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Artykuły w czasopismach na temat "Inertial Gradient Methods"
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Li, Jing, Xiao Wei, Fengpin Wang i Jinjia Wang. "IPGM: Inertial Proximal Gradient Method for Convolutional Dictionary Learning". Electronics 10, nr 23 (3.12.2021): 3021. http://dx.doi.org/10.3390/electronics10233021.
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Inspired by the recent success of the proximal gradient method (PGM) and recent efforts to develop an inertial algorithm, we propose an inertial PGM (IPGM) for convolutional dictionary learning (CDL) by jointly optimizing both an ℓ2-norm data fidelity term and a sparsity term that enforces an ℓ1 penalty. Contrary to other CDL methods, in the proposed approach, the dictionary and needles are updated with an inertial force by the PGM. We obtain a novel derivative formula for the needles and dictionary with respect to the data fidelity term. At the same time, a gradient descent step is designed to add an inertial term. The proximal operation uses the thresholding operation for needles and projects the dictionary to a unit-norm sphere. We prove the convergence property of the proposed IPGM algorithm in a backtracking case. Simulation results show that the proposed IPGM achieves better performance than the PGM and slice-based methods that possess the same structure and are optimized using the alternating-direction method of multipliers (ADMM).
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Zhang, Yanwei, i James N. Moum. "Inertial-Convective Subrange Estimates of Thermal Variance Dissipation Rate from Moored Temperature Measurements". Journal of Atmospheric and Oceanic Technology 27, nr 11 (1.11.2010): 1950–59. http://dx.doi.org/10.1175/2010jtecho746.1.
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Abstract A procedure for estimating thermal variance dissipation rate χT by scaling the inertial-convective subrange of temperature gradient spectra from thermistor measurements on a Tropical Atmosphere Ocean (TAO) equatorial mooring, maintained by NOAA’s National Data Buoy Center, is demonstrated. The inertial-convective subrange of wavenumbers/frequencies is contaminated by the vertical motion induced by the pumping of the surface float by surface gravity waves through the local vertical temperature gradient. The uncontaminated signal can be retrieved by removing the part of the measured signal that is coherent with the signal induced by surface gravity waves, which must be measured independently. An estimate of χT is then obtained by fitting corrected spectra to theoretical temperature gradient spectra over the inertial-convective subrange (0.05 < f < 0.5 Hz); this estimate is referred to as χTIC. Here χTIC was calculated over 120-min intervals and compared with estimates of χTo determined by scaling temperature gradient spectra at high wavenumbers (viscous-convective and viscous-diffusive subranges). Large differences up to a factor of 20 and of unknown origin occur infrequently, especially when both background currents and vertical temperature gradients are weak, but the results herein indicate that 75% of the data pairs are within a factor of 3 of each other. Tests on 15-, 30-, 60-, 120-min intervals demonstrate that differences between the two methods are nearly random, unbiased, and less than estimates of natural variability determined from unrelated experiments at the same location. Because the inertial-convective subrange occupies a lower-frequency range than is typically used for turbulence measurements, the potential for more routine measurements of χT exists. The evaluation of degraded signals (resampled from original measurements) indicates that a particularly important component of such a measurement is the independent resolution of the surface wave–induced signal.
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Kesornprom, Suparat, i Prasit Cholamjiak. "A modified inertial proximal gradient method for minimization problems and applications". AIMS Mathematics 7, nr 5 (2022): 8147–61. http://dx.doi.org/10.3934/math.2022453.
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<abstract><p>In this paper, the aim is to design a new proximal gradient algorithm by using the inertial technique with adaptive stepsize for solving convex minimization problems and prove convergence of the iterates under some suitable assumptions. Some numerical implementations of image deblurring are performed to show the efficiency of the proposed methods.</p></abstract>
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Sheng, Guangrun, Guowei Gao i Boyuan Zhang. "Application of Improved Wavelet Thresholding Method and an RBF Network in the Error Compensating of an MEMS Gyroscope". Micromachines 10, nr 9 (13.09.2019): 608. http://dx.doi.org/10.3390/mi10090608.
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The large random errors in Micro-Electro-Mechanical System (MEMS) gyros are one of the major factors that affect the precision of inertial navigation systems. Based on the indoor inertial navigation system, an improved wavelet threshold de-noising method was proposed and combined with a gradient radial basis function (RBF) neural network to better compensate errors. We analyzed the random errors in an MEMS gyroscope by using Allan variance, and introduced the traditional wavelet threshold methods. Then, we improved the methods and proposed a new threshold function. The new method can be used more effectively to detach white noise and drift error in the error model. Finally, the drift data was modeled and analyzed in combination with the RBF neural network. Experimental results indicate that the method is effective, and this is of great significance for improving the accuracy of indoor inertial navigation based on MEMS gyroscopes.
