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Letteratura scientifica selezionata sul tema "Gradient implicite"

Autore: Grafiati

Pubblicato: 31 agosto 2024

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Articoli di riviste sul tema "Gradient implicite"

Weller, Hilary, e Ava Shahrokhi. "Curl-Free Pressure Gradients over Orography in a Solution of the Fully Compressible Euler Equations with Implicit Treatment of Acoustic and Gravity Waves". Monthly Weather Review 142, n. 12 (1 dicembre 2014): 4439–57. http://dx.doi.org/10.1175/mwr-d-14-00054.1.

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Abstract Steep orography can cause noisy solutions and instability in models of the atmosphere. A new technique for modeling flow over orography is introduced that guarantees curl-free gradients on arbitrary grids, implying that the pressure gradient term is not a spurious source of vorticity. This mimetic property leads to better hydrostatic balance and better energy conservation on test cases using terrain-following grids. Curl-free gradients are achieved by using the covariant components of velocity over orography rather than the usual horizontal and vertical components. In addition, gravity and acoustic waves are treated implicitly without the need for mean and perturbation variables or a hydrostatic reference profile. This enables a straightforward description of the implicit treatment of gravity waves. Results are presented of a resting atmosphere over orography and the curl-free pressure gradient formulation is advantageous. Results of gravity waves over orography are insensitive to the placement of terrain-following layers. The model with implicit gravity waves is stable in strongly stratified conditions, with NΔt up to at least 10 (where N is the Brunt–Väisälä frequency). A warm bubble rising over orography is simulated and the curl-free pressure gradient formulation gives much more accurate results for this test case than a model without this mimetic property.

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Askes, Harm, e Miguel A. Gutiérrez. "Implicit gradient elasticity". International Journal for Numerical Methods in Engineering 67, n. 3 (2006): 400–416. http://dx.doi.org/10.1002/nme.1640.

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Haugh, Jason M., Franca Codazzi, Mary Teruel e Tobias Meyer. "Spatial Sensing in Fibroblasts Mediated by 3′ Phosphoinositides". Journal of Cell Biology 151, n. 6 (11 dicembre 2000): 1269–80. http://dx.doi.org/10.1083/jcb.151.6.1269.

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The directed movement of fibroblasts towards locally released platelet-derived growth factor (PDGF) is a critical event in wound healing. Although recent studies have implicated polarized activation of phosphoinositide (PI) 3-kinase in G protein-mediated chemotaxis, the role of 3′ PI lipids in tyrosine kinase-triggered chemotaxis is not well understood. Using evanescent wave microscopy and green fluorescent protein–tagged Akt pleckstrin homology domain (GFP–AktPH) as a molecular sensor, we show that application of a shallow PDGF gradient triggers a markedly steeper gradient in 3′ PI lipids in the adhesion zone of fibroblasts. Polar GFP–AktPH gradients, as well as a new type of radial gradient, were measured from front to rear and from the periphery to the center of the adhesion zone, respectively. A strong spatial correlation between polarized 3′ PI production and rapid membrane spreading implicates 3′ PI lipids as a direct mediator of polarized migration. Analysis of the temporal changes of 3′ PI gradients in the adhesion zone revealed a fast diffusion coefficient (0.5 μm2/s) and short lifetime of 3′ PIs of <1 min. Together, this study suggests that the tyrosine kinase-coupled directional movement of fibroblasts and their radial membrane activity are controlled by local generation and rapid degradation of 3′ PI second messengers.

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Minervini, Pasquale, Luca Franceschi e Mathias Niepert. "Adaptive Perturbation-Based Gradient Estimation for Discrete Latent Variable Models". Proceedings of the AAAI Conference on Artificial Intelligence 37, n. 8 (26 giugno 2023): 9200–9208. http://dx.doi.org/10.1609/aaai.v37i8.26103.

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The integration of discrete algorithmic components in deep learning architectures has numerous applications. Recently, Implicit Maximum Likelihood Estimation, a class of gradient estimators for discrete exponential family distributions, was proposed by combining implicit differentiation through perturbation with the path-wise gradient estimator. However, due to the finite difference approximation of the gradients, it is especially sensitive to the choice of the finite difference step size, which needs to be specified by the user. In this work, we present Adaptive IMLE (AIMLE), the first adaptive gradient estimator for complex discrete distributions: it adaptively identifies the target distribution for IMLE by trading off the density of gradient information with the degree of bias in the gradient estimates. We empirically evaluate our estimator on synthetic examples, as well as on Learning to Explain, Discrete Variational Auto-Encoders, and Neural Relational Inference tasks. In our experiments, we show that our adaptive gradient estimator can produce faithful estimates while requiring orders of magnitude fewer samples than other gradient estimators.

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Dong, Mingrong, Yixuan Yang, Kai Zeng, Qingwang Wang e Tao Shen. "Implicit Sharpness-Aware Minimization for Domain Generalization". Remote Sensing 16, n. 16 (6 agosto 2024): 2877. http://dx.doi.org/10.3390/rs16162877.

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Domain generalization (DG) aims to learn knowledge from multiple related domains to achieve a robust generalization performance in unseen target domains, which is an effective approach to mitigate domain shift in remote sensing image classification. Although the sharpness-aware minimization (SAM) method enhances DG capability and improves remote sensing image classification performance by promoting the convergence of the loss minimum to a flatter loss surface, the perturbation loss (maximum loss within the neighborhood of a local minimum) of SAM fails to accurately measure the true sharpness of the loss landscape. Furthermore, its variants often overlook gradient conflicts, thereby limiting further improvement in DG performance. In this paper, we introduce implicit sharpness-aware minimization (ISAM), a novel method that addresses the deficiencies of SAM and mitigates gradient conflicts. Specifically, we demonstrate that the discrepancy in training loss during gradient ascent or descent serves as an equivalent measure of the dominant eigenvalue of the Hessian matrix. This discrepancy provides a reliable measure for sharpness. ISAM effectively reduces sharpness and mitigates potential conflicts between gradients by implicitly minimizing the discrepancy between training losses while ensuring a sufficiently low minimum through minimizing perturbation loss. Extensive experiments and analyses demonstrate that ISAM significantly enhances the model’s generalization ability on remote sensing and DG datasets, outperforming existing state-of-the-art methods.

