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1
Yago, Tadayuki, Jianhua Wu, C. Diana Wey, Arkadiusz G. Klopocki, Cheng Zhu et Rodger P. McEver. « Catch bonds govern adhesion through L-selectin at threshold shear ». Journal of Cell Biology 166, no 6 (13 septembre 2004) : 913–23. http://dx.doi.org/10.1083/jcb.200403144.
Texte intégralRésumé :
Flow-enhanced cell adhesion is an unexplained phenomenon that might result from a transport-dependent increase in on-rates or a force-dependent decrease in off-rates of adhesive bonds. L-selectin requires a threshold shear to support leukocyte rolling on P-selectin glycoprotein ligand-1 (PSGL-1) and other vascular ligands. Low forces decrease L-selectin–PSGL-1 off-rates (catch bonds), whereas higher forces increase off-rates (slip bonds). We determined that a force-dependent decrease in off-rates dictated flow-enhanced rolling of L-selectin–bearing microspheres or neutrophils on PSGL-1. Catch bonds enabled increasing force to convert short-lived tethers into longer-lived tethers, which decreased rolling velocities and increased the regularity of rolling steps as shear rose from the threshold to an optimal value. As shear increased above the optimum, transitions to slip bonds shortened tether lifetimes, which increased rolling velocities and decreased rolling regularity. Thus, force-dependent alterations of bond lifetimes govern L-selectin–dependent cell adhesion below and above the shear optimum. These findings establish the first biological function for catch bonds as a mechanism for flow-enhanced cell adhesion.
2
Chen, Shuqi, et Timothy A. Springer. « An Automatic Braking System That Stabilizes Leukocyte Rolling by an Increase in Selectin Bond Number with Shear ». Journal of Cell Biology 144, no 1 (11 janvier 1999) : 185–200. http://dx.doi.org/10.1083/jcb.144.1.185.
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Wall shear stress in postcapillary venules varies widely within and between tissues and in response to inflammation and exercise. However, the speed at which leukocytes roll in vivo has been shown to be almost constant within a wide range of wall shear stress, i.e., force on the cell. Similarly, rolling velocities on purified selectins and their ligands in vitro tend to plateau. This may be important to enable rolling leukocytes to be exposed uniformly to activating stimuli on endothelium, independent of local hemodynamic conditions. Wall shear stress increases the rate of dissociation of individual selectin–ligand tether bonds exponentially (1, 4) thereby destabilizing rolling. We find that this is compensated by a shear-dependent increase in the number of bonds per rolling step. We also find an increase in the number of microvillous tethers to the substrate. This explains (a) the lack of firm adhesion through selectins at low shear stress or high ligand density, and (b) the stability of rolling on selectins to wide variation in wall shear stress and ligand density, in contrast to rolling on antibodies (14). Furthermore, our data successfully predict the threshold wall shear stress below which rolling does not occur. This is a special case of the more general regulation by shear of the number of bonds, in which the number of bonds falls below one.
3
Wu, Tao, Tadayuki Yago, Jun Yang, Jonathan Miner, Leslie Coburn, Jose A. Lopez, Miguel A. Cruz, Larry V. McIntire, Rodger P. McEver et Cheng Zhu. « Glycoprotein Ibα Forms Catch Bonds with von Willebrand Factor A1 Domain but Not with Mutant A1 Domains Exhibiting Properties of Type 2B von Willebrand Disease. » Blood 110, no 11 (16 novembre 2007) : 293. http://dx.doi.org/10.1182/blood.v110.11.293.293.
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Abstract Interactions between glycoprotein Ibα (GPIbα) and von Willebrand factor (VWF) initiate platelet adhesion to injured vascular surfaces, which is enhanced by arterial blood flow. The flow requirement for adhesion is reduced (i.e., gain-of-function) by single-residue substitutions of the VWF-A1 domain, e.g., R543Q that occurs in some patients with type 2B von Willebrand disease (VWD) and R687E that was designed to exhibit type 2B VWD properties. Yet the mechanisms for flow-enhanced adhesion through GPIbα-VWF interactions are not understood. By probing single bonds with atomic force microscopy, we showed that lifetimes of GPIbα/VWF-A1 bonds first increased (catch) and then decreased (slip) with increasing force applied to the bond. Remarkably, the catch bond aspect of the GPIbα/VWF-A1 bonds was eliminated by the R543Q and R687E mutations, which exhibited slip bonds only with prolonged lifetimes at low forces. Flow chamber experiments showed that catch-slip transitional bonds governed flow-enhanced rolling of platelets and GPIbα-coated microspheres on wild-type A1, such that rolling velocities first decreased and then increased with increasing flow. By contrast, slip bonds governed rolling velocities on R543Q and R687E A1 mutants, which increased monotonically with increasing flow. We changed fluid viscosity by adding Ficoll to the medium, tether force by using microspheres of different radii, and platelet deformability by using a chemical fixative. The rolling velocity vs. flow curves aligned with tether force but not with transport parameters and were minimally affected by fixation, which respectively rule out transport-enhanced GPIbα/VWF-A1 bond formation and force-induced enlargement of platelet-surface contact area as the causes for flow-enhanced rolling. Flowing platelets agglutinated with microspheres bearing R543Q and R687E A1 mutants but not with those bearing wild-type A1, suggesting that GPIbα/VWF-A1 catch bonds prevent agglutination of circulating platelets via binding to VWF multimers and that platelet agglutination in patients with type 2B VWD may be explained by the prolonged lifetimes at low forces resulting from elimination of catch bonds in the interactions of GPIbα with VWF-A1 mutants.
4
Lawrence, M. B., et T. A. Springer. « Neutrophils roll on E-selectin. » Journal of Immunology 151, no 11 (1 décembre 1993) : 6338–46. http://dx.doi.org/10.4049/jimmunol.151.11.6338.
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Abstract Using flow conditions that simulate those in post capillary venules, we have found that neutrophils attach and roll on a substrate bearing purified E-selectin. E-selectin resembles P-selectin (CD62) with regard to the dependence of attachment efficiency on wall shear stress and selectin density. In contrast, once attached, neutrophils form rolling adhesions on E-selectin that are much stronger than those on P-selectin. Rolling velocities on E-selectin are slower and have less variance than on P-selectin. With increasing shear stress, rolling velocities reach a plateau level that is dependent on E-selectin density, suggesting that the number of receptor-ligand bonds and the bond dissociation rate limit rolling velocity, and that the bonds are not broken by the applied force.
5
Vivian, R., et C. Auret. « A comparative analysis of returns of various financial asset classes in South Africa : a triumph of bonds ? » Southern African Business Review 18, no 3 (29 janvier 2019) : 175–95. http://dx.doi.org/10.25159/1998-8125/5693.
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There is a popular view that equities always outperform other financial asset classes; especially bonds. This study investigates the performance of three common asset classes to determine whether or not this view is validated in South Africa. Conceptually, the popular view is irrational. If one class consistently and materially outperforms other asset classes, in the absence of other reasons, the other asset classes would disappear. Accordingly, rationally, in the long run and on a risk-adjusted basis, returns on all asset classes should conceptually more or less converge. The results from this study, which concentrates on equities, bonds and cash, show that in South Africa, even before adjusting for risk, there was no material difference between the returns of equities over long bonds over the 27-year period covered by this study (1986–2013). This is equally true for other shorter fixed periods with the end-date (28 February 2013) being the focal point. It is even more evident that bonds outperform equities when a system of rolling periods is used. On a nominal basis (before adjusting for risk), over any randomly selected rolling period, bonds outperform equities in six of the seven categories. This study does not take tax into consideration. After adjusting for risk using the Sharpe ratio or other risk measures, bonds outperformed equities.
6
Lei, X., M. B. Lawrence et C. Dong. « Influence of Cell Deformation on Leukocyte Rolling Adhesion in Shear Flow ». Journal of Biomechanical Engineering 121, no 6 (1 décembre 1999) : 636–43. http://dx.doi.org/10.1115/1.2800866.
