水热合成单晶La1-xCaxMnO3系列纳米线

采用水热法,成功地合成了一系列单晶La1-xCaxMnO3(x=0．3、0．5、0．75)纳米线．X射线衍射(XRD)的结果表明所制备的样品是纯的La1-xCaxMnO3正交相(x=0．3、0．5、0．75)纳米线．透射电子显微镜(TEM)的照片清晰地显示所制备的样品是由大量直径均匀(约90nm)、长度从几微米至几十微米的La1-xCaxMnO3的单晶纳米线构成．La0．5Ca0．5MnO3纳米线清晰的高分辨电子显微镜(HRTEM)的图片表明纳米线的表面是光滑的,没有任何缺陷且La0．5Ca0．5MnO3纳米线沿<100>方向生长．La0．5Ca0．5MnO3纳米线磁测量的结果表明相对于块材来说纳米线的Tc有明显地提高,这是由于晶胞收缩和形状各向异性所致．     

水热合成单晶La 1-x Ca x MnO3系列纳米线

采用水热法，成功地合成了一系列单晶La1-xCaxMnO3（x=0．3、0．5、0．75）纳米线．X射线衍射（XRD）的结果表明所制备的样品是纯的La1-xCaxMnO3正交相（x=0．3、0．5、0．75）纳米线．透射电子显微镜（TEM）的照片清晰地显示所制备的样品是由大量直径均匀（约90nm）、长度从几微米至几十微米的La1-xCaxMnO3的单晶纳米线构成．La0．5Ca0．5MnO3纳米线清晰的高分辨电子显微镜（HRTEM）的图片表明纳米线的表面是光滑的。没有任何缺陷且La0．5Ca0．5MnO3纳米线沿〈100〉方向生长．La0．5Ca0．5MnO3纳米线磁测量的结果表明相对于块材来说纳米线的疋有明显地提高，这是由于晶胞收缩和形状各向异性所致．     

Ca掺杂EuMnO3体系的磁性和磁卡效应研究

采用传统的高温固相反应法制备了钙钛矿氧化物Eu1-xCaxMnO3(x=0,0.1,0.2,0.3,0.4,0.5)多晶体系样品。通过样品的XRD谱线、磁化强度随温度、外加磁场的变化曲线(M-T、M-H)等数据研究了Ca不同掺杂量对钙钛矿氧化物EuMnO3系列多晶样品的居里温度、磁熵变、磁相变等的影响。结果表明,Eu1-xCaxMnO3(x=0,0.1,0.2,0.3,0.4,0.5)系列陶瓷样品呈现良好的单相性,空间点群为Pnma。低浓度掺杂的样品存在一个TC,高浓度掺杂的样品出现两个磁转变点,且由于双交换相互作用,随着Ca的掺杂,TC逐渐增大,当掺杂量达到0.4时,低温下的TC却明显减小。根据-ΔSM和RCP值可知,Eu0.7Ca0.3MnO3是该组样品中比较适合做磁制冷的材料。通过对Loop曲线的分析可知该组样品经历了由一级相变向二级相变转变的过程。     

NaZn13型LaFe基室温磁致冷材料研究进展

介绍了LaFe基室温磁制冷材料在制备和磁热效应方面的研究进展.具有NaZn13型结构的LaFe基化合物中含有高的Fe含量,是良好的软磁材料.LaFe基化合物的居里温度可以通过Co取代Fe或添加非金属元素H、C、B等来提高;应用甩带和其他稀土元素取代La可以缩短制备NaZn13的退火时间.通过调整LaFe基化合物的元素配比可能会制备出具有巨磁热效应的室温磁制冷材料.     

