Relevant bibliographies by topics / Obstruction geometries

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  1. Journal articles
  2. Dissertations / Theses
  3. Book chapters
  4. Conference papers

Academic literature on the topic 'Obstruction geometries'

Author: Grafiati
Published: 19 February 2023

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Journal articles on the topic "Obstruction geometries"

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Trinh, Philippe H., and S. Jonathan Chapman. "New gravity–capillary waves at low speeds. Part 2. Nonlinear geometries." Journal of Fluid Mechanics 724 (April 29, 2013): 392–424. http://dx.doi.org/10.1017/jfm.2013.129.

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AbstractWhen traditional linearized theory is used to study gravity–capillary waves produced by flow past an obstruction, the geometry of the object is assumed to be small in one or several of its dimensions. In order to preserve the nonlinear nature of the obstruction, asymptotic expansions in the low-Froude-number or low-Bond-number limits can be derived, but here, the solutions are waveless to every order. This is because the waves are in fact, exponentially small, and thus beyond-all-orders of regular asymptotics; their formation is a consequence of the divergence of the asymptotic series and the associated Stokes Phenomenon. In Part 1 (Trinh & Chapman, J. Fluid Mech., vol. 724, 2013b, pp. 367–391), we showed how exponential asymptotics could be used to study the problem when the size of the obstruction is first linearized. In this paper, we extend the analysis to the nonlinear problem, thus allowing the full geometry to be considered at leading order. When applied to the classic problem of flow over a step, our analysis reveals the existence of six classes of gravity–capillary waves, two of which share a connection with the usual linearized solutions first discovered by Rayleigh. The new solutions arise due to the availability of multiple singularities in the geometry, coupled with the interplay of gravitational and cohesive effects.
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Dolnik, Milos, Christopher Konow, Noah H. Somberg, and Irving R. Epstein. "Effect of obstructions on growing Turing patterns." Chaos: An Interdisciplinary Journal of Nonlinear Science 32, no. 7 (July 2022): 073127. http://dx.doi.org/10.1063/5.0099753.

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We study how Turing pattern formation on a growing domain is affected by discrete domain discontinuities. We use the Lengyel–Epstein reaction–diffusion model to numerically simulate Turing pattern formation on radially expanding circular domains containing a variety of obstruction geometries, including obstructions spanning the length of the domain, such as walls and slits, and local obstructions, such as small blocks. The pattern formation is significantly affected by the obstructions, leading to novel pattern morphologies. We show that obstructions can induce growth mode switching and disrupt local pattern formation and that these effects depend on the shape and placement of the objects as well as the domain growth rate. This work provides a customizable framework to perform numerical simulations on different types of obstructions and other heterogeneous domains, which may guide future numerical and experimental studies. These results may also provide new insights into biological pattern growth and formation, especially in non-idealized domains containing noise or discontinuities.
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Trinh, Philippe H., and S. Jonathan Chapman. "New gravity–capillary waves at low speeds. Part 1. Linear geometries." Journal of Fluid Mechanics 724 (April 29, 2013): 367–91. http://dx.doi.org/10.1017/jfm.2013.110.

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AbstractWhen traditional linearized theory is used to study gravity–capillary waves produced by flow past an obstruction, the geometry of the object is assumed to be small in one or several of its dimensions. In order to preserve the nonlinear nature of the obstruction, asymptotic expansions in the low-Froude-number or low-Bond-number limits can be derived, but here, the solutions invariably predict a waveless surface at every order. This is because the waves are in fact, exponentially small, and thus beyond-all-orders of regular asymptotics; their formation is a consequence of the divergence of the asymptotic series and the associated Stokes Phenomenon. By applying techniques in exponential asymptotics to this problem, we have discovered the existence of new classes of gravity–capillary waves, from which the usual linear solutions form but a special case. In this paper, we present the initial theory for deriving these waves through a study of gravity–capillary flow over a linearized step. This will be done using two approaches: in the first, we derive the surface waves using the standard method of Fourier transforms; in the second, we derive the same result using exponential asymptotics. Ultimately, these two methods give the same result, but conceptually, they offer different insights into the study of the low-Froude-number, low-Bond-number problem.
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SALEEL, C. A., A. SHAIJA, and S. JAYARAJ. "COMPUTATIONAL SIMULATION OF FLUID FLOW OVER A TRIANGULAR STEP USING IMMERSED BOUNDARY METHOD." International Journal of Computational Methods 10, no. 04 (April 23, 2013): 1350016. http://dx.doi.org/10.1142/s0219876213500163.

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Handling of complex geometries with fluid–solid interaction has been one of the exigent issues in computational fluid dynamics (CFD) because most engineering problems have complex geometries with fluid–solid interaction for the purpose. Two different approaches have been developed for the same hitherto: (i) The unstructured grid method and (ii) the immersed boundary method (IBM). This paper details the IBM for the numerical investigation of two-dimensional laminar flow over a backward facing step and various geometrically configured triangular steps in hydro-dynamically developing regions (entrance region) as well in the hydro-dynamically developed regions through a channel at different Reynolds numbers. The present numerical method is rooted in a finite volume approach on a staggered grid in concert with a fractional step method. Geometrical obstructions are treated as an immersed boundary (IB), both momentum forcing and mass source terms are applied on the obstruction to satisfy the no-slip boundary condition and also to satisfy the continuity for the mesh containing the immersed boundary. Initially, numerically obtained velocity profiles and stream line plots for fluid flow over backward facing step is depicted to show its excellent agreement with the published results in various literatures. There after profiles and plots in the channel with triangular steps are also being unveiled with in depth elucidation. Results are presented for different Reynolds numbers.
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Lehners, Jean-Luc. "No smooth beginning for spacetime." International Journal of Modern Physics D 28, no. 02 (January 2019): 1930005. http://dx.doi.org/10.1142/s0218271819300052.

