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Compressive Stress (compressive + stress)
Kinds of Compressive Stress Selected AbstractsEffects of cyclic dynamic tensile strain on previously compressed inner annulus fibrosus and nucleus pulposus cells of human intervertebral disc,an in vitro studyJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 4 2010Hwan Tak Hee Abstract Our objective was to investigate whether dynamic tensile strain on previously compressed human intervertebral disc (IVD) cells can restore the biosynthetic effects of collagen and glycosaminoglycan. Inner annulus fibrosus (AF) and nucleus pulposus (NP) tissues of adolescent idiopathic scoliosis cases undergoing thoracoscopic discectomy and fusion were cultured on compressive plates. Compressive stress was applied using 0.4 MPa at 1 Hz, for 2 h twice a day for 7 days, to the inner AF and NP tissues, followed by equibiaxial cyclic tensile strain to deform the released cells onto the plate's flexible bottom. With 10% elongation at a rate of 1 Hz, for 2 h twice a day for 7 days, a significant increase in the level of collagen and glycosaminoglycan of the previously compressed inner AF, as well as the level of glycosaminoglycan of the previously compressed NP cells were found. The DNA content and number of endoplasmic reticulum under transmission electron micrograph of the previously compressed inner AF and NP cell were also significantly increased. The results suggested that equibiaxial cyclic tensile strain at a rate of 1 Hz with 10% tensile strain was capable of increasing collagen and glycosaminoglycan synthesis of previously compressed inner AF cells, and glycosaminoglycan synthesis of previously compressed NP cells. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:503,509, 2010 [source] Structural composition and sediment transfer in a composite cirque glacier: Glacier de St. Sorlin, FranceEARTH SURFACE PROCESSES AND LANDFORMS, Issue 13 2008Sam Roberson Abstract This paper considers the links between structure, sediment transport and sediment delivery at Glacier de St. Sorlin, France. Sediment transported by the glacier is concentrated at flow-unit boundaries as medial moraines, controlled by the position of bedrock outcrops in the accumulation area. Rockfall entrained within primary stratification is tightly folded at flow-unit boundaries under high cumulative strains and laterally compressive stress. High cumulative strains and laterally compressive stresses lead to the development of longitudinal foliation from primary stratification. Folding elevates subglacial sediments into foliation-parallel debris ridges, which are exposed in the ablation area. Crevasses and shear planes within the glacier have little control on sediment transport. Debris stripes in the proglacial area are morphologically similar to foliation-parallel debris ridges; however, they are not structurally controlled, but formed by fluvial erosion. The conclusion of this study is that at Glacier de St. Sorlin proglacial sediment-landform associations are subjected to intense syn- and post-depositional modification by high melt-water discharges, hence their composition does not reflect that of sediments melting out at the terminus. The action of melt water limits the potential of the sedimentary record to be used to constrain numerical models of past glacier dynamics in debris-poor glacierized Alpine catchments. Copyright © 2008 John Wiley & Sons, Ltd. [source] Laser shock peening on fatigue crack growth behaviour of aluminium alloyFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 8 2004Y. TAN ABSTRACT The effect of laser shock peening (LPS) in the fatigue crack growth behaviour of a 2024-T3 aluminium alloy with various notch geometries was investigated. LPS was performed under a ,confined ablation mode' using an Nd: glass laser at a laser power density of 5 GW cm,2. A black paint coating layer and water layer was used as a sacrificial and plasma confinement layer, respectively. The shock wave propagates into the material, causing the surface layer to deform plastically, and thereby, develop a residual compressive stress at the surface. The residual compressive stress as a function of depth was measured by X-ray diffraction technique. The fatigue crack initiation life and fatigue crack growth rates of an Al alloy with different preexisting notch configurations were characterized and compared with those of the unpeened material. The results clearly show that LSP is an effective surface treatment technique for suppressing the fatigue crack growth of Al alloys with various preexisting notch configurations. [source] Fretting fatigue behaviour of shot-peened Ti-6Al-4V at room and elevated temperaturesFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 9 2003H. LEE ABSTRACT Fretting fatigue behaviour of shot-peened titanium alloy, Ti-6Al-4V was investigated at room and elevated temperatures. Constant amplitude fretting fatigue tests were conducted over a wide range of maximum stresses, ,max= 333 to 666 MPa with a stress ratio of R= 0.1. Two infrared heaters, placed at the front and back of specimen, were used to heat and maintain temperature of the gage section of specimen at 260 °C. Residual stress measurements by X-ray diffraction method before and after fretting test showed that residual compressive stress was relaxed during fretting fatigue. Elevated