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Добірка наукової літератури з теми "Locally homogenous spaces"

Автор: Grafiati

Опубліковано: 10 березня 2023

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Статті в журналах з теми "Locally homogenous spaces"

Rejali, Ali, and Navid Sabzali. "On the homological and algebraical properties of some Feichtinger algebras." Mathematica Slovaca 71, no. 5 (October 1, 2021): 1211–28. http://dx.doi.org/10.1515/ms-2021-0049.

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Abstract Let G be a locally compact group (not necessarily abelian) and B be a homogeneous Banach space on G, which is in a good situation with respect to a homogeneous function algebra on G. Feichtinger showed that there exists a minimal Banach space B min in the family of all homogenous Banach spaces C on G, containing all elements of B with compact support. In this paper, the amenability and super amenability of B min with respect to the convolution product or with respect to the pointwise product are showed to correspond to amenability, discreteness or finiteness of the group G and conversely. We also prove among other things that B min is a symmetric Segal subalgebra of L 1(G) on an IN-group G, under certain conditions, and we apply our results to study pseudo-amenability and some other homological properties of B min on IN-groups. Furthermore, we determine necessary and sufficient conditions on A under which A min $\mathcal{A}_{\min}$ with the pointwise product is an abstract Segal algebra or Segal algebra in A, whenever A is a homogeneous function algebra with an approximate identity. We apply these results to study amenability of some Feichtinger algebras with respect to the pointwise product.

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Seidel, Hans Peter. "Locally homogeneous ANR-spaces." Archiv der Mathematik 44, no. 1 (January 1985): 79–81. http://dx.doi.org/10.1007/bf01193784.

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Ancel, Fredric D., and David P. Bellamy. "On homogeneous locally conical spaces." Fundamenta Mathematicae 241, no. 1 (2018): 1–15. http://dx.doi.org/10.4064/fm282-4-2017.

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Deng, Shaoqiang, and Joseph A. Wolf. "Locally Symmetric Homogeneous Finsler Spaces." International Mathematics Research Notices 2013, no. 18 (July 24, 2012): 4223–42. http://dx.doi.org/10.1093/imrn/rns179.

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Rodionov, E. D., V. V. Slavskiĭ, and L. N. Chibrikova. "Locally conformally homogeneous pseudo-Riemannian spaces." Siberian Advances in Mathematics 17, no. 3 (September 2007): 186–212. http://dx.doi.org/10.3103/s1055134407030030.

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Nedela, Roman. "Covering spaces of locally homogeneous graphs." Discrete Mathematics 121, no. 1-3 (October 1993): 177–88. http://dx.doi.org/10.1016/0012-365x(93)90550-d.

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Fox, Jeffrey, and Peter Haskell. "Index theory on locally homogeneous spaces." K-Theory 4, no. 6 (November 1990): 547–68. http://dx.doi.org/10.1007/bf00538884.

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Berestovskiǐ, V. N., Denise M. Halverson, and Dušan Repovš. "Locally G-homogeneous Busemann G-spaces." Differential Geometry and its Applications 29, no. 3 (June 2011): 299–318. http://dx.doi.org/10.1016/j.difgeo.2011.03.001.

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Andruchow, Esteban, and Lázaro Recht. "Larotonda spaces: Homogeneous spaces and conditional expectations." International Journal of Mathematics 27, no. 02 (February 2016): 1650002. http://dx.doi.org/10.1142/s0129167x16500026.

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We define a Larotonda space as a quotient space [Formula: see text] of the unitary groups of [Formula: see text]-algebras [Formula: see text] with a faithful unital conditional expectation [Formula: see text] In particular, [Formula: see text] is complemented in [Formula: see text], a fact which implies that [Formula: see text] has [Formula: see text] differentiable structure, with the topology induced by the norm of [Formula: see text]. The conditional expectation also allows one to define a reductive structure (in particular, a linear connection) and a [Formula: see text]-invariant Finsler metric in [Formula: see text]. Given a point [Formula: see text] and a tangent vector [Formula: see text], we consider the problem of whether the geodesic [Formula: see text] of the linear connection satisfying these initial data is (locally) minimal for the metric. We find a sufficient condition. Several examples are given, of locally minimal geodesics.

