基于可调谐多模二极管激光吸收光谱的二氧化碳浓度测量

可调谐二极管激光吸收光谱技术(TDLAS)具有高分辨率、高灵敏度和快速测量等特点,是气体探测中的主流技术。使用多模二极管激光器作为光源,将多模二极管激光吸收光谱技术与关联光谱技术相结合有助于提高测试可靠性和稳定性,同时还可有效解决单模二极管激光器长时间工作时中心波长随外界温度或机械特性的变化而发生偏移的问题。以1 570 nm多模二极管激光器为光源,利用多模二极管激光关联光谱和波长调制的气体测量技术(TMDL-COSPEC-WMS),通过计算待测气体和参考池气体之间二次谐波信号峰值高度之间的关系,实现了对二氧化碳浓度的测量。实验中二氧化碳浓度测量范围在0.6%～30%之间,计算结果表明,二氧化碳浓度与真实浓度值之间具有良好的线性关系,其线性度为0.998 7,线性拟合的斜率为1.061±0.016 8。对二氧化碳与氮气混合气体的连续测量结果表明,系统的探测极限达到335 ppm·m,对同一样品在20 min内的20次连续测量的标准偏差为0.036 7%,表明了系统良好的稳定性,所有测量结果都显示了系统用于二氧化碳气体监测的有效性。     

Proton affinities of fluoro derivatives of benzene,toluene, and<Emphasis Type="Italic">m</Emphasis>-xylene from<Emphasis Type="Italic">ab initio</Emphasis> MP2 calculations

The proton affinity (PA) energies of fluoro derivatives of benzene, toluene, andm-xylene were obtained fromab initio MP2-FC/6-31G^* calculations and compared with experimental results. Protonated forms of the molecules, resulting from different ways of proton addition, were studied. Relative concentrations of isomeric arenonium ions were calculated and compared with the results of NMR studies on arenonium ions in solutions. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1847–1849, November, 2000.     

The aggregartion and catalytic activity of amphiphilic calix[4]resorcinolarenes and phenols in hydrolysis of phosphonous esters in water—dimethylformamide media

The amphiphilic calix[4]resorcinolarenes, aminomethylated calix[4]resorcinolarenes, o-aminomethylphenols, and their quaternary derivatives in water—dimethylformamide media (10—75 vol.% DMF) form aggregates, which catalyze the hydrolysis of phosphonous esters. The ability to self-association and the catalytic activity of the aggregates depend on the hydrophobicity of the amphiphilic compound, the pH of solution, and the content of DMF.     

Determination of Small Amounts of Elements by the Atomic Emission Method with Preliminary Concentration of a Sample

The results of ICP spectrometer measurements of low concentrations of lead and copper in aqueous solutions with preliminary concentration of a sample by means of a flow-injection system are presented. A significant decrease in the detection limits of the indicated elements has been obtained. The influence of different methods used for mathematical processing of the results of measurements on the error in determining elements in aqueous solutions has been investigated.     

Cell-by-cell mapping of carrier concentrations in high-temperature superconductors

The correlation between atomic and electronic structure in the vicinity of grain boundaries in YBa₂Cu₃O_7- is investigated on the scale of the coherence length, using a combination of Z-contrast imaging and electron energy loss spectroscopy in the scanning transmission electron microscope. The detector arrangement of the microscope enables both techniques to be performed simultaneously, allowing the exact crystallographic location of the probe to be determined from the image. As the pre-edge feature of the oxygen K-absorption edge is very sensitive to the partial density of unoccupied states, it can be calibrated to give an accurate measure of local hole concentrations (±5%). Spatial resolution is limited only by the 2.2 Å probe size, thus allowing the electronic properties of the material to be inferred on a scale less than the coherence length. Results are discussed from the study of YBa₂Cu₃O_7- films prepared by laser ablation on yttria-stabilized-zirconia (YSZ) substrates, where a symmetric (near 5) grain boundary shows no significant hole depletion in the boundary region, while an asymmetric (near 17) boundary shows depletion extending over a region far greater than the atomic disorder shown in the image. Application of this technique to the study of interfaces in other superconducting systems is discussed.     

