Computation model of corrosion-fatigue crack growth in thin metallic plates

A computation model of corrosion-fatigue crack growth in thin metallic plates is suggested based on well-known theoretical concepts of fatigue and corrosion fracture and some assumptions. A physicochemical model of this process is constructed, and mathematical relations that describe the kinetics of crack propagation are established. The model agrees with well-known experimental data.Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 30, No. 1, pp. 30–34, January–February, 1994.     

Renal sodium excretion after oral or intravenous sodium loading in sodium-deprived normotensive and spontaneously hypertensive rats

Spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats that had been on a low sodium diet for 3 days were given 1.5 mmol sodium chloride kg-1 body weight either orally or intravenously. The rats receiving an oral sodium load showed a greater natriuresis than those receiving the same saline load intravenously. No increase of renal sodium excretion was observed when the rats received a hypertonic mannitol solution orally. The cumulative sodium excretion during the 8 h following oral loading was two to three times larger in SHR than in WKY, whereas no difference between strains could be demonstrated after giving saline intravenously. Furthermore, after switching from normal to low sodium diet the rate of decrease of renal sodium excretion was greater in SHR than in WKY rats. It is proposed that there exists a gastrointestinal sensory mechanism for sodium controlling the renal sodium excretion. Furthermore, it is suggested that the function of this mechanism differs between SHR and WKY.     

Rat heart-aorta cluster transplantation: a novel model to study transplant rejection

The purpose of this study was to develop a microsurgical cluster model of heart plus entire thoracic aorta transplantation and to compare it to the isolated model of heart transplantation as a tool to study transplant rejection. Thirty-six syngeneic (DA x DA and Lew x Lew) and allogeneic (DA x PVG and DA x Lew) cluster heart-aorta transplants were compared to 43 syngeneic and allogeneic isolated heart grafts. Graft survival, recipient survival and histological data on myocardial and aortic tissues were assessed. There was no statistically significant difference in graft survival between the two models studied (P > 0.05). In the cluster transplants, the aortic component was spared the severity of acute rejection noted for the myocardial counterpart. In conclusion, the results demonstrated that the cluster model was technically feasible and highly reproducible. Additionally, it was possible to apply this model to the study of experimental allograft rejection using novel immunosuppressants. The success of the cluster model in strongly mismatched transplant strain combinations underscores its potential for application in slower rejection combinations, making it particularly suited for chronic rejection studies. The inherent capacity for sampling a broader range of vessel sizes in one animal makes the cluster model more suitable than the isolated models of aorta or heart for application to experimental protocols.     

An exploration of expertise of knowledge workers: towards a definition of the universe of discourse for knowledge acquisition

Abstract. Knowledge systems development and use have been significantly encumbered by the difficulties of eliciting and formalizing the expertise upon which knowledge workers rely. This paper approaches the problem from an examination of the knowledge competencies of knowledge workers in order to define a universe of discourse for knowledge elicitation. It outlines two categories and several types of knowledge that could serve as the foundations for the development of a theory of expertise.     

Visual, cognitive, and neurodevelopmental outcome at 51/2 years in children with perinatal haemorrhagic-ischaemic brain lesions

To determine predictive values of early visual and neurocognitive assessment in children with perinatally acquired haemorrhagic or ischaemic brain lesions selected on the basis of ultrasound, 63 children (37 boys, 26 girls), who had been followed and examined until the age of 18 months, were reexamined at 5 1/2 years. Good correlations between visual and neurodevelopmental assessments at 18 months and at 5 1/2 years were found. When ultrasound abnormalities were combined with early visual and neurocognitive assessment data, good predictive values, especially for the group of children who had grade 2 to 4 leukomalacia, were found for visual acuity and neurodevelopment.     