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In this paper, I will review an obstruction for theories of the beginning of the universe which can be formulated as semiclassical path integrals. Hartle and Hawking’s no boundary proposal and Vilenkin’s tunneling proposal are examples of such theories. Each may be formulated as the quantum amplitude for obtaining a final 3-geometry by integrating over 4-geometries. The result is obtained using a new mathematical tool — Picard–Lefschetz theory — for defining the semiclassical path integral for gravity. The Lorentzian path integral for quantum cosmology with a positive cosmological constant is mathematically meaningful in this approach, but the Euclidean version is not. Framed in this way, the resulting framework and predictions are unique. Unfortunately, the outcome is that primordial gravitational wave fluctuations are unsuppressed.
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Athavale, S. M., and J. S. Strenkowski. "Material Damage-Based Model for Predicting Chip-Breakability." Journal of Manufacturing Science and Engineering 119, no. 4B (November 1, 1997): 675–80. http://dx.doi.org/10.1115/1.2836808.

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A model for predicting the chip breakability potential of groove and obstruction-type tools is described. The potential for a tool to break chips is evaluated in terms of the chip geometry and the damage sustained by the chip as it is formed in the shear zone. The chip geometry is characterized by its thickness-to-radius ratio, and the material damage is evaluated in terms of a normalized accumulated damage factor that is based on a hole growth and coalescence model. The chip thickness-to-radius ratio and the normalized accumulated damage factor are evaluated using a finite element cutting model. A total of 210 cutting tests were conducted to verify the model. Different tools including flat, obstruction, and groove, were tested for cutting of AISI 1020 steel and SS 304 steel. Each of these tool geometries exhibited significantly different chip thickness-to-radius ratios and normalized accumulated damage. Threshold criteria for breaking chips were determined for AISI 1020 and SS 304. For difficult-to-break materials such as stainless, a lower normalized accumulated damage was needed and a higher chip thickness-to-radius ratio was required to break chips. Although the model presented in the paper was developed for orthogonal cutting, it can be readily extended to three dimensional machining processes. Using this approach, a new tool design can be evaluated for its chip breakability potential with much less reliance on prototype building and testing.
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Lappa, Marcello. "Hydrothermal waves in two-dimensional liquid layers with sudden changes in the available cross-section." International Journal of Numerical Methods for Heat & Fluid Flow 27, no. 11 (November 6, 2017): 2629–49. http://dx.doi.org/10.1108/hff-11-2016-0453.

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Purpose Hydrothermal waves represent the preferred mode of instability of the so-called Marangoni flow for a wide range of liquids and conditions. The related features in classical rectangular containers have attracted much attention over recent years owing to the relevance of these oscillatory modes to several techniques used for the production of single crystals of semiconductor or oxide materials. Control or a proper knowledge of convective instabilities in these systems is an essential topic from a material/product properties saving standpoint. The purpose of this study is to improve our understanding of these phenomena in less ordinary circumstances. Design/methodology/approach This short paper reports on a numerical model developed to inquire specifically about the role played by sudden changes in the available cross-section of the shallow cavity hosting the liquid. Although accounting for the spanwise dimension would be necessary to derive quantitative results, the approach is based on the assumption of two-dimensional flow, which, for high-Pr fluids, is believed to retain the essence of the involved physical processes. Findings Results are presented for the case of a fluid with Pr = 15 filling an open container with a single backward-facing or forward-facing step on the bottom wall or with an obstruction located in the centre. It is shown that the presence of steps in the considered geometry can lead to a variety of situations with significant changes in the local spectral content of the flow and even flow stabilization in certain circumstances. The role of thermal boundary conditions is assessed by considering separately adiabatic and conducting conditions for the bottom wall. Originality/value Although a plethora of studies have been appearing over recent years motivated, completely or in part, by a quest to identify new means to mitigate these instabilities and produce accordingly single crystals of higher quality for the industry, unfortunately, most of these research works were focusing on very simple geometries. In the present paper, the causality and interdependence among all the kinematic and thermal effects mentioned above is discussed.
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Mazumder, Sandip. "Methods to Accelerate Ray Tracing in the Monte Carlo Method for Surface-to-Surface Radiation Transport." Journal of Heat Transfer 128, no. 9 (February 9, 2006): 945–52. http://dx.doi.org/10.1115/1.2241978.

