A new concept of integrated cardiopulmonary bypass circuit.

OBJECTIVE: Standard cardiopulmonary bypass (CPB) circuits with their large surface area and volume contribute to postoperative systemic inflammatory reaction and hemodilution. In order to minimize these problems a new approach has been developed resulting in a single disposable, compact arterio-venous loop, which has integral kinetic-assist pumping, oxygenating, air removal, and gross filtration capabilities (CardioVention Inc., Santa Clara, CA, USA). The impact of this system on gas exchange capacity, blood elements and hemolysis is compared to that of a conventional circuit in a model of prolonged perfusion. METHODS: Twelve calves (mean body weight: 72.2+/-3.7 kg) were placed on cardiopulmonary bypass for 6 h with a flow of 5 l/min, and randomly assigned to the CardioVention system (n=6) or a standard CPB circuit (n=6). A standard battery of blood samples was taken before bypass and throughout bypass. Analysis of variance was used for comparison. RESULTS: The hematocrit remained stable throughout the experiment in the CardioVention group, whereas it dropped in the standard group in the early phase of perfusion. When normalized for prebypass values, both profiles differed significantly (P<0.01). Both O2 and CO2 transfers were significantly improved in the CardioVention group (P=0.04 and P<0.001, respectively). There was a slightly higher pressure drop in the CardioVention group but no single value exceeded 112 mmHg. No hemolysis could be detected in either group with all free plasma Hb values below 15 mg/l. Thrombocyte count, when corrected by hematocrit and normalized by prebypass values, exhibited an increased drop in the standard group (P=0.03). CONCLUSION: The CardioVention system with its concept of limited priming volume and exposed foreign surface area, improves gas exchange probably because of the absence of detectable hemodilution, and appears to limit the decrease in the thrombocyte count which may be ascribed to the reduced surface. Despite the volume and surface constraints, no hemolysis could be detected throughout the 6 h full-flow perfusion period.

Development of a simulation tool for torsional vibration of branched power transmission system

In this master's thesis a mechanical model that is driven with variable speed synchronous machine was developed. The developed mechanical model simulates the mechanics of power transmission and its torsional vibrations. The mechanical model was developed for the need of the branched mechanics of a rolling mill and the propulsion system of a tanker. First, the scope of the thesis was to clarify the concepts connected to the mechanical model. The clarified concepts are the variable speed drive, the mechanics of power transmission and the vibrationsin the power transmission. Next, the mechanical model with straight shaft line and twelve moments of inertia that existed in the beginning was developed to be branched considering the case of parallel machines and the case of parallel rolls. Additionally, the model was expanded for the need of moreaccurate simulation to up to thirty moments of inertia. The model was also enhanced to enable three phase short circuit situation of the simulated machine. After that the mechanical model was validated by comparing the results of the developed simulation tool to results of other simulation tools. The compared results are the natural frequencies and mode shapes of torsional vibration, the response of the load torque step and the stress in the mechanical system occurred by the permutation of the magnetic field that is arisen from the three phase short circuit situation. The comparisons were accomplished well and the mechanical model was validated for the compared cases. Further development to be made is to develop the load torque to be time-dependent and to install two frequency converters and two FEM modeled machines to be simulated parallel.

Sähköverkkoyhtiön keskijänniteverkon kehittämissuunnitelma

Tämän työn tavoitteena oli laatia KSS Energia Oy:n keskijänniteverkon kehittämissuunnitelma. Tätä varten selvitettiin verkon nykytila ja sen toimivuus korvaustilanteissa. Suunnitelmaa varten laadittiin verkoston vuoteen 2020 asti ulottuva kuormitusennuste. Kehittämissuunnitelmassa paikannettiin alueet, joilla kuormitettavuus, korvattavuus tai oikosulkukestoisuus olisivat toimivansähkönjakelun esteinä tulevaisuudessa. Työn painopistealueiksi muodostuivat Vuolenkosken, Paimenpolun ja Valkealan alueet. Näiden alueiden kasvavan tehontarpeen tyydyttämiseksi selvitettiin uusien sähköasemien rakentamisvaihtoehtoja. Suunnitelmassa tarkasteltiin ja vertailtiin kolmen uuden sähköaseman rakentamista keskijänniteverkon saneerausvaihtoehtoon. Työssä selvitettiin myös miten alueen kuormituksen kasvun aiheuttama lisätehontarpeen jakelu voidaan hoitaa. Näiden alueiden kuormituksen kasvu edellyttää uusien sähköasemien rakentamista seuraavien 10vuoden kuluessa.

