Fluid flow in T-junction of pipes

The aim of this work is to study flow properties at T-junction of pipe, pressure loss suffered by the flow after passing through T-junction and to study reliability of the classical engineering formulas used to find head loss for T-junction of pipes. In this we have compared our results with CFD software packages with classical formula and made an attempt to determine accuracy of the classical formulas. In this work we have studies head loss in T-junction of pipes with various inlet velocities, head loss in T-junction of pipes when the angle of the junction is slightly different from 90 degrees and T-junction with different area of cross-section of the main pipe and branch pipe. In this work we have simulated the flow at T-junction of pipe with FLUENT and Comsol Multiphysics and observed flow properties inside the T-junction and studied the head loss suffered by fluid flow after passing through the junction. We have also compared pressure (head) losses obtained by classical formulas by A. Vazsonyi and Andrew Gardel and formulas obtained by assuming T-junction as combination of other pipe components and observations obtained from software experiments. One of the purposes of this study is also to study change in pressure loss with change in angle of T-junction. Using software we can have better view of flow inside the junction and study turbulence, kinetic energy, pressure loss etc. Such simulations save a lot of time and can be performed without actually doing the experiment. There were no real life experiments made, the results obtained completely rely on accuracy of software and numerical methods used.

Current-phase relation in graphene Josephson junction

In this thesis, we present the results of high-frequency measurements on superconductor-graphene-superconductor junctions. We obtained the relation between the supercurrent through the junction and the superconducting phase. The relation allowed us to extract true critical current and to determine the transport regime of graphene in our SGS-junction samples at the Dirac point and away from it. An experimental temperature dependence of the current-phase relation is presented. We have calculated theoretical supercurrent-phase relation in the case of ballistic and diffusive junction. For the diffusive case, we have considered short and long limits where the coherence length is larger or smaller than the sample length, respectively.

IGBT-simulaatiomallien soveltuvuus laitetason hyötysuhdesimulaatioihin

Tehoelektroniikkalaitteiden tehon kasvun myötä niiden hyötysuhteesta on tullut yksi niiden tärkeimmistä ominaisuuksista. Suurilla tehoilla prosentuaalisesti pienetkin tehohäviöt ovat merkittäviä ja aiheuttavat laitteen käyttäjälle ylimääräisiä energiakustannuksia ja tarvetta hukkalämmön poistolle. Näistä syistä asiakkaat vaativat hyvällä hyötysuhteella toimivia laitteita, joten laitevalmistajat pyrkivät tekemään niistä sellaisia. Simulaatiomallit ovat arvokkaita työkaluja laitesuunnittelussa. Hyötysuhdeoptimoinnin kannalta tehohäviöt tulisi pystyä mallintamaan, jotta komponenttivalintojen, ohjaustapojen ja pääpiiritopologioiden vaikutusta hyötysuhteeseen voitaisiin arvioida. Tässä työssä perehdytään eristehilabipolaaritransistorista (IGBT) tehtyihin simulaatiomalleihin ja arvioidaan niiden soveltuvuutta IGBT:ssä syntyvien tehohäviöiden mallintamiseen. Lisäksi verrataan mallia mittaukseen ja pohditaan, millaiset vaatimukset simulaatiomalliin todellisuudessa kohdistuvat.

Switching components for medium voltage drives

Nowadays power drives are the essential part almost of all technological processes. Improvement of efficiency and reduction of losses require development of semiconductor switches. It has a particular meaning for the constantly growing market of renewable sources, especially for wind turbines, which demand more powerful semiconductor devices for control with growth of power. Also at present semiconductor switches are the key component in energy transmission, optimization of generation and network connection. The aim of this thesis is to make a survey of contemporary semiconductor components, showing difference in structures, advantages, disadvantages and most suitable applications. There is topical information about voltage, frequency and current limits of different switches. Study tries to compare dimensions and price of different components. Main manufacturers of semiconductor components are presented with the review of devices produced by them, and a conclusion about their availability was made. IGBT is selected as a main component in this study, because nowadays it is the most attractive component for usage in power drives, especially at the low levels of medium voltage. History of development of IGBT structure, static and dynamic characteristics are considered. Thesis tells about assemblies and connection of components and problems which can appear. One of key questions about semiconductor materials and their future development was considered. For the purpose of comparison strong and weak sides of different switches, calculation of losses of IGBT and its basic competitor – IGCT is presented. This master’s thesis makes an effort to answer the question if there are at present possibilities of accurate selection of switches for electrical drives of different rates of power and looks at future possible ways of development of semiconductor market.

