Subatomic Features on the Silicon (111)-(7x7) Surface Observed by Atomic Force Microscopy

The atomic force microscope images surfaces by sensing the forces between a sharp tip and a sample. If the tip-sample interaction is dominated by short-range forces due to the formation of covalent bonds, the image of an individual atom should reflect the angular symmetry of the interaction. Here, we report on a distinct substructure in the images of individual adatoms on silicon (111)-(7x7), two crescents with a spherical envelope. The crescents are interpreted as images of two atomic orbitals of the front atom of the tip. Key for the observation of these subatomic features is a force-detection scheme with superior noise performance and enhanced sensitivity to short-range forces.     

A structural framework for deciphering the link between I-Ag7 and autoimmune diabetes

Susceptibility to murine and human insulin-dependent diabetes mellitus correlates strongly with major histocompatibility complex (MHC) class II I-A or HLA-DQ alleles that lack an aspartic acid at position beta57. I-Ag7 lacks this aspartate and is the only class II allele expressed by the nonobese diabetic mouse. The crystal structure of I-Ag7 was determined at 2.6 angstrom resolution as a complex with a high-affinity peptide from the autoantigen glutamic acid decarboxylase (GAD) 65. I-Ag7 has a substantially wider peptide-binding groove around beta57, which accounts for distinct peptide preferences compared with other MHC class II alleles. Loss of Asp(beta57) leads to an oxyanion hole in I-Ag7 that can be filled by peptide carboxyl residues or, perhaps, through interaction with the T cell receptor.     

Atomic resolution imaging of adsorbates on metal surfaces in air: iodine adsorption on pt(111)

The adsorption of iodine on platinum single crystals was studied with the scanning tunneling microscope (STM) to define the limits of resolution that can be obtained while imaging in air and to set a target resolution for STM imaging of metal surfaces immersed in an electrochemical cell. Two iodine adlattice unit cells of slightly different iodine packing density were clearly imaged: ( radical7 x radical7) R19.1 degrees -I, surface coverage ?(I) = 3/7; and (3 x 3)-I, ?(I) = 4/9. The three iodine atoms in the ( radical7 x radical7) unit cell form a regular hexagonal lattice interatomic distance d(I) = 0.424 nanometer, with two atoms adsorbed in threefold hollow sites and one atom adsorbed at an atop site. The (3 x 3) unit cell showed two different packing arrangements of the four iodine atoms exit. In one of the (3 x 3) structures, the iodine atoms pack to form a hexagonal lattice, d(I) = 0.417 nanometer, with three of the iodine atoms at twofold adsorption sites and one atom at an atop site. Another packing arrangement of iodine into the (3 x 3) unit cell was imaged in which the iodine atoms are not arranged symmetrically.     

SL—2—（7）型套管头结构应力分析

应用有限法对ＳＬ－２－（７）型套管头结构进行应力分析,将套不分成密封结构和承载结构２部分进行有限元应力计算,得到结构整体应力分布情况和单个构件的应力分布情况以及最大应力分布位置,从而为ＳＬ－２－（７）型套管头结构提供了可靠的依据。     

Ultrafast mid-infrared response of YBa(2)Cu(3)O(7-delta)

Optical spectra of high-transition-temperature superconductors in the mid-infrared display a gap of in-plane conductivity whose role for superconductivity remains unresolved. Femtosecond measurements of the mid-infrared reflectivity of YBa(2)Cu(3)O(7-delta) after nonequilibrium optical excitation are used to demonstrate the ultrafast fill-in of this gap and reveal two gap constituents: a picosecond recovery of the superconducting condensate in underdoped and optimally doped material and, in underdoped YBa(2)Cu(3)O(7-delta), an additional subpicosecond component related to pseudogap correlations. The temperature-dependent amplitudes of both contributions correlate with the antiferromagnetic 41-millielectronvolt peak in neutron scattering, supporting the coupling between charges and spin excitations.     

