The effect of topology on estimates of among-site rate variation

Among-site rate variation, as quantified by the gamma-distribution shape parameter,a or , and the ratio of transition rate to transversion rate (Ts/Tv) influence phylogenetic inference. We examine the effect of topology on estimates of these two parameters in 12S rRNA sequences from nine species of mice belonging to the generaOnychomys andPeromyscus by generating 100 random topologies and estimating these parameters using parsimony and maximum-likelihood methods for each of the random topologies. The parsimony-based estimate ofTs/Tv from the well-corroborated topology falls within the distribution of estimates based on random topologies, whereas the maximum-likelihood estimate ofTs/Tv based on the well-corroborated topology lies well outside the distribution of estimates derived from random topologies. TheTs/Tv ratio derived via maximumlikelihood estimation is three times the parsimony-based estimate, suggesting that parsimony-based estimates are severe underestimates even when the correct topology is used. Both parsimony- and likelihood-based estimates of the gamma-distribution shape parameter () are sensitive to topology because the best estimates based on the well-corroborated topology are well outside the distributions of estimates derived from random topologies for both methods. We show that the reason for topology dependence is the presence of long internal branches in the underlying topology.     

Measurements of intracellular ionized calcium in squid giant axons using calcium-selective electrodes

Ca²⁺-selective electrodes have been used to measure free intracellular Ca²⁺ concentrations in squid giant axons. Electrodes made of glass cannulas of about 20 μm in diameter, plugged with a poly(vinyl chloride) gelled sensor were used to impale the axons axially. They showed a Nernstian response to Ca²⁺ down to about 3 μM in solutions containing 0.3 M K⁺ and 0.025 M Na⁺. Sub-Nernstian but useful responses were obtained up to pCa 8. The electrodes showed adequate selectivity to Ca²⁺ over Mg²⁺, H⁺, K⁺ and Na⁺. To calibrate them properly, a set of standard solutions were prepared using different Ca²⁺ buffers (EGTA, HEEDTA, nitrilotriacetic acid) after carefully characterizing their apparent Ca²⁺ association constants under conditions resembling the axoplasmic environment. In fresh axons incubated in artificial seawater containing 4 mM Ca²⁺, the mean resting intracellular ionized calcium concentration was 0.106 μM ($\text{n = 15}$). The Ca²⁺-electrodes were used to investigate effects of different experimental procedures on the [Ca²⁺]_i. The main conclusions are: (i) intact axons can extrude calcium ions at low [Ca²⁺]_i levels by a process independent of external Na⁺; (ii) poisoned axons can extrude calcium ions at high levels of [Ca²⁺]_i by an external Na⁺-dependent process. The level of free intracellular Ca attained at these latter conditions is about an order to magnitude greater than the resting physiological value.     

A New Imprinting Material for Scanning Electron Microscopic Studies

A new imprinting material, “Ther-mocool”, has been used for preparing negative replicas of plant as well as metal surfaces for SEM study. The technique has wide application and gives very good results.     

云南省少数民族皮纹研究—白族等十一个民族皮纹正常值测定

本文报告了云南省白族等11个少数民族14项皮纹正常值参数,并与汉族、北美白人作了比较,进行了统计学分析与聚类分析。结果表明,皮纹这一类遗传性状不仅在各人种之间有显著差异,而且在我国各民族之间也存在显著差异。各民族有自己皮纹的特异性。     

多个数量性状的拓广遗传参数

运用多元分析方法定义了拓广表型方差(?)(generalized phenotypic variance),拓广遗传方差(?)(generalized genetic variance),拓广遗传力(?)(generalized heritability)和拓广遗传相关系数(?)(generalized genetic correlation coefficient): 这些参数可用来对多个数量性状总体的变异、协变异及不同组向量之间的相关性进行轮廓分析(profile analysis)。用棉花和紫花苜蓿的两个实例说明了这些参数的估算和应用。     

