Journal articles on the topic 'Multicontact systems'
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1
Radjai, Farhang. "Multicontact dynamics of granular systems." Computer Physics Communications 121-122 (September 1999): 294–98. http://dx.doi.org/10.1016/s0010-4655(99)00337-9.
2
Carpentier, Justin, and Nicolas Mansard. "Multicontact Locomotion of Legged Robots." IEEE Transactions on Robotics 34, no. 6 (December 2018): 1441–60. http://dx.doi.org/10.1109/tro.2018.2862902.
3
Nekrasov, A. Ya, M. O. Arbuzov, and A. N. Sobolev. "Automatic control of the static loads in multicontact mechanical systems." Russian Engineering Research 35, no. 6 (June 2015): 442–46. http://dx.doi.org/10.3103/s1068798x1506012x.
4
Khlus, V. A., and A. V. Dyomin. "Thermal fluctuations in multicontact Josephson granular systems and ac magnetic susceptibility." Physica C: Superconductivity 185-189 (December 1991): 2441–42. http://dx.doi.org/10.1016/0921-4534(91)91345-5.
5
Al-Wahaibi, Y. M., and A. K. Al-Hadhrami. "Oil Recovery Mechanisms via Multicontact Miscible Gas Injection Process within Lensed Systems." Petroleum Science and Technology 27, no. 15 (October 21, 2009): 1744–56. http://dx.doi.org/10.1080/10916460802637163.
6
Del Prete, Andrea, Steve Tonneau, and Nicolas Mansard. "Zero Step Capturability for Legged Robots in Multicontact." IEEE Transactions on Robotics 34, no. 4 (August 2018): 1021–34. http://dx.doi.org/10.1109/tro.2018.2820687.
7
Vinogradov, Aleksandr Vladimirovich, Alina Vasilevna Vinogradova, and Aleksandr Aleksandrovich Lansberg. "Advanced method of encoding situations in the electric network containing multicontact switching systems." Vesti vysshikh uchebnykh zavedenii Chernozem'ya, no. 1 (2021): 12–30. http://dx.doi.org/10.53015/18159958_2021_1_12.
8
Dindoruk, Birol, Russell Johns, and Franklin M. Orr. "Measurement and Modeling of Minimum Miscibility Pressure: A State-of-the-Art Review." SPE Reservoir Evaluation & Engineering 24, no. 02 (February 10, 2021): 367–89. http://dx.doi.org/10.2118/200462-pa.
Abstract:
Summary This paper gives a critical review of miscibility-measurement techniques published in the open literature along with recommendations and lessons learned. Many of these published methods violate the inherent assumptions for multicontact miscibility (MCM). The confusion often arises from a failure to distinguish between first-contact miscibility (FCM), in which two fluids can be mixed in all proportions without forming two phases, and MCM, in which fluid compositions that arise during the flow of two phases in a porous medium approach a specific critical point within the constraints of the MCM definition. There are many analytical, numerical, correlational, and experimental methods available to estimate the minimum miscibility pressure (MMP) for MCM flow. The numerous available methods, some of which are quite inexpensive, have caused significant misunderstandings in the literature and in practice regarding their ability to estimate MMP. Our experience has shown that the best methods are those that honor the multicontact process (MCM), in which flow interacts with phase behavior in a prescribed way. Good methods that achieve this are slimtube experiments, detailed slimtube simulations, multiple-mixing-cell calculation methods, and the method of characteristics (MOC). Techniques such as the rising-bubble-apparatus (RBA) and vanishing-interfacial-tension (IFT) (VIT) experiments are subject to significant uncertainties, although they can still provide useful information. Numerous MMP correlations have been developed. They should be used with caution for systems similar to those used to develop the correlation. Use for other fluid systems can lead to significant errors. We discuss the advantages and disadvantages of most current methods and show that various combinations of methods can reduce uncertainty.
9
Lorensu, Pedro Javier Perez, Helena Perez Perez, Domingo Navajas Carasa, and Victor Manuel Garcia Marin. "P164 Utility of multicontact cylindrical subdural soft electrodes in electrocorticography for epilepsy surgery." Clinical Neurophysiology 119 (May 2008): S112. http://dx.doi.org/10.1016/s1388-2457(08)60435-6.
10
Alart, Pierre, Michael Barboteu, and Mathieu Renouf. "Parallel Computational Strategies for Multicontact Problems: Applications to Cellular and Granular Media." International Journal for Multiscale Computational Engineering 1, no. 4 (2003): 419–30. http://dx.doi.org/10.1615/intjmultcompeng.v1.i4.70.
11
Яшин, Александр, Aleksandr Yashin, Сергей Баринов, Sergey Barinov, Алексей Киричек, Alexey Kirichek, Алексей Зайцев, and Aleksey Zaytsev. "ENERGETIC REGULARITIES OF PULSE LOADING BY SYSTEMS WITH INTERMEDIATE LINK." Bulletin of Bryansk state technical university 2017, no. 1 (March 31, 2017): 83–90. http://dx.doi.org/10.12737/24896.
Abstract:
The investigations carried out deal with the re-gularity study in the distribution of shock pulse energy at multiple procedures of loading. The experimental researches were carried out on the specially developed test bench in which under all waveguides (or tools) of the shock system there were situated independently (separately) sensors connected with an oscilloscope registering parameters of a shock pulse (a form, amplitude, duration).
As a result it was determined that the increase of the eccentricity in the symmetry axis location of a head and a waveguide (or a tool) and their number in the shock system contributes to the reduction of an energy portion sent to the deformation source. The application of multi-contact schemes of loading allows sending large total energy of a shock pulse to the deformation source to accept conditions of experiment fulfillment.
At that the energy portion of a shock pulse fall-ing to each waveguide (or a tool) in the multicontact scheme as compared with the singlecontact one decreases (for rod-formed waveguides by 20%, and for spherical tools – by 15%) at the installation of each subsequent waveguide (or a tool) in the shock system.
12
Sentis, Luis, Jaeheung Park, and Oussama Khatib. "Compliant Control of Multicontact and Center-of-Mass Behaviors in Humanoid Robots." IEEE Transactions on Robotics 26, no. 3 (June 2010): 483–501. http://dx.doi.org/10.1109/tro.2010.2043757.
13
Zhao, Huihua, Jonathan Horn, Jacob Reher, Victor Paredes, and Aaron D. Ames. "Multicontact Locomotion on Transfemoral Prostheses via Hybrid System Models and Optimization-Based Control." IEEE Transactions on Automation Science and Engineering 13, no. 2 (April 2016): 502–13. http://dx.doi.org/10.1109/tase.2016.2524528.
14
Rannou, Guillaume, Denis Voskov, and Hamdi Tchelepi. "Tie-Line-Based K-Value Method for Compositional Simulation." SPE Journal 18, no. 06 (August 8, 2013): 1112–22. http://dx.doi.org/10.2118/167257-pa.