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Milder, A. L., A. S. Joglekar, W. Rozmus i D. H. Froula. "Qualitative and quantitative enhancement of parameter estimation for model-based diagnostics using automatic differentiation with an application to inertial fusion". Machine Learning: Science and Technology 5, nr 1 (13.02.2024): 015026. http://dx.doi.org/10.1088/2632-2153/ad2493.
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Abstract Parameter estimation using observables is a fundamental concept in the experimental sciences. Mathematical models that represent the physical processes can enable reconstructions of the experimental observables and greatly assist in parameter estimation by turning it into an optimization problem which can be solved by gradient-free or gradient-based methods. In this work, the recent rise in flexible frameworks for developing differentiable scientific computing programs is leveraged in order to dramatically accelerate data analysis of a common experimental diagnostic relevant to laser–plasma and inertial fusion experiments, Thomson scattering. A differentiable Thomson-scattering data analysis tool is developed that uses reverse-mode automatic differentiation (AD) to calculate gradients. By switching from finite differencing to reverse-mode AD, three distinct outcomes are achieved. First, gradient descent is accelerated dramatically to the extent that it enables near real-time usage in laser–plasma experiments. Second, qualitatively novel quantities which require O ( 10 3 ) parameters can now be included in the analysis of data which enables unprecedented measurements of small-scale laser–plasma phenomena. Third, uncertainty estimation approaches that leverage the value of the Hessian become accurate and efficient because reverse-mode AD can be used for calculating the Hessian.
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Ceng, Lu-Chuan, Adrian Petruşel, Ching-Feng Wen i Jen-Chih Yao. "Inertial-Like Subgradient Extragradient Methods for Variational Inequalities and Fixed Points of Asymptotically Nonexpansive and Strictly Pseudocontractive Mappings". Mathematics 7, nr 9 (17.09.2019): 860. http://dx.doi.org/10.3390/math7090860.
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Let VIP indicate the variational inequality problem with Lipschitzian and pseudomonotone operator and let CFPP denote the common fixed-point problem of an asymptotically nonexpansive mapping and a strictly pseudocontractive mapping in a real Hilbert space. Our object in this article is to establish strong convergence results for solving the VIP and CFPP by utilizing an inertial-like gradient-like extragradient method with line-search process. Via suitable assumptions, it is shown that the sequences generated by such a method converge strongly to a common solution of the VIP and CFPP, which also solves a hierarchical variational inequality (HVI).
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Kesornprom, Suparat, Papatsara Inkrong, Uamporn Witthayarat i Prasit Cholamjiak. "A recent proximal gradient algorithm for convex minimization problem using double inertial extrapolations". AIMS Mathematics 9, nr 7 (2024): 18841–59. http://dx.doi.org/10.3934/math.2024917.
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<abstract><p>In this study, we suggest a new class of forward-backward (FB) algorithms designed to solve convex minimization problems. Our method incorporates a linesearch technique, eliminating the need to choose Lipschitz assumptions explicitly. Additionally, we apply double inertial extrapolations to enhance the algorithm's convergence rate. We establish a weak convergence theorem under some mild conditions. Furthermore, we perform numerical tests, and apply the algorithm to image restoration and data classification as a practical application. The experimental results show our approach's superior performance and effectiveness, surpassing some existing methods in the literature.</p></abstract>
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Rasmussen, John, Sebastian Skejø i Rasmus Plenge Waagepetersen. "Predicting Tissue Loads in Running from Inertial Measurement Units". Sensors 23, nr 24 (15.12.2023): 9836. http://dx.doi.org/10.3390/s23249836.
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Background: Runners have high incidence of repetitive load injuries, and habitual runners often use smartwatches with embedded IMU sensors to track their performance and training. If accelerometer information from such IMUs can provide information about individual tissue loads, then running watches may be used to prevent injuries. Methods: We investigate a combined physics-based simulation and data-based method. A total of 285 running trials from 76 real runners are subjected to physics-based simulation to recover forces in the Achilles tendon and patella ligament, and the collected data are used to train and test a data-based model using elastic net and gradient boosting methods. Results: Correlations of up to 0.95 and 0.71 for the patella ligament and Achilles tendon forces, respectively, are obtained, but no single best predictive algorithm can be identified. Conclusions: Prediction of tissues loads based on body-mounted IMUs appears promising but requires further investigation before deployment as a general option for users of running watches to reduce running-related injuries.
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Michielsen, M., C. Aerts i D. M. Bowman. "Probing the temperature gradient in the core boundary layer of stars with gravito-inertial modes". Astronomy & Astrophysics 650 (czerwiec 2021): A175. http://dx.doi.org/10.1051/0004-6361/202039926.
