Outflow boundary conditions for 3D simulations of non-periodic blood flow and pressure fields in deformable arteries

The simulation of blood flow and pressure in arteries requires outflow boundary conditions that incorporate models of downstream domains. We previously described a coupled multidomain method to couple analytical models of the downstream domains with 3D numerical models of the upstream vasculature. This prior work either included pure resistance boundary conditions or impedance boundary conditions based on assumed periodicity of the solution. However, flow and pressure in arteries are not necessarily periodic in time due to heart rate variability, respiration, complex transitional flow or acute physiological changes. We present herein an approach for prescribing lumped parameter outflow boundary conditions that accommodate transient phenomena. We have applied this method to compute haemodynamic quantities in different physiologically relevant cardiovascular models, including patient-specific examples, to study non-periodic flow phenomena often observed in normal subjects and in patients with acquired or congenital cardiovascular disease. The relevance of using boundary conditions that accommodate transient phenomena compared with boundary conditions that assume periodicity of the solution is discussed

Pauli blocking and medium effects in nucleon knockout reactions

We study medium modifications of the nucleon-nucleon (NN) cross sections and their influence on the nucleon knockout reactions. Using the eikonal approximation, we compare the results obtained with free NN cross sections with those obtained with a purely geometrical treatment of Pauli-blocking and with NN obtained with more elaborated Dirac-Bruecker methods. The medium effects are parametrized in terms of the baryon density. We focus on symmetric nuclear matter, although the geometrical Pauli-blocking allows for the treatment of asymmetric nuclear matter. It is shown that medium effects can change the nucleon knockout cross sections and momentum distributions up to 10% in the energy range E=50-300 MeV/nucleon. The effect is more evident in reactions involving halo nuclei.Comment: 10 pages, 9 figures, accepted for publication in Physics Review

3D Radiative Transfer in η\eta Carinae: Application of the SimpleX Algorithm to 3D SPH Simulations of Binary Colliding Winds

Eta Carinae is an ideal astrophysical laboratory for studying massive binary interactions and evolution, and stellar wind-wind collisions. Recent three-dimensional (3D) simulations set the stage for understanding the highly complex 3D flows in $\eta$ Car. Observations of different broad high- and low-ionization forbidden emission lines provide an excellent tool to constrain the orientation of the system, the primary's mass-loss rate, and the ionizing flux of the hot secondary. In this work we present the first steps towards generating synthetic observations to compare with available and future HST/STIS data. We present initial results from full 3D radiative transfer simulations of the interacting winds in $\eta$ Car. We use the SimpleX algorithm to post-process the output from 3D SPH simulations and obtain the ionization fractions of hydrogen and helium assuming three different mass-loss rates for the primary star. The resultant ionization maps of both species constrain the regions where the observed forbidden emission lines can form. Including collisional ionization is necessary to achieve a better description of the ionization states, especially in the areas shielded from the secondary's radiation. We find that reducing the primary's mass-loss rate increases the volume of ionized gas, creating larger areas where the forbidden emission lines can form. We conclude that post processing 3D SPH data with SimpleX is a viable tool to create ionization maps for $\eta$ Car.Comment: 18 pages, 11 figures, accepted for publication in MNRA

Casting light on the ƞ Carinae puzzle

Eta Carinae is one of the most massive and luminous binary systems known. Due to their luminosity both stars posses powerful stellar winds. These winds collide and the combination of their strength and the orbital motion determines the 3D structure of the gas. The interaction of the ionizing photons emitted by the stars with the gas is the topic of this thesis. We use the SimpleX algorithm for radiative transfer to post process hydrodynamic simulations of the wind interaction in Eta Carinae. We show that SimpleX is suitable to investigate the ionization structure of colliding wind binaries. Knowing where the gas is ionized allows us to identify the areas where observed emission and absorption lines might form. This has important implications for several properties of the system, such as the line of sight and the physical parameters of the stars, such as the temperature or mass-loss rate. We also printed 3D models of the interaction region of the two winds and investigated the usage of 3D interactive figures in scientific publications. These tools not only allow for better visualization and understanding of the system, but are also of great help when presenting complex simulation results to non expertsComputational astrophysicsInterstellar matter and star formatio

