阵列式等离子体射流处理芽孢的实验研究北大核心CSCD

研制了一套单极性微秒脉冲阵列式等离子体射流系统,该系统可在大气压下激发产生等离子体射流,实现大面积的灭菌处理。该系统可产生峰值电压20 kV、频率15 kHz的高压脉冲,激发产生的射流均匀稳定,覆盖面积达37.7 cm2,射流长度达6 cm,射流功率为40.05 W,处理5 min可使射流覆盖范围内的枯草芽孢杆菌的芽孢基本全部失去活性。考察了不同参数对灭菌效率的影响,结果表明,灭菌率与工作电压、脉冲频率、处理时间呈正相关,在氦气氛围下有较好的灭菌效果。SEM显示等离子体射流能够对枯草芽孢杆菌的芽孢外壳结构造成损坏,导致芽孢无法正常代谢,最终死亡。     

强碱胁迫枯草芽孢杆菌芽孢致死的拉曼光谱研究

应用单细胞拉曼分析技术结合PCA方法,以枯草芽孢杆菌芽孢为对象,以强碱为诱导剂实时记录芽孢生理变化过程,探究芽孢在强碱胁迫下的致死机制。实验表明,枯草芽孢杆菌芽孢和其萌发后芽孢在一定范围均有一定的耐受强碱能力,但萌发后芽孢的耐受力明显下降,主要原因是释放了维持其抗性及稳定性的特有Ca2+-DPA的保护;芽胞受强碱胁迫也会有少量Ca2+-DPA释放过程的行为特征,但通过分析所记录的光谱数据结果表明,其释放行为不同于由L-丙氨酸引起的芽孢的正常Ca2+-DPA释放过程。通过PCA比较分析强碱胁迫芽孢和萌发后芽孢Ca2+-DPA释放过程,主要是强碱破坏芽孢膜结构,膜损伤后强碱比较容易进到芽孢内部从而破坏蛋白质的主链结构链及核酸;芽孢膜通道也可能受到强碱的伤害,造成微量Ca2+-DPA的释放。     

太赫兹量子级联激光器中有源区上激发态电子向高能级泄漏的研究

利用热力学统计理论和激光器输出特性理论,建立了太赫兹量子级联激光器(THz QCL)有源区中上激发态电子往更高能级电子态泄漏的计算模型,以输出功率度量电子泄漏程度研究分析了晶格温度和量子阱势垒高度对电子泄漏的影响.数值仿真结果表明,晶格温度上升会加剧电子泄漏,并且电子从上激发态泄漏到束缚态的数量大于泄漏到阱外连续态,同时温度的上升也会降低激光输出功率.增加量子阱势垒高度能抑制电子泄漏,并且有源区量子阱结构中存在一个最优量子阱势垒高度. THz QCL经过最优量子阱势垒高度优化后,工作温度得到提升,其输出功率相比于以往的结果也有所提高.研究结果对优化THz QCL有源区结构、抑制电子泄漏和改善激光器输出特性有指导作用.     

温压结合超高压处理对芽孢杀灭作用的研究进展

 详细介绍了温压结合超高压杀菌技术的优点,指出其独特的应用优势,深入完整地综述了温压结合超高压处理对各类细菌芽孢的杀灭作用及动力学研究成果,并对温压结合超高压处理杀灭芽孢的机理做了初步总结。在此基础上,分析了该研究领域尚存在的问题,提出了未来的研究重点和方向。     

快中子辐照对枯草芽孢杆菌DNA损伤研究

采用脉冲场凝胶电泳技术检测并定量分析了CFBR-Ⅱ快中子脉冲堆产生的快中子在不同剂量和剂量率条件下, 对枯草芽孢杆菌黑色变种(ATCC 9372)DNA双链断裂的诱导. 通过DNA释放百分比PR值、DNA断裂水平L值、断裂DNA平均分子量和DNA片段分布等指标的分析, 结果表明：在不同的辐射条件下, DNA片段均明显分布于两个区域, 表明枯草芽孢杆菌黑色变种DNA分子上可能存在对中子辐射较为敏感的位点; 并且随着中子辐射剂量和剂量率的变化, DNA~释放百分比PR值、DNA断裂水平L值和各片段区双链断裂的含量也会发生一定规律性的变化.     

