Das spezifische Brechungsinkrement eines statistischen Methylmethacrylat/Benzylacrylat/Styrol-Terpolymeren

The specific refractive index increments of a random methylmethacrylate/ benzylacrylate/styrene-terpolymer and of the three corresponding homopolymers was measured in several solvents and at six different wavelengths. With the known terpolymer composition and the specific refractive index increments of the homopolymers the specific refractive index increment of the terpolymer is calculated by means of an equation formerly derived. Calculated and experimental values are compared.     

Photosensitivity of thin-film ZnO/CdS/Cu(In, Ga)Se2 solar cells

The photoelectric properties of thin-film ZnO/CdS/Cu(In,Ga)Se₂ solar cells were studied by polarization photoactive absorption spectroscopy. It was shown that the thin-film solar cells have a high efficiency relative to the intensity of unpolarized radiation in the photon energy range from 1.2 to 2.5 eV. The induced photopleochroism coefficient P _I increases with the angle of incidence of the incident radiation as P _I ∼θ ² and at 70° it reaches 17–20% with photon energy 1.3 eV. Oscillations of the photopleochroism were also observed. These results are discussed taking into account the antireflection effect. The results obtained by us make it possible to use such solar cells as wide-band photosensors for linearly polarized radiation and for monitoring the production of high-efficiency, thin-film solar cells based on ternary semiconductors. Fiz. Tekh. Poluprovodn. 31, 806–810 (July 1997)     

Filler cement: The effect of the secondary component on the hydration of Portland cement: Part 2: Fine hydraulic binders

In Part 1 of this paper, it was shown that enhanced hydration was achieved by blending a fine non-hydraulic filler into an ordinary Portland cement. This enhancement was considered to be a particle size effect and associated with the presence of fine particles of filler which provided the additional nucleation sites. The filler, rutile, had a variable cement equivalence and reached a maximum value of 0.9kg/kg after hydration had proceeded for three days. In this second part, the same Portland cement was blended seperately with latent hydraulic binders (two pulverized fuel ashes and a ground granulated blastfurnace slag, a Lurgi slag and a volatilized silica). The apparent overall reactivity of these binders was seen to have two components, the first being the particle size effect with its influence on the hydration of the Portland cement and the second the inherent hydraulicity of the secondary material.     

Hydrodynamic constraints on evolution of chemically mediated interactions between aquatic organisms in unidirectional flows

Two hydrodynamic habitats can be defined in unidirectional flow: (1) A boundary where molecular diffusion dominates is found within roughly 1 mm of solid substrates. The actual thickness of this diffusion boundary is a function of current velocity and topography of the substrates. (2) A zone of turbulent flow is present outside the diffusion boundary where chemicals are rapidly diluted and transported downstream. The mode of chemically mediated interaction between organisms in streams is constrained differently depending on which of these two habitats they occupy. Within a diffusion boundary, reciprocal interaction between small organisms is possible because mixing is low, diffusion flux high, and organisms share the same water. Outside a diffusion boundary, in unidirectional flow, organisms unable to move effectively against flow are only chemically influenced by upstream organisms and can only influence downstream organisms. Organisms that are able to move upstream can interact reciprocally with other organisms, even if one or both organisms are found primarily in areas of turbulent mixing.     

Hemoglobin-fortified biscuits: bioavailability and its effect on iron nutriture in school children

School-age children in Chile received 30 g of wheat-flour biscuits daily through a National School Lunch Program. To improve iron nutrition, these biscuits were fortified with 6% of a bovine hemoglobin concentrate. Hemoglobin iron bioavailability, measured with a double isotope technique, showed that heme-iron absorption in fortified biscuits was high (19.7%). In a pilot field trial, a cohort of 215 school-children received fortified biscuits (30 g) daily during two school periods, and their iron nutrition status was compared with that of children who received non-fortified biscuits (n = 212). Acceptability of both types of biscuits was excellent. Initially, both groups had comparably good iron nutrition. The fortified children presented higher mean ferritin values at the end of the first and second school periods. Good iron stores (serum ferritin greater than or equal to 20 micrograms/lt) were present in 92% and 79% of the fortified and control subjects, respectively (P less than 0.004). The high-iron bioavailability, the good organoleptic characteristics and the biological effect on iron nutriture make this product an appealing alternative to combat iron deficiency.     