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Bertei, Antonio, Andrea Lamorgese e Roberto Mauri. "Constitutive Relations of Thermal and Mass Diffusion". Journal of Non-Equilibrium Thermodynamics 45, n. 1 (28 gennaio 2020): 27–38. http://dx.doi.org/10.1515/jnet-2019-0055.

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AbstractNon-equilibrium thermodynamics provides a general framework for the description of mass and thermal diffusion, thereby including also cross-thermal and material diffusion effects, which are generally modeled through the Onsager coupling terms within the constitutive equations relating heat and mass flux to the gradients of temperature and chemical potential. These so-called Soret and Dufour coefficients are not uniquely defined, though, as they can be derived by adopting one of the several constitutive relations satisfying the principles of non-equilibrium thermodynamics. Therefore, mass diffusion induced by a temperature gradient and heat conduction induced by a composition gradient can be implicitly, and unexpectedly, predicted even in the absence of coupling terms. This study presents a critical analysis of different formulations of the constitutive relations, with special focus on regular binary mixtures. It is shown that, among the different formulations presented, the one which adopts the chemical potential gradient at constant temperature as the driving force for mass diffusion allows for the implicit thermo-diffusion effect to be strictly absent while the resulting Dufour effect is negligibly small. Such a formulation must be preferred to the other ones since cross-coupling effects are predicted only if explicitly introduced via Onsager coupling coefficients.

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Nishikawa, Hiroaki. "From hyperbolic diffusion scheme to gradient method: Implicit Green–Gauss gradients for unstructured grids". Journal of Computational Physics 372 (novembre 2018): 126–60. http://dx.doi.org/10.1016/j.jcp.2018.06.019.

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Gourmel, Olivier, Loic Barthe, Marie-Paule Cani, Brian Wyvill, Adrien Bernhardt, Mathias Paulin e Herbert Grasberger. "A gradient-based implicit blend". ACM Transactions on Graphics 32, n. 2 (aprile 2013): 1–12. http://dx.doi.org/10.1145/2451236.2451238.

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Dandi, Yatin, Luis Barba e Martin Jaggi. "Implicit Gradient Alignment in Distributed and Federated Learning". Proceedings of the AAAI Conference on Artificial Intelligence 36, n. 6 (28 giugno 2022): 6454–62. http://dx.doi.org/10.1609/aaai.v36i6.20597.

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A major obstacle to achieving global convergence in distributed and federated learning is the misalignment of gradients across clients or mini-batches due to heterogeneity and stochasticity of the distributed data. In this work, we show that data heterogeneity can in fact be exploited to improve generalization performance through implicit regularization. One way to alleviate the effects of heterogeneity is to encourage the alignment of gradients across different clients throughout training. Our analysis reveals that this goal can be accomplished by utilizing the right optimization method that replicates the implicit regularization effect of SGD, leading to gradient alignment as well as improvements in test accuracies. Since the existence of this regularization in SGD completely relies on the sequential use of different mini-batches during training, it is inherently absent when training with large mini-batches. To obtain the generalization benefits of this regularization while increasing parallelism, we propose a novel GradAlign algorithm that induces the same implicit regularization while allowing the use of arbitrarily large batches in each update. We experimentally validate the benefits of our algorithm in different distributed and federated learning settings.

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Nelson, J. Bradley. "An alternate derivation of the three‐dimensional Hilbert transform relations from first principles". GEOPHYSICS 51, n. 4 (aprile 1986): 1014–15. http://dx.doi.org/10.1190/1.1442141.

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Several techniques for determining the location, geometry, and strength of a source are based on a knowledge of the magnetic gradients generated by that source. Hood (1965), Bhattacharyya (1966), and Rao et al. (1981) detailed three of these gradient methods. For many years, geophysicists have used the two‐dimensional (2-D) Hilbert transform to approximate the vertical gradient from measurements of the horizontal gradient in the magnetic‐field intensity (Nabighian, 1972; Stanley and Green, 1976; Stanley, 1977; Mohan et al., 1982). This technique is of limited applicability because of the implicit assumption that the source is a linear, 2-D body oriented at right angles to the profile direction.

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Più fonti

Tesi sul tema "Gradient implicite"

Ribeiro, Nogueira Breno. "Non-local damage mechanics with evolving interactions for modeling quasi-brittle materials : anisotropic damage and gradient-enhanced Eikonal approach". Electronic Thesis or Diss., université Paris-Saclay, 2024. http://www.theses.fr/2024UPAST072.