枯草芽孢杆菌双精氨酸转运系统TatAy蛋白的溶液结构

存在于细菌和植物叶绿体中的双精氨酸(Tat)蛋白质转运系统能将底物蛋白以折叠的状态进行跨膜转运。该系统中的单次跨膜膜蛋白 TatA 通过自身寡聚形成转运底物蛋白的通道。该文应用液体核磁共振方法解析了枯草芽孢杆菌 TatAy蛋白在十二烷基胆碱磷酸胶束中的结构,它是由一个跨膜螺旋(TMH)和一个两亲性螺旋(APH)构成的L型结构。通过与已经报道的枯草芽孢杆菌TatAd蛋白的结构比较,该文能够鉴定出参与维持L型构象的重要氨基酸残基,并指出了TatA蛋白家族中若干较为保守的结构特征。在此基础上,该文讨论了保守残基在 TatA 通道形成过程中可能发挥的作用。     

傅里叶变换红外光谱对枯草芽孢杆菌的光学特性研究

使用傅里叶变换红外光谱(FTIR)技术,测量了两种不同浓度的枯草芽孢杆菌的红外透过率谱,根据朗伯-比尔定律计算出它们的质量消光截面,通过算出复折射率的虚部,再使用KK(Kramers-Kronig)关系,导出复折射率的实部,并对实验结果作了分析和讨论。通过研究枯草芽孢杆菌复折射率的测量和分析方法,对于进一步研究生物气溶胶的吸收和散射特性、拓宽生物气溶胶的测量和遥测技术方法,具有重要的意义。     

结香纤维素与木素分布的显微激光拉曼光谱研究

显微激光拉曼光谱技术可以实现纤维素与木素在木材细胞壁中原位状态分布规律的观察研究。首先采用透射电子显微镜(TEM)研究了结香细胞壁的超微结构。进而采用显微激光拉曼光谱技术对细胞壁各层中纤维素与木素分布特点进行了原位分析测定,拉曼图像及光谱分析结果表明,纤维素与木素在细胞壁各形态区分布不均一,纤维素的分布情况与木素相反。     

C波段磁绝缘线振荡器的数值模拟

 利用2维半全电磁PIC程序进行数值模拟，设计了一种C波段磁绝缘线振荡器。该振荡器在阴极电子发射起点加圆环,控制此处电子束的发射密度，来减少电子能量的损耗，改善束-波互作用；逐渐加大慢波结构的后两个叶片的内半径，增大微波群速度，便于谐振腔中的能量输出，提高微波输出效率；采用两个扼流片有效地阻止了微波功率向二极管区泄漏，相应减小了器件的尺寸。当外加电压为430 kV、束流46 kA时，饱和后输出微波平均功率2 GW，频率3.51 GHz，功率转换效率10%。     

超高压处理对冷藏鲈鱼片品质及组织结构变化的影响

为研究超高压处理对冷藏鲈鱼片品质及组织结构变化的影响,将新鲜鲈鱼片经不同超高压(200、250、300MPa,保压时间9min)处理后,置于4℃条件下贮藏。分别于0、4、8、11、13、15d进行样品的理化指标(pH值、硬度、持水力、硫代巴比妥酸(TBA)值、挥发性盐基氮(TVB-N)值)和微生物指标(菌落总数)测定,并结合低场核磁共振技术表征其水分迁移状态,辅以外观及微观结构观察,进行指标间的相关性分析,以综合评价超高压处理对冷藏鲈鱼片品质及组织结构变化的影响。结果显示:随着贮藏时间的延长,样品的pH值呈先降后升的变化趋势,压力大小与pH值变化正相关,与硬度值、持水力负相关;超高压处理能抑制样品的TBA值、TVB-N值及菌落总数的上升,压力越高,抑制效果越显著。低场核磁共振技术结合持水力数据显示:超高压处理后鱼肉水分迁移变化明显;随着压力的增大,鱼肉样品表面呈乳白色,蒸煮效果显著。观察样品肌肉组织的微观结构得出,经超高压处理后,鱼体肌肉组织变得模糊,肌纤维结构紧致无序,其中300MPa处理组样品呈明显凝胶状。超高压处理能抑制样品的脂肪氧化和微生物生长,但会对样品外观、色泽及持水力产生不利影响。进行指标间的相关性分析得到,TVB-N、TBA值和菌落总数能作为判断鲈鱼鲜度的重要指标。比较各组别间的结果差异性,以250MPa、9min超高压处理的综合评价效果相对较好,能使鲈鱼片的冷藏货架期至少延长4d。     

