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1.
OA al-Swayeh MS al-Humayyd AA Mustafa AS al-Tuwaijri RS al-Rashed AT Ali 《Canadian Metallurgical Quarterly》1997,12(7):481-489
Recent evidence suggests that oxygen-derived free radicals are involved in mediating gastric microvascular and parenchymal cell injuries induced by ischaemia and reperfusion. Therefore, the effect of the locally acting anti-ulcer drug, sucralfate, was studied on ischaemia and reperfusion (e.g. induced gastric lesions, intraluminal bleeding, changes in vascular permeability and non-protein sulfhydryl levels in the rat stomach). Allopurinol was used as a known standard antioxidant drug. Rats were subjected to 30 min of gastric ischaemia in the presence of 100 mmol/L hydrochloric acid and reperfusion periods of 15, 30 or 60 min duration. The gastric lesions were assessed microscopically under an inverted microscope. The vascular permeability was quantified by measuring the extravasated Evans blue in the stomach. There were significantly greater numbers of gastric lesions, intraluminal bleeding and leakage of Evans blue during all reperfusion periods as compared with those of ischaemia, with maximum effects occurring at 60 min following reperfusion. Pretreatment with sucralfate (31.25-250 mg/kg, p.o.) or allopurinol (12.5-50 mg/kg, i.p.) 30 min before the procedure, dose-dependently reduced the gastric lesions, intraluminal bleeding, and decreased the vascular permeability induced by ischaemia and reperfusion. Furthermore, sucralfate dose-dependently reverses the ischaemia and reperfusion-induced depletion of mucosal non-protein sulfhydryl levels and inhibited the superoxide radical production in both cell-free xanthine-xanthine oxidase and in the stimulated polymorphonuclear cellular systems. These results suggest that the protection produced by sucralfate against gastric injury may be due to its antioxidant effects. 相似文献
2.
The aim of this paper is to give a general quantitative requirement which the loop gain must satisfy in order to stabilize a given unstable (possibly nonlinear and time-varying) plant, namely that the gain must exceed one. 相似文献
3.
Timothy Thomasma Kurt Hilbrecht 《International Journal of Flexible Manufacturing Systems》1991,3(3-4):231-250
Good methods are needed to specify, test, and debug material-handling control logic. This article surveys a number of representative methods for defining and describing control algorithms for programmable material-handling equipment used in flexible manufacturing systems. The methods are evaluated with regard to their suitability for communication between people and as bases for interfaces to automatic program generators. It is concluded that no single method is entirely satisfactory. Three methods (position diagrams, function block diagrams, and operation networks) have potential to be combined into an effective hybrid approach that minimizes the need for the user to switch between various conceptual models. 相似文献
4.
Effect of flexure induced transverse crack and self-healing on chloride diffusivity of reinforced mortar 总被引:2,自引:0,他引:2
Mustafa Şahmaran 《Journal of Materials Science》2007,42(22):9131-9136
Cracks in reinforced concrete are unavoidable. Durability is of increasing concern in the concrete industry, and it is significantly
affected by the presence of cracks. The corrosion of reinforcing steel due to chloride ions in deicing salts or sea-water
is a major cause of premature deterioration of reinforced concrete structures. Although, it is generally recognized that cracks
accelerate the ingress of chlorides in concrete, a lack of consensus on this subject does not yet allow reliable quantification
of their effects. The present work studies the relationship between crack widths and chloride diffusivity. Flexural load was
introduced to generate cracks of width ranging between 29 and 390 μm. As crack width was increased, the effective diffusion
coefficient was also increased, thus reducing the initiation period of corrosion process. For cracks with widths less than
135 μm, the effect of crack widths on the effective diffusion coefficient of mortar was found to be marginal, whereas for
crack widths higher than 135 μm the effective diffusion coefficient increased rapidly. Therefore, the effect of crack width
on chloride penetration was more pronounced when the crack width is higher than 135 μm. Results also indicate that the relation
between the effective diffusion coefficient and crack width was found to be power function. In addition, a significant amount
of self-healing was observed within the cracks with width below 50 μm subjected to NaCl solution exposure. The present research
may provide insight into developing design criteria for a durable concrete and in predicting service life of a concrete structures. 相似文献
5.
Conceptual damage-sensitive features for structural health monitoring: Laboratory and field demonstrations 总被引:2,自引:0,他引:2
F. Necati Catbas Mustafa Gul Jason L. Burkett 《Mechanical Systems and Signal Processing》2008,22(7):1650-1669
The use of damage-sensitive features to evaluate structural condition or health is a very critical aspect of structural health monitoring. The purpose of this paper is to investigate the potential of two different damage-sensitive features for detecting damage. Different damage scenarios are simulated on a large-scale laboratory structure and a three-span highway bridge for demonstration. The features presented in this paper are the modal flexibility-based deflection and curvature both of which are obtained directly from dynamic properties. In the literature, flexibility associated with mode shapes and mode shapes curvatures have been mostly explored. In this study, multi-input–multi-output dynamic data are used to obtain modal flexibility, which is a close approximation to the actual flexibility. A main novelty is that the curvature is calculated from the deflected shapes using the modal flexibility as opposed to using modal vectors. In this paper, the theory of the methodology is explained and then experimental studies and results are presented. For the experimental studies, the laboratory specimen and the three-span bridge were gradually damaged. It is shown that both deflection and curvature are conceptual and physically meaningful features for damage detection and localization. The issues and the requirements for these features to perform successfully are also presented. 相似文献
6.
7.
The parallel language FORK [1], based on a scalable shared memory model, is a PASCAL-like language with some additional parallel constructs. A PRAM (Parallel Random Access Machine) algorithm can be expressed on a high level of abstraction as a FORK program which is translated into efficient PRAM code guaranteeing theoretically predicted runtimes.
In this paper, we concentrate on those features of the language FORK related to parallelism, such as the group concept, a shared memory access and synchronous or asynchronous execution. We present a trace-based denotational interleaving semantics where processes describe synchronous computations. Processes are created or deleted dynamically and run asynchronously. Interleaving rules reflect the underlying CRCW (concurrent-read-concurrent-write) PRAM model. 相似文献
8.
9.
Summary Potential polymeric herbicides have been synthesized by reacting poly(acrylic acid)s with 3-aniino-1,2,4-triazole and 1-acetyl-5-amino-1,2,4-triazole, respectively. The produced copolymers contained the active moieties as pendant groups in the range of 3 to 27 per cent of weight and with a content of carboxyl groups up to 95 mol-%. The hydrolytic release of 3-amino-1,2,4-triazole was investigated.Part 12: M. Hartmann, H,-J. Bauer, A. Pritzsche and K. Wermann, Makromol. Chem., in press 相似文献
10.
The man-machine dialog is very important for the design process. In this paper a program system, based on the minicomputer KRS 4201 (ROBOTRON), is demonstrated by using an interactive graphical screen. This program system provides the opportunity to analyze and synthesize mechanisms up to 16 links. The application is demonstrated by designing a front-loader-system for a truck. Real-time animation of seven-bar linkages and coupler curves, including velocity and acceleration, are shown. 相似文献