Inverted electron-hole alignment in InAs-GaAs self-assembled quantum dots

New information on the electron-hole wave functions in InAs-GaAs self-assembled quantum dots is deduced from Stark effect spectroscopy. Most unexpectedly it is shown that the hole is localized towards the top of the dot, above the electron, an alignment that is inverted relative to the predictions of all recent calculations. We are able to obtain new information on the structure and composition of buried quantum dots from modeling of the data. We also demonstrate that the excited state transitions arise from lateral quantization and that tuning through the inhomogeneous distribution of dot energies can be achieved by variation of electric field.     

A modification of the secant rule derived from a maximum likelihood principle

An estimate of a zero of a complex function, constructed from ordinate information at distinct abscissae, is found from a Maximum Likelihood estimate relative to a normal probability distribution induced by a weak Gaussian distribution on a related Hilbert space. In the case of two ordinate observations this leads to an estimator structurally similar to the Secant Rule, and asymptotically approaching that rule in certain limiting situations. A correspondingly modified version of Newton's method is also derived, and regional and asymptotic convergence results proved.     

Shot noise in chaotic systems: "classical" to quantum crossover

This paper is devoted to study of the classical-to-quantum crossover of the shot noise in chaotic systems. This crossover is determined by the ratio of the particle dwell time in the system, tau(d), to the characteristic time for diffraction t(E) approximately lambda(-1)|lnh, where lambda is the Lyapunov exponent. The shot noise vanishes when t(E)>tau(d), while it reaches a universal value in the opposite limit. Thus, the Lyapunov exponent of chaotic mesoscopic systems may be found by shot noise measurements.     

Self-organizing silane-siloxane copolymers: Synthesis and behavior in the block and monomolecular layers

Trans tactic cyclolinear organosilicon copolymers with a regular alternation of decamethylcyclohexasiloxane and decamethylcyclosilane units have been synthesized by the heterofunctional polycondensation of trans-2,8-dihydroxydecamethylcyclohexasiloxane with 1,3-or 1,4-dichlorodecamethylcyclohexasilanes. The structure of the copolymers has been studied by ¹H and ²⁹Si NMR, and IR spectroscopy; molecular mass measurements; and elemental analysis. The phase behavior of these copolymers in the block has been examined by DSC, X-ray diffraction, and polarization optical microscopy. It has been demonstrated that the copolymers of interest may exist in the mesomorphic state within a wide temperature interval. The ability of cyclolinear organosilicon copolymers to spread at the water/air interface and to form monolayers has been investigated. It has been shown that cyclosilane units that are structural isomers affect the pattern of surface pressure isotherms of the said copolymers.     

Cuprate/manganite heterostructures

Advances in thin film deposition techniques have made it possible to produce heterostructures of high-temperature superconducting compounds and manganite perovskites. The latter exhibit the phenomenon of colossal magnetoresistance (CMR). The half-metallic character of the CMR compounds results in their carriers being spin polarized. Experiments with these heterostructures have demonstrated that the injection of spin-polarized carriers into high-temperature superconductors results in a reduction of parameters such as the critical current and critical temperature. The experimental situation is reviewed, and open questions are identified.     

Determination of electron affinity of carbonyl radicals by means of negative ion mass spectrometry

Appearance energies of [M-H](-) ions from carbonyl compounds R-CO-R' (R,R' = H, CH(3), NH(2), OH) have been measured by means of negative ion mass spectrometry in resonant electron capture mode. Values of electron affinity of the corresponding radicals, CH(2)&dbond;C(X)O, NH&dbond;C(X)O and O&dbond;C(X)O, have been determined. Copyright 1999 John Wiley & Sons, Ltd.     

A comparison of μSR and thermopower in Hg 1:2:0:1 high‐Tc cuprates

We present the results of μSR measurements of the transverse field relaxation rate below T_c for seven samples of HgBa₂ CuO_4+\delta, spanning the underdoped, optimally doped, and nominally overdoped regions of the superconducting phase. On comparison with the “anomalous” thermopower data for these compounds, we find that nominally “overdoped” Hg 1:2:0:1 resembles underdoped compounds in certain respects. This revised version was published online in August 2006 with corrections to the Cover Date.     

On a system of Klein-Gordon type equations with acoustic boundary conditions

We prove the existence, uniqueness and uniform stabilization of global solutions for a generalized system of Klein-Gordon type equations with acoustic boundary conditions on a portion of the boundary and the Dirichlet boundary condition on the rest.     

Decay of solutions for 2D Navier–Stokes equations posed on Lipschitz and smooth bounded and unbounded domains

Initial–boundary value problems for 2D Navier–Stokes equations posed on bounded and unbounded rectangles as well as on bounded and unbounded smooth domains were considered. The existence and uniqueness of regular global solutions in bounded rectangles and bounded smooth domains as well as exponential decay of solutions on bounded and unbounded domains were established.     

Synthesis and Practical Use of 1H‐1,2,3‐Benzotriazole‐5‐carboxaldehyde for Reductive Amination

A reliable synthetic procedure to obtain multigram quantities of 1H‐1,2,3‐benzotriazole‐5‐carboxaldehyde has been developed. This material can be used in reductive amination reactions with primary and secondary amines to provide good to excellent yields of the desired products without protection of the starting material.