La空位掺杂对La-Ca-Sr-MnO_3磁热性质的影响

用溶胶-凝胶法制备了不同空位掺杂的系列样品La_(0.7-x)Ca_(0.28)Sr_(0.02)MnO_3,研究了La~(3+)空位浓度对样品居里温度和磁热效应的影响。结果表明,在La位掺入少量空位(x0.06),可以实现将样品的居里温度有效调整至室温,同时也促进了样品磁熵变的提高。当La空位掺杂x=0.06时,与未空位掺杂样品相比,居里温度由227 K提高到264 K,近室温,其磁熵变值为3.01 J·kg-1·K-1(外加磁场1 T)。该系列样品在室温附近,较低磁场下,有较强的磁制冷能力。     

La0.8-xNdxNa0.2MnO3的磁卡效应研究

用溶胶-凝胶法制备系列样品La0.8-xNdxNa0.2MnO3(x=0.00,0.05,0.10,0.15和0.20)钙钛矿锰氧化物.研究温度范围在240～340 K、外磁场0～1T下该系列样品的居里温度和磁熵变.发现样品的居里温度TC随x增加而减小,而且x=0.20、温度为295K时,最大磁熵变△SM为1.68 J/kg·K.实验结果表明钙钛矿锰氧化物La0.8-xNdxNa0.2MnO3有可能作为室温下的磁致冷材料的候选者.     

(La0.6Dy0.1)Sr0.3MnO3的磁热效应研究

对庞磁电阻材料(La0.6Dy0．1)Sr0.3MnO3的磁热效应进行了研究．通过不同温度下的等温磁化(M-H)曲线的测量和计算，发现伴随铁磁-顺磁(PM—FM)相变出现大的磁热效应，额外的磁性交换作用将导致额外的磁熵变化．结果表明，(La0.6Dy0．1)Sr0.3MnO3可以作为室温下使用的磁制冷工质候选材料．     

La0.7-xNdxBa0.3MnO3纳米颗粒的居里温度与磁热效应

用溶胶-凝胶法制备了La0.7-xNdxBa0.3MnO3(x=0,0.05,0.10,0.15,0.20,0.25)多晶纳米颗粒,用XRD分析其相结构并计算晶格常数,用VSM测量样品的磁性能并计算磁熵变和居里温度.结果表明,La-Ba-Mn-O系列中适当的Nd掺杂可调整材料的居里温度至室温附近并有效提高其磁熵变.文中对于Nd掺杂对居里温度和磁熵变影响的机理进行了定性的分析.     

La0.67-xCa0.33MnO3系列样品的磁热效应

用溶胶-凝胶法制备了不同空位浓度掺杂的La0.67-xCa0.33MnO3系列样品(x=0.00,0.02,0.06,0.10),用扫描电子显微镜(SEM)观察了样品的形态和颗粒大小,X射线衍射实验结果显示样品为单相钙钛矿结构,用振动样品磁强计(VSM)测量了样品的磁化强度随温度变化的M-T曲线和起始磁化M-H曲线.研究了空位浓度对样品的居里温度Tc和磁熵变的影响.结果表明,空位浓度的掺杂将样品的居里温度Tc提高至室温附近,磁熵变得到增强.对于经历了一级相变的样品La0.67-xCa0 33MnO3(x=0.02),在居里温度Tc(277 K)附近和1T外磁场下,最大磁熵变达到了2.78 J/(kg·K).     

La_(0.64)Ca_(0.28)Sr_(0.02)MnO_3材料的磁热性能

用溶胶-凝胶法制备了空位掺杂的La0.64Ca0.28Sr0.02MnO3材料样品,从结构,磁化曲线,磁相变等方面研究分析其具有大磁熵变的原因。在外加磁场1 T时,该样品磁熵变|ΔSM|达到3.01 J/(kg.K),居里温度TC为264 K。该样品低磁场下在室温附近有较强的制冷力,可作为良好的室温磁制冷材料。     

Estimation of Parameters of Universal Distribution of Moments of Failure of Products

A method is proposed for estimating the parameters of a mixture of exponential and Weibull distributions for which the accuracy of preliminary estimates obtained by graphical analysis is refined in accordance with the criterion of maximum likelihood. The efficiency of the proposed method is supported by the results of statistical modeling.     

