suzaku 2011, Exploring the X-ray
Universe: Suzaku and Beyond
The Global Implications of the Hard X-ray Excess in Type 1 AGN
Recent evidence for a strong 'hard excess' of flux at energies > 20 keV in
some Suzaku observations of type 1 Active Galactic Nuclei (AGN) has motivated
an exploratory study of the phenomenon in the local type 1 AGN population. We
have selected all type 1 AGN in the Swift Burst Alert Telescope (BAT) 58-month
catalog and cross-correlated them with the holdings of the Suzaku public
archive. We find the hard excess phenomenon to be a ubiquitous property of type
1 AGN. Taken together, the spectral hardness and equivalent width of Fe K alpha
emission are consistent with reprocessing by an ensemble of Compton-thick
clouds that partially cover the continuum source. In the context of such a
model, ~ 80 % of the sample has a hardness ratio consistent with > 50% covering
of the continuum by low-ionization, Compton-thick gas. More detailed study of
the three hardest X-ray spectra in our sample reveal a sharp Fe K absorption
edge at ~ 7 keV in each of them, indicating that blurred reflection is not
responsible for the very hard spectral forms. Simple considerations place the
distribution of Compton-thick clouds at or within the optical broad line
region.Comment: Accepted for publication in Ap
Radiation hydrodynamical models of the inner rim in protoplanetary disks
Many stars host planets orbiting within a few astronomical units (AU). The
occurrence rate and distributions of masses and orbits vary greatly with the
host stars mass. These close planets origins are a mystery that motivates
investigating protoplanetary disks central regions. A key factor governing the
conditions near the star is the silicate sublimation front, which largely
determines where the starlight is absorbed, and which is often called the inner
rim. We present the first radiation hydrodynamical modeling of the sublimation
front in the disks around the young intermediate-mass stars called Herbig Ae
stars. The models are axisymmetric, and include starlight heating, silicate
grains sublimating and condensing to equilibrium at the local, time-dependent
temperature and density, and accretion stresses parametrizing the results of
MHD magneto-rotational turbulence models. The results compare well with
radiation hydrostatic solutions, and prove to be dynamically stable. Passing
the model disks into Monte Carlo radiative transfer calculations, we show that
the models satisfy observational constraints on the inner rims location. A
small optically-thin halo of hot dust naturally arises between the inner rim
and the star. The inner rim has a substantial radial extent, corresponding to
several disk scale heights. While the fronts overall position varies with the
stellar luminosity, its radial extent depends on the mass accretion rate. A
pressure maximum develops near the location of thermal ionization at
temperatures about 1000 K. The pressure maximum is capable of halting solid
pebbles radial drift and concentrating them in a zone where temperatures are
sufficiently high for annealing to form crystalline silicates.Comment: accepted for Ap
Study of metallic structural design concepts for an arrow wing supersonic cruise configuration
A structural design study was made, to assess the relative merits of various metallic structural concepts and materials for an advanced supersonic aircraft cruising at Mach 2.7. Preliminary studies were made to ensure compliance of the configuration with general design criteria, integrate the propulsion system with the airframe, select structural concepts and materials, and define an efficient structural arrangement. An advanced computerized structural design system was used, in conjunction with a relatively large, complex finite element model, for detailed analysis and sizing of structural members to satisfy strength and flutter criteria. A baseline aircraft design was developed for assessment of current technology. Criteria, analysis methods, and results are presented. The effect on design methods of using the computerized structural design system was appraised, and recommendations are presented concerning further development of design tools, development of materials and structural concepts, and research on basic technology
Microscale Alfven waves in the solar wind at 1 AU
Analysis of IMP 1 (Explorer 43) plasma and magnetic field fluctuations on a scale of one hour revealed that linearly and circularly polarized Alfven waves are rarely present in the solar wind at 1 AU. The most prevalent microscale fluctuations appeared to be large-amplitude Alfven waves with small but non-zero fluctuations in the magnetic field intensity. These waves are present about 40% of the time and are predominantly propagating away from the sun
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