Direct measurement of the formation length of photons

We report the first observation of a shoulder in the radiation spectrum from GeV electrons in a structured target consisting of two thin and closely spaced foils. The position of the shoulder depends on the target spacing and is directly connected to the finite formation length of a low-energy photon emitted by an ultrarelativistic electron. With the present setup it is possible to control the separation of the foils on a μm scale and hence measure interference effects caused by the macroscopic dimensions of the formation length. Several theoretical groups have predicted this effect using different methods. Our observations have a preference for the modified theory by Blankenbecler but disagree with the results of Baier and Katkov.     

高效液相色谱-串联质谱法测定环境水体中双酚A、辛基酚、壬基酚

建立了高效液相色谱-串联质谱测量水环境中的双酚A(BPA)、辛基酚(OP)、壬基酚(NP)的方法。提取方法基于液-液萃取,流动相为V(甲醇)∶V(水)=90∶10,流速200μL/min,运行时间为5min。质谱用来定量的碎片离子分别为:BPA,212.3;BPA-d16,223.4;OP,106.3;NP,106.3,定量采用内标法。仪器的检出限均为0.7pg,方法检出限均为0.07ng/L。对同一环境样品进行3个不同浓度(10、100、500 ng/L)的加标来测得回收率:BPA 79.4%~84.3%,RSD 2.7%~3.4%;NP 78.9%~112.5%,RSD 1.9%~5.0%;OP69.4%~122.7%,RSD3.4%~11.3%。基于该方法,对大连旅顺地区主要河流和排污口水体中的BPA、NP和OP进行了检测,浓度范围为35.67~753.92ng/L,与国内其他调查区域比酚类物质污染处于中等水平,而低于国外类似调查区域。     

双流化床煤气化试验研究

建立了一套3米高的双流化床煤气化试验装置,煤在鼓泡流化床中热解气化,生成的半焦送入循环流化床中燃烧,两床间采用气动控制阀连接.分别采用神华烟煤、龙口褐煤和大同烟煤进行了试验.煤中的碳转化成煤气和烟气的总转化率达到90%以上;冷煤气效率随着窄气/煤比的提高而增加;采用神华煤时焦油产率可达到1.5%;采用龙口褐煤时气化效果较好,在气化炉空气/煤比为0.3 kg/kg时,冷煤气热值为10.7 MJ/Nm3,冷煤气效率为48%.经过分析计算,龙口褐煤产生煤气中的可燃成分主要来自热解.     

红外窗口和整流罩材料研究现状与发展趋势

介绍红外窗口的三个综合性能评价因子:热破裂品质因子、光畸变品质因子、抗热冲击品质因子;并用它们评价了氟化镁、尖晶石、氮氧化铝、蓝宝石、硫化锌和硒化锌、金刚石等主要的红外窗口和整流罩材料;综述其国内外的研究现状,并对其未来的发展趋势发表了自己的观点.     

Low temperature X-ray diffraction study of CdI2 crystals

Solid state structural transformations in polytypic crystals of cadmium iodide have been investigated at low temperatures using X-ray diffraction techniques. The crystals were cooled to liquid nitrogen and liquid helium temperatures employing three different methods. The results obtained are discussed on the basis of bond dissociation energies of interlayer and intralayer bonds and the possible mode of layer displacements in MX₂-type polytypic crystals.     

超声提取-高效液相色谱法测定土壤中联苯胺的含量北大核心CSCD

取干燥的土壤样品5.00 g,用含有1%(体积分数)氨水和50 mg·L^(-1)硫代硫酸钠(防止联苯胺的氧化)的甲醇溶液(作为提取剂)10 mL超声提取30 min,加冰保持温度低于10℃,静置10 min.取上清液2.0 mL,经0.22μm聚四氟乙烯针式过滤器过滤后,以ZORBAX C_(18)反相色谱柱为固定相,体积比25∶75的乙腈-0.01 mol·L^(-1)乙酸铵溶液的混合液为流动相,直接采用附荧光检测器的高效液相色谱法测定其中联苯胺的含量.结果表明,联苯胺的质量浓度在0.50~50.0μg·L^(-1)内与对应的峰面积呈线性关系,检出限为0.20μg·kg^(-1).按标准加入法对空白土壤样品进行回收试验,回收率为75.9%~99.1%,测定值的相对标准偏差(n=6)均小于4.0%.     

Self-assembling of chain molecules in low dimensions: A Monte Carlo study

We studied the self-assembling of linear chain molecules in insoluble monolayers due to attractive interactions. We used lattice Monte Carlo simulations in a two-dimensional system. The molecules consist of segments occupying adjacent lattice sites. The head segments are confined to move along a line whereas the chain segments can arrange in a plane above the heads. Only one interaction parameter is applied. At high densities and small interaction energy the system shows percolation behavior. At moderate and small densities it can be characterized by a monotonous cluster size distribution. Self-assembling occurs at small densities for strong attractive interactions. The corresponding cluster size distributions indicate preferred cluster sizes which depend upon density and interaction strength. With increasing density the clusters grow. The internal cluster structure depends on the cluster size and the interaction parameter. The clusters tend to minimize their total energy. Molecules at cluster margins contribute less to the cluster energy and are mainly disordered. They cause that the cluster properties strongly depend on the cluster size. Large clusters only have minimum energy if the molecules in the cluster are in stretched-out conformation. With decreasing interaction strength the clusters get disordered thereby producing less energy-minimized domain boundaries.     

A Comparative Study of Existing Polytype Notations with Reference to the CdI2 Polytypes

Existing polytype notations have been critically examined to select a single notation which can describe the CdI₂ structures completely and most conveniently. A comparative study shows that the Zhdanov notation fulfils both the conditions. However, the ambiguities in the similar looking symbols is removed by employing some simple criteria proposed by Jain and Trigunayat for deciding the equivalent structures. Further, being numerical in nature this is the easiest notation to handle.