Modeling the transport phenomena within arterial wall: porous media approach

The transport of macromolecules, such as low-density lipoprotein (LDL), and their accumulation in the layers of the arterial wall play a critical role in the creation and development of atherosclerosis. Atherosclerosis is a disease of large arteries e.g., the aorta, coronary, carotid, and other proximal arteries that involves a distinctive accumulation of LDL and other lipid-bearing materials in the arterial wall. Over time, plaque hardens and narrows the arteries. The flow of oxygen-rich blood to organs and other parts of the body is reduced. This can lead to serious problems, including heart attack, stroke, or even death. It has been proven that the accumulation of macromolecules in the arterial wall depends not only on the ease with which materials enter the wall, but also on the hindrance to the passage of materials out of the wall posed by underlying layers. Therefore, attention was drawn to the fact that the wall structure of large arteries is different than other vessels which are disease-resistant. Atherosclerosis tends to be localized in regions of curvature and branching in arteries where fluid shear stress (shear rate) and other fluid mechanical characteristics deviate from their normal spatial and temporal distribution patterns in straight vessels. On the other hand, the smooth muscle cells (SMCs) residing in the media layer of the arterial wall respond to mechanical stimuli, such as shear stress. Shear stress may affect SMC proliferation and migration from the media layer to intima. This occurs in atherosclerosis and intimal hyperplasia. The study of blood flow and other body fluids and of heat transport through the arterial wall is one of the advanced applications of porous media in recent years. The arterial wall may be modeled in both macroscopic (as a continuous porous medium) and microscopic scales (as a heterogeneous porous medium). In the present study, the governing equations of mass, heat and momentum transport have been solved for different species and interstitial fluid within the arterial wall by means of computational fluid dynamics (CFD). Simulation models are based on the finite element (FE) and finite volume (FV) methods. The wall structure has been modeled by assuming the wall layers as porous media with different properties. In order to study the heat transport through human tissues, the simulations have been carried out for a non-homogeneous model of porous media. The tissue is composed of blood vessels, cells, and an interstitium. The interstitium consists of interstitial fluid and extracellular fibers. Numerical simulations are performed in a two-dimensional (2D) model to realize the effect of the shape and configuration of the discrete phase on the convective and conductive features of heat transfer, e.g. the interstitium of biological tissues. On the other hand, the governing equations of momentum and mass transport have been solved in the heterogeneous porous media model of the media layer, which has a major role in the transport and accumulation of solutes across the arterial wall. The transport of Adenosine 5´-triphosphate (ATP) is simulated across the media layer as a benchmark to observe how SMCs affect on the species mass transport. In addition, the transport of interstitial fluid has been simulated while the deformation of the media layer (due to high blood pressure) and its constituents such as SMCs are also involved in the model. In this context, the effect of pressure variation on shear stress is investigated over SMCs induced by the interstitial flow both in 2D and three-dimensional (3D) geometries for the media layer. The influence of hypertension (high pressure) on the transport of lowdensity lipoprotein (LDL) through deformable arterial wall layers is also studied. This is due to the pressure-driven convective flow across the arterial wall. The intima and media layers are assumed as homogeneous porous media. The results of the present study reveal that ATP concentration over the surface of SMCs and within the bulk of the media layer is significantly dependent on the distribution of cells. Moreover, the shear stress magnitude and distribution over the SMC surface are affected by transmural pressure and the deformation of the media layer of the aorta wall. This work reflects the fact that the second or even subsequent layers of SMCs may bear shear stresses of the same order of magnitude as the first layer does if cells are arranged in an arbitrary manner. This study has brought new insights into the simulation of the arterial wall, as the previous simplifications have been ignored. The configurations of SMCs used here with elliptic cross sections of SMCs closely resemble the physiological conditions of cells. Moreover, the deformation of SMCs with high transmural pressure which follows the media layer compaction has been studied for the first time. On the other hand, results demonstrate that LDL concentration through the intima and media layers changes significantly as wall layers compress with transmural pressure. It was also noticed that the fraction of leaky junctions across the endothelial cells and the area fraction of fenestral pores over the internal elastic lamina affect the LDL distribution dramatically through the thoracic aorta wall. The simulation techniques introduced in this work can also trigger new ideas for simulating porous media involved in any biomedical, biomechanical, chemical, and environmental engineering applications.