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Two different algorithms to accelerate ray tracing in surface-to-surface radiation Monte Carlo calculations are investigated. The first algorithm is the well-known binary spatial partitioning (BSP) algorithm, which recursively bisects the computational domain into a set of hierarchically linked boxes that are then made use of to narrow down the number of ray-surface intersection calculations. The second algorithm is the volume-by-volume advancement (VVA) algorithm. This algorithm is new and employs the volumetric mesh to advance the ray through the computational domain until a legitimate intersection point is found. The algorithms are tested for two classical problems, namely an open box, and a box in a box, in both two-dimensional (2D) and three-dimensional (3D) geometries with various mesh sizes. Both algorithms are found to result in orders of magnitude gains in computational efficiency over direct calculations that do not employ any acceleration strategy. For three-dimensional geometries, the VVA algorithm is found to be clearly superior to BSP, particularly for cases with obstructions within the computational domain. For two-dimensional geometries, the VVA algorithm is found to be superior to the BSP algorithm only when obstructions are present and are densely packed.
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Peszynska, Malgorzata, Joseph Umhoefer, and Choah Shin. "Reduced Model for Properties of Multiscale Porous Media with Changing Geometry." Computation 9, no. 3 (March 3, 2021): 28. http://dx.doi.org/10.3390/computation9030028.

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In this paper, we consider an important problem for modeling complex coupled phenomena in porous media at multiple scales. In particular, we consider flow and transport in the void space between the pores when the pore space is altered by new solid obstructions formed by microbial growth or reactive transport, and we are mostly interested in pore-coating and pore-filling type obstructions, observed in applications to biofilm in porous media and hydrate crystal formation, respectively. We consider the impact of these obstructions on the macroscopic properties of the porous medium, such as porosity, permeability and tortuosity, for which we build an experimental probability distribution with reduced models, which involves three steps: (1) generation of independent realizations of obstructions, followed by, (2) flow and transport simulations at pore-scale, and (3) upscaling. For the first step, we consider three approaches: (1A) direct numerical simulations (DNS) of the PDE model of the actual physical process called BN which forms the obstructions, and two non-DNS methods, which we call (1B) CLPS and (1C) LP. LP is a lattice Ising-type model, and CLPS is a constrained version of an Allen–Cahn model for phase separation with a localization term. Both LP and CLPS are model approximations of BN, and they seek local minima of some nonconvex energy functional, which provide plausible realizations of the obstructed geometry and are tuned heuristically to deliver either pore-coating or pore-filling obstructions. Our methods work with rock-void geometries obtained by imaging, but bypass the need for imaging in real-time, are fairly inexpensive, and can be tailored to other applications. The reduced models LP and CLPS are less computationally expensive than DNS, and can be tuned to the desired fidelity of the probability distributions of upscaled quantities.
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Kluck, C., and T. M. Buzug. "Numerical simulations of airflow in the human pharynx of OSAHS patients." Current Directions in Biomedical Engineering 1, no. 1 (September 1, 2015): 552–55. http://dx.doi.org/10.1515/cdbme-2016-0003.

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AbstractAbstract: Computational Fluid Dynamic simulations are performed in real patient individual pharynx geometries of an Obstructive Sleep Apnea patient. The Navier-Stokes equations as well as the Reynolds Averaged Navier-Stokes equations and k − ∊ and k −ω turbulence models are used. The velocity profile and pressure distribution of the patient without any treatment and the patient wearing a mandibular advancement appliance are compared to each other. The simulation results for the different model conditions all lead to similar results showing the robustness of the numerical solutions. The pressure loss along the pharynx is lower in the presence of a mandibular appliance, which can indicate the reduction of OSAHS severity.
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Dissertations / Theses on the topic "Obstruction geometries"

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Gautam, Sushrut Zubin Sulaksh. "Two geometric obstruction results in harmonic analysis." Diss., Restricted to subscribing institutions, 2009. http://proquest.umi.com/pqdweb?did=1872162601&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.

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Sathaye, Bakul Sathaye. "Obstructions to Riemannian smoothings of locally CAT(0) manifolds." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1531416481628579.

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ROCHA, Jackson Ítalo Tavares da. "Avaliação da geometria nasal em adultos com apneia obstrutiva do sono." Universidade Federal de Pernambuco, 2016. https://repositorio.ufpe.br/handle/123456789/18675.

