To see the other types of publications on this topic, follow the link: Obstruction geometries.
Journal articles on the topic 'Obstruction geometries'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 39 journal articles for your research on the topic 'Obstruction geometries.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse journal articles on a wide variety of disciplines and organise your bibliography correctly.
1
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.
Full textAbstract:
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.
2
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.
Full textAbstract:
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.
3
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.
Full textAbstract:
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.
4
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.
Full textAbstract:
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.
5
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.
Full textAbstract:
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.
6
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.
Full textAbstract:
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.
7
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.
Full textAbstract:
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.
8
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.
Full textAbstract:
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.
9
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.
Full textAbstract:
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.
10
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.
Full textAbstract:
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.
11
Tutzauer, P., S. Becker, T. Niese, O. Deussen, and D. Fritsch. "UNDERSTANDING HUMAN PERCEPTION OF BUILDING CATEGORIES IN VIRTUAL 3D CITIES - A USER STUDY." ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLI-B2 (June 8, 2016): 683–87. http://dx.doi.org/10.5194/isprs-archives-xli-b2-683-2016.
Full textAbstract:
Virtual 3D cities are becoming increasingly important as a means of visually communicating diverse urban-related information. To get a deeper understanding of a human’s cognitive experience of virtual 3D cities, this paper presents a user study on the human ability to perceive building categories (e.g. residential home, office building, building with shops etc.) from geometric 3D building representations. The study reveals various dependencies between geometric properties of the 3D representations and the perceptibility of the building categories. Knowledge about which geometries are relevant, helpful or obstructive for perceiving a specific building category is derived. The importance and usability of such knowledge is demonstrated based on a perception-guided 3D building abstraction process.
12
Tutzauer, P., S. Becker, T. Niese, O. Deussen, and D. Fritsch. "UNDERSTANDING HUMAN PERCEPTION OF BUILDING CATEGORIES IN VIRTUAL 3D CITIES - A USER STUDY." ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLI-B2 (June 8, 2016): 683–87. http://dx.doi.org/10.5194/isprsarchives-xli-b2-683-2016.
Full textAbstract:
Virtual 3D cities are becoming increasingly important as a means of visually communicating diverse urban-related information. To get a deeper understanding of a human’s cognitive experience of virtual 3D cities, this paper presents a user study on the human ability to perceive building categories (e.g. residential home, office building, building with shops etc.) from geometric 3D building representations. The study reveals various dependencies between geometric properties of the 3D representations and the perceptibility of the building categories. Knowledge about which geometries are relevant, helpful or obstructive for perceiving a specific building category is derived. The importance and usability of such knowledge is demonstrated based on a perception-guided 3D building abstraction process.
13
Liu, Hongliang, Mads Henrik Strand Moxness, Victorien Emile Prot, and Bjørn Helge Skallerud. "Palatal implant surgery effectiveness in treatment of obstructive sleep apnea: A numerical method with 3D patient-specific geometries." Journal of Biomechanics 66 (January 2018): 86–94. http://dx.doi.org/10.1016/j.jbiomech.2017.11.006.
Full text
14
Bosse, Léo, Jean Lilensten, Nicolas Gillet, Colette Brogniez, Olivier Pujol, Sylvain Rochat, Alain Delboulbé, Stéphane Curaba, and Magnar Gullikstad Johnsen. "At the source of the polarisation of auroral emissions: experiments and modeling." Journal of Space Weather and Space Climate 12 (2022): 7. http://dx.doi.org/10.1051/swsc/2022004.
Full textAbstract:
A polarised radiative transfer model (POMEROL) has been developed to compute the polarisation measured by a virtual instrument in a given nocturnal environment. This single-scattering model recreates real-world conditions (among them atmospheric and aerosol profiles, light sources with complex geometries at the ground and in the sky, terrain obstructions). It has been successfully tested at mid-latitudes where sky emissions are of weak intensity. We show a series of comparisons between POMEROL predictions and polarisation measurements during two field campaigns in the auroral zone, in both quiet and active conditions. These comparisons show the strength of the model to assess the aerosol characteristics in the lower atmosphere by using a mesospheric line. They also show that three main upper atmosphere emissions must be polarised: the green atomic oxygen line at 557.7 nm and the 1st N2+ negative band at 391.4 nm (purple) and 427.8 nm (blue). This polarisation can be either created directly at the radiative de-excitation or may occur when the non-polarised emission crosses the ionospheric currents. We provide some of the potentialities it offers in the frame of space weather. These require refinements of the preliminary modeling approach considered in the present study.
15
KARIMPOUR, H., and E. JAVDAN. "SIMULATION OF STENOSIS GROWTH IN THE CAROTID ARTERY BY LATTICE BOLTZMANN METHOD." Journal of Mechanics in Medicine and Biology 14, no. 02 (March 10, 2014): 1450016. http://dx.doi.org/10.1142/s021951941450016x.
Full textAbstract:
Atherosclerosis, as the leading cause of mortality, is usually regarded as a systemic disease and several well-identified risk factors have been implicated in its pathogenesis. Low or highly oscillatory wall shear stress has mainly been linked to the development of atherosclerosis. Conditions under which human blood can be considered Newtonian for the purpose of arterial flow modeling are investigated with emphasis on near wall shear stresses. The Lattice Boltzmann method is implemented in parallel for both Newtonian and non-Newtonian models of blood and then examined in the context of steady and oscillatory flows. As the lattice method permits to adjust the morphology of the computational domain during the solving process, the artery walls are reshaped in a recursive manner by the progressive accumulation of deposits according to the conventional OSI criterion. Regions subjected to partial obstructions identified qualitatively well with those susceptible to atherosclerosis in the in vivo sample, thereby approving this criterion by verifying its accumulative effect. The present work demonstrates the suitability of LB method for studying flows across geometries that transform due to atherosclerotic progression and permits to explain the trend of deposit distribution across time.
