低温碱热法制备尖晶石型LiMn2O4纳米棒

以硫酸锰和氢氧化锂为原料,采用碱热法在KOH-NaOH体系中成功地合成了尖晶石型LiMn2O4纳米棒。利用X射线衍射(XRD)和扫描电子显微镜(SEM)对样品的结构与形貌进行了表征,结果表明:反应温度、反应时间和氢氧化锂的用量对产物的结构和形貌有较大影响。     

Ce~(4+)/Ce~(3+)缓冲溶液流动注射电势检测法测定维生素C

以Ce4+ /Ce3 + 氧化还原体系作缓冲溶液 ,用流动注射电势检测法测定了维生素C ,将样品注射于以 0 .1mol/LK2 SO4作支持电解质的Ce4+ /Ce3 + 缓冲溶液试剂流 ,以流通型氧化还原电势检测电极检测维生素C与Ce4+ 反应引起的氧化还原电对的电势变化 ,对 3.0× 10 -4mol/LCe4+ / 3.0× 10 -4mol/LCe3 + 缓冲溶液 ,测定维生素C的线性范围为 1.0× 10 -4～ 6 .0× 10 -4mol/L ,检出限为 1.3× 10 -5mol/L ,相对标准偏差为 0 .36 % (n =4 ) ,分析频率为 12 0次 /小时。     

用计算机程序校正玻璃电极及测定半胱氨酸质子化常数

本文介绍在精密pH电位法测量中用MAGEc计算机程序对玻璃电极进行选择和校正的方法.将该程序和MINIQUAD-82A联合使用,精确测定了L-半胱氨酸在生理条件下(37℃,I=150mmol/L Nacl)的质子化常数:lgβ_(11)=10.149±0.007,lgβ_(12)=18.132±0.012,lgβ_(13)=20.169±0.015.     

Ce^4＋／Ce^3＋缓冲溶液流动注射电势检测法测定维生素C

以Ce4+/Ce3+氧化还原体系作缓冲溶液,用流动注射电势检测法测定了维生素C,将样品注射于以0.1mol/L K2SO4作支持电解质的Ce4+/Ce3+缓冲溶液试剂流, 以流通型氧化还原电势检测电极检测维生素C与Ce4+反应引起的氧化还原电对的电势变化,对3.0×10-4mol/L Ce4+/3.0×10-4mol/L Ce3+缓冲溶液,测定维生素C的线性范围为1.0×10-4～6.0×10-4mol/L,检出限为1.3×10-5mol/L,相对标准偏差为0.36%(n=4),分析频率为120次/小时.     

抗癌药物3-吖啶氨基-5羟甲基苯胺(AHMA)的晶体结构分析

本文用X射线晶体衍射法分析了抗癌药物3-吖啶氨基-5羟甲基苯胺(3-(9-acridiny-lamino)-5-(hydroxymethyl)aniline,AHMA)的分子结构。AHMA的化学式为C_(20)H_(17)N_3O,Mr=315.37。晶体属三斜晶系,空间群为P-1。晶胞参数晶胞参数:α=8.043(2),b=9.949(2),c=11.631(3)A,α=69.78(1)°,β=84.02(1)°,γ=65.70(1)°。经最小二乘修正后得到的R_1值为0.051。在晶体结构中,吖啶环和苯胺环几乎相互垂直,两个环平面之间的两面角为66.5°。这种结构有利于AHMA以嵌插于DNA碱基对的形式与DNA结合。     

谈谈设备利用率的综合考核问题——和吴恒国同志商榷

本刊1992年第10期刊登了吴恒国同志“从设备的经济效益看设备的利用率”一文,从经济效益的角度,对设备利用率进行了探讨。并提出设备利用率计算公式如下: U=T(u)×A(u)×100％ 式中:U——设备利用率T(u)——设备时间利 用率 T(u)=t_1/t_2 × 100％ A(u)——设 备固有能力利用率 A(u)=A_0/A×100％ 其中:t_1——设备有效工作的台时数 t_2——按规定制度设备应工作的台时数 A——在某种条件下设备能达到的最大工 作能力 A_0——在相同条件下设备的实际利用能力 笔者认为,按这一计算不能全面反映设备利用率和经济效益的关系,应该说设备利用率是设备运行生产产品时达到的产值与理论设计产值的比值。如两者相等,设备利用率为100％,但实际上,由于设备在运行过程中有各种各样的损失,要达到100％利用率是     

