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Статті в журналах з теми "Backward Dynamical Approach"
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Attouch, Hédy, Juan Peypouquet, and Patrick Redont. "A Dynamical Approach to an Inertial Forward-Backward Algorithm for Convex Minimization." SIAM Journal on Optimization 24, no. 1 (January 2014): 232–56. http://dx.doi.org/10.1137/130910294.
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KLEMM, M., and P. E. BECKMANN. "THE TOPOLOGY OF BASIN BOUNDARIES IN A CLASS OF THREE-DIMENSIONAL DYNAMICAL SYSTEMS." International Journal of Bifurcation and Chaos 06, no. 01 (January 1996): 161–67. http://dx.doi.org/10.1142/s0218127496001909.
Повний текст джерелаАнотація:
We will develop new methods to determine the topology of the basin boundary in a class of three-dimensional dynamical systems. One approach is to approximate the basin boundary by backward integration. Unfortunately, there are dynamical systems where it is hard to approximate the basin boundary by a numerical backward integration algorithm. We will introduce topological methods which will provide new information about the structure of the basin boundary. The topological invariants which we will use can be numerically computed.
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Rosatti, Giorgio, Daniel Zugliani, Marina Pirulli, and Marta Martinengo. "A new method for evaluating stony debris flow rainfall thresholds: the Backward Dynamical Approach." Heliyon 5, no. 6 (June 2019): e01994. http://dx.doi.org/10.1016/j.heliyon.2019.e01994.
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Boţ, Radu Ioan, Sorin-Mihai Grad, Dennis Meier, and Mathias Staudigl. "Inducing strong convergence of trajectories in dynamical systems associated to monotone inclusions with composite structure." Advances in Nonlinear Analysis 10, no. 1 (August 25, 2020): 450–76. http://dx.doi.org/10.1515/anona-2020-0143.
Повний текст джерелаАнотація:
Abstract In this work we investigate dynamical systems designed to approach the solution sets of inclusion problems involving the sum of two maximally monotone operators. Our aim is to design methods which guarantee strong convergence of trajectories towards the minimum norm solution of the underlying monotone inclusion problem. To that end, we investigate in detail the asymptotic behavior of dynamical systems perturbed by a Tikhonov regularization where either the maximally monotone operators themselves, or the vector field of the dynamical system is regularized. In both cases we prove strong convergence of the trajectories towards minimum norm solutions to an underlying monotone inclusion problem, and we illustrate numerically qualitative differences between these two complementary regularization strategies. The so-constructed dynamical systems are either of Krasnoselskiĭ-Mann, of forward-backward type or of forward-backward-forward type, and with the help of injected regularization we demonstrate seminal results on the strong convergence of Hilbert space valued evolutions designed to solve monotone inclusion and equilibrium problems.
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Martinengo, Marta, Daniel Zugliani, and Giorgio Rosatti. "Uncertainty analysis of a rainfall threshold estimate for stony debris flow based on the backward dynamical approach." Natural Hazards and Earth System Sciences 21, no. 6 (June 3, 2021): 1769–84. http://dx.doi.org/10.5194/nhess-21-1769-2021.
Повний текст джерелаАнотація:
Abstract. A rainfall threshold is a function of some rainfall quantities that provides the conditions beyond which the probability of debris-flow occurrence is considered significant. Many uncertainties may affect the thresholds calibration and, consequently, its robustness. This study aims to assess the uncertainty in the estimate of a rainfall threshold for stony debris flow based on the backward dynamical approach, an innovative method to compute the rainfall duration and averaged intensity strictly related to a measured debris flow. The uncertainty analysis is computed by performing two Monte Carlo cascade simulations: (i) to assess the variability in the event characteristics estimate due to the uncertainty in the backward dynamical approach parameters and data and (ii) to quantify the impact of this variability on the threshold calibration. The application of this procedure to a case study highlights that the variability in the event characteristics can be both low and high. Instead, the threshold coefficients have a low dispersion showing good robustness of the threshold estimate. Moreover, the results suggest that some event features are correlated with the variability of the rainfall event duration and intensity. The proposed method is suitable to analyse the uncertainty of other threshold calibration approaches.
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Tkach, T. B., A. S. Kvasikova, and I. M. Shpinareva. "ON SOME NUMERICAL MODEL TO SOLVING DYNAMICAL EQUATIONS OF NONRELATIVISTIC AND RELATIVISTIC BACKWARD-WAVE TUBE." Photoelectronics, no. 30 (August 21, 2022): 146–51. http://dx.doi.org/10.18524/0235-2435.2021.30.262909.
Повний текст джерелаАнотація:
It is developed an effective computational approach to solution the master corresponding system of differential equations, which describe the nonlinear stationary and non-stationary electromagnetic processes in the nonrelativistic and relativistic backward-wave tubes (carcinotrons) with maximal accounting for the different physical factors such as the relativistic effects, effects of dissipation, the presence of a space charge, wave reflections at the ends of the slowing system, stochastic factors by means including the special elements in a whole system etc as well as the detailed investigation of characteristics (dynamical and topological invariants) of dynamics of a carcinotron in automodulation and chaotic regimes with construction the corresponding bi-furcation diagrams. Below in order to further solve the master system of dynamical equations for carcinotron it is presented in brief the realizing numerical scheme, based on the use of the conservative finite-difference schemes of the "predictor-corrector" type and the sweep algorithm.
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Boţ, Radu Ioan, and Laura Kanzler. "A forward-backward dynamical approach for nonsmooth problems with block structure coupled by a smooth function." Applied Mathematics and Computation 394 (April 2021): 125822. http://dx.doi.org/10.1016/j.amc.2020.125822.