CFD simulation of complex phenomena containing suspensions and flow throughporous media

There is an increasing reliance on computers to solve complex engineering problems. This is because computers, in addition to supporting the development and implementation of adequate and clear models, can especially minimize the financial support required. The ability of computers to perform complex calculations at high speed has enabled the creation of highly complex systems to model real-world phenomena. The complexity of the fluid dynamics problem makes it difficult or impossible to solve equations of an object in a flow exactly. Approximate solutions can be obtained by construction and measurement of prototypes placed in a flow, or by use of a numerical simulation. Since usage of prototypes can be prohibitively time-consuming and expensive, many have turned to simulations to provide insight during the engineering process. In this case the simulation setup and parameters can be altered much more easily than one could with a real-world experiment. The objective of this research work is to develop numerical models for different suspensions (fiber suspensions, blood flow through microvessels and branching geometries, and magnetic fluids), and also fluid flow through porous media. The models will have merit as a scientific tool and will also have practical application in industries. Most of the numerical simulations were done by the commercial software, Fluent, and user defined functions were added to apply a multiscale method and magnetic field. The results from simulation of fiber suspension can elucidate the physics behind the break up of a fiber floc, opening the possibility for developing a meaningful numerical model of the fiber flow. The simulation of blood movement from an arteriole through a venule via a capillary showed that the model based on VOF can successfully predict the deformation and flow of RBCs in an arteriole. Furthermore, the result corresponds to the experimental observation illustrates that the RBC is deformed during the movement. The concluding remarks presented, provide a correct methodology and a mathematical and numerical framework for the simulation of blood flows in branching. Analysis of ferrofluids simulations indicate that the magnetic Soret effect can be even higher than the conventional one and its strength depends on the strength of magnetic field, confirmed experimentally by Völker and Odenbach. It was also shown that when a magnetic field is perpendicular to the temperature gradient, there will be additional increase in the heat transfer compared to the cases where the magnetic field is parallel to the temperature gradient. In addition, the statistical evaluation (Taguchi technique) on magnetic fluids showed that the temperature and initial concentration of the magnetic phase exert the maximum and minimum contribution to the thermodiffusion, respectively. In the simulation of flow through porous media, dimensionless pressure drop was studied at different Reynolds numbers, based on pore permeability and interstitial fluid velocity. The obtained results agreed well with the correlation of Macdonald et al. (1979) for the range of actual flow Reynolds studied. Furthermore, calculated results for the dispersion coefficients in the cylinder geometry were found to be in agreement with those of Seymour and Callaghan.

Drag force and frictional resistances in vertically vibrated dense granular media

The objective of this thesis is to shed light on the vertical vibration of granular materials for potential interest in the power generation industry. The main focus is investigating the drag force and frictional resistance that influence the movement of a granular material (in the form of glass beads) contained in a vessel, which is subjected to sinusoidal oscillation. The thesis is divided into three parts: theoretical analysis, experiments and computer simulations. The theoretical part of this study presents the underlying physical phenomena of the vibration of granular materials. Experiments are designed to determine fundamental parameters that contribute to the behavior of vibrating granular media. Numerical simulations include the use of three different software applications: FLUENT, LS-DYNA and ANSYS Workbench. The goal of these simulations is to test theoretical and semiempirical models for granular materials in order to validate their compatibility with the experimental findings, to assist in predicting their behavior, and to estimate quantities that are hard to measure in laboratory.

Electrochemical Characterisation of Filter Media Properties and Their Exploitation in Enhanced Filtration

Streaming potential measurements for the surface charge characterisation of different filter media types and materials were used. The equipment was developed further so that measurements could be taken along the surfaces, and so that tubular membranes could also be measured. The streaming potential proved to be a very useful tool in the charge analysis of both clean and fouled filter media. Adsorption and fouling could be studied, as could flux, as functions of time. A module to determine the membrane potential was also constructed. The results collected from the experiments conducted with these devices were used in the study of the theory of streaming potential as an electrokinetic phenomenon. Several correction factors, which are derived to take into account the surface conductance and the electrokinetic flow in very narrow capillaries, were tested in practice. The surface materials were studied using FTIR and the results compared with those from the streaming potentials. FTIR analysis was also found to be a useful tool in the characterisation of filters, as well as in the fouling studies. Upon examination of the recorded spectra from different depths in a sample it was possible to determine the adsorption sites. The influence of an external electric field on the cross flow microflltration of a binary protein system was investigated using a membrane electroflltration apparatus. The results showed that a significant improvement could be achieved in membrane filtration by using the measured electrochemical properties to help adjust the process conditions.

De scientia Dei media

Invocatio: kreik.

