Influence of internal degrees of freedom on the structure of one-dimensional systems

Summary The influence of internal degrees of freedom on the behaviour of one-dimensional systems is discussed. For systems with half-filled bands the coupling to internalviz. lattice coordinates decides whether Peierls distortion is caused by intramonomer coordinates or by a lattice coordinate. Thereby the various intramonomer degrees of freedom act cooperatively. We show that there is a small regime of parameters where both kinds of distortion exist simultaneously. For increasing temperature we find that distortions can also move from the lattice coordinate to the intramonomer coordinate.     

Fejér means of functions on noncommutative Vilenkin groups with respect to the character system

Summary It is known that the Fejér means - with respect to the character system of the Walsh, and bounded Vilenkin groups - of an integrable function converge to the function a.e. In this work we discuss analogous problems on the complete product of finite, not necessarily Abelian groups with respect to the character system for functions that are constant on the conjugacy classes. We find that the nonabelian case differs from the commutative case. We prove the a.e. convergence of the (C,1) means of the Fourier series of square integrable functions. We also prove the existence of a function f∊L^q for some q >1 such that sup |σ_n f | = + ∞ a.e. This is a sharp contrast between the Abelian and the nonabelian cases.     

Order Embeddings with Irrational Codomain: Debreu Properties of Real Subsets

The objective of this paper is to investigate the role of the set of irrational numbers as the codomain of order-preserving functions defined on topological totally preordered sets. We will show that although the set of irrational numbers does not satisfy the Debreu property it is still nonetheless true that any lower (respectively, upper) semicontinuous total preorder representable by a real-valued strictly isotone function (semicontinuous or not) also admits a representation by means of a lower (respectively, upper) semicontinuous strictly isotone function that takes values in the set of irrational numbers. These results are obtained by means of a direct construction. Moreover, they can be related to Cantor’s characterization of the real line to obtain much more general results on the semicontinuous Debreu properties of a wide family of subsets of the real line.      

Development of high-repetition-rate LD pumped Nd:YAG laser and its application

High-average-power and high-energy lasers with good beam quality are fundamental tools for pumping high-peak and high-average-power ultrafast Ti:sapphire laser systems. Laser-diode (LD) pumped solid slate lasers with phase conjugation offer a unique combination of efficiency, reliability, and compactness. We present the design details and performance characteristics of a 360-W 1-kHz LD pumped Nd:YAG phase-conjugated laser. We also discuss the basic design aspects and present our preliminary experimental investigations on ultrashort-pulse laser systems.     

Structural and electrical properties of core–shell structured GaP nanowires with outer Ga2O3 oxide layers

This paper presents a review of our current experimental research on GaP nanowires grown by a vapor deposition method. Their structural, electrical, opto-electric transport, and gas-adsorption properties are reviewed. Our structural studies showed that a GaP nanowire consisted of a core–shell structure with a single-crystalline GaP core and an outer Ga₂O₃ layer. The individual GaP nanowires exhibited n-type field effects. Their electron mobilities were in the range of about 6 to 22 cm²/V s at room temperature. When the nanowires were illuminated with an ultraviolet light source, an abrupt increase of conductance occurred resulting from carrier generation in the nanowire and de-adsorption of adsorbed OH^- or O₂ ^- ions on the Ga₂O₃ surface shell. Using an intrinsic Ga₂O₃ shell layer as a gate dielectric, top-gated GaP nanowire field-effect transistors were fabricated and characterized. Like other metal oxide nanowires, the carrier concentration and mobility of GaP nanowires were significantly affected by the surface molecular adsorption of OH or O₂. The GaP nanowire devices were fabricated as sensors for NO₂, NH₃, and H₂ gases by using a simple metal decoration technique. PACS 73.63.-b; 72.80.Ey; 85.35.-p     

Linear sorting withO(logn) processors

A file ofn records can be sorted in linear time givenO(log(n)) processors. Four such algorithms are presented and analyzed. All of them have reasonable hardware requirements; no memory access conflicts are generated; a constant number of communication lines per processor are needed (except for one case); and the space requirements areO(n) orO(n log(log(n))).     

Adsorbed state and vibrational excitation of N2 on Pd(110)

High-resolution vibrational electron energy loss spectroscopy, low-energy electron diffraction and Auger electron spectroscopy have been used to study the interactions of nitrogen with the Pd(110) surface. At 120 K, N₂ is chemisorbed molecularly on the Pd(110) surface, and the (2 × 1)-N₂ structure is formed. Most probably, the N₂ molecules are chemisorbed in the on-top sites of the bulk-like Pd(110) surface in the upright-linear structure. The Pd---N₂ bond energy is estimated to be ˜ 6 kcal/mol. The Pd---N₂ and N---N stretching vibrations of N₂ admolecules on Pd(110) are observed at 30 and 278 meV, respectively. The primary-energy dependence and angle dependence of their excitation cross sections agree reasonably well with the prediction of the dipole theory. The electron beam-induced effects are briefly discussed.     

Reduction of the concentration of slow insulator states in SiO2/InP-MIS structures

The well-known drift phenomena usually found in the InP-metal-insulator-semiconductor (MIS) devices can be explained by the assumption of a spatial and energetical distribution of slow states located within the insulator. The concentration of these states can be reduced by far more than one order of magnitude if a suitable technique of insulator deposition is applied. In this paper we will discuss the influence of the deposition temperature, the spatial separation of sample and plasma (“indirect plasma method”), and the addition of phosphorus into the reaction chamber during the initial period of insulator deposition on the properties of n-type and p-type InP-MIS capacitors. Plasma-enhanced chemical vapor deposited silicon dioxide is used as insulator. The samples were characterized by means of capacitance/voltage (C(V)) and deep level transient spectroscopy (DLTS) measurements. Only minor hysteresis of the C(V) curves and concentrations of slow insulator states of only (1–2)×10¹¹ cm^-2 eV^-1 are measured for the best of our samples.