Dissertations / Theses on the topic 'PHYSICS EXPERIMENTAL'

Experiments were carried out to investigate the modulated nature of cross-waves in a long, deep, rectangular channel with a plane-flap type wavemaker at one end. Poincare sections, power spectra, Lyapunov exponents, correlation dimensions and winding numbers were generated from local wave height data to reveal the temporal behavior of modulated states. Information about the transverse spatial structure was obtained from digital image processing and multiprobe techniques. In general, three frequencies were observed: the subharmonic and two slow modulation frequencies. A one-mode modulation was associated with streamwise variation, and a sloshing modulation was associated with spanwise variation. The interaction of the oscillations produced a pattern of overlapping frequency-locked tongues in parameter space. In some tongues, all three frequencies were locked. The frequency-locked tongues had winding numbers in Farey tree sequences, and the overall picture was similar to the Arnold tongues of one-dimensional circle maps. Near the intersection of the neutral stability curves for two adjacent modes, a standing wave localized on one side of the tank was observed, in agreement with the coupled mode analysis of Ayanle (1989). At large forcing amplitudes or negative detunings, the transverse sloshing motion broke up into more than one soliton-like structure propagating in the spanwise direction and reflected by the sidewalls.

General relativity describes gravity as the curvature of space-time. The theory predicts the existence of gravitational waves (GWs), which can be described as ripples in space-time propagating at the speed of light. So far no direct detection of GWs has been achieved. The sensitivities of the currently leading laser interferometric GW detectors are limited by various noise sources, i.e. seismic, thermal, shot noises etc. Several conceptual studies are underway investigating new techniques that aim to improve sensitivities enough to fulfil the requirements of the next generation of detectors. One of these new techniques under investigation is displacement and frequency noise free interferometry (DFI). This thesis reports on the experimental demonstration of a new method of partial DFI that is effective in the GW detection frequency band. The isolation of a mimicked GW signal from displacement noise of one mirror is demonstrated for a detuned Fabry-Perot cavity. A significant reduction in the displacement noise of the cavity input mirror was achieved by properly combining the reflected and transmitted signals from the cavity. This result represents the first experimental demonstration of this recently proposed DFI scheme, and lays the foundations for future work aimed at implementing DFI schemes in up-coming laser interferometric GW detectors.

TOF neutron diffraction and multinuclear MAS NMR data are combined to investigate the local structure of three silicate based glass forming systems. The effects of experimental resolution on the structural parameters obtained from neutron diffraction data are considered using simulated correlation functions. The Gaussian fit parameters to a peak in T(r) report a smaller peak width and area than that of the Gaussian broadening. This is due to the contribution of the realspace resolution function. This effect is most dramatic for small values of (u 2) 1/2 and Qmax but is negligible for typical values. The experimental uncertainty in measuring Q is considered for TOF neutron diffraction data. ΔQ is considered constant for data measured at several scattering angles. Some of the scattering intensity is transferred to a tail on the low r side of each peak, the magnitude of which increases with ΔQ. The peak fit parameters (position, width and area) change with increasing ΔQ, both before and after removing the gradient at low r. The Q-space resolution at a fixed scattering angle is considered by broadening i(Q) with a Gaussian of width ΔQ/Q=constant. The peak fit parameters change with increasing ΔQ/Q but not significantly at the resolution quoted for the high angle detectors on LAD. The interpretation of experimental data in terms of glass structure is greatly dependant upon an accurate knowledge of the glass composition. It is considered necessary to determine the concentration of all the cation species by a single or combination of techniques. TOF neutron diffraction and 170 MAS NMR data are reported for several (SnO)x(Si02)1-x glasses and a partially crystallised (SnO)(Si02) sample. 29Si, 119Sn MAS NMR and a powder X-ray diffraction data are also presented for the partially crystallised sample. The tin is present as Sn2+ and is three co-ordinated to oxygen at all compositions. The (SnO)x(Si02)1-x glasses are thought to consist of a network of Sn03/3 and Si04/2 polyhedra. The tin polyhedra may form pairs or chains. The local order in the crystalline phase is thought to be similar to that in the glasses. There are two tin and two silicon sites in the crystal phase of approximate composition (SnO)4(Si02). It has not been possible to refine the crystal structure. 29Si MAS NMR data are presented for (Li20)x(SnO)1-x(Si02), (Na20)x(SnO)1-x (Si02) and (K20)x(SnO)1-x(Si02) glasses and TOP neutron diffraction data for (K20)x(SnO)1-x(Si02). The tin is present as Sn2+ and is three co-ordinated at all compositions. Replacing the tin with modifier oxide reduces the 29Si NMR chemical shift. The modifier cation is thought to depolymerise the tin silicate network, associating with the tin to maintain charge neutrality. 29Si and 31p MAS NMR and TOP neutron diffraction data are presented for (K20- 4Si02)x(P205)1-x, (K20-2Si02)x(P205)1-x and (Si02)x(P205)1-x glasses. Each glass contains SiIV and SiVI species, the potassium tetrasilicate-Pjt), glasses also contain SiV species. The proportion of silicon species changed with thermal history. Each glass is thought to consist of a modified phospho silicate network. The potassium disilicate-Pjo, glasses are thought to consist of a continuous network of Si(OP)3(OSi), Si(OP)4(OSi)2, (p-Q2)- and (P-Q4)+ species. The alkali-free phosphosilicate and potassium tetrasilicate-P2O5, glasses are thought to have similar structures but it is not possible to define the phosphate species. It was not possible to distinguish the different species by neutron diffraction. The phosphosilicate network is thought to be more disordered than modified phosphate and modified silicate networks.

