Technique for anisotropic extension of organic crystals: application to temperature dependence of electrical resistance

We have developed a technique for the anisotropic extension of fragile molecular crystals. The pressure medium and the instrument, which extends the pressure medium, are both made from epoxy resin. Since the thermal contraction of our instrument is identical to that of the pressure medium, the strain applied to the pressure medium has no temperature dependence down to 2 K. Therefore, the degree of extension applied to the single crystal at low temperatures is uniquely determined from the degree of extension in the pressure medium and thermal contractions of the epoxy resin and the single crystal at ambient pressure. Using this novel instrument, we have measured the temperature dependence of the electrical resistance of metallic, superconducting, and insulating materials. The experimental results are discussed from the viewpoint of the extension (compression) of the lattice constants along the parallel (perpendicular) direction.     

Variational Bayes solution of linear neural networks and its generalization performance

It is well known that in unidentifiable models, the Bayes estimation provides much better generalization performance than the maximum likelihood (ML) estimation. However, its accurate approximation by Markov chain Monte Carlo methods requires huge computational costs. As an alternative, a tractable approximation method, called the variational Bayes (VB) approach, has recently been proposed and has been attracting attention. Its advantage over the expectation maximization (EM) algorithm, often used for realizing the ML estimation, has been experimentally shown in many applications; nevertheless, it has not yet been theoretically shown. In this letter, through analysis of the simplest unidentifiable models, we theoretically show some properties of the VB approach. We first prove that in three-layer linear neural networks, the VB approach is asymptotically equivalent to a positive-part James-Stein type shrinkage estimation. Then we theoretically clarify its free energy, generalization error, and training error. Comparing them with those of the ML estimation and the Bayes estimation, we discuss the advantage of the VB approach. We also show that unlike in the Bayes estimation, the free energy and the generalization error are less simply related with each other and that in typical cases, the VB free energy well approximates the Bayes one, while the VB generalization error significantly differs from the Bayes one.     

Isolation of penicillin-resistant Streptococcus pneumoniae in Saga Medical School Hospital

A recent nationwide increase in beta-lactams-resistant Streptococcus pneumoniae has attracted a great deal of attention. We studied the drug sensitivity of S. pneumoniae isolated from various clinical specimens in Saga Medical School Hospital between April 1988 and December 1991. To determine the drug sensitivity of the strains, we used a micro-dilution method and determined the MIC. Drug resistance was evaluated using MIC of ampicillin (ABPC) as a reference MIC, and the results were roughly classified into the following three groups: sensitive (< or = 0.1 microgram/ml), moderately resistant (0.2-3.13 micrograms/ml) and highly resistant (> or = 6.25 micrograms/ml). The isolation frequency was calculated on the basis of one strain from one patient. No strain of S. pneumoniae with high resistance against ABPC was found in 1988 (94 strains of S. pneumoniae were isolated) and 1990 (115 strains isolated), but one such strain (0.8%) was found among 129 strains isolated in 1989, and 2 such strains (2.4%) among 84 strains isolated in 1991. Moderately resistant strains were isolated at the frequencies of 12.8%, 15.5%, 22.6%, and 21.4% respectively, in 1988, 1989, 1990, and 1991. A sum of the frequencies of "moderately resistant" and "highly resistant" (2.4%) strains was 23.8% in 1991. The frequency of resistant strains is increasing and the intensity of resistance is also being elevated.     

A pilot survey of 39 Victorian WWTP effluents using a high speed luminescent umu test in conjunction with a novel GC-MS-database technique for automatic identification of micropollutants

In 2007, samples of treated effluent were collected at point of discharge to the environment from 39 wastewater treatment plants (WWTPs) located across Victoria, Australia grouped by treatment type. Sample genotoxicity was assessed with a high-throughput luminescent umu test method using Salmonella typhimurium TL210 strain, with and without addition of a commercially available metabolic activation system. Samples were also screened using a gas chromatographic-mass spectrometric mass-structure database recognition method. A genotoxic response was observed in half of the samples tested without metabolic activation system (相似文献   

Role of frustration in quasi 1D conductor — Charge ordering and/or CDW in (R1,R2-DCNQI)2M (M=Ag, Li, Cu) system —