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Ioan Boţ, Radu, and Ernö Robert Csetnek. "A forward-backward dynamical approach to the minimization of the sum of a nonsmooth convex with a smooth nonconvex function." ESAIM: Control, Optimisation and Calculus of Variations 24, no. 2 (January 22, 2018): 463–77. http://dx.doi.org/10.1051/cocv/2017020.
Повний текст джерелаАнотація:
We address the minimization of the sum of a proper, convex and lower semicontinuous function with a (possibly nonconvex) smooth function from the perspective of an implicit dynamical system of forward-backward type. The latter is formulated by means of the gradient of the smooth function and of the proximal point operator of the nonsmooth one. The trajectory generated by the dynamical system is proved to asymptotically converge to a critical point of the objective, provided a regularization of the latter satisfies the Kurdyka−Łojasiewicz property. Convergence rates for the trajectory in terms of the Łojasiewicz exponent of the regularized objective function are also provided.
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Sharma, Sandeep, and Nitu Kumari. "Backward Bifurcation in a Cholera Model: A Case Study of Outbreak in Zimbabwe and Haiti." International Journal of Bifurcation and Chaos 27, no. 11 (October 2017): 1750170. http://dx.doi.org/10.1142/s021812741750170x.
Повний текст джерелаАнотація:
In this paper, a nonlinear deterministic model is proposed with a saturated treatment function. The expression of the basic reproduction number for the proposed model was obtained. The global dynamics of the proposed model was studied using the basic reproduction number and theory of dynamical systems. It is observed that proposed model exhibits backward bifurcation as multiple endemic equilibrium points exist when [Formula: see text]. The existence of backward bifurcation implies that making [Formula: see text] is not enough for disease eradication. This, in turn, makes it difficult to control the spread of cholera in the community. We also obtain a unique endemic equilibria when [Formula: see text]. The global stability of unique endemic equilibria is performed using the geometric approach. An extensive numerical study is performed to support our analytical results. Finally, we investigate two major cholera outbreaks, Zimbabwe (2008–09) and Haiti (2010), with the help of the present study.
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Gao, Huadong. "Efficient Numerical Solution of Dynamical Ginzburg-Landau Equations under the Lorentz Gauge." Communications in Computational Physics 22, no. 1 (May 3, 2017): 182–201. http://dx.doi.org/10.4208/cicp.oa-2016-0120.
Повний текст джерелаАнотація:
AbstractIn this paper, a new numerical scheme for the time dependent Ginzburg-Landau (GL) equations under the Lorentz gauge is proposed. We first rewrite the original GL equations into a new mixed formulation, which consists of three parabolic equations for the order parameter ψ, the magnetic field σ=curlA, the electric potential θ=divA and a vector ordinary differential equation for the magnetic potential A, respectively. Then, an efficient fully linearized backward Euler finite element method (FEM) is proposed for the mixed GL system, where conventional Lagrange element method is used in spatial discretization. The new approach offers many advantages on both accuracy and efficiency over existing methods for the GL equations under the Lorentz gauge. Three physical variables ψ, σ and θ can be solved accurately and directly. More importantly, the new approach is well suitable for non-convex superconductors. We present a set of numerical examples to confirm these advantages.
Дисертації з теми "Backward Dynamical Approach"
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Liang, Gechun. "A functional approach to backward stochastic dynamics." Thesis, University of Oxford, 2010. http://ora.ox.ac.uk/objects/uuid:afb9af6f-c79c-4204-838d-2a4872c1c796.
Повний текст джерелаАнотація:
In this thesis, we consider a class of stochastic dynamics running backwards, so called backward stochastic differential equations (BSDEs) in the literature. We demonstrate BSDEs can be reformulated as functional differential equations defined on path spaces, and therefore solving BSDEs is equivalent to solving the associated functional differential equations. With such observation we can solve BSDEs on general filtered probability space satisfying the usual conditions, and in particular without the requirement of the martingale representation. We further solve the above functional differential equations numerically, and propose a numerical scheme based on the time discretization and the Picard iteration. This in turn also helps us solve the associated BSDEs numerically. In the second part of the thesis, we consider a class of BSDEs with quadratic growth (QBSDEs). By using the functional differential equation approach introduced in this thesis and the idea of the Cole-Hopf transformation, we first solve the scalar case of such QBSDEs on general filtered probability space satisfying the usual conditions. For a special class of QBSDE systems (not necessarily scalar) in Brownian setting, we do not use such Cole-Hopf transformation at all, and instead introduce the weak solution method, which is to use the strong solutions of forward backward stochastic differential equations (FBSDEs) to construct the weak solutions of such QBSDE systems. Finally we apply the weak solution method to a specific financial problem in the credit risk setting, where we modify the Merton's structural model for credit risk by using the idea of indifference pricing. The valuation and the hedging strategy are characterized by a class of QBSDEs, which we solve by the weak solution method.
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Martinengo, Marta. "Improving some non-structural risk mitigation strategies in mountain regions: debris-flow rainfall thresholds, multi-hazard flooding scenarios and public awareness." Doctoral thesis, Università degli studi di Trento, 2022. http://hdl.handle.net/11572/353702.
