Ammoniumsalze von α-Ketocarbonsäuren eine Klasse neur Photoinitiatoren

Ammoniumsalts of α-ketocarboxylic acids like phenylglyoxylic acid or benzylidenepyruvic acid are splitted under the influence of light into carbondioxide and aldehydes like benzaldehyde or cinnamic aldehyde and into the corresponding amine. This reaction is used for light-induced catalytic hardening of laquers based on polyurethanes.     

Effects of formula diet with varying carbohydrate proportion on gut microflora in man

The effects of conventional food and of formula diet on gut microflora were tested in six healthy persons. In comparison with conventional food, the total gut microflora concentrations slightly increased during formula diet with oligosaccharides. During the periods of formula diet rich in sucrose of maltose, total flora concentrations declined. These changes of total gut microflora were especially caused by the increase and decrease of the enterococci and enterobacteria, the bacteroides showing rather small changes. The concentrations of lactobacteria, sporeforming bacilli and yeasts decreased rapidly with formula diet and did not increase again until normal food was supplied.     

Fluorescence spectroscopy of eumelanins

The fluorescence spectra from different forms of melanin, excited by an argon-ion laser at 488 nm wavelength were measured. The fluorescence intensity and maxima were found to be dependent on the melanin concentration. The location of the fluorescence maxima depends on the type of melanin and its environment. Solubilization of melanin markedly increases its fluorescence emission and it is postulated that an oxidative cleavage of the quinoid structure of the indole moiety present in the melanin is associated both with the solubilization of the pigment as well as with an enhancement of fluorescence.     

On the primary processes of sensitized photopolymerization of vinylmonomers. Laser flash photolysis studies and stationary polymerization experiments

The absorption spectra of the triplets of aromatic ketones used as photosensitizers for the polymerization of unsaturated compounds — benzophenone (BP), 3,3′,4,4′-tetramethoxycarbonylbenzophenone (TMCB) and 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA) — were recorded after irradiation of benzene or acetone solutions of the ketones with 25 ns flashes from a frequency doubled ruby laser (λ = 347,1 nm) at room temperature. Furthermore, the spectra of the respective ketyl radicals were measured. Rate constants of the reaction of triplets with various monomers were measured. Very high rate constants (> 10⁹ 1 · mol^?1 s^?1) were found for styrene (St) and N-vinylpyrrolidone (VP). The triplet energy E_T of these monomers is smaller than E_T of the sensitizers, except the case BP/VP. Other monomers — vinylacetate (VAc), methylmethacrylate (MMA), acrylonitrile (AN) — react relatively slowly with sensitizer triplets (5 × 10⁶ to 1.4 × 10⁸ l · mol^?1 s^?1). It is assumed that these monomers have E_T values higher than the E_T values of the sensitizers. The rate of polymerization v was determined in tetrahydrofuran solutions containing monomer (5 mol/1) and sensitizer (6–7 × 10⁴ mol/1) from stationary experiments with irradiation of light with λ > 320 nm. The probabilities, α_R, for the initiation of polymerization derived from the rate constants of triplet quenching by the monomers were correlated with the measured rates of polymerization. In accordance with expectation it was found that St and VP did not polymerize and that in the cases of VAc, MMA and AN a significant polymerization takes place (in the absence of sensitizer the rates v were negligibly small). For MMA v is proportional to α.     

变压器业务中的质量管理

近年来,我国电力行业发展迅速,如西北750kV示范工程投运;多条±500kV直流输电工程相继开工或投运;三峡工程左岸投运、右岸在建;多项大型水力发电工程开工建设;±800kV特高压直流示范工程、特高压交流试验示范工程获国家发展出和改革委员会准批。电力行业的快速发展促进了设备制造业的发展与进步,尤其是大型变压器产品,无论在产品品种、电压等级方面,还是在配套容量、技术指标方面均取得了很大进步,许多原先依赖进口的变压器产品现在已能实现国产化生产。如750kV示范工程超高压输变电系统中的单相自耦变压器已完全实现国产化;发电机用主变压器已具备生产三相500kV、840MVA的能力;长距离直流输电用±500kV换流变压器实现国产化;背靠背换流站用换流变压器也已能国产化;大型核电站、水电站用变压器已实现国产化;用于交流特高压试验基地的国产1000kV、40MVA的试验变压器已制造完成,进入试验阶段;±800kV特高压直流输电工程所需的双组12脉波油浸式换流变压器的研制正在进行中。同时,许多重点产品在多项科学技术领域填补了国家空白,适应并满足了国内外电力发展的要求,大大提升了国内变压器厂家的核心竞争力与市场占有力,一些先进的变压器产品甚至还出口到了国外,这些成绩的取得着实值得广大国人为之骄傲。然而,我国变压器在制造、选型及运行维护等方面却存在这样或者那样的问题,从而使得变压器的寿命不尽如人意。2005年有10台运行不足10年的变压器发生事故,因制造方面问题所引起的变压器损坏事故台次占总损坏事故台次的83.3%,事故容量占总损坏事故容量的90.3%。国产变压器的可用系数要低于进口变压器可用系数;国产变压器的强迫停运率要高于进口变压器。那么,我国变压器在制造、选型及运行维护等方面具体存在哪些问题呢,又该如何来解决这些问题,有没有成功的经验可借鉴呢,让我们来听一听有关专家的精辟分析与见解吧!     

