排序方式: 共有66条查询结果,搜索用时 15 毫秒
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Terahertz semiconductor-heterostructure laser 总被引:18,自引:0,他引:18
Köhler R Tredicucci A Beltram F Beere HE Linfield EH Davies AG Ritchie DA Iotti RC Rossi F 《Nature》2002,417(6885):156-159
Semiconductor devices have become indispensable for generating electromagnetic radiation in everyday applications. Visible and infrared diode lasers are at the core of information technology, and at the other end of the spectrum, microwave and radio-frequency emitters enable wireless communications. But the terahertz region (1-10 THz; 1 THz = 10(12) Hz) between these ranges has remained largely underdeveloped, despite the identification of various possible applications--for example, chemical detection, astronomy and medical imaging. Progress in this area has been hampered by the lack of compact, low-consumption, solid-state terahertz sources. Here we report a monolithic terahertz injection laser that is based on interminiband transitions in the conduction band of a semiconductor (GaAs/AlGaAs) heterostructure. The prototype demonstrated emits a single mode at 4.4 THz, and already shows high output powers of more than 2 mW with low threshold current densities of about a few hundred A cm(-2) up to 50 K. These results are very promising for extending the present laser concept to continuous-wave and high-temperature operation, which would lead to implementation in practical photonic systems. 相似文献
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Non-redundant role of the long pentraxin PTX3 in anti-fungal innate immune response 总被引:15,自引:0,他引:15
Garlanda C Hirsch E Bozza S Salustri A De Acetis M Nota R Maccagno A Riva F Bottazzi B Peri G Doni A Vago L Botto M De Santis R Carminati P Siracusa G Altruda F Vecchi A Romani L Mantovani A 《Nature》2002,420(6912):182-186
Pentraxins are a superfamily of conserved proteins that are characterized by a cyclic multimeric structure. The classical short pentraxins, C-reactive protein (CRP) and serum amyloid P component (SAP), are acute-phase proteins produced in the liver in response to inflammatory mediators. Short pentraxins regulate innate resistance to microbes and the scavenging of cellular debris and extracellular matrix components. In contrast, long pentraxins have an unrelated, long amino-terminal domain coupled to the carboxy-terminal pentraxin domain, and differ, with respect to short pentraxins, in their gene organization, chromosomal localization, cellular source, and in their stimuli-inducing and ligand-recognition ability. To investigate the in vivo function of the long pentraxin PTX3, we generated mice deficient in Ptx3 by homologous recombination. Ptx3-null mice were susceptible to invasive pulmonary aspergillosis. Ptx3 binds selected microbial agents, including conidia of Aspergillus fumigatus, and we found that susceptibility of Ptx3-null mice was associated with defective recognition of conidia by alveolar macrophages and dendritic cells, as well as inappropriate induction of an adaptive type 2 response. Thus, the long pentraxin Ptx3 is a secreted pattern-recognition receptor that has a non-redundant role in resistance to selected microbial agents, in particular to the opportunistic fungal pathogen Aspergillus fumigatus. 相似文献
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Payne BA Wilson IJ Hateley CA Horvath R Santibanez-Koref M Samuels DC Price DA Chinnery PF 《Nature genetics》2011,43(8):806-810
There is emerging evidence that people with successfully treated HIV infection age prematurely, leading to progressive multi-organ disease, but the reasons for this are not known. Here we show that patients treated with commonly used nucleoside analog anti-retroviral drugs progressively accumulate somatic mitochondrial DNA (mtDNA) mutations, mirroring those seen much later in life caused by normal aging. Ultra-deep re-sequencing by synthesis, combined with single-cell analyses, suggests that the increase in somatic mutation is not caused by increased mutagenesis but might instead be caused by accelerated mtDNA turnover. This leads to the clonal expansion of preexisting age-related somatic mtDNA mutations and a biochemical defect that can affect up to 10% of cells. These observations add weight to the role of somatic mtDNA mutations in the aging process and raise the specter of progressive iatrogenic mitochondrial genetic disease emerging over the next decade. 相似文献
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Prüfer K Munch K Hellmann I Akagi K Miller JR Walenz B Koren S Sutton G Kodira C Winer R Knight JR Mullikin JC Meader SJ Ponting CP Lunter G Higashino S Hobolth A Dutheil J Karakoç E Alkan C Sajjadian S Catacchio CR Ventura M Marques-Bonet T Eichler EE André C Atencia R Mugisha L Junhold J Patterson N Siebauer M Good JM Fischer A Ptak SE Lachmann M Symer DE Mailund T Schierup MH Andrés AM Kelso J Pääbo S 《Nature》2012,486(7404):527-531
Two African apes are the closest living relatives of humans: the chimpanzee (Pan troglodytes) and the bonobo (Pan paniscus). Although they are similar in many respects, bonobos and chimpanzees differ strikingly in key social and sexual behaviours, and for some of these traits they show more similarity with humans than with each other. Here we report the sequencing and assembly of the bonobo genome to study its evolutionary relationship with the chimpanzee and human genomes. We find that more than three per cent of the human genome is more closely related to either the bonobo or the chimpanzee genome than these are to each other. These regions allow various aspects of the ancestry of the two ape species to be reconstructed. In addition, many of the regions that overlap genes may eventually help us understand the genetic basis of phenotypes that humans share with one of the two apes to the exclusion of the other. 相似文献