Global ETD Search

1	Utilidades em \'S\' e os paradoxos do mercado financeiro / S-shaped utilities and the puzzles of the financial markets Farias Neto, João José de 03 December 2007 (has links) Testam-se quatro utilidades com o formato S das curvas de saturação - gama, logística, Cauchy e Cauchy modificada - no modelo básico de apreçamento de ativos de Lucas, com séries temporais do mercado americano. Estabelecendo-se um parâmetro que acompanha o nível de consumo per capita , constata-se que todas resolvem o chamado riskfree puzzle. A gama e a Cauchy modificada saem-se melhor no apreçamento dos 25 ativos do portfolio de Fama e French e esta última é eleita a vencedora, pelas suas propriedades assintóticas e por apresentar coeficiente médio (no sentido cross-section) de aversão relativa ao risco na faixa considerada normal (entre 0 e 5). A Cauchy modificada regulariza a utilidade de Constantinides-Cochrane-Campbel, de formação de hábito, permitindo que o trecho abaixo do consumo habitual seja usado, com isso dispensando o uso de truques para impedir que o consumo suavizado ultrapasse o real. Constatou-se a manutenção daquele coeficiente médio dentro da faixa normal, em um nível pouco abaixo do americano, no caso do mercado brasileiro. Nesse sentido de média crosssection, poderia-se dizer que a utilidade aqui proposta resolve o chamado equity premium puzzle. / Four S-shaped utility functions are tested - gamma, logistic, Cauchy and modified Cauchy - on Lucas asset pricing model with American market time series. Establishing a parameter that follows the level of the per capita consumption, it is shown that all of them solve the so called risk free puzzle. The gamma utility and the modified Cauchy are the ones with better pricing power with respect to Fama and French\'s 25 book-to-market portfolio and the last one is elected the winner, for its asymptotic properties and for exhibiting mean (in the cross-section sense) relative risk aversion coefficient inside the accepted normal range (between 0 and 5). The modified Cauchy utility regularizes the habit-formation Constantinides-Cochrane-Campbel utility function, allowing the usage of the stretch below the habit consumption level, thus doing without the need of tricks to forbid the smoothed consumption series from outgrowing the real one. In the Brazilian market, the mean relative risk aversion coefficient also remains inside the acceptable region, on a slightly lower level. In this mean cross-section sense, it might be possible to state that the utility here proposed solves the equity premium puzzle. Ações Consumo Economia matemática Escolha (teoria econômica) Habit formation Puzzles S-shaped Utility function
2	Utilidades em \'S\' e os paradoxos do mercado financeiro / S-shaped utilities and the puzzles of the financial markets João José de Farias Neto 03 December 2007 (has links) Testam-se quatro utilidades com o formato S das curvas de saturação - gama, logística, Cauchy e Cauchy modificada - no modelo básico de apreçamento de ativos de Lucas, com séries temporais do mercado americano. Estabelecendo-se um parâmetro que acompanha o nível de consumo per capita , constata-se que todas resolvem o chamado riskfree puzzle. A gama e a Cauchy modificada saem-se melhor no apreçamento dos 25 ativos do portfolio de Fama e French e esta última é eleita a vencedora, pelas suas propriedades assintóticas e por apresentar coeficiente médio (no sentido cross-section) de aversão relativa ao risco na faixa considerada normal (entre 0 e 5). A Cauchy modificada regulariza a utilidade de Constantinides-Cochrane-Campbel, de formação de hábito, permitindo que o trecho abaixo do consumo habitual seja usado, com isso dispensando o uso de truques para impedir que o consumo suavizado ultrapasse o real. Constatou-se a manutenção daquele coeficiente médio dentro da faixa normal, em um nível pouco abaixo do americano, no caso do mercado brasileiro. Nesse sentido de média crosssection, poderia-se dizer que a utilidade aqui proposta resolve o chamado equity premium puzzle. / Four S-shaped utility functions are tested - gamma, logistic, Cauchy and modified Cauchy - on Lucas asset pricing model with American market time series. Establishing a parameter that follows the level of the per capita consumption, it is shown that all of them solve the so called risk free puzzle. The gamma utility and the modified Cauchy are the ones with better pricing power with respect to Fama and French\'s 25 book-to-market portfolio and the last one is elected the winner, for its asymptotic properties and for exhibiting mean (in the cross-section