Wave radiation is an important process in many geophysical flows. In particular, it is by wave radiation that flows may adjust to a state for which the dynamics is slow. Such a state is described as “balanced”, meaning there is an approximate balance between the Coriolis force and horizontal pressure gradients, and between buoyancy and vertical pressure gradients. In this thesis, wave radiation processes relevant to these enormously complex flows are studied through the use of some highly simplified models, and a parallel aim is to develop accurate numerical techniques for doing so. This thesis is divided into three main parts. 1. We consider accurate numerical boundary conditions for various equations which support wave radiation to infinity. Particular attention is given to discretely non-reflecting boundary conditions, which are derived directly from a discretised scheme. Such a boundary condition is studied in the case of the 1-d Klein-Gordon equation. The limitations concerning the practical implementation of this scheme are explored and some possible improvements are suggested. A stability analysis is developed which yields a simple stability criterion that is useful when tuning the boundary condition. The practical use of higher-order boundary conditions for the 2-d shallow water equations is also explored; the accuracy of such a method is assessed when combined with a particular interior scheme, and an analysis based on matrix pseudospectra reveals something of the stability of such a method. 2. Large-scale atmospheric and oceanic flows are examples of systems with a wide timescale separation, determined by a small parameter. In addition they both undergo constant random forcing. The five component Lorenz-Krishnamurthy system is a system with a timescale separation controlled by a small parameter, and we employ it as a model of the forced ocean by further adding a random forcing of the slow variables, and introduce wave radiation to infinity by the addition of a dispersive PDE. The dynamics are reduced by deriving balance relations, and numerical experiments are used to assess the effects of energy radiation by fast waves. 3. We study quasimodes, which demonstrate the existence of associated Landau poles of a system. In this thesis, we consider a simple model of wave radiation that exhibits quasimodes, that allows us to derive some explicit analytical results, as opposed to physically realistic geophysical fluid systems for which such results are often unavailable, necessitating recourse to numerical techniques. The growth rates obtained for this system, which is an extension of one considered by Lamb, are confirmed using numerical experiments.

Made available in DSpace on 2014-06-11T19:32:43Z (GMT). No. of bitstreams: 0 Previous issue date: 2002-11Bitstream added on 2014-06-13T20:04:09Z : No. of bitstreams: 1 lunardi_ma_dr_botfca.pdf: 2616577 bytes, checksum: 3ce9de8aa359098429c03603153b828c (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Este experimento foi conduzido, dentro e fora de ambiente protegido, durante o período de 21/04 a 03/11/2000, na área experimental do Departamento de Recursos Naturais da Faculdade de Ciências Agronômicas, UNESP, Campus de Botucatu, São Paulo (latitude 22° 51’ S, longitude 48° 26’ W e altitude de 786 m). O objetivo foi avaliar o efeito do Polietileno de Baixa Densidade com 150 mm de espessura, difusor de luz (PEBD150d), no saldo de energia de ondas longas, assim como no desenvolvimento do pimentão vermelho (Capsicum annuum L.) híbrido Elisa e indicadores de produção da cultura. Os modelos de estimativa do saldo de ondas longas foram obtidos por meio de regressão linear entre os valores medidos deste parâmetro climático, pressão de vapor e temperatura do ar e solo. Os resultados mostraram que em condições de ambiente protegido houve aumento de produção da cultura, em relação ao ocorrido no campo, e significante diferença na transmissividade da energia líquida pela cobertura. Houve redução do fluxo de calor no solo, velocidade do vento, número de horas de insolação, consumo de água, radiação direta e refletida. Contrariamente, a radiação solar difusa teve aumento de 158 %, confirmando o alto efeito difusor do PEBD150d. Os testes dos modelos de estimativa obtidos mostraram alto coeficiente de determinação (r2 > 0,90), tanto para o ambiente protegido como no campo. / This experiment was carried out under field and protected environment conditions in the experimental area of the Natural Resources Department of the Faculty of Agricultural Sciences – UNESP, Campus of Botucatu, São Paulo State, Brazil, from April 21st to November 3rd, 2000. The objective was to assess the effect of the light diffuser polyethylene with 150 μm thickness (PEBD150d), on the long wave radiation estimate, as well as on growth and yield index of the hybrid Elisa of red pepper (Capsicum annuum L.). The long wave radiation models was obtained by linear regression of measured values of this climatic parameter and water vapor pressure, air and soil temperature. The results showed that the protected environmental condition provided gains of yield in relation to field and significant difference in the long wave transmission though the coverage. There was reduction of the heat flux from soil, wind speed, number of hours of sunshine, water consumption, reflected and direct radiation. The diffuse solar radiation had an increment of 158 %, confirming the higher diffuse effect of PEBD150d. The tests of the estimating models obtained for long wave presented high determination coefficient for both environmental conditions (r2 > 0.90).

