Bibliografie tematiche / Sample paths regularity

Letteratura scientifica selezionata sul tema "Sample paths regularity"

Autore: Grafiati

Pubblicato: 15 giugno 2024

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Articoli di riviste sul tema "Sample paths regularity":

Scheuerer, Michael. "Regularity of the sample paths of a general second order random field". Stochastic Processes and their Applications 120, n. 10 (settembre 2010): 1879–97. http://dx.doi.org/10.1016/j.spa.2010.05.009.

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Dalang, Robert C., e Marta Sanz-Solé. "Regularity of the sample paths of a class of second-order spde's". Journal of Functional Analysis 227, n. 2 (ottobre 2005): 304–37. http://dx.doi.org/10.1016/j.jfa.2004.11.015.

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STOEV, STILIAN, e MURAD S. TAQQU. "PATH PROPERTIES OF THE LINEAR MULTIFRACTIONAL STABLE MOTION". Fractals 13, n. 02 (giugno 2005): 157–78. http://dx.doi.org/10.1142/s0218348x05002775.

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Abstract (sommario):

The linear multifractional stable motion (LMSM) processes Y = {Y(t)}t∈ℝ is an α-stable (0 < α < 2) stochastic process, which exhibits local self-similarity, has heavy tails and can have skewed distributions. The process Y is obtained from the well-known class of linear fractional stable motion (LFSM) processes by replacing their self-similarity parameter H by a function of time H(t). We show that the paths of Y(t) are bounded on bounded intervals only if 1/α ≤ H(t) < 1, t ∈ ℝ. In particular, if 0 < α ≤ 1, then Y has everywhere discontinuous paths, with probability one. On the other hand, Y has a version with continuous paths if H(t) is sufficiently regular and 1/α < H(t), t ∈ ℝ. We study the Hölder regularity of the sample paths when these are continuous and establish almost sure bounds on the pointwise and uniform pointwise Hölder exponents of the (random) function Y(t,ω), t ∈ ℝ, in terms of the function H(t) and its corresponding Hölder exponents. The Gaussian multifractional Brownian motion (MBM) processes are LMSM processes when α = 2. We obtain some new results on the Hölder regularity of their paths.

SANZ-SOLÉ, MARTA, e IVÁN TORRECILLA. "A FRACTIONAL POISSON EQUATION: EXISTENCE, REGULARITY AND APPROXIMATIONS OF THE SOLUTION". Stochastics and Dynamics 09, n. 04 (dicembre 2009): 519–48. http://dx.doi.org/10.1142/s0219493709002762.

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We consider a stochastic boundary value elliptic problem on a bounded domain D ⊂ ℝk, driven by a fractional Brownian field with Hurst parameter H = (H1,…,Hk) ∈ [½, 1[k. First, we define the stochastic convolution derived from the Green kernel and prove some properties. Using monotonicity methods, we prove the existence and uniqueness of solution along with regularity of the sample paths. Finally, we propose a sequence of lattice approximations and prove its convergence to the solution of the SPDE at a given rate.

Slaoui, Meryem, e C. A. Tudor. "The linear stochastic heat equation with Hermite noise". Infinite Dimensional Analysis, Quantum Probability and Related Topics 22, n. 03 (settembre 2019): 1950022. http://dx.doi.org/10.1142/s021902571950022x.

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We analyze the solution to the linear stochastic heat equation driven by a multiparameter Hermite process of order [Formula: see text]. This solution is an element of the [Formula: see text]th Wiener chaos. We discuss various properties of the solution, such as the necessary and sufficient condition for its existence, self-similarity, [Formula: see text]-variation and regularity of its sample paths. We will also focus on the probability distribution of the solution, which is non-Gaussian when [Formula: see text].

RUIZ-MEDINA, M. D., J. M. ANGULO e V. V. ANH. "FRACTIONAL RANDOM FIELDS ON DOMAINS WITH FRACTAL BOUNDARY". Infinite Dimensional Analysis, Quantum Probability and Related Topics 07, n. 03 (settembre 2004): 395–417. http://dx.doi.org/10.1142/s0219025704001694.

