89,296 research outputs found
Variational calculation of many-body wave functions and energies from density-functional theory
A generating coordinate is introduced into the exchange-correlation
functional of density-functional theory (DFT). The many-body wave function is
represented as a superposition of Kohn-Sham (KS) Slater determinants arising
from different values of the generating coordinate. This superposition is used
to variationally calculate many-body energies and wave functions from solutions
of the KS equation of DFT. The method works for ground and excited states, and
does not depend on identifying the KS orbitals and energies with physical ones.
Numerical application to the Helium isoelectronic series illustrates the
method's viability and potential.Comment: 4 pages, 2 tables, J. Chem. Phys., accepte
Fluids confined in wedges and by edges: From cluster integrals to thermodynamic properties referred to different regions
Recently, new insights in the relation between the geometry of the vessel
that confines a fluid and its thermodynamic properties were traced through the
study of cluster integrals for inhomogeneous fluids. In this work I analyze the
thermodynamic properties of fluids confined in wedges or by edges, emphasizing
on the question of the region to which these properties refer. In this context,
the relations between the line-thermodynamic properties referred to different
regions are derived as analytic functions of the dihedral angle , for
, which enables a unified approach to both edges and wedges. As
a simple application of these results, I analyze the properties of the confined
gas in the low-density regime. Finally, using recent analytic results for the
second cluster integral of the confined hard sphere fluid, the low density
behavior of the line thermodynamic properties is analytically studied up to
order two in the density for and by adopting different
reference regions.Comment: 8 pages, 7 figure
Warm molecular hydrogen in outflows from Ultraluminous Infrared Galaxies
Ultraluminous infrared galaxies (ULIRGs) show on average three times more
emission in the rotational transitions of molecular hydrogen than expected
based on their star formation rates. Using Spitzer archival data we investigate
the origin of excess warm H_2 emission in 115 ULIRGs of the IRAS 1 Jy sample.
We find a strong correlation between H_2 and [FeII] line luminosities,
suggesting that excess H_2 is produced in shocks propagating within neutral or
partially ionized medium. This view is supported by the correlations between
H_2 and optical line ratios diagnostic of such shocks. The galaxies powered by
star formation and those powered by active nuclei follow the same relationship
between H_2 and [FeII], with emission line width being the major difference
between these classes (about 500 and 1000 km/sec, respectively). We conclude
that excess H_2 emission is produced as the supernovae and active nuclei drive
outflows into the neutral interstellar medium of the ULIRGs. A weak positive
correlation between H_2 and the length of the tidal tails indicates that these
outflows are more likely to be encountered in more advanced mergers, but there
is no evidence for excess H_2 produced as a result of the collision shocks
during the final coalescence.Comment: 16 pages, MNRAS accepted. Complete data tables and Spitzer spectra
are available at http://www.pha.jhu.edu/~zakamska/ULIRGS
Ultrasonic scanner for radial and flat panels
An ultrasonic scanning mechanism is described that scans panels of honeycomb construction or with welded seams. It incorporates a device which by simple adjustment is adapted to scan either a flat panel or a radial panel. The supporting structure takes the form of a pair of spaced rails. An immersion tank is positioned between the rails and below their level. A work holder is mounted in the tank and is adapted to hold the flat or radial panel. A traveling bridge is movable along the rails and a carriage is mounted on the bridge
A monostrain test apparatus
Test apparatus is designed for determining tensile strength, modulus of elasticity, elongation, and thermal coefficient of contraction or expansion of uniformly shaped plastics, adhesives, and foam materials over temperature range of 700 to 90 K (800 to -300). Tests may be used in design quality control, and in evaluation of new adhesives and plastic materials
Efficiency of autonomous soft nano-machines at maximum power
We consider nano-sized artificial or biological machines working in steady
state enforced by imposing non-equilibrium concentrations of solutes or by
applying external forces, torques or electric fields. For unicyclic and
strongly coupled multicyclic machines, efficiency at maximum power is not
bounded by the linear response value 1/2. For strong driving, it can even
approach the thermodynamic limit 1. Quite generally, such machines fall in
three different classes characterized, respectively, as "strong and efficient",
"strong and inefficient", and "balanced". For weakly coupled multicyclic
machines, efficiency at maximum power has lost any universality even in the
linear response regime
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