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Shape Change (shape + change)
Kinds of Shape Change Selected AbstractsShape Change and Color Gamut in Gold Nanorods, Dumbbells, and Dog Bones,ADVANCED FUNCTIONAL MATERIALS, Issue 16 2006X. Xu Abstract It is shown here that deviations from a prolate ellipsoidal shape have a significant effect on the optical properties of gold nanorods. Transitions from rods to ,dumbbell'- or ,phi'-shaped particles lead to a shift in the longitudinal plasmon peak in the blue and red directions, respectively. Development of ,dog-bone' shapes leads to a red-shift and to the development of a third peak. A broad and flexible color gamut can be obtained. [source] Step-Energy Barriers and Particle Shape Changes during CoarseningJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2002Brian W. Sheldon Models of particle shape changes usually do not account for the step-energy barrier associated with adding or removing additional atomic planes from a faceted surface. However, the step-energy barrier can be a substantial limitation when the free energy changes that drive particle shape changes are relatively low. A good example of this is particle coarsening. The analysis presented in this article describes dislocation-free particles with surfaces that have faceted and nonfaceted regions. When the chemical potential differences responsible for shape changes are too small to overcome the step-energy barrier, atomic layers cannot be added or removed from the facets. Even with this constraint, it is possible to add or remove atoms from the particle surface; however, this can cause the particle shape to differ substantially from the traditional equilibrium shape. [source] Electromechanical reshaping of septal cartilage,,THE LARYNGOSCOPE, Issue 11 2003Ki-Hong Kevin Ho BS Abstract Objectives: This study describes the process of tissue electroforming and how shape changes in cartilage can be produced by the application of direct current (DC). The dependence of shape change on voltage and application time is explored. Study Design: Basic investigation using ex vivo porcine septal cartilage grafts and electromechanical cartilage deformation focused on development of a new surgical technique. Methods: Uniform flat porcine nasal septal cartilage specimens were mechanically deformed between two semicircular aluminum electrodes. DC current was applied to establish charge separation and electrical streaming potential. Voltage (0,3.5 V) and application time (0,5 minutes) were varied. Shape change was measured, and shape retention was calculated using analytic representation. The effect of the direction of applied current on shape change was evaluated by switching the polarities of electrodes and using parameters of 0 to 5.5 V and 5 minutes. Temperature during reshaping was monitored with a thermocouple, and surface features were evaluated using light microscopy. Results: Reshaped specimen demonstrated mechanical stability similar to native cartilage tissue. Shape retention strongly correlated with increasing voltage and application time. Only a small current (<0.1 A) through the tissue was measured. Temperature change was less than 2°C during electroforming, suggesting that electroforming likely results from some nonthermal mechanisms. Surface features indicated that electrodeposition may occur depending on electrode material and magnitude of the applied voltage. Conclusions: These findings demonstrate that cartilage can be reshaped through the process we have described as "electroforming" by generating intrinsic differences in charge separation with negligible heat production. [source] Chemical and physical responses to deformation in micaceous quartzites from the Tauern Window, Eastern AlpsJOURNAL OF METAMORPHIC GEOLOGY, Issue 4 2003J. Selverstone Abstract Micaceous quartzites from a subvertical shear zone in the Tauern Window contain abundant quartz clasts derived from dismembered quartz-tourmaline veins. Bulk plane strain deformation affected these rocks at amphibolite facies conditions. Shape changes suggest net shortening of the clasts by 11,64%, with a mean value of 35%. Quartz within the clasts accommodated this strain largely via dislocation creep processes. On the high-stress flanks of the clasts, however, quartz was removed via solution mass transfer (pressure solution) processes; the resulting change in bulk composition allowed growth of porphyroblastic staurolite + chlorite ± kyanite on the clast flanks. Matrix SiO2 contents decrease from c. 83 wt% away from the clasts to 49,58% in the selvages on the clast flanks. The chemical changes are consistent with c. 70% volume loss in the high-stress zones. Calculated shortening values within the clast flanks are similar to the volume-loss estimates, and are greatly in excess of the shortening values calculated from the clasts themselves. Flow laws for dislocation creep versus pressure solution imply large strain-rate gradients and/or differential stress gradients between the matrix and the clast selvages. In a rock containing a large proportion of semirigid clasts, weakening within the clast flanks could dominate rock rheology. In our samples, however, weakening within the selvages was self limiting: (1) growth of strong staurolite porphyroblasts in the selvages protected remaining quartz from dissolution; and (2) overall flattening of the