Effect of Noncondensable Gases on Circulation of Primary Coolant in Nuclear Power Plants in Abnormal Situations

The present study focuses on two effects of the presence of a noncondensable gas on the thermal-hydraulic behavior of thecoolant of the primary circuit of a nuclear reactor in the VVER-440 geometry inabnormal situations. First, steam condensation with the presence of air was studied in the horizontal tubes of the steam generator (SG) of the PACTEL test facility. The French thermal-hydraulic CATHARE code was used to study the heat transfer between the primary and secondary side in conditions derived from preliminary experiments performed by VTT using PACTEL. In natural circulation and single-phase vapor conditions, the injection of a volume of air, equivalent to the totalvolume of the primary side of the SG at the entrance of the hot collector, did not stop the heat transfer from the primary to the secondary side. The calculated results indicate that air is located in the second half-length (from the mid-length of the tubes to the cold collector) in all the tubes of the steam generator The hot collector remained full of steam during the transient. Secondly, the potential release of the nitrogen gas dissolved in the water of the accumulators of the emergency core coolant system of the Loviisa nuclear power plant (NPP) was investigated. The author implemented a model of the dissolution and release ofnitrogen gas in the CATHARE code; the model created by the CATHARE developers. In collaboration with VTT, an analytical experiment was performed with some components of PACTEL to determine, in particular, the value of the release time constant of the nitrogen gas in the depressurization conditions representative of the small and intermediate break transients postulated for the Loviisa NPP. Such transients, with simplified operating procedures, were calculated using the modified CATHARE code for various values of the release time constant used in the dissolution and release model. For the small breaks, nitrogen gas is trapped in thecollectors of the SGs in rather large proportions. There, the levels oscillate until the actuation of the low-pressure injection pumps (LPIS) that refill the primary circuit. In the case of the intermediate breaks, most of the nitrogen gas is expelled at the break and almost no nitrogen gas is trapped in the SGs. In comparison with the cases calculated without taking into account the release of nitrogen gas, the start of the LPIS is delayed by between 1 and 1.75 h. Applicability of the obtained results to the real safety conditions must take into accountthe real operating procedures used in the nuclear power plant.

Torque vibration model of axial-flux surface-mounted permanent magnet synchronous machine

