Does string theory solve the puzzles of black hole evaporation?

We point out that the massive modes of closed superstring theories may play a crucial role in the last stages of black hole evaporation. If the Bekenstein-Hawking entropy describes the true degeneracy of a black hole — implying loss of quantum coherence and the unitary evolution of quantum states-it becomes entropically favorable for an evaporating black hole to make a transition to a state of massive string modes. This in turn may decay into massless modes of the string (radiation) avoiding the naked singularity exposed by black hole evaporation in the semiclassical picture. Alternatively, quantum coherence may be maintained if the entropy of an evaporating black hole is much larger than that given by the Bekenstein-Hawking formula. In that case, however, the transition to massive string modes is unlikely. String theories might thus resolve the difficulty of the naked singularity, but it appears likely that they will still involve loss of quantum coherence.This essay received the first award from the Gravity Research Foundation for the year 1986 — Ed.     

Nonadditivity of bipartite distillable entanglement follows from a conjecture on bound entangled Werner states

Assuming the validity of a conjecture given by DiVincenzo et al. [Phys. Rev. A 61, 062312 (2000)] and by Dür et al. [Phys. Rev. A 61, 062313 (2000)], we show that the distillable entanglement for two bipartite states, each of which individually has zero distillable entanglement, can be nonzero. We show that this also implies that the distillable entanglement is not a convex function. Our example consists of the tensor product of a bound entangled state based on an unextendible product basis with an entangled Werner state which lies in the class of conjectured undistillable states.     

Crystal structure of diserinesulfate monohydrate

The crystal structure of DL-Serine H₂SO₄ · H₂O is determined by single-crystal x-ray diffraction. The intensities of x-ray reflections are measured at three temperatures, namely, 295, 343, and 233 K. The crystal structure of the studied compound is refined using all three sets of intensities. It is demonstrated that, at a temperature of 233 K, the structure transforms into an incommensurately modulated state. This transformation is assumed to be responsible for the disappearance of the piezoresponse at this temperature.     

Finite element simulation of nanostructuring burnishing

Dynamics simulation of burnishing of a thin steel layer beneath an indenter applied with a constant force and then moving with a constant velocity was performed by the finite element method in the plane strain approximation. The indenter was modeled by a perfectly rigid body, and the steel was modeled by an elastoplastic body with isotropic hardening according to an experimentally defined law. The regularities of changes in the stressstrain state of the material near the treated surface were studied and mechanisms of the formation of a nanostructured layer were disclosed. The effect of the friction coefficient and the burnishing force on the height of a bulge of edged material was analyzed. The results of studies agree well with experimental data.     

Localized plastic strain in polycrystalline materials with hole and notches

Analyzed numerically are the localized strain of polycrystalline materials subjected to quasi-static loading. The objective is to study the peculiarities associated with the deformation process close to the stress concentrators such as holes, notches and interfaces of internal structure. Analytical results show that geometry and/or heterogeneous internal structure of material together with the action of maximum shear result in the development of a system of plastically deformed shear bands. Shears and rotations in the regions of strain localization are found to be higher than in other parts of the specimen while rotations are more sensitive to localization.     

The thermodynamics of gravitational radiation

I conjecture, and show for a large class of cases, that given a spacelike hypersurface on which is an arbitrary distribution of linearized gravitons and matter, the latter satisfying the positive energy condition, the expectation value of the number of events in which a graviton is absorbed by or scattered inelastically from the matter within any future time,t, is always less then the expectation value of the number of gravitons in the initial state (except for a set of initial configurations of measure zero). Consequences of this result are: (1) the impossibility of any system containing gravitational radiation reaching thermal equilibrium in a finite time, (2) the absence of an ultraviolet catastrophe for gravitational radiation, (3) the impossibility of measuring accurately the quantum state of the linearized gravitational field, and (4) the impossibility of constructing a gravitational wave laser.This essay received the second award from the Gravity Research Foundation for the year 1983 [Ed.].     

Superspace unmasked: The physical interpretation of supergravity theory

Supergravity admits a geometric formulation in terms of an expanded algebra of functions on ordinary spacetime. This formulation, called graded manifold theory, is equivalent to the usual superspace supergravity constructions but avoids the anticommuting coordinates of superspace. The geometry suggests an operational interpretation of supergravity theory in terms of measurements made by local observers in spacetime.