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Дисертації з теми "Locally homogenous spaces"

Arias, Marco Teresa. "Study of homogeneous DÀtri spaces, of the Jacobi operator on g.o. spaces and the locally homogeneous connections on 2-dimensional manifolds with the help of Mathematica." Doctoral thesis, Universitat de València, 2007. http://hdl.handle.net/10803/9954.

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Nowadays, the concept of homogeneity is one of the fundamental notions in geometry although its meaning must be always specified for the concrete situations. In this thesis, we consider the homogeneity of Riemannian manifolds and the homogeneity of manifolds equipped with affine connections. The first kind of homogeneity means that, for every smooth Riemannian manifold (M, g), its group of isometries I(M) is acting transitively on M. Part I of this thesis fits into this philosophy. Afterwards in Part II, we treat the homogeneity concept of affine connections. This homogeneity means that, for every two points of a manifold, there is an affine diffeomorphism which sends one point into another. In particular, we consider a local version of the homogeneity, that is, we accept that the affine diffeomorphisms are given only locally, i.e., from a neighborhood onto a neighborhood. More specifically, we devote the first Chapter of Part I to make a brief overview of some special kinds of homogeneous Riemannian manifolds which will be of special relevance in Part I and to show how the software MATHEMATICA© becomes useful. For that, we prove that "the three-parameter families of flag manifolds constructed by N. R. Wallach in "Compact homogeneous Riemannian manifols with strictly positive curvature, Ann. of Math. 96 (1972), p. 276-293" are D'Atri spaces if and only if they are naturally reductive spaces. Thus, we improve the previous results given by D'Atri, Nickerson and by Arias-Marco, Naveira.Moreover, in Chapter 2 we obtain the complete 4-dimensional classification of homogeneous spaces of type A. This allows us to prove correctly that every 4-dimensional homogeneous D'Atri space is naturally reductive. Therefore, we correct, complete and improve the results presented by Podestà, Spiro, Bueken and Vanhecke. Chapter 3 is devoted to prove that the curvature operator has constant osculating rank over g.o. spaces. It is mean that a real number 'r' exists such that under some assumptions, the higher order derivatives of the curvature operator from 1 to r are linear independent and from 1 to r + 1 are linear dependent. As a consequence, we also present a method valid on every g.o. space to solve the Jacobi equation. This method extends the method given by Naveira and Tarrío for naturally reductive spaces. In particular, we prove that the Jacobi operator on Kaplan's example (the first known g.o. space that it is not naturally reductive) has constant osculating rank 4. Moreover, we solve the Jacobi equation along a geodesic on Kaplan's example using the new method and the well-known method used by Chavel, Ziller and Berndt,Tricerri, Vanhecke. Therefore, we are able to present the main differences between both methods.In Part II, we classify (locally) all locally homogeneous affine connections with arbitrary torsion on two-dimensional manifolds. Therefore, we generalize the result given by Opozda for torsion-less case. Moreover, from our computations we obtain interesting consequences as the relation between the classifications given for the torsion less-case by Kowalski, Opozda and Vlá ek. In addition, we obtain interesting consequences about flat connections with torsion.In general, the study of these problems sometimes requires a big number of straightforward symbolic computations. In such cases, it is a quite difficult task and a lot of time consuming, try to make correctly this kind of computations by hand. Thus, we try to organize our computations in (possibly) most systematic way so that the whole procedure is not excessively long. Also, because these topics are an ideal subject for a computer-aided research, we are using the software MATHEMATICA©, throughout this work. But we put stress on the full transparency of this procedure.
En esta tesis, se consideran dos tipos bien diferenciados de homogeneidad: la de las variedades riemannianas y la de las variedades afines. El primer tipo de homogeneidad se define como aquel que tiene la propiedad de que el grupo de isometrías actúa transitivamente sobre la variedad. La Parte I, recoge todos los resultados que hemos obtenido en esta dirección. Sin embargo, en la Parte II se presentan los resultados obtenidos sobre conexiones afines homogéneas. Una conexión afín se dice homogénea si para cada par de puntos de la variedad existe un difeomorfismo afín que envía un punto en otro. En este caso, se considera una versión local de homogeneidad. Más específicamente, la Parte I de esta tesis está dedicada a probar que "las familias 3-paramétricas de variedades bandera construidas por Wallach son espacios de D'Atri si y sólo si son espacios naturalmente reductivos". Más aún, en el segundo Capítulo, se obtiene la clasificación completa de los espacios homogéneos de tipo A cuatro dimensionales que permite probar correctamente que todo espacio de D'Atri homogéneo de dimensión cuatro es naturalmente reductivo.Finalmente, en el tercer Capítulo se prueba que en cualquier g.o. espacio el operador curvatura tiene rango osculador constante y, como consecuencia, se presenta un método para resolver la ecuación de Jacobi sobre cualquier g.o. espacio. La Parte II se destina a clasificar (localmente) todas las conexiones afines localmente homogéneas con torsión arbitraria sobre variedades 2-dimensionales. Para finalizar el cuarto Capítulo, se prueban algunos resultados interesantes sobre conexiones llanas con torsión.En general, el estudio de estos problemas requiere a veces, un gran número de cálculos simbólicos aunque sencillos. En dichas ocasiones, realizarlos correctamente a mano es una tarea ardua que requiere mucho tiempo. Por ello, se intenta organizar todos estos cálculos de la manera más sistemática posible de forma que el procedimiento no resulte excesivamente largo. Este tipo de investigación es ideal para utilizar la ayuda del ordenador; así, cuando resulta conveniente, utilizamos la ayuda del software MATHEMATICA para desarrollar con total transparencia el método de resolución que más se adecua a cada uno de los problemas a resolver.