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For random fields with fractional regularity order (respectively, fractional singularity order), an orthogonal decomposition of the associated reproducing kernel Hilbert space with respect to domains with fractal boundary is derived. The approach presented is based on the theory of generalized random fields on fractional Sobolev spaces. The orthogonal decomposition derived is equivalent to the weak-sense Markov condition, in the second-order moment sense, studied in Ref. 50, and based on the concept of splitting Hilbert spaces. A mean-square fractional order differential representation on bounded domains with fractal boundary is also obtained. In the Gaussian case, the random fields studied have fractal sample paths (see Ref. 1). Examples of fractional-order differential models in the class considered are provided.

DUNCAN, T. E., B. PASIK-DUNCAN e B. MASLOWSKI. "FRACTIONAL BROWNIAN MOTION AND STOCHASTIC EQUATIONS IN HILBERT SPACES". Stochastics and Dynamics 02, n. 02 (giugno 2002): 225–50. http://dx.doi.org/10.1142/s0219493702000340.

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In this paper, stochastic differential equations in a Hilbert space with a standard, cylindrical fractional Brownian motion with the Hurst parameter in the interval (1/2,1) are investigated. Existence and uniqueness of mild solutions, continuity of the sample paths and state space regularity of the solutions, and the existence of limiting measures are verified. The equivalence of the probability laws for the solution evaluated at different times and different initial conditions and the convergence of these probability laws to the limiting probability are verified. These results are applied to specific stochastic parabolic and hyperbolic differential equations. The solution of a specific parabolic equation with the fractional Brownian motion only in the boundary condition is shown to have many results that are analogues of the results for a fractional Brownian motion in the domain.

ENGELKE, SEBASTIAN, e JEANNETTE H. C. WOERNER. "A UNIFYING APPROACH TO FRACTIONAL LÉVY PROCESSES". Stochastics and Dynamics 13, n. 02 (4 marzo 2013): 1250017. http://dx.doi.org/10.1142/s0219493712500177.

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Starting from the moving average representation of fractional Brownian motion, there are two different approaches to constructing fractional Lévy processes in the literature. Applying L2-integration theory, one can keep the same moving average kernel and replace the driving Brownian motion by a pure jump Lévy process with finite second moments. Alternatively, in the framework of alpha-stable random measures, the Brownian motion is replaced by an alpha-stable Lévy process and the exponent in the kernel is reparametrized by H - 1/α. We now provide a unified approach taking kernels of the form [Formula: see text], where γ can be chosen according to the existing moments and the Blumenthal–Getoor index of the underlying Lévy process. These processes may exhibit both long and short range dependence. In addition we will examine further properties of the processes, e.g., regularity of the sample paths and the semimartingale property.

Wang, Yasen, Cheng Cheng, Hongwei Sun, Junyang Jin e Huazhen Fang. "Data augmentation-based statistical inference of diffusion processes". Chaos: An Interdisciplinary Journal of Nonlinear Science 33, n. 3 (marzo 2023): 033115. http://dx.doi.org/10.1063/5.0124763.

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The identification of diffusion processes is challenging for many real-world systems with sparsely sampled observation data. In this work, we propose a data augmentation-based sparse Bayesian learning method to identify a class of diffusion processes from sparsely sampled data. We impute latent unsampled diffusion paths between adjacent observations and construct a candidate model for the diffusion processes with the sparsity-inducing prior on model parameters. Given the augmented data and candidate model, we investigate the full joint posterior distribution of all the parameters and latent diffusion paths under a Bayesian learning framework. We then design a Markov chain Monte Carlo sampler with non-degenerate acceptance probability on system dimension to draw samples from the posterior distribution to estimate the parameters and latent diffusion paths. Particularly, the proposed method can handle sparse data that are regularly or irregularly sampled in time. Simulations on the well-known Langevin equation, homogeneous diffusion in a symmetric double-well potential, and stochastic Lotka–Volterra equation demonstrate the effectiveness and considerable accuracy of the proposed method.

Dieker, A. B., e Guido R. Lagos. "A dichotomy for sampling barrier-crossing events of random walks with regularly varying tails". Journal of Applied Probability 54, n. 4 (30 novembre 2017): 1213–32. http://dx.doi.org/10.1017/jpr.2017.60.

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AbstractWe study how to sample paths of a random walk up to the first time it crosses a fixed barrier, in the setting where the step sizes are independent and identically distributed with negative mean and have a regularly varying right tail. We introduce a desirable property for a change of measure to be suitable for exact simulation. We study whether the change of measure of Blanchet and Glynn (2008) satisfies this property and show that it does so if and only if the tail index α of the right tail lies in the interval (1, 3/2).

