Cryogenic scanning tunneling spectroscopy studies of inhomogeneous superconductors

We applied scanning tunneling microscopy and spectroscopy, combined with magnetic susceptibility measurements and Mossbauer spectroscopy, in studies of three superconducting materials. Two belong to a new class of high T_c magnetic-superconductor systems, R_1.4Ce_0.6RuSr₂Cu₂O_10-δ (R=Eu and Gd), which are magnetically ordered at T_N≪T_c. The third is a granular normal-superconductor system, where the superconducting phase is YNi₂B₂C. In this paper we focus on the tunneling measurements, which exhibit large spatial variations of the local electronic properties for all three materials. Albeit, these local measurements also reveal pronounced differences between the third and the first two systems, which will be discussed in view of their macroscopic properties.     

Accurate reanalysis of structures by a preconditioned conjugate gradient method

A preconditioned conjugate gradient (PCG) method that is most suitable for reanalysis of structures is developed. The method presented provides accurate results efficiently. It is easy to implement and can be used in a wide range of applications, including non‐linear analysis and eigenvalue problems. It is shown that the PCG method presented and the combined approximations (CA) method developed recently provide theoretically identical results. Consequently, available results from one method can be applied to the other method. Effective solution procedures developed for the CA method can be used for the PCG method, and various criteria and error bounds developed for conjugate gradient methods can be used for the CA method. Numerical examples show that the condition number of the selected preconditioned matrix is much smaller than the condition number of the original matrix. This property explains the fast convergence and accurate results achieved by the method. Copyright © 2002 John Wiley & Sons, Ltd.     

Behavioral effects of environmental enrichment in randomly bred mice.

Reared 212 randomly bred mice from birth in an enriched environment or in a standard control environment. Ss were tested for open-field activity and defecation, running wheel activity, exploration, and hoarding. After the hoarding tests all Ss were sacrificed and adrenal glands were removed and weighed. Significant main effects due to treatment were found on gross body weight at 38 days of age, open-field activity and defecation, running wheel activity measures, and exploration. Correlational analyses revealed that open-field activity was positively associated with exploratory behavior, and that the 2 activity measures were positively associated. In the control Ss, the running wheel measures were positively associated with hoarding performance. Results are discussed and compared with previous studies of environmental enrichment and mouse behavior. It is concluded that the effects of early enrichment upon open-field activity, running wheel activity, and exploration are well established. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Input–output approach to stability and -gain analysis of systems with time-varying delays

Stability and L₂ (l₂)-gain of linear (continuous-time and discrete-time) systems with uncertain bounded time-varying delays are analyzed under the assumption that the nominal delay values are not equal to zero. The delay derivatives (in the continuous-time) are not assumed to be less than q<1. An input–output approach is applied by introducing a new input–output model, which leads to effective frequency domain and time domain criteria. The new method significantly improves the existing results for delays with derivatives not greater than 1, which were treated in the past as fast-varying delays (without any constraints on the delay derivatives). New bounded real lemmas (BRLs) are derived for systems with state and objective vector delays and norm-bounded uncertainties. Numerical examples illustrate the efficiency of the new method.     

New conditions for delay-derivative-dependent stability

Two recent Lyapunov-based methods have significantly improved the stability analysis of time-delay systems: the delay-fractioning approach of Gouaisbaut and Peaucelle (2006) for systems with constant delays and the convex analysis of systems with time-varying delays of Park and Ko (2007). In this paper we develop a convex optimization approach to stability analysis of linear systems with interval time-varying delay by using the delay partitioning-based Lyapunov–Krasovskii Functionals (LKFs). Novel LKFs are introduced with matrices that depend on the time delays. These functionals allow the derivation of stability conditions that depend on both the upper and lower bounds on delay derivatives.     

Isolation of soybean protein: Effect of processing conditions on yields and purity

The process of soybean-protein isolation, comprising extraction in dilute calcium hydroxide and precipitation with hydrochloric acid at pH 4.5, was evaluated from the viewpoint of the effect of processing conditions on yields and product purity. The course of extraction and the effect of particle size and agitation indicate that the process is quite rapid even when coarse meal is treated under mild agitation. The heattreatment history of the meal is the main factor governing the extraction and isolation yields. The precipitation yield is unaffected by temperature. Two steps of curd washing were found to suffice for maximum product purity. The purity is also improved considerably by preliminary sifting of the meal.     

Electronic structure and self-assembly of cross-linked semiconductor nanocrystal arrays

We studied the electronic level structure of assemblies of InAs quantum dots and CdSe nanorods cross-linked by 1,4-phenylenediamine molecules using scanning tunneling spectroscopy. We found that the bandgap in these arrays is reduced with respect to the corresponding ligand-capped nanocrystal arrays. In addition, a pronounced sub-gap spectral structure commonly appeared which can be attributed to unpassivated nanocrystal surface states or associated with linker-molecule-related levels. The exchange of the ligands by the linker molecules also affected the structural array properties. Most significantly, clusters of close-packed standing CdSe nanorods were formed.     

Visible light-induced charge retention and photocatalysis with hybrid CdSe-Au nanodumbbells

Visible light photocatalysis is a promising route for harnessing of solar energy to perform useful chemical reactions and to convert light to chemical energy. Nanoscale photocatalytic systems used to date were based mostly on oxide semiconductors aided by metal deposition and were operational only under UV illumination. Additionally, the degree of control over particle size and shape was limited. We report visible light photocatalysis using highly controlled hybrid gold-tipped CdSe nanorods (nanodumbbells). Under visible light irradiation, charge separation takes place between the semiconductor and metal parts of the hybrid particles. The charge-separated state was then utilized for direct photoreduction of a model acceptor molecule, methylene blue, or alternatively, retained for later use to perform the reduction reaction in the dark.     

Nutritional upgrading of a new soya-protein isolate—SP55

A series of biochemical and nutritional studies was performed in order to establish the reasons for the poor nutritional quality of the new soya-protein isolate SP55. Moist heat treatment which destroyed the substantial residual anti-tryptic activity present in the SP55 fraction, did not improve the nutritive value of the protein as indicated by rat feeding tests. Furthermore, partial in-vitro-enzymic digestion by papain or by pancreatin of SP55 prior to rat feeding did not alter the poor performance of the preparation. Amino acid analysis indicated that the protein was deficient in several essential amino acids. Subsequent rat feeding studies showed that the nutritional quality of the protein can be highly upgraded by supplementation with sulphur-containing amino acids, tryptophan and threonine.