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Sommaro, Silvia. "Groups of principal homogeneous spaces for some Hopf orders arising from formal groups." Thesis, University of Exeter, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368366.

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Salazar, Malpartida Johan Renzo. "Geodesic deviation equation in locally de Sitter spacetimes." Universidade Estadual Paulista (UNESP), 2018. http://hdl.handle.net/11449/157153.

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Submitted by Johan Renzo Salazar Malpartida (johanrenzosm@gmail.com) on 2018-09-24T18:20:35Z No. of bitstreams: 1 0-Thesis.pdf: 349725 bytes, checksum: a61b999c76db9b574769428cae02bc08 (MD5)
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Como é bem conhecido, a relatividade especial de Einstein, cuja cinemática é governada pelo grupo de Poincaré, deixa de valer na escala de Planck devido à existência de uma escala de comprimento invariante, dada pelo comprimento de Planck. Por essa razão, ela é incapaz de descrever a cinemática naquela escala. Uma solução possível para esse problema, a qual preserva a simetria de Lorentz — e consequentemente a causalidade — é substituir a relatividade especial de Einstein por uma relatividade especial na qual a cinemática é governada pelo grupo de de Sitter. Claro que uma mudança na relatividade especial irá pruduzir mudanças concomitantes na relatividade geral, a qual se torna o que chamamos de relatividade geral modificada por de Sitter. Trabalhando no contexto dessa teoria, o objetivo desse trabalho é deduzir a fórmula geral da aceleração relativa entre duas geodésicas próximas, a qual leva à equação do desvio geodésico modificada por de Sitter. Uma análise simples dos efeitos adicionais induzidos pela cinemática local de de Sitter é apresentada.
As is well-known, the Poincaré invariant Einstein special relativity breaks down at the Planck scale due to the presence of an invariant length, given by the Planck length. For this reason, it is unable to describe the spacetime kinematics at that scale. A possible solution to this problem that preserves Lorentz symmetry — and consequently causality — is arguably to replace the Poincaré invariant Einstein special relativity by a de Sitter invariant special relativity. Of course, a change in special relativity produces concomitant changes in general relativity, which becomes what we have called de Sitter modified general relativity. By working in the context of this theory, the purpose of this work is to deduce the general relative acceleration between nearby geodesics, which leads to the de Sitter modified geodesic deviation equation. A simple analysis of the additional effects induced by the local de Sitter kinematics is presented.
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Routin, Eddy. "Local Tb theorems and Hardy type inequalities." Phd thesis, Université Paris Sud - Paris XI, 2011. http://tel.archives-ouvertes.fr/tel-00656023.

