Fluorine, chlorine and iodine adsorption on the Ge(0 0 1) surface: Comparative study for the coverage of 0.75 and 1 monolayer

Theoretical study of the adsorption of 0.75 and 1 monolayer of F, Cl, and I on the Ge(0 0 1)-p(1×2) surface is presented. Various stable atomic configurations are considered, their surface electronic properties are discussed by means of the density-of-states analysis, and the corresponding STM images are simulated. While the results obtained for Cl and I are similar to those known for Br, the F-covered surfaces exhibit noticeably different features.     

A density functional theory study of CH4 dehydrogenation on Co(1 1 1)

The dehydrogenation of CH₄ on the Co(1 1 1) surface is studied using density functional theory calculation (DFT). It is found that CH₄ is favored to dissociate to CH₃ and then transforms to CH₂ and CH by sequential dehydrogenation, and CH₄ activation into CH₃ and H is the rate-determining step on the Co(1 1 1) surface. CH₂ is quite unstable on Co(1 1 1) surface. CH dehydrogenation into C and H is difficult. CH₃ and H prefer to adsorb on 3-fold hollow hcp and fcc sites, and CH₂, CH and C prefer to adsorb on hcp sites.     

The investigation of oxidized silver nanoparticles prepared by thermal evaporation and radio-frequency sputtering of metallic silver under oxygen

The investigation of oxidized silver nanoparticles by the photoemission (XPS, UPS) and HRTEM methods was performed. The nanoparticles of oxidized silver were obtained in the vacuum chamber by two methods of synthesis: thermal evaporation of silver nanoparticles followed by transferring in convective gas flow and sputtering of oxidized clusters under the action of plasma. Both methods indicated that oxygen interaction with silver nanoparticles depends strongly on its size. It was shown that the chemical bonding of oxygen species stabilized on small particles differs from the oxygen species adsorbed on bulk silver surfaces (monocrystals, foils and large particles). The low charged oxygen with molecular type of bonding stabilizes on particles of size approximately 5 nm and smaller. Increasing particle size leads to the dissociation of molecular oxygen species and the formation of strongly charged oxygen composed of oxide nanoparticles like Ag₂O or AgO type. The presence of extended defects in the microdomain large nanoparticles facilitates the formation of Ag₂O or AgO layers covering metallic nanosilver.     

Preparation of functional composite grafted particles PDMAEMA/SiO2 and preliminarily study on functionality

Micron-sized silica gel particles were first surface-modified with coupling agent, γ-methacryloylpropyl trimethoxysilane (MPS), and the polymerizable double bonds were introduced onto the surfaces of silica gel particles, forming the modified particles MPS-SiO₂. Subsequently, N,N-dimethylaminoethyl methacrylate (DMAEMA) was graft-polymerized on the surfaces of particles MPS-SiO₂ in the manner of “grafting through”, resulting in the grafted particles PDMAEMA/SiO₂. The grafted particles PDMAEMA/SiO₂ were fully characterized with several means. The graft polymerization process of DMAEMA on particles MPS-SiO₂ was studied in detail, and the optimal reaction conditions were determined. Thereafter, the adsorption properties of the grafted particles PDMAEMA/SiO₂ for chromate anion and Cu²⁺ ion were preliminarily examined respectively. The experimental results indicate that the PDMAEMA grafting degree on PDMAEMA/SiO₂ particles is limited because an enwinding polymer layer as a kinetic barrier on the surfaces of silica gel particles will be formed during the graft polymerization, and blocks the graft polymerization. In order to enhance PDMAEMA grafting degree, reaction time and temperature, and the used amount of initiator as well as the monomer concentration should be effectively controlled. The preliminary adsorption tests show that the grafted particles PDMAEMA/SiO₂ are multi-functional. They possess very strong adsorption ability for CrO₄²⁻ anion by right of strong electrostatic interaction, and have also adsorption action towards heavy metal ion by dint of complexing action.     