Synchrotron X-ray high-resolution measurements have been performed to investigate the nature of the insulating state of a quarter-filled quasi-one-dimensional conductor (DI-DCNQI)₂Ag and the π-d interacted conductor (DBr-DCNQI)₂Cu. The two-fold structure in the ground state of (DI-DCNQI)₂Ag system consists of not only charge ordering columns but also monotonic charge dimerized columns caused by frustration among DCNQI columns. On the other hand, Cu salt in the insulating phase realizes a commensurate structure where the Cu charge ordering is coupled with the 3c-CDW in the insulator phase. The frustration among charged columns is restrained by the charge ordering of the Cu ions.     

Application of functionally graded material for solid insulator in gaseous insulation system

Functionally graded materials (FGM) have spatial distribution of a material property in order to achieve efficient stress control. An application of the FGM to a solid insulator (spacer) for a gaseous insulation system, like gas insulated switchgear, is expected to improve electric field (E-field) distribution around the spacer. In this paper, we describe the applicability of the FGM spacer to gas insulated power equipment. In the FGM spacer, we gave spatial distribution of dielectric permittivity to control the E-field distribution inside and outside the spacer. This paper includes following key results for the applications of the FGM. Firstly, E-field simulation results when applying the FGM by a finite element method are presented, in which we show the effective reduction of the maximum field strength by applying the FGM. Next, a fabrication technique of the FGM spacer sample with not only step-by-step but also continuous changes of permittivity is presented by use of centrifugal force. Finally, dielectric breakdown tests using FGM samples which are accurately controlled the spatial distribution of permittivity are carried out under lightning impulse voltage applications. The test result indicates the increase of breakdown voltage (BDV). From these results, we verified the applicability and the fabrication technique of FGM spacer for improvement of the dielectric strength in the gaseous insulation system.     

Constant-ratio-coupled multi-grain digital synchronizer with flexible input-output delay selection for versatility in low-power applications

The constant-ratio-coupled multi-grain digital synchronizer (CRC-MGsynchronizer) is proposed as a means for making high-speed connections with very low power consumption, both among multiple chips such as processors, controllers, and storage devices, and among on-chip modules. The synchronizer not only provides a wide range of operating frequencies, but is fast locking and only occupies a small area on chip. Therefore, it contributes to large reductions in power consumption and costs. It is suitable for use in various low-power systems (e.g., battery-hungry mobile appliances and low-cost consumer electronic products). Three major techniques were applied to the design: 1)a multi-grain structure for the delay elements, which greatly reduces the number of gates while facilitating locking in a very small number of clock cycles;2) constant-ratio-coupled (CRC) delay lines (measurement versus generation)for flexible selection of the input-output delay; and 3) a new lock stage decision circuit (LSDC) scheme, conferring excellent testability. Moreover,the architecture is all-digital, and thus it has high process portability. By applying these techniques to a DDR memory interface circuit for a mobile application processor fabricated in 130-nm technology, we were able to reduce power consumption by 42% and chip area by 65% compared with a conventional implementation. Furthermore, the novel design spans a frequency range covering 12 times the minimum frequency.     

Statistical analysis for multiplicatively modulated nonlinear autoregressive model and its applications to electrophysiological signal analysis in humans

Modulating the dynamics of a nonlinear autoregressive model with a radial basis function (RBF) of exogenous variables is known to reduce the prediction error. Here, RBF is a function that decays to zero exponentially if the deviation between the exogenous variables and a center location becomes large. This paper introduces a class of RBF-based multiplicatively modulated nonlinear autoregressive (mmNAR) models. First, we establish the local asymptotic normality (LAN) for vector conditional heteroscedastic autoregressive nonlinear (CHARN) models, which include the mmNAR and many other well-known time-series models as special cases. Asymptotic optimality for estimation and testing is described in terms of LAN properties. The mmNAR model indicates goodness-of-fit for surface electromyograms (EMG) using electrocorticograms (ECoG) as the exogenous variables. Concretely, it is found that the negative potential of the motor cortex forces change in the frequency of EMG, which is reasonable from a physiological point of view. The proposed mmNAR model fitting is both useful and efficient as a signal-processing technique for extracting information on the action potential, which is associated with the postsynaptic potential.