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排序方式: 共有628条查询结果,搜索用时 15 毫秒
71.
Dominic G.B. Edelen 《International Journal of Engineering Science》1983,21(5):463-470
The traction boundary value problem for spatially finite material bodies is examined in the context of the gauge theory of dislocations. In contrast with classical theory of dislocations in infinite bodies, the boundary conditions for the dislocation fields are shown to have pronounced effects. Expansion in the load parameter that is naturally associated with the applied loading shows that dislocation effects are essentially nonlinear. If the dislocation coupling constant is of the order of the shear modulus or larger, the dislocation density tensor vanishes throughout the body in the linear engineering approximation. A sequence of well-posed linear boundary value problems are shown to provide approximate solutions to any desired degree of accuracy in the load parameter. 相似文献
72.
ErikW. van Hellemond Linda Vermote Wilma Koolen Theo Sonke Ellen Zandvoort Dominic P.H.M. Heuts DickB. Janssen MarcoW. Fraaije 《Advanced Synthesis \u0026amp; Catalysis》2009,351(10):1523-1530
The substrate scope of the flavoprotein alditol oxidase (AldO) from Streptomyces coelicolor A3(2), recombinantly produced in Escherichia coli, was explored. While it has been established that AldO efficiently oxidizes alditols to D ‐aldoses, this study revealed that the enzyme is also active with a broad range of aliphatic and aromatic alcohols. Alcohols containing hydroxy groups at the C‐1 and C‐2 positions like 1,2,4‐butanetriol (Km=170 mM, kcat=4.4 s−1), 1,2‐pentanediol (Km=52 mM, kcat=0.85 s−1) and 1,2‐hexanediol (Km=97 mM, kcat=2.0 s−1) were readily accepted by AldO. Furthermore, the enzyme was highly enantioselective for the oxidation of 1,2‐diols [e.g., for 1‐phenyl‐1,2‐ethanediol the (R)‐enantiomer was preferred with an E‐value of 74]. For several diols the oxidation products were determined by GC‐MS and NMR. Interestingly, for all tested 1,2‐diols the products were found to be the α‐hydroxy acids instead of the expected α‐hydroxy aldehydes. Incubation of (R)‐1‐phenyl‐1,2‐ethanediol with 18O‐labelled water (H218O) revealed that a second enzymatic oxidation step occurs via the hydrate product intermediate. The relaxed substrate specificity, excellent enantioselectivity, and independence of coenzymes make AldO an attractive enzyme for the preparation of optically pure 1,2‐diols and α‐hydroxy acids. 相似文献
73.
74.
Quan-Bao Ma Jürgen Ziegler Bernhard Kaiser Dominic Fertig Wolfram Calvet Eswaran Murugasen Wolfram Jaegermann 《International Journal of Hydrogen Energy》2014
The electrochemical properties of single-crystalline p-type 3C-SiC films on p-Si substrate were investigated as an electrode in H2SO4 aqueous solutions in dark and under white light illumination. The photoelectrochemical (PEC) measurements indicates the p-type 3C-SiC film on p-Si substrate can generate a cathodic photocurrent as a photocathode, which corresponds to hydrogen production, and generate an anodic photocurrent as a photoanode, which corresponds to oxygen evolution. The surface chemical states of the films were investigated by XPS. In order to observe the surface chemical state changes after PEC test, the range of applied potential to the electrode was divided into three zones: −3.6 to 0 V, 0–1.5 V and 1.5–4 V vs. Ag/AgCl. After separated PEC tests in these three areas, XPS shows the surface of the SiC film in the range of −3.6 to 0 V and 0–1.5 V was stable without oxidation except the band bending occurred. But in the range of 1.5–4 V the film surface was oxidized due to anodic oxidation. 相似文献
75.
Dombrowski PM Long W Farley KJ Mahony JD Capitani JF Di Toro DM 《Environmental science & technology》2005,39(7):2169-2176
The Challenger mechanism for the methylation of arsenic is a repeating sequence of a two-electron reduction of pentavalent arsenic As(V) species to trivalent arsenic As(III) species followed by a methylation-oxidation reaction forming the successive methyl As(V) species. This unusual oxidation-reduction sequence prompted an examination of the thermodynamics of these reactions. Quantum chemical methods are employed to estimate the thermodynamic parameters for the methyl arsenic species. The sequence is thermodynamically favored at neutral pH for redox potentials with pe < 0 and methyl cation activities pCH3+ < -3 to -7 depending on the precise situation analyzed. The observed distribution of methyl arsenic species in human urine, which is remarkably constant across many studied populations, can be reproduced using an equilibrium model if the formation of TMA species is prevented. The estimated thermodynamic parameters are sufficiently accurate to evaluate questions of thermodynamic plausibility but not the precise details of speciation. 相似文献
76.
