探讨使用野外随机取样推断随机变量概率分布的数学方法--杂草研究作为一个例子

我们在生态学研究中涉及到的大多数变量呈现出随机性，因而可以认为它们就是随机变量。概率分布是研究随机变量变化规律的基础，如何利用野外取样来推断检验随机变量的分布是本文要解决的主要问题。本文扩展了回归方法的应用，使其能用来推断一个随机变量的分布函数。并且该推断还能被统计检验。作为一个应用实例。该方法被用于确定杂草种子在特定条件下扩散的分布函数。在此条件下，该杂草种子扩散为近似的高斯(正态)分布。     

Haematopoietic stem cells adopt mature haematopoietic fates in ischaemic myocardium

Under conditions of tissue injury, myocardial replication and regeneration have been reported. A growing number of investigators have implicated adult bone marrow (BM) in this process, suggesting that marrow serves as a reservoir for cardiac precursor cells. It remains unclear which BM cell(s) can contribute to myocardium, and whether they do so by transdifferentiation or cell fusion. Here, we studied the ability of c-kit-enriched BM cells, Lin- c-kit+ BM cells and c-kit+ Thy1.1(lo) Lin- Sca-1+ long-term reconstituting haematopoietic stem cells to regenerate myocardium in an infarct model. Cells were isolated from transgenic mice expressing green fluorescent protein (GFP) and injected directly into ischaemic myocardium of wild-type mice. Abundant GFP+ cells were detected in the myocardium after 10 days, but by 30 days, few cells were detectable. These GFP+ cells did not express cardiac tissue-specific markers, but rather, most of them expressed the haematopoietic marker CD45 and myeloid marker Gr-1. We also studied the role of circulating cells in the repair of ischaemic myocardium using GFP+-GFP- parabiotic mice. Again, we found no evidence of myocardial regeneration from blood-borne partner-derived cells. Our data suggest that even in the microenvironment of the injured heart, c-kit-enriched BM cells, Lin- c-kit+ BM cells and c-kit+ Thy1.1(lo) Lin- Sca-1+ long-term reconstituting haematopoietic stem cells adopt only traditional haematopoietic fates.     

Towards sustainability in world fisheries

Fisheries have rarely been 'sustainable'. Rather, fishing has induced serial depletions, long masked by improved technology, geographic expansion and exploitation of previously spurned species lower in the food web. With global catches declining since the late 1980s, continuation of present trends will lead to supply shortfall, for which aquaculture cannot be expected to compensate, and may well exacerbate. Reducing fishing capacity to appropriate levels will require strong reductions of subsidies. Zoning the oceans into unfished marine reserves and areas with limited levels of fishing effort would allow sustainable fisheries, based on resources embedded in functional, diverse ecosystems.     

Pyruvate kinase inhibited by L-cysteine as a marker of tumorigenic human urothelial cell lines

Summary It was found that a decrease in electrophoretic mobility of pyruvate kinase (PK) isoenzyme, and an increase of the sensitivity of this enzyme to L-cysteine, were markers of immortalization and tumorigenic properties, respectively, in human urothelial cell lines characterized by different grades of transformation (TGr) in vitro.     

HIV是如何攻击人体免疫系统的?

在过去15年里，各国政府与研究机构在艾滋病研究方面均投入了大量的财力，科研人员与医生在疾病治疗方面也取得了显著进展，而且对引发艾滋病的HIV病毒是如何感染细胞的也获得了新认识。但是，科学家们对于HIV究竟是怎样导致免疫系统崩溃的，即感染的基本过程还不是十分清楚。多数研究人员坚持认为，HIV能直接杀死被称为协助者的T细胞，或CDe细胞，结果免疫系统因细胞被疯狂置换和取代而出现崩溃。据最新研究显示，C］X细胞分裂的不同途径可能起着更重要的作用。最近，一些研究人员怀疑，病毒有阻断新免疫细胞供给的作用。有些科学家…     

Variation in chromosome number in the sheep headflyHydrotaea irritans (Fallen) (Diptera: Muscidae)

Summary Variation in the number of chromosomes was found in sheep headflies, ranging from 12 to 15 chromosomes. Of these, five pairs were common among all individuals. Among 9 larvae no males were identified.