Membrane properties of structurally modified ceramides : effects on lipid lateral distribution and sphingomyelin-interactions in artificial bilayer membranes

Ceramides comprise a class of sphingolipids that exist only in small amounts in cellular membranes, but which have been associated with important roles in cellular signaling processes. The influences that ceramides have on the physical properties of bilayer membranes reach from altered thermodynamical behavior to significant impacts on the molecular order and lateral distribution of membrane lipids. Along with the idea that the membrane physical state could influence the physiological state of a cell, the membrane properties of ceramides have gained increasing interest. Therefore, membrane phenomena related to ceramides have become a subject of intense study both in cellular as well as in artificial membranes. Artificial bilayers, the so called model membranes, are substantially simpler in terms of contents and spatio-temporal variation than actual cellular membranes, and can be used to give detailed information about the properties of individual lipid species in different environments. This thesis focuses on investigating how the different parts of the ceramide molecule, i.e., the N-linked acyl chain, the long-chain sphingoid base and the membrane-water interface region, govern the interactions and lateral distribution of these lipids in bilayer membranes. With the emphasis on ceramide/sphingomyelin(SM)-interactions, the relevance of the size of the SMhead group for the interaction was also studied. Ceramides with methylbranched N-linked acyl chains, varying length sphingoid bases, or methylated 2N (amide-nitrogen) and 3O (C3-hydroxyl) at the interface region, as well as SMs with decreased head group size, were synthesized and their bilayer properties studied by calorimetric and fluorescence spectroscopic techniques. In brief, the results showed that the packing of the ceramide acyl chains was more sensitive to methyl-branching in the mid part than in the distal end of the N-linked chain, and that disrupting the interfacial structure at the amide-nitrogen, as opposed to the C3-hydroxyl, had greater effect on the interlipid interactions of ceramides. Interestingly, it appeared that the bilayer properties of ceramides could be more sensitive to small alterations in the length of the long-chain base than what was previously reported for the N-linked acyl chain. Furthermore, the data indicated that the SM-head group does not strongly influence the interactions between SMs and ceramides. The results in this thesis illustrate the pivotal role of some essential parts of the ceramide molecules in determining their bilayer properties. The thesis provides increased understanding of the molecular aspects of ceramides that possibly affect their functions in biological membranes, and could relate to distinct effects on cell physiology.

Before internationalisation : reflections of lateral rigidity on managerial decision making

The purpose of the study is to analyse lateral rigidity in the framework of pre-internationalisation to find out its reflections on managerial decision making. The interest of the study lies in the intersection of the meaningful but relatively stagnant concept of lateral rigidity, and the pre-internationalisation phase of companies that has received only a limited amount of research attention. The theoretical basis for the study is drawn from managerial decision making and internationalisation literatures. Firstly, the study aims to define the concept of lateral rigidity in order to secondly find out how it influences managers’ pre-internationalisation decision making. The study is theoretical in nature, and is based solely on literature examination. Concept analysis method is used to determine the attributes of lateral rigidity for the purpose of recognising the concept in the pre-internationalisation framework. The attributes that are found to comprise lateral rigidity are culture, know-how, uncertainty and attitude. Furthermore, these attributes are more specifically found to consist of environmental, personal and operational matters. Through the analysis of the pre-internationalisation literature it is discovered that all the attributes appear there, and present a variety of influences on pre-internationalisation decision making that can be characterised as being negative. The study finds that culture influences managers’ decision making via subjective reasoning and behaviour that stem from a domestic inclination, and via unfamiliarity with foreign markets. Against assumption, home cultural factors, e.g. values and customs, do not appear to have an influence. Know-how is found to influence decision making via managers’ previous experiences, subjective abiding perceptions, and the usage of previous operation patterns. Uncertainty, then again, influences managers’ risk perception, unfamiliarity avoidance, and the scope of potential international operations. Attitude is found to have a robust influence on managerial decision making via the usage of familiar processes and decision regimes, subjective preference of convention, and plausible results of operations. Ergo, the effects of lateral rigidity on managers show to represent an encumbrance in the pre-internationalisation phase; even though internationalisation would take place, the related decisions and actions are highly constrained. Especially the subjectivity of managers is seen to have a meaningful role in the decision making process.