Più fonti

Tesi sul tema "Sample paths regularity":

Bouly, Florent. "Etude fine de processus multifractionnaires non classiques". Electronic Thesis or Diss., Université de Lille (2022-....), 2023. http://www.theses.fr/2023ULILB012.

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Les processus stochastiques multifractionnaires sont des généralisations naturelles desmouvements brownien et brownien fractionnaire. Leur caractéristique essentielle est que leurs propriétés locales peuvent être prescrites via un paramètre fonctionnel et peuvent donc changer significativement d'un point à un autre. Le mouvement brownien multifractionnaire et d'autres processus multifractionnaires classiques sont construitsen remplaçant le paramètre de Hurst constant d'un processus fractionnaire par unefonction qui dépend de la variable qui permet d'indexer le processus. Une importante idée nouvelle est que le paramètre fonctionnel (déterministe ou aléatoire) de tels processus peut être dépendant de la variable d'intégration associée à l'intégrale stochastique qui représente le processus; un tel processus est alors dit multifractionnaire non classique.Ces processus non classiques sont plus complexes à étudier et il n'est pas certain que les méthodes usuelles s'adaptent à ce nouveau contexte. Un objectif important de cette thèse est de réussir à déterminer les exposants de Hölder local et ponctuel de ces processus non classiques pour un événement universel qui ne dépend pas du point considéré. Un autre objectif est l'estimation statistique de leur paramètre de Hurst (qui est parfois aléatoire) à partir d'une trajectoire discrétisée. Enfin, la question de la simulation de tels processus non classiques est également étudiée
Multifractional processes are natural generalisations of Brownian motion and fractional Brownian motion. Their essential feature is that their local properties can be prescribed via a functional parameter and can therefore change significantly from one point to another. Multifractional Brownian motion and other classical multifractional processes are constructed by replacing the constant Hurst parameter of a fractional process by a function that depends on the variable which indexes the process. An important new idea is that the functional parameter (deterministic or random) of such processes can depend on the integration variable associated with the stochastic integral that represents the process; such a process is then said to be non-classical multifractional.These non-classical processes are more complex to study and it is not clear that the usual methods fit this new context. An important objective of this thesis is to determine the local and pointwise Hölder exponents of these non-classical processes for a universal event that does not depend on the location. Another objective is the statistical estimation of their Hurst parameter (which is sometimes random) from a discretized trajectory. Finally, the question of the simulation of such non-classical processes is also presented

Balança, Paul. "Régularité fine de processus stochastiques et analyse 2-microlocale". Phd thesis, Ecole Centrale Paris, 2014. http://tel.archives-ouvertes.fr/tel-00958290.

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Les travaux présentés dans cette thèse s'intéressent à la géométrie fractale de processus stochastiques à travers le prisme d'un outil appelé l'analyse 2-microlocale. Ce dernier est issu d'une autre branche des mathématiques, l'analyse fonctionnelle et l'étude des équations aux dérivées partielles, et s'est avéré être pertinent pour décrire la géométrie fine de fonctions déterministes ou de processus aléatoires, généralisant notamment les exposants de Hölder classiques. Nous envisageons ainsi dans ce manuscrit différentes classes de processus, traitant en premier lieu le cas des martingales continues et de l'intégrale stochastique d'Ito. La régularité 2-microlocale de ces derniers fait notamment apparaître un autre concept, la pseudo frontière 2-microlocale, étroitement lié à son aîné. Nous appliquons également ce formalisme d'étude à une classe de processus gaussiens : le mouvement brownien multifractionnaire. Nous caractérisons ainsi sa régularité 2-microlocale et hölderienne, et déterminons dans un deuxième temps la forme générale de la dimension fractale de ses trajectoires. Dans notre étude portant sur les processus de Lévy, nous combinons le formalisme 2-microlocale à l'analyse multifractale, permettant alors de mettre en évidence des comportements géométriques n'étant pas captés par les outils usuels. Nous obtenons également en corollaire le spectre multifractal des processus fractionnaires de Lévy. Enfin, dans une dernière partie, nous nous intéressons à la définition et aux propriétés de certains processus de Markov multiparamètres, pouvant être plus généralement indicés par des ensembles.