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La prévision de la nucléation et de la propagation des fissures est essentielle pour décrire la réponse des structures dans des conditions de chargement complexes. On observe l'apparition de microfissures diffuses avant la formation d'une macrofissure. Dans le cas de matériaux quasi-fragiles, on observe un comportement adoucissant lié à une perte progressive de rigidité. D'un point de vue thermodynamique, ce comportement peut être décrit de manière continue par une variable d'état d'endommagement. Cependant, les modèles d'endommagement locaux conduisent inévitablement à un problème aux valeurs limites mal posé. Dans un contexte d'éléments finis, les résultats numériques dépendent donc du maillage. Les modèles d'endommagement non locaux permettent d'obtenir des résultats indépendants du maillage en introduisant des interactions de voisinage par le biais d'une longueur interne. Les approches non locales classiques considèrent des interactions isotropes et constantes, ce qui ne permet pas de reproduire correctement l'ensemble du processus de dégradation. Des approches prenant en compte des interactions évolutives existent et peuvent mieux décrire le comportement de la fissuration.Cette thèse vise à fournir des aspects théoriques et numériques pour le développement de modèles d'endommagement à gradient implicite avec interactions évolutives. Tout d'abord, les modèles non-locaux sont étudiés et comparés en analysant les effets de bord et la diffusion de l'endommagement dans un essai d'écaillage unidimensionnel en dynamique explicite.L'approche non-locale Eikonale est étudiée, où les interactions évolutives sont considérées par le biais d'une métrique riemannienne dépendante de l'endommagement. La version avec gradient de ce modèle (ENLG) est ensuite dérivée d'un cadre micromorphe basé sur la géométrie différentielle, conduisant à une expression de dissipation respectant au second principe de la thermodynamique. Une formulation variationnelle simplifiée est développée pour évaluer les capacités du modèle dans des simulations numériques quasi-statiques bidimensionnelles avec endommagement isotrope. Enfin, la régularisation ENLG est couplée à un modèle d'endommagement anisotrope prenant en compte un tenseur d'endommagement de second ordre. L'anisotropie induite est naturellement prise en compte dans le comportement et dans les interactions évolutives. Des simulations en deux et trois dimensions sont étudiées et comparées aux résultats expérimentaux existants dans la littérature, tout en soulignant les aspects numériques associés. Une analyse détaillée décrit les avantages de la prise en compte de l'endommagement anisotrope et des interactions anisotropes dépendantes de l'endommagement
Predicting the cracking nucleation and propagation is essential to describe structural response under complex loading conditions. Diffuse micro-cracks are observed to appear before coalescing into a macro-crack. In the case of quasi-brittle materials, strain-softening behavior is observed and is related to a progressive loss of stiffness. From a thermodynamics viewpoint, this can be described in a continuum way by a damage state variable.However, local continuum damage mechanics models inevitably lead to an ill-posed rate equilibrium problem. In a finite element context, numerical results are, therefore, mesh-dependent. Non-local damage models can recover mesh-independent results by introducing neighborhood interactions through an internal length. Classic non-local approaches consider isotropic and constant interactions, which cannot reproduce the entire degradation process appropriately. Evolving interaction approaches exist and may better describe the cracking behavior. This thesis aims to provide theoretical and numerical aspects for developing evolving interactions gradient-enhanced damage models. Firstly, non-local models are studied and compared by analyzing boundary effects and damage diffusion in a one-dimensional explicit dynamics spalling test.The Eikonal non-local approach is given attention, where evolving interactions are considered through a damage-dependent Riemannian metric. The gradient-enhanced version of this model (ENLG) is then derived from a differential geometry-based micromorphic framework, leading to a dissipation expression fulfilling thermodynamics second principle. A simplified variational formulation is developed to evaluate the model's capabilities in two-dimensional isotropic damage quasi-static numerical simulations. Finally, the ENLG regularization is coupled to an anisotropic damage model considering a second-order damage tensor. Damage-induced anisotropy is naturally considered in the behavior and the evolving interactions. Simulations in two and three-dimensional contexts are studied and compared to existing experimental results from the literature while highlighting the numerical aspects involved. A detailed analysis describes the advantages of considering anisotropic damage and damage-dependent anisotropic interactions

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Charlton, Timothy James. "An implicit Generalised Interpolation Material Point Method for large deformation and gradient elasto-plasticity". Thesis, Durham University, 2018. http://etheses.dur.ac.uk/12824/.

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The ability to correctly capture large deformation behaviour in solids is important in many problems in geotechnical engineering such as slope failure or installation of foundations. The Material Point Method (MPM) is a computational method with particular suitability for modelling problems involving large deformations. In the MPM, a domain is modelled using a set of material points at which state variables are stored and tracked. These material points move through a fixed background grid upon which calculations take place with variables being mapped between the material points and the grid. This thesis sets out to develop the MPM as a method with potential for use in geotechnical problems. Problems are encountered with the original MPM when material points cross between grid cells, and one solution to this is the Generalised Interpolation Material Point (GIMP) method, where material points are able to influence nodes beyond the currently occupied grid cell. Most development of the GIMP method has used an explicit approach, however there are a number of advantages of an implicit approach including larger load steps and improved error control. This thesis focuses on the development of a large deformation elasto-plastic implicit GIMP method. A way of calculating the deformation gradient consistent with the MPM is introduced and convergence is demonstrated using this method which has previously been frequently omitted from MPM research. An alternative way of updating material point domains using the stretch tensor is also proposed. The MPM has a number of similarities to the FEM, and it is often suggested that FEM technologies are trivial to use with the MPM. The MPM can encounter localisations caused by shear banding and, to overcome this, a gradient plasticity approach previously implemented for the FEM is investigated with the GIMP method for the first time. The addition of gradient plasticity to the GIMP method introduces a length scale parameter which governs the width of these shear bands and removes the mesh dependency which is encountered with conventional approaches. It is shown that implementation is possible however, there are a number of problems that are present in the combination of the two methods which should not be overlooked in the future.

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Townshend, Julia Margaret. "A study of implicit memory and temporal gradients in retrograde amnesia and semantic dementia". Thesis, University of Sussex, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.340797.