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Blood cell interaction with vascular endothelium is important in microcirculation, where rolling adhesion of circulating leukocytes along the surface of endothelial cells is a prerequisite for leukocyte emigration under flow conditions. HL-60 cell rolling adhesion to surface-immobilized P-selectin in shear flow was investigated using a side-view flow chamber, which permitted measurements of cell deformation and cell-substrate contact length as well as cell rolling velocity. A two-dimensional model was developed based on the assumption that fluid energy input to a rolling cell was essentially distributed into two parts: cytoplasmic viscous dissipation, and energy needed to break adhesion bonds between the rolling cell and its substrate. The flow fields of extracellular fluid and intracellular cytoplasm were solved using finite element methods with a deformable cell membrane represented by an elastic ring. The adhesion energy loss was calculated based on receptor-ligand kinetics equations. It was found that, as a result of shear-flow-induced cell deformation, cell-substrate contact area under high wall shear stresses (20 dyn/cm2) could be as much as twice of that under low stresses (0.5 dyn/cm2). An increase in contact area may cause more energy dissipation to both adhesion bonds and viscous cytoplasm, whereas the fluid energy input may decrease due to the flattened cell shape. Our model predicts that leukocyte rolling velocity will reach a plateau as shear stress increases, which agrees with both in vivo and in vitro experimental observations.
7
Lou, Jizhong, Tadayuki Yago, Arkadiusz G. Klopocki, Padmaja Mehta, Wei Chen, Veronika I. Zarnitsyna, Nicolai V. Bovin, Cheng Zhu et Rodger P. McEver. « Flow-enhanced adhesion regulated by a selectin interdomain hinge ». Journal of Cell Biology 174, no 7 (21 septembre 2006) : 1107–17. http://dx.doi.org/10.1083/jcb.200606056.
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L-selectin requires a threshold shear to enable leukocytes to tether to and roll on vascular surfaces. Transport mechanisms govern flow-enhanced tethering, whereas force governs flow-enhanced rolling by prolonging the lifetimes of L-selectin–ligand complexes (catch bonds). Using selectin crystal structures, molecular dynamics simulations, site-directed mutagenesis, single-molecule force and kinetics experiments, Monte Carlo modeling, and flow chamber adhesion studies, we show that eliminating a hydrogen bond to increase the flexibility of an interdomain hinge in L-selectin reduced the shear threshold for adhesion via two mechanisms. One affects the on-rate by increasing tethering through greater rotational diffusion. The other affects the off-rate by strengthening rolling through augmented catch bonds with longer lifetimes at smaller forces. By forcing open the hinge angle, ligand may slide across its interface with L-selectin to promote rebinding, thereby providing a mechanism for catch bonds. Thus, allosteric changes remote from the ligand-binding interface regulate both bond formation and dissociation.
8
Li, Long, Wei Kang et Jizeng Wang. « Mechanical Model for Catch-Bond-Mediated Cell Adhesion in Shear Flow ». International Journal of Molecular Sciences 21, no 2 (16 janvier 2020) : 584. http://dx.doi.org/10.3390/ijms21020584.
Texte intégralRésumé :
Catch bond, whose lifetime increases with applied tensile force, can often mediate rolling adhesion of cells in a hydrodynamic environment. However, the mechanical mechanism governing the kinetics of rolling adhesion of cells through catch-bond under shear flow is not yet clear. In this study, a mechanical model is proposed for catch-bond-mediated cell adhesion in shear flow. The stochastic reaction of bond formation and dissociation is described as a Markovian process, whereas the dynamic motion of cells follows classical analytical mechanics. The steady state of cells significantly depends on the shear rate of flow. The upper and lower critical shear rates required for cell detachment and attachment are extracted, respectively. When the shear rate increases from the lower threshold to the upper threshold, cell rolling became slower and more regular, implying the flow-enhanced adhesion phenomenon. Our results suggest that this flow-enhanced stability of rolling adhesion is attributed to the competition between stochastic reactions of bonds and dynamics of cell rolling, instead of force lengthening the lifetime of catch bonds, thereby challenging the current view in understanding the mechanism behind this flow-enhanced adhesion phenomenon. Moreover, the loading history of flow defining bistability of cell adhesion in shear flow is predicted. These theoretical predictions are verified by Monte Carlo simulations and are related to the experimental observations reported in literature.
9
Rutkowski, Marek. « Self-Financing Trading Strategies for Sliding, Rolling-Horizon, and Consol Bonds ». Mathematical Finance 9, no 4 (octobre 1999) : 361–85. http://dx.doi.org/10.1111/1467-9965.00074.
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Tabassum, Hassina, Ruqiang Zou, Asif Mahmood, Zibin Liang et Shaojun Guo. « A catalyst-free synthesis of B, N co-doped graphene nanostructures with tunable dimensions as highly efficient metal free dual electrocatalysts ». Journal of Materials Chemistry A 4, no 42 (2016) : 16469–75. http://dx.doi.org/10.1039/c6ta07214c.
Texte intégralRésumé :
A catalyst-free synthetic strategy of self-squeezing and rolling of B, N co-doped graphene nanosheets to nanotubes was reported, which exhibits tunable dimensions and atomic bonds as metal-free dual electrocatalysts by using polyethylene glycol as the directing agent..
11
Côté, Fabien, Dominique Lévesque et Jean-Pierre Perreault. « Natural 2′,5′-Phosphodiester Bonds Found at the Ligation Sites of Peach Latent Mosaic Viroid ». Journal of Virology 75, no 1 (1 janvier 2001) : 19–25. http://dx.doi.org/10.1128/jvi.75.1.19-25.2001.
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ABSTRACT Peach latent mosaic viroid (PLMVd) is a circular RNA pathogen that replicates in a DNA-independent fashion via a rolling circle mechanism. PLMVd has been shown to self-ligate in vitro primarily via the formation of 2′,5′-phosphodiester bonds; however, in vivo the occurrence and necessity of this nonenzymatic mechanism are not evident. Here, we unequivocally report the presence of 2′,5′-phosphodiester bonds at the ligation site of circular PLMVd strands isolated from infected peach leaves. These bonds serve to close the linear conformers (i.e., intermediates), yielding circular ones. Furthermore, these bonds are shown to stabilize the replicational circular templates, resulting in a significant advantage in terms of viroid viability. Although the mechanism responsible for the formation of these 2′,5′-phosphodiester bonds remains to be elucidated, a hypothesis describing in vivo nonenzymatic self-ligation is proposed. Most significantly, our results clearly show that 2′,5′-phosphodiester bonds are still present in nature and that they are of biological importance.
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Morikis, Vasilios A., Shannon Chase, Ted Wun, Elliot L. Chaikof, John L. Magnani et Scott I. Simon. « Selectin catch-bonds mechanotransduce integrin activation and neutrophil arrest on inflamed endothelium under shear flow ». Blood 130, no 19 (9 novembre 2017) : 2101–10. http://dx.doi.org/10.1182/blood-2017-05-783027.
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Key Points Neutrophils rolling on E-selectin form catch-bonds with L-selectin that mechanosignal β2-integrin bond formation with intracellular adhesion molecule 1. Rivipansel blocks E-selectin recognition of sLex on L-selectin, thereby antagonizing outside-in signaling of high-affinity β2-integrin.
13
Pospieszalska, Maria K., Alexander Zarbock, John E. Pickard et Klaus Ley. « Event-Tracking Model of Adhesion Identifies Load-Bearing Bonds in Rolling Leukocytes ». Microcirculation 16, no 8 (9 novembre 2009) : 781. http://dx.doi.org/10.3109/10739680903298228.
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Pospieszalska, Maria K., Alexander Zarbock, John E. Pickard et Klaus Ley. « Event-Tracking Model of Adhesion Identifies Load-Bearing Bonds in Rolling Leukocytes ». Microcirculation 16, no 2 (janvier 2009) : 115–30. http://dx.doi.org/10.1080/10739680802462792.
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Wachowski, Marcin, Robert Kosturek, Lucjan Śnieżek, Sebastian Mróz, Andrzej Stefanik et Piotr Szota. « The Effect of Post-Weld Hot-Rolling on the Properties of Explosively Welded Mg/Al/Ti Multilayer Composite ». Materials 13, no 8 (19 avril 2020) : 1930. http://dx.doi.org/10.3390/ma13081930.
Texte intégralRésumé :
The paper describes an investigation of an explosively welded Mg/Al/Ti multilayer composite. Following the welding, the composite was subjected to hot-rolling in three different temperatures: 300 °C, 350 °C and 400 °C, with a total relative strain of 30%. The rolling speed was 0.2 m/s. The investigation of the composite properties involves microhardness analysis and mini-specimen tensile tests of the joints. The composite Mg/Al and Al/Ti bonds in the as-welded state and after rolling in 400 °C were subjected to microstructure analysis using scanning electron (SEM) and transmission electron microscopy (TEM). In the Al/Ti interface, the presence of melted zones with localized intermetallic precipitates has been reported in the as-welded state, and it has been stated that hot-rolling results in precipitation of intermetallic particles from the melted zone. The application of the hot-rolling process causes the formation of a continuous layer in the Mg/Al joint, consisting of two intermetallic phases, Mg2Al3 (β) and Mg17Al12 (γ).
