No description available.

Electromagnetic processes induced by electron scattering off few-nucleon systems are theoretically investigated in the non-relativistic formalism. Non-relativistic one-body nuclear current operators are used with a parametrization of nucleon electromagnetic form factors based on recent experimental nucleon scattering data. Electromagnetic form factors of three-nucleon and four-nucleon systems are calculated from elastic electron-nucleus scattering information. Nuclear response functions used in the determination of differential cross sections for inclusive and exclusive quasi-elastic electron-nucleon scattering from the 4He nucleus are also calculated. Final-state interactions in the quasi-elastic nucleon knockout process are explicitly taken into account using the Glauber approximation. The sensitivity of the response functions to the final-state interactions is investigated. The Antisymmetrized Molecular Dynamics approach with angular momentum and parity projection is employed to construct ground state wave functions for the nuclei. A reduced form of the realistic Argonne V18 nucleon-nucleon potential is used to describe nuclear Hamiltonian. A convenient numerical technique of approximating expectation values of nuclear Hamiltonian operators is employed. The constructed wave functions are used to calculate ground-state energies, root-mean-square radii and magnetic dipole moments of selected light nuclei. The theoretical predictions of the nuclear properties for the selected nuclei give a satisfactory description of experimental values. The Glauber approximation is combined with the Antisymmetrized Molecular Dynamics to generate wave functions for scattering states in quasi-elastic scattering processes. The wave functions are then used to study proton knockout reactions in the 4He nucleus. The theoretical predictions of the model reproduce experimental observation quite well. / Physics / Ph D. (Physics)

In recent years, there has been a significant increase in the usage of audience engagement platforms, which have allowed for engaging interactions between presenters and their audiences. The increased popularity of the platforms comes from the fact that engaging and interactive presentations have been shown to improve learning outcomes and create positive presentation experiences. However, using the platforms does not guarantee that your audience is engaged and participating. Given that the added value of engaging presentations only applies if the audience is actually engaged, it increases the need to know if and how engaged your audience is. The usage of audience engagement platforms has allowed for new ways of engagement to be studied. By utilizing the data gathered from the interactive presentation sessions, engagement can be studied and quantified through the modeling of the data. As the usage of audience engagement platforms and the study of presentation engagement is relatively new, there exists a limited amount of labeled data quantifying the level of engagement during presentations. To model the data, machine learning models should therefore be trained to generalize by being exposed to a limited number of presentation samples. This technique of training machine learning models is also referred to as few-shot learning. Distance-based machine learning models are defined in this study as models that make classifications and inferences by calculating distances between observations or observation class representations. Distance-based models have previously shown relatively good performance in few-shot learning applications, and interest therefore lies in expanding their application areas. This study presents a comparative evaluation of distance- and non-distance-based machine learning models given the problem of classifying presentations as being engaged or non-engaged, and estimating presentation class likelihoods in a few-shot learning context. A presentation-level dataset was gathered from the interactive presentation sessions, and each presentation observation was labeled as being engaged or non-engaged. The machine learning models were then trained to model the data and evaluated in terms of how well they were able to generalize to unseen testing samples by being exposed to a limited number of training observations. In particular, their classification and class likelihood estimation performances were evaluated. The results conclude that the distance-based models outperformed the non-distance-based models artificial neural network and relevance-vector machine given the presentation class likelihood estimation problem. The metric learning nearest neighbor classifier was the only distance-based model that outperformed all the non-distance-based models given both the presentation classification and class likelihood estimation problems. / Under de senaste åren har det skett en betydande ökning av användningen av plattformar för publikengagemang, vilket har möjliggjort engagerande interaktioner mellan presentatörer och deras publik. Plattformarnas ökade popularitet kommer från det faktum att engagerande och interaktiva presentationer har visat sig förbättra läranderesultat och skapa positiva presentationsupplevelser. Att använda plattformarna garanterar dock inte att din publik är engagerad och deltagande. Med tanke på att mervärdet av engagerande presentationer bara gäller om publiken faktiskt är engagerad, ökar det behovet av att veta om och hur engagerad din publik är. Användningen av plattformar för publikengagemang har gjort det möjligt att på nya sätt studera engagemang. Genom att använda data som samlats in från de interaktiva presentationssessionerna kan engagemang studeras och kvantifieras genom modellering av data. Eftersom användandet av plattformar för publikengagemang och studien av presentationsengagemang är relativt nytt, finns det en begränsad mängd märkt data som kvantifierar nivån av engagemang under presentationerna. För att modellera datan så bör maskininlärningsmodeller tränas att generalisera genom att utsättas för ett begränsad antal presentations observationer. Denna teknik för att träna inlärningsmodeller kallas också few-shot lärande. Distans-baserade maskininlärningsmodeller definieras i denna studie som modeller som gör klassificeringar genom att beräkna avstånd mellan observationer eller observationsklass representationer. Distans-baserade modeller har tidigare visat relativt goda resultat i few-shot inlärning problem, och intresset ligger därför i att utöka deras tillämpningsområden. Denna studie presenterar en jämförande utvärdering av distans- och icke-distans baserade maskininlärningsmodeller givet problemet med att klassificera presentationer som engagerade eller icke-engagerade, och uppskattning av presentation klasssannolikheter i ett few-shot inlärnings sammanhang. Ett dataset på presentationsnivå samlades in från de interaktiva presentationssessionerna, och varje presentation märktes som engagerad eller icke-engagerad. Maskininlärningsmodellerna tränades sedan för att modellera data och utvärderades i termer av hur väl de kunde generalisera till osedda testobservationer givet att de exponeras mot ett begränsat antal träningsobservationer. I synnerhet utvärderades deras klassificering och uppskattning av klasssannolikheter. Resultaten visade att alla distans-baserade modeller var bättre än de icke-distansbaserade modellerna artificial neural network och relevence-vector machine givet problemet med uppskattning av klasssannolikheter. Den distans-baserade metric learning nearest neighbor klassificeraren var den enda avståndsbaserade modellen som överträffade alla icke-distansbaserade modeller givet problemen med presentations klassificering och klasssannolikhets uppskattning.

Doctor of Philosophy / Department of Physics / Zenghu Chang / The few-cycle femtosecond laser pulse has proved itself to be a powerful tool for controlling the electron dynamics inside atoms and molecules. By applying such few-cycle pulses as a driving field, single isolated attosecond pulses can be produced through the high-order harmonic generation process, which provide a novel tool for capturing the real time electron motion. The first part of the thesis is devoted to the state of the art few-cycle near infrared (NIR) laser pulse development, which includes absolute phase control (carrier-envelope phase stabilization), amplitude control (power stabilization), and relative phase control (pulse compression and shaping). Then the double optical gating (DOG) method for generating single attosecond pulses and the attosecond streaking experiment for characterizing such pulses are presented. Various experimental limitations in the attosecond streaking measurement are illustrated through simulation. Finally by using the single attosecond pulses generated by DOG, an attosecond transient absorption experiment is performed to study the autoionization process of argon. When the delay between a few-cycle NIR pulse and a single attosecond XUV pulse is scanned, the Fano resonance shapes of the argon autoionizing states are modified by the NIR pulse, which shows the direct observation and control of electron-electron correlation in the temporal domain.

Doctor of Philosophy / Department of Physics / Zenghu Chang / In this research, the carrier-envelope phase (CE phase) evolution of the pulse train from a Kerr-lens mode-locked chirped-mirror dispersion compensated Ti:Sapphire laser oscillator was stabilized. The offset frequency corresponding to the rate of change of the CE phase was obtained by spectrally broadening the oscillator pulses in a photonic crystal fiber and interfering the f and 2f components. An offset frequency linewidth of 100 mHz was obtained and could be locked over several hours. The effect of path length drift in the interferometer used for CE phase stabilization of the laser oscillator was investigated. By stabilizing the path length drift, the interferometer noise was reduced by several orders of magnitude. The CE phase drift through a grating-based chirped-pulse multi-pass amplifier was investigated. Varying the grating separation by 1μm in the stretcher was found to cause a shift of 3.7 +/- 1.2 rad of the CE phase. The CE phase could be stabilized to within 160 mrad rms error by feedback controlling the grating separation. By locking the path length in the f-to-2f interferometer used to stabilize the CE phase of the oscillator pulses, the fast (>3 Hz) CE phase drift of the amplified laser pulses was reduced from 79 to 48 mrad. It was also found that the CE phase could be shifted and set to any value within a 2π range by changing the grating separation. Also, the CE phase could be continuously modulated within a 2π range while maintaining a relative phase error of 171 mrad. The CE phase shift of a grating-based compressor was found to be stabilized to 230 mrad rms. The effect of laser power fluctuation on the CE phase measurement was also investigated. It was found that a 1% fluctuation of the laser energy caused a 160 mrad error in the CE phase measurement. A two-step model is proposed to explain the phase-energy coupling in the CE phase measurement. The model explains the experimentally observed dependence of the group delay between the f and 2f pulses on the laser energy. Few-cycle pulses were CE phase stabilized to 134 mrad rms and were used to perform above-threshold ionization and high harmonic generation.

The Internet has fundamentally changed the way of modern communication. Current trends indicate that high-capacity demands are not going to be saturated anytime soon. From Shannon's theory, we know that information capacity is a logarithmic function of signal-to-noise ratio (SNR), but a linear function of the number of dimensions. Ideally, we can increase the capacity by increasing the launch power, however, due to the nonlinear characteristics of silica optical fibers that imposes a constraint on the maximum achievable optical-signal-to-noise ratio (OSNR). So there exists a nonlinear capacity limit on the standard single mode fiber (SSMF). In order to satisfy never ending capacity demands, there are several attempts to employ additional degrees of freedom in transmission system, such as few-mode fibers (FMFs), which can dramatically improve the spectral efficiency. On the other hand, for the given physical links and network equipment, an effective solution to relax the OSNR requirement is based on forward error correction (FEC), as the response to the demands of high speed reliable transmission. In this dissertation, we first discuss the model of FMF with nonlinear effects considered. Secondly, we simulate the FMF based OFDM system with various compensation and modulation schemes. Thirdly, we propose tandem-turbo-product nonbinary byte-interleaved coded modulation (BICM) for next-generation high-speed optical transmission systems. Fourthly, we study the Q factor and mutual information as threshold in BICM scheme. Lastly, an experimental study of the limits of nonlinearity compensation with digital signal processing has been conducted.

Com o objetivo de investigar a fotoprodução de kaons na região de energias intermediarias, foram realizadas medidas de seção de choque de fotoprodução de híperons utilizando o deutério como alvo, entre 0,50 e 2,95GeV. Para obtenção das medidas foi utilizado o acelerador de elétrons do TJNAF (Thomas Jefferson National Accelerator Facility) localizado na Virginia, USA. Foram obtidas seções de choque de fotoprodução para as reações gama(p, K+)lambda, gama(p, K+)sigmaº, sigma(n, K+)lambda-. Observou-se a estrutura de interferência na proximidade do limiar de produção de \'lambdaº, previsto teoricamente. As seções de choque obtidas foram comparadas com o modelo teórico existente fornecendo informações fundamentais para uma elaboração teórica mais consistente. Foram ainda, observados lambda(1385) com grande resolução abrindo possibilidade de realizar um estudo muito interessante desta produção. / Kaon photoproduction on deuterium was investigated and the differential cross sections were determined using the data obtained in Hall B at TJNAF (Thomas Jefferson National Accelerator Facility). Real photons were produced in the range covered from 0.50 to 2.95GeV. The cross section for kaon production reactions gama(p, K+ ) lambda, gama(p, K+ ) \'sigmaº, sigma(n, K+)lambda- were obtained. The interference structure near the production of lambdaº, predicted theoretically, was revealed. Theoretical model was compared to the cross section obtained and fundamental informations became available in order to improve the consistence of the model existent. At last, lambda(1385) were identified with good resolution conducting to interesting investigation in the future.