Effect of carbohydrates and glycerol on the stability and surface properties of lyophilized liposomes

Summary The interaction of permeant molecules such as glycerol and urea and nonpermeants such as trehalose, sucrose, lactose and glucose with dipalmitoylphosphatidylcholine (DPPC) and egg yolk phosphatidylcholine (EPC) bilayers was studied by means of infrared spectroscopy in solid samples. The properties of the liposomes formed upon rehydration in different polyol solutions were determined by dynamic light scattering, fluorescence anisotropy, absorbance at 450 nm and merocyanine 540 spectra.Phospholipid samples dehydrated in the presence of urea and glycerol give v _1/2 values for the antisymmetric stretch (P=0 stretch) in the IR spectra; lower values are found for hydrated phospholipids.In contrast, the same procedure in the presence of carbohydrates, gives v _1/2 values close or higher to those found for hydrated phospholipids, following the sequence glucose>sucrose>trehalose. This order is similar to that found in hydrated bilayers for the 570/500 nm ratio determined in the MC 540 spectra as a function of the number of OH equatorial groups of the sugars.Liposomes lyophilized in the presence of those carbohydrates and rehydrated in buffer solution showed an increase in the 570/530 absorbance ratio in the MC spectra at temperatures below that corresponding to the gel-liquid crystalline transition. This is interpreted as an exposure of hydrophobic regions due to the carbohydrate-phospholipid interaction. In these conditions, the size at which liposomes spontaneously stabilize is a function of the type and concentration of the polyols in the aqueous solution. These changes in size are connected with packing and mechanical constraints of the bilayer for some of the sugars assayed.Similar results to those obtained with lyophilized liposomes were found after aging liposomes in high sugar concentration solutions. A clear distinction can be made between the effect of permeant and nonpermeant molecules in regard to size, packing and hydrophobic region exposure.     

Some improvements in calculating the plant stand surface albedo and its influence on ground surface temperature

It is shown that better results are obtained in calculating the surface albedo of a plant stand for near-infrared solar radiation using the modified two-stream approximation in favor of the Schwarzschild one. These evaluations of the plant stand surface albedo were obtained by assuming the values for scattering parameters of upward ₀ and diffusive solar radiation in the plant stand, by applying the delta-Eddington approximation. However, more accurate evaluations of ₀ and can be obtained by using Rayleigh's phase scattering functions for radiative scattering in a plant stand. Furthermore, much attention is devoted to testing the influence of the plant stand albedo for the visible part of solar radiation (for which the Schwarzchild approximation is valid) on ground surface temperature. The ground surface temperature was calculated by the force-restore method; the greatest ground surface temperature corrections were obtained in cases where the surface beneath the plant stand is covered with snow. The influence on ground surface temperature of high absorption and scattering in dense plant stands with horizontal foliage was also tested. Again significant corrections of ground surface temperature were obtained, taking into consideration the given characteristics of a plant stand compared to a standard albedo value.List of symbols A albedo of direct radiation in plant canopy - A _D albedo of diffuse radiation in plant canopy - A _p albedo of the ground surface - A _Q total albedo in plant canopy - a proportion of gaps in plant canopy characteristic of surface evaporation - _w constant - parameter of upward scattering diffuse radiation - ₀ parameter of upward scattering direct radiation - C _g soil volumetric heat capacity - C _p air specific heat - C _DH aerodynamic transfer coefficient for heat - C _DE aerodynamic transfer coefficient for moisture - d depth of soil - sun's declination - azimuth of incident radiation - azimuth of diffuse radiation - characteristic of the radiative sources - G foliage orientation function - g parameter in delta-Eddington approximation - g _z parameter for near-infrared radiation - _L scattering phase function radiation - _D diffuse solar radiation flux - _G soil heat flux - _H air sensible heat flux - _L air latent heat flux - _O solar constant - _R net longwave radiation flux - _S direct solar radiation flux - h _o height of the sun - i intensity of diffuse radiation - k von Karman constant - L leaf area index - L _v coefficient for latent heat of evaporation - _g soil heat conductivity - n/N relative cloudiness - solid angle - frequency of temperature wave - Q _a specific humidity of air - Q _w specific humidity of saturated air - R _L coefficient of plant reflectivity - r direction of diffuse radiation - direction of incident radiation - r _o direction of solar radiation - r _s resistance of the leaf stomata - p _o air density - S intensity of direct solar radiation - Stefan-Boltzman constant - T _a air temperature - T _G ground surface temperature - T _c cloud temperature - T ₁ feaf temperature - T _* air temperature scale - t time - t time step - zenith angle of diffuse radiation - zenith angle of incident radiation - ₀ zenith angle of solar radiation - U _* friction velocity scale - V near-surface wind velocity - W _g soil water content - W _L scattering coefficient in plant canopy - W _sat saturated soil water content - z vertical direction     

