970 resultados para Retaining walls


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[ES] Se han documentado unos 180 metros de muralla que corresponde a los alzados este y norte. También se incluye el interior de dos puertas de acceso, el muro exterior del cementerio y parte de los muros de la iglesia.

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Alternative scaffolds are non-antibody proteins that can be engineered to bind new targets. They have found useful niches in the therapeutic space due to their smaller size and the ease with which they can be engineered to be bispecific. We sought a new scaffold that could be used for therapeutic ends and chose the C2 discoidin domain of factor VIII, which is well studied and of human origin. Using yeast surface display, we engineered the C2 domain to bind to αvβ3 integrin with a 16 nM affinity while retaining its thermal stability and monomeric nature. We obtained a crystal structure of the engineered domain at 2.1 Å resolution. We have christened this discoidin domain alternative scaffold the “discobody.”

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The purpose of this work is to extend experimental and theoretical understanding of horizontal Bloch line (HBL) motion in magnetic bubble materials. The present theory of HBL motion is reviewed, and then extended to include transient effects in which the internal domain wall structure changes with time. This is accomplished by numerically solving the equations of motion for the internal azimuthal angle ɸ and the wall position q as functions of z, the coordinate perpendicular to the thin-film material, and time. The effects of HBL's on domain wall motion are investigated by comparing results from wall oscillation experiments with those from the theory. In these experiments, a bias field pulse is used to make a step change in equilibrium position of either bubble or stripe domain walls, and the wall response is measured by using transient photography. During the initial response, the dynamic wall structure closely resembles the initial static structure. The wall accelerates to a relatively high velocity (≈20 m/sec), resulting in a short (≈22 nsec ) section of initial rapid motion. An HBL gradually forms near one of the film surfaces as a result of local dynamic properties, and moves along the wall surface toward the film center. The presence of this structure produces low-frequency, triangular-shaped oscillations in which the experimental wall velocity is nearly constant, vs≈ 5-8 m/sec. If the HBL reaches the opposite surface, i.e., if the average internal angle reaches an integer multiple of π, the momentum stored in the HBL is lost, and the wall chirality is reversed. This results in abrupt transitions to overdamped motion and changes in wall chirality, which are observed as a function of bias pulse amplitude. The pulse amplitude at which the nth punch- through occurs just as the wall reaches equilibrium is given within 0.2 0e by Hn = (2vsH'/γ)1/2 • (nπ)1/2 + Hsv), where H' is the effective field gradient from the surrounding domains, and Hsv is a small (less than 0.03 0e), effective drag field. Observations of wall oscillation in the presence of in-plane fields parallel to the wall show that HBL formation is suppressed by fields greater than about 40 0e (≈2πMs), resulting in the high-frequency, sinusoidal oscillations associated with a simple internal wall structure.

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Part I of this thesis deals with 3 topics concerning the luminescence from bound multi-exciton complexes in Si. Part II presents a model for the decay of electron-hole droplets in pure and doped Ge.

Part I.

We present high resolution photoluminescence data for Si doped With Al, Ga, and In. We observe emission lines due to recombination of electron-hole pairs in bound excitons and satellite lines which have been interpreted in terms of complexes of several excitons bound to an impurity. The bound exciton luminescence in Si:Ga and Si:Al consists of three emission lines due to transitions from the ground state and two low lying excited states. In Si:Ga, we observe a second triplet of emission lines which precisely mirror the triplet due to the bound exciton. This second triplet is interpreted as due to decay of a two exciton complex into the bound exciton. The observation of the second complete triplet in Si:Ga conclusively demonstrates that more than one exciton will bind to an impurity. Similar results are found for Si:Al. The energy of the lines show that the second exciton is less tightly bound than the first in Si:Ga. Other lines are observed at lower energies. The assumption of ground state to ground-state transitions for the lower energy lines is shown to produce a complicated dependence of binding energy of the last exciton on the number of excitons in a complex. No line attributable to the decay of a two exciton complex is observed in Si:In.

We present measurements of the bound exciton lifetimes for the four common acceptors in Si and for the first two bound multi-exciton complexes in Si:Ga and Si:Al. These results are shown to be in agreement with a calculation by Osbourn and Smith of Auger transition rates for acceptor bound excitons in Si. Kinetics determine the relative populations of complexes of various sizes and work functions, at temperatures which do not allow them to thermalize with respect to one another. It is shown that kinetic limitations may make it impossible to form two-exciton complexes in Si:In from a gas of free excitons.

