Determination of SIF in a cracked plane orthotropic strip by the Wiener-Hopf technique

The stress intensity factor for a long cracked strip was determined within the context of the linear orthotropic clasticity. The body had the form of an infinite strip containing a semi-infinite crack at the middle distance of the strip faces. Fourier transforms in combination with the Wiener-Hopf technique were employed to evaluate asymptotically the cleavage stress and its intensity at the crack tip.

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Résumé On détermine le facteur d'intensité d'entaille relatif à une longue bande fissurée, dans un contexte d'élasticité linéaire et orthotrope. On considère un corps ayant la forme d'une bande infinie et comportant une fissure semi-infinie à mi-distance des faces de la bande. On recourt à une transformée de Fourier en combinaison avec la technique de Wiener-Hopf pour évaluer par voie asymptotique la tension de clivage et son intensité à l'extrémité de la fissure.

     

The potential for a generic approach to certification of safety critical systems in the transportation sector

This paper investigates the potential for common treatment of certification of safety critical programmable electronic systems in the transportation industries. It contains a comparative review of new, emerging international standards that are likely to influence certification procedures in the railway, automotive and aerospace sectors in the future. These include the EUROCAE/SAE aerospace guidelines, the CENELEC railway standards and IEC-61508, the draft international standard on safety related systems. The review identifies the common and divergent requirements for certification among these standards. Based on significant commonalities, we have developed a common process model for the development, assessment and certification of safety critical programmable electronic systems which could be acceptable in the framework of each standard in consideration. The proposed model contains a system development and a safety assessment process which rationalises and unifies the common requirements among the standards in these areas. In addition, it defines a common evolutionary process for the development of the system's safety case. The safety case process determines how the evidence produced in the progression of safety assessment can be structured in order to form an overall convincing argument about the safety of the system. We conclude that it is possible to use this model as the basis of a generic method for the certification of systems across the transportation sector and outline a suitable approach to such certification.     

Greater rate of decline in maximal aerobic capacity with age in physically active vs. sedentary healthy women

Using a meta-analytic approach, we recently reported that the rate of decline in maximal oxygen uptake (VO2 max) with age in healthy women is greatest in the most physically active and smallest in the least active when expressed in milliliters per kilogram per minute per decade. We tested this hypothesis prospectively under well-controlled laboratory conditions by studying 156 healthy, nonobese women (age 20-75 yr): 84 endurance-trained runners (ET) and 72 sedentary subjects (S). ET were matched across the age range for age-adjusted 10-km running performance. Body mass was positively related with age in S but not in ET. Fat-free mass was not different with age in ET or S. Maximal respiratory exchange ratio and rating of perceived exertion were similar across age in ET and S, suggesting equivalent voluntary maximal efforts. There was a significant but modest decline in running mileage, frequency, and speed with advancing age in ET. VO2 max (ml . kg-1 . min-1) was inversely related to age (P < 0.001) in ET (r = -0.82) and S (r = -0.71) and was higher at any age in ET. Consistent with our meta-analysic findings, the absolute rate of decline in VO2 max was greater in ET (-5.7 ml . kg-1 . min-1 . decade-1) compared with S (-3.2 ml . kg-1 . min-1 . decade-1; P < 0. 01), but the relative (%) rate of decline was similar (-9.7 vs -9. 1%/decade; not significant). The greater absolute rate of decline in VO2 max in ET compared with S was not associated with a greater rate of decline in maximal heart rate (-5.6 vs. -6.2 beats . min-1 . decade-1), nor was it related to training factors. The present cross-sectional findings provide additional evidence that the absolute, but not the relative, rate of decline in maximal aerobic capacity with age may be greater in highly physically active women compared with their sedentary healthy peers. This difference does not appear to be related to age-associated changes in maximal heart rate, body composition, or training factors.     