16
Si, Xiuhua April, and Jinxiang Xi. "Deciphering Exhaled Aerosol Fingerprints for Early Diagnosis and Personalized Therapeutics of Obstructive Respiratory Diseases in Small Airways." Journal of Nanotheranostics 2, no. 3 (June 22, 2021): 94–117. http://dx.doi.org/10.3390/jnt2030007.
Full textAbstract:
Respiratory diseases often show no apparent symptoms at their early stages and are usually diagnosed when permanent damages have been made to the lungs. A major site of lung pathogenesis is the small airways, which make it highly challenging to detect using current techniques due to the diseases’ location (inaccessibility to biopsy) and size (below normal CT/MRI resolution). In this review, we present a new method for lung disease detection and treatment in small airways based on exhaled aerosols, whose patterns are uniquely related to the health of the lungs. Proof-of-concept studies are first presented in idealized lung geometries. We subsequently describe the recent developments in feature extraction and classification of the exhaled aerosol images to establish the relationship between the images and the underlying airway remodeling. Different feature extraction algorithms (aerosol density, fractal dimension, principal mode analysis, and dynamic mode decomposition) and machine learning approaches (support vector machine, random forest, and convolutional neural network) are elaborated upon. Finally, future studies and frequent questions related to clinical applications of the proposed aerosol breath testing are discussed from the authors’ perspective. The proposed breath testing has clinical advantages over conventional approaches, such as easy-to-perform, non-invasive, providing real-time feedback, and is promising in detecting symptomless lung diseases at early stages.
17
Toledo, Mauricio J., and Valeria Isamitt. "A Proposal for Controlling Work Progress on Excavation Projects Using Digital Photographs." Advanced Engineering Forum 21 (March 2017): 397–404. http://dx.doi.org/10.4028/www.scientific.net/aef.21.397.
Full textAbstract:
Current practice in excavation projects is characterized by a deficient control of work progress that includes estimates of daily work progress by indirect means such as manual records of truck movements, estimates of soil swelling and occasional topographic measurements (usually at start and end of projects). In this article we propose a procedure to calculate earth work volume and progress by using geotagged digital photographs taken at the construction site. This methodology helps construction managers to improve excavation progress control and it systematizes excavation records. The procedure is grounded on literature review, the experience gained from controlled experiments and its application on a case study. With a relatively low effort (approx. 3 hrs.) the proposal enabled us to measure excavation work progress from around 50 geotagged digital photos with a precision of about 8-10% as compared to the traditional excavation volume estimate obtained from truck movement records. Best results were realized for large earth movements recorded on a weekly basis. Precision decreased for small earth movements (e.g., daily work progress control). The proposal includes recommendations for capturing the digital photos; formation of a point cloud model using photogrammetric software; formation of a mesh model and calculation of the excavation volume. Considerations for obstructing construction equipment and complex geometries are included.
18
Yang, Fan, Mahdieh Babaiasl, and John P. Swensen. "Fracture-Directed Steerable Needles." Journal of Medical Robotics Research 04, no. 01 (March 2019): 1842002. http://dx.doi.org/10.1142/s2424905x18420023.
Full textAbstract:
Steerable needles hold the promise of improving the accuracy of both therapies and biopsies as they are able to steer to a target location around obstructions, correct for disturbances, and account for movement of internal organs. However, their ability to make late-insertion corrections has always been limited by the lower bound on the attainable radius of curvature. This paper presents a new class of steerable needle insertion where the objective is to first control the direction of tissue fracture with an inner stylet and later follow with the hollow needle. This method is shown to be able to achieve radius of curvature as low as 6.9[Formula: see text]mm across a range of tissue stiffnesses and the radius of curvature is controllable from the lower bound up to a near infinite radius of curvature based on the stylet/needle step size. The approach of “fracture-directed” steerable needles indicates the promise of the technique for providing a tissue-agnostic method of achieving high steerability that can account for variability in tissues during a typical procedure and achieve radii of curvature unattainable through current bevel-tipped techniques. A variety of inner stylet geometries are investigated using tissue phantoms with multiple stiffnesses and discrete-step kinematic models of motion are derived heuristically from the experiments. The key finding presented is that it is the geometry of the stylet and the tuning of the bending stiffnesses of both the stylet and the tube, relative to the stiffness of the tissue, that allow for such small radius of curvature even in very soft tissues.
19
Poorbahrami, Kamran, David G. Mummy, Sean B. Fain, and Jessica M. Oakes. "Patient-specific modeling of aerosol delivery in healthy and asthmatic adults." Journal of Applied Physiology 127, no. 6 (December 1, 2019): 1720–32. http://dx.doi.org/10.1152/japplphysiol.00221.2019.