quartz clasts probably decreased the resolved shear stress on the flanks to values near those of the matrix, which would have reduced the driving force for solution-transfer creep. Extreme chemical changes nonetheless occurred over short distances. The necessity of maintaining strain compatibility may lead to significant localized dissolution in rocks containing rheologic heterogeneities, and overall weakening of the rocks may result. Solution-transfer creep may be a major process whereby weakening and strain localization occur during deep-crustal metamorphism of polymineralic rocks. [source] Effects of cadmium on formation of the ventral body wall in chick embryos and their prevention by zinc pretreatmentBIRTH DEFECTS RESEARCH, Issue 2 2001Jennifer Thompson Background Cadmium (Cd) is an established experimental teratogen whose effects can be reversed by pretreatment with zinc. Mesodermal development is a frequently reported target for Cd teratogenicity. The aim of this study was to examine the mechanisms of Cd induced body wall defects in chick embryos. Methods Chick embryos in shell-less culture were treated with 50 ,l of cadmium acetate (8.9 × 10,5 M Cd2+) at 60-hr incubation (H.-H. stages 16,17). Controls received equimolar sodium acetate. Other embryos were treated with various concentrations of zinc acetate and then with Cd or NaAc 1 hrs later. Development was evaluated 48 hrs later. Resin-embedded 1-,m sections were examined at earlier stages. Results Cd caused embryolethality (35%), ventral body wall defect with malpositioned lower limbs (40%), and weight reduction in survivors. After 4-hr treatment with Cd, breakdown of junctions between peridermal cells with rounding up and desquamation occurred. Shape changes were also seen in the basal layer of the ectoderm. At 4 hr, cell death was evident in lateral plate mesoderm, somites, and neuroepithelium; the lateral plate mesoderm began to grow dorsally, carrying the attached limb buds with it. Zn pretreatment protected against the lethal, teratogenic, and growth-retarding effects of Cd, as well as ectodermal changes and cell death. Conclusions Cd disrupts peridermal cell adhesion and induces cell death in the mesoderm. This may result in abnormal growth of lateral plate mesoderm and in a body wall defect. Zn pretreatment prevents both the gross teratogenic effects and the cellular changes, most likely by competition with Cd. Teratology 64:87,97, 2001. © 2001 Wiley-Liss, Inc. [source] QUANTITATIVE GENETICS OF PLASTRON SHAPE IN SLIDER TURTLES (TRACHEMYS SCRIPTA)EVOLUTION, Issue 3 2006Erin M. Myers Abstract Shape variation is widespread in nature and embodies both a response to and a source for evolution and natural selection. To detect patterns of shape evolution, one must assess the quantitative genetic underpinnings of shape variation as well as the selective environment that the organisms have experienced. Here we used geometric morphometrics to assess variation in plastron shell shape in 1314 neonatal slider turtles (Trachemys scripta) from 162 clutches of laboratory-incubated eggs from two nesting areas. Multivariate analysis of variance indicated that nesting area has a limited role in describing plastron shape variation among clutches, whereas differences between individual clutches were highly significant, suggesting a prominent clutch effect. The covariation between plastron shape and several possible maternal effect variables (yolk hormone levels and egg dimensions) was assessed for a subset of clutches and found to be negligible. We subsequently employed several recently proposed methods for estimating heritability from shape variables, and generalized a univariate approach to accommodate unequal sample sizes. Univariate estimates of shape heritability based on Procrustes distances yielded large values for both nesting populations (h2, 0.86), and multivariate estimates of maximal additive heritability were also large for both nesting populations (h2max, 0.57). We also estimated the dominant trend in heritable shape change for each nesting population and found that the direction of shape evolution was not the same for the two sites. Therefore, although the magnitude of shape evolution was similar between nesting populations, the manner in which plastron shape is evolving is not. We conclude that the univariate approach for assessing quantitative genetic parameters from geometric morphometric data has limited utility, because it is unable to accurately describe how shape is evolving. [source] THE EVOLUTION OF DEVELOPMENT: TWO PORTRAITS OF SKULL OSSIFICATION IN PIPOID FROGSEVOLUTION, Issue 12 2002Jennifer Yeh Abstract., Development creates morphology, and the study of developmental processes has repeatedly shed light on patterns of morphological evolution. However, development itself evolves as well, often concomitantly with changes in life history or in morphology. In this paper, two approaches are used to examine the evolution of skull development in pipoid frogs. Pipoids have highly unusual morphologies and life histories compared to other frogs, and their development also proves to be remarkable. First, a phylogenetic examination of skull bone ossification sequences reveals that jaw ossification occurs significantly earlier in pipoids than in other frogs; this represents a reversal to the primitive vertebrate condition. Early jaw ossification