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In this thesis, we study local Tb theorems for singular integral operators in the setting of spaces of homogeneous type. We give a direct proof of the local Tb theorem with L^2 integrability on the pseudo- accretive system. Our argument relies on the Beylkin-Coifman-Rokhlin algorithm applied in adapted Haar wavelet basis and some stopping time results. Motivated by questions of S. Hofmann, we extend it to the case when the integrability conditions are lower than 2, with an additional weak boundedness type hypothesis, which incorporates some Hardy type inequalities. We study the possibility of relaxing the support conditions on the pseudo-accretive system to a slight enlargement of the dyadic cubes. We also give a result in the case when, for practical reasons, hypotheses on the pseudo-accretive system are made on balls rather than dyadic cubes. Finally we study the particular case of perfect dyadic operators for which the proof gets much simpler. Our argument gives us the opportunity to study Hardy type inequalities. The latter are well known in the Euclidean setting, but seem to have been overlooked in spaces of homogeneous type. We prove that they hold without restriction in the dyadic setting. In the more general case of a ball B and its corona 2B\B, they can be obtained from some geometric conditions relative to the distribution of points in the homogeneous space. For example, we prove that some relative layer decay property suffices. We also prove that this property is implied by the monotone geodesic property of Tessera. Finally, we give some explicit examples and counterexamples in the complex plane to illustrate the relationship between the geometry of the homogeneous space and the validity of the Hardy type inequalities.

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Liang, Yongqi. "Principe local-global pour les zéro-cycles." Phd thesis, Université Paris Sud - Paris XI, 2011. http://tel.archives-ouvertes.fr/tel-00630560.

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Dans cette thèse, nous nous intéressons à l'étude de l'arithmétique (le principe de Hasse, l'approximation faible, et l'obstruction de Brauer-Manin) des zéro-cycles sur les variétés algébriques définies sur des corps de nombres. Nous introduisons la notion de sous-ensemble hilbertien généralisé. En utilisant la méthode de fibration, nous démontrons que l'obstruction de Brauer-Manin est la seule au principe de Hasse et à l'approximation faible pour les zéro-cycles de degré 1; et établissons l'exactitude d'une suite de type global-local concernant les groupes de Chow des zéro-cycles, pour certaines variétés qui admettent une structure de fibration au-dessus d'une courbe lisse ou au-dessus de l'espace projectif, où les hypothèses arithmétiques sont posées seulement sur les fibres au-dessus d'un sous-ensemble hilbertien généralisé.De plus, nous relions l'arithmétique des points rationnels et l'arithmétique des zérocycles de degré 1 sur les variétés géométriquement rationnellement connexes. Comme application, nous trouvons que l'obstruction de Brauer-Manin est la seule au principe de Hasse et à l'approximation faible pour les zéro-cycles de degré 1 sur- les espaces homogènes d'un groupe algébrique linéaire à stabilisateur connexe,- certains fibrés en surfaces de Châtelet au-dessus d'une courbe lisse ou au-dessus de l'espace projectif (en particulier, les solides de Poonen).

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Pediconi, Francesco. "Geometric aspects of locally homogeneous Riemannian spaces." Doctoral thesis, 2020. http://hdl.handle.net/2158/1197175.

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The subject of this thesis is the study of some geometric problems arising in the context of locally and globally homogeneous Riemannian spaces. In particular, we are mainly interested in investigate the interplay between curvature conditions and the compactness of some classes of locally homogeneous spaces, with respect to appropriate topologies.

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Книги з теми "Locally homogenous spaces"

1938-, Griffiths Phillip, and Kerr Matthew D. 1975-, eds. Hodge theory, complex geometry, and representation theory. Providence, Rhode Island: Published for the Conference Board of the Mathematical Sciences by the American Mathematical Society, 2013.

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From Frenet to Cartan: The Method of Moving Frames. American Mathematical Society, 2017.

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Частини книг з теми "Locally homogenous spaces"

Hamrouni, Hatem, and Firas Sadki. "Self-Chabauty-isolated Locally Compact Groups." In Geometric and Harmonic Analysis on Homogeneous Spaces, 57–70. Cham: Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-26562-5_2.

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Hasegawa, Keizo, and Yoshinobu Kamishima. "Locally Conformally Kähler Structures on Homogeneous Spaces." In Geometry and Analysis on Manifolds, 353–72. Cham: Springer International Publishing, 2015. http://dx.doi.org/10.1007/978-3-319-11523-8_13.

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Katsuda, Atsushi. "A pinching problem for locally homogeneous spaces." In Curvature and Topology of Riemannian Manifolds, 150–55. Berlin, Heidelberg: Springer Berlin Heidelberg, 1986. http://dx.doi.org/10.1007/bfb0075652.

