Effect of phases on the dynamic evolution of a Lambda system with spontaneously generated coherence

The dynamic evolution of a A system coupled by two strong coherent fields is investigated by taking spontaneously generated coherence (SGC) into account. By numericaly simulation, it is shown that the relative phase of the two coherent fields affects significantly the time scale to the coherent population trapping state. In addition, an analytical expression to the evolution rate which is consistent with the numerical results is given. (c) 2005 Elsevier B.V. All rights reserved.

The distribution and ages of regional lithologies in the lunar maria

A research program was designed (1) to map regional lithological units of the lunar surface based on measurements of spatial variations in spectral reflectance, and, (2) to establish the sequence of the formation of such lithological units from measurements of the accumulated affects of impacting bodies.

Spectral reflectance data were obtained by scanning luminance variations over the lunar surface at three wavelengths (0.4µ, 0.52µ, and 0.7µ). These luminance measurements were reduced to normalized spectral reflectance values relative to a standard area in More Serenitotis. The spectral type of each lunar area was identified from the shape of its reflectance spectrum. From these data lithological units or regions of constant color were identified. The maria fall into two major spectral classes: circular moria like More Serenitotis contain S-type or red material and thin, irregular, expansive maria like Mare Tranquillitatis contain T-type or blue material. Four distinct subtypes of S-type reflectances and two of T-type reflectances exist. As these six subtypes occur in a number of lunar regions, it is concluded that they represent specific types of material rather than some homologous set of a few end members.

The relative ages or sequence of formation of these more units were established from measurements of the accumulated impacts which have occurred since more formation. A model was developed which relates the integrated flux of particles which hove impacted a surface to the distribution of craters as functions of size and shape. Erosion of craters is caused chiefly by small bodies which produce negligible individual changes in crater shape. Hence the shape of a crater can be used to estimate the total number of small impacts that have occurred since the crater was formed. Relative ages of a surface can then be obtained from measurements of the slopes of the walls of the oldest craters formed on the surface. The results show that different maria and regions within them were emplaced at different times. An approximate absolute time scale was derived from Apollo 11 crystallization ages under an assumption of a constant rote of impacting for the last 4 x 10^9 yrs. Assuming, constant flux, the period of mare formation lasted from over 4 x 10^9 yrs to about 1.5 x 10^9 yrs ago.

A synthesis of the results of relative age measurements and of spectral reflectance mapping shows that (1) the formation of the lunar maria occurred in three stages; material of only one spectral type was deposited in each stage, (2) two distinct kinds of maria exist, each type distinguished by morphology, structure, gravity anomalies, time of formation, and spectral reflectance type, and (3) individual maria have complicated histories; they contain a variety of lithic units emplaced at different times.

Mechanistic aspects of the Ziegler-Natta polymerization

The isotope effect on propagation rate was determined for four homogeneous ethylene polymerization systems. The catalytic system Cp_2Ti(Et)Cl + EtA1Cl_2 has a k^H_p/k^D_p = 1.035 ± 0.03. This result strongly supports an insertion mechanism which does not involve a hydrogen migration during the rate determining step of propagation (Cossee mechanism). Three metal-alkyl free systems were also studied. The catalyst I_2 (PMe_3)_3Ta(neopentylidene)(H) has a k^H_p/k^D_p = 1.709. It is interpreted as a primary isotope effect involving a non-linear a-hydrogen migration during the rate determining step of propagation (Green mechanism). The lanthanide complexes Cp*_2LuMe•Et_2O and Cp*_2YbMe•Et_2O have a k^H_p/k^D_p = 1.46 and 1.25, respectively. They are interpreted as primary isotope effects due to a partial hydrogen migration during the rate determining step of propagation.

The presence of a precoordination or other intermediate species during the polymerization of ethylene by the mentioned metal-alkyl free catalysts was sought by low temperature NMR spectroscopy. However, no evidence for such species was found. If they exist, their concentrations are very small or their lifetimes are shorter than the NMR time scale.

