A novel monochromator for experiments with ultrashort X‐ray pulses

Aiming at advancing storage‐ring‐based ultrafast X‐ray science, over the past few years many upgrades have been undertaken to continue improving beamline performance and photon flux at the Femtoslicing facility at BESSY II. In this article the particular design upgrade of one of the key optical components, the zone‐plate monochromator (ZPM) beamline, is reported. The beamline is devoted to optical pump/soft X‐ray probe applications with 100 fs (FWHM) X‐ray pulses in the soft X‐ray range at variable polarization. A novel approach consisting of an array of nine off‐axis reflection zone plates is used for a gapless coverage of the spectral range between 410 and 1333 eV at a designed resolution of E/ΔE = 500 and a pulse elongation of only 30 fs. With the upgrade of the ZPM the following was achieved: a smaller focus, an improved spectral resolution and bandwidth as well as excellent long‐term stability. The beamline will enable a new class of ultrafast applications with variable optical excitation wavelength and variable polarization.     

Spectrophotometric Studies of the Energy Consumed During Oxidative Degradation of D-Fructose

ABSTRACT

Mechanistic investigation of the oxidative degradation of d-fructose (D-Fruc) has been studied by spectrophotometric technique. Molecular mechanics (MM +) calculations suggest that the potential energy (PE/kcal mol^?1) of the d-fruc (opening structure) is at least three (3.71) times more stable than the PE of the cycling structure of the same matrix. The oxidation constant (K _ox) of the anionic form of the d-Fruc (Fruc-NaOH) is about seven times greater than that of the protonated form (Fruc-H₂SO₄). Therefore, the anionic form is more highly oxidizable than is the cationic form of this matrix. The limit of detection can be as low as 18 ppm (mg L^?1) of d-Fruc. This is about 60 times lower than the blood sugar level (BSL) or 100 times lower than that reported previously. The proposed procedure was applied successfully for the oxidation of D-Fruc in uni-fructose powder. The anionic form of D-Fruc (Fruc-NaOH) has the ability to store energy about 744.72 kJ g^?1 h at 608 nm in a condensed lightweight form. Kinetic parameters of the oxidative degradation of the anionic form of D-Fruc at different concentration were deduced. A number of models were used to evaluate the kinetic parameters. The mechanism of the degradation of D-Fruc is explained on the basis of kinetic parameters.     

Zerstörungsfreie risstiefenbestimmung in Betonbauwerken mittels Radiotracerverfahren

At the Leipzig Technical University a method was developed, which allows to determine nondestructive the crack depth in concrete up to 15 cm. Based on a radiotracer technique the access to only one side of the object is required. The labelling of artificial-made cracks was carried out by use of a transport medium (not miscible with water) on the base of methyl isobutyl ketone (MIBK) and In- 113m as radionuclide. For the calculation of crack depth, measure-geometrical parameters were used. The improvement of the reliability of building-diagnostical interpretation using radio-physical parameters is described. A first application is provided for concrete structures below chemical equipments built as a barrier against ecologically harmful substances (petrol tanks). The intersectional aspect of further qualifications of the technique is emphasized.     

The role of cool-flame chemistry in quasi-steady combustion and extinction of n-heptane droplets

Experiments on the combustion of large n-heptane droplets, performed by the National Aeronautics and Space Administration in the International Space Station, revealed a second stage of continued quasi-steady burning, supported by low-temperature chemistry, that follows radiative extinction of the first stage of burning, which is supported by normal hot-flame chemistry. The second stage of combustion experienced diffusive extinction, after which a large vapour cloud was observed to form around the droplet. In the present work, a 770-step reduced chemical-kinetic mechanism and a new 62-step skeletal chemical-kinetic mechanism, developed as an extension of an earlier 56-step mechanism, are employed to calculate the droplet burning rates, flame structures, and extinction diameters for this cool-flame regime. The calculations are performed for quasi-steady burning with the mixture fraction as the independent variable, which is then related to the physical variables of droplet combustion. The predictions with the new mechanism, which agree well with measured autoignition times, reveal that, in decreasing order of abundance, H₂O, CO, H₂O₂, CH₂O, and C₂H₄ are the principal reaction products during the low-temperature stage and that, during this stage, there is substantial leakage of n-heptane and O₂ through the flame, and very little production of CO₂ with no soot in the mechanism. The fuel leakage has been suggested to be the source of the observed vapour cloud that forms after flame extinction. While the new skeletal chemical-kinetic mechanism facilitates understanding of the chemical kinetics and predicts ignition times well, its predicted droplet diameters at extinction are appreciably larger than observed experimentally, but predictions with the 770-step reduced chemical-kinetic mechanism are in reasonably good agreement with experiment. The computations show how the key ketohydroperoxide compounds control the diffusion-flame structure and its extinction.     