Orientador: João Francisco Escobedo / Este experimento foi conduzido, dentro e fora de ambiente protegido, durante o período de 21/04 a 03/11/2000, na área experimental do Departamento de Recursos Naturais da Faculdade de Ciências Agronômicas, UNESP, Campus de Botucatu, São Paulo (latitude 22° 51' S, longitude 48° 26' W e altitude de 786 m). O objetivo foi avaliar o efeito do Polietileno de Baixa Densidade com 150 mm de espessura, difusor de luz (PEBD150d), no saldo de energia de ondas longas, assim como no desenvolvimento do pimentão vermelho (Capsicum annuum L.) híbrido Elisa e indicadores de produção da cultura. Os modelos de estimativa do saldo de ondas longas foram obtidos por meio de regressão linear entre os valores medidos deste parâmetro climático, pressão de vapor e temperatura do ar e solo. Os resultados mostraram que em condições de ambiente protegido houve aumento de produção da cultura, em relação ao ocorrido no campo, e significante diferença na transmissividade da energia líquida pela cobertura. Houve redução do fluxo de calor no solo, velocidade do vento, número de horas de insolação, consumo de água, radiação direta e refletida. Contrariamente, a radiação solar difusa teve aumento de 158 %, confirmando o alto efeito difusor do PEBD150d. Os testes dos modelos de estimativa obtidos mostraram alto coeficiente de determinação (r2 > 0,90), tanto para o ambiente protegido como no campo. / Resumo: This experiment was carried out under field and protected environment conditions in the experimental area of the Natural Resources Department of the Faculty of Agricultural Sciences - UNESP, Campus of Botucatu, São Paulo State, Brazil, from April 21st to November 3rd, 2000. The objective was to assess the effect of the light diffuser polyethylene with 150 μm thickness (PEBD150d), on the long wave radiation estimate, as well as on growth and yield index of the hybrid Elisa of red pepper (Capsicum annuum L.). The long wave radiation models was obtained by linear regression of measured values of this climatic parameter and water vapor pressure, air and soil temperature. The results showed that the protected environmental condition provided gains of yield in relation to field and significant difference in the long wave transmission though the coverage. There was reduction of the heat flux from soil, wind speed, number of hours of sunshine, water consumption, reflected and direct radiation. The diffuse solar radiation had an increment of 158 %, confirming the higher diffuse effect of PEBD150d. The tests of the estimating models obtained for long wave presented high determination coefficient for both environmental conditions (r2 > 0.90). / Doutor

No description available.

No description available.

Two of the principal phenomena observed and exploited in the field of spintronics are giant magnetoresistance (GMR) and spin transfer torque (STT). With GMR, the resistance of a magnetic multilayer is affected by the relative orientation of its magnetic layers due to (electron) spin dependent scattering. For the STT effect, a spin-polarized electric current is used to alter the magnetic state of a ferromagnet. Together, GMR and STT are at the foundation of numerous technologies, and they hold promise for many more applications. To achieve the high current densities (~10¹² A/m²) that are necessary to observe STT effects, point contacts – constricted electrical pathways (~1–100 nm in diameter) between conducting materials – are often used because of their small cross-sectional areas. In this sense, we have explored STT in bilayer magnetic nanopillars, where an electric current was used to induce precession of a ferromagnetic layer. This precessional state was detected as an increase in resistance of the device, akin to GMR. Temperature dependent measurements of the onset of precession shed light on the activation mechanism, but raised further questions about its detailed theory. Point contacts can also be used as local sources or detectors of electrons. In this context, we have observed transverse electron focusing (TEF) in a single crystal of bismuth. TEF is a k-selective technique for studying electron scattering from within materials. Using lithographically fabricated point contacts, we have studied the temperature dependence of the relaxation time for ballistic electrons from 4.2 to 100 K. These measurements indicated a transition between electron-electron dominated scattering at low temperatures and electron-phonon scattering as the Debye temperature was approached. We present preliminary work toward a TEF experiment to measure spin dependent scattering from a non-magnet/magnet interface. We also investigated spin wave propagation in thin, magnetic waveguide structures. At the boundary between the waveguide and continuous magnetic film, spin wave rays were found to radiate into the film, or to reflect and form standing waves in the waveguide. A circular defect in the waveguide was observed to cause diffraction of spin waves, generating an interference pattern of higher modes of oscillation. / text

