Global ETD Search

31	Gamma spectroscopy and lifetime measurements in the doubly-odd 194tl nucleus, revealing possible chiral symmetry breaking Masiteng, Paulus Lukisi January 2013 (has links) Philosophiae Doctor - PhD / In the first experiment high spin states in 194Tl, excited through the 181Ta (18O, 5n) heavyion fusion evaporation reaction were studied using the AFRODITE array at iThemba LABS. The γ-γ coincidences, RAD ratios and linear polarization measurements were carried out and the previously known level scheme of 194Tl was significantly extended. A total of five rotational bands four of which are new were observed. A pair of rotational bands associated with the πh9/2 ⊗ νi−1 13/2 configuration at lower spins and with the πh9/2 ⊗ νi−3 13/2 configuration at higher spins was found and interpreted as the first possible chiral bands followed above the band crossing. The two 4-quasiparticle bands show exceptionally close near-degeneracy in the excitation energies. Furthermore close similarity is also found in their alignments and B(M1)/B(E2) reduced transition probability ratios. In the second experiment lifetimes in 194Tl were measured using the DSAM technique with the excited states in this nucleus populated through the 181Ta (18O, 5n) reaction. A total of 25 lifetimes and 30 reduced transition probabilities of magnetic dipole B(M1) and electric quadrupole B(E2) have been evaluated. Furthermore B(M1) and B(E2) reduced transition probabilities in Bands 1 and 4, which have been regarded as chiral candidates, were found to be close to each other and reveals strong splitting along spin values. This further supports the proposed chiral nature of these two bands. High-spin states Level scheme Linear polarisation Angular momentum Excitation energies Near-degeneracy Rotational bands Transition probability ratios Chirality Doppler shift attenuation method Lifetimes
32	Softwarový přijímač pro dálkový průzkum Země v pásmu X / X-band Earth Observation Satellite Software Defined Receiver Zedka, Radim January 2019 (has links) Práce se zabývá procesem návrhu digitálního přijímače pro signály družic dálkového průzkumu Země v pásmu X. V první části je uveden seznam družic které umožnují příjem vědeckých dat pomocí amatérských neautorizovaných stanic. Jsou zde vypsány základní signálové parametry některých družic, z nichž EOS-PM-1 je zvolena jako hlavní objekt pro návrh přijímače. Ve druhé části je použit software MATLAB pro simulaci družicového O-QPSK signálu v základním pásmu, mechanizmu kompenzace kmitočtového ofsetu, synchronizaci nosné, symbolové synchronizaci, rámcové synchronizaci a odstranění fázové dvojznačnosti vlivem modulace. Třetí část práce pojednává detailněji o implementaci jednotlivých bloků přijímače do FPGA při použití aritmetky s pevnou řádovou čárkou. Je zde popsána metoda pro verifikaci celého designu v reálném čase a závěrem je zde uvedeno porovnání výsledků měření touto metodou a výsledků simulace.
33	Analýza přenosu mobilního digitálního rozhlasového vysílání / Analysis of the transmission in the mobile digital audio broadcasting Kresta, Daniel January 2016 (has links) This thesis deals with an analysis of a system called Digital Audio Broadcast and describes its mathematical model created in MATLAB program. In the first part basic blocks of a transmitter and a receiver are analyzed along with their principles. Then different types of transmission channels for static, portable and mobile receivers are described. The second part contains description of the DAB mathematical model itself. Individual blocks are described in the order of the DAB signal path, from the transmitter through the transmission channel to the receiver side. In this part the graphical user interface is also described. In the final part the results of experimental measurements and simulations are presented.
34	Turbulence measurements in fiber suspension flows : experimental methods and results Fällman, Monika Carina January 2009 (has links) Turbulent mixing is present in many pulp and paper processes. It is a particularly important factor in the design and improvements of the paper machine headbox, influencing the final paper structure. During this project, experimental methods to quantify the effect of fibers on turbulent suspension flows have been developed, and then used for studying turbulent mixing in fiber suspensions. A technique that uses microprobes to measure passive scalar mixing of salt for the characterization of turbulent fluctuations in a fiber suspension flow has been developed: Conductivity micro-probes have been built and turbulence measurements have been performed in simple jet and wake flows, studying turbulent mixing between the two streams of pulp suspension, of which one has been doped with salt. A relatively new technique to measure fluid velocity non-intrusively in opaque fluids has also been tested. The technique makes use of ultrasonic pulses to obtain velocity information through the Doppler-shift of reflected pulses. The main efforts reported on in the thesis are focused on method design and development as well as method evaluation. fluid flow turbulent turbulence paper pulp fiber fibre suspension two-phase experimental conductivity micro-probes passive scalar ultrasonic Doppler shift Fluid Mechanics and Acoustics Strömningsmekanik och akustik