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Guivarc’h, Yves, and C. R. E. Raja. "Polynomial Growth, Recurrence and Ergodicity for Random Walks on Locally Compact Groups and Homogeneous Spaces." In Random Walks, Boundaries and Spectra, 65–74. Basel: Springer Basel, 2011. http://dx.doi.org/10.1007/978-3-0346-0244-0_4.

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"Locally homogeneous spaces." In Ergodic Theory, Groups, and Geometry, 53–59. Providence, Rhode Island: American Mathematical Society, 2008. http://dx.doi.org/10.1090/cbms/109/08.

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Riihentaus, Juhani. "Quasinearly subharmonic functions in locally uniformly homogeneous spaces." In Subharmonic Functions, Generalizations, Holomorphic Functions, Meromorphic Functions, and Properties, 119–30. BENTHAM SCIENCE PUBLISHERS, 2021. http://dx.doi.org/10.2174/9789811498701121010013.

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"Contributions to the spectral geometry of locally homogeneous spaces." In Space – Time – Matter, 69–89. De Gruyter, 2018. http://dx.doi.org/10.1515/9783110452150-003.

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"The Geodesic Flow of Riemannian Locally Symmetric Spaces." In Ergodic Theory and Topological Dynamics of Group Actions on Homogeneous Spaces, 36–79. Cambridge University Press, 2000. http://dx.doi.org/10.1017/cbo9780511758898.003.

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Koyagi, Mikiya. "Traveling Citizens." In Iran in Motion, 163–89. Stanford University Press, 2021. http://dx.doi.org/10.11126/stanford/9781503613133.003.0008.

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In chapter 7, themes of space, practice, and subjectivity fully converge. Railway passengers continued to shape new subjectivities as they made mundane bodily motions within the railway space while moving across provincial, national, and transnational spaces. Rather than creating a homogeneous, Europeanized experience of railway journeys as desired by advocates of the New Civilization, encounters in the railway space produced differentiated traveling publics who identified with local, national, and transnational communities simultaneously. Thus, the Trans-Iranian Railway not only integrated the nation but also fostered new connectivities that transcended the nation.

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Zinn-Justin, Jean. "Generalized non-linear σ-models in two dimensions." In Quantum Field Theory and Critical Phenomena, 692–720. Oxford University Press, 2021. http://dx.doi.org/10.1093/oso/9780198834625.003.0029.

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This chapter describes the formal properties, and discusses the renormalization, of quantum field theories (QFT) based on homogeneous spaces: coset spaces of the form G/H, where G is a compact Lie group and H a Lie subgroup. In physics, they appear naturally in the case of spontaneous symmetry breaking, and describe the interaction between Goldstone modes. Homogeneous spaces are associated with non-linear realizations of group representations. There exist natural ways to embed these manifolds in flat Euclidean spaces, spaces in which the symmetry group acts linearly. As in the example of the non-linear σ-model, this embedding is first used, because the renormalization properties are simpler, and the physical interpretation of the more direct correlation functions. Then, in a generic parametrization, the renormalization problem is solved by the introduction of a Becchi–Rouet–Stora–Tyutin (BRST)-like symmetry with anticommuting (Grassmann) parameters, which also plays an essential role in quantized gauge theories. The more specific properties of models corresponding to a special class of homogeneous spaces, symmetric spaces (like the non-linear σ-model), are studied. These models are characterized by the uniqueness of the metric and thus, of the classical action. In two dimensions, from the classical field equations an infinite number of non-local conservation laws can be derived. The field and the unique coupling renormalization group (RG) functions are calculated at one-loop order, in two dimensions, and shown to imply asymptotic freedom.

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Тези доповідей конференцій з теми "Locally homogenous spaces"

Buryachenko, Valeriy A. "Generalized Method of Effective Field in Linear Peridynamic Micromechanics of Random Structure Composites." In ASME 2020 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/imece2020-24574.

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Abstract A statistically homogeneous random matrix medium with the bond-based peridynamic properties of constituents is considered. For the media subjected to remote homogeneous volumetric boundary loading, one proved that the effective behavior of this media is governing by conventional effective constitutive equation which is the same as for the local elasticity theory. The average is performed over the surface of the extended inclusion phase rather than over an entire space. Any spatial derivatives of displacement fields are not required. The basic hypotheses of locally elastic micromechanics are generalized to their peri-static counterparts. In particular, in the generalized method of effective field proposed, the effective field is evaluated from self-consistent estimations by the use of closing of a corresponding integral equation in the framework of the quasi-crystalline approximation. In so doing, the classical effective field hypothesis is relaxed, and the hypothesis of the ellipsoidal symmetry of the random structure of CMs is not used. One demonstrates some similarity and difference with respect to other methods (the dilute approximation and Mori-Tanaka approach) proposed before in peridynamic micromechanics of CMs. Comparative numerical analyses of these methods are performed for 1D case.