Capitoli di libri sul tema "Sample paths regularity":

Bhattacharya, Rabi, e Edward Waymire. "Regularity of Markov Process Sample Paths". In Continuous Parameter Markov Processes and Stochastic Differential Equations, 35–39. Cham: Springer International Publishing, 2023. http://dx.doi.org/10.1007/978-3-031-33296-8_3.

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Stroock, Daniel W., e S. R. Srinivasa Varadhan. "Markov Processes, Regularity of Their Sample Paths, and the Wiener Measure". In Multidimensional Diffusion Processes, 46–64. Berlin, Heidelberg: Springer Berlin Heidelberg, 1997. http://dx.doi.org/10.1007/3-540-28999-2_3.

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Bhattacharya, Rabi, e Edward C. Waymire. "The Kolmogorov–Chentsov Theorem and Sample Path Regularity". In Graduate Texts in Mathematics, 61–70. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-78939-8_6.

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Gao, Y., J. Xiang, Z. Yu, G. Han e H. Jing. "Influence of Carbon Nanotubes on the Fracture Surface Characteristics of Cementitious Composites Under the Brazilian Split Test". In Lecture Notes in Civil Engineering, 503–12. Singapore: Springer Nature Singapore, 2023. http://dx.doi.org/10.1007/978-981-99-3330-3_53.

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AbstractTo better analyze the reinforcing mechanisms of carbon nanotubes (CNTs) in cementitious composites, the micromorphological characteristics of the fracture surface of cement-based specimens under the Brazilian split test were investigated. The results demonstrated that the addition of CNTs promoted nucleation and pore filling effects that optimized the pore structure and inhibited the development of microcracks in the cement matrix during loading. Due to the ultra-high specific surface area and bridging effects of CNTs, the formation of hydration products was promoted, internal microcracks and micropores were effectively reduced, and the regularity and integrity of the samples also improved. Therefore, under tensile loading, CNT-reinforced cementitious composites absorbed more energy, resulting in more complex stress paths and rougher fracture surfaces.

"Regularity of sample paths of a stochastic process". In Translations of Mathematical Monographs, 73–128. Providence, Rhode Island: American Mathematical Society, 2000. http://dx.doi.org/10.1090/mmono/188/03.

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Jones, Brad A. "In Search of Common Happiness". In Resisting Independence, 70–103. Cornell University Press, 2021. http://dx.doi.org/10.7591/cornell/9781501754012.003.0004.

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This chapter investigates how, in the absence of a shared discourse of Loyalism, Britons in the Atlantic were confronted with a crisis of identity in the late 1760s and early 1770s. Britons were reared in a shared political culture that regularly framed political controversies as a struggle between popish tyranny and Protestant liberty. This was certainly true during celebrations of the repeal of the unpopular Stamp Act, which many perceived as detrimental to the political and economic well-being of their empire. But by 1773, the inhabitants of New York City, Glasgow, Kingston, and Halifax had begun to pursue different and often competing paths in the ongoing crisis, which demonstrated the tenuous nature of popular British loyalty in the latter half of the eighteenth century. In the absence of a common shared enemy, these same subjects reverted to far more local and conflicting understandings of Britishness, which were defined most crucially by events that directly concerned their communities.

Mallick, Rwitabrata. "Tea Rhizospheres and Their Functional Role in Tea Gardens". In Data Science for Agricultural Innovation and Productivity, 163–74. BENTHAM SCIENCE PUBLISHERS, 2024. http://dx.doi.org/10.2174/9789815196177124010011.

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Darjeeling tea (Camellia sinensis) is famous worldwide for its excellent aroma and taste, and out of that, the best quality tea is produced in the Kurseong hill area. A year-long analysis of soil samples collected from different sites was done by applying the plate-count method in terms of colony-forming units for determining the presence of microbial population within soils cultivating tea on a monthly basis. Coordination in specific microbes might also be responsible for the impact. Fungi, bacteria, and actinomycetes – these three groups of microbes were tested during the process. Results showed that the neo tea plant, rhizosphere and rhizosphere of several other perpetual plants of various ages, flourishing in age-old tea gardens, seemed to expedite the growth of microbes. At present, the tea rhizosphere has been tested thoroughly, specifically in relation to plant-microbe response. Counter to the common outcomes, rhizosphere and soil ratios were found to be regularly less than 1 in samples collected from age-old tea gardens, showing an overall -ve rhizosphere impact. The finding of the 'negative rhizosphere effect' in old tea bushes is a significant and novel nature of the tea rhizosphere. The -ve impact on the rhizosphere of aged tea bushes does not seem to be a regular phenomenon that is related to the aging of plants generally but might be distinctive particular to tea plants. Other important and associated features include colonization of tea, rhizosphere, soil pH, etc. Supremacy of a certain population of microbes, an affinity towards a section of general opponents constitutes a good instance of reciprocated selection in the natural environment. These discoveries have unlocked newer paths for extended research in the field of 'rhizosphere microbiology'. The present study is an attempt to evaluate the transforming features coupled with the microbial activity and diversity in the tea rhizosphere and significant implications in the tea industry.

