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Contact Length (contact + length)
Selected AbstractsPositively Charged Material Surfaces Generated by Plasma Polymerized Allylamine Enhance Vinculin Mobility in Vital Human Osteoblastss,ADVANCED ENGINEERING MATERIALS, Issue 8 2010Henrike Rebl Abstract Several studies suggest that the modification of an implant surface by chemical means plays an important role in bone tissue engineering. Previously we have shown that osteoblast cell adhesion and spreading can strongly be increased by a positively charged surface. Cell adhesion and migration are two vital processes that are completely dependent on coordinated formation of focal adhesions. Changes in the organization of the actin cytoskeleton and the focal adhesions are essential for numerous cellular processes including cell motility and tissue morphogenesis. We examined the mobility of the cytoskeletally associated protein vinculin on functionalized surfaces using plasma polymerized allylamine (PPAAm), a homogenous plasma polymer layer with randomly distributed amino groups. In living, GFP,vinculin transfected osteoblastic cells we determined a significant increase in vinculin mobility and vinculin contact length on PPAAm compared to collagen I coated surfaces during the initial adhesion phase. We suggest that positive charges control the cell physiology which seems to be dominant over the integrin receptor binding to collagen I. The results emphasize the role of the surface charge for the design of artificial scaffolds in bone repair. [source] Fretting fatigue limit as a short crack problem at the edge of contactFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 5 2004Y. KONDO ABSTRACT This paper proposes a local stress concept to evaluate the fretting fatigue limit for contact edge cracks. A unique S,N curve based on the local stress could be obtained for a contact edge crack irrespective of mechanical factors such as contact pressure, relative slip, contact length, specimen size and loading type. The analytical background for the local stress concept was studied using FEM analysis. It was shown that the local stress uniquely determined the ,K change due to crack growth as well as the stress distribution near the contact edge. The condition that determined the fretting fatigue limit was predicted by combining the ,K change due to crack growth and the ,Kth for a short crack. The formation of a non-propagating crack at the fatigue limit was predicted by the model and it was experimentally confirmed by a long-life fretting fatigue test. [source] Similarities of stress concentrations in contact at round punches and fatigue at notches: implications to fretting fatigue crack initiationFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 7 2000Giannakopoulos A linear elastic model of the stress concentration due to contact between a rounded flat punch and a homogeneous substrate is presented, with the aim of investigating fretting fatigue crack initiation in contacting parts of vibrating structures including turbine engines. The asymptotic forms for the stress fields in the vicinity of a rounded punch-on-flat substrate are derived for both normal and tangential loading, using both analytical and finite element methods. Under the action of the normal load, P, the ensuing contact is of width 2b which includes an initial flat part of width 2a. The asymptotic stress fields for the sharply rounded flat punch contact have certain similarities with the asymptotic stress fields around the tip of a blunt crack. The analysis showed that the maximum tensile stress, which occurs at the contact boundary due to tangential load Q, is proportional to a mode II stress intensity factor of a sharp punch divided by the square root of the additional contact length due to the roundness of the punch, Q/(,(b,,,a),,b). The fretting fatigue crack initiation can then be investigated by relating the maximum tensile stress with the fatigue endurance stress. The result is analogous to that of Barsom and McNicol where the notched fatigue endurance stress was correlated with the stress intensity factor and the square root of the notch-tip radius. The proposed methodology establishes a ,notch analogue' by making a connection between fretting fatigue at a rounded punch/flat contact and crack initiation at a notch tip and uses fracture mechanics concepts. Conditions of validity of the present model are established both to avoid yielding and to account for the finite thickness of the substrate. The predictions of the model are compared with fretting fatigue experiments on Ti,6Al,4V and shown to be in good agreement. [source] Estimating error in measuring thermal conductivity using a T-type nanosensorHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 5 2009Yohei Ito Abstract We discuss the measurement error caused by fabrication and measurement of a T-type nanosensor with a suspended sub-micrometer Pt hot film that was developed to measure the thermal properties of individual nanowire materials. Comparison of numerical simulation and one-dimensional analysis revealed that the thermal conductivity of nanowire material such as a carbon nanotube is calculated to be 17% lower. As an example, the thermal conductivity measurement result for a SiC nanowire is reported. The error caused by contact thermal resistance is found to depend on the contact length and can be as great as 20%. It can be said that future measuring can have higher reliability by correcting the estimated measurement error. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20228 [source] Lateral magnocellular nucleus of the anterior neostriatum (LMAN) in the zebra finch: Neuronal connectivity and the emergence of sex differences in cell morphologyMICROSCOPY RESEARCH AND TECHNIQUE, Issue 6 2001Barbara E. Nixdorf-Bergweiler Abstract The song system of birds provides a model system to study basic mechanisms of neuronal plasticity and development underlying learned behavior. Song learning and production involve discrete sets of interconnected nuclei in the avian brain. One of these nuclei, the lateral magnocellular nucleus of the anterior neostriatum (LMAN), is the output of the so-called anterior forebrain pathway known to be essential for learning and maintenance of song, both processes depending on auditory feedback. In zebra finches, only males sing and this sexually dimorphic behavior is mirrored by sexual dimorphism in neuronal structure that develops during ontogeny. Female zebra finches are not able to sing and nuclei of the song system are strongly reduced in size or even lacking, when compared to male brains. Only LMAN can be delineated as easily in females as in males. Since female zebra finches, despite being unable to sing, recognize song just as males do and form a memory for song (model acquisition) early in life, LMAN is a putative candidate for song acquisition in both sexes. Therefore, development of LMAN was studied at the cellular and ultrastructural level in both male and female zebra finches. Regressive development of dendritic spines, enlargement of neuronal cell body and nuclei size, as well as changes at the nucleolar level are events all occurring exclusively in males, when song learning progresses. The decline in synapse number and the augmentation in synaptic contact length at synapses in LMAN in males are indicative for synaptic plasticity, whereas in females synapse number and synaptic contact length remain unchanged. Microsc. Res. Tech. 54:335,353, 2001. © 2001 Wiley-Liss, Inc. [source] Influence of post-extrusion parameters on the final morphology of polystyrene/high density polyethylene blendsPOLYMER ENGINEERING & SCIENCE, Issue 10 2003H. Padilla-Lopez The deformation of the dispersed phase in polystyrene/high density polyethylene (PS/HDPE) blends produced by ribbon extrusion was studied numerically and experimentally. A mathematical model for the deformation of the dispersed phase in ribbon extrusion processing of polymer blends was developed assuming uniaxial deformation of the ribbon and the equilibrium shapes of the dispersed particles with a pressure balance over a drop. Simulated morphologies as function of the post-extrusion parameters were obtained and compared with experiments. The analysis of the ribbon extrusion process showed that parameters such as draw ratio (DR) and ribbon-water contact length (X) significantly influence the ribbon dimensions, the extensional stress, and the stretching force. The results also showed that deformation and coalescence of the dispersed phase in the ribbon extrusion processing of polymer blends increase at higher DR and/or lower X values. The comparison between the model and the experimental morphologies of PS/HDPE produced a good agreement. [source] Enhanced Bone Bonding of the Hydroxyapatite/,-Tricalcium Phosphate Composite by Electrical Polarization in Rabbit Long BoneARTIFICIAL ORGANS, Issue 6 2010Hideki Sagawa Abstract A review of the osteogenic cell activity and new bone growth in the regions bordering negatively charged surfaces of polarized Hydroxyapatite/,-tricalcium phosphate (HA/TCP) composites implanted in the long bone in rabbits was conducted. Polarized and non-polarized HA/TCP specimens were implanted into the right and left femoral condyle, respectively (each n = 10). After 3 and 6 weeks, five rabbits were sacrificed in each group, and histological analysis was administered. Large cuboidal-shaped osteoblastic cells were predominantly observed lining the newly formed bone on the negatively charged surface (N-surface) in the polarized HA/TCP implants. The TRAP-positive multinucleated cells were observed extensively in the newly formed bone on the N-surfaces compared with the 0-surface and adhered directly to the HA/TCP composite. The bone area (B.Ar) value, newly formed bone area contacting the implant, and contact length (C.Le) value, percentage length of newly formed bone directly attaching to the implant, on both the 0- and N-surface increased significantly with time in each group. Both the B.Ar and C.Le value on the N-surface were significantly greater than those on the 0-surface after 3 and 6 weeks. The number of TRAP-positive cells/total length value on the N-surface was significantly greater than that on the 0-surface after 3 and 6 weeks postoperatively. It is hypothesized that electrical charge acquired by electrical polarization treatment may modify the biochemical and biophysical processes of the osteogenic cells, resulting in enhanced new bone formation and direct bonding between the recipient bone and implants. 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