In order that the radius and thus ununiform structure of the teeth and otherelectrical and magnetic parts of the machine may be taken into consideration the calculation of an axial flux permanent magnet machine is, conventionally, doneby means of 3D FEM-methods. This calculation procedure, however, requires a lotof time and computer recourses. This study proves that also analytical methods can be applied to perform the calculation successfully. The procedure of the analytical calculation can be summarized into following steps: first the magnet is divided into slices, which makes the calculation for each section individually, and then the parts are submitted to calculation of the final results. It is obvious that using this method can save a lot of designing and calculating time. Thecalculation program is designed to model the magnetic and electrical circuits of surface mounted axial flux permanent magnet synchronous machines in such a way, that it takes into account possible magnetic saturation of the iron parts. Theresult of the calculation is the torque of the motor including the vibrations. The motor geometry and the materials and either the torque or pole angle are defined and the motor can be fed with an arbitrary shape and amplitude of three-phase currents. There are no limits for the size and number of the pole pairs nor for many other factors. The calculation steps and the number of different sections of the magnet are selectable, but the calculation time is strongly depending on this. The results are compared to the measurements of real prototypes. The permanent magnet creates part of the flux in the magnetic circuit. The form and amplitude of the flux density in the air-gap depends on the geometry and material of the magnetic circuit, on the length of the air-gap and remanence flux density of the magnet. Slotting is taken into account by using the Carter factor in the slot opening area. The calculation is simple and fast if the shape of the magnetis a square and has no skew in relation to the stator slots. With a more complicated magnet shape the calculation has to be done in several sections. It is clear that according to the increasing number of sections also the result will become more accurate. In a radial flux motor all sections of the magnets create force with a same radius. In the case of an axial flux motor, each radial section creates force with a different radius and the torque is the sum of these. The magnetic circuit of the motor, consisting of the stator iron, rotor iron, air-gap, magnet and the slot, is modelled with a reluctance net, which considers the saturation of the iron. This means, that several iterations, in which the permeability is updated, has to be done in order to get final results. The motor torque is calculated using the instantaneous linkage flux and stator currents. Flux linkage is called the part of the flux that is created by the permanent magnets and the stator currents passing through the coils in stator teeth. The angle between this flux and the phase currents define the torque created by the magnetic circuit. Due to the winding structure of the stator and in order to limit the leakage flux the slot openings of the stator are normally not made of ferromagnetic material even though, in some cases, semimagnetic slot wedges are used. In the slot opening faces the flux enters the iron almost normally (tangentially with respect to the rotor flux) creating tangential forces in the rotor. This phenomenon iscalled cogging. The flux in the slot opening area on the different sides of theopening and in the different slot openings is not equal and so these forces do not compensate each other. In the calculation it is assumed that the flux entering the left side of the opening is the component left from the geometrical centre of the slot. This torque component together with the torque component calculated using the Lorenz force make the total torque of the motor. It is easy to assume that when all the magnet edges, where the derivative component of the magnet flux density is at its highest, enter the slot openings at the same time, this will have as a result a considerable cogging torque. To reduce the cogging torquethe magnet edges can be shaped so that they are not parallel to the stator slots, which is the common way to solve the problem. In doing so, the edge may be spread along the whole slot pitch and thus also the high derivative component willbe spread to occur equally along the rotation. Besides forming the magnets theymay also be placed somewhat asymmetric on the rotor surface. The asymmetric distribution can be made in many different ways. All the magnets may have a different deflection of the symmetrical centre point or they can be for example shiftedin pairs. There are some factors that limit the deflection. The first is that the magnets cannot overlap. The magnet shape and the relative width compared to the pole define the deflection in this case. The other factor is that a shifting of the poles limits the maximum torque of the motor. If the edges of adjacent magnets are very close to each other the leakage flux from one pole to the other increases reducing thus the air-gap magnetization. The asymmetric model needs some assumptions and simplifications in order to limit the size of the model and calculation time. The reluctance net is made for symmetric distribution. If the magnets are distributed asymmetrically the flux in the different pole pairs will not be exactly the same. Therefore, the assumption that the flux flows from the edges of the model to the next pole pairs, in the calculation model from one edgeto the other, is not correct. If it were wished for that this fact should be considered in multi-pole pair machines, this would mean that all the poles, in other words the whole machine, should be modelled in reluctance net. The error resulting from this wrong assumption is, nevertheless, irrelevant.

Spectral analysis of the angular distribution function of back reflectors for thin film silicon solar cells

Nowadays, one of the most important challenges to enhance the efficiency of thin film silicon solar cells is to increase the short circuit intensity by means of optical confinement methods, such as textured back-reflector structures. In this work, two possible textured structures to be used as back reflectors for n-i-p solar cells have been optically analyzed and compared to a smooth one by using a system which is able to measure the angular distribution function (ADF) of the scattered light in a wide spectral range (350-1000 nm). The accurate analysis of the ADF data corresponding to the reflector structures and to the μc-Si:H films deposited onto them allows the optical losses due to the reflector absorption and its effectiveness in increasing light absorption in the μc-Si:H layer, mainly at long wavelengths, to be quantified.

