地面铷原子钟稳定性和一致性研究

研究了铷原子钟的稳定性和一致性。重点对稳定度的不同表示方法进行了比较,对同一铷原子钟不同寿命时期的稳定性、同一类型多个铷原子钟的稳定性进行了比较,研究了断续工作铷原子钟的频率稳定性、漂移率和一致性。     

浅谈计量标准稳定性的考核方法

本文阐述了根据拟开展的检定项目不同,应采用不同的方法对稳定性进行考核。     

汽轮机汽水系统实时仿真分析

本文利用数字仿真技术对汽轮机汽水系统的稳定性问题进行了非线性数学模型的仿真实验,对比了几种不同结构的系统的稳定性,提出了提高稳定性的方法.同时提出了一种简化的线性化动态数学模型,供方案设计时使用.     

试件-加载系统相互作用对实时子结构试验系统稳定性影响

实时子结构试验将易于建模部分进行数值仿真,剩余部分进行物理试验,从而间接增强了既有设备的试验能力。加载系统与试验试件动力特性的耦合是影响子结构系统稳定性的关键问题。现有稳定性分析方法忽略了其耦合效应对稳定性分析精度的影响。该文建立了作动器、振动台与物理试件间的动力耦合模型,建立了可考虑耦合动力特性的稳定性分析方法,通过试验与理论分析验证了该方法的准确性。基于该方法分别讨论了试件-加载系统相互作用对基于作动器和振动台的子结构试验系统稳定性影响。分析结果表明:试件-加载系统相互作用在不同条件对子结构试验系统稳定性会不同程度的降低或提高,需要特别考虑。     

预应力作用下深基坑桩锚支护结构整体稳定性分析研究

深基坑桩锚支护结构中诸多研究是基于预应力锚杆或基坑稳定性的,对锚杆预应力与基坑稳定性之间的相互影响、相互作用的系统研究并不多见。以此出发,分析桩锚支护结构受力性能,引入附加应力法,将施加于锚杆上的预应力等效为土体中的附加应力,建立考虑预应力作用的深基坑桩锚支护结构整体稳定性计算模型,推导计算公式。并应用于工程实例,与不同方法相对比,结果表明:该文方法能较好地反映出预应力的变化对基坑整体稳定性安全系数的影响,可实时掌握不同施工阶段中基坑安全性的动态变化情况,同时也说明该方法是合理的、可行的。     

静态质量法水流量标准装置微小流量稳定性研究

微小流量稳定性是如今越来越多小口径流量计高准确度测量的基础.本文重点对两种稳压方式(稳压容器和高位水箱)、不同压力下微小流量的稳定性研究.稳定性计算方法依据JJG 164-2000《液体流量标准装置检定规程》中"各累积时间之间流量稳定性的检定方法"进行计算,并对实验结果进行进一步分析.实验结果表明,采用高位水箱稳压,压...     

HPLC外标法测定异香兰素含量及其稳定性研究

目的：测定异香兰素的含量并对其进行稳定性考察。方法：采用HPLC外标法测定异香兰素的含量,通过将样品置于光照、不同温度、湿度下考察异香兰素的稳定性。结果：含量测定方法可行,稳定性考察表明异香兰素在潮湿空气中会缓慢氧化。     

随机缺陷模态法在弦支穹顶稳定性计算中的应用

初始几何缺陷对弦支穹顶的稳定性能有较大的影响。在结构整体稳定性计算中,利用随机缺陷模态法为结构施加合理的初始几何缺陷是该文的主要研究目的。首先采用一致缺陷模态法,在不同初始几何缺陷下,对肋环2型弦支穹顶结构进行稳定性能分析,然后讨论随机缺陷模态中方差的取值方法,并利用该方法对肋环2型弦支穹顶结构进行了210种不同初始几何缺陷下的稳定性能分析,两种分析方法所施加缺陷的最大值均为结构跨度的1/300。分析结果表明:结构的初始几何缺陷对结构的稳定性能影响较大,考虑初始几何缺陷后结构稳定性能为完善结构的50%左右,且采用一致缺陷模态法时也需通过考虑不同缺陷分布形式的多次计算才能合理评估结构的稳定性能,建议在跨度较大、较为复杂的结构中采用随机模态法来考虑初始几何缺陷对结构稳定性能的影响。     

小行星探测器附着碎石层的稳定性分析方法EI北大核心CSCD

小行星探测器在星体表面的稳固附着是探测任务的关键所在。以某型小行星探测器为研究对象,将离散元方法和多体动力学仿真方法相结合,建立了同时考虑缓冲机构作用和碎石层碰撞作用的耦合仿真模型,用来分析小行星探测器在碎石层的附着稳定性。而后,给出了探测器附着稳定性的综合评价参数,并在此基础上,针对典型附着工况,采用耦合仿真模型分析了探测器的附着稳定性。在特定的竖直速度下,通过全因子试验设计方法选取样本点,基于耦合仿真模型的计算结果,利用三阶多项式建立性能评价参数关于不同碎石层坡度、探测器水平速度和偏航角的代理模型,并利用代理模型确定了探测器的附着稳定性边界,分析了不同工况参数下的稳定性边界变化趋势。最后,根据稳定性边界分析结果,确定了三组恶劣附着工况,并在此基础上分析了竖直速度对附着稳定性的影响。该研究方法对于我国未来小行星附着探测任务的顺利开展具有一定的指导意义。     