Power semiconductor nonlinearities in active du/dt output filtering

This doctoral thesis introduces an improved control principle for active du/dt output filtering in variable-speed AC drives, together with performance comparisons with previous filtering methods. The effects of power semiconductor nonlinearities on the output filtering performance are investigated. The nonlinearities include the timing deviation and the voltage pulse waveform distortion in the variable-speed AC drive output bridge. Active du/dt output filtering (ADUDT) is a method to mitigate motor overvoltages in variable-speed AC drives with long motor cables. It is a quite recent addition to the du/dt reduction methods available. This thesis improves on the existing control method for the filter, and concentrates on the lowvoltage (below 1 kV AC) two-level voltage-source inverter implementation of the method. The ADUDT uses narrow voltage pulses having a duration in the order of a microsecond from an IGBT (insulated gate bipolar transistor) inverter to control the output voltage of a tuned LC filter circuit. The filter output voltage has thus increased slope transition times at the rising and falling edges, with an opportunity of no overshoot. The effect of the longer slope transition times is a reduction in the du/dt of the voltage fed to the motor cable. Lower du/dt values result in a reduction in the overvoltage effects on the motor terminals. Compared with traditional output filtering methods to accomplish this task, the active du/dt filtering provides lower inductance values and a smaller physical size of the filter itself. The filter circuit weight can also be reduced. However, the power semiconductor nonlinearities skew the filter control pulse pattern, resulting in control deviation. This deviation introduces unwanted overshoot and resonance in the filter. The controlmethod proposed in this thesis is able to directly compensate for the dead time-induced zero-current clamping (ZCC) effect in the pulse pattern. It gives more flexibility to the pattern structure, which could help in the timing deviation compensation design. Previous studies have shown that when a motor load current flows in the filter circuit and the inverter, the phase leg blanking times distort the voltage pulse sequence fed to the filter input. These blanking times are caused by excessively large dead time values between the IGBT control pulses. Moreover, the various switching timing distortions, present in realworld electronics when operating with a microsecond timescale, bring additional skew to the control. Left uncompensated, this results in distortion of the filter input voltage and a filter self-induced overvoltage in the form of an overshoot. This overshoot adds to the voltage appearing at the motor terminals, thus increasing the transient voltage amplitude at the motor. This doctoral thesis investigates the magnitude of such timing deviation effects. If the motor load current is left uncompensated in the control, the filter output voltage can overshoot up to double the input voltage amplitude. IGBT nonlinearities were observed to cause a smaller overshoot, in the order of 30%. This thesis introduces an improved ADUDT control method that is able to compensate for phase leg blanking times, giving flexibility to the pulse pattern structure and dead times. The control method is still sensitive to timing deviations, and their effect is investigated. A simple approach of using a fixed delay compensation value was tried in the test setup measurements. The ADUDT method with the new control algorithm was found to work in an actual motor drive application. Judging by the simulation results, with the delay compensation, the method should ultimately enable an output voltage performance and a du/dt reduction that are free from residual overshoot effects. The proposed control algorithm is not strictly required for successful ADUDT operation: It is possible to precalculate the pulse patterns by iteration and then for instance store them into a look-up table inside the control electronics. Rather, the newly developed control method is a mathematical tool for solving the ADUDT control pulses. It does not contain the timing deviation compensation (from the logic-level command to the phase leg output voltage), and as such is not able to remove the timing deviation effects that cause error and overshoot in the filter. When the timing deviation compensation has to be tuned-in in the control pattern, the precalculated iteration method could prove simpler and equally good (or even better) compared with the mathematical solution with a separate timing compensation module. One of the key findings in this thesis is the conclusion that the correctness of the pulse pattern structure, in the sense of ZCC and predicted pulse timings, cannot be separated from the timing deviations. The usefulness of the correctly calculated pattern is reduced by the voltage edge timing errors. The doctoral thesis provides an introductory background chapter on variable-speed AC drives and the problem of motor overvoltages and takes a look at traditional solutions for overvoltage mitigation. Previous results related to the active du/dt filtering are discussed. The basic operation principle and design of the filter have been studied previously. The effect of load current in the filter and the basic idea of compensation have been presented in the past. However, there was no direct way of including the dead time in the control (except for solving the pulse pattern manually by iteration), and the magnitude of nonlinearity effects had not been investigated. The enhanced control principle with the dead time handling capability and a case study of the test setup timing deviations are the main contributions of this doctoral thesis. The simulation and experimental setup results show that the proposed control method can be used in an actual drive. Loss measurements and a comparison of active du/dt output filtering with traditional output filtering methods are also presented in the work. Two different ADUDT filter designs are included, with ferrite core and air core inductors. Other filters included in the tests were a passive du/dtfilter and a passive sine filter. The loss measurements incorporated a silicon carbide diode-equipped IGBT module, and the results show lower losses with these new device technologies. The new control principle was measured in a 43 A load current motor drive system and was able to bring the filter output peak voltage from 980 V (the previous control principle) down to 680 V in a 540 V average DC link voltage variable-speed drive. A 200 m motor cable was used, and the filter losses for the active du/dt methods were 111W–126 W versus 184 W for the passive du/dt. In terms of inverter and filter losses, the active du/dt filtering method had a 1.82-fold increase in losses compared with an all-passive traditional du/dt output filter. The filter mass with the active du/dt method was 17% (2.4 kg, air-core inductors) compared with 14 kg of the passive du/dt method filter. Silicon carbide freewheeling diodes were found to reduce the inverter losses in the active du/dt filtering by 18% compared with the same IGBT module with silicon diodes. For a 200 m cable length, the average peak voltage at the motor terminals was 1050 V with no filter, 960 V for the all-passive du/dt filter, and 700 V for the active du/dt filtering applying the new control principle.