Повний текст джерелаАнотація:
Hydrogeological hazards are quite diffuse rainfall-induced phenomena that affect mountain regions and can severely impact these territories, producing damages and sometimes casualties. For this reason, hydrogeological risk reduction is crucial. Mitigation strategies aim to reduce hydrogeological risk to an acceptable level and can be classified into structural and non-structural measures. This work focuses on enhancing some non-structural risk mitigation measures for mountain areas: debris-flow rainfall thresholds, as a part of an Early Warning System (EWS), multivariate rainfall scenarios with multi-hazard mapping purpose and public awareness. Regarding debris-flow rainfall thresholds, an innovative calibration method, a suitable uncertainty analysis and a proper validation process are developed. The Backward Dynamical Approach (BDA), a physical-based calibration method, is introduced and a threshold is obtained for a study area. The BDA robustness is then tested by assessing the uncertainty in the threshold estimate. Finally, the calibrated threshold's reliability and its possible forecast use are assessed using a proper validation process. The findings set the stage for using the BDA approach to calibrate debris-flow rainfall thresholds usable in operational EWS. Regarding hazard mapping, a multivariate statistical model is developed to construct multivariate rainfall scenarios with a multi-hazards mapping purpose. A confluence between a debris-flow-prone creek and a flood-prone river is considered. The multivariate statistical model is built by combining the Simplified Metastatistical Extreme Value approach and a copula approach. The obtained rainfall scenarios are promising to be used to build multi-hazard maps. Finally, the public awareness within the LIFE FRANCA (Flood Risk ANticipation and Communication in the Alps) European project is briefly considered. The project action considered in this work focuses on training and communication activities aimed at providing a multidisciplinary view of hydrogeological risk through the holding of courses and seminars.
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Le, Pendu Mikaël. "Backward compatible approaches for the compression of high dynamic range videos." Thesis, Rennes 1, 2016. http://www.theses.fr/2016REN1S002/document.
Повний текст джерелаАнотація:
Les technologies d'écran ont connu récemment une évolution rapide. De la télévision 3D à l'Ultra Haute Définition, la tendance est maintenant aux écrans HDR (pour ''High Dynamic Range'') permettant de reproduire une gamme de luminance bien plus élevée que les écrans classiques. L'émergence de cette technologie implique de nouveaux travaux de standardisation dans le domaine de la compression vidéo. Une question essentielle pour la distribution à grande échelle de contenu HDR est celle de la rétro-compatibilité. Tandis que la future génération d'écrans de télévision sera adaptée à ce nouveau format, il est nécessaire de permettre aux équipements plus anciens de décoder et afficher une version du même contenu dont la dynamique a été préalablement réduite par un procédé appelé ''tone mapping''. Cette thèse vise à explorer les schémas de compression HDR rétro-compatibles. Dans une première approche, un algorithme de tone mapping spécifié par l'encodeur est appliqué à l'image HDR. L'image générée, alors appelée LDR (pour ''Low Dynamic Range''), peut être encodée et décodée dans un format classique. L'encodeur transmet par ailleurs une quantité réduite d'information permettant à un décodeur HDR d'inverser l'opération de tone mapping et de reconstruire une version HDR. L'étude de ces schémas est axée sur la définition de méthodes de tone mapping optimisées pour les performances de compression. La suite de la thèse se concentre sur l'approche scalable dans laquelle les deux versions sont fournies à l'encodeur sans connaissance à priori sur l'opérateur de tone mapping utilisé. Le producteur garde donc le contrôle sur la création du contenu LDR. Cette version LDR est d'abord compressée comme une première couche. L'image reconstruite est utilisée par le codeur scalable pour compresser plus efficacement la couche HDR grâce à un mécanisme de prédiction inter-couches. Notre approche locale et non linéaire nous permet d'améliorer les performances de codage par rapport aux méthodes scalables existantes, en particulier dans le cas où un tone mapping complexe est utilisé pour générer la version LDRIn recent years, the display technologies have been rapidly evolving. From 3D television to Ultra High Definition, the trend is now towards High Dynamic Range (HDR) displays that can reproduce a luminance range far beyond the capabilities of conventional displays. The emergence of this technology involves new standardization effort in the field of video compression. In terms of large scale content distribution, the question of backward compatibility is critical. While the future generation of television displays will be adapted to this new format, it is necessary to enable the older equipment to decode and display a version of the same content whose dynamic range has been previously reduced by a process called “tone mapping”. This thesis aims at exploring the backward compatible HDR compression schemes. In a first approach, a tone mapping operator specified by the encoder is applied to the HDR image. The resulting image, called Low Dynamic Range (LDR), can then be encoded and decoded in a conventional format. The encoder additionally transmits a small amount of information enabling a HDR capable decoder to inverse the tone mapping operator and retrieve the HDR version. The study of these schemes is directed towards the definition of tone mapping operators optimized for the compression performance. We then focus on scalable approaches, where both versions are given to the encoder without prior knowledge on the tone mapping operator used. The producer thus keeps full control on the LDR content creation process. This LDR version is compressed as a first layer. The reconstructed image is used by the scalable encoder to compress the HDR layer efficiently by performing inter-layer predictions. Thanks to a local and non-linear approach, the proposed schemes improve the coding performance compared to the existing scalable methods, especially in the case where a complex tone mapping is used for generating the LDR version
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Fonley, Morgan Rae. "Effects of oscillatory forcing on hydrologic systems under extreme conditions: a mathematical modeling approach." Diss., University of Iowa, 2015. https://ir.uiowa.edu/etd/2075.
Повний текст джерелаАнотація:
At the large watershed scale, we emphasize the effects of flow through a river network on streamflow under dry conditions. An immediate consequence of assuming dry conditions is that evapotranspiration causes flow in the river network to exhibit oscillations. When all links in the river network combine their flow patterns, the oscillations interact in ways that change the timing and amplitude of the streamflow waves at the watershed outlet. The geometric shape of the river network is particularly important, so we develop an analytic solution for streamflow which emphasizes that importance.
Doing hydrology backward is a strategy recently developed by several researchers to deal with uncertainty in measurements of forcing terms applied to hydrologic models. The strategy has also been applied to resolve the assumption of homogeneity on realistic catchments that exhibit many heterogeneous properties. In this work, we demonstrate hydrology in the backward direction applied to two examples: using streamflow at the catchment scale to determine runoff at the hillslope scale and using the hillslope runoff to infer the applied evapotranspiration forcing under the assumption of dry conditions. In order to work across scales, we utilize the analytic solution for streamflow at the outlet of a river network. At the hillslope scale, we develop a soil model to create fluxes consistent with observed soil processes.