Abstract:
Summary The thermodynamic behavior of multicomponent multiphase systems is highly nonlinear, and the coupling to the flow equations is quite complex; as a result, equation-of-state (EOS) -based simulations can be computationally prohibitive. We describe a new K-value method that captures the compositional dependence of the phase behavior. Specifically, we propose a method for selecting compositions used in the tabulation of K-values and define an operator that interpolates the K-values as a function of pressure and composition. The method employs the minimal critical pressure (MCP) to detect supercritical compositions, which allows for effective modeling of multicontact miscible displacements. We compare our K-value approach with standard EOS compositional simulation for several isothermal problems, and we demonstrate the efficiency and accuracy of the proposed method.
15
Baumberger, Tristan, and Christiane Caroli. "Multicontact Solid Friction: A Macroscopic Probe of Pinning and Dissipation on the Mesoscopic Scale." MRS Bulletin 23, no. 6 (June 1998): 41–46. http://dx.doi.org/10.1557/s0883769400030621.
Abstract:
In this article, we review the present status of experimental and theoretical work on friction at the interface between extended macroscopic bodies, rough on the micrometer scale. We show that systematic detailed studies of low-velocity friction using dynamical systems analysis, together with their shear response in the static state, provide a tool for investigating the physical processes taking place on the mesoscopic scale of real contacts between rough surfaces. This approach should shed light on the enduring question of the relationship between macroscopic friction and microscopic dissipative mechanisms. This still open issue has come back to the fore during the last decades, following considerable progress due to the development of “molecular tribometers.Bowden and Tabor pointed out that, because nominally flat surfaces are in general rough on small scales, the real area of contact Ar (Figure 1) is only a small fraction ϕ of apparent contact area A0. On the other hand, they postulated the existence of a stressσs characteristic of the shear strength of the interface between a given couple of solids. Hence the friction force:In this framework, the Amontons-Coulomb (AC) law F = μFN amounts to stating that Ar is proportional to the normal load FN where μ is the coefficient of friction.When considering soft metals, Bowden and Tabor noticed that ϕ ≪ 1 entails that the nominal local pressure p on the real contacts—of the order of FN/(ϕA0)–generally overcomes the yield strength Y so that the contacting asperities flow plastically until p = H≈ 3Y, the “hardness” of the (softer) material. So, Ar = FN/H.
16
Greenwood, P., D. Childs, K. M. Groom, B. J. Stevens, M. Hopkinson, and R. A. Hogg. "Tuning Superluminescent Diode Characteristics for Optical Coherence Tomography Systems by Utilizing a Multicontact Device Incorporating Wavelength-Modulated Quantum Dots." IEEE Journal of Selected Topics in Quantum Electronics 15, no. 3 (2009): 757–63. http://dx.doi.org/10.1109/jstqe.2009.2013481.
17
Fernbach, Pierre, Steve Tonneau, Olivier Stasse, Justin Carpentier, and Michel Taix. "C-CROC: Continuous and Convex Resolution of Centroidal Dynamic Trajectories for Legged Robots in Multicontact Scenarios." IEEE Transactions on Robotics 36, no. 3 (June 2020): 676–91. http://dx.doi.org/10.1109/tro.2020.2964787.
18
Li, Kejun, Maegan Tucker, Rachel Gehlhar, Yisong Yue, and Aaron D. Ames. "Natural Multicontact Walking for Robotic Assistive Devices via Musculoskeletal Models and Hybrid Zero Dynamics." IEEE Robotics and Automation Letters 7, no. 2 (April 2022): 4283–90. http://dx.doi.org/10.1109/lra.2022.3149568.
19
Pluskota, Elzbieta, Dmitry A. Soloviev, and Edward F. Plow. "Convergence of the adhesive and fibrinolytic systems: recognition of urokinase by integrin αMβ2 as well as by the urokinase receptor regulates cell adhesion and migration." Blood 101, no. 4 (February 15, 2003): 1582–90. http://dx.doi.org/10.1182/blood-2002-06-1842.
Abstract:
Previous studies demonstrated that integrin αMβ2 (CD11b/18, Mac-1) forms a physical complex with the urokinase-type plasminogen activator receptor (uPAR/CD87) on leukocytes. In this study, we used human peripheral blood neutrophils and transfected cells expressing αMβ2, uPAR, or both receptors to show that the integrin can directly interact with urokinase (uPA). We demonstrate that αMβ2 supported adhesion and migration of these cells to uPA, and, in each case, blockade of αMβ2 suppressed the response. Within uPA, both the kringle and proteolytic domains are recognized by αMβ2, which are distinct from the growth factor domain that binds to uPAR. Within the αM subunit of the integrin, the I domain interacts with uPA, which is distinct from the region that interacts with uPAR. On cells expressing uPAR and αMβ2, both receptors mediated adhesion and migration. This cooperation was particularly apparent in the responses of neutrophils to uPA, where blockade of αMβ2 reduced uPAR-mediated responses and engagement of uPAR enhanced recognition of uPA by αMβ2. Thus, recognition of uPA by αMβ2 allows for formation of a multicontact trimolecular complex, in which a single uPA ligand may bind simultaneously to both uPAR and αMβ2. This complex may play an important role in the control of inflammatory cell migration and vascular homeostasis.
20
Givre, S. J., J. C. Arezzo, and C. E. Schroeder. "Effects of wavelength on the timing and laminar distribution of illuminance-evoked activity in macaque V1." Visual Neuroscience 12, no. 2 (March 1995): 229–39. http://dx.doi.org/10.1017/s0952523800007914.
Abstract:
AbstractResponses to full-field colored flashes (red, blue, and green) were compared with those to illuminancematched white flashes in area V1, optic radiations, and the lateral geniculate nucleus of two alert macaques. Laminar profiles of visual evoked potentials (VEPs), current source density, and multiunit activity were obtained using multicontact electrodes capable of sampling from all layers of cortex or lateral geniculate nucleus, simultaneously. In striate cortex, stimulation with colored flash enhanced transmembrane current flow dramatically in both layer 4c and the supragranular laminae. Stimulation with red evoked the largest enhancement in every electrode penetration. The mean peak amplitudes of current sinks evoked by red were 203% and 537% of those evoked by white light in layer 4c and the supragranular laminae, respectively. Color effects in VI were preceded by an initial epoch of wavelength-insensitive activity. In layer 4c, the red effect reached significance, on average, at 47 ms, or ≈24 ms after the onset of transmembrane current flow. In the supragranular layers, the red effect reached significance, on average, at 55 ms, or ≈14 ms after the onset of current flow. Recordings from optic radiations in the white matter below V1 and from lateral geniculate nucleus showed no significant difference in the responses to color and illuminance-matched white light. Enhancement of supragranular current flow with color stimulation increased the contribution of these laminae to the generation of the surface VHP. Comparison of the surface VHP wave forms evoked by white and color stimuli may, therefore, help to differentiate the responses of the granular and supragranular laminae.
