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1.
The problem of time's arrow historico-critically reexamined 总被引:1,自引:1,他引:0
Roberto Torretti 《Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics》2007,38(4):732-756
Responding to Hasok Chang's vision of the history and philosophy of science (HPS) as the continuation of science by other means, I illustrate the methods of HPS and their utility through a historico-critical examination of the problem of “time's arrow”, that is to say, the problem posed by the claim by Boltzmann and others that the temporal asymmetry of many physical processes and indeed the very possibility of identifying each of the two directions we distinguish in time must have a ground in the laws of nature. I claim that this problem has proved intractable chiefly because the standard mathematical representation of time employed in the formulation of the laws of nature “forgets” one of the connotations of the word ‘time’ as it is used in ordinary language and in experimental physics. 相似文献
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Parton LE Ye CP Coppari R Enriori PJ Choi B Zhang CY Xu C Vianna CR Balthasar N Lee CE Elmquist JK Cowley MA Lowell BB 《Nature》2007,449(7159):228-232
A subset of neurons in the brain, known as 'glucose-excited' neurons, depolarize and increase their firing rate in response to increases in extracellular glucose. Similar to insulin secretion by pancreatic beta-cells, glucose excitation of neurons is driven by ATP-mediated closure of ATP-sensitive potassium (K(ATP)) channels. Although beta-cell-like glucose sensing in neurons is well established, its physiological relevance and contribution to disease states such as type 2 diabetes remain unknown. To address these issues, we disrupted glucose sensing in glucose-excited pro-opiomelanocortin (POMC) neurons via transgenic expression of a mutant Kir6.2 subunit (encoded by the Kcnj11 gene) that prevents ATP-mediated closure of K(ATP) channels. Here we show that this genetic manipulation impaired the whole-body response to a systemic glucose load, demonstrating a role for glucose sensing by POMC neurons in the overall physiological control of blood glucose. We also found that glucose sensing by POMC neurons became defective in obese mice on a high-fat diet, suggesting that loss of glucose sensing by neurons has a role in the development of type 2 diabetes. The mechanism for obesity-induced loss of glucose sensing in POMC neurons involves uncoupling protein 2 (UCP2), a mitochondrial protein that impairs glucose-stimulated ATP production. UCP2 negatively regulates glucose sensing in POMC neurons. We found that genetic deletion of Ucp2 prevents obesity-induced loss of glucose sensing, and that acute pharmacological inhibition of UCP2 reverses loss of glucose sensing. We conclude that obesity-induced, UCP2-mediated loss of glucose sensing in glucose-excited neurons might have a pathogenic role in the development of type 2 diabetes. 相似文献
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Gianluca L. Perrucci Erica Rurali Aoife Gowran Alessandro Pini Carlo Antona Roberto Chiesa Giulio Pompilio Patrizia Nigro 《Cellular and molecular life sciences : CMLS》2017,74(2):267-277
Marfan syndrome (MFS) is a connective tissue disorder with multiple organ manifestations. The genetic cause of this syndrome is the mutation of the FBN1 gene, encoding the extracellular matrix (ECM) protein fibrillin-1. This genetic alteration leads to the degeneration of microfibril structures and ECM integrity in the tunica media of the aorta. Indeed, thoracic aortic aneurysm and dissection represent the leading cause of death in MFS patients. To date, the most effective treatment option for this pathology is the surgical substitution of the damaged aorta. To highlight novel therapeutic targets, we review the molecular mechanisms related to MFS etiology in vascular smooth muscle cells, the foremost cellular type involved in MFS pathogenesis. 相似文献
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Water has many kinetic and thermodynamic properties that exhibit an anomalous dependence on temperature, in particular in the supercooled phase. These anomalies have long been interpreted in terms of underlying structural causes, and their experimental characterization points to the existence of a singularity at a temperature of about 225 K. Further insights into the nature and origin of this singularity might be gained by completely characterizing the structural relaxation in supercooled water. But until now, such a characterization has only been realized in simulations that agree with the predictions of simple mode-coupling theory; unambiguous experimental support for this surprising conclusion is, however, not yet available. Here we report time-resolved optical Kerr effect measurements that unambiguously demonstrate that the structural relaxation of liquid and weakly supercooled water follows the behaviour predicted by simple mode-coupling theory. Our findings thus support the interpretation of the singularity as a purely dynamical transition. That is, the anomalous behaviour of weakly supercooled water can be explained using a fully dynamic model and without needing to invoke a thermodynamic origin. In this regard, water behaves like many other, normal molecular liquids that are fragile glass-formers. 相似文献
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The delayed release of the National Account data for GDP is an impediment to the early understanding of the economic situation. In the short run, this information gap may be at least partially eliminated by bridge models (BM) which exploit the information content of timely updated monthly indicators. In this paper we examine the forecasting ability of BM for GDP growth in the G7 countries and compare their performance to that of univariate and multivariate statistical benchmark models. We run four alternative one‐quarter‐ahead forecasting experiments to assess BM performance in situations as close as possible to the actual forecasting activity. BM are estimated for GDP both for single countries (USA, Japan, Germany, France, UK, Italy and Canada), and area‐wide (G7, European Union, and Euro area). BM forecasting ability is always superior to that of benchmark models, provided that at least some monthly indicator data are available over the forecasting horizon. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
6.
