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突发模式误码测试仪与一般连续误码测试仪不同,其接收端在误码比对前要实现在十几位内,对具有相位跳变特点的信号进行时钟提取和数据恢复,并且在误码比对时须滤除前导码和定界符,仅对有效数据进行误码统计。本文提出一种基于FPGA实现的高速突发模式误码测试仪设计方案,并介绍该方案的总体设计过程,以及FPGA中主要功能逻辑模块的工作原理和控制系统的设计。该测试仪应用于1.25GHz GPON系统突发式光接收模块的误码测试中,具有较好的性能和实际意义。 相似文献
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Family of G protein {alpha} chains: amphipathic analysis and predicted structure of functional domains 总被引:7,自引:0,他引:7
Masters Susan B.; Stroud Robert M.; Bourne Henry R. 《Protein engineering, design & selection : PEDS》1986,1(1):47-54
The G proteins transduce hormonal and other signals into regulationof enzymes such as adenylyl cyclase and retinal cGMP phosphodiesterase.Each G protein contains an subunit that binds and hydrolyzesguanine nucleotides and interacts with ß subunitsand specific receptor and effector proteins. Amphipathic andsecondary structure analysis of the primary sequences of fivedifferent chains (bovine s, t1 and t2, mouse i, and rat o)predicted the secondary structure of a composite chain (avg).The chains contain four short regions of sequence homologousto regions in the GDP binding domain of bacterial elongationfactor Tu (EF-Tu). Similarities between the predicted secondarystructures of these regions in avg and the known secondary structureof EF-Tu allowed us to construct a three-dimensional model ofthe GDP binding domain of avg. Identification of the GDP bindingdomain of avg defined three additional domains in the compositepolypeptide. The first includes the amino terminal 41 residuesof avg, with a predicted am phipathic helical structure; thisdomain may control binding of the chains to the ßcomplex. The second domain, containing predicted ßstrands and helices, several of which are strongly amphipathic,probably contains sequences responsible for interaction of chains with effector enzymes. The predicted structure of thethird domain, containing the carhoxy terminal 100 amino acids,is predominantly ß sheet with an amphipathic helixat the carboxy terminus. We propose that this domain is reponsiblefor receptor binding. Our model should help direct further experimentsinto the structure and function of the G protein chain. 相似文献
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There are various difficulties involved with comparing the effects of short-lived and long-lived atmospheric species on climate. Global warming potentials (GWPs) can be computed for pulse emissions of short-lived species. However, if the focus is on the long-term effect of a pulse emission occurring today, GWPs do not factor in the fact that if a radiative forcing is applied for a short period, the climate system has time to relax back to equilibrium. The concept of global temperature change potential (GTP) at a time horizon for an emission pulse has been proposed to circumvent this problem. Here we show how GTPs can be used to compare black carbon (BC) and CO2 emissions and the methodology is illustrated with two concrete examples. In particular we discuss a trade-off situation where a decrease in BC emissions is associated with a fuel penalty and therefore an additional CO2 emission. A parameter—which depends on the BC radiative effects, the BC emission reduction and the additional CO2 emission—is defined and can be compared to a critical parameter to assess whether or not the BC emission reduction wins over the fuel penalty for various time horizons. We show how this concept can be generalised to compare the climate effects of carbon dioxide against a set of short-lived species and to account for differences in climate efficacy. Finally, the need for additional research is discussed in the light of current uncertainties. 相似文献
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