LISN-keinoverkko

Tämä opinnäytetyö käsittelee keinoverkon suunnittelua, rakentamista, testausta ja toimintaa ja näihin liittyvää teoria- ja standarditietoa. Keinoverkko rakennettiin MSc Elec-tronics Oy:lle, sillä yritys tarvitsi kaupallista keinoverkkoa monipuolisemman keinoverkon. Kaupalliset keinoverkot ovat usein yksivaiheisia eivätkä kestä tarpeeksi suuria virtoja. Yrityksen tarkoituksena on käyttää keinoverkkoa alustaviin johtuvien häiriöiden mittauksiin rakentamilleen- ja suunnitteilla oleville tehoelektroniikkalaitteille. Keinoverkko toimii sähköverkon ja testattavana olevan laitteen välissä. Keinoverkko tuottaa testattavalle laitteelle stabiilin 50Ω impedanssin. Se myös estää sähköverkon häiriöiden pääsyn mittalaitteelle ja näin saadaan spektrianalysaattorilla mitattua vain testattavan laitteen aiheuttamat johtuvat häiriöt. Keinoverkon toimintavarmuus ja turvallisuus testattiin ennen laitteen käyttöä. Keinoverkolle tehtiin useita referenssimittauksia, joissa verrattiin aina saman testilaitteen tuottamia häiriöitä eri keinoverkoilla. Mittauksia tehtiin Tampereen ammattikorkeakoulun suurjännitelaboratoriossa, sekä yrityksen testaustiloissa. Samasta testattavasta laitteesta löytyi myös aiempaa mittausdataa, standardin mukaisella mittausmenetelmällä. Kaikkia tuloksia verrattiin keskenään. Turvallisuus varmistettiin tutkimalla maadoituksen jatkuvuus, lämpömittaus suurella kuormituksella sekä läpilyöntilujuus. Keinoverkko toimii erittäin hyvin ja riittävällä tarkkuudella alustaviin johtuvien häiriöiden mittauksiin. Mittalaitteen ominaisuudet ovat vähäiset ja käyttöliittymä on epävakaa. Yrityksen tarkoituksena onkin hankkia monipuolisempi mittalaite.The purpose of the thesis was to design, build and test line impedance stabilization network (LISN). The study also focused on LISN functions. The LISN was built for MSc Electronics Oy. The company needed a LISN with better features than of commercial LISN. Commercial LISNs are usually only single phase networks and they lack the capability for high current. The LISN is used for preliminary testing at products development stage. It is used for testing power electronic devices that conduct emissions. Conducted emissions must be below international standards limits. The purpose of LISN is to connect the equipment under test (EUT) to a measuring device. LISN provides stable input impedance (50Ω) for EUT. Power electronic devices causes’ noise to the input, which in this case is LISN. With LISN attached, we can measure conducted emissions according to standard. One of line impedance stabilization networks function is to filter incoming noise from a power grid. With these noises filtered, the measurement shows only emissions, produced by EUT. There are international standards which defines products electromagnetic compatibility (EMC). All products must meet these standards. The product must work properly in the environment, it has been designed for. Devices must work properly under electromagnetic interference (EMI) not to mention those disturbance noises that device produces. These interference levels can only be measured with appropriate LISN. The most important target was to make it safe for user and get the functions needed with preliminary conducted emissions measurements. The LISN works very well and its accuracy is sufficient for preliminary measurements. The measuring device has a lack of features needed, for example its frequency range is too narrow. The user interface is also unstable. The purpose is to get a measuring device with more functions as soon as possible

Solving eigenvalue problems on curved surfaces using the Closest Point Method

Eigenvalue problems are fundamental to mathematics and science. We present a simple algorithm for determining eigenvalues and eigenfunctions of the Laplace--Beltrami operator on rather general curved surfaces. Our algorithm, which is based on the Closest Point Method, relies on an embedding of the surface in a higher-dimensional space, where standard Cartesian finite difference and interpolation schemes can be easily applied. We show that there is a one-to-one correspondence between a problem defined in the embedding space and the original surface problem. For open surfaces, we present a simple way to impose Dirichlet and Neumann boundary conditions while maintaining second-order accuracy. Convergence studies and a series of examples demonstrate the effectiveness and generality of our approach