21
Alston, R. B., G. P. Kokolis, and C. F. James. "CO2 Minimum Miscibility Pressure: A Correlation for Impure CO2 Streams and Live Oil Systems." Society of Petroleum Engineers Journal 25, no. 02 (April 1, 1985): 268–74. http://dx.doi.org/10.2118/11959-pa.
Abstract:
Abstract This paper presents an empirically derived correlation for estimating the minimum pressure required for multicontact miscible (MCM) displacement of live oil systems by pure or impure CO2 streams. Minimum miscibility pressure (MMP) has been correlated with temperature, oil C5+ molecular weight, volatile oil fraction, intermediate oil fraction, and composition of the CO2 stream. The effects of temperature and oil C5+ molecular weight on pure CO2 MMP have been well documented. However, CO2 sources are rarely pure, and solution gas usually is present in reservoir oils. The correlation presented in this paper accounts for the additional effects on MMP caused by the presence of volatile components (methane, C1; and N2) and intermediate components (ethane, C2; propane, C3; butane, C4; hydrogen sulfide, H2S; and CO2) in the reservoir oil. This correlation also is capable of estimating MMP for a contaminated or enriched CO2 stream on the basis of the pure CO2 MMP. Introduction Miscible displacements using hydrocarbon solvents have been described in the literature by many authors.1–6 The use of a slim tube apparatus for the establishment of MMP requirements for enriched or vaporizing gas drives was presented by Deffrenne et al.5 and Yarborough and Smith.7 Rutherford8 referred to these systems as conditionally miscible processes. The initial work of Rathmell et al.9 and Ballard and Smith10 illustrated that the mechanisms of CO2 displacements are similar to those of high-pressure MCM vaporizing gas drives. Since the high solubility of CO2 in reservoir oils diminishes the pressure required for miscibility to occur, a CO2 vaporizing gas drive can operate in the same manner as a lean-gas injection process, but at significantly lower pressures. Correlations for the prediction of MMP requirements for CO2 flooding are extremely helpful in the screening of candidate reservoirs for CO2 floods. Holm and Josendal11 were the first to introduce a method for estimating the MMP required for CO2 displacing oil. Other correlations for CO2 MMP have been introduced by the Natl. Petroleum Council,12 Yellig and Metcalfe,13 and Johnson and Pollin,14 as well as a new correlation from Holm and Josendal.15,16 This paper presents an empirical approach to MMP estimation. Included in this study are the effects of solution gas (live oil systems) and the effects of impure CO2 sources. Concepts of Miscible Displacement Miscible displacement is represented most easily by a ternary diagram. A pseudoternary diagram for a hypothetical hydrocarbon system is shown in Fig. 1. This is a pseudoternary representation since the apexes do not consist of pure components, but it can be used to qualitatively describe the process of miscible displacement. Fig. 1 has been divided into three areas: Zone 1, Zone 2, and Zone 3. Zone 1 represents the area of first-contact miscibility. Any solvent falling within this region can be mixed with the reservoir oil shown, such that any and all mixtures will fall outside of the two-phase region. Zone 2 represents the region of multicontact miscibility. Solvents within this area, while not initially miscible in all proportions with the reservoir oil, eventually will achieve miscibility through the repeated contacts of the reservoir oil and equilibrium fluids. There are two types of MCM processes: vaporizing gas drive, where the solvent is enriched by components vaporized from the reservoir oil, and condensing or enriched gas drive, where the solvent contributes to the enrichment of the reservoir fluid.17 Commercially viable CO2-miscible EOR processes are usually of the MCM type, because reservoir pressure requirements for this process are significantly lower than required for first contact miscibility. Zone 3 represents the area of immiscible displacement. Displacement of the reservoir oil by an fluid falling within Zone 3 will result in multiphase flow. The mass transfer between the oil and displacing fluid is such that miscibility cannot be achieved.
22
Park, Jaeheung, and Oussama Khatib. "Robot multiple contact control." Robotica 26, no. 5 (September 2008): 667–77. http://dx.doi.org/10.1017/s0263574708004281.
Abstract:
SUMMARYThis paper addresses the problem of contact force control for multiple contacts distributed over multiple links in a robot. This is of importance when performing complex tasks in unstructured environment, particularly in humanoid robot applications. The proposed multicontact control framework provides a new way of defining the operational space coordinates, which facilitates the specification of multiple contact control. The contact force space on multiple links is constructed as an operational space for the highest priority task. Motion control, given lower priority, can be executed using the rest of degree of freedom within the null-space of the force control. The dynamic control structure, then, provides a means to control each contact force and motion independently. This dynamic decoupling enables each contact force controller to utilize linear control theories. In particular, the contact force controllers adopt full state feedback control and estimation methods to produce robust performance with respect to modeling and parameter uncertainties. The effectiveness of the multiple contact control framework was demonstrated using a PUMA560 manipulator, with multiple contacts on the end-effector and third link. The demonstrated tasks involved controlling each of the contact forces with null-space motion.
23
Brogliato, Bernard, Hongjian Zhang, and Caishan Liu. "Analysis of a generalized kinematic impact law for multibody-multicontact systems, with application to the planar rocking block and chains of balls." Multibody System Dynamics 27, no. 3 (January 24, 2012): 351–82. http://dx.doi.org/10.1007/s11044-012-9301-3.
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Jessen, Kristian, and Erling Halfdan Stenby. "Fluid Characterization for Miscible EOR Projects and CO2 Sequestration." SPE Reservoir Evaluation & Engineering 10, no. 05 (October 1, 2007): 482–88. http://dx.doi.org/10.2118/97192-pa.
