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Shearing
Kinds of Shearing Terms modified by Shearing Selected AbstractsBiological Sustainability of Live Shearing of Vicuña in PeruCONSERVATION BIOLOGY, Issue 1 2007CATHERINE TERESA SAHLEY Andes; conservación basada en comunidades; Vicugna vicugna Abstract:,The vicuña's (Vicugna vicugna) fiber is highly valued as an export product that is made into luxury fabric and clothing. The price of fiber in 2004 was $566/kg, which makes the fiber a potentially important source of income for Andean agropastoral communities and serves as an incentive to allow vicuña grazing on high-elevation Andean landscapes. It is presumed that a shorn vicuña has little value for poachers, so shearing vicuñas could serve as a disincentive to poaching. Thus, the supply of vicuña fiber may be sustainable if it is procured through live shearing, which should serve as a powerful conservation tool. We evaluated the effects of capture and shearing on the demography of vicuña in one site located in the Salinas Aguada Blanca Reserve, Arequipa, Peru, where vicuñas were captured and shorn in spring and then returned to the wild. We conducted fixed-width line-transect censuses from 1997 to 2003 of this population. We compared the proportion of young born to females that were shorn versus females that were unshorn for the 3 years in which shearing occurred. We evaluated the effect of capture and shearing on proportion of young born to shorn and unshorn females at a second site, Picotani, Puno. The wild population in Arequipa that underwent capture and shearing showed a steady increase in total population and average density between 1997 and 2003. No significant difference was found between the proportion of young per female for shorn and unshorn females at either site. We conclude that in spring, capture and live shearing of vicuñas can be biologically sustainable. Further research is needed to determine whether shearing during winter months is biologically sustainable. Resumen:,La fibra de vicuña (Vicugna vicugna) tiene gran valor como un producto de exportación que es transformado en tela y ropa de lujo. El precio de la fibra en 2004 era de $566/kg, lo que hace que la fibra sea una fuente de ingreso potencialmente importante para comunidades agropastoriles Andinas y servir como un incentivo para permitir el pastoreo de vicuñas en paisajes Andinos elevados. Se presume que una vicuña trasquilada tiene poco valor para cazadores furtivos, por lo que el trasquilado de vicuñas pudiera servir como un desincentivo para la caza furtiva. Por lo tanto, el abastecimiento de fibra de vicuña puede ser sustentable si se obtiene del trasquilado de animales vivos, y el trasquilado de animales vivos debería ser una poderosa herramienta de conservación. Evaluamos los efectos de la captura y trasquilado sobre la demografía de vicuñas en un sitio localizado en la Reserva Salinas Aguada Blanca, Arequipa, Perú, donde las vicuñas fueron capturadas y trasquiladas en primavera y liberadas. Realizamos censos de esta población en transectos lineales de ancho fijo de 1997 a 2003. Comparamos la proporción de crías de hembras trasquiladas con las de hembras no trasquiladas durante los 3 años en que ocurrió el trasquilado. Evaluamos el efecto de la captura y trasquilado sobre la proporción de crías de hembras trasquiladas y no trasquiladas en un segundo sitio, Picotani, Puno. La población silvestre en Arequipa que fue capturada y trasquilada mostró un incremento constante en la población total y la densidad promedio entre 1997 y 2003. No se encontró diferencia significativa entre la proporción de crías por hembra para hembras trasquiladas y no trasquiladas en ningún sitio. Concluimos que en la primavera, la captura y trasquilado de vicuñas vivas puede ser biológicamente sostenible. Se requiere más investigación para determinar si el trasquilado durante el invierno es biológicamente sostenible. [source] Shearing flows of a dry granular material,hypoplastic constitutive theory and numerical simulationsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 14 2006Chung Fang Abstract In the present study, the Goodman,Cowin theory is extended to incorporate plastic features to construct an elasto-visco-plastic constitutive model for flowing dry granular materials. A thermodynamic analysis, based on the Müller,Liu entropy principle, is performed to derive the equilibrium expressions of the constitutive variables. Non-equilibrium responses are proposed by use of a quasi-linear theory, in particular a hypoplastic-type relation is introduced to model the internal friction and plastic effects. It is illustrated that the Goodman,Cowin theory can appropriately be extended to include frictional effects into the evolution equation of the volume fraction (i.e. the so-called balance of equilibrated force) and the equilibrium expression of the Cauchy stress tensor. The implemented model is applied to investigate conventional steady isothermal granular flows with incompressible grains, namely simple plane shear, inclined gravity-driven and vertical channel-flows, respectively. Numerical results show that the hypoplastic effect plays a significant role in the behaviour of a flowing granular material. The obtained profiles of the velocity and the volume fraction with hypoplastic features are usually sharper and the shear-thinning effect is more significant than that without such plastic effects. This points at the possible wide applicability of the present model in the fields of granular materials and soil mechanics. In addition, the present paper also provides a framework for a possible extension of the hypoplastic theories which can be further undertaken. Copyright © 2006 John Wiley & Sons, Ltd. [source] Morphology in Immiscible Polymer Blends During Solidification of an Amorphous Dispersed Phase under ShearingTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2002Yves Deyrail Abstract Solidification under shear of dispersed polycarbonate (PC) fibers in copolymer polyethylene-methyl acrylate matrix (EMA) was investigated using a hot optical shear device. First, the deformation of PC droplets and its modeling under isothermal conditions were studied for comprehension purposes. Overall agreement with literature models was found and the main influence of the viscosity ratio has been stressed. Second, the morphology control through dynamic quenching was experimented. It consists of solidifying the amorphous PC dispersed phase under shear flow. Break-up times of PC fibers were taken into account. Shear rate and quenching-time balance was demonstrated. Thus, during dynamic solidification, a fibrillar morphology could be obtained through rapid quenching. Long quenching times allow nodular morphology, whose size depends on the shear rate used. PC rods can be obtained by adjusting the shear rate during dynamic quenching. La solidification sous cisaillement du polycarbonate (PC) dispersé dans une matrice copolymère éthylène-acétate de vinyle (EMA) a été suivie à l'aide d'un microscope et d'une platine de cisaillement chauffante. Dans un premier temps la déformation isotherme de billes de PC pour