Discrete modeling of crack bridging by a discontinuous platelet with a controlled interface

Crack bridging by discontinuous fibers can make brittle materials tougher by transferring stresses from the crack tip to elsewhere in the matrix material. One important aspect of crack bridging is the nature of the interface between the fibers and the matrix material. In this paper, a two-dimensional numerical model of bridging a Mode I loaded crack by linear elastic discontinuous platelets is developed for two different types of interfaces. The first type is a perfectly bonded interface. The second type is an imperfect interface described as a stick–slip interface. A shear-lag model to predict platelet pullout is developed in detail to verify the numerical implementation of the stick–slip interface. An example of a crack tip bridged by a platelet is examined for both interfaces. The perfectly bonded interface will reduce the Stress Intensity Factor (SIF) of the crack greatly but introduces new stress concentrations at the platelet ends. The stick–slip interface can be tailored to also reduce the SIF while not introducing new stress concentrations.     

A study on performance characteristics of granular-media trickling filters

Mass transfer within microbial films is described using Monod type biological kinetics in terms of the properties of packing material and the feed solution. For this purpose computer techniques have been first developed for the numerical evaluation of the normalized biofilm mathematical model. A second-order partial differential equation describing the mechanism of dispersion phenomena inside the liquid layer is then solved to determine the mass transfer coefficient. The application of the theory to experimental data reported in literature has also been demonstrated using the values of mass transfer coefficients and the computer programs developed.     

Non‐Uniform‐Sampling Ultrahigh Resolution TOCSY NMR: Analysis of Complex Mixtures at Microgram Levels

Non‐uniform sampling in combination with homonuclear broadband decoupling along an indirect dimension, and indirect covariance processing are used to record ultrahigh resolution two‐dimensional TOCSY spectra in less than half an hour, for typical sample concentrations in the mm range. TOCSY correlations belonging to protons separated by as little as ≈2 Hz can be distinctly discerned. The utility of the technique for low concentrations has been demonstrated.     

Element concentrations of dry-grind corn-processing streams

The dry-grind corn process is one of two technologies used to convert corn into ethanol. In his process, all kernel components are processed through several sequential steps, including fermentation. Only one coproduct (distillers’ dried grains with solubles [DDGS]) is available for marketing. DDGS provide income to offset costs of processing; issues that affect marketing have implications in the economic viability of dry-grind plants. Two issues relate to elements in DDGS: high concentrations and excessive variation. Data on element concentrations in dry-grind processing streams could be helpful in addressing these concerns. The objective of this study was to determine element concentrations in primary process streams from dry-grind plants. Samples of corn, ground corn, beer, wet grains, syrup, and DDGS were obtained from nine dry-grind plants, and element concentrations were determinined. The concentrations of most elements in corn were not different among processing plants and were similar to published data. However, for the processing streams, there were differences in several element concentrations among processing plants. The concentrations of most elements in beer were about three times those of corn, due to the disappearance of starch during fermentation. Syrup had the highest element concentrations. Variations in element contents of DDGS and parent streams were due to processing conditions and not corn. Appropriate processing of thin stillage (the parent stream of syrup) could reduce the element content of DDGS.     

头发中甲状腺激素和类固醇激素的高效液相色谱串联质谱检测

基于高效液相色谱-串联质谱（HPLC-MS/MS）,开发了一种灵敏、可靠的方法,用于同时测定人类头发中的甲状腺和类固醇激素,包括甲状腺素（T4）、3,3′,5-三碘甲状腺原氨酸（T3）、3,3′,5′-三碘甲状腺原氨酸（rT3）、3,3′-二碘甲状腺原氨酸（3,3′-T2）、L-甲状腺原氨酸（T0）、皮质醇（F）和可的松（E）。头发用量20 mg,使用甲醇/氨水（体积比95∶5）在40℃下孵育24 h。采用电喷雾离子源,在多反应监测模式和正离子模式下进行定量分析。在甲醇/纯水（体积比80∶20,含0.2 mmol/L乙酸铵）的等度洗脱条件下,7种待测物分离良好。该方法检测上述7种激素的检测限在0.3～1.9 pg/mg,定量限在1.1～6.5 pg/mg;日内、日间变异系数均小于10%,回收率在89.4%～109.1%之间;稳定性、残留效应均符合检测标准要求。运用该方法检测140名被试的头发样本,所有被试的T0、F和E均可定量检测,而T4、T3、rT3和3,3′-T2的含量非常低,均在定量限附近,仅在少量被试中可被检出。