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Aims. We investigated the thermal and chemical structure in the near-core region of stars with a convective core by means of gravito-inertial modes. We determined the probing power of different asteroseismic observables and fitting methodologies. We focus on the case of the B-type star KIC 7760680, rotating at a quarter of its critical rotation velocity. Methods. We computed grids of 1D stellar structure and evolution models for two different prescriptions of the temperature gradient and mixing profile in the near-core region. We determined which of these prescriptions is preferred according to the prograde dipole modes detected in 4 yr Kepler photometry of KIC 7760680. We considered different sets of asteroseismic observables and compared the outcomes of the regression problem for a χ2 and a Mahalanobis distance merit function, where the latter takes into account realistic uncertainties for the theoretical predictions and the former does not. Results. Period spacings of modes with consecutive radial order offer a better diagnostic than mode periods or mode frequencies for asteroseismic modelling of stars revealing only high-order gravito-inertial modes. We find KIC 7760680 to reveal a radiative temperature gradient in models with convective boundary mixing, but less complex models without such mixing are statistically preferred for this rotating star, revealing extremely low vertical envelope mixing. Conclusions. Our results strongly suggest the use of measured individual period spacing values for modes of consecutive radial order as an asteroseismic diagnostic for stellar modelling of B-type pulsators with gravito-inertial modes.
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Neuwirth, Christina, Cory Snyder, Wolfgang Kremser, Richard Brunauer, Helmut Holzer i Thomas Stöggl. "Classification of Alpine Skiing Styles Using GNSS and Inertial Measurement Units". Sensors 20, nr 15 (29.07.2020): 4232. http://dx.doi.org/10.3390/s20154232.
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In alpine skiing, four commonly used turning styles are snowplow, snowplow-steering, drifting and carving. They differ significantly in speed, directional control and difficulty to execute. While they are visually distinguishable, data-driven classification is underexplored. The aim of this work is to classify alpine skiing styles based on a global navigation satellite system (GNSS) and inertial measurement units (IMU). Data of 2000 turns of 20 advanced or expert skiers were collected with two IMU sensors on the upper cuff of each ski boot and a mobile phone with GNSS. After feature extraction and feature selection, turn style classification was applied separately for parallel (drifted or carved) and non-parallel (snowplow or snowplow-steering) turns. The most important features for style classification were identified via recursive feature elimination. Three different classification methods were then tested and compared: Decision trees, random forests and gradient boosted decision trees. Classification accuracies were lowest for the decision tree and similar for the random forests and gradient boosted classification trees, which both achieved accuracies of more than 93% in the parallel classification task and 88% in the non-parallel case. While the accuracy might be improved by considering slope and weather conditions, these first results suggest that IMU data can classify alpine skiing styles reasonably well.
Rozprawy doktorskie na temat "Inertial Gradient Methods"
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Maulen, Soto Rodrigo. "A dynamical system perspective οn stοchastic and iΙnertial methοds fοr optimizatiοn". Electronic Thesis or Diss., Normandie, 2024. http://www.theses.fr/2024NORMC220.
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Motivé par l'omniprésence de l'optimisation dans de nombreux domaines de la science et de l'ingénierie, en particulier dans la science des données, ce manuscrit de thèse exploite le lien étroit entre les systèmes dynamiques dissipatifs à temps continu et les algorithmes d'optimisation pour fournir une analyse systématique du comportement global et local de plusieurs systèmes du premier et du second ordre, en se concentrant sur le cadre convexe, stochastique et en dimension infinie d'une part, et le cadre non convexe, déterministe et en dimension finie d'autre part. Pour les problèmes de minimisation convexe stochastique dans des espaces de Hilbert réels séparables de dimension infinie, notre proposition clé est de les analyser à travers le prisme des équations différentielles stochastiques (EDS) et des inclusions différentielles stochastiques (IDS), ainsi que de leurs variantes inertielles. Nous considérons d'abord les problèmes convexes différentiables lisses et les EDS du premier ordre, en démontrant une convergence faible presque sûre vers les minimiseurs sous hypothèse d'intégrabilité du bruit et en fournissant une analyse globale et locale complète de la complexité. Nous étudions également des problèmes convexes non lisses composites utilisant des IDS du premier ordre et montrons que, sous des conditions d'intégrabilité du bruit, la convergence faible presque sûre des trajectoires vers les minimiseurs, et avec la régularisation de Tikhonov la convergence forte presque sûre des trajectoires vers la solution de norme minimale. Nous développons ensuite un cadre mathématique unifié