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Vestin, Albin, and Gustav Strandberg. "Evaluation of Target Tracking Using Multiple Sensors and Non-Causal Algorithms." Thesis, Linköpings universitet, Reglerteknik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-160020.
Повний текст джерелаАнотація:
Today, the main research field for the automotive industry is to find solutions for active safety. In order to perceive the surrounding environment, tracking nearby traffic objects plays an important role. Validation of the tracking performance is often done in staged traffic scenarios, where additional sensors, mounted on the vehicles, are used to obtain their true positions and velocities. The difficulty of evaluating the tracking performance complicates its development. An alternative approach studied in this thesis, is to record sequences and use non-causal algorithms, such as smoothing, instead of filtering to estimate the true target states. With this method, validation data for online, causal, target tracking algorithms can be obtained for all traffic scenarios without the need of extra sensors. We investigate how non-causal algorithms affects the target tracking performance using multiple sensors and dynamic models of different complexity. This is done to evaluate real-time methods against estimates obtained from non-causal filtering. Two different measurement units, a monocular camera and a LIDAR sensor, and two dynamic models are evaluated and compared using both causal and non-causal methods. The system is tested in two single object scenarios where ground truth is available and in three multi object scenarios without ground truth. Results from the two single object scenarios shows that tracking using only a monocular camera performs poorly since it is unable to measure the distance to objects. Here, a complementary LIDAR sensor improves the tracking performance significantly. The dynamic models are shown to have a small impact on the tracking performance, while the non-causal application gives a distinct improvement when tracking objects at large distances. Since the sequence can be reversed, the non-causal estimates are propagated from more certain states when the target is closer to the ego vehicle. For multiple object tracking, we find that correct associations between measurements and tracks are crucial for improving the tracking performance with non-causal algorithms.
Книги з теми "Backward Dynamical Approach"
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Lazer, David, and Stefan Wojcik. Political Networks and Computational Social Science. Edited by Jennifer Nicoll Victor, Alexander H. Montgomery, and Mark Lubell. Oxford University Press, 2017. http://dx.doi.org/10.1093/oxfordhb/9780190228217.013.9.
Повний текст джерелаАнотація:
The last half century has witnessed the digitization of human life, with a sharp inflection point being the widespread adoption of the Internet. In the wake of this digitization the phrase “big data” has been coined. Because many big data are explicitly or implicitly relational, this digitization of humanity has been critical in the increase in the study of networks. Further, since this digitization process continues not only forward but backward (e.g., through the scanning of millions of books and news periodicals going back for centuries), it is likely that the social sciences will be recentered over the next generation around computational approaches to data emphasizing (1) the relational aspects of human behavior, (2) phenomena that exist on societal scales rather than just individual ones, and (3) the dynamics of human behavior. This chapter discusses, in particular, the potential transformation of political science in these directions.
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Sheth, Falguni A. Unruly Women. Oxford University Press, 2022. http://dx.doi.org/10.1093/oso/9780197547137.001.0001.
Повний текст джерелаАнотація:
Drawing upon Michel Foucault’s accounts of governmentality and neoliberalism, liberal feminist and colonial “civilizing” narratives, and tacit juridical racial dismissal toward visibly Muslim women, this book explores the neocolonial and racial-cultural aesthetics of power as directed toward women of color and Black women. Even as neocolonialism incorporates without acknowledgment the anti-Blackness and settler-colonial roots of its past, along with an anti-immigrationist sentiment—it does not do so overtly. Rather it does so through a range of biopolitical, ontopolitical, and globalizing neoliberal economic norms. Focusing on the discrimination claims of Muslim women, this study examines juridical and political approaches that dismiss Muslim women and other populations of color as culturally backward, misguided in their thinking, and gratuitously nonconformist. Likewise, it analyses the experience of excruciation undergone by the addressees of racial dismissal. Excruciation names the phenomena by which vulnerable populations are pressed into hopeless performances of cultural assimilation. Racial dismissal is excavated through legal opinions, court transcripts, and other encounters between Muslim women and the state. This work finds that the racial address of dismissal and the phenomena of excruciation have been pivotal to a liberal juridical order that otherwise claims neutrality. By concentrating on the treatment of Muslim women, this book uncovers dynamics of social and racial division which have inhabited and bolstered liberal legal neutrality from its inception. This book’s framework, while focusing on Muslim women in the United States, is a template for understanding how exclusion is juridically implemented for other racialized and marginalized populations.
Частини книг з теми "Backward Dynamical Approach"
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Al-Shudeifat, Mohammad A., Oleg Shiryayev, Tariq Alzarooni, and Chandrasekhar Nataraj. "Full Spectrum Analysis for Studying the Backward Whirl in Accelerated Rotor Systems." In Perspectives in Dynamical Systems II: Mathematical and Numerical Approaches, 37–47. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-77310-6_4.
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Glushkov, Alexander V., Andrey V. Tsudik, Valentin B. Ternovsky, Dmytro V. Astaykin, Andrii V. Bondarenko, Dmytro V. Danylenko, and Vasily V. Buyadzhi. "Deterministic Chaos, Bifurcations and Strange Attractors in Nonlinear Dynamics of Relativistic Backward-Wave Tube." In Perspectives in Dynamical Systems II: Mathematical and Numerical Approaches, 125–35. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-77310-6_12.