Full textAbstract:
The magnitude and regional heterogeneity of airway obstructions in severe asthmatics is likely linked to insufficient drug delivery, as evidenced by the inability to mitigate exacerbations with inhaled aerosol medications. To understand the correlation between morphometric features, airflow distribution, and inhaled dosimetry, we perform dynamic computational simulations in two healthy and four asthmatic subjects. Models incorporate computed tomography-based and patient-specific central airway geometries and hyperpolarized 3He MRI-measured segmental ventilation defect percentages (SVDPs), implemented as resistance boundary conditions. Particles [diameters ( dp) = 1, 3, and 5 μm] are simulated throughout inhalation, and we record their initial conditions, both spatially and temporally, with their fate in the lung. Predictions highlight that total central airway deposition is the same between the healthy subjects (26.6%, dp = 3 μm) but variable among the asthmatic subjects (ranging from 5.9% to 59.3%, dp = 3 μm). We found that by preferentially releasing the particles during times of fast or slow inhalation rates we enhance either central airway deposition percentages or peripheral particle delivery, respectively. These predictions highlight the potential to identify with simulations patients who may not receive adequate therapeutic dosages with inhaled aerosol medication and therefore identify patients who may benefit from alternative treatment strategies. Furthermore, by improving regional dose levels, we may be able to preferentially deliver drugs to the airways in need, reducing associated adverse side effects. NEW & NOTEWORTHY Although it is evident that exacerbation mitigation is unsuccessful in some asthmatics, it remains unclear whether or not these patients receive adequate dosages of inhaled therapeutics. By coupling MRI and computed tomography data with patient-specific computational models, our predictions highlight the large intersubject variability, specifically in severe asthma.
20
Herfray, Yannick. "Carrollian manifolds and null infinity: A view from Cartan geometry." Classical and Quantum Gravity, April 2, 2022. http://dx.doi.org/10.1088/1361-6382/ac635f.
Full textAbstract:
Abstract We discuss three different (conformally) Carrollian geometries and their relation to null infinity from the unifying perspective of Cartan geometry. Null infinity \emph{per se} comes with numerous redundancies in its intrinsic geometry and the two other Carrollian geometries can be recovered by making successive choices of gauge. This clarifies the extent to which one can think of null infinity as being a (strongly) Carrollian geometry and we investigate the implications for the corresponding Cartan geometries. The perspective taken, which is that characteristic data for gravity at null infinity are equivalent to a Cartan geometry for the Poincaré group, gives a precise geometrical content to the fundamental fact that ``gravitational radiation is the obstruction to having the Poincaré group as asymptotic symmetries''.
21
Hung, Sheng Po, and Wei-Hsin Tien. "Visualization of Three-Dimensional Acoustic Streaming Flow Patterns around an Inclined Triangular Obstruction using Digital In-Line Holographic Micro-Particle Tracking Velocimetry." 14th International Symposium on Particle Image Velocimetry 1, no. 1 (August 1, 2021). http://dx.doi.org/10.18409/ispiv.v1i1.59.
Full textAbstract:
Acoustic Streaming is a flow phenomenon with many applications in the field of microfluidics, such as micro mixing[1, 2] and particle manipulation[3]. With the manufacturing techniques evolves, more complicated geometries can be designed for microfluidic device and 3-D acoustic streaming patterns may occurs. In this study, 3-D trajectories of particle induced by acoustic streaming around an inclined triangular obstruction in a microchannel were visualized by a volumetric tracking method using Digital Inline Holographic Microscopy (DIHM)[4-6]. The triangular obstruction has a tip angle of 20° and an inclined angle of 30°. The acoustic streaming is created under 12 kHz oscillation of a piezo plate driven by 20V voltage. Illuminated by a 450nm continuous laser, the magnified hologram of the motion of 1.79μm tracer particles was recorded by a low-cost 10X industrial microscope with a machine vision camera of 10 fps (frames per second). Using RayleighSommerfeld back-propagation method[7], particle locations was reconstructed frame by frame and 3-D tracking of individual particles was performed afterwards. The trajectories of each particle were reconstructed to reveal the vortical structure of the acoustic streaming flow. For the current system setup, the measurable range was estimated to be 550×685×840 μm3. The 3-D location reconstruction accuracy was verified with a calibration target and the location sensitivity was found to be linear throughout the measurable range. Reconstruction at different depth locations show that the dick-shaped calibration dots and the spherical polystyrene particles have different intensity profiles. The calibration dots show local minimum of intensity at the correct depth location, while polystyrene particles show local maximum of intensity instead. Resolved particle trajectories show that the acoustic streaming flows cause particles to move with 3-D spiral shaped motions near the side of the triangular obstruction, while particles away from the obstruction shows planar motions.
22
Chassagne, Fanette, Sujatha Buddhe, Lester Permut, David MCMULLAN, Stephen P. Seslar, and Alberto Aliseda. "Abstract 10570: A New Method for Planning the Surgical Repair of Pediatric Aortic Coarctation: In vitro Design and Performance Evaluation." Circulation 144, Suppl_1 (November 16, 2021). http://dx.doi.org/10.1161/circ.144.suppl_1.10570.
Full textAbstract:
Introduction: The surgical treatment of severe aortic coarctation associated with arch hypoplasia combines resection of the stenosed tissue and enlargement of the aortic arch with a patch, designed by the surgeon in the OR. This work aims at creating an a priori design method for the patch and evaluating the success of the treatment by measuring the restoration of flow. Methods: Treatment was virtually implemented on segmented patient’s CT images based on the surgeons’ experience, identifying the zone to resect and the start of the lumen-widening, and optimized through CFD simulations The optimal patch geometry template was 3D-printed and used to perform surgery on in vitro silicon models of the aorta. Repairs were performed by an experienced surgeon using two patch geometries: the optimal patch template designed by our methodology and the patch designed by experience (traditional method). The geometry of the lumen resulting from the surgery was obtained from micro-CTs of the models. Finally, CFD simulations were performed for these geometries to evaluate the two repairs. Results: All repairs showed significant increases in aortic flowrate and decreases in pressure gradient. The virtually repaired geometry resulted in a 3-fold increase in flowrate and complete resolution of the obstruction. The traditional repair and the optimal patch repair showed similar effects on flow rate (+300%), and the traditional repair showed no remaining pressure gradient. All repairs reduced the stenosis-induced jet. However, the traditional repair led to large recirculation zones, potentially increasing the risk of thrombosis and pathological aortic remodeling. Conclusion: A novel method, combining in vitro and in silico approaches, was created to help surgical planning. This approach predicted flow and pressure gradients for the evaluation of the repair, but also provided the flow topology that should be taken into consideration to avoid hemodynamics-related complications.