16
Clark, Rachael A., Harold P. Erickson et Timothy A. Springer. « Tenascin Supports Lymphocyte Rolling ». Journal of Cell Biology 137, no 3 (5 mai 1997) : 755–65. http://dx.doi.org/10.1083/jcb.137.3.755.
Texte intégralRésumé :
Tenascin is a large extracellular matrix molecule expressed at specific sites in the adult, including immune system tissues such as the bone marrow, thymus, spleen, and T cell areas of lymph nodes. Tenascin has been reported to have both adhesive and anti-adhesive effects in static assays. We report here that tenascin supports the tethering and rolling of lymphocytes and lymphoblastic cell lines under flow conditions. Binding was calcium dependent and was not inhibited by treatment of lymphocytes with O-glycoprotease or a panel of glycosidases including neuraminidase and heparitinase but was inhibited by treatment of cells with proteinase K. Binding was to the fibrinogen-like terminal domain of tenascin as determined by antibody blocking studies and binding to recombinant tenascin proteins. When compared to rolling of the same cell type on E-selectin, rolling on tenascin was found to be smoother at all shear stresses tested, suggesting that cells formed a larger number of bonds on the tenascin substrate than on the E-selectin substrate. When protein plating densities were adjusted to give similar profiles of cell detachment under increasing shears, the density of tenascin was 8.5-fold greater than that of E-selectin. Binding to tenascin was not dependent on any molecules previously identified as tenascin receptors and is likely to involve a novel tenascin receptor on lymphocytes. We postulate that the ability of tenascin to support lymphocyte rolling may reflect its ability to support cell migration and that this interaction may be used by lymphocytes migrating through secondary lymphoid organs.
17
Dwir, Oren, Ariel Solomon, Shmuel Mangan, Geoffrey S. Kansas, Ulrich S. Schwarz et Ronen Alon. « Avidity enhancement of L-selectin bonds by flow ». Journal of Cell Biology 163, no 3 (3 novembre 2003) : 649–59. http://dx.doi.org/10.1083/jcb.200303134.
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L-selectin is a key lectin essential for leukocyte capture and rolling on vessel walls. Functional adhesion of L-selectin requires a minimal threshold of hydrodynamic shear. Using high temporal resolution videomicroscopy, we now report that L-selectin engages its ligands through exceptionally labile adhesive bonds (tethers) even below this shear threshold. These tethers share a lifetime of 4 ms on distinct physiological ligands, two orders of magnitude shorter than the lifetime of the P-selectin–PSGL-1 bond. Below threshold shear, tether duration is not shortened by elevated shear stresses. However, above the shear threshold, selectin tethers undergo 14-fold stabilization by shear-driven leukocyte transport. Notably, the cytoplasmic tail of L-selectin contributes to this stabilization only above the shear threshold. These properties are not shared by P-selectin– or VLA-4–mediated tethers. L-selectin tethers appear adapted to undergo rapid avidity enhancement by cellular transport, a specialized mechanism not used by any other known adhesion receptor.
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Muzychuk, Vasyl. « STUDY OF THE DEFORMED STATE CONNECTION OF THE PISTON WITH THE ROD OF THE UNREGULATED PISTON PUMP ». Vibrations in engineering and technology, no 3(98) (30 octobre 2020) : 95–103. http://dx.doi.org/10.37128/2306-8744-2020-3-10.
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The technological processes of cold rolling of precision workpieces and ring parts, rolling of pipes, rolling of piston-connecting rod axial-rotor piston pump, which are a kind of processing of metals by pressure and contain changes in the shape of workpieces according to performing relative to the axis of the workpiece radial rotational motion. The workpiece can remain stationary or rotate. It is shown that by means of technological process of rolling of pipes, unrolling of preparations various hollow axisymmetric metal products receive, the specified processes are combined by the mechanism of deformation, namely: at them two deformations of compression and one - tension are realized. This mechanical deformation scheme creates favorable conditions for plastic deformation, because intercrystalline displacements are difficult, leading to the violation of mechanical bonds, and plastic deformation occurs mainly due to intracrystalline displacements. It is shown that in the process of connecting the piston-connecting rod in compliance with the process parameters (output supply pressure, feed rate, leaving time) the value of the specified gap either exceeds the maximum value or decreases to the value at which the next operation of the piston-connecting rod spell. The deformed state in the technological operation of rolling the piston-connecting rod pair at different stages of shape change is studied, the process control mechanism is revealed, which prevents the defect in the form of deviation from the regulated gap after rolling between the piston and the connecting rod. The used resource of plasticity at different stages of rolling is calculated, the deformability of the piston workpiece in the rolling process is estimated.
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Pawar, Parag, Sameer Jadhav, Charles D. Eggleton et Konstantinos Konstantopoulos. « Roles of cell and microvillus deformation and receptor-ligand binding kinetics in cell rolling ». American Journal of Physiology-Heart and Circulatory Physiology 295, no 4 (octobre 2008) : H1439—H1450. http://dx.doi.org/10.1152/ajpheart.91536.2007.
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Polymorphonuclear leukocyte (PMN) recruitment to sites of inflammation is initiated by selectin-mediated PMN tethering and rolling on activated endothelium under flow. Cell rolling is modulated by bulk cell deformation (mesoscale), microvillus deformability (microscale), and receptor-ligand binding kinetics (nanoscale). Selectin-ligand bonds exhibit a catch-slip bond behavior, and their dissociation is governed not only by the force but also by the force history. Whereas previous theoretical models have studied the significance of these three “length scales” in isolation, how their interplay affects cell rolling has yet to be resolved. We therefore developed a three-dimensional computational model that integrates the aforementioned length scales to delineate their relative contributions to PMN rolling. Our simulations predict that the catch-slip bond behavior and to a lesser extent bulk cell deformation are responsible for the shear threshold phenomenon. Cells bearing deformable rather than rigid microvilli roll slower only at high P-selectin site densities and elevated levels of shear (≥400 s−1). The more compliant cells (membrance stiffness = 1.2 dyn/cm) rolled slower than cells with a membrane stiffness of 3.0 dyn/cm at shear rates >50 s−1. In summary, our model demonstrates that cell rolling over a ligand-coated surface is a highly coordinated process characterized by a complex interplay between forces acting on three distinct length scales.
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KING, MICHAEL R. « SCALE INVARIANCE IN SELECTIN-MEDIATED LEUKOCYTE ROLLING ». Fractals 12, no 02 (juin 2004) : 235–41. http://dx.doi.org/10.1142/s0218348x04002525.
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White blood cells slowly roll along the walls of blood vessels, due to the coordinated formation and breakage of chemical selectin-carbohydrate bonds. Using detailed computer simulations of cells rolling on a selectin surface under flow, we show the time series of the cell translational velocity to be fractal in nature over time scales ranging from 22–211 ms. A rescaled range analysis was performed to determine the Hurst exponent of the velocity time series, for simulations of cells rolling on either a uniform or punctate distribution of P-selectin molecules. The rolling behavior was found to exhibit two very distinct regimes, with a negative Hurst exponent ranging from -(1.2-0.6) over time scales of 23-27 ms, and a positive Hurst exponent of +0.47±0.03 over time scales of 27-211 ms. The short-time Hurst exponent was found to be a strong function of the molecular distribution and also a function of average molecular density, while the long-time Hurst exponent was unchanged over all conditions studied. The implication is that the short-time adhesive behavior of cells interacting with a reactive surface is sensitive to the spatial arrangement of molecules, and the total number of molecules on the surface.
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Erlwein-Sayer, Christina. « Macroeconomic News Sentiment : Enhanced Risk Assessment for Sovereign Bonds ». Risks 6, no 4 (7 décembre 2018) : 141. http://dx.doi.org/10.3390/risks6040141.
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We enhance the modelling and risk assessment of sovereign bond spreads by taking into account quantitative information gained from macro-economic news sentiment. We investigate sovereign bonds spreads of five European countries and improve the prediction of spread changes by incorporating news sentiment from relevant entities and macro-economic topics. In particular, we create daily news sentiment series from sentiment scores as well as positive and negative news volume and investigate their effects on yield spreads and spread volatility. We conduct a correlation and rolling correlation analysis between sovereign bond spreads and accumulated sentiment series and analyse changing correlation patterns over time. Market regimes are detected through correlation series and the impact of news sentiment on sovereign bonds in different market circumstances is investigated. We find best-suited external variables for forecasts in an ARIMAX model set-up. Error measures for forecasts of spread changes and volatility proxies are improved when sentiment is considered. These findings are then utilised to monitor sovereign bonds from European countries and detect changing risks through time.