IGBT:N KYLLÄSTYSVALVONTA

Tässä työssä on tutkittu IGBT-modulin kyllästysvalvontaa. Periaatteellisena erona yleisesti käytössä olevaan IGBT:n kyllästysvalvontamenetelmään on valvonnan perustuminen IGBT-modulin läpi kulkevaan virtaan, sen yli olevan jännitteen mittaamisen asemesta. IGBT-modulin läpi kulkeva virta aiheuttaa pienen jännitehäviön IGBT-modulin sisällä olevassa DC-miinuskiskossa. Jännitehäviön suuruus riippuu modulin läpi kulkevan virran suuruudesta. Jännitehäviö voidaan mitata kahden mittapisteen välisenä jännite-erona. Kun jännite-ero mittapisteiden välillä kasvaa tarpeeksi suureksi, IGBT:n voidaan olettaa olevan oikosulussa ja laukaisu voidaan suorittaa. Kyllästystilan havaitsemista kuitenkin vaikeuttaa se, että kyseisen DC-miinuskiskon läpi kulkee moottorivirta. Moottorivirran aiheuttamat jännite-erot on pystyttävä erottamaan luotettavasti oikosulkutilanteesta. Lisäksi komponentin ylikuormitettavuusvaatimukset lisäävät kytkennän toteuttamisen vaikeutta. Komponenttia voidaan hetkellisesti ylikuormittaa moninkertaisella nimellisvirralla eikä tämäkään tilanne saa johtaa laukaisuun.Kyllästysvalvonta toteutetaan taajuusmuuttajaan, joka on tunnetusti varsin häiriöinen ympäristö. DC-miinuskiskon mittapisteiden välissä on tämän johdosta havaittavissa virrasta riippuvan jännite-eron lisäksi erittäin voimakkaita kytkentäilmiöistä johtuvia häiriöitä. Myös muiden IGBT-modulien kytkentäilmiöistä johtuvat häiriöt kytkeytyvät kyllästysvalvontakytkentään ja vaikeuttavat osaltaan sen toteuttamista.

Converter Supply Transformer For LVDC Distribution System

This master’s thesis is focused on optimizing the parameters of a distribution transformer with respect to low voltage direct current (LVDC) distribution system. One of the main parts of low voltage direct current (LVDC) distribution system is transformer. It is studied from several viewpoints like filtering capabilities of harmonics caused by rectifier, losses and short circuit current limiting Determining available short circuit currents is one of the most important aspects of designing power distribution systems. Short circuits and their effects must be considered in selecting electrical equipment, circuit protection and other devices.

Vaasan Sähköverkko Oy:n keskijänniteverkon nykytilan määritys sekä kehittämissuunnitelma käyttövarmuuden näkökulmasta

Tämän työn tavoitteena on analysoida Vaasan Sähköverkko Oy:n keskijänniteverkon nykytila sekä selvittää verkon kehittämisen suuntaviivoja. Nykytilan määrityksessä selvitetään kuormitettavuusasteet, jännitteenalenemat, häviöt oiko- ja maasulkusuojauksen toimivuus sekä keskeytyskustannukset. Nykytilan määrityksen apuna käytettiin verkkotietojärjestelmä Xpowerin tehojako-, oikosulku- ja maasulkulaskentoja. Nykytila on määritetty sekä normaalissa kytkentätilanteessa, että tilanteessa jossa yksi sähköasema kerrallaan on poissa käytöstä. Nykytilan määrityksen perusteella voidaan todeta, että normaalissa kytkentätilanteessa keskijänniteverkko täyttää suurilta osin sille asetetut tekniset reunaehdot, jotka ovat jännitteenalenema, kuormitettavuus, oikosulkukestoisuus sekä oiko- ja maasulkusuojauksen havahtuvaisuus. Jotta reunaehdot toteutuisivat kokonaisuudessaan, tulee oikosulkukestottomien lähtöjen releasetteluja muuttaa tai vaihtaa oikosulkukestottomat johto-osuudet suurempi poikkipintaiseen johtimeen. Nykytilan määrityksen perusteella neljän päämuuntajan kuormitettavuusaste on yli 90 %, joten näiden asemien alueiden kehitystä tulee tarkkailla. Sähköasemien korvaustarkastelun perusteella viiden sähköaseman korvaus tuottaa ongelmia jo nykyisillä huippukuormilla. Työssä tehtyjen selvitystöiden perusteella Vaasan Sähköverkko Oy:n keskijänniteverkkoon lisättiin 10 maastokatkaisijaa sekä selvitettiin verkon mahdollisia tulevaisuuden kehittämisen suuntaviivoja.

