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Mechanical Resistance (mechanical + resistance)
Selected AbstractsImpaired mastication modifies the dynamics of bolus formationEUROPEAN JOURNAL OF ORAL SCIENCES, Issue 3 2006Claude Yven Mastication is a complex sensory-motor activity whereby a food product is transformed into a bolus. Consumers mainly perceive the sensory properties of the food during the intra-oral manipulation of the product. Consequently, the quality of the chewing process could have consequences on the perception of sensory properties and food choice. By focusing on meat products, this study aimed to analyze the influence of dental status on (i) dynamic adaptation of the chewing behavior (evaluated by electromyography) to the changes in texture during bolus formation and (ii) bolus properties (mechanical resistance and saliva incorporation) obtained from meat of different initial textures. Two groups of subjects (dentate subjects and denture wearers), known to present highly different chewing efficiency, were compared. For both groups, salivary flow rates were evaluated at rest and after stimulation by chewing (paraffin and meat). The salivary flow rates, assessed during chewing of a nonedible matrix (paraffin), were a good predictor of salivary flow rates induced by meat chewing for both groups of subjects. Salivary flow rates were not affected by the dental status. In contrast, the chewing behavior varied between groups. For denture wearers, the chewing pattern was strongly impaired and not adapted to the changes in meat structure during bolus formation. Denture wearers swallowed less fragmented boli than dentate subjects, but boli had a similar level of moisture for both groups of subjects. [source] Structural fire design according to Eurocode 5,design rules and their backgroundFIRE AND MATERIALS, Issue 3 2005Jürgen KönigArticle first published online: 18 NOV 200 Abstract This paper gives a review of the design rules of EN 1995-1-2, the future common code of practice for the fire design of timber structures in the Member States of the EU and EFTA, and makes reference to relevant research background. Compared with the European pre-standard ENV 1995-1-2, the new EN 1995-1-2 has undergone considerable changes. Charring is dealt with in a more systematic way and different stages of protection and charring rates are applied. For the determination of cross-sectional strength and stiffness properties, two alternative rules are given, either by implicitly taking into account their reduction due to elevated temperature by reducing the residual cross-section by a zero-strength zone, or by calculating modification factors for strength and stiffness parameters. Design rules for charring and modification factors are also given for timber frame members of wall and floor assemblies with cavities filled with insulation. A modified components additive method has been included for the verification of the separating function. The design rules for connections have been systemized by introducing simple relationships between the load-bearing capacity (mechanical resistance) and time. The code provides for advanced calculation methods for thermal and structural analysis by giving thermal and thermo-mechanical properties for FE analyses. The code also gives some limited design rules for natural fire scenarios using parametric fire curves. Copyright © 2004 John Wiley & Sons, Ltd. [source] Lesion development in stems of rough- and smooth-barked Eucalyptus nitens following artificial inoculations with canker fungiFOREST PATHOLOGY, Issue 3 2001Z. Q. Yuan A study of lesion development in stems of Eucalyptus nitens following artificial inoculations with canker fungi was carried out on 16-year-old plantation trees. In a first trial cambium bark wounds on smooth- and rough-barked trees were inoculated with the mycelium of nine species of canker fungi, including Endothia gyrosa. In a second trial spores or mycelium of E. gyrosa were applied directly onto undamaged or superficially wounded bark surfaces. Infection subsequent to artificial inoculation via wounding (whatever the wounding technique or type of inoculum) resulted in significantly larger external lesions (mean lesion area up to 35.6 cm2 20 months after inoculation) on smooth bark compared with those on rough bark (up to 19.0 cm2). Microscopic studies of infected rough and smooth bark suggest that, once smooth bark is compromised by wounding and artificial inoculation, the particular anatomical structure of smooth bark may offer less mechanical resistance to post-penetration hyphal spread in comparison with rough bark. It is