temperature induced more residual stress relaxation, which, in turn, decreased fretting fatigue life significantly at 260 °C. Finite element analysis (FEA) showed that the longitudinal tensile stress, ,xx varied with the depth inside the specimen from contact surface during fretting fatigue and the largest ,xx could exist away from the contact surface in a certain situation. A critical plane based fatigue crack initiation model, modified shear stress range parameter (MSSR), was computed from FEA results to characterize fretting fatigue crack initiation behaviour. It showed that stress relaxation during test affected fretting fatigue life and location of crack initiation significantly. MSSR parameter also predicted crack initiation location, which matched with experimental observations and the number of cycles for crack initiation, which showed the appropriate trend with the experimental observations at both temperatures. [source] The creation of an asymmetric hydraulic fracture as a result of driving stress gradientsGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2009T. Fischer SUMMARY Hydraulic fracture stimulation is frequently performed in hydrocarbon reservoirs and geothermal systems to increase the permeability of the rock formation. These hydraulic fractures are often mapped by hypocentres of induced microearthquakes. In some cases microseismicity exhibits asymmetry relative to the injection well, which can be interpreted by unequal conditions for fracture growth at opposite sides of the well or by observation effects. Here we investigate the role of the lateral change of the minimum compressive stress. We use a simple model to describe the relation among the lateral stress gradient, the mean viscous pressure gradients in the fracture wings, the fracture geometry, and the net pressure in the fracture. Our model predicts a faster fracture growth in the direction of decreasing stress and a limited growth in the opposite direction. We derive a simple relationship to estimate the lateral stress gradient from the injection pressure and the shape of the seismic hypocentre cloud. The model is tested by microseismic data obtained during stimulation of a Canyon Sands gas field in West Texas. Using a maximum likelihood method we fit the parameters of the asymmetric fracture model to the space,time pattern of hypocentres. The estimated stress gradients per metre are in the range from 0.008 to 0.010 times the bottom-hole injection overpressure (8,10 kPa m,1 assuming the net pressure of 1 MPa). Such large horizontal gradients in the order of the hydrostatic gradient could be caused by the inhomogeneous extraction of gas resulting in a lateral change of the effective normal stress acting normal to the fracture wall. [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] In situ stress measurements in a borehole close to the Nojima FaultISLAND ARC, Issue 3-4 2001Hiroaki Tsukahara AbstractIn situ stress was measured close to the fault associated with the 1995 Kobe Earthquake (Hyogo-ken Nanbu earthquake; January 1995; M7.2) using the hydraulic fracturing method. The measurements were made approximately 2 years after the earthquake. The measured points were approximately 40 m from the fault plane at depths of about 1500 m. The maximum and the minimum horizontal compressive stresses were 45 MPa and 31 MPa, respectively. The maximum compressive stress and the maximum shear stress are very small in comparison with those of other seismically active areas. The azimuth of the maximum horizontal compressive stress was estimated from the observed azimuths of well bore breakouts at depths between 1400 m and 1600 m and was found to be N135° (clockwise). The maximum stress axis is perpendicular to the fault strike, N45°. These features are interpreted in terms of a small frictional coefficient of the fault. The shear stress on the fault was released and dropped almost to zero during the earthquake and it has not yet recovered. Zero shear stress on the fault plane resulted from the perpendicular orientation of one of the principal stress to the fault plane. [source] Quantitative microstructural and texture characterization by X-ray diffraction of polycrystalline ferroelectric thin filmsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2004Jesús Ricote Texture becomes an important issue in ferroelectric materials as it greatly influences the physical properties of polycrystalline films. The use of advanced methods of analysis of the X-ray diffraction profiles, namely quantitative texture analysis or the recently developed combined approach, allows access to quantitative information on the different components of the global texture and to more accurate values of structural and microstructural parameters of both the ferroelectric film and the substrate, not available by more conventional methods of analysis. The results obtained allow important conclusions to be drawn regarding the mechanisms that lead to the development of preferred orientations in thin films and, also, the correlation between them and the ferroelectric behaviour. For example, it is observed that the inducement of a strong ,111, texture component does not mean the complete disappearance of the so-called `natural' ,100,, ,001, components, and that the ratio between the contributions to the global texture of these two components can be changed by the presence