Littérature scientifique sur le sujet « Rolling bonds »
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Articles de revues sur le sujet "Rolling bonds"
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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..
Thèses sur le sujet "Rolling bonds"
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Raso, Vanessa. « An optimal Markovian consumption-investment problem in a market with longevity bonds ». Doctoral thesis, Luiss Guido Carli, 2011. http://hdl.handle.net/11385/200887.
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Market, portfolio and arbitrage. Short rate models. Survival models. Financial and mortality risk models. The Optimal Portfolio. The Optimal Portfolio: the CRRA utility case. The Optimal Portfolio: a numerical simulation of the CRRA utility case.
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Cavagnini, Rossana. « Stochastic programming models for distribution logistics, bikesharing and production management ». Doctoral thesis, Università degli studi di Bergamo, 2019. http://hdl.handle.net/10446/128677.
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In this thesis, we study four different problems, all characterized by the presence of uncertainty. The first two of them deal with a distribution system in which transshipment and/or backordering are allowed. For the first problem, we propose a two-stage stochastic program, we provide complexity results and we show that considering uncertainty explicitly in the model leads to better solutions with respect to the ones provided by the corresponding deterministic program, especially if limited recourse actions are admitted. For the second distribution problem, we propose a multi-stage stochastic model. As the complexity increases with the number of stages, we first derive optimal policies useful for solving two polynomially solvable cases. Then, for the general case, we show that the rolling horizon heuristic performs well by properly decomposing the time horizon. For the third problem, we derive a two-stage stochastic model to optimize the allocation and rebalancing activities in a bikesharing system. After showing the benefits of modeling uncertainty, we compare the solution of our stochastic program with the one obtained by Newsvendor model-based heuristics and with the real implemented system. For the fourth problem, we propose a two-stage stochastic programming model that quantifies the impact of worker assignment decisions to produce through an exponential stochastic learning curve. After linearizing it through a mixed integer program that can be solved efficiently, we perform a rigorously designed computational study and statistical analysis to derive tactics and managerial insights for how an organization should plan its production operations about assignment, cross-training and practicing. Finally, given the complexity of solving stochastic integer programs (even for the two-stage case), we propose a methodology in order to obtain monotonic chains of lower bounds for problems hard to be solved and we present some preliminary results based on instances from the literature.
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Nakhaeinejad, Mohsen. « Fault detection and model-based diagnostics in nonlinear dynamic systems ». Thesis, 2010. http://hdl.handle.net/2152/ETD-UT-2010-12-2208.
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Modeling, fault assessment, and diagnostics of rolling element bearings and induction motors were studied. Dynamic model of rolling element bearings with faults were developed using vector bond graphs. The model incorporates gyroscopic and centrifugal effects, contact deflections and forces, contact slip and separations, and localized faults. Dents and pits on inner race, outer race and balls were modeled through surface profile changes. Experiments with healthy and faulty bearings validated the model. Bearing load zones under various radial loads and clearances were simulated. The model was used to study dynamics of faulty bearings. Effects of type, size and shape of faults on the vibration response and on dynamics of contacts in presence of localized faults were studied.
A signal processing algorithm, called feature plot, based on variable window averaging and time feature extraction was proposed for diagnostics of rolling element bearings. Conducting experiments, faults such as dents, pits, and rough surfaces on inner race, balls, and outer race were detected and isolated using the feature plot technique. Time features such as shape factor, skewness, Kurtosis, peak value, crest factor, impulse factor and mean absolute deviation were used in feature plots. Performance of feature plots in bearing fault detection when finite numbers of samples are available was shown. Results suggest that the feature plot technique can detect and isolate localized faults and rough surface defects in rolling element bearings. The proposed diagnostic algorithm has the potential for other applications such as gearbox.
A model-based diagnostic framework consisting of modeling, non-linear observability analysis, and parameter tuning was developed for three-phase induction motors. A bond graph model was developed and verified with experiments. Nonlinear observability based on Lie derivatives identified the most observable configuration of sensors and parameters. Continuous-discrete Extended Kalman Filter (EKF) technique was used for parameter tuning to detect stator and rotor faults, bearing friction, and mechanical loads from currents and speed signals. A dynamic process noise technique based on the validation index was implemented for EKF. Complex step Jacobian technique improved computational performance of EKF and observability analysis. Results suggest that motor faults, bearing rotational friction, and mechanical load of induction motors can be detected using model-based diagnostics as long as the configuration of sensors and parameters is observable.text
Livres sur le sujet "Rolling bonds"
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Rolling the bones : Poems. Tampa : University of Tampa Press, 2010.
