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Rolling
Kinds of Rolling Terms modified by Rolling Selected AbstractsPhysical 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] Constituent Particle Break-Up During Hot Rolling of AA 5182,ADVANCED ENGINEERING MATERIALS, Issue 1-2 2010Nicolas Moulin Aluminum sheet is currently used for body panels on a number of mass-produced vehicles, in particular for closure panels. AA5xxx alloys always contain coarse inter-metallic particles (Alx(Fe,Mn)ySi, Mg2Si) after casting. In the present work inter-metallic particle break-up during hot reversible rolling of AA5182 alloy sheets has been analyzed. The sizes and shapes of inter-metallic particles in as-cast and industrially hot rolled AA5182 alloys sheets were characterized by 3D X-ray tomography observations. The relation between particle break-up and particle morphology was then analyzed statistically and by a micromechanical finite element (FE)-based model. The essential outcomes of the statistical approach may be summarized as follows. The inter-metallic particle population may be described by five morphological parameters. Secondly the comparison of the particle morphology in as cast and industrially rolled sheets leads to the definition of five classes. The evolution of each particle class as function of the rolling strain is provided. The statistical analysis shows which particles break-up. The stresses and strains in inter-metallic particles, embedded in an elasto-viscoplastic aluminum matrix submitted to plane strain compression, were analyzed by an FE model. A new failure criterion was proposed. The essential outcomes of the mechanical approach are as follows: a precise description of stress concentration mechanisms in nonconvex particles, a close description of the parameters controlling particle break-up, and finally a simplified classification of the failure behavior. [source] Hardness Variation and Strain Distribution in Magnesium Alloy AZ31 Processed by Multi-pass Caliber Rolling,ADVANCED ENGINEERING MATERIALS, Issue 8 2009Tadanobu Inoue The evolution of microstructure and hardness with equivalent strain was studied in magnesium alloy AZ31 bars fabricated using a process of multi-pass caliber rolling at 473 K. The inhomogeneity of hardness throughout the cross section in the rolled bars was very similar to that of the strain predicted from FE simulation. The caliber rolling produced a fine-grain structure below 2.5 µm in a bulk sample with a length of over 1000 mm. [source] Verhalten laserschockverfestigter und festgewalzter Randschichten der Ti-Legierung Ti-6Al-4V bei schwingender Beanspruchung unter erhöhten TemperaturenMATERIALWISSENSCHAFT UND WERKSTOFFTECHNIK, Issue 6 2003I. Altenberger Laser Shock Peening; Deep Rolling; Residual Stresses; Ti-6-4 Abstract Es ist seit langem bekannt, dass mechanische Oberflächenbehandlungen wie etwa Festwalzen, Kugelstrahlen oder Laserschockoberflächenbehandlungen, um nur einige zu nennen, das Ermüdungsverhalten hochbeanspruchter metallischer Bauteile entscheidend verbessern können. Insbesondere Festwalzen und Laserschockoberflächenbehandlungen haben sich als besonders wirksam herausgestellt, da sie tiefe Druckeigenspannungs- und Verfestigungsprofile sowie eine vergleichsweise glatte Oberflächentopographie erzeugen. Tatsächlich wird z.,B. das Festwalzen bereits serienmässig zur Erhöhung der Schwingfestigkeit von Stählen, wie etwa beim Festwalzen von Kurbelwellen, eingesetzt. Obwohl die meisten Arbeiten zum Festwalzen sich mit Stählen beschäftigen, wurde dieses Verfahren in jüngerer Zeit auch auf eine Reihe von Titanwerkstoffen erfolgreich angewendet. Die vorliegenden Untersuchungen beschäftigen sich mit dem Einfluss von Festwalzbehandlungen auf das Niedrig- und Hochlastwechselermüdungsverhalten der wichtigsten kommerziellen Titanlegierung Ti-6Al-4V, wobei besonderes Augenmerk auf die thermische und mechanische Stabilität randnaher Eigenspannungszustände und Mikrostrukturen gerichtet wurde. Zusätzlich werden erste Ergebnisse zum Eigenspannungszustand und zur Schwingfestigkeit lasergeschockter Ti-6Al-4V-Proben präsentiert und mit Resultaten festgewalzter Zustände verglichen. Ausserdem wird untersucht, ob die Oberflächenbehandlungen auch bei erhöhten Temperaturen (bis 450,°C) ihre Wirksamkeit zur Verbesserung der Schwingfestigkeit behalten. Basierend auf Wechselverformungs- und Lebensdaueruntersuchungen, in Kombination mit Röntgendiffraktometrie und In-situ -Transmissionselektronenmikroskopie, lässt sich feststellen, dass Laserschockoberflächenbehandlungen und insbesondere Festwalzen die Rissbildung und Ausbreitung in hochtemperaturschwingbeanspruchtem Ti-6Al-4V trotz eines fast völligen Druckeigenspannungsabbaus wirkungsvoll hemmt. Daraus lässt sich ableiten, dass zusätzlich zu Eigenspannungen vor allem randnahe Mikrostrukturen, welche im Falle von mechanisch randschichtverfestigtem Ti-6Al-4V durch sehr hohe Versetzungsdichten und Nanokristallite gekennzeichnet ist, einen wesentlichen Einfluss bei der Lebensdauererhöhung durch Randschichtverfestigung haben. Residual stress stability and near-surface microstructures in high temperature fatigued mechanically surface treated Ti-6Al-4V It is well known that mechanical surface treatments, such as deep rolling, shot peening and laser