35	Radio channel modeling for mobile ad hoc wireless networks Sng, Sin Hie 06 1900 (has links) Approved for public release; distribution is unlimited / The radio channel places fundamental limitations on the performance of mobile ad hoc wireless networks. In the mobile radio environment, fading due to multipath delay spread impairs received signals. The purpose of this thesis is to develop a radio channel model and examine the effect of various parameters on channel behavior that is representative of environments in which mobile ad hoc wireless networks operate. The various physical phenomena considered are outdoor environments, fading and multipath propagation, type of terrains, and mobility (Doppler shift). A channel model based on a Tapped Delay Line (TDL) structure was developed and implemented in the MATLAB programming language, and the performance of the time-varying channel was studied by plotting the signal constellations. The simulation results indicate that the number of taps required in the TDL is 8 or less and the carrier frequency did not influence the performance significantly. The Jakes Doppler spectrum should be used in urban environments with high mobility; the Gaussian Doppler spectrum is the choice for low mobility urban environments and for the hilly terrain under both low and high mobility. / Civilian, Singapore Ministry of Defense Wireless communication systems Wireless LANs Mobile communication systems Doppler effect Ad hoc wireless networks Rayleigh and Rician distribution MATLAB Mobile radio channel Tapped delay line Doppler shift Jakes power spectrum Multipath and fading
36	Ultracold Neutral Plasma Evolution in an External Magnetic Field Pak, Chanhyun 26 June 2023 (has links) (PDF) We study the expansion velocity and ion temperature evolution of ultracold neutral plasmas (UNPs) of calcium atoms under the influence of a uniform magnetic field that ranges up to 200 G. In the experiments, we use a magneto-optical trap (MOT) to capture the neutral atoms and laser-induced fluorescence (LIF) to take images of the plasma. We vary the magnetic field strengths and the initial electron temperatures and observe the plasma evolution in time. We compare the ion temperature evolution to the theory introduced in the paper by Pohl et. al. [Phys. Rev. A 70, 033416 (2004)]. The evolution of the gradient of expansion velocity suggests the presence of ion acoustic waves (IAWs). We speculate that our measurements showing that the ion temperature remains relatively high throughout the evolution is a biproduct of the IAW. Coulomb coupling parameter Debye screening length ultracold neutral plasma alkaline earth metals magneto-optical trap laser-induced fluorescence Zeeman shift frequency comb Nd:YAG-pumped dye laser Doppler shift Doppler broadening Voigt profile ion acoustic waves Physical Sciences and Mathematics
37	Pokročilé algoritmy zpracování signálů pro družicovou komunikaci / Advanced Algorithms for Satellite Communication Signal Processing Záplata, Filip January 2016 (has links) Dizertační práce je zaměřena na softwarově definované přijímače určené k úzkopásmové družicové komunikaci. Komunikační kanály družicových spojů zahrnujících komunikaci s hlubokým vesmírem jsou zatíženy vysokými úrovněmi šumu, typicky modelovaného AWGN, a silným Dopplerovým posuvem signálu způsobeným mimořádnou rychlostí pohybu objektu. Dizertační práce představuje možné postupy řešení výpočetně efektivní digitální downkonverze úzkopásmových signálů a systému odhadu kmitočtu nosné úzkopásmových signálů zatížených Dopplerovým posuvem v řádu násobků šířky pásma signálu. Popis navrhovaných algoritmů zahrnuje analytický postup jejich vývoje a tam, kde je to možné, i analytické hodnocení jejich chování. Algoritmy jsou modelovány v prostředí MATLAB Simulink a tyto modely jsou využity pro ověření vlastností simulacemi. Modely byly také využity k experimentálním testům na reálném signálu přijatém z družice PSAT v laboratoři experimentálních družic na ústavu radioelektroniky.
38	One-Dimensional Velocity Distributions of Fast Ions under RF Heating Including Doppler Shift in Tokamaks Bähner, Lukas January 2022 (has links) The goal of nuclear fusion research is to create a clean and virtually limitless energy source. In order to that, a plasma must be heated to hundreds of millions degrees Celsius. A commonly used heating mechanism is ion cyclotron resonance heating, where antennas emit radio waves into the plasma. The wave can resonate with the ions at their cyclotron frequency, which leads to wave absorption. In order to investigate and improve the heating, one can perform computer simulations. FEMIC is a finite element model for ICRH that calculates the wave field created by the antennas. However, this code does not take into account how the wave modifies the velocity distribution of the plasma. Therefore, a time-independent Fokker-Planck solver is implemented that computes the fast ion distribution due to the incident wave field calculated with FEMIC. The novelty of this code is to include Doppler shift, which influences where ions resonate and how they are heated. / Målet med fusionsforskningen är att skapa en ren energikälla som kan producera obegränsade mängder energi. För detta krävs att ett plasma värms till hundratals miljoner grader Celsius. En vanlig teknik för att värma plasmat är joncyklotronuppvärmning, där en antenn emitterar radiovågor som propagerar in i plasmat. Om vågen är i resonans med jonernas cyklotronrörelse leder detta till att vågen absorberas av jonerna. För att studera och utveckla denna uppvärmningsteknik kan man använda datorsimuleringar. FEMIC är en kod baserad på den finita elementmetoden som beräknar vågfälten som skapas av antennen. Med denna kod kan vi dock inte beräkna hur vågen påverkar jonernas fördelningsfunktioner. Därför har en Fokker-Planck-lösare implementerats som kan beräkna fördelningen av snabba joner som accelererats av vågfältet från FEMIC. Det nya i denna modell är att koden tar hänsyn till Dopplerskiftet, vilket påverkar var jonerna är i resonans med vågen och hur de värms upp. plasma fusion ICRH Ion Cyclotron Resonance Heating RF radio frequency Fokker-Planck equation Fokker-Planck solver quasilinear operator Coulomb collision Doppler shift velocity distribution local temperature plasma fusion ICRH joncyklotronuppvärmning RF radiofrekvens Fokker-Planck-ekvationen Fokker-Planck-lösare kvasilinjär operator Coulombkollisioner Dopplerskift hastighetsfördelning lokal temperatur Elektroteknik och elektronik

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