"国家点火装置"开始运转

“国家点火装置”计划约在15年前提出设想,现在这个装置正在建造,其初始运转十分成功,超出每个人的预计。在第一批四束激光运转中,激光系统的各个方面,从光束质量到能量结构,都符合设计规格。最终它将有192个光束．其已完成的2％的光束发射．已产生世界最高的激光能量。     

The polymerase chain reaction: Applications for the detection of foodborne pathogens

Faster methods for the detection of foodborne microbial pathogens are needed. The polymerase chain reaction (PCR) can amplify specific segments of DNA and is used to detect and identify bacterial genes responsible for causing diseases in humans. The major features and requirements for the PCR are described along with a number of important variations. A considerable number of PCR‐based assays have been developed, but they have been applied most often to clinical and environmental samples and more rarely for the detection of foodborne microorganisms. Much of the difficulty in implementing PCR for the analysis of food samples lies in the problems encountered during the preparation of template DNAs from food matrices; a variety of approaches and considerations are examined. PCR methods developed for the detection and identification of particular bacteria, viruses, and parasites found in foods are described and discussed, and the major features of these reactions are summarized.     

Modeling net energy efficiencies as quantitative characteristics in lactating cows

To date, researchers have measured net efficiencies of energy conversion using data from animals in energy chambers. The expense of this approach prevents the establishment of a large data base for quantitative studies. Our purpose was to investigate models that would enable us to use data collectable in normal field conditions to compare dairy cattle for their net energetic efficiency. Data from 357 Holstein cows in seven herds and in various parities consisted of daily measures of DM intake, net energy intake, milk production, biweekly measures of milk components, and bimonthly BW. Eighteen alternative multiple regression models were fitted to each of the cows to estimate simultaneously net efficiency of energy conversion for maintenance, lactation, pregnancy, and BW change during positive energy balance period, negative energy balance period, and whole lactation. Results from several fitted models approximated closely literature results based on data from cows in energy chambers. These comparative results suggest that it is possible to estimate efficiency of energy conversion on individual cows using data obtained from normal animal management situations.     

Mikromethode zur quantitativen Bestimmung von Coffein

Zusammenfassung Zur quantitativen Bestimmung von Coffein in biologischem Material wird ein kombiniertes Verfahren aus Dünnschichtchromatographie und Densitometrie beschrieben. Das Verfahren läßt Bestimmungen im Nanogramm-Bereich zu. Das Probenvolumen liegt unter 100 l.Die Proben — Capillarblut — werden zunächst mit dem gleichen Volumen Chloroform extrahiert. Anschließend wird das Coffein mittels Dünnschichtchromatographie von Begleitstoffen und störenden Substanzen abgetrennt. Es werden Kieselgel-60-Fertigplatten und Chlorofom/Aceton (9 + 1; v/v) als Fließmittel verwendet, dabei beträgt die Laufzeit 30 min.Die quantitative densitometrische Auswertung erfolgt durch Remissionsmessung bei 273 nm. Im Bereich von 10–60 ng Coffein/Fleck verläuft die Eichkurve linear. 1 mg/I Coffein kann noch sicher quantitativ erfaßt werden. Die Nachweisgrenze liegt bei 0,1 mg/1.

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A quantitative micromethod for the caffeine determination

Summary A combined procedure with thin-layer-chromatography and densitometry is described for the quantitative estimation of caffeine in biological material. This method ist applicable in the nanogram range. Test samples of less than 100 l may be used. The samples (capillary-blood) are extracted with the same volume of chloroform. Caffeine is separated from interfering compounds by thin-layer-chromatography. Commercial silica-60-plates with chloroform/acetone (9 + 1; v/v) as solvent are used. The running time is about 30 min. The quantitative densitometric determinations are performed in the remission mode at 273 nm. In the range from 10 to 60 ng/spot the calibration curve is linear. Accurate quantitative data will be obtained even at concentrations of 1 mg/1 caffeine. The detection limit is at about 0.1 mg/1.

     

Reliability considerations of III-nitride microelectronic devices

The success of III-nitride optoelectronic devices paths the way towards emerging devices in microelectronics. These devices are currently at the threshold to commercialization, therefore reliability considerations are becoming increasingly important. This paper reviews the material and process technology of III-nitride microelectronic devices in the scope of reliability. Since statistical reliability data are lacking in the current state of research the review starts with a summary of how reliability can be designed into process modules being relevant for microelectronic devices. This includes a discussion of the most important issues of material growth, metallization, implantation, dry etching and surface passivation. The subsequent chapter focuses to microelectronic devices and highlights technological challenges that have to be met in order to obtain reliable devices. Finally, results of lifetime experiments (thermal aging) demonstrate that III-nitride devices have the potential for reliable operation even at elevated temperatures up to 400°C.