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Liu, Hong Xi, Ye Hua Jiang, Rong Zhou, Zu Lai Li et Bao Yin Tang. « Investigating the Mechanical Property and Rolling Contact Fatigue Life of Diamond-Like Carbon Films on Bearing Steel ». Materials Science Forum 575-578 (avril 2008) : 990–95. http://dx.doi.org/10.4028/www.scientific.net/msf.575-578.990.
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Microstructure and properties of plasma immersion ion implantation and deposition diamond-like carbon (DLC) films on bearing steel substrate were studied. Raman spectroscopy analysis indicates that PIII&D DLC consists of a mixture of amorphous and crystalline phases, with a variable ratio of sp2/sp3 carbon bonds, and the sp3 bonds content more than 10%. The nanohardness (H) and the elastic modulus (E) of DLC films measurement indicate that the maximum H (E) value is 40GPa (430GPa). The corrosion polarization curves prove that the corrosion resistance of DLC samples is much better than that of substrate. The friction and wear behaviors and rolling contact fatigue (RCF) life of these samples show that the friction coefficient decrease from 0.87 to 0.2; the L10 , L50 , La and L life of treated sample increases by 9.1, 3.2, 2.5 and 2.4 times, respectively. The RCF life scatter extent of treated samples is improved significantly.
23
Reboux, S., G. Richardson et O. E. Jensen. « Bond tilting and sliding friction in a model of cell adhesion ». Proceedings of the Royal Society A : Mathematical, Physical and Engineering Sciences 464, no 2090 (4 décembre 2007) : 447–67. http://dx.doi.org/10.1098/rspa.2007.0210.
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As a simple theoretical model of a cell adhering to a biological interface, we consider a rigid cylinder moving in a viscous shear flow near a wall. Adhesion forces arise through intermolecular bonds between receptors on the cell and their ligands on the wall, which form flexible tethers that can stretch and tilt as the base of the cell moves past the wall; binding kinetics is assumed to follow a standard model for slip bonds. By introducing a finite resistance to bond tilting, we use our model to explore the territory between previous theoretical models that allow for either zero or infinite resistance to bond rotation. A microscale calculation (for two parallel sliding plates) reveals a nonlinear force–speed relation arising from bond formation, tilting and breakage. Two distinct types of macroscale cell motion are then predicted: either bonds adhere strongly and the cell rolls (or tank treads) over the wall without slipping, or the cell moves near its free-stream speed with bonds providing weak frictional resistance to sliding. The model predicts bistability between these two states, implying that at critical shear rates the system can switch abruptly between rolling and free sliding, and suggesting that sliding friction arising through bond tilting may play a significant dynamical role in some cell-adhesion applications.
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Shapovalov, Vladimir, Petr Shcherbak, Pavel Kharlamov, Tatiana Sajamova et Denis Ryabysh. « Improving the energy efficiency of power transmissions of a rolling stock on the basis of dynamic anisotropy of frictional contact ». E3S Web of Conferences 104 (2019) : 01002. http://dx.doi.org/10.1051/e3sconf/201910401002.
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The analysis showed the following tendencies of development and energy efficiency of designs of gearboxes for track machines: provision of a maximum level of efficiency, removal of rupture of a stream of the passed capacity, provision of a high level of reliability, decrease of power input on gearbox work, provision of convenience, simplicity of service and steering, engine braking maintenance, and also maintenance of a relatively low cost. The above-mentioned tasks are performed by including clutch pinion gears with the built in frictional amplifier elements in an automatic gearbox, and also during the effect of dynamic anisotropy of frictional bonds. Besides a torque transfer, the clutch gear carries out a safety clutch function. That means that there is sliding at a high rotational power. Factor of strengthening of the given link is Кstr → ∞ due to occurence of dynamic anisotropy of frictional bonds. Physical and mechanical characteristics of contacting surfaces are formed in the course of dynamic interaction of roughnesses in friction units at modes of dry and boundary friction. Essential-nonlinear friction processes, interconnected with dynamic processes on the contact area, define values of target characteristics of frictional system. They can fluctuate in a very wide range. The friction factor fmp for the same friction units at preservation of constant conditions and friction parameters can vary from zero to infinity that is an essence of dynamic anisotropy of frictional bonds.
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Tangelder, GJ, et KE Arfors. « Inhibition of leukocyte rolling in venules by protamine and sulfated polysaccharides ». Blood 77, no 7 (1 avril 1991) : 1565–71. http://dx.doi.org/10.1182/blood.v77.7.1565.1565.
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Abstract Intravital video microscopy was used to investigate leukocyte margination in 80 mesenteric venules (19 to 54 microns) of 50 anesthetized rabbits. After intravenous (IV) bolus injection, sulfated polysaccharides reduced in a reversible and dose-dependent way the number of leukocytes rolling slowly along the venular wall. The presence of sulfate groups is essential because other negatively charged or neutral polysaccharides had no effect. It was not caused by an increase in RBC velocity or chelation of divalent cations. Inhibition by sulfated dextrans (n = 7) was independent of molecular weight (mol wt 13,000 to 500,000) but was influenced by the average number of sulfate groups per monosaccharide. With substitution 0.13, the 90%-inhibition dose was 104 mg/kg, with 0.7 it was 56 mg/kg, and between substitution 1 and 2 it ranged from 20 to 23 mg/kg. At 100 mg/kg, plasma concentration was 0.6 to 0.7 mg/mL. Xylan sulfate (mol wt 6,000, substitution 1.8) gave 90% inhibition at 11 mg/kg, and heparin gave 90% inhibition at 97 mg/kg. Duration of inhibition (0.5 to 2 hours) depended on mol wt and appeared to be related to plasma clearance. Because protamine also inhibited rolling (12 mg/kg; less than 10 minutes), we propose that repetitive formation and breakup of ionic bonds between sulfate groups and positively charged amino acids is involved in leukocyte rolling. During inhibition of rolling, systemic lymphocyte/monocyte levels appeared to increase. Granulocyte counts did not change, indicating that rolling is not the main mechanism responsible for the marginal granulocyte pool.
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Tangelder, GJ, et KE Arfors. « Inhibition of leukocyte rolling in venules by protamine and sulfated polysaccharides ». Blood 77, no 7 (1 avril 1991) : 1565–71. http://dx.doi.org/10.1182/blood.v77.7.1565.bloodjournal7771565.
Texte intégralRésumé :
Intravital video microscopy was used to investigate leukocyte margination in 80 mesenteric venules (19 to 54 microns) of 50 anesthetized rabbits. After intravenous (IV) bolus injection, sulfated polysaccharides reduced in a reversible and dose-dependent way the number of leukocytes rolling slowly along the venular wall. The presence of sulfate groups is essential because other negatively charged or neutral polysaccharides had no effect. It was not caused by an increase in RBC velocity or chelation of divalent cations. Inhibition by sulfated dextrans (n = 7) was independent of molecular weight (mol wt 13,000 to 500,000) but was influenced by the average number of sulfate groups per monosaccharide. With substitution 0.13, the 90%-inhibition dose was 104 mg/kg, with 0.7 it was 56 mg/kg, and between substitution 1 and 2 it ranged from 20 to 23 mg/kg. At 100 mg/kg, plasma concentration was 0.6 to 0.7 mg/mL. Xylan sulfate (mol wt 6,000, substitution 1.8) gave 90% inhibition at 11 mg/kg, and heparin gave 90% inhibition at 97 mg/kg. Duration of inhibition (0.5 to 2 hours) depended on mol wt and appeared to be related to plasma clearance. Because protamine also inhibited rolling (12 mg/kg; less than 10 minutes), we propose that repetitive formation and breakup of ionic bonds between sulfate groups and positively charged amino acids is involved in leukocyte rolling. During inhibition of rolling, systemic lymphocyte/monocyte levels appeared to increase. Granulocyte counts did not change, indicating that rolling is not the main mechanism responsible for the marginal granulocyte pool.
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Dixit, Neha, et Scott Simon. « The LFA-1/ICAM-1 bond : A Spatio-Temporal Cue in PMN Recruitment in Acute Inflammation (140.3) ». Journal of Immunology 184, no 1_Supplement (1 avril 2010) : 140.3. http://dx.doi.org/10.4049/jimmunol.184.supp.140.3.