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Christopher, Buckley. Rolling the bones : Poems. Tampa : University of Tampa Press, 2010.
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Rolling the bones : A memoir. Toronto : General Karma, 2010.
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Rolling the bones : A novel. South Royalton, Vt : Steerforth Press, 2001.
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Gardner, Erle Stanley. The case of the rolling bones. Boston, Mass : G.K. Hall, 1986.
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Gardner, Erle Stanley. The case of the rolling bones. Bath : Lythway, 1986.
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Gardner, Erle Stanley. The case of the rolling bones. New York : Ballantine Books, 1985.
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New Jersey. Legislature. General Assembly. Agriculture and Natural Resources Committee. Public hearing before Assembly Agriculture and Natural Resources Committee : Assembly bill no. 2143, the Green Acres, Farmland and Historic Preservation, and Lake, Stream, and Dam Restoration Bond Act of 1998 : authorizes $210 million in bonds for those purposes, and appropriates $5,000. Trenton, N.J. (PO Box 068, Trenton 08625-0068) : The Unit, 1998.
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1932-1991, Bonis Bob, dir. The lost Rolling Stones photographs : The Bob Bonis archive, 1964-1966. New York : It Books, 2010.
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Only a few bones : A true account of the Rolling Fork tragedy and its aftermath. Washington, DC : Direct Descent, 2000.
Trouver le texte intégralChapitres de livres sur le sujet "Rolling bonds"
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Consoli, Sergio, Luca Tiozzo Pezzoli et Elisa Tosetti. « Information Extraction From the GDELT Database to Analyse EU Sovereign Bond Markets ». Dans Mining Data for Financial Applications, 55–67. Cham : Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-66981-2_5.
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AbstractIn this contribution we provide an overview of a currently on-going project related to the development of a methodology for building economic and financial indicators capturing investor’s emotions and topics popularity which are useful to analyse the sovereign bond markets of countries in the EU.These alternative indicators are obtained from the Global Data on Events, Location, and Tone (GDELT) database, which is a real-time, open-source, large-scale repository of global human society for open research which monitors worlds broadcast, print, and web news, creating a free open platform for computing on the entire world’s media. After providing an overview of the method under development, some preliminary findings related to the use case of Italy are also given. The use case reveals initial good performance of our methodology for the forecasting of the Italian sovereign bond market using the information extracted from GDELT and a deep Long Short-Term Memory Network opportunely trained and validated with a rolling window approach to best accounting for non-linearities in the data.
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Swartz, Michael D. « Bubbling Blood and Rolling Bones : Agency and Teleology in Rabbinic Myth ». Dans Ancient Myth. Media, Transformations and Sense-Constructions, 432–52. Berlin, New York : Walter de Gruyter, 2009. http://dx.doi.org/10.1515/9783110217247.5.432.
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Ganghoffer, Jean-François. « Mechanical Models of Cell Adhesion Incorporating Nonlinear Behavior and Stochastic Rupture of the Bonds ». Dans Handbook of Research on Computational and Systems Biology, 599–627. IGI Global, 2011. http://dx.doi.org/10.4018/978-1-60960-491-2.ch027.
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The rolling of a single biological cell is analysed using modelling of the local kinetics of successive attachment and detachment of bonds occurring at the interface between a single cell and the wall of an ECM (extracellular matrix). Those kinetics correspond to a succession of creations and ruptures of ligand-receptor molecular connections under the combined effects of mechanical, physical (both specific and non-specific), and chemical external interactions. A three-dimensional model of the interfacial molecular rupture and adhesion kinetic events is developed in the present contribution. From a mechanical point of view, this chapter works under the assumption that the cell-wall interface is composed of two elastic shells, namely the wall and the cell membrane, linked by rheological elements representing the molecular bonds. Both the time and space fluctuations of several parameters related to the mutual affinity of ligands and receptors are described by stochastic field theory; especially, the individual rupture limits of the bonds are modelled in Fourier space from the spectral distribution of power. The bonds are modelled as macromolecular chains undergoing a nonlinear elastic deformation according to the commonly used freely joined chains model, while the cell membrane facing the ECM wall is modelled as a linear elastic plate. The cell itself is represented by an equivalent constant rigidity. Numerical simulations predict the sequence of broken bonds, as well as the newly established connections on the ‘adhesive part’ of the interface. The interplay between adhesion and rupture entails a rolling phenomenon. In the last part of this chapter, a model of the deformation induced by the random fluctuation of the protrusion force resulting from the variation of affinity with chemiotactic sources is calculated, using stochastic finite element methods in combination with the theory of Gaussian random variables.