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Rastgoftar, Hossein, and Suhada Jayasuriya. "Evolution of Multi Agent Systems Under a New Communication Topology." In ASME 2014 Dynamic Systems and Control Conference. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/dscc2014-6140.

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In this paper, a multi agent system (MAS) is considered as particles of a continuum deforming under a specific class of homeomorphic mappings, called a homogenous transformation. We have recently showed how a desired homogenous mapping of the MAS in a n–D space can be prescribed by transient positions of n + 1 leaders placed at the vertices of a n–D polytope, called leading polytope [1–9]. In this article, we first minimize the acceleration norm with (i) initial and final positions of the leaders known and (ii) leaders (located at the vertices of the leading polytope) are constrained to move in such a way that the initial volume of the leading polytope is preserved during evolution. The followers learn the leader-determined homogenous map through local communication with each follower modeled as a double integrator. Proposed is a communication topology that requires every follower agent to update its position based on communication with n + 1 local agents. The weights of communication are uniquely specified by the initial positions of the agents. Simulation of a MAS moving in a plane validates the proposed communication topology.

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Endo, Masaya, Takahiro Tsukahara, and Yasuo Kawaguchi. "Relationship Between Diffusing-Material Lumps and Organized Structures in Turbulent Flow." In ASME/JSME/KSME 2015 Joint Fluids Engineering Conference. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/ajkfluids2015-24432.

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When a material spreads in the turbulent flow, its instantaneous concentration distribution becomes not homogenous in space, and areas with high concentration containing sudden change of the concentration are formed by the local intense turbulence. In this study, we extracted such localized high-concentration areas by a conditional sampling technique, and observed the behavior of the areas. In order to realize the scalar diffusion in quasi homogeneous isotropic turbulent flow, a model experiment was performed in a water channel flow. Fluorescent dye was introduced from a nozzle located at the center of the channel, and the concentration images of the dye were obtained at several downstream positions by PLIF measurement. To extract areas of high concentration containing a sudden change of the concentration, three types of analysis techniques including the conditional sampling technique were applied to PLIF images. By the conditional sampling technique, we can extract areas of high concentration, which cannot be identified by the other two kind methods, and the effectiveness of this technique was proved. It was found that the areas extracted by the conditional sampling technique appear as lumps. The spanwise numerical probability distribution of the lumps roughly follows the Gaussian distribution, and the peak of the distribution decreases while its standard variation increases as streamwise distance increases. This result implies that performing extraction of areas with high concentration appropriately would enable to realize the material diffusing process as a Lagrange particle and provide a prediction method about the material diffusion source and the damage of the pollutant.

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Schlu¨ter, Michael, So¨ren Scheid, and Norbert Ra¨biger. "Local Bubble Dynamics in Two-Phase Flows." In ASME 2002 Joint U.S.-European Fluids Engineering Division Conference. ASMEDC, 2002. http://dx.doi.org/10.1115/fedsm2002-31240.

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For the development of environmentally sustainable processes e.g. in chemical engineering or biotechnology detailed knowledge of hydrodynamics and mass transfer is essential. A calculation of the exact design layout of reactors and processes required for multiphase flows has been impossible to achieve because of the complex transient coupling between the continuous and dispersed phases. Due to the lack of exact models to describe local and transient phenomena the calculation of hydrodynamics and mass transfer is over-simplified by using time- and space-averaged data, thus neglecting important facts. Recently developed measurement techniques allow the investigation of these local effects in multiphase flows and indicate that e.g. the behavior and slip velocity of fluid particles in a particle swarm differ from the behavior of single particles and depend on particle hold-up and flow conditions of the continuous phase. Measurements in two-phase flows in co-current and counter-current flow have shown that generally used models for homogeneous flow are dissatisfying.

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Giuffrida, Giada, and Rosa Caponetto. "A look on the intrinsic sustainability of Aeolian vernacular architecture." In HERITAGE2022 International Conference on Vernacular Heritage: Culture, People and Sustainability. Valencia: Universitat Politècnica de València, 2022. http://dx.doi.org/10.4995/heritage2022.2022.15190.