Texte intégralRésumé :
Abstract Polymorphonuclear leukocyte (PMN) adhesion to the inflamed endothelium is in part mediated by LFA-1(CD11a/CD18) which recognizes its ligand ICAM-1. It has long been known that ICAM-1 rapidly forms homodimers and this conformation supports stable bonds specifically with high affinity LFA-1 on the PMN in the presence of shear flow. We hypothesize that shear stress on these dimeric pairs of bonds between high affinity LFA-1 and ICAM-1 result in intracellular signaling that serves as a gatekeeper in the transition from PMN arrest to a migratory phenotype. Imaging PMN rolling on an inflammatory mimetic substrate expressing allosteric activating and blocking antibodies to CD18 under shear flow revealed that calcium flux as well as Talin recruitment was mediated primarily through shear stress acting on high affinity CD18 bonds. Immunofluorescence revealed colocalization of cytoplasmic F-actin, Talin, Rap-1, and phospho-Src within regions correlating with high affinity clusters of LFA-1. In summary, these data sets reveal that an integrin mediated outside-in signal is dependent on shear and the affinity of LFA-1 for its ligand ICAM-1 and that a minimum dimerization of high affinity LFA-1/ICAM-1 bonds elicits the assembly of a macromolecular complex that provides a key navigational step in the transition from PMN arrest to a migratory phenotype.
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Zhao, Yihua, Shu Chien, Richard Skalak et Herbert H. Lipowsky. « Leukocyte Rolling in Rat Mesentery Venules : Distribution of Adhesion Bonds and the Effects of Cytoactive Agents ». Annals of Biomedical Engineering 29, no 5 (mai 2001) : 360–72. http://dx.doi.org/10.1114/1.1366676.
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Madhavan, Vinodh, et Rakesh Arrawatia. « Relative Efficiency of G8 Sovereign Credit Default Swaps and Bond Scrips : An Adaptive Market Hypothesis Perspective ». Studies in Microeconomics 4, no 2 (26 septembre 2016) : 127–50. http://dx.doi.org/10.1177/2321022216649479.
Texte intégralRésumé :
This article is aimed at examining the degree of efficiency exhibited by the sovereign credit default swaps (SCDS) and the sovereign bonds (SBs) pertaining to the G8 countries, namely, US, UK, Japan, Germany, Italy, France and Russia, from an Adaptive Market Hypothesis (AMH) perspective. At the outset, the authors employ rolling AR(1)–GARCH(1,1) filter so as to remove short-term dependency in the different time series considered for this study. The AR(1)–GARCH(1,1)-filtered rolling standardized residuals were then subjected to Mandelbrot’s classical R/S test so as to obtain rolling Hurst exponents. Subsequently, the evolving efficiencies of G8 SCDS and SB scrips as reflected by the scrip-wise rolling Hurst exponents are made available. In doing so, scrip-wise transient inefficiencies, as characterized by periods that exhibit strong evidence of long memory, were identified. The authors then offer a ranking of G8 SCDS and SB scrips, in the decreasing order of relative efficiency, based on proportion of scrip-wise rolling windows that exhibited strong evidence of long memory. The findings pertaining to this study are as follows. First, SBs pertaining to UK, Japan, US, France and Russia were found to be the most efficient, while SBs pertaining to Russia were found to be the least efficient. Second, when it comes to SCDS, Russian SCDS scrips were found to be relatively more efficient than the Russian SBs. Having said so, G8 SCDS scrips pertaining to the other countries were found to be inefficient vis-à-vis their respective SBs. Of all the G8 countries, US was the only country wherein no strong evidence of long memory was witnessed in SCDS and/or SB scrips. Finally, there is discernable difference in the degree of efficiency exhibited by G8 SCDS scrips vis-à-vis their underlying reference obligations (ROs).
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Zhao, Yanling, Yuan Jin, Chengyi Pan, Chuanwang Wu, Xueyu Yuan, Gang Zhou et Wenguang Han. « Characterization of Bond Fracture in Discrete Groove Wear of Cageless Ball Bearings ». Materials 15, no 19 (27 septembre 2022) : 6711. http://dx.doi.org/10.3390/ma15196711.
Texte intégralRésumé :
Cageless ball bearings with discrete grooves in the outer raceway enable the dispersion of rolling elements. Once worn, the discrete groove can cause the rolling element to discretely fail. This paper presents the discrete element method to investigate the wear of discrete grooves in cageless bearings from the standpoint of bond fracture. In conjunction with the structural characteristics of bearing races with discrete slots, we propose a hexagonal close-spaced spherical particle arrangement, in which the discrete slots are discretized into particles of the same size that are connected by bonds. The contact model and contact force equation between the rolling elements and the aggregate elements are established, and the external force on the aggregate elements is calculated. Under the influence of an external force and the arrangement of particles in the aggregate element, the internal force transfer equation of different layers and different particles is derived, and the internal force of the particles in the aggregate unit is calculated. In accordance with Hertz–Mindline theory, the bonding model of discrete groove particles is established, the size of the particle shedding cohesive force during bond fracture is determined, and the wear degree of discrete grooves is characterized by comparing the cohesive force and internal force. Numerical solutions and wear tests are combined. Bond fracture can accurately characterize the wear of discrete grooves. This approach offers theoretical guidance for cageless bearing design.
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Nandini Seal et Soumya Mukherjee. « A Study on the Performance of Mutual Funds of Indian AMCs ». Management Journal for Advanced Research 2, no 6 (31 décembre 2022) : 16–23. http://dx.doi.org/10.54741/mjar.2.6.4.
Texte intégralRésumé :
A mutual fund is a pool of money managed by an Asset Management Company (AMC) that collect funds from different individuals as well as institutional investors, and invest those funds in various securities, capital assets such as bonds, real estates, stocks as well as in mutual funds. Most of the Asset Management Companies have different categories of equity mutual funds depending upon the risk associated with such investments. In this case, trailing return and rolling return indicate the performance of a mutual fund. However, a long-term investor has to consider other factors associated with such mutual funds (like asset under management, expenses ratio, number of stocks, and experience of the management) to finalise the selection of mutual funds.
In this research paper, an attempt has been made to identify the relationship among the performance of selected equity mutual funds and the parameters considered by the investors for selecting the fund. 't-statistic’ has been used to identify such relationship.
This research shows that there is no relationship between trailing return of any kinds of Equity mutual funds and the selected parameters by the investors. However, number of stocks and experience of management have a little impact on the rolling return of equity large cap mutual funds and Assets under management has a little impact on rolling return in case of mid-cap mutual fund only.
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Shash, Mayssa, et Hasan Hsamou. « Experimental study on triblogical behaviors of PA6 and PTFE polymers in the case of rolling friction ». Association of Arab Universities Journal of Engineering Sciences 27, no 3 (30 septembre 2020) : 138–49. http://dx.doi.org/10.33261/jaaru.2020.27.3.015.
Texte intégralRésumé :
Rolling/sliding contacts, such as rolling-element bearings or gears, are a keystone of many machines, which could not properly operate in absence of these components. Machine elements of this kind are typically made of certain variants of steel, whereby hardening processes are carried out in order to increase lifetime and reduce wear. Furthermore, proper lubrication of these tribo-systems is inevitable in order to guarantee a safe operation throughout the component’s lifetime. In recent years high performance polymers, such as Polyether ether ketone (PEEK) or polyamid 46 (PA46), have become an option for application in rolling/sliding contacts. Due to the low density and effective manufacturing processes, such as injection moulding, polymers enable lightweight design solutions under relatively low cost. A comparative investigation based on tribological properties including the friction and wear behaviour of two polymers (Polyamide 6, Polytetrafluoroethylene) was researched in this study. Where samples were prepared by machining for precast cylinders of these materials, and experiments were carried out using a device designed for this purpose, with two parameters (rolling speeds and loads) in select. The morphology of the polymeric transfer film which plays a lubricating role in the dry operation conditions was observed for both materials. The obtained results showed that the friction feature of PTFE was better than that of PA 6 which released high sounds during testing duo to adhesion bonds with metallic counterface. The main wear mechanism of polyamide was micro mechanical machining and deformation, while was adhesive wear for PTFE, and the wear rate of PTFE was very high compared to PA 6 which suffered from delamination wear in some cases
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Jurkšas, Linas, Deimantė Teresienė et Rasa Kanapickiene. « Liquidity risk : Intraday liquidity and price spillovers in euro area sovereign bond markets ». Risk Governance and Control : Financial Markets and Institutions 11, no 2 (2021) : 18–31. http://dx.doi.org/10.22495/rgcv11i2p2.