An embedding technique for the solution of reaction-fiffusion equations on algebraic surfaces with isolated singularities

In this paper we construct a parametrization-free embedding technique for numerically evolving reaction-diffusion PDEs defined on algebraic curves that possess an isolated singularity. In our approach, we first desingularize the curve by appealing to techniques from algebraic geometry.\ud We create a family of smooth curves in higher dimensional space that correspond to the original curve by projection. Following this, we pose the analogous reaction-diffusion PDE on each member of this family and show that the solutions (their projection onto the original domain) approximate the solution of the original problem. Finally, we compute these approximants numerically by applying the Closest Point Method which is an embedding technique for solving PDEs on smooth surfaces of arbitrary dimension or codimension, and is thus suitable for our situation. In addition, we discuss the potential to generalize the techniques presented for higher-dimensional surfaces with multiple singularities

LDL aggregation susceptibility as a novel risk factor for atherosclerosis

Atherosclerotic cardiovascular disease (ASCVD) is the leading worldwide cause of mortality and morbidity, being both an economic burden for healthcare systems and a source of great individual suffering. The low density lipoprotein cholesterol (LDL-C) concentration in plasma is a causal and modifiable risk factor for ASCVD. Atherogenesis is initiated and then driven by retention, modification, and aggregation of low density lipoprotein (LDL) particles in the arterial intima. Experimental work by our group and others has demonstrated that aggregated LDL particles can induce lipid accumulation in macrophages and this can also activate intimal cells and thereby induce inflammation in the arterial wall. Here, it was hypothesized that it is not only the plasma concentration of LDL particles that influences atherogenesis, but also their characteristics. This thesis aims at testing whether subjects with aggregation-prone LDL have an increased risk for ASCVD and/or ASCVD death. For this purpose, a method to measure LDL aggregation susceptibility was developed, and it was further studied if LDL aggregation susceptibility is modifiable. In addition, it is studied here if LDL aggregates cause a heightened inflammatory response in cells present in the artery wall. The first publication was a hypothesis-generating study, where it was discovered that LDL particles from ASCVD patients are more prone to aggregate in comparison to those from healthy individuals, and importantly, that aggregation-prone LDL predicted future ASCVD death in a group of patients with established ASCVD. It was found that the aggregation-prone LDL particles are rich in sphingolipids but have less phosphatidylcholines than their aggregation-resistant LDL counterparts. Three interventions in animal models aimed at altering the LDL composition, were observed not only to lower the susceptibility LDL particles to aggregate but also to slow the development of atherosclerosis. Similar compositional changes induced in humans by proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibition or adoption of a healthy Nordic diet also lowered the LDL aggregation susceptibility. In the second publication it was demonstrated that genetic background, here ethnicity, influenced LDL aggregation susceptibility. LDL particles from South Asians were more prone to aggregate compared to those from white Caucasians, a finding that may partly explain why South Asians are at higher risk for ASCVD. The third study was a dietary intervention to investigate if different macronutrients could alter LDL particles aggregation susceptibility. Saturated fats were found to increase LDL aggregation, while unsaturated fats or simple sugars had no effect. In addition, the consumption of plant stanol esters, that are known to