Abstract:
Summary Accurate performance prediction of miscible enhanced-oil-recovery (EOR) projects or CO2 sequestration in depleted oil and gas reservoirs relies in part on the ability of an equation-of-state (EOS) model to adequately represent the properties of a wide range of mixtures of the resident fluid and the injected fluid(s). The mixtures that form when gas displaces oil in a porous medium will, in many cases, differ significantly from compositions created in swelling tests and other standard pressure/volume/temperature (PVT) experiments. Multicontact experiments (e.g., slimtube displacements) are often used to condition an EOS model before application in performance evaluation of miscible displacements. However, no clear understanding exists of the impact on the resultant accuracy of the selected characterization procedure when the fluid description is subsequently included in reservoir simulation. In this paper, we present a detailed analysis of the quality of two different characterization procedures over a broad range of reservoir fluids (13 samples) for which experimental swelling-test and slimtube-displacement data are available. We explore the impact of including swelling-test and slimtube experiments in the data reduction and demonstrate that for some gas/oil systems, swelling tests do not contribute to a more accurate prediction of multicontact miscibility. Finally, we report on the impact that use of EOS models based on different characterization procedures can have on recovery predictions from dynamic 1D displacement calculations. Introduction During the past few decades, a significant effort has been invested in the studies and development of improved-oil-recovery processes. From a technical point of view, gas injection can be a very efficient method for improving the oil production, particularly in the case when miscibility develops during the displacement process. The lowest pressure at which a gas should be injected into the reservoir to obtain the multicontact miscible displacement—the minimum miscibility pressure (MMP)—has consequently attained a very important status in EOR studies. Various methods for measuring and calculating the MMP have been proposed in the literature. Many of these are based on simplifications such as the ternary representation of the compositional space. This method fails to honor the existence of a combined mechanism controlling the development of miscibility in real reservoir fluids. Zick (1986) and Stalkup (1987) described the existence of the condensing/vaporizing mechanism. They showed that the development of miscibility (MMP) in multicomponent gas-displacement processes could, independent of the mechanism controlling the development of miscibility, be predicted accurately by 1D compositional simulations. A semianalytical method for predicting the MMP was later presented by Wang and Orr (1997), who played an important role in the development and application of the analytical theory of gas-injection processes. Jessen et al. (1998) subsequently developed an efficient algorithm for performing these calculations, reducing the MMP calculation time to a few seconds even for fluid descriptions of 10 components or more. Later, Jessen et al. (2001) used this approach to generate approximate solutions to the dispersion-free, 1D-displacement problem for multicomponent gas-injection processes. Analytical and numerical methods for predicting the performance of a gas-injection process depend on an EOS to predict the phase behavior of the mixtures that form in the course of a displacement process. The role of the phase behavior in relation to numerical diffusion in compositional reservoir simulation has been pointed out previously by Stalkup (1990) and by Stalkup et al. (1990). Recently, Jessen et al. (2004) proposed a method to quantify the interplay of the phase behavior and numerical diffusion in a finite-difference simulation of a gas-injection process. By analyzing the phase behavior of the injection-gas/reservoir-fluid system, a measure of the impact, referred to as the dispersive distance, can be calculated. The dispersive distance is useful when designing and interpreting large-scale compositional reservoir simulations.
25
Zhang, Kaiyi, Bahareh Nojabaei, Kaveh Ahmadi, and Russell T. Johns. "Effect of Gas/Oil Capillary Pressure on Minimum Miscibility Pressure for Tight Reservoirs." SPE Journal 25, no. 02 (December 31, 2019): 820–31. http://dx.doi.org/10.2118/199354-pa.
Abstract:
Summary Shale and tight reservoir rocks have pore throats on the order of nanometers, and, subsequently, a large capillary pressure. When the permeability is ultralow (k < 200 nd), as in many shale reservoirs, diffusion might dominate over advection, so that the gas injection might no longer be controlled by the multicontact minimum miscibility pressure (MMP). For gasfloods in tight reservoirs, where k > 200 nd and capillary pressure is still large, however, advection likely dominates over diffusive transport, so that the MMP once again becomes important. This paper focuses on the latter case to demonstrate that the capillary pressure, which has an impact on the fluid pressure/volume/temperature (PVT) behavior, can also alter the MMP. The results show that the calculation of the MMP for reservoirs with nanopores is affected by the gas/oil capillary pressure, owing to alteration of the key tie lines in the displacement; however, the change in the MMP is not significant. The MMP is calculated using three methods: the method of characteristics (MOC); multiple mixing cells; and slimtube simulations. The MOC method relies on solving hyperbolic equations, so the gas/oil capillary pressure is assumed to be constant along all tie lines (saturation variations are not accounted for). Thus, the MOC method is not accurate away from the MMP but becomes accurate as the MMP is approached when one of the key tie lines first intersects a critical point (where the capillary pressure then becomes zero, making saturation variations immaterial there). Even though the capillary pressure is zero for this key tie line, its phase compositions (and, hence, the MMP) are impacted by the alteration of all other key tie lines in the composition space by the gas/oil capillary pressure. The reason for the change in the MMP is illustrated graphically for quaternary systems, in which the MMP values from the three methods agree well. The 1D simulations (typically slimtube simulations) show an agreement with these calculations as well. We also demonstrate the impact of capillary pressure on CO2-MMP for real reservoir fluids. The effect of large gas/oil capillary pressure on the characteristics of immiscible displacements, which occur at pressures well below the MMP, is discussed.
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Glaso, O. "Generalized Minimum Miscibility Pressure Correlation (includes associated papers 15845 and 16287 )." Society of Petroleum Engineers Journal 25, no. 06 (December 1, 1985): 927–34. http://dx.doi.org/10.2118/12893-pa.
Abstract:
Abstract This paper presents a generalized correlation for predicting the minimum miscibility pressure (MMP) required for predicting the minimum miscibility pressure (MMP) required for multicontact miscible displacement of reservoir fluids by hydrocarbon, CO2, or N2 gas. The equations are derived from graphical correlations given by Benham et al. and give MMP as a function of reservoir temperature, C7+ molecular weight of the oil, mole percent methane in the injection gas, and the molecular weight of the intermediates (C2 through C6) in the gas. CO2 and N2 are represented in the current correlation by "equivalent" methane/propane- and methane/ethane-mixture injection gases, respectively. The study shows that for hydrocarbon systems, paraffinicity has an effect on MMP. In the equations, the C7+ paraffinicity has an effect on MMP. In the equations, the C7+ molecular weight of the oil is corrected to a K factor of 11.95, thereby accounting for varying paraffinicity. An additional temperature effect on N2 MMP is related to the API gravity of the oil. The N2 correlation, however, is not tested against measured MMP data other than those used to develop the equation and should be used with care. A correlation that accounts for the additional effect on CO2 MMP caused by the presence of intermediate components in the reservoir oil is presented. Predicted MMP's from the correlations developed are compared to experimental slim-tube