sense) relative risk aversion coefficient inside the accepted normal range (between 0 and 5). The modified Cauchy utility regularizes the habit-formation Constantinides-Cochrane-Campbel utility function, allowing the usage of the stretch below the habit consumption level, thus doing without the need of tricks to forbid the smoothed consumption series from outgrowing the real one. In the Brazilian market, the mean relative risk aversion coefficient also remains inside the acceptable region, on a slightly lower level. In this mean cross-section sense, it might be possible to state that the utility here proposed solves the equity premium puzzle. Ações Consumo Economia matemática Escolha (teoria econômica) Habit formation Puzzles S-shaped Utility function
3	Alternate Stable States in Ecological Systems Sasi, Sarath 11 August 2012 (has links) In this thesis we study two reaction-diffusion models that have been used to analyze the existence of alternate stable states in ecosystems. The first model describes the steady states of a logistic growth model with grazing in a spatially homogeneous ecosystem. It also describes the dynamics of the fish population with natural predation. The second model describes phosphorus cycling in stratified lakes. The same equation has also been used to describe the colonization of barren soils in drylands by vegetation. In this study we discuss the existence of multiple positive solutions, leading to the occurrence of S-shaped bifurcation curves. We were able to show that both the models have alternate stable states for certain ranges of parameter values. We also introduce a constant yield harvesting term to the first model and discuss the existence of positive solutions including the occurrence of a Sigma-shaped bifurcation curve in the case of a one-dimensional model. Again we were able to establish that for certain ranges of parameter values the model has alternate stable states. Thus we establish analytically that the above models are capable of describing the phenomena of alternate stable states in ecological systems. We prove our results by the method of sub-super solutions and quadrature method. Boundary value problems Spatial ecology S-shaped bifurcation Method of sub-super solutions Quadrature method
4	Modelling and forecasting human populations using sigmoid models Raeside, Robert January 1987 (has links) Early this century "S-shaped" curves, sigmoids, gained popularity among demographers. However, by 1940, the approach had "fallen out of favour", being criticised for giving poor results and having no theoretical validity. It was also considered that models of total population were of little practical interest, the main forecasting procedure currently adopted being the bottom-up "cohort-component" method. In the light of poor forecasting performance from component methods, a re-assessment is given in this thesis of the use of simple trend models. A suitable means of fitting these models to census data is developed, using a non-linear least squares algorithm based on minimisation of a proportionately weighted residual sum of squares. It is demonstrated that useful models can be obtained from which, by using a top-down methodology, component populations and vital components can be derived. When these models are recast in a recursive parameterisation, it is shown that forecasts can be obtained which, it is argued, are superior to existing official projections. Regarding theoretical validity, it is argued that sigmoid models relate closely to Malthusian theory and give a mathematical statement of the demographic transition. In order to judge the suitability of extrapolating from sigmoid models, a framework using Catastrophe Theory is developed. It is found that such a framework allows one qualitatively to model population changes resulting from subtle changes in influencing variables. The use of Catastrophe Theory has advantages over conventional demographic models as it allows a more holistic approach to population modelling. 519
