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Softening
Kinds of Softening Terms modified by Softening Selected AbstractsACTIVITIES OF ,-GALACTOSIDASE AND ,-L-ARABINOFURANOSIDASE, ETHYLENE BIOSYNTHETIC ENZYMES DURING PEACH RIPENING AND SOFTENINGJOURNAL OF FOOD PROCESSING AND PRESERVATION, Issue 5 2006CHANG-HAI JIN ABSTRACT A study was conducted to determine changes in firmness, ethylene and ethylene biosynthetic enzymes, and the activities of ,-galactosidase (,-GAL) and ,-L-arabinofuranosidase (,-AF) during peach ripening and softening. The activities of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase, ACC oxidase and polygalacturonase increased in parallel with ethylene production and declined in firmness during peach ripening, and they appeared at maximum simultaneously at maturity IV. ,-GAL activity was high in unripe peach fruit and it experienced an overall decline during peach ripening. While ,-AF activity changed placidly at the initial stage (maturity I,III), after that it experienced a rapid increasing stage. The preliminary result indicated that ,-GAL and ,-AF, as well as ethylene biosynthetic enzymes, may be involved in the ripening and softening of peach fruit. [source] THE EFFECT OF PROXY-VOICE INTERVENTION ON COUPLE SOFTENING IN THE CONTEXT OF ENACTMENTSJOURNAL OF MARITAL AND FAMILY THERAPY, Issue 4 2006Ryan B. Seedall In this study we evaluated the effectiveness of proxy voice (therapist acting as client's "voice") intervention, embedded within couple enactments, on client-perceived softening. The primary research question was whether use of proxy voice would be more likely to bring about softening, or if its use was counterintuitive to enactment conceptualization and would elicit struggle behavior (e.g., withdrawal or negativity). Results indicate that proxy voice has a significant, positive association with softening and is inversely related to withdrawal or negativity. Preliminary findings suggest that proxy voice intervention embedded within a fluid, carefully delineated, and discriminating model of enactments effectively facilitates essential elements of couple interaction (expression of primary affect and articulation of self-concept and attachment threats) while promoting self-reliant couple interaction and increased softening. [source] COMPARISON OF MECHANICAL TESTS FOR EVALUATING TEXTURAL CHANGES IN POTATOES DURING THERMAL SOFTENINGJOURNAL OF TEXTURE STUDIES, Issue 6 2002W. K. SOLOMON ABSTRACT The changes in the texture of cylindrical samples of potato tissues immersed in water at 60, 70, 80 and 90C for up to 80 min were monitored at each temperature in terms of tangent modulus of elasticity in axial and radial compression tests, and elasticity and viscosity parameters in creep and stress relaxation tests. The magnitude of all mechanical test parameters decreased with an increase in heating time and temperature. The creep and stress relaxation responses of individual potato samples were adequately represented by respective mechanical models (R2= 0.94 to 0.99). The mechanical test parameters followed apparent first-order degradation kinetics due to the effect of thermal softening, and the rate constant was used as an index of the sensitivity of a mechanical test. The radial compression test was relatively more sensitive than the axial test. Based on an overall comparison, the parameters from creep and stress relaxation tests were found to be the most sensitive in describing the textural changes during thermal softening of potatoes. [source] Elementary Mechanisms behind the High-Temperature Deformation Behavior of Lutetium-Doped Silicon NitrideJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2003Giuseppe Pezzotti Intergranular sliding and diffusive mechanisms behind the deformation behavior of a commercially available lutetium-doped silicon nitride were investigated and discussed. A method of locating and separating phenomena critical for mechanical relaxation at elevated temperatures was applied; the method was based on low-frequency forced-vibration damping measurements. The potentiality of lutetium addition for improving the deformation resistance of silicon nitride was clearly reflected in the high-temperature damping behavior of the investigated polycrystal. Softening of intergranular lutetium silicate phases located at multigrain junctions, which resulted in a grain-boundary sliding peak, occurred at remarkably high temperatures (>1725 K). This phenomenon, partly overlapping diffusional flow, was followed by further damping relaxation with the melting of the lutetium silicates. Subsequent grain growth was also detected at temperatures >2100 K. Torsional creep results, collected up to 2100 K, consistently proved the presence of a "locking" effect by lutetium silicates with the sliding of silicon nitride grain boundaries below 1873 K. [source] English Hypothetical Universalism: John Preston the Softening of Reformed Theology.THE HEYTHROP JOURNAL, Issue 1 2010By Jonathon D. Moore, John Owen: Reformed Catholic, Renaissance Man (Great Theologians Series). No abstract is available for this article. [source] Molecular biology of grape berry ripeningAUSTRALIAN JOURNAL OF GRAPE AND WINE RESEARCH, Issue 2 2000SIMON P. ROBINSON Abstract Grapevines produce non-climacteric fruit that exhibit a double sigmoidal pattern of growth. Ripening occurs during the second growth phase when grapes change colour, start to soften, accumulate reducing sugars, metabolise organic acids and synthesise flavour compounds. Unlike many other fruit, grapes ripen while the berries are still expanding, and as with most non-climacteric