shock peening, can significantly improve the fatigue behavior of highly-stressed metallic components. Deep rolling is particularly attractive since it is possible to generate, near the surface, deep compressive residual stresses and work hardened layers while retaining a relatively smooth surface finish. In the present investigation, the effect of deep rolling on the low-cycle and high-cycle fatigue behavior of a Ti-6Al-4V alloy is examined, with particular emphasis on the thermal and mechanical stability of the residual stress states and the near-surface microstructures. Preliminary results on laser shock peened Ti-6Al-4V are also presented for comparison. Particular emphasis is devoted to the question of whether such surface treatments are effective for improving the fatigue properties at elevated temperatures up to ,450,°C, i.e., at an homologous temperature of ,0.4 T/Tm (where Tm is the melting temperature). Based on cyclic deformation and stress/life (S/N) fatigue behavior, together with the X-ray diffraction and in situ transmission electron microscopy observations of the microstructure, it was found that deep rolling can be quite effective in retarding the initiation and initial propagation of fatigue cracks in Ti-6Al-4V at such higher temperatures, despite the almost complete relaxation of the near-surface residual stresses. In the absence of such stresses, it is shown that the near-surface microstructures, which in Ti-6Al-4V consist of a layer of work hardened nanoscale grains, play a critical role in the enhancement of fatigue life by mechanical surface treatment. [source] Rolling over stock index futures contractsTHE JOURNAL OF FUTURES MARKETS, Issue 7 2009Óscar Carchano Derivative contracts have a finite life limited by their maturity. The construction of continuous series, however, is crucial for academic and trading purposes. In this study, we analyze the relevance of the choice of the rollover date, defined as the point in time when we switch from the front contract series to the next one. We have used five different methodologies in order to construct five different return series of stock index futures contracts. The results show that, regardless of the criterion applied, there are not significant differences between the resultant series. Therefore, the least complex method can be used in order to reach the same conclusions. © 2009 Wiley Periodicals, Inc. Jrl Fut Mark 28:684,694, 2009 [source] Nonablative Acne Scar Reduction after a Series of Treatments with a Short-Pulsed 1,064-nm Neodymium:YAG LaserDERMATOLOGIC SURGERY, Issue 8 2006GRAEME M. LIPPER MD BACKGROUND Effective treatment of facial acne scarring presents a major challenge. Nonablative lasers and radiofrequency devices work by thermally stimulating dermal collagen remodeling, thereby softening acne scars in a minimally invasive fashion. One such laser, a 1,064-nm short-pulsed Nd:YAG, uses rapidly scanned low-energy infrared pulses to heat the dermis selectively through the normal dermal microvasculature. OBJECTIVE In this pilot study, the safety and efficacy of a novel short-pulsed Nd:YAG laser were investigated for the treatment of moderate to severe facial acne scarring. MATERIALS AND METHODS Nine of 10 enrolled patients with moderate to severe facial acne scarring received eight sequential 1,064-nm Nd:YAG treatments (laser parameters 14 J/cm2, 0.3 milliseconds, 5-mm spot size, 7-Hz pulse rate, 2,000 pulses per side of face). Patients were graded for the presence and severity of three scar morphologies: superficial (rolling), medium-depth (boxcar), and deep (ice pick). Outcome measures included blinded evaluation of before and after photographs by three physician observers (scar severity score) and patient self-assessment. RESULTS Acne scarring improved in 100% of the nine patients completing the study. Scar severity scores improved by a mean of 29.36% (95% confidence interval, 16.93%,41.79%; p=.006); 89% of patients noted greater than 10% scar improvement. No treatment-related adverse events were seen. CONCLUSION Our findings support the use of a short-pulsed, low-fluence 1,064-nm Nd:YAG laser as a safe, effective treatment for facial acne scarring. Scar improvement was noted in all treated subjects with minimal discomfort and no downtime. This protocol appears to be most effective at reducing scar depth and softening scar contours. [source] Approach to procedures in neonatesDERMATOLOGIC THERAPY, Issue 2 2005Valerie B. Lyon ABSTRACT:, Physical constraints and metabolic differences in neonates require that special attention is given to performing procedures in this patient group. Neonates have a thinner dermis and a greater surface-to-weight ratio, allowing for easier invasion through the skin barrier. The enzymes for metabolism of agents and defense against organisms inside the body are not fully developed in infants. Very premature neonates also have less circulating albumin, making the effective concentration of circulating agent even greater. The infant is prone to unanticipated movement during procedures, such as rolling on the procedure table. The neonatal period is the most common time period for malformations to become manifest on the skin, and invasion of some of these lesions can produce morbidity. These and other factors affect