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This thesis sets out to test some of the predictions proposed by a recent connectionist model of memory and amnesia. The model proposes a time limited role for the hippocampus in memory consolidation in which memories once dependent on the hippocampus become independent of the hippocampus over time and fully supported by the neocortex. The predictions that are made by the model are that there will be memories in retrograde amnesia that are only available through implicit tests of memory; that implicit memory in retrograde amnesia will show a temporal gradient; that semantic dementia patients will show a 'reverse temporal gradient' in retrograde amnesia; and that implicit learning in semantic dementia will be impaired. Chapter 1 reviews some of the current literature relevant to these predictions. Chapter 2 contains the psychometric details of the patient groups taking part, relating these to the underlying neuropathology. Chapter 3 describes three studies which examine recognition and familiarity of famous faces and names from the retrograde period and temporal gradients in familiarity responses. The results are discussed in terms of face and name recognition models. Chapter 4 describes a study that provides evidence of implicit knowledge of famous faces using an indirect method of testing. Chapter 5 is a single-case study using a reaction time measure for new words introduced into the English language during the retrograde period. Chapter 6 is a single-case study of a patient with semantic dementia. The three experiments in this chapter investigate implicit learning in a repetition priming task and the relationship between forced choice recognition of famous faces and famous names. Finally, Chapter 7 discusses the findings in terms of the predictions of the connectionist model of memory and amnesia. The conclusion is that whilst there is evidence of implicit memory in retrograde amnesia, this is unlikely to show a temporal gradient. The prediction that there would be a 'reverse temporal gradient' and impaired implicit memory in semantic dementia was not upheld, and this is discussed in terms of the underlying neuropathology and how it relates to this and other models of memory.

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Jackson, Sarah Marie. "The Influence of Implicit and Explicit Gender Bias on Grading, and the Effectiveness of Rubrics for Reducing Bias". Wright State University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=wright1464731201.

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De, Santis Dante. "Development of a high-order residual distribution method for Navier-Stokes and RANS equations". Phd thesis, Université Sciences et Technologies - Bordeaux I, 2013. http://tel.archives-ouvertes.fr/tel-00946171.

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The construction of compact high-order Residual Distribution schemes for the discretizationof steady multidimensional advection-diffusion problems on unstructuredgrids is presented. Linear and non-linear scheme are considered. A piecewise continuouspolynomial approximation of the solution is adopted and a gradient reconstructionprocedure is used in order to have a continuous representation of both thenumerical solution and its gradient. It is shown that the gradient must be reconstructedwith the same accuracy of the solution, otherwise the formal accuracy ofthe numerical scheme is lost in applications in which diffusive effects prevail overthe advective ones, and when advection and diffusion are equally important. Thenthe method is extended to systems of equations, with particular emphasis on theNavier-Stokes and RANS equations. The accuracy, efficiency, and robustness of theimplicit RD solver is demonstrated using a variety of challenging aerodynamic testproblems.

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Haley, James. "To Curve or Not to Curve? The Effect of College Science Grading Policies on Implicit Theories of Intelligence, Perceived Classroom Goal Structures, and Self-efficacy". Thesis, Boston College, 2015. http://hdl.handle.net/2345/bc-ir:104165.

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Thesis advisor: George M. Barnett
There is currently a shortage of students graduating with STEM (science, technology, engineering, or mathematics) degrees, particularly women and students of color. Approximately half of students who begin a STEM major eventually switch out. Many switchers cite the competitiveness, grading curves, and weed-out culture of introductory STEM classes as reasons for the switch. Variables known to influence resilience include a student's implicit theory of intelligence and achievement goal orientation. Incremental theory (belief that intelligence is malleable) and mastery goals (pursuit of increased competence) are more adaptive in challenging classroom contexts. This dissertation investigates the role that college science grading policies and messages about the importance of effort play in shaping both implicit theories and achievement goal orientation. College students (N = 425) were randomly assigned to read one of three grading scenarios: (1) a "mastery" scenario, which used criterion-referenced grading, permitted tests to be retaken, and included a strong effort message; (2) a "norm" scenario, which used norm-referenced grading (grading on the curve); or (3) an "effort" scenario, which combined a strong effort message with the norm-referenced policies. The dependent variables included implicit theories of intelligence, perceived classroom goal structure, and self-efficacy. A different sample of students (N = 15) were randomly assigned a scenario to read, asked to verbalize their thoughts, and responded to questions in a semi-structured interview. Results showed that students reading the mastery scenario were more likely to endorse an incremental theory of intelligence, perceived greater mastery goal structure, and had higher self-efficacy. The effort message had no effect on self-efficacy, implicit theory, and most of the goal structure measures. The interviews revealed that it was the retake policy in the mastery scenario and the competitive atmosphere in the norm-referenced scenarios that were likely driving the results. Competitive grading policies appear to be incompatible with mastery goals, cooperative learning, and a belief in the efficacy of effort. Implications for college STEM instruction are discussed
Thesis (PhD) — Boston College, 2015
Submitted to: Boston College. Lynch School of Education
Discipline: Teacher Education, Special Education, Curriculum and Instruction

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De, Santis Dante. "Schémas d'ordre élevé distribuant le résidu pour la résolution des équations de Navier-Stokes et Navier-Stokes moyennées (RANS)". Phd thesis, Université Sciences et Technologies - Bordeaux I, 2013. http://tel.archives-ouvertes.fr/tel-00935419.

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Cette thèse présente la construction de schémas distribuant le résidu (RD) d'ordre très élevés, pour la discrétisation d'équations d'advection-diffusion multidimensionnelles et stationnaires sur maillages non structurés. Des schémas linéaires ainsi que des schémas non linéaires sont considérés. Une approximation de la solution polynomiale par morceaux et continue sur chaque élément est adoptée, de plus une procédure de reconstruction du gradient que celle de la solution numérique est utilisée afin d'avoir une représentation continue de la solution numérique et de son gradient. Il est montré que le gradient doit être reconstruit avec la même précision de la solution, sans quoi la précision formel du schéma numérique est perdue dans les cas où les effets de diffusion prévalent sur les effets d'advection, et aussi quand l'advection et la diffusion sont également importants. Ensuite, la méthode est étendue à des systèmes d'équations, en particulier aux équations de Navier-Stokes et aux équations RANS. La précision, l'efficacité et la robustesse du solveur RD implicite sont démontrées sur plusieurs cas tests.

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Cai, Shang-Gui. "Computational fluid-structure interaction with the moving immersed boundary method". Thesis, Compiègne, 2016. http://www.theses.fr/2016COMP2276/document.