fruit, ripening does not appear to be controlled by ethylene. Sugars and amino acids that accumulate in grapes during ripening are imported via the phloem, while many secondary metabolites are synthesised within the berry itself. Grapes import sucrose but accumulate hexoses. Conversion of sucrose to hexoses is most likely catalysed by invertase. cDNAs encoding vacuolar invertases have been isolated from grape berries. Expression of these genes and an increase in invertase activity occur before veraison, so it seems unlikely that synthesis of this enzyme is a controlling factor for sugar accumulation during ripening. Proteins that transport sugars into the berry vacuole may regulate sugar accumulation, and cDNAs encoding both sucrose and hexose transporters have been isolated from ripening grape berries. Determination of the role of these transporters may reveal the pathway of sugar accumulation in grapes. Anthocyanins are only synthesised in the skin of red grapes after veraison. Analysis of the patterns of expression of genes in the flavonoid pathway has shown that there is a dramatic increase in expression of many of these genes in skin cells at veraison. Expression of the gene encoding a glycosyl transferase involved in the lasts steps of anthocyanin synthesis was absolutely correlated with anthocyanin synthesis and may explain the lack of anthocyanin synthesis in white grapes and in the flesh of most red grapes. We infer that the synthesis of anthocyanins is regulated at the transcription level and is likely to be controlled by regulatory genes. Softening of fruit generally results from changes in the properties of cell walls. Analysis of the cell walls of grapes during ripening suggests that there are no dramatic changes in polysaccharide composition but modification of specific components may contribute to softening. A number of proteins are newly synthesised in grapes during ripening and several of these proteins have now been identified. The most abundant are pathogenesis-related (PR) proteins, including chitinases and thaumatin-like proteins. Expression of genes encoding a number of PR proteins increased dramatically in grapes during ripening. It is not clear what role the PR proteins play during ripening but they may provide resistance to pathogens. Differential screening of a post-veraison grape berry cDNA library has also identified ripening-related genes, some of which encode proline-rich cell wall proteins. Other grape ripening-related genes have homologues that are induced by stress in other plants. These studies indicate that a dramatic change in gene expression occurs in grape berries at veraison and suggest that ripening involves a coordinated increase in transcription of a number of different genes. [source] A unified bounding surface plasticity model for unsaturated soilsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 3 2006A.R. Russell Abstract A unified constitutive model for unsaturated soils is presented in a critical state framework using the concepts of effective stress and bounding surface plasticity theory. Consideration is given to the effects of unsaturation and particle crushing in the definition of the critical state. A simple isotropic elastic rule is adopted. A loading surface and a bounding surface of the same shape are defined using simple and versatile functions. The bounding surface and elastic rules lead to the existence of a limiting isotropic compression line, towards which the stress trajectories of all isotropic compression load paths approach. A non-associated flow rule of the same general form is assumed for all soil types. Isotropic hardening/softening occurs due to changes in plastic volumetric strains as well as suction for some unsaturated soils, enabling the phenomenon of volumetric collapse upon wetting to be accounted for. The model is used to simulate the stress,strain behaviour observed in unsaturated speswhite kaolin subjected to three triaxial test load paths. The fit between simulation and experiment is improved compared to that of other constitutive models developed using conventional Cam-Clay-based plasticity theory and calibrated using the same set of data. Also, the model is used to simulate to a high degree of accuracy the stress,strain behaviour observed in unsaturated Kurnell sand subjected to two triaxial test load paths and the oedometric compression load path. For oedometric compression theoretical simulations indicate that the suction was not sufficiently large to cause samples to separate from the confining ring. Copyright © 2005 John Wiley & Sons, Ltd. [source] Compaction of cell shape occurs before decrease of elasticity in CHO-K1 cells treated with actin cytoskeleton disrupting drug cytochalasin DCYTOSKELETON, Issue 4 2009Christian Schulze Abstract The actin filaments of the cytoskeleton form a highly dynamic polymer scaffold which is actively involved in many essential mechanisms such as cell migration, transport, mitosis, and mechanosensitivity. We treated CHO-K1 cells with different concentrations of the actin cytoskeleton disrupting drug cytochalasin D. Then investigating the cells' elastic behaviour by scanning force microscopy-based rheology we confirmed for high cytochalasin D concentrations (,1.5 ,M) a significant decrease of mechanical stability. At lower concentrations we measured no significant softening, but flattening and a horizontal contraction was observable even at low concentrations (,0.3 ,M) of cytochalasin D. The observed changes in cell shape resulted in a lower cell volume, showing that there is compensation by volume for small decreases in cytoskeletal