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Magnetotunneling in a Two-Dimensional Electron-Hole System Near Equilibrium
We have measured the zero-bias differential tunneling conductance of
InAs/AlSb/GaS b/AlSb/InAs heterostructures at low temperatures (1.7K < T < 60K)
and unde r a magnetic field at various angles with the heterostructure's
interfaces. Shubni kov-de Haas oscillations in the magnetoconductance reveal
the two-dimensional (2D) character of the electrons accumulated at the InAs
interfaces and yield their num ber in each of them. The temperature dependence
of the oscillations suggests the f ormation of a field-induced energy gap at
the Fermi level, similar to that observe d before in simpler 2D-2D tunneling
systems. A calculation of the magnetoconductan ce that considers different 2D
densities in the two InAs electrodes agrees with th e main observations, but
fails to explain features that might be related to the pr esence of 2D holes in
the GaSb region.Comment: 4 papes, 3 eps figures. Submit to Phys. Rev.
Toward the AdS/CFT gravity dual for High Energy Collisions: I.Falling into the AdS
In the context of the AdS/CFT correspondence we discuss the gravity dual of a
high energy collision in a strongly coupled SYM gauge theory. We
suggest a setting in which two colliding objects are made of non-dynamical
heavy quarks and antiquarks, which allows to treat the process in classical
string approximation. Collision ``debris'' consist of closed as well as open
strings. If the latter have ends on two outgoing charges, and thus are being
``stretched'' along the collision axes. We discuss motion in AdS of some simple
objects first -- massless and massive particles -- and then focus on open
strings. We study the latter in a considerable detail, concluding that they
rapidly become ``rectangular'' in proper time -spatial rapidity
coordinates with well separated fragmentation part and a near-free-falling
rapidity-independent central part. Assuming that in the collisions of ``walls''
of charges multiple stretching strings are created, we also consider the motion
of a 3d stretching membrane. We then argue that a complete solution can be
approximated by two different vacuum solutions of Einstein eqns, with matter
membrane separating them. We identify one of this solution with
Janik-Peschanski stretching black hole solution, and show that all objects
approach its (retreating) horizon in an universal manner.Comment: v2 was redone, with new material and different introduction. It now
includes introduction to the second paper of the series as well, in which we
calculate "holograms" of falling objects, namely their stress tensor on the
boundar
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The effect of weld residual stresses and their re-distribution with crack growth during fatigue under constant amplitude loading
In this work the evolution of the residual stresses in a MIG-welded 2024-T3 aluminium alloy M(T) specimen during in situ fatigue crack growth at constant load amplitude has been measured with neutron diffraction. The plastic relaxation and plasticity-induced residual stresses associated with the fatigue loading were found to be small compared with the stresses arising due to elastic re-distribution of the initial residual stress field. The elastic re-distribution was modelled with a finite element simulation and a good correlation between the experimentally-determined and the modelled stresses was found. A significant mean stress effect on the fatigue crack growth rate was seen and this was also accurately predicted using the measured initial residual stresses
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