Neutron activation analysis of trace elements in cataracts

The knowledge of the role of trace elements is a necessary condition for the investigation of cataract etiopathogenesis. The deposition of trace elements in eye lens may be influenced by many vital factors and, therefore, the effect of sex, age and locality on the content of these elements was investigated. The determinations of elements were carried out by instrumental neutron activation analysis, and the results were evaluated with the aid of statistical tests. The effect of locality being taken as a set of local ecological factors has been proved as a dominant factor.     

Determination of Homoisoflavonoids in Ophiopogon japonicus by RP-HPLC

The homoisoflavonoid content of 14 samples of Ophiopogon japonicus collected from different parts of China have been investigated. Three principal homoisoflavonoids, methylophiopogonanone A, methylophiopogonanone B, and 6-aldehydo-isoophiopogonanone A, were analyzed simultaneously by reversed-phase high-performance liquid chromatography with a binary mixture of acetonitrile and 0.3% aqueous acetic acid as mobile phase. The recovery of the method was 98.5–102.6% and good linearity (r > 0.9990) was obtained for all the homoisoflavonoids over a relatively wide concentration range. The results indicated that the homoisoflavonoid content of Ophiopogon japonicus varied significantly from species to species, and from locality to locality. The quality and identity of Ophiopogon japonicus from the herb market can be determined from the homoisoflavonoid content.     

The pore structure in processed Victorian Brown coal

Changes in the pore structure of Victorian Brown coal when upgraded with heated gases under pressure are investigated. We show that the results obtained from ultra-small-angle neutron scattering (USANS) measurements agree with previous results using small-angle X-ray scattering results but that USANS may also be used to investigate the meso porosity. Findings from small-angle scattering are confirmed using electron microscopy. We also show evidence from electron diffraction that thermal conditions within the brown coals during the upgrade procedure may be far more extreme than previously thought.     

大黄酸铜(Ⅱ)配合物与血清白蛋白的相互作用

采用荧光光谱法和紫外光谱法研究了大黄酸铜配合物与牛血清白蛋白之间的相互作用.大黄酸铜配合物能显著猝灭牛血清白蛋白的内源荧光并以静态猝灭为主;计算了298 K和309 K温度下结合常数、结合位点,根据热力学参数判断大黄酸铜配合物与牛血清白蛋白之间具有较强的疏水作用力;依据F?rster的偶极-偶极非辐射能量转移理论,计算出大黄酸铜在蛋白质中结合位置与色氨酸残基间的距离为3.21 nm, 表明大黄酸铜的部分片段能够插入蛋白质分子内部;用同步荧光光谱和圆二色光谱技术探讨了大黄酸铜对牛血清白蛋白构象的影响.     

Synthesis of colloidal nanoscaled copper-indium-gallium-selenide (CIGS) particles for photovoltaic applications

In this work, Cu(In,Ga)Se(2) (CIGS) nanoparticles were synthesized using a wet chemical method. The method is based on a non-vacuum thermal process that does not use selenization. The effects of temperature, source materials, and growth conditions on the phase and particle size were investigated. X-ray diffraction results confirm the formation of a tetragonal CIGS structure as the main phase with the purity more than 99% obtained by energy-dispersive X-ray spectroscopy (EDX). The morphology and size of the samples were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Using these methods, 20-80nm particles were obtained. Through measurements of the absorption spectra of CIGS nanoparticles, the band gap of the synthesized material was determined to be about 1.44eV, which corresponds to an acceptable wavelength region for absorber layers in solar cells.     

Surface modification of nanoclays by catalytically active transition metal ions

A unique class of nanoclays was prepared by modification of pristine clays or organoclays (Cloisite C20A) with transition metal ions (TMIs). The composition, structure, morphology and thermal properties of TMI-modified nanoclays were investigated by atomic absorption spectroscopy (AAS), elemental analysis (EA), scanning electron microscopy (SEM), small-angle X-ray scattering (SAXS), wide-angle X-ray diffraction (WAXD), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC) and X-ray absorption near-edge structure (XANES) spectroscopy. The content of TMIs in modified clays was found to be close to the limiting value of ion exchange capacity. SEM and X-ray results confirmed that TMIs were located between the mineral layers instead of being adsorbed on the surface of clay particles. TGA results indicated that the TMI treatment of organoclays could significantly increase the thermal stability, which was more pronounced in air than in nitrogen. Temperature-resolved SAXS measurements revealed that the presence of TMIs increased the onset temperature of structural degradation. The higher thermal stability of TMI-modified organoclays can be attributed to the change in the thermal degradation mechanism, resulting in a decrease in the yield of volatile products and the formation of char facilitated by the presence of catalytically active TMIs.     