几种食用植物油发热量的测定

利用WZR-1A型精密微电脑量热计系统地测量了10种食用植物油的恒容燃烧热.准确称取一定量的基准物质,放入氧弹中充人高压纯氧,将测试样品在氧弹中完全燃烧,并记录燃烧前后时间与量热计温度变化数据,运用仪器所带的数据处理软件计算出仪器热容量,然后再准确称取一定量的食用植物油,装入已准确测定热值的燃烧胶囊中后,将测试数据用自编的计算机处理程序对测试数据处理,从而得到食用植物油的燃烧热值.此法准确、简便、实用,可用于日常检测工作.     

奶制品热值测定

利用WZR-1A型精密微电脑量热计系统地测量了8种奶制品的恒容燃烧热.准确称取一定量的基准物质,放入氧弹中充入高压纯氧,将测试样品在氧弹中完全燃烧,并记录燃烧前后时间与量热计温度变化数据,利用仪器自带的数据处理软件计算出仪器热容量,然后再准确称取一定量的奶制品,装入已准确测定热值的燃烧胶囊中后,将测试数据用自编的计算机处理程序对测试数据处理,从而得到奶制品的燃烧热值.此法准确、简便、实用,可用于日常检测工作.     

2-氨基苯硫酚NIR-SERS光谱及其在纳米银表面吸附行为分析

本文采用静电自组装的方法制备了二维纳米银膜。UV-vis吸收光谱显示其等离子体共振吸收带位于400+900nm的光谱范围,延伸到了近红外区,可以较好的匹配785nm的近红外激发光源。以该纳米银膜为基底,对2-氨基苯硫酚(2-ATP)分子进行了近红外表面增强拉曼散射(NIR-SERS)检测,获得了重复性良好的NIR-SERS光谱图。实验表明:以2-ATP为探针分子时,该纳米银膜的NIR-SERS增强因子达到2.19×109。同时,本文采用密度泛函理论(DFT),以B3LYP/6-31G为基函数,对2-ATP分子进行结构优化和普通拉曼光谱(NR)计算,发现理论值和实验值吻合较好。此外,对2-ATP的NIR-SERS谱带进行了归属分析,发现当2-ATP分子在纳米银表面吸附时,是以-SH基团吸附到银表面,且同时-SH基团会被纳米银氧化。     

Box-modeling of bone and tooth phosphate oxygen isotope compositions as a function of environmental and physiological parameters*

A time-dependent box model is developed to calculate oxygen isotope compositions of bone phosphate as a function of environmental and physiological parameters. Input and output oxygen fluxes related to body water and bone reservoirs are scaled to the body mass. The oxygen fluxes are evaluated by stoichiometric scaling to the calcium accretion and resorption rates, assuming a pure hydroxylapatite composition for the bone and tooth mineral. The model shows how the diet composition, body mass, ambient relative humidity and temperature may control the oxygen isotope composition of bone phosphate. The model also computes how bones and teeth record short-term variations in relative humidity, air temperature and δ¹⁸O of drinking water, depending on body mass. The documented diversity of oxygen isotope fractionation equations for vertebrates is accounted for by our model when for each specimen the physiological and diet parameters are adjusted in the living range of environmental conditions.     

吸气剂在高真空多层绝热LNG槽车内吸附性能研究

为了利用吸附等温线理论模型模拟高真空多层绝热LNG槽车内吸气剂的吸附过程,对在真空技术中常用的等温式进行了分析研究。通过实验获得吸气剂在室温下的吸氢等温线,同时利用实验数据得到考虑分子间作用力的BET模型中的参数值。将模型结果与实验数据进行对比分析,结果表明:考虑分子间作用力的BET模型不能用作高真空多层绝热LNG槽车真空夹层内吸气剂吸附量的计算。利用Temkin和Freundlich等温式分段对实验数据进行拟合,对于1#吸气剂,拟合方程式计算得出的吸附量与实验数据的相对误差仅为2.6%,表明拟合方程能够对吸气剂在室温下的吸氢量进行准确预测。     

5kW/4.5K氦制冷系统外纯化器吸附筒设计

纯化器设计的关键是求解吸附剂对吸工质的吸附容量。文中根据朗格缪尔方程式,对活性炭在78K温度下对氮、氧等杂质的吸附容量进行了计算与分析,研究杂质气体中氮、氢比例对吸附容量的影响。在计算结果基础上,对吸附筒进行机械结构设计和应力分析。