Identification of the products from the reaction of chlorine with the silicon(111)-(7x7) surface

The various products from the reaction of chlorine (Cl) with the adatom layer of the Si(111)-(7x7) surface have been identified with scanning tunneling microscopy (STM). Initially, a single Cl atom reacts with the adatom dangling bond. At higher surface coverage, additional Cl atoms insert themselves into the Si-Si backbonds between the adatom and rest-atom layers, producing adatoms that have reacted with two or three Cl atoms. These products are characterized by different registries with respect to the underlying rest layer and appear in STM images as adatoms of different sizes, consistent with the breaking of Si-Si backbonds and the formation ofnew Si-Cl bonds.     

Identification of Molecular Markers Linked to the Wilt Resistance Gene FuJ7(t)in Flax

A cross between wilt resistant flax variety Jinya7 and susceptible variety Jinyal was made for mapping wilt resistance gene(s).The inoculation test of F1 and F2 progeny proved that the resistance of Jinya7 to wilt is controlled by two dominant genes.With 48 EcoRⅠ/MseⅠ primer combinations,amplified fragment length polymorphisms(AFLP)analysis was performed on two parents and their F2 resistance and susceptibility bulks.A total of about 3 300 distinguishable bands were amplified,of which three bands had stable differences.The genetic linkage analysis of the three polymorphic DNA fragments with the resistance gene(s)was made in the F2 segregating population derived from the cross between Jinya7 and Jinyal.The DNA fragment AG/CAG was found closely linked to one of the wilt-resistant genes,which with a genetic distance of 5.2 cm,was tentatively named FuJ7(t).The cloned fragment AG/CAG was sequenced and then converted successfully to a sequence characterized amplified region(SCAR)marker,which can be used more conveniently in the identification and marker-assisted selection for the wilt resistance gene FuJ7(t)to flax wilt.     

Size-Specific Infrared Spectra of Benzene-(H2O)n Clusters (n = 1 through 7): Evidence for Noncyclic (H2O)n Structures

Resonant ion-dip infrared spectroscopy has been used to record size-specific infrared spectra of C(6)H(6)-(H(2)O)n clusters with n = 1 through 7 in the O-H stretch region. The O-H stretch spectra show a dramatic dependence on cluster size. For the n = 3 to 5 clusters, the transitions can be divided into three types-attributable to free, pi hydrogen-bonded, and single donor water-water O-H stretches-consistent with a C(6)H(6)-(H(2)O)n structure in which benzene is on the surface of a cyclic (H(2)O)n cluster. In n = 6 and 7 clusters, the spectra show distinct new transitions in the 3500 to 3600 wave number region. After comparison of these results with the predictions of ab initio calculations on (H(2)O)n clusters, these new transitions have been assigned to double donor O-H stretches associated with the formation of a more compact, noncyclic structure beginning with (H(2)O)(6). This is the same size cluster for which ab initio calculations predict that a changeover to noncyclic (H(2)O)n structures will occur.     

7个绵羊微卫星DNA标记在绵(山)羊群体中的多态性检测

选择分别位于绵羊2,4,6,9,17和19号染色体上的7个微卫星标记OarFCB11,OarFCB128,MAF70,OarAE101,MAF33,OarFCB48和OarFCB304,对湖羊、同羊及长江三角洲白山羊的典型群随机样本相应位点进行了PCR检测。结果表明,每个微卫星座位发现7个以上等位基因,且均存在多态;湖羊、同羊、长江三角洲白山羊群体杂合度(H)分别为0.9092,0.9177和0.8867,相应的群体基因平均多态信息含量(PIC)分别为0.9024,0.9116和0.8774,有效等位基因数(Ne)分别为11.7723,12.4538和11.6104,均以同羊为最高;以产生有效条带为标志,随机样本的PCR扩增效率存在明显的群体间和座位间差异,以长江三角洲白山羊和OarFCB128座位为最高;以7个座位微卫星等位基因频率推算群体间标准遗传距离,山羊与绵羊群体间遗传距离远大于绵羊群体之间,湖羊、同羊间亲缘距离系数R为0.1998。研究结果提示:选择的7个微卫星DNA座位均为多态座位;以7个微卫星标记为测度,湖羊、同羊及长江三角洲白山羊具有丰富的遗传多态性;7个微卫星标记可进一步用于绵山羊近缘种间遗传分析研究。     