Locality of exchange matrices for common Gaussian basis sets

This article investigates a new approach to local approximations to exchange. When a finite basis set is introduced, any operator may be regarded as equivalent to a local operator if its matrix can be reproduced as the matrix of a multiplicative function operator. The expectation values of such operators can be determined from the electron density. Any matrix can be divided into local and nonlocal components, in a way dependent on linear dependencies among basis-set products. A measure of locality is provided by the ratio of the norm of the local component to that of the whole matrix. The local contribution to an expectation value can also be compared with the total. The self-consistent field exchange matrices and their expectation values for atoms Li through Ne and for LiH and HF with several Cartesian Gaussian basis sets were investigated in this way, and for the atoms, the exchange supermatrix was also examined. It has been found in all cases that the matrices and expectation values are more than 92% local; most are more than 99% local. © 1997 John Wiley & Sons, Inc.     

Thermal behaviour of corn starch granules under action of fungal α-amylase

Corn starch, partially hydrolyzed by fungal α-amylase was investigated by using thermal analysis, microscopy and X-ray diffraction. After enzymatic treatment lower degradation onset temperatures were observed. DSC analysis showed almost similar range of gelatinization temperature, however, the enthalpies of gelatinization increased for the partially hydrolyzed starch granules. According to the X-ray diffraction analysis, stronger cereal pattern peaks were recognized after enzymatic digestion. The results suggested that the hydrolysis was more pronounced in the amorphous part of the starch granules.     

In situ phosphorus K-edge X-ray absorption spectroscopy studies of calcium–phosphate formation and transformation on the surface of bacterial cellulose nanofibers

In this work, for the first time, in situ formation and transformation process of embryo calcium phosphate (Ca–P) minerals on three-dimensional bacterial cellulose nanofibers was investigated. Combined with XRD, X-ray absorption near-edge structure results revealed that the embryo precursor was amorphous calcium phosphate which was subsequently converted to β-tricalcium phosphate, octacalcium phosphate, and finally to the more thermodynamically stable form of hydroxyapatite. The methodology reported herein may be extended to the studies of Ca–P and other minerals on various substrates.     

Application of large-area avalanche photodiodes to X-ray spectrometry of muonic atoms

Large-area avalanche photodiodes have been investigated as 1.9-keV X-ray detectors for the muonic hydrogen Lamb-shift experiment. We report experimental tests carried out for evaluation of the avalanche photodiode capabilities for X-ray detection in the intense radiation and low counting rate environment of experiments with muonic atoms. Several muonic atoms were used and it was shown that the electronic background of muonic atom X-ray spectra can be reduced simply by timing the X-ray signal against the gate signal produced by the muon entrance. Furthermore, the background can be eliminated using coincidences between the X-ray signal and the signal resulting from the electron due to the muon decay. This coincidence discrimination results, however, in a reduction of the X-ray detection efficiency.     

Geometric structure determination of N694C lipoxygenase: a comparative near-edge X-ray absorption spectroscopy and extended X-ray absorption fine structure study

The mononuclear nonheme iron active site of N694C soybean lipoxygenase (sLO1) has been investigated in the resting ferrous form using a combination of Fe-K-pre-edge, near-edge (using the minuit X-ray absorption near-edge full multiple-scattering approach), and extended X-ray absorption fine structure (EXAFS) methods. The results indicate that the active site is six-coordinate (6C) with a large perturbation in the first-shell bond distances in comparison to the more ordered octahedral site in wild-type sLO1. Upon mutation of the asparagine to cysteine, the short Fe-O interaction with asparagine is replaced by a weak Fe-(H(2)O), which leads to a distorted 6C site with an effective 5C ligand field. In addition, it is shown that near-edge multiple scattering analysis can give important three-dimensional structural information, which usually cannot be accessed using EXAFS analysis. It is further shown that, relative to EXAFS, near-edge analysis is more sensitive to partial coordination numbers and can be potentially used as a tool for structure determination in a mixture of chemical species.     