23
Jensen, David, and Dhruv Ranganathan. "Brill-Noether theory for curves of a fixed gonality." Forum of Mathematics, Pi 9 (2021). http://dx.doi.org/10.1017/fmp.2020.14.
Full textAbstract:
Abstract We prove a generalisation of the Brill-Noether theorem for the variety of special divisors $W^r_d(C)$ on a general curve C of prescribed gonality. Our main theorem gives a closed formula for the dimension of $W^r_d(C)$ . We build on previous work of Pflueger, who used an analysis of the tropical divisor theory of special chains of cycles to give upper bounds on the dimensions of Brill-Noether varieties on such curves. We prove his conjecture, that this upper bound is achieved for a general curve. Our methods introduce logarithmic stable maps as a systematic tool in Brill-Noether theory. A precise relation between the divisor theory on chains of cycles and the corresponding tropical maps theory is exploited to prove new regeneration theorems for linear series with negative Brill-Noether number. The strategy involves blending an analysis of obstruction theories for logarithmic stable maps with the geometry of Berkovich curves. To show the utility of these methods, we provide a short new derivation of lifting for special divisors on a chain of cycles with generic edge lengths, proved using different techniques by Cartwright, Jensen, and Payne. A crucial technical result is a new realisability theorem for tropical stable maps in obstructed geometries, generalising a well-known theorem of Speyer on genus $1$ curves to arbitrary genus.
24
Jensen, David, and Dhruv Ranganathan. "Brill-Noether theory for curves of a fixed gonality." Forum of Mathematics, Pi 9 (2021). http://dx.doi.org/10.1017/fmp.2020.14.
Full textAbstract:
Abstract We prove a generalisation of the Brill-Noether theorem for the variety of special divisors $W^r_d(C)$ on a general curve C of prescribed gonality. Our main theorem gives a closed formula for the dimension of $W^r_d(C)$ . We build on previous work of Pflueger, who used an analysis of the tropical divisor theory of special chains of cycles to give upper bounds on the dimensions of Brill-Noether varieties on such curves. We prove his conjecture, that this upper bound is achieved for a general curve. Our methods introduce logarithmic stable maps as a systematic tool in Brill-Noether theory. A precise relation between the divisor theory on chains of cycles and the corresponding tropical maps theory is exploited to prove new regeneration theorems for linear series with negative Brill-Noether number. The strategy involves blending an analysis of obstruction theories for logarithmic stable maps with the geometry of Berkovich curves. To show the utility of these methods, we provide a short new derivation of lifting for special divisors on a chain of cycles with generic edge lengths, proved using different techniques by Cartwright, Jensen, and Payne. A crucial technical result is a new realisability theorem for tropical stable maps in obstructed geometries, generalising a well-known theorem of Speyer on genus $1$ curves to arbitrary genus.
25
Bik, Arthur, and Henrik Eisenmann. "The geometries of Jordan nets and Jordan webs." Annali di Matematica Pura ed Applicata (1923 -), April 6, 2022. http://dx.doi.org/10.1007/s10231-022-01204-y.
Full textAbstract:
AbstractA Jordan net (resp. web) is an embedding of a unital Jordan algebra of dimension 3 (resp. 4) into the space $${\mathbb{S}}^n$$ S n of symmetric $$n\times n$$ n × n matrices. We study the geometries of Jordan nets and webs: we classify the congruence orbits of Jordan nets (resp. webs) in $${\mathbb{S}}^n$$ S n for $$n\le 7$$ n ≤ 7 (resp. $$n\le 5$$ n ≤ 5 ), we find degenerations between these orbits and list obstructions to the existence of such degenerations. For Jordan nets in $$\mathbb{S}^n$$ S n for $$n\le 5$$ n ≤ 5 , these obstructions show that our list of degenerations is complete . For $$n=6$$ n = 6 , the existence of one degeneration is still undetermined. To explore further, we used an algorithm that indicates numerically whether a degeneration between two orbits exists. We verified this algorithm using all known degenerations and obstructions and then used it to compute the degenerations between Jordan nets in $$\mathbb {S}^7$$ S 7 and Jordan webs in $$\mathbb {S}^n$$ S n for $$n=4,5$$ n = 4 , 5 .
26
Rouleau, Leonie, Monica Farcas, Jean-Claude Tardif, Rosaire Mongrain, and Richard L. Leask. "Endothelial Cell Morphologic Response to Asymmetric Stenosis Hemodynamics: Effects of Spatial Wall Shear Stress Gradients." Journal of Biomechanical Engineering 132, no. 8 (July 29, 2010). http://dx.doi.org/10.1115/1.4001891.