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Dans cette thèse, une nouvelle méthode de frontières immergées a été développée pour la simulation d'interaction fluide-structure, appelée la méthode de frontières immergées mobiles (en langage anglo-saxon: MIBM). L'objectif principal de cette nouvelle méthode est de déplacer arbitrairement les solides à géométrie complexe dans un fluide visqueux incompressible, sans remailler le domaine fluide. Cette nouvelle méthode a l'avantage d'imposer la condition de non-glissement à l'interface d'une manière exacte via une force sans introduire des constantes artificielles modélisant la structure rigide. Cet avantage conduit également à la satisfaction de la condition CFL avec un pas de temps plus grand. Pour un calcul précis de la force induite par les frontières mobiles, un système linéaire a été introduit et résolu par la méthode de gradient conjugué. La méthode proposée peut être intégrée facilement dans des solveurs résolvant les équations de Navier-Stokes. Dans ce travail la MIBM a été mise en œuvre en couplage avec un solveur fluide utilisant une méthode de projection adaptée pour obtenir des solutions d'ordre deux en temps et en espace. Le champ de pression a été obtenu par l'équation de Poisson qui a été résolue à l'aide de la méthode du gradient conjugué préconditionné par la méthode multi-grille. La combinaison de ces deux méthodes a permis un gain de temps considérable par rapport aux méthodes classiques de la résolution des systèmes linéaires. De plus le code de calcul développé a été parallélisé sur l'unité graphique GPU équipée de la bibliothèque CUDA pour aboutir à des hautes performances de calcul. Enfin, comme application de nos travaux sur la MIBM, nous avons étudié le couplage "fort" d'interaction fluide-structure (IFS). Pour ce type de couplage, un schéma implicite partitionné a été adopté dans lequel les conditions à l'interface sont satisfaites via un schéma de type "point fixe". Pour réduire le temps de calcul inhérent à cette application, un nouveau schéma de couplage a été proposé pour éviter la résolution de l'équation de Poisson durant les itérations du "point fixe". Cette nouvelle façon de résoudre les problèmes IFS a montré des performances prometteuses pour des systèmes en IFS complexe
In this thesis a novel non-body conforming mesh formulation is developed, called the moving immersed boundary method (MIBM), for the numerical simulation of fluid-structure interaction (FSI). The primary goal is to enable solids of complex shape to move arbitrarily in an incompressible viscous fluid, without fitting the solid boundary motion with dynamic meshes. This novel method enforces the no-slip boundary condition exactly at the fluid-solid interface with a boundary force, without introducing any artificial constants to the rigid body formulation. As a result, large time step can be used in current method. To determine the boundary force more efficiently in case of moving boundaries, an additional moving force equation is derived and the resulting system is solved by the conjugate gradient method. The proposed method is highly portable and can be integrated into any fluid solver as a plug-in. In the present thesis, the MIBM is implemented in the fluid solver based on the projection method. In order to obtain results of high accuracy, the rotational incremental pressure correction projection method is adopted, which is free of numerical boundary layer and is second order accurate. To accelerate the calculation of the pressure Poisson equation, the multi-grid method is employed as a preconditioner together with the conjugate gradient method as a solver. The code is further parallelized on the graphics processing unit (GPU) with the CUDA library to enjoy high performance computing. At last, the proposed MIBM is applied to the study of two-way FSI problem. For stability and modularity reasons, a partitioned implicit scheme is selected for this strongly coupled problem. The interface matching of fluid and solid variables is realized through a fixed point iteration. To reduce the computational cost, a novel efficient coupling scheme is proposed by removing the time-consuming pressure Poisson equation from this fixed point interaction. The proposed method has shown a promising performance in modeling complex FSI system

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Singh, Manish Kumar. "Implicit Gradient Reconstruction for Unstructured Mesh Finite Volume Method". Thesis, 2022. https://etd.iisc.ac.in/handle/2005/5934.

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In the present work, an Implicit Gradient Reconstruction (IGR) method is proposed in the context of Finite Volume Methodology (FVM). There are three computationally intensive steps involved in a typical finite volume framework for a spatially second-order accurate upwind scheme. These are solution reconstruction, solution limiting and flux finding. Solution re- construction involves determination of gradients while solution limiting requires comparison of double precision numbers. Further, computation of gradient and solution limiting is cell based procedure while flux finding is edge/face based procedure. The proposed IGR procedure, which is edge/face based procedure, integrates all these steps obviating explicit reconstruction and limiting steps resulting in a considerable reduction in computational effort and associated memory footprint. In the modified CIR (MCIR) scheme of linear convection equation, a parameter φ is in- troduced to control dissipation. The IGR procedure is derived from the MCIR scheme. The relation between the φ parameter and solution reconstruction in a finite volume procedure is systematically established. The methodology is extended to multidimensions, where the use of φ implicitly represents a reconstruction step. Hence, this procedure is referred to as Implicit Gradient Reconstruction. In addition, it is brought out that the use of φ also serves the purpose of solution limiting. The spatial accuracy of this procedure is demonstrated by computing the 2-D circular convection problem. The methodology, when extended to the Euler equations of Gas dynamics, results in the reconstruction of the characteristic variables. Consequently, three steps in the computation of explicit residual, namely, solution reconstruction, limiting and flux computation, are seamlessly merged into a single step. Owing to its significantly smaller memory footprint, the procedure is particularly relevant to large scale parallel computing. This procedure can be effortlessly incorporated into any of the existing finite volume solvers where inviscid flux formulation is based on characteristic decomposition. The capability of IGR procedure is established through several test cases involving inviscid and viscous flow computations in one and two dimensions. The results obtained from IGR procedure are compared with reconstruction based solvers and wind tunnel data wherever available. The IGR procedure produces results comparable to the classical reconstruction based procedure. The aforementioned IGR procedure is applicable to any flux formulation involving charac- teristic decomposition. An Edge Based Reconstruction Limiting (EBRL) is proposed for flux formulation not involving characteristic decomposition. This procedure is very simple and does not require classical diamond path reconstruction. The results obtained from EBRL based Roe and AUSM Plus flux formulation on transonic viscous flow over RAE 2822 airfoil are very good and compare well with wind tunnel experiments.