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Riad, Maha, Saeedeh Ghanadbashi, and Fatemeh Golpayegani. "Run-Time Norms Synthesis in Dynamic Environments with Changing Objectives." In Communications in Computer and Information Science, 462–74. Cham: Springer Nature Switzerland, 2023. http://dx.doi.org/10.1007/978-3-031-26438-2_36.
Повний текст джерелаАнотація:
AbstractNormative Multi-Agent Systems (NorMAS) can model real-world applications as multi-agent systems and facilitate the coordination of the social behaviour of various entities (agents) interacting in an environment using norms. Aligning such norms with the objectives of the agents is crucially important to ensure that applying the norms would not affect the achievement of their objectives. However, when the environment is dynamic, agents can face unseen situations and might need to change their objectives accordingly. Therefore, it becomes more challenging to understand the change, synthesise norms, and align them with such dynamic objectives. This paper introduces a Dynamic Objectives and Norms Synthesizer and Reasoner (DONSR) model to align objectives and norms using a utility-based approach. An ontology-based schema, forward reasoning, and backward reasoning are used to identify the change in the environment and synthesise new objectives. Case-based reasoning enables the dynamic changing and reasoning of previously created objectives and synthesising norms. DONSR is evaluated using multiple simulated traffic scenarios, including different unseen situations (emergency events).Results show that norms can be synthesised and maintained efficiently while the objectives are being created and changed. Further, DONSR showed its efficacy in handling unseen situations, creating new objectives, and aligning them with the created norms.
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Jin, Shangzhu, Jike Ge, and Jun Peng. "A New Fuzzy Rule Interpolation Approach to Terrorism Risk Assessment." In Violent Extremism, 351–72. IGI Global, 2019. http://dx.doi.org/10.4018/978-1-5225-7119-3.ch019.
Повний текст джерелаАнотація:
Terrorist attacks launched by extremist groups or individuals have caused catastrophic consequences worldwide. Terrorism risk assessment therefore plays a crucial role in national and international security. Fuzzy reasoning based terrorism risk assessment systems offer a significant potential of providing decision support in combating terrorism, where highly complex situations may be involved. Nevertheless, little has been done in developing and applying an integrated hierarchical bidirectional (forward/backward) fuzzy rule interpolation mechanism that is tailored to suit decision support for terrorism risk assessment. This paper presents such an integrated approach that is capable of dealing with dynamic and insufficient information in the risk assessing process. In particular, the hierarchical system implementing the proposed techniques can predict the likelihood of terrorism attacks on different segments of focused attention. The results of an experimental investigation of this implemented system are represented, demonstrating the potential and efficacy of the proposed approach.
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Ugurlu, Barkan, and Atsuo Kawamura. "Prototyping and Real-Time Implementation of Bipedal Humanoid Robots." In Prototyping of Robotic Systems, 146–81. IGI Global, 2012. http://dx.doi.org/10.4018/978-1-4666-0176-5.ch006.
Повний текст джерелаАнотація:
This chapter is aimed at describing a contemporary bipedal humanoid robot prototyping technology, accompanied with a mathematically rigorous method to generate real-time walking, jumping, and running trajectories that can be applied to this type of robots. The main strategy in this method is to maintain the overall dynamic equilibrium and to prevent undesired rotational actions for the purpose of smooth maneuvering capabilities while the robot is in motion. In order to reach this goal, Zero Moment Point criterion is utilized in spherical coordinates, so that it is possible to fully exploit its properties by the help of Euler’s equations of motions. Such a strategy allows for characterization of the rotational inertia and therefore the associated angular momentum rate change terms, so that undesired torso angle fluctuations during walking and running are well suppressed. It enables prevention of backwards-hopping actions during jumping as well. To validate the proposed approach, the authors performed simulations using a precise 3D simulator and conducted experiments on an actual bipedal robot. Results indicated that the method is superior to classical methods in terms of suppressing undesired rotational actions, such as torso angle fluctuations and backwards-hopping.
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Félix Mora-Camino and Luiz Gustavo Zelaya Cruz. "Advances in Data Processing for Airlines Revenue Management." In Computational Models, Software Engineering, and Advanced Technologies in Air Transportation, 132–45. IGI Global, 2010. http://dx.doi.org/10.4018/978-1-60566-800-0.ch008.
Повний текст джерелаАнотація:
In this communication advances in data processing techniques applied to Airlines Revenue Management are displayed. The general introduction presents a brief review of Airlines Revenue Management. The first of the paper introduces the problem of updating the probability distributions of demand for reservations. This updating process, facing the stochastic nature of demand for travel, is a cornerstone for the design of an efficient on-line decision support system to control the reservation process for a flight by an airline. The considered problem is formulated as a dual geometric problem to which an unconstrained nonconvex, primal geometric problem is associated. A genetic algorithm optimization approach is proposed to solve the primal geometric problem, and then the classical geometric primal-dual transformations provide the solution to the initial problem. Then, the second part of the paper considers the design of a new Decision Support System for improving the reservation control process of airlines. A new recursive Dynamic Programming model for maximum expected revenue evaluation is defined, which, contrarily to other approaches, takes explicitly into account daily booking request arrivals. A practical Backward Dynamic Programming algorithm is established, leading to the design of an on-line optimisation module for Revenue Management. In this study two cases are considered. The first one considers that fare classes are not physically confined and the obtained results are extended in the second case to cover the situations where confinement of fare classes (Business Class and Economy Class) is applied.
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Jabari, Farkhondeh, Heresh Seyedia, Sajad Najafi Ravadanegh, and Behnam Mohammadi Ivatloo. "Stochastic Contingency Analysis Based on Voltage Stability Assessment in Islanded Power System Considering Load Uncertainty Using MCS and k-PEM." In Advances in Computer and Electrical Engineering, 12–36. IGI Global, 2016. http://dx.doi.org/10.4018/978-1-4666-9911-3.ch002.