Nabokov, Isabelle. "Last Rites For Commanding Relationships". In Religion Against the Self, 55–69. Oxford University PressNew York, NY, 2000. http://dx.doi.org/10.1093/oso/9780195113648.003.0005.

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Abstract On a full-moon night in the Tamil month of Mii.ci (February), Nagaji scheduled Laksmi’s “removal ” rite.1 The breeze during my motorscooter ride to his sanctuary east of Gingee was cool and dry. The path was utterly deserted; in the late hours when Nagaji conducted these rituals every one was fast asleep. Nor were these rituals casual spectacles; people without business there avoided them. Only some dogs barked at my silent passage through a succession of villages leading me to the ciimi’s grove. Laksmi and her father were standing motionless with several other visitors around a camp fire. That night two women (including Laksmi) and seven men had arrived together with clusters of immediate relatives. No one talked, but they stared wide-eyed at me, completely bewildered why I would record such an inauspicious even dangerous ritual. But Nagaji, who understood and even exploited my research for his own ends, explained that I was learning how he dealt with enemy sorcerers and their demons. His job was to stop spells, mine was to be an attentive but neutral spectator. His patients nodded in approval. As Nagaji waited for the midnight hour the air of expectation only intensified. That was when the original spells were cast, he once told me. Since Nagaji considered each ritual a counterattack on an opposing sorcerer, he had to strike back at the same time and in like manner. When I pointed out that he had personally not witnessed the evil sorcerer’s ritual, Nagaji explained that the tutelary goddess guided his actions.2 But for this healing, his supernatural assistant was not the goddess Sakti who regularly spoke during his biweekly divining seances, but the goddess Kali-well known throughout Tamilnadu for her bloody battles against demons. Yet when acting as exorcist he did not identify with Ka.Ii but retained his own male, human consciousness and personality.

"television, constrained at the time from such a move by Independent Broadcasting Association regulations (Willock 1992). Coronation Street and Crossroads had been stripped across three evenings, and EastEnders across two. Stripping across five days/nights had long been common in Australian television. This was first done for Number 96 (1972–1977) by Ian Holmes, later the Grundy Organisation’s president. So successful was the stripping of Neighbours across five days that the same principle has since been adopted in the UK for Home and Away. David Liddiment, Head of Entertainment at Granada, which produces Coronation Street and Families, both Neighbours competitors, went so far as to say: “In future, no-one will contemplate running a daytime serial in the UK except as a strip. It’s inevitable that you build success more quickly when you strip a soap” (Liddiment 1989: 20). Second, on scheduling, Loughton made the schedules more cost-effective by repeating each edition daily (Patterson 1992). “The time-slots chosen by the BBC were 1.30 pm, with a repeat the following morning at 9.05. It attracted a typical audience of housewives, shift workers, the unemployed, people home sick” (Oram 1988: 48). After the unexpected success of Neighbours’ first year, it was decided to reschedule the next morning repeat for the same evening, at 5:35 p.m. This was to cater for working mothers, but most of all for schoolchildren who had previously played truant to watch the series. The most famous story attributes the schedule change to the representations made to no less than Michael Grade himself by his daughter. Rescheduled in January 1988, Neighbours nearly doubled its audience to 16.25 million within six weeks. By Christmas 1988, audiences topped 20 million. Five-day stripping and repeat screenings, then, offered a regularity and familiarity significant in capturing such huge audiences, representing one-third of the UK population. The third precondition was the UK “mediascape.” This included a very broad familiarity with Australian soaps. When Neighbours was launched on October 27, 1986, The Sullivans, A Country Practice, Young Doctors, Flying Doctors, Richmond Hills, Prisoner: Cell Block H, and others had broadened the paths already beaten by many Australian films released in the UK. Michael Collins, executive in charge of production at JNP, producers of A Country Practice, maintains that the serial, screened in the UK since 1983, “was a forerunner in getting audiences used to Australian drama” (Collins 1991). And one factor contributing to Neighbours’s topping the ratings late in 1988 would have been the demise of Crossroads, the British soap created by Reg Watson, in spring 1988 after a twenty-four-year run. Fourth, tabloids, television, and un(der)employment. Under Thatcher and Murdoch, the tabloid press in Britain expanded in the mid-1980s, producing what one television executive described, albeit parodically, as “one page of news, one page of sex, and twenty-two pages of television and sport” (Patterson 1992). So when Neighbours was stripped over five days, “the papers really noticed it” (Willock 1992). Together with Woman, Woman’s Day, Jackie, Scoop, and other teen magazines, the tabloids ran myriad stories on Kylie, Jason, Peter O’Brien, and so on, as is indicated by the three sample headlines from three successive days:". In To Be Continued..., 113. Routledge, 2002. http://dx.doi.org/10.4324/9780203131855-15.