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« Papa Was a Rolling Stone ». Dans Built on Bones. Bloomsbury Sigma, 2017. http://dx.doi.org/10.5040/9781472948311.0005.
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Swartz, Michael D. « Bubbling Blood and Rolling Bones ». Dans The Signifying Creator, 75–90. NYU Press, 2012. http://dx.doi.org/10.18574/nyu/9780814740934.003.0005.
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Elizondo Griest, Stephanie. « The Bonder and the Dealer ». Dans All the Agents and Saints. University of North Carolina Press, 2017. http://dx.doi.org/10.5149/northcarolina/9781469631592.003.0006.
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A chance meeting with a bail bond agent turned French restaurateur in Falfurrias, Texas, turns the author onto the drug economy in South Texas. After an overview of Mexico’s Drug War, which claimed at least 60,000 lives during the presidency of Felipe Calderon, the author investigates the case of a local drug runner who got caught rolling bags of cocaine into the breakfast tacos he sold out of his taqueria in South Texas. She also expands on Chimamanda Ngozi Adichie’s concept of “the danger of a single story.”
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Gutsalenko, Yuriy, et Tetyana Tretyak. « FORMATION OF WORKING SURFACES AND RESEARCH OF QUALITATIVE INDICATORS OF NON-EVOLVENT GEARS (REVIEW AND PROSPECTS OF DEVELOPMENT) ». Dans Integration of traditional and innovation processes of development of modern science. Publishing House “Baltija Publishing”, 2020. http://dx.doi.org/10.30525/978-9934-26-021-6-35.
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From the standpoint of the development of possibilities of application in theory and practice, the works of Prof. B. A. Perepelitsa from Kharkov Polytechnic Institute and his disciples to develop an applied methodology of multiparameter mappings in relation to the profiling and functioning of complex curvilinear objects and transmission mechanisms in mechanical engineering, mainly with examples of gears, are presented. The work substantiates the relevance of the study of gears with a complex non-involute profile of the side surfaces of the teeth, which in some applications have advantages over involute gears and are devoid of some of their drawbacks associated with quality indicators. A technique for obtaining mating surfaces of the teeth of non-invasive gears as envelopes of the specified surfaces of the teeth of tools is described. A scheme for forming pairs of non-involute gears, from which a gearing can be composed, is proposed. At the same time, diamond-abrasive tools are considered as shaping the working gear profile in its cutting according to the copying scheme and finishing according to the rolling honing scheme. In the first case, the profile of a special shaped tool on a high-strength metal bond is supported by a master electrode according to the scheme of the anodic connection of the tool into the electric circuit of dressing, similar to diamond spark grinding. In the second case, the use of gear wheels-hones on elastic ligaments is shown. It is shown that to obtain the mating surfaces of the teeth of two non-involute gears, two tool rails can be used with the profiles of the side surfaces of the teeth opposite to each other. As a nonlinear profile of the tooth lateral surface of the tool rail, some part of one of the simulated flat kinematic curves is considered. A description of the program developed in accordance with the described method is given, which allows you to calculate the geometric characteristics of the shaped profiles of the gear pair wheels, visualize the shaping process, and also determine the quality indicators of the gearing. Thus, the prerequisites were created for choosing from the resulting geometric modeling of the curve field of such tooth profiles of the tools, which would provide the most rational combination of the tooth profiles of the gears processed by them and the required quality parameters of the gear teeth. The results of the study of the pressure ratio between the teeth of a gear and the overlap ratio of gears when choosing the shape of the tooth profiles are presented. A series of numerical experiments for gearing, formed by pairs of tool rails with different profiles of the side surfaces of the teeth straight, convex and concave, as well as convex-concave were performed. It is shown that non-involute gearing can have large reduced radii of curvature (and consequently smaller pressure coefficients) at the points of tangency of the profiles compared to involute gearing with a slight increase or decrease in the gearing overlap ratio. The most preferable is the variant of the rails with convex and concave tooth profiles, which provides the best values of both quality indicators of the engagement.
