一种新型多工作模式的Wilkinson功分器设计

设计了一种新型的具有多工作模式的Wilkinson功分器电路,该电路通过将传统的Wilkinson功分器与有限数量的单刀单掷开关进行合理的组合,并通过控制这些射频开关,进而使得该电路具有Wilkinson和两个微带直通的工作模式。同时,对具有任意功分比的多工作模式的Wilkinson功分器进行了理论分析,并使用是德公司的ADS仿真工具验证了微带线的各个电长度对微带直通模式下的性能(如插损、回波损耗)的影响。验证了在等分情况下的多工作模式的Wilkinson功分器在各种工作模式下的性能。     

基于导纳矩阵的任意端口阻抗等分功分器设计

为减小非50Ω功分器电路尺寸,研究了任意端口阻抗等分功分器。理论证明了若等分功分器的输出端口之间只使用电阻连接,不能同时实现任意端口阻抗匹配和输出端口隔离。提出了一种新的任意端口阻抗等分功分器结构。在隔离电阻两端串联不同的微带线,在各端口加载短路/开路短截线。利用此结构同时实现了各端口匹配与输出端口之间的互相隔离。基于导纳矩阵推导了该功分器的设计公式,并据此设计研制了中心频率为1 GHz,端口阻抗分别为30Ω、53Ω、47Ω的等分功分器。该文方法设计的功分器电路尺寸比传统设计方法减小了约66%。测试结果验证了该等分功分器结构简单有效。     

基于SS-CML的双频Wilkinson功分器研究

为了设计出结构紧凑且制作加工灵活方便的双频功分器结构,该文提出了一种基于短路短截线加载耦合微带线(Shorted stub loaded coupled microstrip lines,SS-CML)单元的新型双频Wilkinson功分器。在运用奇偶模分析法对SS-CML单元的等效相位及等效特性阻抗分析的基础上,推导出采用该单元设计双频Wilkinson功分器的解析公式,讨论了该功分器工作频率比的适用范围。最后设计加工并测试了一个工作于1.43 GHz和2.57 GHz的双频Wilkinson功分器,测试与仿真结果吻合良好。该功分器可适用于工作频率比较小的情况。     

Ku波段Wilkinson功分器仿真与设计

针对现有功分器设计方法存在的一些不足,提出一个Ku波段的一分四功分器的设计要求。结合ADS软件的速度快与HFSS的准确2个优点,协同使用2个仿真软件进行仿真,通过参数优化在短周期内设计一个Ku波段的一分四的Wilkinson微带线功分器。设计版图和腔体图并进行加工组装,通过调试测量该功分器最终达到设计目标:工作带宽为16~18 GHz,在工作带内驻波小于1.3,传输损耗小于7.1 dB,4个端口的隔离度大于17.5 dB。测试结果验证了该功分器设计方法的可行性。     

新型双频Wilkinson微带功分器研究

为了使Wilkinson功分器能够在两个任意的频率点上对纯电阻负载实现理想的阻抗匹配,该文利用双节传输线的双频阻抗变换特性,并在输出端口并联开路微带线,设计了一种具有高隔离度的双频Wilkinson微带功分器.基于奇-偶模分析方法获得双频功分器解析设计公式,然后研制了一个工作频率为2.0 GHz和4.2 GHz的双频Wilkinson微带功分器.测试结果表明:其在两个中心工作频率的传榆衰减分别为3.5 dB和3.8 dB;各个端口的回波损耗和隔离度在频率1.9～2.1 GHz和4.1～4.3 GHz的范围内均优于15 dB.     

基于AWR仿真软件的功分器设计与仿真

给出了一种基于带状线设计一分为二等功率功分器的方法,讨论了功分器的基本原理和设计步骤,并利用AWR软件设计了一种2～6G带状功分器,对相关S参数进行分析和优化,得出可供工程应用的设计模型,最后对设计样品进行检测,获得较好的结果,为分析设计功分器提供了参考.     