Two titanocene (alkenyl)chlorides (hexenyl 1 and heptenyl 2 were prepared from titanocene dichloride and a THF solution of the corresponding alkenylmagnesium chloride. They do not cyclize in solution when alone, but cyclization to their respective titanocene(methyl(cycloalkyl) chlorides occurs readily in the presence of a Lewis acid. It is demonstrated that such cyclization occurs with the alkenyl ligand within the coordination sphere of the titanium atom. Cyclization of 1 with EtAlCl_2 at 0°C occurs in less than 95 msec (ethylene insertion time), as shown by the presence of 97% cyclopentyl-capped oligomers when polymerizing ethylene with this system. Some alkyl exchange occurs (3%). Cyclization of 2 is slower under the same reaction conditions and is not complete in 95 msec as shown by the presence of both cyclohexyl-capped oligomers (35%) and odd number α-olefin oligomers (50%). Alkyl exchange is more extensive as evidenced by the even number n-alkanes (15%).

Cyclization of 2-d_1 (titanocene(hept-6-en-1-yl-1-d_1)chloride) with EtA1Cl_2 demonstrated that for this system there is no α-hydrogen participation during said process. The cyclization is believed to occur by a Cossee-type mechanism. There was no evidence for precoordination of the alkenyl double bond during the cyclization process.

O acesso aos exames de alta complexidade nos planos de saúde privados na perspectiva dos usuários

A dissertação trata do acesso aos serviços de alta complexidade, particularmente os exames diagnósticos e complementares, estudado entre usuários de planos de saúde privados que buscam atendimento e diagnóstico especializado. Desde a década de 80 o usuário do sistema público de saúde vem procurando a saúde suplementar. Contudo, afirmar que o acesso é garantido no domínio privado, através da contratação dos planos de saúde, é uma incerteza que rodeia a inspiração para esta pesquisa, que se justifica pela relevância de ações que possibilitem a melhora da qualidade regulatória dos planos de saúde, a partir do controle social de seus usuários. O objetivo geral é analisar as percepções do acesso aos exames de alta complexidade nos serviços de saúde privados entre usuários de planos de saúde. Os objetivos específicos são descrever as percepções dos usuários de planos de saúde acerca do acesso aos exames de alta complexidade; analisar as motivações dos usuários de planos de saúde privados para a realização de exames de alta complexidade através da rede privada de assistência; e analisar o nível de satisfação dos usuários de planos de saúde quanto ao acesso aos exames de alta complexidade. A metodologia é qualitativa-descritiva, onde a amostra foi de trinta usuários de planos de saúde, acima de 18 anos, selecionados no campo de estudo no ano de 2010. O cenário de estudo foi um laboratório privado de medicina diagnóstica no Rio de Janeiro. As técnicas de coleta de dados utilizadas foram formulário e entrevista individual estruturada. A análise do formulário foi realizada através de estatística descritiva, e as entrevistas através da análise de conteúdo temática-categorial. Os usuários de plano de saúde declararam que o acesso é garantido com facilidade para os exames de alta complexidade. Suas principais motivações para a realização desses exames na rede privada de assistência foram caracterizadas pela rapidez de atendimento, flexibilidade e facilidade de marcação pela internet, telefone ou pessoalmente no laboratório estudado, pronta entrega dos resultados, dificuldade e morosidade do atendimento do SUS, localização do prestador credenciado próxima de bairros residenciais ou do trabalho, resolutividade diagnóstica de imagem de excelência, possibilidade de escolha pelo usuário entre as modalidades aberta e fechada de ressonância magnética e tomografia computadorizada, além da densitometria óssea que foram facilmente acessíveis a todos os sujeitos da pesquisa. O nível de satisfação foi correspondido com a rapidez na realização dos exames em caráter eletivo e de urgência quase equiparados na escala de tempo de acordo com os usuários. Contudo, embora as notas de avaliação dos usuários quanto aos seus planos de saúde tenham sido altas, foram abordadas algumas dificuldades, tais como: prazos de validade dos pedidos médicos com datação prévia; solicitações de senhas de autorização pela operadora; burocracia nos procedimentos de agendamento; dificuldades de acesso para tratamentos como implantes, fisioterapia, RPG, pilates, home care, consultas de check up; negação de reembolsos; restrição de materiais cirúrgicos, em especial as próteses e órteses; e restrições específicas de grau para cirurgias de miopia. Conclui-se que o atendimento rápido dos exames de imagem de alto custo na amostra foi descrito como satisfatório, embora a percepção de rapidez possa variar em função do tipo de produto do plano de saúde privado contratado, com necessidade de melhoria regulatória em alguns aspectos pontuais da saúde suplementar.