We present direct thermodynamic measurements of the work functions of bound multi-exciton complexes in Al, B, P and Li doped Si. We find that in general the work functions are smaller than previously believed. These data remove one obstacle to the bound multi-exciton complex picture which has been the need to explain the very large apparent work functions for the larger complexes obtained by assuming that some of the observed lines are ground-state to ground-state transitions. None of the measured work functions exceed that of the electron-hole liquid.

Part II.

A new model for the decay of electron-hole-droplets in Ge is presented. The model is based on the existence of a cloud of droplets within the crystal and incorporates exciton flow among the drops in the cloud and the diffusion of excitons away from the cloud. It is able to fit the experimental luminescence decays for pure Ge at different temperatures and pump powers while retaining physically reasonable parameters for the drops. It predicts the shrinkage of the cloud at higher temperatures which has been verified by spatially and temporally resolved infrared absorption experiments. The model also accounts for the nearly exponential decay of electron-hole-droplets in lightly doped Ge at higher temperatures.

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[ES]Comparativa de las alternativas disponibles para la construcción de un edificio, con el objetivo de optimizar el diseño disminuyendo las pérdidas de energía. De los distintos tipos de construcciones posibles, la investigación se centra en una vivienda unifamiliar. El trabajo aborda, por una parte, el diseño de la envolvente de la vivienda con las técnicas eficientes y los materiales mejor ajustados a la zona de edificación; y por otra, la selección del sistema de calefacción y de agua caliente sanitaria (ACS). Se opta por bloques de tierra comprimida, aislante de celulosa y enlucido de arcilla para las paredes, así como por una caldera de pellets para el sistema de calefacción y una instalación de energía solar térmica para el ACS.

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[ES] El conjunto de dos edificios divididos en varias estancias, un canal de captación de aguas y un puente, todo ello arruinado. Los muros aún se mantienen en pie aunque ya no quedan restos de los tejados ni del mobiliario, maquinaria o decoración.

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The two-pulse stimulated radiation of dense (10^9/cm^3 < ne ≤ 10^(11) /cm^3) nonuniform neon and argon afterglow plasma columns longitudinally immersed in a magnetic field is studied. The magnetic field is very homogeneous over the plasma volume (∆B/B~.01%). If the S-band microwave pulses' center frequency is such that they resonantly excite a narrow band of plasma upper hybrid oscillations close to the maximum upper hybrid frequency of the column, strong two pulse echoes are observed. This new echo process is called the upper hybrid echo. The echo spectrum, echo power and echo width were studied as a function of the pulse peak power P, pulse separation τ, relative density (ω_(po)/ω)^2, and relative cyclotron frequency (ω_c/ω). The complex but systematic variations of the echo properties as a function of the above-mentioned parameters arc found to be in qualitative agreement with those predicted by a theory of Gould and Blum based upon a simple nonuniform unidimensional cold plasma slab model. The possible effects of electron neutral and electron ion collisions not retained in the theoretical model are discussed.

The existence of a new type of cyclotron echo, different from that of Hill and Kaplan and not predicted by the Blum and Gould model is documented. It is believed to be also of a collective effect nature and can probably be described in terms of a theory retaining some hot plasma effects.

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[EU]Proiektu honen helburua etxebizitzetako barne hormen dimentsionamendu berritzailearen azterketa bat egitea da, orain arte erabilitako horma klasikoen ezaugarriak mantenduz, diseinu optimoagoa lortzeko asmoa izanda, material kantitatearen murrizketa bat bilatuz. Hau burutzeko diseinatua dagoen igeltsuzko horma bat hartuko da oinarri modura eta honen moldeaketa bat eginez, eta isolatzaile industrial biren arteko konparaketa bat aurrera eroanez, berregite optimo bat sortuko da, beharrezko suaren kontrako ezaugarri mekaniko eta termikoak betetzen dituena.

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Part I

Regression analyses are performed on in vivo hemodialysis data for the transfer of creatinine, urea, uric acid and inorganic phosphate to determine the effects of variations in certain parameters on the efficiency of dialysis with a Kiil dialyzer. In calculating the mass transfer rates across the membrane, the effects of cell-plasma mass transfer kinetics are considered. The concept of the effective permeability coefficient for the red cell membrane is introduced to account for these effects. A discussion of the consequences of neglecting cell-plasma kinetics, as has been done to date in the literature, is presented.