of tensile or compressive stress during crystallization of the films. The relative contributions of these texture components are also related to the final properties of the ferroelectric films. [source] Compressive response and energy absorption of foam EPDMJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2007Biqin Wang Abstract Ethylene,propylene,diene terpolymer foam was prepared by two different processing routes. The microstructure and mechanical properties of the foams with wide relative density ranging from 0.11 to 0.62 have been studied via scanning electron microscopy and mechanical testing, respectively. Scanning electron microscopy shows that the foam with lower relative density has a unique bimodal cell size structure, which the larger cells inlay among the smaller cells, while the foam articles with higher relative density have thicker cell walls with few small cells. The compressive stress,strain curves show that the foam articles with lower relative density have three regimes: linear elastic, a wide slightly rising plateau, and densification, while the foam articles with higher relative density have only two regimes: the longer linear elastic and densification. The relative modulus increases with the increase in the relative density. The contribution of the gas trapped in the cell to the modulus could be neglected. The energy absorbed per unit volume is relationship with the permitted stress and the relative density. The efficiency and the ideality parameter were evaluated from the compressive stress,strain plots. The parameters were plotted against stress to obtain maximum efficiency and the maximum ideality region, which can be used for optimizing the choice for practical applications in cushioning and packaging. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 [source] The constrictor dorsalis musculature and basipterygoid articulation in SphenodonJOURNAL OF MORPHOLOGY, Issue 3 2010Peter JohnstonArticle first published online: 5 OCT 200 Abstract The constrictor internus dorsalis (CID) trigeminal muscles in vertebrates lie between the braincase and the palatoquadrate bar, and in reptiles they are believed to function in the relative movements between braincase and maxillary segment known as kinesis. In amniote taxa, the presence of a synovial basipterygoid articulation (BPA) correlates with presence of the CID. Previous descriptions of the CID in the tuatara Sphenodon (Rhynchocephalia) are inconsistent regarding presence, size and direction, particularly of the m. protractor pterygoidei. The Sphenodon skull is reported to be akinetic. The CID was investigated in Sphenodon by examination of sectioned embryonic and hatchling material, and by dissection of fixed specimens. Osteological correlates of CID muscles and morphology of the BPA were examined on disarticulated skulls and on CT scan images. The vectors of action of these muscles in relation to the BPA were projected onto CT images. Mm. levator bulbi and levator pterygoidei are found to be similar to most previous descriptions, but m. protractor pterygoidei was found in a different position, lying entirely medial to the palatoquadrate bar. The insertions of mm. levator pterygoidei and protractor pterygoidei are visible on the disarticulated pterygoid bone. The BPA is mobile only by rotation around the horizontal axis of the joints themselves; metakinesis is not possible in the Sphenodon skull. M. protractor pterygoidei appears to either resist or recognize lateral displacement of the BPA. M. levator ptergyoidei is placed to resist dorsal displacement of the braincase at the BPA, or torsion of the braincase around its longitudinal axis. The BPA appears to be a means to direct compressive stress via the base of the braincase and occipital condyle to the cervical spine in Sphenodon, and probably in its direct ancestors. Metakinesis may never have been a feature of the lepidosaur skull. J. Morphol., 2010. © 2009 Wiley-Liss, Inc. [source] Micro-computed tomography evaluation of vertebral end-plate trabecular bone changes in a porcine asymmetric vertebral tetherJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 2 2010Jean-Michel Laffosse Abstract We conducted a micro-CT analysis of subchondral bone of the vertebral end-plates after application of compressive stress. Thoracic and lumbar vertebral units were instrumented by carrying out left asymmetric tether in eleven 4-week-old pigs. After 3 months of growth, instrumented units and control units were harvested. Micro-CT study of subchondral bone was performed on one central and two lateral specimens (fixated side and non-fixated side). In control units, bone volume fraction (BV/TV), number of trabeculae (Tb.N), trabecular thickness (Tb.Th), and degree of anisotropy (DA) were significantly higher, whereas intertrabecular space (Tb.Sp) was significantly lower in center than in periphery. No significant difference between the fixated and non-fixated sides was found. In instrumented units, BV/TV, Tb.N, Tb.Th, and DA were significantly higher in center than in periphery. BV/TV, Tb.N, and Conn.D were significantly higher in fixated than in non-fixated side, while Tb.Sp was significantly lower. We noted BV/TV, Tb.N, and Tb.Th significantly lower, and Tb.Sp significantly higher, in the instrumented levels. This study showed, in instrumented units, two opposing processes generating a reorganization of the trabecular network. First, an osteolytic process (decrease in BV/TV, Tb.N, Tb.Th) by stress-shielding, greater in center and on non-fixated side. Second, an osteogenic process (higher BV/TV, Tb.N, Conn.D, and lower Tb.Sp) due to the compressive loading induced by growth on the fixated side. This study demonstrates the densification of the trabecular bone tissue of the vertebral end-plates after compressive loading, and illustrates the potential risks of excessively rigid spinal instrumentation which may induce premature osteopenia. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:232,240, 2010 [source] Differential effects of static and dynamic compression on meniscal cell gene expressionJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 6 2003Maureen L. Upton Abstract Cells of the meniscus are exposed to a wide range of time-varying mechanical stimuli that may regulate their metabolic activity in vivo. In this study, the biological response of the meniscus to compressive stimuli was evaluated in vitro, using a well-controlled explant culture system. Gene expression for relevant extracellular matrix proteins was quantified using real-time RT-PCR following a 24 h period of applied static (0.1 MPa compressive stress) or dynamic compression (0.08,0.16 MPa). Static and dynamic compression were found to differentially regulate mRNA levels for specific proteins of the extracellular matrix. Decreased mRNA levels were observed for decorin (,2.1 fold-difference) and type II collagen (,4.0 fold-difference) following 24 h of dynamic compression. Decorin mRNA levels also decreased following static compression (,4.5 fold-difference), as did mRNA levels for both types I (,3.3 fold-difference) and II collagen (,4.0 fold-difference). Following either static or dynamic compression, mRNA levels for aggrecan, biglycan and cytoskeletal proteins were unchanged. It is noteworthy that static compression was associated with a 2.6 fold-increase in mRNA levels for collagenase, or MMP-1, suggesting that the homeostatic balance between collagen biosynthesis and catabolism was altered by the mechanical stimuli. These findings demonstrate that the biosynthetic response of the meniscus to compression is regulated, in part, at the transcriptional level and that transcription of types I and II collagen as well as decorin may be regulated by common mechanical stimuli. © 2003 Orthopaedic Research Society. Published by Elsevier Science Ltd. All rights reserved. [source] Effect of compressibility on performance of hydraulic wash columnsAICHE JOURNAL, Issue 7 2002L. van Oord-Knol In a hydraulic wash column the solid crystals are separated from the mother liquor by filtration in the top section of the column. Remaining impurities are removed via countercurrent washing of the crystals in the bottom section. Since compressibility limits the capacity of a wash column, this phenomenon needs to be quantified and modeled rigorously. The compressibility of the bed was determined from the porosity profile and the liquid-pressure profile inside the wash column. The porosity of the bed decreases from 0.65 to 0.3 during transport of the bed. This is associated with a decrease in local bed permeability by a factor of 10. The compressibility of the bed, therefore, partly explains the large ratio between the average permeability above and below the wash front. Compressibility coefficients make it possible to relate the compressive stress to the porosity and permeability in the top section of the bed. These coefficients are, therefore, incorporated in a model to successfully predict the capacity of a wash column with a compressible bed. [source] Synthesis of hafnium tungstate by a CO2 laser and its microstructure and Raman spectroscopic studyJOURNAL OF RAMAN SPECTROSCOPY, Issue 7 2008E. J. Liang Abstract Densely packed hafnium tungstate blocks were synthesized by rapid solidification with a CO2 laser. It is shown that the optimum synthesis conditions for HfW2O8 are around 700 W laser power and 1 mm/s scan speed. Scanning electron microscopy (SEM) observation shows that the blocks consist of oriented nano-threads/rods that grew horizontally on the surface region and vertically in the interior. The orientations of the nanostructures are governed by the heat transfer directions on the surface and in the interior. Raman spectroscopic and X-ray diffraction studies show that the samples solidified in the cubic structure with minor contents of the orthorhombic phase. This is explained by a compressive stress induced during the rapid solidification process due to a sudden drop of temperature of the molten pool to the ambient. The stress is estimated to be about 0.6 GPa by comparison with high-pressure Raman study. Some specific Raman bands appear in the samples synthesized with the laser synthetic route but not in the sample by solid-state reaction. Copyright © 2008 John Wiley & Sons, Ltd. [source] Preparation of Highly Dense PZN,PZT Thick Films by the Aerosol Deposition Method Using Excess-PbO PowderJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2007Jong-Jin Choi Lead zinc niobate,lead zirconate titanate thick films with a thickness of 50,100 ,m were deposited on silicon and alumina substrates using the aerosol deposition method. The effects of excess lead oxide (PbO) on stress relaxation during postannealing were studied. Excess PbO content