pour analyser la dynamique inertielle stochastique du second ordre via la reparamétrisation temporelle et le moyennage de la dynamique stochastique du premier ordre, ce qui permet d'obtenir une convergence faible presque sûre des trajectoires vers les minimiseurs et une convergence rapide des valeurs et des gradients. Ces résultats sont étendus à des EDS plus générales du second ordre avec un amortissement visqueux et Hessien, en utilisant une analyse de Lyapunov spécifique pour prouver la convergence et établir de nouveaux taux de convergence. Enfin, nous étudions des problèmes d'optimisation déterministes non convexes et proposons plusieurs algorithmes inertiels pour les résoudre, dérivés d'équations différentielles ordinaires (EDO) du second ordre combinant à la fois un amortissement visqueux sans vanité et un amortissement géométrique piloté par le Hessien, sous des formes explicites et implicites. Nous prouvons d'abord la convergence des trajectoires en temps continu des EDO vers un point critique pour des objectives vérifiant la propriété de Kurdyka-Lojasiewicz (KL) avec des taux explicites, et génériquement vers un minimum local si l'objective est Morse. De plus, nous proposons des schémas algorithmiques par une discrétisation appropriée de ces EDO et montrons que toutes les propriétés précédentes des trajectoires en temps continu sont toujours valables dans le cadre discret sous réserve d'un choix approprié de la taille du pasMotivated by the ubiquity of optimization in many areas of science and engineering, particularly in data science, this thesis exploits the close link between continuous-time dissipative dynamical systems and optimization algorithms to provide a systematic analysis of the global and local behavior of several first- and second-order systems, focusing on convex, stochastic, and infinite-dimensional settings on the one hand, and non-convex, deterministic, and finite-dimensional settings on the other hand. For stochastic convex minimization problems in infinite-dimensional separable real Hilbert spaces, our key proposal is to analyze them through the lens of stochastic differential equations (SDEs) and inclusions (SDIs), as well as their inertial variants. We first consider smooth differentiable convex problems and first-order SDEs, demonstrating almost sure weak convergence towards minimizers under integrability of the noise and providing a comprehensive global and local complexity analysis. We also study composite non-smooth convex problems using first-order SDIs, and show under integrability conditions on the noise, almost sure weak convergence of the trajectory towards a minimizer, with Tikhonov regularization almost sure strong convergence of trajectory to the minimal norm solution. We then turn to developing a unified mathematical framework for analyzing second-order stochastic inertial dynamics via time scaling and averaging of stochastic first-order dynamics, achieving almost sure weak convergence of trajectories towards minimizers and fast convergence of values and gradients. These results are extended to more general second-order SDEs with viscous and Hessian-driven damping, utilizing a dedicated Lyapunov analysis to prove convergence and establish new convergence rates. Finally, we study deterministic non-convex optimization problems and propose several inertial algorithms to solve them derived from second-order ordinary differential equations (ODEs) combining both non-vanishing viscous damping and geometric Hessian-driven damping in explicit and implicit forms. We first prove convergence of the continuous-time trajectories of the ODEs to a critical point under the Kurdyka-Lojasiewicz (KL) property with explicit rates, and generically to a local minimum under a Morse condition. Moreover, we propose algorithmic schemes by appropriate discretization of these ODEs and show that all previous properties of the continuous-time trajectories still hold in the discrete setting under a proper choice of the stepsize
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Anjo, Luiz Fernando Resende dos Santos. "Modelo hidraulico para transitorios lentos em conduto forçado". [s.n.], 2008. http://repositorio.unicamp.br/jspui/handle/REPOSIP/258182.
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Orientador: Edevar Luvizotto JuniorTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Civil, Arquitetura e Urbanismo
Made available in DSpace on 2018-08-11T21:41:10Z (GMT). No. of bitstreams: 1 Anjo_LuizFernandoResendedosSantos_D.pdf: 3588080 bytes, checksum: 122271523488dc8a40a0d509bd1b0cf8 (MD5) Previous issue date: 2008
Resumo: Este texto descreve as etapas que objetivam a utilização da estrutura originalmenteproposta por Todini e Pilati no chamado método gradiente (MG), utilizado para análise em regime permanente em instalações a condutos forçados, na formulação de um modelo dinâmico inercial rígido (MDIR), para a análise de escoamentos transitórios lentos neste tipo de instalação. São apresentadas as bases teóricas para esta nova modelação, justificadas através do equacionamento geral do escoamento fluido em condutos forçados. Os resultados obtidos pelo MDIR são comparados com os resultados obtidos pelo programa EPANET que utiliza o método gradiente. Discussões a respeito da importância da incorporação do efeito de inércia são apresentadas através de um estudo de casos, no caso de modelação hidráulica, e para análises de qualidade decorrentes desta.