différentes températures a été étudiée, ainsi que sa modélisation. Une bonne corrélation avec les modèles issus de la littérature a été obtenue. L'importance du rapport des viscosités a été ainsi soulignée. Dans un second temps le contrôle de la morphologie par le procédé de « refroidissement dynamique » a été expérimenté. Celui-ci consiste à solidifier le PC sous cisaillement pendant le refroidissement. Les temps de rupture des fibres de PC ont été considérés et l'importance du couple gradient de cisaillement-temps de refroidissement sur le contrôle de la morphologie a été mis en évidence. Pendant la solidification, un refroidissement rapide permet d'obtenir une morphologie fibrillaire. [source] Shearing of a Frova Intubating Introducer by a Bronchocath double lumen tubeANAESTHESIA, Issue 2 2006H. Vlachtsis No abstract is available for this article. [source] Biological Sustainability of Live Shearing of Vicuña in PeruCONSERVATION BIOLOGY, Issue 1 2007CATHERINE TERESA SAHLEY Andes; conservación basada en comunidades; Vicugna vicugna Abstract:,The vicuña's (Vicugna vicugna) fiber is highly valued as an export product that is made into luxury fabric and clothing. The price of fiber in 2004 was $566/kg, which makes the fiber a potentially important source of income for Andean agropastoral communities and serves as an incentive to allow vicuña grazing on high-elevation Andean landscapes. It is presumed that a shorn vicuña has little value for poachers, so shearing vicuñas could serve as a disincentive to poaching. Thus, the supply of vicuña fiber may be sustainable if it is procured through live shearing, which should serve as a powerful conservation tool. We evaluated the effects of capture and shearing on the demography of vicuña in one site located in the Salinas Aguada Blanca Reserve, Arequipa, Peru, where vicuñas were captured and shorn in spring and then returned to the wild. We conducted fixed-width line-transect censuses from 1997 to 2003 of this population. We compared the proportion of young born to females that were shorn versus females that were unshorn for the 3 years in which shearing occurred. We evaluated the effect of capture and shearing on proportion of young born to shorn and unshorn females at a second site, Picotani, Puno. The wild population in Arequipa that underwent capture and shearing showed a steady increase in total population and average density between 1997 and 2003. No significant difference was found between the proportion of young per female for shorn and unshorn females at either site. We conclude that in spring, capture and live shearing of vicuñas can be biologically sustainable. Further research is needed to determine whether shearing during winter months is biologically sustainable. Resumen:,La fibra de vicuña (Vicugna vicugna) tiene gran valor como un producto de exportación que es transformado en tela y ropa de lujo. El precio de la fibra en 2004 era de $566/kg, lo que hace que la fibra sea una fuente de ingreso potencialmente importante para comunidades agropastoriles Andinas y servir como un incentivo para permitir el pastoreo de vicuñas en paisajes Andinos elevados. Se presume que una vicuña trasquilada tiene poco valor para cazadores furtivos, por lo que el trasquilado de vicuñas pudiera servir como un desincentivo para la caza furtiva. Por lo tanto, el abastecimiento de fibra de vicuña puede ser sustentable si se obtiene del trasquilado de animales vivos, y el trasquilado de animales vivos debería ser una poderosa herramienta de conservación. Evaluamos los efectos de la captura y trasquilado sobre la demografía de vicuñas en un sitio localizado en la Reserva Salinas Aguada Blanca, Arequipa, Perú, donde las vicuñas fueron capturadas y trasquiladas en primavera y liberadas. Realizamos censos de esta población en transectos lineales de ancho fijo de 1997 a 2003. Comparamos la proporción de crías de hembras trasquiladas con las de hembras no trasquiladas durante los 3 años en que ocurrió el trasquilado. Evaluamos el efecto de la captura y trasquilado sobre la proporción de crías de hembras trasquiladas y no trasquiladas en un segundo sitio, Picotani, Puno. La población silvestre en Arequipa que fue capturada y trasquilada mostró un incremento constante en la población total y la densidad promedio entre 1997 y 2003. No se encontró diferencia significativa entre la proporción de crías por hembra para hembras trasquiladas y no trasquiladas en ningún sitio. Concluimos que en la primavera, la captura y trasquilado de vicuñas vivas puede ser biológicamente sostenible. Se requiere más investigación para determinar si el trasquilado durante el invierno es biológicamente sostenible. [source] Modelling increased soil cohesion due to roots with EUROSEMEARTH SURFACE PROCESSES AND LANDFORMS, Issue 13 2008S. De Baets Abstract As organic root exudates cause soil particles to adhere firmly to root surfaces, roots significantly increase soil strength and therefore also increase the resistance of the topsoil to erosion by concentrated flow. This paper aims at contributing to a better prediction of the root effects on soil erosion rates in the EUROSEM model, as the input values accounting for roots, presented in the user manual, do not account for differences in root density or root architecture. Recent research indicates that small changes in root density or differences in root architecture considerably influence soil erosion rates during concentrated flow. The approach for incorporating the root effects into this model is based on a comparison of measured soil detachment rates for bare and for root-permeated topsoil samples with predicted erosion rates under the same flow conditions using the erosion equation of EUROSEM. Through backwards calculation, transport capacity efficiencies and corresponding soil cohesion values can be assessed for bare and root-permeated topsoils respectively. The results are promising and present soil cohesion values that are in accordance with reported values in the literature for the same soil type (silt loam). The results show that grass roots provide a larger increase in soil cohesion as compared with tap-rooted species and that the increase in soil cohesion is not significantly different under wet and dry soil conditions, either for fibrous root systems or for tap root systems. Power and exponential relationships are established between measured root density values and the corresponding calculated soil cohesion values, reflecting the effects of roots on the resistance of the topsoil to concentrated flow incision. These relationships enable one to incorporate the root effect into the soil erosion model EUROSEM, through adapting the soil cohesion input value. A scenario analysis shows that the contribution of roots to soil cohesion is very important for preventing soil loss and reducing runoff volume. The increase in soil shear strength due to the binding effect of roots on soil particles is two orders of magnitude lower as compared with soil reinforcement achieved when roots mobilize their tensile strength during soil shearing and root breakage. Copyright © 2008 John Wiley & Sons, Ltd. [source] A