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1.
Strong lensing as a tool to study the early universe : written report
Brankica Apostolova, 2023, raz. nal. na višji ali visoki šoli

Ključne besede: strong lensing, astrophysics, Roman Space Telescope, galaxy clustersv, galaxies
Objavljeno v RUNG: 23.08.2023; Ogledov: 626; Prenosov: 0
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Charge transport characterization of P3HT thin-film organic semiconductor : Written report: in fulfilment of diploma seminar 1FAF29 requirement
Matija Filipčič, 2021, raz. nal. na višji ali visoki šoli

Opis: The focus of this diploma seminar is to describe different types of charge transport theory and models used for finding mobility in semiconductors, more specifically focused on P3HT thin-film organic semiconductor. It also describes the time-of-flight method, which was used to measure the experimental data for P3HT with time dependent current I(t) curve. Another data set was obtained by performing Kinetic Monte Carlo (KMC) simulations using Miller-Abrahams hopping formalism. KMC was used to determine the material disorder, simulate I(t) curve and transit time for every charge carrier. Simulated data, different transit times and mobilities were then finally compared with experimental, in order to find agreements between the two.
Ključne besede: charge transport, P3HT, thin-film organic semiconductor
Objavljeno v RUNG: 15.09.2021; Ogledov: 2240; Prenosov: 0
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Vibrational spectra of am-Al 2 O 3 : tuning a parametric model. : Written report: in fulfillment of Diploma Seminar 1FAF29 requirements
Kurtović Jasmin, 2021, raz. nal. na višji ali visoki šoli

Opis: The present diploma seminar work has been dedicated first to the implementation of a procedure to calculate the vibrational density of states of two structural models of vitreous SiO 2 (v- SiO 2 ) and amorphous Al 2 O 3 (am-Al 2 O 3 ) models, and next to tune a parametric model for the calculation of the infrared (IR) spectra of am-Al 2 O 3 , in particular of the imaginary part of the dielectric function. The ground state of both structural models is obtained by relaxing the atomic structure by using the conjugate gradient method as implemented in the LAMMPS code. Vibrational frequencies and modes are obtained, in the harmonic approximation, by diagonalizing the dynamical matrices calculated for the given v-SiO 2 and am-Al 2 O 3 structural models. Dynamical matrices are obtained through a finite differences approach and vibrational density of states are plotted by applying Gaussian broadening. The calculation of the dielectric function requires the knowledge of the vibrational frequencies as well as the knowledge of the dynamical (or Born) charge tensors related to the atoms of the am-Al 2 O 3 structural model. For the latter model, a parametrization of the ab-initio Born charge tensors has been carried out with the purpose to allow for the fast calculation of the IR spectrum of any other am- Al 2 O 3 model without the need to calculate for it the Born charge tensors using expensive ab- initio methods. The parametrization of Born charge tensors takes into account, for aluminium atoms, only of the isotropic charge which depends on coordination number and average Al- O bond length of aluminium atoms, while for oxygen atoms coordinated to three Al atoms (75%), dynamical charges are parametrized also by the area bounded by aluminium atoms nearest neighbours of the 3-coordinated oxygen atom. Moreover for analyzing the dynamical charge tensors of 3-coordinated oxygen atoms a decomposition in terms of the representations of the spatial rotations was used. The IR spectrum obtained by means of the above described parametrization provides a good approximation to the IR spectrum obtained by using the ab- initio calculated dynamical charges, as it differs from it, on average, by around 5.1% which is much better (12%) than using a average isotropic charge model (i.e. diagonal Born charge tensors where each diagonal element is one third of the average isotropic charge).
Ključne besede: Vibrational spectra, am-Al 2 O 3, parametric model
Objavljeno v RUNG: 15.09.2021; Ogledov: 1927; Prenosov: 0
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8.
Least-square fit : written report
Aleksander Đorđević, 2021, raz. nal. na višji ali visoki šoli

Ključne besede: least-square fit, non-linear regression, Levenberg-Marquardt algorithm
Objavljeno v RUNG: 28.06.2021; Ogledov: 2161; Prenosov: 0
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Kvantni Hallov pojav v 2D materialih : diplomski seminar
Matevž Rupnik, 2021, raz. nal. na višji ali visoki šoli

Ključne besede: kvantni Hallov pojav, 2D materiali, Schrödingerjeva enačba, elektroni v električnem in magnetnem polju, grafen, Diracova enačba
Objavljeno v RUNG: 28.06.2021; Ogledov: 2110; Prenosov: 0
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10.
Space weather research with the Pierre Auger Observatory
Miha Živec, 2019, magistrsko delo

Opis: Space weather refers to environmental conditions in the interplanetary space and Earth’s magnetosphere, ionosphere and exosphere and can influence the performance and reliability of electronics based technological systems. The major role in space weather changes plays the solar wind, a stream of charged particles (mostly electrons and protons) with energies of approximately 1 keV, that can cause geomagnetic storms and auroras. During their entry into the atmosphere, high energy cosmic rays collide with atomic nuclei of atmospheric gasses. When scattering occurs extensive air showers are created. Those cascades of secondary particles create flashes of light due to the Cherenkov effect as well as excite molecules of nitrogen gas in atmosphere, which then glow in fluorescent light. In order to observe the light created by air showers, it has to be collected with telescopes. The particles from the cascades that reach ground can be detected with surface detectors. The Pierre Auger Observatory is the largest observatory for cosmic ray measurements. It is located in Argentinian pampas covering an area of 3000 km2. It consists of 1660 surface detectors and 27 fluorescence telescopes. For cosmic rays with energies above few 1017 eV, a precise reconstruction of energy and direction of primary particle is achievable. Observatory also allows measurement of flux of incoming particles down to primary energies in ca. 10 GeV - 10 TeV interval, with a median energy ca. 80-90 GeV. This measurement capability is called "scaler" mode, since the corresponding data consist of scaler counted cascade particles with deposited energy between 15 and 100 MeV, at the average rate of 2 kHz per individual surface detector. For the purpose of this master thesis I compared the data from scaler mode measurements with measurements of neutron monitors, which are commonly used for space weather observations. With the correlation received from the comparison, I showed that scaler mode operation of Pierre Auger observatory can be used to monitor space weather events such as solar cycle and the decreases in the observed galactic cosmic ray intensity due to solar wind (Forbush decrease).
Ključne besede: Pierre Auger Observatory, cosmic rays, space weather, Forbush decrease
Objavljeno v RUNG: 17.09.2019; Ogledov: 4955; Prenosov: 181
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