Thematische Bibliographien / Symmetric random walk

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Auswahl der wissenschaftlichen Literatur zum Thema „Symmetric random walk“

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Veröffentlicht am 15. Dezember 2023

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Zeitschriftenartikel zum Thema "Symmetric random walk"

LI, KEQIN. „PERFORMANCE ANALYSIS AND EVALUATION OF RANDOM WALK ALGORITHMS ON WIRELESS NETWORKS“. International Journal of Foundations of Computer Science 23, Nr. 04 (Juni 2012): 779–802. http://dx.doi.org/10.1142/s0129054112400369.

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We propose a model of dynamically evolving random networks and give an analytical result of the cover time of the simple random walk algorithm on a dynamic random symmetric planar point graph. Our dynamic network model considers random node distribution and random node mobility. We analyze the cover time of the parallel random walk algorithm on a complete network and show by numerical data that k parallel random walks reduce the cover time by almost a factor of k. We present simulation results for four random walk algorithms on random asymmetric planar point graphs. These algorithms include the simple random walk algorithm, the intelligent random walk algorithm, the parallel random walk algorithm, and the parallel intelligent random walk algorithm. Our random network model considers random node distribution and random battery transmission power. Performance measures include normalized cover time, probability distribution of the length of random walks, and load distribution.

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Zygmunt, Marcin J. „Non symmetric random walk on infinite graph“. Opuscula Mathematica 31, Nr. 4 (2011): 669. http://dx.doi.org/10.7494/opmath.2011.31.4.669.

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Godrèche, Claude, und Jean-Marc Luck. „Survival probability of random walks and Lévy flights with stochastic resetting“. Journal of Statistical Mechanics: Theory and Experiment 2022, Nr. 7 (01.07.2022): 073201. http://dx.doi.org/10.1088/1742-5468/ac7a2a.

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Abstract We perform a thorough analysis of the survival probability of symmetric random walks with stochastic resetting, defined as the probability for the walker not to cross the origin up to time n. For continuous symmetric distributions of step lengths with either finite (random walks) or infinite variance (Lévy flights), this probability can be expressed in terms of the survival probability of the walk without resetting, given by Sparre Andersen theory. It is therefore universal, i.e. independent of the step length distribution. We analyze this survival probability at depth, deriving both exact results at finite times and asymptotic late-time results. We also investigate the case where the step length distribution is symmetric but not continuous, focusing our attention onto arithmetic distributions generating random walks on the lattice of integers. We investigate in detail the example of the simple Polya walk and propose an algebraic approach for lattice walks with a larger range.

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YANG, ZHIHUI. „LARGE DEVIATION ASYMPTOTICS FOR RANDOM-WALK TYPE PERTURBATIONS“. Stochastics and Dynamics 07, Nr. 01 (März 2007): 75–89. http://dx.doi.org/10.1142/s0219493707001950.

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Symmetric random walks can be arranged to converge to a Wiener process in the area of normal deviation. However, random walks and Wiener processes have, in general, different asymptotics of the large deviation probabilities. The action functionals for random-walks and Wiener processes are compared in this paper. The correction term is calculated. Exit problem and stochastic resonance for random-walk-type perturbation are also considered and compared with the white-noise-type perturbation.

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Telcs, András, und Nicholas C. Wormald. „Branching and tree indexed random walks on fractals“. Journal of Applied Probability 36, Nr. 4 (Dezember 1999): 999–1011. http://dx.doi.org/10.1239/jap/1032374750.

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This paper deals with the recurrence of branching random walks on polynomially growing graphs. Amongst other things, we demonstrate the strong recurrence of tree indexed random walks determined by the resistance properties of spherically symmetric graphs. Several branching walk models are considered to show how the branching mechanism influences the recurrence behaviour.

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Telcs, András, und Nicholas C. Wormald. „Branching and tree indexed random walks on fractals“. Journal of Applied Probability 36, Nr. 04 (Dezember 1999): 999–1011. http://dx.doi.org/10.1017/s0021900200017812.

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Hilário, Marcelo R., Daniel Kious und Augusto Teixeira. „Random Walk on the Simple Symmetric Exclusion Process“. Communications in Mathematical Physics 379, Nr. 1 (26.08.2020): 61–101. http://dx.doi.org/10.1007/s00220-020-03833-x.