Elintarviketehtaan sähköverkon selvitys ja kehittämissuunnitelma

Työssä selvitetään elintarviketehtaan sähköverkon kunto sen suurimpien sähkönsyöttöjen osalta ja lasketaan oikosulkuvirtojen suuruus, kaapeleiden kuormitettavuus ja jännitteenalenemat verkon eri osissa. Laskentatulosten analysoinnin jälkeen esitetään korjaavat toimenpiteet löydettyjen epäkohtien osalta. Lisäksi tarkastellaan tehtaan energiankulutusta ja suunniteltujen energiansäästöehdotuksien vaikutuksia sähköverkon toimintaan. Työssä arvioidaan myös verkon eri osienvikaantumisen vaikutusta tehtaan tuotantoon ja esitetään parannuskeinoja verkon luotettavuuden parantamiseksi. Lopuksi on esitelty suunnitelma sähköverkon laajentamiselle ja käyty läpi tulevien investointien sähköteknistä mitoitusta ja vaikutusta verkon tulevaan tilaan.

Parallella, dynamiska representationer i gymnasiefysiken : implementering av ett interaktivt datorverktyg i didaktiska situationer och uppfattning av effektivt lärande

The computer is a useful tool in the teaching of upper secondary school physics, and should not have a subordinate role in students' learning process. However, computers and computer-based tools are often not available when they could serve their purpose best in the ongoing teaching. Another problem is the fact that commercially available tools are not usable in the way the teacher wants. The aim of this thesis was to try out a novel teaching scenario in a complicated subject in physics, electrodynamics. The didactic engineering of the thesis consisted of developing a computer-based simulation and training material, implementing the tool in physics teaching and investigating its effectiveness in the learning process. The design-based research method, didactic engineering (Artigue, 1994), which is based on the theoryof didactical situations (Brousseau, 1997), was used as a frame of reference for the design of this type of teaching product. In designing the simulation tool a general spreadsheet program was used. The design was based on parallel, dynamic representations of the physics behind the function of an AC series circuit in both graphical and numerical form. The tool, which was furnished with possibilities to control the representations in an interactive way, was hypothesized to activate the students and promote the effectiveness of their learning. An effect variable was constructed in order to measure the students' and teachers' conceptions of learning effectiveness. The empirical study was twofold. Twelve physics students, who attended a course in electrodynamics in an upper secondary school, participated in a class experiment with the computer-based tool implemented in three modes of didactical situations: practice, concept introduction and assessment. The main goal of the didactical situations was to have students solve problems and study the function of AC series circuits, taking responsibility for theirown learning process. In the teacher study eighteen Swedish speaking physics teachers evaluated the didactic potential of the computer-based tool and the accompanying paper-based material without using them in their physics teaching. Quantitative and qualitative data were collected using questionnaires, observations and interviews. The result of the studies showed that both the group of students and the teachers had generally positive conceptions of learning effectiveness. The students' conceptions were more positive in the practice situation than in the concept introduction situation, a setting that was more explorative. However, it turned out that the students' conceptions were also positive in the more complex assessment situation. This had not been hypothesized. A deeper analysis of data from observations and interviews showed that one of the students in each pair was more active than the other, taking more initiative and more responsibilityfor the student-student and student-computer interaction. These active studentshad strong, positive conceptions of learning effectiveness in each of the threedidactical situations. The group of less active students had a weak but positive conception in the first iv two situations, but a negative conception in the assessment situation, thus corroborating the hypothesis ad hoc. The teacher study revealed that computers were seldom used in physics teaching and that computer programs were in short supply. The use of a computer was considered time-consuming. As long as physics teaching with computer-based tools has to take place in special computer rooms, the use of such tools will remain limited. The affordance is enhanced when the physical dimensions as well as the performance of the computer are optimised. As a consequence, the computer then becomes a real learning tool for each pair of students, smoothly integrated into the ongoing teaching in the same space where teaching normally takes place. With more interactive support from the teacher, the computer-based parallel, dynamic representations will be efficient in promoting the learning process of the students with focus on qualitative reasoning - an often neglected part of the learning process of the students in upper secondary school physics.