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Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2017-04-27T15:57:25Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) DISSERTACAO MESTRADO 2016 - JACKSON ITALO T ROCHA.pdf: 2594938 bytes, checksum: 75e029c72bf805464c1a4ed0313636dd (MD5)
Made available in DSpace on 2017-04-27T15:57:25Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) DISSERTACAO MESTRADO 2016 - JACKSON ITALO T ROCHA.pdf: 2594938 bytes, checksum: 75e029c72bf805464c1a4ed0313636dd (MD5) Previous issue date: 2016-06-10
A apneia obstrutiva do sono (AOS) é uma disfunção da respiração que gera interrupções no sono, consequentes quadros de hipersonolência diurna, além de disfunções cardiovasculares. Sua etiologia ainda é desconhecida, sendo descrita como multifatorial. Ainda assim, o seu diagnóstico é bastante preciso e realizado por meio de um exame padrão-ouro, a polissonografia. Muitos estudos têm investigado outros procedimentos diagnósticos que permitam complementar a bateria de exames já existentes com a finalidade de facilitar e permitir um diagnóstico e intervenção cada vez mais precoces na AOS. Com isto, a rinometria acústica (RA), que permite mensurar a geometria nasal, surge como possibilidade de cumprir tais objetivos quando aplicada em pacientes com AOS. Este é um estudo transversal analítico e seu objetivo foi comparar as medidas rinométricas entre indivíduos sem e com AOS e correlacionar o volume (V) e a área de secção transversal mínima (ASTM) das cavidades nasais com a gravidade e sintomas da AOS. Para compor a amostra, foram convidados pacientes sem AOS e diagnosticados com AOS, em diferentes graus, acompanhados no ambulatório de Pneumologia do Hospital Otávio de Freitas nos últimos dois anos. A pesquisa foi realizada em conjunto na clínica de fonoaudiologia da Universidade Federal de Pernambuco. Os indivíduos foram divididos em dois grupos: grupo 1 (sem AOS e AOS leve; n=10) e grupo 2 (AOS moderada e grave; n=10). A coleta dos dados de cada paciente foi realizada por meio da busca de prontuário, identificando sexo, idade, escala de sonolência de Epworth (ESE) e os resultados da polissonografia e, em seguida, era realizada a RA. A análise do estudo foi feita por meio de estatística descritiva e inferencial com auxílio do software SPSS, versão 18.0. A aderência dos dados aos padrões de normalidade e homogeneidade foi testada pelo teste de Shapiro-Wilk e Levene, respectivamente. A comparação entre os grupos foi realizada com o teste de Mann-Whitney e a correlação entre as variáveis com o coeficiente de correlação de Spearman. As diferenças foram assumidas quando p<0,05. Não foi encontrada diferença entre os grupos estudados nos valores totais da área de secção transversa mínima (ASTM) (grupo 1: 1,71cm² [0,93; 2,84cm²] vs. grupo 2: 1,47cm² [0,87; 2,60cm²]) e do volume (V) (grupo1: 19,25cm³ [12,50-36,15cm³] e grupo 2: 24,82cm³ [7,58- 32,48cm³]). Não houve correlação entre o índice apneia e hipopneia (IAH) e ASTM (r = 0,044; p>0,05), nem entre o IAH e V (r = 0,323, p>0,05). Não foi possível observar correlação entre a ESE e ASTM (r = -0,064; p>0,05), nem entre a ESE e V (r = -0,115, p>0,05). Na amostra estudada, em indivíduos sem queixa de obstrução nasal, a geometria nasal não apresentou correlação com a gravidade ou com os sintomas da AOS.
Obstructive sleep apnea (OSA) is a disorder of breathing during sleep characterized by several interruptions in sleep, daytime sleepiness, and cardiovascular disorders. The etiology is described as multifactorial and the diagnosis is assessed by gold standard polysomnography measures. However, many studies have been developed to find other coadjuvants diagnostics procedures for the early detection of OSA. Acoustic rhinometry (AR) allows the assessment of nasal geometry and emerge as a new possibility to help in the diagnosis of OSA patients. Therefore, the aim of this study was to compare rhinometric measures between subjects with and without OSA and to correlate nasal geometry with the symptoms and the severity of OSA. This is an analytical cross-sectional study and the objective is to analyze the rhinometric characteristics in subjects with OSA. Consecutive patients diagnosed with, different levels of OSA severity, and patients diagnosed without OSA followed at the Hospital Otavio de Freitas (HOF) in the last 2 years. The subjects were divided into two groups: group 1 (patients without OSA/mild OSA; n=10) and group 2 (moderate/severe OSA; n=10). The baseline data were collected for each patient first identifying data such as gender, age, Epworth sleepiness scale (ESS) and the results of polysomnography. Then, the patients were also submitted to AR. Statistical analysis was performed using SPSS (Version 18, IBM, NY USA). Shapiro Wilk test was used to determine the distributions of continuous variables were normally. Levene test was used for the evaluation of homogeneity of variances. Between-group differences in continuous data were assessed using Mann-Whitney test and the associations were examined with Spearman correlation coefficient. Statistical tests were considered significant when p < 0.05. No difference was found between the groups studied in the total value of the minimum cross-sectional area (MCSA) (group 1: 1,71cm² [0.93; 2,84cm²] vs. group 2: 1,47cm² [0.87; 2 , 60cm²]) and volume (V) (group1: 19,25cm³ [12,5036,15cm³] and group 2: 24,82cm³ [7,58- 32,48cm³]). There was no correlation between the apnea hypopnea index (AHI) and MCSA (r = 0.044; p> 0.05) nor between AHI and V (r = 0.323, p> 0.05). Could not observe correlation between ESS and MSCA (r = -0.064; p> 0.05) or between the ESS and V (r = -0.115, p> 0.05). In the sample studied in individuals without complaints of nasal obstruction, nasal geometry was not correlated with the severity or symptoms of OSA. Keywords: Acous
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Powell, Mark Andrew. "Second order algebraic knot concordance group." Thesis, University of Edinburgh, 2011. http://hdl.handle.net/1842/5030.

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Let Knots be the abelian monoid of isotopy classes of knots S1 ⊂ S3 under connected sum, and let C be the topological knot concordance group of knots modulo slice knots. Cochran-Orr-Teichner [COT03] defined a filtration of C: C ⊃ F(0) ⊃ F(0.5) ⊃ F(1) ⊃ F(1.5) ⊃ F(2) ⊃ . . .The quotient C/F(0.5) is isomorphic to Levine’s algebraic concordance group AC1 [Lev69]; F(0.5) is the algebraically slice knots. The quotient C/F(1.5) contains all metabelian concordance obstructions. The Cochran-Orr-Teichner (1.5)-level two stage obstructions map the concordance class of a knot to a pointed set (COT (C/1.5),U). We define an abelian monoid of chain complexes P, with a monoid homomorphism Knots → P. We then define an algebraic concordance equivalence relation on P and therefore a group AC2 := P/ ~, our second order algebraic knot concordance group. The results of this thesis can be summarised in the following diagram: . That is, we define a group homomorphism C → AC2 which factors through C/F(1.5). We can extract the two stage Cochran-Orr-Teichner obstruction theory from AC2: the dotted arrows are morphisms of pointed sets. Our second order algebraic knot concordance group AC2 is a single stage obstruction group.
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Zahnd, Stephane. "Descente de torseurs, gerbes et points rationnels." Phd thesis, Université des Sciences et Technologie de Lille - Lille I, 2003. http://tel.archives-ouvertes.fr/tel-00004163.

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Soient $k$ un corps de caractéristique nulle et $G$ un $k$-groupe algébrique linéaire. Il est bien connu que si $G$ est abélien, les torseurs sous $G_(X)$ sur un $k$-schéma $\pi:X\rightarrow \textup(Spec)\;k$ fournissent une obstruction à l'existence de points $k$-rationnels sur $X$, puisque la suite spectrale de Leray donne dans les bons cas (\textit(e.g.) $X$ propre) une suite exacte de groupes sur laquelle on peut directement lire l'obstruction à ce qu'un $\bar(G)_(X)$-torseur $\bar(P)\rightarrow\bar(X)$ de corps des modules $k$ soit défini sur $k$, \textit(i.e.) qu'il provienne par extension des scalaires à la cl(ô)ture algébrique $\bar(k)$ de $k$ d'un $G_(X)$-torseur $P\rightarrow X$. Le point crucial est que cette obstruction est mesurée par une gerbe, qui est neutre lorsque $X$ possède un point $k$-rationnel. On essaye ici d'étendre ce résultat au cas non-commutatif, et on en déduit (sous certaines conditions) des obstructions cohomologiques non-abéliennes à l'existence de points $k$-rationnels sur $X$, et des résultats sur la descente des torseurs.
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Robbeloth, Michael Christopher. "Recognition of Incomplete Objects based on Synthesis of Views Using a Geometric Based Local-Global Graphs." Wright State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=wright1557509373174391.

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(9808835), Mohd Kabir. "Flow characteristics of Newtonian and non-Newtonian fluids in a channel with obstruction at the entry." Thesis, 2004. https://figshare.com/articles/thesis/Flow_characteristics_of_Newtonian_and_non-Newtonian_fluids_in_a_channel_with_obstruction_at_the_entry/21721064.

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This study investigates the flow phenomena in a channel with an obstruction at the entry which is placed in another wider parallel walled channel. When obstructed, the flow phenomena inside the channel were observed to be reverse, forward or stagnant depending on the position of the obstruction. The parameters that influence the flow inside and around the test channel are: - the size and shape of the obstruction geometries, the gap between the test channel and the obstruction geometry, the Reynolds number and the length of the test channel. Knowledge of these flow phenomena has the potential benefit in the control of various flows in process engineering applications.

Experimental investigations of these flow parameters were carried out in an open channel rig. Fluids used in the investigations were a Newtonian fluid (water) and two non-Newtonian fluids, namely polyacrylamide solution (0.03% by weight) and mixed solution (xanthan gum, magna floc 139 and magna floc 1011). The polyacrylamide solution and mixed solution had similar viscosity and both show a power-law behavior, however their elastic behavior was different.

Experimental studies of these flows include the velocity measurement and the flow visualization analysis. The velocity measurement provides the quantitative information whereas flow visualization provides the qualitative information of the flow. Numerical simulations of these flow phenomena were also carried out using a CFD software and comparisons are made with the experimental results.

The influence of the size and shapes of the obstruction geometries; and the gap to width (g/w) ratio on the magnitude of the velocity ratio (ViNo: inside/outside velocity of the test channel) was studied. Obstruction geometries used were semicircle, triangle, circle and various shapes of rectangles. The g/w ratios ranging from 0.5 to 8 were selected as a set of distances from the test channel. The influence of the Reynolds numbers on the value of the velocity ratio was investigated. The effect of the test channel length on the velocity ratio was also investigated at the Reynolds number of 2000 for the above specified g/w ratios.

The flow inside the test channel was observed to be forward, reverse or stagnant for both Newtonian fluid (water) and Non-Newtonian fluids. The 'flat plate' obstruction geometry produced the maximum reverse flow inside the test channel compared with other obstruction geometries for both Newtonian and non-Newtonian fluids. The magnitude of the reverse flow for both non-Newtonian fluids used in this study is observed to be half of the magnitude of the reverse flow for water. The maximum reverse flow for non-Newtonian fluids occurs at g/w ratio of 1.0 whereas for Newtonian fluid (water) it occurs at g/w ratio of 1.5.)

The two flow parameters namely, the size and shapes of the obstruction geometries and the gap between the test channel and the obstruction geometries have the strongest influence on the flow phenomena. The Reynolds number has also a strong influence whereas the test channel length has a negligible influence on the flow phenomena.

The numerical simulations using CFD-ACE+ found that the numerically predicted streamlines and velocity vectors of the flow phenomena are in good agreement with the streak lines of the flow visualization images. It was also found that the numerical model used for this study can be generally applied for the prediction of the flow behaviour in the channel with obstruction at the entry.

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Franklin, Bridget. "Obstructions to the Concordance of Satellite Knots." Thesis, 2012. http://hdl.handle.net/1911/64620.

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Formulas which derive common concordance invariants for satellite knots tend to lose information regarding the axis a of the satellite operation R(a,J). The Alexander polynomial, the Blanchfield linking form, and Casson-Gordon invariants all fail to distinguish concordance classes of satellites obtained by slightly varying the axis. By applying higher-order invariants and using filtrations of the knot concordance group, satellite concordance may be distinguished by determining which term of the derived series of the fundamental group of the knot complement the axes lie. There is less hope when the axes lie in the same term. We introduce new conditions to distinguish these latter classes by considering the axes in higher-order Alexander modules in three situations. In the first case, we find that R(a,J) and R(b,J) are non-concordant when a and b have distinct orders viewed as elements of the classical Alexander module of R. In the second, we show that R(a,J) and R(b,J) may be distinguished when the classical Blanchfield form of a with itself differs from that of b with itself. Ultimately, this allows us to find infinitely many concordance classes of R(-,J) whenever R has nontrivial Alexander polynomial. Finally, we find sufficient conditions to distinguish these satellites when the axes represent equivalent elements of the classical Alexander module by analyzing higher-order Alexander modules and localizations thereof.
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Amiss, David Scott Cameron. "Obstructions to Motion Planning by the Continuation Method." Thesis, 2012. http://hdl.handle.net/1974/7703.

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The subject of this thesis is the motion planning algorithm known as the continuation method. To solve motion planning problems, the continuation method proceeds by lifting curves in state space to curves in control space; the lifted curves are the solutions of special initial value problems called path-lifting equations. To validate this procedure, three distinct obstructions must be overcome. The first obstruction is that the endpoint maps of the control system under study must be twice continuously differentiable. By extending a result of A. Margheri, we show that this differentiability property is satisfied by an inclusive class of time-varying fully nonlinear control systems. The second obstruction is the existence of singular controls, which are simply the singular points of a fixed endpoint map. Rather than attempting to completely characterize such controls, we demonstrate how to isolate control systems for which no controls are singular. To this end, we build on the work of S. A. Vakhrameev to obtain a necessary and sufficient condition. In particular, this result accommodates time-varying fully nonlinear control systems. The final obstruction is that the solutions of path-lifting equations may not exist globally. To study this problem, we work under the standing assumption that the control system under study is control-affine. By extending a result of Y. Chitour, we show that the question of global existence can be resolved by examining Lie bracket configurations and momentum functions. Finally, we show that if the control system under study is completely unobstructed with respect to a fixed motion planning problem, then its corresponding endpoint map is a fiber bundle. In this sense, we obtain a necessary condition for unobstructed motion planning by the continuation method.
Thesis (Ph.D, Chemical Engineering) -- Queen's University, 2012-12-18 20:53:43.272
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Book chapters on the topic "Obstruction geometries"

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Andrzejewski, Pawel. "Equivariant finiteness obstruction and its geometric applications - A survey." In Lecture Notes in Mathematics, 20–37. Berlin, Heidelberg: Springer Berlin Heidelberg, 1991. http://dx.doi.org/10.1007/bfb0084735.

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Mulmuley, Ketan, and Milind Sohoni. "Geometric Complexity Theory, P vs. NP and Explicit Obstructions." In Advances in Algebra and Geometry, 239–61. Gurgaon: Hindustan Book Agency, 2003. http://dx.doi.org/10.1007/978-93-86279-12-5_20.

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Ranicki, Andrew. "THE EVEN-DIMENSIONAL SURGERY OBSTRUCTION." In Algebraic and Geometric Surgery, 247–301. Oxford University Press, 2002. http://dx.doi.org/10.1093/acprof:oso/9780198509240.003.0011.

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Ranicki, Andrew. "THE ODD-DIMENSIONAL SURGERY OBSTRUCTION." In Algebraic and Geometric Surgery, 302–39. Oxford University Press, 2002. http://dx.doi.org/10.1093/acprof:oso/9780198509240.003.0012.

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Duchin, Moon. "Hyperbolic Groups." In Office Hours with a Geometric Group Theorist. Princeton University Press, 2017. http://dx.doi.org/10.23943/princeton/9780691158662.003.0009.

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This chapter deals with hyperbolic groups. It begins with an overview of curvature, a fundamental way of understanding the intrinsic geometry of manifolds, and its three regimes—positive, zero, and negative. In terms of surfaces, each regime corresponds to the sphere, the plane, and the saddle, respectively. The chapter proceeds by considering the definition of hyperbolicity in terms of triangles in trees, thin triangles, insize, the four-point condition, and invariance. It then looks at some examples of groups and spaces that are δ‎–hyperbolic and some obstructions to δ‎–hyperbolicity. It also explores surface groups and some qualitative geometric properties of hyperbolic spaces before concluding with an analysis of a property of hyperbolic groups that seems combinatorial: every hyperbolic group possesses an algorithm to solve the word problem. The discussion includes exercises and research projects.
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Conference papers on the topic "Obstruction geometries"

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Stark, Henry, and Peyma Oskoui-Fard. "Geometry-Free X-Ray Reconstruction Using the Theory of Convex Projections." In Machine Vision. Washington, D.C.: Optica Publishing Group, 1987. http://dx.doi.org/10.1364/mv.1987.tha5.

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In problems involving inspection by x-ray tomography it may not always be possible to obtain a full set of parallel-beam or fan-beam views from which to reconstruct an image. This may occur because of: 1) external obstructions; 2) internal obstruction; and 3) restricted data acquisition times. Yet typical reconstruction algorithms such as convolution-back projection (CBP) or the direct Fourier method (DFM) are based on specific geometries and a full set of views.
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Malikov, German, Vladimir Lisienko, Roman Koptelov, Jakov Kalugin, and Raymond Viskanta. "A Numerical Investigation of Ray Tracing Method in a View Factor Calculation Procedure for Zonal Radiation Heat Transfer in Complex Systems." In ASME 2009 International Mechanical Engineering Congress and Exposition. ASMEDC, 2009. http://dx.doi.org/10.1115/imece2009-10429.

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In this paper a variety of well known computer graphics algorithms (Binary Spatial Partitioning-BSP, Bounding Box-BB, and direct method of sequential search) for ray tracing are studied numerically in the context of the view factor calculations for the zonal method of radiation heat transfer analysis in complex industrial furnace geometries. The paper reports on a modified BSP algorithm which takes into account the specific types of obstructions and their arrangement in different types of metallurgical furnaces. The modified algorithm enhances the ray tracing calculations by two to three orders of magnitude. An universal algorithm to obtain an intersection with a polyhedron obstruction is developed. The method is tested for simple three dimensional and complex furnace geometries.
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Doerffer, S. S., D. C. Groeneveld, K. F. Rudzinski, I. L. Pioro, and J. W. Martin. "Some Aspects of Critical-Heat-Flux Enhancement in Tubes." In ASME 2000 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2000. http://dx.doi.org/10.1115/imece2000-1518.

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Abstract This paper summarizes the effects of various types or numbers of critical-heat-flux (CHF)-enhancing inserts in tubular geometries. The impact of inserts on CHF is frequently expressed by an enhancement ratio K: the ratio of CHF with an insert to the CHF in a bare tube for the same local flow conditions. The impact on K of the following parameters was investigated: (i) fluid type (Freon-134a, water), (ii) axial spacing between inserts, (iii) shape of the insert, (iv) flow blockage of the insert, (v) number of similar/dissimilar insert planes upstream, and (vi) impact of flow conditions. The spacing and flow-obstruction area were found to be the major geometric factors that affected K: by decreasing the relative spacing, L/D, to 16, K can reach a value of from 2 to 3, depending on the flow-obstruction area. Among flow parameters, the critical quality, xc, usually has a strong effect on K: K can increase from a value of 1 to 3, when xc increases from 0 to 0.4 for a mass flux G ≥ 2 Mg/m2s. For G &lt; 2 Mg/m2s, CHF enhancement can disappear or become negative (K &lt; 1). No cumulative effect was found on K for a series of upstream insert planes. CHF enhancement does not depend on fluid type, provided that the conditions in the fluids meet the CHF fluid-to-fluid modelling requirements.
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Saini, Satyam, Kaustubh K. Adsul, Pardeep Shahi, Amirreza Niazmand, Pratik Bansode, and Dereje Agonafer. "CFD Modeling of the Distribution of Airborne Particulate Contaminants Inside Data Center Hardware." In ASME 2020 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/ipack2020-2590.

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Abstract Modern-day data center administrators are finding it increasingly difficult to lower the costs incurred in mechanical cooling of their IT equipment. This is especially true for high-performance computing facilities like Artificial Intelligence, Bitcoin Mining, and Deep Learning, etc. Airside Economization or free air cooling has been out there as a technology for a long time now to reduce the mechanical cooling costs. In free air cooling, under favorable ambient conditions of temperature and humidity, outside air can be used for cooling the IT equipment. In doing so, the IT equipment is exposed to sub-micron particulate/gaseous contaminants that might enter the data center facility with the cooling airflow. The present investigation uses a computational approach to model the airflow paths of particulate contaminants entering inside the IT equipment using a commercially available CFD code. A Discrete Phase Particle modeling approach is chosen to calculate trajectories of the dispersed contaminants. Standard RANS approach is used to model the airflow in the airflow and the particles are superimposed on the flow field by the CFD solver using Lagrangian particle tracking. The server geometry was modeled in 2-D with a combination of rectangular and cylindrical obstructions. This was done to comprehend the effect of change in the obstruction type and aspect ratio on particle distribution. Identifying such discrete areas of contaminant proliferation based on concentration fields due to changing geometries will help with the mitigation of particulate contamination related failures in data centers.
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Rouleau, Leonie, Joanna Rossi, Jean-Claude Tardif, Rosaire Mongrain, and Richard L. Leask. "Inflammatory Response of Endothelial Cells to Wall Shear Stress in Three Dimensional Stenotic Models." In ASME 2009 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2009. http://dx.doi.org/10.1115/sbc2009-206669.

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Endothelial cells (ECs) are believed to respond differentially to hemodynamic forces in the vascular tree. Once atherosclerotic plaque has formed in a vessel, the obstruction creates complex spatial gradients in wall shear stress (WSS). In vitro models have used mostly unrealistic and simplified geometries, which cannot reproduce accurately physiological conditions. The objective of this study was to expose ECs to the complex WSS pattern created by an asymmetric stenosis. Endothelial cells were grown and exposed for different times to physiological steady flows in straight dynamic controls and in idealized asymmetric stenosis models. Cell morphology was noticeably different in the regions with spatial WSS gradients, being more randomly oriented and of cobblestone shape. Inflammatory molecule expression was also altered by exposure to shear and endothelial nitric oxide synthase (eNOS) was upregulated by its presence. A regional response in terms of inflammation was observed through confocal microscopy. This work provides a more realistic model to study endothelial cell response to spatial and temporal WSS gradients that are present in vivo and is an important advancement towards a better understanding of the mechanisms involved in coronary artery disease.
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Chen, Po-Hsin, and Ming-Wen Chang. "Projective effect of a Ronchi ruling with an extended light source." In OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1989. http://dx.doi.org/10.1364/oam.1989.thm6.

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In the production of moire fringes by the obstruction theory, the relationship between the light source and a single Ronchi ruling is observed. A uniform extended light source is imaged by a TV camera with the insertion of a grating between light source and camera. The image of the light source overlaps the projection of the grating. When the grating moves away from the light source, the image pattern varies periodically with the change in distance between light source and grating. The effect can be explained with geometric optics imaging theory combined with the geometric projection principle of the point source to an obstructing object.
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Ferreira, Ana C. M., Senhorinha F. C. F. Teixeira, and Jose´ C. F. Teixeira. "Contributions to the Study of Blood Flow in the Abdominal Aorta and Its Branches." In ASME 2009 International Mechanical Engineering Congress and Exposition. ASMEDC, 2009. http://dx.doi.org/10.1115/imece2009-13028.

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Cardiovascular diseases are a major cause of death. Their development through the deposition of plaques onto the arteries and the subsequent formation of stenosis greatly affects the blood flow in the vascular system. Blood flow patterns depend on different factors, being the rheological characteristics of blood one of the most important. Although various publications have been dedicated to the study of blood flow in various geometries, they mostly assume the arteries as a rigid boundary. In the present work, the effect of the artery’s wall deformation upon the flow patterns is investigated. Therefore, the prime goal of this study consists in the development of numerical models able to predict the blood flow in the region of abdominal aorta under deformable boundaries. The simulation was performed using adaptative dynamic meshes into the finite volume FLUENT software, in order to evaluate the influence of increasing the stenosis degree in the blood flow. The results show the influence of the deformable boundary upon the length and location of the recirculation zone downstream of the stenosis and also in the wall shear stress distribution and pressure drop across the obstruction. An experimental test facility was developed in order to validate the numerical results. A cam profile coupled with electro valves duplicates the periodic flow of the cardiac cycle observed in the iliac bifurcation. The results evidence that the severity of the stenosis affects the distribution of the velocity profiles across the obstructed vessel’s section. It is also shown that the development of recirculation areas increases with the stenosis degree in post stenotic regions.
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Nanda, Aditya, and M. Amin Karami. "Energy Harvesting From Arterial Blood Pressure for Embedded Brain Sensing." In ASME 2016 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/detc2016-60573.

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This paper investigates energy harvesting from arterial blood pressure via the piezoelectric effect for the purpose of powering embedded micro-sensors in the brain. Blood flow is highly dynamic and arterial blood pressure varies, in the average human blood vessel, from 120 mm of Hg to 80 mm of Hg and we look at transduction of this pressure variation to electric energy via the piezoelectric effect. We propose two different geometries for this purpose. Initially, we look at the energy harvested by a cylinder, coated with PVDF (Polyvinylidene fluoride) patches, placed inside an artery acted upon by blood pressure. The arrangement is similar to that of a stent which is a cylinder placed in veins and arteries to prevent obstruction in blood flow. The governing equations of the harvester are obtained using Hamilton’s principle. Pressure acting in arteries is radially directed and this is used to simplify the governing equations. Specifically, radial pressure directed on the inner wall of the cylinder is assumed to excite only the radial breathing mode of vibration. Using this, the transfer function relating pressure to the induced voltage across the surface of the harvester is derived and the power harvested by the cylindrical harvester is obtained for different shunt resistances. However, the natural frequency of the radial breathing mode (RBM) is found to be very high and the harvested power at the frequencies of interest (3 Hz – 20 Hz) is very low. To decrease the natural frequency, we propose a novel streaked cylinder design that involves cutting the cylinder along the length, transforming it to a curved beam with an opening angle of 360 deg.. The governing equations corresponding to a circular curved beam, with PVDF patches on top and bottom surfaces, are derived using Hamilton’s principle and modal analysis is used to obtain the transfer function relating radial pressure to induced voltage. We validate the derived transfer function by evaluating the harvested power for a beam with very large radius of curvature; in which case, the curved beam becomes a straight beam and the harvested power is compared with the same for a straight beam (which exists in the literature). Further, we conduct design analyses and obtain the power as the geometric parameters of the harvester are varied for the purpose of optimizing the dimensions of harvester for maximal power generation. The power harvested by the harvester, at lower frequencies is deemed to be satisfactory.
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Burgisser, Peter, Christian Ikenmeyer, and Greta Panova. "No Occurrence Obstructions in Geometric Complexity Theory." In 2016 IEEE 57th Annual Symposium on Foundations of Computer Science (FOCS). IEEE, 2016. http://dx.doi.org/10.1109/focs.2016.49.

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Reusser, R. S., D. E. Chimenti, S. D. Holland, R. A. Roberts, Donald O. Thompson, and Dale E. Chimenti. "PLATE WAVE TRANSMISSION∕REFLECTION AT GEOMETRIC OBSTRUCTIONS: EXPERIMENT." In REVIEW OF PROGRESS IN QUANTITATIVE NONDESTRUCTIVE EVALUATION VOLUME 29. AIP, 2010. http://dx.doi.org/10.1063/1.3362361.

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