下肢外骨骼系统稳定性分析和步态控制研究

本文在传统ZMP稳定性判据的基础上对ZMP稳定性判据进行了改进,建立了人的外界干扰因素对系统稳定性的影响的数学模型,然后对下肢外骨骼人机系统的运动过程稳定性进行研究,按最大稳定裕量原则对步态进行优化。为了在不同情况下保持平衡,提出了步幅、调整新的控制措施。通过仿真实例验证了所提出方法的正确可行性。     

几种活性炭吸附剂工作苯容的比较

测定了几种优质活性炭在食品级CO2中的工作苯容（即穿透苯容,穿透指标为苯含量≤0．02×10^-6）,同时观察其在不同温度下的解吸过程。     

空气清新气雾剂中苯系物的安全风险评估

采用气相色谱-质谱法定量分析30批次空气清新气雾剂中苯系物的含量,并通过模拟喷洒试验,采用美国EPA常用的吸入暴露模型进行风险分析.通过比较不同场景下对不同人群的危害程度得出,在车内使用空气清新气雾剂对婴幼儿的危害风险最高.因此,建议有婴幼儿乘坐的车内空间避免使用空气清新气雾剂.     

Transport and fate of volatile organic chemicals in unsaturated, nonisothermal, salty porous media: 2. Experimental and numerical studies for benzene.

Simultaneous transport in soil of heat, water, potassium chloride, and benzene was studied experimentally and numerically. A laboratory experiment permitted observation of temperature, water content, chloride concentration and benzene concentration distributions in soil. A numerical model based upon newly developed transport theory was used to simulate the observed data. Transport of benzene in soils was simulated numerically under isothermal and nonisothermal conditions. Simulated results for benzene were compared with experimental data. Experiments were conducted in sealed aluminum columns (0.05-m I.D. and 0.20-m length) with sterilized salinized unsaturated Fayette soil. The soil had initial water content of 0.22 m(3)/m(3) and initial inorganic solute concentration of 0.20 mol/kg. Benzene was injected at one end of each soil column (top end) to provide 143 g/m(3)gas. The results of this study indicated that transport models need to include the effect of temperature and temperature gradient to describe the movement of volatile chemicals in soils.     

炭包覆TiO2复合物对低浓度苯的光催化降解

通过将TiO2粉末和聚乙二醇混合,随后在氮气气氛下热处理合成了炭包覆TiO2.利用粉末X射线衍射、紫外-可见漫反射光谱、透射电子显微镜和氮吸附对炭包覆TiO2复合物样品进行了表征,并研究了其对浓度为～1.2×10-5苯的光催化活性.结果表明:炭包覆量受热处理温度和聚乙二醇用量的影响,随着温度的升高和聚乙二醇量的减少而减少;TiO2的结晶度随着温度的升高而提高,但是炭包覆对TiO2晶体的生长有抑制作用.炭包覆锐钛矿样品比纯TiO2表现出对苯更高的光催化活性,这是由于炭吸附作用导致锐钛矿颗粒周围的苯浓度增加以及包覆炭可导致电荷的有效分离;另一个原因是锐钛矿相结晶度的提高.因此,要获得对苯具有高光催化活性的炭包覆TiO2需要综合考虑碳含量和锐钛矿晶体结构.

Abstract：

Carbon-coated TiO2 was synthesized by mixing TiO2 powders and polyethylene glycol,followed by heat treatment in nitrogen atmosphere. All samples were characterized by powder X-ray diffraction,UV diffuse reflectance spectroscopy,high-resolution transmission electron microscopy,and nitrogen adsorption. The photocatalytic activity of carbon-coated TiO2 for benzene degradation was investigated with a benzene concentration of ～ 1.2 × 10-5. Results showed that the residual carbon content was influenced greatly by heat treatment temperature (HTT)and the amount of PEG,which decreased and increased with increasing the temperature and the amount of PEG,respectively. The crystallinity of TiO2 was improved when the HTT increased. However,the carbon residue had an inhibition effect on the crystal growth of TiO2. The carbon-coated anatase samples were shown to exhibit higher photocatalytic activities than the pristine TiO2 because of the adsorption enrichment of benzene by carbon around the anatase particles and of the effective charge separation due to the electronic conduction of carbon. Another important factor affecting photocatalytic activity was the crystallinity of the anatase phase. High photocatalytic activity for benzene requires a balance between the carbon content and the anatase crystalline structure.     