亚麻抗枯萎病基因FuJ7(t)的分子标记

 用高抗枯萎病亚麻品种“晋亚 7号”与高感枯萎病品种“晋亚 1号”配制杂交组合 ,接种鉴定其正反交F1代以及F2 代分离群体的枯萎病发生情况 ,结果表明 ,晋亚 7号对枯萎病的抗性属于细胞核遗传 ,受 2个显性基因控制。用 4 8个EcoRI/MseI引物组合对“晋亚 7号”、“晋亚 1号”两个亲本及其F2 代抗病和感病基因池进行AFLP分析 ,共扩增出约 330 0条可分辨的带 ,其中 3条为稳定的差异。用“晋亚 7号”和“晋亚 1号”杂交产生的F2 代分离群体对 3个特异条带与目的基因的遗传连锁性进行分析 ,发现特异条带AG/CAG与暂定名为FuJ7(t)的抗枯萎病基因紧密连锁 ,二者之间的遗传距离为 5 .2cM。将AG/CAG片段回收、克隆和测序 ,成功地将其转化为SCAR标记 ,可以更加方便地用于对FuJ7(t)基因的分子检测和标记辅助选择。     

Quantitative measurement of short-range chemical bonding forces

We report direct force measurements of the formation of a chemical bond. The experiments were performed using a low-temperature atomic force microscope, a silicon tip, and a silicon (111) 7x7 surface. The measured site-dependent attractive short-range force, which attains a maximum value of 2.1 nanonewtons, is in good agreement with first-principles calculations of an incipient covalent bond in an analogous model system. The resolution was sufficient to distinguish differences in the interaction potential between inequivalent adatoms, demonstrating the ability of atomic force microscopy to provide quantitative, atomic-scale information on surface chemical reactivity.     

Energy dependence of abstractive versus dissociative chemisorption of fluorine molecules on the silicon (111)-(7x7) surface

Scanning tunneling microscopy and monoenergetic molecular beams have been used to obtain real-space atomic images of the competition between abstractive and dissociative chemisorption. The size distribution of Si-F adsorbates on the Si(111)-(7x7) surface was examined as a function of the incident translational energy of the F(2) molecules. For F(2) molecules with 0.03 electron volt of incident energy, the dominant adsorbate sites were isolated Si-F species. As an F(2) molecule with low translational energy collides with the surface, abstraction occurs and only one of the F atoms chemisorbs; the other is ejected into the gas phase. For F(2) molecules with 0.27 electron volt of incident energy, many adjacent Si-F adsorbates (dimer sites) were observed because F(2) molecules with high translational energy collide with the surface and chemisorb dissociatively so that both F atoms react to form adjacent Si-F adsorbates. For halogens with very high incident energy (0.5-electron volt Br(2)), dissociative chemisorption is the dominant adsorption mechanism and dimer sites account for nearly all adsorbates.     

超声波辐射合成7-(3-溴丙氧基)异黄酮

以苯乙酸和间苯二酚为起始原料,用三氟化硼乙醚作溶剂和催化剂,在超声波辐射下＂一锅法＂合成了7-羟基异黄酮（2）,产率92.5%,然后将其在DMF/丙酮的混合溶剂中,以碳酸钾为缩合剂,在超声波辐射下与1,3-二溴丙烷反应合成7-（3-溴丙氧基）异黄酮（3）,产率78.6%,其结构通过1HNMR和13CNMR进行确证。该合成方法具有反应条件温和、反应时间短、后处理简便、产率高等优点,具有广泛的应用前景。     

7-(3-芳基)丙烯酰氧基-4-甲基香豆素的合成

合成7-(3-芳基)丙烯酰氧基-4-甲基香豆素类化合物.方法:以酰氯法,经酯化反应,制得7种相应香豆素类化合物.结果:结构经元素分析、红外光谱、紫外光谱确定7种化合物(Ⅲa—Ⅲg)未见文献报道.结论:用酰氯法制备7-(3-芳基)丙烯酰氧基-4-甲基香豆素类化合物是简便易行的.     

