Spin angular impulse due to spin-dependent reflection off a barrier

The spin-dependent elastic reflection of quasi two-dimensional electrons from a lateral impenetrable barrier in the presence of band-structure spin-orbit coupling results in a spin angular impulse exerted on the electrons which is proportional to the nontrivial difference between the electrons' momentum and velocity. Even for an unpolarized incoming beam we find that the spin angular impulse is nonzero when averaged over all components of the reflected beam. We present a detailed analysis of the kinematics of this process.Comment: 4 pages, 2 figures, final versio

Analogical acts as conceptual strategies in science, engineering and the humanities

The composing models which operate by means of analogy are identified. The importance of analogical acts in the prewriting stage of the composing process is discussed. The relations between analogical acts and concept formation are explored. A basic correspondence between the analogical thinking employed in successful learning and analogical thinking as a composing strategy is discussed. Teaching analogical acts as conceptual strategies for exploring problems and generating the form and content of discourse is presented in support of the contention that writing is a unique mode of learning

Parsimonious Segmentation of Time Series' by Potts Models

Typical problems in the analysis of data sets like time-series or images crucially rely on the extraction of primitive features based on segmentation. Variational approaches are a popular and convenient framework in which such problems can be studied. We focus on Potts models as simple nontrivial instances. The discussion proceeds along two data sets from brain mapping and functional genomics

Pressurized bellows flat contact heat exchanger interface

Disclosed is an interdigitated plate-type heat exchanger interface. The interface includes a modular interconnect to thermally connect a pair or pairs of plate-type heat exchangers to a second single or multiple plate-type heat exchanger. The modular interconnect comprises a series of parallel, plate-type heat exchangers arranged in pairs to form a slot therebetween. The plate-type heat exchangers of the second heat exchanger insert into the slots of the modular interconnect. Bellows are provided between the pairs of fins of the modular interconnect so that when the bellows are pressurized, they drive the plate-type heat exchangers of the modular interconnect toward one another, thus closing upon the second heat exchanger plates. Each end of the bellows has a part thereof a thin, membrane diaphragm which readily conforms to the contours of the heat exchanger plates of the modular interconnect when the bellows is pressurized. This ensures an even distribution of pressure on the heat exchangers of the modular interconnect thus creating substantially planar contact between the two heat exchangers. The effect of the interface of the present invention is to provide a dry connection between two heat exchangers whereby the rate of heat transfer can be varied by varying the pressure within the bellows

Electron spin orientation under in-plane optical excitation in GaAs quantum wells

We study the optical orientation of electron spins in GaAs/AlGaAs quantum wells for excitation in the growth direction and for in-plane excitation. Time- and polarization-resolved photoluminescence excitation measurements show, for resonant excitation of the heavy-hole conduction band transition, a negligible degree of electron spin polarization for in-plane excitation and nearly 100% for excitation in the growth direction. For resonant excitation of the light-hole conduction band transition, the excited electron spin polarization has the same (opposite) direction for in-plane excitation (in the growth direction) as for excitation into the continuum. The experimental results are well explained by an accurate multiband theory of excitonic absorption taking fully into account electron-hole Coulomb correlations and heavy-hole light-hole coupling.Comment: 10 pages, 4 figures, final versio

The INTEGRAL Core Observing Programme

The Core Programme of the INTEGRAL mission is defined as the portion of the scientific programme covering the guaranteed time observations for the INTEGRAL Science Working Team. This paper describes the current status of the Core Programme preparations and summarizes the key elements of the observing programme.Comment: Contributed paper, 3rd INTEGRAL Workshop, Taormina/Sicily, Sep 1998, to be published in Astrophys. Letters & Communications, 199

Quantum black holes from null expansion operators

Using a recently developed quantization of spherically symmetric gravity coupled to a scalar field, we give a construction of null expansion operators that allow a definition of general, fully dynamical quantum black holes. These operators capture the intuitive idea that classical black holes are defined by the presence of trapped surfaces, that is surfaces from which light cannot escape outward. They thus provide a mechanism for classifying quantum states of the system into those that describe quantum black holes and those that do not. We find that quantum horizons fluctuate, confirming long-held heuristic expectations. We also give explicit examples of quantum black hole states. The work sets a framework for addressing the puzzles of black hole physics in a fully quantized dynamical setting.Comment: 5 pages, version to appear in CQ