Models and modelling for process limits in metal forming

Modelling of metal forming processes is an essential task of production engineering. Due to the latest technological developments, a huge variety of models is already available and extending continuously. Thus, it is important to find a suitable model. This paper gives an overview on the common classification and characterization of modelling and models in metal forming, as well as introduces a model selection procedure. Based on this classification, various relevant process limits for metal forming are investigated regarding existing models. The conclusion of the paper shows open topics as well as upcoming challenges in modelling process limits in metal forming.     

Comparison of charge distributions in CIGS thin-film solar cells with ZnS/(Zn,Mg)O and CdS/i-ZnO buffers

The commonly used CdS/i-ZnO buffer system in Cu(In,Ga)Se₂ (CIGS) thin-film solar cells was substituted by ZnS/(Zn,Mg)O. ZnS has a higher transmission in the short wavelength range due to the higher bandgap energy E_g = 3.7 eV compared to CdS with E_g = 2.4 eV. Unfortunately, in our experiments the resulting gain in short-circuit current density j_SC as the result of reduced absorption losses in the blue wavelength region is mostly accompanied by a decrease in open-circuit voltage V_OC of the devices with ZnS buffer. This contribution discusses possible explanations for the systematically lower open-circuit voltages of the devices with a ZnS buffer layer.The carrier collection properties of the devices with a ZnS buffer were investigated by electron beam induced current measurements in the junction configuration. The maximum of the collection probability for ZnS cells is located in the CIGS bulk and not near the buffer/CIGS interface like for solar cells with CdS buffer. Additionally, we observed a larger space charge width compared to devices with a CdS buffer. This finding concurs with the considerably lower capacitance values and also lower charge densities in ZnS-buffered devices, as determined by capacitance voltage measurements.Based on these findings, the main reason for the lower open-circuit voltages of our ZnS devices is that the charge densities are lower than for the CdS/i-ZnO cells.     

241Am migration in a sandy aquifer studied by long-term column experiments

The migration behavior of 241Am(III) in a sandy aquifer was studied under near-natural conditions by long-term column experiments of more than 1 year duration. Columns with 50 cm length and 5 cm in diameter were packed with aeolian quartz sand and equilibrated with two different groundwaters having an original dissolved organic carbon concentration (DOC) of 1.1 and 7.2 mg x dm(-3), respectively,from the Gorleben site (Lower Saxony, Germany). In each experiment, 1 cm3 of Am-spiked groundwater ([Am] = 0.2 to 2 micromol x dm(-3)) was injected into the column. The flow rate of the groundwater was adjusted to 0.28 m x d(-1). A small colloid-borne Am fraction was found to elute together with tritiated water. After 414 and 559 days, respectively, the experiments were terminated. Whereas the nonsorbing tracer of tritiated water would have covered a distance of about 350 m in that time period, the maximum of the Am activity was detected between 32 and 40 mm column length. Applying selective dissolution analysis to the sand surface, Am was found to be preferentially bound to iron hydroxide/oxide sites. From this Am distribution, a retardation factor R of about 10(4) was determined and compared to static batch experiments. The Am breakthrough was calculated forthe conditions of the column experiment     

Permeability Comparison of Natural and Artificial Pinus Radiata Forest Litters

Forest litter flammability metrics have been extensively studied under laboratory conditions, but little research has been conducted in quantifying the difference between artificially reconstructed litters and natural litters. In order to assess the fire spread behaviour of natural litter beds, a sampling method was designed to obtain almost unperturbed radiata pine litters. As permeability is expected to affect flammability, this property was used for comparison between natural and artificially reconstructed litters. The pressure drop of airflow through undisturbed litter samples was measured in the vertical and horizontal direction for different flow velocities. The permeability of the specimens was obtained by fitting experimental values to the Forchheimer equation. It was found that for natural litter samples the horizontal permeability is almost unaffected by bulk density, while the vertical permeability is a decaying linear function of bulk density. It was further found that the permeability of artificially reconstructed litter samples depends exponentially on the bulk density of the sample. Surface to volume ratio, density and porosity of both types of litter are also informed, and qualitative comparison between them is given. Surface to volume ratio as well as density and porosity were notably different between natural and reconstructed litters.