Evaluation of optical properties of highly scattering media by moments of distributions of times of flight of photons

A novel method for the determination of the optical properties of tissue from time-domain measurements is presented. The data analysis is based on the evaluation of the first moment and the second centralized moment, i.e., the mean time of flight and the variance of the measured distribution of times of flight (DTOF) of photons injected by short (picosecond) laser pulses. Analytical expressions are derived for calculation of absorption and of reduced scattering coefficients from these moments by application of diffusion theory for infinite and semi-infinite homogeneous media. The proposed method was tested on experimental data obtained with phantoms, and results for absorption and reduced scattering coefficients obtained by the proposed method are compared with those obtained by fitting of the same data with analytical solutions of the diffusion equation. Furthermore, the accuracy of the moment analysis was investigated for a range of integration limits of the DTOF. The moment analysis may serve as a comparatively fast method for evaluating optical properties with sufficient accuracy and can be used, e.g., for on-line monitoring of optical properties of biological tissue.     

Analysis of the rate of propagation of the wave of change of boiling modes

An approximate analytical expression is derived for the velocity of the front of the wave of change of boiling modes on a rod and on a plate. The impact of the Thomson effect and of the heater orientation in the gravity field is included. Adequate agreement is demonstrated between the derived relations and experimental data.     

Estimation of potentialities of methods of summation of direct measurement errors

Conventional methods for summation of direct measurement errors are considered. Conditions under which these methods provide consistent results are stated. It is proposed to utilize for characteristic of the total error, its interval estimator or the half-sum of the value obtained by adding up its arithmetic and geometric random errors.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 10–12, April, 1995.     

空压机轴承箱蜗壳温度探头油封改造

由于空压机进气侧轴承箱蜗壳温度探头密封效果不好,使空压机及其后续管道受到油污染。后将温度探头的O形圈密封改为骨架油封,杜绝了轴承箱漏油问题。文章简介空压机的结构和技术参数,详细介绍了骨架油封的制作和优点。     

Characteristics of mechanical properties of materials in studies of conditions of attainment of marginal states

It is shown that conditions of attainment of marginal states in the material of structural components are formulated on the basis of analysis of force and deformation criteria of formation and development of destruction. The parameters of these criteria are data on types of structural materials, standard and special characteristics of their mechanical properties, structural forms of considered elements of the equipment, and their operating stress loading. In this case, the construction of a system of state equations for describing interrelation of current damage, external actions, and responses to them is based on the concept of calculating variations in properties of materials at all stages of the design life cycle.     

Determination of parameters of microstructural inhomogeneity of deformation of metals by the method of modeling

The article suggests a method of evaluating the microstructural inhomogeneity of deformation of metals by modeling. The method includes the measurement of deformations of metal according to meshes of a dividing grid with small base and the calculation of the distribution parameters of microdeformations in model representation. It is shown that the modeling method makes it possible objectively to evaluate the microinhomogeneity of deformation of metals independently of the chosen mesh size of the dividing grid. New structural characteristics are introduced: the base and wave of variation expressing the degree of crumbling or amalgamation of metal grains by inhomogeneity of deformation.Translated from Problemy Prochnosti, No. 7, pp. 40–44, July, 1991.     

水三相点复现的不确定度评定

水三相点是开尔文热力学温度的唯一基准点，也是ITS-90国际温标重要的定义固定点。因此，水三相点不确定度分析对整个温标的建立、温度量值传递起着至关重要的作用。近3年来，中国计量科学研究院研制出一系列高质量的水三相点容器，加强了水三相点的研究，为不确定度的分析提供了更为可靠的实验依据。同时，不确定度的分析也是客观评价新研制容器性能的一个重要指标。因此，根据实验结果对新研制容器所复现的水三相点进行了不确定度评定。评定结果表明，其扩展不确定度为0．16mK(k=2．69，P=0．99)。