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Identification of fatigue crack propagation modes by means of roughness measurements

Antunes, F. V.; Ramalho, A.; Ferreira, J. M.
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Artigo de Revista Científica Formato: aplication/PDF
ENG
Relevância na Pesquisa
36.45%
This paper is a study of the applicability of fracture surface roughness measurements to identify the crack propagation mode in nickel base superalloys (transgranular, intergranular or mixed). The results obtained indicated that this technique can be used as an alternative or as a complement to standard fractography. The best roughness parameters for identifying the crack propagation mode are average roughness, mean roughness depth and mean height profile peak (Ra, Rz and Rpm). Analysis of roughness spectra in terms of the frequency range showed that the amplitude values of the profiles with wavelengths identical to the grain size are significant when propagation is intergranular. The roughness measurements were used to study the influence of loading frequency and stress state on the fatigue crack propagation mode occurring in Inconel 718 tested at 600°C.; http://www.sciencedirect.com/science/article/B6V35-41ST109-6/1/4695f61f2b3e59463aa24ef462c9fdc5

Metodologia de caracterização da propagação acústica em tubulações de transporte de fluidos bifásicos gás-líquido; Methodology of characterization of acoustic propagation in pipelines for transporting two-phase gas-liquid fluids

Martins, Jaqueline Costa
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 04/02/2011 PT
Relevância na Pesquisa
36.45%
Este trabalho tem como objetivo global contribuir para o desenvolvimento do estudo da propagação de ondas em dutos de transporte de fluidos, especialmente oleodutos e gasodutos, através da análise da atenuação acústica e da velocidade de propagação da onda. Para isso, foram feitos ensaios experimentais, tanto em escoamento mono quanto bifásico, variando-se a vazão do escoamento em uma linha de testes de 1500 metros e 50 mm de diâmetro, para aquisição de sinais gerados a partir do fechamento de válvulas de simulação de vazamentos em pontos ao longo da tubulação. Para análise da atenuação acústica foi proposta uma metodologia baseada na medição do coeficiente de amortecimento temporal das ondas de pressão como subsídio para o cálculo do coeficiente de atenuação, através da utilização de um único sensor de pressão. Esta metodologia foi validada pela medição direta do coeficiente de atenuação e os resultados mostram uma excelente concordância em escoamentos monofásicos. Para os testes em escoamento bifásico não foi possível aplicar esta metodologia devido ao forte amortecimento das ondas de pressão, sendo feitas apenas medições diretas da atenuação com resultados fenomenologicamente coerentes. A velocidade de propagação acústica para escoamento monofásico foi influenciada pela presença de gás dissolvido e bolhas de cavitação...

Propagação de raios cósmicos extragaláticos; Propagation of the extragalactic cosmic rays

Anjos, Rita de Cássia dos
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 26/06/2014 PT
Relevância na Pesquisa
36.45%
Recentemente, o Observatório Pierre Auger tem medido espectro de energia de Raios Cósmicos Ultra Energéticos (Ultra High Energy Cosmic Rays - UHECR) (E > 1019 eV) com grande acurácia. No entanto, o estudo de raios cósmicos ultra energéticos na Terra tem uma forte dependência do estudo de sua propagação no Universo. Neste trabalho, abordamos o estudo da propagação de raios cósmicos em diferentes aspectos. Núcleos em alta energia interagem com os campos de radiação no caminho da fonte à Terra. A interação mais importante é a fotodesintegração. Na primeira parte, implementamos de maneira analítica e numérica a solução da razão de fotodesintegração e fizemos uso da solução numérica em um programa de Monte Carlo. Mostramos soluções baseadas na parametrização das seções de choque por uma função Gaussiana e por uma função Lorenztiana. Comparamos nossos resultados com trabalhos prévios da literatura. O seguinte estudo mostrou que sob a hipótese de propagação quase-linear e utilizando várias distribuições de fontes no céu, a latitude do observatório: tem influência no fluxo total medido por um observatório; impõe um limite na capacidade de medida de anisotropia e tem um efeito negligenciável na medida do XMax. No terceiro estudo...

