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G. E. Risinger P. N. Parker H. H. Hsieh 《Cellular and molecular life sciences : CMLS》1965,21(8):434-434
Zusammenfassung Es wird die Isolierung eines neuen fluoreszierenden Thiaminderivates beschrieben. 相似文献
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The separation of the effects of environmental variability from the impacts of fishing has been elusive, but is essential for sound fisheries management. We distinguish environmental effects from fishing effects by comparing the temporal variability of exploited versus unexploited fish stocks living in the same environments. Using the unique suite of 50-year-long larval fish surveys from the California Cooperative Oceanic Fisheries Investigations we analyse fishing as a treatment effect in a long-term ecological experiment. Here we present evidence from the marine environment that exploited species exhibit higher temporal variability in abundance than unexploited species. This remains true after accounting for life-history effects, abundance, ecological traits and phylogeny. The increased variability of exploited populations is probably caused by fishery-induced truncation of the age structure, which reduces the capacity of populations to buffer environmental events. Therefore, to avoid collapse, fisheries must be managed not only to sustain the total viable biomass but also to prevent the significant truncation of age structure. The double jeopardy of fishing to potentially deplete stock sizes and, more immediately, to amplify the peaks and valleys of population variability, calls for a precautionary management approach. 相似文献
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iASPP oncoprotein is a key inhibitor of p53 conserved from worm to human 总被引:39,自引:0,他引:39
Bergamaschi D Samuels Y O'Neil NJ Trigiante G Crook T Hsieh JK O'Connor DJ Zhong S Campargue I Tomlinson ML Kuwabara PE Lu X 《Nature genetics》2003,33(2):162-167
We have previously shown that ASPP1 and ASPP2 are specific activators of p53; one mechanism by which wild-type p53 is tolerated in human breast carcinomas is through loss of ASPP activity. We have further shown that 53BP2, which corresponds to a C-terminal fragment of ASPP2, acts as a dominant negative inhibitor of p53 (ref. 1). Hence, an inhibitory form of ASPP resembling 53BP2 could allow cells to bypass the tumor-suppressor functions of p53 and the ASPP proteins. Here, we characterize such a protein, iASPP (inhibitory member of the ASPP family), encoded by PPP1R13L in humans and ape-1 in Caenorhabditis elegans. iASPP is an evolutionarily conserved inhibitor of p53; inhibition of iASPP by RNA-mediated interference or antisense RNA in C. elegans or human cells, respectively, induces p53-dependent apoptosis. Moreover, iASPP is an oncoprotein that cooperates with Ras, E1A and E7, but not mutant p53, to transform cells in vitro. Increased expression of iASPP also confers resistance to ultraviolet radiation and to cisplatin-induced apoptosis. iASPP expression is upregulated in human breast carcinomas expressing wild-type p53 and normal levels of ASPP. Inhibition of iASPP could provide an important new strategy for treating tumors expressing wild-type p53. 相似文献
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Why fishing magnifies fluctuations in fish abundance 总被引:1,自引:0,他引:1
Anderson CN Hsieh CH Sandin SA Hewitt R Hollowed A Beddington J May RM Sugihara G 《Nature》2008,452(7189):835-839
It is now clear that fished populations can fluctuate more than unharvested stocks. However, it is not clear why. Here we distinguish among three major competing mechanisms for this phenomenon, by using the 50-year California Cooperative Oceanic Fisheries Investigations (CalCOFI) larval fish record. First, variable fishing pressure directly increases variability in exploited populations. Second, commercial fishing can decrease the average body size and age of a stock, causing the truncated population to track environmental fluctuations directly. Third, age-truncated or juvenescent populations have increasingly unstable population dynamics because of changing demographic parameters such as intrinsic growth rates. We find no evidence for the first hypothesis, limited evidence for the second and strong evidence for the third. Therefore, in California Current fisheries, increased temporal variability in the population does not arise from variable exploitation, nor does it reflect direct environmental tracking. More fundamentally, it arises from increased instability in dynamics. This finding has implications for resource management as an empirical example of how selective harvesting can alter the basic dynamics of exploited populations, and lead to unstable booms and busts that can precede systematic declines in stock levels. 相似文献
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据DNA序列中核苷酸短程关闻为主及其进化依赖性,本提出了一个以少核苷酸频数为基础的进化距离的定义,据此用35个物种的16S(18S)RNA序列构建进化树,得到了和生物学公认的进化树一致的结果。最佳的树为用7-8核苷频数作为距离定义构建而成,这意味着存在着一些7-8核苷酸组成的字串,它们与进化强相关。论的最后部分把这些进化相关字串全部找出。 相似文献
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Ping‐Hung Hsieh 《Journal of forecasting》2001,20(7):485-499
Risk managers are often concerned about tail probabilities of asset return distributions, in particular the frequency and severity of extreme returns. In this article, we propose a model that integrates extreme value theory and point processes to model the frequency and severity of exchange rate returns. The proposed model is applied to daily spot exchange rate series and the parameters of interest, such as the tail index, the mean size and rate of occurrence of extreme returns, are estimated using maximum likelihood estimation. We study the impact of recent currency crises on the frequency and severity of the series and find that, during 1995–9, the frequency of extreme daily Japanese yen–US dollar spot exchange rate returns increases twofold, and the time duration of high volatility persists longer for the Japanese yen series than for the Swiss franc and Danish krone series. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
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When electrons are subject to a large external magnetic field, the conventional charge quantum Hall effect dictates that an electronic excitation gap is generated in the sample bulk, but metallic conduction is permitted at the boundary. Recent theoretical models suggest that certain bulk insulators with large spin-orbit interactions may also naturally support conducting topological boundary states in the quantum limit, which opens up the possibility for studying unusual quantum Hall-like phenomena in zero external magnetic fields. Bulk Bi(1-x)Sb(x) single crystals are predicted to be prime candidates for one such unusual Hall phase of matter known as the topological insulator. The hallmark of a topological insulator is the existence of metallic surface states that are higher-dimensional analogues of the edge states that characterize a quantum spin Hall insulator. In addition to its interesting boundary states, the bulk of Bi(1-x)Sb(x) is predicted to exhibit three-dimensional Dirac particles, another topic of heightened current interest following the new findings in two-dimensional graphene and charge quantum Hall fractionalization observed in pure bismuth. However, despite numerous transport and magnetic measurements on the Bi(1-x)Sb(x) family since the 1960s, no direct evidence of either topological Hall states or bulk Dirac particles has been found. Here, using incident-photon-energy-modulated angle-resolved photoemission spectroscopy (IPEM-ARPES), we report the direct observation of massive Dirac particles in the bulk of Bi(0.9)Sb(0.1), locate the Kramers points at the sample's boundary and provide a comprehensive mapping of the Dirac insulator's gapless surface electron bands. These findings taken together suggest that the observed surface state on the boundary of the bulk insulator is a realization of the 'topological metal'. They also suggest that this material has potential application in developing next-generation quantum computing devices that may incorporate 'light-like' bulk carriers and spin-textured surface currents. 相似文献