Repository Junction Broker

Poster at Open Repositories 2014, Helsinki, Finland, June 9-13, 2014

ERBB4 mutations in cancer and amyotrophic lateral sclerosis

ErbB receptor tyrosine kinases, epidermal growth factor receptor (EGFR, also known as ErbB1), ErbB2 (HER2 or NEU), ErbB3 (HER3), and ErbB4 (HER4), transduce signals borne by extracellular ligands into central cellular responses such as proliferation, survival, differentiation, and apoptosis. Mutations in ERBB genes are frequently detected in human malignant diseases of epithelial and neural origin, making ErbB receptors important drug targets. Targeting EGFR and ErbB2 has been successful in eg. lung and breast cancer, respectively, and mutations in these genes can be used to select patients that are responsive to the targeted treatment. Although somatic ERBB4 mutations have been found in many high-incidence cancers such as melanoma, lung cancer, and colorectal cancer and germ-line ERBB4 mutations have been linked to neuronal disorders and cancer, ErbB4 has generally been neglected as a potential drug target. Thus, the consequences of ERBB4 mutations on ErbB4 biology are largely unknown. This thesis aimed to elucidate the functional consequences and assess the clinical significance of somatic and germ-line ERBB4 mutations in the context of cancer and amyotrophic lateral sclerosis. The results of this study indicated that cancer-associated ERBB4 mutations can promote aberrant ErbB4 function by activating the receptor or inducing qualitative changes in ErbB4 signaling. ERBB4 mutations increased survival or decreased differentiation in vitro, suggesting that ERBB4 mutations can be oncogenic. Importantly, the potentially oncogenic mutations were located in various subdomains in ErbB4, possibly providing explanation for the characteristic scattered pattern of mutations in ERBB4. This study also demonstrated that hereditary variation in ERBB4 gene can have a significant effect on the prognosis of breast cancer. In addition, it was shown that hereditary or de novo germ-line ERBB4 mutations that predispose to amyotrophic lateral sclerosis inhibit ErbB4 activity. Together, these results suggest that ErbB4 should be considered as a novel drug target in cancer and amyotrophic lateral sclerosis.

Prenatal and perinatal risk factors for bipolar disorder

Bipolar disorder (BPD) is a severe mental disorder associated with considerable morbidity and mortality. Prenatal insults have been shown to be associated with later development of mental disorders and there is a growing interest in the potential role of prenatal and perinatal risk factors in the development of BPD. The aims of this thesis were to describe the overall study design of the Finnish Prenatal Study of Bipolar Disorders (FIPS-B) and demographic characteristics of the sample. Furthermore, it was aimed to examine the association of parental age, parental age difference, perinatal complications and maternal smoking during pregnancy with BPD. This thesis is based on FIPS-B, a nested case-control study using several nationwide registers. The cases included all people born in Finland between January 1st 1983 and December 31st 1998 and diagnosed with BPD according to the Finnish Hospital Discharge Register (FHDR) before December 31st 2008. Controls for this study were people who were without BPD, schizophrenia or diagnoses related to these disorders, identified from the Population Register Centre (PRC), and matched two-fold to the cases on sex, date of birth (+/- 30 days), and residence in Finland on the first day of diagnosis of the matched case. Conditional logistic regression models were used to examine the association between risk factors and BPD. This study included 1887 BPD cases and 3774 matched controls. The mean age at diagnosis was 19.3 years and females accounted for 68% of the cases. Mothers with the lowest educational level had the highest odds of having BPD in offspring. Being born in Eastern and Southern region of Finland increased the odds of having BPD later in life. A U-shaped distribution of odds ratio was observed between paternal age and BPD in the unadjusted analysis. Maternal age and parental age difference was not associated with BPD. Birth by planned caesarean section was associated with increased odd of BPD. Smoking during pregnancy was not associated with BPD in the adjusted analyses. Region of birth and maternal educational level were associated with BPD. Both young and old father’s age was associated with BPD. Most perinatal complications and maternal smoking during pregnancy were not associated with BPD. The findings of this thesis, considered together with previous literature, suggest that the pre- and perinatal risk factor profile varies among different psychiatric disorders.

Modification of a quantum efficiency measurement system for multi-junction solar cells

In this thesis the basic structure and operational principals of single- and multi-junction solar cells are considered and discussed. Main properties and characteristics of solar cells are briefly described. Modified equipment for measuring the quantum efficiency for multi-junction solar cell is presented. Results of experimental research single- and multi-junction solar cells are described.