S波段3dB微带功分器的设计

介绍一款S波段3dB微带功分器的设计方法和过程,仿真结果表明了应用ADS进行设计有效性和可行性。     

一种新颖的带状线功分器等效电路分析方法

带状线功分器结构中包含直角拐角和T型接头不连续性部分,会引入相应的不连续性传输损耗,传统的分析方法并没有考虑这部分损耗,导致分析结果不够准确.针对这个问题,提出了一种新颖的带状线功分器等效电路分析方法.在已获得的微带开路线不连续性等效电路模型及理论的基础上,提出了带状线功分器参考面T′区域的等效电路模型,并推导出了带状线功分器散射参数的计算公式.经实例验证发现,该等效电路分析法所得结果与仿真软件HFSS仿真结果吻合良好,带状线功分器散射参数的平均误差小于2%,这充分表明了该等效电路模型的正确性和有效性.     

一分六功分器的设计与实现

设计制作了一个ku频段一分六功分器,进行理论模型计算后,利用仿真软件进行优化,加工电路板和金属壳体,使用改进的安装工艺,最终得到实物,测试其性能,验证了整个设计与实现过程的可行性。     

分配路数和分配比均可重构功分器设计

为了改善功率分配比可重构功分器结构复杂、分配比例离散且所能应用范围受限等问题，基于可调反射移相器的特性参数分析，提出了一种新型的可重构功率分配器，只需要通过改变反射系数即可实现该功分器的分配路数和功率分配比例可调谐。设计分析了基于π型变换网络的可调反射移相器，通过改变调谐变容二极管两边的外置偏置电压进而实现反射系数可调，设计了一款分配路数和分配比多功能可重构功分器。与传统功分器相比，实现了功分器的多功能、功分比大范围内调谐和调谐方便等特点。通过先进设计系统（advanced design system，ADS）版图设计和实物加工测试，所设计的可重构功分器实现了1-5路分配路数可调，同时每一路功率分配比等功率输出（1 ∶1）和分配比在17.1~-33.1 dB和-16.7~33.3 dB可调输出，且实物结果与仿真结果基本吻合。     

高温注氢对钒合金微观结构的影响

研究了500℃高温条件下注氢对V-4Cr、V-4Ti和V-4Cr-4Ti三种合金微观结构的影响。在注氢实验之前,V-4Cr合金的基体清晰干净,而V-4Ti和V-4Cr-4Ti两种合金的基体中则出现很多相互平行和垂直的针状析出相,且大部分析出相周围都存在着位错。在500℃注氢实验之后,V-4Cr合金基体中出现大量的分布不均的黑色点状缺陷和缺陷簇,而V-4Ti和V-4Cr-4Ti两种合金的基体中除产生点状缺陷外,还出现高密度的气泡,且V-4Cr-4Ti合金中气泡的平均尺寸要稍小一些。另外,V-4Ti和V-4Cr-4Ti合金基体中原有的析出相在注氢实验之后都发生不同程度的溶解。在观察V-4Cr-4Ti合金基体中气泡分布规律时发现,在距离晶界25 nm的范围内几乎看不到气泡的存在,由此推断晶界的存在可以抑制氢气泡等辐照缺陷的产生。     

Functional cloning of TUG as a regulator of GLUT4 glucose transporter trafficking

Insulin stimulates glucose uptake in fat and muscle by mobilizing the GLUT4 glucose transporter. GLUT4 is sequestered intracellularly in the absence of insulin, and is redistributed to the plasma membrane within minutes of insulin stimulation. But the trafficking mechanisms that control GLUT4 sequestration have remained elusive. Here we describe a functional screen to identify proteins that modulate GLUT4 distribution, and identify TUG as a putative tether, containing a UBX domain, for GLUT4. In truncated form, TUG acts in a dominant-negative manner to inhibit insulin-stimulated GLUT4 redistribution in Chinese hamster ovary cells and 3T3-L1 adipocytes. Full-length TUG forms a complex specifically with GLUT4; in 3T3-L1 adipocytes, this complex is present in unstimulated cells and is largely disassembled by insulin. Endogenous TUG is localized with the insulin-mobilizable pool of GLUT4 in unstimulated 3T3-L1 adipocytes, and is not mobilized to the plasma membrane by insulin. Distinct regions of TUG are required to bind GLUT4 and to retain GLUT4 intracellularly in transfected, non-adipose cells. Our data suggest that TUG traps endocytosed GLUT4 and tethers it intracellularly, and that insulin mobilizes this pool of retained GLUT4 by releasing this tether.     