Ultrastructure of the siphonaceous green alga Halimeda cuneata,with emphasis on the cytoskeleton

Cytoplasm streaming is a fundamental process for the transport of molecules and organelles in plant cells. In vegetative filaments of the coenocytic green alga, Halimeda cuneata Hering, the spatial organisation of microtubules in the cytoplasmic layer, was observed under transmission electron microscopy. A cross section of a cortical filament shows a tubular cell wall enclosing a peripheral layer of cytoplasm with numerous chloroplasts, amyloplasts, nuclei, mitochondria and microtubules surrounding a small central vacuole. Towards the thallus medulla the central vacuole enlarges considerably and the cytoplasm becomes gradually reduced to a thin parietal layer, the number of organelles is reduced and the quantity of microtubules increases. Therefore, most of the thallus volume is occupied by the huge central vacuole which extends throughout the coenocytic filaments. Microtubules run longitudinally, being about 0.05 μm from each other. Some microtubules were observed in close association to cell organelles.     

Ultrastructure of spined conidia and hyphae of the rice false smut fungus Ustilaginoidea virens

Spined conidia and hyphae of Ustilaginoidea virens were examined by light and electron microscopy. Bright-field light microscopy showed that conidia were round to elliptical and warty on the surface with diameters approximately ranging from 3 to 5 microm. Scanning electron microscopy revealed the globose to irregularly rounded and ornamented conidia with prominent spines. The spines were pointed at the apex or irregularly curved, and approximately 200-500 nm long. Ultrastructure of spined conidia and hyphae revealed by transmission electron microscopy showed lipid globules and vacuoles in the cytoplasm enclosed by an electron-transparent cell wall. Conspicuous electron-dense spines were evident on the surface of conidia, and had obclavate or irregularly protruding shapes with varying heights along the conidial cell wall. Microfibrillar structures with stretching or branching patterns were evident in the spine matrix. Some conidia were interconnected by spines from the neighboring conidia by their extended outgrowth. Hyphae had concentric bodies that showed an electron-transparent core surrounded by an electron-dense layer. One or more intrahyphal hyphae were found in hyphal cytoplasm. The fungus is thought to form concentric bodies and intrahyphal hyphae as survival mechanisms against the water- and nutrient-deficient environments that may occur in the necrotic regions of host plants.     

Identification by TEM and EELS of the products formed at the surface of a carbon electrode during its reduction in MClO4-EC and MBF4-EC electrolytes (M = Li, Na)

The electrochemical intercalation of lithium and sodium into graphite was carried out using a liquid electrolyte containing ethylene carbonate (EC) as solvent and MClO4 or MBF4 (M = Li, Na) as salts. The first intercalation of alkali metals into graphite is accompanied with irreversible reactions attributed to the reduction of the electrolyte. These reactions contribute to the development of a passivating layer, formed on graphite surface prior to intercalation. This layer is impervious to solvent molecules but allows alkali ions to diffuse through its bulk. The surface chemistry of the electrodes was characterized using transmission electron microscopy (image, selected area electron diffraction) as well as EELS. The effect of the nature of the alkali salts on the properties of the passivating layer is studied.     

Novel approaches for low cost fabrication of SOI

Two trials for low cost manufacture of silicon-on-insulator (SOI) wafers were implemented. Low dose separation by implantation of oxygen (SIMOX) procedure has been conducted on a beam-line ion implanter with mass analyzer. The energy dependence of the formed SOI structure was studied at varied implant dosages. The integrity of the buried oxide (BOX) layer was examined by transmission electron microscopy (TEM) and the threading dislocation in the top silicon layer was evaluated by Secco technique. The results indicated that not only the implanted oxygen dose but also the oxygen ion energy plays an important role in the formation of SOI structure with good crystallinity of top silicon, sharp Si/SiO₂ interfaces and highly integrated BOX layer free of silicon inclusion. For separation by plasma implantation of oxygen (SPIMOX) approach, water plasma, rather than oxygen plasma, was employed to avoid oxygen spread in the implant depth profile. The SPIMOX process using water plasma was carried out on a beam-line ion implanter without mass selector to simulate the plasma implantation procedure. Cross-sectional TEM study revealed that uniform BOX layer was formed under single crystal silicon superficial layer with the present approach. The interfaces between silicon superficial layer, BOX layer and bulk silicon were smooth and sharp. An implant dose window has been identified for fabricating the desirable SOI structure.     