Robeao Pompoli Andrea Farnetani Nicola Prodi 《华南理工大学学报(自然科学版)》2007,35(B10):5-10
论述了古希腊与古罗马的剧场音质.该研究是由欧共体资助的ERATO项目“古代剧场和表演场所声学遗产的鉴定、评价与振兴”的一部分.该项目对古希腊与古罗马剧场进行了较详尽的调研.文中通过对若干保存得最好的古罗马剧场,如土耳其阿斯彭多斯剧场以及约旦杰拉斯南方剧场测量的脉冲响应进行深入的分析,探讨了其典型构造.同时对西塔库萨剧场建立了1:20的模型,进行了专门的声学测量. 相似文献
7.
Genome sequence and analysis of the tuber crop potato 总被引:11,自引:0,他引:11
Potato Genome Sequencing Consortium Xu X Pan S Cheng S Zhang B Mu D Ni P Zhang G Yang S Li R Wang J Orjeda G Guzman F Torres M Lozano R Ponce O Martinez D De la Cruz G Chakrabarti SK Patil VU Skryabin KG Kuznetsov BB Ravin NV Kolganova TV Beletsky AV Mardanov AV Di Genova A Bolser DM Martin DM Li G Yang Y Kuang H Hu Q Xiong X Bishop GJ Sagredo B Mejía N Zagorski W Gromadka R Gawor J Szczesny P Huang S Zhang Z Liang C He J Li Y He Y Xu J Zhang Y Xie B Du Y Qu D Bonierbale M Ghislain M 《Nature》2011,475(7355):189-195
Potato (Solanum tuberosum L.) is the world's most important non-grain food crop and is central to global food security. It is clonally propagated, highly heterozygous, autotetraploid, and suffers acute inbreeding depression. Here we use a homozygous doubled-monoploid potato clone to sequence and assemble 86% of the 844-megabase genome. We predict 39,031 protein-coding genes and present evidence for at least two genome duplication events indicative of a palaeopolyploid origin. As the first genome sequence of an asterid, the potato genome reveals 2,642 genes specific to this large angiosperm clade. We also sequenced a heterozygous diploid clone and show that gene presence/absence variants and other potentially deleterious mutations occur frequently and are a likely cause of inbreeding depression. Gene family expansion, tissue-specific expression and recruitment of genes to new pathways contributed to the evolution of tuber development. The potato genome sequence provides a platform for genetic improvement of this vital crop. 相似文献
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Haploinsufficiency of ATP1A2 encoding the Na+/K+ pump alpha2 subunit associated with familial hemiplegic migraine type 2 总被引:22,自引:0,他引:22
De Fusco M Marconi R Silvestri L Atorino L Rampoldi L Morgante L Ballabio A Aridon P Casari G 《Nature genetics》2003,33(2):192-196
Headache attacks and autonomic dysfunctions characterize migraine, a very common, disabling disorder with a prevalence of 12% in the general population of Western countries. About 20% of individuals affected with migraine experience aura, a visual or sensory-motor neurological dysfunction that usually precedes or accompanies the headache. Although the mode of transmission is controversial, population-based and twin studies have implicated genetic factors, especially in migraine with aura. Familial hemiplegic migraine is a hereditary form of migraine characterized by aura and some hemiparesis. Here we show that mutations in the gene ATP1A2 that encodes the alpha2 subunit of the Na+/K+ pump are associated with familial hemiplegic migraine type 2 (FHM2) linked to chromosome 1q23 (OMIM 602481). Functional data indicate that the putative pathogenetic mechanism is triggered by a loss of function of a single allele of ATP1A2. This is the first report associating mutations of Na+K+ pump subunits to genetic diseases. 相似文献