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CICERI, ANDREA. "Il ruolo del wine packaging nel processo decisionale: confronto tra consumatori danesi e italiani integrando metodologia tradizionale e di neuromarketing". Doctoral thesis, 2017. http://hdl.handle.net/10808/22423.

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La ricerca realizzata ha preso in esame il processo decisionale del vino, focalizzandosi in particolar modo sul ruolo che ha l’aspetto estetico del packaging. Si è deciso da un lato di prendere a oggetto di studio questo prodotto, in quanto connotato da una elevata percezione di rischio. Dall’altro, si è ristretto l’ambito decisionale al solo packaging, poiché è un elemento che assume un ruolo del tutto peculiare e fondamentale nel processo decisionale di questo prodotto. Bottiglie con soluzioni estetiche gradite hanno infatti una maggiore probabilità di essere scelte, una maggiore disponibilità a pagare (DAP) e una maggiore propensione all’acquisto. Lo studio parte da un gap di ricerca. Sino ad oggi, la ricerca sul vino in generale e sul suo packaging nello specifico, ha adottato metodi di ricerca tradizionali quali i self report o i questionari, che la ricerca stessa, ha evidenziato avere il limite di cogliere soltanto la parte razionale e consapevole dei processi decisionali. Partendo da questa premessa, l’approccio che si è utilizzato in questa ricerca ha combinato le metodologie di ricerca classica con la metodologia di neuromarketing, permettendo così di esplorare con maggiore affidabilità la tematica di ricerca. La ricerca si è svolta a Milano e a Copenaghen. Si è deciso di confrontare questi due gruppi di partecipanti (millenials e tutti consumatori di vino) perché caratterizzati da abitudini di consumo radicalmente differenti. Da un lato, l’Italia in cui il consumo di vino è un elemento culturale tipico e dall’altro la Danimarca in cui questo prodotto ha un ruolo del tutto marginale negli stili di consumo. Lo studio ha previsto due fasi. Una prima fase (316 partecipanti, 146 danesi e 170 italiani), finalizzata a raccogliere le abitudini di consumo dei rispettivi gruppi di ricerca e a classificare in termini di moderno e tradizionale (la classificazione più comune che si segue per definire il packaging del vino) le soluzioni grafiche realizzate per essere poi usate nella seconda fase della ricerca. La seconda fase (120 partecipanti, 52 danesi e 68 italiani), si è svolta presso due centri di ricerca dell’Università IULM e della Copenaghen Business School. In questa seconda fase i partecipanti sono stati profilati per livello di conoscenza (basso) e di coinvolgimento (basso) verso questo prodotto. Si è optato per questo target per diversi motivi: perché rappresentativo del consumatore medio, perché è un segmento di consumatori in forte crescita e infine perché per questi consumatori il packaging è importante quanto il prodotto stesso. Il protocollo di ricerca prevedeva la somministrazione di un totale di 24 soluzioni grafiche di packaging, combinate tra loro a coppie, abbinando una soluzione grafica moderna a una tradizionale. Il partecipante aveva 4 secondi per esprimere la preferenza di scelta rispetto a ciascuna delle 12 coppie di soluzioni grafiche. I dati eye tracking e di attivazione fisiologica (SC) sono stati raccolti durante questa fase. Successivamente il partecipante compilava un questionario finalizzato a cogliere per ciascuna soluzione grafica: il gradimento, la propensione all’acquisto e la disponibilità a pagare. Gli obiettivi della ricerca erano due. Il primo verificare se target differenti (per genere e nazionalità) avevano preferenze differenti rispetto alle soluzioni grafiche testate. In particolare le ipotesi di ricerca, derivate da questo primo obiettivo erano due e ipotizzavano rispettivamente che i partecipanti danesi e le partecipanti donne avessero una preferenza maggiore per soluzioni grafiche moderne. Il secondo obiettivo era quello di esplorare il processo decisionale, analizzando in particolar modo la difficoltà nel portare a termine la scelta. Sono state definite due ipotesi di ricerca che ipotizzavano una maggiore difficoltà decisionale per partecipanti danesi e partecipanti donne. I risultati non hanno confermato le prime due ipotesi. Tutti i partecipanti, indiscriminatamente da sesso o nazionalità hanno espresso una netta preferenza per le soluzioni grafiche tradizionali, risultati supportati sia dai dati indiretti eye tracking (la cui analisi ha adottato come framework teorico il gaze bias effect) che dai dati verbali dei self report. Differenze significative e in linea con le ultime due ipotesi di ricerca sono state invece trovate per quanto riguarda il processo decisionale.

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Libri sul tema "Gradient implicite"

1929-, Chung T. J., e United States. National Aeronautics and Space Administration., a cura di. Flowfield-dependent mixed explicit-implicit (FDMEI) algorithm for computational fluid dynamics: Final report ... [Washington, DC: National Aeronautics and Space Administration, 1997.

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Baysal, Oktay. Efficient gradient-based shape optimization methodology using inviscid/viscous CFD: Summary of research report for the period of March 9, 1995 to March 8, 1997, grant# NCC-1-211. Norfolk, Va: Dept. of Aerospace Engineering, College of Engineering and Technology, Old Dominion University, 1997.

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United States. National Aeronautics and Space Administration., a cura di. Efficient gradient-based shape optimization methodology using inviscid/viscous CFD: Summary of research report for the period of March 9, 1995 to March 8, 1997, grant# NCC-1-211. Norfolk, Va: Dept. of Aerospace Engineering, College of Engineering and Technology, Old Dominion University, 1997.

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Townshend, Julia Margaret. A study of implicit memory and temporal gradients in retrograde amnesia and semantic dementia. 2001.