the choice of the type of procedure used, the timing for intervention, and the approach to intervention in this age group. This article reviews the important considerations for approaching procedures and offers suggestions for safe and effective methods of reliably producing the intended outcome. [source] Young children who abandon error behaviourally still have to free themselves mentally: a retrospective test for inhibition in intuitive physicsDEVELOPMENTAL SCIENCE, Issue 3 2004Norman H. Freeman When preschoolers overcome persistent error, subsequent patterns of correct choices may identify how the error had been overcome. Children who no longer misrepresented a ball rolling down a bent tube as though it could only fall vertically, were asked sometimes to approach and sometimes to avoid where the ball landed. All children showed requisite task-switching flexibility. The pattern of 4-year-olds' correct choices among different places showed unnecessary avoidance of any place that would previously have tempted them into a vertical-approach error, 5-year-olds rebounded into a reversal, and 7-year-olds were flexible. The data attest to an inhibition mechanism, ruling out competing possibilities. [source] SLIC-1/sorting nexin,20: A novel sorting nexin that directs subcellular distribution of PSGL-1EUROPEAN JOURNAL OF IMMUNOLOGY, Issue 2 2008Ulrich Abstract P-Selectin glycoprotein ligand-1 (PSGL-1) is a mucin-like glycoprotein expressed on the surface of leukocytes that serves as the major ligand for the selectin family of adhesion molecules and functions in leukocyte tethering and rolling on activated endothelium and platelets. Previous studies have implicated the highly conserved cytoplasmic domain of PSGL-1 in regulating outside-in signaling of integrin activation. However, molecules that physically and functionally interact with this domain are not completely defined. Using a yeast two-hybrid screen with the cytoplasmic domain of PSGL-1 as bait, a novel protein designated selectin ligand interactor cytoplasmic-1 (SLIC-1) was isolated. Computer-based homology search revealed that SLIC-1 was the human orthologue for the previously identified mouse sorting nexin,20. Direct interaction between SLIC-1 and PSGL-1 was specific as indicated by co-immunoprecipitation and motif mapping. Colocalization experiments demonstrated that SLIC-1 contains a Phox homology domain that binds phosphoinositides and targets the PSGL-1/SLIC-1 complex to endosomes. Deficiency in the murine homologue of SLIC-1 did not modulate PSGL-1-dependent signaling nor alter neutrophil adhesion through PSGL-1. We conclude that SLIC-1 serves as a sorting molecule that cycles PSGL-1 into endosomes with no impact on leukocyte recruitment. [source] T lymphocyte rolling and recruitment into peripheral lymph nodes is regulated by a saturable density of L-selectin (CD62L)EUROPEAN JOURNAL OF IMMUNOLOGY, Issue 5 2007Elena Galkina Dr. Abstract L-selectin mediates tethering and rolling of lymphocytes in high endothelial venules (HEV) of lymph nodes (LN) and of leukocytes at inflammatory sites. We used transgenic mice expressing varying levels of wild-type or a non-cleavable mutant form of L-selectin on T cells to determine the relationship between L-selectin density, tethering and rolling, and migration into LN. T cells expressing supraphysiological levels of either wild-type or non-cleavable L-selectin showed rolling parameters similar to C57BL/6 T cells in hydrodynamic flow assays and during rolling in Peyer's patch HEV. In contrast, PMA- or antigen-activated T cells and L-selectin+/, T cells expressing subphysiological levels of L-selectin showed reduced numbers of rolling cells with increased rolling velocity. Short-term homing studies showed that elevated expression of L-selectin above physiological levels had no effect on T cell migration to LN; however, low L-selectin expression resulted in reduced T cell homing to LN. Thus, T lymphocyte migration into LN is regulated by the density of cell surface L-selectin. In addition, there is a saturable density of L-selectin required for optimal homing to PLN in C57BL/6 mice, the L-selectin level on circulating naive T cells promotes optimal homing, and increased expression above saturating levels promotes no further increase in T cell recruitment. [source] CD4+CD25+ regulatory T cells suppress contact hypersensitivity reactions by blocking influx of effector T cells into inflamed tissueEUROPEAN JOURNAL OF IMMUNOLOGY, Issue 11 2006Sabine Ring Dr. Abstract CD4+CD25+ regulatory T cells (Treg) exert suppressive functions on effector T cells in vitro and in vivo. However, the exact cellular events that mediate this inhibitory action remain largely unclear. To elucidate these events, we used intravital microscopy in a model of contact hypersensitivity (CHS) and visualized the leukocyte-endothelium interaction at the site of antigen challenge in awake C57BL/6 mice. Injection of Treg i.v. into sensitized mice at the time of local hapten challenge significantly inhibited rolling and adhesion of endogenous leukocytes to the endothelium. A similar inhibition of leukocyte recruitment could be recorded after injection of Treg-derived tissue culture supernatant. Thus, these data indicate that soluble factors may account for the suppressive