in pipoids is hypothesized to result from the absence of certain larval specializations possessed by other frogs, combined with unusual larval feeding behaviors. Second, thin-plate spline morphometric studies of ontogenetic shape change reveal important differences between pipoid skull development and that of other frogs. In the course of frog evolution, there has been a shift away from salamander-like patterns of ontogenetic shape change. The pipoids represent the culmination of this trend, and their morphologies are highly derived in numerous respects. This study represents the first detailed examination of the evolution of skull development in a diverse vertebrate clade within a phylogenetic framework. It is also the first study to examine ossification sequences across vertebrates, and the first to use thin-plate spline morphometrics to quantitatively describe ontogenetic trajectories. [source] Involvement of Cdc42 and Rac small G proteins in invadopodia formation of RPMI7951 cellsGENES TO CELLS, Issue 12 2003Hirokazu Nakahara Background:, Invadopodia are membrane protrusions into the extracellular matrix by aggressive tumour cells. These structures are associated with sites of matrix degradation and invasiveness of malignant tumour cells in an in vitro fibronectin degradation/invasion assay. The Rho family small G proteins, consisting of the Rho, Rac and Cdc42 subfamilies, are implicated in various cell functions, such as cell shape change, adhesion, and motility, through reorganization of the actin cytoskeleton. We studied the roles of the Rho family small G proteins in invadopodia formation. Results:, We first demonstrated that invadopodia of RPMI7951 human melanoma cells extended into the matrix substratum on a vertical view using a laser scanning confocal microscope system. We confirmed that invadopodia were rich in actin filaments (F-actin) and visualized clearly with F-actin staining on a vertical view as well as on a horizontal view. We then studied the roles of Rho, Rac, and Cdc42 in invasiveness of the same cell line. In the in vitro fibronectin degradation/invasion assay, a dominant active mutant of Cdc42 enhanced dot-like degradation, whereas a dominant active mutant of Rac enhanced diffuse-type degradation. Furthermore, frabin, a GDP/GTP exchange protein for Cdc42 with F-actin-binding activity, enhanced both dot-like and diffuse-type degradation. However, a dominant active mutant of Rho did not affect the fibronectin degradation. Moreover, inhibition of phosphatidylinositol-3 kinase (PI3K) disrupted the Rac and Cdc42-dependent actin structures and blocked the fibronectin degradation. Conclusion:, These results suggest that Cdc42 and Rac play important roles in fibronectin degradation and invasiveness in a coordinate manner through the frabin-Cdc42/Rac-PI3K signalling pathway. [source] Measuring Similarity Among Various Shapes Based on Geometric MatchingGEOGRAPHICAL ANALYSIS, Issue 4 2005Zuoquan Zhao The purpose of this article is to examine how to measure the degree of similarity among various shapes, including for the first time those that are fragmented and perforated, by the overlap-based elongation index. It is argued that complete removal of the effects of position, size, and orientation on shape, which is essential for the calibration of shape similarity, can be achieved by a shape similarity index that varies continuously with changes in shape. After examining the characteristics of shape change, it is demonstrated that the elongation index is sensitive to changes in the shape of two spatial objects only when the centroids of the two objects are coincident. Two related rules of shape similarity are then presented. The applicability of the elongation index is evaluated by comparing several simple and complex shapes. The principal contribution of this article is that for the first time similarity among various shapes, fragmented or perforated, can be identified using the elongation index. [source] One-Step Process for Creating Triple-Shape Capability of AB Polymer NetworksADVANCED FUNCTIONAL MATERIALS, Issue 1 2009Marc Behl Abstract Triple-shape polymers can move from a first shape (A) to a second shape (B) and from there to a third shape (C), where both shape changes are induced by temperature increases. This triple-shape capability is obtained for multiphase polymer networks after application of a complex thermomechanical programming process, which consists of two steps; these steps create shapes (B) and (A), while shape (C) is defined by the covalent crosslinks of the polymer network. Here, the creation of the triple-shape capability for an AB polymer network system by a simple one-step process similar to a conventional dual-shape programming process is reported. The polymer networks are based on poly(, -caprolactone) (PCL) and poly(cyclohexyl methacrylate); favorable compositions for obtaining a triple shape effect have a PCL content between 35 and 60 wt%. This finding substantially facilitates handling of the triple-shape technology and is an important step toward the realization of potential applications in which more than one shape change is required. [source] Martensitic Phase Transformation of Isolated HfO2, ZrO2, and HfxZr1,,,xO2 (0,<,x,<,1) Nanocrystals,ADVANCED FUNCTIONAL MATERIALS, Issue 10 2005J. Tang Abstract We previously reported that, during the reactions to make