displacement data from the literature and from our displacement tests on North Sea gas/oil systems. These displacement tests have been performed with a packed slim tube, where the effect of viscous fingering is reduced to a minimum. Introduction Multicontact miscibility is represented most easily with a ternary diagram, where the composition of the driving or displaced fluid is altered. This is obtained by vaporization of light hydrocarbon components into a driving gas or by condensation of hydrocarbon components from a driving gas into the reservoir oil. Miscibility between reservoir oils and hydrocarbon gases is achieved either by vaporization or by condensing-gas-drive mechanism, depending on the reservoir oil and injection-gas composition. With N2 and CO2, miscibility is obtained by vaporization, but with CO2, miscibility usually is achieved at lower pressure because CO2 extracts much higher-molecular-weight hydrocarbons from the reservoir oil than N2 gas. The prediction of miscibility conditions from ternary diagrams is based on experimentally determined or calculated gas and liquid compositions of a reservoir-oil/injection-gas mixture. The experimental gas and liquid equilibrium data are not easy to obtain and are often time-consuming to determine, especially near the plait point. The method for calculating gas and liquid data with point. The method for calculating gas and liquid data with equations of state to predict miscibility relies largely on gas and liquid compositions near the plait-point region. It is generally accepted that such data may not be sufficiently accurate. Flow experiments offer the most reliable method to determine the pressure required for miscibility with CO2, N 2, and hydrocarbon gas. The slim-tube method has been most widely used to determine miscibility. Different experimental procedures and interpretation criteria, however, have ted to different definitions of miscibility and have caused considerable confusion. The limitation of the slim-tube test and the problems associated with miscible displacement in porous media have been described by several authors. Phase behavior and mechanisms of miscible flooding with CO2, N2, and hydrocarbon gas have also been described by several authors. Correlations for predicting MMP have been proposed by a number of investigators and are important tools in the selection of potential reservoirs for gas miscible flooding. Therefore, the correlations must be as accurate as possible. Several CO2 MMP correlations have been published, but none of these can be used with enough published, but none of these can be used with enough confidence for final project design. They are useful, however, for screening and preliminary work. Correlations on CO2 miscible flooding have shown temperature to be the most important parameter but they disagree regarding the effect of oil type (e.g., C7+ properties of the oil). Compared with CO2 miscible flooding, very little has been published on high-pressure hydrocarbon gas miscible flooding. A recent publication gives a correlation for predicting MMP with lean hydrocarbon gases and nitrogen. In 1960, Benham et al. presented empirical curves that can estimate miscibility conditions for reservoir oils that are displaced by rich gas within a pressure range of 1,500 to 3,000 psia [10.34 to 20.68 MPa]. They assumed a limiting tie line (at the critical composition on a ternary diagram) parallel to the C1–C7+ axis and estimated mole percent methane in the injection gas from calculated percent methane in the injection gas from calculated critical points with pressure, temperature, molecular weights of C2 through C4 in the gas, and the C5+ molecular weight of the oil as variables. From Benham et al.'s data, the proposed equations have been derived for predicting MMP. SPEJ P. 927
27
Tsao, Jeffrey, and Charles J. Lumsden. "CRYSTAL: Building Multicontext Virtual Environments." Presence: Teleoperators and Virtual Environments 6, no. 1 (February 1997): 57–72. http://dx.doi.org/10.1162/pres.1997.6.1.57.
Abstract:
Current virtual environment systems are, for the most part, dedicated to specific applications such as engineering or surgery. The CRYSTAL project applied the concept of crystals, or 3D “windows,” to segment the virtual world into independent volumes, which may interact with each other. The contents of individual crystals can be very different from crystal to crystal, so the resulting virtual environment (VE) is not restricted to any unique context, and it is suitable as a general-purpose workspace. Crystals are created and owned by independent programs called modules, which serve as functional elements of the VE. There are basic modules to provide common functions, such as navigation, wand control, and so on. Extra modules can be launched to add content and functionality to the VE, and the modules can also be terminated interactively. Unlike “pipelined” systems for VE design, CRYSTAL modules are designed to self-assemble and resolve any interface conflicts automatically. As a result, they do not place a high demand on user proficiency in customizing VEs for a variety of uses.
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Wen, Huichao. "An Improved Machine Translation Model and its Application in Japanese Multi-Context Translation." Security and Communication Networks 2022 (August 2, 2022): 1–10. http://dx.doi.org/10.1155/2022/8364278.
Abstract:
In order to further improve the application of machine translation model in Japanese translation, analytic analysis method is adopted to optimize the original machine translation model. The improved machine translation model is used to analyze and describe Japanese translation. Finally, the optimized machine translation model is used to analyze Japanese multicontext. The relevant indexes and parameters were extracted and verified, and finally the model was verified by relevant experiments. The results show that the vector variation graph with different parameters can be divided into slow decline stage, stable change stage, and fast decline stage according to the increase of iteration number and the influence of corresponding change trend. In addition, it can be seen from the value of PE curve that the influence of parameter pe is the least, while the influence of corresponding re parameter is the greatest. The multicontext index of Japanese has the greatest influence on Japanese fluency and the least influence on Japanese keywords, and the trend of influence is parabolic. The application curve of the optimized machine translation model to Japanese in multiple contexts shows that different parameters have different effects on Japanese, which should be represented by the positive parameter V. Finally, the accuracy of the model is verified by experimental data. The above research can provide support for the application of machine learning in different fields and also provide research ideas for the multicontext translation of Japanese.
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Jessen, Kristian, and Franklin M. Orr. "On Interfacial-Tension Measurements to Estimate Minimum Miscibility Pressures." SPE Reservoir Evaluation & Engineering 11, no. 05 (October 1, 2008): 933–39. http://dx.doi.org/10.2118/110725-pa.
Abstract:
Summary Measurements of the interfacial tension (IFT) of mixtures of a reservoir fluid and injection gas at various pressures have been proposed as an experimental method for predicting the minimum miscibility pressure (MMP) in an experiment referred to as the vanishing-IFT (VIT) technique. In this paper, we analyze the accuracy and reliability of the VIT approach using phase equilibrium and slimtube experimental observations and equation-of-state (EOS) calculations of the behavior of VIT experiments for the same systems. We consider 13 gas/oil systems for which phase equilibrium and density data and slimtube measurements of the MMP are available. We show that tuned EOS characterizations using 15 components to represent the gas/oil systems yield calculations of phase compositions and densities and calculated MMPs that reproduce the experimental observations accurately. We assume that IFTs can be calculated with a parachor expression, and we simulate the behavior of a series of VIT experiments with different mixture compositions in the VIT cell. We show that compositions of mixtures created in the VIT cell are not, in general, critical mixtures and that calculated estimates of the MMP obtained by the VIT approach depend strongly on the composition of the mixture used in the experiment. We show also that those MMP estimates may or may not differ significantly from values obtained in slimtube displacements. Fortuitously chosen mixture compositions can result in VIT-experiment estimates that agree well with slimtube MMPs, while for other mixtures, the error of the estimates can be quite large. In particular, we show that errors in the VIT-technique estimate of the MMP are often large for gas/oil systems for which the first-contact miscibility pressure (FCMP) is much larger than the slimtube MMP. We conclude, therefore, that the VIT experiment is not a reliable single source of information regarding the development of multicontact miscibility in multicomponent gas/oil displacements. Introduction Many oil fields are now candidates for enhanced-oil-recovery processes such as tertiary gasfloods or miscible water-alternating-gas injection schemes. The MMP is an important parameter in the design and implementation of these displacement processes and, hence, it is equally important that the MMP be determined by a method that is both reliable and accurate. Several methods have been proposed for measurement of the MMP. The slimtube-displacement experiment is the most commonly used approach (Yellig and Metcalfe 1980; Holm and Josendal 1982; Orr et al. 1982). Because of the time-consuming process of performing multiple slimtube-displacement experiments, alternative experimental approaches have been proposed. Some investigators have suggested use of a rising-bubble experiment, in which observations of bubbles of injection gas rising through oil (Christiansen and Haines 1987; Eakin and Mitch 1988; Novosad et al. 1990; Sibbald et al. 1991; Mihcakan and Poettmann 1994), are a basis of a method for determining the MMP. Zhou and Orr (1988) concluded that the changes in bubble behavior observed in the rising-bubble experiment are caused primarily by changes in IFT as components in the bubble dissolve in the oil and components in the oil transfer to the bubble. They showed that rising-bubble experiments could be used to measure the MMP for vaporizing gas drives, but are less accurate for condensing gas drives, while a drop of oil falling through gas could be used to determine the MMP for condensing gas drives. Whether either a falling-drop or a rising-bubble experiment could be used to determine the MMP accurately in condensing/vaporizing gas drives such as those described by Zick (1986), Stalkup (1987), and Johns et al. (1993) has not been determined. Rao and coworkers proposed a different use of IFT observations to determine the MMP (Rao 1997, 1999; Rao and Lee 2002, 2003; Ayirala et al. 2003; Ayirala and Rao 2004, 2006a, 2006b; Sequeira 2006). They measured IFTs for pendant drops of oil suspended in a cell containing a two-phase mixture of the injection gas and the oil. In that approach, known as the VIT experiment, the IFT is measured at a sequence of pressures, and the MMP is taken to be the pressure at which the IFT plotted as a function of pressure extrapolates to zero IFT. Orr and Jessen (2007) presented an analysis of the VIT technique based on EOS calculations for well-characterized ternary and quaternary gas/oil systems and demonstrated that the VIT experiment may give estimates of the MMP that differ significantly from the MMP based on critical tie-lines for condensing, vaporizing, and condensing/vaporizing gas drives. In this paper, we extend the analysis of Orr and Jessen (2007) and calculate the IFT behavior that would be observed in the VIT experiment for gas displacements of multicomponent crude-oil systems. We assess the accuracy of MMP estimated by the VIT approach for 13 multicomponent gas/oil displacements for which experimental phase-equilibrium and slimtube data are available, and we demonstrate that for these multicomponent crude-oil systems, the VIT approach can give estimates of the MMP that are close to the actual MMP or that are significantly in error, depending on the compositions of mixtures created in the equilibrium cell.
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Deng, Shangju, and Jiwei Qin. "Matrix factorization completed multicontext data for tensor-enhanced recommendation." Journal of Intelligent & Fuzzy Systems 41, no. 6 (December 16, 2021): 6727–38. http://dx.doi.org/10.3233/jifs-210641.
Abstract:
Tensors have been explored to share latent user-item relations and have been shown to be effective for recommendation. Tensors suffer from sparsity and cold start problems in real recommendation scenarios; therefore, researchers and engineers usually use matrix factorization to address these issues and improve the performance of recommender systems. In this paper, we propose matrix factorization completed multicontext data for tensor-enhanced algorithm a using matrix factorization combined with a multicontext data method for tensor-enhanced recommendation. To take advantage of existing user-item data, we add the context time and trust to enrich the interactive data via matrix factorization. In addition, Our approach is a high-dimensional tensor framework that further mines the latent relations from the user-item-trust-time tensor to improve recommendation performance. Through extensive experiments on real-world datasets, we demonstrated the superiority of our approach in predicting user preferences. This method is also shown to be able to maintain satisfactory performance even if user-item interactions are sparse.
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Fan, Xiaocong, Michael McNeese, Bingjun Sun, Timothy Hanratty, Laurel Allender, and John Yen. "Human–Agent Collaboration for Time-Stressed Multicontext Decision Making." IEEE Transactions on Systems, Man, and Cybernetics - Part A: Systems and Humans 40, no. 2 (March 2010): 306–20. http://dx.doi.org/10.1109/tsmca.2009.2035302.
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Johns, R. T., P. Sah, and R. Solano. "Effect of Dispersion on Local Displacement Efficiency for Multicomponent Enriched-Gas Floods Above the Minimum Miscibility Enrichment." SPE Reservoir Evaluation & Engineering 5, no. 01 (February 1, 2002): 4–10. http://dx.doi.org/10.2118/75806-pa.
Abstract:
Summary Recent research on four-component 1D displacements has shown that enriching the gas above the minimum miscibility enrichment (MME) can increase oil recovery substantially for certain systems. Research has shown further that the oil-recovery increase can be very sensitive to the level of dispersion at the enrichment chosen. The main focus of this paper is to extend the research on four-component systems to displacements of multicomponent oils and gases in which the recovery is affected by dispersion and enrichment. We consider here a 12-component oil displaced by solvents enriched above the MME. For this case, the increase in recovery (displacement efficiency) above the MME can be as large as 15% original oil in place (OOIP), depending on the level of mixing. The methodology outlined can be used as a screening tool to determine whether a significant benefit may exist and whether further 2D and 3D studies are warranted. A secondary focus of the paper is to examine in detail how dispersion affects recoveries and displacement mechanisms for the 4- and 12-component systems. We show that for the case of the four-component model, the displacement mechanism changes from a combined condensing/vaporizing (CV) displacement to a strictly condensing one as enrichment increases above the MME. We also show how to quantify the percentage of the CV displacement that is vaporizing or condensing by calculating the compositional distances between key tie lines identified from "dispersion- free" theory. Introduction The objective of enriched-gas floods is to achieve a multicontact miscible (MCM) displacement by a sufficient enrichment of the gas with intermediate components. If a near-MCM process occurs, then a highly efficient local displacement can be achieved. Because the local displacement efficiency is one of the primary factors that govern ultimate recovery, it is very important to quantify how mixing the oil and gas in reservoirs can adversely impact the efficiency of the MCM process. One of the key variables in enriched-gas floods, therefore, is the optimum enrichment for a highly efficient displacement. Slimtube experiments are often used to help determine the optimum enrichment. Because these experiments typically show that the