Novel organic-inorganic glasses

The preparation and properties of novel organic-inorganic glasses with phenyl groups covalently bonded to phosphorus in an inorganic glass are presented. Phenyl phosphonic acid (PPA) can be incorporated into tin and zinc fluorophosphate glasses (MO/MF₂/PO_2.5PPA) at levels up to 72 mol%. The T _g's of these glasses range from below room temperature to near 200°C depending on glass composition. For low melt glasses, these glasses have low moisture absorption and may solubilize dyes, organic photoconductors, NLO molecules, and pharmaceuticals. Several applications have been considered.     

Should laparoscopic appendectomy be avoided for complicated appendicitis in children?

BACKGROUND/PURPOSE: Laparoscopic appendectomy is becoming the preferred technique for treating acute appendicitis. However, recent literature on adults suggests that laparoscopic appendectomy may increase the risk for postoperative infectious complications in complicated (gangrenous or perforated) cases. This study was undertaken to compare the results of open versus laparoscopic appendectomy for complicated appendicitis in children. METHODS: A retrospective review from two institutions was performed for all children treated operatively for complicated appendicitis from January 1994 through November 1996. RESULTS: Fifty-six cases were identified. Twenty-seven children underwent laparoscopic appendectomy, whereas 22 underwent open appendectomy. Seven children underwent conversion from laparoscopic to open surgery. Operating times and length of hospital stay did not differ significantly between the laparoscopic and open groups. Postoperative complications developed in 24 children (42.8%). Complications were more frequent after laparoscopic appendectomy compared with open appendectomy (56% v 18%, P = .002). A postoperative intraabdominal abscess (IAA) developed in 14 children (25%). An IAA occurred in two children after open appendectomy compared with 11 children after laparoscopic appendectomy (9% v 41%, P = .01). CONCLUSION: The findings suggest that laparoscopic appendectomy should be avoided in children who have complicated appendicitis because of the increased risk for postoperative intraabdominal abscesses. The authors propose a prospective, randomized trial to verify this finding.     

Energy,economic and environmental performance of heating systems in Greek buildings

The introduction of natural gas in the Greek energy market broadened the options in the field of space heating. Residents in five major Greek cities can choose from a variety of different fuels and systems for heating their houses or working spaces; 12 more cities will be connected to the gas network within the next 5 years. Considering that space heating is the major energy consuming activity in the Greek building sector and that the environmental constrains imposed by the Kyoto protocol will be met only with difficulty, if at all, a strategy concerning the developments in space heating seems to be necessary. This however presupposes an elaborate analysis of the overall performance of the alternative systems, taking into consideration the particular conditions of the Greek energy system and the ‘established’ way of designing residential and mixed-use buildings. The present paper aims to present the empirical comparative results related to the three most popular heating systems operated in Greek multi-apartment and mixed-use buildings, which use three different fuels, respectively: a central oil-fired boiler, a unitary gas-fired boiler and unitary heat pumps.     

Small-scale crack blunting at a bimaterial interface with Coulomb friction

The deformation field near the tip of a tensional crack impinging upon a normally loaded bimaterial frictional interface is studied. By allowing the two materials to slide with respect to each other along the interface the high stresses around the crack tip are relaxed. The region of slip as well as the stress distribution inside the slip zone is obtained as a function of the far field loading parameter.     

Bonding behaviour of chemically modified wood particles for board production

The objective of this paper was to evaluate the bonding behaviour of chemically modified wood particles towards an isocyanate resin system, as determined from internal bond strength of the board, and to determine which resin system, isocyanate or formaldehyde is suitable for use in boards made from modified raw material. It was found that chemical modification of wood chips and strands did not significantly affect the bonding efficiency of isocyanate resin, but the bonding efficiency of formaldehyde resins was strongly influenced. This behaviour can be a consequence of the usage of a less pH dependent resin that is fully cured during hot pressing in combination with the high mobility of the resin which causes penetration to considerable depth into compressed particles repairing weak zones, which are created during the modification process as chips are exposed to elevated temperatures, by sticking them together. It is suggested therefore, that the isocyanate resin system is more suitable for use in boards made from modified raw material than the formaldehyde resin system.