Full textAbstract:
Endothelial cells are known to respond to hemodynamic forces. Their phenotype has been suggested to differ between atheroprone and atheroprotective regions of the vasculature, which are characterized by the local hemodynamic environment. Once an atherosclerotic plaque has formed in a vessel, the obstruction creates complex spatial gradients in wall shear stress. Endothelial cell response to wall shear stress may be linked to the stability of coronary plaques. Unfortunately, in vitro studies of the endothelial cell involvement in plaque stability have been limited by unrealistic and simplified geometries, which cannot reproduce accurately the hemodynamics created by a coronary stenosis. Hence, in an attempt to better replicate the spatial wall shear stress gradient patterns in an atherosclerotic region, a three dimensional asymmetric stenosis model was created. Human abdominal aortic endothelial cells were exposed to steady flow (Re=50, 100, and 200 and τ=4.5 dyn/cm2, 9 dyn/cm2, and 18 dyn/cm2) in idealized 50% asymmetric stenosis and straight/tubular in vitro models. Local morphological changes that occur due to magnitude, duration, and spatial gradients were quantified to identify differences in cell response. In the one dimensional flow regions, where flow is fully developed and uniform wall shear stress is observed, cells aligned in flow direction and had a spindlelike shape when compared with static controls. Morphological changes were progressive and a function of time and magnitude in these regions. Cells were more randomly oriented and had a more cobblestone shape in regions of spatial wall shear stress gradients. These regions were present, both proximal and distal, at the stenosis and on the wall opposite to the stenosis. The response of endothelial cells to spatial wall shear stress gradients both in regions of acceleration and deceleration and without flow recirculation has not been previously reported. This study shows the dependence of endothelial cell morphology on spatial wall shear stress gradients and demonstrates that care must be taken to account for altered phenotype due to geometric features. These results may help explain plaque stability, as cells in shoulder regions near an atherosclerotic plaque had a cobblestone morphology indicating that they may be more permeable to subendothelial transport and express prothrombotic factors, which would increase the risk of atherothrombosis.
27
Praveen Kumar, G. V., and L. Mathew. "3D CAD Based Conceptual Design of a Novel Aortic Valve Stent." Journal of Medical Devices 3, no. 2 (June 1, 2009). http://dx.doi.org/10.1115/1.3135156.
Full textAbstract:
Vascular support structures are an important tool for treating valve stenosis. A large population of patients are treated for valvular disease and the principal mode of treatment is the use of percutaneous valvuloplasty. Stent devices are proving to be an improved treatment method; these devices now account for 20% of treatments in Europe. This new technology provides highly effective results at minimal cost and short duration of hospitalization. Accurate and reliable structural analysis provides essential information to the design team in an environment where in vivio experimentation is extremely expensive, or impossible. This paper describe the design of vascular support structure (stents), to provide designers with estimates of the critical parameters which are essential to restore the functions of the endothelium of the Aorta during and after implantation without injuring it. Stent geometries were uniquely defined using the following parameters. (a) Diameter of the aorta; (b) Distance between the aortic root and the coronary artery roots; (c) Position of the coronary arteries; (d) Diameter of the coronaries; (e) Stent–Endothelium Mechanics. Keeping these parameters into consideration a novel stent model was designed to suit its requirement for percutaneous replacement. The 3D geometry of the repeatable units of the stent was generated using SOLIDWORKS modeling software. Using the repeating unit geometry of each stent design, solid models were generated. The unit consisted of 8 lips with two non crossing struts making a circular diameter of 16 mm at the center and 18 mm at either ends. The upper and the lower portions of the prosthesis has a high radial force, the upper portion flared to fix the stent firmly in the ascending aorta and the lower portion to expand against the calcified leaflets and to avoid recoil. The middle portion which bears the valve is constrained and narrower to avoid obstruction of the coronary arteries. This varying diameter of different parts of the stent creates the blunt hooks at either end of the stent. The methodology described in this paper is proposed as a method to compare and analyze the existing stents and the ones proposed here. However, further analysis and studies are needed before these stents are fabricated and deployed. Animal experiments are being planned currently for this purpose.
28
Mahmood, Fiaz, and Huasi Hu. "Obstructed View Factor Calculations for Multiple Obstructions in Closed Cavities." Journal of Nuclear Engineering and Radiation Science 5, no. 1 (January 1, 2019). http://dx.doi.org/10.1115/1.4041563.
Full textAbstract:
The inertial confinement fusion (ICF) program has been mainly concentrating on the indirect drive approach for the last three decades, due to relaxed requirements on driver-beam uniformity and reduced sensitivity to hydrodynamic instabilities. The optimal designs are important for maximum conversion of driving energy to X-rays, and finally, symmetrical irradiation of the capsule. The view factor (VF) evaluation is an important parameter providing significant radiation heat transport information in specific geometries. The present study is aimed at the VF calculations for closed cavities. The VF calculations include the case of energy transfer from one infinitesimal surface element of the enclosure to other similar infinitesimal surface elements of the cavity. Similarly, the obstructed VF is also calculated when multiple obstructions are present in the cavity. Two distinct computer programs are developed by programming in FORTRAN-90 to evaluate unobstructed VF and obstructed VF for a square geometry. The calculations are based on the crossed strings method, which is more reliable for simple geometries. The shadow effect method is used for the obstructed VF calculations. The results of the developed programs are benchmarked using the summation rule. In the case of no obstacles in the cavity, VF calculations solely obey the summation rule. However, in the presence of obstacles in the cavity, obstructed VF calculations showed the acceptable difference in comparison with the summation rule.
29
Anderson, Peter, Sidney Fels, and Sheldon Green. "Implementation and Validation of a 1D Fluid Model for Collapsible Channels." Journal of Biomechanical Engineering 135, no. 11 (October 1, 2013). http://dx.doi.org/10.1115/1.4025326.
Full textAbstract:
A 1D fluid model is implemented for the purpose of fluid-structure interaction (FSI) simulations in complex and completely collapsible geometries, particularly targeting the case of obstructive sleep apnea (OSA). The fluid mechanics are solved separately from any solid mechanics, making possible the use of a highly complex and/or black-box solver for the solid mechanics. The fluid model is temporally discretized with a second-order scheme and spatially discretized with an asymmetrical fourth-order scheme that is robust in highly uneven geometries. A completely collapsing and reopening geometry is handled smoothly using a modified area function. The numerical implementation is tested with two driven-geometry cases: (1) an inviscid analytical solution and (2) a completely closing geometry with viscous flow. Three-dimensional fluid simulations in static geometries are performed to examine the assumptions of the 1D model, and with a well-defined pressure-recovery constant the 1D model agrees well with 3D models. The model is very fast computationally, is robust, and is recommended for OSA simulations where the bulk flow pressure is primarily of interest.
