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71.
Biphasic, mixed gels of agarose and gelatin were prepared, and their mechanical behaviour in tensile tests was determined, up to failure, utilising four decades of (constant) strain rate. The behaviour of pure agarose and pure gelatin in such tests has been determined previously. Suitable ‘blending-laws’ relating the small deformation shear modulus of the composite to the moduli of the component phases have also been discussed elsewhere. This report extends the latter treatment to the more aggressive large deformation regime, deriving bounds for modulus and break stress which closely model observed behaviour. 相似文献
72.
Louise M. Canfield Judy M. Hopkinson Anne F. Lima Gail S. Martin Kyoto Sugimoto Jeanne Burr Larry Clark Daniel L. McGee 《Lipids》1990,25(7):406-411
A quantitative method was developed for the assay of vitamin K in human colostrum and milk. The procedure combines preparative
and analytical chromatography on silica gel in a nitrogen atmosphere followed by reversed phase high performance liquid chromatography
(HPLC). Two HPLC steps were used: gradient separation with ultraviolet (UV) detection followed by isocratic separation detected
electrochemically. Due to co-migrating impurities, UV detection alone is insufficient for identification of vitamin K. Exogenous
vitamin K was shown to equilibrate with endogenous vitamin K in the samples. A statistical method was incorporated to control
for experimental variability. Vitamin K1 was analyzed in 16 pooled milk samples from 7 donors and in individual samples from 15 donors at 1 month post-partrum. Vitamin
K1 was present at 2.94±1.94 and 3.15±2.87 ng/mL in pools and in individuals, respectively. Menaquinones, the bacterial form
of the vitamin, were not detected. The significance of experimental variation to studies of vitamin K in individuals is discussed. 相似文献
73.
Identification and elimination by site-directed mutagenesis of thermolabile aspartyl bonds in Aspergillus awamori glucoamylase 总被引:2,自引:0,他引:2
Chen Hsiu-mei; Ford Clark; Reilly Peter J. 《Protein engineering, design & selection : PEDS》1995,8(6):575-582
Both Dative Aspergillus niger glucoamylase and wild-type Aspergillusawamori glucoamylase expressed in Saccharo-myces cerevisiae,which have identical primary structures, undergo hydrolysisat aspartyl bonds at low pH values and elevated temperatures.In native A.niger enzyme the Aspl26Glyl27 bond was preferentiallycleaved at pH 3.5,while at pH 4.5 cleavage of the Asp257Pro258and Asp293Gly294 bonds was dominant. In wild-type A.awamoriglucoamylase, cleavage of the latter was dominant at both pH3.5 and 4.5. Site-directed mutations Aspl26Glu and Glyl27Alain wild-type enzyme decreased specific activities by 60 and30%, respectively, and increased irreversible thermoinactivationrates 3- to 4-fold at pH 4.5. Replacement of Asp257 with Gluand Asp293 with Glu or Gin decreased specific activities by20%, but greatly reduced cleavage of the Asp257Pro258and Asp293Gly294 bonds. The Asp257Glu mutant was producedvery slowly and was more thermostable than wildtype glucoamylaseat pH 4.5up to 70°C. Replacement of Asp293 with either Gluor Gln significantly raised protein production and slightlyincreased thermostability at pH 3.5 and 4.5, but not at pH5. 相似文献
74.
Ultrafiltration of lake water for potable water production 总被引:1,自引:0,他引:1
Ultrafiltration with coagulation or powdered activated carbon pretreatment is used to treat water from a public water supply. While UF without pretreatment is effective in removing turbidity, pretreatment prior to UF greatly enhances the removal of natural organic matter and trihalomethane precursors. Short-term flux loss can be minimized with backflushing, while long-term irreversible fouling seems to be affected most by the type of membrane polymer. 相似文献
75.