Investigação da propagação estável de trinca pelo método da cunha em refratários: tijolo e concreto; Investigation of stable crack propagation by the wedge splitting method in brick and concrete refractories

Ribeiro, Giseli Cristina
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 28/11/2014 PT
Relevância na Pesquisa
36.6%
Refratários são materiais com microestrutura heterogênea constituída de uma fração grosseira, os agregados, e de uma fração mais fina, a matriz, em que ambas exercem papéis fundamentais nas propriedades dos refratários, sendo a resistência ao dano por choque térmico, uma das mais importantes. Para avaliar essa questão crítica dos refratários há necessidade de se conhecer bem seu comportamento à propagação de trinca, principalmente quando submetido a uma tensão. Porém, devido à complexidade da estrutura desses materiais, o comportamento das regiões à frente e atrás da ponta da trinca sempre foi muito discutido, só que essa discussão sempre fez uso de modelos e simulações computacionais, já que é prevista uma zona de processo, em que diferentes mecanismos podem absorver energia aumentando a resistência à propagação da trinca principal. Nesta tese foi proposto o estudo experimental do comportamento da propagação de trinca em refratários, visando entender os mecanismos de resistência à propagação de trinca e o caminho das trincas propagantes, utilizando o método da cunha para propagação estável da trinca, que é o mais adequado para essa classe de materiais. Para isso foram utilizados, dois refratários distintos: tijolo e concreto...

Propagação de trinca por fadiga do concreto reforçado com baixos teores de fibra; Fatigue crack propagation of fiber reinforced concrete with low content of fibers

Marco Antonio Carnio
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 05/02/2009 PT
Relevância na Pesquisa
36.52%
O concreto reforçado com fibras (CRF) é um compósito constituído de duas fases: concreto (matriz) e fibras (reforço). As fibras são elementos descontínuos de vários aspectos geométricos e materiais, destacando-se atualmente as fibras metálicas (aço) e as fibras sintéticas (polipropileno). Em geral, os teores de fibras em volume adicionados à matriz se dividem em: baixos teores - até 0,5%; médios teores - entre 0,5% e 1% e altos teores - acima de 1%. Dentre as aplicações do CRF com baixos teores, a utilização em pavimentos de concreto é a mais significativa, cuja solicitação predominante é cíclica. O estudo da fadiga se divide em iniciação da trinca, propagação da trinca e fratura final, e a vida em fadiga (Nf) é caracterizada pela soma do número de ciclos até a fratura. Dessa forma, como no estudo da fadiga do CRF a maioria dos trabalhos se concentra na obtenção de seu comportamento por meio das curvas S-N (tensão em função do número de ciclos até a fratura), este trabalho tem como objetivo estudar experimentalmente a propagação da trinca por fadiga dos CRFs com baixos teores, por meio de ensaios de flexão em corpos-de-prova prismáticos de seção quadrada, submetidos a carga cíclica com freqüência de 20 Hz e razão de carga R = 0...

Role of the intercalated disc in cardiac propagation and arrhythmogenesis

Kleber, Andre G.; Saffitz, Jeffrey E.
Fonte: Frontiers Media S.A. Publicador: Frontiers Media S.A.
Tipo: Artigo de Revista Científica
EN_US
Relevância na Pesquisa
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This review article discusses mechanisms underlying impulse propagation in cardiac muscle with specific emphasis on the role of the cardiac cell-to-cell junction, called the “intercalated disc.”The first part of this review deals with the role of gap junction channels, formed by connexin proteins, as a determinant of impulse propagation. It is shown that, depending on the underlying structure of the cellular network, decreasing the conductance of gap junction channels (so-called “electrical uncoupling”) may either only slow, or additionally stabilize propagation and reverse unidirectional propagation block to bidirectional propagation. This is because the safety factor for propagation increases with decreasing intercellular electrical conductance. The role of heterogeneous connexin expression, which may be present in disease states, is also discussed. The hypothesis that so-called ephaptic impulse transmission plays a role in heart and can substitute for electrical coupling has been revived recently. Whereas ephaptic transmission can be demonstrated in theoretical simulations, direct experimental evidence has not yet been presented. The second part of this review deals with the interaction of three protein complexes at the intercalated disc: (1) desmosomal and adherens junction proteins...