Loss of p16Ink4a with retention of p19Arf predisposes mice to tumorigenesis.

The cyclin-dependent kinase inhibitor p16INK4a can induce senescence of human cells, and its loss by deletion, mutation or epigenetic silencing is among the most frequently observed molecular lesions in human cancer. Overlapping reading frames in the INK4A/ARF gene encode p16INK4a and a distinct tumour-suppressor protein, p19ARF (ref. 3). Here we describe the generation and characterization of a p16Ink4a-specific knockout mouse that retains normal p19Arf function. Mice lacking p16Ink4a were born with the expected mendelian distribution and exhibited normal development except for thymic hyperplasia. T cells deficient in p16Ink4a exhibited enhanced mitogenic responsiveness, consistent with the established role of p16Ink4a in constraining cellular proliferation. In contrast to mouse embryo fibroblasts (MEFs) deficient in p19Arf (ref. 4), p16Ink4a-null MEFs possessed normal growth characteristics and remained susceptible to Ras-induced senescence. Compared with wild-type MEFs, p16Ink4a-null MEFs exhibited an increased rate of immortalization, although this rate was less than that observed previously for cells null for Ink4a/Arf, p19Arf or p53 (refs 4, 5). Furthermore, p16Ink4a deficiency was associated with an increased incidence of spontaneous and carcinogen-induced cancers. These data establish that p16Ink4a, along with p19Arf, functions as a tumour suppressor in mice.     

固氮酶反应中铁蛋白与MgATP配位的化学模拟

以[Fe_4S_4(SCH_2Ph)_4]~(-2)作为氧化态铁蛋白4Fe-4S中心的模型化合物,化学模拟研究表明,ATP能与[Fe_4S_4(SCH_2Ph)_4]~(-2)原子簇结合,促进原子簇与亚甲蓝之间的氧化还原反应速率,并敏化原子簇中的Fe(Ⅱ),使其易与亚铁螯合剂反应,用正庚烧作萃取刑,在原子簇-ATP体系没有检测到游离的HSCH_2Ph,ATP没有置换原子簇中的—SCH_2Ph,这表明作为电子活化剂的ATP可能通过其磷酸根与Fe_4S_4原子簇结合。     

On the Structure of Cyclic Codes over F_q+uF_q+vF_q+uvF_q

In this paper,cyclic codes over the ring R=F4+uF4+vF4+uvF4 are discussed where the ring R is not a finite chain ring.By studying the polynomial ring Rn=(F4+uF4+vF4+uvF4) and using the corresponding relationship between the cyclic codes in R and the ideals in,cyclic codes over the ring R are characterized.Finally,a Gray-map is obtained and the image of cyclic codes in R is characterized.     

C2H4与TiCl4络合体系的CNDO／2计算

采用ＣＮＤＯ／２法计算乙烯在Ｚｉｅｇｌｅｒ－Ｎａｔｔａ催化剂主体（ＴｉＣｌ４）上的络合反应机理．计算结果为：乙烯和四氯化钛单体处于优化构型时的能量分别为－１７．０７３２ａ．ｕ．和－６８．８５４０ａ．ｕ．，乙烯Ｃ＝Ｃ双键的Ｍｕｌｉｋｅｎ键级为１．１７３；络合体系处于优化构型时的能量为－８６．０１４６ａ．ｕ．，与吸附前单体乙烯和四氯化钛的能值相比，乙烯在四氯化钛上的吸附热为－２２９．３ｋＪ／ｍｏｌ，乙烯Ｃ＝Ｃ双键的Ｍｕｌ－ｌｉｋｅｎ键级为１．０９５，与络合前相比受到了削弱．通过计算所得的分子轨道能级、轨道特征以及Ｍｕｌｉｋｅｎ约化重叠集居等数据，分析了催化剂的催化机理。     

Quadruplex structure of Oxytricha telomeric DNA oligonucleotides.