A prototype wind-powered reverse osmosis desalination system was constructed and tested on Coconut Island off the northern coast of Oahu, Hawaii, for brackish water desalination. The system has four major subsystems: a multi-vaned windmill/pump, a flow/pressure stabilizer, a reverse osmosis module, and a control mechanism. The feedback control mechanism, developed by this study, allowed this prototype system to be operated satisfactorily under mild ambient wind of 5 m/s or less. No auxiliary power source was needed. The system operational data showed that at an average wind speed of 5 m/s, brackish feedwater at a total dissolved solids concentration of 3000 mg/1 and at a flow rate of 13 1/min could be processed by this system. The average rejection rate of this prototype system was 97% and the average recovery ratio was 20%. The energy efficiency of the system was measured at 3 5%, which is comparable to the typical energy efficiency of well-operated multi-vaned windmills. Generally, the system's energy efficiency decreases as wind speed increases. 相似文献
76.
Effect of amino acid deletions in the O-glycosylated region of Aspergillus awamori glucoamylase 总被引:1,自引:0,他引:1
Libby Carol Baker; Cornett Catherine A.G.; Reilly Peter J.; Ford Clark 《Protein engineering, design & selection : PEDS》1994,7(9):1109-1114
Aspergillus awamori glucoamylase (GA) contains globular catalyticand starch-binding domains (residues 1471 and 509616,respectively). A heavily O-glycosylated sequence comprises twoparts. The first (residues 441471) in the crystal structurewraps around an /-barrel formed by residues 1440. Thesecond (residues 472508) is an extended, semi-rigid linkerbetween the two domains. To investigate the functional roleof this linker, we made internal deletions to remove residues466512 (GA1), 485512 (GA2) and 466483 (GA3).GA2 and GA3 were expressed in Saccharomyces cerevisiae culturesupernatants at 60 and 20% the wild-type level, respectively,while GA1 was almost undetectable. Western blots comparing extracellularand intracellular fractions indicated that the region deletedin GA3 was critical for secretion, while the region deletedin GA2 contributed to the production of a stable enzyme structure.The activities of purified GA2 and GA3 on soluble and insolublestarch were similar to those of wild-type GA, indicating thatfor soluble starch their deletions did not affect the catalyticdomain and for insoluble starch the linker does not coordinatethe activities of the catalytic and starch-binding domains.The deletions had a significant negative effect on GA2 and GA3thermos tabilities. 相似文献
77.
本文是美国著名艺术理论家、批评家T.J.克拉克同名著作修订版的导论部分,探讨了印象派绘画与巴黎的关系. 相似文献
78.
Clark A. Updike M.S. Ram B. Bhagat Ph.D. Martin J. Pechersky Ph.D. Maurice F. Amateau Ph.D. 《JOM Journal of the Minerals, Metals and Materials Society》1990,42(3):42-46
Metal-matrix composites may offer better damping properties than unreinforced alloys. Because damping properties (and metal-matrix composites) are becoming important in airframe design, the damping capabilities of a number of aluminum-matrix composites were measured over a wide range of frequencies at low strain amplitudes, using a new laser vibrometer technique. Silicon carbide and alumina reinforcements resulted in a material with damping properties similar to that of unreinforced aluminum 6061-T6, but unidirectional and planar-random graphite continuous-fiber reinforcements increased the damping by 5 and 14 times, respectively. The increased damping of the continuous fiber composites is attributed to the absence of interfacial reaction resulting from the high-pressure infiltration method used for their manufacture. 相似文献
79.
W. Hui P.J.-H. Hu † T.H.K. Clark ‡ K.Y. Tam‡ & J. Milton§ 《Journal of Computer Assisted Learning》2008,24(3):245-259
Abstract A field experiment compares the effectiveness and satisfaction associated with technology-assisted learning with that of face-to-face learning. The empirical evidence suggests that technology-assisted learning effectiveness depends on the target knowledge category. Building on Kolb's experiential learning model, we show that technology-assisted learning improves students' acquisition of knowledge that demands abstract conceptualization and reflective observation but adversely affects their ability to obtain knowledge that requires concrete experience. Technology-assisted learning better supports vocabulary learning than face-to-face learning but is comparatively less effective in developing listening comprehension skills. In addition, according to empirical tests, perceived ease of learning and learning community support significantly predict both perceived learning effectiveness and learning satisfaction. Overall, the results support our hypotheses and research model and suggest instructors should consider the target knowledge when considering technology-assisted learning options or designing a Web-based course. In addition, a supportive learning community can make technology-assisted learning easier for students and increase their learning satisfaction. 相似文献
80.