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951.
The synthesis and characterization of 27 novel polystyrene resin-supported optically active phase transfer catalysts is described. The first group of five catalytic species are essentially supported tetraethylene oxide derivatives each carrying a terminal chiral group. The second group consists of resins loaded with a protected galactose function along with a range of onium salt and oligoether catalysts. The third group are analogous to the second with a protected fructose residue replacing the galactose one. In the fourth group some attempt has been made to define the stereochemical relationship between the chiral species and the catalytic one, by attaching a chiral diphosphine to the support. Similarly, a phosphinated sugar, ephedrine and quinine have been attached. In the final group a chiral acetal function has been synthesized on the resin, and this function subsequently modified with a phosphonium salt and an oligoether each as the phase transfer catalytic species. In general good loadings were achieved as indicated by changes in elemental analyses and shifts in the infra-red absorption spectra of resins. 相似文献
952.
953.
In recent years the variety of cheeses available on the UK market has increased dramatically, the range available widening to meet consumer demand. However, the relationships between intended use and appropriateness of cheeses and other factors determining choice have received little attention. Using the repertory grid method, appropriateness of a range of cheeses was examined. This methodology also facilitated study of attributes, related to intended use, providing insights into characteristics influencing perceptions of appropriateness. Eight significant Use Factors discriminated between cheeses in terms of appropriateness for different uses, with textural and melting properties being major determinants of appropriateness. A range of Cheddar cheeses, the most popular UK variety, also differed in appropriateness. 相似文献
954.
The levels of higher alcohols, fatty acids and esters formed in a small-scale whisky fermentation which had been inoculated with different amounts of yeast was investigated. The total level of higher alcohols increased with increasing inoculum levels. However, the relative levels of propanol, isobutanol, amyl alcohols and 2-phenyl ethanol were unaffected. The levels of octanoic, decanoic and dodecanoic acids and their ethyl esters were depressed at inoculum levels above 2 × 107 cells ml?1. Varying the inoculum levels did not have a consistent effect on the acetate esters of the higher alcohols. However, the highest values were obtained at inoculum levels 4 × 107 cells ml?1. 相似文献
955.
M El-Metwally R Shafiee-Nick NJ Pyne BL Furman 《Canadian Metallurgical Quarterly》1997,324(2-3):227-232
We have examined in rats the effects of Org 9935 (4,5-dihydro-6-(5,6-dimethoxy-benzo[b]-thien-2-yl)-methyl-1-(2H)-p yridazinone), a selective inhibitor of type 3 phosphodiesterase (phosphodiesterase 3) and Org 30029 (N-hydroxy-5,6-dimethoxy-benzo[b]-thiophene-2-carboximidamide HCl), an inhibitor of phosphodiesterase 3/4 on rat plasma insulin and glucose concentrations in pentobarbitone-anaesthetised rats and on insulin secretion by rat isolated islets. We have also compared their effects on islet phosphodiesterase activity. Org 9935 (0.1 and 1.0 mg kg(-1) i.v. 15 min previously) dose dependently elevated fasting and post-glucose (0.25 g kg(-1) i.v.) plasma insulin concentrations. Org 30029 in a dose of 10 mg kg(-1), but not 1 mg kg(-1), also increased plasma insulin concentrations. Neither drug modified either fasting or post-glucose plasma glucose concentrations. Each drug augmented glucose-induced insulin release by rat isolated islets in a static incubation system, with approximate EC50 values of 1.5 microM for Org 9935 and 20 microM for Org 30029. Phosphodiesterase activity, in both supernatant and pellet fractions of islet homogenates, was inhibited concentration dependently by each drug. Although the shape of the concentration-inhibition curve for Org 30029 precluded estimation of an IC50 value, this drug was clearly much less potent than Org 9935 (IC50 about 50 nM) in inhibiting islet phosphodiesterase activity. We conclude that the increase in plasma insulin produced by each drug is a consequence of augmented insulin secretion, probably secondary to inhibition of phosphodiesterase 3 in the islet beta cell, with a resultant elevation in cAMP. The failure of the drugs to modify plasma glucose may be due to concomitant inhibition of cAMP phosphodiesterase in liver and adipose tissue. 相似文献
956.
In this paper, we present a prototype system that has been developed to support geometric configuration of objects at the early stages of design. Guided by the general principle of minimum commitment, this system assists in the iterative development of alternative geometric configurations based on approximately or precisely defined information. The system has been evaluated in the context of computer enclosure design. 相似文献
957.
The thermotolerances of two different cell forms of Listeria monocytogenes (serotype 4b) grown at 37 and 42.8 degrees C in commercially pasteurized and laboratory-tyndallized whole milk (WM) were investigated. Test strains, after growth at 37 or 42.8 degreesC, were suspended in WM at concentrations of approximately 1.5 x 10(8) to 3.0 x 10(8) cells/ml and were then heated at 56, 60, and 63 degrees C for various exposure times. Survival was determined by enumeration on tryptone-soya-yeast extract agar and Listeria selective agar, and D values (decimal reduction times) and Z values (numbers of degrees Celsius required to cause a 10-fold change in the D value) were calculated. Higher average recovery and higher D values (i.e., seen as a 2.5- to 3-fold increase in thermotolerance) were obtained when cells were grown at 42.8 degrees C prior to heat treatment. A relationship was observed between thermotolerance and cell morphology of L. monocytogenes. Atypical Listeria cell types (consisting predominantly of long cell chains measuring up to 60 micron in length) associated with rough (R) culture variants were shown to be 1.2-fold more thermotolerant than the typical dispersed cell form associated with normal smooth (S) cultures (P = 0.001). The thermal death-time (TDT) curves of R-cell forms contained a tail section in addition to the shoulder section characteristic of TDT curves of normal single to paired cells (i.e., S form). The factors shown to influence the thermoresistance of suspended Listeria cells (P = 0.001) were as follows: growth and heating temperatures, type of plating medium, recovery method, and cell morphology. Regression analysis of nonlinear data can underestimate survival of L. monocytogenes; the end point recovery method was shown to be a better method for determining thermotolerance because it takes both shoulders and tails into consideration. Despite their enhanced heat resistance, atypical R-cell forms of L. monocytogenes were unable to survive the low-temperature, long-time pasteurization process when freely suspended and heated in WM. 相似文献
958.
Dielectric measurements are reported on the effect of addition of glass (wool and beads) to a rubber modified epoxy resin. A parallel study of the influence of the addition of polydimethylsiloxane is also reported. It is found that there are significant shifts in the position of the dielectric relaxation associated with the acrylonitrile/butadiene phase. Analysis of the data indicates that the activation energy of the relaxation is little affected by the additives and the observed effects can be explained by the change in internal field brought about by the addition of filler through its effect on the permittivity of the material. 相似文献
959.
The microprocessor is ideally suited to automating the collection of data, the control of processes and the measurement of important parameters in industry. A number of applications are presented here, where development and research work is carried out using a microcomputer made up of a Z80 microprocessor with additional circuit boards. The applications are in the areas of data acquisition, control and measurement of variables. 相似文献
960.
Achim Ilchmann 《Systems & Control Letters》1990,14(5):437-443
Adaptive high gain stabilizers for classes of linear time-invariant state space systems are presented. The classes cover multi-input—multi-output systems where the state dimension is not known. Only standard assumptions such as minimum phase and known respectively unknown sign are required. The main result is, that the adaptive control laws of Byrnes and Willems can be modified to produce a gurantee of exponentially decaying states. 相似文献