New Insights from Aperiodic Variability of Young Stars

Nearly all young stars are variable, with the variability traditionally divided into two classes: periodic variables and aperiodic or "irregular" variables. Periodic variables have been studied extensively, typically using periodograms, while aperiodic variables have received much less attention due to a lack of standard statistical tools. However, aperiodic variability can serve as a powerful probe of young star accretion physics and inner circumstellar disk structure. For my dissertation, I analyzed data from a large-scale, long-term survey of the nearby North America Nebula complex, using Palomar Transient Factory photometric time series collected on a nightly or every few night cadence over several years. This survey is the most thorough exploration of variability in a sample of thousands of young stars over time baselines of days to years, revealing a rich array of lightcurve shapes, amplitudes, and timescales.

I have constrained the timescale distribution of all young variables, periodic and aperiodic, on timescales from less than a day to ~100 days. I have shown that the distribution of timescales for aperiodic variables peaks at a few days, with relatively few (~15%) sources dominated by variability on tens of days or longer. My constraints on aperiodic timescale distributions are based on two new tools, magnitude- vs. time-difference (Δm-Δt) plots and peak-finding plots, for describing aperiodic lightcurves; this thesis provides simulations of their performance and presents recommendations on how to apply them to aperiodic signals in other time series data sets. In addition, I have measured the error introduced into colors or SEDs from combining photometry of variable sources taken at different epochs. These are the first quantitative results to be presented on the distributions in amplitude and time scale for young aperiodic variables, particularly those varying on timescales of weeks to months.

Lock Acquisition and Sensitivity Analysis of Advanced LIGO Interferometers

Laser interferometer gravitational wave observatory (LIGO) consists of two complex large-scale laser interferometers designed for direct detection of gravitational waves from distant astrophysical sources in the frequency range 10Hz - 5kHz. Direct detection of space-time ripples will support Einstein's general theory of relativity and provide invaluable information and new insight into physics of the Universe.

Initial phase of LIGO started in 2002, and since then data was collected during six science runs. Instrument sensitivity was improving from run to run due to the effort of commissioning team. Initial LIGO has reached designed sensitivity during the last science run, which ended in October 2010.

In parallel with commissioning and data analysis with the initial detector, LIGO group worked on research and development of the next generation detectors. Major instrument upgrade from initial to advanced LIGO started in 2010 and lasted till 2014.

This thesis describes results of commissioning work done at LIGO Livingston site from 2013 until 2015 in parallel with and after the installation of the instrument. This thesis also discusses new techniques and tools developed at the 40m prototype including adaptive filtering, estimation of quantization noise in digital filters and design of isolation kits for ground seismometers.

The first part of this thesis is devoted to the description of methods for bringing interferometer to the linear regime when collection of data becomes possible. States of longitudinal and angular controls of interferometer degrees of freedom during lock acquisition process and in low noise configuration are discussed in details.

Once interferometer is locked and transitioned to low noise regime, instrument produces astrophysics data that should be calibrated to units of meters or strain. The second part of this thesis describes online calibration technique set up in both observatories to monitor the quality of the collected data in real time. Sensitivity analysis was done to understand and eliminate noise sources of the instrument.

Coupling of noise sources to gravitational wave channel can be reduced if robust feedforward and optimal feedback control loops are implemented. The last part of this thesis describes static and adaptive feedforward noise cancellation techniques applied to Advanced LIGO interferometers and tested at the 40m prototype. Applications of optimal time domain feedback control techniques and estimators to aLIGO control loops are also discussed.

Commissioning work is still ongoing at the sites. First science run of advanced LIGO is planned for September 2015 and will last for 3-4 months. This run will be followed by a set of small instrument upgrades that will be installed on a time scale of few months. Second science run will start in spring 2016 and last for about 6 months. Since current sensitivity of advanced LIGO is already more than factor of 3 higher compared to initial detectors and keeps improving on a monthly basis, upcoming science runs have a good chance for the first direct detection of gravitational waves.

