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51.
Friedrich Otto 《Theory of Computing Systems》1987,20(1):253-260
WhenC is a concurrency relation on alphabet , then */=
C
is a free partially commutative monoid. Here we show that it is decidable in polynomial time whether or not there exists a finite canonical rewriting systemR on such that the congruences
R
*
generated byR and =
C
induced byC coincide. Further, in case such a systemR exists, one such system can be determined in polynomial time. 相似文献
52.
A Kaolin-filled, high-density polyethylene (HDPE) system was used to illustrate the influence of particulates on modulus and toughness of the bulk material. A variation of filler content, particulate size and coupling quality for two HDPE-matrix systems with different viscosity led to a strong dependency of elastic modulus and fracture toughness under various testing conditions, e.g. static loading, fatigue and impact.
A stiffness improvement with increasing filler content was achieved by all coupling qualities. The developed Kaolin reinforcement of HDPE with optimised coupling offers an improvement of the stiffness and toughness under all investigated loading conditions. The degree of improvement depends on the particulate size and matrix viscosity. The energy dissipation mechanisms were investigated by fractographic analysis. 相似文献
A stiffness improvement with increasing filler content was achieved by all coupling qualities. The developed Kaolin reinforcement of HDPE with optimised coupling offers an improvement of the stiffness and toughness under all investigated loading conditions. The degree of improvement depends on the particulate size and matrix viscosity. The energy dissipation mechanisms were investigated by fractographic analysis. 相似文献
53.
Effect of moisture and particle size on the extractability of oils from seeds with supercritical CO2
J. M. Snyder J. P. Friedrich D. D. Christianson 《Journal of the American Oil Chemists' Society》1984,61(12):1851-1856
Moisture level and particle size of soybeans, peanuts and cottonseed were correlated with the extraction rate and yield of
oil when extracted with supercritical carbon dioxide (SC-CO2) at a constant temperature (50 C) and pressure (8000 psig). The rate of extraction and ultimate oil yields were quite low
with cracked soybeans. However, good extraction rates and nearly theoretical oil yields were obtained from ground or thinly
flaked (<0.010″) seeds. Moisture levels between 3% and 12% had little effect on extracability. Oil composition was not influenced
by either parameter. Scanning electron microscopy was used to study seed structure before and after extraction with SC-CO2. Micrographs of SC-CO2-extracted seeds were similar to hexane-extracted seeds.
Presented at the AOCS Meeting, May 1983, Chicago. 相似文献
54.
Monoalkyl esters of linseed-oil-derived C18-saturated cyclic acids (HCal), described in earlier work, showed promise as lubricant base stocks for turbine aircraft as
set forth in the military specification MIL-L-7808E. These esters, however, did not exhibit the increased oxidative stability
and higher viscosity required by the more recent specification MIL-L-23699.
Six diol esters of HCal have now been prepared. Both hindered and unhindered dihydric alcohols were used, including ethylene
glycol, 1,4-cyclohexanedimethanol, 1,4-benzenedimethanol, 2,3-dimethyl-1,3-propanediol and 2,2,4,4-tetramethyl-1,3-cyclobutanediol
(I). The viscosities of these esters at 210F ranged from 10.1 to 19.6 centistokes and the pour points, from −35 to −62F. Oxidative
stabilities at 400F were determined with 0.5% each of phenyl-a-napthylamine (PANA) andp,p’-dioctyldiphenylamine as inhibitors. The esters of the unhindered diols had poor stability, whereas esters of the hindered
diols, in particular I, exhibited excellent resistance to the formation of acidic decomposition products and sludge. Although
the HCal ester of I by itself is too viscous to meet specification MIL-L-23699, its ASTM slope (0.650) is excellent. Blends
of this material with less viscous hindered esters, commercially available, may find application as lubricants for high-performance
turbine engines used in various aircraft.
Presented at the AOCS Meeting in Los Angeles, 1966.
No. Utiliz. Res. Dev. Div., ARS, USDA. 相似文献
55.
E. N. Frankel R. A. Awl J. P. Friedrich 《Journal of the American Oil Chemists' Society》1979,56(12):965-969
The use of Cr(CO)6 was investigated to convert polyunsaturated fats intocis unsaturated products. With methyl sorbate, the same order of selectivity for the formation ofcis-3-hexenoate was demonstrated for Cr(CO)6 as for the arene-Cr(CO)3 complexes. With conjugated fatty esters, the stereoselectivity of Cr(CO)6 toward thetrans, trans diene system was particularly high in acetone. However, this solvent was not suitable at elevated temperatures required to
hydrogenatecis, trans- andcis, cis-conjugated dienes (175 C) and nonconjugated soybean oil (200 C). Reaction parameters were analyzed statistically to optimize
hydrogenation of methyl sorbate and soybean oil. To achieve acceptable oxidative stability, it is necessary to reduce the
linolenate constituent of soybean oil below 1–3%. When this is done commercially with conventional heterogenous catalysts,
the hydrogenated products contain more than 15%trans unsaturation. By hydrogenating soybean oil with Cr(CO)6 (200 C, 500 psi H2, 1% catalyst in hexane solution), the product contains less than 3% each of linolenate andtrans unsaturation. Recycling of Cr(CO)6 catalyst by sublimation was carried through three hydrogenations of soybean oil, but, about 10% of the chromium was lost
in each cycle by decomposition. The hydrogenation mechanism of Cr(CO)6 is compared with that of arene-Cr(CO)3 complexes.
Presented in part at Seventh Conference on Catalysis in Organic Syntheses, Chicago, Illinois, June 5–7, 1978. 相似文献
56.