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Abstract We investigate the long-term behavior of a random walker evolving on top of the simple symmetric exclusion process (SSEP) at equilibrium, in dimension one. At each jump, the random walker is subject to a drift that depends on whether it is sitting on top of a particle or a hole, so that its asymptotic behavior is expected to depend on the density $$\rho \in [0, 1]$$ ρ ∈ [ 0 , 1 ] of the underlying SSEP. Our first result is a law of large numbers (LLN) for the random walker for all densities $$\rho $$ ρ except for at most two values $$\rho _-, \rho _+ \in [0, 1]$$ ρ - , ρ + ∈ [ 0 , 1 ] . The asymptotic speed we obtain in our LLN is a monotone function of $$\rho $$ ρ . Also, $$\rho _-$$ ρ - and $$\rho _+$$ ρ + are characterized as the two points at which the speed may jump to (or from) zero. Furthermore, for all the values of densities where the random walk experiences a non-zero speed, we can prove that it satisfies a functional central limit theorem (CLT). For the special case in which the density is 1/2 and the jump distribution on an empty site and on an occupied site are symmetric to each other, we prove a LLN with zero limiting speed. We also prove similar LLN and CLT results for a different environment, given by a family of independent simple symmetric random walks in equilibrium.

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Fujita, Takahiko. „A random walk analogue of Lévy’s Theorem“. Studia Scientiarum Mathematicarum Hungarica 45, Nr. 2 (01.06.2008): 223–33. http://dx.doi.org/10.1556/sscmath.45.2008.2.50.

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In this paper we will give a simple symmetric random walk analogue of Lévy’s Theorem. We will give a new definition of a local time of the simple symmetric random walk. We apply a discrete Itô formula to some absolute value like function to obtain a discrete Tanaka formula. Results in this paper rely upon a discrete Skorokhod reflection argument. This random walk analogue of Lévy’s theorem was already obtained by G. Simons ([14]) but it is still worth noting because we will use a discrete stochastic analysis to obtain it and this method is applicable to other research. We note some connection with previous results by Csáki, Révész, Csörgő and Szabados. Finally we observe that the discrete Lévy transformation in the present version is not ergodic. Lastly we give a Lévy-type theorem for simple nonsymmetric random walk using a discrete bang-bang process.

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ISHIMURA, N., und N. YOSHIDA. „ON THE CONVERGENCE OF DISCRETE PROCESSES WITH MULTIPLE INDEPENDENT VARIABLES“. ANZIAM Journal 58, Nr. 3-4 (06.03.2017): 379–85. http://dx.doi.org/10.1017/s1446181116000389.

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We discuss discrete stochastic processes with two independent variables: one is the standard symmetric random walk, and the other is the Poisson process. Convergence of discrete stochastic processes is analysed, such that the symmetric random walk tends to the standard Brownian motion. We show that a discrete analogue of Ito’s formula converges to the corresponding continuous formula.

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Fang, Xiao, Han L. Gan, Susan Holmes, Haiyan Huang, Erol Peköz, Adrian Röllin und Wenpin Tang. „Arcsine laws for random walks generated from random permutations with applications to genomics“. Journal of Applied Probability 58, Nr. 4 (22.11.2021): 851–67. http://dx.doi.org/10.1017/jpr.2021.14.

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AbstractA classical result for the simple symmetric random walk with 2n steps is that the number of steps above the origin, the time of the last visit to the origin, and the time of the maximum height all have exactly the same distribution and converge when scaled to the arcsine law. Motivated by applications in genomics, we study the distributions of these statistics for the non-Markovian random walk generated from the ascents and descents of a uniform random permutation and a Mallows(q) permutation and show that they have the same asymptotic distributions as for the simple random walk. We also give an unexpected conjecture, along with numerical evidence and a partial proof in special cases, for the result that the number of steps above the origin by step 2n for the uniform permutation generated walk has exactly the same discrete arcsine distribution as for the simple random walk, even though the other statistics for these walks have very different laws. We also give explicit error bounds to the limit theorems using Stein’s method for the arcsine distribution, as well as functional central limit theorems and a strong embedding of the Mallows(q) permutation which is of independent interest.

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Dissertationen zum Thema "Symmetric random walk"

Jamshidpey, Arash. „Population Dynamics in Random Environment, Random Walks on Symmetric Group, and Phylogeny Reconstruction“. Thesis, Université d'Ottawa / University of Ottawa, 2016. http://hdl.handle.net/10393/34623.