A physical model for the Kiil dialyzer is presented in order to calculate the available membrane area for mass transfer, the linear blood and dialysate velocities, and other variables. The equations used to determine the independent variables of the regression analyses are presented. The potential dependent variables in the analyses are discussed.

Regression analyses were carried out considering overall mass-transfer coefficients, dialysances, relative dialysances, and relative permeabilities for each substance as the dependent variables. The independent variables were linear blood velocity, linear dialysate velocity, the pressure difference across the membrane, the elapsed time of dialysis, the blood hematocrit, and the arterial plasma concentrations of each substance transferred. The resulting correlations are tabulated, presented graphically, and discussed. The implications of these correlations are discussed from the viewpoint of a research investigator and from the viewpoint of patient treatment.

Recommendations for further experimental work are presented.

Part II

The interfacial structure of concurrent air-water flow in a two-inch diameter horizontal tube in the wavy flow regime has been measured using resistance wave gages. The median water depth, r.m.s. wave height, wave frequency, extrema frequency, and wave velocity have been measured as functions of air and water flow rates. Reynolds numbers, Froude numbers, Weber numbers, and bulk velocities for each phase may be calculated from these measurements. No theory for wave formation and propagation available in the literature was sufficient to describe these results.

The water surface level distribution generally is not adequately represented as a stationary Gaussian process. Five types of deviation from the Gaussian process function were noted in this work. The presence of the tube walls and the relatively large interfacial shear stresses precludes the use of simple statistical analyses to describe the interfacial structure. A detailed study of the behavior of individual fluid elements near the interface may be necessary to describe adequately wavy two-phase flow in systems similar to the one used in this work.

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O afrouxamento dos parafusos protéticos é descrito na literatura como uma das complicações mais frequentes das próteses sobre implantes. Durante sua confecção, os profissionais sentem necessidade de remover várias vezes as próteses e/ou componentes protéticos, soltando e re-apertando os parafusos repetidamente. O principal objetivo deste trabalho foi avaliar a variação do torque de remoção de parafusos de fixação de pilares protéticos a implantes osteointegráveis após sucessivos ciclos de parafusamento e desparafusamento. Outro objetivo foi avaliar a influência do hexágono da base do pilar no torque de remoção dos parafusos. Para isso, foram utilizados 20 implantes de plataforma regular com hexágono externo e 20 pilares protéticos sextavados, que foram parafusados aos implantes com um parafuso de titânio, aplicando-se a este um torque de 32Ncm, por meio de um torquímetro digital. Os conjuntos implante/pilar/parafuso foram divididos em dois grupos: (1) pilares cujo hexágono da base foram removidos e (2) pilares convencionais, com hexágono na base. Cada conjunto recebeu uma restauração provisória e foi submetido a ciclagem mecânica por 15 minutos. Depois, os parafusos foram removidos, medindo-se o torque de remoção. Esta sequência foi repetida dez vezes e então o parafuso foi trocado por outro sem uso, e mais um ciclo foi realizado. Uma análise de regressão linear demonstrou nos dois grupos uma queda do torque de remoção do parafuso ao longo dos repetidos ciclos de inserção/remoção. A comparação entre os coeficientes da regressão nos dois grupos não revelou diferença entre eles. Também não houve diferença entre as médias das 5 últimas repetições e o 11 ciclo, com o parafuso novo. Concluiu-se que (1) repetidos parafusamentos e desparafusamentos promoveram a diminuição progressiva do torque de remoção dos parafusos, (2) a troca do parafuso por outro sem uso após dez ciclos de inserção/remoção não aumentou sua resistência ao afrouxamento, e (3) a remoção do hexágono da base do pilar protético não exerceu nenhum efeito sobre o torque de remoção do parafuso.