Advanced orbital pipe welding

Since the introduction of automatic orbital welding in pipeline application in 1961, significant improvements have been obtained in orbital pipe welding systems. Requirement of more productive welding systems for pipeline application forces manufacturers to innovate new advanced systems and welding processes for orbital welding method. Various methods have been used to make welding process adaptive, such as visual sensing, passive visual sensing, real-time intelligent control, scan welding technique, multi laser vision sensor, thermal scanning, adaptive image processing, neural network model, machine vision, and optical sensing. Numerous studies are reviewed and discussed in this Master’s thesis and based on a wide range of experiments which already have been accomplished by different researches the vision sensor are reported to be the best choice for adaptive orbital pipe welding system. Also, in this study the most welding processes as well as the most pipe variations welded by orbital welding systems mainly for oil and gas pipeline applications are explained. The welding results show that Gas Metal Arc Welding (GMAW) and its variants like Surface Tension Transfer (STT) and modified short circuit are the most preferred processes in the welding of root pass and can be replaced to the Gas Tungsten Arc Welding (GTAW) in many applications. Furthermore, dual-tandem gas metal arc welding technique is currently considered the most efficient method in the welding of fill pass. Orbital GTAW process mostly is applied for applications ranging from single run welding of thin walled stainless tubes to multi run welding of thick walled pipes. Flux cored arc welding process is faster process with higher deposition rate and recently this process is getting more popular in pipe welding applications. Also, combination of gas metal arc welding and Nd:YAG laser has shown acceptable results in girth welding of land pipelines for oil and gas industry. This Master’s thesis can be implemented as a guideline in welding of pipes and tubes to achieve higher quality and efficiency. Also, this research can be used as a base material for future investigations to supplement present finding.

Chelyabinsk CHP-3 “locked power” problem solving

All over the world power systems become bigger and bigger every day. New equipment is installed, new feeders are constructed, new power units are installed. Some old elements of the network, however, are not changed in time. As a result, “bottlenecks” for capacity transmission can occur. By locked power problem the situation when a power plant has installed capacity exceeding the power it can actually deliver is usually meant. Regime, scheme or even technical restrictions-related issues usually cause this kind of problem. It is really important, since from the regime point of view it is typical decision to have a mobile capacity reserve, in case of malfunctions. And, what can be even more significant, power plant owner (JSC Fortum in our case) losses his money because of selling less electrical energy. The goal of master`s thesis is to analyze the current state of Chelyabinsk power system and the CHP-3 (Combined Heat and Power plant) in particular in relation with it`s ability to deliver the whole capacity of the CHP in it`s existing state and also taking into consideration the prospect of power unit 3 installation by the fourth quarter of 2010. The thesis contains some general information about the UPS of Russia, CPS of Ural, power system of Chelyabinsk and the Chelyabinsk region itself. Then the CHP-3 is described from technical point of view with it`s equipment observation. Regimes for the nowadays power system and for the system after the power unit 3 installation are reviewed. The problems occurring are described and, finally, a solution is offered.

Pricing anomalies in the Finnish stock market

The aim of this thesis is to examine whether the pricing anomalies exists in the Finnish stock markets by comparing the performance of quantile portfolios that are formed on the basis of either individual valuation ratios, composite value measures or combined value and momentum indicators. All the research papers included in the thesis show evidence of value anomalies in the Finnish stock markets. In the first paper, the sample of stocks over the 1991-2006 period is divided into quintile portfolios based on four individual valuation ratios (i.e., E/P, EBITDA/EV, B/P, and S/P) and three hybrids of them (i.e. composite value measures). The results show the superiority of composite value measures as selection criterion for value stocks, particularly when EBITDA/EV is employed as earnings multiple. The main focus of the second paper is on the impact of the holding period length on performance of value strategies. As an extension to the first paper, two more individual ratios (i.e. CF/P and D/P) are included in the comparative analysis. The sample of stocks over 1993- 2008 period is divided into tercile portfolios based on six individual valuation ratios and three hybrids of them. The use of either dividend yield criterion or one of three composite value measures being examined results in best value portfolio performance according to all performance metrics used. Parallel to the findings of many international studies, our results from performance comparisons indicate that for the sample data employed, the yearly reformation of portfolios is not necessarily optimal in order to maximally gain from the value premium. Instead, the value investor may extend his holding period up to 5 years without any decrease in long-term portfolio performance. The same holds also for the results of the third paper that examines the applicability of data envelopment analysis (DEA) method in discriminating the undervalued stocks from overvalued ones. The fourth paper examines the added value of combining price momentum with various value strategies. Taking account of the price momentum improves the performance of value portfolios in most cases. The performance improvement is greatest for value portfolios that are formed on the basis of the 3-composite value measure which consists of D/P, B/P and EBITDA/EV ratios. The risk-adjusted performance can be enhanced further by following 130/30 long-short strategy in which the long position of value winner stocks is leveraged by 30 percentages while simultaneously selling short glamour loser stocks by the same amount. Average return of the long-short position proved to be more than double stock market average coupled with the volatility decrease. The fifth paper offers a new approach to combine value and momentum indicators into a single portfolio-formation criterion using different variants of DEA models. The results throughout the 1994-2010 sample period shows that the top-tercile portfolios outperform both the market portfolio and the corresponding bottom-tercile portfolios. In addition, the middle-tercile portfolios also outperform the comparable bottom-tercile portfolios when DEA models are used as a basis for stock classification criteria. To my knowledge, such strong performance differences have not been reported in earlier peer-reviewed studies that have employed the comparable quantile approach of dividing stocks into portfolios. Consistently with the previous literature, the division of the full sample period into bullish and bearish periods reveals that the top-quantile DEA portfolios lose far less of their value during the bearish conditions than do the corresponding bottom portfolios. The sixth paper extends the sample period employed in the fourth paper by one year (i.e. 1993- 2009) covering also the first years of the recent financial crisis. It contributes to the fourth paper by examining the impact of the stock market conditions on the main results. Consistently with the fifth paper, value portfolios lose much less of their value during bearish conditions than do stocks on average. The inclusion of a momentum criterion somewhat adds value to an investor during bullish conditions, but this added value turns to negative during bearish conditions. During bear market periods some of the value loser portfolios perform even better than their value winner counterparts. Furthermore, the results show that the recent financial crisis has reduced the added value of using combinations of momentum and value indicators as portfolio formation criteria. However, since the stock markets have historically been bullish more often than bearish, the combination of the value and momentum criteria has paid off to the investor despite the fact that its added value during bearish periods is negative, on an average.