nanocrystals of HfO2 and Hf-rich HfxZr1,,,xO2, a tetragonal-to-monoclinic phase transformation occurs that is accompanied by a shape change of the particles (faceted spherical to nanorods) when the temperature at which the reaction is conducted is changed from 340,to 400,°C. We now conclude that this concomitant phase and shape change is a result of the martensitic transformation of isolated nanocrystals in a hot liquid, where twinning plays a crucial role in accommodating the shape-change-induced strain. That such change was not observed during the reactions forming ZrO2 and Zr-rich HfxZr1,,,xO2 nanocrystals is attributed to the higher driving force needed in those instances compared to that needed for producing HfO2 and Hf-rich HfxZr1,,,xO2 nanocrystals. We also report here the post-synthesis, heat-induced phase transformation of HfxZr1,,,xO2 (0,<,x,<,1) nanocrystals. As temperature increases, all the tetragonal nanocrystals transform to the monoclinic phase accompanied by an increase in particle size (as evidenced by X-ray diffraction and transmission electron microscopy), which confirms that there is a critical size for the phase transformation to occur. When the monoclinic nanorods are heated above a certain temperature the grains grow considerably; under certain conditions a small amount of tetragonal phase appears. [source] A Continuous Flow Synthesis of Micrometer-Sized Actuators from Liquid Crystalline ElastomersADVANCED MATERIALS, Issue 47 2009Christian Ohm We demonstrate the use of a microfluidic setup to prepare monodisperse and spherical beads from a liquid crystalline elastomer. These particles show a strong and reversible shape change into a cigar-like conformation during the transition into the isotropic phase. These properies are a result of the monodomainic alignment of the mesogens in the flow field of the microfluidic setup. [source] A fictitious energy approach for shape optimizationINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 3 2010M. Scherer Abstract This paper deals with shape optimization of continuous structures. As in early works on shape optimization, coordinates of boundary nodes of the FE-domain are directly chosen as design variables. Convergence problems and problems with jagged shapes are eliminated by a new regularization technique: an artificial inequality constraint added to the optimization problem limits a fictitious total strain energy that measures the shape change of the design with respect to a reference design. The energy constraint defines a feasible design space whose size can be varied by one parameter, the upper energy limit. By construction, the proposed regularization is applicable to a wide range of problems; although in this paper, the application is restricted to linear elastostatic problems. Copyright © 2009 John Wiley & Sons, Ltd. [source] Reversible Infrared Actuation of Carbon Nanotube,Liquid Crystalline Elastomer Nanocomposites,ADVANCED MATERIALS, Issue 12 2008Liqiang Yang Nanocomposite films comprising polymer-functionalized single-walled carbon-nanotubes (SWNTs) and liquid crystal elastomers (LCEs) show a reversible IR-induced strain (,,30%) at very low SWNT loading levels (,0.2 wt%). SWNTs can efficiently transform absorbed IR light into thermal energy, thereby serving as a nanoscale heat-source and thermal- conduction pathway. The absorbed thermal-energy induced a nematic, isotropic phase-transition, generating a shape change in the nanocomposite film. [source] An Artificial Muscle with Lamellar Structure Based on a Nematic Triblock Copolymer,ADVANCED MATERIALS, Issue 21 2004M.-H. Li A muscle-like material with a lamellar structure has been prepared for the first time from a liquid-crystalline triblock copolymer. The material consists of a repeated series of nematic-polymer blocks and conventional rubber blocks. The motor for the contraction is the reversible macromolecular-chain shape change, from stretched to spherical, of the nematic polymer that occurs at the nematic-to-isotropic phase transition. [source] The pattern of endocranial ontogenetic shape changes in humansJOURNAL OF ANATOMY, Issue 3 2009Simon Neubauer Abstract Humans show a unique pattern of brain growth that differentiates us from all other primates. In this study, we use virtual endocasts to provide a detailed description of shape changes during human postnatal ontogeny with geometric morphometric methods. Using CT scans of 108 dried human crania ranging in age from newborns to adults and several hundred landmarks and semi-landmarks, we find that the endocranial ontogenetic trajectory is curvilinear with two bends, separating three distinct phases of shape change. We test to what extent endocranial shape change is driven by size increase and whether the curved ontogenetic trajectory can be explained by a simple model of modular development of the endocranial base and the endocranial vault. The hypothesis that endocranial shape change is driven exclusively by brain growth is not supported; we find changes in endocranial shape after adult size has been attained and that the transition from high rates to low rates of size increase does not correspond to one of the shape trajectory bends. The ontogenetic trajectory of the endocranial vault analyzed separately is nearly linear; the trajectory of the endocranial base, in contrast, is curved. The endocranial vault therefore