Texte intégralRésumé :
The purpose of this paper is to determine the cross-market liquidity and price spillover effects across euro area sovereign bond markets. The analysis is carried out with the constructed minute frequency order-book dataset from 2011 until 2018. This derived dataset covers the six largest euro area markets for benchmark 10-year sovereign bonds. To estimate the cross-market spillover effect between sovereign bonds, it was decided to use the empirical approach proposed by Diebold and Yilmaz (2012) and combine it with the vector error correction model (VECM). We also employed the panel regression model to identify why some bond markets had a higher spillover effect while others were smaller. The dependent variable was the daily average spillover effect of a particular bond. As the spillover effects vary highly across different bonds, country-specific fixed effects were used, and the clustered standard errors were calculated for robustness reasons. Lastly, the cross-market spillovers were analyzed daily to compare them with the results of the model with intraday data. The analysis was performed with rolling 100-day window variance decompositions and a 10-day forecast horizon for six sovereign bonds and the overnight indexed swap (OIS) market. The results of the created time-series model revealed that intraday cross-market spillovers exist but are relatively weak, especially in the case of liquidity spillovers. As the cross-market linkages became much more robust with the model using daily data, the liquidity or price disbalances between different markets are usually corrected on longer intervals than minutes. Distance between countries is the most important explanatory variable and is negatively linked to the magnitude of both liquidity and price spillovers. These findings should be of particular interest to bond market investors, risk managers, and analysts who try to scrutinize the liquidity and price transmission mechanism of sovereign bonds in their portfolios.
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Sundd, Prithu, Edgar Gutierrez, Maria Pospieszalska, Alexander Groisman et Klaus Ley. « Stressed and Compressed Molecular Bonds Revealed in Footprints of Rolling Neutrophils using Total Internal Reflection Fluorescence Microscopy ». Biophysical Journal 98, no 3 (janvier 2010) : 595a. http://dx.doi.org/10.1016/j.bpj.2009.12.3236.
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Shapovalov, V. V., V. I. Kolesnikov, P. V. Kharlamov, R. A. Kornienko et A. M. Petrik. « Improving the efficiency of the path - rolling stock system based on the implementation of anisotropic frictional bonds ». IOP Conference Series : Materials Science and Engineering 900 (4 septembre 2020) : 012011. http://dx.doi.org/10.1088/1757-899x/900/1/012011.
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Lawrence, Michael Brandeau, Jeffrey A. Divietro, Richard S. Larson et Larry A. Sklar. « Immobilized SDF-1α Triggers Rapid VLA-4 Affinity Increases to Stabilize Lymphocyte Tethers on VCAM-1 and Subsequently Initiate Firm Adhesion (97.7) ». Journal of Immunology 178, no 1_Supplement (1 avril 2007) : S190. http://dx.doi.org/10.4049/jimmunol.178.supp.97.7.
Texte intégralRésumé :
Abstract The integrin VLA-4 (?4?1) mediates tethering and rolling events as well as firm adhesion of leukocytes to VCAM-1. Unlike selectins, VLA-4 integrin-mediated lymphocyte adhesiveness can be modulated by chemokines through intracellular signaling pathways. To investigate the effects of the chemokine Stromal cell Derived Factor-1? (SDF-1?) on VLA-4-mediated lymphocyte adhesion; human peripheral blood lymphocytes (PBL) were flowed over VCAM-1 substrates in a parallel plate flow chamber with surface immobilized SDF-1?, a potent activator of firm adhesion. The initial tethering interactions had a median lifetime of 200 ms, consistent with the half-life of low affinity VLA-4-VCAM-1 bonds. Immobilized SDF-1? acted within the lifetime of a primary tether to stabilize initial tethering interactions, increasing the likelihood a PBL would remain interacting with the surface. As expected, the immobilized SDF-1? also increased the ratio of PBL firm adhesion to rolling. An LDV peptide-based small molecule that preferentially binds high affinity VLA-4 reduced PBL firm adhesion to VCAM-1 by 90%. The reduction in firm adhesion due to blockage of high affinity VLA-4 was paralleled by a four-fold increase in the fraction of rolling PBL. SDF-1? activation of PBL firm adhesion on VCAM-1 depended on induction of high affinity VLA-4 rather than recruitment of a pre-existing pool of high affinity VLA-4 as previously thought. Supported by NIH R01 HL54614.
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Vaseghi, Majid, Hossein Zand et Mahmood Sameezadeh. « Mechanical bonding in cold roll-cladding of tri-layered brass/steel/brass composite ». International Journal of Materials Research 111, no 10 (1 octobre 2020) : 826–32. http://dx.doi.org/10.1515/ijmr-2020-1111006.
Texte intégralRésumé :
Abstract In this paper, brass/steel/brass clad-composite was fabricated using a cold roll-bonding process. Composite sheets were roll-bonded at reduction ratios between 37 and 72% at room temperature from strips of 150 mm in length and 30 mm wide, in one pass without lubrication. The threshold deformation for successful bonding was at a thickness reduction of 48% and peel strengths of the bonds were measured to be approximately 12 N cm-1, and it was found to escalate with an increase in the rolling reduction. The optimum reduction in thickness was ~66% wherein the peel strength was ~33 N cm-1. Various techniques such as optical and electron microscopy were implemented to analyze and investigate the effects of the reduction in thickness and the joining mechanism. The results showed that an increased reduction in thickness in rolling leads to an increase in the joining strength. Furthermore, increasing the brass plate thickness negatively affects the joining strength. A Cu peak on the peeled-off steel surface and the presence of Fe on the peeled-off brass surface strongly suggest that the major bonding between brass and steel was mechanically induced metallurgical bonding.
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Khuzwayo, Bhekinkosi, et Eben Mare. « Aspects of volatility targeting for South African equity investors ». South African Journal of Economic and Management Sciences 17, no 5 (28 novembre 2014) : 691–99. http://dx.doi.org/10.4102/sajems.v17i5.662.
Texte intégralRésumé :
We consider so-called volatility targeting strategies in the South African equity market. These strategies are aimed at keeping the volatility of a portfolio consisting of a risky asset, typically an equity index, and cash fixed. This is done by changing the allocation of the assets based on an indicator of the future volatility of the risky asset. We use the three month rolling implied volatility as an indicator of future volatility to influence our asset allocation. We compare investments based on different volatility targets to the performance of bonds, equities, property as well as the Absolute Return peer mean. We examine risk and return characteristics of the volatility targeting strategy as compared to different asset classes.
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Fredrickson, Becky J., Jing-Fei Dong, Larry V. McIntire et José A. López. « Shear-Dependent Rolling on von Willebrand Factor of Mammalian Cells Expressing the Platelet Glycoprotein Ib-IX-V Complex ». Blood 92, no 10 (15 novembre 1998) : 3684–93. http://dx.doi.org/10.1182/blood.v92.10.3684.
Texte intégralRésumé :
Abstract Mural thrombi form on exposed arterial subendothelium by a two-step process of platelet adhesion and aggregation. At high shear stresses such as are found in stenotic arteries, both steps are mediated by von Willebrand factor (vWF). Platelets initially adhere on vWF affixed to the subendothelial matrix through the glycoprotein (GP) Ib-IX-V complex. To examine the role of the GP Ib-IX-V complex under dynamic conditions, we modeled initial platelet adhesion at shear stresses ranging from 2 to 40 dyn/cm2 using vWF-coated glass slides, mammalian cells expressing full or partial GP Ib-IX-V complexes, and a parallel plate flow chamber with phase contrast video microscopy and digital image processing. Mammalian cells expressing the full complex tethered and rolled on the vWF substrate, whereas control cells did not. The rolling was completely inhibited by the monoclonal GP Ib antibody, AK2, or the vWF antibody, 5D2, both shown previously to block vWF-dependent platelet aggregation. Other GP Ib antibodies, WM23 and SZ2, did not significantly change the number or mean velocity of rolling cells. At low levels of GP Ib surface expression, cells expressing the full complex rolled slower than cells expressing the complex without GP V, indicating that GP V strengthens the interactions with the vWF surface under these conditions. Preshearing vWF for 5 minutes at 40 dyn/cm2 immediately before introducing cells into the chamber did not significantly change the number or the mean velocity of rolling cells. Inhibiting sulfation of the tyrosine residues within the GP Ib subunit reduced the number but did not change the mean velocity of the rolling cells. Our results indicate that, under the conditions of these experiments, bonds between vWF and GP Ib constantly form and break under fluid shear stress. Additionally, our results suggest that GP Ib-IX-V complexes behave like selectin receptors in their ability to mediate smooth rolling while cells maintain continuous surface contact. Such a mechanism, in vivo, would allow platelets to slow down and eventually arrest on the blood vessel wall. The system described provides a valuable approach for investigating the structure-function relationship of individual receptors and ligands in the process of platelet adhesion and thrombosis.