Повний текст джерелаАнотація:
Increased electricity demands and economic operation of large power systems in a deregulated environment with a limited investment in transmission expansion planning causes interconnected power grids to be operated closer to their stability limits. Meanwhile, the loads uncertainty will affect the static and dynamic stabilities. Therefore, if there is no emergency corrective control in time, occurrence of wide area contingency may lead to the catastrophic cascading outages. Studies show that many wide area blackouts which led to massive economic losses may have been prevented by a fast feasible controlled islanding decision making. This chapter introduces a novel computationally efficient approach for separating of bulk power system into several stable sections following a severe disturbance. The splitting strategy reduces the large initial search space to an interface boundary network considering coherency of synchronous generators and network graph simplification. Then, a novel islanding scenario generator algorithm denoted as BEM (Backward Elimination Method) based on PMEAs (Primary Maximum Expansion Areas) has been applied to generate all proper islanding solutions in the simplified network graph. The PPF (Probabilistic Power Flow) based on Newton-Raphson method and Q-V modal analysis has been used to evaluate the steady-state stability of created islands in each generated scenario. BICA (Binary Imperialistic Competitive Algorithm) has then been applied to minimize total load-generation mismatch considering integrity, voltage permitted range and steady-state voltage stability constraints. The best solution has then been applied to split the entire power network. A novel stochastic contingency analysis of islands based on PSVI (Probability of Static Voltage Instability) using MCS (Monte Carlo Simulation) and k-PEM (k-Point Estimate Method) have been proposed to identify the critical PQ buses and severe contingencies. In these approaches, the ITM (Inverse Transform Method) has been used to model uncertain loads with normal probability distribution function in optimal islanded power system. The robustness, effectiveness and capability of the proposed approaches have been validated on the New England 39-bus standard power system.
Тези доповідей конференцій з теми "Backward Dynamical Approach"
1
Gunter, Edgar J., and Wen Jeng Chen. "Dynamic Analysis of an 1150 MW Turbine-Generator." In ASME 2005 Power Conference. ASMEDC, 2005. http://dx.doi.org/10.1115/pwr2005-50142.
Повний текст джерелаАнотація:
This paper presents the dynamical analysis of an 11-bearing 1,150 MW turbine-generator system. Original studies of this system yielded information on the system critical speeds and mode shapes. These calculations were first generated by the transfer matrix method. It was found that the transfer matrix method is unsuited for the analysis of large turbine-generators for a number of reasons. The first is the problem of convergence of the modes with a large number of mass stations. The second is that the iteration procedure misses modes that are closely spaced. In the study of the dynamical behavior of large T-G sets, it was determined that it was necessary to include the foundation or bearing pedestal effects. This not possible with the transfer matrix method due to the numerical problems associated with branched elements of the supports. The system critical speeds were computed using a structural finite element program. This approach could generate the system modes, but is not capable of computing damped eigenvalues, unbalance response, or to perform accurate time transient analysis to evaluate system motion and bearing forces transmitted due to blade loss. With the recent enhancements to the PC-based finite element program DyRoBeS, it is now possible to perform both linear and nonlinear time transient studies on large turbine-generator systems, as well as damped eigenvalue analysis and unbalance response. In the calculation of the undamped critical speeds, it was observed that there can be as many as 12 undamped modes in the operating speed range. Not all of these modes need to be of concern. A mode is of concern if it has a low log decrement damping and is in the vicinity of the operating speed, or that it has a negative log decrement which indicates that it may be unstable. In order to compute the damped complex 3-dimensional eigenvalues of the system, the 8 bearing stiffness and damping coefficients for the 11 bearings must be known. These values were computed for each bearing and are then used in the calculation of the damped modes. Instead of considering only 12 modes, one must compute the first 30 complex modes to span the frequency range of interest. These modes represent forward, mixed, and backward modes. Only several of these modes are of concern. There are several forward modes that are near the operating speed and have high exciter and LP turbine motion. These modes also have low log decrements which makes them of concern, particularly as regards to a suddenly applied unbalance. A time transient analysis is required in order to assess the TG response at running speed due to a sudden unbalance, such as caused by blade loss. One of the limitations with structural finite element programs is that transient analysis is accomplished by assuming a set of undamped modes. One is then required to assume a percent of modal damping for each mode. This approach may be acceptable for structural systems, but it is not acceptable for a rotor dynamics analysis in which the bearings have high damping in addition to the bearing cross-coupling coefficients which structural FEA programs can not handle. A time transient analysis was performed using DyRoBeS to simulate 6 cycles of shaft motion. In this simulation of LP3 blade loss at running speed, one of the system modes around 1,600 CPM was excited to the extent that exciter damage could occur, leading to system failure. It is concluded that exciters of this class may be insufficiently supported and also have insufficient damping to withstand blade loss.
2
Gragg, Jared, Jingzhou (James) Yang, and Guolai Yang. "Probabilistic Approach for Digital Human Kinematic and Dynamic Reliabilities." In ASME 2012 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/detc2012-70560.
Повний текст джерелаАнотація:
Traditionally, deterministic methods have been applied in digital human modeling (DHM). Transforming the deterministic approach of digital human modeling into a probabilistic approach is natural since there is inherent uncertainty and variability associated with DHM problems. Typically, deterministic studies in this field ignore this uncertainty or try to limit the uncertainty by employing optimization procedures. Due to the variability in the inputs, a deterministic study may not be enough to account for the uncertainty in the system. Probabilistic design techniques allow the designer to predict the likelihood of an outcome while also accounting for uncertainty, in contrast to deterministic studies. The purpose of this study is to incorporate probabilistic approaches to a deterministic DHM problem that has already been studied, analyzing human kinematics and dynamics. The problem is transformed into a probabilistic approach where the human kinematic and dynamic reliabilities are determined. The kinematic reliability refers to the probability that the human end-effector position (and/or orientation) falls within a specified distance from the desired position (and/or orientation) in an inverse kinematic problem. The dynamic reliability refers to the probability that the human end-effector position (and/or velocity) falls within a specified distance from the desired position (and/or velocity) along a specified trajectory in the workspace. The dynamic equations of motion for DHM are derived by the Lagrangian backward recursive dynamics formulation.
