37,444 research outputs found
Opaque Service Virtualisation: A Practical Tool for Emulating Endpoint Systems
Large enterprise software systems make many complex interactions with other
services in their environment. Developing and testing for production-like
conditions is therefore a very challenging task. Current approaches include
emulation of dependent services using either explicit modelling or
record-and-replay approaches. Models require deep knowledge of the target
services while record-and-replay is limited in accuracy. Both face
developmental and scaling issues. We present a new technique that improves the
accuracy of record-and-replay approaches, without requiring prior knowledge of
the service protocols. The approach uses Multiple Sequence Alignment to derive
message prototypes from recorded system interactions and a scheme to match
incoming request messages against prototypes to generate response messages. We
use a modified Needleman-Wunsch algorithm for distance calculation during
message matching. Our approach has shown greater than 99% accuracy for four
evaluated enterprise system messaging protocols. The approach has been
successfully integrated into the CA Service Virtualization commercial product
to complement its existing techniques.Comment: In Proceedings of the 38th International Conference on Software
Engineering Companion (pp. 202-211). arXiv admin note: text overlap with
arXiv:1510.0142
An experimental study for a miniature Stirling refrigerator
Experimental results of a miniature two-stage Stirling cryocooler are introduced. The influence of filling gas pressure and refrigeration temperature on the refrigerating capacity along with the relationship between parameters was measured. The valley pressure corresponding to the lowest refrigeration temperature and the cooldown time versus operating pressure are discussed. The coefficient of performance and thermodynamic efficiency of the cryocooler are calculated based on experimental data
Investigation for the puzzling abundance pattern of the neutron-capture elements in the ultra metal-poor star: CS 30322-023
The s-enhanced and very metal-poor star CS 30322-023 shows a puzzling
abundance pattern of the neutron-capture elements, i.e. several neutron-capture
elements such as Ba, Pb etc. show enhancement, but other neutron-capture
elements such as Sr, Eu etc. exhibit deficient with respect to iron. The study
to this sample star could make people gain a better understanding of s- and
r-process nucleosynthesis at low metallicity. Using a parametric model, we find
that the abundance pattern of the neutron-capture elements could be best
explained by a star that was polluted by an AGB star and the CS 30322-023
binary system formed in a molecular cloud which had never been polluted by
r-process material. The lack of r-process material also indicates that the AGB
companion cannot have undergone a type-1.5 supernova, and thus must have had an
initial mass below 4.0M, while the strong N overabundance and the
absence of a strong C overabundance indicate that the companion's initial mass
was larger than 2.0M. The smaller s-process component coefficient of
this star illustrates that there is less accreted material of this star from
the AGB companion, and the sample star should be formed in the binary system
with larger initial orbital separation where the accretion-induced collapse
(AIC) mechanism can not work.Comment: 13 pages, 2 figure
X-ray Flares from Markarian 501
Motivated by the recent finding of hierarchical X-ray flaring phenomenon in
Mrk 421, we conducted a systematic search for X-ray flares from Mrk 501,
another well-known TeV blazar, by making use of the rich {\em RXTE} archival
database. We detected flares over a wide range of timescales, from months down
to minutes, as in the case of Mrk 421. However, the flares do not seem to occur
nearly as frequently in Mrk 501 as in Mrk 421 on any of the timescales. The
flaring hierarchy also seems apparent in Mrk 501, suggesting that it might be
common among TeV blazars. The results seem to imply a scale-invariant physical
origin of the flares (large or small). The X-ray spectrum of the source shows a
general trend of hardening toward the peak of long-duration flares, with
indication of spectral hysteresis, which is often seen in TeV blazars. However,
the data are not of sufficient quality to allow us to draw definitive
conclusions about spectral variability associated with more rapid but weaker
flares. We critically examine a reported sub-hour X-ray flare from Mrk 501, in
light of intense background flaring activity at the time of the observation,
and concluded that the flare is likely an artifact. On the other hand, we did
identify a rapid X-ray flare that appears to be real. It lasted only for about
15 minutes, during which the flux of the source varied by about 30%.
Sub-structures are apparent in its profile, implying variabilities on even
shorter timescales. Such rapid variabilities of Mrk 501 place severe
constraints on the physical properties of the flaring region in the jet, which
have serious implications on the emission models proposed for TeV blazars.Comment: 23 pages, 11 figures, accepted for publication in Ap
Compensation of Effective Field in the Field-Induced Superconductor k-(BETS)2FeBr4 Observed by 77Se NMR
We report results of 77Se NMR frequency shift in the normal state of the
organic charge-transfer-salt k-(BETS)2FeBr4 which shows magnetic field-induced
superconductivity (FISC). From a simple mean field analysis, we determined the
field and the temperature dependences of the magnetization m_{pi} of the \pi
conduction electrons on BETS molecules. We found that the Fe spins are
antiferromagnetically coupled to the pi electrons and determined the exchange
field to be J = -2.3T/mu_B. The exchange field from the fully saturated Fe
moments (5 mu_B) is compensated by an external field of 12T. This is close to
the central field of the FISC phase, consistent with the Jaccarino-Peter local
field-compensation mechanism for FISC (Phys. Rev. Lett. 9, 290 (1962))
Dirac-Surface-State-Dominated Spin to Charge Current Conversion in the Topological Insulator Films at Room Temperature
We report the spin to charge current conversation in an intrinsic topological
insulator (TI) film at room temperature. The spin
currents are generated in a thin layer of permalloy (Py) by two different
processes, spin pumping (SPE) and spin Seebeck effects (SSE). In the first we
use microwave-driven ferromagnetic resonance of the Py film to generate a SPE
spin current that is injected into the TI layer in
direct contact with Py. In the second we use the SSE in the longitudinal
configuration in Py without contamination by the Nernst effect made possible
with a thin NiO layer between the Py and layers.
The spin-to-charge current conversion is attributed to the inverse Edelstein
effect (IEE) made possible by the spin-momentum locking in the electron Fermi
contours due to the Rashba field. The measurements by the two techniques yield
very similar values for the IEE parameter, which are larger than the reported
values in the previous studies on topological insulators.Comment: 18 pages and 7 figure
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