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The vernacular architecture of the Aeolian Islands can be seen as the result of a stratification of empirical knowledge, linked to socio-economic, cultural, and environmental needs of local communities. This homogeneous and specific heritage is characterised by a constructive code which is the direct expression of the necessities dictated by the geo-morphological context, the environmental conditions and the availability of local resources. These constraints have strongly influenced the local “modus aedificandi”, characterised by an intrinsic sustainability. In particular, adaptation to local orography and climate, and to main wind directions, has promoted the adoption of several bioclimatic strategies (as the use of massive walls and roofs, cross ventilation and shading systems provided by verandas/porches) and of resources reuse (like rainwater collection). The smart use of traditional and locally available natural building materials for the realisation of the main constructive elements is another manifestation of this heritage sustainability. But the arrival of "modernity" (closely linked to industrialisation) has often compromised these aspects, neglecting the concept of continuous maintenance, choosing new, synthetic and (quite often) not compatible materials for recovery interventions, repurposing spaces and substituting and/or altering original uses. This contribution highlights the sustainability of Aeolian architecture and the traditional technical solutions used in this peculiar archipelago composed by volcanic islands. It also reports some "bad practices" introduced in the 60s and 70s to refurbish traditional buildings. Finally,a programmatic and more conscious approach to the recovery of Aeolian architecture, by the use of more compatible and sustainable interventions, is proposed. This choice is fundamental to respect the memory of vernacular heritage in general and, in particular, of Aeolian one, included in the UNESCO World Heritage Site list since 2000.

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Qin, Jian-Rong, S. T. John Yu, and Ming-Chia Lai. "Simulation of Transient Cavitating Water-Hammer Pipe Flow." In ASME 1999 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1999. http://dx.doi.org/10.1115/imece1999-1234.

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Abstract Direct calculations of the transient cavitating water-hammer pipe flows using the Space-Time Conservation Element and Solution Element method, or the CE/SE method for short, is reported. The principles of the CE/SE method is treating space and time as one entity, and the calculation of flow properties is based on the local and global space-time flux conservation. As a contrast to the modern upwind schemes, no Riemann solver is used, thus the logic of the present scheme for cavitating flows is much simpler. Two numerical examples are reported in this paper: (1) a hydraulic shock problem, and (2) a cavitating pipe flow. For the hydraulic shock problem, we demonstrate the capability of the CE/SE method for capturing contact discontinuities in cavitating fluids. For the pipe flows, a two-phase homogeneous equilibrium cavitation model is employed. In both cases, numerical results compared favorably with the experimental data and analytical solution.

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Coppo Leite, Victor, and Elia Merzari. "The Effect of Varying Viscosity in Turbulent Channel Flow." In ASME 2020 Fluids Engineering Division Summer Meeting collocated with the ASME 2020 Heat Transfer Summer Conference and the ASME 2020 18th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/fedsm2020-20228.

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Abstract In this article we examine channel flow subject to spatially varying viscosity in the streamwise direction. The Reynolds number is imposed locally with three different ramps. The setup is reminiscent of transient channel flow, but with a space-dependent viscosity rather than a time dependent viscosity. It is also relevant to various applications in nuclear engineering and in particular in test reactors, where the viscosity changes significantly in the streamwise direction, and there is a severe lack of Direct Numerical Simulation (DNS) data to benchmark turbulence models in these conditions. As part of this work we set up a novel benchmark case: the channel is extended in the stream-wise direction up to 20π. The viscosity is kept constant in the first 4π region. This inlet region is used as a cyclic region to obtain a fully developed flow profile at the beginning of the ramping region. In the ramping region the Reynolds number is linearly increased along the channel. The flow is homogenous in the spanwise direction, while it is non-homogenous in the stream-wise and wall-normal direction. We perform here Direct Numerical Simulation (DNS) with Nek5000, a spectral-element computational fluid dynamics (CFD) code developed at Argonne National Laboratory. In this study, specific focus is given to the investigation of turbulence properties and structures in the near-wall region along the flow direction. Turbulent statistics are collected and investigated. Similarly to transient channel flow, the results show that a variation in the Reynolds across a channel does not cause an immediate change in the size of turbulent structures in the ramp region and a delay is in fact observed in both wall shear and friction Reynolds number. The results from the present study are compared with a correlation available in the literature for the friction velocity and as a function of the Reynolds number.