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This thesis concerns applications of some probabilistic tools to phylogeny reconstruction and population genetics. Modelling the evolution of species by continuous-time random walks on the signed permutation groups, we study the asymptotic medians of a set of random permutations sampled from simple random walks at time 0.25cn, for c> 0. Running k independent random walks all starting at identity, we prove that the medians approximate the ancestor (identity permutation) up to time 0.25n, while there exists a constant c>1 after which the medians loose credibility as an estimator. We study the median of a set of random permutations on the symmetric group endowed with different metrics. In particular, for a special metric of dissimilarity, called breakpoint, where the space is not geodesic, we find a large group of medians of random permutations using the concept of partial geodesics (or geodesic patches). Also, we study the Fleming-Viot process in random environment (FVRE) via martingale and duality methods. We develop the duality method to the case of time-dependent and quenched martingale problems. Using a family of dual processes we prove the convergence of the Moran processes in random environments to FVRE in Skorokhod topology. We also study the long-time behaviour of FVRE and prove the existence of equilibrium for the joint annealed-environment process and prove an ergodic theorem for the latter.

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SOUZA, RODRIGO MARINHO DE. „MIXING TIMES FOR RANDOM WALKS ON THE SYMMETRIC GROUP“. PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2017. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=33139@1.

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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
PROGRAMA DE EXCELENCIA ACADEMICA
O objetivo desta dissertação é apresentar algumas técnicas e ferramentas para a obtenção de cotas superiores e inferiores para tempos de mistura de cadeias de Markov. Para que isso se torne mais interessante, apresentaremos estes conceitos através de cadeias de Markov que atuam sobre o grupo simétrico, que podem ser vistas como embaralhamentos de cartas. Ademais, usaremos um destes embaralhamentos como toy model para o processo de exclusão simples simétrico, o que nos ajudará a determinar os tempos de mistura do embaralhamento e do famoso sistema de partículas.
The aim of this dissertation is to introduce some techniques and tools to obtain upper and lower bounds for Markov chains mixing times. To make it more interesting, we introduce these concepts through Markov chains that act on the symmetric group, which can be seen as card shuffles. Furthermore, we use one of these shuffles as a toy model for the symmetric simple exclusion process, which helps us to determine mixing times for the shuffle and for the famous particle system.

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Klyachko, Alexander A., und klyachko@fen bilkent edu tr. „Random Walks on Symmetric Spaces and Inequalities for Matrix Spectra“. ESI preprints, 2000. ftp://ftp.esi.ac.at/pub/Preprints/esi900.ps.

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Frączyk, Mikołaj. „Benjamini-Schramm convergence of locally symmetric spaces“. Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS233/document.

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Le sujet principal de ce mémoire est le comportement asymptotique de la géométrie et topologie des variétés localement symétriques Gamma\ X quand le volume tend vers l’infini. Notre premier résultat porte sur la convergence Benjamini-Schramm des 2 ou 3-variétés hyperboliques arithmétiques. Une suite d'espaces localement symétriques (Gamma_n\ X) converge Benjamini-Schramm vers l'espace symétrique X si pour chaque R>0 la limite de \Vol((\Gamma\X)_{
The main theme of this work is the study of geometry and topology of locally symmetric spaces Gamma\ X as ther volume Vol(\Gamma\ X) tends to infinity. Our first main result concerns the Benjamini-Schramm convergence for arithmetic hyperbolic 2 or 3-manifolds. A sequence of locally symmetric spaces (Gamma_n\ X) converges Benjamini-Schramm to X if and only if for every radius R>0 the limit Vol((Gamma\ X)_{

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Zarka, Benjamin. „La propriété de décroissance rapide hybride pour les groupes discrets“. Electronic Thesis or Diss., Université Côte d'Azur, 2023. http://www.theses.fr/2023COAZ4057.