机床零件的袖珍计算机计算程序(八)

螺旋齿轮传动的几何计算 1.概述 机床用螺旋齿轮传动,通常轴交角δ=90°,机床设计中所用轴交角为90°的螺旋齿轮传动用改变螺旋角的办法来配凑中心距。已知:Z1,Z2,ma,A。求βf1,βf2 由于[2]第200页5.4.—49式: 是含βf1的一元函数的超越方程。用计算机数值计算方法解方程:简单,快速,准确。 程序运行后输出所求参数:βf1,βf2并输出齿顶圆直径,分度圆直径,公法线长度和跨齿数。2.变量表(表1-10) 3.螺旋齿轮传动的几何计算框图(图1-13) 4.原程序 5.计算实例及按键操作步骤 [例]:已知一对螺旋齿轮传动参数为:δ=90°,mn=2mm,Z1=18,Z2=54,A=…     

元素分析-同位素质谱测定蜂蜜中碳-4植物糖含量的能力验证结果与分析

目的:为了评价实验室检测蜂蜜中碳-4植物糖含量的技术能力和水平,设计和组织了蜂蜜中碳-4植物糖含量测定的能力验证项目。方法:评价考核的样品中δ^(13)C_(h)值和δ^(13)C_(P)值的均匀性、稳定性,保证考核的样品在整个计划周期内稳定、满足能力验证要求的。通过本次能力验证计划的实施,采用Z比分的法来对11个省、直辖市的19家实验室的测定能力和结果进行评判。结果:在参加能力验证的实验室中,δ^(13)C_(h)和δ^(13)C_(P)首次测定的满意率为78.9%,后补测总体满意率为94.7%。结论:参加实验室中大多数检测能力结果是满意的,这表明蜂蜜中碳-4植物糖含量测定水平总体良好。通过对离群结果的技术分析,也可以帮助实验室查找实验误差原因并进行整改。     

光学膜吸收率与散射率测量台

西德LEYBOLD-HERAEUS高真空技术公司研究与生产一种名叫“LAMABS”的激光测量台,用于测定光学膜层的吸收与散射,其测量精度已达到吸收率A=士0.01％,散射率S=±1×10~(-5)。测量台的测量原理如下: ①吸收测量原理: 被测量样品用足够功率的氩离子激光器(输出功率约为1瓦)照射后,对由于吸收而产生的温升进行测量,就可直接测得介质反射镜的吸收。温升可用电阻温度计     

B_4C-SiC复相陶瓷的制备与性能

采用粒径为10.22μm的B_4C粉和粒径为1.07μm的β-SiC粉,通过球磨混合后用真空热压烧结工艺,在1 900～2 100℃制备了纯B_4C陶瓷和B_4C-20%SiC复相陶瓷,并进行了相结构分析和力学性能测试。结果表明:SiC的添加对B_4C陶瓷的致密度影响不大,当烧结温度为2 100℃时,纯B_4C陶瓷和B_4C-20%SiC复相陶瓷的相对密度分别为87.9%和87.0%;孔隙率显著地影响B_4C基陶瓷的力学性能,抗弯强度σ_w与孔隙率θ的关系符合公式σ_w=257exp(-2.18θ)。     

Measurement and optimization of atmospheric plasma sprayed CoMoCrSi coatings parameters on Ti-6Al-4V substrates affecting microstructural and properties using hybrid abductor induction mechanism