suggested that at a pre-penetration stage under natural conditions spores of E. gyrosa more easily infect rough bark via cracks associated with this type of bark but not present in smooth bark. Développement des lésions sur les troncs d'Eucalyptus nitens àécorce lisse ou rugueuse, après inoculation par des champignons agents de chancre L'étude a été conduite en plantation sur des arbres de 16 ans. Dans un premier essai, des blessures de l'écorce jusqu'au cambium sur des arbres àécorce lisse ou rugueuse, ont été inoculées avec le mycélium de 9 espèces de champignons agents de chancre, dont Endothia gyrosa. Dans un deuxième essai, des spores ou du mycélium de E. gyrosa ont été appliqués directement sur l'écorce intacte ou blessée seulement superficiellement. Quel que soit la technique d'inoculation ou le type d'inoculum, l'infection a été plus importante extérieurement (surface moyenne jusqu'à 35,6 cm2 après 20 mois) chez les écorces lisses que chez les rugueuses (jusqu'à 19,0 cm2). L'étude microscopique des écorces infectées suggérait qu'à condition que l'écorce lisse soit impliquée dans la blessure, sa structure anatomique particulière offre moins de résistance mécanique à la post-pénétration mycélienne que l'écorce rugueuse. Il est suggéré qu'au stade de la pré-pénétration en conditions naturelles, les spores de E. gyrosa infectent plus facilement l'écorce rugueuse à la faveur des fissures qui sont présentes chez ce type d'écorce mais absentes chez les écorces lisses. Entwicklung von Läsionen am Stamm von rauh- und glattrindigen Individuen von Eucalyptus nitens nach künstlicher Inokulation mit krebserregenden Pilzen Es wurde die Entwicklung von Läsionen an Stämmen 16jähriger Eucalyptus nitens -Pflanzungen nach künstlicher Inokulation mit Krebserregern untersucht. In einem ersten Versuch wurden an rauh- und glattrindigen Bäumen Rindenwunden, die bis zum Kambium reichten, mit Myzel von neun Arten krebserregender Pilze, einschliesslich Endothia gyrosa, beimpft. In einem zweiten Versuch wurden Sporen oder Myzel von E. gyrosa direkt auf unverletzte oder nur oberflächlich verletzte Rinde aufgebracht. Künstliche Inokulation von Wunden (unabhängig von der Methode der künstlichen Verwundung oder der Art des Inokulums) führte zu signifikant grösseren, äusseren Wunden auf glatter (durchschnittliche Läsionsfläche 35.6 cm2 20 Monate nach Inokulation) als auf rauher Rinde (bis 19.0 cm2). Mikroskopische Untersuchungen zeigten, dass glatte Rinde gegen die Ausbreitung von Pilzhyphen mechanisch weniger resistent ist als rauhe Rinde. Unter natürlichen Bedingungen dürften dagegen Sporen von E. gyrosa Bäume mit rauher Rinde leichter durch vorhandene Rindenrisse infizieren, die bei glatter Rinde fehlen. [source] A finite element analysis of ferrule design on restoration resistance and distribution of stress within a rootINTERNATIONAL ENDODONTIC JOURNAL, Issue 6 2006I. Ichim Abstract Aim, To analyse the effect of ferrule height upon the mechanical resistance and stress distribution within a root to explain variations in the pattern of root fracture. Methodology, An extracted, intact, caries free, maxillary right central incisor was scanned by laser and then reconstructed on a computer to produce a model of the tooth and associated periodontal ligament. A simulated post/core/crown restoration was constructed on conventional tooth preparations with various ferrules. The crown was loaded with a simulated 500 N force and the simulated displacement of components and the tensile and compressive stress within the tooth structure were recorded. Results, Without a ferrule preparation, the simulated crown tilted to the labial and rotated distally. With increasing ferrule height the displacement and rotation of the crown reduced in conventional and crown-lengthening models with maximum reduction occurring when the ferrule height reached 1.5 mm. In ferrule models, higher levels of tensile stress developed in internal (by a factor of 8) and mid-root palatal (by a factor of 90) dentine at the cervical margin of the preparation. With an increase in ferrule height, the area of tensile stress within the palatal mid-dentine expanded towards the cervical margin. Similar patterns and stress values were recorded for the crown-lengthening models. Conclusion, The study confirms that a ferrule increases the mechanical resistance of a post/core/crown restoration. However a ferrule creates a larger area of palatal dentine under tensile stress that may be a favourable condition for a crack to develop. Crown-lengthening did not alter the levels or pattern of stress within compared with conventional ferrule preparations. [source] Development