Structure of dispersion media by nuclear magnetic resonance

The change of the diamagnetic shielding constant of a benzene molecule interacting with the solid phase surface is calculated.Notation _d diamagnetic shielding constant - e, m_e electron charge and mass, respectively - c speed of light - _b ^o benzene wave function - _m ^o and _m ^o* eigenfunctions of benzene molecule and their conjugates - W_mo matrix elements of the perturbation operator - E _o ^o energy of the ground state of a benzene molecule - e _m ^o energy of the excited states of a benzene molecule - a ₀ Bohr radius Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 41, No. 3, pp. 476–482, September, 1981.     

Environmental stress cracking of PVC: Effects of natural gas with different amounts of benzene

Craze initiation, craze growth and ultimate fracture were studied in PVC (Polyvinylchloride) and PVC-CPE (PVC blend with 10% chlorinated polyethylene) under a constant load in air and in natural gas enriched with benzene. The craze initiation results are similar for PVC and PVC-CPE. The craze initiation stress is decreased dramatically at high benzene concentrations ( 25000 p.p.m.). Preferential and enhanced sorption of benzene molecules near surface inhomogeneities, the craze initiators, are held responsible for this phenomenon. Initial crazegrowth rates in natural gas enriched with benzene increase compared to those in air. However, in all the environments studied, a limited logarithmic craze growth is observed, and growth seems limited to this constant logarithmic interval. The logarithmic craze growth and the termination of craze growth are attributed to a reduction of the stress at the craze tip. The failure mode of PVC and PVC-CPE in air and in gas with 5000–6000 p.p.m. benzene is yielding. A brittle branch appears in the failure curve (failure stress against loading time) in the more concentrated benzene vapours. This branch is attributed to a reduction in the stability of the crazes.     

Toxicity assessment of volatile organic compounds and polycyclic aromatic hydrocarbons in motorcycle exhaust

This study investigates the toxicity of various pollutant species from motorcycle exhaust via dose-response analysis and margin of safety using Escherichia coli DH5 alpha. The toxicity evaluation of the major components of motorcycle exhaust volatile organic compounds (VOCs), collected with impinger, and polycyclic aromatic hydrocarbons (PAHs), collected with filter and XAD-2, is essential to determine emission standards for motorcycles. The toxicity of benzene (B), toluene (T), ethyl benzene (E) and xylene (X) was selected for comparison as standard VOCs emitted from motorcycles. In addition, three types of reformulated gasoline (high oxygenate and high benzene content (No. 1), low oxygen and high benzene (No. 2), and low oxygen and low benzene (No. 3) were prepared to reveal combined toxicity of individual compositions. Motorcycle exhaust is significantly more toxic than BTEX due to the highly toxic VOCs generated from incomplete combustion. Overall toxicity evaluation showed that the toxicity, indicated as EC50, was approximately as follows: PAHs>two-stroke engines>four-stroke engines>BTEX.     

Surface oxygen in the growth of plasma polymerised thin films

Three different types of non-oxygen containing monomers were plasma polymerised into thin films and then studied using X-ray photoelectron spectroscopy (XPS) to determine the surface oxygen content. These three monomers were benzene, ferrocene, and octafluorocyclobutane. Depth profiling was also used to investigate the oxygen content into the bulk of the films by analysing the newly formed film surfaces after different amounts of argon ion sputtering. The initial oxygen concentration on the surface of the ferrocene films was the largest of the three (>20 at.%) while octafluorocyclobutane films had only a small concentration at the surface (∼0.4 at.%). The benzene films had an intermediate concentration (∼4 at.%). Affinity for oxygen on the benzene films is due to residual activated species including free radicals and dangling bond sites on the film surface. Depth profiling showed a rapid reduction of oxygen (to ∼0.2 at.%) a short distance into the benzene films, indicating that the oxygen adsorbed on the surface after film deposition and exposure to the ambient. For the ferrocene films, a substantial amount of oxygen remained with depth, indicating that oxygen was incorporated into the film during deposition. Due to the chemical nature of fluorine, the as-deposited octafluorocyclobutane films did not exhibit significant affinity towards oxygen.     

食品添加剂二氧化碳中苯气体标准物质性能评价方法的研究

介绍了食品添加剂二氧化碳中苯气体标准物质的分析方法和性能评价方法。采用美国Agilent6890N气相色谱仪、FID检测器,在最佳色谱实验条件下对苯的检测限小于10×10^-9,线性误差小于2%。还给出了二氧化碳中苯气体标准物质均匀性、一致性、稳定性（随时间、压力变化）的考察结果。研究成果表明二氧化碳中苯气体标准物质重量配制的相对扩展不确定度小于1.7%。     

基于群论方法的苯分子振动模式研究

苯(C₆H₆)作为大气和室内环境中的主要污染物,具有强烈致癌性,是大气环境主要监测的内容之一。基于群论方法分析建立一种苯分子的泛频跃迁谱线计算方法,利用苯分子简正振动模式与光谱活性,获得30个振动模式的振动频率及其不可约表示。基于D₆点群乘法规则,给出苯分子泛频跃迁的振动模式、光谱活性与谱线位置,为后续精确测量近红外区域苯分子未知谱线跃迁提供了数据与理论支撑。