A hybrid artificial intelligence method (AIM) is used to optimize the atmospheric plasma spraying (APS) processing parameters for CoMoCrSi coatings deposited on Ti-6Al-4V substrates. In the proposed approach, the Taguchi design method is used to obtain an initial solution for the optimal set of APS parameters. The true optimal values of the spray distance, chamber pressure, current, argon gas flow rate and hydrogen gas flow rate are then obtained using an artificial neural network (ANN) and genetic algorithm (GA). The coatings deposited using the processing parameters determined using the Taguchi design method alone have a porosity of 8.5%. However, following the ANN/GA optimization procedure, the porosity reduces to just 5.6%. The XRD analysis results show that the as-sprayed coatings contain Cr₃Si phase as a result of the high-temperature plasma flame. In addition, it is shown that the structure of the Ti phase in the coating transforms from a α-Ti crystal structure (i.e., HCP) to a β-Ti crystal structure (i.e., BCC) during thermal treatment at temperatures to 1200 °C. Finally, it is shown that the hardness of the annealed coatings increases with both an increasing annealing time and an increasing annealing temperature. The higher hardness under higher temperature conditions is attributed to the precipitation of Cr₃Si phase. Overall, the coatings obtained in the present study using the optimal spray-coating parameters have a low porosity, a high hardness and a good thermal stability at high temperatures.     

Effects of Temperature and Humidity on the Characterization of C-4 Explosive Threats

Both the quantity and the amount of time that an explosive is present on the surface of a material is dependent upon the amount of explosive originally deposited on the surface, the adhesive forces, temperature and humidity, as well as other environmental factors. This laboratory study focused on evaluating RDX crystal morphology changes resulting from variations in temperature and humidity conditions of the sample. The temperature and humidity conditions were controlled using a Tenney THRJ environmental chamber and a Tenney T11RC-1.5 environmental chamber. These chambers allow the temperature and humidity to be held within ±3?°C and ±5?% RH. The temperature and humidity conditions used for this test series were: 4?°C/40?%RH, 21?°C/20?%RH (samples left on benchtop), 21?°C/70?%RH, 21?°C/95?%RH, 35?°C/40?%RH, 35?°C/70?%RH, and 35?°C/95?%RH. These temperature and humidity set points were chosen to represent a wide range of conditions that may be found in real world scenarios. C-4 (RDX crystals and binder material) was deposited on the surface of one of six substrates by placing a fingerprint from the explosive block onto the matrix surface. The substrates were chosen to provide a range of items that are commonly used. Six substrate types were used during these tests: 50?% cotton/50?% polyester as found in T-shirts, 100?% cotton with a smooth surface such as that found in a cotton dress shirt, 100?% cotton on a rough surface such as that found on canvas or denim, suede leather such as might be found on jackets, purses, or shoes, painted metal obtained from a car hood, and a computer diskette. The samples were not pre-cleaned prior to testing and contained sizing agents, and in the case of the metal: oil, dirt, scratches, and rust spots. The substrates were photographed at various stages of testing, using a Zeiss Discover V12 stereoscope with Axiocam ICc1 3 megapixel digital camera, to determine any changes in the crystalline morphology. Some of the samples were examined using scanning electron microscopy and atomic force microscopy in an attempt to determine how the explosive was bound to the substrate. This is the second article in a series on the effects of temperature and relative humidity on trace explosive threats.     

Epifluorescence microscopy study of a quadruple node of triple junctions of grain boundaries in a Eu2+‐doped Kcl:Kbr solid solution by using the doping ion as a fluorochrome