oil-recovery increase beyond the MME is minimal, the optimum enrichment is often taken to be the MME. Other factors, such as the availability of solvents in the field and surface facility considerations, also can impact the choice of enrichment. Recent results by Johns et al.1 show that the slimtube results may be misleading because of the scaleup of dispersion from the laboratory to the field scale. Mixing by dispersion and other mechanisms is likely much greater in the field than the level of dispersion found in laboratory cores. Oil and gas mixing in a reservoir can be caused by mechanisms such as molecular diffusion, mechanical dispersion, gravity crossflow, viscous crossflow, and capillary crossflow.2 Several authors have examined the effect of mixing and enrichment above the MME on oil recovery. Johns et al.1 considered the effect of dispersion on recovery in 1D displacements. They showed that the "knee" in the recovery curve from slimtube experiments depends on the level of dispersion. For small dispersivities typical of slimtubes, the knee occurs at the MME. For greater levels of mixing, they showed that the knee could occur at enrichments much greater than the MME. Chang3 matched coreflood displacements with reservoir simulations at different enrichments. He showed that recovery increased sharply for enrichments above the MME. Chang concluded that the increased recoveries were caused by higher displacement and sweep efficiencies as the enrichment level increased. The better sweep efficiency was attributed to increased gas density with enrichment. Jerauld4 also observed an increase in recovery above the MME. Giraud et al.5 observed that the highest recovery occurred at pressures above the minimum miscibility pressure (MMP). Stalkup2 showed that significant additional recovery might be obtained by injecting enriched gases above the MME. A significant increase in recovery occurred for longitudinal dispersivities as low as 0.3 ft, when the solvent and water were injected in slugs. He also concluded that mixing of the solvent and the oil by viscous crossflow during water alternating gas (WAG) might dominate other mixing mechanisms in the reservoir (i.e., dispersion). Numerous other papers also have examined the effect of viscous crossflow, capillary pressure, diffusion, gravity, heterogeneities, and numerical grids on recovery.6–19 The main focus of this paper is to extend the work for four-component systems to displacements of a 12-component oil by solvents enriched above the MME. The effects of realistic levels of dispersive mixing on the displacement efficiency of the floods are examined. The slope in the recovery curves is used to quantify the effect of dispersion on the displacement efficiency. We also show how dispersion and enrichment affect the CV displacement mechanisms. The displacement mechanisms of the miscible process are quantified exactly for the first time using dispersion-free theory. We use numerical dispersion in this research to mimic physical dispersion. Analytical and Numerical Models The numerical solutions for 1D flow are calculated with the U. of Texas at Austin Compositional Simulator (UTCOMP), a compositional simulator that includes volume change on mixing.20 Analytical solutions to dispersion-free flow in one dimension are solved using hyperbolic conservation equations with the assumptions stated by Helfferich.21 The analytical solutions are used to find the MME and the key tie lines in the displacement.22–26
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Cinar, Yildiray, and Franklin M. Orr. "Measurement of Three-Phase Relative Permeability with IFT Variation." SPE Reservoir Evaluation & Engineering 8, no. 01 (February 1, 2005): 33–43. http://dx.doi.org/10.2118/89419-pa.
Abstract:
Summary In this paper, we present results of an experimental investigation of the effects of variations in interfacial tension (IFT) on three-phase relative permeability. We report results that demonstrate the effect of low IFT between two of three phases on the three-phase relative permeabilities. To create three-phase systems in which IFT can be con-trolled systematically, we used a quaternary liquid system composed of hexadecane(C16), n-butanol (NBA), water (H2O), and isopropanol (IPA). Measured equilibrium phase compositions and IFTs are reported. The reported phase behavior of the quaternary system shows that the H2O-rich phase should represent the "gas" phase, the NBA-rich phase should represent the "oil" phase, and the C16-rich phase should represent the "aqueous" phase. Therefore, we used oil-wet Teflon (PTFE) bead packs to simulate the fluid flow in a water-wet oil reservoir. We determined phase saturations and three-phase relative permeabilities from recovery and pressure-drop data using an extension of the combined Welge/Johnson-Bossler-Naumann (JBN) method to three-phase flow. Measured three-phase relative permeabilities are reported. The experimental results indicate that the wetting-phase relative permeability was not affected by IFT variation, whereas the other two-phase relative permeabilities were clearly affected. As IFT decreases, the oil and gas phases become more mobile at the same phase saturations. For gas/oil IFTs in the range of 0.03 to 2.3 mN/m, we observed an approximately 10-fold increase in the oil and gas relative permeabilities against an approximately 100-fold decrease in the IFT. Introduction Variations in gas and oil relative permeabilities as a function of IFT are of particular importance in the area of compositional processes such as high-pressure gas injection, where oil and gas compositions can vary significantly both spatially and temporally. Because gas-injection processes routinely include three-phase flow (either because the reservoir has been water-flooded previously or because water is injected alternately with gas to improve overall reservoir sweep efficiency), the effect of IFT variations on three-phase relative permeabilities must be delineated if the performance of the gas-injection process is to be predicted accurately. The development of multicontact miscibility in a gas-injection process will create zones of low IFT between gas and oil phases in the presence of water. Although there have been studies of the effect of low IFT on two-phase relative permeability,1–14 there are limited experimental data published so far analyzing the effect of low IFT on three-phase relative permeabilities.15,16 Most authors have focused on the effect of IFT on oil and solvent relative permeabilities.17 Experimental results show that residual oil saturation and relative permeability are strongly affected by IFT, especially when the IFT is lower than approximately 0.1 mN/m (corresponding to a range of capillary number of 10–2 to 10–3). Bardon and Longeron3 observed that oil relative permeability increased linearly as IFT was reduced from approximately 12.5 mN/m to 0.04 mN/m and that for IFT below 0.04, the oil relative permeability curves shifted more rapidly with further reductions in IFT. Later, Asar and Handy6 showed that oil relative permeability curves began to shift as IFT was reduced below 0.18 mN/m for a gas/condensate system near the critical point. Delshad et al.15 presented experimental data for low-IFT three-phase relative permeabilities in Berea sandstone cores. They used a brine/oil/surfactant/alcohol mixture that included a microemulsion and excess oil and brine. The measurements were done at steady-state conditions with a constant capillary number of 10–2 between the microemulsion and other phases. The IFTs of microemulsion/oil and microemulsion/brine were low, whereas the IFT between oil and brine was high. They concluded that low-IFT three-phase relative permeabilities are functions of their own saturations only. Amin and Smith18 recently have published experimental data showing that the IFTs for each binary mixture of brine, oil, and gas phases vary as pressure increases(Fig. 1). Fig. 1 shows that the IFT of a gas/oil pair decreases as the pressure increases, whereas the IFTs of the gas/brine and oil/brine pairs approach each other.
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Ayub, Shahanaz, R. Jagadeesh Kannan, Shitharth S, Raed Alsini, Tawfiq Hasanin, and Choragudi Sasidhar. "LSTM-Based RNN Framework to Remove Motion Artifacts in Dynamic Multicontrast MR Images with Registration Model." Wireless Communications and Mobile Computing 2022 (May 4, 2022): 1–12. http://dx.doi.org/10.1155/2022/5906877.