The telomeres of most eukaryotes contain a repeating G-rich sequence with the consensus d(T/A)1-4G1-8, of which 12-16 bases form a 3' single-strand overhang beyond the telomeric duplex. It has been proposed that these G-rich oligonucleotides associate to form four-stranded structures from one, two or four individual strands and that these structures may be relevant in vivo. The proposed structures contain Hoogsteen base-paired G-quartets, precedent for which has been in the literature for many years. Here we use 1H NMR spectroscopy to study the conformations of the DNA oligonucleotides d(G4T4G4) (Oxy-1.5) and d(G4T4G4T4G4T4G4) (Oxy-3.5) which contain the Oxytricha telomere repeat (T4G4). We find that these molecules fold to form a symmetrical bimolecular and an intramolecular quadruplex, respectively. Both structures have four G-quartets formed from nucleotides that are alternately syn and anti along each strand. This arrangement differs from earlier models in which the strands are alternately all syn or all anti. The T4 loops in Oxy-1.5 are on opposite ends of the quadruplex and loop diagonally across the G-quartet, resulting in adjacent strands being alternately parallel and antiparallel.     

Crystal structure of a human membrane protein involved in cysteinyl leukotriene biosynthesis

The cysteinyl leukotrienes, namely leukotriene (LT)C4 and its metabolites LTD4 and LTE4, the components of slow-reacting substance of anaphylaxis, are lipid mediators of smooth muscle constriction and inflammation, particularly implicated in bronchial asthma. LTC4 synthase (LTC4S), the pivotal enzyme for the biosynthesis of LTC4 (ref. 10), is an 18-kDa integral nuclear membrane protein that belongs to a superfamily of membrane-associated proteins in eicosanoid and glutathione metabolism that includes 5-lipoxygenase-activating protein, microsomal glutathione S-transferases (MGSTs), and microsomal prostaglandin E synthase 1 (ref. 13). LTC4S conjugates glutathione to LTA4, the endogenous substrate derived from arachidonic acid through the 5-lipoxygenase pathway. In contrast with MGST2 and MGST3 (refs 15, 16), LTC4S does not conjugate glutathione to xenobiotics. Here we show the atomic structure of human LTC4S in a complex with glutathione at 3.3 A resolution by X-ray crystallography and provide insights into the high substrate specificity for glutathione and LTA4 that distinguishes LTC4S from other MGSTs. The LTC4S monomer has four transmembrane alpha-helices and forms a threefold symmetric trimer as a unit with functional domains across each interface. Glutathione resides in a U-shaped conformation within an interface between adjacent monomers, and this binding is stabilized by a loop structure at the top of the interface. LTA4 would fit into the interface so that Arg 104 of one monomer activates glutathione to provide the thiolate anion that attacks C6 of LTA4 to form a thioether bond, and Arg 31 in the neighbouring monomer donates a proton to form a hydroxyl group at C5, resulting in 5(S)-hydroxy-6(R)-S-glutathionyl-7,9-trans-11,14-cis-eicosatetraenoic acid (LTC4). These findings provide a structural basis for the development of LTC4S inhibitors for a proinflammatory pathway mediated by three cysteinyl leukotriene ligands whose stability and potency are different and by multiple cysteinyl leukotriene receptors whose functions may be non-redundant.     

一种含吡啶环和三氟甲基取代基的芳香二胺的合成与表征

以4-三氟甲基苯甲醛、4'-硝基苯乙酮和醋酸铵为原料,在冰醋酸介质中,通过改进的Chichibabin反应得到了二硝基化合物4-(4-三氟甲基苯基)-2,6-二(4-胺基苯基)吡啶(TMPBNPP),继而用Pd/C和水合肼将TMPBNPP进行还原,成功合成了一种新型含吡啶环和三氟甲基侧基的芳香二胺4-(4-三氟甲基苯基)-2,6-二(4-胺基苯基)吡啶(TMPBAPP),2步反应总收率为48;,并用核磁共振谱、红外光谱和X-射线衍射等手段对其结构进行了分析表征.