Evaluation of image signal-to-noise ratio in time-of-flight PET

In PET imaging Noise Equivalent Counts (NEC) is a common image quality index, derived to be proportional to image SNR 2 and used as an index of general system performance. Many studies have shown that TOF information leads to reduced noise, faster image convergence, and improved SNR. However, the original NEC formula does not account for any contribution of timing resolution to the final image quality, and modified versions of the formula have been proposed to account for the reduction in noise variance and increased sensitivity due to TOF information. In this study, we aim to investigate the relationship between NEC and image SNR in uniform phantoms when OSEM and TOF OSEM image reconstruction is applied. Two cylindrical uniform phantoms, 20 and 35 cm in diameter, were acquired over a wide range of activity levels on a Philips Gemini TF PET scanner. Multiple realizations of the original scans were obtained through bootstrapping and reconstructed with OSEM and TOF OSEM algorithms to obtain mean and standard deviation images. The ratio of the mean value in a central ROI over both images was taken as a measure of image SNR. NEC was calculated from the original data using both the classical and a TOF-adapted formula. The results show that Trues have a better proportionality with image SNR 2 than NEC and TOF NEC in the considered range of activities. Timing resolution and Random fraction appear to have a limited influence on image SNR, but the usage of a matched TOF kernel in reconstruction is found to be necessary to maximize the gain

A reduced-order modeling for efficient design study of artificial valve in enlarged ventricular outflow tracts

A computational approach is proposed for efficient design study of a reducer stent to be percutaneously implanted in enlarged right ventricular outflow tracts (RVOT). The need for such a device is driven by the absence of bovine or artificial valves which could be implanted in these RVOT to replace the absent or incompetent native valve, as is often the case over time after Tetralogy of Fallot repair. Hemodynamics are simulated in the stented RVOT via a reduce order model based on proper orthogonal decomposition (POD), while the artificial valve is modeled as a thin resistive surface. The reduced order model is obtained from the numerical solution on a reference device configuration, then varying the geometrical parameters (diameter) for design purposes. To validate the approach, forces exerted on the valve and on the reducer are monitored, varying with geometrical parameters, and compared with the results of full CFD simulations. Such an approach could also be useful for uncertainty quantification

Efficient blood flow simulations for the design of stented valve reducer in enlarged ventricular outflow tracts

Tetralogy of Fallot is a congenital heart disease characterized over time, after the initial repair, by the absence of a functioning pulmonary valve, which causes regurgitation, and by progressive enlargement of the right ventricle and pulmonary arteries. Due to this pathological anatomy, available transcatheter valves are usually too small to be deployed in the enlarged right ventricular outflow tracts (RVOT). To avoid surgical valve replacement, an alternative consists in implanting a reducer prior to or in combination with a transcatheter valve. We describe a computational model to study the effect of a stented valve RVOT reducer on the hemodynamics in enlarged ventricular outflow tracts. To this aim, blood flow in the right ventricular outflow tract is modeled via the incompressible Navier--Stokes equations coupled to a simplified valve model, numerically solved with a standard finite element method and with a reduced order model based on Proper Orthogonal Decomposition (POD). Numerical simulations are based on a patient geometry obtained from medical imaging and boundary conditions tuned according to measurements of inlet flow rates and pressures. Different geometrical models of the reducer are built, varying its length and/or diameter, and compared with the initial device-free state. Simulations thus investigate multiple device configurations and describe the effect of geometry on hemodynamics. Forces exerted on the valve and on the reducer are monitored, varying with geometrical parameters. Results support the thesis that the reducer does not introduce significant pressure gradients, as was found in animal experiments. Finally, we demonstrate how computational complexity can be reduced with POD

Os signos que possuem o uso condicionado ao protocolo de certificação : uma análise do caso Angus