BOILING IN CHANNEL WITH POROUS MATRIX

Experimental data on heat transfer and pressure drop in the case of forced-convection boiling in a channel with a porous matrix are presented. Correlations for the experimental data are given. Example calculation of thermohydrautic characteristics of a heat exchanger with a highly conductive porous matrix has been done using the obtained experimental data. Results of these calculations are presented.     

Development of low concentrated solar photovoltaic system with lead acid battery as storage device

Energy storage system powered by renewable energies is a viable option to meet energy requirement without addition of carbon footprints to the environment. This study involves development of theoretical and computational models for a solar photovoltaic (PV) system coupled with a lead acid battery. The study commenced with selection of most appropriate lead acid battery and PV system for installation in a representative location in Riyadh, Kingdom of Saudi Arabia. Various technical and economic parameters were assessed and calculated by computational approach. The optimized lead acid battery was integrated with low concentration solar PV panels (CPV) followed by a feasibility study. Theoretical model was developed for the integrated system to calculate various parameters of the CPV and lead acid battery. Technical and economic assessment of this coupled unit was calculated using a theoretical approach. The developed model was then subjected to computational approach for verification and validation analysis of the integrated system. The detailed assessment of batteries and integrated system show the applicability of this system in Riyadh region. The research will be extended to develop energy storage systems for remote areas using lead acid batteries.     

轮背空腔-密封气对CAES向心涡轮变工况流动损失的影响

本文以国内首套MW级压缩空气储能(CAES)系统末级向心涡轮为研究对象,通过数值模拟分析了变工况条件下轮背空腔-密封气对等熵效率和流场结构的影响.结果表明:在求解中考虑轮背空腔-密封气结构能够使等熵效率数值解的偏差减小0.7%;随涡轮进口压力增加,轮背空腔泄漏流由叶片吸力面中部叶高区域逐渐向轮毂转移,流动损失先增加后减小;合理降低轮背空腔泄漏气体的轴向速度,能够减弱轮背空腔-密封气结构对等熵效率的负面影响,使向心涡轮在较宽的变工况范围内都保持高效运行.     

无水坝抽水蓄能系统高压溶气问题研究

无水坝抽水蓄能系统利用封闭容器内的高压气体构建虚拟水坝,是兼具压缩空气储能和抽水蓄能优点的新型储能系统。但该系统的封闭容器内水和气在高压状态共存有可能造成水中溶气,从而对水轮机造成汽蚀等破坏。本文采用实际气体状态方程及分子动力学模拟方法,研究了宽广的压力、温度范围下气体在水中的溶解及扩散规律,揭示了水中气体溶解量随时间和水深的变化规律。研究结果表明释能结束后保证水-气共容舱内剩余水的高度大于0.5 m时,高压溶气不会对水轮机产生危害,该结论对系统的工程应用及推广具有指导意义。     

Heat conduction in a rock mass with an annular hot water store

Vast subterranean caverns may be used for hot water storage in distinct heating schemes; such caverns can be annular, with a central pillar. This paper considers the quasi-steady solution of the heat conduction equation for this geometry with periodic temperature variations     

体全息存储系统读出图像的放大率的补偿算法研究

在1∶1体全息存储系统的读出过程中,保证图像的不失真和降低误码率是最关键的问题。提出了一种新颖的放大率补偿算法,定量分析了放大率偏移误差对图像的影响,并通过理论推导和实验模拟证明了这一算法的可行性。