Abstract: This research describes the stages which aim the use of the original structure proposed by Todini and Pilati in the so called gradient method (GM), used in the analysis in steady state of pipe networks, in the formulation of an inertial rigid dynamic model (IRDM) to analyse slow transients in this type of installation. The theoretical bases are presented for this new method, justified by the general equation of fluids flow in pipes networks. The results obtained by the MDIR are compared to the results obtained in the EPANET program, which uses the gradient method. Discussion on the importance of the incorporation of the inertia effect are presented through a study case of hydraulic modelation and for quality analysis which derived from it.
Doutorado
Recursos Hidricos
Doutor em Engenharia Civil
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Gaujour, Etienne. "Evaluation des sources d'espèces et des déterminants de la diversité végétale des parcelles agricoles : interchamps, stock semencier, pratiques agricoles et paysage de l'Installation Expérimentale Inra ASTER Mirecourt". Thesis, Vandoeuvre-les-Nancy, INPL, 2010. http://www.theses.fr/2010INPL020N/document.
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L'un des moyens pour faire face à la réduction de l'utilisation d'intrants de synthèse est de favoriser durablement les services agro-écologiques de la diversité végétale. Pour cela, l'agriculteur devra adapter ses modes de gestion. Ma thèse s'inscrit dans l'objectif finalisé d'apporter à l'agriculteur, de l'aide à la gestion de cette diversité végétale sur le territoire de son exploitation. Je me suis fixé 2 objectifs de recherche : i) vérifier si les interchamps et le stock semencier constituent des sources d'espèces pour le centre des parcelles agricoles et ii) quantifier l'influence de la dynamique de deux grands groupes de facteurs, représentée sous la forme de trajectoires de parcelles, sur la diversité végétale : les pratiques agricoles et les caractéristiques de la mosaïque paysagère.J'ai mené ce travail sur l'ensemble du parcellaire de l'Installation Expérimentale de l'Inra ASTER Mirecourt, dont les systèmes de production (polyculture-élevage bovin laitier) sont convertis à l'agriculture biologique depuis 2004. J'ai caractérisé la végétation - en place dans les interchamps et au centre des parcelles, et dans le stock semencier - des parcelles en prairies permanentes et en champs cultivés selon deux approches complémentaires : taxonomique au rang de l'espèce et fonctionnelle à partir de sept propriétés rendant compte de la dissémination, de l'établissement et de la survie des espèces végétales. J'ai caractérisé les trajectoires des parcelles, sur une durée de neuf ans, soit à partir des pratiques agricoles mises en œuvre chaque année, soit à partir des caractéristiques annuelles de la mosaïque paysagère. Cette mosaïque correspond aux différentes occupations du sol obtenues à partir de relevés de terrain ou d'enquêtes auprès des exploitants.Je montre que le stock semencier et les interchamps ne constituent pas des sources potentielles d'espèces végétales pour le centre des parcelles, champs cultivés ou prairies permanentes. En revanche, ce sont des refuges importants pour une grande partie des espèces prairiales. Au vu de mes résultats, je fais l'hypothèse que les interchamps sont des puits d'espèces adventices en champs cultivés. J'ai également mis en évidence que le gradient fonctionnel de la végétation prairiale entre la bordure et le centre s'étend jusqu'à 2 m seulement.Enfin, la diversité végétale des parcelles étudiées est principalement influencée par la trajectoire des parcelles selon les caractéristiques de la mosaïque paysagère et par les pratiques agricoles mises en œuvre durant l'année en cours. Les caractéristiques du sol ont un rôle très minoritaire. Ces trois groupes de facteurs expliquent à eux seuls plus des trois quarts de la variabilité de la composition fonctionnelle de la végétation.La gestion de la diversité végétale des parcelles agricoles d'une exploitation peut donc être menée en partie par l'agriculteur. Cependant, compte-tenu des effets de la trajectoire des parcelles selon les caractéristiques paysagères, il est nécessaire de mettre aussi en place une gestion collective de la végétation entre les différents acteurs partageant le territoireOne of the means to offset the decrease of pesticide use is to favour agro-ecological services of plant diversity. In this aim, farmer will have to adapt its farming management. My work partly answers to the following applied objective: to bring to the farmer some advices for the management of plant diversity on the farm territory. I have two scientific objectives: i) to verify if field boundaries and soil seed bank are potential sources of plant species for field centres; ii) to quantify the relative influence of dynamics of two factor groups, characterized as field paths, on plant diversity: farming practices and characteristics of landscape mosaïc.I have carried out this study on the experimental farm of INRA ASTER Mirecourt. Its farming systems (mixed crop-dairy systems) have been converted to organic farming since 2004. I have characterized vegetation - established vegetation in field boundaries and in field centres, and vegetation in the soil seed bank - of permanent grasslands and arable fields with complementary approaches: taxonomical approach based on the species, and functional approach based on seven functional properties about dispersal, establishment and persistence of plant species. I have characterized field paths, along nine years, either from farming practices set up on field, either from annual characteristics of landscape mosaïc. I have represented this landscape mosaïc as a mosaïc of distinct land-uses. All of them and their spatialization have been determined from farmer surveys or landscape observations.My results show that soil seed bank and field bboundaries are not potential sources of plant species for field centres, in both permanent grasslands and arable fields. On the other hand, they are efficient refuges for a large part of grassland species. According to my results, I hypothesize that field boudaries are species sinks in arable fields. I also highlight that functional gradient of grassland vegetation in the field edge, between field margins and field centres, is spread until 2 m only.Finally, plant diversity in studied fields is mainly influenced by field path according landscape mosaïc and by farming practices set up the same year of vegetation sampling. Soil characteristics have a minor influence. These three groups of influent factors explain more than 75 % of the functional composition variability of the vegetation in field centres.The management of plant diversity in agricultural fields of a given farm can be partly reach by the farmer. However, according to the effects of field paths about landscape mosaïc, it is necessary to set up a collective management of plant diversity with all actors sharing the studied territory
