Attraction, with boundaries

We study the basin of attraction of static extremal black holes, in the concrete setting of the STU model. By finding a connection to a decoupled Toda-like system and solving it exactly, we find a simple way to characterize the attraction basin via competing behaviors of certain parameters. The boundaries of attraction arise in the various limits where these parameters degenerate to zero. We find that these boundaries are generalizations of the recently introduced (extremal) subtracted geometry: the warp factors still exhibit asymptotic integer power law behaviors, but the powers can be different from one. As we cross over one of these boundaries ('generalized subttractors'), the solutions turn unstable and start blowing up at finite radius and lose their asymptotic region. Our results are fully analytic, but we also solve a simpler theory where the attraction basin is lower dimensional and easy to visualize, and present a simple picture that illustrates many of the basic ideas.

Higher spin cosmology

We construct cosmological solutions of higher spin gravity in 2 + 1 dimensional de Sitter space. We show that a consistent thermodynamics can be obtained for their horizons by demanding appropriate holonomy conditions. This is equivalent to demanding the integrability of the Euclidean boundary conformal field theory partition function, and it reduces to Gibbons-Hawking thermodynamics in the spin-2 case. By using the prescription of Maldacena, we relate the thermodynamics of these solutions to those of higher spin black holes in AdS(3).

Observation of a reversible isomorphous phase transition and an interplay of ``sigma-holes'' and ``pi-holes'' in Fmoc-Leu-psiCH2-NCS]

Fmoc-Leu-psiCH2NCS] undergoes a reversible isomorphous phase transition upon cooling. The crystal structure at 100 K displays a short N=C=S center dot center dot center dot N=C=S intermolecular interaction, which has been characterized based on experimental charge density analysis, as a stabilizing interaction with both sigma-holes and pi-holes acting cooperatively.

Heat kernels on the AdS(2) cone and logarithmic corrections to extremal black hole entropy

We develop new techniques to efficiently evaluate heat kernel coefficients for the Laplacian in the short-time expansion on spheres and hyperboloids with conical singularities. We then apply these techniques to explicitly compute the logarithmic contribution to black hole entropy from an N = 4 vector multiplet about a Z(N) orbifold of the near-horizon geometry of quarter-BPS black holes in N = 4 supergravity. We find that this vanishes, matching perfectly with the prediction from the microstate counting. We also discuss possible generalisations of our heat kernel results to higher-spin fields over ZN orbifolds of higher-dimensional spheres and hyperboloids.

Using internal fibre geometry to improve the performance of pin-loaded holes in composite materials

The anisotropic nature of fibre reinforced composites leads to large stress concentrations around pin-loaded holes through standard weave cloths. Proper understanding of how this anisotropic nature affects the load distribution around holes can be utilised to reduce these con-centrations if sufficient thought is given to the internal fibre geometry near to the hole. Such local reinforcements need not be highly complex and can be readily produced without excessive effort, producing significant improvements in performance. © 1996 Kluwer Academic Publishers.

Experimental investigation on bubble coalescence under nonuniform temperature distribution in reduced gravity

Results on bubble coalescences from the space experiment of thermocapillary bubble migration conducted on board the Chinese 22nd recoverable satellite are presented in this paper. Some coalescences of large spherical bubbles under microgravity are observed through bubbles staying at the upper side of the test cell. The data of bubble coalescence time are recorded and compared with theoretical predictions, which is based on a theory to describe the tendency of coalescence connected to chemical potential difference. It is implied that the theory is applicable for the experimental data of bubble coalescence. Moreover, the angle between the line of two bubble centers and temperature gradient falled mostly in the range 20 degrees-40 degrees. (C) 2007 Elsevier Inc. All rights reserved.

Topics in quantum gravity

We study some aspects of conformal field theory, wormhole physics and two-dimensional random surfaces. Inspite of being rather different, these topics serve as examples of the issues that are involved, both at high and low energy scales, in formulating a quantum theory of gravity. In conformal field theory we show that fusion and braiding properties can be used to determine the operator product coefficients of the non-diagonal Wess-Zumino-Witten models. In wormhole physics we show how Coleman's proposed probability distribution would result in wormholes determining the value of ^θQCD. We attempt such a calculation and find the most probable value of ^θQCD to be π. This hints at a potential conflict with nature. In random surfaces we explore the behaviour of conformal field theories coupled to gravity and calculate some partition functions and correlation functions. Our results throw some light on the transition that is believed to occur when the central charge of the matter theory gets larger than one.

Electron spin relaxation by nuclei and holes in single InAs quantum dots

Electron spin relaxation of charged excitons X+ and X2+ are investigated by time-resolved and polarization-resolved photoluminescence spectroscopy. For X+ configuration, the electron spin relaxation shows a typical decay curve induced by hyperfine interaction with nuclei, whereas for X2+ state the electron spin relaxation is affected not only by nuclei but also by electron-hole exchange interaction, leading to a power-law time dependence.

Greatly enhanced resonant tunneling of photo-excited holes in a three-barrier resonant tunneling structure

By integrating a resonant tunneling diode with a 1.2 mu m-thick slightly doped n-type GaAs layer in a three-barrier, two-well resonant tunneling structure, the resonant tunneling of photo-excited holes exhibits a value of peak-to-valley current ratio (PVCR) as high as 36. A vast number of photo-excited holes generated in this 1.2 mu m-thick slightly doped n-type GaAs layer, and the quantization of hole levels in a 23nm-thick quantum well on the outgoing side of hole tunneling out off the resonant tunneling diode which greatly depressed the valley current of the holes, are thought to be responsible for such greatly enhanced PVCR.

Resonant tunneling of holes in GaMnAs-related double- barrier structures

Using the multiband quantum transmitting boundary method (MQTBM), hole resonant tunneling through AlGaAs/GaMnAs junctions is investigated theoretically. Because of band-edge splitting in the DMS layer, the current for holes with different spins are tuned in resonance at different biases. The bound levels of the "light" hole in the quantum well region turned out to be dominant in the tunneling channel for both "heavy" and "light" holes. The resonant tunneling structure can be used as a spin filter for holes for adjusting the Fermi energy and the thickness of the junctions.

Different transfer paths for thermally activated electrons and holes in self-organized Ge/Si(001) islands in a multilayer structure

We investigated the temperature dependence (10-250 K) of the photoluminescence (PL) emission spectrum of self-organized Ge/Si(001) islands in a multilayer structure. With elevated temperature, we find that the thermally activated holes and electrons are gathered by the Ge islands in different ways. The holes drift from the wetting layer into the islands, while the electrons, confined in Si due to type-II band alignment, leak into the Ge islands by the electrostatic interaction with the holes accumulated there. It results in an increase of the integrated intensity of island-related PL at a certain temperature range and a reduction of the phonon energy in the phonon-assisted PL of the islands by involving a type-I transition into a type-II transition. (C) 2001 American Institute of Physics.

Resonant tunneling of holes in GaMnAs-related double- barrier structures

Using the multiband quantum transmitting boundary method (MQTBM), hole resonant tunneling through AlGaAs/GaMnAs junctions is investigated theoretically. Because of band-edge splitting in the DMS layer, the current for holes with different spins are tuned in resonance at different biases. The bound levels of the "light" hole in the quantum well region turned out to be dominant in the tunneling channel for both "heavy" and "light" holes. The resonant tunneling structure can be used as a spin filter for holes for adjusting the Fermi energy and the thickness of the junctions.