Submitted by Emanuel Varela Cardoso (emanuel.varela@ufcg.edu.br) on 2018-08-15T16:36:49Z No. of bitstreams: 1 ANTONIO MARCOS DELFINO DE ANDRADE – TESE (PPGMet) 2017.pdf: 3321439 bytes, checksum: 641b9755396203a4dd27ac62503ca9e8 (MD5) / Made available in DSpace on 2018-08-15T16:36:49Z (GMT). No. of bitstreams: 1 ANTONIO MARCOS DELFINO DE ANDRADE – TESE (PPGMet) 2017.pdf: 3321439 bytes, checksum: 641b9755396203a4dd27ac62503ca9e8 (MD5) Previous issue date: 2016-02-19 / Capes / A radiação de onda longa incidente (L↓) é seguramente a componente do balanço de radiação mais difícil de ser medida. Portanto, diferentes formulações têm sido propostas para estimá-la. Desta maneira, avaliou-se neste estudo o desempenho de várias formulações para a estimativa dos fluxos de L↓ e sua a interação com outras variáveis medidas, bem como as interações da temperatura do ar e da pressão de vapor d’água junto à L↓. Neste estudo foi utilizada a análise pela transformada em ondeletas (TO) como ferramenta matemática para a análise de variações locais de energia dentro das séries temporais aqui estudadas, pela sua decomposição no tempo-frequência-espaço. Para investigar a correlação entre duas séries (L↓ com a temperatura do ar e da L↓ medida com as estimadas por cada modelo), empregou-se transformada cruzada em ondeletas e a coerência e fase em ondeletas. Os dados deste estudo compreendem o período de 01 de janeiro a 31 de dezembro de 2009, e são provenientes da torre micrometeorológica (K34) pertencente ao Experimento de Grande Escala da Biosfera Atmosfera na Amazônia (LBA) em Manaus, Amazonas. A TO revelou que no período de 36 horas, para todo período analisado, um persistente, homogêneo e forte espectro energético entre a L↓ e a temperatura do ar, onde se constatou uma sinergia entre essas variáveis. Constatou -se ainda que a precipitação e a pressão de vapor d’água exercem bastante influencia nos fluxos de L↓, principalmente na estação chuvosa. A análise através da transformada cruzada e de coerência e fase em ondeletas no período de 32 a 64 horas. Já nos modelos ajustados foram no período de 16 a 64 horas. Os modelos propostos para condições de céu claro, com o uso de seus coeficientes originais, mostraram tendência em subestimar os fluxos de L↓ medidos. Com os ajustes nos coeficientes, os modelos expuseram uma melhora nas estimativas nos fluxos de L↓.Para os modelos propostos para condições de céu nublado, estes exibiram um desempenho regular. / The downward longwave radiation (L↓) component really is difficult of the net radiation the measured. Therefore, different parameterizations have been proposed to estimate it. Thus, in this study we evaluated the performance of various parameterizations for the L↓ flows estimated and their interaction with other variables measured as well as the air temperature and water vapour pressure interactions with L↓. In this study we used by wavelet transform (WT) analysis as mathematical tool for energy of local variations analysis in the studied time series here by their frequency time-space decomposition. To investigate the correlation between two series (L↓ with air temperature and between L↓ measured with estimated), we used crosswavelet transform and coherency wavelets and phase angle. The datasets used in this study are of the January 01 to December 31 of 2009, measured from micrometeorological tower (named K34) controlled by Large Scale Biosphere Atmosphere experiment in Amazonia (LBA) from Manaus city, Amazonas. The WT showed that in 36 hours period, for the entire period analyzed, a persistent, smooth and strong energy spectrum between L↓ and the air temperature, which demonstrated a synergy between these variables. It was also found that precipitation and water vapour pressure exert enough on L↓ flows influence, especially in the wet season. The crosswavelet transform and coherency wavelets and phase angle analysis at 32 to 64 hours period. Already in adjusted models were in the 16-64 hours period. With the adjustable coefficients, according to the environmental study area conditions, the models presents an improvement in the L↓ flows estimates. The cloudy skies models proposed, they exhibited a regular performance.