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It is the first time in China that the phase variations and phase shift of microwave cavity in a miniature Rb fountain frequency standard are studied, considering the effect of imperfect metallic walls. Wall losses in the microwave cavity lead to small traveling wave components that deliver power from the cavity feed to the walls of cavity. The small traveling wave components produce a microradian distribution of phase throughout the cavity ity, and therefore distributed cavity phase shifts need to be considered. The microwave cavity is a TE011 circular cylinder copper cavity, with round cut-hole of end plates (14mm in diameter) for access for the atomic flux and two small apertures in the center of the side wall for coupling in microwave power. After attenuation alpha is calculated, field variations in cavity are solved. The field variations of the cavity are given. At the same time, the influences of loaded quality factor QL and diameter/height (2a/d) of the microwave cavity on the phase variations and phase shift are considered. According to the phase variation and phase shift of microwave cavity we select the parameters of cavity, diameter 2a = 69.2mm, height d = 34.6mm, QL = 5000, which will result in an uncertainty delta(Delta f / f0 ) < 4.7 x 10(-17) and meets the requirement for the miniature Rb fountain frequency standard with accuracy 10(-15).

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Fluvial systems form landscapes and sedimentary deposits with a rich hierarchy of structures that extend from grain- to valley scale. Large-scale pattern formation in fluvial systems is commonly attributed to forcing by external factors, including climate change, tectonic uplift, and sea-level change. Yet over geologic timescales, rivers may also develop large-scale erosional and depositional patterns that do not bear on environmental history. This dissertation uses a combination of numerical modeling and topographic analysis to identify and quantify patterns in river valleys that form as a consequence of river meandering alone, under constant external forcing. Chapter 2 identifies a numerical artifact in existing, grid-based models that represent the co-evolution of river channel migration and bank strength over geologic timescales. A new, vector-based technique for bank-material tracking is shown to improve predictions for the evolution of meander belts, floodplains, sedimentary deposits formed by aggrading channels, and bedrock river valleys, particularly when spatial contrasts in bank strength are strong. Chapters 3 and 4 apply this numerical technique to establishing valley topography formed by a vertically incising, meandering river subject to constant external forcing—which should serve as the null hypothesis for valley evolution. In Chapter 3, this scenario is shown to explain a variety of common bedrock river valley types and smaller-scale features within them—including entrenched channels, long-wavelength, arcuate scars in valley walls, and bedrock-cored river terraces. Chapter 4 describes the age and geometric statistics of river terraces formed by meandering with constant external forcing, and compares them to terraces in natural river valleys. The frequency of intrinsic terrace formation by meandering is shown to reflect a characteristic relief-generation timescale, and terrace length is identified as a key criterion for distinguishing these terraces from terraces formed by externally forced pulses of vertical incision. In a separate study, Chapter 5 utilizes image and topographic data from the Mars Reconnaissance Orbiter to quantitatively identify spatial structures in the polar layered deposits of Mars, and identifies sequences of beds, consistently 1-2 meters thick, that have accumulated hundreds of kilometers apart in the north polar layered deposits.

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Semiconductor technology scaling has enabled drastic growth in the computational capacity of integrated circuits (ICs). This constant growth drives an increasing demand for high bandwidth communication between ICs. Electrical channel bandwidth has not been able to keep up with this demand, making I/O link design more challenging. Interconnects which employ optical channels have negligible frequency dependent loss and provide a potential solution to this I/O bandwidth problem. Apart from the type of channel, efficient high-speed communication also relies on generation and distribution of multi-phase, high-speed, and high-quality clock signals. In the multi-gigahertz frequency range, conventional clocking techniques have encountered several design challenges in terms of power consumption, skew and jitter. Injection-locking is a promising technique to address these design challenges for gigahertz clocking. However, its small locking range has been a major contributor in preventing its ubiquitous acceptance.

In the first part of this dissertation we describe a wideband injection locking scheme in an LC oscillator. Phase locked loop (PLL) and injection locking elements are combined symbiotically to achieve wide locking range while retaining the simplicity of the latter. This method does not require a phase frequency detector or a loop filter to achieve phase lock. A mathematical analysis of the system is presented and the expression for new locking range is derived. A locking range of 13.4 GHz–17.2 GHz (25%) and an average jitter tracking bandwidth of up to 400 MHz are measured in a high-Q LC oscillator. This architecture is used to generate quadrature phases from a single clock without any frequency division. It also provides high frequency jitter filtering while retaining the low frequency correlated jitter essential for forwarded clock receivers.

To improve the locking range of an injection locked ring oscillator; QLL (Quadrature locked loop) is introduced. The inherent dynamics of injection locked quadrature ring oscillator are used to improve its locking range from 5% (7-7.4GHz) to 90% (4-11GHz). The QLL is used to generate accurate clock phases for a four channel optical receiver using a forwarded clock at quarter-rate. The QLL drives an injection locked oscillator (ILO) at each channel without any repeaters for local quadrature clock generation. Each local ILO has deskew capability for phase alignment. The optical-receiver uses the inherent frequency to voltage conversion provided by the QLL to dynamically body bias its devices. A wide locking range of the QLL helps to achieve a reliable data-rate of 16-32Gb/s and adaptive body biasing aids in maintaining an ultra-low power consumption of 153pJ/bit.

From the optical receiver we move on to discussing a non-linear equalization technique for a vertical-cavity surface-emitting laser (VCSEL) based optical transmitter, to enable low-power, high-speed optical transmission. A non-linear time domain optical model of the VCSEL is built and evaluated for accuracy. The modelling shows that, while conventional FIR-based pre-emphasis works well for LTI electrical channels, it is not optimum for the non-linear optical frequency response of the VCSEL. Based on the simulations of the model an optimum equalization methodology is derived. The equalization technique is used to achieve a data-rate of 20Gb/s with power efficiency of 0.77pJ/bit.

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O presente estudo tem como objeto o Programa Bolsa Família, buscando captar, junto aos usuários, as suas impressões acerca deste, que é o carro-chefe dos programas sociais do atual governo federal. Com base nos pressupostos de que o Bolsa Família tem forte apelo popular; é legitimado em larga escala por diferentes segmentos sociais e tem centralidade no campo da Assistência Social, a hipótese é de que os usuários, enquanto beneficiários diretos do Programa tendem à sua defesa, apesar de dificuldades e problemas que possam apontar. Muitos estudos têm debatido o Bolsa Família, mas ressentem-se de uma abordagem que coloque em cena os usuários. Para a realização deste estudo, que tem como referência o materialismo histórico-dialético, foram investigados diversos autores acerca do tema Política Social e diversos documentos de fontes primárias, como jornais, legislação e material institucional, bem como, pesquisa junto aos usuários do Bolsa Família que utilizam o Centro de Referência da Assistência Social (CREAS) Arlindo Rodrigues, na Tijuca, Rio de Janeiro, como local para aquisição e manutenção do benefício do Programa. A pesquisa, entre outros elementos, aponta para uma aceitação deste, ainda que haja alguns questionamentos e objeções por parte dos usuários. A procura ao CREAS é constante e intensa configurando o centro de referência como espaço central de atendimento ao Bolsa Família.

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A expansão rápida da maxila cirurgicamente assistida tornou-se amplamente utilizada e muito aceitável no tratamento da deficiência maxilar de pacientes adolescentes e adultos. Diversas técnicas cirúrgicas foram propostas ao longo dos anos com o objetivo de solucionar este problema de forma eficiente, com estabilidade dos resultados e baixa morbidade. Controvérsias em relação ao procedimento cirúrgico persistem, principalmente relacionadas a quais osteotomias devem ser realizadas para se obter bons resultados. O objetivo deste trabalho foi avaliar os resultados da expansão ortocirúrgica da maxila realizando osteotomias nas paredes laterais da maxila e na sutura palatina mediana. Foram selecionados dezessete pacientes adultos portadores de deficiência transversa maxilar, com média de idade de 24 anos e 8 meses; todos foram submetidos a exames de tomografia computadorizada convencional e moldagens maxilares previamente ao procedimento cirúrgico e após três meses, no mínimo, do término de ativação e estabilização do aparelho expansor. As medidas do pós-cirúrgico foram confrontadas com as do pré-cirúrgico e os resultados foram comparados e analisados estatisticamente. Foi obtida a expansão desejada clinicamente em todos os pacientes. No entanto, a quantidade de expansão na região de molares foi estatisticamente maior nas áreas referentes aos dentes, enquanto que os resultados obtidos referentes aos caninos se mostraram similares nas três regiões maxilares avaliadas. Quando comparadas às regiões de caninos e molares entre si, a expansão intercaninos foi maior na altura dos forames palatinos e o inverso ocorreu nas regiões de processo alveolar e dentária, nas quais a expansão intermolar foi maior.