Ao observar uma embalagem contendo o signo “Angus” é comum que o consumidor não saiba exatamente o que este signo indica, se uma marca, um tipo de produto, padrão de qualidade ou somente uma raça animal. Atualmente, Angus é designativo de uma raça animal, e que, em tese, só pode ser utilizado pelo produtor que tiver se submetido à certificação da Associação responsável no Brasil pelo controle desta raça. Contudo, verifica-se, na prática, o uso indiscriminado e muitas vezes irregular, bem como encontram-se registros de marca concedidos contendo o referido signo. Em face disso, questiona-se: quais são as implicações da concessão, por parte do INPI, de marcas compostas por signos cujo significado remete à nomenclatura de uso regulado, como é o caso da raça Angus, que é objeto de rastreabilidade e certificação? Para aprofundar o debate, torna-se necessário primeiramente compreender o instituto da Propriedade Intelectual e os requisitos para registro de marca, além de analisar o direito regulatório referente à identificação de raça bovina em produtos ou serviços do ramo alimentício, especificamente da raça “Angus”. Ainda, faz-se necessário investigar a existência de uma relação entre as normas referentes ao registro de marca e normas referentes à rotulagem e certificação da raça bovina Angus. Com isso, por meio de um levantamento bibliográfico, normativo e jurisprudencial-administrativo, pretende-se compreender as implicações do registro do signo “Angus” como marca. Como resultados da pesquisa, observa-se a ausência de norma que impeça o INPI de conceder marcas sem que seja possível atestar a existência de certificação do produto identificado pela raça angus, notadamente por parte da Associação Brasileira de Angus. Todavia, a legislação vigente determina ao INPI o dever de observar o princípio da veracidade, a fim de garantir uma concorrência leal no mercado e proteger o consumidor para que este não seja induzido em erro. Ao não reconhecer que o uso do signo angus depende de protocolo de rastreabilidade e correspondente certificação, cria-se um cenário favorável para que os produtores/criadores de carne animal não observem as normativas sobre rotulagem de carne animal e induzam o mercado como um todo em erro quanto à qualidade do produto ofertado.When observing a package containing the term “Angus”, it is common for the consumer not to know exactly what this sign indicates, whether a brand, a type of product, quality standard or just an animal breed. Currently, Angus is the designation of an animal breed, which, in theory, can only be used by the producer who has submitted himself to the certification of the Association responsible in Brazil for the control of this breed. However, in practice, indiscriminate and irregular use is verified, as well as granted trademark registrations containing the referred term. Therefore, the question emerges: what are the implications of granting, by the INPI, brands composed of terms whose meaning refers to the nomenclature of regulated use, as is the case of the Angus breed, which is subject to traceability and certification? To deepen the debate, it becomes necessary to comprehend, at first, the Intellectual Property institute and the requirements for trademark registration, in addition to analyzing the regulatory law regarding the identification of the bovine breed in products or services in the food industry, specifically the “Angus” breed. Even so, it is necessary to investigate the existence of a relationship between the norms referring to trademark registration and norms referring to the labeling and certification of the Angus bovine breed. Hence, through a bibliographical, normative and administrative jurisprudential survey, it is intended to understand the implications of registering the term “Angus” as a trademark. As result, it is observed the absence of a rule that prevents the INPI from granting marks without it being possible to attest to the existence of certification of the product identified by the Angus breed, notably by the Associação Brasileira de Angus. However, current legislation determines to INPI the duty to observe the principle of truthfulness, in order to guarantee a fair competition in the market and protect consumers so that they are not misled. By not acknowledging that the use of the angus sign depends on a traceability protocol and corresponding certification, a favorable scenario is created so that animal meat producers/breeders do not observe the regulations on animal meat labeling and induce the market as a whole to error as to the quality of the product offered

Aerosols in Healthy and Emphysematous In Silico Pulmonary Acinar Rat Models

International audienceThere has been relatively little attention given on predicting particle deposition in the respiratory zone of the diseased lungs despite the high prevalence of chronic obstructive pulmonary disease (COPD). Increased alveolar volume and deterioration of alveolar septum, characteristic of emphysema, may alter the amount and location of particle deposition compared to healthy lungs, which is particularly important for toxic or therapeutic aerosols. In an attempt to shed new light on aerosol transport and deposition in emphysematous lungs, we performed numerical simulations in models of healthy and emphysematous acini motivated by recent experimental lobar-level data in rats~\citep{OakesEmp}. Compared to healthy acinar structures, models of emphysematous subacini were created by removing inter-septal alveolar walls and enhancing the alveolar volume in either a homogeneous or heterogeneous fashion. Flow waveforms and particle properties were implemented to match the experimental data. The occurrence of flow separation and recirculation within alveolar cavities was found in proximal generations of the healthy zones, in contrast to the radial-like airflows observed in the diseased regions. In agreement with experimental data, simulations point to particle deposition concentrations that are more heterogeneously distributed in the diseased models compared with the healthy one. Yet, simulations predicted less deposition in the emphysematous models in contrast to some experimental studies, a likely consequence due to the shallower penetration depths and modified flow topologies in disease compared to health. These spatial-temporal particle transport simulations provide new insight on deposition in the emphysematous acini and shed light on experimental observations