Ultra-short pulse propagation in multi-level media

Clader, B. David (1980 - ); Eberly, Joseph H. (1935 - )
Fonte: University of Rochester Publicador: University of Rochester
Tipo: Tese de Doutorado Formato: Number of Pages:xiii, 117 leaves
ENG
Relevância na Pesquisa
36.52%
Thesis (Ph. D.)--University of Rochester. Dept. of Physics and Astronomy, 2008.; We consider the propagation of short, intense laser pulses through media consisting of two-level and three-level atoms. We derive the coupled Maxwell-Bloch (MB) equations, which describe such propagation. Many different physical situations have been studied by analyzing various limiting cases of these equations. Most of the recent work has relied on steady-state or adiabatic assumptions to simplify the analysis of the MB equations. However rapid progress has been made in recent years in developing analytic solution techniques that do not require these simplifications, such as Bäcklund transformations, inverse scattering methods, and Darboux transformations. We use the Bäcklund solution method, to derive soliton solutions to the MB equations for various physical situations of interest in multi-level media. In addition we examine the experimental applicability of the exact solutions by numerically integrating the MB equations for more physically realistic pulse shapes and media preparations that may not permit analytic solutions. In two-level inverted gain media, we derive a pulse solution with group velocity exceeding the speed of light in vacuum (fast light). Numerical results confirm that such a pulse can exhibit fractional peak advances exceeding one pulse width despite spontaneous instabilities such as superfluorescence and stimulated instabilities related to the McCall-Hahn area theorem. In three-level Λ type media we derive soliton solutions for two pulses propagating through a medium prepared in an arbitrary mixed-state of the two ground states. We include a tunable parameter in the solutions that allows one to vary the medium between completely mixed state and completely pure-state superpositions known as “phaseonium”. This flexibility allows one to study the interplay between stimulated Raman scattering...

Quantitative ultrasound imaging during shear wave propagation for application related to breast cancer diagnosis

Alavi Dorcheh, Marzieh
Fonte: Université de Montréal Publicador: Université de Montréal
Tipo: Thèse ou Mémoire numérique / Electronic Thesis or Dissertation
EN
Relevância na Pesquisa
36.64%
Dans le contexte de la caractérisation des tissus mammaires, on peut se demander ce que l’examen d’un attribut en échographie quantitative (« quantitative ultrasound » - QUS) d’un milieu diffusant (tel un tissu biologique mou) pendant la propagation d’une onde de cisaillement ajoute à son pouvoir discriminant. Ce travail présente une étude du comportement variable temporel de trois paramètres statistiques (l’intensité moyenne, le paramètre de structure et le paramètre de regroupement des diffuseurs) d’un modèle général pour l’enveloppe écho de l’onde ultrasonore rétrodiffusée (c.-à-d., la K-distribution homodyne) sous la propagation des ondes de cisaillement. Des ondes de cisaillement transitoires ont été générés en utilisant la mèthode d’ imagerie de cisaillement supersonique ( «supersonic shear imaging » - SSI) dans trois fantômes in-vitro macroscopiquement homogènes imitant le sein avec des propriétés mécaniques différentes, et deux fantômes ex-vivo hétérogénes avec tumeurs de souris incluses dans un milieu environnant d’agargélatine. Une comparaison de l’étendue des trois paramètres de la K-distribution homodyne avec et sans propagation d’ondes de cisaillement a montré que les paramètres étaient significativement (p < 0...