I. Electron spin relaxation studies of manganese(II) complexes in acetonitrile. II. Nuclear spin relaxation studies of bromine in tetrabromomanganese(II) in acetonitrile

Magnetic resonance techniques have given us a powerful means for investigating dynamical processes in gases, liquids and solids. Dynamical effects manifest themselves in both resonance line shifts and linewidths, and, accordingly, require detailed analyses to extract desired information. The success of a magnetic resonance experiment depends critically on relaxation mechanisms to maintain thermal equilibrium between spin states. Consequently, there must be an interaction between the excited spin states and their immediate molecular environment which promote changes in spin orientation while excess magnetic energy is coupled into other degrees of freedom by non-radiative processes. This is well known as spin-lattice relaxation. Certain dynamical processes cause fluctuations in the spin state energy levels leading to spin-spin relaxation and, here again, the environment at the molecular level plays a significant role in the magnitude of interaction. Relatively few electron spin relaxation studies of solutions have been conducted and the present work is addressed toward the extension of our knowledge in this area and the retrieval of dynamical information from line shape analyses on a time scale comparable to diffusion controlled phenomena.

Specifically, the electron spin relaxation of three Mn⁺²3d⁵ complexes, Mn(CH₃CN)₆⁺², MnCl₄^-2 in acetonitrile has been studied in considerable detail. The effective spin Hamiltonian constants were carefully evaluated under a wide range of experimental conditions. Resonance widths of these Mn⁺² complexes were studied in the presence of various excess ligand ions and as a function of concentration, viscosity, temperature and frequency (X-band, ~9.5 Ԍ Hz and K-band, ~35 Ԍ Hz).

A number of interesting conclusions were drawn from these studies. For the Et₄NCl-₄^-2 system several relaxation mechanisms leading to resonance broadening were observed. One source appears to arise through spin-orbit interactions caused by modulation of the ligand field resulting from transient distortions of the complex imparted by solvent fluctuations in the immediate surroundings of the paramagnetic ion. An additional spin relaxation was assigned to the formation of ion pairs [Et₄N⁺…MnCl₄^-2] and it was possible to estimate the dissociation constant for this specie in acetonitrile.

The Bu₄NBr-MnBr₄^-2 study was considerably more interesting. As in the former case, solvent fluctuations and ion-pairing of the paramagnetic complex [Bu₄N⁺…MnBr₄^-2] provide significant relaxation for the electronic spin system. Most interesting, without doubt, is the onset of a new relaxation mechanism leading to resonance broadening which is best interpreted as chemical exchange. Thus, assuming that resonance widths were simply governed by electron spin state lifetimes, we were able to extract dynamical information from an interaction in which the initial and final states are the same

MnBr₄^-2 + Br^- = MnBr₄^-2 + Br^-.

The bimolecular rate constants were obtained at six different temperatures and their magnitudes suggested that the exchange is probably diffusion controlled with essentially a zero energy of activation. The most important source of spin relaxation in this system stems directly from dipolar interactions between the manganese 3d⁵ electrons. Moreover, the dipolar broadening is strongly frequency dependent indicating a deviation between the transverse and longitudinal relaxation times. We are led to the conclusion that the 3d⁵ spin states of ion-paired MnBr₄^-2 are significantly correlated so that dynamical processes are also entering the picture. It was possible to estimate the correlation time, ^Td, characterizing this dynamical process.

In Part II we study nuclear magnetic relaxation of bromine ions in the MnBr4-2-Bu4NBr-acetonitrile system. Essentially we monitor the 79Br and 81Br linewidths in response to the [MnBr4-2]/[Br-] ratio with the express purpose of supporting our contention that exchange is occurring between "free" bromine ions in the solvent and bromine in the first coordination sphere of the paramagnetic anion. The complexity of the system elicited a two-part study: (1) the linewidth behavior of Bu4NBr in anhydrous CH3CN in the absence of MnBr4-2 and (2) in the presence of MnBr4-2. It was concluded in study (1) that dynamical association, Bu4NBr k1= Bu4N+ + Br-, was modulating field-gradient interactions at frequencies high enough to provide an estimation of the unimolecular rate constant, k1. A comparison of the two isotopic bromine linewidth-mole fraction results led to the conclusion that quadrupole interactions provided the dominant relaxation mechanism. In study (2) the "residual" bromine linewidths for both 79Br and 81Br are clearly controlled by quadrupole interactions which appear to be modulated by very rapid dynamical processes other than molecular reorientation. We conclude that the "residual" linewidth has its origin in chemical exchange and that bromine nuclei exchange rapidly between a "free" solvated ion and the paramagnetic complex, MnBr4-2.