Actes de conférences sur le sujet "Rolling bonds"
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Pappu, Vijay, et Prosenjit Bagchi. « Capture, Deformation, Rolling and Detachment of a Cell on an Adhesive Surface in a Shear Flow ». Dans ASME 2008 International Mechanical Engineering Congress and Exposition. ASMEDC, 2008. http://dx.doi.org/10.1115/imece2008-67742.
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Three-dimensional computational modeling and simulation using front tracking method are presented on the motion of a deformable cell over an adhesive surface in a shear flow. The numerical method couples a Navier-Stokes flow solver with cell membrane mechanics, and a Monte Carlo simulation to capture stochastic formation and breakage of receptor/ligand bonds. The entire range of events during cell adhesion, namely, initial arrest of a free-flowing cell, slow rolling of an adherent cell, and detachment off the surface is simulated. Simulations are conducted to signify the role of hydrodynamic lift force that exists for a deformable particle in a wall-bounded flow. Three sets of numerical experiments are presented. In the first set, we consider the initial arrest of the cell, and show that the time needed for the cell to arrest increases with increasing Ca, but rapidly drops and saturates for higher bond strength. In the second set, we consider quasi-steady rolling motion of the cell, and predict the experimentally observed “stop and go” motion of the rolling leukocytes which is characterized by intermittent pauses and sudden jumps in cell velocity. In the third set we consider the detachment of the cell from the surface upon breakage of bonds. The bond strength needed to prevent the detachment of an adherent cell is computed and shown to be maximum for an intermediate Ca.
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Strano, Matteo, Juan S. Sanchez, Valerio Mussi et Michele Monno. « A Comprehensive Experimental Study on the Effect of Process Parameters in Warm Roll Bonding of Aluminum Sheets ». Dans ASME 2014 International Manufacturing Science and Engineering Conference collocated with the JSME 2014 International Conference on Materials and Processing and the 42nd North American Manufacturing Research Conference. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/msec2014-4000.
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Roll bonding of aluminum sheets is a technology with actual and potential applications in several fields, such as the production of special materials or all-aluminum channeled products. The strength of the rolled bonds clearly depends on the main process parameters, including the rolling conditions (entry temperature, reduction, speed, etc.) and the pre-rolling treatment conditions (annealing temperature and time, surface preparation technique, etc.). The purpose of this paper is to further investigate, experimentally, the effect of additional parameters that have been generally neglected by the scientific literature, such as the initial wall thickness of the sheets and the post-rolling heat treatment. An extensive plan of experiments has been designed for evaluating the simultaneous effect of several process variables. The results have been analyzed with a statistical approach, using the strength of the bond as the main response variable, evaluated though peel tests. The analysis demonstrated that thicker sheets are easier to weld than thin sheets. The study also proved that a prolonged post-rolling heat treatment is useful to enhance the bond strength (by solid state diffusion), but only if a good mechanical bond has already been obtained by rolling. Furthermore, the surface quality of the rolled products has been measured and correlated to the strength of the bond.
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Skierczynski, Boguslaw A. « Probability Density of the Rolling Velocity of the Cell ». Dans ASME 1998 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1998. http://dx.doi.org/10.1115/imece1998-0056.
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Abstract Rolling of the cell under flow conditions is an important process in PMN emigration. It is a finely regulated process involving membrane receptors and cell-matrix recognition. Several models have been proposed to explain how the strength and lifetime of the bonds in receptor-mediated cell-substratum are related to cell rolling velocity (Hammer, 1992, Tozeren, 1992, Zhao, 1995). The paper presents a simple model of the cell rolling based on the experimental measurements that will allow to gain information relevant to the molecular processes underlying the rolling motion of the cell.
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Shao, Jin-Yu, et Baoyu Liu. « Cellular Membrane Tether Retraction : Experiment and Model ». Dans ASME 2012 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/sbc2012-80760.