effects. Accordingly we found that IL-10, but not TGF-,, was produced by Treg upon stimulation and that addition of anti-IL-10 antibodies abrogated the suppressive effects of Treg and tissue culture supernatant in CHS reactions. Moreover, CD4+CD25+ T cells isolated from IL-10,/, mice were not able to suppress the immune response induced by hapten treatment in C57BL/6 mice. In conclusion, our data suggest that cytokine-dependent rather than cell-cell contact-dependent mechanisms play a pivotal role in the suppression of CHS reactions by Treg in vivo. [source] Cost-Affordable Technique Involving Equal Channel Angular Pressing for the Manufacturing of Ultrafine Grained Sheets of an Al,Li,Mg,Sc Alloy,ADVANCED ENGINEERING MATERIALS, Issue 8 2010Rustam Kaibyshev A two-step process consisting of modified equal channel angular pressing (ECAP) and subsequent isothermal rolling (IR) was developed to produce thin sheets of aluminum alloys with ultra-fine grained (UFG) structure. Significant increase in the efficiency of ECAP was attained by using flat billets and a back pressure system. The incorporation of final IR into technologic route provides a reduced strain which is necessary to impose for the fabrication of thin sheets with UFG structure. In addition, it allows producing relatively "long billets." In order to demonstrate the feasibility of this technique an Al,5.1Mg,2.1Li,0.17Sc,0.08Zr (wt %) alloy was subjected to ECAP at 325,°C to a total strain of ,8 using processing route CX. The operation time of this processing did not exceed 15,min. Subsequent IR at the same temperature with a total reduction of 88% was applied to produce thin sheets with a 1.8,mm thickness and an average size of recrystallized grains of ,1.6,µm. These sheets exhibit extraordinary high superplastic ductilities. In addition, this material demonstrated almost isotropic mechanical behavior at room temperature. The maximum elongation-to-failure of ,2700% was attained at a temperature of 450,°C and an initial strain rate of 1.4,×,10,2 s,1. Thus it was demonstrated that the two-step processing consisting of ECAP with a back pressure followed by IR was a simple technique providing potential capability for the fabrication of superplastic sheets from an Al,Mg,Li,Sc alloy on a commercial scale. [source] Nanoscale Grain Refinement and H-Sorption Properties of MgH2 Processed by High-Pressure Torsion and Other Mechanical Routes,ADVANCED ENGINEERING MATERIALS, Issue 8 2010Daniel Rodrigo Leiva MgH2 is a promising material for solid-state hydrogen storage due to its high gravimetric and volumetric storage capacity and its relatively low cost. Severe plastic deformation (SPD) processing techniques are being explored as an alternative to high-energy ball-milling (HEBM) in order to obtain more air resistant materials and reduce processing times. In this work, Mg, MgH2, and MgH2,Fe mixtures were severely mechanically processed by different techniques such as high-pressure torsion (HPT), extensive cold forging, and cold rolling. A very significant grain refinement was achieved when using MgH2 instead of Mg as raw material. The mean crystallite sizes observed ranged from 10 to 30,nm, depending on the processing conditions. Enhanced H-sorption properties were observed for the MgH2 -based nanocomposites processed by HPT when compared with MgH2 mixtures. Additionally, cold forging and cold rolling also proved effective in nanostructuring MgH2. These results suggest a high potential for innovative application with the use of low cost mechanical processing routes to produce Mg-based nanomaterials with attractive hydrogen storage properties. [source] Recrystallization Modeling of AA8XXX Alloys with Cellular Automata Considering Recovering Kinetics,ADVANCED ENGINEERING MATERIALS, Issue 3 2010Carmen Schäfer A through-process modeling scheme for the prediction of recrystallization textures and microstructures after final annealing, subsequent to cold rolling is proposed and applied to a commercial AlFeSi alloy. The heart of the setup is a cellular automaton for modeling of recrystallization which considers changes in dislocation density by recovery and changes in Zener and solute drag due to microchemistry evolution. However, recrystallization is the crucial point in the whole setup, since it leads to significant changes in microstructure and texture. The simulated results are compared to experiments. [source] Constituent Particle Break-Up During Hot Rolling of AA 5182,ADVANCED ENGINEERING MATERIALS, Issue 1-2 2010Nicolas Moulin Aluminum sheet is currently used for body panels on a number of mass-produced vehicles, in particular for closure panels. AA5xxx alloys always contain coarse inter-metallic particles (Alx(Fe,Mn)ySi, Mg2Si) after casting. In the present work inter-metallic particle break-up during hot reversible rolling of AA5182 alloy sheets has been analyzed. The sizes and shapes of inter-metallic particles in as-cast and industrially hot rolled AA5182 alloys sheets were characterized by 3D X-ray tomography observations. The relation between particle break-up and particle morphology was then analyzed statistically and by a micromechanical finite element (FE)-based model. The essential outcomes of the statistical approach may be summarized as follows. The inter-metallic