Stimuli-Responsive, Photoluminescent, Anthracene-Based Liquid Crystal: Emission Color Determined by Thermal and Mechanical ProcessesADVANCED FUNCTIONAL MATERIALS, Issue 12 2009Yoshimitsu Sagara Abstract Here, a photoluminescent liquid crystal that exhibits a change of emission color on the metastable,stable phase transition induced by external stimuli is prepared. A 2,6-diethynylanthracene derivative with amide groups and dendritic side chains exhibits a columnar phase on slow cooling from the isotropic phase and shows blue emission in this columnar phase. In contrast, a cubic phase is obtained by rapid cooling from the isotropic phase. In the cubic phase, the 2,6-diethynylanthracene cores form excimers, resulting in yellow emission. While the columnar phase is a stable liquid-crystalline (LC) phase, the cubic phase is a metastable LC phase. It is found that a change of the photoluminescent color from yellow to blue is observed on the cubic-columnar phase transition induced by heating or mechanical shearing for this 2,6-diethynylanthracene derivative in the cubic phase. This change of photoluminescent color is ascribed to the inhibition of excimer formation on the metastable,stable LC phase transition. [source] Deformation during exhumation of medium- and high-grade metamorphic rocks in the Variscan chain in northern Sardinia (Italy)GEOLOGICAL JOURNAL, Issue 3 2009Rodolfo Carosi Abstract The Anglona and SW Gallura regions represent key places to investigate the tectonic evolution of medium- and high-grade metamorphic rocks cropping out in northern Sardinia (Italy). From south to north we distinguish two different metamorphic complexes recording similar deformation histories but different metamorphic evolution: the Medium Grade Metamorphic Complex (MGMC) and the High Grade Metamorphic Complex (HGMC). After the initial collisional stage (D1 deformation phase), both complexes were affected by three contractional deformational phases (D2, D3 and D4) followed by later extensional tectonics. The D2 deformation phase was the most significant event producing an important deformation partitioning that produced localized shearing and folding domains at the boundary between the two metamorphic complexes. We highlight the presence of two previously undocumented systems of shear belts with different kinematics but analogous orientation in the axial zone of Sardinia. They became active at the boundary between the MGMC and HGMC from the beginning of D2. They formed a transpressive regime responsible for the exhumation of the medium- and high-grade metamorphic rocks, and overall represent a change from orthogonal to orogen-parallel tectonic transport. Copyright © 2008 John Wiley & Sons, Ltd. [source] Localized ductile thrusting north of the Variscan Front, Ross Island, southwest IrelandGEOLOGICAL JOURNAL, Issue 1 2003Paul A. M. Nex Abstract Two thrusts occur on Ross Island: the Head of Ross Thrust and the more southerly Ross Island Thrust. These lie to the north of the Killarney,Mallow Fault (KMF), the boundary frequently interpreted as the Variscan Front. The Ross Island Thrust, exposed in outcrop and in seven borehole cores, has emplaced dark blue,grey limestones of the Courceyan Ballysteen Formation over pale grey,brown Rockfield Limestone Formation of Chadian,Holkerian age. These lithologies at Ross Island exhibit a continuum of deformation at both the micro- and macro-scale, beginning with the generation of a spaced cleavage, formed during layer parallel shortening, that was subsequently rotated into parallelism with fold axial planes. Extensional microstructures are predominant in thin section and are associated with attenuation of the fold limb. Calcite veins are also attenuated and lie parallel to a mylonitic fabric close to the thrust plane. Lithological boundaries, the prominent pressure solution cleavage and the southerly dipping limb of an asymmetrical antiform are all parallel and form a composite planar anisotropy. This has controlled the location of the ductile Ross Island Thrust, which formed during the attenuation and shearing of a common fold limb. Ductile thrusts within the limestones at Ross Island contrast with the reactivation of basin-margin extensional faults further to the south along the major KMF. The Ross Island Thrust is considered to result from deformation ahead of the major northerly propagating Variscan décollement thrust and does not necessitate a continuous décollement structure north of the KMF. Mineralization at Ross Island exhibits remobilization associated with the formation of a pressure-solution cleavage and probably pre-dates thrusting. Copyright © 2003 John Wiley & Sons, Ltd. [source] The role of friction and secondary flaws on deflection and re-initiation of hydraulic fractures at orthogonal pre-existing fracturesGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2006Xi Zhang SUMMARY In this study, we explore the nature of plane-strain hydraulic fracture growth in the presence of pre-existing fractures such as joints without or with secondary flaws. The 2-D plane-strain fracture studied can be taken as a cross-section through the short dimensions of an elongated 3-D fracture or as an approximate representation of the leading edge of a 3-D fracture where the edge curvature is negligible. The fluid-driven fracture intersects a pre-existing fracture to which it is initially perpendicular and is assumed not to immediately cross, but is rather deflected into the pre-existing fracture. The intersection results in branching of the fracture and associated fluid flow into the pre-existing fracture. Further growth results in opening and frictional sliding along the pre-existing fracture. Fracture propagation in an impermeable homogeneous elastic medium and fluid invasion into a pre-existing fracture are both driven by an incompressible, Newtonian fluid injected at a constant rate. The frictional stress on the surfaces of pre-existing fractures is assumed to obey the Coulomb law. The governing equations for quasi-static fluid-driven fracture growth are given and a scaling is introduced to help identify important parameters. The displacement discontinuity method and the finite difference method are employed to deal with this coupling mechanism of rock fracture and fluid flow. In order to account for fluid lag, a method for separately tracking the crack tip and the fluid front is included in the numerical model. Numerical results are obtained for internal pressure, frictional contact stresses, opening and shear displacements, and fluid lag size, as well as for fracture re-initiation from secondary flaws. After fracture intersection, the hydraulic fracture growth mode changes from tensile to shearing. This contributes to increased injection pressure and to a reduction in fracture width. In the presence of pre-existing fractures, the fluid-driven cracks can be arrested or retarded in growth rate as a result of diversion of fluid flow into and frictional sliding along the pre-existing fractures. Frictional behaviour significantly affects the ability of the fluid to enter or penetrate the pre-existing fracture only for those situations where the fluid front is within