was varied from 0 to 5 mol%. The as-deposited film had a fairly dense microstructure with nanosized grains. The films deposited on silicon were annealed at temperatures of 700°C, and the films deposited on sapphire were annealed at 900°C in an electrical furnace. The annealed film was detached and cracks were generated due to the high residual compressive stress and thermal stress induced by thermal expansion coefficient mismatch. However, the film deposited using powder containing 2% of excess PbO showed no cracking or detachment from the substrate after the postannealing process. The PbO evaporation at elevated temperature during the postannealing process seemed to have reduced the residual compressive stress. The remanent polarization and relative dielectric constant of the 50 ,m thick films annealed at 900°C were 43.1 ,C/cm2 and 1400, respectively, which were comparable with the values of a bulk specimen prepared by a powder sintering process. [source] Ion-Exchanged Glass Laminates that Exhibit a Threshold StrengthJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2007Scott P. Fillery Glass laminates, fabricated to include periodic thin layers containing biaxial compressive stresses, exhibit a threshold strength, i.e., a stress below which failure will not occur. Ion-exchange treatments in KNO3 at 350°,450°C for periods of 3,72 h were used to create residual compressive stresses at the surface of soda lime silicate glass sheets. Wafer direct bonding of the ion-exchanged glass sheets resulted in glass laminates with thin layers of compressive stress adjacent to the glass interface and perpendicular to the laminate top surface. Critical strain energy release measurements of the bonded interface were used to optimize the bonding temperature/time to avoid significant relaxation of the stress produced by ion exchange. Stress profiles, determined via the wafer curvature measurement method, showed a residual compressive stress maximum of 328 MPa for an ion exchange temperature of 450°C. The threshold flexural strength of the ion exchanged glass laminates was determined to be 112 MPa after the introduction of indentation cracks with indent loads ranging from 1 to 5 kg. In contrast to similar ceramic laminates, where cracks either propagate across the compressive layer or bifurcate within the compressive layer, the cracks in the glass laminates were deflected along the interface between the bonded sheets. [source] Thermal Cycling Damage Mechanisms of C/SiC Composites in Displacement Constraint and Oxidizing AtmosphereJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2006Hui Mei A constraint stress of 62.5 MPa is created on a three-dimensional C/SiC composite specimen whose both ends are fixed when temperature is cycled between 900° and 1200°C. The cyclic stress results in a maximum damage strain of 0.06% within 50 cycles owing to coating and matrix cracking, fiber debonding, sliding, and breaking in the composite. This constrained specimen elongation also leads to a final compressive stress of 14 MPa on the composite through a decrease in the baseline constraint stress. Wet oxygen atmosphere at a high cyclic temperature, concomitant with stresses, can aggravate the damage situation by alternate oxidation between internal and external fibers in composites. [source] Constrained Sintering of Low-Temperature Co-Fired CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2006Aravind Mohanram This paper discusses the effect of uniaxial compressive stress and pressureless constraint on the microstructure, density, and shrinkage anisotropy during the sintering of two commercial low-temperature co-fired ceramic (LTCC) systems, i.e., Heraeus CT2000 (CT) and DuPont 951Tape (DU). Under uniaxial compression, the ratio of axial to transverse shrinkage of DU is significantly higher than that of CT. A simple linear viscous theory was used to estimate the change in the strain rates produced by the external stress and the stress required to produce zero shrinkage. The theory was found to overestimate the measured stress-induced strain rates. The uniaxial compressive stress required for zero overall shrinkage was estimated to be ,60 kPa for DU and 80 kPa for CT. The estimate for the DU materials was in good agreement with the experimental data, but there was significant deviation for the CT material. Higher viscosity and higher constraining stresses led to lower densities in pressure-less constrained CT specimens compared with DU. [source] Evaluation of articular cartilage repair using biodegradable nanofibrous scaffolds in a swine model: a pilot studyJOURNAL OF TISSUE ENGINEERING AND REGENERATIVE MEDICINE, Issue 1 2009Wan-Ju Li Abstract The aim of this study was to evaluate a cell-seeded nanofibrous scaffold for cartilage repair in vivo. We used a biodegradable poly(,-caprolactone) (PCL) nanofibrous scaffold seeded with allogeneic chondrocytes or xenogeneic human mesenchymal stem cells (MSCs), or acellular PCL scaffolds, with no implant as a control to repair iatrogenic, 7 mm full-thickness cartilage defects in a swine model. Six months after implantation, MSC-seeded constructs showed the most complete repair in the defects compared to other groups. Macroscopically, the MSC-seeded constructs regenerated hyaline cartilage-like tissue and restored a smooth cartilage surface, while the chondrocyte-seeded constructs produced