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Flowfield-dependent mixed explicit-implicit (FDMEI) algorithm for computational fluid dynamics: Final report ... [Washington, DC: National Aeronautics and Space Administration, 1997.

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Flowfield-dependent mixed explicit-implicit (FDMEI) algorithm for computational fluid dynamics: Final report ... [Washington, DC: National Aeronautics and Space Administration, 1997.

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Mann, Peter. Matrices. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198822370.003.0031.

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This chapter looks at the calculus of a function of two or more variables, which is the subject of partial differentiation. The partial derivative of a function is the rate of change of the function with respect to the distance in the direction of a particular coordinate axis and is symbolised with the sign ∂. The chapter spends time on the implicit function theorem, since it is relied upon heavily elsewhere in the text. Lagrange multipliers are used to solve constrained optimisation problems. Topics include critical points, the product rule, the chain rule, directional derivatives, hypersurfaces and Taylor’s theorem. In addition, the chapter discusses Jacobian matrices, the inverse function theorem, gradients, level sets and Hessian matrices.

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Efficient gradient-based shape optimization methodology using inviscid/viscous CFD: Summary of research report for the period of March 9, 1995 to March 8, 1997, grant# NCC-1-211. Norfolk, Va: Dept. of Aerospace Engineering, College of Engineering and Technology, Old Dominion University, 1997.

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Capitoli di libri sul tema "Gradient implicite"

Lyu, Yueming, e Ivor W. Tsang. "Black-Box Optimizer with Stochastic Implicit Natural Gradient". In Machine Learning and Knowledge Discovery in Databases. Research Track, 217–32. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-86523-8_14.

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Hillman, M., e J. S. Chen. "An Implicit Gradient Meshfree Formulation for Convection-Dominated Problems". In Advances in Computational Fluid-Structure Interaction and Flow Simulation, 25–37. Cham: Springer International Publishing, 2016. http://dx.doi.org/10.1007/978-3-319-40827-9_3.

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Bayer, Hakan, Benedikt Faltin e Markus König. "Automated Extraction of Bridge Gradient from Drawings Using Deep Learning". In CONVR 2023 - Proceedings of the 23rd International Conference on Construction Applications of Virtual Reality, 683–90. Florence: Firenze University Press, 2023. http://dx.doi.org/10.36253/979-12-215-0289-3.68.

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Digital methods such as Building Information Modeling (BIM) can be leveraged, to improve the efficiency of maintenance planning of bridges. However, this requires digital building models, which are rarely available. Consequently, these models must be created retrospectively, which is time-consuming when done manually. Naturally, there is a great interest in the industry to automate the process of retro-digitization. This paper contributes to these efforts by proposing a multistage pipeline to automatically extract the gradient of a bridge from pixel-based construction drawings using deep learning. The bridge gradient, a key element of the structure’s axis, is critical for describing the elevation profile and axis slope. This information is implicitly contained in the longitudinal view of bridge drawings as gradient symbols. To extract this information, the well-established object detection model YOLOv5 is employed to locate the gradient symbols inside the drawings. Subsequently, EasyOCR and heuristic rules are applied to extract the relevant gradient parameters associated with each detected symbol. The extracted parameters are then exported in a machine-interpretable format to facilitate seamless integration into other applications. The results show a promising 98% accuracy in symbol detection and an overall accuracy of 70%. Consequently, the pipeline represents a significant advance in automating the retro-digitization process for existing bridges by reducing the time and effort required

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Nguyen, Quoc-Son. "Quasi-static Evolution, Variational Principles and Implicit Scheme in Gradient Plasticity". In Springer Series in Solid and Structural Mechanics, 143–52. Cham: Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-48884-4_7.

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Medvedev, Dmitry, e Alexander D’yakonov. "Learning to Generate Synthetic Training Data Using Gradient Matching and Implicit Differentiation". In Communications in Computer and Information Science, 138–50. Cham: Springer International Publishing, 2022. http://dx.doi.org/10.1007/978-3-031-15168-2_12.

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Zhou, Jincheng, e Maoxing Zheng. "Federated Learning with Class Balanced Loss Optimized by Implicit Stochastic Gradient Descent". In Communications in Computer and Information Science, 121–35. Singapore: Springer Nature Singapore, 2023. http://dx.doi.org/10.1007/978-981-99-0405-1_9.

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Wu, Jiaying, Xiatao Kang, Jingying Xiao e Jiayi Yao. "Gradient Coupled Flow: Performance Boosting on Network Pruning by Utilizing Implicit Loss Decrease". In Neural Information Processing, 231–43. Singapore: Springer Nature Singapore, 2023. http://dx.doi.org/10.1007/978-981-99-8082-6_18.

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Hahn, Jooyoung, Karol Mikula, Peter Frolkovič e Branislav Basara. "Semi-implicit Level Set Method with Inflow-Based Gradient in a Polyhedron Mesh". In Springer Proceedings in Mathematics & Statistics, 81–89. Cham: Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-57394-6_9.

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Chen, ZhenLi, Antoine Devesa, Michael Meyer, Eric Lauer, Stefan Hickel, Christian Stemmer e Nikolaus A. Adams. "Wall Modelling for Implicit Large Eddy Simulation of Favourable and Adverse Pressure Gradient Flows". In ERCOFTAC Series, 337–46. Dordrecht: Springer Netherlands, 2011. http://dx.doi.org/10.1007/978-90-481-9603-6_35.

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Atti di convegni sul tema "Gradient implicite"

Nishikawa, Hiroaki. "Updates to Implicit Edge-Based Gradient Methods". In AIAA SCITECH 2024 Forum. Reston, Virginia: American Institute of Aeronautics and Astronautics, 2024. http://dx.doi.org/10.2514/6.2024-1748.

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Ajmani, Kumud, e Meng-Sing Liou. "Implicit conjugate-gradient solvers on distributed-memory architectures". In 12th Computational Fluid Dynamics Conference. Reston, Virigina: American Institute of Aeronautics and Astronautics, 1995. http://dx.doi.org/10.2514/6.1995-1695.