strength resulting from reduced numbers or lengths of actin filaments. These results suggest that the characteristic functions defining a cell's mechanical stability such as mechanosensitivity can be maintained via small changes in cell volume in order to counter fluctuations in cytoskeletal composition. Cell Motil. Cytoskeleton 2009. © 2009 Wiley-Liss, Inc. [source] The Effect of Full-Face Broadband Light Treatments Alone and in Combination With Bilateral Crow's Feet Botulinum Toxin Type A ChemodenervationDERMATOLOGIC SURGERY, Issue 3 2004Jean Carruthers MD Background. Broadband light (BBL; Intense Pulsed Light; Lumenis Ltd., Yokneam, Israel) is a powerful, nonablative, light-based technology that targets melanin and hemoglobin and stimulates the formation of collagen and elastin. Botulinum toxin type A (BTX-A; BOTOX; Allergan Inc., Irvine, CA) treatment of the lateral periocular region relaxes the vertical fibers of the orbicularis oculi and results in softening of the lateral orbital crow's feet rhytides and widening of the palpebral aperture. Objective. To compare the effects of full-face BBL in combination with BTX-A and BBL alone in female subjects with Fitzpatrick I,III skin types, Glogau II,III rhytides, and significant associated facial lentigines and telangiectasia. Methods. This was a prospective, randomized study of 30 women with moderate to severe crow's feet rhytides. Half of the subjects were treated with BTX-A and BBL and the other half with BBL alone. Their response was assessed clinically and photographically. Skin biopsies of the temporal skin were taken from two subjects in each group and were stained with Masson trichrome. Results. Patients treated with a combination of BTX-A and BBL experienced a better response to treatment, both at rest and on maximum smile, as well as a slightly improved response in associated lentigines, telangiectasia, pore size, and facial skin texture compared with patients who received BBL treatment alone. Skin biopsies showed an increase in dermal collagen in each group. Conclusions. The patients in this study benefited from both treatments. Although BBL led to a remarkable improvement in full-face telangiectasias, lentigines, and skin texture, the improvement increased in all categories with combination therapy. In addition, an added improvement in the full-face aesthetic with both BTX-A and BBL therapy combined was obvious. These results suggest that both treatments,although evidently complementary,may also act synergistically to produce optimal clinical effects, revolutionizing the treatment of facial aging. [source] Design of passive systems for control of inelastic structuresEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 6 2009Gian Paolo Cimellaro Abstract A design strategy for control of buildings experiencing inelastic deformations during seismic response is formulated. The strategy is using weakened, and/or softened, elements in a structural system while adding passive energy dissipation devices (e.g. viscous fluid devices, etc.) in order to control simultaneously accelerations and deformations response during seismic events. A design methodology is developed to determine the locations and the magnitude of weakening and/or softening of structural elements and the added damping while insuring structural stability. A two-stage design procedure is suggested: (i) first using a nonlinear active control algorithm, to determine the new structural parameters while insuring stability, then (ii) determine the properties of equivalent structural parameters of passive system, which can be implemented by removing or weakening some structural elements, or connections, and by addition of energy dissipation systems. Passive dampers and weakened elements are designed using an optimization algorithm to obtain a response as close as possible to an actively controlled system. A case study of a five-story building subjected to El Centro ground motion, as well as to an ensemble of simulated ground motions, is presented to illustrate the procedure. The results show that following the design strategy, a control of both peak inter-story drifts and total accelerations can be obtained. Copyright © 2008 John Wiley & Sons, Ltd. [source] Hysteretic models that incorporate strength and stiffness deteriorationEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 12 2005Luis F. Ibarra Abstract This paper presents the description, calibration and application of relatively simple hysteretic models that include strength and stiffness deterioration properties, features that are critical for demand predictions as a structural system approaches collapse. Three of the basic hysteretic models used in seismic demand evaluation are modified to include deterioration properties: bilinear, peak-oriented, and pinching. The modified models include most of the sources of deterioration: i.e. various modes of cyclic deterioration and softening of the post-yielding stiffness, and also account for a residual strength after deterioration. The models incorporate an energy-based deterioration parameter that controls four cyclic deterioration modes: basic strength, post-capping strength, unloading stiffness, and accelerated reloading stiffness deterioration. Calibration of the hysteretic models on steel, plywood, and reinforced-concrete components demonstrates that the proposed models are capable of simulating the main characteristics that influence deterioration. An application of a peak-oriented deterioration model in the seismic evaluation of single-degree-of-freedom (SDOF) systems is illustrated. The advantages of using deteriorating