Texte intégralRésumé :
During leukocyte rolling on the endothelium, membrane tethers can be extracted simultaneously from both leukocytes and endothelial cells because of the force imposed by the blood flow [1]. Tether extraction has been shown to stabilize leukocyte rolling by increasing the lifetime of the adhesive selectin-ligand bonds that mediate leukocyte rolling [2]. Over the past two decades, tether extraction has been studied extensively, both experimentally and theoretically. In contrast, much less is known about tether retraction.
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Pappu, Vijay, et Prosenjit Bagchi. « 3D Computational Modeling and Simulation of Cell Motion on Adhesive Surfaces in Shear Flow ». Dans ASME 2008 Fluids Engineering Division Summer Meeting collocated with the Heat Transfer, Energy Sustainability, and 3rd Energy Nanotechnology Conferences. ASMEDC, 2008. http://dx.doi.org/10.1115/fedsm2008-55113.
Texte intégralRésumé :
A three-dimensional computational fluid dynamic (CFD) model is presented to simulate transient rolling adhesion and deformation of leukocytes over a P-selectin coated surface in shear flow. The computational model is based on immersed boundary method for cell deformation, and stochastic Monte Carlo simulation for receptor/ligand interaction. The model is shown to predict the characteristic ‘stop-and-go’ motion of rolling leukocytes. The objective here is to understand the coupling between external shear flow, cell deformation, microvilli deformation and various biophysical parameters that govern the formation of selectin bonds. We observe that compliant cells roll more stably with lesser fluctuations. Adhesion is seen to occur via multiple tethers, but often one tether is sufficient to support rolling. The force loading on individual microvillus is not continuous, rather occurs in steps. Further, it is also shown that only the microvilli whose undeformed length is above a certain cut off length, participate in bond formation and the cutoff length reduces with increasing cell rigidity.
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Karnik, Rohit, Seungpyo Hong, Suman Bose, Huanan Zhang, Ying Mei, Daniel G. Anderson, Jeffrey M. Karp et Robert Langer. « Microfluidic Separation of Cells by Rolling on Patterned Receptors ». Dans ASME 2008 6th International Conference on Nanochannels, Microchannels, and Minichannels. ASMEDC, 2008. http://dx.doi.org/10.1115/icnmm2008-62217.
Texte intégralRésumé :
Cell separation based on markers present on the cell surface has extensive biological applications. However, current separation methods involve labeling and label removal steps which are often slow and intrusive. We envisioned that the ability to control the direction of transport of cells based on specific receptors on the cell surface without labeling and label removal steps would enable simple continuous-flow microfluidic cell separation systems with minimal processing steps and active components. We therefore explored whether receptor patterning could be used to direct the transport of cells in a label-free manner through the formation of transient receptor-ligand bonds that result in cell rolling.
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Xu, J., et H. Zhang. « Computational Modeling of Dynamic Cell Adhesion, Deformation, and Rolling Under Blood Flow in a Micro-Channel ». Dans ASME 2003 International Mechanical Engineering Congress and Exposition. ASMEDC, 2003. http://dx.doi.org/10.1115/imece2003-41221.
Texte intégralRésumé :
Cell adhesion to postcapillary vascular endothelium in the fluid dynamic environment is an important event in many physiological and pathological processes, e.g. leukocyte emigration is critical for the successful host defense against tissue injury and infection. Since cell-blood interaction is strongly coupled with cell adhesion in the microchannel, we have developed an integrated mathematical model of cell adhesion, deformation, and rolling. Cells are modeled as elastic solids interacting with the flat wall of a micro-channel. The ligand-receptor bonds between the cell and micro-channel wall are simulated as many simple springs. The formation and dissociation rates of bonds are characterized by a reversible kinetic model (Dembo et al., 1988).
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Gupta, Vijay K., et Charles D. Eggleton. « A 3-D Computational Model of L-Selectin-PSGL-1 Dependent Homotypic Leukocyte Binding and Rupture in Shear Flow ». Dans ASME 2012 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/sbc2012-80862.
