Scanning tunneling microscopy of electrodeposited ceramic superlattices

Cleaved cross sections of nanometer-scale ceramic superlattices fabricated from materials of the lead-thallium-oxygen system were imaged in the scanning tunneling microscope (STM). The apparent height differences between the layers were attributed to composition-dependent variations in local electrical properties. For a typical superlattice, the measured modulation wavelength was 10.6 nanometers by STM and 10.8 nanometers by x-ray diffraction. The apparent height profile for potentiostatically deposited superlattices was more square than that for galvanostatically deposited samples. These results suggest that the composition follows the applied potential more closely than it follows the applied current. The x-ray diffraction pattern of a superlattice produced under potential control had satellites out to the fourth order around the (420) Bragg reflection.     

A bacterium that can grow by using arsenic instead of phosphorus

Life is mostly composed of the elements carbon, hydrogen, nitrogen, oxygen, sulfur, and phosphorus. Although these six elements make up nucleic acids, proteins, and lipids and thus the bulk of living matter, it is theoretically possible that some other elements in the periodic table could serve the same functions. Here, we describe a bacterium, strain GFAJ-1 of the Halomonadaceae, isolated from Mono Lake, California, that is able to substitute arsenic for phosphorus to sustain its growth. Our data show evidence for arsenate in macromolecules that normally contain phosphate, most notably nucleic acids and proteins. Exchange of one of the major bio-elements may have profound evolutionary and geochemical importance.     

龟纹瓢虫成虫对高粱蚜的捕食作用

室内条件下进行了龟纹瓢虫成虫对高粱蚜的捕食功能反应与搜寻效应试验。结果表明,龟纹瓢虫雌雄成虫的捕食功能反应均符合HollingⅡ型方程;龟纹瓢虫成虫的捕食量随猎物密度的增加而增加,而搜寻效应随之降低。龟纹瓢虫雌雄成虫处理1头高粱蚜虫所需的时间(Th)分别为0.017 d和0.024 d;瞬间攻击率(a)分别为1.661和2.967;最大日捕食量分别为58.824头和41.667头。龟纹瓢虫的捕食量受种内干扰影响,随着龟纹瓢虫密度的增加,单头平均捕食量呈下降趋势。在龟纹瓢虫成虫2头/皿时,分摊竞争强度(I)仅为0.0689,说明此密度下龟纹瓢虫成虫捕食高粱蚜时种内干扰效应很低。     

伪狂犬病病毒吉林分离株感染BHK-21细胞的超微结构变化

以猪伪狂犬病病毒(PRV)吉林分离株PRV-JL感染体外培养的BHK-21细胞为模型,通过透射电镜对PRV的形态发生学和宿主细胞超微结构的动态变化规律进行研究。结果显示,PRV能导致BHK-21细胞圆缩,并发生细胞融合,形成合胞体;电镜观察到的病毒粒子呈球形或椭圆形,成熟的病毒粒子直径大小为140~210 nm,未成熟病毒粒子直径为90~150 nm,多呈中空状,部分呈致密核芯。病毒吸附于细胞后以膜融合的方式进入细胞,在胞核内复制,装配好的病毒粒子以出芽的方式离开细胞核,获得最初的囊膜,进入胞浆;在胞浆内的病毒粒子又利用高尔基体的膜结构合成第2层囊膜,形成完整的病毒粒子;最后包裹有完整病毒粒子的高尔基囊泡与细胞膜发生融合,将病毒粒子释放到细胞外。感染细胞超微结构变化主要表现为:细胞胞浆空泡增多,内质网扩张,线粒体增生、嵴肿胀、脱落,最后空泡化,整个细胞裂解、破碎。     

水浴法提取怀菊花总黄酮工艺研究

以芦丁为对照品,正交设计优化怀菊花中总黄酮水浴提取条件,于505 nm处采用紫外分光光度法测定总黄酮的含量。结果表明,总黄酮在0～50μg/mL范围内,吸光度与浓度呈良好的线性关系,水浴法提取怀菊花总黄酮的最佳提取条件为A1B1C3,即温度60℃、乙醇浓度60%、料液比1∶10、提取2次、提取1 h,提取率为109.74 mg/g。回归方程为:y=0.01058x-0.01233,R2=0.9973,平均加标回收率为98.16%,RSD为0.210%。该方法成本低,无污染,操作简便,结果准确,可作为怀菊花的质量控制方法。     

Electrodeposited defect chemistry superlattices

Nanometer-scale layered structures based on thallium(III) oxide were electrodeposited in a beaker at room temperature by pulsing the applied potential during deposition. The conducting metal oxide samples were superlattices, with layers as thin as 6.7 nanometers. The defect chemistry was a function of the applied overpotential: High overpotentials favored oxygen vacancies, whereas low overpotentials favored cation interstitials. The transition from one defect chemistry to another in this nonequilibrium process occurred in the same potential range (100 to 120 millivolts) in which the rate of the back electron transfer reaction became significant. The epitaxial structures have the high carrier density and low electronic dimensionality of high transition temperature superconductors.     

农业用地供给侧改革的可行举措探讨

通过梳理我国农业用地在利用中所存在的制度层面、利用层面、管理层面和其他层面的问题,结合我国推进农业用地实行供给侧改革的目的,从4个方面制度供给、利用供给、管理供给和其他供给提出我国在实行农业用地供给侧改革的可行举措,为我国推进农业用地的供给侧改革提供理论依据。