Radio propagation in fire environments.

Boan, Jonathan Alexander
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2009
Relevância na Pesquisa
36.6%
Radio propagation in the presence of fire is known to be problematic to communications. In this thesis we use both experimental and theoretical approaches to examine and understand radio propagation in fire environments. Propagation is examined for three small scale fires with broadband equipment operating from 50MHz to 1GHz. Results for line of sight propagation show a strong interaction of fire with electromagnetic propagation. The next section develops electromagnetic modelling of the fire environment. A model of the combustion induced plasma is developed, as well as a refractive index model of the surrounding atmosphere of a fire. Simple propagation calculations are undertaken, using the developed fire models, to provide an intial understanding of propagation in fire environments. The next portion of the thesis considers propagation using a more rigorous electromagnetic simulation technique. A modified Finite Difference Time Domain method is presented and is utilised to examine three dimensional propagation in the small scale fire experiments. The outcome is a more solid understanding of propagation and the contributing factors. The last portion of the thesis is the application of the above electromagnetic modelling and simulation methods to bushfire scenarios. Various scenarios that are problematic to radio communication are examined. Discussion and recommendations are made concerning radio communication frequency selection and considerations for propagation in fire environments.; Thesis (Ph.D.) -- University of Adelaide...

Electro-optic propagation through highly aberrant media.

Isterling, William Martin
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2010
Relevância na Pesquisa
36.56%
Infrared guided, or “heat seeking” missiles, have posed a threat to aircraft ever since their inception. However, the proliferation of man portable shoulder launching infrared guided missiles has increased the threat level against both military and civilian aircraft. Furthermore, advanced variants of the missiles are less susceptible to decoy against traditional countermeasures such as flares. To counter the threat, advances in laser technology have allowed the development of small, robust and powerful infrared lasers that have been developed into laser defence systems that can be fitted to aircraft. These systems, Directed InfraRed CounterMeasures (DIRCM), detect the incoming missile and direct modulated infrared energy, in the form of a laser beam, on to the missile sensor to disrupt the missile’s guidance. The defence system works well in laboratory settings, and through normal atmosphere, but effects of a highly aberrant propagation path on the laser beam’s temporal and spatial quality need to be considered. In particular, scenarios may arise where the laser beam must pass through the hot, turbulent gases of the engine exhaust, the plume. Some initial system studies highlight the problem but have not reported on the individual effects of the various laser and flow parameters in this high temperature...

Propagation effects on HF Skywave MIMO radar.

Tomei, Sonia
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2014
Relevância na Pesquisa
36.49%
MIMO technology has been suggested as an effective tool to overcome some of the issues typical of conventional OTH skywave radars. The advantages of the application of MIMO technology to HF Skywave radars is based on the transmission of multiple linearly independent waveforms and their separation at the receiver. Notwithstanding, the high instability of the ionosphere is responsible for severe signal fading and degradation that can prevent the separation with consequences on the radar performance. The present thesis is concerned with the problem of the effects of ionospheric propagation, which are analyzed from a theoretical point of view at first, through the description of the ionosphere morphology and the disturbances that affect the ionospheric electron density structure. The relation between structural variations in the ionosphere and the transmitted signal parameters has been then derived. A radar signal simulator has been realized accordingly to the signal model proposed in the thesis. The results of the thesis concern three different aspects of propagation in HF MIMO radars. The orthogonality of the transmitted waveforms after ionospheric propagation is analyzed first, while the effects of ionospheric propagation on the results of conventional beamforming is studied secondly. The performance of the radar receiver are evaluated in terms of ROCs in case of multipath propagation and compared to the single path case.; Thesis (Ph.D.) -- University of Adelaide...

