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51.
52.
Markert Yvonne; Koditz Jens; Ulbrich-Hofmann Renate; Arnold Ulrich 《Protein engineering, design & selection : PEDS》2003,16(12):1041-1046
The virtue of the so-called proline concept andthe charge concept for stabilizing protease-susceptibleregions of a protein structure was compared on bovine pancreaticribonuclease A. Alanine 20 and serine 21, both of whichare located in a loop that is susceptible to the unspecificproteases subtilisin Carlsberg, subtilisin BPN', proteinaseK and elastase, were replaced with proline or lysine by site-directedmutagenesis. The rate constant of proteolysis was decreasedby up to three orders of magnitude for the proline mutants dependingon the site of the mutation and the protease used. In contrast,substitution by lysine increased the proteolytic resistanceby only one order of magnitude characterizing the prolineconcept as superior to the charge concept.Although the four applied proteases are considered to be unspecific,the degree of stabilization of the ribonuclease molecule variedconsiderably, indicating the impact of individual differencesin their substrate specificity on the proteolytic resistanceand degradation pathway of the target protein. Received May 12, 2003; revised October 23, 2003; accepted October 30, 2003 相似文献
53.
Summary
This article reports the synthesis of novel hydrophilic end-branched poly(ethylene glycol)s, in aqueous media by atom transfer
radical polymerization (ATRP). Poly(ethylene glycol)s with molecular weights 10,000 and 16,000 were end-functionalized and
used as bifunctional initiators for the polymerization of a poly(ethylene glycol) macromonomer with a molecular weight of
2,000 (PEGMA), either by aqueous ATRP or in a watedmethanol (l/l V/V) mixture. For both macroinitiators a DP of 10 was the
target, giving an average of 5 branches in each end. The rates of polymerization were of the same order of magnitude when
the polymerizations were initiated by either of the two macroinitiators in watedmethanol (l/l V/V). When a bifunctional oligo(ethy1ene
glycol) initiator (Mn = 600) was used to study the polymerization of PEGMA in water/methanol a reduction in the rate of polymerization was observed
indicating an influence of the molecular weight of the initiator on the rate of polymerization.
Received 25 Maich 2002/Revised 8 November 2002/Accepted 8 November 2002
Correspondence to Jorgen Kops 相似文献
54.
Felix Schmutzler Christopher Zschiesche Juliane Titus David Poppitz Jens Freiding Rainer Rakoczy Andreas Reitzmann Roger Gläser 《化学,工程师,技术》2021,93(6):981-989
The hydroisomerization of two long-chain n-alkane mixtures was investigated over bifunctional Pt/H-ZSM-5 catalysts before and after dealumination of preshaped zeolite/binder pellets. The hydroisomerization over the dealuminated catalysts leads to more isomers and less cracking products. Consequently, higher ratios of multi- to mono-branched isomerization products are formed as expected for large- rather than medium-pore zeolites. This indicates a higher availability of space in the vicinity of the active sites and provides an attractive route to make medium-pore zeolites suitable for upgrading higher boiling hydrocarbon feeds. 相似文献
55.
This article investigates the prediction of the crack growth angle of an existing internal crack under mixed mode loading at the crack tip for an unfilled ethylene propylene diene terpolymer rubber (EPDM). For the realization of mixed mode loading, the cracks of the uniaxial loaded specimens were oriented with different angles to the loading direction. The energy density factor was used as a potential criterion for determining the crack growth angle. The determination of the strain energy density factor was carried out simulatively in Abaqus. The second-order Ogden model was used to describe the rubber-like material behavior. The relative local minimum of the strain energy density factor provides the possible growth angle. The experimental investigations show that the initial cracks grow orthogonally to the loading direction for the different crack orientation angles. For the crack orientation angle parallel to the load direction, the crack growth was observed because the strong stretching of the specimen caused strong necking in the crack region. The crack growth for the remaining crack orientation angles were induced due to shear loading at the crack tip. The predictive angle of different crack orientation angles shows very good accordance to the measured crack growth angles. 相似文献
56.
BRINKSMEIER Ekkard WALTER André NOWAG Lutz S 《金属热处理》2004,29(8):66-72
通过旋转试验和有限元分析介绍了工件在切削加工过程中产生的畸变情况,分析了工件的装夹方式、切削速度、切削深度和进刀量对100Cr6钢环圆度的影响。通过去应力退火释放冷加工诱发的残余应力后工件的圆度与切削参数有关。另外测试了被试验环的表面残余应力,其表面残余应力与装夹方式有关。将测量的装夹力作为计算参数输入,通过有限元分析方法测试了装夹方式对工件变形的影响。协同测量结果示出了装夹方式影响工件变形的一个主要因素,表面残余应力与工件的径向变形有关,最大的拉伸应力位于夹口位置。旋转切削试验结果表明,提高切削速度圆度会稍有增加;随着切削深度的加大,圆度呈下降趋势,尽管切削力增加了;进给量的增加会导致更高的切削力,因此圆度值也增加;常规的去应力退火可使被加工环的圆度值增加。 相似文献
57.
F. H. Spedding A. H. Daane K. W. Herrmann 《JOM Journal of the Minerals, Metals and Materials Society》1957,9(7):895-897
The electrical resistivities of high purity lanthanum, cerium, praseodymium, and neodymium were investigated as a function of temperature over the range from room temperature to near the melting points of the metals. Transformation temperatures were observed in these metals which were confirmed by supplementary X-ray diffraction studies. 相似文献
58.
59.
Jens Petter Johansen Petter Grytten Almklov Abdul Basit Mohammad 《Cognition, Technology & Work》2016,18(2):333-350
This paper explores how different forms of anticipatory work contribute to reliability in high-risk space operations. It is based on ethnographic field work, participant observation and interviews supplemented with video recordings from a control room responsible for operating a microgravity greenhouse at the International Space Station (ISS). Drawing on examples from different stages of a biological experiment on the ISS, we demonstrate how engineers, researchers and technicians work to anticipate and proactively mitigate possible problems. Space research is expensive and risky. The experiments are planned over the course of many years by a globally distributed network of organizations. Owing to the inaccessibility of the ISS, every trivial detail that could possibly cause a problem is subject to scrutiny. We discuss what we label anticipatory work: practices constituted of an entanglement of cognitive, social and technical elements involved in anticipating and proactively mitigating everything that might go wrong. We show how the nature of anticipatory work changes between planning and the operational phases of an experiment. In the planning phase, operators inscribe their anticipation into technology and procedures. In the operational phase, we show how troubleshooting involves the ability to look ahead in the evolving temporal trajectory of the ISS operations and to juggle pre-planned fixes along these trajectories. A key objective of this paper is to illustrate how anticipation is shared between humans and different forms of technology. Moreover, it illustrates the importance of including considerations of temporality in safety and reliability research. 相似文献
60.
“Simply, people can no longer remember passwords good enough to reliably defend against dictionary attacks, and are much more secure if they choose a password too complicated to remember and then write it down. We’re all good at securing small pieces of paper. I recommend that people write their passwords down on a small piece of paper, and keep it with their other valuable small pieces of paper: in their wallet.” 相似文献