reduce the LDL-C concentration, was found to decrease the LDL aggregation susceptibility. This thesis propose that the aggregation susceptibility of LDL particles is a novel modifiable risk factor of ASCVD; its assessment may add predictive power to the conventional ASCVD risk estimation. The evaluation of this biomarker may facilitate the identification of those patients who would benefit most from aggressive LDL-C-lowering therapies.Ateroskleroosi eli valtimonkovettumatauti on maailman yleisin kuolinsyy ja se kehittyy vuosien kuluessa lapsuudesta lähtien. Plasman LDL-hiukkasten kolesterolipitoisuus on merkittävä riskitekijä taudin kehittymiselle, mikä on näytetty geneettisissä, epidemiologisissa ja kliinisissä tutkimuksissa. LDL-hiukkasten pitoisuus valtimon seinämän sisäkerroksessa, intimassa, on sama kuin plasmassa. LDL-hiukkasten kertyminen valtimon seinämään alkaa plasman LDL kolesteroli pitoisuuden ollessa suurempi kuin fysiologinen LDL kolesteroli pitoisuus (1-1,5 mmol/l). Intimassa LDL-hiukkaset takertuvat solunulkoiseen tukiverkkoon ja ovat alttiita entsymaattisille ja hapettaville muutoksille. Muuntuneet LDL-hiukkaset ovat alttiita aggregoitumaan eli takertumaan toisiinsa, ja aggregoituneet LDL-hiukkaset puolestaan tarttuvat entistä tiukemmin soluväliaineeseen. LDL-hiukkasten kerääntyminen intimaan houkuttelee paikalle makrofageja, jotka fagosytosoivat erityisesti aggregoituneita hiukkasia, mikä johtaa vaahtosolujen muodostumiseen ja paikalliseen tulehdukseen. Valtimoplakkien tiedetään sisältävän aggregoituneita LDL-hiukkasia ja eläinkokeissa on näytetty, että plasman LDL aggregoituu valtimon seinämässä vain kahden tunnin kuluessa siitä, kun eläimeen injektoidaan LDL-hiukkasia ja plasman LDL-kolesterolipitoisuus kohoaa. Tässä väitöskirjatyössä kehitin menetelmän mitata LDL-hiukkasten aggregoitumisherkkyyttä verinäytteistä. Osoitin, että LDL-hiukkasten herkkyys aggregoitua vaihtelee ihmisten välillä ja johtuu eroista LDL-hiukkasten pinnan rasvojen suhteista, fosfatidyylikoliinien ja sfingomyeliinien suhteellisesta osuudesta. Sfingomyeliiniä paljon sisältävät LDL-hiukkaset aggregoituvat herkemmin, ja fosfatidyylikoliinia paljon sisältävät LDL-hiukkaset hitaammin. Osoitin, että LDL-hiukkaset aggregoituvat herkemmin sepelvaltimotautipotilailla kuin terveillä verrokeilla ja mikä tärkeintä, LDL- hiukkasten aggregoitumisherkkyys ennusti tulevaa sydänkuolemaa sepelvaltimotautia sairastavilla potilailla. LDL-hiukkasten aggregoitumisherkkyys osoittautui itsenäiseksi riskitekijäksi, eikä korreloinut esimerkiksi plasman LDL-kolesterolipitoisuuden tai iän kanssa, eikä eronnut miesten ja naisten välillä. Lisäksi osoitin, että LDL-hiukkasten herkkyys aggregoitua riippuu mahdollisesti ainakin osittain geneettisistä tekijöistä, sillä eteläaasialaisten LDL aggregoitui herkemmin kuin länsimaalaisten. Kliinisesti on tärkeää tietää voiko LDL-hiukkasten aggregoitumisherkkyyteen vaikuttaa elintavoilla tai lääkityksellä. Näytin tässä työssä, että ravinnon rasvoilla on merkitystä, sillä tyydyttyneet rasvat huononsivat LDL-hiukkasten laatua ja lisäsivät LDL-hiukkasten aggregoitumisherkkyyttä. Pohjoismainen terveellinen ruokavalio, erityisesti siihen kuuluvat kasviöljyt paransivat LDL- hiukkasten laatua ja vähensivät aggregoitumista. PCSK9 (proprotein convertase subtilisin/kexin 9) estäjä, plasman kolesterolipitoisuutta laskeva monoklonaalinen vasta- ainelääke vähensi LDL-hiukkasten aggregoitumista parantamalla LDL-hiukkasten laatua. Lisäksi havaittiin, että kasviöljypohjaisen kasvistanolia sisältävän levitteen käyttö puolestaan paransi LDL-hiukkasten laatua ja vähensi LDL-hiukkasten aggregoitumisherkkyyttä. Tämä väitöskirjatyö esittelee LDL-hiukkasten aggregoitumisherkkyyden uutena muokattavissa olevana riskitekijänä ateroskleroottisille valtimosairauksille. LDL- hiukkasten aggregoitumisherkkyys voi tulevaisuudessa auttaa tunnistamaan potilaat, jotka hyötyisivät eniten aggressivisesta LDL kolesterolia alentavasta lääkityksestä

