环境因子对锌酵母生长影响潜力预测Ⅱ.基于模糊关系方程

在构造环境因子温度、pH、溶氧对锌酵母菌体生长评价的隶属函数的基础上,通过求解模糊关系方程,预测环境因子对菌体生长影响潜力。     

Comparison of dwarf bamboos (Indocalamus sp.) leaf parameters to determine relationship between spatial density of plants and total leaf area per plant

The relationship between spatial density and size of plants is an important topic in plant ecology. The self‐thinning rule suggests a ?3/2 power between average biomass and density or a ?1/2 power between stand yield and density. However, the self‐thinning rule based on total leaf area per plant and density of plants has been neglected presumably because of the lack of a method that can accurately estimate the total leaf area per plant. We aimed to find the relationship between spatial density of plants and total leaf area per plant. We also attempted to provide a novel model for accurately describing the leaf shape of bamboos. We proposed a simplified Gielis equation with only two parameters to describe the leaf shape of bamboos one model parameter represented the overall ratio of leaf width to leaf length. Using this method, we compared some leaf parameters (leaf shape, number of leaves per plant, ratio of total leaf weight to aboveground weight per plant, and total leaf area per plant) of four bamboo species of genus Indocalamus Nakai (I. pedalis (Keng) P.C. Keng, I. pumilus Q.H. Dai and C.F. Keng, I. barbatus McClure, and I. victorialis P.C. Keng). We also explored the possible correlation between spatial density and total leaf area per plant using log‐linear regression. We found that the simplified Gielis equation fit the leaf shape of four bamboo species very well. Although all these four species belonged to the same genus, there were still significant differences in leaf shape. Significant differences also existed in leaf area per plant, ratio of leaf weight to aboveground weight per plant, and leaf length. In addition, we found that the total leaf area per plant decreased with increased spatial density. Therefore, we directly demonstrated the self‐thinning rule to improve light interception.     

ESTIMATING PHENOTYPIC SELECTION IN AGE‐STRUCTURED POPULATIONS BY REMOVING TRANSIENT FLUCTUATIONS

An extension of the selection differential in the Robertson–Price equation for the mean phenotype in an age‐structured population is provided. Temporal changes in the mean phenotype caused by transient fluctuations in the age‐distribution and variation in mean phenotype among age classes, which can mistakenly be interpreted as selection, will disappear if reproductive value weighting is applied. Changes in any weighted mean phenotype in an age‐structured population may be decomposed into between‐ and within‐age class components. Using reproductive value weighting the between‐age class component becomes pure noise, generated by previous genetic drift or fluctuating selection. This component, which we call transient quasi‐selection, can therefore be omitted when estimating age‐specific selection on fecundity or viability within age classes. The final response can be computed at the time of selection, but can not be observed until lifetime reproduction is realized unless the heritability is one. The generality of these results is illustrated further by our derivation of the selection differential for the continuous time age‐structured model with general age‐dependent weights. A simple simulation example as well as estimation of selection components in a house sparrow population illustrates the applicability of the theory to analyze selection on the mean phenotype in fluctuating age‐structured populations.     

Faster-than-anticipated Na/Cl diffusion across lipid bilayers in vesicles

Maintenance of electrochemical potential gradients across lipid membranes is critical for signal transduction and energy generation in biological systems. However, because ions with widely varying membrane permeabilities all contribute to the electrostatic potential, it can be difficult to measure the influence of diffusion of a single ion type across the bilayer. To understand the electrodiffusion of H⁺ across lipid bilayers, we used a pH-sensitive fluorophore to monitor the lumenal pH in vesicles after a stepwise change in the bulk pH. In vesicles containing the ion channel gramicidin, the lumenal pH rapidly approached the external pH. In contrast, the lumen of intact vesicles showed a two stage pH response: an initial rapid change occurred over ~ 1 min, followed by a much slower change over ~ 24 h. We provide a quantitative interpretation of these results based on the Goldman–Hodgkin–Katz ion fluxes discharging the electrical capacitance of the bilayer membrane. This interpretation provides an estimate of the permeability of the membranes to Na⁺ and Cl⁻ ions of ~ 10^− 8 cm/s, which is ~ 3 orders of magnitude faster than previous reports. We discuss possible mechanisms to account for this considerably higher permeability in vesicle membranes.     

