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.

Coatings on Composites

Polymer based composite materials coated with thin layers of wear resistant materials have been proposed as replacements for steel components for certain applications with the advantage of reduced mass. Magnetron sputtered coatings can be successfully deposited on composite materials. Nevertheless there are number of issues which must be addressed such as limited temperature, which the composite can withstand because of the epoxy binder which is used, the adhesion of the coating to the composite and the limited mechanical support, the hard coating can obtain from the relatively soft epoxy. We have investigated the deposition of chromium nitride, titanium carbide and titanium doped DLC coatings on carbon fibre reinforced composites and various polymers. The adhesion of the coatings has been studied by the pull-off adhesion tester. In general, the failure mechanism has been noticed to be due to the cohesive failure for a wide range of conditions. The wear behavior of the coatings has been noticed to be complicated. Wear tests on coated composites have shown that where the reinforcing fibres are near the surface, the composite samples do not perform well due to breakage of the fibres from the polymer matrix. A fibre free surface has been noticed to improve the wear resistance.

Biopolttoaineilla toimiva Stirling-voimalaitos

Stirling-moottori on ns. kuumailma moottori, joka toimii kaasun lämpötilaeron avulla. Kuumailma moottorin erityispiirteitä on laitteen ulkopuolella tapahtuva palaminen, josta lämpö johdetaan moottorille. Yleensä polttoaineena on käytetty vähän likaavaa polttoainetta esim. maakaasua mutta fossiilisten polttoaineiden kallistumisen ja niistä aiheutuvien päästöjen vuoksi niiden korvaaminen biopolttoaineella on tullut ajankohtaiseksi aiheeksi. Biopolttoaineiden likaavuuden takia niillä ei kuitenkaan voida lämmittää Stirling-moottoria suoraan vaan tarvitaan ylimääräinen lämmönsiirrin. Tämä diplomityö suoritettiin Lappeenrannan teknilliselle yliopistolle ja sen tarkoituksena oli tutkia juuri tähän laitteistoon suunnitellun, Stirling-moottorin ja polttokammion välisen lämmönsiirtimen suoritusarvoja ja likaantumista. Lisäksi työssä tutkittiin lämmönsiirtimeltä Stirling-moottorille menevien ilmaputkien lämpöhäviöitä. Työssä tultiin siihen tulokseen, että tämän tyyppinen lämmönsiirrin on suoritusarvoiltaan keskiverto kaasu-kaasu lämmönsiirrintä parempi ja ei likaannu erityisen nopeasti. Lämpöhäviöt olivat toisaalta merkittävämmässä asemassa kuin likaantuminen. Suurista lämpötiloista johtuva eristeiden lämmöneristyskyvyn heikkeneminen tai lämmönsiirtimen vuoto aiheutti merkittäviä lämpöhäviöitä.

Trigger and data link system for CMS Resistive Plate Chambers at the LHC accelerator

The purpose of the work was to realize a high-speed digital data transfer system for RPC muon chambers in the CMS experiment on CERN’s new LHC accelerator. This large scale system took many years and many stages of prototyping to develop, and required the participation of tens of people. The system interfaces to Frontend Boards (FEB) at the 200,000-channel detector and to the trigger and readout electronics in the control room of the experiment. The distance between these two is about 80 metres and the speed required for the optic links was pushing the limits of available technology when the project was started. Here, as in many other aspects of the design, it was assumed that the features of readily available commercial components would develop in the course of the design work, just as they did. By choosing a high speed it was possible to multiplex the data from some the chambers into the same fibres to reduce the number of links needed. Further reduction was achieved by employing zero suppression and data compression, and a total of only 660 optical links were needed. Another requirement, which conflicted somewhat with choosing the components a late as possible was that the design needed to be radiation tolerant to an ionizing dose of 100 Gy and to a have a moderate tolerance to Single Event Effects (SEEs). This required some radiation test campaigns, and eventually led to ASICs being chosen for some of the critical parts. The system was made to be as reconfigurable as possible. The reconfiguration needs to be done from a distance as the electronics is not accessible except for some short and rare service breaks once the accelerator starts running. Therefore reconfigurable logic is extensively used, and the firmware development for the FPGAs constituted a sizable part of the work. Some special techniques needed to be used there too, to achieve the required radiation tolerance. The system has been demonstrated to work in several laboratory and beam tests, and now we are waiting to see it in action when the LHC will start running in the autumn 2008.