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Un groupe finiment engendré G a la propriété RD lorsque l'algèbre de Sobolev du groupe H^s(G) s'injecte dans la C^*-algèbre réduite C^*_r(G). Cette inclusion permet de contrôler la norme de l'opérateur de convolution sur l^2(G) par des normes l^2 pondérées, et induit des isomorphismes en K-théorie. Il est connu que la présence de sous-groupes moyennables à croissance sur-polynomiale est une obstruction à cette propriété. Parallèlement à cela, on dispose toujours d'une inclusion canonique de l^1(G) dans C^*_r(G), mais cette estimation est en général moins fine que celle donnée par RD, et l'existence d'isomorphismes de K-théorie découlant de cette inclusion est un problème généralement ouvert qui est souvent issu de la combinaison des conjectures de Bost et Baum-Connes. C'est pourquoi, dans cette thèse, nous présenterons une version relative de la propriété RD appelée propriété RD_H basée sur une interpolation entre les normes l^1 et l^2 paramétrée par un sous-groupe H de G. Nous verrons que cette propriété peut être vue comme une généralisation aux cas des sous-groupes non distingués du fait que le quotient G/H ait la propriété RD. Nous étudierons certaines propriétés géométriques liées à l'espace G/H permettant de déduire ou d'infirmer la propriété RD_H. En particulier, nous nous pencherons sur le cas où H est un sous-groupe co-moyennable de G et le cas où G est un groupe relativement hyperbolique par rapport au sous-groupe H. Nous montrerons que la propriété RD_H nous permet d'obtenir une famille d'isomorphismes en K-théorie paramétrée par le choix du sous-groupe H, et d'obtenir une borne inférieure concernant la probabilité de retour dans le sous-groupe H d'une marche aléatoire symétrique. Une autre partie de la thèse est consacrée à l'existence d'un isomorphisme entre les groupes de K-théorie des algèbres l^1(G) et C^*_r(G) où l'on prouve la véracité de ce résultat pour certains produits semi-directs en combinant deux types de suites exactes sans faire intervenir les conjectures de Bost et Baum-Connes
A finitely generated group G has the property RD when the Sobolev space H^s(G) embeds in the group reduced C^*-algebra C^*_r(G). This embedding induces isomorphisms in K-theory, and allows to upper-bound the operator norm of the convolution on l^2(G) by weighted l^2 norms. It is known that if G contains an amenable subgroup with superpolynomial growth, then G cannot have property RD. In another hand, we always have the canonical inclusion of l^1(G) in C^*_r(G), but this estimation is generally less optimal than the estimation given by the property RD, and in most of cases, it needs to combine Bost and Baum-Connes conjectures to know if that inclusion induces K-theory isomorphisms. That's the reason why, in this thesis, we define a relative version of property RD by using an interpolation norm between l^1 and l^2 which depends on a subgroup H of G, and we call that property: property RD_H. We will see that property RD_H can be seen as an analogue for non-normal subgroups to the fact that G/H has property RD, and we will study what kind of geometric properties on G/H can imply or deny the property RD_H. In particular, we care about the case where H is a co-amenable subgroup of G, and the case where G is relatively hyperbolic with respect to H. We will show that property RD_H induces isomorphisms in K-theory, and gives us a lower bound concerning the return probability in the subgroup H for a symmetric random walk. Another part of the thesis is devoted to show that if G is a certain kind of semi-direct product, the inclusion l^1(G)subset C^*_r(G) induces isomorphisms in K-theory, we prove this statement by using two types of exact sequences without using Bost and Baum-Connes conjectures

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Gioev, Dimitri. „Generalizations of Szego Limit Theorem : Higher Order Terms and Discontinuous Symbols“. Doctoral thesis, KTH, Mathematics, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3123.

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Lin, Li-Chen, und 林涖晨. „Symmetric Covering in a Simple Random Walk“. Thesis, 2013. http://ndltd.ncl.edu.tw/handle/43638124361429621617.

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碩士
國立彰化師範大學
數學系所
101
Let Sn be the position of a simple random walk (starting at 0) at time n, and let Ln = min 0in Si, Rn = max 0in Si. The range of the walk at time n is then the interval [Ln;Rn]. Dene N to be the stopping time when the range of the walk becomes a symmetric interval of the form [

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Huang, Ming-Cheng, und 黃明正. „On The Study Of 2-Dimensional Symmetric Random Walk And Its Applications“. Thesis, 2001. http://ndltd.ncl.edu.tw/handle/02873174228987968869.