acts as one developmental module during human postnatal ontogeny. Our data suggest that the cranial base comprises several submodules that follow their own temporally and/or spatially disjunct growth trajectories. [source] Reactive mold filling in resin transfer molding processes with edge effectsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2009Yanyu Ding Abstract Reactive mold filling is one of the important stages in resin transfer molding processes, in which resin curing and edge effects are important characteristics. On the basis of previous work, volume-averaging momentum equations involving viscous and inertia terms were adopted to describe the resin flow in fiber preform, and modified governing equations derived from the Navier,Stokes equations are introduced to describe the resin flow in the edge channel. A dual-Arrhenius viscosity model is newly introduced to describe the chemorheological behavior of a modified bismaleimide resin. The influence of the curing reaction and processing parameters on the resin flow patterns was investigated. The results indicate that, under constant-flow velocity conditions, the curing reaction caused an obvious increase in the injection pressure and its influencing degree was greater with increasing resin temperature or preform permeability. Both a small change in the resin viscosity and the alteration of the injection flow velocity hardly affected the resin flow front. However, the variation of the preform permeability caused an obvious shape change in the resin flow front. The simulated results were in agreement with the experimental results. This study was helpful for optimizing the reactive mold-filling conditions. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Thrombogenic and atherogenic activities of lysophosphatidic acidJOURNAL OF CELLULAR BIOCHEMISTRY, Issue 6 2004Wolfgang Siess Abstract Lysophosphatidic acid (LPA) has been identified as a biologically active lipid in mildly-oxidized LDL, human atherosclerotic lesions, and the supernatant of activated platelets. The evidence that LPA has thrombogenic and atherogenic activities has increased substantially in recent years. Supporting the thrombogenic activity of LPA, analysis of the core region of human carotid plaques revealed recently the presence of alkyl- and acyl-molecular species from LPA with high platelet-activating potency (16:0 alkyl-LPA, 20:4 acyl-LPA). LPA, lipid extracts of atherosclerotic plaques, and the lipid-rich core elicited shape change and, in synergy with other platelet stimuli, aggregation of isolated platelets. This effect was completely abrogated by prior incubation of platelets with LPA receptor antagonists. Furthermore, LPA at concentrations approaching those found in vivo, induced platelet shape change, aggregation, and platelet-monocyte aggregate formation in blood. LPA-stimulated platelet aggregation was mediated by the ADP-stimulated activation of the P2Y1 and P2Y12 receptors. Supporting its atherogenic activity, LPA is a mitogen and motogen to vascular smooth muscle cells (VSMCs) and an activator of endothelial cells and macrophages. Recently, LPA has been identified as an agonist of the peroxisome proliferator activating receptor , (PPAR,), which is a key regulator of atherogenesis. LPA elicits progressive neointima formation, which is fully abolished by GW9662, an antagonist of PPAR,. We propose that LPA plays a central role in eliciting vascular remodeling and atherogenesis. Furthermore, upon rupture of lipid-rich atherosclerotic plaques, LPA may trigger platelet aggregation and intra-arterial thrombus formation. Antagonists of LPA receptors might be useful in preventing LPA-elicited thrombus formation and neointima formation in patients with cardiovascular diseases. © 2004 Wiley-Liss, Inc. [source] Evolution of bite performance in turtlesJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 6 2002A. Herrel Abstract Among vertebrates, there is often a tight correlation between variation in cranial morphology and diet. Yet, the relationships between morphological characteristics and feeding performance are usually only inferred from biomechanical models. Here, we empirically test whether differences in body dimensions are correlated with bite performance and trophic ecology for a large number of turtle species. A comparative phylogenetic analysis indicates that turtles with carnivorous and durophagous diets are capable of biting harder than species with other diets. This pattern is consistent with the hypothesis that an evolutionary increase in bite performance has allowed certain turtles to consume harder or larger prey. Changes in carapace length tend to be associated with proportional changes in linear head dimensions (no shape change). However, maximum bite force tends to change in proportion to length cubed, rather than length squared, implying that changes in body size are associated with changes in the design of the jaw apparatus. After the effect of body size is accounted for in the analysis, only changes in head height are significantly correlated with changes in bite force. Additionally, our data suggest that the ability to bite hard might trade off with the ability to feed on fast agile prey. Rather than being the direct result of conflicting biomechanical or physiological demands for force and speed, this trade-off may be mediated through the constraints