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121.
Massive stars end their short lives in spectacular explosions--supernovae--that synthesize new elements and drive galaxy evolution. Historically, supernovae were discovered mainly through their 'delayed' optical light (some days after the burst of neutrinos that marks the actual event), preventing observations in the first moments following the explosion. As a result, the progenitors of some supernovae and the events leading up to their violent demise remain intensely debated. Here we report the serendipitous discovery of a supernova at the time of the explosion, marked by an extremely luminous X-ray outburst. We attribute the outburst to the 'break-out' of the supernova shock wave from the progenitor star, and show that the inferred rate of such events agrees with that of all core-collapse supernovae. We predict that future wide-field X-ray surveys will catch each year hundreds of supernovae in the act of exploding.  相似文献   
122.
Historically, variable and transient sources have both surprised astronomers and provided new views of the heavens. Here we report the discovery of an optical transient in the outskirts of the lenticular galaxy Messier 85 in the Virgo cluster. With a peak absolute R magnitude of -12, this event is distinctly brighter than novae, but fainter than type Ia supernovae (which are expected in a population of old stars in lenticular galaxies). Archival images of the field do not show a luminous star at that position with an upper limit in the g filter of about -4.1 mag, so it is unlikely to be a giant eruption from a luminous blue variable star. Over a two-month period, the transient source emitted radiation energy of almost 10(47) erg and subsequently faded in the optical sky. It is similar to, but six times more luminous at peak than, an enigmatic transient in the galaxy M31 (ref. 1). A possible origin of M85 OT2006-1 is a stellar merger. If so, searches for similar events in nearby galaxies will not only allow study of the physics of hyper-Eddington sources, but also probe an important phase in the evolution of stellar binary systems.  相似文献   
123.
Y Liu  J H Gao  M Liotti  Y Pu  P T Fox 《Nature》1999,400(6742):364-367
Many tasks require rapid and fine-tuned adjustment of motor performance based on incoming sensory information. This process of sensorimotor adaptation engages two parallel subcorticocortical neural circuits, involving the cerebellum and basal ganglia, respectively. How these distributed circuits are functionally coordinated has not been shown in humans. The cerebellum and basal ganglia show very similar convergence of input-output organization, which presents an ideal neuroimaging model for the study of parallel processing at a systems level. Here we used functional magnetic resonance imaging to measure the temporal coherence of brain activity during a tactile discrimination task. We found that, whereas the prefrontal cortex maintained a high level of activation, output activities in the cerebellum and basal ganglia showed different phasic patterns. Moreover, cerebellar activity significantly correlated with the activity of the supplementary motor area but not with that of the primary motor cortex; in contrast, basal ganglia activity was more strongly associated with the activity of the primary motor cortex than with that of the supplementary motor area. These results demonstrate temporally partitioned activity in the cerebellum and basal ganglia, implicating functional independence in the parallel subcortical outputs. This further supports the idea of task-related dynamic reconfiguration of large-scale neural networks.  相似文献   
124.
Carotid intima media thickness (cIMT) and plaque determined by ultrasonography are established measures of subclinical atherosclerosis that each predicts future cardiovascular disease events. We conducted a meta-analysis of genome-wide association data in 31,211 participants of European ancestry from nine large studies in the setting of the Cohorts for Heart and Aging Research in Genomic Epidemiology (CHARGE) Consortium. We then sought additional evidence to support our findings among 11,273 individuals using data from seven additional studies. In the combined meta-analysis, we identified three genomic regions associated with common carotid intima media thickness and two different regions associated with the presence of carotid plaque (P < 5 × 10(-8)). The associated SNPs mapped in or near genes related to cellular signaling, lipid metabolism and blood pressure homeostasis, and two of the regions were associated with coronary artery disease (P < 0.006) in the Coronary Artery Disease Genome-Wide Replication and Meta-Analysis (CARDIoGRAM) consortium. Our findings may provide new insight into pathways leading to subclinical atherosclerosis and subsequent cardiovascular events.  相似文献   
125.
The era of sphingolipid-based therapeutics is upon us. A large body of work has been accumulating that demonstrates the distinct biological roles of sphingolipids in maintaining a homeostatic environment and in responding to environmental stimuli to regulate cellular processes. It is thus necessary to further investigate alterations in sphingolipid-metabolism in pathological conditions and, in turn, try to exploit altered sphingolipid-metabolizing enzymes and their metabolites as therapeutic targets. This review will examine how advances in the fields of drug delivery, drug discovery, synthetic chemistry, enzyme replacement therapy, immunobiology, infectious disease and nanotechnology have delivered the potential and promise of utilizing and/or targeting sphingolipid metabolites as therapies for diverse diseases.  相似文献   
126.
Habitat degradation and climate change are thought to be altering the distributions and abundances of animals and plants throughout the world, but their combined impacts have not been assessed for any species assemblage. Here we evaluated changes in the distribution sizes and abundances of 46 species of butterflies that approach their northern climatic range margins in Britain-where changes in climate and habitat are opposing forces. These insects might be expected to have responded positively to climate warming over the past 30 years, yet three-quarters of them declined: negative responses to habitat loss have outweighed positive responses to climate warming. Half of the species that were mobile and habitat generalists increased their distribution sites over this period (consistent with a climate explanation), whereas the other generalists and 89% of the habitat specialists declined in distribution size (consistent with habitat limitation). Changes in population abundances closely matched changes in distributions. The dual forces of habitat modification and climate change are likely to cause specialists to decline, leaving biological communities with reduced numbers of species and dominated by mobile and widespread habitat generalists.  相似文献   
127.
Understanding the determinants of healthy mental ageing is a priority for society today. So far, we know that intelligence differences show high stability from childhood to old age and there are estimates of the genetic contribution to intelligence at different ages. However, attempts to discover whether genetic causes contribute to differences in cognitive ageing have been relatively uninformative. Here we provide an estimate of the genetic and environmental contributions to stability and change in intelligence across most of the human lifetime. We used genome-wide single nucleotide polymorphism (SNP) data from 1,940 unrelated individuals whose intelligence was measured in childhood (age 11 years) and again in old age (age 65, 70 or 79 years). We use a statistical method that allows genetic (co)variance to be estimated from SNP data on unrelated individuals. We estimate that causal genetic variants in linkage disequilibrium with common SNPs account for 0.24 of the variation in cognitive ability change from childhood to old age. Using bivariate analysis, we estimate a genetic correlation between intelligence at age 11 years and in old age of 0.62. These estimates, derived from rarely available data on lifetime cognitive measures, warrant the search for genetic causes of cognitive stability and change.  相似文献   
128.
129.
以一个基于面向对象的企业集成模型为研究背景,针对企业物料管理的实际,运用面向对象的系统设计方法和面向对象的程度设计语言C ̄(++)和ROCK,在计算机上实现了相应的物料采购系统。  相似文献   
130.
R Acharya  E Fry  D Stuart  G Fox  D Rowlands  F Brown 《Nature》1989,337(6209):709-716
The structure of foot-and-mouth disease virus has been determined at close to atomic resolution by X-ray diffraction without experimental phase information. The virus shows similarities with other picornaviruses but also several unique features. The canyon or pit found in other picornaviruses is absent; this has important implications for cell attachment. The most immunogenic portion of the capsid, which acts as a potent peptide vaccine, forms a disordered protrusion on the virus surface.  相似文献   
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