Aperfeiçoamento da previsão global em séries temporais caóticas

A previsão de valores futuros em séries temporais produzidas por sistemas caóticos pode ser aplicada em diversas áreas do conhecimento como Astronomia, Economia, Física, Medicina, Meteorologia e Oceanografia. O método empregado consiste na reconstrução do espaço de fase seguido de um termo de melhoria da previsão. As rotinas utilizadas para a previsão e análise nesta linha de pesquisa fazem parte do pacote TimeS, que apresenta resultados encorajadores nas suas aplicações. O aperfeiçoamento das rotinas computacionais do pacote com vistas à melhoria da acurácia obtida e à redução do tempo computacional é construído a partir da investigação criteriosa da minimização empregada na obtenção do mapa global. As bases matemáticas são estabelecidas e novas rotinas computacionais são criadas. São ampliadas as possibilidades de funções de ajuste que podem incluir termos transcendentais nos componentes dos vetores reconstruídos e também possuir termos lineares ou não lineares nos parâmetros de ajuste. O ganho de eficiência atingido permite a realização de previsões e análises que respondem a perguntas importantes relacionadas ao método de previsão e ampliam a possibilidade de aplicações a séries reais.

Safety net or debt net?: ties between marketing and credit in coastal Bangladesh

Three fishing communities in coastal Bangladesh namely: 1) Hindu community near Chittagong; 2) Muslim community in Rehania; and 3) Bhuddist community of Rakhaipara were studied, and each shared the same credit marketing system.

A criação dos números e sua evolução Matemática: de escrava a rainha das ciências.

Este trabalho aborda, de maneira bem sucinta e objetiva, a história da evolução dos números desde o primeiro risco em um osso, até chegar na forma atual como os conhecemos. Ao longo de aproximadamente 30.000 anos de existência, os sistemas de numeração, suas bases e representações sofreram inúmeras modificações, adequando-se ao contexto histórico vigente. Podemos citar a mentalidade científica da época, a necessidade da conquista de territórios, religiões e crenças e necessidades básicas da vida cotidiana. Deste modo, mostramos uma corrente histórica que tenta explicar como e porque a ideia de número se modifica com o tempo, sempre tendo em vista os fatores que motivaram tais mudanças e quais benefícios (ou malefícios) trouxeram consigo. Com um capítulo dedicado a cada uma das mais importantes civilizações que contribuíram para o crescimento da matemática e, sempre que possível, em ordem cronológica de acontecimentos, o leitor consegue ter uma boa ideia de como uma civilização influencia a outra e como um povo posterior pôde apoiar-se nos conhecimentos adquiridos dos antepassados para produzir seus próprios algorítimos e teoremas.

Compulsory heterosexuality and Caribbean queer identities: an investigation of Achy Obejas's Memory mambo and Shani Mootoo's Valmiki's daughter

Esta dissertação pretende investigar de que forma idéias construídas socialmente impõem a heterossexualidade e afetam indivíduos não heterosexuais das ilhas Caribenhas, conforme ilustrado nos romances Memory Mambo, da Cubana-Americana Achy Obejas e Valmikis Daughters, da Trinitária-Canadense Shani Mootoo. Este trabalho se concentra na análise de políticas sexuais ligadas à homossexualidade tanto nas ilhas do Caribe quanto nos Estados Unidos da América. Em Memory Mambo, a protagonista Juani Casas deseja entender como sua condição de exilada cubana molda sua identidade sexual e como seu lesbianismo afeta seus relacionamentos familiares e amorosos. Reconstruindo sua história através de uma memória não confiável, Juani procura descobrir como sua sexualidade e sua nacionalidade estão ligadas, para que ela possa conciliar as duas. Em Valmikis Daughter, Viveka Krishnu e seu pai Valmiki Krishnu tentam esconder seus verdadeiros desejos por causa dos comportamentos supostamente corretos que foram designados tanto para homens quanto para mulheres em Trinidad, e mais especificamente na sociedade indo-caribenha. Pai e filha sofrem com a opressão e tentam não se tornarem vítimas de homofobia constante, ele escondendo sua sexualidade e ela deixando a ilha. Assim, através da representação literária, Obejas e Mootoo participam de uma discussão necessária sobre as consequencias das políticas sexuais na construção identitária de Caribenhos que vivem nas ilhas ou em destinos diaspóricos

Condições de contorno tipo albedo para cálculos globais de reatores nucleares com o modelo de dois grupos de energia na formulação de transporte SN em geometria bidimensional cartesiana