a certain distance from the intersecting point. Importantly, fluid penetration requires higher injection pressure for frictionally weak pre-existing fractures. Fracture re-initiation from secondary flaws can reduce the injection pressure, but re-initiation is suppressed by large sliding on pre-existing fractures that are frictionally weak. [source] Numerical simulations of simple shear with non-coaxial soil modelsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 1 2006Yunming Yang Abstract This paper investigates the effects of a non-coaxial model on simulated stress,strain behaviour of granular materials subject to simple shearing under various initial conditions. In most cases, a significant difference of predictions between coaxial and non-coaxial modelling is found during the early stage in shearing. With the increase in shearing, non-coaxial simulations approach and tend to coincide with coaxial simulations. It is also found that the roles of non-coaxial modelling in simulating simple shear behaviour are considerably influenced by hardening rules, flow rules, initial static lateral pressure coefficients. In some cases, the non-coaxial modelling gives a similar simulation as the coaxial modelling. In other cases, the non-coaxial modelling decreases the hardening response or softening response of materials, compared with the coaxial modelling. Under certain conditions, the predicted peak strength of materials with non-coaxial modelling is larger than that for coaxial modelling. Some of these observations can be attributed to the amount of principal stress rotation in various cases analysed. Others can be attributed to the difference between the directions of the non-coaxial plastic flow and those for coaxial plastic flow. Copyright © 2005 John Wiley & Sons, Ltd. [source] Friction and degradation of rock joint surfaces under shear loadsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 10 2001F. Homand Abstract The morpho-mechanical behaviour of one artificial granite joint with hammered surfaces, one artificial regularly undulated joint and one natural schist joint was studied. The hammered granite joints underwent 5 cycles of direct shear under 3 normal stress levels ranging between 0.3 and 4 MPa. The regularly undulated joint underwent 10 cycles of shear under 6 normal stress levels ranging between 0.5 and 5 MPa and the natural schist replicas underwent a monotonics shear under 5 normal stress levels ranging between 0.4 and 2.4 MPa. These direct shear tests were performed using a new computer-controlled 3D-shear apparatus. To characterize the morphology evolution of the sheared joints, a laser sensor profilometer was used to perform surface data measurements prior to and after each shear test. Based on a new characterization of joint surface roughness viewed as a combination of primary and secondary roughness and termed by the joint surface roughness, SRs, one parameter termed ,joint surface degradation', Dw, has been defined to quantify the degradation of the sheared joints. Examinations of SRs and Dw prior to and after shearing indicate that the hammered surfaces are more damaged than the two other surfaces. The peak strength of hammered joint with zero-dilatancy, therefore, significantly differs from the classical formulation of dilatant joint strength. An attempt has been made to model the peak strength of hammered joint surfaces and dilatant joints with regard to their surface degradation in the course of shearing and two peak strength criteria are proposed. Input parameters are initial morphology and initial surface roughness. For the hammered surfaces, the degradation mechanism is dominant over the phenomenon of dilatancy, whereas for a dilatant joint both mechanisms are present. A comparison between the proposed models and the experimental results indicates a relatively good agreement. In particular, compared to the well-known shear strength criteria of Ladanyi and Archambault or Saeb, these classical criteria significantly underestimate and overestimate the observed peak strength, respectively, under low and high normal stress levels. In addition and based on our experimental investigations, we put forward a model to predict the evolution of joint morphology and the degree of degradation during the course of shearing. Degradations of the artificial undulated joint and the natural schist joint enable us to verify the proposed model with a relatively good agreement. Finally, the model of Ladanyi and Archambault dealing with the proportion of total joint area sheared through asperities, as, once again, tends to underestimate the observed degradation. Copyright © 2001 John Wiley & Sons, Ltd. [source] Detection of hazelnut DNA traces in chocolate by PCRINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 6 2003Lieve Herman Summary By use of the DneasyTM Plant Tissue kit (Qiagen Inc.) plant DNA could be extracted from chocolate and related matrices. The polymerase chain reaction (PCR) detection of mitochondrial plant DNA is directly correlated with the length of the amplified fragment indicating shearing of DNA during chocolate production. Hazelnut DNA could be specifically detected in chocolate matrices with primers derived from the intron between exon B and C of the mitochondrial gene nad1. Specificity was confirmed towards individual chocolate ingredients and in 20 hazelnut negative chocolates. From taxonomically closely related plant species, only Carpinus turczaninovii, Ostrya carpinifolia and Corylus americana showed cross reaction, this was because of the identical sequence of the nad1 fragment. Application of extra MgCl2 throughout the DNA extraction procedure and of a specially designed Mg2+ buffered PCR, increased the detection sensitivity of co-processed hazelnut in chocolate to 0.001% or 10 ppm. [source] Influence of the length of the plasticating system on selected characteristics of an autothermal extrusion processADVANCES IN POLYMER TECHNOLOGY, Issue 1 2005Janusz W. Sikora Abstract The presented paper aims to determine the influence of the length of the plasticating system on the course of an autothermal extrusion process. Three special screws were used, of the relationship of the length of the operating part to diameter of the screw L/D = 20, 25, and 30, with a tip for intensive shearing and mixing, assigned for polyethylene processing, and five screw rotation frequencies were applied. The conducted research consisted of the measurement, during the extrusion, of the factors studied directly and in the calculation, and on their basis, the values characterizing this process. It is stated that the change of the length of the plasticating system in a significant way influences the dependences determining polymer flow rate, temperature and pressure of the processed polymer, extrusion velocity, specific energy consumption, and energy efficiency of the extruder; that is, the whole characteristic of an autothermal extrusion process. © 2005 Wiley Periodicals, Inc. Adv Polym Techn 24:21,28, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/.adv20021 [source] Physical characterization of starch extrudates as a function of melting