Quantifying relationships between traits and explicitly measured gradients of stress and disturbance in early successional plant communities

Questions: How can one explicitly quantify, and separately measure, stress and disturbance gradients? How do these gradients affect functional composition in early successional plant communities and to what extent? Can we accurately predict trait composition from knowledge of these gradients? Location: Southern Quebec, Canada. Methods: Using eight environmental variables measured in 48 early successional plant communities, we estimated stress and disturbance gradients through structural equation modelling. We then measured 10 functional traits on the most abundant species of these 48 communities and calculated their community‐level mean and variance weighted by the relative abundance of each species. Finally, we related these community‐weighted means and variances to the estimated stress and disturbance gradients using general linear models or generalized additive models. Results: We obtained a well‐fitting measurement model of the stress and disturbance gradients existing in our sites. Of the 10 studied traits, only average plant reproductive height was strongly correlated with the stress (r²=0.464) and disturbance (r²=0.543) gradients. Leaf traits were not significantly related to either the stress or disturbance gradients. Conclusions: The well‐fitting measurement model of the stress and disturbance gradients, combined with the generally weak trait–environment linkages, suggests that community assembly in these early successional plant communities is driven primarily by stochastic processes linked to the history of arrival of propagules and not to trait‐based environmental filtering.     

The stereodynamics of 1,2‐dipropyldiaziridines

N‐alkylated trans‐diaziridines are an intriguing class of compounds with two stereogenic nitrogen atoms which easily interconvert. In the course of our investigations of the nature of the interconversion process via nitrogen inversion or electrocyclic ring opening ring closure, we synthesized and characterized the three constitutionally isomeric diaziridines 1,2‐di‐n‐propyldiaziridine 1 , 1‐isopropyl‐2‐n‐propyldiaziridine 2 , and 1,2‐diisopropyldiaziridine 3 to study the influence of the substituents on the interconversion barriers. Enantiomer separation was achieved by enantioselective gas chromatography on the chiral stationary phase Chirasil‐β‐Dex with high separation factors α (1‐isopropyl‐2‐n‐propyldiaziridine: 1.18; 1, 2‐diisopropyldiaziridine: 1.24; 100°C 50 kPa He) for the isopropyl substituted diaziridines. These compounds showed pronounced plateau formation between 100 and 150°C, and peak coalescence at elevated temperatures. The enantiomerization barriers ΔG? and activation parameters ΔH? and ΔS? were determined by enantioselective dynamic gas chromatography (DGC) and direct evaluation of the elution profiles using the unified equation implemented in the software DCXplorer. Interestingly, 1‐isopropyl‐2‐n‐propyldiaziridine and 1,2‐diisopropyldiaziridine exhibit similar high interconversion barriers ΔG? (100°C) of 128.3 ± 0.4 kJ mol^?1 and 129.8 ± 0.4 kJ mol^?1, respectively, which indicates that two sterically demanding substituents do not substantially increase the barrier as expected for a distinct nitrogen inversion process. Chirality, 2010. © 2009 Wiley‐Liss, Inc.     

Estimating Haplotype Effects for Survival Data

Summary Genetic association studies often investigate the effect of haplotypes on an outcome of interest. Haplotypes are not observed directly, and this complicates the inclusion of such effects in survival models. We describe a new estimating equations approach for Cox's regression model to assess haplotype effects for survival data. These estimating equations are simple to implement and avoid the use of the EM algorithm, which may be slow in the context of the semiparametric Cox model with incomplete covariate information. These estimating equations also lead to easily computable, direct estimators of standard errors, and thus overcome some of the difficulty in obtaining variance estimators based on the EM algorithm in this setting. We also develop an easily implemented goodness‐of‐fit procedure for Cox's regression model including haplotype effects. Finally, we apply the procedures presented in this article to investigate possible haplotype effects of the PAF‐receptor on cardiovascular events in patients with coronary artery disease, and compare our results to those based on the EM algorithm.