Os eventos de fissão nuclear, resultados da interação dos nêutrons com os núcleos dos átomos do meio hospedeiro multiplicativo, não estão presentes em algumas regiões dos reatores nucleares, e.g., moderador, refletor, e meios estruturais. Nesses domínios espaciais não há geração de potência nuclear térmica e, além disso, comprometem a eficiência computacional dos cálculos globais de reatores nucleares. Propomos nesta tese uma estratégia visando a aumentar a eficiência computacional dessas simulações eliminando os cálculos numéricos explícitos no interior das regiões não-multiplicativas (baffle e refletor) em torno do núcleo ativo. Apresentamos algumas modelagens e discutimos a eficiência da aplicação dessas condições de contorno aproximadas tipo albedo para uma e duas regiões nãomultiplicativas, na formulação de ordenadas discretas (SN) para problemas de autovalor a dois grupos de energia em geometria bidimensional cartesiana. A denominação Albedo, palavra de origem latina para alvura, foi originalmente definida como a fração da luz incidente que é refletida difusamente por uma superfície. Esta denominação latina permaneceu como o termo científico usual em astronomia e, nesta tese, este conceito é estendido para reflexão de nêutrons. Estas condições de contorno tipo albedo SN não-convencional substituem aproximadamente as regiões de baffle e refletor no em torno do núcleo ativo do reator, desprezando os termos de fuga transversal no interior dessas regiões. Se o problema, em particular, não possui termos de fuga transversal, i.e., trata-se de um problema unidimensional, então as condições de contorno albedo, como propostas nesta tese, são exatas. Por eficiência computacional entende-se a análise da precisão dos resultados numéricos em comparação com o tempo de execução computacional de cada simulação de um dado problema-modelo. Resultados numéricos considerando dois problemas-modelo com de simetria são considerados para ilustrar esta análise de eficiência.

Active learning of model evidence using Bayesian quadrature

Numerical integration is a key component of many problems in scientific computing, statistical modelling, and machine learning. Bayesian Quadrature is a modelbased method for numerical integration which, relative to standard Monte Carlo methods, offers increased sample efficiency and a more robust estimate of the uncertainty in the estimated integral. We propose a novel Bayesian Quadrature approach for numerical integration when the integrand is non-negative, such as the case of computing the marginal likelihood, predictive distribution, or normalising constant of a probabilistic model. Our approach approximately marginalises the quadrature model's hyperparameters in closed form, and introduces an active learning scheme to optimally select function evaluations, as opposed to using Monte Carlo samples. We demonstrate our method on both a number of synthetic benchmarks and a real scientific problem from astronomy.

Control of lunar and martian dust - Experimental insights from artificial and natural cyanobacterial and algal crusts in the desert of Inner Mongolia, China

Studies on the colonization of environmentally extreme ground surfaces were conducted in a Mars-like desert area of Inner Mongolia, People's Republic of China, with microalgae and cyanobacteria. We collected and mass-cultured cyanobacterial strains from these regions and investigated their ability to form desert crusts artificially. These crusts had the capacity to resist sand wind erosion after just 15 days of growth. Similar to the surface of some Chinese deserts, the surface of Mars is characterized by a layer of fine dust, which will challenge future human exploration activities, particularly in confined spaces that will include greenhouses and habitats. We discuss the use of such crusts for the local control of desert sands in enclosed spaces on Mars. These experiments suggest innovative new directions in the applied use of microbe-mineral interactions to advance the human exploration and settlement of space.

A simple closed aquatic ecosystem (CAES) for space

A closed aquatic ecosystem (CAES) was developed to stud), the effects of microgravity on the function of closed ecosystems aboard the Chinese retrieved satellite and on the spacecraft SHENZHOU-II. These systems housed a small freshwater snail (Bulinus australianus) and an autotrophic green algae (Chlorella pyrenoidosa). The results of the test on the satellite were that the concentration of algae changed little, but that the snails died during the experiments. We then sought to optimize the function of the control system, the cultural conditions and the data acquisition system and carried out an experiment on the spacecraft SHENZHOU-II. Using various sensors to monitor the CAES, real-time data regarding the operation of the CAES in microgravity was acquired. In addition, all on-board Ig centrifuge was included to identify gravity-related factors. It was found that microgravity is the major factor affecting the operation of the CAES in space. The change in biomass of the primary producer during each day in microgravity was larger than that of the control groups. The mean biomass concentration per day in the microgravity group decreased, but that of the control groups increased for several days and then leveled off. Space effects on the biomass of a primary producer may be a result of microgravity effects leading to increasing metabolic rates of the consumer combined with decreases in photosynthesis. (c) 2007 COSPAR. Published by Elsevier Ltd. All rights reserved.

The response of antioxidant systems in Nostoc sphaeroides against UV-B radiation and the protective effects of exogenous antioxidants

UV radiation is one of many harmful factors found in space that are detrimental to organisms on earth in space exploration. In the present work, we examined the role of antioxidant system in Nostoc sphaeroides Kutz (Cyanobacterium) and the effects of exogenously applied antioxidant molecules on its photosynthetic rate under UV-B radiation. It was found that UV-B radiation promoted the activity of antioxidant system to protect photosystem 11 (PSII) and exogenously applied antioxidant: sodium nitroprusside (SNP) and N-acetylcysteine (NAC) had an obvious protection on PSII activity under UV-B radiation. The activity of superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), peroxidase (POD, EC 1.11.1.7) and content of NIDA (malondialdehyde) and ASC (ascorbate) were improved by 0.5 mM and 1 mM SNP, but 0.1 mM SNP decreased the activity of antioxidant system. Addition of exogenous NAC decreased the activity of SOD, POD, CAT and the content MDA and ASC. In contrast, exogenously applied NAC increased GSH content. The results suggest that exogenous SNP and NAC may protect algae by different mechanisms: SNP may play double roles as both sources of reactive free radicals as well as ROS scavengers in mediating the protective role of PSII on algae under UV-B radiation. On the other hand, NAC functions as an antioxidant or precursor of glutathione, which could protect PSII directly from UV-B radiation. (c) 2007 COSPAR, Published by Elsevier Ltd. All rights reserved.