Liposomal membranes XI. A suggestion to structural characteristics of acido-thermophilic bacterial membranes

To understand the role of ω-cyclohexyl fatty acid residue of lipids in acido-thermophilic bacterial membranes, three unusual phosphatidylcholines, 1,2-di-11-cyclohexylundecanoyl-l-α-phosphatidylcholine (11_CYPC), 1,2-di-13-cyclohexyltridecanoyl-l-α-phosphatidylcholine (13_CYPC), and 1–13-cyclohexyltridecanoyl-2–11-cyclohexylundecanoyl-l-α-phosphatidylcholine (1–13_CY-2–11_CYPC) were prepared and the steady-state fluorescence anisotropy of 1,6-diphenylhexatriene (DPH) in the hydrophobic domain of these liposomal bilayers was determined. Compared with the case of dipalmitoyl (DPPC) or dimyristoyl phosphatidylcholine (DMPC), introducing the ω-cyclohexyl moiety onto lecithins makes the bilayers fluid below the phase transition temperature, while immobilizes them above the phase transition temperatures. The properties of the unusual phosphatidylcholine liposomes suggested by the steady-state fluorescence anisotropy investigation were in good agreement with those obtained from the thermotropic and permeability investigations. Results obtained are discussed from the view point of the role and function of lipid membranes of acido-thermophilic bacteria which contain unusual fatty acids.     

Parameter estimation in surface exchange models using nonlinear inversion: how many parameters can we estimate and which measurements are most useful?

Models of mass and energy exchanges between the biosphere and the atmosphere generally contain a nonlinear dependence between fluxes and model parameters, and thus estimation of these parameters from measurements in a heterogeneous landscape depends on the scale of the observations. The scale‐dependence of a typical surface‐exchange model (the CSIRO Biospheric Model, CBM) is examined using the diurnal variation of hourly fluxes of CO₂, latent heat, sensible heat and soil heat. The fluxes were measured using micrometeorological techniques over six sites in a grazing/pasture system in SE Australia during a period of three weeks in 1995. Nonlinear parameter inversion was used to determine model parameters. Analysis of the covariance of the estimates of the parameters and the unexplained residuals of the model showed that a maximum of three or four parameters could be determined independently from the observations for all six sites. Estimates of a key model parameter, j_max, the mean of maximum potential electron transport rate of all leaves within the canopy, was best determined by the measurements of net CO₂ flux at all sites examined. Measurements of ground heat flux provide little information about any of the model parameters in CBM. Because of nonlinearities in the surface exchange model, calculated fluxes will be in error if parameters for the component vegetation types are simply averaged in proportion to their areal fraction. The magnitude of these errors was examined for CBM using a hypothetical land surface consisting of two surface types, each with different parameter values. Predictions of net CO₂, latent heat and ground heat fluxes using a linear combination of model parameters for the two surface types were quite similar with those found using optimal estimates of the parameters for the landscape, but were significantly poorer for sensible heat fluxes.