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Taha Sochi

Publications and source records attributed to Taha Sochi.

At least 55 records · Page 3Linked to original sources
arXiv2013

Flow of Navier-Stokes Fluids in Converging-Diverging Distensible Tubes

We use a method based on the lubrication approximation in conjunction with a residual-based mass-continuity iterative solution scheme to compute the flow rate and pressure field in distensible converging-diverging tubes for Navier-Stokes fluids. We employ an analytical formula derived from a one-dimensional version of the Navier-Stokes equations to describe the underlying flow model that provides the residual function. This formula correlates the flow rate to the boundary pressures in straight cylindrical elastic tubes with constant-radius. We validate our findings by the convergence toward a final solution with fine discretization as well as by comparison to the Poiseuille-type flow in its convergence toward analytic solutions found earlier in rigid converging-diverging tubes. We also tested the method on limiting special cases of cylindrical elastic tubes with constant-radius where the numerical solutions converged to the expected analytical solutions. The distensible model has also been endorsed by its convergence toward the rigid Poiseuille-type model with increasing the tube wall stiffness. Lubrication-based one-dimensional finite element method was also used for verification. In this investigation five converging-diverging geometries are used for demonstration, validation and as prototypes for modeling converging-diverging geometries in general.

physics.flu-dyn↗
arXiv2013

Pore-Scale Modeling of Navier-Stokes Flow in Distensible Networks and Porous Media

In this paper, a pore-scale network modeling method, based on the flow continuity residual in conjunction with a Newton-Raphson non-linear iterative solving technique, is proposed and used to obtain the pressure and flow fields in a network of interconnected distensible ducts representing, for instance, blood vasculature or deformable porous media. A previously derived analytical expression correlating boundary pressures to volumetric flow rate in compliant tubes for a pressure-area constitutive elastic relation has been used to represent the underlying flow model. Comparison to a preceding equivalent method, the one-dimensional Navier-Stokes finite element, was made and the results were analyzed. The advantages of the new method have been highlighted and practical computational issues, related mainly to the rate and speed of convergence, have been discussed.

physics.flu-dyn↗
arXiv2013

Fluid Flow at Branching Junctions

The flow of fluids at branching junctions plays important kinematic and dynamic roles in most biological and industrial flow systems. The present paper highlights some key issues related to the flow of fluids at these junctions with special emphasis on the biological flow networks particularly blood transportation vasculature.

physics.flu-dyn↗
arXiv2013

Methods for Analyzing Resonances in Atomic Scattering

Resonances, which are also described as autoionizing or quasi-bound states, play an important role in the scattering of atoms and ions with electrons. The current article is an overview of the main methods, including a recently-proposed one, that are used to find and analyze resonances.

physics.atom-ph↗
arXiv2013

Comparing Poiseuille with 1D Navier-Stokes Flow in Rigid and Distensible Tubes and Networks

A comparison is made between the Hagen-Poiseuille flow in rigid tubes and networks on one side and the time-independent one-dimensional Navier-Stokes flow in elastic tubes and networks on the other. Analytical relations, a Poiseuille network flow model and two finite element Navier-Stokes one-dimensional flow models have been developed and used in this investigation. The comparison highlights the differences between Poiseuille and one-dimensional Navier-Stokes flow models which may have been unjustifiably treated as equivalent in some studies.

physics.flu-dyn↗
arXiv2013

Flow of Navier-Stokes Fluids in Cylindrical Elastic Tubes

Analytical expressions correlating the volumetric flow rate to the inlet and outlet pressures are derived for the time-independent flow of Newtonian fluids in cylindrically-shaped elastic tubes using a one-dimensional Navier-Stokes flow model with two pressure-area constitutive relations. These expressions for elastic tubes are the equivalent of Poiseuille and Poiseuille-type expressions for rigid tubes which were previously derived for the flow of Newtonian and non-Newtonian fluids under various flow conditions. Formulae and procedures for identifying the pressure field and tube geometric profile are also presented. The results are validated by a finite element method implementation. Sensible trends in the analytical and numerical results are observed and documented.