of hydrogel patch for controlled release of alpha-hydroxy acid contained in tamarind fruit pulp extractINTERNATIONAL JOURNAL OF COSMETIC SCIENCE, Issue 2 2005J. Viyoch Synopsis The aim of this study was to develop hydrogel patch using crosslinked chitosan,starch as polymeric matrix for controlling the release of the natural alpha-hydroxy acid (AHA) contained in the extract of tamarind's fruit pulp. The chitosan (MW 100 000) was blended with corn, tapioca or rice starch in various ratios and then crosslinked with glutaraldehyde. The physical characteristics, mechanical resistance, bio-adhesion property and surface morphology of the prepared hydrogel patches with and without the extract were investigated. The release patterns of the hydrogel patches containing the extract were investigated by measuring the amount of tartaric acid, a major AHA present in the tamarind's fruit pulp extract, accumulated in the receptor medium of the vertical diffusion cell at various time intervals over a period of 6 h. The results indicated that the formulations of chitosan : corn starch 4.5 : 0.5 with glutaraldehyde 0.02% w/w (C4.5C0.5G0.02) or 0.04% w/w (C4.5C0.5G0.04), chitosan : tapioca starch 4.5 : 0.5 with glutaraldehyde 0.04% w/w (C4.5T0.5G0.04) or 0.05% w/w (C4.5T0.5G0.05), and chitosan : rice starch 4.5 : 0.5 with glutaraldehyde 0.04% w/w (C4.5R0.5G0.04) and chitosan : rice starch 4.0 : 1.0 with glutaraldehyde 0.03% w/w (C4.0R1.0G0.03) provided the flexible and elastic patches with good bio-adhesive property. The tensile strength values ranged from 5 to15 N mm,2 and the elasticity ranged from 30 to 60%. The addition of the extract in these formulations significantly increased the tensile strength values of the obtained patches. The patch of C4.0R1.0G0.03 formulation containing the extract showed relatively highest porosity, corresponding to its highest amount (12.02 ± 0.33 mg) and rate (0.452 ± 0.012 mg mm,2 min,1/2) of tartaric acid released. The amounts of tartaric acid released from the developed hydrogel patches were proportional to a square root of time (Higuchi's model), particularly the release from C4.0R1.0G0.03 (R2, 0.9978 ± 0.0020) and C4.5R0.5G0.04 (R2, 0.9961 ± 0.0024) patches. Résumé Le but de cette étude était de développer un patch hydrogel en utilisant, en tant que matrice polymère, un mélange chitosane/amidon réticulé pour le contrôle du relargage d', -hydroxyacide naturel contenu dans l'extrait de la pulpe du fruit du tamarinier. Du chitosane (MW 100 000) a été mélangéà des farines de maïs, de tapioca ou de riz dans différentes proportions, les mélanges ont été réticulés avec du glutaraldéhyde. Les caractéristiques physiques, résistance mécanique, propriétés de bio adhésion et morphologie de surface des patchs hydrogels préparés avec et sans extrait ont étéétudiées. Le profil de relargage des patchs hydrogels contenant l'extrait a étéétudié en mesurant la quantité d'acide tartarique, , -aminoacide majoritaire présent dans l'extrait, accumulé dans le milieu récepteur d'une cellule à diffusion verticale en fonction du temps sur une période de 6 heures. Les résultats ont montré que les formulations contenant: ,,un mélange chitosane/amidon de maïs dans un rapport 4.5 : 0.5 réticulé avec 0.02% ou 0.04% poids/poids de glutaraldéhyde (respectivement C4.5C0.5G0.02 et C4.5 C0.5 G0.04) ou ,,un mélange de chitosane/amidon de tapioca dans un rapport 4.5 : 0.5 réticulé avec 0.04% ou 0.05% poids/poids de glutaraldéhyde (C4.5T0.5 G0.04ou C4.5 T0.5 G0.05) ,,ainsi que le mélange chitosane/amidon de riz dans un rapport 4.5 : 0.5 réticulé avec 0.04% poids/poids de glutaraldehyde (C4.5R0.5 G0.04) ,,et le mélange chitosane/amidon de riz dans un rapport 4.0 : 1.0 réticulé avec 0,03% poids/poids de glutaraldehyde (C4.0 R1.0 G0.03) conduisaient à des patchs flexibles et élastiques avec de bonnes propriétés bio adhésives. Leur résistance mécanique varie de 5 à 15 N/m2 et leur élasticité de 30 à 60%. L'addition de l'extrait de fruit à ces formules augmente significativement la résistance mécanique des patchs. Le patch C4.0R1.0 G0.03 contenant l'extrait montre la plus grande porosité correspondant à la quantité d'acide tartarique relargué la plus élevée (12.02 ± 0.33 mg), ainsi qu'à la plus grande vitesse de relargage (0.452 ± 0.012 mg mm- 2 mn- 1/2). Les quantités d'acide tartarique relarguées à partir de patchs hydrogels développés sont proportionnelles à la racine carrée du temps (modèle d'Higuchi), en particulier pour les patchs C4.0 R1.0G0.03 (R2, 0.9978 ± 0.0020) et C4.5R0.5 C0.004 (R2, 0.9061 ± 0.0024). [source] The innervation of FGF-induced additional limbs in the chick embryoJOURNAL OF