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碩士
國立中正大學
數學研究所
89
Abstract In this paper, I want to introduce a new method to solve 2-dimensional random walk Markov chains. The new method is called left-right alternative Markov chains whose state space is rearranged to a two-dimensional array. For a process moves to one of lateral direction and a vertical direction alternatively, we rearrange the state space to a lattice block. Then by using left-right alternative Markov chain model, we may solve this process to use less memory space and few numbers of multiplications than a tradition model does. Keywords: Two-Dimensional Random Walk Markov Chains, Markov chains, Stationary Distribution, Limiting Probability, Left-Right Alternative Markov Chains, Traffic Lights.

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Buchteile zum Thema "Symmetric random walk"

Schinazi, Rinaldo B. „The Simple Symmetric Random Walk“. In Classical and Spatial Stochastic Processes, 47–65. New York, NY: Springer New York, 2014. http://dx.doi.org/10.1007/978-1-4939-1869-0_3.

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Gorenflo, Rudolf, und Francesco Mainardi. „Random walk models approximating symmetric space-fractional diffusion processes“. In Problems and Methods in Mathematical Physics, 120–45. Basel: Birkhäuser Basel, 2001. http://dx.doi.org/10.1007/978-3-0348-8276-7_10.

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Pinsky, Ross G. „The Arcsine Laws for the One-Dimensional Simple Symmetric Random Walk“. In Universitext, 35–48. Cham: Springer International Publishing, 2014. http://dx.doi.org/10.1007/978-3-319-07965-3_4.

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Lanchier, Nicolas. „Symmetric simple random walks“. In Stochastic Modeling, 129–39. Cham: Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-50038-6_8.

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Guivarc’h, Yves, Lizhen Ji und J. C. Taylor. „Random Walks and Ground State Properties“. In Compactification of Symmetric Spaces, 213–30. Boston, MA: Birkhäuser Boston, 1998. http://dx.doi.org/10.1007/978-1-4612-2452-5_14.

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Guivarc’h, Yves, Lizhen Ji und J. C. Taylor. „Harnack Inequality, Martin’s Method and The Positive Spectrum for Random Walks“. In Compactification of Symmetric Spaces, 165–85. Boston, MA: Birkhäuser Boston, 1998. http://dx.doi.org/10.1007/978-1-4612-2452-5_11.

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Chen, Zhen-Qing, Takashi Kumagai, Laurent Saloff-Coste, Jian Wang und Tianyi Zheng. „Symmetric Lévy Processes on Nilpotent Groups“. In Limit Theorems for Some Long Range Random Walks on Torsion Free Nilpotent Groups, 71–92. Cham: Springer Nature Switzerland, 2023. http://dx.doi.org/10.1007/978-3-031-43332-0_7.

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Laurent, Clément, Alejandro F. Ramírez, Christophe Sabot und Santiago Saglietti. „Velocity Estimates for Symmetric Random Walks at Low Ballistic Disorder“. In Springer Proceedings in Mathematics & Statistics, 274–325. Singapore: Springer Singapore, 2019. http://dx.doi.org/10.1007/978-981-15-0302-3_11.

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Yarovaya, Elena. „Critical and Subcritical Branching Symmetric Random Walks on d-Dimensional Lattices“. In Advances in Data Analysis, 157–68. Boston: Birkhäuser Boston, 2009. http://dx.doi.org/10.1007/978-0-8176-4799-5_15.

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Frisch, Uriel, und Hélène Frisch. „Universality of escape from a half-space for symmetrical random walks“. In Lévy Flights and Related Topics in Physics, 262–68. Berlin, Heidelberg: Springer Berlin Heidelberg, 1995. http://dx.doi.org/10.1007/3-540-59222-9_39.

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Konferenzberichte zum Thema "Symmetric random walk"

Zhao, Zimeng. „Limiting process of symmetric simple random walk“. In International Conference on Statistics, Applied Mathematics, and Computing Science (CSAMCS 2021), herausgegeben von Ke Chen, Nan Lin, Romeo Meštrović, Teresa A. Oliveira, Fengjie Cen und Hong-Ming Yin. SPIE, 2022. http://dx.doi.org/10.1117/12.2628023.

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Chu, Steven. „A random walk in science“. In ART AND SYMMETRY IN EXPERIMENTAL PHYSICS. AIP, 2001. http://dx.doi.org/10.1063/1.1426791.