Texte intégralRésumé :
Cell adhesion plays a pivotal role in diverse biological processes, including inflammation, tumor metastasis, arteriosclerosis, and thrombosis. Changes in cell adhesion can be the defining event in a wide range of diseases, including cancer, atherosclerosis, osteoporosis, and arthritis. Cells are exposed constantly to hemodynamic/hydrodynamic forces and the balance between the dispersive hydrodynamic forces and the adhesive forces generated by the interactions of membrane-bound receptors and their ligands determines cell adhesion. Therefore to develop novel tissue engineering based approaches for therapeutic interventions in thrombotic disorders, inflammatory, and a wide range of other diseases, it is crucial to understand the complex interplay among blood flow, cell adhesion, and vascular biology at the molecular level. In response to tissue injury or infection, polymorphonuclear (PMN) leukocytes are recruited from the bloodstream to the site of inflammation through interactions between cell surface receptors and complementary ligands expressed on the surface of the endothelium [1]. PMN-PMN interactions also contribute to the process of recruitment. It has been shown that PMNs rolling on activated endothelium cells can mediate secondary capture of PMNs flowing in the free blood stream through homotypic interactions [2]. This is mediated by L-selectin (ligand) binding to PSGL-1 (receptor) between a free-stream PMN and one already adherent to the endothelium cells [3]. Both PSGL-1 and L-selectin adhesion molecules are concentrated on tips of PMN microvilli [4]. Homotypic PMN aggregation in vivo or in vitro is supported by multiple L-selectin–PSGL-1 bondings between pairs of microvilli. The ultimate objective of our work is to develop software that can simulate the adhesion of cells colliding under hydrodynamic forces that can be used to investigate the complex interplay among the physical mechanisms and scales involved in the adhesion process. However, cell-cell adhesion is a complex phenomenon involving the interplay of bond kinetics and hydrodynamics. Hence, as a first step we recently developed a 3-D computational model based on the Immersed Boundary Method to simulate adhesion-detachment of two PMN cells in quiescent conditions and the exposing the cells to external pulling forces and shear flow in order to investigate the behavior of the nano-scale molecular bonds to forces applied at the cellular scale [5]. Our simulations predicted that the total number of bonds formed is dependent on the number of available receptors (PSGL-1) when ligands (L-selectin) are in excess, while the excess amount of ligands controls the rate of bond formation [5]. Increasing equilibrium bond length causes an increased intercellular contact area hence results in a higher number of receptor-ligand bonds [5]. Off-rates control the average number of bonds by modulating bond lifetimes while On-rate constants determine the rate of bond formation [5]. An applied external pulling force leads to time-dependent on- and off-rates and causes bond rupture [5]. It was shown that the time required for bond rupture in response to an applied external force is inversely proportional to the applied external force and decreases with increasing offrate [5]. Fig. 1 shows the time evolution of the total number of bonds formed for various values of NRmv (number of receptor) and NLmv (number of ligand). As expected, the total number of bonds formed at equilibrium is dependent on NRmv when NLmv is in excess. In this particular case study since two pairs (or four) microvilli each with NRmv are involved in adhesion hence the equilibrium bond number is approximately 4NRmv. It is noticed that for NRmv = 50, as we vary NLmv the mean value of the total number of bonds at equilibrium does not change appreciably. However, it can be noticed from Fig. 1 that for NRmv = 50, as the excess number of ligands (NLmv) increases there is a slight increase in the rate of bond formation due to the increase in probability of bond formation. Having developed confidence in the ability of the numerical method to simulate the adhesion of two cells that can form up to 200 bonds, we apply the method to study the effect of shear rate on the detachment of two cells. In particular, we first would like to establish the minimum shear rate needed for the two cells to detach for a given number of bonds between them. Fig. 2 shows the variation of force per bond at no rupture with number of bonds for various shear rates indicated. It is seen that at a given shear rate as the number of bonds increases the force per bond at no rupture decreases. This is attributed to the fact that force caused by shear flow is shared equally among the existing bonds. Further, it is seen that a given number of bonds as the shear rate increases the force per bond at no rupture increases. This is due to the fact that at a given number of bonds between the cells as we increase the shear rate the force caused by the flow increases hence the force per bond increases. We further notice that at shear rate = 3000 s−1 cells attached either by a single bond or by two bonds detach while they don’t for higher (> 2) number of bonds. This clearly demonstrate that there is a minimum shear rate needed to detach cells adhered by a given number of bonds. The higher the number of bonds, the higher the minimum shear rate for complete detachment of cells. For example, from Fig. 2 is it clear that for the cells adhered by two and five bonds the minimum shear rate needed for complete detachment of these two cells are 3000 s−1 and 6000 s−1, respectively.
