Emission, kinetic and magnetic phenomena in rare-earth and transition metal doped ZnSe single crystals

In this work emission, optical, electrical and magnetic properties of the d- and f- elements doped zinc selenide crystals were investigated within a wide temperature range. Doping was performed in various technological processes: during the growth by chemical vapor transport method; by thermal diffusion from the Bi or Zn melt. Concentration of the doping impurity in the crystals was controlled by amount of the dopant in the source material or by its concentration in the doping media. Special interest in the work was paid to the influence of the different concentrations of Cr and Yb impurities on ZnSe crystals’ properties, correlations between observed effects and similarities with the Ni, Mn and Gd dopants are analysed. Possibility of formation of the excitons bound to the doping d-ions was shown. In contrast to this, it was observed that f-elements do not bound excitons, but prevent formation of excitons bound to some uncontrolled impurities. A mechanism of Cr doping impurity interaction with background impurities and zinc selenide structural defects was proposed based on experimental data. An assumption about resonant energy transfer between double charged chromium ions and complexes based on crystals’ vacancy defects was made. A correlation between emission and magnetic properties of the d- ions doped samples was established. Based on this correlation a mechanism explaining the concentration quench of the emission was proposed. It was found that f-ions bind electrically active shallow and deep donor and acceptor states of background impurity to electrically neutral complexes. This may be observed as “purification” of ZnSe crystals by doping with the rare-earth elements, resulting i tendency of the properties of f-ion doped crystals to the properties of intrinsic crystals, but with smaller concentration of uncontrolled native and impurity defects. A possible interpretation of this effect was proposed. It was shown that selenium substituting impurities decrease efficiency of the Yb doping. Based on this experimental results an attempt to determine ytterbium ion surroundings in the crystal lattice was made. It was shown that co-doping of zinc selenide crystals with the d- and f- ions leads to the combination of the impurities influence on the material’s properties. On the basis of obtained data an interaction mechanism of the d- and f-elements co-dopants was proposed. Guided by the model of the ytterbium ion incorporation in the selenide sublattice of the ZnSe crystals, an assumption about stabilization of single charged chromium ions in the zinc sublattice crystal nodes, by means of formation of the local charge compensating clusters, was made.

Eleohjaus Google Cardboard-virtuaaliympäristöön käyttäen älypuhelimen kameraa

Tässä opinnäytetyössä on toteutettu ja arvioitu virtuaalitodellisuuteen soveltuvaa käyttöliittymää. Motivaationa työlle oli Google Cardboardin mahdollistama todentuntuinen virtuaalikokemus älypuhelimen hinnalla. Cardboard-ympäristöön ei kuitenkaan ollut olemassa kattavaa käyttöliittymää ja tämän työn tavoitteena olikin selvittää, onko älypuhelimen kameraa mahdollista käyttää eleohjauksen toteuttamiseen niin että ohjaus on käytettävyydeltään kelvollinen ja se tukee läsnäolon tunteen syntymistä. Asian selvittämiseksi kehitettiin testipeli, jolla eleohjausta verrattiin Cardboardin oletuskäyttöliittymään. Koehenkilöt saavuttivat ehdotetulla käyttöliittymällä testipelissä keskimäärin 45-% korkeampia pistemääriä ja lisäksi he arvioivat sen olleen toimiva ja sen synnyttämän läsnäolon tunteen olleen voimakkaampaa.

The influence of high cable penetration in distribution networks on earth fault currents and the operation of relay protection.

Recent Storms in Nordic countries were a reason of long power outages in huge territories. After these disasters distribution networks' operators faced with a problem how to provide adequate quality of supply in such situation. The decision of utilization cable lines rather than overhead lines were made, which brings new features to distribution networks. The main idea of this work is a complex analysis of medium voltage distribution networks with long cable lines. High value of cable’s specific capacitance and length of lines determine such problems as: high values of earth fault currents, excessive amount of reactive power flow from distribution to transmission network, possibility of a high voltage level at the receiving end of cable feeders. However the core tasks was to estimate functional ability of the earth fault protection and the possibility to utilize simplified formulas for operating setting calculations in this network. In order to provide justify solution or evaluation of mentioned above problems corresponding calculations were made and in order to analyze behavior of relay protection principles PSCAD model of the examined network have been created. Evaluation of the voltage rise in the end of a cable line have educed absence of a dangerous increase in a voltage level, while excessive value of reactive power can be a reason of final penalty according to the Finish regulations. It was proved and calculated that for this networks compensation of earth fault currents should be implemented. In PSCAD models of the electrical grid with isolated neutral, central compensation and hybrid compensation were created. For the network with hybrid compensation methodology which allows to select number and rated power of distributed arc suppression coils have been offered. Based on the obtained results from experiments it was determined that in order to guarantee selective and reliable operation of the relay protection should be utilized hybrid compensation with connection of high-ohmic resistor. Directional and admittance based relay protection were tested under these conditions and advantageous of the novel protection were revealed. However, for electrical grids with extensive cabling necessity of a complex approach to the relay protection were explained and illustrated. Thus, in order to organize reliable earth fault protection is recommended to utilize both intermittent and conventional relay protection with operational settings calculated by the use of simplified formulas.

Verkkosivujen automaattinen nopeusoptimointi Google PageSpeed -työkaluilla

Toukokuussa 2015 verkkosivujen keskimääräinen latauskoko ylitti ensimmäistä kertaa kahden megatavun rajan Internetin historian aikana. Verkkosivujen keskimääräinen latauskoko on ollut jatkuvassa kasvussa, vaikka yhä enemmän verkkosivuja selataan epäluotettavilla mobiiliyhteyksillä tai hitailla päätelaitteilla. Tässä tutkielmassa esitellään verkkosivujen latausnopeuteen vaikuttavia tekijöitä ja kuinka näitä tekijöitä voidaan optimoida nopeamman Internetin saavuttamiseksi. Verkkosivujen latausnopeuteen vaikuttavia kriteerejä on paljon ja kriteerit vaihtelevat sivustokohtaisesti. Verkkosivujen nopeusoptimointi on teknistä ja kriteerien monimuotoisuuden ja vaihtelevuuden johdosta automaattinen nopeusoptimointi on vaikeaa. Tutkielmassa esitellään tähän ongelmaan yhtenä ratkaisuna Googlen tarjoamat PageSpeed -työkalut. PageSpeed -työkaluista esitellään kaksi keskeistä työkalua: Google PageSpeed Insights -metriikkatyökalu, joka mittaa sivuston lataus- ja renderöintinopeutta ja Google PageSpeed Module -palvelinmoduuli, joka tekee automaattista nopeusoptimointia reaaliaikaisesti HTTP-palvelimen yhteydessä.