3
Grover, Piyush. "Stability Analysis in Mean-Field Games via an Evans Function Approach." In ASME 2018 Dynamic Systems and Control Conference. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/dscc2018-8926.
Повний текст джерелаАнотація:
This work is concerned with stability analysis of stationary and time-varying equilibria in a class of mean-field games that relate to multi-agent control problems of flocking and swarming. The mean-field game framework is a non-cooperative model of distributed optimal control in large populations, and characterizes the optimal control for a representative agent in Nash-equilibrium with the population. A mean-field game model is described by a coupled PDE system of forward-in-time Fokker-Planck (FP) equation for density of agents, and a backward-in-time Hamilton-Jacobi-Bellman (HJB) equation for control. The linear stability analysis of fixed points of these equations typically proceeds via numerical computation of spectrum of the linearized MFG operator. We explore the Evans function approach that provides a geometric alternative to solving the characteristic equation.
4
Spakovsky, Z. S. "Backward Traveling Rotating Stall Waves in Centrifugal Compressors." In ASME Turbo Expo 2002: Power for Land, Sea, and Air. ASMEDC, 2002. http://dx.doi.org/10.1115/gt2002-30379.
Повний текст джерелаАнотація:
Rotating stall waves that travel against the direction of rotor rotation are reported for the first time and a new, low-order analytical approach to model centrifugal compressor stability is introduced. The model is capable of dealing with unsteady radially swirling flows and the dynamic effects of impeller-diffuser component interaction as it occurs in centrifugal compression systems. A simple coupling criterion is developed from first principles to explain the interaction mechanism important for system stability. The model findings together with experimental data explain the mechanism for first-ever observed backward traveling rotating stall in centrifugal compressors with vaned diffusers. Based on the low-order model predictions, an air injection scheme between the impeller and the vaned diffuser is designed for the NASA Glenn CC3 high-speed centrifugal compressor. The steady air injection experiments show an increase of 25% in surge-margin with an injection mass flow of 0.5% of the compressor mass flow. In addition, it is experimentally demonstrated that this injection scheme is robust to impeller tip-clearance effects and that a reduced number of injectors can be applied for similar gains in surge-margin. The results presented in this paper firmly establish the connection between the experimentally observed dynamic phenomena in the NASA CC3 centrifugal compressor and a first principles based coupling criterion. In addition, guidelines are given for the design of centrifugal compressors with enhanced stability.
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Wang, Fengxia, and Saeed Onsorynezhad. "Backward Mechanical-Electric Coupling Effect of a Frequency-Up-Conversion Piezoelectric Energy Harvester." In ASME 2019 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/detc2019-97867.
Повний текст джерелаАнотація:
Abstract This paper developed an analytical model for a frequency-up-conversion piezoelectric energy harvester (PEH) composed of a piezoelectric bimorph and a stopper as shown in Fig.1. The whole system was subjected to a harmonic excitation. A bimodal approach was adopted to animate the beam stopper reaction. When the tip of the bimorph vibrates in free space or impacts with the stopper, a cantilever beam function was adopted. On the other hand, if the tip of the bimorph sticks with the stopper, a clamped-pinned beam function was applied to model the piezoelectric bimorph. To exam the effect of backward mechanical-electric coupling on power output, the dynamics and output energies are compared for two cases: 1) neglecting the backward mechanical-electric coupling effect in the model; 2) including the backward mechanical-electric coupling effect in the model. To obtain maximum output energy, the steady-state analytical solutions were studied to obtain the optimum gap between the piezoelectric beam and the stopper. From the results, we found that if the beam impacts and/or sticks with the stopper, the PEH model without the backward mechanical-electric coupling will exaggerate the output energy.
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Ward, Greg. "A general approach to backwards-compatible delivery of high dynamic range images and video." In ACM SIGGRAPH 2008 classes. New York, New York, USA: ACM Press, 2008. http://dx.doi.org/10.1145/1401132.1401172.
Повний текст джерела
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Krishna, C. Vamsi, and Santosh Hemchandra. "Reduced Order Modelling of Combustion Instability in a Backward Facing Step Combustor." In ASME 2013 Gas Turbine India Conference. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/gtindia2013-3559.
Повний текст джерелаАнотація:
This paper develops a fully coupled time domain Reduced Order Modelling (ROM) approach to model unsteady combustion dynamics in a backward facing step combustor. The acoustic field equations are projected onto the canonical acoustic eigenmodes of the systems to obtain a coupled system of modal evolution equations. The heat release response of the flame is modelled using the G-equation approach. Vortical velocity fluctuations that arise due to shear layer rollup downstream of the step are modelled using a simplified 1D-advection equation whose phase speed is determined from a linear, local, temporal stability analysis of the shear layer, just downstream of the step. The hydrodynamic stability analysis reveals a abrupt change in the value of disturbance phase speed from unity for Re < Recrit to 0.5 for Re > Recrit, where Recrit for the present geometry was found to be ≈ 10425. The results for self-excited flame response show highly wrinkled flame shapes that are qualitatively similar to those seen in prior experiments of acoustically forced flames. The effect of constructive and destructive interference between the two contributions to flame surface wrinkling results in high amplitude wrinkles for the case when Kc → 1.