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Gupta, Vijay K., et Charles D. Eggleton. « A Numerical Method for Coupling Nano-Scale Molecular Binding With Mesoscale Cellular Deformation ». Dans ASME 2009 International Mechanical Engineering Congress and Exposition. ASMEDC, 2009. http://dx.doi.org/10.1115/imece2009-13296.
Texte intégralRésumé :
Cell adhesion plays a pivotal role in diverse biological processes, including inflammation and thrombosis. Changes in cell adhesion can be the defining event in a wide range of diseases, including cancer, osteoporosis, atherosclerosis, and arthritis. Cells are exposed constantly to hemodynamic/hydrodynamic forces and the balance between the dispersive hydrodynamic forces and the adhesive forces generated by the interactions of membrane-bound receptors and their ligands determines cell adhesion. The ultimate objective of our work is to develop software that can simulate the adhesion of cells colliding under hydrodynamic forces that can be used to investigate the complex interplay among the physical mechanisms and scales involved in the adhesion process. Here, we review the development of a multi-scale model combining Monte-Carlo models of molecular binding with the Immersed Boundary Method for cellular-hydrodynamic interactions. This model predicted for the first time that the rolling of more compliant cells is relatively smoother and slower compared to cells with stiffer membranes, due to increased cell-substrate contact area. At the molecular level, we show that the average number of bonds per cell as well as per single microvillus decreases with increasing membrane stiffness. The numerical model was modified to compare the effects of different kinetic models of molecular binding on cell rolling. Simulations predict that the catch-slip bond behavior and to a lesser extent bulk cell deformation are responsible for the shear threshold phenomenon. In bulk flow, shear rate has been shown to critically affect the kinetics and receptor specificity of cell-cell interactions. We are currently simulating the adhesion of two PMN cells in quiescent conditions and the exposing the cells to external pulling forces and shear flow in order to investigate the behavior of the nano-scale molecular bonds to forces applied at the cellular scale.
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Lu, Xiaoxing, et Zhong Hu. « Evaluation of Mechanical Behaviors of Single-Walled Carbon Nanotubes by Finite Element Analysis ». Dans ASME 2010 International Mechanical Engineering Congress and Exposition. ASMEDC, 2010. http://dx.doi.org/10.1115/imece2010-37766.
Texte intégralRésumé :
Based on molecular mechanics, a three-dimensional finite element model for armchair, zigzag and chiral single-walled carbon nanotubes (SWCNTs) has been developed, in which the carbon nanotubes (CNTs), when subjected to load, behave like space-frame structures. The bending stiffness of the graphite layer has been considered. The potentials associated with the atomic interactions within a CNT were evaluated by the strain energies of beam elements which serve as structural substitutions of covalent bonds. The out-of-plane deformation (inversion) of the bonds was distinguished from the in-plane deformation by considering an elliptical cross-section for the beam elements. The elastic moduli of beam elements are determined by using a linkage between molecular and continuum mechanics. A closed form solution of the sectional properties of the beam element was derived analytically and verified through the analysis of rolling a graphite sheet into a carbon nanotube. This method was validated by its application to a graphene model, and Young’s modulus of the model was found, showing agreement with the known values of graphite. Modeling of the elastic deformation of SWCNTs reveals that Young’s moduli and the shear modulus of CNTs vary with the tube diameter and are affected by their helicity. With increasing tube diameter, Young’s moduli of both armchair and zigzag CNTs are increasing monotonically and approaching to the Young’s modulus of graphite, which are in agreement with the existing theoretical and experimental results. The rolling energy per atom was computed by finite element analysis. By comparing mechanical properties with circular cross section models, it is found that the computational results of the proposed elliptical cross-section model are closer to the results from the atomistic computations. The proposed model is valid for problems where the effect of local bending of the graphite layer in a CNT is significant. This research work shows that the proposed finite element model may provide a valuable tool for studying the mechanical behaviors of CNTs and their integration in nano-composites.