38,737 research outputs found
Coulomb drag in double quantum wells with a perpendicular magnetic field
Momentum transfer due to electron-electron interaction (Coulomb drag) between
two quantum wells, separated by a distance , in the presence of a
perpendicular magnetic field, is studied at low temperatures. We find besides
the well known Shubnikov-de Haas oscillations, which also appear in the drag
effect, the momentum transfer is markedly enhanced by the magnetic field.Comment: 8 pages, Revtex, 4 Postscript figures are available upon request,
Accepted by Mod. Phys. Lett.
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
Gluon GPDs and Exclusive Photoproduction of a Quarkonium in Forward Region
Forward photoproduction of can be used to extract Generalized Parton
Distributions(GPD's) of gluons. We analyze the process at twist-3 level and
study relevant classifications of twist-3 gluon GPD's. At leading power or
twist-2 level the produced is transversely polarized. We find that at
twist-3 the produced is longitudinally polarized. Our study shows that
in high energy limit the twist-3 amplitude is only suppressed by the inverse
power of the heavy quark mass relatively to the twist-2 amplitude. This
indicates that the power correction to the cross-section of unpolarized
can have a sizeable effect. We have also derived the amplitude of the
production of at twist-3, but the result contains end-point
singularities. The production of other quarkonia has been briefly discussed.Comment: Discussions of results are adde
Local rectification of heat flux
We present a chain-of-atoms model where heat is rectified, with different
fluxes from the hot to the cold baths located at the chain boundaries when the
temperature bias is reversed. The chain is homogeneous except for boundary
effects and a local modification of the interactions at one site, the
"impurity". The rectification mechanism is due here to the localized impurity,
the only asymmetrical element of the structure, apart from the externally
imposed temperature bias, and does not rely on putting in contact different
materials or other known mechanisms such as grading or long-range interactions.
The effect survives if all interaction forces are linear except the ones for
the impurity.Comment: 5 pages, 5 figure
Evidence for "Propeller" Effects In X-ray Pulsars GX 1+4 And GROJ1744-28
We present observational evidence for "propeller" effects in two X-ray
pulsars, GX 1+4 and GROJ1744-28. Both sources were monitored regularly by the
Rossi X-ray Timing Explorer (RXTE) throughout a decaying period in the X-ray
brightness. Quite remarkably, strong X-ray pulsation became unmeasurable when
total X-ray flux had dropped below a certain threshold. Such a phenomenon is a
clear indication of the propeller effects which take place when pulsar
magnetosphere grows beyond the co-rotation radius as a result of the decrease
in mass accretion rate and centrifugal force prevents accreting matter from
reaching the magnetic poles. The entire process should simply reverse as the
accretion rate increases. Indeed, steady X-ray pulsation was reestablished as
the sources emerged from the non-pulsating faint state. These data allow us to
directly derive the surface polar magnetic field strength for both pulsars:
3.1E+13 G for GX 1+4 and 2.4E+11 G for GROJ1744-28. The results are likely to
be accurate to within a factor of 2, with the total uncertainty dominated by
the uncertainty in estimating the distances to the sources. Possible mechanisms
for the persistent emission observed in the faint state are discussed in light
of the extreme magnetic properties of the sources.Comment: 12 pages including 3 ps figures. To appear in ApJ Letters Vol. 48
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