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MIAO, WEIWEN, YULIA R. GEL und JOSEPH L. GASTWIRTH. „A NEW TEST OF SYMMETRY ABOUT AN UNKNOWN MEDIAN“. In Random Walk, Sequential Analysis and Related Topics - A Festschrift in Honor of Yuan-Shih Chow. WORLD SCIENTIFIC, 2006. http://dx.doi.org/10.1142/9789812772558_0013.

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Yasuda, Kazunori, und Noriyasu Mori. „Fiber Orientation and Concentration Distribution in a Concentrated Suspension Flow Through a Complex Geometry“. In ASME/JSME 2003 4th Joint Fluids Summer Engineering Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/fedsm2003-45778.

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Distributions of fiber orientation and fiber concentration in slit flows of concentrated suspensions were measured. Slit channels were used in the experiments: a channel with an abrupt expansion and a crank geometry with six L-shaped corners. Such channels are usually used in a polymer processing. For visualization of fibers, an index-of-refraction matching method was employed, and tracer fibers having birefringence were suspended to observe between crossed polarizers. When fibers flow through an abrupt expansion, they rapidly orient in the direction perpendicular to the flow direction near the centerline. The fiber orientation, however, returns to the flow direction in the downstream region. In the L-shaped corner, fibers randomly orient because of the decelerating flow. In the downstream region of the L-shaped corner, fiber orientation is not symmetric with respect to the centerline. This seems to result from fiber-fiber interactions in the concentrated suspension. The fiber concentration is uniform over a width of a channel except adjacent to the side wall in the concentrated suspension, while it has a maximum apart from the side wall in the dilute suspension.

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Lawandy, N. M. „Mechanism for efficient second harmonic generation in Ge- and P-doped optical fibers“. In OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1988. http://dx.doi.org/10.1364/oam.1988.fs4.

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The discovery by Osterberg and Margulis of efficient (>5%) conversion of 1.06-μm light to the second harmonic (0.532 μm) in a P2O5:GeO2:SiO2 glass fiber has resulted in an interesting yet unexplained physical effect. We believe that the defect responsible for this effect is a clathrate structure or interstitial trapping of a GeO molecule. The maximum doping of ~10% mol of GeO2 into the SiO2 network may result in extra GeO molecules, which are interstitially trapped during preform fabrication. The GeO molecule has an inter-nuclear separation of 1.786 and 1.650 Å in its ground (A1∑+)and excited (X1∑+) states, respectively. GeO is rotationally frozen in its A1∑+ state, while multiphoton optical excitation of the X1∑+ state (~2600 Å) by three photons (2ω + ω + ω) at 1.06 μm allows the GeO guest molecule to reorient itself. The threshold for preparation is believed to be due to the onset of a parametric instability in vibrational Raman scattering (~1 GW/ cm2). The symmetry of the diffusional reorientation process of the GeO molecule is broken by its dependence on the 2ω field strength, which is in turn coupled to the local ensemble orientations of the GeO molecules. This process results in an asymmetric angular random walk, which preferentially self-organizes the fiber to maximize its doubling efficiency. Phosphorous oxygen hole centers are two-photon pumped at 1.06 μm and emit photons between 2 and 2.5 eV helping to initiate the reorientation.

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Arora, Prince, Prashant Parmeshwar Atkale, Badri Prasad Patel und Suhail Ahmad. „Response Analysis of Composite Blades of Offshore VAWT Using CFD and FSI for the Indian Ocean“. In ASME 2023 42nd International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2023. http://dx.doi.org/10.1115/omae2023-104820.

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Abstract Conventional HAWTs dominate the wind industry commercially, whereas VAWTs are receiving researchers’ interest now across the globe due to their inherent advantages over HAWTs. VAWTs are more suitable for the offshore environment due to their omnidirectionality and lower center of gravity. The centrifugal forces play a dominant role in the bending of the vertical axis wind turbine blades in addition to aerodynamic forces. Thus, there is a scope for the optimization of VAWT blades’ wall thickness and material such that the contributions of aerodynamic and centrifugal forces in the bending of blades are equalized. Further, the probabilistic nature of the wind causes more complexities in the system. So far, many studies have been performed employing computational fluid dynamics and FSI approaches to analyze VAWTs. However, only a few publications give insight into its structural behaviour as a result of interaction with the random nature of the wind velocity. The present study is carried out in two steps. The first step involves the probabilistic analysis of the actual wind speed of 13 months (1 November 2017 to 30 November 2018) recorded using LIDAR in the Gulf of Khambhat, in the Indian Ocean. The probabilistic wind data is then used to estimate the wind-induced pressure on blades using the standard commercial CFD tool, ANSYS Fluent considering a three-bladed vertical axis wind turbine with a symmetrical NACA airfoil. The aerodynamic pressure is estimated based on the Reynolds-Averaged Navier Stokes (RANS) equations. The latter part of the study involves structural analysis of the hollow composite blades of VAWT due to the aerodynamic pressure estimated from the first part and centrifugal forces due to rotation. The risk of failure arises due to the exceedance of stresses/strains beyond a threshold. Each hollow blade is modeled with different layers of material and thickness to minimize the blade mass such that the stresses/deflections are within the allowable limits and blades do not exhibit dynamic instabilities such as flutter. The study will be useful for an improved and efficient design of the VAWT in an Indian offshore environment.