mostly fibrocartilage-like tissue with a discontinuous superficial cartilage contour. Incomplete repair containing fibrocartilage or fibrous tissue was found in the acellular constructs and the no-implant control group. Quantitative histological evaluation showed overall higher scores for the chondrocyte- and MSC-seeded constructs than the acellular construct and the no-implant groups. Mechanical testing showed the highest equilibrium compressive stress of 1.5 MPa in the regenerated cartilage produced by the MSC-seeded constructs, compared to 1.2 MPa in the chondrocyte-seeded constructs, 1.0 MPa in the acellular constructs and 0.2 MPa in the no-implant group. No evidence of immune reaction to the allogeneically- and xenogeneically-derived regenerated cartilage was observed, possibly related to the immunosuppressive activities of MSCs, suggesting the feasibility of allogeneic or xenogeneic transplantation of MSCs for cell-based therapy. Taken together, our results showed that biodegradable nanofibrous scaffolds seeded with MSCs effectively repair cartilage defects in vivo, and that the current approach is promising for cartilage repair. Copyright © 2008 John Wiley & Sons, Ltd. [source] Long-Term Properties of Butt-Welded Poly(propylene)MACROMOLECULAR MATERIALS & ENGINEERING, Issue 4 2003Ernst Schmachtenberg Abstract It is still not clear why the long-term properties of plastic weld seams can only be differentiated by the very expensive medium tensile creep tests. One hypothesis for justifying this is based on the change in the structure of the weld seam surroundings, another cites the consumption of antioxidants and the following ageing in the weld seam area to be responsible for this. Butt-welded weld seams made of poly(propylene) were systematically produced under different process parameters. Corresponding to the particular hypothesis, these weld seams were then analyzed in various ways to find correlations or to prove one of the hypotheses. Regarding their short-term weld seam quality, the analyzed weld seams could not be differentiated through short-term tensile or short-term bend test. However, the medium tensile creep tests showed significant differences in both time until failure and long-term weld seam quality. Under long-term loading, the start of the brittle crack could be detected in most weld seams in the fine spherulite-zone or between this zone and the area of the flow lines. This demonstrated again that only long-term tests are suitable for examining different weld seam qualities. Depending on the welding parameters, times until failure decline with increasing heated-tool temperature and heating time. Though these parameters lead to a higher consumption of antioxidants in the weld seam, a degradation was not detected in the breaking area. In fact, increasing heated-tool temperatures and heating times, as well as higher joining pressures lead to a change in the internal structure of the material. This can be seen in morphological structure analyses in the larger bend of the entire weld seam area. A larger bend, however, correlates with higher residual stresses in the weld seam. In the medium tensile creep tests, these residual stresses as well as the tensile stress in the border region and the compressive stress in the middle are superimposed by the tensile stress resulting from the test stress. Thus a greater bend of the weld seam area and higher residual stresses in the weld seam itself lead to shorter times until failure in medium tensile creep tests. Schematic representation of the formation of residual stresses in a weld seam and residual stresses in the different bended weld seam areas. [source] Improved electromigration failure in Al based interconnectsPHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 2 2007Yong Tae Kim Abstract Electromigration (EM) failure in Al interconnects is significantly improved by inserting a WN film between Al and the interlayer dielectric: over 90% of test samples failed with the Al/TiN/Ti interconnects, whereas the failure rate of the Al film on WN is reduced to less than 13% under the stress con- ditions of 9 MA/cm2 and 225 °C, and the EM lifetime is also much extended at the same conditions. Experimental results suggest that higher activation energy, no hillocks and compressive stress are responsible for the improved electromigration performance in the Al/WN interconnect. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Photoluminescence from InGaN/GaN MQWs on sapphire and membranes fabricated by laser lift-offPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2004Tongjun Yu Abstract Photoluminescence and Raman scattering spectra of InGaN/GaN MQWs on sapphire and membranes free of substrate fabricated by laser lift-off have been studied. It is observed that photoluminescence peak of 850 °C annealed sample red-shifts from that of as grown sample, while in the case of membrane samples, the luminescence peak blue-shifts when annealed at 700 °C. In Raman scattering spectra, InGaN/GaN MQWs film without sapphire substrate has a lower E2 mode frequency (569.3 cm,1) than that of the films with substrate (570.8 cm,1), which indicates that compressive stress in the films releases partially when the sapphire substrate is taken off. It is believed that the piezoelectric field decrease leads to the blue-shift in luminescence spectra. Compared with the samples with sapphire substrate, the free-standing membranes showed blue-shift of luminescence peak after relatively low temperature annealing, because the piezoelectric field reduced more easily in the films without substrate. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Effect of growth temperature of AlN interlayers on the properties of GaN epilayers grown on c-plane sapphire by metal organic chemical vapor depositionPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2010J. S. Xue Abstract The effect of growth temperature of AlN interlayers on the properties of GaN epilayers grown on c-plane sapphire by metal organic chemical vapor deposition has been investigated by high resolution X-ray diffraction (HRXRD) and Raman spectroscopy. It is concluded that the crystalline quality of GaN epilayers is improved significantly by using the high temperature AlN (HT-AlN) interlayer in GaN buffers. The density of threading dislocation is reduced especially for edge type dislocations. Higher compressive stress exists in GaN epilayers with HT-AlN interlayer than with low temperature AlN (LT-AlN) interlayer, which is related to the reduction of strain relaxation caused by the formation of misfit dislocation. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Luminescence and vibrational properties of erbium-implanted nanoporous GaNPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008C. B. Soh Abstract Implantation of erbium (Er) into GaN is useful in creating selected areas to emit at the green, yellow and infrared wavelengths. Enhanced erbium activation is obtained when erbium is implanted into porous GaN formed by electrochemical etching than into as-grown GaN. This is due to the increase in surface areas for light extraction and the availability of more free surfaces to accommodate strain when it is annealed. Furnace annealing at 1100 °C for 30 mins in nitrogen gives rise to higher band-edge photoluminescence intensity. Apart from the host GaN phonon modes, we have also observed disorder-induced lattice vibrations at 170, 200 and 350-365 cm,1 from Er-implanted porous GaN. The E2 (high) mode of GaN also shifts towards higher energy at higher annealing temperatures, indicative of more erbium occupying the VGa site (ionic radii of Er > Ga) and hence increasing the compressive stress in the GaN crystal lattice. The prominent defect-induced local vibrational modes in Er-doped nanoporous GaN are also observed in ultraviolet resonant Raman scattering. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Decorated vacancy clusters in Si and thin C films grown on Si studied by depth profiling positron annihilation spectroscopiesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2007R. S. Brusa Abstract The combined use of different depth profiling positron annihilation spectroscopies give insight on distribution, type and decoration of open-volume defects. Applications regarding defects produced in modified silicon and at the interface between deposited thin films and the silicon substrate are presented. The attention is focused on selected systems and situations potentially related to technological developments: a) identification of decorated vacancy clusters in silicon implanted by light-ion (He, He+H) and evolution of the clusters with the thermal treatments; b) release of compressive stress through vacancy-like defects formation at the interface during the growth of thin (10-200 nm thick) carbon films. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Multilayer Diffusion Barrier Coatings on Poly(propylene) with Improved Temperature DurabilityPLASMA PROCESSES AND POLYMERS, Issue S1 2009Lutz Körner Abstract The improvement of temperature durability for autoclaving of silicon oxide (SiOx) diffusion barrier coatings on poly(propylene) (PP) by deposition of thin amorphous hydrogenated carbon-nitrogen (a-C:N:H) intermediate layers was investigated. Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy revealed terminating amino and nitrile groups responsible for low compressive stress in a-C:N:H. Uniaxial tensile tests showed a higher crack onset strain (COS) for a-C:N:H of 2.7% compared to 0.7% for SiOx. Best temperature durability was achieved by a three-layer coating from a-C:N:H, an intermediate layer deposited by a mixture of N2, C2H2, hexamethyldisiloxane (HMDSO), and a SiOx layer. The oxygen transmission rate (OTR) was only increased from 6 to 22 cm3·m,2·d,1·bar,1 after exposure to 140,°C for 30 min, whereas for single SiOx barrier coatings, severe loss of barrier properties of 1,040 cm3·m,2·d,1·bar,1 was evidenced due to the formation of cracks. [source] Normal Faulting Type Earthquake Activities in the Tibetan Plateau and Its Tectonic ImplicationACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 1 2010Jiren XU Abstract: This paper analyzes various earthquake fault types, mechanism solutions, stress field as well as other geophysical data to study the crust movement in the Tibetan plateau and its tectonic implications. The results show that a lot of normal faulting type earthquakes concentrate in the central Tibetan plateau. Many of them are nearly perfect normal fault events. The strikes of the fault planes of the normal faulting earthquakes are almost in the N-S direction based on the analyses of the equal area projection diagrams of fault plane solutions. It implies that the dislocation slip vectors