A typical quadruple node (QN) of triple junctions (TJs) of grain boundaries (GBs) in a Eu²⁺‐doped KCl_0.52Br_0.48 solid solution is investigated from the geometrical point of view by epifluorescence microscopy using the doping ion as a fluorochrome. The excitation and fluorescence optical properties of the fluorochrome were previously characterised by spectrophotometry whereas the structural nature of the studied material as well as its Bravais lattice type, unit cell size and long‐range translational order degree was determined by X‐ray diffraction. A three‐dimensional reconstruction was built from the microscopy images of different optical cross‐sections of the studied arrangement of crystal defects. In the close vicinity of the QN, the studied arrangement of crystal defects adopts the geometry of a collapsed tristetrahedron which, centred at the QN, has its legs along the TJs and, hence, has its faces as collapsed in pairs into the GBs. The angles defined by different TJ couples as well as the dihedral angles defined by the different GB couples meeting in every TJ were measured at the QN site. All, the image recording and stacking as well as the measuring procedures are carefully described. The measured TJ angles (97°, 117°, 95°, 117°, 99° and 130° ± 2°) depart from the characteristic angle (109.47°) of a tetrahedron whereas the measured GB angles (101°, 119°, 140°; 125°, 127°, 108°; 133°, 109°, 119°; 129°, 99° and 132° ± 2°) depart from the angular argument (120°) of a 3‐fold symmetry rotation indicating that, in the close neighbourhood of the QN, the studied arrangement of crystal defects is structurally unstable. Such an instability is associated with an observed mismatch in orientation (by angles of 20°, 15°, 33° and 30° ± 2°) between the TJs and some <111> zone axis matrix lattice crystallographic directions ([], [11], [11] and [11]), respectively). Local variations in anionic composition, existing within the solid solution matrix, are discussed to be responsible for this mismatching and, therefore, for the observed structural instability.     

Electron microscopic studies of CuS nanocrystals formed in Langmuir-Blodgett films

The morphology and structure of CuS crystals formed during sulfidation of copper behenate films obtained by the Langmuir-Blodgett (LB) method have been studied using high resolution electron microscopy. The average size of these crystals is about 3 nm and increases by a factor of approximately 2.2 after annealing at a temperature of 150 °C or above. Analysis of interplanar distances has shown that in the range of annealing temperatures of 150–200 °C, CuS nanocrystals have a P6_3/mmc hexagonal crystal lattice with parameters a = 0.38 nm and c = 1.64 nm. At annealing temperatures of 250 °C or above, the Cu₂S crystalline phase begins to form, in addition to CuS nanocrystals. The proportion of this phase increases with increasing annealing temperature. Cu₂S nanocrystals have a hexagonal crystal lattice type with the P6_3/mmc spatial group and unit cell parameters a = 0.39 nm and c = 0.68 nm. Quantitative evaluation of copper and sulfur in individual CuS and Cu₂S nanocrystals was performed by local analysis of characteristic X-ray spectra.     

Trigonal catalase crystals: a new molecular packing assignment obtained from sections preserved with tannic acid

The molecular packing of a trigonal crystal form of catalase initially studied by Longley [1] has been re-evaluated. Sections of crystals fixed and preserved with tannic acid were obtained parallel to the (001) and (100) planes. Specimens prepared by either conventional or low temperature embedding maintained 20 A resolution after sectioning. The space group of the crystals is either P3(1)21 or P3(2)21 and the observed unit cell parameters for (001) and (100) are a = b = 174 A, gamma = 119 degrees and b = 189 A, c = 248 A with alpha = 89.5 degrees. Computer-based reconstructions of two principal projections coupled with crystal density measurements allowed the deduction that there is one catalase tetramer per asymmetric unit. The crystal structure consists of 6 molecules packed closely about a common triad screw axis. This interpretation differs from that proposed by Longley [J. Mol. Biol. 30 (1967) 323], because thin sections of embedded crystals were assumed a priori to be positively stained in the early work; in actuality the sections were negatively stained. We also demonstrate that tannic acid fixation can lead to well preserved, positively stained crystal sections under certain conditions.     