particle population may be described by five morphological parameters. Secondly the comparison of the particle morphology in as cast and industrially rolled sheets leads to the definition of five classes. The evolution of each particle class as function of the rolling strain is provided. The statistical analysis shows which particles break-up. The stresses and strains in inter-metallic particles, embedded in an elasto-viscoplastic aluminum matrix submitted to plane strain compression, were analyzed by an FE model. A new failure criterion was proposed. The essential outcomes of the mechanical approach are as follows: a precise description of stress concentration mechanisms in nonconvex particles, a close description of the parameters controlling particle break-up, and finally a simplified classification of the failure behavior. [source] Hardness Variation and Strain Distribution in Magnesium Alloy AZ31 Processed by Multi-pass Caliber Rolling,ADVANCED ENGINEERING MATERIALS, Issue 8 2009Tadanobu Inoue The evolution of microstructure and hardness with equivalent strain was studied in magnesium alloy AZ31 bars fabricated using a process of multi-pass caliber rolling at 473 K. The inhomogeneity of hardness throughout the cross section in the rolled bars was very similar to that of the strain predicted from FE simulation. The caliber rolling produced a fine-grain structure below 2.5 µm in a bulk sample with a length of over 1000 mm. [source] Achieving Low Temperature Superplasticity from Ca-Containing Magnesium Alloy Sheets,ADVANCED ENGINEERING MATERIALS, Issue 7 2009Woo-Jin Kim The application of hot extrusion and high-speed-ratio differential speed rolling (HRDSR) to a Ca-containing Mg -3Al1Zn magnesium alloy, processed by electromagnetic casting in the presence of electromagnetic stirring, produced a novel microstructure, composed of an ultrafine grain size of less than 1,,m and very fine (Al,Mg)2Ca particles that were uniformly and densely distributed over the matrix. The HRDSR processed alloy exhibited excellent superplasticity at relatively low temperatures (below 523,K). [source] Core loss estimation in three-phase transformer using vector hysteresis model and classical loss model incorporated in 2D magnetodynamicsEUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 2 2003O. Deblecker This paper deals with the computation of the magnetic field and core loss in a three-phase three-limb transformer at no-load. The computational algorithm consists of the vector hysteresis model incorporated in 2D magneto-dynamics via the differential reluctivity tensor. The hysteretic nonlinearity is handled by a simple iteration scheme. The eddy-current losses in the laminated steel core are accounted for by considering an additional conductivity matrix in the FE equations. The magnetisation-dependant vector Preisach model with an analytical expression for the distribution function is adopted for describing the hysteretic constitutive law in the rolling and transverse directions of the laminations. The parameters and mean field term are fitted on the basis of a set of BH-symmetric (quasistatic) loops. Numerical results are presented that confirm the effectiveness of the proposed method for the no-load simulation of the transformer in the transient and the steady-states. [source] The effects of macrolocalization of deformation in Al-based composites with Al2O3 inclusionsFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 4 2003YE. YE. ABSTRACT Using a television optical TOMSC system, regular features of localization of macroplastic deformation are studied in composite aluminum-based materials with hard inclusions of Al2O3 under tension. Before investigation, the specimens are subjected to cold rolling, tempering for 30 min at 500 °C with subsequent cooling in air, and annealing at 550 °C during 2 h with subsequent cooling in furnace. It is shown that the tempered and annealed alloys exhibit mobile centers of active macrolocalization long before the formation of a stationary neck preceding material fracture. Physical mesomechanics, relying on the concepts of the leading role of different-scale stress concentrators that relax and develop in a loaded heterogeneous material, is capable of providing a qualitative description of macrolocalization development. [source] The effect of contact load reduction on the fatigue life of pearlitic rail steel in lubricated rolling,sliding contactFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 8 2000D. I. Fletcher Twin-disc contact simulation tests were carried out to investigate the influence of contact pressure variation on rail steel fatigue life. Both a colloidal suspension of molybdenum disulphide in an oil carrier fluid (similar to a commercial flange lubrication product) and water were used as lubricants. It was found that the reduction from 1500 to 900 MPa of the maximum Hertzian contact pressure (at which a molybdenum,disulphide-lubricated and previously worn rail sample was tested) extended the fatigue life of the rail steel by over five times. For water lubrication a similar reduction in contact pressure produced only a marginal increase in fatigue life. The results were found to be in qualitative agreement with the predictions of the newly developed Three Mechanism (TM) model of rolling