Streszczenia konferencji na temat "Inertial Gradient Methods"
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Xu, Ling. "Recursive parameter estimation methods based on gradient search for estimating system parameters of first-order inertial control systems". W 2021 40th Chinese Control Conference (CCC). IEEE, 2021. http://dx.doi.org/10.23919/ccc52363.2021.9549830.
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Ghose, K., i H. R. Shea. "A Micromachined Earth Sensor Based on Measuring the Gravity Gradient Torque". W ASME 2009 International Mechanical Engineering Congress and Exposition. ASMEDC, 2009. http://dx.doi.org/10.1115/imece2009-12762.
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We present the fabrication and testing of a novel MEMS inertial sensor that directly measures the gravity gradient in low Earth orbit in order to sense the relative orientation of a satellite with respect to the Earth. Instead of the current Earth sensing methods that determine the Earth vector by sensing the Earth’s IR emission, we present a much lighter and more compact MEMS-based approach that determine the Earth vector by measuring the Gravity Gradient Torque on an elongated silicon proof mass. Current Earth sensors require optical access on multiple faces of the satellite. This MEMS-based approach does not require optical access.
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Broc, Daniel, i Gianluca Artini. "Fluid Structure Interaction for Tubes Bundles: Different Homogenization Methods". W ASME 2017 Pressure Vessels and Piping Conference. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/pvp2017-65727.
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ASTRID is a project for an industrial prototype of a 600 MWe sodium cooled Fast Reactor, led by CEA. An important program is in progress for the development and the validation of numerical tools for the simulation of the dynamic mechanical behavior of the Fast Reactor cores, with both experimental and numerical parts. The cores are constituted of Fuel Assemblies (of FA) and Neutronic Shields (or NS) immersed in the primary coolant (sodium), which circulates inside the Fluid Assemblies. The FA and the NS are slender structures, which may be considered as beams, form a mechanical point of view. The dynamic behavior of this system has to be understood, for design and safety studies. Two main movements have to be considered: global horizontal movements under a seismic excitation, and opening of the core. The fluid leads to complex interactions between the structures in the whole core. The dynamic behavior of the core is also strongly influenced by contacts between the beams and by the sodium, which limit the relative displacements. Numerical methods and models are built to describe and simulate this dynamic behavior. The validation of the numerical tools is based on the results of different experimental programs, already performed or in progress. The paper is mainly devoted to the modeling of the Fluid Structure Interaction phenomena in the Fast Reactor cores. Tubes bundles immersed in a dense fluid are very common in the nuclear industry (reactor cores and steam generators). In the case of an external excitation (earthquake or shock) the presence of the fluid leads to “inertial effects” with lower natural frequencies, and “dissipative effects”, with higher damping. The geometry of a tubes bundle is complex, which may lead to very huge sizes for the numerical models. Many works have been made during the last decades to develop homogenization, in order to simplify the problem. Theoretical analyses are presented on different simplifications and assumptions which can be made in the homogenization approach. The accuracy of the different assumptions depends of the conditions of the system: fluid flow or fluid at rest, small or large displacements of the structure. In the general case, it is theoretically necessary to consider the Navier Stokes equations: the fluid flow is fully nonlinear. Models have been developed during the last years, based on the Euler linear equations, corresponding to a fluid at rest, with small displacements of the structure. Only the inertial effects are theoretically described but the dissipative effects may be taken into account by using a Rayleigh damping. Different theoretical analyses show that, even in the case of a nonlinear fluid flow, the linear potential flow models may be used as linear equivalent models. In the cases with an important head loss in the fluid flow through the tubes, the fluid movement is mainly driven by the important forces exchanged with the structure and by the pressure gradient. The global equations of the system are close to the equations used for porous media, like the Darcy equations. An important condition to get a relevant model is to describe globally the energy balance in the system. The energy given to the fluid by the solid correspond to a variation of kinetic energy in the fluid and to energy dissipation in the fluid. Attention will be paid to the cases where the tubes bundle is in interaction with free fluid, without tubes. The global equation of the system has to be accurate for the tubes bundle and for the free fluid also.