A least-squares implicit RBF-FD closest point method and applications to PDEs on moving surfaces

The closest point method (Ruuth and Merriman, J. Comput. Phys. 227(3):1943-1961, [2008]) is an embedding method developed to solve a variety of partial differential equations (PDEs) on smooth surfaces, using a closest point representation of the surface and standard Cartesian grid methods in the embedding space. Recently, a closest point method with explicit time-stepping was proposed that uses finite differences derived from radial basis functions (RBF-FD). Here, we propose a least-squares implicit formulation of the closest point method to impose the constant-along-normal extension of the solution on the surface into the embedding space. Our proposed method is particularly flexible with respect to the choice of the computational grid in the embedding space. In particular, we may compute over a computational tube that contains problematic nodes. This fact enables us to combine the proposed method with the grid based particle method (Leung and Zhao, J. Comput. Phys. 228(8):2993-3024, [2009]) to obtain a numerical method for approximating PDEs on moving surfaces. We present a number of examples to illustrate the numerical convergence properties of our proposed method. Experiments for advection-diffusion equations and Cahn-Hilliard equations that are strongly coupled to the velocity of the surface are also presented

Spatially partitioned embedded Runge-Kutta Methods

We study spatially partitioned embedded Runge–Kutta (SPERK) schemes for partial differential equations (PDEs), in which each of the component schemes is applied over a different part of the spatial domain. Such methods may be convenient for problems in which the smoothness of the solution or the magnitudes of the PDE coefficients vary strongly in space. We focus on embedded partitioned methods as they offer greater efficiency and avoid the order reduction that may occur in non-embedded schemes. We demonstrate that the lack of conservation in partitioned schemes can lead to non-physical effects and propose conservative additive schemes based on partitioning the fluxes rather than the ordinary differential equations. A variety of SPERK schemes are presented, including an embedded pair suitable for the time evolution of fifth-order weighted non-oscillatory (WENO) spatial discretizations. Numerical experiments are provided to support the theory

High-order TVD and TVB linear multistep methods

We consider linear multistep methods that possess the TVD (total variation diminishing) or TVB (total variation bounded) properties, or related general monotonicity and boundedness properties. Strict monotonicity or TVD, in terms of arbitrary starting values for the multistep schemes, is only valid for a small class of methods, under very stringent step size restrictions. This makes them uncompetitive to the TVD Runge-Kutta methods. By relaxing these strict monotonicity requirements a larger class of methods can be considered, including many methods of practical interest. In this paper we construct linear multistep methods of high-order (up to six) that possess relaxed monotonicity or boundedness properties with optimal step size conditions. Numerical experiments show that the new schemes perform much better than the classical TVD multistep schemes. Moreover there is a substantial gain in efficiency compared to recently constructed TVD Runge-Kutta methods

On monotonicity and boundedness properties of linear multistep methods

Simon Fraser University, Burnaby, British Columbia, V5A 1S6 Canada. Abstract: In this paper an analysis is provided of nonlinear monotonicity and boundedness properties for linear multistep methods. Instead of strict monotonicity for arbitrary starting values we shall focus on generalized monotonicity or boundedness with Runge-Kutta starting procedures. This allows many multistep methods of practical interest to be included in the theory. In a related manner, we also consider contractivity and stability in arbitrary norms