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11.
Crosslinking of tissue-derived biomaterials in 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) 总被引:2,自引:0,他引:2
J. M. Lee H. H. L. Edwards C. A. Pereira S. I. Samii 《Journal of materials science. Materials in medicine》1996,7(9):531-541
In contrast to bifunctional reagents such as glutaraldehyde or polyfunctional reagents such as polyepoxides, carbodiimides belong to the class of zero-length crosslinkers which modify amino acid side-groups to permit crosslink formation, but do not remain as part of that linkage. The authors have compared the effects of 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) and glutaraldehyde (the de facto industrial standard crosslinker) on the hydrothermal, biochemical, and uniaxial mechanical properties of bovine pericardium. EDC crosslinking was optimized for maximum increase in collagen denaturation temperature using variables of pH, concentration, and ratio of EDC to N-hydroxysuccinimide (NHS): a reagent for formation of activated esters. EDC and glutaraldehyde crosslinked materials were subjected to hydrothermal denaturation tests, biochemical degradation by enzymes (collagenase, trypsin) and CNBr, amino acid analysis for unreacted lysine, and to high strain rate mechanical tests including: large deformation stress-strain studies (0.1 to 10 Hz), stress relaxation experiments (loading time 0.1 s) and small deformation forced vibration (1 and 10 Hz). A protocol for EDC crosslinking was developed which used 1.15% EDC (2:1 EDC:NHS) at pH 5.5 for 24 h. The increase in denaturation temperature for EDC (from 69.7±1.2°C to 86.0±0.3°C) was equivalent to that produced by glutaraldehyde (85.3±0.4°C). Both treatments equivalently increased resistance to collagenase and CNBr degradation; however, after denaturation, the EDC-treated tissue was slightly more resistant to collagenase, and markedly more resistant to trypsin. EDC-treated materials were more extensible and more elastic than glutaraldehyde-treated materials. Despite the differences in crosslinking mechanism, EDC and glutaraldehyde-treated materials are very similar. Subtle but intriguing differences in biochemical structure remain to be investigated. 相似文献
12.
Electronic commerce is an important application that has evolved significantly recently. However, electronic commerce systems
are complex and difficult to be correctly designed. Guaranteeing the correctness of an e-commerce system is not an easy task
due to the great amount of scenarios where errors occur, many of them very subtle. In this work we presents a methodology
that uses formal-method techniques, specifically symbolic model checking, to design electronic commerce applications and to automatically verify them. Also, a model checking pattern hierarchy has
been developed—it specifies patterns to construct and verify the formal model of e-commerce systems. We consider this research
the first step to the development of a framework, which will integrate the methodology, an e-commerce specification language
based on business rules, and a model checker.
Adriano Pereira received the B.S. and M.S. degrees in computer science in 2000 and 2002, respectively, and he is currently pursuing the Ph.D.
degree in computer science from the Federal University of Minas Gerais, Belo Horizonte, Brazil. His current interests are
on performance analysis and modeling of e-business and distributed systems, and formal methods.
Mark Song received the B.S., M.S. and Ph.D. degrees in computer science from the Federal University of Minas Gerais, Belo Horizonte,
Brazil. His current interests are on distributed systems and formal methods – especially BMC (Bounded Model Checking).
Gustavo Franco received the B.S. and M.S. degrees in computer science in 2001 and 2004, respectively, from the Federal University of Minas
Gerais, Belo Horizonte, Brazil. His research was on modeling the user behavior of e-business and distributed systems, and
formal methods. Actually his current interests are on software engeneering and project management of IT projects. 相似文献
13.
14.
In this paper, an original spatial shape error-concealment technique, to be used in the context of object-based image and video coding schemes, is proposed. In this technique, it is assumed that the shape of the corrupted object at hand is in the form of a binary alpha plane, in which some of the shape data is missing due to channel errors. From this alpha plane, a contour corresponding to the border of the object can be extracted. However, due to errors, some parts of the contour will be missing and, therefore, the contour will be broken. The proposed technique relies on the interpolation of the missing contours with Bézier curves, which is done based on the available surrounding contours. After all the missing parts of the contour have been interpolated, the concealed alpha plane can be easily reconstructed from the fully recovered contour and used instead of the erroneous one improving the final subjective impact. 相似文献
15.