Applications of nuclear magnetic resonance spectroscopy to the study of medium-sized rings. I. Conformational properties of cycloheptane. II. Conformational properties of cycloöctane

Conformational equilibrium in medium-sized rings has been investigated by the temperature variation of the fluorine-19 n.m.r. spectra of 1, 1-difluorocycloalkanes and various substituted derivatives of them. Inversion has been found to be fast on the n.m.r. time scale at -180˚ for 1, 1-difluorocycloheptane, but slow for 1, 1-difluoro-4, 4-dimethylcycloheptane at -150˚. At low temperature, the latter compound affords a single AB pattern with a chemical-shift difference of 841 cps. which has been interpreted in terms of the twist-chair conformation with the methyl groups on the axis position and the fluorine atoms in the 4-position. At room temperature, the n.m.r. spectrum of 1, 1-difluoro-4-t-butylcycloheptane affords an AB pattern with a chemical-shift difference of 185 cps. The presence of distinct trans and gauche couplings from the adjacent hydrogens has been interpreted to suggest the existence of a single predominant form, the twist chair with the fluorine atoms on the axis position.

Investigation of 1, 1-difluorocycloöctane and 1, 1, 4, 4-tetrafluorocycloöctane has led to the detection of two kinetic processes both having activation energies of 8-10 kcal./mole but quite different A values. In light of these results eleven different conformations of cycloöctane along with a detailed description of the ways in which they may be interconverted are discussed. An interpretation involving the twist-boat conformation rapidly equilibrating through the saddle and the parallel-boat forms at room temperature is compatible with the results.

Optimization and Control of Power Flow in Distribution Networks

Climate change is arguably the most critical issue facing our generation and the next. As we move towards a sustainable future, the grid is rapidly evolving with the integration of more and more renewable energy resources and the emergence of electric vehicles. In particular, large scale adoption of residential and commercial solar photovoltaics (PV) plants is completely changing the traditional slowly-varying unidirectional power flow nature of distribution systems. High share of intermittent renewables pose several technical challenges, including voltage and frequency control. But along with these challenges, renewable generators also bring with them millions of new DC-AC inverter controllers each year. These fast power electronic devices can provide an unprecedented opportunity to increase energy efficiency and improve power quality, if combined with well-designed inverter control algorithms. The main goal of this dissertation is to develop scalable power flow optimization and control methods that achieve system-wide efficiency, reliability, and robustness for power distribution networks of future with high penetration of distributed inverter-based renewable generators.

Proposed solutions to power flow control problems in the literature range from fully centralized to fully local ones. In this thesis, we will focus on the two ends of this spectrum. In the first half of this thesis (chapters 2 and 3), we seek optimal solutions to voltage control problems provided a centralized architecture with complete information. These solutions are particularly important for better understanding the overall system behavior and can serve as a benchmark to compare the performance of other control methods against. To this end, we first propose a branch flow model (BFM) for the analysis and optimization of radial and meshed networks. This model leads to a new approach to solve optimal power flow (OPF) problems using a two step relaxation procedure, which has proven to be both reliable and computationally efficient in dealing with the non-convexity of power flow equations in radial and weakly-meshed distribution networks. We will then apply the results to fast time- scale inverter var control problem and evaluate the performance on real-world circuits in Southern California Edison’s service territory.

The second half (chapters 4 and 5), however, is dedicated to study local control approaches, as they are the only options available for immediate implementation on today’s distribution networks that lack sufficient monitoring and communication infrastructure. In particular, we will follow a reverse and forward engineering approach to study the recently proposed piecewise linear volt/var control curves. It is the aim of this dissertation to tackle some key problems in these two areas and contribute by providing rigorous theoretical basis for future work.