Submitted by Marco Antonio Oliveira da Silva (maosilva@ipen.br) on 2017-11-09T11:36:10Z No. of bitstreams: 0 / Made available in DSpace on 2017-11-09T11:36:10Z (GMT). No. of bitstreams: 0 / Revestimentos superficiais são aplicados à muitas ferramentas de usinagem na indústria metalúrgica com o intuito de melhorar a eficiência de corte e aumentar sua vida útil. Neste trabalho foram realizados testes para remoção do recobrimento de nitreto de titânio alumínio (TiAlN) em pastilhas de carboneto de tungstênio (WC-Co), utilizando um feixe laser de pulsos ultracurtos. Após a determinação dos limiares de dano do filme e do substrato foram ablacionados na superfície do recobrimento, traços utilizando duas condições de ablação. Inicialmente operou-se no regime de baixa fluência do filme, e posteriormente no regime de baixa fluência do substrato, muito abaixo do limiar do filme, aplicando-se alta sobreposição de pulsos. Um sistema de espectroscopia de emissão atômica induzida por laser (LIBS) foi montado para monitoramento dos materiais presentes no plasma gerado pelo laser, porém o sistema não apresentou sensibilidade suficiente para leitura da baixa intensidade do plasma proveniente do processo e não foi utilizado. Após a análise dos traços por microscopia eletrônica, perfilometria óptica e espectroscopia por fluorescência de Raios-X, não foi possível determinar um processo seguro para realizar a remoção seletiva do filme em questão, porém, devido aos dados obtidos e observações dos resultados em alguns traços, novas possibilidades foram levantadas, abrindo a discussão para a realização de trabalhos futuros. / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

The east-west oriented cloud bands in the tropics are called the Inter-tropical Con-vergence Zones (ITCZ). Till recently, the ITCZ has been assumed to have a simple vertical structure with convergence near the surface boundary layer and divergence near the tropopause. Recent work has shown that the ITCZ can have a complex ver-tical structure with multi-level ows. This complex structure has a profound impact on the mass, momentum and energy budget in the ITCZ. This thesis addresses the factors that govern the shallow meridional circulation that occurs in the ITCZ and the mechanisms that govern the abrupt poleward transition and the gradual poleward migration . The shallow meridional circulation forms when the boundary layer ow that con-verges in the ITCZ, rises above the boundary layer and diverges in the lower tropo-sphere. The ow above the boundary layer is in the direction opposite to the direction of the ow within the boundary layer. Some authors have argued that this is caused by the reversal of pressure gradients just above the boundary layer in response to strong sea surface temperature gradients. This hypothesis neglects the eect of plan-etary rotation on the ow and was found to be insucient to explain the formation of shallow meridional circulation. In the east Pacic ocean, the shallow circulation forms only to the south of the ITCZ when the ITCZ forms away from the equator, while it is absent when the ITCZ forms close to the equator. The aqua-planet simulations of the equatorial and the o-equatorial ITCZ were conducted using Community Atmosphere Model (CAM 3.0). The model used the Eulerian dynamical core with T42 horizontal resolution and 26 levels in vertical. Each simulation was run for 3 years and analysis of last six months was presented. The simulations reproduced the contrast in the vertical structure of the equatorial and o-equatorial ITCZ. The shallow circulation was simulated with-out the reversal of pressure gradients and the SST gradients were weakest when the shallow circulation was simulated. We have proposed a new mechanism for the exis-tence of shallow meridional circulation in the ITCZ. We have argued that, in Earth's atmosphere, the mean horizontal ow generally occurs in the direction perpendicular to the direction of applied pressure gradient due to the action of Coriolis force. If the local rotational eects of the ow (relative vorticity) cancels the action of the Coriolis force, then a ow along the pressure gradient is possible. We demonstrated that this condition was satised only to the south of the ITCZ when it forms away from the equator. The ITCZ is characterized by the maximum mass convergence in the boundary layer. The mass convergence is mainly caused by the deceleration of poleward ow in the boundary layer. When the ITCZ forms close to the equator, the ow in the boundary layer is a resultant of vector addition of three forces, a pressure gradient force in the north-south direction (i.e., the ow towards low pressure), a Coriolis force which acts in the east-west direction( perpendicular to the direction of the ow), and surface friction which opposes the resultant ow. When the ITCZ forms away from the equator a three way balance does not capture the dynamics of ow. As the poleward ow is accelerated towards low pressure, it has to advect a considerable amount of zonal momentum with it which acts to retard the poleward ow. This eect of advection of zonal momentum has to be included in the force balance to obtain an accurate estimate of the ow and associated convergence. The ITCZ acts like a heat engine. The energy is gained near the surface, some energy is transported towards pole while some is utilized in driving the meridional circulation. The rest is rejected near the tropopause. The transport within the troposphere occurs through the vertical or horizontal advection of the energy due to vertical and horizontal motions respectively. Our analysis of the ITCZ suggests that; a large amount of transport occurs through horizontal motions that was neglected in the previous studies. The detailed analysis suggests that the latent energy in the form of mass of water vapor is exported out of the ITCZ at dierent levels in association with the multilevel ows. The equatorial and the o-equatorial ITCZ are dierent because, evaporation is larger in the o-equatorial ITCZ when compared to the equatorial ITCZ. The ITCZ shows a strong sub-seasonal variability in its location in the Indian Ocean and the west Pacic Ocean during boreal summer. There are two favorable locations, one near the equator and another away from the equator, for formation of the ITCZ. The equatorial ITCZ either propagates abruptly or gradually to the o-equatorial location. A detailed analysis of moisture and momentum budget of the simulated abrupt and gradual propagations enabled us to separate the role of thermo-dynamic and dynamic processes. We found that, if the equatorial ITCZ would propa-gate abruptly or gradually to the o-equatorial location is decided by the availability of the water vapor in the boundary layer between the two locations of the ITCZ, i.e., by the thermodynamic processes. But, such a transition to the o-equatorial location is allowed only when the constraints imposed by the re-adjustment in the circulation are satised. In simple terms, these constraints emerge due to two processes. 1. The Earth (lower boundary of the atmosphere) spins at maximum eective radius near the equator. As a result, the atmosphere gains maximum angular momentum near the equator (`zonal momentum' in Cartesian co-ordinates) . The ITCZ is one of the primary avenues to transport the zonal momentum from the lower troposphere to the upper troposphere. When the favorable location of ITCZ is near the equator, the location of ITCZ and the location where atmosphere gains maximum zonal momentum are coincident. The ITCZ and associated meridional circulation transports the zonal momentum upwards which is then transported polewards. As the favorable location of ITCZ moves away from the equator, the two locations are die rent. As a result, the atmospheric ow has to re-adjust so that the zonal momentum is transported from the equator to the favorable location of the ITCZ which then transports it upwards and polewards. In summary, this thesis proposes a new mechanism for the generation of shallow meridional circulation, the abrupt transition and the gradual propagations of the ITCZ.