An efficient method for calculating NMR lineshapes from anisotropic second rank tensor interactions is presented. The algorithm produces lineshapes from asymmetric tensors by summing those from symmetric tensors. This approach significantly reduces the calculation time, greatly facilitating iterative nonlinear least squares fitting of experimental spectra. This algorithm has been modified to produce partially relaxed lineshapes and spectra of partially ordered samples.;Calculations for rapidly spinning samples show that spin-lattice relaxation time ( T1Z ) anisotropy varies with the angle between the spinning axis and the external field. When the rate of molecular motion is in the extreme narrowing limit, measurement of T1Z anisotropies for two different values of the spinning angle allows the determination of two linear combinations of the three static spectral densities, J0(0), J1(0) and J2(0). Experimental results for ferrocene demonstrate the utility of these linear combinations in the investigation of molecular dynamics with natural abundance 13C NMR. For ferrocene-d 10, deuteron T1Z and quadrupolar order relaxation time ( T1Q ) anisotropies, along with the relaxation time of the 13C magic angle spinning (MAS) peak, provide sufficient information to determine the orientation dependence of all three individual spectral densities. The experimental results include the first determination of J 0(0) in a solid sample.;A variety of experimental techniques were used in an investigation of the polyimides LaRC-IA, LaRC-TPI and LaRC-SI and related model compounds. Magic angle spinning was used to acquire 13C isotropic chemical shift spectra of these materials. The spectra were assigned as completely as possible. In addition, the principal components of some shielding tensors were measured using variable angle correlation spectroscopy. of those studied, LaRC-SI is the only polymer that is soluble. However, after it is heated past its glass transition temperature, LaRC-SI becomes insoluble. Experiments were performed in an attempt to identify causes of this behavior. 1H and 13C NMR spectra of soluble and insoluble LaRC-SI are significantly different when magnetization from nuclei in rigid regions of the polymer is suppressed. Hydration studies of LaRC-SI and LaRC-IA show that absorbed water plasticizes these polymers.

Sound propagation is a complex subject, especially in an enclosure. The study of room acoustics involves not only a research into how sound is propagated in a room, but also a search into how to measure sound under different condition and how to control sound in the case of various wall materials. For an acoustical environment, there are three separated parts: sound sources, room acoustics, and the listens. These three items form a source-medium-receiver chain, which is typical for most of communication models. In this thesis, the image method is applied to predict the acoustical quality of a real room, and the experiment for room acoustic measurement is set up. The simulation model using image method proved the design of the measurement system is efficient for room acoustics.

Beams of light can carry spin and orbital angular momentum. Spin angular momentum describes how the direction of the electric field rotates about the propagation axis, while orbital angular momentum describes the rotation of the field amplitude pattern. These concepts are well understood for monochromatic beams, but previous theoretical studies have constructed polychromatic superpositions where the connection between angular momentum and rotation of the electric field becomes much less clear. These states are superpositions of two states of light carrying opposite signs of angular momentum and slightly detuned frequencies. They rotate at the typically small detuning frequency and thus we call them slowly rotating modes of light. Strangely, some of these modes appear to rotate in the direction opposing the sign of their angular momentum, while others exhibit overall rotation with no angular momentum at all! These findings have been the subject of some controversy, and in 2012, Susanna Todaro (HMC ’12) and I began work on trying to shed light on this “angular momentum paradox." In this thesis, I extend previous work in theory, simulation, and experiment. Via theory and modeling in Mathematica, I present a possible intuitive explanation for the angular momentum paradox. I also present experimental realization of slowly rotating spin superpositions, and outline the steps necessary to generate slowly rotating orbital angular momentum superpositions.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2013.
Cataloged from PDF version of thesis.
Includes bibliographical references (page 77).
In optical communications, two measures of efficiency are commonly at odds. The first is the photon information efficiency (in bits/photon) which measures the information that each detected photon conveys; the second is the spectral efficiency (in bits/s/Hz) which measures the bit rate achieved under limited bandwidth. One interesting communication protocol which can simultaneously obtain high information efficiency without sacrificing spectral efficiency, however, is spatial pulse-position- modulation (spatial-PPM), in which information is encoded into the spatial modes of light and sent through free space between transmitter and receiver. This thesis aims to lay the groundwork for an experimental design to achieve efficient spatial-PPM free-space optical communication using 1550 nm light at the single photon level. We focus on presenting and evaluating a transmitter-receiver design by giving a precise characterization of its operation, properties, and limitations.
by Edwin Ng.
S.B.

The advances in nanoscience and nanotechnology in recent decades have renewed the interests in the optical properties of metals. Today, the field known as Plasmonics studies the control and manipulation of the electromagnetic near-fields of metallic nanostructures in order to realize novel subwavelength optical applications. In particular, this thesis explores the phenomenon of plasmon resonance for molecular sensing. Surface plasmon resonance (SPR) on flat metal surfaces is used for index-of-refraction sensing and localized surface plasmon resonance (LSPR) on metal nanospheres can produce surface-enhanced Raman scattering (SERS). The operation principles and the experimental evaluation of two SPR sensing devices are presented. An integrated sensor and a 2D wavelength-angle modulated version were estimated to have an angular sensitivity of 126°/RIU and 91°/RIU, respectively. Furthermore, through an implementation of a full vector multiple-multipole light scattering method, useful for the calculations of the field focusing efficiency between assemblies of metal nanospheres, we showed that optical frequency electric fields can be enhanced in gold nanoparticle assemblies by an order of 450 in nanometer volumes. Keywords: surface plasmons, plasmonics, optical biosensors, surface-enhanced Raman scattering, optics of metals, nanophotonics, nanomaterials, classical electrodynamics
L'avancée des nanosciences et de la nanotechnologie au cours des dernières décennies a suscité un renouvellement de l'intérêt pour les propriétés optiques des métaux. Aujourd'hui, la Plasmonique cherche à contrôler les champs proches électromagnétiques des nanostructures métalliques afin de bénéficier des nouvelles applications reposant sur l'optique de sous-longueur d'onde. En particulier, ce mémoire explore l'utilisation de la résonance à plasmons pour la capture des molécules. L'étude se divise en la résonance à plasmons de surface (SPR) pour des surfaces métalliques planes et pour des nanosphères métalliques. Ces deux méthodes permettent de créer des capteurs sensibles aux variations d'indice de réfraction et d'autres qui reposent sur des effets non-linéaires tels que la diffusion Raman exaltée de surface (SERS). Suite à l'introduction des bases, l'opération ainsi que des résultats expérimentaux de deux capteurs à plasmons de surface sont présentés. Un capteur intégré et une version 2D avec modulation de longueur d'onde et de l'angle possèdent une sensibilité angulaire d'environ 126°/RIU et 91°/RIU, respectivement. Par la suite, la réalisation de la méthode du multiple-multipole, utile pour évaluer l'efficacité de la concentration des champs entre des nanosphères métalliques, est discutée. Une amélioration de la concentration de champ optique de l'ordre de 450 par des nanospheres d'or est présentée. Mots-clés: plasmon de surface, plasmonique, biocapteurs optiques, diffusion Raman exaltée de surface, optique des métaux, nanophotonique, nanomatériel, électro-dynamique classique

The ability of optical systems to obtain images of desired objects is sometimes limited by the presence of background radiation. The background radiation can arise from scattering, self-radiation, or out-of-focus images, all originating from regions axially displaced from the object plane of interest. Techniques such as confocal microscopy, computer image reconstruction, various holographic techniques, and timegating tomography are all being developed in order to address the problem. Some of the prior techniques have been successfully applied in various fields where the imaging problem is encountered. All of the prior techniques have some advantages and some disadvantages. Recently, a new technique of background compensation has been proposed that utilizes controlled phase shifts in the pupil plane of the imaging instrument to distinguish in-focus radiation from background radiation. The new technique can potentially offer several advantages over the prior techniques, and may be applicable in situations for which no other technique is suitable. The present work describes the technique and reviews some relevant theoretical aspects and theoretical predictions for the technique. In addition, an experiment to test the basic concepts of the technique is described. The experiment consists of several discrete phases, and the results of the experiment are compared to the theoretical predictions. The results of each phase of the present experiment support the theoretical expectations for the technique, and it is concluded that the technique should be further investigated. The technique appears to represent a novel and potentially far-reaching alternative method by which the problem of imaging in the presence of undesired background radiation can be successfully addressed.

LIMA, L. P. P. Olimpíadas de Física e o Ensino de Física Experimental. 2017. 248 f. Dissertação (Mestrado Nacional Profissional em Ensino de Física) - Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2017.
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The Scientific Olympiad is a tool used in many countries of the world to optimize teaching / learning processes and to encourage high school students, or equivalent, to pursue technological careers. In Brazil, the Brazilian Physics Olympiad (OBF) is an important program maintained by the Brazilian Society of Physics that aims to contribute to the development of Physics teaching. One of the main objectives of the OBF is to prepare students to compete in International Physics Olympiads. These competitions are important because they provide a benchmark for assessing the world- wide physics teaching we are practicing. However, there is a lack in the available literature of works that do this evaluation at world level. Thus, in this work, first, an analysis was made of the success of the OBF in the preparation of students through the results obtained in the International Physics Olympiad (IPhO). Positive and negative points were investigated, aiming to construct an educational product that contributes to the improvement of the program. We analyzed the performance of Brazil in the editions in which it participated and verified whether there was evolution in the overall performance. Then, we analyze the performance separately in the Theoretical and Experimental tests, comparing with the overall performance. We also analyzed the results in a school's OBF 2016 and compared it with the overall results of all participants. The analysis indicated that the contribution should be made in the teaching of Experimental Physics. Finally, as an final product of this work, an experimental physics booklet was developed for teachers and high school students. The handout addresses the concepts of experimental physics in a language appropriate to high school students and teachers.
Dissertação de Mestrado apresentada ao Programa de Pós-Graduação em Ensino de Física da Pró-Reitoria de Pesquisa e Pós-Graduação da Universidade Federal do Ceará no Curso de Mestrado Profissional de Ensino de Física (MNPEF), como parte dos requisitos necessários à obtenção do título de Mestre em Ensino de Física. As Olimpíadas Científicas são uma ferramenta utilizada, em vários países do mundo, na otimização dos processos de ensino/aprendizagem e no incentivo para que alunos do ensino médio, ou equivalente, sigam carreiras tecnológicas. No Brasil, a Olimpíada Brasileira de Física (OBF) é um importante programa mantido pela Sociedade Brasileira de Física que visa contribuir para o desenvolvimento do ensino de Física. Um dos principais objetivos da OBF é preparar os alunos para competirem em Olimpíadas Internacionais de Física. Essas competições são importantes porque fornecem um parâmetro para avaliarmos em nível mundial o ensino de Física que estamos praticando. No entanto, há uma carência na literatura disponível de trabalhos que façam esta avaliação em nível mundial. Assim, neste trabalho, primeiramente, foi feita uma análise do sucesso da OBF na preparação dos alunos através dos resultados obtidos nas Olimpíadas Internacionais de Física (International Physics Olympiad – IPhO). Foram investigados pontos positivos e negativos, com objetivo de construir um produto educacional que contribua para o aprimoramento do programa. Analisamos por dois diferentes critérios o desempenho do Brasil nas edições em que ele participou e verificamos se houve evolução no desempenho geral. Então, analisamos o desempenho separadamente nas provas Teórica e Experimental, comparando com o desempenho global. Também, analisamos os resultados na OBF 2016 de uma escola e comparamos com os resultados globais de todos os participantes. A análise indicou que a contribuição deveria ser feita no ensino de Física Experimental. Por fim, foi desenvolvido, como produto final deste trabalho, uma apostila de Física Experimental destinada aos professores e alunos do ensino médio. A apostila aborda os conceitos de Física experimental em uma linguagem adequada aos alunos e professores do ensino médio.

