1,031 research outputs found
Photoproduction of jets and the virtual structure of the photon
We compute the ratio between the direct and the resolved photon components of
single jet and dijet production in collisions for the kinematical range
covered by the most recent ZEUS data. We analyse the phenomenological
consequences of different models for the structure of virtual photons in these
observables and compare them with the available data. We also comment on the
correlation between the so called and the `true'
, that can be inferred from the data.Comment: epsfig, 5 figure
Study of controlled diffusion stator blading. 1. Aerodynamic and mechanical design report
Pratt & Whitney Aircraft is conducting a test program for NASA in order to demonstrate that a controlled-diffusion stator provides low losses at high loadings and Mach numbers. The technology has shown great promise in wind tunnel tests. Details of the design of the controlled diffusion stator vanes and the multiple-circular-arc rotor blades are presented. The stage, including stator and rotor, was designed to be suitable for the first-stage of an advanced multistage, high-pressure compressor
The Possible White Dwarf-Neutron Star Connection
The current status of the problem of whether neutron stars can form, in close
binary systems, by accretion-induced collapse (AIC) of white dwarfs is
examined. We find that, in principle, both initially cold C+O white dwarfs in
the high-mass tail of their mass distribution in binaries and O+Ne+Mg white
dwarfs can produce neutron stars. Which fractions of neutron stars in different
types of binaries (or descendants from binaries) might originate from this
process remains uncertain.Comment: 6 pages. To appear in "White Dwarfs", ed. J. Isern, M. Hernanz, and
E. Garcia-Berro (Dordrecht: Kluwer
Core compressor exit stage study, 2
A total of two three-stage compressors were designed and tested to determine the effects of aspect ratio on compressor performance. The first compressor was designed with an aspect ratio of 0.81; the other, with an aspect ratio of 1.22. Both compressors had a hub-tip ratio of 0.915, representative of the rear stages of a core compressor, and both were designed to achieve a 15.0% surge margin at design pressure ratios of 1.357 and 1.324, respectively, at a mean wheel speed of 167 m/sec. At design speed the 0.81 aspect ratio compressor achieved a pressure ratio of 1.346 at a corrected flow of 4.28 kg/sec and an adiabatic efficiency of 86.1%. The 1.22 aspect ratio design achieved a pressure ratio of 1.314 at 4.35 kg/sec flow and 87.0% adiabatic efficiency. Surge margin to peak efficiency was 24.0% with the lower aspect ratio blading, compared with 12.4% with the higher aspect ratio blading
Tau Be or not Tau Be? - A Perspective on Service Compatibility and Substitutability
One of the main open research issues in Service Oriented Computing is to
propose automated techniques to analyse service interfaces. A first problem,
called compatibility, aims at determining whether a set of services (two in
this paper) can be composed together and interact with each other as expected.
Another related problem is to check the substitutability of one service with
another. These problems are especially difficult when behavioural descriptions
(i.e., message calls and their ordering) are taken into account in service
interfaces. Interfaces should capture as faithfully as possible the service
behaviour to make their automated analysis possible while not exhibiting
implementation details. In this position paper, we choose Labelled Transition
Systems to specify the behavioural part of service interfaces. In particular,
we show that internal behaviours (tau transitions) are necessary in these
transition systems in order to detect subtle errors that may occur when
composing a set of services together. We also show that tau transitions should
be handled differently in the compatibility and substitutability problem: the
former problem requires to check if the compatibility is preserved every time a
tau transition is traversed in one interface, whereas the latter requires a
precise analysis of tau branchings in order to make the substitution preserve
the properties (e.g., a compatibility notion) which were ensured before
replacement.Comment: In Proceedings WCSI 2010, arXiv:1010.233
Nickel-Rich Outflows Produced by the Accretion-Induced Collapse of White Dwarfs: Lightcurves and Spectra
The accretion-induced collapse (AIC) of a white dwarf to form a neutron star
can leave behind a rotationally supported disk with mass of up to ~ 0.1 M_sun.
The disk is initially composed of free nucleons but as it accretes and spreads
to larger radii, the free nucleons recombine to form helium, releasing
sufficient energy to unbind the remaining disk. Most of the ejected mass fuses
to form Ni56 and other iron group elements. We present spherically symmetric
radiative transfer calculations of the transient powered by the radioactive
heating of this ejecta. For an ejecta mass of 1e-2 M_sun (3e-3 M_sun), the
lightcurve peaks after <~ 1 day with a peak bolometric luminosity ~ 2e41 erg/s
(~ 5e40 erg/s), i.e., a "kilonova"; the decay time is ~ 4 (2) days. Overall,
the spectra redden with time reaching U-V ~ 4 after ~ 1 day; the optical colors
(B-V) are, however, somewhat blue. Near the peak in the lightcurve, the spectra
are dominated by Doppler broadened Nickel features, with no distinct spectral
lines present. At ~ 3-5 days, strong Calcium lines are present in the infrared,
although the Calcium mass fraction is only ~ 1e-4.5. If rotationally supported
disks are a common byproduct of AIC, current and upcoming transient surveys
such as the Palomar Transient Factory should detect a few AIC per year for an
AIC rate of ~ 1e-2 of the Type Ia rate. We discuss ways of distinguishing AIC
from other rapid, faint transients, including .Ia's and the ejecta from binary
neutron star mergers.Comment: 9 pages, 4 figures, 1 table, now accepted to MNRA
Identification of the companion stars of Type Ia supernovae
The nature of the binary systems giving rise to Type Ia supernovae (SNeIa)
remains an unsolved problem. In this {\it Letter} we calculate, from the
statistics of initial conditions (masses and binary separations), the mass,
luminosity, and velocity distributions of the possible binary companions
(main-sequence star, subgiant, red giant) following the explosion of the white
dwarf which gives rise to the SNeIa. Those companions could be detected from
either their proper or their radial motions, by means of high-precision
astrometric and radial-velocity measurements in young, nearby supernova
remnants. Peculiar velocities typically ranging from 100 to 450 km s
should be expected, which places proper-motion measurements within reach of HST
instruments and makes radial-velocity ones feasible with 2.5-4m class
telescopes from the ground. Detections would solve the long-standing problem of
which kind of binaries do produce SNeIa and clear up the way to accurate
physical modeling of the explosions.Comment: 17 pages, incl. 2 figures. Submittet to ApJ (Letters
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