146,472 research outputs found
Interface refactoring in performance-constrained web services
This paper presents the development of REF-WS an approach to enable a Web Service provider to reliably evolve their service through the application of refactoring transformations. REF-WS is intended to aid service providers, particularly in a reliability and performance constrained domain as it permits upgraded ’non-backwards compatible’ services to be deployed into a performance constrained network where existing consumers depend on an older version of the service interface. In order for this to be successful, the refactoring and message mediation needs to occur without affecting functional compatibility with the services’ consumers, and must operate within the performance overhead expected of the original service, introducing as little latency as possible. Furthermore, compared to a manually programmed solution, the presented approach enables the service developer to apply and parameterize refactorings with a level of confidence that they will not produce an invalid or ’corrupt’ transformation of messages. This is achieved through the use of preconditions for the defined refactorings
Profiles of thermal line emission from advection dominated accretion flows
Recently, Narayan & Raymond (1999) proposed that the thermal emission lines
from the hot plasma in advection dominated accretion flows (ADAFs) are
potentially observable with the next generation of X-ray observatories, with
which the physical properties of some X-ray sources can be probed. In ADAFs,
the temperature of the ion is so high that the thermal broadening of the line
is important. We calculate the profiles of thermal line emission from ADAFs, in
which both the thermal and Doppler broadening have been considered. It is found
that the double-peaked profiles are present for high inclination angles between
the axis of disk and the line of sight. The double-peaked profiles are smeared
in low inclination cases, and completely disappear while the inclination angle
is less than , where the thermal and turbulent broadening dominated
on the line profiles. We also note that the thermal line profile is affected by
the location of the transition radius of ADAF. The self-similar
height-integrated disk structure and the emissivity with power-law dependence
of radius are adopted in our calculations. The results obtained in this work
can be used as a diagnosis on the future X-ray observations of the thermal
lines. Some important physical quantities of ADAFs could be inferred from
future thermal line observations.Comment: 7 page
Quantum spin mixing in a binary mixture of spin-1 atomic condensates
We study quantum spin mixing in a binary mixture of spin-1 condensates
including coherent interspecies mixing process, using the familiar spinor
condensates of Rb and Na atoms in the ground lower hyperfine F=1
manifolds as prototype examples. Within the single spatial mode approximation
for each of the two spinor condensates, the mixing dynamics reduce to that of
three coupled nonlinear pendulums with clear physical interpretations. Using
suitably prepared initial states, it is possible to determine the interspecies
singlet-pairing as well as spin-exchange interactions from the subsequent
mixing dynamics.Comment: 6 pages, 3 figure
Narrow-line Seyfert 1 Galaxies and the M_BH - sigma Relation
We have studied the location of narrow-line Seyfert 1 (NLS1) galaxies and
broad-line Seyfert 1 (BLS1) galaxies on the M_BH - sigma relation of non-active
galaxies. We find that NLS1 galaxies as a class - as well as the BLS1 galaxies
of our comparison sample - do follow the M_BH-sigma relation of non-active
galaxies if we use the width of the [SII]6716,6731 emission lines as surrogate
for stellar velocity dispersion, sigma_*. We also find that the width of
[OIII]5007 is a good surrogate for sigma_*, but only after (a) removal of
asymmetric blue wings, and, more important, after (b) excluding core [OIII]
lines with strong blueshifts (i.e., excluding galaxies which have their [OIII]
velocity fields dominated by radial motions, presumably outflows). The same
galaxies which are extreme outliers in [OIII] still follow the M_BH - sigma
relation in [SII]. We confirm previous findings that NLS1 galaxies are
systematically off-set from the M_BH - sigma relation if the full [OIII]
profile is used to measure sigma. We systematically investigate the influence
of several parameters on the NSL1 galaxies' location on the M_BH - sigma plane:
[OIII]_core blueshift, L/L_Edd, intensity ratio FeII/H_beta, NLR density, and
absolute magnitude. Implications for NLS1 models and for their evolution along
the M_BH - sigma relation are discussed.Comment: ApJ Letters, in press (3 figures, one in colour
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