I. The effect of N,N,N',N' -tetramethylethylenediamine on the Schlenk Equilibrium. II. The nature of the Di-Grignard reagent

I. The influence of N,N,N’,N’-tetramethylethylenediamine on the Schlenk equilibrium

The equilibrium between ethylmagnesium bromide, diethylmagnesium, and magnesium bromide has been studied by nuclear magnetic resonance spectroscopy. The interconversion of the species is very fast on the nmr time scale, and only an averaged spectrum is observed for the ethyl species. When N,N,N’,N’-tetramethylethylenediamine is added to solutions of these reagents in tetrahydrofuran, the rate of interconversion is reduced. At temperatures near -50°, two ethylmagnesium species have been observed. These are attributed to the different ethyl groups in ethylmagnesium bromide and diethylmagnesium, two of the species involved in the Schlenk equilibrium of Grignard reagents.

II. The nature of di-Grignard reagents

Di-Grignard reagents have been examined by nuclear magnetic resonance spectroscopy in an attempt to prove that dialkylmagnesium reagents are in equilibrium with alkylmagnesium halides. The di-Grignard reagents of compounds such as 1,4-dibromobutane have been investigated. The dialkylmagnesium form of this di-Grignard reagent can exist as an intramolecular cyclic species, tetramethylene-magnesium. This cyclic form would give an nmr spectrum different from that of the classical alkylmagnesium halide di-Grignard reagent. In dimethyl ether-tetrahydrofuran solutions of di-Grignard reagents containing N N,N,N’,N’-Tetramethylethylenediamine, evidence has been found for the existence of an intramolecular dialkylmagnesium species. This species is rapidly equilibrating with other forms, but at low temperatures, the rates of interconversion are reduced. Two species can be seen in the nmr spectrum at -50°. One is the cyclic species; the other is an open form.

Inversion of the carbon at the carbon-magnesium bond in di-Grignard reagents has also been studied. This process is much faster than in corresponding monofunctional Grignard reagents.

I. Configurational stability and redistribution equilibria in organomagnesium compounds. II. Redistribution equilibria in organocadmium compounds

I. CONFIGURATIONAL STABILITY AND REDISTRIBUTION EQUILIBRIA IN ORGANOMAGNESIUM COMPOUNDS

The dependence of the rate of inversion of a dialkylmagnesium compound on the solvent has been studied.

Examination of the temperature dependence of the nuclear magnetic resonance spectrum of 1-phenyl-2-propylmagnesium bromide in diethyl ether solution indicates that inversion of configuration at the methylene group of this Grignard reagent occurs with an approximate rate of 2 sec^-1 at room temperature. This is the first example of a rapid inversion rate in a secondary Grignard reagent.

The rates of exchange of alkyl groups between dineopentylmagnesium and di-s-butylmagnesium, bis-(2-methylbutyl)-magnesium and bis-(4, 4-dimethyl-2-pentyl)-magnesium respectively in diethyl ether solution were found to be fast on the nmr time scale. However, the alkyl group exchange rate was found to be slow in a diethyl ether solution of dineopentylmagnesium and bis-(2-methylbutyl)-magnesium containing N, N, N', N'-tetramethylethylenediamine. The unsymmetrical species neopentyl-2-methylbutyl-magnesium was observed at room temperature in the nmr spectrum of the solution containing the diamine.

II. REDISTRIBUTION EQUILIBRIA IN ORGANOCADMIUM COMPOUNDS

The exchange of methyl groups in dimethylcadmium has been studied by nuclear magnetic resonance spectroscopy. Activation parameters for the methyl group exchange have been measured for a neat sample and for a solution in tetrahydrofuran. The exchange is faster in the basic solvent tetrahydrofuran relative to the neat sample and in tetrahydrofuran solution is retarded by the solvating agent N, N, N’, N’-tetramethylethylenediamine and greatly increased by cadmium bromide. The addition of methanol to a solution of dimethylcadmium in tetrahydrofuran appears to have very little effect on the rate of exchange. The exchange was found to proceed with retention of configuration. The rate-limiting step for the exchange of methyl groups in a basic solvent appears to be the dissociation of coordinating solvent from dimethylcadmium.