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Fredrickson, Becky J., Jing-Fei Dong, Larry V. McIntire et José A. López. « Shear-Dependent Rolling on von Willebrand Factor of Mammalian Cells Expressing the Platelet Glycoprotein Ib-IX-V Complex ». Blood 92, no 10 (15 novembre 1998) : 3684–93. http://dx.doi.org/10.1182/blood.v92.10.3684.422k39_3684_3693.
Texte intégralRésumé :
Mural thrombi form on exposed arterial subendothelium by a two-step process of platelet adhesion and aggregation. At high shear stresses such as are found in stenotic arteries, both steps are mediated by von Willebrand factor (vWF). Platelets initially adhere on vWF affixed to the subendothelial matrix through the glycoprotein (GP) Ib-IX-V complex. To examine the role of the GP Ib-IX-V complex under dynamic conditions, we modeled initial platelet adhesion at shear stresses ranging from 2 to 40 dyn/cm2 using vWF-coated glass slides, mammalian cells expressing full or partial GP Ib-IX-V complexes, and a parallel plate flow chamber with phase contrast video microscopy and digital image processing. Mammalian cells expressing the full complex tethered and rolled on the vWF substrate, whereas control cells did not. The rolling was completely inhibited by the monoclonal GP Ib antibody, AK2, or the vWF antibody, 5D2, both shown previously to block vWF-dependent platelet aggregation. Other GP Ib antibodies, WM23 and SZ2, did not significantly change the number or mean velocity of rolling cells. At low levels of GP Ib surface expression, cells expressing the full complex rolled slower than cells expressing the complex without GP V, indicating that GP V strengthens the interactions with the vWF surface under these conditions. Preshearing vWF for 5 minutes at 40 dyn/cm2 immediately before introducing cells into the chamber did not significantly change the number or the mean velocity of rolling cells. Inhibiting sulfation of the tyrosine residues within the GP Ib subunit reduced the number but did not change the mean velocity of the rolling cells. Our results indicate that, under the conditions of these experiments, bonds between vWF and GP Ib constantly form and break under fluid shear stress. Additionally, our results suggest that GP Ib-IX-V complexes behave like selectin receptors in their ability to mediate smooth rolling while cells maintain continuous surface contact. Such a mechanism, in vivo, would allow platelets to slow down and eventually arrest on the blood vessel wall. The system described provides a valuable approach for investigating the structure-function relationship of individual receptors and ligands in the process of platelet adhesion and thrombosis.
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Wang, Zimeng, Shumei Kang, Meiling Xu, Yanqiang Cheng et Ming Dong. « Effect of Heat Treatment on Microstructure and Properties of Clad Plates 316L/Q370qE ». Materials 12, no 9 (12 mai 2019) : 1556. http://dx.doi.org/10.3390/ma12091556.
Texte intégralRésumé :
Mechanical properties of Q370qE carbon steel can be improved by cladding it with 316L stainless steel. After rolling these materials together, microstructure, hardness, shear strength, and corrosion properties of the cladded metals were evaluated. Hardness and shear tests were performed according to appropriate standards to evaluate the bonds. The results show that the remarkable diffusion of Ni and Cr formed a hard transition zone. The width of this diffusion zone increases with increasing temperature. The shear strength of the clad interface reached a minimum of 385 MPa. In addition, the surfaces of samples were examined by neutral salt spray (NSS) tests and potentiodynamic polarization tests to examine corrosion behavior. The 316L side primarily exhibited pitting corrosion, while the Q370qE side was dominated by uniform corrosion.
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Rivera-Díaz-del-Castillo, Pedro E. J., et Sybrand van der Zwaag. « A Statistical Mechanics Theory of Grain Deformation and Its Prediction of Dynamical Recovery and Recrystallization ». Materials Science Forum 467-470 (octobre 2004) : 87–92. http://dx.doi.org/10.4028/www.scientific.net/msf.467-470.87.
Texte intégralRésumé :
A novel statistical mechanics approach to quantify the effects of hot rolling and deformation on the formation of dislocations in a single grain scenario is presented. The dislocations are dealt as equilibrium defects in the crystal structure, which is assumed to be deformed via the formation of dislocations or single atom displacements at the grain boundary, which involve breaking their bonds and are thus termed “bond breaking atoms”. The deformation process is applied to steels of a variety of grain size and dislocations densities. The model has the capacity to describe the grain energy increase as a function of crystallography, grain sizes, temperature and degree of deformation, providing thus an aid in predicting the conditions for dynamic recovery and recrystallization.
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Bernal-Ortega, Pilar, M. Mar Bernal, Anke Blume, Antonio González-Jiménez, Pilar Posadas, Rodrigo Navarro et Juan L. Valentín. « Sulfur-Modified Carbon Nanotubes for the Development of Advanced Elastomeric Materials ». Polymers 13, no 5 (7 mars 2021) : 821. http://dx.doi.org/10.3390/polym13050821.
Texte intégralRésumé :
The outstanding properties of carbon nanotubes (CNTs) present some limitations when introduced into rubber matrices, especially when these nano-particles are applied in high-performance tire tread compounds. Their tendency to agglomerate into bundles due to van der Waals interactions, the strong influence of CNT on the vulcanization process, and the adsorptive nature of filler–rubber interactions contribute to increase the energy dissipation phenomena on rubber–CNT compounds. Consequently, their expected performance in terms of rolling resistance is limited. To overcome these three important issues, the CNT have been surface-modified with oxygen-bearing groups and sulfur, resulting in an improvement in the key properties of these rubber compounds for their use in tire tread applications. A deep characterization of these new materials using functionalized CNT as filler was carried out by using a combination of mechanical, equilibrium swelling and low-field NMR experiments. The outcome of this research revealed that the formation of covalent bonds between the rubber matrix and the nano-particles by the introduction of sulfur at the CNT surface has positive effects on the viscoelastic behavior and the network structure of the rubber compounds, by a decrease of both the loss factor at 60 °C (rolling resistance) and the non-elastic defects, while increasing the crosslink density of the new compounds.
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Liu, Zhao, Alexander Kraemer, Kai F. Karhausen, Holger Aretz, Marco Teller et Gerhard Hirt. « A New Coupled Thermal Stress FE-Model for Investigating the Influence of Non-Isothermal Conditions on Bond Strength and Bonding Status of the First Pass in Roll Bonding ». Key Engineering Materials 767 (avril 2018) : 301–8. http://dx.doi.org/10.4028/www.scientific.net/kem.767.301.
Texte intégralRésumé :
Roll bonding is a joining-by-forming process to permanently join two or more layers of different materials by hot or cold rolling. One of the typical industrial applications is aluminium sheets for heat exchangers in automobiles. During roll bonding the layers are fed into the rolling stand with parallel surfaces. Due to the plastic deformation in the roll gap metallic bonds between the layers are achieved. Several theoretical models have been published to describe the process, e.g. Zhang & Bay. These models have mostly been developed for cold rolling and describe the bond strength based on surface enlargement, contact pressure and flow stress. Since these models are developed for cold rolling, they are not temperature depending. Heat exchange is usually neglected and de-bonding after the roll gap is not accounted for. However, for hot roll bonding the above mentioned assumptions do not hold true. To understand the mechanisms of hot roll bonding industrial and laboratory scale investigations have previously been conducted. Based on the findings a FE framework for hot roll bonding was developed. This FE framework accounts for the possibility of de-bonding after the roll gap but is restricted to isothermal conditions. However, for a roll bonding simulation it is essential to take the temperature influence into consideration. Therefore, this paper presents an extended version of the FE framework which accounts for temperature dependent material flow, compatible definition of thermal & mechanical interactions and bonding status related heat exchange. To verify the new features of the extended FE framework a roll bonding test case is employed. Mechanical and thermal interactions as well as the current flow stress are calculated in subroutines in order to enable a fully coupled thermal stress simulation. The results show that with this extended FE framework the influence of non-isothermal conditions on material flow and bonding status as well as the feedback effects of bonding status to heat exchange have been successfully integrated in hot roll bonding simulations. This fully coupled thermal stress simulation is the first step towards multi-pass roll bonding simulations.
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Карпов, В. В., А. В. Бандура et Р. А. Эварестов. « Неэмпирические расчеты структуры и устойчивости нанотрубок на основе монохалькогенидов галлия ». Физика твердого тела 62, no 6 (2020) : 908. http://dx.doi.org/10.21883/ftt.2020.06.49346.023.