physics.flu-dyn↗
arXiv2013

One-Dimensional Navier-Stokes Finite Element Flow Model

This technical report documents the theoretical, computational, and practical aspects of the one-dimensional Navier-Stokes finite element flow model. The document is particularly useful to those who are interested in implementing, validating and utilizing this relatively-simple and widely-used model.

physics.flu-dyn↗
arXiv2013

New program with new approach for spectral data analysis

This article presents a high-throughput computer program, called EasyDD, for batch processing, analyzing and visualizing of spectral data; particularly those related to the new generation of synchrotron detectors and X-ray powder diffraction applications. This computing tool is designed for the treatment of large volumes of data in reasonable time with affordable computational resources. A case study in which this program was used to process and analyze powder diffraction data obtained from the ESRF synchrotron on an alumina-based nickel nanoparticle catalysis system is also presented for demonstration. The development of this computing tool, with the associated protocols, is inspired by a novel approach in spectral data analysis.

physics.data-an↗
arXiv2013

Using Euler-Lagrange Variational Principle to Obtain Flow Relations for Generalized Newtonian Fluids

Euler-Lagrange variational principle is used to obtain analytical and numerical flow relations in cylindrical tubes. The method is based on minimizing the total stress in the flow duct using the fluid constitutive relation between stress and rate of strain. Newtonian and non-Newtonian fluid models; which include power law, Bingham, Herschel-Bulkley, Carreau and Cross; are used for demonstration.

physics.flu-dyn↗
arXiv2012

Dielectronic Recombination Lines of C+

The current paper presents atomic data generated to investigate the recombination lines of C II in the spectra of planetary nebulae. These data include energies of bound and autoionizing states, oscillator strengths and radiative transition probabilities, autoionization probabilities, and recombination coefficients. The R-matrix method of electron scattering theory was used to describe the C2+ plus electron system.

physics.atom-ph↗
arXiv2012

Electron Temperatures and Free-Electron Energy Distributions of Nebulae from C II Dielectronic Recombination Lines

A recently generated theoretical line list of C II dielectronic recombination lines together with observational data gathered from the literature is used to investigate the electron temperature in a range of astronomical objects, mainly planetary nebulae. The electron temperature is obtained by a least-squares optimisation using all the reliable observed lines in each object. In addition, the subset of lines arising directly from autoionising states is used to directly determine the free-electron energy distribution which is then compared with various theoretical possibilities. The method described here can potentially determine whether there are departures from Maxwell-Boltzmann distributions in some nebulae, as has been recently proposed. Using published observations of the three planetary nebulae where the relevant lines are recorded, we find that the data are best matched by Maxwell-Boltzmann distributions but that the uncertainties are sufficiently large at present that kappa-distributions or two-component nebular models are not excluded.

astro-ph.SR↗
arXiv2012

Newtonian Flow in Converging-Diverging Capillaries

The one-dimensional Navier-Stokes equations are used to derive analytical expressions for the relation between pressure and volumetric flow rate in capillaries of five different converging-diverging axisymmetric geometries for Newtonian fluids. The results are compared to previously-derived expressions for the same geometries using the lubrication approximation. The results of the one-dimensional Navier-Stokes are identical to those obtained from the lubrication approximation within a non-dimensional numerical factor. The derived flow expressions have also been validated by comparison to numerical solutions obtained from discretization with numerical integration. Moreover, they have been certified by testing the convergence of solutions as the converging-diverging geometries approach the limiting straight geometry.