30
Hume, David, John M. Mackay, and Romain Tessera. "Poincaré profiles of Lie groups and a coarse geometric dichotomy." Geometric and Functional Analysis, September 27, 2022. http://dx.doi.org/10.1007/s00039-022-00617-4.
Full textAbstract:
AbstractPoincaré profiles are analytically defined invariants, which provide obstructions to the existence of coarse embeddings between metric spaces. We calculate them for all connected unimodular Lie groups, Baumslag–Solitar groups and Thurston geometries, demonstrating two substantially different types of behaviour. For Lie groups, our dichotomy extends both the rank one versus higher rank dichotomy for semisimple Lie groups and the polynomial versus exponential growth dichotomy for solvable unimodular Lie groups. We provide equivalent algebraic, quasi-isometric and coarse geometric formulations of this dichotomy. As a consequence, we deduce that for groups of the form $$N\times S$$ N × S , where N is a connected nilpotent Lie group, and S is a rank one simple Lie group, both the growth exponent of N, and the conformal dimension of S are non-decreasing under coarse embeddings. These results are new even for quasi-isometric embeddings and give obstructions which in many cases improve those previously obtained by Buyalo–Schroeder.
31
Mojumder, Joy, Lei Fan, Thuy Nguyen, Kenneth S. Campbell, Jonathan F. Wenk, Julius M. Guccione, Theodore Abraham, and Lik Chuan Lee. "Computational analysis of ventricular mechanics in hypertrophic cardiomyopathy patients." Scientific Reports 13, no. 1 (January 18, 2023). http://dx.doi.org/10.1038/s41598-023-28037-w.
Full textAbstract:
AbstractHypertrophic cardiomyopathy (HCM) is a genetic heart disease that is associated with many pathological features, such as a reduction in global longitudinal strain (GLS), myofiber disarray and hypertrophy. The effects of these features on left ventricle (LV) function are, however, not clear in two phenotypes of HCM, namely, obstructive and non-obstructive. To address this issue, we developed patient-specific computational models of the LV using clinical measurements from 2 female HCM patients and a control subject. Left ventricular mechanics was described using an active stress formulation and myofiber disarray was described using a structural tensor in the constitutive models. Unloaded LV configuration for each subject was first determined from their respective end-diastole LV geometries segmented from the cardiac magnetic resonance images, and an empirical single-beat estimation of the end-diastolic pressure volume relationship. The LV was then connected to a closed-loop circulatory model and calibrated using the clinically measured LV pressure and volume waveforms, peak GLS and blood pressure. Without consideration of myofiber disarray, peak myofiber tension was found to be lowest in the obstructive HCM subject (60 kPa), followed by the non-obstructive subject (242 kPa) and the control subject (375 kPa). With increasing myofiber disarray, we found that peak tension has to increase in the HCM models to match the clinical measurements. In the obstructive HCM patient, however, peak tension was still depressed (cf. normal subject) at the largest degree of myofiber disarray found in the clinic. The computational modeling workflow proposed here can be used in future studies with more HCM patient data.
32
Zhou, Aitao, Meng Zhang, Kai Wang, and Derek Elsworth. "Near-source characteristics of two-phase gas–solid outbursts in roadways." International Journal of Coal Science & Technology, September 29, 2020. http://dx.doi.org/10.1007/s40789-020-00362-9.
Full textAbstract:
Abstract Coal and gas outbursts compromise two-phase gas–solid mixtures as they propagate as shock waves and flows from their sources. Propagation is influenced by the form of the outburst, proximity to source, the structure and form of the transmitting roadways and the influence of obstacles. The following characterizes the propagation of coal and gas outbursts as two-phase gas–solid flows proximal to source where the coupled effects of pulverized coal and gas flows dominate behavior. The characteristics of shock wave propagation and attenuation were systematically examined for varied roadway geometries using experiments and numerical models. The results demonstrate that the geometry of roadway obstructions is significant and may result in partial compression and sometimes secondary overpressurization in blocked and small corner roadways leading to significant attenuation of outburst shock waves. The shock waves attenuate slowly in both straight and abruptly expanding roadways and more significantly in T-shaped roadways. The most significant attenuation appears in small angle corners and bifurcations in roadways with the largest attenuation occurring in blocked roadways. These results provide basic parameters for simplifying transport in complex roadway networks in the far-field, and guidance for the design of coal and gas outburst prevention facilities and emergency rescue.
33
Rovenskaya, Olga, and Giulio Croce. "Numerical Investigation of Microflow Over Rough Surfaces: Coupling Approach." Journal of Heat Transfer 135, no. 10 (September 11, 2013). http://dx.doi.org/10.1115/1.4024500.
Full textAbstract:
A numerical analysis of the flow field in rough microchannel is carried out decomposing the computational physical domain into kinetic and continuum subdomains. Each domain size is determined by the value of a proper threshold parameter, based on the local Knudsen number and local gradients of macroparameters. This switching parameter is computed from a preliminary Navier–Stokes (NS) solution throughout the whole physical domain. The solution is then advanced in time simultaneously in both kinetic and continuum domains: The coupling is achieved by matching half fluxes at the interface of the kinetic and Navier–Stokes domains, taking care of the conservation of momentum, energy, and mass through the interface. The roughness geometry is modeled as a series of triangular obstructions with a relative roughness up to a maximum of 5% of the channel height. A wide range of Mach numbers is considered, from nearly incompressible to chocked flow conditions 0.001 ≤ Ma ≤ 0.75 and a Reynolds number up to 170. To estimate rarefaction effect, the flow at Knudsen number ranging from 0.01 to 0.08 and fixed pressure ratio has been considered. Accuracy and discrepancies between full Navier–Stokes, kinetic, and coupled solutions are discussed, assessing the range of applicability of first order slip condition in rough geometries. The effect of the roughness is discussed via Poiseuille number as a function of local Knudsen and Mach numbers.
