Zur Probenchemie von Stickstoffverbindungen für die emissionsspektrometrische Isotopenanalyse des Stickstoffs

In einer Übersicht werden diewichtigsten Verfahren zurprobenchemischen Aufbereitung ¹⁵N-markierter Verbindungen wiedergegeben. Im Anschluß daran wird eine bewährte Mikormethode zur Probenchemie von Stickstoffverbindungen für die optische Isotopenanalyse des Stickstoffs beschrieben, die auf der Oxydation von Ammoniumchlorid mittels Natriumhypobromit zu N₂ beruht und Stickstoffmengen von etwa · 10^?6 Mol für eine Probe benötigt. Aufbau der Apparatur und Arbeitsweise werden eingehend erläutert.     

“110警车配置及巡逻方案”评阅综述

介绍2009年全国研究生数学建模竞赛D题的命题思路及解题方法,并对评阅结果进行了综合评述.     

Heavy-tailed longitudinal data modeling using copulas

In this paper, we consider “heavy-tailed” data, that is, data where extreme values are likely to occur. Heavy-tailed data have been analyzed using flexible distributions such as the generalized beta of the second kind, the generalized gamma and the Burr. These distributions allow us to handle data with either positive or negative skewness, as well as heavy tails. Moreover, it has been shown that they can also accommodate cross-sectional regression models by allowing functions of explanatory variables to serve as distribution parameters.The objective of this paper is to extend this literature to accommodate longitudinal data, where one observes repeated observations of cross-sectional data. Specifically, we use copulas to model the dependencies over time, and heavy-tailed regression models to represent the marginal distributions. We also introduce model exploration techniques to help us with the initial choice of the copula and a goodness-of-fit test of elliptical copulas for model validation. In a longitudinal data context, we argue that elliptical copulas will be typically preferred to the Archimedean copulas. To illustrate our methods, Wisconsin nursing homes utilization data from 1995 to 2001 are analyzed. These data exhibit long tails and negative skewness and so help us to motivate the need for our new techniques. We find that time and the nursing home facility size as measured through the number of beds and square footage are important predictors of future utilization. Moreover, using our parametric model, we provide not only point predictions but also an entire predictive distribution.     

P110钢CO2腐蚀产物膜的XPS分析

为了确定CO2腐蚀产物膜的组成及不同层次结构中成分和含量的差异,采用P110钢在高温高压腐蚀静态釜中制备CO2腐蚀产物膜,利用SEM观察了腐蚀产物膜的表面和断面形貌,结合XRD分析结果,通过XPS研究了两层结构膜的化学组成差异。结果表明,腐蚀产物膜断面呈现双层结构;膜层的主要成分是FeCO3,还有少量的CaCO3和铁的氧化物,但内层CaCO3较多且夹杂着Fe3C和单质Fe,外层氧化物稍多;通过内外层Ca^2＋含量差异推断出内层腐蚀膜优先形成。     

The Ab Initio Studies of NO Chemisorption on TiO2(110) Surface

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Efficient lasing action from Rhodamine-110 (Rh-110) impregnated sol-gel silica samples prepared by dip method

Rhodamine-110/sol-gel samples are prepared by sol-gel technique using dip method. Concentration dependent photophysical studies of these samples have indicated about the least possibility of aggregate formation. The lasing action of Rh-110 in silica samples is studied as a function of dye concentration. An efficient laser emission is observed when the samples are transversely pumped at 337.1 nm and 1.5 Hz repetition rate using a nitrogen laser (400 μJ energy/pulse and 4 ns pulse duration). The maximum of 166% laser efficiency of dye doped sol-gel samples compared to Rhodamine-6G (Rh-6G) in methanol is achieved. The photostability is also measured by using N₂ laser at 1 Hz and it is found nearly 165 pulses. The possible reasons for the photodegradation of the dye molecules are discussed in detail.     

Short-range order in non-stoichiometric amorphous silicon oxynitride and silicon-rich nitride

By de-convoluting the Si 2p X-ray photoelectronic spectra, it was found that the short-range order in amorphous silicon oxynitride (SiO_xN_y) films with different compositions can be quantitatively described by the random bonding model. In this model the SiO_xN_y consists of five types of randomly distributed tetrahedra and it indicates that metal-oxide-semiconductor transistor with this gate dielectric will not result in any gigantic potential fluctuation in the conduction channel. On the contrary, the structure of silicon-rich silicon nitride SiN_x can only be described by the random mixture model where the local composition fluctuations in this film will result in gigantic potential contra-variant fluctuation.     

Structural change of OH-free fused quartz tube by blowing with hydrogen-oxygen flame

The effect of blowing with a hydrogen-oxygen flame on the structure of an OH-free fused quartz tube was studied by microscopic spectroscopy. The number of OH groups increased within 1000 μm from the outside surface (OSS). The peak decomposition of the IR absorption at around 3600 cm⁻¹ showed that most OH structures were ‘free SiOH’ without the hydrogen bond, and H₂O molecules were also distributed throughout the cross section. The distribution of the fictive temperature, T_F, in the cross section was measured from the peak position of infrared absorption at ≈2200 cm⁻¹. T_F before blowing was ≈1420 K, which is near the strain point, except in the region within 200 μm from the OSS, where T_F steeply decreases approaching the OSS. After blowing, the values of T_F became greater than those before blowing, increasing steeply from the OSS and having a maximum at ≈1000 μm. The steep change near the OSS must be caused by the shorter structural relaxation time due to the SiOH introduced by blowing and H₂O vapor in the flame. The distribution of the intensities of Raman bands at 495 (D₁) and 606 cm⁻¹ (D₂) derived from the planar four- and three-member rings was also measured.     

Temperature dependence of the tribological properties of laser re-melted Al-Cu-Fe quasicrystalline plasma sprayed coatings

The aim of this study was to investigate the effect of temperature on tribological properties of plasma-sprayed Al-Cu-Fe quasicrystal (QC) coating after laser re-melting treatment. The laser treatment resulted in a more uniform, denser and harder microstructure than that of the as-sprayed coatings. Tribological experiments on the coatings were conducted under reciprocating motion at high frequency in the temperature range from 25 to 650 °C. Remarkable influence of temperature on the friction behavior of the coating was recorded and analyzed. Microstructural analysis indicated that the wear mechanisms of the re-melted QC coatings changed from abrasive wear at room temperature, to adhesive wear at 400 °C and severe adhesive wear at 650 °C owing to the material transfer of the counterpart ball. It was also observed that the ratio of the icosahedral (i)-phase to β-Al₅₀(Fe,Cu)₅₀ phase in the coating was higher after test at 400 °C than that at 650 °C. The variation of the ratio i/β of coating and of the property of the counterpart ball and coating with the temperature are the two main factors influencing the wear mechanisms and value of the friction coefficient.     

X-ray absorption and Raman characterizations of TeO2-Ga2O3 glasses

The thermodynamic properties of transparent glasses prepared in the TeO₂-Ga₂O₃ system were investigated by differential scanning calorimetry. The change of the thermal parameters as a function of the chemical composition is discussed. Raman and both Te L_III and Ga K edge X-ray absorption spectroscopies at room temperature were used to examine the short range order. Analyses of the spectra suggest that the addition of Ga₂O₃ content to the TeO₂ glass matrix induces the transformation of trigonal bipyramids (TeO₄E, E=lone electronic pair 5s² of Te) to trigonal pyramids (TeO₃E) with formation of Te-O-Ga bridging bonds. Furthermore, Ga K edge XANES and EXAFS studies show that Ga atoms exhibit both tetrahedral (GaO₄) and octahedral (GaO₆) environments.