ANATOMY, Issue 1 2003B. W. Turney Abstract Motoneurones that supply the vertebrate limb innervate their muscle targets in a highly reproducible manner. As development proceeds, these limb-specific motoneurones send out axons, which grow towards the developing limb and then congregate at its base to form the plexus. In the plexus, in response to unknown positional cues, these axons rearrange, often changing their original spatial relationships, before sorting out to emerge in the defined nerve trunks that innervate the limb. Several proposals have been put forward to explain how this reproducible innervation pattern is achieved. These include (1) that early differences in the motoneurone identity dictate their future axonal trajectories, (2) that axons actively respond to attractive or repulsive positional cues provided by the limb bud itself, or (3) that motor axons are passively deployed, following pathways of least mechanical resistance. We have addressed the question of the relative roles of motoneurone identity and the signals that the axons encounter on their journey towards the limb bud. Using the developing chick embryo as our experimental model we tested the effect of providing an additional limb target for motor axons leaving the flank level of the spinal cord. To do this we placed FGF-soaked beads in the presumptive flank of 2-day-old chick embryos. This treatment induces an additional limb containing muscles. We investigated whether such additional limbs are innervated and by which neurones. We show that rather than the additional limbs being solely supplied by axons diverted from the two existing limb plexuses, motoneurones that normally supply the flank alter their trajectories to enter the induced limb. Once in the limb, axons respond to positional cues within the bud to generate the stereotypical innervation pattern. Our results show that the tendency of ,flank' motoneurones to innervate flank can be overcome by the presence of an additional limb. [source] Composites of rigid polyurethane foam and cellulose fiber residueJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2010M. C. Silva Abstract Rigid polyurethane composite foams were prepared with cellulose fibers as a filler. The cellulose fibers were an industrial residue of blanched cellulose pulp production. The influence of the cellulose fiber concentration on the structural, thermal, mechanical, and morphological properties of the foams was investigated. We also studied the influence of the cellulose fibers on the foam's resistance to fungal attack by placing a suspension of known fungus in contact with the surface of the foam and following the morphological evolution as a function of time (for 60 days). The increase in the cellulose filler concentration in the foams, up to 16% w/w with respect to the polyol, changed their properties as follows: (1) the cell size decreased, (2) the thermooxidative stability and mechanical properties remained approximately constant, (3) the thermal conductivity decreased slightly, and (4) fungal growth was observed. Therefore, a cellulosic fibrous industrial residue was rationally valorized as a filler in classical rigid polyurethane foams; this yielded materials with mechanical resistance and a susceptibility to fungi in a wet environment. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Effects of chitosan solution concentration and incorporation of chitin and glycerol on dense chitosan membrane propertiesJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 2 2007Paula Rulf Marreco Dallan Abstract The aim of this work was to perform a systematic study about the effects induced by chitosan solution concentration and by chitin or glycerol incorporation on dense chitosan membranes with potential use as burn dressings. The membrane properties analyzed were total raw material cost, thickness, morphology, swelling ratio, tensile strength, percentage of strain at break, crystallinity, in vitro enzymatic degradation with lysozyme, and in vitro Vero cells adhesion. While the use of the most concentrated chitosan solution (2.5% w/w) increased membrane cost, it also improved the biomaterial mechanical resistance and ductility, as well as reduced membrane degradation when exposed for 2 months to lysozyme. The remaining evaluated properties were not affected by initial chitosan solution concentration. Chitin incorporation, on the other hand, reduced the membranes cost, swelling ratio, mechanical properties, and crystallinity, resulting in thicker biomaterials with irregular surface more easily degradable when exposed to lysozyme. Glycerol incorporation also reduced the membranes cost and crystallinity and increased membranes degradability after exposure to lysozyme. Strong Vero cells adhesion was not observed in any of the tested membrane formulations. The overall results indicate that the majority of the prepared membranes meet the performance requirements of temporary nonbiodegradable burn dressings (e.g. adequate values of mechanical resistance and ductility, low values of in vitro cellular adhesion on their surfaces, low extent of degradation when exposed to lysozyme solution, and high stability in aqueous solutions). © 2006 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2007 [source] Amylin and Bone Metabolism in Streptozotocin-Induced Diabetic RatsJOURNAL OF BONE AND MINERAL RESEARCH, Issue 5 2001Marie-Noëlle Horcajada-Molteni Abstract Amylin (AMY) is a 37 amino acid peptide cosecreted with insulin (INS) by pancreatic ,-cells and absent in type 1 diabetes, a condition frequently associated with osteopenia. AMY binds to calcitonin receptors, lowers plasma calcium concentration, inhibits osteoclast activity, and stimulates osteoblasts. In the present study, we examined the effects of AMY replacement on bone loss in a streptozotocin (STZ)-induced rodent model type 1 diabetes. Of 50 male Wistar rats studied, 40 were made diabetic with intraperitoneal STZ (50 mg/kg; plasma glucose concentrations >11 mM within 5 days). Ten nondiabetic control (CONT) rats received citrate buffer without STZ. Diabetic rats were divided into four groups (n = 10/group) and injected subcutaneously with rat AMY (45 mg/kg), INS (12 U/kg), both (same doses), or saline (STZ; diabetic controls) once per day. After 40 days of treatment and five 24-h periods of urine collection for deoxypyridinoline (DPD), the animals were killed, blood was sampled, and femurs were removed. The left femur was tested for mechanical resistance (three-point bending). The right femur was tested for total, diaphyseal (cortical bone), and metaphyseal (trabecular bone) bone densities using dual-energy X-ray absorptiometry (DXA). Bone was ashed to determine total bone mineral (calcium) content. None of the treatments had any significant effect on femoral length and diameter. Untreated diabetic rats (STZ; 145 ± 7N) had lower bone strength than did nondiabetic CONT (164 ± 38; p < 0.05). Total bone mineral density (BMD; g/cm2) was significantly lower in STZ (0. 2523 ± 0. 0076) than in CONT (0.2826 ± 0.0055), as were metaphyseal and diaphyseal densities. Diabetic rats treated with AMY, INS, or both had bone strengths and bone densities that were indistinguishable from those in nondiabetic CONT. Changes in bone mineral content paralleled those for total BMD (T-BMD). Plasma osteocalcin (OC) concentration, a marker for osteoblastic activity, was markedly lower in untreated diabetic rats (7. 6 ± 0. 9 ng/ml); p < 0. 05) than in nondiabetic CONT (29. 8 ± 1. 7; p < 0. 05) or than in AMY (20. 1 ± 0. 7; p < 0. 05). Urinary DPD excretion, a marker for bone resorption, was similar in untreated and AMY-treated diabetic rats (35.0 ± 3.1 vs. 35.1 ± 4.4 nmol/mmol creatinine), intermediate in rats treated with INS (49.9 ± 2.7), and normalized in diabetic rats treated with both agents (58.8 ± 8.9 vs. 63.2 ± 4.5 in CONT). Thus, in our STZ rat model of diabetic osteopenia, addition of AMY improved bone indices apparently by both inhibiting resorption and stimulating bone formation. [source] Skull anatomy of the miniaturized gecko Sphaerodactylus roosevelti (Squamata: Gekkota)JOURNAL OF MORPHOLOGY, Issue 11 2008Juan D. Daza Abstract A detailed description of the skull and jaw of the gecko Sphaerodactylus roosevelti is presented. The bones are described articulated and isolated with special consideration given to the type of suture among joining elements. S. roosevelti was compared with 109 gekkotan species to evaluate the osteological variation and to find characters for cladistic analysis. Changes in the skull associated with the miniaturization process are discussed within the sphaerodactylid geckos. A noticeable increase of overlapping sutures was observed in the snout of the smallest sphaerodactylids compared to other gekkotans. This pattern is convergent with that in miniaturized pygopodids and may be attributed to adaptations for decreasing mechanical resistance of the cranium during feeding or burrowing. New cranial characters support Sphaerodactylinae as a monophyletic group and should be useful for resolving questions such as their relationship with other gekkotans. J. Morphol. 269:1340,1364, 2008. © 2008 Wiley-Liss, Inc. [source] Effect of freeze-drying and gamma irradiation on the mechanical properties of human cancellous boneJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 3 2000O. Cornu Freeze-drying and gamma irradiation are commonly used for preservation and sterilization in bone banking. The cumulative effects of preparation and sterilization of cancellous graft material have not been adequately studied, despite the clinical importance of graft material in orthopaedic surgery. Taking benefit from the symmetry of the left and right femoral heads, the influence of lipid extraction followed by freeze-drying of a femoral head and a final 25-kGy gamma irradiation was determined, with the nonirradiated, nonprocessed counterpart as the control. Five hundred and fifty-six compression tests were performed (137 pairs for the first treatment and 141 pairs for the second). Mechanical tests were performed after 30 minutes of rehydration in saline solution. Freeze-dried femoral heads that had undergone lipid extraction experienced reductions of 18.9 and 20.2% in ultimate strength and stiffness, respectively. Unexpectedly, the work to failure did not decrease after this treatment. The addition of gamma irradiation resulted in a mean drop of 42.5% in ultimate strength. Stiffness of the processed bone was not modified by the final irradiation, with an insignificant drop of 24%, whereas work to failure was reduced by a mean of 71.8%. Freeze-dried bone was a bit less strong and stiff than its frozen control. Its work to failure was not reduced, due to more deformation in the nonlinear domain, and it was not brittle after 30 minutes of rehydration. Final irradiation of the freeze-dried bone weakened its mechanical resistance, namely by the loss of its capacity to absorb the energy (in a plastic way) and a subsequent greater brittleness. [source] MECHANICAL CHARACTERIZATION OF SHREDDED WHEATJOURNAL OF TEXTURE STUDIES, Issue 5 2008J.B. LAURINDO ABSTRACT The purpose of the study was to evaluate a methodology for mechanical characterization of brittle foods with strong anisotropy. Spoon-sized pieces of three commercial brands of dry shredded wheat were chosen for the demonstration. They were compressed along their three principal axes, individually and grouped in the same orientation. The force-displacement curves in the three directions were all irregular and irreproducible but had discernible features characteristic of the specimen's orientation. When tested as constrained groups, these features could change, depending on the compression direction, reflecting on the contribution of the broken structure's remnants to the specimen's mechanical resistance. The assemblies' force-displacement curves were all smoother than those of the individual particles, a result of the "averaging effect." The overall force level could not be predicted from the number of pieces because of differences in the specimens' post-failure response to added deformation. The jaggedness of the normalized (dimensionless) force oscillations record was quantified in terms of an apparent Kolmogorov (fractal) dimension, determined with the box counting algorithm. Its value strongly depended on the smoothing model's goodness fit if the fit was too close, but not if it only captured the general shape of the force-displacement curve. PRACTICAL APPLICATIONS Despite the irregular and irreproducible mechanical signature of shredded wheat and the dependence on the specimens' orientation, it is still possible to characterize the products' mechanical properties in a way that distinguishes between their overall strength and brittleness. The described method could help to quantify textural differences between these and other brittle food products, and probably identify the conditions under which crunchiness would be maintained or lost. [source] Correlated changes in skeletal muscle connective tissue and flesh texture during starvation and re-feeding in brown trout (Salmo trutta) reared in seawaterJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 11 2004Jérôme Bugeon Abstract Quantitative and qualitative changes to muscle and collagen were analysed following starvation and re-feeding of brown trout (Salmo trutta) reared in seawater. Fish were submitted to starvation for 2 months followed by re-feeding for 1 month and compared with a control group continuously fed. Classical effects of starvation on growth and morphometrics traits were observed with only a partial recovery of these parameters after 1 month of re-feeding. Muscle composition of starved fish was significantly affected (lower dry matter content and higher post-mortem pH) compared with control fish and was partially recovered in re-fed fish compared with continuously fed fish. Muscle structure and composition were affected with thinner muscle fibre and higher connective tissue content for the starved fish but similar thickness of myosepta compared with the control group. No difference was observed after 1 month of re-feeding. Characteristics of the connective tissue were significantly affected by starvation (more high weight molecular collagen form, higher thermal stability of skin collagen). These differences remained significant after the re-feeding period. Starved fish showed also higher mechanical resistance of the raw flesh compared with the control group, but no difference in rheological measurements was observed after 1 month of re-feeding. The changes in texture and their relationships with muscle composition, muscle structure and collagen characteristics are discussed. Copyright © 2004 Society of Chemical Industry [source] Nanoindentation response of compound semiconductorsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2007E. Le Bourhis Abstract The paper reviews the nanoindentation behaviour of III-V semiconductors under concentrated load and its implication for optoelectronic-device design. We consider first, fundamental aspects involved into the mechanical resistance to contact loading of semiconductor single crystals (elastic-plastic transition, indentation strain, hardness-yield relationship). The paper then describes recent applicative studies aimed at improving the heterostructure quality used in optoelectronic applications and emphasizes the so-called mechanical design (alloying and compliant substructure). (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Mechanical Study of High Resistance Silicon Carbide Based Multi-Nano-Layers Grown by Multifrequency PACVDPLASMA PROCESSES AND POLYMERS, Issue S1 2009Farida Rebib Abstract Titanium alloys are commonly used to lighten aeronautical structures. Unfortunately, their poor tribological properties need to confer onto the surface both high mechanical resistance under load and low friction/low wear against other metals. Based on amorphous silicon carbide (a-SiC:H), periodic multi-nano-coatings have been found to be candidates for this use. Such coatings were deposited on Ti surfaces using multifrequency plasma CVD devices. Scratch-testing measurements have revealed that the critical loads corresponding to cohesive/adhesive cracks are significantly increased using multilayered stacks. Fretting-wear tests also revealed the influence of multilayer architecture and preliminary analysis of wear tracks and material transfers leaded to a first classification of the coatings. [source] Mechanically unfolding proteins: The effect of unfolding history and the supramolecular scaffoldPROTEIN SCIENCE, Issue 12 2002Rebecca C. Zinober Abstract The mechanical resistance of a folded domain in a polyprotein of five mutant I27 domains (C47S, C63S I27)5is shown to depend on the unfolding history of the protein. This observation can be understood on the basis of competition between two effects, that of the changing number of domains attempting to unfold, and the progressive increase in the compliance of the polyprotein as domains unfold. We present Monte Carlo simulations that show the effect and experimental data that verify these observations. The results are confirmed using an analytical model based on transition state theory. The model and simulations also predict that the mechanical resistance of a domain depends on the stiffness of the surrounding scaffold that holds the domain in vivo, and on the length of the unfolded domain. Together, these additional factors that influence the mechanical resistance of proteins have important consequences for our understanding of natural proteins that have evolved to withstand force. [source] Experimentelle Untersuchungen zum Schubtragverhalten dünner Scheiben aus Ultrahochfestem Beton,BETON- UND STAHLBETONBAU, Issue 9 2009Julia Heidrich Dipl.-Ing. Versuche; Baustoffe Abstract Ultrahochfester Beton ist ein Baustoff mit herausragenden mechanischen Eigenschaften. Weit gespannte Brückentragwerke mit schlanken Stegen aus Ultrahochfestem Beton sind denkbar. Dadurch kann Eigengewicht und Material gespart werden. Die Lebensdauer der Brücken würde aufgrund der Widerstandsfähigkeit gegen mechanische und chemische Einflüsse steigen. Die Zug- und die Druckfestigkeit wurden inzwischen in einigen Forschungsarbeiten untersucht. Demgegenüber gibt es noch kaum Erkenntnisse zum Schubtragverhalten. Auch existieren noch keine Normen oder Vorschriften dazu. Eine Arbeit am Institut für Betonbau der TU-Graz befasst sich mit der Schubtragfähigkeit von schlanken, nicht beulgefährdeten Scheiben