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991.
Walter Gsele Wolfgang Egel-Hess Klaus Wintermantel Friedrich Richard Faulhaber Alfons Mersmann 《化学,工程师,技术》1990,62(7):544-552
Formation of solids by crystallization and precipitation. Formation of solids from solutions can take place by crystallization or precipitation. The principal factor is the relationship between solubility and supersaturation. In crystallization, the solubility of the crystallising substance is so high that the formation of solids occurs largely in the metastable zone in the immediate vicinity of the solubility limits. Crystal growth and nucleation are functions of supersaturation. If a high supersaturation is required at low substance-specific growth rates for an adequate crystal growth, high nucleation rates and hence small crystals will result. On this basis, the authors present information for the specific design of crystallization processes. In contrast, the solubility of the precipitated product must be very low for precipitation. Direct crystal formation is possible only for substance systems of high solubility. As a rule, however, the precipitated substance is so insoluble that solids are formed via amorphous intermediates. The results of a large number of experiments show the influence of various parameters of the precipitation process on the filtrability of the precipitated product. 相似文献
992.
Reinvestigation confirms action of Δ11-desaturases in spruce budworm moth sex pheromone biosynthesis
The biosynthesis of a large number of sex pheromone components of various moth species has been shown to start with common fatty acids and involve chain shortening by two carbons and introduction of a double bond at the 11–12 position. A recent report indicates that one of these common components, (E)-11-tetradecenyl acetate, is present in the eastern spruce budworm,Choristoneurafumiferana, but is not made by this pathway. Reinvestigation of this insect using in vivo and in vitro techniques indicates that the acetate indeed is made by a sequence of reactions similar to that used in other leafroller moths. In fact, evidence was found for the presence of several 11-desaturase systems in spruce budworm. One produced a large quantity of (Z)-11-hexadecanoic acid, and another produced (E)-11-tetradecanoic acid. It is not known if the small amount of (Z)-11-tetradecanoic acid is produced by either of those two systems or by a third system. A comparison with other species showed that cabbage looper moths have only the first system, redbanded leafroller moths use the last two systems, and European corn borer moths have all three. 相似文献
993.
Walter A. Pons Jr. F. H. Thurber Carroll L. Hoffpauir 《Journal of the American Oil Chemists' Society》1955,32(2):98-103
Summary A study has been made of the relation between processing conditions and the chemical characteristics of cottonseed meals and
oils produced by prepressing-solvent extraction. Twenty-six complete sets of mill samples of known processing history and
representative of the production at 11 mills were used in the investigation.
Cooking conditions were the major factor influencing the distribution of the gossypol between the meal and oil. Reduction
in free gossypol during cooking was due to binding with meal components while that occurring during prepressing and solvent
extraction resulted mainly from removal of gossypol in the prepressed and solvent-extracted oils.
Nitrogen solubility data, which have been suggested as a measure of protein damage, indicated that the major change or reduction
in nitrogen solubility occurred during cooking. Very little reduction was noted for prepressing or solvent extraction. The
reduction in nitrogen solubility during prepressing is much smaller than that previously reported for normal screw-pressing
operations.
Prepressed oils gave lower refining losses and lower refined and bleached color than did the solvent-extracted oils. Bleach
color reversion, after storage of crude oils for 30 days at 100°F., was greater for solvent-extracted than for prepressed
oils.
A number of meals exhibited the desirable characteristics of low free gossypol content and high nitrogen solubility. Values
calculated for chemical indexes of protein quality, as suggested by Lyman and associates (11), indicate that many of the meals
should have good protein quality.
Presented at the 45th Annual Meeting of the American Oil Chemists' Society, April 11–14, 1954, San Antonio, Tex.
One of the laboratories of the Southern Utilization Research Branch, Agricultural Research Service, U. S. Department of Agriculture. 相似文献
994.
Zeynep Ozkan Araci Anne F. Runge Walter J. Doherty III S. Scott Saavedra 《Israel journal of chemistry》2006,46(3):249-255
Potential modulated attenuated total reflectance (PM-ATR) spectroscopy has been employed to study charge transfer processes in Prussian blue (PB) films deposited on indium tin oxide (ITO) electrodes. PM-ATR is a planar waveguide-based spectroelectrochemical technique in which the optical response of an electroactive film is measured as a function of applied potential and modulation frequency. The multiple internal reflection geometry of PM-ATR provides a significant sensitivity advantage over the single external reflectance geometry that has been employed in most prior electroreflectance studies. The apparent electron transfer rate of PB on ITO obtained using PM-ATR was compared to that obtained with conventional cyclic voltammetry; the respective rates, 0.33 ± 0.15 s−1 (n = 3) and 0.71 ± 0.37 s−1 (n = 10), are in good agreement. 相似文献
995.