imposed by the need to retract the head into the shell for defensive purposes. [source] Ontogenetic allometries and shape changes in the suckermouth armoured catfish Ancistruscf.triradiatus Eigenmann (Loricariidae, Siluriformes), related to suckermouth attachment and yolk-sac sizeJOURNAL OF FISH BIOLOGY, Issue 4 2008T. Geerinckx Early life-history stages of the loricariid catfish Ancistruscf.triradiatus are described, from pre-hatch embryos to juveniles. The descriptions, as well as metric characters, indicate that the free-swimming embryonic stage is followed directly by the juvenile stage, without a true larval stage or metamorphosis. Intense, but gradual ontogenetic head-shape changes are present during the embryonic and free-living embryonic stages: the suckermouth gradually shifts from an almost rostral to a ventral position. The external and internal transformations related to this shape change are considered an adaptation to both the loricariid algae-scraping feeding mode and the need of suckermouth functioning from the moment of hatching, when a ventrally situated suckermouth would be disadvantageous, as a large yolk sac is present. [source] Morphological changes during postembryonic development in two species of neotropical harvestmen (Opiliones, Laniatores, Cranaidae)JOURNAL OF MORPHOLOGY, Issue 9 2009Victor R. Townsend Jr. Abstract Morphological changes during postembryonic development in the Cranaidae are described on the basis of the examination of an incomplete series of larvae, nymphs, and adults of Phareicranaus calcariferus and Santinezia serratotibialis. The life histories of these species are hypothesized to consist of six nymphal stages, featuring the appearance of secondary male sexual characteristics in the antepenultimate nymph (N5). Color and body shape change dramatically during development. Growth rates for nymphs based upon leg measurements were similar for both species. In S. serratotibialis, the greatest increase in leg size occurred from larva to 1st nymph. The tarsomeres of legs I,IV varied by 1,2 segments per leg for each nymph stage, with the number of tarsal segments increased by 1,2 segments at each stage. Adults had nearly twice as many tarsomeres on leg II than other legs. Ontogenetic changes were observed in the armature of the proximal cheliceral segment, ocularium, pedipalp, opisthosoma, distitarsus III and IV, and leg IV. Morphological changes in postembryonic development in cranaid harvestmen are similar to those reported for other Laniatores. J. Morphol., 2009. © 2009 Wiley-Liss, Inc. [source] Pelvic growth: Ontogeny of size and shape sexual dimorphism in rat pelvesJOURNAL OF MORPHOLOGY, Issue 1 2007S. Berdnikovs Abstract The mammalian pelvis is sexually dimorphic with respect to both size and shape. Yet little is known about the differences in postnatal growth and bone remodeling that generate adult sexual dimorphism in pelvic bones. We used Sprague-Dawley laboratory rats (Rattus norvegicus), a species that exhibits gross pelvic size and shape dimorphism, as a model to quantify pelvic morphology throughout ontogeny. We employed landmark-based geometric morphometrics methodology on digitized landmarks from radiographs to test for sexual dimorphism in size and shape, and to examine differences in the rates, magnitudes, and directional patterns of shape change during growth. On the basis of statistical significance testing, the sexes became different with respect to pelvic shape by 36 days of age, earlier than the onset of size dimorphism (45 days), although visible shape differences were observed as early as at 22 days. Males achieved larger pelvic sizes by growing faster throughout ontogeny. However, the rates of shape change in the pelvis were greater in females for nearly all time intervals scrutinized. We found that trajectories of shape change were parallel in the two sexes until age of 45 days, suggesting that both sexes underwent similar bone remodeling until puberty. After 45 days, but before reproductive maturity, shape change trajectories diverged because of specific changes in the female pelvic shape, possibly due to the influence of estrogens. Pattern of male pelvic bone remodeling remained the same throughout ontogeny, suggesting that androgen effects on male pelvic morphology were constant and did not contribute to specific shape changes at puberty. These results could be used to direct additional research on the mechanisms that generate skeletal dimorphisms at different levels of biological organization. J. Morphol., 2006. © 2006 Wiley-Liss, Inc. [source] Chondrocranial development in larval Rana sylvatica (Anura: Ranidae): Morphometric analysis of cranial allometry and ontogenetic shape changeJOURNAL OF MORPHOLOGY, Issue 2 2002Peter M. Larson Abstract This study provides baseline quantitative data on the morphological development of the chondrocranium in a larval anuran. Both linear and geometric morphometric methods are used to quantitatively analyze size-related shape change in a complete developmental series of larvae of the wood frog, Rana sylvatica. The null hypothesis of isometry was rejected in all geometric morphometric and most linear morphometric analyses. Reduced major axis regressions of 11 linear chondrocranial measurements on size indicate a mixture of allometric and isometric scaling. Measurements in the otic and oral regions tend to