Overcompensation and population cycles in an ungulate.

Although theoretical studies show that overcompensatory density-dependent mechanisms can potentially generate regular or chaotic fluctuations in animal numbers, the majority of realistic single-species models of invertebrate populations are not overcompensatory enough to cause sustained population cycles. The possibility that overcompensation may generate cycles or chaos in vertebrate populations has seldom been considered. Here we show that highly overcompensatng density-dependent mortality can generate recurrent population crashes consistent with those observed in a naturally limited population of Soay sheep. The observed interval of three or more years between crashes points to sharp 'focusing' of mortality over a narrow range of population density.     

On the limitations of comparing mean square forecast errors

Linear models are invariant under non-singular, scale-preserving linear transformations, whereas mean square forecast errors (MSFEs) are not. Different rankings may result across models or methods from choosing alternative yet isomorphic representations of a process. One approach can dominate others for comparisons in levels, yet lose to another for differences, to a second for cointegrating vectors and to a third for combinations of variables. The potential for switches in ranking is related to criticisms of the inadequacy of MSFE against encompassing criteria, which are invariant under linear transforms and entail MSFE dominance. An invariant evaluation criterion which avoids misleading outcomes is examined in a Monte Carlo study of forecasting methods.     

特征结构提取的高阶Hopfield神经网络实现

本文首先建立了特征结构提取问题的罚函数表示，通过对罚函数求极小可以求得原始协方差矩阵的主特征向量及其对应的特征值。为了求得其他特征结构，特构造了一个协方差矩阵序列。如果将罚函数展开并进行整理，高阶Ｈｏｐｆｉｅｌｄ神经网络可被引入到特征结构提取中。这种方法比较直观，它将网络稳定时的输出与所求协方差矩阵的主特征向量的各个分量相对应，而网络稳定时的能量则对应于协方差矩阵的迹与所求特征值之差，计算机仿真结果验证了这种方法的正确性。     

过渡金属乙酰丙酮配合物引发淀粉与烯基单体接枝共聚

研究了Ｍｎ（Ⅲ）、Ｃｏ（Ⅲ）、Ｃｒ（Ⅲ）和Ｖ（Ⅳ）的乙酰丙酮配合物引发淀粉与ＭＭＡ、ＡＮ、ＡＭ和ＡＡ接枝共聚合反应的引发活性。实验表明，４种引发体系中，Ｍｎ（ａｃａｃ）３的引发活性最佳，它可以有效地引发淀粉与上述４种单体的接枝共聚合反应，并获得较高的ＰＧ；Ｃｏ（ａｃａｃ）３和Ｃｒ（ａｃａｃ）３仅对水溶性烯基单体ＡＭ、ＡＡ有良好的引发活性；Ｖｏ（ａｃａｃ）２对４种单体的引发活性均较低。４种单体中，水     

灰铸铁的应力屈服曲面及其三维热弹塑性应力解析

对原有的灰铸铁件应力屈服曲面进行了合理的简化,使其在理论上合理,工程应用上更为方便。建立了灰铸铁件三维非稳态热弹塑性应力场的有限元方法。以灰铸铁哑铃件为对象,用新屈服曲面对其应力发展过程进行了模拟,且比较了用新旧屈服面计算得到的结果。     

Choroidal and iris angioarchitecture of the newt: A scanning electron-microscopic study of vascular corrosion casts

The corrosion cast technique provided for the first time an excellent three-dimensional visualization of the vascular pattern of the choroid and iris in the newt eye. The results show the presence of a single arterial afference to the choroidal and iris capillaries: the ophthalmic artery is the origin fo both ciliary arteries and the long posterior ciliary artery. Slightly behind the equatorial circumference of the eyeball the venous drainage consists of a single vessel on the dorsal side and two distinct vessels on the ventral one. It receives blood from both iris and choroid. The surface of the plastic endocasts shows some details of fine luminal structures of the endothelial cells. Shallow depressions may be regarded as imprints of endothelial cell nuclei, and they are distinctly different for arteries and capillaries. The angioarchitecture of the newt eye differs from that of brain in that hairpin-shaped capillary loops are not observed at all.     

小麦群体连续选择效应的综合分析

本试验对由信谷核不育基因构成的异效群体内４个性状进行连续两轮歧化选择，并将所得数据进行群体综合分析。结果表明：整个群体的平均表现和变异程度未发明显变化；但群体分布状况有一定改变，尤其是每穗粒数的分布数化较为明显；株高和千粒重的有效因子数估计基本符合小麦遗传实际表现，每穗粒数的有效有效因子数估计略低，说明此性状遗传背景较为简单。     

巷道底板上锚杆布置形式对预防底鼓效果的模拟研究

本文采用三个边界元模型对巷道底板上锚杆的不同布置形式对防治底鼓的效果进行了模拟研究。根据研究结果,提出采用在巷道底板上分期安装锚杆的方法,可有效地防治巷道底鼓。本文对巷道底鼓产生机理和防治措施的研究结果,具有一定的理论价值和应用参考价值。     

Phenological studies of selected savanna mosses of south-western Nigeria

It was established that there is little diversity of bryophytes in the derived savanna. Mosses were found in the sampling sites, whereas liverworts were rarely observed. The reproductive methods of four dominant sexually reproducing savanna mosses —Archidium ohioense, Bryum coronatum, Fissidens minutifolius andTrachycarpidium tisserantii were monitored over two consecutive rainy seasons. Protonemal and gametophyte production were noticed in the field in March/April, and capsule dehiscence and spore dispersal occurred in September/October. The sequential stages of development, starting with gametangial production and ending with the falling of the dehisced capsules, occurred within the rainy season. However,A. ohioense andT. tisserantii did not discharge their spores easily (cleistocarpous), unlike the stegocarpous speciesB. coronatum andF. minutifolius. Water availability and possibly high humidity may have contributed to growth. The short period between sex organ formation and dehiscence of capsule seen in these studies, compared with the longer period in some temperate mosses, may be an advantage for bryophytes in a savanna environment.     

转台轴线标定及综合标定矩阵的生成——用于三维计算机视觉系统

提出利用标定平面的两个角度可交出转台轴线,通过交出的轴线,标定出光-象平面轴线的关系,并给出测量点通过平移、旋转再进入标定矩阵的一个新的转换矩阵。