contact fatigue, which is introduced here. This model combines the mechanisms of ratcheting and the fracture mechanics-based mechanisms of both shear stress- and tensile stress-driven, fluid-assisted, crack growth. [source] Modelling blowing snow redistribution to prairie wetlandsHYDROLOGICAL PROCESSES, Issue 18 2009X. Fang Abstract Blowing snow transports and sublimates a substantial portion of the seasonal snowfall in the prairies of western Canada. Snow redistribution is an important feature of prairie hydrology as deep snowdrifts provide a source of meltwater to replenish ponds and generate streamflow in this dry region. The spatial distribution of snow water equivalent in the spring is therefore of great interest. A test of the distributed and aggregated modelling strategies for blowing snow transport and sublimation was conducted at the St. Denis National Wildlife Area in the rolling, internally drained prairie pothole region east of Saskatoon, Saskatchewan, Canada. A LiDAR-based DEM and aerial photograph-based vegetation cover map were available for this region. A coupled complex windflow and blowing snow model was run with 262,144 6 m × 6 m grid cells to produce spatially distributed estimates of seasonal blowing snow transport and sublimation. The calculation was then aggregated to seven landscape units that represented the major influences of surface roughness, topography and fetch on blowing snow transport and sublimation. Both the distributed and aggregated simulations predicted similar end-of-winter snow water equivalent with substantial redistribution of blowing snow from exposed sparsely vegetated sites across topographic drainage divides to the densely vegetated pothole wetlands. Both simulations also agreed well with snow survey observations. While the distributed calculations provide a fascinating and detailed visual image of the interaction of complex landscapes and blowing snow redistribution and sublimation, it is clear that blowing snow transport and sublimation calculations can be successfully aggregated to the spatial scale of the major landscape units in this environment. This means that meso and macroscale hydrological models can represent blowing snow redistribution successfully in the prairies. Copyright © 2009 John Wiley & Sons, Ltd. [source] GlcNAc6ST-1-mediated decoration of MAdCAM-1 protein with L-selectin ligand carbohydrates directs disease activity of ulcerative colitisINFLAMMATORY BOWEL DISEASES, Issue 5 2009Motohiro Kobayashi MD Abstract Background: A diffuse lymphocyte infiltrate is 1 of the characteristic features of ulcerative colitis (UC). Such lymphocyte recruitment requires lymphocyte rolling mediated by L-selectin ligand carbohydrates (6-sulfo sialyl Lewis X-capped O -glycans) and/or mucosal addressin cell adhesion molecule 1 (MAdCAM-1) expressed on high endothelial venule (HEV)-like vessels. The present study was undertaken to elucidate the role of MAdCAM-1 posttranslationally modified ("decorated") with L-selectin ligand carbohydrates in UC pathogenesis and consequent clinical outcomes. Methods: Biopsy specimens composed of active and remission phases of UC as well as normal colonic mucosa were immunostained for CD34, MAdCAM-1, and MECA-79, and the immunostained sections were quantitatively analyzed. Reverse-transcriptase polymerase chain reaction (RT-PCR) was carried out to evaluate transcripts of MAdCAM-1 and N -acetylglucosamine-6- O -sulfotransferases (GlcNAc6STs). CHO and Lec2 cells transfected with CD34 and MAdCAM-1 together with enzymes involved in L-selectin ligand carbohydrate biosynthesis were analyzed by immunofluorescence, FACS, and Western blotting to characterize the biochemical properties of GlcNAc6STs. Results: The number of MAdCAM-1+ vessels was increased in UC, with no significant difference between active and remission phases. An increased ratio of MECA-79+ to MAdCAM-1+ vessels with preferential GlcNAc6ST-1 transcripts was observed in the active phase of UC compared to the remission phase. MAdCAM-1 protein was colocalized with L-selectin ligand carbohydrates at the luminal surface of HEV-like vessels in situ. GlcNAc6ST-1 preferentially utilizes MAdCAM-1 as a scaffold protein for GlcNAc-6- O -sulfation in L-selectin ligand carbohydrate biosynthesis. Conclusions: UC disease activity is not regulated by expression of MAdCAM-1 protein itself, but rather by GlcNAc6ST-1-mediated decoration of MAdCAM-1 protein with L-selectin ligand carbohydrates. (Inflamm Bowel Dis 2008) [source] Down-regulation of endothelial adhesion molecules and leukocyte adhesion by treatment with superoxide dismutase is beneficial in chronic immune experimental colitisINFLAMMATORY BOWEL DISEASES, Issue 10 2005Joaquim Seguí PhD Abstract Modulation of adhesion molecule expression that govern trafficking of leukocytes into the inflamed intestine is envisioned as a new strategy for treatment of inflammatory bowel disease (IBD). This study was designed to determine the impact of reducing oxidative stress on adhesion molecules expression and leukocyte recruitment in experimental chronic colitis. For that purpose, colitic interleukin-10 knockout and wild-type mice were studied. Groups of animals were treated with Cu/Zn superoxide dismutase (SOD1) 13 mg/kg/d or vehicle for either 7 or 14 days. Expression