Oh no, Notch again!

The Notch receptor signaling pathway is important for morphogenesis and development of many organs and tissues in most if not all multicellular species. The classical view holds that Notch signaling keeps cells in an undifferentiated state. Recently, however, this notion has been challenged in the nervous system by two sets of observations: Notch plays an active role in the differentiation of glial cells,(1-4) and Notch influences the length and organisation of neuronal processes.(5-7) In this review, we analyse these recent data and discuss how Notch signaling may be able to perform such quite different tasks during nervous system development. BioEssays 23:3-7, 2001.     

Comparative flexibility,extension, and conformation of some simple polysaccharide chains

Realistic polymer chain models are developed for several polysaccharides to illustrate, using perspective drawings of representative chain conformations, the wide range of configuration, extension, and flexibility found in chains of the polysaccharide class. A method for incorporating the gauche or exo-anomeric effect into polysaccharide conformational energy functions is described, and a novel measure of directional correlation and pseudohelical persistence is utilized to help distinguish the differences in chain configuration observed among the polysaccharides compared.     

A simple chemically,defined medium for the growth of Aphanomyces euteiches and some other oomycetes

A chemically-defined medium composed of glutathione, D-glucose, DL-asparagine, calcium and magnesium chlorides, and monobasic and dibasic potassium phosphates supported growth of several species of filamentous fungi which include seven isolates ofAphanomyces euteiches and single isolates ofA. leavis, A. stellatus, Achlya ambisexualis and several species ofPythium. Some growth occurred if a stoichiometric equivalent of the amino acids contained in glutathione were substituted for it. Dithiothreitol, a compound which keeps glutathione in the reduced form, inhibited growth ofA. euteiches at the concentrations tested. Replacement of the medium with a solution of known ionic composition caused the fungal colonies to produce and release zoospores and to produce oospores.     

饲养五种夜蛾科昆虫的一种简易人工饲料

以黄豆粉、酵母粉及麦麸粉等为主要营养成分 ,研制和筛选出了一种既可工厂化饲养斜纹夜蛾幼虫 ,又可大量饲养甜菜夜蛾、银纹夜蛾、粉纹夜蛾和棉铃虫幼虫的简易人工半合成饲料。利用该饲料目前已实现了工厂化饲养斜纹夜蛾幼虫增殖斜纹夜蛾核多角体病毒     

Detection of Atmospheric Oh Radicals

The detection of atmospheric OH radicals by laser long path absorption spectroscopy is described. This technique is specific to OH and easily calibrated. In various field measurements from below the detection limit (5*10⁵/cm³) up to 8.7* 10⁶ OH radicals/cm¹ have been observed. Measurements of meteorologic parameters and mixing ratios of other trace gases simultaneously with OH allow comparison of observed OH levels with reaction kinetic model calculations.     

MD Simulations of Liquids with Td,Oh Molecular Symmetry

Abstract

A new method is proposed for the calculation of intermolecular interactions in Molecular Dynamics simulations of liquids with T_d, O_h molecular symmetry. The new algorithm is based on the separation of the pair potential into a short-range and a long-range contribution described by a site-site and a spherical centre-centre potential model respectively using an additional cutoff distance. Test calculations for the Lennard-Jones fluids CCl₄ and SF₆ show significant savings in CPU time. We compare thermodynamic properties, pair correlation functions and a few dynamic autocorrelation functions obtained with the novel strategy with results of the commonly used algorithm for systems containing 864 molecules. Since no significant differences appear the new algorithm may be suggested as a useful contribution to the area of Molecular Dynamics simulation of liquids with these rather high molecular symmetries.     

The convergence in distribution of some simple epidemics

A group of n susceptible individuals exposed to a contagious disease isconsidered. It is assumed that at each point in time one or more susceptible individuals can contract the disease. The progress of this simple batch epidemic is modeled by a stochastic process X_n(t), t[0, ∞), representing the number of infectiveindividuals at time t. In this paper our analysis is restricted to simple batch epidemics with transition rates given by [α²X_n(t){n −X_n(t) +X_n(0)}]^1/2, t[0, ∞), α(0, ∞). This class of simple batch epidemics generalizes a model used and motivated by McNeil (1972) to describe simple epidemic situations. It is shown for this class of simple batch epidemics, that X_n(t), with suitable standardization, converges in distribution as n→∞ to a normal random variable for all t(0, t₀), and t₀ is evaluated.     

Counting phylogenetic invariants in some simple cases.

An informal degrees of freedom argument is used to count the number of phylogenetic invariants in cases where we have three or four species and can assume a Jukes-Cantor model of base substitution with or without a molecular clock. A number of simple cases are treated and in each the number of invariants can be found. Two new classes of invariants are found: non-phylogenetic cubic invariants testing independence of evolutionary events in different lineages, and linear phylogenetic invariants which occur when there is a molecular clock. Most of the linear invariants found by Cavender (1989, Molec. Biol. Evol. 6, 301-316) turn out in the Jukes-Cantor case to be simple tests of symmetry of the substitution model, and not phylogenetic invariants.     

13C NMR Analysis of some simple tetrahydroisoquinolines

¹³C NMR resonances of 15 simple tetrahydroisoquinolines have been assigned on the basis of chemical shift theory, ¹³C-¹H coupling constants     

A comparison of some quick and simple threshold selection methods for stained cells

The segmentation accuracy of four fast and simple gray-scale threshold selection methods were compared using a data base of stained cervical cell images. Some postprocessing was applied to the segmented images to increase the accuracy of the nuclear segmentation. The most accurate method correctly segmented the cytoplasm of 81% of the cell images and the nuclei of 78% of the cell images in the data base.