In this thesis, I have developed a range of theoretical and numerical techniques for modelling the behaviour of partially coherent optical systems and multi-mode detectors. The numerical simulations were carried out for the ultra-low-noise Transition Edge Sensors (TESs) being proposed for use on the SAFARI instrument on the cooled aperture infrared space telescope SPICA (34 - 210 μm). The optical behaviour of the SAFARI system is described in terms of the optical modes of the telescope, as distinct from the optical modes of the detector. The performance of the TESs were assessed in terms of signal power, background power and photon noise. To establish a method for precisely characterising and calibrating ultra-low-noise TESs, a cryogenic test system was designed and engineered to measure the optical efficiencies of the SAFARI TESs. The multi-mode, partially coherent illumination conditions of the measurement system were engineered to be precisely the same as those of the telescope. A major difference between the test system and the telescope’s optics is that the telescope will have focusing elements, but the test system was designed to avoid focusing elements in order to keep the optical path as clean as possible. The theoretical formalism and numerical models were adapted accordingly to address this difference. The numerical simulations show that the test system could provide near identical optical performance as that of the telescope system even though the focusing elements were absent. I also performed experimental measurements to investigate the optical efficiencies of the multi-mode TESs. The detectors worked exceedingly well in all respects with satisfactory optical efficiencies. In addition, it has been shown that the optical model provides a good description of the optical behaviour of the test system and detectors. Further modal analysis was developed to study losses in the multi-mode horns. The optical behaviour of the waveguide-mounted thin absorbing films in the far-infrared was modelled using a mode-matching method.

The diploma thesis is aimed at the teaching methods used in the setting of schools with few classes. The theoretical part engages in the issue of teaching methods, their characteristics, historical development and classification according to various authors. Selected teaching methods are then described in bigger detail. The next section is devoted to the schools with few classes. They are viewed here as community schools or as a pedagogic alternative, the thesis describes the history of schools with few classes and both advantages and disadvantages of their aktivity. The practical part of the thesis was realized via an observing method. The aim of this section of the thesis was to map teaching methods use dat three selected schools with few classes. Results are presented via an analysis of observed classes and chart, which contains the most widely used teaching methods at individual schools.

Com o objetivo de investigar a fotoprodução de kaons na região de energias intermediarias, foram realizadas medidas de seção de choque de fotoprodução de híperons utilizando o deutério como alvo, entre 0,50 e 2,95GeV. Para obtenção das medidas foi utilizado o acelerador de elétrons do TJNAF (Thomas Jefferson National Accelerator Facility) localizado na Virginia, USA. Foram obtidas seções de choque de fotoprodução para as reações gama(p, K+)lambda, gama(p, K+)sigmaº, sigma(n, K+)lambda-. Observou-se a estrutura de interferência na proximidade do limiar de produção de \'lambdaº, previsto teoricamente. As seções de choque obtidas foram comparadas com o modelo teórico existente fornecendo informações fundamentais para uma elaboração teórica mais consistente. Foram ainda, observados lambda(1385) com grande resolução abrindo possibilidade de realizar um estudo muito interessante desta produção. / Kaon photoproduction on deuterium was investigated and the differential cross sections were determined using the data obtained in Hall B at TJNAF (Thomas Jefferson National Accelerator Facility). Real photons were produced in the range covered from 0.50 to 2.95GeV. The cross section for kaon production reactions gama(p, K+ ) lambda, gama(p, K+ ) \'sigmaº, sigma(n, K+)lambda- were obtained. The interference structure near the production of lambdaº, predicted theoretically, was revealed. Theoretical model was compared to the cross section obtained and fundamental informations became available in order to improve the consistence of the model existent. At last, lambda(1385) were identified with good resolution conducting to interesting investigation in the future.