An increase of utilization efficiency of X-ray beam

The features of absorbed dose field formation in objects irradiated with scanned X-ray beams at double—and four-sided irradiation were investigated both analytically and by Monte Carlo methods. An analytical approach uses an angular/spectrum X-ray characteristics calculated with PENELOPE, JEANT 4 and ModeXR codes. It was shown that the special angular orientation of electron beam incidence on the X-ray converter leads to X-ray dose smoothing on the surface of the irradiated object. At the same time, a double-sided irradiation can provide high X-ray beam efficiency at dose uniformity ration (DUR) <1.5 for sizeable object thickness. At four-sided irradiation, the angular orientation of electron beam incidence on the X-ray converter should be changed so as to focus the electrons to the center of the converter. At this mode X-ray beam efficiency is more than 60%.     

The Dirac equation in quantum chemistry: strategies to overcome the current computational problems

A perspective on the use of the relativistic Dirac equation in quantum chemistry is given. It is demonstrated that many of the computational problems that plague the current implementations of the different electronic structure methods can be overcome by utilizing the locality of the small component wave function and density. Possible applications of such new and more efficient formulations are discussed.     

高性能Bi3+掺杂改性PbO2电极的制备及表征

采用电沉积法制备了金属Bi3+改性PbO2(Bi-PbO2)电极,并通过扫描电镜(SEM)、X射线能谱(EDS)、X射线光电子能谱(XPS)、X射线衍射(XRD)、紫外-可见漫反射(UV-VisDRS)、荧光光谱(FP)、莫特-肖特基(Mott-Schottky)曲线、电化学阻抗谱(EIS)和线性极化扫描(LSV)等方法表征了其微结构和电化学性能.SEM、EDS和XPS结果表明,Bi3+以Bi2O3的形式掺杂进入PbO2镀层,同时其掺杂改性可明显改善PbO2镀层的微结构,使电极表面颗粒细化;XRD和UV-VisDRS分析结果显示Bi3+掺杂改性后,PbO2晶体的晶胞参数发生变化,同时禁带宽度(Eg)变小;荧光光谱分析表明Bi-PbO2电极可促进羟基自由基的产生,增强电极降解有机物的催化活性;电化学性能测试显示,Bi3+改性PbO2电极电催化活性的提升与电极的平带电势(Efb)负移、活性表面积增大、电化学反应电阻减小和析氧电位提高有关.     

Thermoanalytical investigation of cavity filling natrolite group minerals in basalts

Cavity filling natrolites in basalts from several localities of Balaton Highland were investigated by different methods. The measurements of different thermal parameters (corrected decomposition temperature and activation energy) were first applied for natrolite. Energy dispersive spectroscopy (EDS) was used for the observation of chemical composition. Few of the minerals are regular, ordered natrolite, the majority proved to be so called ‘tetranatrolite’. According to our observations both natrolite and ‘tetranatrolite’ may appear in the same locality and chemical inhomogenity can be demonstrated within a single natrolite needle.     

Decomposition pathways of Z-selective ruthenium metathesis catalysts

The decomposition of a Z-selective ruthenium metathesis catalyst and structurally similar analogues has been investigated utilizing X-ray crystallography and density functional theory. Isolated X-ray crystal structures suggest that recently reported C-H activated catalysts undergo decomposition via insertion of the alkylidene moiety into the chelating ruthenium-carbon bond followed by hydride elimination, which is supported by theoretical calculations. The resulting ruthenium hydride intermediates have been implicated in previously observed olefin migration, and thus lead to unwanted byproducts in cross metathesis reactions. Preventing these decomposition modes will be essential in the design of more active and selective Z-selective catalysts.     

Methods for Characterizing the 3-D Morphology of Polymer Composites

3-dimensional visualization of polymer morphology is of increasing interest in the polymer community because it provides a deeper insight into the arrangement of the phases in heterophasic polymeric materials, for example in composites. Depending on the size of the fillers, an adequate method offering a good compromise between suitable resolution and observable volume must be selected. Different polypropylene composites filled with long glass fibres, mica and talcum particles were investigated. Four methods were applied to account for the different filler sizes. For composites containing fillers larger than several micrometers, i.e. glass fibres and mica particles, X-ray tomography offers a very good combination of visibility and volume. Serial sectioning by polishing in combination with light optical microscopy can be an alternative if no X-ray equipment is available. This combined method has the disadvantage, however, that the imaged volume is smaller and involves more effort, which makes it unsuitable for routine observations. The much smaller talcum particles with thicknesses down to 200 nm were investigated by coupling focused ion beam (FIB) milling and scanning electron microscopy (SEM) and by insitu ultramicrotomy in the SEM. Both methods led to good and comparable results.     