Rashba electron transport in one-dimensional quantum waveguides

The properties of Rashba wave function in the planar one-dimensional waveguide are studied, and the following results are obtained. Due to the Rashba effect, the plane waves of electron with the energy E divide into two kinds of waves with the wave vectors k(1)=k(0)+k(delta) and k(2)=k(0)-k(delta), where k(delta) is proportional to the Rashba coefficient, and their spin orientations are +pi/2 (spin up) and -pi/2 (spin down) with respect to the circuit, respectively. If there is gate or ferromagnetic contact in the circuit, the Rashba wave function becomes standing wave form exp(+/- ik(delta)l)sin[k(0)(l-L)], where L is the position coordinate of the gate or contact. Unlike the electron without considering the spin, the phase of the Rashba plane or standing wave function depends on the direction angle theta of the circuit. The travel velocity of the Rashba waves with the wave vector k(1) or k(2) are the same hk(0)/m*. The boundary conditions of the Rashba wave functions at the intersection of circuits are given from the continuity of wave functions and the conservation of current density. Using the boundary conditions of Rashba wave functions we study the transmission and reflection probabilities of Rashba electron moving in several structures, and find the interference effects of the two Rashba waves with different wave vectors caused by ferromagnetic contact or the gate. Lastly we derive the general theory of multiple branches structure. The theory can be used to design various spin polarized devices.

Spin injection in the multiple quantum-well LED structure with the Fe/AlO (x) injector

A spin-injection/-detection device has been fabricated based on the multiple quantum well light emitting diode (LED) structure. It is found that only a broad electroluminescence (EL) peak of a full width at half maximum of 8.6 nm appears at the wavelength of 801 nm in EL spectra with a circular luminescence polarization degree of 18%, despite PL spectra always show three well resolved peaks. The kinetic energy gained by injected electrons and holes in their drift along opposite directions broadens the EL peak, and makes three EL peaks converge together. The same process also destroys the injected spin polarization of electrons mainly dominated by the Bir-Aronov-Pikus spin relaxing mechanism.

Ultrafast photo-induced turning of magnetization and its relaxation dynamics in GaMnAs

We report that, by linearly polarized pumping of different wavelengths, Kerr transients appear at zero magnetic field only in the case when GaMnAs samples are initialized at 3 K by first applying a 0.8 Tesla field and then returning to zero field. We find that, instead of magnetization precession, the near-band gap excitation induces a coherent out-of-plane turning of magnetization, which shows very long relaxation dynamics with no precession. When photon energy increases, the peak value of the Kerr transient increases, but it decays rapidly to the original slow transient seen under the near-band-gap excitation.

Antibunching and blinking from a single colloidal CdSe quantum dot

We have investigated the optical properties of single CdSe/ZnS nanocrystals by conducting combinations of experiments on antibunching and photoluminescence intermittence under different experimental conditions. Based on photoluminescence in an antibunching experiment, we analyzed the emission lifetime of QDs by using stretched exponentials. The difference between the parameters obtained from average lifetimes and stretched exponents were analyzed by considering the effect of nonradiative emission. An Auger-assisted tunneling model was used to explain the power law exponents of off time distribution. The power law exponent under high excitation power was correlated with a higher Auger ionization rate. Using the parameters obtained from stretched exponential function and power law, the antibunching phenomena at different time and under different excitation intensity were analyzed.

The growth temperatures dependence of optical and electrical properties of InN films

InN films grown on sapphire at different substrate temperatures from 550 degrees C to 700 degrees C by metalorganic chemical vapor deposition were investigated. The low-temperature GaN nucleation layer with high-temperature annealing (1100 degrees C) was used as a buffer for main InN layer growth. X-ray diffraction and Raman scattering measurements reveal that the quality of InN films can be improved by increasing the growth temperature to 600 degrees C. Further high substrate temperatures may promote the thermal decomposition of InN films and result in poor crystallinity and surface morphology. The photoluminescence and Hall measurements were employed to characterize the optical and electrical properties of InN films, which also indicates strong growth temperature dependence. The InN films grown at temperature of 600 degrees C show not only a high mobility with low carrier concentration, but also a strong infrared emission band located around 0.7 eV. For a 600 nm thick InN film grown at 600 degrees C, the Hall mobility achieves up to 938 cm(2)/Vs with electron concentration of 3.9 x 10(18) cm(-3).