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Mononen, Teemu, Jouni Mattila i Antti Kolu. "Blade Control for Surface Profile Tracking by Heavy-Duty Bulldozers". W ASME/BATH 2021 Symposium on Fluid Power and Motion Control. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/fpmc2021-68656.
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Abstract The bulldozer is a heavy-duty earthmoving machine used in ground surface profiling and soil manipulation. Tracking the desired surface gradients with the hydraulically actuated manipulator while compensating for the mobile base motion is important in high-performance surface grading and traction control. In this paper, we present an approach for surface elevation tracking control for earthmoving work done by bulldozers using inertial measurement units (IMUs) and roof mounted global navigation satellite system (GNSS) antennas. We use mapping between the desired surface profile and hydraulic actuator velocities using the elevation surface and its gradient, the mobile manipulator Jacobian, and mobile base pose estimation by the extended Kalman filter (EKF) framework. With the proposed method, a relatively simple low-level actuator space control scheme can produce sufficient accuracy in varying elevation requirements besides leveling work. In an experimental setup, flat and uneven surface profiles were followed with average errors below 2 cm computed using kinematics. An external GNSS survey gave a coarse verification of the actual surface profile, showing average errors below 4 cm. This paper demonstrates a blade controller on a heavy-duty tracked vehicle with high manipulator inertia, hydraulic dynamics, and body vibrations. The experimental results validate the efficacy of the proposed method, also revealing the needs for further development.
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Sun, Yixiong, Wenhua Yang, Sheng Sun, Liang Zhang, Wenbin Zhao, Shuai Jin, Jin Lei i Jinkang Cheng. "The Influences of Key Factors on the Gas Diffusion in the Material Irradiation Test Based on the Regulation of Gas Composition". W 2024 31st International Conference on Nuclear Engineering. American Society of Mechanical Engineers, 2024. http://dx.doi.org/10.1115/icone31-135739.
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Abstract Material irradiation test requires to design device structure to ensure that the specimen temperature can meet requirements. Gas composition regulation is one of the main temperature control methods. Temperature gradient is established through the gas gap between the specimens and coolant, and the thermal conductivity of gap can be changed by regulating the gas composition, thereby controlling the specimen temperature. The study takes the annular gas gap of a typical material irradiation device as the research object, adopts computational fluid dynamics (CFD) method to simulate the gas diffusion process, and analyzes the influences of key factors such as type of gas inflated, gas inflation rate and volume on gas diffusion behavior during the process of gas composition regulation. Helium floats because of its lower density than the mixed gas, and argon sinks because of its higher density. For the same working conditions, argon will diffuse to a farther location under the action of greater inertial force. The higher the gas inflation rate, the wider the range of gas diffusion to the surroundings at the bottom of the device, the faster the diffusion rate in the gas gap, and the longer the diffusion distance. The volume of only affects the final diffusion state. The higher the gas inflation volume, the mole fraction of the corresponding gas will continue to increase.
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Chang, J., Bo Zhao, Fei Yu, R. Zhang i P. Wu. "A hybrid grading calibration method of FOG-IMU and its experimental verification". W 2017 DGON Inertial Sensors and Systems (ISS). IEEE, 2017. http://dx.doi.org/10.1109/inertialsensors.2017.8171498.
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Wasfy, Tamer M. "Modeling Continuum Multibody Systems Using the Finite Element Method and Element Convected Frames". W ASME 1994 Design Technical Conferences collocated with the ASME 1994 International Computers in Engineering Conference and Exhibition and the ASME 1994 8th Annual Database Symposium. American Society of Mechanical Engineers, 1994. http://dx.doi.org/10.1115/detc1994-0273.
