矩阵的加号逆理论在参数估计中的应用

本文从矩阵的加号逆理论出发,根据求矛盾线性方程组最佳逼近解的方法,建立起一种新的参数估计方法,同时给出了显著性检验方法,这种方法更简单更精确．     

不健全资料的参数关联分析法

首先建立相关变量取值随时序变化的数学模型,而后,利用模型中能够反映变量几何形状的适宜参数,提出了参数关联度的概念．从而解决了观测值非一一对应、且不齐的相关变量关联分析问题．同时给出一种较高拟合精度的非等间隔序列的灰色建模方法．     

生物种群动态微分方程模型参数估计方法

本文以数值分析和最优化技术的有机结合为基础,提出了一种新的对动态微分方程模型直接进行数据拟合和参数估计方法,并以Logistic微分方程、生物种间竞争关系微分方程以及一种复合形态的Logistic微分方程为例进行了数据拟合试验．结果表明,该方法对各种动态微分方程模型均能进行最优拟合分析并求解其参数．同时发现,以前有的作者〔1,2,3,4,5〕提出的方法所得到的参数估计值存在系统误差且误差较大．     

Derivation and testing of pair potentials for protein folding. When is the quasichemical approximation correct?

Many existing derivations of knowledge-based statistical pair potentials invoke the quasichemical approximation to estimate the expected side-chain contact frequency if there were no amino acid pair-specific interactions. At first glance, the quasichemical approximation that treats the residues in a protein as being disconnected and expresses the side-chain contact probability as being proportional to the product of the mole fractions of the pair of residues would appear to be rather severe. To investigate the validity of this approximation, we introduce two new reference states in which no specific pair interactions between amino acids are allowed, but in which the connectivity of the protein chain is retained. The first estimates the expected number of side-chain contracts by treating the protein as a Gaussian random coil polymer. The second, more realistic reference state includes the effects of chain connectivity, secondary structure, and chain compactness by estimating the expected side-chain contrast probability by placing the sequence of interest in each member of a library of structures of comparable compactness to the native conformation. The side-chain contact maps are not allowed to readjust to the sequence of interest, i.e., the side chains cannot repack. This situation would hold rigorously if all amino acids were the same size. Both reference states effectively permit the factorization of the side-chain contact probability into sequence-dependent and structure-dependent terms. Then, because the sequence distribution of amino acids in proteins is random, the quasichemical approximation to each of these reference states is shown to be excellent. Thus, the range of validity of the quasichemical approximation is determined by the magnitude of the side-chain repacking term, which is, at present, unknown. Finally, the performance of these two sets of pair interaction potentials as well as side-chain contact fraction-based interaction scales is assessed by inverse folding tests both without and with allowing for gaps.     

Germination responses of a seed population of Taraxacum officinale Weber to constant temperatures including the supra-optimal range

Abstract The germination responses of a nondormant fraction of a seed population of Taraxacum officinale Weber at constant temperatures in the range 7–34°C were analysed through a time-course study. Maximal percentage germination (approximately 90%) was attained at temperatures 10–18°C, where simple linear relationships were observed between the temperature and the germination rates, i.e. the reciprocals of the time taken to germinate by subpopulations with 20–80% germination. There was a variation in the required ‘thermal times’ (θ) which characterized the linear relationships, the distribution of which could be approximated for the seed population by the following distribution function: where m is the median of the distribution, and A is a shape parameter characterizing the pattern of the distribution. Final percentage germination decreased with increasing temperature from 20 to 32°C, where the final percentage germination vs. temperature plotted on a normal probability scale yielded a straight line, indicating the normality of the distribution of the upper limit temperature in the seed population. The estimated mean and standard deviation were 27.25 ± 3.75°C. The rate of germination for the subpopulation with 20–80% germination also decreased with increases in the temperature from 22 to 30°C. If the relationships between the temperature within this range and the rate for the subpopulations with 20–80% germination were approximated by the regression lines, the negative ‘thermal time’ characterizing the yielded linear relationship would have a distribution which could be approximated by the same function with the required thermal time for the relationship of suboptimal range. The parameters m and A for the negative ‘thermal time’ were determined to be 2870 K h and 1.7 × 10^-10 K^-3 h^-3.     

Differences in membrane unsaturated fatty acids and electron spin resonance in different types of myeloid leukemia cells

The fatty acid composition and some physical properties of intact cells and isolated plasma membranes of two types of mouse myeloid leukemia cell clone grown in culture have been examined. One clone type, MGI⁺D⁺, can be induced by the macrophage and granulocyte-inducing protein (MGI) to differentiate into mature macrophages and granulocytes. The other clone type, MGI⁺D^?, could not be induced to differentiate into mature cells. A two-fold increase in the ratio of saturated fatty acid to unsaturated fatty acid was found in the MGI⁺D^? compared to the MGI⁺D⁺ clones. The MGI⁺D^? clones produced an unusual polyunsaturated C_20:5 fatty acid at 28°C, whereas the MGI⁺D⁺ clones did not grow at this temperature. The cells and their isolated plasma membranes were studied by electron spin resonance. The motion of the 5-nitroxide stearate spin label was found to be higher in the intact cells and in the membranes of MGI⁺D^? clones than of the MGI⁺D⁺ clones. The cells of MGI⁺D⁺ clones showed a similar freedom of motion to normal myeloblasts from the bone marrow. The results indicate that myeloid leukemia cells which differ in their competence to be induced to differentiate into mature cells have different physical properties of their plasma membranes and that this is correlated with their fatty acid acyl chain composition.     

The effects of cholesterol on the time-resolved emission anisotropy of 12-(9-anthroyloxy)stearic acid in dipalmitoylphosphatidylcholine bilayers

The time-resolved fluorescence emission anisotropy of 12-(9-anthroyloxy)stearic acid (12-AS) and 1,6-diphenyl-1,3,5-hexatriene (DPH) have been measured in dipalmitoylphosphatidylcholine liposomes in the presence and absence of 40 mol% cholesterol at temperatures above and below the phase transition temperature (41°C). By using a synchronously-pumped mode-locked frequency-doubled dye laser and single photon counting detection with an excitation response function of 300 picosecond, rotational correlation times down to less than 1 nanosecond could be resolved. Whereas DPH showed only small changes in the limiting anisotropy on the addition of cholesterol, 12-AS showed significant increases in this parameter with the effect being potentiated at higher temperatures. This difference in behaviour has been attributed to a fluorophore-cholesterol interaction that resulted in a change in the fluorophore geometry. Not only do DPH and 12-AS sense different depolarizing rotations due to the different directions of their emission dipoles but also differ in their lipid interactions which alter their limiting anisotropies. The implication is that the comparison of steady-state anisotropy measurements between chemically identical fluorophores in different lipid environments may be complicated by molecular distortions that change the motions to which the steady-state fluorescence parameters will be sensitive.     

线性规划法在植物生态学数学模型参数估计中的应用初探

本文提出了一种植物生态学数学模型参数估计的新方法——线性规划法,并结合最小二乘法对模型参数的估计进行了实例分析。认为某种程度上前者更优于后者。是一种值得进一步研究的方法。