The equilibrium between methylcadmium bromide, dimethylcadmium and cadmium bromide in tetrahydrofuran solution has also been studied. At room temperature the interconversion of the species is very fast on the nmr time scale but at -100° distinct absorptions for methylcadmium bromide and imethylcadmium are observed.

The species ethylmethylcadmium has been observed in the nmr spectrum.

The rate of exchange of vinyl groups in a solution of divinylcadmium in tetrahydrofuran has been found to be fast on the nmr time scale.

A uniform phase representation for the harmonic model in speech synthesis applications

Feature-based vocoders, e.g., STRAIGHT, offer a way to manipulate the perceived characteristics of the speech signal in speech transformation and synthesis. For the harmonic model, which provide excellent perceived quality, features for the amplitude parameters already exist (e.g., Line Spectral Frequencies (LSF), Mel-Frequency Cepstral Coefficients (MFCC)). However, because of the wrapping of the phase parameters, phase features are more difficult to design. To randomize the phase of the harmonic model during synthesis, a voicing feature is commonly used, which distinguishes voiced and unvoiced segments. However, voice production allows smooth transitions between voiced/unvoiced states which makes voicing segmentation sometimes tricky to estimate. In this article, two-phase features are suggested to represent the phase of the harmonic model in a uniform way, without voicing decision. The synthesis quality of the resulting vocoder has been evaluated, using subjective listening tests, in the context of resynthesis, pitch scaling, and Hidden Markov Model (HMM)-based synthesis. The experiments show that the suggested signal model is comparable to STRAIGHT or even better in some scenarios. They also reveal some limitations of the harmonic framework itself in the case of high fundamental frequencies.

Observation of ultrafast carrier dynamics in amorphous Ge2Sb2Te5 films induced by femtosecond laser pulses

The femtosecond pump-probe technique was used to study the carrier dynamics of amorphous Ge2Sb2Te5 films. With carrier density at around 10(20)-10(21) cm(-3), carriers were excited within 1 ps and recovered to the initial state for less than 3 ns. On the picosecond time scale, the carrier relaxation consists of two components: a fast process within 5 ps and a slow process after 5 ps. The relaxation time of the fast component is a function of carrier density, which increases from 1.9 to 4.3 ps for the carrier density changing from 9.7x10(20) cm(-3) to 3.1x10(21) cm(-3). A possible interpretation of the relaxation processes is elucidated. In the first 5 ps the relaxation process is dominated by an intraband carrier relaxation and the carrier trapping. It is followed by a recombination process of trapped carriers at later delay time. (c) 2007 American Institute of Physics.

Circulação e fluxo de material particulado em suspensão no principal canal de acesso à baía de Sepetiba

Entre 06/08/11 e 25/02/12 foram obtidas séries temporais contínuas de intensidade e direção das correntes e intensidade do eco ao longo de toda a coluna dágua, e medições, de temperatura e pressão, próximas ao fundo, na região adjacente ao canal de acesso à baía de Sepetiba (230'16.5"S e 4359'29.4"W, profundidade local de aproximadamente 25 m) através da utilização de um perfilador acústico ADCP (Acoustic Doppler Current Profiler), modelo WorkHorse BroadBand Sentinel (600 kHz, Teledyne-RDI). A partir dos dados adquiridos, observou-se a existência de correntes intensas próximo ao fundo (até 1,02 m/s), principalmente durante os períodos de enchente sob condições de sizígia, que são fortemente influenciadas pela orientação do canal de navegação. A análise das séries temporais das componentes da velocidade mostraram, em conformidade ao relatado por alguns autores, que esta é uma baía cuja circulação é fortemente influenciada pela dinâmica da maré sendo M2, M4, M6 e M8 as principais componentes harmônicas que atuam no sistema. Além disso, observou-se significativa assimetria da maré, sendo os períodos de enchente consideravelmente mais curtos e associados às correntes mais intensas, o que permite concluir que no setor investigado da baía de Sepetiba há dominância de enchente. Outra característica interessante da área de estudo relaciona-se à observação de que ventos intensos de S-SO são responsáveis pelo empilhamento de água no interior da baía, sendo que altura do nível da superfície da água apresenta relação direta com as variações da pressão atmosférica local. Em diversos períodos, quando há atuação de ventos de E-NE é possível encontrar Água Central do Atlântico Sul (ACAS) no interior da baía de Sepetiba, desde a sua entrada principal até as adjacências da ilha Guaíba. Além disso, foram identificadas diversas oscilações de baixa frequência que puderam ser associadas à variação da pressão atmosférica. Oscilações de alta frequência foram associadas à dinâmica da maré, a co-oscilações da maré e ao vento. Em relação à concentração de Material Particulado em Suspensão (MPS), durante os períodos de sizígia foram registradas as maiores concentrações material particulado na coluna dágua. Durante os períodos de sizígia, o fluxo de MPS é mais pronunciado do que durante as quadraturas, sendo que, independente do período da maré, o fluxo cumulativo de material particulado em suspensão é dirigido para o interior da baía de Sepetiba. Considerando o alinhamento dos vetores de velocidade em conformidade a direção preferencial do canal de navegação, tem-se que o fluxo cumulativo de MPS varia entre dirigido para SE na região próxima ao fundo, a dirigido para NE próximo ao topo da coluna dágua, o que sugere a deflexão do movimento das correntes em consequência do atrito. Ao longo de um dia, o fluxo do material particulado é mais pronunciado durante as enchentes, quando há aumento das tensões cisalhantes que atuam sobre o leito da baía redisponibilizando para a coluna dágua o material que estava depositado no fundo.