transitions and extrusion conditionsADVANCES IN POLYMER TECHNOLOGY, Issue 4 2004Stéphanie Blanche Abstract The objective of this study was to investigate the relationships between starch melt transition characteristics, extrusion conditions, and final product properties. Cornstarch was extruded using a corotating twin-screw extruder at varying moisture content, medium/high screw configuration, and 300/400-rpm screw speeds. Extrudates were evaluated for bulk density, expansion ratio, cell structure, bending strength, thermal and pasting properties. Temperature change (,T) was defined as the temperature difference between the native starch melting temperature and its melt temperature just behind the die during extrusion at a given moisture content. ,T was significantly affected by starch moisture content and mechanical shearing, which controlled the melting behavior of the starch in the barrel. Amylose,lipid complex formation during extrusion increased as ,T increased and leveled off at ,T of about 20°C. Pasting peak viscosity of the starch extrudates decreased as ,T increased and leveled off at ,T of about 15°C. Within the same range of mechanical shearing intensity, extrudate bulk density and bending strength decreased linearly as ,T increased. Extrudate expansion was negatively correlated to bulk density. © 2004 Wiley Periodicals, Inc. Adv Polym Techn 23: 277,290, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20017 [source] Facile method to manipulate the molecular weight and practical mass production of chitosan by mechanical shearing and concurrent ultrafiltration treatmentJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2010Min Lang Tsai Abstract The objective of this study was to propose a facile method to manipulate the molecular weight and practical mass production of chitosan by mechanical shearing and concurrent ultrafiltration (UF) treatment. The proposed method was based on the degradation rate and rate constant of various process variables, such as: solution temperature, reaction time, concentration of chitosan solution, with or without concurrent removal of degraded fragments during mechanical shearing. The result obtained was that the degradation rate constant was 1.8,6.0 times higher for those using UF to remove smaller degraded molecules concurrently during treatment, than that without UF treatment. The degradation rate constant increased with increasing solution temperature; however, the solution temperature should not exceed than 50°C to prevent the undesired color changes of the resulting product. A method combining mechanical shearing/UF treatment at 50°C and ultrasonic radiation or microfluidization/UF treatment at 30°C is proposed here for a facile method to manipulate the molecular weight of the resultant chitosan with an energy saving, efficient and practical mass production. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Modeling UHMWPE wear debris generationJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 2 2007H. Baudriller Abstract It is widely recognized that polyethylene wear debris is one of the main causes of long-term prosthesis loosening. The noxious bioreactivity associated with this debris is determined by its size, shape, and quantity. The aim of this study was to develop a numerical tool that can be used to investigate the primary polyethylene wear mechanisms involved. This model illustrates the formation of varying flow of polyethylene debris with various shapes and sizes caused by elementary mechanical processes. Instead of using the classical continuum mechanics formulation for this purpose, we used a divided materials approach to simulate debris production and release. This approach involves complex nonlinear bulk behaviors, frictional adhesive contact, and characterizes material damage as a loss of adhesion. All the associated models were validated with various benchmark tests. The examples given show the ability of the numerical model to generate debris of various shapes and sizes such as those observed in implant retrieval studies. Most of wear mechanisms such as abrasion, adhesion, and the shearing off of micro-asperities can be described using this approach. Furthermore, it could be applied to study the effects of friction couples, macroscopic geometries, and material processing (e.g. irradiation) on wear. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2007 [source] Linear stability analysis of two-layer rectilinear flow in slot coatingAICHE JOURNAL, Issue 10 2010Jaewook Nam Abstract Two-layer coating occurs in many products. Ideally, the liquids are deposited onto the substrate simultaneously. In the case of two-layer slot coating, the interlayer between the coating liquids is subjected to enormous shearing. This may lead to flow instabilities that ruin the product. It is important to map the regions of the parameter space at which the flow is unstable. Most of the stability analyses of two-layer rectilinear flow consider the position of the interlayer as an independent parameter. Classical results cannot be applied directly in coating flows. We present a linear stability analysis of two-layer rectilinear flow considering the flow rates as an independent parameter. The predicted neutral-stability curves define the region of stable flow as a function of the operating parameters. The range of coating operating conditions is restricted further, when the condition for the desirable interlayer separation point location are considered together with the stability condition. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source] Microfabric characteristics and rheological significance of ultra-high-pressure metamorphosed jadeite-quartzite and eclogite from Shuanghe, Dabie Mountains, ChinaJOURNAL OF METAMORPHIC GEOLOGY, Issue 2 2010L. WANG Abstract Quantitative analysis of the structural evolution of jadeite-quartzite, a rare ultra-high pressure (UHP) rock type from the Dabie Mountains of eastern China, sheds light on the formation and evolution of UHP orogenic belts worldwide. Geological mapping of the Shuanghe area, where jadeite-quartzites crop out, was carried out to determine the spatial relationships between different UHP rocks within this orogen. The deformation mechanisms of jadeite-quartzite, geodynamical parameters (stress, strain, strain rate), and microstructure including lattice preferred orientation (LPO) were determined from six jadeite-quartzite samples from the Shuanghe area. LPOs of clinopyroxene (jadeite and omphacite), garnet, rutile and quartz from these jadeite-quartzite samples are compared with those of three eclogites preserving different degrees of deformation from the Shuanghe area. Microstructural LPOs of jadeite, omphacite, garnet, rutile and quartz were determined using electron backscattered diffraction (EBSD) analysis. Quartz fabrics were largely recrystallized during late, low-grade stages of deformation, whereas garnet shows no strong LPO patterns. Rutile fabrics show a weak LS fabric along [001]. Jadeite and omphacite show the strongest eclogite facies LPO patterns, suggesting that they may provide important information about mantle deformation patterns and control the rheology of deeply subducted continental crust. Microstructural data show that the jadeite LPO patterns are similar to those of omphacite and vary between L- and S-types, which correlate with prolate and oblate grain shape fabrics (SPO); quartz LPOs are monoclinic. Microstructural analysis using TEM shows that the dominant slip systems of jadeite in one sample are (100)[001], (110)[001] and (1 1 0)1/2[110], while in another sample, no dislocations are observed. Abundant dislocations in quartz were accommodated by the dominant slip system (0001)[110], indicating basal glide and represents regional shearing during the exhumation process. This suggests that dislocation creep is the dominant fundamental deformation mechanism in jadeite under UHP conditions. The protoliths of jadeite-quartzite, metasedimentary rocks from the northern passive continental margin of the Yangtze craton, experienced the same deep subduction and were deformed under similar rheological conditions as other UHP eclogite, marble and paragneiss. Experimental UHP deformation of quartzo-feldspathic gneiss with a chemical composition similar to the bulk continental crust has shown that the formation of a jadeite,stishovite rock is associated with a density increase of the host rock similar to the eclogite conversion from basaltic protoliths. The resulting rock can be denser than the surrounding mantle pyrolite up to depths of 660 km (24 GPa). Thus, processes of deep continental subduction may be better-understood through understanding the rheology and mechanical behaviour of jadeite. Jadeite-quartzites such as those from the Shuanghe may be exhumed remnants of deeply-subducted slabs of continental crust, other parts of which subducted past the ,depth of no return', and remain in the deep mantle. [source] Timing and nature of fluid flow and alteration during Mesoproterozoic shear zone formation, Olary Domain, South AustraliaJOURNAL OF METAMORPHIC GEOLOGY, Issue 3 2005C. CLARK Abstract The development of shear zones at mid-crustal levels in the Proterozoic Willyama Supergroup was synchronous with widespread fluid flow resulting in albitization and calcsilicate alteration. Monazite dating of shear zone fabrics reveal that they formed at 1582 ± 22 Ma, at the end of the Olarian D3 deformational event and immediately prior to the emplacement of regional S-type granites. Two stages of fluid flow are identified in the area: first an albitizing event which involved the addition of Na and loss of Si, K and Fe; and a second phase of calcsilicate alteration with additions of Ca, Fe, Mg and Si and removal of Na. Fluid fluxes calculated for albitization and calcsilicate alteration were 5.56 × 109 to 1.02 × 1010 mol m,2 and 2.57 × 108,5.20 × 109 mol m,2 respectively. These fluxes are consistent with estimates for fluid flow through mid-crustal shear zones in other terranes. The fluids associated with shearing and alteration are calculated to have ,18O and ,D values ranging between +8 and +11,, and ,33 and ,42,, respectively, and ,Nd values between ,2.24 and ,8.11. Our results indicate that fluids were derived from metamorphic dehydration of the Willyama Supergroup metasediments. Fluid generation occurred during prograde metamorphism of deeper crustal rocks at or near peak pressure conditions. Shear zones acted as conduits for major crustal fluid flow to shallow levels where peak metamorphic conditions had been attained earlier leading to the apparent ,retrograde' fluid-flow event. Thus, the peak metamorphism conditions at upper and lower crustal levels were achieved at differing times, prior to regional granite formation, during the same orogenic cycle leading to the formation of retrograde mineral assemblages during shearing. [source] Evolution of a crustal-scale transpressive shear zone in the Albany,Fraser Orogen, SW Australia: 2.JOURNAL OF METAMORPHIC GEOLOGY, Issue 8 2004Mawson cratons, Tectonic history of the Coramup Gneiss, a kinematic framework for Mesoproterozoic collision of the West Australian Abstract Within the Albany,Fraser Orogen of southwestern Australia, the Coramup Gneiss is a NE,SW trending zone of high-strain rocks that preserves a detailed record of orogenesis related to Mesoproterozoic convergence of the West Australian and Mawson cratons. New structural, metamorphic and U,Pb SHRIMP zircon age data establish that the Coramup Gneiss underwent high-grade tectonism during both Stage I (c. 1290 Ma) and Stage II (c. 1170 Ma) of the Albany,Fraser Orogeny. Stage I commenced with c. 1300 Ma high- T, low- P M1a metamorphism during extension, and the formation of small-scale ptygmatic folds within a subhorizontal S1a gneissosity. High- P M1b metamorphism at c. 1290 Ma was accompanied by the transposition and shearing of S1a into a composite, shallow SE-dipping S1b foliation, and the development of tight recumbent F1b folds with S1-parallel axial surfaces and asymmetries indicating NW-directed thrusting. The preservation of a similar P,T,time record in the Fraser Complex (NE of the Coramup Gneiss) is consistent with large-scale, NW-directed Stage I thrusting of the Mawson Craton margin over the south-eastern edge of the West Australian Craton. Stage II tectonism in the western Coramup Gneiss involved high- T, low- P M2a metamorphism and the formation of subvertical SE-dipping D2 shear zones, shallow SW-plunging L2 mineral stretching lineations, and NW-verging F2 folds with S2-parallel axial surfaces. A synkinematic pegmatite dyke emplaced into a D2 shear zone yielded a U,Pb SHRIMP zircon age of 1168 ± 12 Ma. Kinematic indicators suggest a combination of pure shear flattening perpendicular to S2, and dextral simple shear. However, contemporaneous structures elsewhere in the Albany,Fraser Orogen are consistent with continued NW,SE convergence at craton-scale during Stage II, and oblique compression in the Coramup Gneiss is attributed to the arcuate geometry of the orogen-scale deformation front. [source] Hydrothermal alteration, fluid flow and volume change in shear zones: the layered mafic,ultramafic Kettara intrusion (Jebilet Massif, Variscan belt, Morocco)JOURNAL OF METAMORPHIC GEOLOGY, Issue 1 2004A. Essaifi Abstract During emplacement and cooling, the layered mafic,ultramafic Kettara intrusion (Jebilet, Morocco) underwent coeval effects of deformation and pervasive fluid infiltration at the scale of the intrusion. In the zones not affected by deformation, primary minerals (olivine, plagioclase, clinopyroxene) were partially or totally altered into Ca-amphibole, Mg-chlorite and CaAl-silicates. In the zones of active deformation (centimetre-scale shear zones), focused fluid flow transformed the metacumulates (peridotites and leucogabbros) into ultramylonites where insoluble primary minerals (ilmenite, spinel and apatite) persist in a Ca-amphibole-rich matrix. Mass-balance calculations indicate that shearing was accompanied by up to 200% volume gain; the ultramylonites being enriched in Si, Ca, Mg, and Fe, and depleted in Na and K. The gains in Ca and Mg and losses in Na and K are consistent with fluid flow in the direction of increasing temperature. When the intrusion had cooled to temperatures prevailing in the country rock (lower greenschist facies), deformation was still active along the shear zones. Intense intragranular fracturing in the shear zone walls and subsequent fluid infiltration allowed shear zones to thicken to metre-scale shear zones with time. The inner parts of the shear zones were transformed into chlorite-rich ultramylonites. In the shear zone walls, muscovite crystallized at the expense of Ca,Al silicates, while calcite and quartz were deposited in ,en echelon' veins. Mass-balance calculations indicate that formation of the chlorite-rich shear zones was accompanied by up to 60% volume loss near the centre of the shear zones; the ultramylonites being enriched in Fe and depleted in Si, Ca, Mg, Na and K while the shear zones walls are enriched in K and depleted in Ca and Si. The alteration observed in, and adjacent to the chlorite shear zones is consistent with an upward migrating regional fluid which flows laterally into the shear zone walls. Isotopic (Sr, O) signatures inferred for the fluid indicate it was deeply equilibrated with host lithologies. [source] Metamorphism and microstructures along a high-temperature metamorphic field gradient: the north,eastern boundary of the Královský hvozd unit (Bohemian Massif, Czech Republic)JOURNAL OF METAMORPHIC GEOLOGY, Issue 4 2002D. Scheuvens Abstract A metamorphic field gradient has been investigated in the Moldanubian zone of the central European Variscides encompassing, from base to the top, a staurolite,kyanite zone, a muscovite,sillimanite zone, a K-feldspar,sillimanite zone, and a K-feldspar,cordierite zone, respectively. The observed reaction textures in the anatectic metapsammopelites of the higher grade zones are fully compatible with experimental data and petrogenetic grids that are based on fluid-absent melting reactions. From structural and microstructural observations it can be concluded that the boundary between the kyanite,staurolite zone and the muscovite- and K-feldspar,sillimanite zones coincides with an important switch in deformation mechanism(s). Besides minor syn-anatectic shearing (melt-enhanced deformation), microstructural criteria point (a) to a switch in deformation mechanism from rotation recrystallization (climb-accommodated dislocation creep) to prism P,T conditions of decompression of the Limpopo high-grade terrane: record from shear zonesJOURNAL OF METAMORPHIC GEOLOGY, Issue 3 2001C. A. Smit Abstract The Southern Marginal Zone of the late Archean Limpopo Belt of southern Africa is an example of a high-grade gneiss terrane in which both upper and lower crustal deformational processes can be studied. This marginal zone consists of large thrust sheets of complexly folded low-strain gneisses, bound by an imbricate system of kilometre-wide deep crustal shear zones characterized by the presence of high-strain gneisses (,primary straight gneisses'). These shear zones developed during the decompression stage of this high-grade terrane. Low- and high-strain gneisses both contain similar reaction textures that formed under different kinematic conditions during decompression. Evidence for the early M1/D1 metamorphic phase (> 2690 Ma) is rarely preserved in low-strain gneisses as a uniform orientation of relict Al-rich orthopyroxene in the matrix and quartz and plagioclase inclusions in the cores of early (M1) Mg-rich garnet porphyroblasts. This rare fabric formed at >,820 °C and >,7.5 kbar. The retrograde M2/D2 metamorphic fabric (2630,2670 Ma) is well developed in high-strain gneisses from deep crustal shear zones and is microscopically recognized by the presence of reaction textures that formed synkinematically during shear deformation: M2 sigmoid-shaped reaction textures with oriented cordierite,orthopyroxene symplectites formed after the early M1 Mg-rich garnet porphyroblasts, and syn-decompression M2 pencil-shaped garnet with oriented inclusions of sillimanite and quartz formed after cordierite under conditions of near-isobaric cooling at 750,630 °C and 6,5 kbar. The symplectites and pencil-shaped garnet are oriented parallel to the shear fabric and in the stretching direction. Low-strain gneisses from thrust sheets show similar M2 decompression cooling and near-isobaric cooling reaction textures that formed within the same P,T range, but under low-strain conditions, as shown by their pseudo-idioblastic shapes that reflect the contours of completely replaced M1 garnet and randomly oriented cordierite,orthopyroxene symplectites. The presence of similar reaction textures reflecting low-strain conditions in gneisses from thrust sheets and high-strain conditions in primary straight gneisses suggests that most of the strain during decompression was partitioned into the bounding shear zones. A younger M3/D3 mylonitic fabric (< 2637 Ma) in unhydrated mylonites is characterized by brittle deformation of garnet porphyroclasts and ductile deformation of the quartz,plagioclase,biotite matrix developed at <,600 °C, as the result of post-decompression shearing under epidote,amphibolite facies conditions. [source] Evolution of the Pan-African Wadi Haimur metamorphic sole, Eastern Desert, EgyptJOURNAL OF METAMORPHIC GEOLOGY, Issue 6 2000H. Abd El-Naby By comparison with the general features of metamorphic soles (e.g. vertical and lateral extension, metamorphic grade and diagnostic mineral parageneses, deformation and dominant rock types), it is inferred that the amphibolites, metagabbros and hornblendites of the Wadi Um Ghalaga,Wadi Haimur area in the southern part of the Eastern Desert of Egypt represent the metamorphic sole of the Wadi Haimur ophiolite belt. The overlying ultramafic rocks represent overthrusted mantle peridotite. Mineral compositions and thermobarometric studies indicate that the rocks of the metamorphic sole record metamorphic conditions typical of such an environment. The highest P,T conditions (c. 700 °C and 6.5,8.5 kbar) are preserved in clinopyroxene amphibolites and garnet amphibolites from the top of the metamorphic sole, which is exposed in the southern part of the study area. The massive amphibolites and metagabbros further north (Wadi Haimur) represent the basal parts of the sole and show the lowest P,T conditions (450,620 °C and 4.7,7.8 kbar). The sole is the product of dynamothermal metamorphism associated with the tectonic displacement of ultramafic rocks. Heat was derived mainly from the hot overlying mantle peridotites, and an inverted P,T gradient was caused by dynamic shearing during ophiolite emplacement. Sm/Nd dating of whole-rock,metamorphic mineral pairs yields similar ages of c. 630 Ma for clinopyroxene and hornblende, which is interpreted as a lower age limit for ophiolite formation and an upper age limit for metamorphism. A younger Sm/Nd age for a garnet-bearing rock (c. 590 Ma) is interpreted as reflecting a meaningful cooling age close to the metamorphic peak. Hornblende K/Ar ages in the range 570,550 Ma may reflect thermal events during late orogenic granite magmatism. [source] Deformation of nasal septal cartilage during masticationJOURNAL OF MORPHOLOGY, Issue 10 2009Ayman A. Al Dayeh Abstract The cartilaginous nasal septum plays a major role in structural integrity and growth of the face, but its internal location has made physiologic study difficult. By surgically implanting transducers in 10 miniature pigs (Sus scrofa), we recorded in vivo strains generated in the nasal septum during mastication and masseter stimulation. The goals were (1) to determine whether the cartilage should be considered as a vertical strut supporting the nasal cavity and preventing its collapse, or as a damper of stresses generated during mastication and (2) to shed light on the overall pattern of snout deformation during mastication. Strains were recorded simultaneously at the septo-ethmoid junction and nasofrontal suture during mastication. A third location in the anterior part of the cartilage was added during masseter stimulation and manipulation. Contraction of jaw closing muscles during mastication was accompanied by anteroposterior compressive strains (around ,1,000 ,,) in the septo-ethmoid junction. Both the orientation and the magnitude of the strain suggest that the septum does not act as a vertical strut but may act in absorbing loads generated during mastication. The results from masseter stimulation and manipulation further suggest that the masticatory strain pattern arises from a combination of dorsal bending and/or shearing and anteroposterior compression of the snout. J. Morphol., 2009. © 2009 Wiley-Liss, Inc. [source] A Facile Route to Synthesize the Ti5NbO14 Nanosheets by Mechanical Cleavage ProcessJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2010Na Zhang Layered and rod-like K3Ti5NbO14 was synthesized via the solid-state chemistry, and it was exfoliated into nanosheets through a novel mechanical cleavage technology. X-ray diffraction was utilized to determine the phase changes of all the specimen during the total process, and the microstructure of the samples was analyzed by scanning electron microscope and transmission electron microscope. The formation mechanism was also discussed in detail, the results indicated that the compression and shearing should play a main function in the crack and the cleavage of the aggregated layered compound. UV,vis absorption spectroscopy was used to monitor the consecutive buildup of the (PEI/Ti5NbO14)n film. The resulting quasi-linear increase at the top absorbance as a function of the sequential assembly number for the multilayer film indicated that the nanosheet had deposited uniformly in each dipping cycle. The photocatalytic activity of K3Ti5NbO14 -related products was examined. Compared with original layered compound, nanosheet precipitate had good property under irradiation of ultraviolet light. [source] Early Mesozoic evolution of alivincular bivalve ligaments and its implications for the timing of the ,Mesozoic marine revolution'LETHAIA, Issue 2 2004MICHAEL HAUTMANN The early Mesozoic radiation of the Pteriomorphia was accompanied and furthered by the development of several new types of alivincular ligaments. These new types evolved as modifications of the primitive alivincular-areate (new term) ligament, which is characterized by an ontogenetic shift of both the central resilium and the straight lateral ligament in the direction of main shell growth. Arching of the attachment surface of the ligament led to the alivincular-arcuate (new term) ligament type, which has been realized by the Ostreidae only. By contrast, a replacement of the lateral ligament by hinge teeth, limiting the (primary) ligament to a central groove (alivincular-fossate, new term), has evolved independently in three families (Dimyidae, Plicatulidae and Spondylidae). Functionally, both kinds of modification effectively impede shearing of the valves and are interpreted as an antipredatory adaptation advantageous in the cemented habit of these families. The alivincular-alate (new term) ligament of the Entoliidae and Pectinidae differs from the other types of alivincular ligaments by different growth directions of resilium and lateral ligament, which result in an internal position of the resilium suitable for fast and powerful opening of the valves. This arrangement is an important prerequisite for effective swimming, which, in its turn, is a behaviour chiefly used to escape from predator attacks. The simultaneous early Mesozoic appearance of different antipredatory adaptations within independent clades hints at increased predator pressure as a stimulant and may therefore point to a contemporaneous proliferation of durophagous predators. Hence, an important aspect of the ,Mesozoic marine revolution' might have started earlier than previously thought. [source] Influence of Coupling Agents on Melt Flow Behavior of Natural Fiber CompositesMACROMOLECULAR MATERIALS & ENGINEERING, Issue 5 2007Velichko Hristov Abstract The influence of coupling agents on the melt rheological properties of natural fiber composites has been investigated in this work using capillary and rotational rheometers. Scanning electron microscopy was also employed to supplement the rheological data. It was found that molecular weight and molecular weight distribution of the polymer matrix and coupling agent characteristics influence the filler wetting and the melt flow properties of the filled composites. Generally, low molecular weight and narrow molecular weight distribution polyethylene matrix provides relatively larger increase of the viscosity of the composites. Coupling agents tend to increase the resistance to shearing, but wall slip effects may interfere with the measured values, especially at very high filler loadings. Entrance pressure loss in capillaries is also influenced by polymer matrix and coupling agent used. [source] Mineralogy, petrology, and thermal evolution of the Benton LL6 chondriteMETEORITICS & PLANETARY SCIENCE, Issue S7 2003Erin L. WALTON Internally, the meteorite comprises light-colored, subangular to subrounded clasts embedded in a dark grey-colored matrix. Clasts comprise the same mineral phases as the matrix, as well as chondrules and larger (50,100 ,m) single mineral grains (mainly olivine and orthopyroxene). Composite (polyphase) clasts can be several millimeters in length. Numerous examples of post-brecciation and post-annealing shearing and displacement at the micron to millimeter scale occur in the form of shock veins. Benton is a shock stage S3 chondrite, which experienced shock pressures on the order of 15,20 GPa, with an estimated post-shock temperature increase of 100,150°C. Benton's history comprises a sequence of events as follows: 1) chondrule formation and initial assembly; 2) brecciation; 3) thermal metamorphism; and 4) shock veining. Events (2) and (4) can be equated with distinct impact events, the former representing bombardment of target material that remained in situ or collisionally fragmented during metamorphism, and then gravitationally reassembled, the latter probably with release from the source body to yield a meteorite. Thermal metamorphism post-dates brecciation. The mean equilibration temperature recorded in the Benton LL6 chondrite is 890°C, obtained using the two pyroxene geothermometer. [source]
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