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Russell, P. St J., and T. A. Birks. "A Hamiltonian Approach to Propagation in Chirped and Non-Uniform Bragg Grating Structures." In Photosensitivity and Quadratic Nonlinearity in Glass Waveguides. Washington, D.C.: Optica Publishing Group, 1995. http://dx.doi.org/10.1364/pqn.1995.pmd.2.

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One current and evolving use of fibre gratings is for chirped grating dispersion compensation[1]. Another is in the formation of effective λ/4 lasing cavities for DFB fibre lasers by imposing a slow local perturbation on the grating parameters[2], In both cases the essential analytical problem is the same: How to treat the behaviour of light in spatially heterogeneous Bragg gratings? In this paper an approach is developed based on the Hamiltonian optics elegantly summarised by a number of authors, including notably Arnaud in his 1976 book Beam and Fibre Optics[3]. The Hamiltonian approach can be applied where the dispersion relation in the homogeneous structure is known, and where, in the heterogeneous real structure, parameters like average index vary slowly in space. It is essentially an analytical method for stepping through a non-uniform structure, matching phase velocities normal to the gradient of the heterogeneity at each step, and propagating along the local group velocity to the next point.

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Yan, Chaoxing, Changqi Yan, Licheng Sun, and Yang Wang. "Experimental Study on Resistance Characteristics in a 3 × 3 Rod Bundle." In 2014 22nd International Conference on Nuclear Engineering. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/icone22-30295.

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Experimental study on resistance of air-water two-phase flow in a vertical 3 × 3 rod bundle was carried out under normal temperature and pressure. The rod diameter and pitch were 8 mm and 11 mm, respectively. The ranges of gas and liquid superficial velocity were 0.013∼3.763 m/s and 0.076∼1.792 m/s, respectively. The result indicated that the existing correlations for calculating frictional coefficient in the rod bundle and local resistance coefficient could not give favorable predictions on the single-phase experimental data. For the case of two-phase flow, eight correlations for calculating two-phase equivalent viscosity poorly predicted the frictional pressure drop, with the mean absolute errors around 60%. Meanwhile, the eight classical two-phase viscosity formulae were evaluated against the local pressure drop at spacer grid. It is shown that Dukler model predicted the experimental data well in the range of Rel<9000 while McAdams correlation was the best for Rel⩾9000. For all the experimental data, Dukler model provided the best prediction with MRE of 29.03%. Furthermore, approaches to calculate two-phase frictional pressure drop and local resistance were proposed by considering mass quality, two-phase Reynolds number and densities in homogenous flow model, resulting in a good agreement with the experimental data.

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Wang, Di, and Xuewu Cao. "Preliminary Analysis of Hydrogen Distribution During Severe Accident Induced by Loss of Coolant Accident." In 2017 25th International Conference on Nuclear Engineering. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/icone25-66497.

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During hypothetical severe accidents in nuclear power plants, a large amount of hydrogen is generated rapidly as a result of Zirconium-Steam reaction and released into the containment. Hydrogen mixes with air and may come into combustion or detonation under proper conditions, which threatens the integrity of containment. Therefore, getting detailed hydrogen flow and distribution in various physical mechanisms is a key issue to resolve the hydrogen risk in containment and compartments. To study local hydrogen distribution in the containment of advanced passive PWR, an analysis model is built by 3-dimensional CFD code. Computational domain is divided by structured grid which contains over 100,000 cells. the shape and surface area of walls and obstacles of steel shell and internal structure, which have great impact on gas flow and heat transfer, are included. Hydrogen distribution in containment simulating with different turbulence models is studied, the result shows that during large amount of hydrogen release stage. In hydrogen distribution result simulating with algebraic model, hydrogen is all gathered in the dome and the peak concentration reaches 17%. When k-ε model is adopted, the peak concentration in the dome is 8%, hydrogen stratification is established in whole large space. Besides, hydrogen distribution near source also shows algebraic model cannot simulate turbulence diffusion in local compartment. It is more reasonable choosing k-ε model to study hydrogen behavior in containment. Based on adopted k-ε model, the effect of steam on hydrogen distribution is investigated. With steam injection, the hydrogen distribution is more homogeneous in upper space and average concentration is lower. In local compartment, due to diffusion enhanced by steam, the hydrogen concentration is higher in the bottom.

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