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Li, Peiyan, Xu Liang e Haochen Song. "A Survey on Implicit Bias of Gradient Descent". In 2022 14th International Conference on Computer Research and Development (ICCRD). IEEE, 2022. http://dx.doi.org/10.1109/iccrd54409.2022.9730384.

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York, William D., e James H. Leylek. "Numerical Prediction of Mainstream Pressure Gradient Effects in Film Cooling". In ASME 1999 International Gas Turbine and Aeroengine Congress and Exhibition. American Society of Mechanical Engineers, 1999. http://dx.doi.org/10.1115/99-gt-166.

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A documented, systematic, computational methodology is applied to singularly investigate the effects of mainstream pressure gradients on film cooling over a flat surface for realistic gas turbine parameters. Key aspects of the study include: (1) validation of the ability of computational fluid dynamics to simulate film cooling in regions of mainstream pressure gradients, accomplished through the isolation of this parameter and the careful modeling of a published experimental study; (2) documentation of the effects of the applied pressure gradient on film cooling adiabatic effectiveness, as compared to the zero-pressure gradient case; and (3) detailed discussion of the pertinent physical mechanisms involved, with appropriate flowfield results. The imposed pressure gradient is typical of the suction surface of a gas turbine airfoil, with a strong favorable pressure gradient (the acceleration parameter was K = 1.5×10−6 at injection) transitioning to a mild adverse pressure gradient region beyond 30 diameters downstream. A single row of cylindrical film-cooling holes had an injection angle of 35°, with hole length-to-diameter ratio of 4.0 and a lateral spacing of 3.0 diameters. The simulated mass flux ratios were M = 0.6, 1.0, and 1.5, and the density ratio was held constant at 1.6. Solutions were obtained using a multi-block, multi-topology grid and a pressure-correction based, fully-implicit Navier-Stokes solver. A “realizeable” k-ε turbulence model, which eliminates the documented unrealistic turbulence production of the standard k-ε model in regions of large flow strain, was employed to obtain practical results economically. The applied pressure gradient resulted in a small advantage in center-line effectiveness, while laterally averaged effectiveness was slightly lower as compared to the zero-pressure gradient reference case. The results of this study demonstrate the ability of the applied computational methodology to accurately model film cooling in the presence of mainstream pressure gradients and resolve one of the key fundamental issues in turbine airfoil film cooling.

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Yi, Sung-Jae, e Moon-Sun Chung. "An Advanced Semi-Implicit Method for Two-Phase Flow Calculation". In 2010 14th International Heat Transfer Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/ihtc14-22009.

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Introducing the interfacial pressure jump terms based on the surface tension into the momentum equations of two-phase two-fluid model, the system of governing equations is turned mathematically into the hyperbolic system. The eigenvalues of the equation system become always real representing the void wave and the pressure wave propagation speeds as shown in the present authors’ reference: Numerical Heat Transfer —Part B, vol. 40, pp. 83–97. To solve the interfacial pressure jump terms with void fraction gradients implicitly, the conventional semi-implicit method should be modified as an intermediate iteration method for void fraction at fractional time step. Owing to this modified numerical scheme with surface tension effect, the advanced semi-implicit method (ASIM) then becomes stable without conventional additive terms. As a consequence, including the interfacial pressure jump terms with the advanced semi-implicit method, the numerical solutions of typical two-phase problems can be more stable and sound than those calculated exclusively by using any other terms like virtual mass, or artificial viscosity.

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Nishikawa, Hiroaki. "Implicit Edge-Based Gradients for Simplex Grids". In AIAA AVIATION 2020 FORUM. Reston, Virginia: American Institute of Aeronautics and Astronautics, 2020. http://dx.doi.org/10.2514/6.2020-3048.

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El Gheche, Mireille, Giovanni Chierchia e Pascal Frossard. "Stochastic Gradient Descent for Spectral Embedding with Implicit Orthogonality Constraint". In ICASSP 2019 - 2019 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP). IEEE, 2019. http://dx.doi.org/10.1109/icassp.2019.8683286.

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Sommer, Christiane, Lu Sang, David Schubert e Daniel Cremers. "Gradient-SDF: A Semi-Implicit Surface Representation for 3D Reconstruction". In 2022 IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR). IEEE, 2022. http://dx.doi.org/10.1109/cvpr52688.2022.00618.

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Tsaknakis, Ioannis, Prashant Khanduri e Mingyi Hong. "An Implicit Gradient-Type Method for Linearly Constrained Bilevel Problems". In ICASSP 2022 - 2022 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP). IEEE, 2022. http://dx.doi.org/10.1109/icassp43922.2022.9747013.

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Eaton, Brandon, Michael R. von Spakovsky, Michael W. Ellis, Douglas J. Nelson, Benoit Olsommer e Nathan Siegel. "One-Dimensional, Transient Model of Heat, Mass, and Charge Transfer in a Proton Exchange Membrane". In ASME 2001 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2001. http://dx.doi.org/10.1115/imece2001/aes-23652.

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Abstract A transient, one-dimensional, model of the membrane of a proton exchange membrane fuel cell is presented. The role of the membrane is to transport protons from the anode to cathode of the fuel cell while preventing the transport of other reactants. The membrane is modeled assuming mono-phase, multi-species flow. For water transport, the principle driving forces modeled are a convective force, an osmotic force (i.e. diffusion), and an electric force. The first of these results from a pressure gradient, the second from a concentration gradient, and the third from the migration of protons from anode to cathode and their effect (drag) on the dipole water molecules. Equations are developed for the conservation of protons and water, the conservation of thermal energy, and the variation of proton potential within the membrane. The model is solved using a fully implicit finite difference approach. Results showing the effects of current density, pressure gradients, water and heat fluxes, and fuel cell start-up on water concentration, temperature, and proton potential across the membrane are presented.

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