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Kasac, J., J. Deur, B. Novakovic, and I. Kolmanovsky. "A BPTT-Like Optimal Control Algorithm With Vehicle Dynamics Control Application." In ASME 2008 International Mechanical Engineering Congress and Exposition. ASMEDC, 2008. http://dx.doi.org/10.1115/imece2008-67319.
Повний текст джерелаАнотація:
The paper presents a gradient-based numerical algorithm for optimal control of nonlinear multivariable systems with control and state vectors constraints. The algorithm has a backward-in-time recurrent structure similar to the backpropagation-through-time (BPTT) algorithm, which is mostly used as a learning algorithm for dynamic neural networks. This paper presents an enhancement of the basic optimization algorithm. Our enhanced algorithm uses high-order Adams time-discretization schemes instead of the basic Euler discretization method, and a numerical calculation of Jacobians as an alternative to analytical Jacobians. Two examples are considered to illustrate the algorithm and its performance. The first example is that of a tubular reactor, for which an analytical solution is available, which can be readily used for validation of our approach. The second example is related to controlling vehicle dynamics based on a realistic high order model.
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Bayly, Philip V., Keith A. Young, and Jeremiah E. Halley. "Tool Oscillation and the Formation of Lobed Holes in a Quasi-Static Model of Reaming." In ASME 1999 Design Engineering Technical Conferences. American Society of Mechanical Engineers, 1999. http://dx.doi.org/10.1115/detc99/vib-8061.
Повний текст джерелаАнотація:
Abstract A quasi-static model of reaming is used to explain oscillation of the tool during cutting and the resulting roundness errors in reamed holes. Tools with N evenly-spaced teeth often produce holes with N+1 or N-1 “lobes”. These profiles correspond, respectively, to forward or backward whirl of the tool at N cycles/rev. Other whirl harmonics (2N cycles/rev, e.g.) are occasionally seen as well. The quasi-static model is motivated by the observations that relatively large oscillations occur at frequencies well below the natural frequency of the tool, and that in this regime the wavelength of the hole profile is largely independent of both cutting speed and tool natural frequency. In the quasi-static approach, inertial and viscous damping forces are neglected, but the system remains dynamic because regenerative (time-delayed) cutting and rubbing forces are included. The model leads to an eigenvalue problem with forward and backward whirl solutions that closely resemble the tool behavior seen in practice.
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Gavrea, B., D. Negrut, and F. A. Potra. "The Newmark Integration Method for Simulation of Multibody Systems: Analytical Considerations." In ASME 2005 International Mechanical Engineering Congress and Exposition. ASMEDC, 2005. http://dx.doi.org/10.1115/imece2005-81770.
Повний текст джерелаАнотація:
When simulating the behavior of a mechanical system, the time evolution of the generalized coordinates used to represent the configuration of the model is computed as the solution of a combined set of ordinary differential and algebraic equations (DAEs). There are several ways in which the numerical solution of the resulting index 3 DAE problem can be approached. The most well-known and time-honored algorithms are the direct discretization approach, and the state-space reduction approach, respectively. In the latter, the problem is reduced to a minimal set of potentially new generalized coordinates in which the problem assumes the form of a pure second order set of Ordinary Differential Equations (ODE). This approach is very accurate, but computationally intensive, especially when dealing with large mechanical systems that contain flexible parts, stiff components, and contact/impact. The direct discretization approach is less but nevertheless sufficiently accurate yet significantly faster, and it is the approach that is considered in this paper. In the context of direct discretization methods, approaches based on the Backward Differentiation Formulas (BDF) have been the traditional choice for more than 20 years. This paper proposes a new approach in which BDF methods are replaced by the Newmark formulas. Local convergence analysis is carried out for the proposed method, and step-size control, error estimation, and nonlinear system solution related issues are discussed in detail. A series of two simple models are used to validate the method. The global convergence analysis and a computational-efficiency comparison with the most widely used numerical integrator available in the MSC.ADAMS commercial simulation package are forthcoming. The new method has been implemented successfully for industrial strength Dynamic Analysis simulations in the 2005 version of the MSC.ADAMS software and used very effectively for the simulation of systems with more than 15,000 differential-algebraic equations.
Звіти організацій з теми "Backward Dynamical Approach"
1
An Input Linearized Powertrain Model for the Optimal Control of Hybrid Electric Vehicles. SAE International, March 2022. http://dx.doi.org/10.4271/2022-01-0741.
Повний текст джерелаАнотація:
Models of hybrid powertrains are used to establish the best combination of conventional engine power and electric motor power for the current driving situation. The model is characteristic for having two control inputs and one output constraint: the total torque should be equal to the torque requested by the driver. To eliminate the constraint, several alternative formulations are used, considering engine power or motor power or even the ratio between them as a single control input. From this input and the constraint, both power levels can be deduced. There are different popular choices for this one control input. This paper presents a novel model based on an input linearizing transformation. It is demonstrably superior to alternative model forms, in that the core dynamics of the model (battery state of energy) are linear, and the non-linearities of the model are pushed into the inputs and outputs in a Wiener/Hammerstein form. The output non-linearities can be approximated using a quadratic model, which creates a problem in the linear-quadratic framework. This facilitates the direct application of linear control approaches such as LQR control, predictive control, or Model Predictive Control (MPC). The paper demonstrates the approach using the ELectrified Vehicle library for sImulation and Optimization (ELVIO). It is an open-source MATLAB/Simulink library designed for the quick and easy simulation and optimization of different powertrain and drivetrain architectures. It follows a modelling methodology that combines backward-facing and forward-facing signal path, which means that no driver model is required. The results show that the approximated solution provides a performance that is very close to the solution of the original problem except for extreme parts of the operating range (in which case the solution tends to be driven by constraints anyway).