Texte intégralRésumé :
For the first time first-principles calculations were performed to get the dependences of strain energy and band gap of achiral nanotubes obtained by rolling up monolayers of gallium (II) sulfide and selenide. The hybrid density functional method (with 13% of the Hartree-Fock exchange) within the CRYSTAL17 computer code was used. The empirical Grimme correction was applied to describe the dispersion interactions between layers accurately. As a result of simulations of nanotubes with different chirality and different diameters, the minimum diameters of the stable single-walled nanotubes were determined, which retain the continuity of the chemical bonds on the outer nanotube surface. It was shown that the strain energy dependence on a diameter obeys a classical law of inverse squares and is the same for «zigzag» and «armchair» nanotubes.
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Pietryga, Michael, Johannes Lohmar et Gerhard Hirt. « A New FE-Model for the Investigation of Bond Formation and Failure in Roll Bonding Processes ». Materials Science Forum 854 (mai 2016) : 152–57. http://dx.doi.org/10.4028/www.scientific.net/msf.854.152.
Texte intégralRésumé :
Roll bonding is a process to join two or more different materials permanently in a rolling process. A typical industrial application is the manufacturing of aluminum sheets for heat exchangers in cars where the solder is joined onto a base layer by roll bonding. From a modelling point of view the challenge is to describe the bond formation and failure of the different material layers within a FE-process model. Most methods established today either tie the different layers together or treat them as completely separate. The problem for both assumptions is that they are not applicable to describe the influence of tangential stresses that can cause layer shifting and occur in addition to the normal stresses within the roll gap. To overcome these restrictions in this paper a 2D FE-model is presented that integrates an adapted contact formulation being able to join two bodies that are completely separated at the start of the simulation. The contact formulation is contained in a user subroutine that models bond formation by adhesion in dependence of material flow and load. Additionally if the deformation conditions are detrimental already established bonds can fail. This FE-model is then used to investigate the process boundaries of the first passes of a typical rolling schedule in terms of achievable height reductions. The results show that passes with unfavorable height reduction introduce tensile and shear stresses that can lead to incomplete bonding or can even destroy the bond entirely. It is expected that, with adequate calibration, the developed FE-model can be used to identify conditions that are profitable for bond formation in roll bonding prior to production and hence can lead to shorter rolling schedules with higher robustness.
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Hassanabadi, Majid, Mohammad Najafi, Sohrab Nikazar, Sadaf Saeedi Garakani et Ghodratollah Hashemi Motlagh. « Impact of Placement of Aminopropyl Triethoxy Silane and Tetraethoxy Silicate on SSBR Chains : Analysis of Rolling Resistance, Wet Grip, and Abrasion Resistance ». Advances in Polymer Technology 2022 (5 avril 2022) : 1–16. http://dx.doi.org/10.1155/2022/1566042.
Texte intégralRésumé :
Solution styrene-butadiene rubber (SBR) and silica filler have attracted a significant attention because of their superior properties in cured rubber mixtures used in automobile tire industry. One of the challenges ahead of using these materials is the hard dispersion of silica with its polar surface in SBR nonpolar rubber. In the present study, the synthesis of styrene-butadiene rubber by solution polymerization method with polymer chain modification using copolymer functionalization was performed. For this purpose, two materials, namely, aminopropyl triethoxy silane (APTES) and tetraethoxy silicate (TEOS), were employed to improve the silica dispersion in the mixture. The results of postsynthesis structural tests show the successful placement of functional groups on the polymer chain. The results of mechanical, dynamic, and imaging analyses of the cured mixtures showed an improvement in the APTES-containing samples rolling resistance, wet surface grip, and abrasion resistance by 39%, 18%, and 17%, respectively, due to having stronger physical and chemical bonds with silica and also the usage of end agents in the polymer chain. The samples containing TEOS had also better results than the conventional SBR rubber. In addition, a sample containing emulsion styrene-butadiene rubber was prepared to compare its properties with those of the solution SBR. Another SBR sample containing silane coupling agent was also prepared to investigate its performance compared to that of the agents placed on the polymer chain. The abrasion resistance, rolling resistance, and wet grip of the coupling agent containing sample showed 2%, 10%, and 30% improvement, respectively, which were very close to those of the sample containing the TEOS agent. In this work, various techniques including, rheometry, wear, rolling, hardness, bound rubber content, dynamic mechanical thermal analysis (DMTA), and field emission scanning electron microscopy (FE-SEM) were employed to analyze the synthesized rubber.
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Xu, Gang, et Jin-Yu Shao. « Human neutrophil surface protrusion under a point load : location independence and viscoelasticity ». American Journal of Physiology-Cell Physiology 295, no 5 (novembre 2008) : C1434—C1444. http://dx.doi.org/10.1152/ajpcell.00136.2008.
Texte intégralRésumé :
Mechanical properties of neutrophils have been recognized as key contributors to stabilizing neutrophil rolling on the endothelium during the inflammatory response. In particular, accumulating evidence suggests that surface protrusion and tether extraction from neutrophils facilitate stable rolling by relieving the disruptive forces on adhesive bonds. Using a customized optical trap setup, we applied piconewton-level pulling forces on targeted receptors that were located either on the microvillus tip (CD162) or intermicrovillus surface of neutrophils (CD18 and CD44). Under a constant force-loading rate, there always occurred an initial tent-like surface protrusion that was terminated either by rupture of the adhesion or by a “yield” or “crossover” to tether extraction. The corresponding protrusional stiffness of neutrophils was found to be between 0.06 and 0.11 pN/nm, depending on the force-loading rate and the cytoskeletal integrity, but not on the force location, the medium osmolality, nor the temperature increase from 22°C to 37°C. More importantly, we found that neutrophil surface protrusion was accompanied by force relaxation and hysteresis. In addition, the crossover force did not change much in the range of force-loading rates studied, and the protrusional stiffness of lymphocytes was similar to that of neutrophils. These results show that neutrophil surface protrusion is essentially viscoelastic, with a protrusional stiffness that stems primarily from the actin cortex, and the crossover force is independent of the receptor-cytoskeleton interaction.
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Slámová, Margarita, Petr Homola, P. Sláma, Miroslav Karlík, Miroslav Cieslar, Yoshitatsu Ohara et Nobuhiro Tsuji. « Accumulative Roll Bonding of AA8006, AA8011 and AA5754 Sheets ». Materials Science Forum 519-521 (juillet 2006) : 1227–32. http://dx.doi.org/10.4028/www.scientific.net/msf.519-521.1227.
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Accumulative Roll Bonding (ARB) is a technique of grain refinement by severe plastic deformation, which involves multiple repetitions of surface treatment, stacking, rolling, and cutting. The rolling with 50% reduction in thickness bonds the sheets. After several cycles, ultrafine-grained (UFG) materials are produced. Since ARB enables the production of large amounts of UFG materials, its adoption into industrial practice is favoured. ARB has been successfully used for preparation of UFG sheets from different ingot cast aluminium alloys. Twin-roll casting (TRC) is a cost and energy effective method for manufacturing aluminium sheets. Fine particles and small grain size are intrinsic for TRC sheets making them good starting materials for ARB. The paper presents the results of a research aimed at investigating the feasibility of ARB processing of three TRC alloys, AA8006, AA8011 and AA5754, at ambient temperature. The microstructure and properties of the ARB were investigated by means of light and transmission electron microscopy and hardness measurements. AA8006 specimens were ARB processed without any problems. Sound sheets of AA8011 alloy were also obtained even after 8 cycles of ARB. The AA5754 alloy suffered from severe edge and notch cracking since the first cycle. The work hardening of AA8006 alloy saturated after the 3rd cycle, whereas the hardness of AA5754 alloy increased steadily up to the 5th cycle. Monotonous increase in strength up to 280 MPa was observed in the ARB processed AA8011 alloy.
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XUE, Juan, Chuanyu WANG et Lan WANG. « Optimal Investment Strategy of Defined Contribution Pension Based on Bequest Motivation and Loss Aversion ». Wuhan University Journal of Natural Sciences 27, no 4 (août 2022) : 321–30. http://dx.doi.org/10.1051/wujns/2022274321.
Texte intégralRésumé :
Under the S-shaped utility of loss aversion, this paper considers the bequest motivation of pension plan participants, random salary income before retirement and the substitution rate between receiving pension benefits after retirement and wages before retirement, and studies the optimal investment strategy of defined contribution (DC) pension. Assuming that pension funds can invest in a financial market consisting of three assets (risk-free asset cash, rolling bonds and stocks), inflation is considered by discount. Under the S-shaped utility, the Lagrange method is used to find the terminal optimal surplus of pensions in retirement, so as to find the terminal optimal wealth, and then the martingale method is used to find the optimal wealth process and investment strategy. Finally, a sensitivity analysis is carried out on the the influence of bequest motivation and loss aversion on the optimal investment strategy of DC pension.