Fournier D Halasz A Thiboutot S Ampleman G Manno D Hawari J 《Environmental science & technology》2004,38(15):4130-4133
Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) is a recalcitrant energetic chemical that tends to accumulate in soil, close to the surface. The present study describes the aerobic biodegradability of HMX using Phanerochaete chrysosporium. When added to 7 day old static P. chrysosporium liquid cultures, HMX (600 nmol) degraded within 25 days of incubation. The removal of HMX was concomitant with the formation of transient amounts of its mono-nitroso derivative (1-NO-HMX). The latter apparently degraded via two potential routes: the first involved N-denitration followed by hydrolytic ring cleavage, and the second involved alpha-hydroxylation prior to ring cleavage. The degradation of 1-NO-HMX gave the ring-cleavage product 4-nitro-2,4-diazabutanal (NDAB), nitrite (NO2 -), nitrous oxide (N2O), and formaldehyde (HCHO). Using [14C]-HMX, we obtained 14CO2 (70% in 50 days), representing three C atoms of HMX. Incubation of real soils, contaminated with either HMX (403 micromol kg(-1)) (military base soil) or HMX (3057 micromol kg(-1)), and RDX (342 micromol kg(-1)) (ammunition soil) with the fungus led to 75 and 19.8% mineralization of HMX (liberated 14CO2), respectively, also via the intermediary formation of 1-NO-HMX. Mineralization in the latter soil increased to 35% after the addition of glucose, indicating that a fungus-based remediation process for heavily contaminated soils is promising. The present findings improve our understanding about the degradation pathway of HMX and demonstrate the utility of using the robust and versatile fungus P. chrysosporium to develop effective remediation processes for the removal of HMX. 相似文献
77.
Dawei Ji Jingying Ma Min Xu Dominic Agyei 《Comprehensive Reviews in Food Science and Food Safety》2021,20(1):369-400
Proteins displayed on the cell surface of lactic acid bacteria (LAB) perform diverse and important biochemical roles. Among these, the cell-envelope proteinases (CEPs) are one of the most widely studied and most exploited for biotechnological applications. CEPs are important players in the proteolytic system of LAB, because they are required by LAB to degrade proteins in the growth media into peptides and/or amino acids required for the nitrogen nutrition of LAB. The most important area of application of CEPs is therefore in protein hydrolysis, especially in dairy products. Also, the physical location of CEPs (i.e., being cell-envelope anchored) allows for relatively easy downstream processing (e.g., extraction) of CEPs. This review describes the biochemical features and organization of CEPs and how this fits them for the purpose of protein hydrolysis. It begins with a focus on the genetic organization and expression of CEPs. The catalytic behavior and cleavage specificities of CEPs from various LAB are also discussed. Following this, the extraction and purification of most CEPs reported to date is described. The industrial applications of CEPs in food technology, health promotion, as well as in the growing area of water purification are discussed. Techniques for improving the production and catalytic efficiency of CEPs are also given an important place in this review. 相似文献
78.
John A. Osaheni Dominic O. Onukwuli Alfred A. Susu 《Petroleum Science and Technology》1999,17(7):759-781
An estimate of the quantity of toxic coke deposited on fresh and regenerated Pt/Alj2O3 catalyst has been determined for methylcyclopentane (MCP) reforming in a Berty CSTR at 390°C, W/F=0·11 g min cm-3, total pressure of 1 atm and MCP partial pressure of 9·2 × 10-2 atm in H2 or N2 carrier. Eleven cycles consisting each of catalyst deactivation, regeneration and reduction were investigated with 3 in H2 and 8 in N2. Oxidizable (primary) coke deposits were higher in N2. However, higher levels of toxic (secondary) coke were deposited in H2. The ratio of oxidizable to toxic coke lies between 1-15×103 in H2 and 22 - 55 × 103 in N2 The coke-time profiles for secondary coke removal exhibited maxima suggestive of three types of secondary coke with varying reactivity in H2. Furthermore, the results strongly suggest that the cokes were layered on acidic coke forming sites with the solid phase transformation of primary to secondary coke occurring at the catalyst-coke interface. 相似文献
79.
80.