Barkhausen-kohinamittaus ja hiontapalamiset

Tiivistelmä. Hiontapalaminen on teollisuudessa merkittävä ongelma. Hiontapalamisessa kappaleen pinnassa vaikuttavat jännitykset kääntyvät kappaletta vahvistavista puristavista jännityksistä vetojännityksiksi. Tämän lisäksi kappaleen mikrokovuus alenee. Hiontapalamista voidaan mitata monella tapaa. Näistä yksi yleisesti käytössä oleva menetelmä on Barkhausen-kohinamittaus. Tässä kandidaatintyössä käydään läpi Barkhausen-kohinamittauksen hyödyntämistä hiontapalamisten havaitsemisessa, arvioinnissa ja luokittelussa. Tämän lisäksi luotiin kolmeen luokkaan jaetun BN-mittausdatan pohjalta luokittelumalli sekä päätöksentekopuun että logistisen regression avulla. Tällä pyrittiin vastaamaan siihen, toimiiko tässä tilanteessa kaksivaiheinen luokittelu paremmin kuin yhtäaikainen luokittelu. Mallien toimintaa arvioitiin sekaannusmatriisien avulla käyttäen holdout-ristivalidointia. Tämän lisäksi luotiin esimerkkimalli koko dataa käyttäen. Mallit suoriutuivat luokittelusta hyvin. Päätöksentekopuumallin keskimääräiset tarkkuudet opetusdatalle ja testausdatalle olivat 97,40 % ja 89,82 %. Merkittäviä eroja tässä työssä muodostettujen mallien ja kirjallisuudessa esitetyn mallin välillä ei ollut. Kumpikaan malli ei luokitellut testausdatan luokkaa 3 kovin hyvin. Mallien käyttäytymisestä huomattiin, että luokkien 1 ja 2 erottelussa mallit käyttivät lähinnä BN-mittauksen RMS-arvon muutosta. Luokan 2 ja 3 erotus taas tapahtui piikin sijainnin avulla. Mallit todettiin melko toimiviksi ja luotettaviksi. Näin osoitettiin taas eri asteisten hiontapalamisten luokittelun onnistuvan BN:n piirteiden avulla.Barkhausen noise measurement and grinding burns. Abstract. Grinding burn is major problem in industry. In grinding burn, residual stresses in surface region of the object, turn from reinforcing compressive stresses to tensile stresses. In addition, surfaces micro hardness decreases. Grinding burns can be measured in many ways. One of those methods is a nondestructive method that uses magnetic Barkhausen noise (BN), Barkhausen noise measurement. In this bachelor’s thesis Barkhausen noise measurement usage for detection, validation and classification of grinding burns was investigated. Grinding burn classification models were created with logistic regression and with decision tree for BN data separated into 3 categories. Models were made to answer if two phase classification works better ii this situation than simultaneous classification. Classification models performed well. For example, decision trees average performance for teaching data and validation data was 97,40% and 89,82%. Big differences between the models and model of Santa-Aho et al. (2023) were not found. No model could predict testing data’s class 3 well. This was probably because of the small number of class 3 data points. Interesting behaviour of the models was found. The distinction between class 1 and class 2 was made almost completely using the RMS value and distinction between class 2 and class 3 was made almost completely using the peak position of Barkhausen profile. The models were quite good and reliable, so it was shown again that grinding burn classification can be done with Barkhausen noise features

Kadanoff-Baym approach to double-excitations in finite systems

We benchmark many-body perturbation theory by studying neutral, as well as non-neutral, excitations of finite lattice systems. The neutral excitation spectra are obtained by time-propagating the Kadanoff-Baym equations in the Hartree-Fock and second Born approximations. Our method is equivalent to solving the Bethe-Salpeter equation with a high-level kernel while respecting self-consistently, which guarantees the fulfillment of a frequency sum rule. As a result, we find that a time-local method, such as Hartree-Fock, can give incomplete spectra, while already the second Born, which is the simplest time-nonlocal approximation, reproduces well most of the additional excitations, which are characterized as double-excitations.Comment: 20 pages, 10 figure

Linking formal child care characteristics to children's socioemotional well-being: A comparative perspective

Most research on formal child care and children’s outcomes has focused on single countries. We, however, contend that policy context may moderate the association between formal child care characteristics and children’s socioemotional well-being. We examined this by comparing the Netherlands, Finland and the UK; three countries that differ regarding family policies. Of these three countries, Finland was recently ranked highest (ranked 1st) with regards to quality of child care in a recent analysis by the Economist ,followed by the UK (ranked 3rd) and then the Netherlands (ranked 7th) .We hypothesized that children who attend child - care settings in countries with higher- uality formal child- are provision would generally show better socioemotional outcomes. Data from the comparative ‘F amilies 24/7’ survey were used, including 990 parents with children aged 0–12. We distinguished between two age groups in our analysis. Results indicated that, compared to the UK, longer hours in formal care were less beneficial in the Netherlands. Furthermore, spen ding time in formal care during nonstandard hours was more harmful for children in Finland compared to the UK. Lastly, receiving care from multiple caregivers was more disruptive for British children than for Dutch children. No differences were found between Finland and the Netherlands