Laser-driven particle acceleration is an area of increasing research interest given the recent development of short pulse high intensity lasers. A significant difficulty in this field is given by the exceptionally large instantaneous dose rates which such particle beams can produce. This represents a challenge for standard dosimetry techniques and more sophisticated procedures need to be explored. In this thesis I present novel detection and characterisation methods using a combination of GafChromic films, TLD chips, nuclear activation and Monte Carlo simulations, applicable to laser-driven beams. Part of the work is focused on the detection of laserdriven protons used to irradiate V79 cells in order to determine the feasibility of laser-driven proton therapy. A dosimetry method involving GafChromic films and numerical simulations has been appositely developed and used to obtain cell survival results, which are in agreement with those obtained by conventionally accelerated proton beams. Another part is dedicated to the detection and characterisation of laser-driven electron and X-ray beams. An innovative simulation method to obtain the temperature of the electrons accelerated by the laser, and predict the subsequently generated X-ray beam, has been developed and compared with the acquired experimental data.

The thesis is focused on the investigation of structural properties of AuPd nanoparticles via theoretical and experimental studies. For the first system, the 98-atom AuPd nanoclusters, a theoretical analysis has been employed to study the energetics and segregation effects and to assess how typical is the Leary Tetrahedron (LT). Although this motif is the most stable at the empirical level, it loses stability at the DFT level against FCC or Marks Decahedron. The second system is the Au24Pd1 nanoclusters. Theoretically, by performing a search at the DFT level using Basin Hopping Monte Carlo, we identified pyramidal cage structures as putative global minima, where Pd sits in the core and Au occupies surface positions. The Löwdin analysis emphasized charge transfer between Pd and Au, explaining the enhanced catalytic activity with respect to Au25 clusters. Experimentally, STEM has been employed for the structural characterization of Au24Pd1 clusters supported on Multiwall Carbon Nanotubes. Whenever possible, we have tried to link the experimental analysis to the theoretical findings. The third system has been the evaporated AuPd nanoparticles. We observed that the annealing process led to the formation of L12 ordered phases as well as layered and core-shell structures. This study aimed to bring an insight on the segregation and energetics effects of AuPd nanoparticles with potential applications in nanocatalysis.

Measurements of Higgs boson production and decay rates are presented using the proton-proton collision data collected by the ATLAS experiment during LHC Run I, corresponding to 4.5 fb\(^-\)\(^1\) at 7 TeV and 20.3 fb\(^-\)\(^1\) at 8 TeV. Under certain assumptions, the coupling strengths of the Higgs boson to Standard Model particles are also probed. The H -> ZZ\(^(\)\(^*\)\(^)\)\(_-\)\(_>\) 4I final state, where I = e, mu, is discussed, and is observed with a significance corresponding to 8.1 standard deviations. The Higgs boson production rate, relative to the Standard Model prediction, is measured to be mu = 1.44\(^+\)\(^0\)\(^.\)\(^4\)\(^0\)\(_-\)\(_0\)\(_.\)\(_3\)\(_3\) at the ATLAS best-fit value for the measurement of the Higgs boson mass, m\(_H\) = 125.36 GeV. The various Higgs boson production and decay modes studied by the ATLAS experiment are also combined. The couplings of the Higgs boson are probed in a number of benchmark models, where a good agreement with the Standard Model prediction is observed for each model considered. The Higgs boson coupling measurements are also used to place constraints on a number of beyond the Standard Model theories, and are combined with direct searches for invisible Higgs boson decays to place a limit on the Higgs boson branching ratio to invisible final states.