Yhdessä ja liikkeellä. Mobiili sosiaalinen media

Sosiaalinen media viittaa verkkopalveluihin, joiden toiminta perustuu käyttäjien ja käyttäjäyhteisöjen aktiiviseen sosiaaliseen vuorovaikutukseen. Matkapuhelimien kautta sosiaalinen media on liikkeellä ja pitää käyttäjät yhdessä ajasta ja paikasta riippumatta. Sosiaalisen median vetovoima perustuu siihen, että ihmiset jakavat tietoja, kuvia, videota ja ääntä sekä kommentoivat ja jatkavat viestiketjuja. Yhdessä ja liikkeellä -kirja tarkastelee sosiaalisen median uusinta ilmiötä, videoiden jakamista kännykkäpalvelun kautta. Mobiilit videot voivat kertoa jaetuista elämyksistä, konserteista, benji-hypyistä tai jazz-festivaalin vessajonosta. Liikkuva kuva kertoo usein enemmän kuin useampi valokuva, ja monen käyttäjän videokuva samasta tapahtumasta voi jo kertoa monipolvisen tarinan. Yhdessä ja liikkeellä esittelee Mobile Social Media -tutkimushankkeen tuloksia. Tavoitteena on ollut tutkia, millaiset tekijät tukevat mobiilin sosiaalisen median käyttöä ja miten sosiaalista mediaa hyödynnetään matkapuhelimilla, miten sosiaalisen median yhteisö voi muodostaa kännykkävideoista yhteisen tarinan, millaisia teknologisia haasteita mobiilin sosiaalisen median käytölle on. Tutkimushanke on CAT - Culture Art and Technology -verkoston yhteistyötä. Verkostoon kuuluvat Aalto-yliopiston, Tampereen teknillisen yliopiston ja Turun yliopiston Porin yksiköt.

Utilizing social media in software documentation and knowledge management

This Master’s thesis studies the possibilities that social media tools can bring to help knowledge management in software development companies. It will introduce the most popular tools of social media and their usage possibilities in companies, not forgetting the possible downsides. One relevant aspect in this study is to investigate the possibilities of social media to help converting existing tacit knowledge into explicit. The purpose of the work is to create a proposal of social media utilization for a mid-sized software company, which has not utilized social media tools before. To be able to create the proposal, employees of the company are interviewed and a survey is executed to analyze the current situation. In addition a pilot project for trying out new social media tools is executed. The final result of this thesis introduces a tailored solution for the target company to start utilizing social media in its documentation and knowledge sharing processes. This new solution consists of multiple individual suggestions that are categorized and prioritized based on the significance and benefit that they bring to the company.

Seriedebatt i 1950-talets Finland : en studie i barndom, media och reglering

I avhandlingen granskas den debatt som fördes om seriemediet och serieläsandet i Finland från början av 1950-talet till början av 1960-talet. Serietidningen var då ett nytt medium och föranledde en oro beträffande barns läsvanor. ”Seriefrågan” diskuterades i pressen och problematiken engagerade barnskyddsorganisationer och forskare, behandlades i riksdagen och undersöktes av en statlig kommitté. De olika debattuttrycken analyseras i studien. Avhandlingens teoretiska perspektiv är styrningsanalytiskt och bygger på diskussionen om regementalitet (governmentality). I studien granskas hur seriemediet, barndom och regleringen av dessa kom att definieras i behandlingen av det s.k. serieproblemet. Serierna definierades som ett problematiskt medium på ett flertal sätt. De huvudsakliga argumenten mot serierna var dels att de förstörde barns läsförmåga, dels att de budskap som serierna förmedlade till barnen var av fel slag. Enligt kritiken var serierna språkligt fattiga och innehållsmässigt alltför våldsamma. Följaktligen utgjorde serierna ett hot mot barnen. Barnen kom ur detta perspektiv att definieras som inkompetenta medieanvändare och i behov av skydd. I debatten upplyftes olika sätt att lösa och reglera problemet. Man undersökte problematiken och upplyste allmänheten om den, man försökte påverka serieutgivarna och man påkallade censur. Seriedebatten och den verksamhet som debattörerna ägnade sig åt ledde dock inte till synbara resultat, t.ex. ny lagstiftning eller förändringar i seriemarknaden. Ändå dog debatten i början av 1960-talet. Problemet med de serieläsande barnen hanterades m.a.o. genom själva debatten. Samtidigt uteblev mera drastiska former av reglering. Ett övergripande syfte för analysen av den kunskap som skapades i debatten – dess varierande förståelse av seriemedium, barndom och reglering – är att erbjuda infallsvinklar till aktuella diskussioner om och farhågor angående barns mediebruk. Med fokus på bredden hos debattens uttryck och de diskursiva ramarna för problematiseringen av barns serieläsande ger avhandlingen perspektiv på den med jämna mellanrum uppdykande frågeställningen om barns mediebruk.