Celso M. F. Lapa Cludio M. N. A. Pereira Paulo F. Frutuoso e Melo 《Reliability Engineering & System Safety》2003,81(1):103-109
In order to maximize systems average availability during a given period of time, it has recently been developed a non-periodic surveillance test optimization methodology based on genetic algorithms (GA). The fact of allowing non-periodic tests turns the solution space much more flexible and schedules can be better adjusted, providing gains in the overall system average availability, when compared to those obtained by an optimized periodic test scheme. This approach, however, turns the optimization problem more complex. Hence, the use of a powerful optimization technique, such as GA, is required.Considering that some particular features of certain systems can turn it advisable to introduce other specific constraints in the optimization problem, this work investigates the application of seasonal constraints for the set of the Emergency Diesel Generation of a typical four-loop pressurized water reactor in order to planning and optimizing its surveillance test policy. In this analysis, the growth of the blackout accident probability during summer, due to electrical power demand increases, was considered. Here, the used model penalizes surveillance test interventions when the blackout probability is higher.Results demonstrate the ability of the method in adapting the surveillance test policy to seasonal constraints. The knowledge acquired by the GA during the searching process has lead to test schedules that drastically minimize test interventions at periods of high blackout probability. It is compensated by more frequent redistributed tests through the periods of low blackout probability in order to improve on the overall average availability at the system level. 相似文献
16.
Schottky diodes were built on different polycrystalline diamond films grown by Microwave Plasma and Hot Filament Chemical Vapor Deposition and their electrical properties were studied. The barrier height increased with the diamond film quality and the corresponding ideality factor decreased. Even though the lower-quality HFCVD film displayed poor rectifying properties, it was found to be much less sensitive to variations in the operating conditions (air vs. vacuum). The activation energies of the films depend on morphological parameters, as preferable grain size or orientation. The bulk conduction also depends on the quality of the deposited films, changing from ohmic to trap-free or shallow trap SCLC and SCLC with an exponential distribution of traps. The hypothesis of using the electrical measurements as an indicator for film quality has been discussed. 相似文献
17.
We compute the temperature dependent magnetic susceptibility of the single-impurity, two-channel Anderson model with an alternative multi-step numerical renormalization-group transformation, previously applied only to the two-impurity single-channel Kondo model. Compared with the traditional transformation, the new procedure requires substantially less memory and computational time, and opens therefore perspectives for the application of the numerical renormalization-group procedure to more complex Hamiltonians. 相似文献
18.
Presentation of our experience in three cases of urocolpos (acquired pudendal lip fusion), a series numerically equivalent to the total number of cases published until now. All patients in our series were older women and presented complete fusion of the small pudendal lips, with only a small pointed puncture in the lower part of the vulva. The main clinical signs and symptoms in our series were: urinary infection in 100%, false incontinence in 66% due to output of urine retained in the vagina, a symptom that has not been described earlier, and acute urine retention in 33%. All patients were successfully treated by means of surgical loosening of the fusioned lips and application of topical estrogens. An analysis is made of clinical and pathoanatomical features which differentiate this entity from the sclerotic and atrophic lichen. Finally, an etiopathogenic hypothesis is raised to explain the fusion acquired by the small pudendal lips in the urocolpos. 相似文献
19.
Alfredo D. Mazzoni Esteban E Aglietti Enrique Pereira 《Journal of the American Ceramic Society》1993,76(9):2337-2340
β'-Sialons are phases of the Si-Al-O-N system. The carbonitriding of clays and kaolins is a preparation method. The reaction mechanism of clay carbonitriding is verified by means of the relation among crystalline phases formed and the weight loss produced in the samples during the reaction. Two clays were previously mixed with carbon black and pressed into pellets, flowing through N2 atmosphere, at five temperatures within the range 1335–1427°C. The phases formed (XRD)—mullite, SiC, β'A-sialon, and oxynitrides—were related to the weight loss measured in the pellet independently of reaction temperature and time. The β'A-sialon and the nitrogenous phases were formed from SiC and mullite. A z value decrease for β'A-sialon was observed during reaction progression. 相似文献
20.