Submitted by Marco Antonio Oliveira da Silva (maosilva@ipen.br) on 2016-12-21T11:51:34Z No. of bitstreams: 0 / Made available in DSpace on 2016-12-21T11:51:34Z (GMT). No. of bitstreams: 0 / Os radionuclídeos naturais das séries radioativas do 238U e do 232Th têm sido aplicados com sucesso como traçadores de processos ambientais atuais e mudanças climáticas. O 210Pb (meia-vida de 22,2 anos) é empregado na técnica de datação geocronológica de testemunhos sedimentares dos últimos 100-150 anos e na determinação de taxa de sedimentação. As concentrações dos isótopos 226Ra e 228Ra (meia-vida de 1.600 anos e 5,75 anos, respectivamente) auxiliam no cálculo das atividades de 210Pb em excesso no sedimento e auxiliam na identificação de processos marinhos importantes, como, por exemplo, a intrusão de água subterrânea. Neste trabalho foram quantificadas as concentrações de atividade de 226Ra, 228Ra e 210Pb em quatro testemunhos marinhos curtos coletados desde a plataforma continental até o talude superior do Atlântico Sudoeste. A partir dos resultados obtidos, as taxas de sedimentação em cada local e as idades de cada fatia de sedimento foram determinadas pelo método de datação geocronológica com 210Pb. As amostras sedimentares sofreram digestão total ácida em microondas. A separação radioquímica sequencial de 226Ra, 228Ra e 210Pb foi realizada com a obtenção dos precipitados de Ba(Ra)SO4 e PbCrO4. As medidas α total do 226Ra e β total do 228Ra e do 210Pb a partir dos precipitados foram feitas em um detector proporcional de fluxo gasoso de baixa radiação de fundo. Com relação aos testemunhos analisados, as concentrações de atividade dos radionuclídeos variaram de 14 Bq.kg-1 a 154 Bq.kg-1 para o 226Ra; de 17 Bq.kg-1 a 45 Bq.kg-1 para o 228Ra; de 20 Bq.kg-1 a 2.073 Bq.kg-1 para o 210Pb. Valores altos de 210Pb foram encontrados no topo de todos os perfis sedimentares, proveniente principalmente da deposição atmosférica. Os dados coletados neste trabalho estão na mesma faixa de grandeza de outros relacionados a medições de 226Ra, 228Ra, 210Pb em áreas não contaminadas do Oceano Atlântico Sudoeste. As taxas de sedimentação diminuíram com o aumento da profundidade de coluna dágua, cujos valores variaram de 0,049 cm.ano-1 a 0,40 cm.ano-1. / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP