Home About us Contact
|
Home About us Contact | ||
|
|
||
High Strains (high + strain)
Terms modified by High Strains Selected AbstractsThe Effect of In Vivo Mechanical Loading on Estrogen Receptor , Expression in Rat Ulnar Osteocytes,,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 9 2002P. J. Ehrlich Abstract The presence of estrogen receptor , (ER,) in osteocytes was identified immunocytochemically in transverse sections from 560 to 860 ,m distal to the midshaft of normal neonatal and adult male and female rat ulnas (n = 3 of each) and from adult male rat ulnas that had been exposed to 10 days of in vivo daily 10-minute periods of cyclic loading producing peak strains of either ,3000 (n = 3) or ,4000 microstrain (n = 5). Each animal ambulated normally between loading periods, and its contralateral ulna was used as a control. In animals in which limbs were subject to normal locomotor loading alone, 14 ±1.2% SEM of all osteocytes in each bone section were ER, positive. There was no influence of either gender (p = 0.725) or age (p = 0.577) and no interaction between them (p = 0.658). In bones in which normal locomotion was supplemented by short periods of artificial loading, fewer osteocytes expressed ER, (7.5 ± 0.91% SEM) than in contralateral control limbs, which received locomotor loading alone (14 ± 1.68% SEM; p = 0.01; median difference, 6.43; 95% CI, 2.60, 10.25). The distribution of osteocytes expressing ER, was uniform across all sections and thus did not reflect local peak strain magnitude. This suggests that osteocytes respond to strain as a population, rather than as individual strain-responsive cells. These data are consistent with the hypothesis that ER, is involved in bone cells' responses to mechanical strain. High strains appear to decrease ER, expression. In osteoporotic bone, the high strains assumed to accompany postmenopausal bone loss may reduce ER, levels and therefore impair the capacity for appropriate adaptive remodeling. [source] A Novel Hydrogel with High Mechanical Strength: A Macromolecular Microsphere Composite Hydrogel,ADVANCED MATERIALS, Issue 12 2007T. Huang A novel hydrogel with a new, well- defined network structure is prepared through a two-step method in which the radiation-peroxidized macromolecular microspheres act as both initiators and crosslinkers. The macromolecular microsphere composite hydrogel (see figure) can effectively dissipate applied mechanical stress and has extremely high mechanical strength. Some of the hydrogels can nearly completely recover their original shapes, even after an extremely high strain (99.7%) in compression tests. [source] NO emission characteristics in counterflow diffusion flame of blended fuel of H2/CO2/ArINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 3 2002Jeong Park Abstract Flame structure and NO emission characteristics in counterflow diffusion flame of blended fuel of H2/CO2/Ar have been numerically simulated with detailed chemistry. The combination of H2, CO2 and Ar as fuel is selected to clearly display the contribution of hydrocarbon products to flame structure and NO emission characteristics due to the breakdown of CO2. A radiative heat loss term is involved to correctly describe the flame dynamics especially at low strain rates. The detailed chemistry adopts the reaction mechanism of GRI 2.11, which consists of 49 species and 279 elementary reactions. All mechanisms including thermal, NO2, N2O and Fenimore are taken into account to separately evaluate the effects of CO2 addition on NO emission characteristics. The increase of added CO2 quantity causes flame temperature to fall since at high strain rates a diluent effect is prevailing and at low strain rates the breakdown of CO2 produces relatively populous hydrocarbon products and thus the existence of hydrocarbon products inhibits chain branching. It is also found that the contribution of NO production by N2O and NO2 mechanisms are negligible and that thermal mechanism is concentrated on only the reaction zone. As strain rate and CO2 quantity increase, NO production is remarkably augmented. Copyright © 2002 John Wiley & Sons, Ltd. [source] Mechanical loading stimulates ecto-ATPase activity in human tendon cellsJOURNAL OF CELLULAR BIOCHEMISTRY, Issue 1 2005M. Tsuzaki Abstract Response to external stimuli such as mechanical signals is critical for normal function of cells, especially when subjected to repetitive motion. Tenocytes receive mechanical stimuli from the load-bearing matrix as tension, compression, and shear stress during tendon gliding. Overloading a tendon by high strain, shear, or repetitive motion can cause matrix damage. Injury may induce cytokine expression, matrix metalloproteinase (MMP) expression and activation resulting in loss of biomechanical properties. These changes may result in tendinosis or tendinopathy. Alternatively, an immediate effector molecule may exist that acts in a signal-dampening pathway. Adenosine 5,-triphosphate (ATP) is a candidate signal blocker of mechanical stimuli. ATP suppresses load-inducible inflammatory genes in human tendon cells in vitro. ATP and other extracellular nucleotide signaling are regulated efficiently by two distinct mechanisms: purinoceptors via specific receptor,ligand binding and ecto-nucleotidases via the hydrolysis of specific nucleotide substrates. ATP is released from tendon cells by mechanical loading or by uridine 5,-triphosphate (UTP) stimulation. We hypothesized that mechanical loading might stimulate ecto-ATPase activity. Human tendon cells of surface epitenon (TSC) and internal compartment (TIF) were cyclically stretched (1 Hz, 0.035 strain, 2 h) with or without ATP. Aliquots of the supernatant fluids were collected at various time points, and ATP concentration (ATP) was determined by a luciferin-luciferase bioluminescence assay. Total RNA was isolated from TSC and TIF (three patients) and mRNA expression for ecto-nucleotidase was analyzed by RT-PCR. Human tendon cells secreted ATP in vitro (0.5,1 nM). Exogenous ATP was hydrolyzed within minutes. Mechanical load stimulated ATPase activity. ATP was hydrolyzed in mechanically loaded cultures at a significantly greater rate compared to no load controls. Tenocytes (TSC and TIF) expressed ecto-nucleotidase mRNA (ENTPD3 and ENPP1, ENPP2). These data suggest that motion may release ATP from tendon cells in vivo, where ecto-ATPase may also be activated to hydrolyze ATP quickly. Ecto-ATPase may act as a co-modulator in ATP load-signal modulation by regulating the half-life of extracellular purine nucleotides. The extracellular ATP/ATPase system may be important for tendon homeostasis by protecting tendon cells from responding to excessive load signals and activating injurious pathways. © 2005 Wiley-Liss, Inc. [source] Reaction localization and softening of texturally hardened mylonites in a reactivated fault zone, central ArgentinaJOURNAL OF METAMORPHIC GEOLOGY, Issue 6 2005S. J. WHITMEYER Abstract The Tres Arboles ductile fault zone in the Eastern Sierras Pampeanas, central Argentina, experienced multiple ductile deformation and faulting events that involved a variety of textural and reaction hardening and softening processes. Much of the fault zone is characterized by a (D2) ultramylonite, composed of fine-grained biotite + plagioclase, that lacks a well-defined preferred orientation. The D2 fabric consists of a strong network of intergrown and interlocking grains that show little textural evidence for dislocation or dissolution creep. These ultramylonites contain gneissic rock fragments and porphyroclasts of plagioclase, sillimanite and garnet inherited from the gneissic and migmatitic protolith (D1) of the hangingwall. The assemblage of garnet + sillimanite + biotite suggests that D1-related fabrics developed under upper amphibolite facies conditions, and the persistence of biotite + garnet + sillimanite + plagioclase suggests that the ultramylonite of D2 developed under middle amphibolite facies conditions. Greenschist facies, mylonitic shear bands (D3) locally overprint D2 ultramylonites. Fine-grained folia of muscovite + chlorite ± biotite truncate earlier biotite + plagioclase textures, and coarser-grained muscovite partially replaces relic sillimanite grains. Anorthite content of shear band (D3) plagioclase is c. An30, distinct from D1 and D2 plagioclase (c. An35). The anorthite content of D3 plagioclase is consistent with a pervasive grain boundary fluid that facilitated partial replacement of plagioclase by muscovite. Biotite is partially replaced by muscovite and/or chlorite, particularly in areas of inferred high strain. Quartz precipitated in porphyroclast pressure shadows and ribbons that help define the mylonitic fabric. All D3 reactions require the introduction of H+ and/or H2O, indicating an open system, and typically result in a volume decrease. Syntectonic D3 muscovite + quartz + chlorite preferentially grew in an orientation favourable for strain localization, which produced a strong textural softening. Strain localization occurred only where reactions progressed with the infiltration of aqueous fluids, on a scale of hundreds of micrometre. Local fracturing and microseismicity may have induced reactivation of the fault zone and the initial introduction of fluids. However, the predominant greenschist facies deformation (D3) along discrete shear bands was primarily a consequence of the localization of replacement reactions in a partially open system. [source] In Situ Transmission Electron Microscopy of Electric Field-Triggered Reversible Domain Formation in Bi-Based Lead-Free PiezoceramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2010Jens Kling A lead-free piezoelectric 0.91(Bi1/2Na1/2)TiO3,0.06BaTiO3,0.03(K0.5Na0.5)NbO3 ceramic with high strain was examined in situ under an applied electric field using the transmission electron microscope. No domain structure is observed without an electric field, but an alternating electric field leads to the reversible formation of a lamellar domain structure. Correlations to polarization and strain hysteresis loop measurements indicate an electric field-induced phase transition from a nonpolar to a ferroelectric state and vice versa. [source] Boundary characteristics in Heavily Deformed Metals,ADVANCED ENGINEERING MATERIALS, Issue 5 2003G. Winther Abstract The potential of creating nanostructured metals by plastic deformation to very high strains is currently the subject of intensive research. An important part of this research concerns evolution of the characteristics of deformation induced boundaries, in particular boundary spacing and boundary misorientation. The aim of this paper is to give an overview of the present understanding of the relations between these characteristics, the microscopic deformation mechanisms and the macroscopic deformation mode. [source] High-Strain Lead-free Antiferroelectric ElectrostrictorsADVANCED MATERIALS, Issue 46 2009Shan-Tao Zhang Research on lead-free piezoceramics has dramatically increased over the last years due to stringent legislation demanding to phase out current lead-containing piezoceramics. The use of electrostrictive materials for electric-field induced strain has been largely overlooked. In this paper we demonstrate that electrostrictive materials around a ferroelectric,antiferroelectric transition are capable of providing high strains over a wide temperature regime that was not accessible before. [source] Experimental investigation of slip-stick behaviour in granular materialsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 14 2006Khalid A. Alshibli Abstract This paper presents the results of an experimental programme to study load oscillation in granular materials. Spherical glass beads were used in the investigation. Cylindrical specimens were compressed under axisymmetric triaxial loading condition at 25,100,250 and 400 kPa confining pressures. The test parameters included: (i) particle size; (ii) gradation (uniform versus non-uniform specimens); (iii) confining pressure; (iv) loading rate; and (v) specimen density. In general, a slight post-peak principal stress softening was observed as well as a continuous volume increase (dilation) even at relatively high strains. This appears to be caused by the uniform shape and smooth surface of the spherical particles. Load oscillations were observed in the very small, small, and well-graded beads at each confining pressure. For the medium beads, the oscillations appeared at high confining pressure (250 and 400 kPa), and they did not appear in the large beads. The influences of the confining pressure, loading rate, particle size, gradation and specimen density on load oscillation are presented and discussed. Copyright © 2006 John Wiley & Sons, Ltd. [source] The influence of in situ modification of silica on filler network and dynamic mechanical properties of silica-filled solution styrene,butadiene rubberJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008You-Ping Wu Abstract The influence of in situ modification of silica with bis-(3-(triethoxysilyl)-propyl)-tetrasulfide (TESPT) on filler network in silica filled solution SBR compound was investigated. In situ modification greatly increased the bound rubber content. TEM observation of silica gel showed that bridging and interlocking of absorbed chains on the surface of silica particles formed the filler network. Rubber processing analyzer (RPA) was used to characterize the filler network and interaction between silica and rubber by strain and temperature sweeps. In situ modification improved the dispersion of silica, and in the meantime, the chemical bonds were formed between silica and rubber, which conferred the stability of silica dispersion during the processing. Compared to the compound without in situ modification, the compound with in situ modification of silica exhibited higher tan , at low strains and lower tan , at high strains, which can be explained in terms of filler network in the compounds. After in situ modification, DMTA results showed silica-filled SSBR vulcanizate exhibited higher tan , in the temperature range of ,30 to 10°C, and RPA results showed that it had lower tan , at 60°C when the strain was more than 3%. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] The Effect of In Vivo Mechanical Loading on Estrogen Receptor , Expression in Rat Ulnar Osteocytes,,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 9 2002P. J. Ehrlich Abstract The presence of estrogen receptor , (ER,) in osteocytes was identified immunocytochemically in transverse sections from 560 to 860 ,m distal to the midshaft of normal neonatal and adult male and female rat ulnas (n = 3 of each) and from adult male rat ulnas that had been exposed to 10 days of in vivo daily 10-minute periods of cyclic loading producing peak strains of either ,3000 (n = 3) or ,4000 microstrain (n = 5). Each animal ambulated normally between loading periods, and its contralateral ulna was used as a control. In animals in which limbs were