Bleach Imaged Plasmon Propagation (BlIPP) of Metallic Nanoparticle Waveguides

Solis, David
Fonte: Universidade Rice Publicador: Universidade Rice
ENG
Relevância na Pesquisa
36.57%
The high speed transfer of information in materials with dimensions below the sub-diffraction limit is essential for future technological developments. Metallic nanoparticle (NP) waveguides serve a unique role in efficient energy transfer in this size regime. Light may be confined to metallic structures and propagate along the surface of the waveguide via propagating plasmon waves known as surface plasmon polaritons (SPPs). Plasmon propagation of energy in metallic structures is not perfect however and damping losses from the waveguide material lead to a characteristic exponential decay in the plasmon near field intensity. This decay length is known as the propagation length and serves as an excellent metric to compare various waveguide materials and structures to one another at particular excitation wavelengths. This thesis presents recent work in the development of a novel measurement technique termed bleach imaged plasmon propagation (BlIPP). BlIPP uses the photobleaching property of fluorophores and far field fluorescence microscopy to probe the near-field intensity of propagating plasmons and determine the propagation length. The experimental setup, image analysis, conditions, and application of BlIPP are developed within this thesis and an in depth review of the 1-photon photobleaching mechanism is also investigated. The BlIPP method is used to investigate long plasmon propagation lengths along straight chains of tightly packed Au NPs through the coupling of light to sub-radiant propagating modes...

Indoor propagation simulation software

Calle, Juan Carlos
Fonte: Monterey, California. Naval Postgraduate School Publicador: Monterey, California. Naval Postgraduate School
Tipo: Tese de Doutorado Formato: xiv, 47 p.;28 cm.
EN_US
Relevância na Pesquisa
36.54%
Approved for public release; distribution is unlimited; Computer simulation can be used to predict the signal strength in complex indoor environments. Signal propagation prediction is essential for determining the coverage of WLAN's (Wireless Local Area Networks). Increasing use of WLANs within infrastructures that have been built prior to the installation of the wireless networks requires measurements, semi-empirical models, or computer simulations to determine the number and location of access points for optimum coverage. In cases where the infrastructure has yet to be built (as in a new class of ships) the simulation may be the only option for WLAN coverage prediction. In such a case, blueprints may be used in conjunction with the indoor propagation simulation software in order to predict the best places to install the access points. The indoor propagation simulation software differs from the outdoor propagation software used for the cellular networks because of the differences in the characteristics of indoor and outdoor propagation channels. This thesis explains the characteristics and structure of a Wireless Local Area Network and presents the computer simulation results the 2.4 GHz wireless signal propagation inside an enclosed space. A building at the Naval Postgraduate School...

Investigation of propagation in foliage using simulation techniques

Chan, Chung Wei
Fonte: Monterey, California. Naval Postgraduate School Publicador: Monterey, California. Naval Postgraduate School
Formato: xxii, 91 p. : ill. (chiefly col.) ; 28 cm.
Relevância na Pesquisa
36.49%
In a foliage environment, radio wave propagation is subjected to fading on both large-scales and small-scales that impair the quality and reliability of data link transmission. This has implications in many military applications. An example is the performance of communications links and unmanned aerial vehicle radio links when the ground forces are operating in foliage environments. The purpose of this research is to evaluate some simple models for propagation of radio waves in foliage using an electromagnetic field simulation application. The three dimensional (3D) electromagnetic field simulation application, CST Studio Suite, was used in the modeling and simulation process. Specifically, the CST Microwave Studio module was used to model the forest using dielectric blocks. Various combinations of forest dimensions, material dielectric parameters and antenna placements were simulated to obtain propagation models of radio waves in foliage environment. The simulation models are compared to three empirical models presented in the literature for propagation in foliage environment. Using the simulation model, we examined the coverage diagram for a transmitter antenna immersed in foliage. The results show that the proposed simulation models provide a rough approximation to radiowave propagation in an actual rainforest environment. Based on the simulated results...