Electroexplosive Carburizing of Iron: Surface Relief,Phase Composition and Defect Substructure

Surface relief, phase composition and defect substructure of the surface layer of iron specimens are investigated using scanning and transmission electron microscopy after high-energy electroexplosive carburizing treatment. The structure formed is shown to exhibit a conspicuous gradient character resulting from variations in carbon content with the layer depth. It is found out that a liquid melt of the sublayer of nanocrystalline structure is formed at the boundary of the melt pool. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 36–41, September, 2005.     

Structure of alumina nanowires synthesized by chemical etching of anodic alumina membrane

We report the structure of alumina nanowires (ANWs) synthesized by the chemical etching of an anodic alumina membrane (AAM). The AAM was prepared by the two-step anodization method followed by the lift-off process. The field emission transmission electron microscopy analyses showed that the AAM consists of a gel-like structure, an outer layer, and an inner layer, which are distinguished by their anion impurity concentration. The fabricated ANWs appeared to have a two-oxide-layer structure, similar to the core-shell structure in a coaxial cable. The inner oxide layer may be composed of relatively pure alumina and the outer oxide layer of the byproducts of the reaction between alumina and the anodization or etching solution. The fabricated ANWs have a flexible nature, with some of them being sufficiently malleable to form L-shaped ANWs. One possible formation process of the two-oxide-layer structured ANW is discussed.     

Epitaxial growth of boron-doped graphene by thermal decomposition of B4C

We grew graphene by thermal decomposition of B(4)C and investigated its features by high-resolution transmission electron microscope observations. At temperatures higher than 1600 °C in a vacuum, B(4)C decomposes and graphene forms epitaxially on its surface. The number and the morphology of the graphene layers depend on the surface orientation. An electron diffraction technique revealed the presence of a superstructure with a two-times larger unit cell, which is consistent with the structure of BC(3). We have directly confirmed boron in the graphene layers by electron energy loss spectroscopy measurements and boron-mapping experiments.     

双层弹性支撑板的水下宽带隔声

为实现水下宽带隔声,提出了一种由弹性元件支撑两块刚性端板构成的双层弹性支撑板结构。采用弹簧振子振动分析法和声传播理论,建立了平面波入射的水下隔声理论模型,分析了结构参数对隔声量的影响规律,结果表明足够小的弹性元件单位面积弹性系数或足够大的端板单位面积质量都可以连续一致地提高隔声量.仿真分析了双层弹性支撑板的振动位移和声输入阻抗,比较了双层弹性支撑板与连续介质层的隔声特性,结果表明,降低弹性元件质量,有助于在低频段消除半波全透射现象.在同厚度、同质量、同静态压缩率条件下,双层弹性支撑板能更好的降低两侧流体的振动及声耦合,隔声频带更宽,带内一致性更好,隔声量更大.      

Towards the demonstration of actuator properties of a single carbon nanotube

Owing to its huge elastic modulus, good conductivity and large free surface area per mass, a single carbon single-walled nanotube (SWNT) should present optimal intrinsic actuation properties. Our aim is to demonstrate the viability of such a single nanotube-based actuator (“nano-actuator”). To achieve this goal, the primary focus was on how to obtain and manipulate an isolated and suspended SWNT. Several strategies have been attempted to produce such nanotubes (NTs), among them the “stamping” of tubes on functionalised substrates, or the direct growth of tubes from an oxide catalyst layer on a pre-designed substrate. Characterisation of these structures was carried out by atomic force microscopy, scanning electron microscopy and transmission electron microscopy. Manipulation of NT on flat surfaces was first demonstrated, before attempts were made to probe the suspended NTs. The final and most important step will be the use of an atomic force microscope to probe the deformation of the nanotube which should occur under a bias voltage in an electrochemical cell.     

Electron leakage and double-exchange ferromagnetism at the interface between a metal and an antiferromagnetic insulator: CaRuO3/CaMnO3

Density-functional electronic structure studies of a prototype interface between a paramagnetic metal and an antiferromagnetic (AFM) insulator (CaRuO(3)/CaMnO(3)) reveal the exponential leakage of the metallic electrons into the insulator side. The leaked electrons in turn control the magnetism at the interface via the ferromagnetic (FM) Anderson-Hasegawa double exchange, which competes with the AFM superexchange of the bulk CaMnO3. The competition produces a FM interfacial CaMnO3 layer (possibly canted); but beyond this layer, the electron penetration is insufficient to alter the bulk magnetism.