of vascular cell adhesion molecule-1 and mucosal addressin cell adhesion molecule-1 were determined; leukocyte-endothelial cell interactions in colonic venules were studied with intravital microscopy; and changes in colon pathology and biomarkers of colitis severity were determined. Development of colitis was associated with a marked increase in endothelial vascular cell adhesion molecule-1 and mucosal addressin cell adhesion molecule-1 expression, which were significantly reduced by treatment with SOD1. The increase in leukocyte rolling and adhesion in colonic venules of colitic mice were significantly reduced by administration of SOD1. This treatment markedly reduced colonic lipid hydroperoxidation, myeoloperoxidase activity, and plasma levels of serum amyloid A protein and resulted in significant, although modest, reductions in histologic damage score. The therapeutic value of SOD1 when administered prophylactically was assessed in the dextran sulfate sodium model of colitis with similar positive results. These results indicate that SOD1 affords significant amelioration of colonic inflammatory changes in experimental colitis. Down-regulation of adhesion molecule expression, reduction of lipid hydroperoxidation, and recruitment of leukocytes into the inflamed intestine contribute to this beneficial effect. [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] A micromechanical study of rolling and sliding contacts in assemblies of oval granulesINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 5 2003Hossein M. Shodja Abstract The evolution of the microstructure of an assembly of cohesionless granular materials with associated pores, which carry the overall applied stresses through frictional contacts is a complex phenomenon. The macroscopic flow of such materials take place by the virtue of the relative rolling and sliding of the grains on the micro-scale. A new discrete element method for biaxial compression simulations of random assemblies of oval particles with mixed sizes is introduced. During the course of deformation, the new positions of the grains are determined by employing the static equilibrium equations. A key aspect of the method is that, it is formulated for ellipse cross-sectional particles, hence desirable inherent anisotropies are possible. A robust algorithm for the determination of the contact points between neighbouring grains is given. Employing the present methodology, many aspects of the behaviour of two-dimensional assemblies of oval cross-sectional rods have been successfully addressed. The effects of initial void ratio, interparticle friction angle, aspect ratio, and bedding angle on the rolling and sliding contacts are examined. The distribution of normals to the rolling and sliding contacts have different patterns and are concentrated along directions, which are approximately perpendicular to one another. On the other hand, the distribution of all contact normals (combined rolling and sliding) are close to that of rolling contacts, which confirm that rolling is the dominant mechanism. This phenomenon becomes more pronounced for higher intergranular friction angle. Characteristics of the rolling and sliding contacts are also discussed in the context of the force angle, which is the inclination of contact force with respect to the contact normal. Copyright © 2003 John Wiley & Sons, Ltd. [source] Strip layer method for simulation of the three-dimensional deformations of plate and strip rollingINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 3 2004Liu Hong-Min Abstract A new method,the strip layer method (SLM) is used to simulate the three-dimensional deformations of plate and strip rolling process. The rolling deformation zone is divided evenly into a number of layers along the altitudinal direction of plate or strip, every layer plate (strip) is divided into a number of streamline strip elements along metal flow traces, and the streamline strip elements are mapped onto the corresponding rectangle strip elements for analysis and computation. The longitudinal distribution model of the metal lateral displacement is constructed to be a quartic curve, its lateral distribution is expressed as the third-power spline function, and its altitudinal distribution is fitted to be a parabolic curve. Based on the flow theory of plastic mechanics, the three-dimensional deformations and stresses of the deformation zone are analysed and formulated. Compared with the streamline strip element method (SSEM), the strip layer method considers the uneven distributions of stresses and deformations along altitudinal direction, and realizes an accurate analysis and computation. The simulation examples indicate that the method and the model of this paper are in accord with facts, and provide a new reliable engineering-computation method for a three-dimensional mechanics simulation of plate and strip rolling process. Copyright © 2004 John Wiley & Sons, Ltd. [source] Numerical analysis of a new Eulerian,Lagrangian finite element method applied to steady-state hot rolling processesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 5 2005Josef Synka Abstract A finite element code for steady-state hot rolling processes of rigid,visco-plastic materials under plane,strain conditions was developed in a