scale with negative allometry and those associated with the palatoquadrate and muscular process scale with isometry or positive allometry. Geometric morphometric analyses, based on a set of 11 chondrocranial landmarks, include linear regression of relative warp scores and multivariate regression of partial warp scores and uniform components on log centroid size. Body size explains about one-quarter to one-third of the total shape variation found in the sample. Areas of regional shape transformation (e.g., palatoquadrate, otic region, trabecular horns) are identified by thin-plate spline deformation grids and are concordant with linear morphometric results. Thus, the anuran chondrocranium is not a static structure during premetamorphic stages and allometric patterns generally follow scaling predictions for tetrapod cranial development. Potential implications regarding larval functional morphology, cranial development, and chondrocranial evolution in anurans are discussed. J. Morphol. 252:131,144, 2002. © 2002 Wiley-Liss, Inc. [source] Role of Vanadium Carbide Additive during Sintering of WC,Co: Mechanism of Grain Growth InhibitionJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2003Hyoung R. Lee In a WC,Co specimen, the shape of WC crystals was a triangular prism with truncated corners. When VC was added to inhibit grain growth, the crystal shape changed to a triangular prism without truncation. This shape change was related to the variation of edge energy, which has a significant influence on the coarsening process of WC grains. [source] Differential phosphorylation of myosin light chain (Thr)18 and (Ser)19 and functional implications in plateletsJOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 10 2010T. M. GETZ Summary. Background:, Myosin IIA is an essential platelet contractile protein that is regulated by phosphorylation of its regulatory light chain (MLC) on residues (Thr)18 and (Ser)19 via the myosin light chain kinase (MLCK). Objective:, The present study was carried out to elucidate the mechanisms regulating MLC (Ser)19 and (Thr)18 phosphorylation and the functional consequence of each phosphorylation event in platelets. Results:, Induction of 2MeSADP-induced shape change occurs within 5 s along with robust phosphorylation of MLC (Ser)19 with minimal phosphorylation of MLC (Thr)18. Selective activation of G12/13 produces both slow shape change and comparably slow MLC (Thr)18 and (Ser)19 phosphorylation. Stimulation with agonists that trigger ATP secretion caused rapid MLC (Ser)19 phosphorylation while MLC (Thr)18 phosphorylation was coincident with secretion. Platelets treated with p160ROCK inhibitor Y-27632 exhibited a partial inhibition in secretion and had a substantial inhibition in MLC (Thr)18 phosphorylation without effecting MLC (Ser)19 phosphorylation. These data suggest that phosphorylation of MLC (Ser)19 is downstream of Gq/Ca2+ -dependent mechanisms and sufficient for shape change, whereas MLC (Thr)18 phosphorylation is substantially downstream of G12/13 -regulated Rho kinase pathways and necessary, probably in concert with MLC (Ser)19 phosphorylation, for full contractile activity leading to dense granule secretion. Overall, we suggest that the amplitude of the platelet contractile response is differentially regulated by a least two different signaling pathways, which lead to different phosphorylation patterns of the myosin light chain, and this mechanism results in a graded response rather than a simple on/off switch. [source] (N)-methanocarba-2MeSADP (MRS2365) is a subtype-specific agonist that induces rapid desensitization of the P2Y1 receptor of human plateletsJOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 4 2006D. M. BOURDON Summary., Adenosine diphosphate (ADP) initiates and maintains sustained aggregation of platelets through simultaneous activation of both the Gq -coupled P2Y1 receptor and the Gi -coupled P2Y12 receptor. We recently described the synthesis and P2Y1 receptor-specific agonist activity of (N)-methanocarba-2MeSADP (MRS2365). Consequences of selective activation of the P2Y1 receptor by MRS2365 have been further examined in human platelets. Whereas MRS2365 alone only induced shape change, addition of MRS2365 following epinephrine treatment, which activates the Gi/z -linked, ,2A -adrenergic receptor, resulted in sustained aggregation that was indistinguishable from that observed with ADP. Conversely, the platelet shape change promoted by ADP in the presence of the GPIIb/IIIa antagonist eptifibatide was similar to that promoted by MRS2365. Preaddition of the high affinity P2Y1 receptor antagonist MRS2500 inhibited the effect of MRS2365, whereas addition of MRS2500 subsequent to MRS2365 reversed the MRS2365-induced shape change. Preactivation of the P2Y1 receptor with MRS2365 for 2 min resulted in marked loss of capacity of ADP to induce aggregation as evidenced by a greater than 20-fold rightward shift in the concentration effect curve of ADP. This inhibitory effect of P2Y1 receptor activation was dependent on the concentration of MRS2365 (EC50 = 34 nm). The inhibitory effect of preincubation with MRS2365 was circumvented by activation of the Gq -coupled 5-HT2A receptor suggesting that MRS2365 induces loss of the ADP response as a consequence of desensitization of the Gq -coupled P2Y1 receptor. The time course of MRS2365-induced loss of aggregation