Smith AR Yang R Yang H Dick A Neugebauer J Lambrecht WR 《Microscopy research and technique》2005,66(2-3):72-84
The Mn3N2 (010) surface has been studied using spin-polarized scanning tunneling microscopy at the atomic scale. The principle objective of this work is to elucidate the properties and potential of this technique to measure atomic-scale magnetic structures. The experimental approach involves the use of a combined molecular beam epitaxy/scanning tunneling microscopy system that allows the study of atomically clean magnetic surfaces. Several key findings have been obtained. First, both magnetic and non-magnetic atomic-scale information has been obtained in a single spin-polarized image. Magnetic modulation of the height profile having an antiferromagnetic super-period of c = 12.14 A (6 atomic rows) together with a non-magnetic superstructure having a period of c/2 = 6.07 A (3 atomic rows) was observed. Methods of separation of magnetic and non-magnetic profiles are presented. Second, bias voltage-dependent spin-polarized images show a reversal of the magnetic modulation at a particular voltage. This reversal is clearly due to a change in the sign of the magnetic term in the tunnel current. Since this term depends on both the tip's as well as the sample's magnetic local density of states, the reversal can be caused by either the sample or the tip. Third, the shape of the line profile was found to vary with the bias voltage, which is related to the energy-dependent spin contribution from the 2 chemically inequivalent Mn sites on the surface. Overall, the results shown here expand the application of the method of spin-polarized scanning tunneling microscopy to measure atomic-scale magnetic structures. 相似文献
996.
High purity copper single crystals were eroded at 30° to a (111) face using glass spheres 210 μm in diameter travelling at a velocity of 133 m s?1. Detailed scanning electron microscopy of both eroded surfaces and metallographic sections has been performed together with transmission electron microscopy of erosion debris. It was observed that there was extensive surface shear that led to ripple formation, folding of the surface, subsurface crack propagation and material loss by flaking similar to delamination wear. Direct evidence was obtained for recrystallization of the surface layers. 相似文献
997.
Fluorescence resonance energy transfer (FRET) allows the user to investigate interactions between fluorescent partners. One crucial issue when calculating sensitized emission FRET is the correction for spectral bleed-throughs (SBTs), which requires to calculate the ratios between the intensities in the FRET and in the donor or acceptor settings, when only the donor or acceptor are present. Theoretically, SBT ratios should be constant. However, experimentally, these ratios can vary as a function of fluorophore intensity, and assuming constant values may hinder precise FRET calculation. One possible cause for such a variation is the use of a microscope set-up with different photomultipliers for the donor and FRET channels, a set-up allowing higher speed acquisitions on very dynamic fluorescent molecules in living cells. Herein, we show that the bias introduced by the differential response of the two PMTs can be circumvented by a simple modeling of the SBT ratios as a function of fluorophore intensity. Another important issue when performing FRET is the localization of FRET within the cell or a population of cells. We hence developed a freely available ImageJ plug-in, called PixFRET, that allows a simple and rapid determination of SBT parameters and the display of normalized FRET images. The usefulness of this modeling and of the plug-in are exemplified by the study of FRET in a system where two interacting nuclear receptors labeled with ECFP and EYFP are coexpressed in living cells. 相似文献
998.
999.
Signo T. Reis Walter M. Pontuschka Andrea Moguš‐Milanković Carmen S. M. Partiti 《Journal of the American Ceramic Society》2017,100(5):1976-1981
This paper reports a study and discusses the role of Fe ions in the inhibition of corrosion of iron phosphate glasses. The structure of the 40Fe2O3–60P2O5 (mol%) glass, having a confirmed dissolution rate in aqueous solution at 90°C superior to borosilicate glasses, was investigated. Samples were crystallized at characteristic temperatures defined by differential thermal analysis and analyzed by X‐ray diffraction. Crystalline phases of Fe2Fe[P2O7]2 and Fe4[P2O7]3 were detected. The hyperfine parameters from the Mössbauer spectrum indicate that both Fe2+ and Fe3+ ions are in octahedral coordination, and 18% of the Fe3+ ions in the starting batch are reduced to Fe2+ ions after melting. The broad and symmetric spectra centered in g≈2.0 from the EPR measurements indicate the presence of two or more Fe interacting ions occupying sites of relatively high local symmetry. 相似文献
1000.
Synthesis and Characterization of Novel Surfactants Based on 2-Hydroxy-4-(methylthio)butanoic Acid: 2. Non-ionic Surfactants
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