34
Kondle, Satyanarayana, Jorge L. Alvarado, and Charles Marsh. "Laminar Heat Transfer Behavior of a Phase Change Material Fluid in Microchannels With Staggered Pins." Journal of Heat Transfer 139, no. 6 (February 28, 2017). http://dx.doi.org/10.1115/1.4035441.
Full textAbstract:
Microchannels have been studied extensively for a variety of heat transfer applications including electronic cooling. Many configurations of microchannels have been studied and compared for their effectiveness in terms of heat removal. Recently, the use of staggered pins in microchannels has gained considerable traction, since they can promote internal flow fluctuations that enhance internal heat transfer. Furthermore, staggered pins in microchannels have shown higher heat removal characteristics because of the continuous breaking and formation of the heat transfer fluid boundary layer. However, they also exhibit higher pressure drop because the pins act as flow obstructions. This paper presents numerical results of two characteristic staggered 100-μm pins (square and circular) in microchannels. The heat transfer performance of a single phase fluid (SPF) in microchannels with staggered pins, and the corresponding pressure drop characteristics are presented. Furthermore, a phase change material (PCM, n-eicosane) fluid was also considered by implementing the effective specific heat capacity model approach to account for the corresponding phase change process of PCM fluid. Comparisons of the heat transfer characteristics of single phase fluid and PCM fluid are presented for two different pin geometries and three different Reynolds numbers. Circular pins were found to be more effective in terms of heat transfer by exhibiting higher Nusselt number. Microchannels with circular pins were also found to have lower pressure drop compared to the square-pin microchannels.
35
Sankar, Maathangi, and Sandip Mazumder. "Solution of the Radiative Transfer Equation in Three-Dimensional Participating Media Using a Hybrid Discrete Ordinates: Spherical Harmonics Method." Journal of Heat Transfer 134, no. 11 (September 28, 2012). http://dx.doi.org/10.1115/1.4007129.
Full textAbstract:
In this article, a new hybrid solution to the radiative transfer equation (RTE) is proposed. Following the modified differential approximation (MDA), the radiation intensity is first split into two components: a “wall” component, and a “medium” component. Traditionally, the wall component is determined using a viewfactor-based surface-to-surface exchange formulation, while the medium component is determined by invoking the first-order spherical harmonics (P1) approximation. Recent studies have shown that although the MDA approach is accurate over a large range of optical thicknesses, it is prohibitive for complex three-dimensional geometry with obstructions, both from a computational efficiency as well as memory standpoint. The inefficiency stems from the use of the viewfactor-based approach for determination of the wall-emitted component. In this work, instead, the wall component is determined directly using the control angle discrete ordinates method (CADOM). The new hybrid method was validated for both two-dimensional (2D) and three-dimensional (3D) geometries against benchmark Monte Carlo results for gray media in which the optical thickness was varied over a large range. In all cases, the accuracy of the hybrid method was found to be within a few percent of Monte Carlo results, and comparable to the solutions of the RTE obtained directly using CADOM. Finally, the new hybrid method was explored for 3D nongray media in the presence of reflecting walls and various scattering albedos. As a noteworthy advantage, irrespective of the conditions used, it was always found to be computationally more efficient than standalone CADOM and up to 15 times more efficient than standalone CADOM for optically thick media with strong scattering.
36
Krause, Andrew L., Eamonn A. Gaffney, and Benjamin J. Walker. "Concentration-Dependent Domain Evolution in Reaction–Diffusion Systems." Bulletin of Mathematical Biology 85, no. 2 (January 2023). http://dx.doi.org/10.1007/s11538-022-01115-2.
Full textAbstract:
AbstractPattern formation has been extensively studied in the context of evolving (time-dependent) domains in recent years, with domain growth implicated in ameliorating problems of pattern robustness and selection, in addition to more realistic modelling in developmental biology. Most work to date has considered prescribed domains evolving as given functions of time, but not the scenario of concentration-dependent dynamics, which is also highly relevant in a developmental setting. Here, we study such concentration-dependent domain evolution for reaction–diffusion systems to elucidate fundamental aspects of these more complex models. We pose a general form of one-dimensional domain evolution and extend this to N-dimensional manifolds under mild constitutive assumptions in lieu of developing a full tissue-mechanical model. In the 1D case, we are able to extend linear stability analysis around homogeneous equilibria, though this is of limited utility in understanding complex pattern dynamics in fast growth regimes. We numerically demonstrate a variety of dynamical behaviours in 1D and 2D planar geometries, giving rise to several new phenomena, especially near regimes of critical bifurcation boundaries such as peak-splitting instabilities. For sufficiently fast growth and contraction, concentration-dependence can have an enormous impact on the nonlinear dynamics of the system both qualitatively and quantitatively. We highlight crucial differences between 1D evolution and higher-dimensional models, explaining obstructions for linear analysis and underscoring the importance of careful constitutive choices in defining domain evolution in higher dimensions. We raise important questions in the modelling and analysis of biological systems, in addition to numerous mathematical questions that appear tractable in the one-dimensional setting, but are vastly more difficult for higher-dimensional models.