DFM(A)- aspects for a fixed electrical attenuator design

The goal of this paper is to describe a complete and extensive prototype design of a fixed electrical attenuator. The paper starts by describing the function and by giving some basic information about the attenuators. After a comprehensive description of the component, the facts of reverse engineering are discussed. The method itself is applied to ease manufacturing and design stages of this component. Information about materials and applied manufacturing technologies are also included in this report. By applying some specified DFMA-aspects the final design turned out to be a potential prototype device to be manufactured and for further analyse.

DFM(A)- aspects for a microwave waveguide ring resonator design

In this research manufacturability analysis is made for an E-plane waveguide ring resonator. About the electrical characteristics of the waveguide ring resonator is discussed. Possibilities to utilize concurrent engineering method both for designing and making manufacturability analysis for MW- and RF-components are discussed. For helping to establish the necessary guidelines for easy manufacturing and assembly of the waveguide ring resonator a specialised DFM(A)-questionnaire is generated. The questionnaire gives also new information for collaborative designing approach in MW-/RF- engineering. The advantages and disadvantages of the concurrent engineering design method are evaluated in the research.

DFM(A)- aspects for a horn antenna design

In this paper aspects of design for manufacturability and assembly (DFMA) are applied to the design of coaxially fed standard gain horn antenna for 1.70 - 2.60 GHz. Possibilities to utilize cross-technological approach method is examined. Methods of DFMA for laser processing are covered and practical design guides and methods are developed. Antenna construction for easy manufacturing and specialized performance is shown. Required dimensions and tolerances are discussed and suitable materials for laser processing are selected.

DFM(A)- aspects for an sma connector design

In this research, manufacturability analysis is made for an SMA connector. Analysis and aspects of applying virtual prototyping for an SMA connector design and manufacturing are also investigated. Special questionnaires for the component and machining are made in order to enable necessary information to ensure DFM(A) –aspects of products. The aspects of easy manufacturing for machining the SMA connector are collected. Material selection is discussed, and manufacturing stages of prototype manufacturing are presented. The main focus of this research is on prototype manufacturing, but also aspects considering volume production are discussed. A special purpose SMA connector is designed for printed circuit board edge mounting.

Trust in inter-organizational relationships

Trust in inter-organizational collaborative relationships has attracted substantial research interest among academics and practitioners. Previous studies have concentrated on the benefits of trust to business outcomes and economic performance, as it is considered to be a source of competitive advantage. Despite this increased level of interest, there is no consensus, much less overall agreement, about how it should be conceptualized or about the number of dimensions it incorporates. On the inter-organizational level there is an obvious challenge in defining both the trusting party and the objects of trust. Thus, the notion of trust as an under-theorized and poorly understood phenomenon still holds. Hence, the motivation of this study was fuelled by the need to increase our knowledge and understanding of the role and nature of trust in inter-organizational collaborative relationships. It is posited that there is a call for more understanding about its antecedents and consequences, as well as about the very concept in inter-organizational collaborative relationships. The study is divided into two parts. The first part gives a general overview, and the second part comprises four research publications. Both qualitative and quantitative research methodology is utilized. A multi-method research design was used because it provides different levels of data and different perspectives on the phenomenon. The results of this study reveal that trust incorporates three dimensions on both the individual and the organizational level: capability, goodwill, and self-reference. Trust develops from the reputation and behavior of the trusted party. It appears from this study that trust is clearly directed towards both individual boundary spanners and the counterpart company itself – i.e. not only to one or the other. The trusting party, on the other hand, is always an individual, and not the organization per se. Trust increases collaboration benefits and lowers collaboration drawbacks, thus having a positive effect on relationship performance. The major contribution of this study lies in uncovering the critical points and drawbacks in prior research and thereby in responding to the highlighted challenges. The way in which these challenges were addressed offers contributions to three major issues in the emerging theory of trust in the inter-organizational context: firstly, this study clarifies the trustor-trustee discussion; secondly, it conceptualizes trust as existing on both individual and organizational levels; and thirdly, it provides more information about the antecedents of trust and the ways in which it affects relationship performance.

