乌江河谷岩溶发育特征研究

乌江是长江上游的一条支流,水力资源丰富,全流域碳酸盐岩分布面积占70%,岩溶发育是影响坝址工程地质条件的重要因素.乌江是一深切峡谷,具特定的岩溶发育特征,如河谷深部洞穴发育;河谷类型对岩溶发育有所制约等.本文通过河谷深部洞穴成因的研究,提出了它可能的分布部位;对中更新世以来古气候古环境的研究,提出主要岩溶发育期和古水文网在河谷岩溶发育中的作用.并探讨库坝勘测中第四纪地质、古水文网调查的重要性.     

SC支撑辊板形控制效果的研究

为了更有效的控制板形,我们开发了一种新的支撑辊,称为SC支撑辊。它可以应用于普通四辊轧机、HCW轧机上,也可用作HC轧机的中间支撑辊。本文比较精确的计算了SC支撑辊的变形,并对SC支撑辊的板形控制效果进行了研究。     

Indication of drier periods on Mars from the chemistry and mineralogy of atmospheric dust

The ubiquitous atmospheric dust on Mars is well mixed by periodic global dust storms, and such dust carries information about the environment in which it once formed and hence about the history of water on Mars. The Mars Exploration Rovers have permanent magnets to collect atmospheric dust for investigation by instruments on the rovers. Here we report results from M?ssbauer spectroscopy and X-ray fluorescence of dust particles captured from the martian atmosphere by the magnets. The dust on the magnets contains magnetite and olivine; this indicates a basaltic origin of the dust and shows that magnetite, not maghemite, is the mineral mainly responsible for the magnetic properties of the dust. Furthermore, the dust on the magnets contains some ferric oxides, probably including nanocrystalline phases, so some alteration or oxidation of the basaltic dust seems to have occurred. The presence of olivine indicates that liquid water did not play a dominant role in the processes that formed the atmospheric dust.     

DNMT1 and DNMT3b cooperate to silence genes in human cancer cells

Inactivation of tumour suppressor genes is central to the development of all common forms of human cancer. This inactivation often results from epigenetic silencing associated with hypermethylation rather than intragenic mutations. In human cells, the mechanisms underlying locus-specific or global methylation patterns remain unclear. The prototypic DNA methyltransferase, Dnmt1, accounts for most methylation in mouse cells, but human cancer cells lacking DNMT1 retain significant genomic methylation and associated gene silencing. We disrupted the human DNMT3b gene in a colorectal cancer cell line. This deletion reduced global DNA methylation by less than 3%. Surprisingly, however, genetic disruption of both DNMT1 and DNMT3b nearly eliminated methyltransferase activity, and reduced genomic DNA methylation by greater than 95%. These marked changes resulted in demethylation of repeated sequences, loss of insulin-like growth factor II (IGF2) imprinting, abrogation of silencing of the tumour suppressor gene p16INK4a, and growth suppression. Here we demonstrate that two enzymes cooperatively maintain DNA methylation and gene silencing in human cancer cells, and provide compelling evidence that such methylation is essential for optimal neoplastic proliferation.     

Autoregulated instability of beta-tubulin mRNAs by recognition of the nascent amino terminus of beta-tubulin

Tubulin synthesis in animal cells is controlled by an autoregulatory mechanism that modulates the stability of polysome-bound tubulin messenger RNAs. The beta-tubulin RNAs are selectively targeted as substrates for destabilization not through the recognition of specific RNA sequences, but rather through co-translational recognition of the amino-terminal beta-tubulin tetrapeptide after its emergence from the ribosome. This motif is likely to be used in other systems where RNA degradation is coupled to ribosome attachment and translation.     

An antineoplastic C14-labeled methylhydrazine derivative in P815 mouse leukemia. a metabolic study

Zusammenfassung Die endst?ndige N-Methyl-Gruppe von 1-Methyl-C¹⁴-2-p-(isopropylcarbamoyl)benzylhydrazin-Hydrochlorid (MBH) (Ro 4-6467) erwies sich in In-vivo-Experimenten metabolisch labil, wird teilweise oxydiert und Bestandteil des Formiatpools.      

The evolution of alternative parasitic life histories in large blue butterflies

Large blue (Maculinea) butterflies are highly endangered throughout the Palaearctic region, and have been the focus of intense conservation research. In addition, their extraordinary parasitic lifestyles make them ideal for studies of life history evolution. Early instars consume flower buds of specific host plants, but later instars live in ant nests where they either devour the brood (predators), or are fed mouth-to-mouth by the adult ants (cuckoos). Here we present the phylogeny for the group, which shows that it is a monophyletic clade nested within Phengaris, a rare Oriental genus whose species have similar life histories. Cuckoo species are likely to have evolved from predatory ancestors. As early as five million years ago, two Maculinea clades diverged, leading to the different parasitic strategies seen in the genus today. Contrary to current belief, the two recognized cuckoo species show little genetic divergence and are probably a single ecologically differentiated species. On the other hand, some of the predatory morphospecies exhibit considerable genetic divergence and may contain cryptic species. These findings have important implications for conservation and reintroduction efforts.