Propagation modeling of wireless systems in shipboard compartments

Chaabane, Adnen
Fonte: Monterey California. Naval Postgraduate School Publicador: Monterey California. Naval Postgraduate School
Tipo: Tese de Doutorado Formato: xx, 93 p. : ill. (some col.)
Relevância na Pesquisa
36.49%
Approved for public release, distribution is unlimited; In today's navy, it is becoming more and more important to reach all areas onboard a ship with key technical resources. In order to accomplish this goal, the already existing physical networks need to be complemented with wireless capability. A sophisticated Wireless Local Area Network (WLAN) can provide that vital connectivity to the ship's network resources from almost anywhere on the ship. It would allow sailors to access critical information and immediately communicate with others throughout the ship from any standard wireless device (PDA, laptop and many other hand-held devices). In addition, WLANs greatly mitigate problems due to physical damage to wires or fiber optic cables that are used today. Because the navy's emphasis is on building ships with reduced manning, advanced technology, and lower cost in mind, the idea of a WLAN, which has a deep impact on all those areas, has been of a growing interest to the Navy. The purpose of this thesis is to analyze, model, and simulate a wireless environment on board a variety of naval ship compartments, using the Urbana code. Starting from known inputs (frequency, ship compartment geometry, material properties, propagation computation model...

Propagação não linear de pulsos em estruturas 1D com band gap fotônico; Nonlinear pulse propagation in one-dimensional photonic band gap structures

John Jairo Lozada Vera
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 17/08/2009 PT
Relevância na Pesquisa
36.52%
Estuda-se a interação entre pulsos ópticos ultracurtos e materiais com band gap fotônico, considerando-se a propagação de luz através de estruturas unidimensionais, compostas de uma super-rede dielétrica periódica cuja célula unitária consiste em um par de camadas com diferentes índices de refração n1e n2, respectivamente. Em particular considera-se o caso em que n2, por exemplo, é um material com não linearidade X (3). É bem sabido que a largura e a localização dos band gaps dependem fundamentalmente do contraste entre os índices de refração d n = | n1 - n1 | e, atribuindo-se a n2 um índice de refração dependente da intensidade, conseguimos controlar dinamicamente a largura do band gap com o pulso de luz incidente. Portanto, a idéia básica é investigar a dinâmica de propagação nas vizinhanças de um band gap dependente da intensidade para aplicações importantes no projeto de dispositivos fotônicos, como por exemplo limitadores de luz e switches puramente ópticos. Dentro do formalismo de Maxwell, experimentos computacionais são feitos considerando a propagação de campos ópticos através de super-redes que possuem não linearidades do tipo Kerr, assim como saturável. Esta última é importante para a descrição da interação com pulsos muito intensos já que neste caso a mudança induzida no índice de refração depende de não linearidades de ordem mais alta e...

Automatic LEFM crack propagation method based on local Lepp–Delaunay mesh refinement

Rivara Zúñiga, María Cecilia; Elgueta, Marcelo; Azócar, David
Fonte: ELSEVIER Publicador: ELSEVIER
Tipo: Artículo de revista
EN
Relevância na Pesquisa
36.49%
A numerical method for 2D LEFM crack propagation simulation is presented. This uses a Lepp–Delaunay based mesh refinement algorithm for triangular meshes which allows both the generation of the initial mesh and the local modification of the current mesh as the crack propagates. For any triangle t, Lepp(t) (Longest Edge Propagation Path of t) is a finite, ordered list of increasing longest edge neighbor triangles, that allows to find a pair of triangles over which mesh refinement operations are easily and locally performed. This is particularly useful for fracture mechanics analysis, where high gradients of element size are needed. The crack propagation is simulated by using a finite element model for each crack propagation step, then the mesh near the crack tip is modified to take into account the crack advance. Stress intensify factors are calculated using the displacement extrapolation technique while the crack propagation angle is calculated using the maximum circumferential stress method. Empirical testing shows that the behavior of the method is in complete agreement with experimental results reported in the literature. Good results are obtained in terms of accuracy and mesh element size across the geometry during the process.