利用Bac-to-Bac杆状病毒系统超量表达家蚕let-7簇microRNAs

【目的】利用Bac-to-Bac杆状病毒表达系统超量表达家蚕（Bombyx mori）let-7 簇（cluster）microRNAs：bmo-let-7、bmo-miR-100和bmo-miR-2795,为研究家蚕microRNA的功能提供参考。【方法】克隆家蚕let-7 miRNA簇（bmo-let-7 cluster,bmo-let-7-C）上各miRNA前体(pri-let-7、pri-miR-100与pri-miR-2795)和bmo-let-7-C全长序列,以红色荧光蛋白(red fluorescent protein,RFP)基因为报告基因,昆虫细胞表达载体pFastBac1为穿梭载体,通过Tn7转座子把目的基因和报告基因转座到杆状病毒A. californica nucleopolyhedrovirus (AcNPV)基因组上,获得各重组杆状病毒质粒（recombinant baculovirus plasmid,rBacmid）：Bac-let-7、Bac-miR-100、Bac-miR-2795和Bac-let-7-C。将重组Bacmid转染草地贪夜蛾（Spodoptera frugiperda）卵巢细胞系Sf9,72 h后用荧光显微镜检查红色荧光蛋白信号,荧光定量PCR检测miRNAs的表达。对转染的Sf9细胞进行、离心、收集上清液,获得具感染力的重组病毒,用于侵染新培养的Sf9细胞和注射家蚕幼虫个体,72 h后用荧光显微镜检查红色荧光蛋白信号,荧光定量PCR检测miRNAs的表达。【结果】成功将bmo-let-7-C上各miRNA前体和bmo-let-7-C全长序列构建到杆状病毒基因组上,获得了各miRNA及bmo-let-7-C的过量表达载体。将各重组过量表达载体分别转染草地贪夜蛾细胞系Sf9,72 h后在显微镜下观察到了红色荧光蛋白信号,荧光定量PCR检测结果表明各miRNA显著过量表达;通过离心收集的各miRNA重组过量表达病毒粒子感染新培养的Sf9细胞72 h后检测到了更强的红色荧光蛋白信号,定量PCR结果表明各miRNA均显著过量表达。将各miRNA的重组病毒注射到家蚕5龄1 d幼虫体内后,均能显著超量表达相应miRNA,但注射Bac-let-7-C后只有miR-2795显著过量表达,并有明显的组织差异性,在丝腺中没有过量表达,在脂肪体、血液和中肠中显著过量表达。【结论】利用杆状病毒过量表达系统在草地贪夜蛾细胞系Sf9和家蚕个体中超量表达了家蚕let-7簇miRNAs,为研究家蚕let-7簇和其他miRNAs的产生机制和功能提供了参考。     

Structure of the Reduced TiO2(110) Surface Determined by Scanning Tunneling Microscopy

The scanning tunneling microscope has been used to image a reduced TiO(2)(110) surface in ultrahigh vacuum. Structural units with periodicities rangng from 21 to 3.4 angstroms have been clearly imaged, demonstrating that atomic resolution imaging of an ionic, wide band gap (3.2 electron volts) semiconductor is possible. The observed surface structures can be explained by a model involving ordered arrangements of two-dimensional defects known as crystallographic shear planes and indicate that the topography of nonstoichiometric oxide surfaces can be complex.     

基于T7 RNA聚合酶的传染性法氏囊病病毒反向遗传系统的建立

    为了建立传染性法氏囊病病毒反向遗传系统,应用PCR法在鸡传染性法氏囊病病毒基因组A、B两节段的5'末端和3'末端分别引入T7启动子和核酶HDV序列,然后分别将含有T7启动子和核酶HDV序列的A、B节段构建到载体PT-Pluc当中,构建感染性载体PT-mA和PT-mB.在脂质体介导下将PT-mA和PT-mB共转染经痘病毒vTF7-3(含T7 RNA聚合酶基因,能稳定表达T7 RNA聚合酶)预先感染1 h的vero细胞.细胞病变观测、间接免疫荧光试验、电镜观察和分子标记检测证实成功实现了鸡传染性法氏囊病病毒的遗传拯救.     