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Tsugawa, Takuji. „Search of High Efficiency Design by Another Specific Speed Design“. In ASME-JSME-KSME 2019 8th Joint Fluids Engineering Conference. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/ajkfluids2019-4645.

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Abstract Quite a lot of design parameters exist when the designer designs the best performance impeller and guidevane. Finally, it is necessary to decide the detail 3D shape of impeller and guidevane. The best flow conditions of the flow velocity and the flow angle at the impeller inlet and outlet are designed as first step before impeller detailed 3D shape is designed. The detailed 3D shape is not necessary in this study. The optimum meridian shape has been found, assuming that the total loss head is addition of the blade-to-blade diffusion loss head and the hub-tip axial-symmetrical annular surface friction loss head. That is, the meridian shape is mainly decided depending on the blade-to-blade flow condition on hub surface, mean surface and tip surface. Main design parameters that decide the meridian shape is built in the loss head equation by diffusion factor and all the design parameters relate closely respectively. The value of the design parameters can be set at random for loss head calculation in a usual optimization technique. But, the loss head in the combination of the limited value design parameters can be calculated in this method. Therefore, the great change of design parameter value is not permitted in this optimum process, and the increment of all the design parameters is set respectively and the optimization of the design parameter is advanced from an initial value of the design parameters changing the value of design parameters little by little. Therefore, there is a possibility that the best solution becomes a local best solution and the influence of an initial condition value cannot be removed. In this method, it is necessary for coming out from the local best solution that the value of all the design parameters changes from an initial value to a largely different value. The specific speed influences all the other design parameters. So, the specific speed is changed gradually in restriction optimum process. In FEDSM2014-21030, the impeller blade number was assumed to be a variable real number design parameter and the specific speed that was the specification as constant value become a variable design parameter equally to other design parameters. In AJK2015-09034, the impeller outlet diameter and impeller rotational speed were assumed to be a variable optimum design parameters. As a result, all the design parameters became variable. Optimization was executed from two different initial conditions to study the initial value dependency whether the obtained two optimum solution became the same. In FEDSM2016-7518, one initial value of the specific speed was assumed to be 916 and it was confirmed to obtain the solution from the specific speed 200 to the specific speed 3000 as the variable wide range design parameter by restriction. The design parameter of mixed flow angle of impeller inlet was not change at the beginning of calculation and changed rapidly in the latter half of the calculation. The cause of the mixed flow angle of impeller inlet value jump was uncertainty. In FEDSM2017-69024, the influence of the surface roughness of the axial-symmetrical hub and tip wall was examined. The impeller blade number, the guidevane blade number and mixed flow angle of impeller inlet were able to change by restriction, and the influence of the impeller blade number and the guidevane blade number was examined. The mixed flow angle of impeller inlet was assumed 0 degrees (axial-flow) to avoid the parameter value jump. In this paper, the specific speed design parameter become the restriction design parameter. The specific speed as restriction parameter has been changed from the lower bound value to the upper bound value to come out from a local best solution. The efficiency extended to the specific speed whole area is able to be improved by the influence of the another middle specific speed with the highest efficiency. It is found that the value of the change increment at the specific speed as restriction parameter is important very much executed by the several kind of specific speed increment. In order to improve the design parameters of traditional impeller and guidevane in the future, it is convenient that total head and flow rate are new optimum design parameters instead of impeller outlet diameter and impeller rotational speed. The impeller rotational speed can be calculated by specific speed and total head.

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