Rouhintasorvauksen säätöjärjestelmä

Tässä työssä kuvataan menetelmä, jonka avulla on mahdollista sorvausprosessista mitattujen signaalien perusteella muokata lastuamisprosessin parametreja siten, että prosessissa mahdollisesti esiintyvät ongelmatilanteet korjataan. Työ on tehty osana Feedchip-tutkimushanketta ja tukeutuu tutkimushankkeessa aiemmin tehtyyn työhön vaadittavien korjaustoimenpiteiden, signaaleja mittaavien antureiden instrumentoinnin sekä alustavan ongelmatilanteiden ominaispiirteiden signaaleista tunnistuksen osalta. Tämä työ keskittyy esittelemään toiminnot, joiden avulla aiemmat tulokset voidaan koota yhteen kokonaisuuteen. Järjestelmän toiminta edellyttää sen osien toiminnan korkean tason koordinointia. Lisäksi määritellään päättelyjärjestelmä, joka kykenee mitatuista arvoista tunnistettujen ongelmatilanteiden esiintymisasteiden perusteella määrittämään tarvittavat toimenpiteet ongelmatilanteiden poistamiseksi. Kandidaatintyön rinnalla toteutetaan ohjelmisto Lappeenrannan teknillisen yliopiston konepajatekniikan laboratorion sorvausjärjestelmän yhteyteen rakennetun prototyyppilaitteiston ohjaamiseksi.

Knowledge sharing in virtual communities

The Internet has transformed the scope, boundaries and dynamics of social and economic interactions. It is argued to have broadened the notion of the community from physical, colocated groups towards collectives that are able to transcend time and space, i.e. virtual communities. Even if virtual communities have been on the academic agenda for a couple of decades, there is still surprisingly little research on knowledge sharing within them. In addition, prior research has largely neglected the complex dynamics between Internet-based communication channels and the surrounding communities in which they are embedded. This thesis aims at building a better understanding of knowledge sharing supported by conversational technologies in intra-organisational virtual communities and external virtual communities supporting relationships with customers. The focus is thus on knowledge sharing in types of virtual communities that seem to be of relevance to business organisations. The study consists of two parts. The first part introduces the research topic and discusses the overall results. The second part comprises seven research publications. Qualitative research methods are used throughout the study. The results of the study indicate that investigation of the processes of knowledge sharing in virtual communities requires a socio-technical perspective, combining the individual, social and technological levels, and understanding the interplay between them. It is claimed that collective knowledge in virtual communities creates the enabling structure for knowledge sharing, and forms the invisible structure of the community on the basis of which it operates. It consists of a shared context, social capital and a unique community culture. The Internet does not inevitably erode social interaction: it seems that supporting social relationships by means of communication technology is a matter of quantity rather than quality. In order to provide access to external knowledge and expertise, firms need to open themselves up to an array of Internet-based conversations, and to consider the relevance of virtual communities to their businesses.

