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61.
Pichia sorbitophila grows rapidly in the presence of very high NaCl concentrations. Under these conditions, even when the K(+) concentration is low, P. sorbitophila cells can maintain low Na(+) and high K(+) contents. This remarkable capacity of P. sorbitophila fails when the external pH is not acidic. This indicates that Na(+) efflux is mediated by an electroneutral Na(+)/H(+) antiporter. We have cloned and sequenced two genes designated as PsNHA1 and PsNHA2, which probably encode two antiporters of this type. The genes present high similarity with the corresponding genes from other yeasts. The heterologous expression of PsNHA1 or PsNHA2 in a Saccharomyces cerevisiae mutant lacking the Na(+) efflux systems and sensitive to high concentrations of Na(+) and K(+) rescued the tolerance and the ability to extrude both cations. The Accession Nos of the sequenced DNA fragments are: PsNHA1, AJ496431; PsNHA2, AJ496432. (TC 2.A.36) Copyright 2002 John Wiley & Sons, Ltd. 相似文献
62.
Equations that describe the photobleaching of photochromic layers illuminated by Gaussian laser beams are given. The photochromic samples are made of thionine, triethanolamine, and polyvinyl alcohol and follow simple kinetics law. Spatial absorbance and time-dependent power transmittance are well described by the developed equations. The model is used to calculate the Gaussian dimension of helium-neon laser beams from kinetics data. 相似文献
63.
An auto-adaptive multidomain pseudo-spectral technique is considered in order to solve the linear stability problem of viscous compressible flows. Both the locations of the interfaces and the parameters of the mappings in each subdomain are adapted by minimizing the H
2
-norm of the calculated solution. Such method provides automatically—this is the key point—the best polynomial interpolation of the basic state the stability of which is studied. It turns out that the whole procedure is needed to obtain reliable results. The method is first validated against results available in the literature (both viscous incompressible and inviscid compressible Rayleigh–Taylor configurations). The efficiency of the numerical method is illustrated with results on the linear stability of the compressible viscous diffusive Rayleigh–Taylor flow where no analytical or numerical results are available. New results showing the influence of stratification, viscosity, diffusity between species and thermal diffusivity are presented. 相似文献
64.
Philippe Lenoir Stphane Bila Dominique Baillargeat Serge Verdeyme 《国际射频与微波计算机辅助工程杂志》2005,15(3):278-285
This article presents an electromagnetic tool for the synthesis of manifold multiplexers — the dynamic inverter. By associating this model with the classical circuit model of the filter, the broadband behaviour of each filter can be analysed rapidly and then optimised accurately for an efficient synthesis of the manifold multiplexer. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2005. 相似文献
65.
Serge Zhuiykov 《International Journal of Applied Ceramic Technology》2006,3(5):401-411
Yttria-stabilized zirconia (YSZ)-based ceramic gas sensors operating at high temperatures have been well established in many applications over the last 30 years. This article aims to provide an electron model of the solid electrolytes with oxygen-ionic conductivity used in gas sensors to simulate contact phenomena on the boundary of a YSZ/metal electrode interface within the solid-state zone theory. The primary focus of this article is modelling and assessment of the ability of a YSZ-based electrolyte to control oxygen potentials at low temperatures in different environments. The proposed model allows the necessary information with regard to the electrolyte/metal electrode interface and about the character of the electronic conductivity to be obtained. The model also describes that the character of the electronic conductivity in solid electrolytes usually depends on two mechanisms of charge transfer: electrons transfer in the conductivity zone, separated from the valent zone in the solid electrolyte by the wide enough forbidden zone, and the spasmodic transitions of electrons from one local level to another within the forbidden zone. 相似文献
66.
Normalized cuts in 3-D for spinal MRI segmentation 总被引:1,自引:0,他引:1
Segmentation of medical images has become an indispensable process to perform quantitative analysis of images of human organs and their functions. Normalized Cuts (NCut) is a spectral graph theoretic method that readily admits combinations of different features for image segmentation. The computational demand imposed by NCut has been successfully alleviated with the Nystr?m approximation method for applications different than medical imaging. In this paper we discuss the application of NCut with the Nystr?m approximation method to segment vertebral bodies from sagittal T1-weighted magnetic resonance images of the spine. The magnetic resonance images were preprocessed by the anisotropic diffusion algorithm, and three-dimensional local histograms of brightness was chosen as the segmentation feature. Results of the segmentation as well as limitations and challenges in this area are presented. 相似文献
67.
Time evolution of reflective thermal lenses and measurement of thermal diffusivity in bulk solids 总被引:2,自引:0,他引:2
A simple method for optically measuring the thermal diffusivity of solids is demonstrated. The thermal displacement created on a substrate by a focused laser beam is determined from the divergence that it induces in a weak probe beam. The dynamics of the surface lens and the amplitude of the probe beam's divergence are then used to determine the thermal diffusivity of the substrate. Several materials that span a wide range of thermal properties are studied. 相似文献
68.
We investigated the effect of trace metals (Fe, Mn, Cu, Zn and Mo) on the denitrification unit at the Montreal Biodome. Two dosages of the five trace metals were tested on a denitrifying bacterial population which was extracted from the denitrification unit and cultured in 250 mL chemostats with artificial seawater. The low dosage showed a 20% increase in the denitrification rate whereas the high dosage had a more pronounced effect with a 250% increase. No increase in bacterial growth was observed, suggesting that the trace metals had an effect on the denitrification activity. When the trace metals were tested separately, only iron had a significant effect similar to the increase in the denitrification rate observed when the five trace metals were added. The combination of Fe and Mn caused a small but significant increase compared to the five trace metals. We then tested the effect of adding Fe, Mn and Cu to the denitrification unit at the Montreal Biodome. A high dosage of these trace metals showed a 250% increase in the denitrification rate, which went from 200 to 700 g NO(x)-N/d. Our results showed that the addition of trace metals is crucial for denitrification activities. 相似文献
69.
The goal of this article is to evaluate the relevance of claims concerning the existence of cultural biases in IQ tests. The article has four parts. We first introduce the meaning of the concept of bias in psychometrics by differentiating three inaccurate conceptualizations--equalitarist, standardization and culturalist--that often underlie conclusions about the existence of cultural biases in IQ tests. We then examine potential biases associated with pragmatic validity, conceptual validity, and test administration. Following this examination of the available evidence related to biases affecting the validity of IQ tests, the clear conclusion is that claims often made about the existence of cultural biases in IQ tests are unjustified. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
70.
We consider the max-plus analogue of the eigenproblem for matrix pencils, A???x?=?λ???B???x. We show that the spectrum of (A,B) (i.e., the set of possible values of λ), which is a finite union of intervals, can be computed in pseudo-polynomial number of operations, by a (pseudo-polynomial) number of calls to an oracle that computes the value of a mean payoff game. The proof relies on the introduction of a spectral function, which we interpret in terms of the least Chebyshev distance between A???x and λ???B???x. The spectrum is obtained as the zero level set of this function. 相似文献