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Atti di convegni sul tema "Sample paths regularity":

Polder, Jan Willem, e Hans Broekhuisen. "Tip-Fillet Interference in Cylindrical Gears". In ASME 2003 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/detc2003/ptg-48060.

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The occurrence of severe tip-fillet interference which could not be explained by existing formulas, and the tendency of modern design rules to go up to the geometrical limits, were reasons to develop three new views. The old geometrical condition proved to be incorrect. It required the usable flank to exceed the active flank, which guarantied only a correct mating on the line of action. However, while the involute flanks are mating regularly in an arbitrary position, then outside the line of action the tip of the pinion may penetrate the fillet of the mating gear. The possible tip-fillet interference is not restricted to one single position, but takes up a certain part of the path of action. The deduction of a completely new geometrical condition was based on a positive free distance between tip and fillet in each position. Secondly, a condition based exclusively on nominal dimensions did not suffice. The neglect of inaccuracies and deformations was as irresponsible as neglecting functional backlash in any conventional gear pair. Emphatically, the geometrical condition has to answer the same influences. Therefore, a new algorithm includes a relation with maximal backlash. Thirdly, by introducing a quality dependent backlash function in a geometrical condition, there will be more necessity to standardize a clear backlash-related tolerance system than in the past was required for the minimal functional backlash.

Beckers, Benoit. "Las escalas de la luz". In International Conference Virtual City and Territory. Barcelona: Centre de Política de Sòl i Valoracions, 2009. http://dx.doi.org/10.5821/ctv.7584.

