31,175 research outputs found
Thirteen-color narrow-band photometry of one thousand bright stars
Thirteen-color narrow-band photometry of one thousand bright star
Recovering the stationary phase condition for accurately obtaining scattering and tunneling times
The stationary phase method is often employed for computing tunneling {\em
phase} times of analytically-continuous {\em gaussian} or infinite-bandwidth
step pulses which collide with a potential barrier. The indiscriminate
utilization of this method without considering the barrier boundary effects
leads to some misconceptions in the interpretation of the phase times. After
reexamining the above barrier diffusion problem where we notice the wave packet
collision necessarily leads to the possibility of multiple reflected and
transmitted wave packets, we study the phase times for tunneling/reflecting
particles in a framework where an idea of multiple wave packet decomposition is
recovered. To partially overcome the analytical incongruities which rise up
when tunneling phase time expressions are obtained, we present a theoretical
exercise involving a symmetrical collision between two identical wave packets
and a one dimensional squared potential barrier where the scattered wave
packets can be recomposed by summing the amplitudes of simultaneously reflected
and transmitted waves.Comment: 32 pages, 5 figures, 1 tabl
Multiple Application Propfan Study (MAPS): Advanced tactical transport
This study was conducted to ascertain potential benefits of a propfan propulsion system application to a blended wing/body military tactical transport. Based on a design cruise Mach no. of 0.75 for the design mission, the results indicate a significant advantage in various figures of merit for the propfan over those of a comparable technology turbofan. Although the propfan has a 1.6 percent greater takeoff gross weight, its life cycle cost is 5.3 percent smaller, partly because of a 27 percent smaller specific fuel consumption. When employed on alternate missions, the propfan configuration offers significantly improved flexibility and capability: an increase in sea level penetration distance of more than 100 percent, or in time-on-station of 24 percent, or in deployment payload of 38 percent
âsome kind of thing it aint us but yet its in usâ: David Mitchell, Russell Hoban, and metafiction after the millennium
This article appraises the debt that David Mitchellâs Cloud Atlas owes to the novels of Russell Hoban, including, but not limited to, Riddley Walker. After clearly mapping a history of Hobanâs philosophical perspectives and Mitchellâs inter-textual genre-impersonation practice, the article assesses the degree to which Mitchellâs metatextual methods indicate a nostalgia for by-gone radical aesthetics rather than reaching for new modes of its own. The article not only proposes several new backdrops against which Mitchellâs novel can be read but also conducts the first in-depth appraisal of Mitchellâs formal linguistic replication of Riddley Walker
Strategy bifurcation and spatial inhomogeneity in a simple model of competing sellers
We present a simple one-parameter model for spatially localised evolving
agents competing for spatially localised resources. The model considers selling
agents able to evolve their pricing strategy in competition for a fixed market.
Despite its simplicity, the model displays extraordinarily rich behavior. In
addition to ``cheap'' sellers pricing to cover their costs, ``expensive''
sellers spontaneously appear to exploit short-term favorable situations. These
expensive sellers ``speciate'' into discrete price bands. As well as variety in
pricing strategy, the ``cheap'' sellers evolve a strongly correlated spatial
structure, which in turn creates niches for their expensive competitors. Thus
an entire ecosystem of coexisting, discrete, symmetry-breaking strategies
arises.Comment: 6 pages, 6 figures, epl2; 1 new figure, include nash equilibrium
analysis, typo fixe
Quantifying structural damage from self-irradiation in a plutonium superconductor
The 18.5 K superconductor PuCoGa5 has many unusual properties, including
those due to damage induced by self-irradiation. The superconducting transition
temperature decreases sharply with time, suggesting a radiation-induced Frenkel
defect concentration much larger than predicted by current radiation damage
theories. Extended x-ray absorption fine-structure measurements demonstrate
that while the local crystal structure in fresh material is well ordered, aged
material is disordered much more strongly than expected from simple defects,
consistent with strong disorder throughout the damage cascade region. These
data highlight the potential impact of local lattice distortions relative to
defects on the properties of irradiated materials and underscore the need for
more atomic-resolution structural comparisons between radiation damage
experiments and theory.Comment: 7 pages, 5 figures, to be published in PR
Mission-oriented requirements for updating MIL-H-8501. Volume 1: STI proposed structure
The structure of a new flying and ground handling qualities specification for military rotorcraft is presented. This preliminary specification structure is intended to evolve into a replacement for specification MIL-H-8501A. The new structure is designed to accommodate a variety of rotorcraft types, mission flight phases, flight envelopes, and flight environmental characteristics and to provide criteria for three levels of flying qualities, a systematic treatment of failures and reliability, both conventional and multiaxis controllers, and external vision aids which may also incorporate synthetic display content. Existing and new criteria were incorporated into the new structure wherever they could be substantiated
Shocks and sonic booms in the intracluster medium: X-ray shells and radio galaxy activity
Motivated by hydrodynamic simulations, we discuss the X-ray appearance of
radio galaxies embedded in the intracluster medium (ICM) of a galaxy cluster.
We distinguish three regimes. In the early life of a powerful source, the
entire radio cocoon is expanding supersonically and hence drives a strong shock
into the ICM. Eventually, the sides of the cocoon become subsonic and the ICM
is disturbed by the sonic booms of the jet's working surface. In both of these
regimes, X-ray observations would find an X-ray shell. In the strong shock
regime, this shell will be hot and relatively thin. However, in the weak shock
(sonic-boom) regime, the shell will be approximately the same temperature as
the undisturbed ICM. If a cooling flow is present, the observed shell may even
be cooler than the undisturbed ICM due to the lifting of cooler material into
the shell from the inner (cooler) regions of the cluster. In the third and
final regime, the cocoon has collapsed and no well-defined X-ray shell will be
seen. We discuss ways of estimating the power and age of the source once its
regime of behavior has been determined.Comment: 4 pages, submitted for publication in Astrophysical Journal. Full
paper (including figure) can be obtained from
http://rocinante.Colorado.EDU/~chris/papers/xray_hydro.p
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