math-ph↗
arXiv2012

Atomic and Molecular Aspects of Astronomical Spectra

In the first section we present the atomic part where a C2+ atomic target was prepared and used to generate theoretical data to investigate recombination lines arising from electron-ion collisions in thin plasma. R-matrix method was used to describe the C2+ plus electron system. Theoretical data concerning bound and autoionizing states were generated in the intermediate-coupling approximation. The data were used to generate dielectronic recombination data for C+ which include transition lines, oscillator strengths, radiative transition probabilities, emissivities and dielectronic recombination coefficients. The data were cast in a line list containing 6187 optically-allowed transitions which include many C II lines observed in astronomical spectra. This line list was used to analyze the spectra from a number of astronomical objects, mainly planetary nebulae, and identify their electron temperature. The electron temperature investigation was also extended to include free electron energy analysis to investigate the long-standing problem of discrepancy between the results of recombination and forbidden lines analysis and its possible connection to the electron distribution. In the second section we present the results of our molecular investigation; the generation of a comprehensive, calculated line list of frequencies and transition probabilities for H2D+. The line list contains over 22 million rotational-vibrational transitions occurring between more than 33 thousand energy levels and covers frequencies up to 18500 cm-1. About 15% of these levels are fully assigned with approximate rotational and vibrational quantum numbers. A temperature-dependent partition function and cooling function are presented. Temperature-dependent synthetic spectra for the temperatures T=100, 500, 1000 and 2000 K in the frequency range 0-10000 cm-1 were also generated and presented graphically.

physics.atom-ph↗
arXiv2012

Recombination Lines of CII in the Spectra of Planetary Nebulae

The current report presents the work to investigate the recombination lines of CII in the spectra of planetary nebulae. Two CIII targets were prepared and used to generate theoretical data required in the investigation of recombination lines that arise from collisions between electrons and ions in thin plasma found in planetary nebulae and other astrophysical objects. One of these targets contains 9 atomic terms while the other contains 26 terms. For each one of these targets, theoretical data concerning bound and autoionizing states were generated in the intermediate coupling approximation by R-matrix and Autostructure codes and compared to experimental data. The comparison revealed very good agreement. These theoretical data were then used to generate emissivity data and compare it to the carbon recombination lines found in the observational line list of Zhang et al [2005] on the planetary nebula NGC 7027. The main tool used in this analysis is the `Emissivity' code which is a program developed by the author [2010] in the course of this investigation to calculate the emissivity of transition lines from resonances and subsequent cascade decay. The results of the analysis from both targets using a least-squares optimization technique indicate a temperature of 10200-10500K of the line-emitting region.

physics.atom-ph↗
arXiv2011

Testing the Connectivity of Networks

In this article we discuss general strategies and computer algorithms to test the connectivity of unstructured networks which consist of a number of segments connected through randomly distributed nodes.

cs.DS↗
arXiv2011

Slip at Fluid-Solid Interface

The `no-slip' is a fundamental assumption and generally-accepted boundary condition in rheology, tribology and fluid mechanics with strong experimental support. The violations of this condition, however, are widely recognized in many situations, especially in the flow of non-Newtonian fluids. Wall slip could lead to large errors and flow instabilities, such as sharkskin formation and spurt flow, and hence complicates the analysis of fluid systems and introduces serious practical difficulties. In this article, we discuss slip at fluid-solid interface in an attempt to highlight the main issues related to this diverse complex phenomenon and its implications.

physics.flu-dyn↗
arXiv2010

High Throughput Software for Powder Diffraction and its Application to Heterogeneous Catalysis

In this thesis we investigate high throughput computational methods for processing large quantities of data collected from synchrotrons and their application to spectral analysis of powder diffraction data. We also present the main product of this PhD programme, specifically a software called 'EasyDD' developed by the author. This software was created to meet the increasing demand on data processing and analysis capabilities as required by modern detectors which produce huge quantities of data. Modern detectors coupled with the high intensity X-ray sources available at synchrotrons have led to the situation where datasets can be collected in ever shorter time scales and in ever larger numbers. Such large volumes of datasets pose a data processing bottleneck which augments with current and future instrument development. EasyDD has achieved its objectives and made significant contributions to scientific research. It can also be used as a model for more mature attempts in the future. EasyDD is currently in use by a number of researchers in a number of academic and research institutions to process high-energy diffraction data. These include data collected by different techniques such as Energy Dispersive Diffraction, Angle Dispersive Diffraction and Computer Aided Tomography. EasyDD has already been used in a number of published studies, and is currently in use by the High Energy X-Ray Imaging Technology project. The software was also used by the author to process and analyse datasets collected from synchrotron radiation facilities. In this regard, the thesis presents novel scientific research involving the use of EasyDD to handle large diffraction datasets in the study of alumina-supported metal oxide catalyst bodies. These data were collected using Tomographic Energy Dispersive Diffraction Imaging and Computer Aided Tomography techniques.

physics.data-an↗