of the normal faulting type events have quite great components in the E-W direction. The extension is probably an eastward extensional motion, mainly a tectonic active regime in the altitudes of the plateau. The tensional stress in the E-W or WNW-ESE direction predominates the earthquake occurrence in the normal event region of the central plateau. A number of thrust fault and strike-slip fault type earthquakes with strong compressive stress nearly in the NNE-SSW direction occurred on the edges of the plateau. The eastward extensional motion in the Tibetan plateau is attributable to the eastward movement of materials in the upper mantle based onseismo-tomographic results. The eastward extensional motion in the Tibetan plateau may be related to the eastward extrusion of hotter mantle materials beneath the east boundary of the plateau. The northward motion of the Tibetan plateau shortened in the N-S direction probably encounters strong obstructions at the western and northern margins. Extensional motions from the relaxation of the topography and/or gravitational collapse in the altitudes of the plateau occur hardly in the N-S direction. The obstruction for the plateau to move eastward is rather weak [source] Growth and Properties of TiCl4 -Derived CVD Titanium Oxide Films at Different CO2/H2 Inputs,CHEMICAL VAPOR DEPOSITION, Issue 5 2003D.-H. Kuo Abstract Crystalline titanium oxide films with a thickness of 0.09,0.55,,m were prepared at temperatures below 500,°C by CVD using a mixture of titanium tetrachloride (TiCl4), carbon dioxide (CO2), and hydrogen (H2) as reactants. Film thickness decreased with increasing substrate temperature and CO2/H2 input. Nanosized microstructure was obtained at high CO2/H2 input due to the growth retardation of reacted HO-TiCl3* by the unreacted TiCl4 and CO2. That film composition, i.e., the O/Ti ratio, increased with temperature and the CO2/H2 input can be explained by growth kinetics. Unlike film thickness, internal film stress increased with increasing substrate temperature. Adhesion was controlled by compressive internal stress due to the weak bonding between film and substrate. Two growth mechanisms are proposed to explain the tensile and compressive stress states in films produced by CVD. The adsorption-controlled reaction has a film in compressive stress that increases with an increase in temperature. On the other hand, thermally activated CVD produces a film in tensile stress that decreases with an increase in substrate temperature. [source] Influence of nanocrystalization on magnetoelastic Villari effect in Fe73.5Nb3Cu1Si13.5B9 alloyCRYSTAL RESEARCH AND TECHNOLOGY, Issue 3-5 2003R. Szewczyk Abstract The results of an investigation of the influence of thermal annealing on the magnetoelastic properties of Fe73.5Nb3Cu1Si13.5B9 soft magnetic alloy in both amorphous and nanocrystalline state are presented. A new method developed was used to apply uniform compressive stresses to the investigated ring core made of the alloy. The compressive stresses produced by external mechanical forces were applied perpendicularly to the direction of the magnetizing field. Due to the uniform distribution of stresses in the core brittle nanocrystalline alloys may be tested for stresses up to 10 MPa. The results revealed, that process of nanocrystallisation causes significant increase in the stress sensitivity of the Fe73.5Nb3Cu1Si13.5B9 alloy. Moreover the influence of stresses caused by external forces is more significant at relatively low values of the magnetizing field suggesting that these nanocrystalline soft magnetic materials are stress sensitive in the range of technical operation of inductive components based on such materials. [source] Structural composition and sediment transfer in a composite cirque glacier: Glacier de St. Sorlin, FranceEARTH SURFACE PROCESSES AND LANDFORMS, Issue 13 2008Sam Roberson Abstract This paper considers the links between structure, sediment transport and sediment delivery at Glacier de St. Sorlin, France. Sediment transported by the glacier is concentrated at flow-unit boundaries as medial moraines, controlled by the position of bedrock outcrops in the accumulation area. Rockfall entrained within primary stratification is tightly folded at flow-unit boundaries under high cumulative strains and laterally compressive stress. High cumulative strains and laterally compressive stresses lead to the development of longitudinal foliation from primary stratification. Folding elevates subglacial sediments into foliation-parallel debris ridges, which are exposed in the ablation area. Crevasses and shear planes within the glacier have little control on sediment transport. Debris stripes in the proglacial area are morphologically similar to foliation-parallel debris ridges; however, they are not structurally controlled, but formed by fluvial erosion. The conclusion of this study is that at Glacier de St. Sorlin proglacial sediment-landform associations are subjected to intense syn- and post-depositional modification by high melt-water discharges, hence their composition does not reflect that of sediments melting out at the terminus. The action of melt water limits the potential of the sedimentary record to be used to constrain numerical models of past glacier dynamics in debris-poor glacierized Alpine catchments. 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