A.J. Dickinson L.P.L. Carrette J.A. Collins K.A. Friedrich U. Stimming 《Journal of Applied Electrochemistry》2004,34(10):975-980
This paper describes the effects of varying the Pt to Ru ratio in carbon-supported catalysts for methanol oxidation as a function of temperature. Previously these effects were studied in isolation, but now it is shown that the composition of a given catalyst as a function of temperature is extremely important for its activity towards methanol oxidation. Platinum rich 3:2 atomic ratio catalysts perform better than a 1:1 catalyst at 25 °C, where only Pt is believed to be active towards methanol dehydrogenation, since this process is a highly thermally activated process on Ru sites. This result is reversed at 65 °C, where the 1:1 catalyst displays much higher currents across the entire range of polarization. This may result from methanol dehydrogenation occurring on both Ru and Pt sites at higher temperatures. At an intermediate temperature, 45 °C, the 3:2 catalyst is seen to perform better at lower current values, while the 1:1 catalyst is superior at higher current densities, with the crossover occurring at 62 A g–1. As a consequence, when designing fuel cell catalysts, the composition of the catalyst employed should be tailored with respect to the exact operating conditions, in order to promote optimum fuel cell performance. 相似文献
57.
E. N. Frankel J. P. Friedrich T. R. Bessler W. F. Kwolek N. L. Holy 《Journal of the American Oil Chemists' Society》1980,57(10):349-354
New polymer-bound hydrogenation catalysts were made by complexing PdCl2, RhCl3·3H2O, or NiCl2 with anthranilic acid anchored to chloromethylated polystyrene. The Pd(II) and Ni(II) polymers were reduced to the corresponding
Pd(O) and Ni(O) catalysts with NaBH4. In the hydrogenation of methyl sorbate, these polymer catalysts were highly selective for the formation of methyl 2-hexenoate.
The diene to monoene selectivity decreased in the order: Pd(II), Pd(O), Rh(I), Ni(II), Ni(O). Kinetic studies support 1,2-reduction
of the Δ4 double bond of sorbate as the main path of hydrogenation. In the hydrogenation of soybean esters, the Pd(II) polymer
catalysts proved superior because they were more active than the Ni(II) polymers and produced lesstrans unsaturation than the Rh(I) polymers. Hydrogenation with Pd(II) polymers at 50~100 C and 50 to 100 psi H2 decreased the linolenate content below 3% and increasedtrans unsaturation to 10~26%. The linolenate to linoleate selectivity ranged from 1.6 to 3.2. Reaction parameters were analyzed
statistically to optimize hydrogenation. Recycling through 2 or 3 hydrogenations of soybean esters was demonstrated with the
Pd(II) polymers. In comparison with commercial Pd-on-alumina, the Pd(II) polymers were less active and as selective in the
hydrogenation of soybean esters but more selective in the hydrogenation of methyl sorbate.
Presented at ISF-AOCS Meeting, New York, April 1980. 相似文献
58.
The concept of solubility parameter, developed by Hansen, has been applied to the determination of solubility diagram of polysulfone and sulfonated polysulfone. Data showing the effect of various parameters such as thermodynamic quality of the solvent, casting solution composition and viscosity, solvent evaporation period and precipitation bath composition, on membrane structure and performance have been presented. By adjusting these parameters a wide variety of sulfonated polysulfone membranes useful for both ultrafiltration and reverse osmosis applications could be obtained. 相似文献
59.
Tjeenk Marjjke Leuveling; Bulsink Yvonne B. M.; Slotboom Arend J.; Verheij Hubertus M.; Haas Gerard H.de; Demleitner Gaby; Gotz Friedrich 《Protein engineering, design & selection : PEDS》1994,7(4):579-583
The Staphylococcus hyicus lipase is an acyl hydrolase with broadsubstrate specificity including neutral glycerides and phospholipids.To obtain further insight into the mechanism of action of thisenzyme, we tested several sulfonyl fluorides as active site-directedinhibitors. The enzyme is resistant to the well-known serineprotease/esterase inhibitor phenylmethanesulfonyl fluoride (PMSF),but is rapidly inactivated by hexadecylsulfonyl fluoride. Thekinetics of inactivation were studied in Triton X-100 micelles.Inactivation is fast and the rate of inactivation is constantover the pH range where this lipase is active. Metal ions likeCa2+ and Sr2+ do not appreciably influence the rate of inactivation,although the enzymatic activity is significantly increased,suggesting a structural role for these ions. The S.hyicus lipasecontains a consensus sequence G-H/Y-S-X-G. Substitution by site-directedmutagenesis of this serine (Ser369) by a cysteine resulted ina mutant with only 0.2% residual activity. The activity of thismutant could not be inhibited with water-soluble sulfhydrylreagents either in the presence or absence of Triton X-100 micelles.In the presence of Triton X-100 micelles, inactivation of themutant occurred with 4-nitrophenylhexadecyl disulfide (t1/2= 125 min) while the wild-type enzyme does not react at all.We conclude that Ser369 is the active site residue and thatin water this residue is inaccessible. Only after interfacialactivation Ser369 (or Cys369) becomes exposed and reacts withirreversible inhibitors. 相似文献
60.
在纳米Al2O3、Si3N4、SiC填充环氧树脂复合材料体系中,纳米粒子表面活性及粒子与环氧树脂之间的相互作用影响着环氧树脂的固化过程.本文利用傅立叶红外光谱表征了纳米粒子与环氧树脂之间的化学作用情况,并利用差视扫描量热仪研究了不同纳米粒子/环氧树脂复合材料的固化动力学.结果表明,具有相对最强表面活性的纳米Al2O3粒子与基体之间的相互作用最强,同时该粒子对环氧树脂固化过程的促进作用最显著. 相似文献