Jännitevälipiiritaajuusmuuttajan moottorikaapelin maksimipituuden määrittely

Työssä tutkitaan, kuinka pitkää moottorikaapelia on jännitevälipiiritaajuusmuuttajan kanssa mahdollista käyttää niin, että määritellyt reunaehdot vielä toteutuvat. Tavoitteena on tuottaa tietoa myynnille, markkinoinnille, tuotehallinnalle sekä tuoteylläpidolle siitä, miten taajuus-muuttaja toimii pidemmillä moottorikaapeleilla kuin valmistaja suosittelee. Tutkitut moottori-kaapelipituudet olivat 175…1025 metriä ja tutkitut laitteet nimellislähtövirroiltaan 2,4...25 A. Työssä aihetta käsitellään jänniteheijastusten näkökulmasta. Lisäksi tutkitaan moottorikaapelin pituuden vaikutusta taajuusmuuttajan eri komponenttien lämpenemiseen. Taajuusmuuttajan toiminnallisuutta arvioidaan moottorin suunnanvaihtojen avulla sekä turvallista toimintaa oikosulkutestein. Tutkittujen taajuusmuuttajien kohdalla on mahdollista käyttää taajuusmuuttajavalmistajan suositusta pidempiä moottorikaapeleita. Moottoriliittimien ylijännitteitä aiheuttavat jännite-heijastukset eivät aiheuttaneet raja-arvoja ylittäviä huippujännitteitä tutkituilla laitekokoon-panoilla. Myös lämpötilannousu oli maltillista tai jopa vähäistä taajuusmuuttajasta mitatuilla komponenteilla. Moottorisäätö havaittiin toimintakykyiseksi pidemmilläkin moottorikaape-leilla, tosin moottorin vääntömomentti heikkeni moottorikaapelien pituutta kasvatettaessa. Virranmittaus toimi hyvin myös pitkillä kaapeleilla, tuottaen vikalaukaisun kaikissa tehdyissä oikosulkutilanteissa. Moottorin ja taajuusmuuttajan melutaso nousivat moottorikaapelien pi-tuutta kasvatettaessa, vaikkakin moottorin käynti oli tasaista ja katkotonta Moottorikaapelin pituutta voidaan kasvattaa 325 metriin kaikissa tutkituissa laitteissa ilman, että mikään tutkittu ominaisuus vielä olennaisesti heikkenisi. Vielä 525 metrin moottorikaape-leita on mahdollista käyttää, mutta tällöin vääntömomentin tuotto on jo heikompaa.