Transport of arginine and ornithine into isolated mitochondria of Saccharomyces cerevisiae

In this work we have characterised the transport of L-arginine and L-ornithine into mitochondria isolated from a wild-type Saccharomyces cerevisiae strain and an isogenic arg11 knock-out mutant. The Arg11 protein (Arg11p) is a mitochondrial carrier required for arginine biosynthesis [Crabeel, M., Soetens, O., De Rijcke, M., Pratiwi, R. & Pankiewicz, R. (1996) J. Biol. Chem. 271, 25011-25019]. Reconstitution experiments have confirmed that it is an L-ornithine carrier also transporting L-arginine and L-lysine by order of decreasing affinity, but not L-histidine [Palmieri, L., De Marco, V., Iacobazzi, V., Palmieri, F., Runswick, M. & Walker, J. (1997) FEBS Lett. 410, 447-451]. Evidence is presented here that the mitochondrial inner membrane contains an L-arginine and L-ornithine transporting system distinct from Arg11p, in keeping with the arginine leaky phenotype of arg11 knock-out mutants. The newly characterised carrier, which we propose to name Bac1p (basic amino acid carrier), behaves as an antiporter catalysing the electroneutral exchange of the basic amino acids L-arginine, L-lysine, L-ornithine and L-histidine and displays the highest affinity for L-arginine (Km of 30 microM). L-Arginine uptake has a pH optimum in the range of 7.5-9 and is inhibited by several sulphydryl reagents, by pyridoxal 5'-phosphate and by cations.     

Dynamic Reservation Multiple Access (DRMA): A new multiple access scheme for Personal Communication System (PCS)

To improve the spectrum efficiency of integrated voice and data services in Personal Communication System (PCS), several reservation-type multiple access schemes, such as Packet Reservation Multiple Access (PRMA), Dynamic Time Division Multiple Access (D-TDMA), Resource Auction Multiple Access (RAMA), etc., have been proposed. PRMA uses the data packet itself to make a channel reservation, and is inefficient in that each unsuccessful reservation wastes one slot. However, it does not have a fixed reservation overhead and offers shorter access delay. On the other hand, fixed reservation overhead is unavoidable in both RAMA and D-TDMA. Compared to D-TDMA and PRMA, RAMA is superior in the sense that its slot assignment is independent of the traffic load. But its implementation is difficult. With these observations, a new reservation protocol, called Dynamic Reservation Multiple Access (DRMA), is proposed in this paper. With this new protocol, the success probability of channel access is greatly improved at the expense of slightly increased system complexity. It solves the problem of inefficiency in PRMA, but without introducing the fixed reservation overhead as in D-TDMA and RAMA. In addition, it is more suited to the dynamic behavior of the integrated traffic because there is no fixed boundary between voice and data slots (which is mandatory in D-TDMA and RAMA). Our numerical results indicate that its performance is superior to the existing reservation protocols, especially in the integrated traffic scenario. Moreover, the soft capacity feature is exhibited when the traffic load increases.     

Practical constraints in growth of lightwave networks

The amount of fiber required, propagation delay, and length of the longest link are significant design constraints in spatially large networks. This paper examines these characteristics from the viewpoint of growth and compares basic networks with hierarchical ones in terms of these characteristics. Results show that, when considering growth from three nodes, a star network randomly placed with a uniform distribution uses less fiber than a dual ring until there are 57 nodes. As the networks become large, the star has the smallest propagation delay and the dual ring uses the least amount of fiber. A two-level network having a star on the upper level and dual rings on the lower network level performs well in both categories by using 1.38 times as much fiber as the dual ring and having 1.65 times the propagation delay of a star as the number of nodes becomes large     

Choosing an optimal set of libraries [software reliability]

This paper presents optimization models for selecting a subset of software libraries, viz, collections of programs, residing on floppy disks or compact disks, available on the market. Each library contains a variety of programs whose reliabilities are assumed to be known. The objective is to maximize the reliability of the computer system subject to a budget constraint on the total cost of the libraries selected. The paper includes six models, each of which applies to a different software structure and assumptions. A detailed branch and bound algorithm for solving one of the six models is described; it contains a simple greedy-procedure for generating an initial solution     

Measurement of the gravitational constant with a torsion balance

We present results of ten years of measurements of the gravitational constant made using an evacuated torsion balance. We obtained the valueG=(6.6729±0.0005)·10⁻¹¹ N·m²·kg⁻². We have determined the major destabilizing factors accompanying the measurement process and have estimated the contribution from different sources of error. Translated from Izmeritel'naya Tekhnika, No. 10, pp. 3–9, October, 1996.