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Variando con el paso del día y del año, la luz del Sol y del cielo modula, visual y energéticamente, los territorios, las ciudades y los edificios. ¿Cómo sintetizar y manejar en el proyecto estas informaciones donde se mezcla el azar de las nubes pasajeras con la regularidad astronómica de los trayectos solares? En cuanto a las herramientas de simulación, el mayor avance de estos últimos años se ha producido en los programas de renderización, con los cuales nos vemos forzados a construir la iluminación de una escena a partir de distintos componentes, cada uno de los cuales requiriendo su propia algorítmica: luz directa del Sol, obertura al cielo, reflexión difusa y especular de Sol y cielo. Veremos primero que la mejor manera de entrar estos componentes en una lógica de diseño (y ya no solamente de análisis) consiste en aprovechar las propiedades geométricas de diferentes proyecciones: estereográfica, equivalente, ortogonal, gnomónica, isócrona,… Recordaremos también que el componente aparentemente más sencillo – los trayectos solares – nos conduce ya a un problema de cinco dimensiones. Con el ejemplo del programa “Heliodon 2”, [Beckers & Masset, 2009], indicaremos las formas de diseñar con la doble geometría del Sol y del cielo. Por el crecimiento y la necesaria densificación de nuestras ciudades, nuevos problemas se hacen sensibles: el derecho de todos a ver el cielo, el ahorro energético, la captación y distribución de la energía solar – la ciudad se considera entonces como fuente de energía, y ya no solamente como lugar de consumo –, el control del impacto mutuo entre la ciudad y la atmósfera. Con este último tema, nos encontramos frente a lo que los físicos llaman un “problema multiescala”; es decir: un mismo fenómeno, como el de la isla de calor, es el producto de innumerables contribuciones, las cuales se han de estudiar conjuntamente y de forma simultánea a escalas tan distintas que ya no las gobiernan las mismas ecuaciones. Habrá que aprender a construir edificios pensando en la ciudad, ciudades pensando en el territorio, y concebir el mismo territorio a partir de las ciudades, cuyos buenos o malos procederes modelan hasta los campos más distantes, y el planeta entero. By their continuous transformations along the day and the year, Sun and sky light are modeling, visually and energetically, the cities and buildings. How this information can be synthesized and used in the project, considering together the random occurrence of the passing clouds and the astronomical regularity of the sun paths? Regarding to the simulation tools, the main progress in late years has been produced in the render software, that force the users to separate the different components of light in any construction of an illuminated scene, using the opportune algorithms for direct Sun light, sky aperture, diffuse and specular reflections of Sun and sky. It will be first shown how the best mode of introducing these components into a design logic consists in taking advantage of the geometrical properties of different projections, as the stereographic, equivalent, orthographic, gnomonic or isochronal ones. It will be also remembered that the apparently simplest problem – Sun paths – conduces the architect to a five dimensions problem. With the example of “Heliodon 2” software, [Beckers & Masset, 2009], it will be shown how to design with the double geometry of Sun paths and sky light. Due to the growth and necessary densification of our cities, new problems are appearing: the right for everybody to see the sky, the energies economy, the solar energy collect and distribution – cities are then considered as energy sources and not only as consummation places –, the control of the mutual impact between the city and the atmosphere. With this last theme, we are in front of a “multiscale problem”, as say the physics when a unique problem, as the urban heat island, is the product of innumerable contributions that have to be studied together and simultaneously in so different scales that they are not governed yet by the same equations. We must listen to build architectures thinking on the city, cities thinking on the territory, and to conceive the territory itself from the cities, because our good or bad urban ideas model the most distant countries, and the entire planet.

Darwish, Abdallah Magdy, Ahmed Kamal Khalil, Mohamed El-Hussein El-Dessouky, Islam Ibrahim Mohamed e Tamer Hosny Abdelhalem. "Preventing Halite Scaling in Offshore Pipelines Using Integrated Scale Management System and Modeling – Case Study from Gulf of Suez, Egypt". In Offshore Technology Conference Asia. OTC, 2022. http://dx.doi.org/10.4043/31455-ms.

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Abstract Halite scaling has a dreadful impact on production pipelines. Produced water from Nubia formation in "E" field has high level of total dissolved solids (TDS) concentration. Halite scale causes complete blockage of the flow paths, integrity complications and periodic production interruption. Pipeline pigging and flushing with fresh water were performed frequently to eliminate blockage and restore production. An offshore platform with six online gas lifted wells; two high rate wells are producing from Nubia formation through the production pipeline and the remaining low rate wells are producing from other formations with a lower TDS through the test pipeline. High saline water flows through the production pipeline and cools down to seabed temperature resulting in halite precipitation, which regularly blocks the pipeline and requires repetitive fresh water flushing and pigging operations. Laboratory water analysis and scale tendency were conducted in conjunction with a pipeline network model to predict the halite precipitation temperature, actual friction coefficient and optimum fluid mixing and dilution strategy. The combination of complete water analysis, scale tendency, real time remote monitoring system and pipeline network modeling showed that halite scaling started inside the subsea pipeline nearby the platform. The model matching revealed a high friction coefficient, which indicated partial plugging of the production pipeline. The model sensitivity analysis predicted that diluting the supersaturated water by mixing it with other wells’ lower salinity waters – into the same pipeline, would drop the mixture salinity with no halite scaling along the pipeline. As a result, the strategy of mixing was selected and optimized based on the modeling results and water compatibility tests to reduce losses due to back pressure and to minimize the risk of hard scale deposition. For more than a year, no halite has precipitated, which resulted in an uninterrupted production and allowed well testing of the remaining wells discretely through the test pipeline. This paper demonstrates a comprehensive case in which halite scaling issues were predicted and mitigated through an integrated scale management system. The operating expenditures of pipeline flushing and pigging operations and oil losses were decreased due to interrupted production.

Arghir, Mihai, e Antoine Mariot. "Theoretical Analysis of the Static Characteristics of the Carbon Segmented Seal". In ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/gt2016-56643.

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The segmented carbon seal is regularly used for sealing bearing chambers of aeronautical turboengines or as part of a buffer seal in space turbopumps. The seal operates with contaminated air or with an inert gas and is made of many identic carbon segments (generally three or six) with reciprocally overlapping ends. The segments are serrated against the rotor by the pressure difference between the upstream and the downstream chambers and by a circumferential (garter) spring. The pressure difference and an axial spring press the segments also against the stator. The inner cylindrical surface of each segment is provided with pads that create an aerodynamic lift proportional to the rotor speed. Following this lift force, the segments of the seal are pushed away from the rotor and the seal opens. The contact between the rotor and the segments is lost and an axial leakage path is thus created. Although it was developed since long, a model for calculating the characteristics of the segmented seal is completely absent from the scientific literature. The goal of the present work is to fill this gap at least for the static characteristics (leakage and torque). The analysis is carried out for a single segment of the seal by supposing that all the segments have the same characteristics. Each segment has a planar motion (i.e. three degrees of freedom) and therefore the film thickness under each pad is not uniform. Given the stationary operating conditions (pressure difference and rotation speed), the present model calculates the equilibrium position of each segment on the bases of the lift and of the friction force acting on the pads, of the friction forces acting on the nose of the seal and of the radial and axial springs. Once found the static equilibrium position, the leakage and the torque of the seal are calculated. A parametric study enlightens the importance of the pad waviness, of the pocket depth and of the spring forces on the characteristics of the segmented seal.

Al-Busaidi, Salim, Qasim Hinaai, Rajeev Ranjan Kumar, Ying Ru Chen, Redha Hasan Al Lawatia, Dai Guo Yu, Amit Kumar Singh e Surej Kumar Subbiah. "Successful Drilling Campaign of High Angled Wells in Tight Gas Fields using 3D Geomechanical Modeling and Real-Time Monitoring". In SPE/IADC Middle East Drilling Technology Conference and Exhibition. SPE, 2021. http://dx.doi.org/10.2118/202123-ms.

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Abstract The field under study is witnessing an increasing trend in NPT events while drilling vertical wells through high stressed shale formations and the underlying depleted sandstone reservoir in the same section. The field has multiple sets of faults with lateral variations in stress azimuth and completion quality with the regional strike-slip regime. High angled wells are being planned to increase reservoir coverage and perform hydro fracturing. This paper provides details of capturing stress regime variation along with the effects of depletion in offset wells and identify suitable azimuth of planned well with drilling risks through a 3D geomechanical study. Comprehensive 1D mechanical earth models are constructed using open hole logs, core data and available hydro-fracturing results for wells in the field. Rock mechanical properties have been calibrated at well scale as per core data. Poro-elastic horizontal strain method at well scale indicates a strike-slip to reverse fault variation with significant horizontal stress anisotropy as evident from the closure pressure range of 9,500 psi to 12,500 psi. 3D numerical geomechanical model has been constructed considering structural discontinuities, rock mechanical properties and formation pressure to estimate the principal stresses. Stress direction data from dipole sonic measurements and breakout azimuth from borehole image logs are used for calibration in 3D model incorporating faults. Stress path for depletion has been estimated. Results from the study suggested change in casing policy specifically to have a liner isolating the overburden formations where more than 800 m should be drilled prior to entering the depleted reservoir formation. 3D geomechanical analysis reckons that the mud weight should be in the range of 12.7 kPa/m to 13.1 kPa/m during building up the well profile at 80 deg inclination in overlying shale while 1D study suggesting a range of 13.2 kPa/m to 13.7 kPa/m. Along well path at 80deg to 90deg deviation within reservoir layer toward minimum horizontal stress azimuth, mud weight requirement was found to be much lower at 11.5 kPa/m to 12.1 kPa/m. Apart from mud weight, BHA and chemicals were optimized to avoid differential sticking and better hole cleaning for respective sections. Actual mud weight used was in the range of 12.8 kPa/m to 13.1 kPa/m for building up with no torque and drag issue while running liner and BHA trips. Mud weight was maintained in the range of 11.5 kPa/m to 11.8 kPa/m in the horizontal section with minimum breakouts and smoother hole condition. Cuttings shape and size analysis were performed regularly to check well behavior and manage downhole pressure higher than shear failure limit. Using 3D Geomechanical study and continuous monitoring of drilling parameters in near real-time, the buildup and reservoir sections have been drilled within schedule with no major NPT event and saved at least one week of rig days.