subject to normal locomotor loading alone, 14 ±1.2% SEM of all osteocytes in each bone section were ER, positive. There was no influence of either gender (p = 0.725) or age (p = 0.577) and no interaction between them (p = 0.658). In bones in which normal locomotion was supplemented by short periods of artificial loading, fewer osteocytes expressed ER, (7.5 ± 0.91% SEM) than in contralateral control limbs, which received locomotor loading alone (14 ± 1.68% SEM; p = 0.01; median difference, 6.43; 95% CI, 2.60, 10.25). The distribution of osteocytes expressing ER, was uniform across all sections and thus did not reflect local peak strain magnitude. This suggests that osteocytes respond to strain as a population, rather than as individual strain-responsive cells. These data are consistent with the hypothesis that ER, is involved in bone cells' responses to mechanical strain. High strains appear to decrease ER, expression. In osteoporotic bone, the high strains assumed to accompany postmenopausal bone loss may reduce ER, levels and therefore impair the capacity for appropriate adaptive remodeling. [source] Neurophysiological and biomechanical characterization of goat cervical facet joint capsulesJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 4 2005Ying Lu Abstract Cervical facet joints have been implicated as a major source of pain after whiplash injury. We sought to identify facet joint capsule receptors in the cervical spine and quantify their responses to capsular deformation. The response of mechanosensitive afferents in C5,C6 facet joint capsules to craniocaudal stretch (0.5 mm/s) was examined in anaesthetized adult goats. Capsular afferents were characterized into Group III and IV based on their conduction velocity. Two-dimensional strains across the capsules during stretch were obtained by a stereoimaging technique and finite element modeling. 17 (53%) Group III and 14 (56%) Group IV afferents were identified with low strain thresholds of 0.107 ± 0.033 and 0.100 ± 0.046. A subpopulation of low-strain-threshold afferents had discharge rate saturation at the strains of 0.388 ± 0.121 (n = 9, Group III) and 0.341 ± 0.159 (n = 9, Group IV). Two (8%) Group IV units responded only to high strains (0.460 ± 0.170). 15 (47%) Group III and 9 (36%) Group IV units could not be excited even by noxious capsular stretch. Simple linear regressions were conducted with capsular load and principal strain as independent variables and neural response of low-strain-threshold afferents as the dependent variable. Correlation coefficients (R2) were 0.73 ± 0.11 with load, and 0.82 ± 0.12 with principal strain. The stiffness of the C5,C6 capsules was 16.8 ± 11.4 N/mm. Our results indicate that sensory receptors in cervical facet joint capsules are not only capable of signaling a graded physiological mechanical stimulus, but may also elieit pain sensation under excessive deformation. © 2005 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved. [source] Masticatory stress and the mechanics of "wishboning" in colobine jawsAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 3 2009David J. Daegling Abstract Cercopithecoid monkeys experience relatively high strains along the lingual aspect of the mandibular symphysis because of lateral transverse bending of the mandibular corpora ("wishboning") during mastication. Hylander (Am J Phys Anthropol 64 (1984) 1,46; Am Zool 25 (1985) 315,330) demonstrated that the distribution of strains arising from wishboning loads is comprehensible with reference to the mechanics of curved beams. Theory of curved beams suggests that lingual tensile strains are some multiple of labial compressive strains, yet limitations of experimental methods and uncertainty in estimating parameters needed for theoretical calculations have confounded attempts to characterize the magnitude of this disparity of normal strains. We evaluate the theoretical disparity of normal strains in wishboning in comparison to in vitro strains collected under controlled loads for a sample of mandibles representing two colobine species (N = 6). These data suggest that in colobine monkeys, maximum normal lingual strains should be at least twice maximum labial strains. In addition, we reexamine the distribution of symphyseal stress under an assumption of asymmetric bending, a general approach for calculation of stress appropriate for members that lack a plane of symmetry and are bent along an axis that is not coincident with the member's principal axes. Under asymmetric bending in colobine mandibles, the effect of symphyseal inclination on lingual strain is mitigating at the superior transverse torus and exacerbating at the inferior transverse torus. Relative compliance of colobine mandibular bone further supports the hypothesis that the structural and material properties of the colobine mandibular symphysis do not represent a morphological strategy for minimizing masticatory strain. Am J Phys Anthropol, 2009. © 2008 Wiley-Liss, Inc. [source] | ||||||||||||||||