hysteretic models for obtaining the response of highly inelastic systems are discussed. Copyright © 2005 John Wiley & Sons, Ltd. [source] Identification of soil degradation during earthquake excitations by Bayesian inferenceEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 6 2003Jianye Ching Abstract A Bayesian inference approach is introduced to identify soil degradation behaviours at four downhole array sites. The approach of inference is based on a parametric time-varying infinite impulse response filter model. The approach is shown to be adaptive to the changes of filter parameters and noise amplitudes. Four sites, including the Lotung (Taiwan), Chiba (Japan), Garner Valley (California), and Treasure Island (California) sites with downhole seismic arrays are analysed. Our results show two major types of soil degradation behaviour: the well-known strain-dependent softening, and reduction in stiffness that is not instantaneously recoverable. It is also found that both types of soil degradation are more pronounced in sandy soils than in clayey soils. The mechanism for the second type of soil degradation is not yet clear to the authors and suggested to be further studied. Copyright © 2003 John Wiley & Sons, Ltd. [source] Localization analysis in softening RC frame structuresEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 2 2003Ali R. Khaloo Abstract This paper discusses the sensitivity of softening reinforced concrete frame structures to the changes in input ground motion and investigates the possibility of localizations for this type of structure in static and dynamic analysis. A finite element model is used in which the sections resisting force are calculated using a proposed differential hysteretic model. This model is especially developed for modelling softening behaviour under cyclic loading. To obtain parameters of the differential model the moment,curvature of each section is evaluated using a microplane constitutive law for concrete and bi-linear elasto-plastic law for reinforcements. The capability of the procedure is verified by comparing results with available experimental data at element level, which shows good accuracy of the procedure. The effect of possible changes in ground motion is assessed using a non-stationary Kanai,Tajimi process. This process is used to generate ground motions with approximately the same amplitude and frequency content evolution as those of base ground motion. The possibility of localization in static and dynamic loading is investigated using two structures. A measure for the possibility of localization in code-designed structures is obtained. This study indicates that localization may occur in ordinary moment-resisting structures located in high seismic zones. Localization may result in substantial drift in global response and instability due to P,, effect. Also, it is shown that the structure becomes very sensitive to the input ground motion. It is concluded that allowance by some design codes of the use of ordinary moment-resisting frames in regions with high seismicity should be revised or improvements should be made in the detailing requirements at critical sections of these structures. Copyright © 2002 John Wiley & Sons, Ltd. [source] Usury legislation, cash, and credit: the development of the female investor in the late Tudor and Stuart periods1ECONOMIC HISTORY REVIEW, Issue 2 2008JUDITH SPICKSLEY This article uses testamentary evidence from Lincoln diocesan court between the 1570s and the 1690s to examine links between inheritance, a rise in money-lending amongst single women, and an increase in the proportion of women that never married. Two trends emerge: first, more fathers after the 1570s chose to bequeath cash to their daughters; second, they were more likely to restrict access to this portion by age rather than marriage. Assisted by a softening of attitudes towards interest-bearing lending, these changes offered some single women a measure of financial independence that may have impacted on their marriage decisions. [source] Synthesis and characterization of imidazolinium surfactants derived from tallow fatty acids and diethylenetriamineEUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 10 2008Divya Bajpai Abstract This paper describes the synthesis of long-chain dialkylamido imidazolines based on tallow fatty acids and diethylenetriamine, followed by their quaternization. Imidazolines were obtained by non-solvent microwave synthesis using calcium oxide as support, which were then quaternized by using dimethyl sulfate as a quaternizing agent and iso -propanol as a solvent, to produce cationic imidazolinium salts. The synthesized cationic imidazoline surfactants were evaluated for yield and cationic content. The instrumental techniques, viz. FT-IR and 1H-NMR, verified the formation of imidazolines and their subsequent quaternization. The surface-active and performance properties of the cationic imidazolines in terms of critical micelle concentration, surface tension, dispersibility, emulsion stability, softening, rewettability and antistatic properties were also reported. [source] Equal Channel Angular Pressing of a Mg,3Al,1Zn Alloy with Back Pressure,ADVANCED ENGINEERING MATERIALS, Issue 8 2010Feng Kang Abstract An extruded Mg,3Al,1Zn alloy bar is subjected to 1,4 passes equal channel angular pressing (ECAP) with or without 125,MPa backpressure via route Bc at 200,°C. Both strength and ductility are significantly increased after ECAP with backpressure; this is in strong contrast to the case of ECAP without backpressure, where significant improvement in ductility is accompanied by obvious decrease in yield strength from texture softening. Compared to ECAP without backpressure, much enhanced grain refinement, and the split of the dominant texture component of (0002) pole were observed with scatter intensity peaks in the case after ECAP with backpressure. This turns out to be resulted mainly from the activation of new slip system together with enhanced dynamic recrystallization under the effect of backpressure. The improvement of both strength and ductility in Mg,3Al,1Zn alloy through ECAP with back pressure provides a better approach to meet the engineering requests on comprehensive performance of this light alloy. [source] Physical and Numerical Simulation of Cold Rolling of an AlFeSi Alloy in Consideration of Static Recovery,ADVANCED ENGINEERING MATERIALS, Issue 3 2010Christoph Heering The influence of static recovery on the yield stress of AA8079 was investigated in lab-scale cold rolling experiments. The yield stress of AA8079 in the cold rolling process is affected by static recovery, but the softening caused by static recovery is completely compensated in the subsequent cold rolling pass. Thus, the effect of static recovery on the yield stress of the final product is of minor importance. For the TPM, the kinetics of static recovery of the AlFeSi alloy AA8079 were determined for different temperatures and strain rates. The measured softening kinetics were then implemented in the physically based flow stress model 3IVM+. This flow stress model was extended with an empirical approach for static recovery to enable the through-process modeling of cold-rolled aluminum in consideration of static recovery. Future work will focus on physically based modeling of static recovery without using empirical approaches. [source] Enamel dissolution in citric acid as a function of calcium and phosphate concentrations and degree of saturation with respect to hydroxyapatiteEUROPEAN JOURNAL OF ORAL SCIENCES, Issue 5 2003Michele E. Barbour The aim of this study was to investigate enamel dissolution in citric acid solutions as a function of solution calcium and phosphate concentrations and degree of saturation with respect to hydroxyapatite (DSHA). The primary relevance of the study is the development of soft drinks with reduced erosive potential. Nanoindentation was used to investigate changes in the hardness of polished human enamel surfaces after 120 s and 300 s exposure to solutions with pH 3.30 and a range of calcium and phosphate concentrations. All solutions were undersaturated with respect to hydroxyapatite, with 0.000 , DSHA , 0.295. A complex dependence of enamel softening on calcium concentration was observed. Substantial enamel softening occurred in solutions with calcium concentrations equal to or less than 120 mm (DSHA , 0.104), but there was little or no statistically significant softening of the enamel for calcium concentrations over 120 mm. This condition may be applicable to soft drink formulation. Furthermore, solutions with DSHA = 0.101 and different calcium/phosphate ratios resulted in different degrees of softening of the enamel. Hence, contrary to assumptions made in many models, enamel dissolution is not simply a function of DSHA, and individual calcium and phosphate concentrations are critical. [source] Stress-Dependent Elastic Properties of Porous Microcracked Ceramics,ADVANCED ENGINEERING MATERIALS, Issue 12 2009Irina Pozdnyakova Abstract Although ceramics are considered linear elastic materials, we have observed a non-linear pseudo-elastic behavior in porous cellular microcracked ceramics such as , -eucryptite. This is attributed to the evolution of microstructure in these materials. This behavior is particularly different from that of non-microcracked ceramics such as silicon carbide. It is shown that in microcracked materials two processes, namely stiffening and softening, always compete when a compressive external load is applied. The first regime is attributed to microcrack closure, and the second to microcracks opening, i.e. to a damage introduced by the applied stress. On the other hand rather a continuous damage is observed in the non-microcracked case. A comparison has been done between the microscopic (as measured by neutron diffraction) and the macroscopic stress-strain response. Also, it has been found that at constant load a significant strain relaxation occurs, which has two timescales, possibly driven by the two phenomena quoted above. Indeed, no such relaxation is observed for non-microcracked SiC. Implications of these findings are discussed. [source] Fatigue strength of Inconel 718 at elevated temperaturesFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 3 2000Kawagoishi The strength of Inconel 718 under rotary bending fatigue is investigated at room temperature, 300, 500 and 600 °C in air. It is found that in the long-life region, the fatigue strength of a plain specimen is much higher at elevated temperatures than at room temperature, though the static strength decreases with the increase in temperature. The effect of temperature on the fatigue strength is examined in terms of the initiation and early growth behaviour of a small crack. The results are discussed in relation to the competition between the softening of the nickel matrix (, phase) and the surface oxidation at elevated temperatures. [source] Cover Picture: Spectroscopic and Photophysical Properties of a Highly Derivatized C60 Fullerol (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 1 2006Mater. Abstract The photo-oxidative stress in aqueous milieus can readily be generated in the presence of newly synthesized highly derivatized fullerenes (fullerols) reported in the Full Paper by Vileno and co-workers on p.,120. Their basic structural and photophysical properties were characterized using a range of methods, including X-ray photoelectron and IR spectroscopies, and electron spin resonance. Moreover, a significant drop of the local stiffness of a living cell was monitored using atomic force microscopy. This cell softening was attributed to the early effects of the photo-oxidative stress. Hydroxylated C60 molecules, also called fullerols, are a class of water-soluble fullerenes. Here we report the synthesis in acidic conditions of a highly derivatized fullerol (up to 36 carbons per C60 are oxidized). Spectroscopic investigations (X-ray photoelectron spectroscopy and infrared absorption) highlight the coexistence of both acidic and basic forms for the hydroxyl addends of derivatized C60. pH titrimetry reveals that, at millimolar concentrations, only ten protons per fullerol molecule are labile. Such a low value, as compared to 36 hydroxyl groups, is explained by the formation of clusters. A UV-vis absorption study performed over a large range of concentrations also points to the aggregation phenomenon. Moreover, this study shows that the clusters of fullerols appear at relatively low (micromolar) concentrations. An electron spin resonance (ESR) study, based on the attack of singlet oxygen (1,g) on 2,2,6,6-tetramethyl-4-piperidinol (TMP-OH), has proved the potential of hydroxylated C60 for performing efficient generation of singlet oxygen in aqueous solution. ESR measurements, which allow detection and quantification of 1,g, have also revealed the generation of reactive oxygen species (ROS). The yield of generation of 1,g and ROS is strongly correlated to the concentration of fullerol, thus also pointing to the aggregation of fullerol molecules. Exposing glioblastoma cells to oxidative stress in the presence of hydroxylated C60 and visible light has also been performed. Atomic force microscopy is used to monitor the relevant diminishment of the Young's modulus values for cells exposed to the oxidative stress. These results point to a possible application field of fullerols for performing bio-oxidations. [source] Processing of Bulk Metallic GlassADVANCED MATERIALS, Issue 14 2010Jan Schroers Abstract Bulk metallic glass (BMG) formers are multicomponent alloys that vitrify with remarkable ease during solidification. Technological interest in these materials has been generated by their unique properties, which often surpass those of conventional structural materials. The metastable nature of BMGs, however, has imposed a barrier to broad commercial adoption, particularly where the processing requirements of these alloys conflict with conventional metal processing methods. Research on the crystallization of BMG formers has uncovered novel thermoplastic forming (TPF)-based processing opportunities. Unique among metal processing methods, TPF utilizes the dramatic softening exhibited by a BMG as it approaches its glass-transition temperature and decouples the rapid cooling required to form a glass from the forming step. This article reviews crystallization processes in BMG former and summarizes and compares TPF-based processing methods. Finally, an assessment of scientific and technological advancements required for broader commercial utilization of BMGs will be made. [source] A destructuration theory and its application to SANICLAY modelINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 10 2010Mahdi Taiebat Abstract Many natural clays have an undisturbed shear strength in excess of the remoulded strength. Destructuration modeling provides a means to account for such sensitivity in a constitutive model. This paper extends the SANICLAY model to include destructuration. Two distinct types of destructuration are considered: isotropic and frictional. The former is a concept already presented in relation to other models and in essence constitutes a mechanism of isotropic softening of the yield surface with destructuration. The latter refers to the reduction of the critical stress ratio reflecting the effect of destructuration on the friction angle, and is believed to be a novel proposition. Both the types depend on a measure of destructuration rate expressed in terms of combined plastic volumetric and deviatoric strain rates. The SANICLAY model itself is generalized from its previous form by additional dependence of the yield surface on the third isotropic stress invariant. Such a generalization allows to obtain as particular cases simplified model versions of lower complexity including one with a single surface and associative flow rule, by simply setting accordingly parameters of the generalized version. A detailed calibration procedure of the relatively few model constants is presented, and the performance of three versions of the model, in descending order of complexity, is validated by comparison of simulations to various data for oedometric consolidation followed by triaxial undrained compression and extension tests on two structured clays. Copyright © 2009 John Wiley & Sons, Ltd. [source] Damage-viscoplastic consistency model for rock fracture in heterogeneous rocks under dynamic loadingINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 10 2010Timo Saksala Abstract This paper presents a damage-viscoplastic consistency model for numerical simulation of brittle fracture in heterogeneous rocks. The model is based on a combination of the recent viscoplastic consistency model by Wang and the isotropic damage concept with separate damage variables in tension and compression. This approach does not suffer from ill-posedness, caused by strain softening, of the underlying boundary/initial value problem since viscoplasticity provides the regularization by introducing a length scale effect under dynamic loading conditions. The model uses the Mohr,Coulomb yield criterion with the Rankine criterion as a tensile cut-off. The damage law in compression is calibrated via the degradation index concept of Fang and Harrison. Thereby, the model is able to capture the brittle-to-ductile transition occurring in confined compression at a certain level of confinement. The heterogeneity of rock is accounted for by the statistical approach based on the Weibull distribution. Numerical simulations of confined compression test in plane strain conditions demonstrate a good agreement with the experiments at both the material point and structural levels as the fracture modes are realistically predicted. Copyright © 2009 John Wiley & Sons, Ltd. [source] Numerical modeling of seismic triggering, evolution, and deposition of rapid landslides: Application to Higashi,Takezawa (2004)INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 4 2010Nikos Gerolymos Abstract A mathematical model is developed for the dynamic analysis of earthquake-triggered rapid landslides, considering two mechanically coupled systems: (a) the accelerating deformable body of the slide and (b) the rapidly deforming shear band at the base of the slide. The main body of the slide is considered as a one-phase mixture of Newtonian incompressible fluids and Coulomb solids sliding on a plane of variable inclination. The evolution of the landslide is modeled via a depth-integrated model of the Savage,Hutter type coupled with: (a) a cyclic hysteretic constitutive model of the Bouc,Wen type and (b) Voellmy's rheology for the deformation of the material within the shear band. The original shallow-water equations that govern the landslide motion are appropriately reformulated to account for inertial forces due to seismic loading, and to allow for a smooth transition between the active and the passive state. The capability of the developed model is tested against the Higashi,Takezawa landslide. Triggered by the 2004 Niigata-ken Chuetsu earthquake, the slide produced about 100m displacement of a large wedge from an originally rather mild slope. The mechanism of material softening inside the shear band responsible for the surprisingly large run-out of the landslide is described by a set of equations for grain crushing-induced pore-water pressures. The back-analysis reveals interesting patterns on the flow dynamics, and the numerical results compare well with field observations. It is shown that the mechanism of material softening is a crucial factor for the initiation and evolution of the landslide, while viscoplastic frictional resistance is a key requirement for successfully reproducing the field data. Copyright © 2009 John Wiley & Sons, Ltd. [source] Micromechanical analysis of failure propagation in frictional granular materialsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 15 2009Antoinette Tordesillas Abstract The extent to which the evolution of instabilities and failure across multiple length scales can be reproduced with the aid of a bifurcation analysis is examined. We adopt an elastoplastic micropolar constitutive model, recently developed for dense cohesionless granular materials within the framework of thermomicromechanics. The internal variables and their evolution laws are conceived from a direct consideration of the dissipative mechanism of force chain buckling. The resulting constitutive law is cast entirely in terms of the particle scale properties. It thus presents a unique opportunity to test the potential of micromechanical continuum formulations to reproduce key stages in the deformation history: the development of material instabilities and failure following an initially homogeneous deformation. Progression of failure, initiating from frictional sliding and rolling at contacts, followed by the buckling of force chains, through to macroscopic strain softening and shear banding, is reproduced. Bifurcation point, marking the onset of shear banding, occurred shortly after the peak stress ratio. A wide range of material parameters was examined to show the effect of particle scale properties on the progression of failure. Model predictions on the thickness and angle of inclination of the shear band and the structural evolution inside the band, namely the latitudinal distribution of particle rotations and the angular distributions of contacts and the normal contact forces, are consistent with observations from numerical simulations and experiments. Copyright © 2009 John Wiley & Sons, Ltd. [source] Implicit integration of a mixed isotropic,kinematic hardening plasticity model for structured claysINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 10 2008Angelo Amorosi Abstract In recent years, a number of constitutive models have been proposed to describe mathematically the mechanical response of natural clays. Some of these models are characterized by complex formulations, often leading to non-trivial problems in their numerical integration in finite elements codes. The paper describes a fully implicit stress-point algorithm for the numerical integration of a single-surface mixed isotropic,kinematic hardening plasticity model for structured clays. The formulation of the model stems from a compromise between its capability of reproducing the larger number of features characterizing the behaviour of structured clays and the possibility of developing a robust integration algorithm for its implementation in a finite elements code. The model is characterized by an ellipsoid-shaped yield function, inside which a stress-dependent reversible stiffness is accounted for by a non-linear hyperelastic formulation. The isotropic part of the hardening law extends the standard Cam-Clay one to include plastic strain-driven softening due to bond degradation, while the kinematic hardening part controls the evolution of the position of the yield surface in the stress space. The proposed algorithm allows the consistent linearization of the constitutive equations guaranteeing the quadratic rate of asymptotic convergence in the global-level Newton,Raphson iterative procedure. The accuracy and the convergence properties of the proposed algorithm are evaluated with reference to the numerical simulations of single element tests and the analysis of a typical geotechnical boundary value problem. Copyright © 2007 John Wiley & Sons, Ltd. [source] Creep of saturated materials as a chemically enhanced rate-dependent damage processINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 14 2007Liang Bo Hu Abstract Material behaviour that exhibits characteristics of creep induced by a spontaneous mineral dissolution enhanced by material damage is studied. It is believed that the characteristic rates of the chemical processes involved determine the time-rate dependence of the resulting strain. A basic model of a combined chemo-plastic softening and chemically enhanced deviatoric strain hardening for saturated geomaterials is presented. Chemical softening is postulated to occur as a consequence of the net mass removal resulting from dissolution and precipitation of specific minerals occurring at the damage-generated inter-phase interfaces. Closed and open systems are discussed. In the former case, deformation at constant stress results entirely from a local compensation mechanism between the chemical softening and strain hardening. The classical three stages of creep are interpreted in terms of mechanisms of dissolution and precipitation, as well as the variation in the reaction surface areas involved in the mass exchange. In an open system, the above local mechanism is enhanced by the removal of mass via diffusion of species affecting the mass balance. Such a system is addressed via a boundary value problem as shown in an example. Copyright © 2007 John Wiley & Sons, Ltd. [source] Numerical studies of shear banding in interface shear tests using a new strain calculation method,INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 12 2007Jianfeng Wang Abstract Strain localization is closely associated with the stress,strain behaviour of an interphase system subject to quasi-static direct interface shear, especially after peak stress state is reached. This behaviour is important because it is closely related to deformations experienced by geotechnical composite structures. This paper presents a study using two-dimensional discrete element method (DEM) simulations on the strain localization of an idealized interphase system composed of densely packed spherical particles in contact with rough manufactured surfaces. The manufactured surface is made up of regular or irregular triangular asperities with varying slopes. A new simple method of strain calculation is used in this study to generate strain field inside a simulated direct interface shear box. This method accounts for particle rotation and captures strain localization features at high resolution. Results show that strain localization begins with the onset of non-linear stress,strain behaviour. A distinct but discontinuous shear band emerges above the rough surface just before the peak stress state, which becomes more expansive and coherent with post-peak strain softening. It is found that the shear bands developed by surfaces with smaller roughness are much thinner than those developed by surfaces with greater roughness. The maximum thickness of the intense shear zone is observed to be about 8,10 median particle diameters. The shear band orientations, which are mainly dominated by the rough boundary surface, are parallel with the zero extension direction, which are horizontally oriented. Published in 2007 by John Wiley & Sons, Ltd. [source] Experimental investigation of slip-stick behaviour in granular materialsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 14 2006Khalid A. Alshibli Abstract This paper presents the results of an experimental programme to study load oscillation in granular materials. Spherical glass beads were used in the investigation. Cylindrical specimens were compressed under axisymmetric triaxial loading condition at 25,100,250 and 400 kPa confining pressures. The test parameters included: (i) particle size; (ii) gradation (uniform versus non-uniform specimens); (iii) confining pressure; (iv) loading rate; and (v) specimen density. In general, a slight post-peak principal stress softening was observed as well as a continuous volume increase (dilation) even at relatively high strains. This appears to be caused by the uniform shape and smooth surface of the spherical particles. Load oscillations were observed in the very small, small, and well-graded beads at each confining pressure. For the medium beads, the oscillations appeared at high confining pressure (250 and 400 kPa), and they did not appear in the large beads. The influences of the confining pressure, loading rate, particle size, gradation and specimen density on load oscillation are presented and discussed. Copyright © 2006 John Wiley & Sons, Ltd. [source] | |||||||||||||||||||||||||||||||