Acoustical properties of a long rectangular cavity of constant cross-section immersed in a thick boundary layer

An experimental investigation was undertaken to examine the effect of cavity length on flow oscillations produced by an open cavity placed within a subsonic turbulent boundary layer. A narrow rectangular cavity with a constant width to depth ratio, W/D, of 1 was placed within a thick fully developed turbulent boundary layer with a corresponding Re_θ=10.5×10³. Pressure time histories were acquired for six separate cavity lengths (or L/D values) using microphone type pressure transducers. The spectral character of these signals was analyzed in terms of their magnitude and frequency content. This study indicates that large changes in the fluctuating pressure level can occur as L/D is varied from 1.47 to 8.73. A state of acoustic resonance was only observed at L/D=1.47, while fluid-acoustic resonance occurred at L/D between 1.47 and 8.73. Relative SPL calculations indicate that energy within the cavity was increased by approximately 60% over this L/D range. It is also suggested that this increase was a result of vortical structure shedding and growth. In addition, the location of maximum unsteadiness was estimated to coincide with the location of vortical structure saturation.     

单晶硅料摆辅助多金刚线切片的锯切力模型研究

料摆辅助多金刚线切片技术是实现硬脆材料高精高效加工行之有效的工艺技术,探明其工艺参数、锯切力和切片质量的定量关系,具有重要的现实意义。在研究金刚线运动轨迹的基础上,推导了考虑线弓影响的切割长度变化公式;结合压痕断裂力学和试验研究,建立并验证了料摆辅助切片的锯切力模型。开展了不同工艺参数对锯切力的影响分析,结果表明,料摆辅助加工可以降低锯切力近50%;摆动角度对最大切割力的影响较小,但摆角增大会加剧"锯齿形波动"周期内的锯切力极值幅度,摆动角速度对"锯齿形波动"的周期影响较大;在恒定进给速度条件下,进给速度越高,锯切力越大;在变速进给条件下,最大锯切力可降低12%左右。进一步进行了摆角分别为0°、3°、5°和7°的多金刚线切割单晶硅实验,试验表明,料摆辅助切片加工有助于减少硅片表面因脆性崩裂产生的表面材料破损、深凹坑等缺陷;相较于普通切片加工,在摆角5°工况时,工件的表面粗糙度和硬化层厚度最大分别降低30.1%和20.1%。     

X射线椭圆弯晶谱仪实验研究

利用椭圆从一个焦点发射出的光线经椭圆面反射必汇聚于另一焦点的性质,设计了基于620～6200eV的X射线椭圆弯晶谱仪.文中分析了系统原理,完成了谱仪光学色散系统、探测系统及仪器的研制.采用KAP、LiF、PET、MiCa作为色散元件,其2d值在0.4～2.6nm、Bragg角为30°～67.5°,晶体尺寸为120×8×0.2mm,偏心率为0.9586,焦距1350mm,光程长1456mm,分析器基底材料用数控铣床加工.实验在上海"神光Ⅱ"号装置上实施,激光能量为150J,波长为0.35mm,真空度为3×10^-3Pa.为达到光学对准,采用了小点光源以及精密望远镜对中.实验结果显示出金靶在0.63～0.79nm范围,其分辨力(△λ/λ)达到了1/486.谱的分辨力还与晶体特征和激光靶源尺寸有关.谱仪性能良好、使用方便、简单,具有高的收集效率和分辨能力,能够有效获取激光惯性约束聚变中激光等离子体发射光谱的丰富信息.     

A study of Ar + C2H4 and Xe + CF4 gas mixtures

Mixtures of Ar + 40 ppm C₂H₄ and 50% Xe + 50%CF₄ have been investigated. The spatial distributions of photoelectron clouds produced by primary scintillations on α- and β-particle tracks, as well as the distributions of photoelectron clouds due to photons from avalanches at the pin anode, have been measured for the first time. For a mixture of 50% Xe + 50%CF₄, it has been shown for the first time that CF₄ is a photosensitive dopant in a mixture with Xe. For a mixture of Xe + CF₄ (1: 1), the maximum electron multiplication factors at the pin anode are K(β)^max = 3 × 10⁴ and K(α)^max = 3 × 10³ at a pressure of 1 atm (abs.) and K(β)^max = 10⁴ and K(α)^max = 4 × 10³ at a pressure of 10 atm (abs.)