Let-7d在牙鲆变态发育期间的表达及靶基因预测

MicroRNAs(miRNAs)通过抑制编码基因的转录调控关键的生物学进程。研究发现,let-7是时序发育过程中的重要调控因子,在促进幼体向成体转变的发育过程中起着极其重要的作用。利用Solexa测序技术从牙鲆中成功鉴定出let-7家族的10个成员((let-7a,let-7b,let-7c,let-7d,let-7e,let-7f,let-7g,let-7h,let-7i,let-7j)。相对于let-7家族其他成员,let-7d的拷贝数最多,推测其在牙鲆发育过程中扮演着更重要的角色。运用实时荧光定量PCR方法分析let-7d在牙鲆变态发育不同时期的表达,结果发现,在对照组和甲状腺激素处理组,let-7d的表达模式类似:前5个时期(孵化后17 d,17dph;变态Ⅰ期,20 dph;变态Ⅱ期,23 dph;变态Ⅲ期,29 dph;变态Ⅳ期,36dph)表达量逐渐上升;变态晚期(36 dph)达到高峰;变态结束(41 dph)表达量呈现下降的趋势。定量结果显示,甲状腺激素下调let-7d的表达,与对照组呈显著性差异(P<0.05)。对牙鲆不同组织中let-7d的表达情况分析表明,let-7d主要存在于牙鲆的头部(脑,鳃,心脏)。靶基因预测发现,在目前已公布的482条牙鲆mRNA序列中,其中有30条mRNA的3’非翻译区(3’-UTRs)存在let-7d结合位点。这些预测的靶基因涉及到发育过程的许多方面:蛋白折叠,细胞分化,信号转导,病毒免疫反应和信号通路等。这些结果说明,let-7d在调控牙鲆从仔鱼向稚鱼转变的变态发育过程中起着极其重要的作用。     

四川泸州桂圆的RAPD分析

[目的]对四川泸州桂圆及广西桂圆进行品种鉴定和亲缘关系分析。[方法]以泸州黄舣、海潮、潮河、张坝和广西桂圆品种为试验材料,通过CTAB法提取其叶片总DNA,采用改良的RAPD(随机扩增多态性DNA)技术,筛选重复性好的20条随机引物,并改变从退火到延伸的ramp参数,对5个不同产地的桂圆叶片总基因组DNA进行RAPD分析。[结果]PCR扩增共产生124条清晰可见、重复性好的条带,多态性条带72条占58%,同时,检测出5个桂圆样本的特异RAPD条带;降低ramp参数可以提高PCR产物的分辨率和产量。根据124条计分条带产生遗传关系聚类图,5个产地桂圆的相似系数介于0.59～0.80之间;通过UPGMA聚类分析结果显示,广西桂圆位于聚类树的基部,而泸州4个产地桂圆聚成姐妹支,海潮桂圆与张坝桂圆形成一支,潮河桂圆与黄舣桂圆形成另外一支,相似系数分别为0.80和0.78。[结论]该研究结果表明,泸州桂圆隶属于两大基因池,改良的RAPD技术能有效的进行桂圆品种鉴定及其亲缘关系分析。     

pYLTAC7载体在水稻品种农垦58S转化中应用的研究

利用TAC(transformation-competent artificial chromosome)载体pYLTAC7，将明恢63的35kb基因组片段通过农杆菌介导的方法导人水稻品种农垦58S中，对pYLTAC7载体直接用于水稻遗传转化的可行性进行了探索性研究。本试验中，pYLTAC7载体转化效率为10．1％，转基因植株R代PCR及Southern分析表明，外源片段已稳定整合到基因组中，从而证明pYLTAC7载体可以在水稻遗传转化中应用。