5	Dual Segment S-Shaped Aperture-Coupled Cylindrical Dielectric Resonator Antenna for X-Band Applications Majeed, Asmaa H., Abdullah, Abdulkareem S., Elmegri, Fauzi, Sayidmarie, Khalil H., Abd-Alhameed, Raed, Noras, James M. 12 October 2015 (has links) Yes / A new low-cost dual-segmented dielectric resonator (DR) antenna design is proposed for wideband applications in the X-band region. Two DRs coupled to an S-shaped slot introduce interesting features. The antenna performance was characterized in terms of the reflection coefficient, gain, and radiation pattern, and detailed simulation studies indicate excellent antenna performance from 7.66 GHz to 11.2 GHz (37.5% fractional bandwidth) with a maximum gain of 6.0 dBi at 10.6 GHz while the fabricated prototype has a matched bandwidth from 7.8 GHz to 11.85 GHz (41% fractional bandwidth) and maximum gain of 6dBi. The antenna is compact, size 1 x 0.83 x 0.327 time the wavelength at 10 GHz. The two DR segments may be located on the same side or on opposite sides of the substrate, giving respectively improved gain or more uniform field patterns. Experimental testing of the prototype performance showed reasonable agreement with the predicted performance. S-shaped slot coupling L-shaped feed line HEM11δ mode X-band
6	Fabrication of Nano Josephson Junctions Using the Femtosecond Laser Technique on High Tc Superconducting YBCO Thin films Umenne, Patrice 27 February 2018 (has links) This PhD work involves the utilization of the femtosecond laser technique to fabricate the novel S-shaped Josephson Junctions on the high - T_C superconducting YBCO thin films. Initially, it was envisaged as the title states to fabricate nano sized Josephson Junctions using this femtosecond laser technique. However in this PhD work, micron sized (1 – 2 µm) and near nano sized (500 – 800 nm) Josephson Junctions where achieved. / University of South Africa / Electrical and Mining Engineering Josephson Junction Femtsosecond laser Beam Collimation Shapiro Steps Micron Constrictions submicron constrictions nano constrictions S-shaped constrictions Critical Current ablation threshold
7	Wafer-level heterogeneous integration of MEMS actuators Braun, Stefan January 2010 (has links) This thesis presents methods for the wafer-level integration of shape memory alloy (SMA) and electrostatic actuators to functionalize MEMS devices. The integration methods are based on heterogeneous integration, which is the integration of different materials and technologies. Background information about the actuators and the integration method is provided. SMA microactuators offer the highest work density of all MEMS actuators, however, they are not yet a standard MEMS material, partially due to the lack of proper wafer-level integration methods. This thesis presents methods for the wafer-level heterogeneous integration of bulk SMA sheets and wires with silicon microstructures. First concepts and experiments are presented for integrating SMA actuators with knife gate microvalves, which are introduced in this thesis. These microvalves feature a gate moving out-of-plane to regulate a gas flow and first measurements indicate outstanding pneumatic performance in relation to the consumed silicon footprint area. This part of the work also includes a novel technique for the footprint and thickness independent selective release of Au-Si eutectically bonded microstructures based on localized electrochemical etching. Electrostatic actuators are presented to functionalize MEMS crossbar switches, which are intended for the automated reconfiguration of copper-wire telecommunication networks and must allow to interconnect a number of input lines to a number of output lines in any combination desired. Following the concepts of heterogeneous integration, the device is divided into two parts which are fabricated separately and then assembled. One part contains an array of double-pole single-throw S-shaped actuator MEMS switches. The other part contains a signal line routing network which is interconnected by the switches after assembly of the two parts. The assembly is based on patterned adhesive wafer bonding and results in wafer-level encapsulation of the switch array. During operation, the switches in these arrays must be individually addressable. Instead of controlling each element with individual control lines, this thesis investigates a row/column addressing scheme to individually pull in or pull out single electrostatic actuators in the array with maximum operational reliability, determined by the statistical parameters of the pull-in and pull-out characteristics of the actuators. / QC20100729 Microelectromechanical systems MEMS silicon wafer-level integration heterogeneous integration transfer integration packaging assembly wafer bonding adhesive bonding eutectic bonding release etching electrochemical etching microvalves microactuator Shape Memory Alloy SMA NITINOL TiNi NiTi cold-state reset bias spring stress layers crossbar switch routing switch switch array electrostatic actuator S-shaped actuator zipper actuator addressing transfer stamping blue tape Computer engineering Datorteknik

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