37
Tucker, Michelle L., David G. Wilson, Shawn K. Reinink, and James L. Carmalt. "Computed tomographic geometrical analysis of surgical treatments for equine recurrent laryngeal neuropathy." American Journal of Veterinary Research, February 8, 2022, 1–7. http://dx.doi.org/10.2460/ajvr.21.03.0040.
Full textAbstract:
Abstract OBJECTIVES To characterize the 3-D geometry of the equine larynx replicating laryngeal hemiplegia and 4 surgical interventions by use of CT under steady-state airflow conditions. Secondly, to use fluid mechanic principles of flow through a constriction to establish the relationship between measured airflow geometries with impedance for each surgical procedure. SAMPLE 10 cadaveric horse larynges. PROCEDURES While CT scans were performed, inhalation during exercise conditions was replicated for each of the following 5 conditions: laryngeal hemiplegia, left laryngoplasty with ventriculocordectomy, left laryngoplasty with ipsilateral ventriculocordectomy and arytenoid corniculectomy, corniculectomy, and partial arytenoidectomy for each larynx while CT scans were performed. Laryngeal impedance was calculated, and selected cross-sectional areas were measured along each larynx for each test. Measured areas and constriction characteristics were analyzed with respect to impedance using a multilevel, mixed-effects model. RESULTS Incident angle, entrance coefficient, outlet coefficient, friction coefficient, orifice thickness, and surgical procedure were significantly associated with upper airway impedance in the bivariable model. The multivariate model showed a significant influence of incident angle, entrance coefficient, and surgical procedure on impedance; however, the orifice thickness became nonsignificant within the model. CLINICAL RELEVANCE Laryngeal impedance was significantly associated with the entrance configuration for each procedure. This suggested that the equine upper airway, despite having a highly complex geometry, adheres to fluid dynamic principles applying to constrictions within pipe flow. These underlying flow characteristics may explain the clinical outcomes observed in some patients, and lead to areas of improvement in the treatment of obstructive upper airway disease in horses.
38
Rajendran, Rahul R., and Arindam Banerjee. "Effect of Non-Newtonian Dynamics on the Clearance of Mucus From Bifurcating Lung Airway Models." Journal of Biomechanical Engineering 143, no. 2 (November 11, 2020). http://dx.doi.org/10.1115/1.4048474.
Full textAbstract:
Abstract Mucus hypersecretion is a common pathophysiological manifestation of several obstructive airway diseases in which the mucociliary clearance is impaired, and the airflow generated by a cough or a forced expiratory maneuver called the huff is primarily responsible for clearing mucus. This airflow driven clearance of mucus is a complex process that is affected by the mucus rheology, airflow rate, airway geometry, and gravity. This study examines the role of mucus rheology in the transport and distribution of mucus in idealized 3D airway geometries. The complex air-mucus interface was tracked by the volume-of-fluid (VOF) model, and the turbulence in the core airflow was modeled using the k–ω shear stress transport (SST) model. Mucus was modeled as a shear-thinning liquid by using a power-law model. The computational model was validated using in vitro experimental data available in the literature. Gravity-dominated eccentric core-annular flow was observed with the core biased toward the outer wall in the inclined daughter branches of the bifurcation models, which transitions into concentric core-annular flow in the trachea. The increase in tangential shear at the interface due to the secondary flow structures developed in the flow divider location resulted in a region of enhanced mucus clearance with reduced mucus layer thickness. Secondary flow developed due to the curvature in the airway geometry resulted in a local redistribution of mucus that reduced the eccentricity. The accumulation of mucus around the carinal ridges and the regions with reduced clearance are sites with the potential for microbial growth.
39
Lee, Hyun Woo, Jimyung Park, Eun Jin Jang, and Chang-Hoon Lee. "Comparisons of exacerbations and mortality among LAMA/LABA combinations in stable chronic obstructive pulmonary disease: systematic review and Bayesian network meta-analysis." Respiratory Research 21, no. 1 (November 25, 2020). http://dx.doi.org/10.1186/s12931-020-01540-8.
Full textAbstract:
Abstract Background Only few randomized controlled trials (RCTs) for head-to-head comparison have been conducted between various combinations of long-acting muscarinic antagonists (LAMAs) and long-acting beta-agonists (LABAs). Our study was conducted to compare acute exacerbation and all-cause mortality among different LAMA/LABA regimens using Bayesian network meta-analysis (NMA). Methods We searched Medline, EMBASE, and the Cochrane library (search date: July 1, 2019). We included parallel-group RCTs comparing LAMA/LABA combinations with other inhaled drugs in the stable COPD for ≥ 48 weeks. Two different network geometries were used. The geometry of network (A) had nodes of individual drugs or their combination, while that of network (B) combined all other treatments except LAMA/LABA into each drug class. This study was prospectively registered in PROSPERO; CRD42019126753. Results We included 16 RCTs involving a total of 39,065 patients with stable COPD. Six combinations of LAMA/LABA were identified: tiotropium/salmeterol, glycopyrrolate/indacaterol, umeclidinium/vilanterol, tiotropium/olodaterol, aclidinium/formoterol, and glycopyrrolate/formoterol. We found that umeclidinium/vilanterol was associated with a lower risk of total exacerbations than other LAMA/LABAs in the NMA using network (A) (level of evidence: low or moderate). However, the significant differences were not present in the NMA of network (B). There were no significant differences among the LAMA/LABA combinations in terms of the number of moderate to severe exacerbations, all-cause mortality, major adverse cardiovascular events, or pneumonia. Conclusions The present NMA including all available RCTs provided that there is no strong evidence suggesting different benefits among LAMA/LABAs in patients with stable COPD who have been followed up for 48 weeks or more. Trial registration: This study was prospectively registered in PROSPERO; CRD42019126753.