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Abstract A new method for predicting the dynamic response of flexible multibody systems is developed. The method can account for large rigid-body motion and large deflections. The method is based on the Finite Element Method and the use of a new type of element convected frames. Continuum type elements are used to model the multibody system. The motion of the “nodes” is referred to a global inertial reference frame. D’Alembert principle is used to derive the system’s equations of motion, by invoking the equilibrium, at the nodes, of inertia forces, structural (internal) forces and externally applied forces. Structural forces on a node are calculated from the state of deformation of the elements surrounding that node. Each element has a convected frame which translates and rotates with it. This frame is used to extract the flexible deformation of the element from the total element motion. The orientation of a convected frame is found using the deformation gradient tensor and the Polar decomposition theorem. The equations of motion are solved along with constraint equations using a direct implicit iterative integration scheme. A numerical example is solved to demonstrate some of the features of the new method.
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Reeks, Michael W. "Comparison of Recent Model Equations for Particle Deposition in a Turbulent Boundary Layer With Those Based on the PDF Approach". W ASME/JSME 2003 4th Joint Fluids Summer Engineering Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/fedsm2003-45734.
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Comparisons are made between the Advection-Diffusion Equation (ADE) approach for particle transport and the two fluid model approach based on the PDF method. In principal the ADE approach offers a simpler way of calculating the inertial deposition of particles in a turbulent boundary layer than that based on the PDF approach. However the ADE equations that have recently been used are only strictly valid for a simple Gaussian process when particle inertia is small. Using a prescribed but in general non-Gaussian random particle velocity field, it is shown that the net particle mass flux contains an extra drift term to that from the mean velocity of the particle velocity field, associated with the compressibility of the velocity field. Furthermore the diffusive flux in general depends not only upon the gradient of the mean concentration (true only for a Gaussian random flow field) but also upon higher order derivatives whose relative contribution depends on diffusion coefficients Dijk... etc. These coefficients depend upon the statistical moments associated with random displacements and compressibility of the particle flow field along particle trajectories which in turn depend upon particle inertia. In contrast the PDF approach offers the advantage of using a simple gradient (Gaussian) approximation in particle phase space which can lead to a non-Gaussian spatial dispersion process when particle inertia is important. Conditions based on the particle mean free path are derived for which a simple ADE is appropriate. Some of the features of particle transport in an inhomogeneous turbulent flow are illustrated by examining particle dispersion in a random flow field composed of pairs of counter rotating vortices which has an rms velocity which increase linearly from a stagnation point.
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Hussain, Md Yahia, i Roger E. Khayat. "Effect of Wall Movement on a Jet Depositing on a Moving Wall at Moderate Reynolds Number". W ASME 2010 3rd Joint US-European Fluids Engineering Summer Meeting collocated with 8th International Conference on Nanochannels, Microchannels, and Minichannels. ASMEDC, 2010. http://dx.doi.org/10.1115/fedsm-icnmm2010-30731.
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The steady flow of a moderately inertial jet depositing on a moving wall, is examined theoretically near channel exit. The free surface jet emerges from a channel and adheres to a wall, which may move in the same or opposite direction to the acting channel pressure gradient. The problem is solved using the method of matched asymptotic expansions. The small parameter involved in the expansions is the inverse Reynolds number. The flow field is obtained as a composite expansion by matching the flow in the boundary layer regions near the free surface, with the flow in the core region. The influence of inertia and wall velocity on the shape of the free surface, the velocity and stress is emphasized. It is found that the viscous relaxation length is essentially uninfluenced by the velocity of a forward moving wall. In contrast, it diminishes rapidly with the velocity of a backward moving wall.
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Ahmed, Moinuddin, i Roger E. Khayat. "Flow of a Thin Viscoelastic Jet". W ASME 2010 3rd Joint US-European Fluids Engineering Summer Meeting collocated with 8th International Conference on Nanochannels, Microchannels, and Minichannels. ASMEDC, 2010. http://dx.doi.org/10.1115/fedsm-icnmm2010-30505.
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The influence of elasticity and inertia for steady flow of a thin viscoelastic fluid jet is examined theoretically. The fluid is assumed to emerge from a vertical channel and driven by a pressure gradient and/or gravity. The boundary-layer equations are generalized for a viscoelastic thin film obeying the Oldroyd-b constitutive model. Special emphasis is placed on the initial stages of jet development. The formulation and simulation are carried out for two-dimensional jet flow in order to better understand the intricate wave and flow structures for a viscoelastic jet. In contrast to the commonly used depth-averaging solution method, the strong nonlinearities are preserved in the present formulation as the viscoelastic boundary-layer equations are solved by expanding the flow field in terms of orthonormal shape functions. It is found that for a steady viscoelastic jet, a reduction in inertia or a rise in elasticity leads to the emergence of surface waviness and excessive normal stress, which leads to the formation of sharp gradients in the velocity and shear stress. These gradients can be sufficiently substantial to cause a discontinuity or shock in the flow. During transition, the surface profiles adhere earlier to the shape of the final steady state instead of a traveling wave, the transition between the two states takes the form of a standing wave, which grows essentially in amplitude only.