Recent results of synchrotron radiation induced total reflection X-ray fluorescence analysis at HASYLAB,beamline L

At the Hamburger Synchrotronstrahlungslabor (HASYLAB), Beamline L, a vacuum chamber for synchrotron radiation-induced total reflection X-ray fluorescence analysis, is now available which can easily be installed using the adjustment components for microanalysis present at this beamline. The detector is now in the final version of a Vortex silicon drift detector with 50-mm² active area from Radiant Detector Technologies. With the Ni/C multilayer monochromator set to 17 keV extrapolated detection limits of 8 fg were obtained using the 50-mm² silicon drift detector with 1000 s live time on a sample containing 100 pg of Ni.Various applications are presented, especially of samples which are available in very small amounts: As synchrotron radiation-induced total reflection X-ray fluorescence analysis is much more sensitive than tube-excited total reflection X-ray fluorescence analysis, the sampling time of aerosol samples can be diminished, resulting in a more precise time resolution of atmospheric events. Aerosols, directly sampled on Si reflectors in an impactor were investigated. A further application was the determination of contamination elements in a slurry of high-purity Al₂O₃. No digestion is required; the sample is pipetted and dried before analysis. A comparison with laboratory total reflection X-ray fluorescence analysis showed the higher sensitivity of synchrotron radiation-induced total reflection X-ray fluorescence analysis, more contamination elements could be detected. Using the Si-111 crystal monochromator also available at beamline L, XANES measurements to determine the chemical state were performed. This is only possible with lower sensitivity as the flux transmitted by the crystal monochromator is about a factor of 100 lower than that transmitted by the multilayer monochromator. Preliminary results of X-ray absorption near-edge structure measurements for As in xylem sap from cucumber plants fed with As(III) and As(V) are reported. Detection limits of 170 ng/l of As in xylem sap were achieved.     

Ce0.5-xZr0.5-xBa2xO2负载TiO2光催化降解气相苯

在密闭不锈钢反应器内研究了Ce0.5-xZr0.5-xBa2xO2负载锐钛型TiO2光催化降解气相苯的性能.确定了该系列光催化剂的最佳Ba含量,并应用X射线衍射、紫外-可见漫反射光谱以及X射线光电子能谱对催化剂进行了表征.结果表明,TiO2在载体表面均匀分散.在210~400 nm范围内,TiO2/Ce0.5-xZr0.5-xBa2xO2比TiO2吸收更多的紫外光.TiO2/Ce0.5-xZr0.5-x-Ba2xO2包含Ti和O两种元素,TiO2/Ce0.5-xZr0.5-xBa2xO2的Ti 2p结合能向低能端偏移.Ce0.5-xZr0.5-xBa2xO2表面负载TiO2能有效提高催化剂的光催化活性.Ce0.5-xZr0.5-xBa2xO2的作用是转移电子和使催化剂在紫外区的吸收增强.     

Ignition and combustion characteristics of compound of magnesium and boron

Compound of magnesium and boron (MB) is promising to be the ideal substitute of amorphous boron which is usually used as the raw material of boron-based fuel-rich propellants. In this study, the physical characteristics of MB and amorphous boron were studied by the scanning electron microscope, X-ray diffraction and X-ray photoelectron spectroscopy. The thermal reaction characteristics and the ignition and combustion characteristics were investigated through TG/DSC experiments and laser ignition experiments. The experimental results show that the MB particle is much more regular than amorphous boron, which favors for the preparation of boron-based fuel-rich propellants. Magnesium exists in the form of elementary substance, and boron oxide is produced during the preparation of MB which results in the longer ignition delay time of MB. The content of magnesium and the pressure have effects on the MB combustion performance. Although the combustion of magnesium can provide much heat for the combustion of boron, MB with moderate content of magnesium shows the best combustion performance. On the contrast, the ignition delay time of MB is independent on the content of magnesium and the pressure.