Strain-induced quantum confinement of electron gases

Zero-dimensional electron gases have been fabricated by the strain-patterning of a GaAs/AlAs heterojunction using amorphous carbon stressors. We have used steady-state, time-resolved and temperature-dependent photoluminescence measurements to probe the occupied density of states of the electron gases. We observe a novel lateral confinement mechanism and efficient transfer of modulation-doped electrons from the regions between the stressors to the quantum dots. In finite magnetic fields we have mapped the evolution of the electron states from which we estimate the number of electrons per dot to be 15.     

Effect test spaces

An effect test space, or E-test space, for short, is a generalization of a test space that is able to describe unsharp measurements. Effects in an E-test space correspond to yes-no measurements, and observables correspond to general measurements that may have more than two values. Sharpness, compatibility, and orthogonality of effects are considered. It is shown that every observable is determined by its eigenvalues and eigeneffects. The spectrum of an observable is studied and special types of observables are investigated. Orthocomplements and a natural local sum on an E-test space are introduced. Relationships between the resulting structures and previously studied frameworks are presented.     

Synthesis and biological evaluation of unnatural canthine alkaloids

Employing a ‘one-pot’ microwave-assisted protocol, unnatural canthine alkaloids with biological activities beyond the natural products have been prepared. This report describes unnatural canthine alkaloid analogs as selective, allosteric Akt kinase inhibitors.     

Magneto-optics of zero-dimensional electron systems

Photoluminescence spectroscopy has been used to probe the occupied electron states below the Fermi energy of zero-dimensional electron systems (0DESs) in both zero and finite magnetic fields. The arrays of modulation-doped quantum dots investigated were fabricated by both reactive-ion etching and strain-confining GaAs heterojunctions with a -layer of Be present in the GaAs, in order to improve luminescence efficiency. For the etched quantum dots we show that the low magnetic field dispersion T) of the acceptor recombination line is directly related to the magnetic field dependence of the total ground-state energy of interacting electrons in the quantum dots. For the strain-confined 0DESs we have mapped the magneto-dispersion of the quantum confined electron states to reveal 15 electrons per dot.     

Rashba spin-splitting in narrow gap III–V semiconductor quantum wells

Using Kane's 8-band k·p theory and the envelope function approximation we derive a tight binding Hamiltonian for III–V semiconductor quantum well structures, which accurately models band structure and spin–orbit coupling. By applying a potential difference across the well we have calculated the Rashba spin-splitting in the lowest conduction subband. For identical well widths the Rashba splitting in InSb is shown to be approximately twice that of InAs and, in all cases, passes through a weak maximum with increasing quasimomentum.     

Asymptotics for logical limit laws: When the growth of the components is in an RT class

Compton's method of proving monadic second-order limit laws is based on analyzing the generating function of a class of finite structures. For applications of his deeper results we previously relied on asymptotics obtained using Cauchy's integral formula. In this paper we develop elementary techniques, based on a Tauberian theorem of Schur, that significantly extend the classes of structures for which we know that Compton's theory can be applied.

     

Inverse cubic law for the distribution of stock price variations

The probability distribution of stock price changes is studied by analyzing a database (the Trades and Quotes Database) documenting every trade for all stocks in three major US stock markets, for the two year period January 1994 - December 1995. A sample of 40 million data points is extracted, which is substantially larger than studied hitherto. We find an asymptotic power-law behavior for the cumulative distribution with an exponent , well outside the Lévy regime . Received: 23 April 1998 / Revised and Accepted: 24 April 1998     

Economic Fluctuations and Statistical Physics: The Puzzle of Large Fluctuations

We present an overview of recent research applying ideas of statistical physics to try to better understand puzzles regarding economic fluctuations. One of these puzzles is how to describe outliers, phenomena that lie outside of patterns of statistical regularity. We review evidence consistent with the possibility that such outliers may not exist. This possibility is supported by recent analysis of a database containing the bid, ask, and sale price of each trade of every stock. Further, the data support the picture of economic fluctuations, due to Plerou et al., in which a financial market alternates between being in an “equilibrium phase” where market behavior is split roughly equally between buying and selling, and an “out-of-equilibrium phase” where the market is mainly either buying or selling.     

Cofinality changes required for a large set of unapproachable ordinals below

In , assume that is a strong limit cardinal and . Let be the set of approachable ordinals less than . An open question of M. Foreman is whether can be non-stationary in some and preserving extension of . It is shown here that if is such an outer model, then is infinite, for each positive integer .

     

Graph partitioning induced phase transitions

We study the percolation properties of graph partitioning on random regular graphs with N vertices of degree k. Optimal graph partitioning is directly related to optimal attack and immunization of complex networks. We find that for any partitioning process (even if nonoptimal) that partitions the graph into essentially equal sized connected components (clusters), the system undergoes a percolation phase transition at f = fc = 1-2/k where f is the fraction of edges removed to partition the graph. For optimal partitioning, at the percolation threshold, we find S approximately N 0.4 where S is the size of the clusters and l approximately N 0.25 where l is their diameter. Also, we find that S undergoes multiple nonpercolation transitions for f相似文献