Modeling reaction kinetics and mass transfer in ozonation in water solutions

This dissertation is based on four articles dealing with modeling of ozonation. The literature part of this considers some models for hydrodynamics in bubble column simulation. A literature review of methods for obtaining mass transfer coefficients is presented. The methods presented to obtain mass transfer are general models and can be applied to any gas-liquid system. Ozonation reaction models and methods for obtaining stoichiometric coefficients and reaction rate coefficients for ozonation reactions are discussed in the final section of the literature part. In the first article, ozone gas-liquid mass transfer into water in a bubble column was investigated for different pH values. A more general method for estimation of mass transfer and Henry’s coefficient was developed from the Beltrán method. The ozone volumetric mass transfer coefficient and the Henry’s coefficient were determined simultaneously by parameter estimation using a nonlinear optimization method. A minor dependence of the Henry’s law constant on pH was detected at the pH range 4 - 9. In the second article, a new method using the axial dispersion model for estimation of ozone self-decomposition kinetics in a semi-batch bubble column reactor was developed. The reaction rate coefficients for literature equations of ozone decomposition and the gas phase dispersion coefficient were estimated and compared with the literature data. The reaction order in the pH range 7-10 with respect to ozone 1.12 and 0.51 the hydroxyl ion were obtained, which is in good agreement with literature. The model parameters were determined by parameter estimation using a nonlinear optimization method. Sensitivity analysis was conducted using object function method to obtain information about the reliability and identifiability of the estimated parameters. In the third article, the reaction rate coefficients and the stoichiometric coefficients in the reaction of ozone with the model component p-nitrophenol were estimated at low pH of water using nonlinear optimization. A novel method for estimation of multireaction model parameters in ozonation was developed. In this method the concentration of unknown intermediate compounds is presented as a residual COD (chemical oxygen demand) calculated from the measured COD and the theoretical COD for the known species. The decomposition rate of p-nitrophenol on the pathway producing hydroquinone was found to be about two times faster than the p-nitrophenol decomposition rate on the pathway producing 4- nitrocatechol. In the fourth article, the reaction kinetics of p-nitrophenol ozonation was studied in a bubble column at pH 2. Using the new reaction kinetic model presented in the previous article, the reaction kinetic parameters, rate coefficients, and stoichiometric coefficients as well as the mass transfer coefficient were estimated with nonlinear estimation. The decomposition rate of pnitrophenol was found to be equal both on the pathway producing hydroquinone and on the path way producing 4-nitrocathecol. Comparison of the rate coefficients with the case at initial pH 5 indicates that the p-nitrophenol degradation producing 4- nitrocathecol is more selective towards molecular ozone than the reaction producing hydroquinone. The identifiability and reliability of the estimated parameters were analyzed with the Marcov chain Monte Carlo (MCMC) method. @All rights reserved. No part of the publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior permission of the author.

Tuulivoimakäyttö sähköverkon vikatilanteissa

Tämä työ on tehty Lappeenrannan teknillisessä yliopistossa, meneillään olevan tuulivoimalasimulaattorin kehitystyön yhteydessä. Työssä käydään läpi simulaattorissa käytettyjen generaattorisillan ja verkkosillan säätöperiaatteita, tehdään katsaus siirtoverkon jännitevikoihin sekä tuulivoimalan toimintaan näissä vikatilanteissa. Työn varsinainen tutkimuskohde on verkkosillan säädön toiminnan simuloiminen siirtoverkon jännitevioissa ja säädön parannusehdotukset.

Market Opportunities for Paper Industry in Radio Frequency Identification

The paper industry has been experiencing remarkable structural changes since paper demand growth has ceased and some markets are declining. One reason behind the declined demand is the Internet, which has partially substituted the newspaper as a source of information. Paper products alone can no longer provide livelihood, and the paper industry has to find new business areas. In this research, we studied radio frequency identification (RFID), and the market opportunities it could provide for paper industry. The research combined a quantitative industry analysis and qualitative interviews. RFID is a growing industry in the beginning of its life cycle, in which value chains and technologies still evolve significantly. The industry is going to concentrate on the future, and in the long term RFID-identifiers will probably be printed on paper substrate or directly onto products. Paper industry has the chance to enter the RFID industry, but it has to obtain the required competences, for example through acquisitions. The business potential RFID offers to paper industry is inadequate, and while reviewing new strategic options, the paper industry must consider more options, for example the entire printed intelligence.