罗氏沼虾幼苗体内一种极小病毒的序列测定与分析

从患罗氏沼虾幼苗肌肉白浊病的幼虾体内分离到两种病毒颗粒,诺达病毒(MrNV)和直径只有15nm的小病毒颗粒(extrasmallvirus,XSV),本文通过建立病毒cDNA文库获得XSV基因组的部分序列,在此基础上合成探针,用从病虾组织中提取的总PNA进行Northern杂交,结果表明XSV基因组至少包括两条RNA片段.利用不同的方法对XSV的两端序列进行克隆和测定,分别得到了872、831和662bp3个相互重叠的序列片段,这3个序列的阅读框编码一个相同的大小在17×103左右的蛋白.     

虾肝肠胞虫感染病理特征、18S rRNA基因序列及系统进化树分析

为调查浙江省部分地区虾肝肠胞虫(Enterocytozoon hepatopenaei,EHP)暴发来源及与其他宿主来源的微孢子虫进化关系,本研究利用形态学特征和分子鉴定,尝试对引起浙江多地凡纳对虾生长缓慢综合征的病原进行探究.同时基于18S rRNA基因序列分析该病原与其他地区及其他宿主来源微孢子虫的进化关系.结果显...     

SrTiO_3(001)衬底上多层FeSe薄膜的分子束外延生长

近几年,由于用分子束外延法在SrTiO_3衬底表面制备的单层FeSe具有很高的超导转变温度而引发了极大的研究热潮,随之而来的是对多层FeSe薄膜日益增长的研究兴趣.但目前还没有对成功生长高质量多层FeSe薄膜的详细报道.本文利用高能电子衍射仪(RHEED)实时监控在不同生长条件下制备的多层FeSe薄膜,发现在FeSe薄膜的生长初期,RHEED图像的强度演化基本符合台阶密度模型的描述特征,即台阶密度ρ正相关于衍射条纹强度.FeSe(02)衍射条纹的强度在第一生长周期内呈现稳定而明显的峰型振荡,而且不受高能电子掠射角的影响,最适合用来标定FeSe薄膜的厚度.结合扫描隧道显微镜对FeSe薄膜质量的原位观察,确定了制备多层FeSe薄膜的最佳生长条件,为FeSe薄膜的物性研究提供了重要的材料基础.     

Topological Dirac surface states in ternary compounds GeBi2Te4, SnBi2Te4 and Sn0.571Bi2.286Se4

Using high-resolution angle-resolved and time-resolved photoemission spectroscopy, we have studied the low-energy band structures in occupied and unoccupied states of three ternary compounds GeBi₂Te₄, SnBi₂Te₄ and Sn_0.571Bi_2.286Se₄ near the Fermi level. In previously confirmed topological insulator GeBi₂Te₄ compounds, we confirmed the existence of the Dirac surface state and found that the bulk energy gap is much larger than that in the first-principles calculations. In SnBi₂Te₄ compounds, the Dirac surface state was observed, consistent with the first-principles calculations, indicating that it is a topological insulator. The experimental detected bulk gap is a little bit larger than that in calculations. In Sn_0.571Bi_2.286Se₄ compounds, our measurements suggest that this nonstoichiometric compound is a topological insulator although the stoichiometric SnBi₂Se₄ compound was proposed to be topological trivial.     

Two-dimensional topological insulators with large bulk energy gap

Two-dimensional(2D) topological insulators(TTs,or quantum spin Hall insulators) are special insulators that possess bulk 2D electronic energy gap and time-reversal symmetry protected one-dimensional(1D) edge state.Carriers in the edge state have the property of spin-momentum locking,enabling dissipation-free conduction along the 1D edge.The existence of 2D TIs was confirmed by experiments in semiconductor quantum wells.However,the 2D bulk gaps in those quantum wells are extremely small,greatly limiting potential application in future electronics and spintronics.Despite this limitation,2D TIs with a large bulk gap attracted plenty of interest.In this paper,recent progress in searching for TIs with a large bulk gap is reviewed briefly.We start by introducing some theoretical predictions of these new materials and then discuss some recent important achievements in crystal growth and characterization.     

Metastable Face-Centered Cubic Structure and Structural Transition of Sn on 2H-NbSe_2(0001)

Surface structures and properties of Sn islands grown on superconducting substrate 2H-NbSe_2(0001)are studied using low temperature scanning tunneling microscopy or spectroscopy.The pure face-centered cubic(fee)structure of Sn surface is obtained.Superconductivity is also detected on the fcc-Sn(111)surface,and the size of superconducting gap on the Sn surface is nearly the same as that on the superconducting substrate.Furthermore,phase transition occurs from fcc-Sn(111)toβ-Sn(001)by keeping the sample at room temperature for a certain time.Due to the strain relaxation on theβ-Sn islands,both the in-plane unit cell and out-of-plane structures distort,and the height of surface atoms varies periodically to form a universal ripple structure.     

Topological edge states and electronic structures of a 2D topological insulator： Single-bilayer Bi （111）

Providing the strong spin-orbital interaction, Bismuth is the key element in the family of three-dimensional topological insulators. At the same time, Bismuth itself also has very unusual behavior, existing from the thinnest unit to bulk crystals. Ultrathin Bi （111） bilayers have been theoretically proposed as a two-dimensional topological insulator. The related experimental realization achieved only recently, by growing Bi （111） ultrathin bilayers on topological insulator Bi2Te3 or Bi2Se3 substrates. In this review, we started from the growth mode of Bi （111） bilayers and reviewed our recent progress in the studies of the electronic structures and the one-dimensional topological edge states using scanning tunneling microscopy/spectroscopy （STM/STS）, angle-resolved photoemission spectroscopy （ARPES）, and first principles calculations.     

Surface Structure and Reconstructions of HgTe(111) Surfaces

Hg Te(111) surface is comprehensively studied by scanning tunneling microscopy/spectroscopy(STS).In addition to th√e prim√itive(1 × 1)√ hexagonal lattice,six reconstructed surface structures are observed:(2 × 2),2 × 1,4 × 1,3 ×(1/2)3,2(1/2)2 × 2 and (1/2)11 × 2.The(2 × 2) reconstructed lattice maintains the primitive hexagonal symmetry,whi√le the lattices of the other five reconstructions are rectangular.Moreover,the topographic features of the3 ×(1/2)3 reconstruction are bias dependent,indicating that they have both topographic and electronic origins.The STSs obtained at different reconstructed surfaces show a universal dip feature with size ～100 mV,which may be attributed to the surface distortion.Our results reveal the atomic structure and complex reconstructions of the cleaved Hg Te(111) surfaces,which paves the way to understand the rich properties of Hg Te crystal.     

Band Structures of Ultrathin Bi(110) Films on Black Phosphorus Substrates Using Angle-Resolved Photoemission Spectroscopy

The band structures of two-monolayer Bi(110) films on black phosphorus substrates are studied using angleresolved photoemission spectroscopy. Within the band gap of bulk black phosphorus, the electronic states near the Fermi level are dominated by the Bi(110) film. The band dispersions revealed by our data suggest that the orientation of the Bi(110) film is aligned with the black phosphorus substrate. The electronic structures of the Bi(110) film strongly deviate from the band calculations of the free-standing Bi(110) film, suggesting that the substrate can significantly affect the electronic states in the Bi(110) film. Our data show that there are no non-trivial electronic states in Bi(110) films grown on black phosphorus substrates.     

空气绝热指数的计算机测量

通过采用温度传感器和计算机实时测量分析技术对热力学绝热瞬态过程进行观测， 以便较准确地测量得到空气的绝热指数．