Non-uniform Interstitial Loading in Cardiac Microstructure During Impulse Propagation

Roberts, Sarah F.
Fonte: Universidade Duke Publicador: Universidade Duke
Tipo: Dissertação Formato: 6946498 bytes; application/pdf
Publicado em //2009 EN_US
Relevância na Pesquisa
36.52%

Impulse propagation in cardiac muscle is determined not only by the excitable properties of the myocyte membrane, but also by the gross and fine structure of cardiac muscle. Ionic diffusion pathways are defined by the muscle's interconnected myocytes and interweaving interstitial spaces. Resistive variations arising from spatial changes in tissue structure, including geometry, composition and electrical properties have a significant impact on the success or failure of impulse propagation. Although much as been learned about the impact of discrete resistive architecture of the intracellular space, the role of the interstitial space in the spread of electrical activity is less well understood or appreciated at the microscopic scale.

The interstitial space, or interstitium, occupies from 20-25% of the total heart volume.

The structural and material composition of the interstitial space is both complex and

heterogeneous, encompassing non-myocyte cell structures and a conglomeration of

extracellular matrix proteins. The spatial distribution of the interstitium can vary from confined spaces between abutting myocytes and tightly packed cardiac fibers to large gaps between cardiac bundles and sheets

This work presents a discrete multidomain formulation that describes the three-dimensional ionic diffusion pathways between connected myocytes within a variable interstitial physiology and morphology. Unlike classically used continuous and discontinuous models of impulse propagation...

Modeling holographic grating imaging systems using the angular spectrum propagation method

Blasiak, Thomas
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado Formato: 1341527 bytes; application/pdf
EN_US
Relevância na Pesquisa
36.54%
The goal of this research was to describe the angular spectrum propagation method for the numerical calculation of scalar optical propagation phenomena. The angular spectrum propagation method has some advantages over the Fresnel propagation method for modeling low F# optical systems and non-paraxial systems. An example of one such system was modeled, namely the diffraction and propagation from a holographic diffraction grating. To accomplish this goal MATLAB® code was developed to implement the angular spectrum propagation method. Some classical imaging problems such as diffraction from a rectangular aperture, Talbot imaging, focal shift for converging beam illumination, and two beam interference were described in detail in order to demonstrate the capabilities of this method. Results from modeling the image formation of a holographic diffraction grating were compared to a ZEMAX® ray trace model.

Simulating elastic wave propagation in boreholes: Fundamentals of seismic response and quantitative interpretation of well log data

Ávila-Carrera,Rafael; Spurlin,James H.; Valle-Molina,Celestino
Fonte: Instituto de Geofísica, UNAM Publicador: Instituto de Geofísica, UNAM
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2011 EN
Relevância na Pesquisa
36.49%
An analytic formulation oriented to understand the diffraction, dispersion and attenuation of borehole propagation modes is presented. The main aim of this article is to report to the scientific community the fundamentals of the seismic response at the well neighborhood, excited by an internal point source and present novelty simulation results compared against real data. An important, but not widely exploited technique to carefully investigate the elastic wave propagation in petroleum wells is the logging of sonic waveforms. The appropriate treatment and adequate processing of such microseismograms allow the extraction of useful information to characterize and understand the rock formation and is crucial on taking of decisions in the hydrocarbon production chain. In this work, the study of borehole wave propagation is based in the performing numerical simulations with the so-called Discrete Wave-number method applied to various cases of representative wells in Mexican reservoirs. The contributions of this investigation are: (1) to evince in the seismograms the strong effect of diffraction and dispersion of elastic waves, even working with the homogeneous isotropic case, (2) to describe in frequency and time domains, the propagation of waves generated by a point source in a cylindrical borehole filled with fluid...