Abstract:
Today, many people under the age of 10 are being examined for brain-related issues, including tumours, without displaying any symptoms. It is not unusual for children to develop brain-related concerns such as tumours and central nervous system disorders, which may affect 15% of the population. Medical experts believe that the irregular eating habits (junk food) and the consumption of pesticide-tainted fruits and vegetables are to blame. The human body is naturally resistant to harmful gears, but only up to a point. If it exceeds the limit, a cell manipulation process is automatically initiated that can remove dangerous inactive tissues from the cell membrane and later grows into tumour blockage in the human body. Thus, the adoption of an advanced computer-based diagnostic system is highly recommended in order to generate visually enhanced images for anomaly identification and infectious tissue segmentation. In most cases, an MR image is chosen since it is easier to distinguish between affected and nonaffected tissue. Conventional convolution neural network (CCNN) mapping and feature extraction are difficult because of the vast volume of data. In addition, it takes a lengthy time for the MRI scanning process to obtain diverse positions for anomaly identification. Aside from the discomfort, the patient may experience motion abnormalities. Recurrent neural network (RNN) classifies tumour regions into several isolated portions much faster and more accurately, so that it can be prevented. To remove motion artefacts from dynamic multicontrast MR images, a novel long short-term memory- (LSTM-) based RNN framework is introduced in this research. With this method, the MR image’s visual quality is improved over CCNN while simultaneously mapping a larger volume and extracting more quiet characteristics than CCNN can. DC-CNN, SMSR-CNN, FMSI-CNN, and DRCA-CNN results are compared. For both low and high signal-to-noise ratios, the suggested LSTM-based RNN framework has gained reasonable feature intelligibility (SNRs). In comparison to previous approaches, it requires less computing and has higher accuracy when it comes to detecting infected portions.
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Chi, Nai-Wen, and Alicia A. Grandey. "Emotional Labor Predicts Service Performance Depending on Activation and Inhibition Regulatory Fit." Journal of Management 45, no. 2 (October 12, 2016): 673–700. http://dx.doi.org/10.1177/0149206316672530.
Abstract:
When service providers regulate their moods and expressions (i.e., deep acting and surface acting), are they better performers? Drawing on the framework of activation-inhibition regulatory systems and regulatory fit, we propose (a) that deep acting represents an activation-oriented regulation strategy and surface acting, an inhibition-oriented regulation strategy; (b) that these strategies have separate pathways to desirable performance (i.e., affective delivery) and counterproductive performance (i.e., service sabotage), respectively; and (c) that performance is optimized when momentary regulation strategies are aligned with activation- and inhibition-oriented traits. Empirically, across two studies, we employ a multilevel approach (i.e., within- and between-person), a multisource approach (i.e., self, coworker, customer), and a multicontext approach (i.e., banks and restaurants) to test regulatory fit as applied to emotional labor. In two studies, we support separate activation and inhibition pathways, plus regulatory fit, in that deep acting is beneficial to affective delivery for those higher in two activation traits—namely, extraversion and openness—and that surface acting predicts service sabotage for those lower in an inhibition trait: conscientiousness. We empirically rule out mood as the explanation for these effects, propose future research to apply regulatory fit to other outcomes and contexts, and suggest practical implications for services.
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Zheng, Yu, and Chee-Meng Chew. "Fast Equilibrium Test and Force Distribution for Multicontact Robotic Systems." Journal of Mechanisms and Robotics 2, no. 2 (March 24, 2010). http://dx.doi.org/10.1115/1.4001089.
Abstract:
In the research of multicontact robotic systems, the equilibrium test and contact force distribution are two fundamental problems, which need to determine the existence of feasible contact forces subject to the friction constraint, and their optimal values for counterbalancing the other wrenches applied on the system and maintaining the system in equilibrium. All the wrenches, except those generated by the contact forces, can be treated as a whole, called the external wrench. The external wrench is time-varying in a dynamic system and both problems usually must be solved in real time. This paper presents an efficient procedure for solving the two problems. Using the linearized friction model, the resultant wrenches that can be produced by all contacts constitute a polyhedral convex cone in six-dimensional wrench space. Given an external wrench, the procedure computes the minimum distance between the wrench cone and the required equilibrating wrench, which is equal but opposite to the external wrench. The zero distance implies that the equilibrating wrench lies in the wrench cone, and that the external wrench can be resisted by contacts. Then, a set of linearly independent wrench vectors in the wrench cone are also determined, such that the equilibrating wrench can be written as their positive combination. This procedure always terminates in finite iterations and runs very fast, even in six-dimensional wrench space. Based on it, two contact force distribution methods are provided. One combines the procedure with the linear programming technique, yielding optimal contact forces with linear time complexity. The other directly utilizes the procedure without the aid of any general optimization technique, yielding suboptimal contact forces with nearly constant time complexity. Effective strategies are suggested to ensure the solution continuity.
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Ponton, Brahayam, Majid Khadiv, Avadesh Meduri, and Ludovic Righetti. "Efficient Multicontact Pattern Generation With Sequential Convex Approximations of the Centroidal Dynamics." IEEE Transactions on Robotics, 2021, 1–19. http://dx.doi.org/10.1109/tro.2020.3048125.
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Rouxel, Quentin, Kai Yuan, Ruoshi Wen, and Zhibin Li. "Multicontact Motion Retargeting Using Whole-Body Optimization of Full Kinematics and Sequential Force Equilibrium." IEEE/ASME Transactions on Mechatronics, 2022, 1–11. http://dx.doi.org/10.1109/tmech.2022.3152844.
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Kim, Daekyoo, Ronald Triolo, and Hamid Charkhkar. "Plantar somatosensory restoration enhances gait, speed perception, and motor adaptation." Science Robotics 8, no. 83 (October 18, 2023). http://dx.doi.org/10.1126/scirobotics.adf8997.
Abstract:
Lower limb loss is a major insult to the body’s nervous and musculoskeletal systems. Despite technological advances in prosthesis design, artificial limbs are not yet integrated into the body’s physiological systems. Therefore, lower limb amputees (LLAs) experience lower balance confidence, higher fear of falls, and impaired gait compared with their able-bodied peers (ABs). Previous studies have demonstrated that restored sensations perceived as originating directly from the missing limb via neural interfaces improve balance and performance in certain ambulatory tasks; however, the effects of such evoked sensations on neural circuitries involved in the locomotor activity are not well understood. In this work, we investigated the effects of plantar sensation elicited by peripheral nerve stimulation delivered by multicontact nerve cuff electrodes on gait symmetry and stability, speed perception, and motor adaptation. We found that restored plantar sensation increased stance time and propulsive force on the prosthetic side, improved gait symmetry, and yielded an enhanced perception of prosthetic limb movement. Our results show that the locomotor adaptation among LLAs with plantar sensation became similar to that of ABs. These findings suggest that our peripheral nerve–based approach to elicit plantar sensation directly affects central nervous pathways involved in locomotion and motor adaptation during walking. Our neuroprosthesis provided a unique model to investigate the role of somatosensation in the lower limb during walking and its effects on perceptual recalibration after a locomotor adaptation task. Furthermore, we demonstrated how plantar sensation in LLAs could effectively increase mobility, improve walking dynamics, and possibly reduce fall risks.
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Dimitri, Giovanna Maria, Simeon Spasov, Andrea Duggento, Luca Passamonti, Pietro Lió, and Nicola Toschi. "Multimodal and multicontrast image fusion via deep generative models." Information Fusion, July 2022. http://dx.doi.org/10.1016/j.inffus.2022.07.017.