aus Ultrahochfestem Beton. Shear Carrying Capacity of Ultra High Performance Concrete Ultra High Performance Concrete is a building material with fantastic mechanical properties. Slender, durable Bridges with large spans and thin webs are imaginable. The life cycle will increase because of the chemical and mechanical resistance. The tension and compression strength are well investigated, but there are less investigations about the shear carrying capacity. One research work at the Institute for Structural Concrete of Graz University of Technology deals with the shear carrying capacity of thin Panels without buckling risk. [source] Beton unter hohen Temperaturen , eine Frage der TunnelsicherheitBETON- UND STAHLBETONBAU, Issue 2 2006Konrad Bergmeister Prof. Dipl.-Ing. Die Sicherheit in den Tunnels wird einerseits durch das Verhalten der Benützer und andererseits durch die Konstruktion und Ausstattung bestimmt. Neben der Modellierung des Verhaltens und der Anwendung von Sicherheitstheorien in Tunnel gilt es, organisatorische und erzieherische Maßnahmen in der Planungs-, Ausführungs- und Betriebsphase zu setzen. Durch die extreme Hitzeentwicklung können die Einbauten und das Tunneltragwerk beschädigt werden. Dabei kann es zu Betonabplatzungen (spalling) und zum Ablösen von Betonstücken bzw. Verankerungen kommen. In diesem Beitrag werden unterschiedliche Spritzbetone -experimentell unter hohen Temperaturen untersucht. Dabei zeigt sich, daß die Dichte und die Porenverteilung sowie die Zugkapazität der Betonformulierung von ausschlaggebender Bedeutung sind. Concrete exposed to high Temperatures , a safety Issue of tunnels The safety of tunnels is related to the behaviour of the users as well as to the construction and the equipment, which may be damaged due to heat impact. Concrete spalling decreases the effects of corrosion protection and the bonding of the reinforcement, and the load capacity is also diminished. Predictions about possible concrete spalling and failure mechanism often are based on experimental research. The crucial parameters for concrete spalling are the gas pressure in the pores, the physical properties e. g. water absorption at 20 °C and after 1000 °C and the mechanical resistance. In a full scale fire test in a highway tunnel there have been investigated various shotcrete mixtures. Pore size and distribution have been determined with the Mercury Intrusion (MIP) Porosimeter, whereas the permeability was calculated using the results of the MIP at different temperatures. It could be shown, that the moisture in the pore system and the physical and chemical adsorpted water in the matrix as well as in the aggregates evaporates under external increase of temperature and thus leading to higher pressure. Fire resistant shotcrete for use in tunnel shells should exhibit a certain volume of open pores in order to equalize the vapour pressure. [source] Influence of implant diameter on surrounding boneCLINICAL ORAL IMPLANTS RESEARCH, Issue 5 2007Jeff Brink Abstract Objectives: Implant osseointegration is dependent upon various factors, such as bone quality and type of implant surface. It is also subject to adaptation in response to changes in bone metabolism or transmission of masticatory forces. Understanding of long-term physiologic adjustment is critical to prevention of potential loss of osseointegration, especially because excessive occlusal forces lead to failure. To address this issue, wide-diameter implants were introduced in part with the hope that greater total implant surface would offer mechanical resistance. Yet, there is little evidence that variation in diameter translates into a different bone response in the implant vicinity. Therefore, this study aimed at comparing the impact of implant diameter on surrounding bone. Material and methods: Twenty standard (3.75 mm) and 20 wide (5 mm) implants were placed using an animal model. Histomorphometry was performed to establish initial bone density (IBD), bone to implant contact (BIC) and adjacent bone density (ABD). Results: BIC was 71% and 73%, whereas ABD was 65% and 52%, for standard and wide implants, respectively. These differences were not statistically different (P>0.05). Correlation with IBD was then investigated. BIC was not correlated with IBD. ABD was not correlated to IBD for standard implants (r2=0.126), but it was correlated with wide implants (r2=0.82). In addition, a 1 : 1 ratio between IBD and ABD was found for wide implants. It can be concluded, within the limits of this study, that ABD may be influenced by implant diameter, perhaps due to differences in force dissipation. [source] | ||||||||||||||||||||||