response to epinephrine was similar to that observed with ADP. These results further demonstrate the P2Y1 receptor selectivity of MRS2365 and illustrate the occurrence of agonist-induced desensitization of the P2Y1 receptor of human platelets studied in the absence of P2Y12 receptor activation . [source] A differential role of the platelet ADP receptors P2Y1 and P2Y12 in Rac activationJOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 10 2005C. SOULET Summary., The dynamics of the actin cytoskeleton, largely controlled by the Rho family of small GTPases (Rho, Rac and Cdc42), is critical for the regulation of platelet responses such as shape change, adhesion, spreading and aggregation. Here, we investigated the role of adenosine diphosphate (ADP), a major co-activator of platelets, on the activation of Rac. ADP rapidly activated Rac in a dose-dependent manner and independently of GPIIb/IIIa and phosphoinositide 3-kinase. ADP alone, used as a primary agonist, activated Rac and its effector PAK via its P2Y1 receptor, through a Gq -dependent pathway and independently of P2Y12. The P2Y12 receptor appeared unable to activate the GTPase per se as also observed for the adenosine triphosphate receptor P2X1. Conversely, secreted ADP strongly potentiated Rac activation induced by Fc,RIIa clustering or TRAP via its P2Y12 receptor, the target of antithrombotic thienopyridines. Stimulation of the ,2A -adrenergic receptor/Gz pathway by epinephrine was able to replace the P2Y12/Gi -mediated pathway to amplify Rac activation by Fc,RIIa or by the thrombin receptor PAR-1. This co-activation appeared necessary to reach a full stimulation of Rac as well as PAK activation and actin polymerization and was blocked by a G-protein ,, subunits scavenger peptide. [source] Further evidence that fibrillar collagen is unable to promote platelet shape change and aggregation in the absence of secondary agonistsJOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 9 2005P. OHLMANN [source] Lipid rafts are required in G,i signaling downstream of the P2Y12 receptor during ADP-mediated platelet activationJOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 5 2005T. M. QUINTON Summary., ADP is important in propagating hemostasis upon its secretion from activated platelets in response to other agonists. Lipid rafts are microdomains within the plasma membrane that are rich in cholesterol and sphingolipids, and have been implicated in the stimulatory mechanisms of platelet agonists. We sought to determine the importance of lipid rafts in ADP-mediated platelet activation via the G protein-coupled P2Y1 and P2Y12 receptors using lipid raft disruption by cholesterol depletion with methyl- , -cyclodextrin. Stimulation of cholesterol-depleted platelets with ADP resulted in a reduction in the extent of aggregation but no difference in the extent of shape change or intracellular calcium release. Furthermore, repletion of cholesterol to previously depleted membranes restored ADP-mediated platelet aggregation. In addition, P2Y12-mediated inhibition of cAMP formation was significantly decreased upon cholesterol depletion from platelets. Stimulation of cholesterol-depleted platelets with agonists that depend upon G,i activation for full activation displayed significant loss of aggregation and secretion, but showed restoration when simultaneously stimulated with the G,z -coupled agonist epinephrine. Finally, G,i preferentially localizes to lipid rafts as determined by sucrose density centrifugation. We conclude that G,i signaling downstream of P2Y12 activation, but not G,q or G,z signaling downstream of P2Y1 or ,2A activation, respectively, has a requirement for lipid rafts that is necessary for its function in ADP-mediated platelet activation. [source] The P2Y1 receptor plays an essential role in the platelet shape change induced by collagen when TxA2 formation is preventedJOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 6 2004P. Mangin Summary., ADP and TxA2 are secondary agonists which play an important role as cofactors when platelets are activated by agonists such as collagen or thrombin. The aim of the present study was to characterize the role of the ADP receptor P2Y1 in collagen-induced activation of washed platelets. Inhibition of P2Y1 alone with the selective antagonist MRS2179 prolonged the lag phase preceding aggregation in response to low or high concentrations of fibrillar collagen, without affecting the maximum amplitude of aggregation or secretion. A combination of MRS2179 and aspirin resulted in complete inhibition of platelet shape change at low and high collagen concentrations, together with a profound decrease in aggregation and secretion. Scanning electron microscopy showed that these platelets had conserved the discoid morphology typical of the resting state. A lack of shape change was also observed in aspirin-treated P2Y1 - and G,q -deficient mouse platelets and in ,-storage pool-deficient platelets from Fawn Hooded rats. In contrast, when the second ADP receptor P2Y12 was inhibited with AR-C69931MX, aspirin-treated platelets were still able to change shape and displayed only a moderate decrease in aggregation and secretion. In conclusion, this study provides evidence that collagen requires not only the TxA2 receptor Tp,, but also P2Y1, to induce platelet shape change. [source] | ||||||||||||||||||||||||||||||||||||||||