Aplicação de múltiplas ferramentas no estudo do transporte de sedimentos na margem interna da restinga da Marambaia (baía de Sepetiba, RJ)

Dados sedimentológicos e hidrodinâmicos foram utilizados para estudar a dinâmica sedimentar da margem interna da restinga da Marambaia (baía de Sepetiba, Rio de Janeiro, SE Brasil). Foram realizadas três campanhas amostrais para coleta de sedimentos ao longo da restinga da Marambaia e na área submersa adjacente. Adicionalmente, em dezembro de 2013, três fundeios simultâneos para aquisição de dados hidrodinâmicos foram conduzidos paralelamente à restinga, ao longo da profundidade média de 6,5 metros. As medições abrangeram dois ciclos de maré (25 horas), incluindo perfilagem com CTDs, perfilagem correntométrica e coleta de amostras de água para determinação das concentrações do material particulado em suspensão. A partir do processamento das amostras de sedimentos em laboratório, foram obtidos os parâmetros estatísticos (média, desvio-padrão e assimetria) para o detalhamento da caracterização sedimentológica da área de estudo, bem como a aplicação de um modelo de tendência direcional de transporte de sedimentos (GisedTrend). A restinga apresenta areias médias e bem selecionadas, enquanto as amostras coletadas na porção submersa, em profundidades maiores que 2 m, passam de areias finas e bem selecionadas a siltes finos e mal selecionados em maiores profundidades. Quatro casos de tendência de transporte foram explorados em um total de 14 possibilidades e os mais significativos foram analisados com o intuito de identificar áreas de acumulação e remoção de sedimentos, podendo estar associados aos processos responsáveis pelo transporte de sedimentos, tais como correntes geradas pelos ventos locais, marés e dispersão de plumas de sedimentos em suspensão. Os dados hidrodinâmicos, durante o período amostrado, permitiram observar o complexo padrão de circulação existente, especialmente na área adjacente à área central da restinga. Dentre as observações realizadas, verificou-se a ocorrência de assimetria da maré, fato já documentado em trabalhos anteriores conduzidos próximo ao principal canal de acesso à baia, com períodos de enchente mais curtos e períodos de vazante mais longos. Diferentemente do que foi reportado nestes trabalhos, os períodos de vazante foram associados às correntes de maior intensidade. As concentrações de material particulado em suspensão situaram-se, em média, entre 10 e 20 mg/L tanto em superfície como próximo ao fundo; no entanto, suas variações temporais não apresentaram qualquer relação com as fases da maré. Possíveis áreas de convergência e divergência da circulação / células de transporte de sedimentos foram identificadas e comparadas aos vetores de tendência de transporte obtidos através do modelo GisedTrend, com resultados satisfatórios.