mixed Eulerian,Lagrangian framework. This special set up allows for a direct calculation of the local deformations occurring at the free surfaces outside the contact region between the strip and the work roll. It further simplifies the implementation of displacement boundary conditions, such as the impenetrability condition. When applied to different practical hot rolling situations, ranging from thick slab to ultra-thin strip rolling, the velocity,displacement based model (briefly denoted as vu-model) in this mixed Eulerian,Lagrangian reference system proves to be a robust and efficient method. The vu-model is validated against a solely velocity-based model (vv-model) and against elementary methods based on the Kármán,Siebel and Orowan differential equations. The latter methods, when calibrated, are known to be in line with experimental results for homogeneous deformation cases. For a massive deformation it is further validated against the commercial finite-element software package Abaqus/Explicit. It is shown that the results obtained with the vu-model are in excellent agreement with the predictions of the vv-model and that the vu-model is even more robust than its vv-counterpart. Throughout the study we assumed a rigid cylindrical work roll; only for the homogeneous test case, we also investigated the effect of an elastically deformable work roll within the frame of the Jortner Green's function method. The new modelling approach combines the advantages of conventional Eulerian and Lagrangian modelling concepts and can be extended to three dimensions in a straightforward manner. Copyright © 2004 John Wiley & Sons, Ltd. [source] Kinematics of Robot Fingers with Circular Rolling Contact JointsJOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 6 2003Curtis L. Collins This paper examines the kinematics of robot fingers that use RR subassemblies coupled by rolling contact to provide versatile one degree-of-freedom mechanical joints. A three degree-of-freedom robot finger constructed with these joints is a 6R planar chain with the R-joints coupled together in pairs. The focus is on coupling based on pure rolling of circular cylinders which can be realized by friction contact, gearing, or cable tendons. We derive the forward, inverse and rate kinematics for this 3(RR) open chain. We then focus on the two degree-of-freedom 2(RR) case to illustrate the geometry of the system. An example design of a robot finger that incorporates these joints in order to provide compact movement is provided. © 2003 Wiley Periodicals, Inc. [source] Ranking the contributing risk factors in venous thrombosis in terms of therapeutic potential: Virchow's triad revisitedJOURNAL OF OBSTETRICS AND GYNAECOLOGY RESEARCH (ELECTRONIC), Issue 2 2006Masaki Kiyomura Abstract Aim: Thromboemoblism is an attendant feature of a variety of pathological conditions. We reconsidered Virchow's pathogenetic triad of stasis, humoral factors and vascular wall pathologies in the light of platelet behavior in vivo. Methods: Rat mesenteric microcirculation was examined by intravital microscopy. After isolated rat platelets had been injected i.v. into rats, their behavior in venules was examined under the following conditions: stasis from pressure, hemoconcentration from erythropoietin injections, or endothelial damage from tumor necrosis factor-,. Results: In the endothelial damage group, platelets displayed transient adhesion and rolling, while some platelets exhibited stationary adhesion to venular endothelium. The stasis and hemoconcentration groups exhibited only a slight change in adhesive response. Conclusion: Endothelial dysfunction appears to be the most important contributing factor in the development of venous thrombosis. As such, targeting this dysfunction is suggested for therapeutic intervention. [source] Characterization of Phytoplasmas Associated With Almond Diseases in IranJOURNAL OF PHYTOPATHOLOGY, Issue 11-12 2009L. Zirak Abstract In recent years, almond witches'-broom disease has been prevalent in almond growing areas in the centre and south of Iran. Furthermore, almond trees showing different symptoms of phytoplasma diseases such as little leaf, leaf rolling, dieback of branches, rosette and yellowing were observed in the central regions of Iran. DNA isolated from symptomatic almond trees was used to amplify 16S rDNA and 16S-23S rDNA intergenic spacer (IS) fragments by nested polymerase chain reaction (PCR) using phytoplasma universal primer pairs (P1/P7, R16F2/R2, PA2F/R and NPA2F/R). Phytoplasmas were detected in symptomatic almonds in two major almond-growing regions, Isfahan and ChaharMahal-O-Bakhtiari. Restriction fragment length polymorphism analyses of nested PCR products using endonuclease enzymes HpaII and TaqI revealed that phytoplasmas associated with infected almonds are genetically different. Sequence analyses of amplified fragments of 16S rDNA and IS region indicated that the almond phytoplasmas in Iran are closely related to ,Candidatus (Ca.) Phytoplasma aurantifolia', ,Ca. Phytoplasma phoenicium', ,Ca. Phytoplasma solani' and ,Ca. Phytoplasma trifolii'. The phytoplasmas related to ,Ca. Phytoplasma aurantifolia' were more prevalent than other phytoplasmas in the central regions of Iran. [source] | ||||||||||||||||||||||||||||||||||||||||