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71.
The phylogenetic history of immunodeficiency viruses 总被引:19,自引:0,他引:19
Knowledge of the phylogenetic history of the human immunodeficiency viruses (HIV-1 and HIV-2) is important for our understanding of the epidemiology of AIDS, the disease caused by these viruses. Reconstruction of the evolutionary tree is hampered, however, by two problems. One is the high variation in nucleotide sequence between the known HIV isolates which can create formidable difficulties in identifying homologous genomic sites that may be used in a molecular phylogenetic reconstruction. Another impediment has been the lack of unequivocal time calibration points: there is only a sparse 'fossil record' for HIV and limited historical epidemiological data. We have largely overcome these difficulties by: (1) a thorough optimal-sequence alignment analysis; (2) the inclusion of sequences of an early (1976) HIV-1 isolate, a recent (1986) HIV-2 isolate and two simian immunodeficiency viruses (SIV) along with five other HIV-1 isolates; and (3) the reconstruction of a minimum-length evolutionary tree based on the envelope-gene variable positions. We conclude that HIV-1 may have evolved from its common ancestor with HIV-2 as recently as 40 years ago. 相似文献
72.
对Vincent D. Blondel等提出的B算法的特点及机理进行了分析, 讨论了节点属性对社群结构探测的可能影响. 进而通过重构初始化网络, 控制节点(社群)合并过程两个方面, 对B算法进行了改进, 获得更优的模块性指标及对应的社群划分. 经计算机模拟网络与实际网络的社群结构探测, 结果表明所提改进算法有效可用, 能在获得较大模块性指标的同时, 获得较好的社群划分结果, 且拥有更低的运算时间. 相似文献
73.
Novel microbial communities of the Haakon Mosby mud volcano and their role as a methane sink 总被引:5,自引:0,他引:5
Niemann H Lösekann T de Beer D Elvert M Nadalig T Knittel K Amann R Sauter EJ Schlüter M Klages M Foucher JP Boetius A 《Nature》2006,443(7113):854-858
Mud volcanism is an important natural source of the greenhouse gas methane to the hydrosphere and atmosphere. Recent investigations show that the number of active submarine mud volcanoes might be much higher than anticipated (for example, see refs 3-5), and that gas emitted from deep-sea seeps might reach the upper mixed ocean. Unfortunately, global methane emission from active submarine mud volcanoes cannot be quantified because their number and gas release are unknown. It is also unclear how efficiently methane-oxidizing microorganisms remove methane. Here we investigate the methane-emitting Haakon Mosby Mud Volcano (HMMV, Barents Sea, 72 degrees N, 14 degrees 44' E; 1,250 m water depth) to provide quantitative estimates of the in situ composition, distribution and activity of methanotrophs in relation to gas emission. The HMMV hosts three key communities: aerobic methanotrophic bacteria (Methylococcales), anaerobic methanotrophic archaea (ANME-2) thriving below siboglinid tubeworms, and a previously undescribed clade of archaea (ANME-3) associated with bacterial mats. We found that the upward flow of sulphate- and oxygen-free mud volcano fluids restricts the availability of these electron acceptors for methane oxidation, and hence the habitat range of methanotrophs. This mechanism limits the capacity of the microbial methane filter at active marine mud volcanoes to <40% of the total flux. 相似文献
74.
A selective jumonji H3K27 demethylase inhibitor modulates the proinflammatory macrophage response 总被引:1,自引:0,他引:1
L Kruidenier CW Chung Z Cheng J Liddle K Che G Joberty M Bantscheff C Bountra A Bridges H Diallo D Eberhard S Hutchinson E Jones R Katso M Leveridge PK Mander J Mosley C Ramirez-Molina P Rowland CJ Schofield RJ Sheppard JE Smith C Swales R Tanner P Thomas A Tumber G Drewes U Oppermann DJ Patel K Lee DM Wilson 《Nature》2012,488(7411):404-408
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Halik M Klauk H Zschieschang U Schmid G Dehm C Schütz M Maisch S Effenberger F Brunnbauer M Stellacci F 《Nature》2004,431(7011):963-966
Organic thin film transistors (TFTs) are of interest for a variety of large-area electronic applications, such as displays, sensors and electronic barcodes. One of the key problems with existing organic TFTs is their large operating voltage, which often exceeds 20 V. This is due to poor capacitive coupling through relatively thick gate dielectric layers: these dielectrics are usually either inorganic oxides or nitrides, or insulating polymers, and are often thicker than 100 nm to minimize gate leakage currents. Here we demonstrate a manufacturing process for TFTs with a 2.5-nm-thick molecular self-assembled monolayer (SAM) gate dielectric and a high-mobility organic semiconductor (pentacene). These TFTs operate with supply voltages of less than 2 V, yet have gate currents that are lower than those of advanced silicon field-effect transistors with SiO2 dielectrics. These results should therefore increase the prospects of using organic TFTs in low-power applications (such as portable devices). Moreover, molecular SAMs may even be of interest for advanced silicon transistors where the continued reduction in dielectric thickness leads to ever greater gate leakage and power dissipation. 相似文献
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The contribution of product and industry knowledge to the accuracy of sales forecasting was investigated by examining the company forecasts of a leading manufacturer and marketer of consumable products. The company forecasts of 18 products produced by a meeting of marketing, sales, and production personnel were compared with those generated by the same company personnel when denied specific product knowledge and with the forecasts of selected judgemental and statistical time series methods. Results indicated that product knowledge contributed significantly to forecast accuracy and that the forecast accuracy of company personnel who possessed industry forecasting knowledge (but not product knowledge) was not significantly different from the time series based methods. Furthermore, the company forecasts were more accurate than averages of the judgemental and statistical time series forecasts. These results point to the importance of specific product information to forecast accuracy and accordingly call into question the continuing strong emphasis on improving extrapolation techniques without consideration of the inclusion of non-time series knowledge. 相似文献