Gain and noise spectral density in an electronic parametric amplifier with added white noise

In this paper, we discuss the behavior of a linear classical parametric amplifier (PA) in the presence of white noise and give theoretical estimates of the noise spectral density based on approximate Green's functions obtained by using averaging techniques. Furthermore, we give analytical estimates for parametric amplification bandwidth of the amplifier and for the noisy precursors to instability. To validate our theory we compare the analytical results with experimental data obtained in an analog circuit. We describe the implementation details and the setup used in the experimental study of the amplifier. Near the threshold to the first parametric instability, and in degenerate-mode amplification, the PA achieved very high gains in a very narrow bandwidth centered on its resonance frequency. In quasi-degenerate mode amplification, we obtained lower values of gain, but with a wider bandwidth that is tunable. The experimental data were accurately described by the predictions of the model. Moreover, we noticed spectral components in the output signal of the amplifier which are due to noise precursors of instability. The position, width, and magnitude of these components are in agreement with the noise spectral density obtained by the theory proposed here

Heating and thermal squeezing in parametrically-driven oscillators with added noise

In this paper we report a theoretical model based on Green functions, Floquet theory and averaging techniques up to second order that describes the dynamics of parametrically-driven oscillators with added thermal noise. Quantitative estimates for heating and quadrature thermal noise squeezing near and below the transition line of the first parametric instability zone of the oscillator are given. Furthermore, we give an intuitive explanation as to why heating and thermal squeezing occur. For small amplitudes of the parametric pump the Floquet multipliers are complex conjugate of each other with a constant magnitude. As the pump amplitude is increased past a threshold value in the stable zone near the first parametric instability, the two Floquet multipliers become real and have different magnitudes. This creates two different effective dissipation rates (one smaller and the other larger than the real dissipation rate) along the stable manifolds of the first-return Poincare map. We also show that the statistical average of the input power due to thermal noise is constant and independent of the pump amplitude and frequency. The combination of these effects cause most of heating and thermal squeezing. Very good agreement between analytical and numerical estimates of the thermal fluctuations is achieved.Comment: Submitted to Phys. Rev. E, 29 pages, 12 figures. arXiv admin note: substantial text overlap with arXiv:1108.484

Amplification in parametrically-driven resonators near instability based on Floquet theory and Green's functions

Here we use Floquet theory to calculate the response of parametrically-driven time-periodic systems near the onset of parametric instability to an added external ac signal or white noise. We provide new estimates, based on the Green's function method, for the response of the system in the frequency domain. Furthermore, we write novel expressions for the power and the noise spectral densities. We validate our theoretical results by comparing our predictions for the specific cases of a single degree of freedom parametric amplifier and of the parametric amplifier coupled to a harmonic oscillator with the numerical integration results and with analytical approximate results obtained via the averaging method up to second order.Comment: 19 pages, 4 figure

Signal to noise ratio in parametrically-driven oscillators

Here we report a theoretical model based on Green's functions and averaging techniques that gives ana- lytical estimates to the signal to noise ratio (SNR) near the first parametric instability zone in parametrically- driven oscillators in the presence of added ac drive and added thermal noise. The signal term is given by the response of the parametrically-driven oscillator to the added ac drive, while the noise term has two dif- ferent measures: one is dc and the other is ac. The dc measure of noise is given by a time-average of the statistically-averaged fluctuations of the position of the parametric oscillator due to thermal noise. The ac measure of noise is given by the amplitude of the statistically-averaged fluctuations at the frequency of the parametric pump. We observe a strong dependence of the SNR on the phase between the external drive and the parametric pump, for some range of the phase there is a high SNR, while for other values of phase the SNR remains flat or decreases with increasing pump amplitude. Very good agreement between analytical estimates and numerical results is achieved.Comment: Submitted to Phys. Rev.

MÉTRICAS DA PAISAGEM NA CARACTERIZAÇÃO DA EVOLUÇÃO DA OCUPAÇÃO DA AMAZÔNIA

Land use and land cover change in the tropics has severe impact on the environment. Landscape metrics had been used for land use and land cover change characterization. This work had the objective of characterizing the evolution of the landscape of an area of the center-eastern of the State of Pará, from 1973 to 1997, based on landscape metrics calculated by using a specific software. A drastic decrease of the forest area was observed, accompanied by a significant increase of the pasture areas. The number of patches of the study area increased, while the medium size of the patches of the landscape decreased. The edge density also presented a great increase. The average distance between nearest neighbors did not vary much for the forest class along the years, however, it was observed a decrease in the average distance between pasture patches. Only 5% of the forest area were located over 500 m far from a border, in 1997, what indicates an intense degradation of the forest in the studied area. Key words: Landscape Ecology, Land Use and Land Cover Change, Amazonia, Remote Sensing.As mudanças de uso e cobertura da terra nos trópicos resultam em vários impactos sobre o meio-ambiente. Uma forma de caracterizar mudanças de uso e cobertura da terra é utilizando-se métricas da paisagem. Este trabalho teve como objetivo caracterizar a evolução da paisagem de uma área do centro-leste do Estado do Pará, no período de 1973 a 1997, utilizado-se métricas da paisagem calculadas através de software específico. Observou-se uma diminuição drástica da área de floresta, acompanhada por um aumento significativo das áreas de pastagem. O número de manchas da área de estudo aumentou, enquanto que o tamanho médio das manchas da paisagem diminuiu. A densidade de bordas também apresentou um grande aumento. A distância média entre vizinhos mais próximos, ao longo dos anos, não apresentou uma grande variação para a classe floresta, tendo sido, contudo, observada uma diminuição da distância média entre as manchas de pasto no período estudado. Apenas 5% da área de floresta encontrava-se a mais de 500 m de uma borda, no ano de 1997, o que implica numa intensa degradação da floresta na área estudada. Palavras chave: Ecologia da Paisagem, Mudança de Uso e Cobertura da Terra, Amazônia, Sensoriamento Remoto

Brazilian Federal District cocaine chemical profiling : mass balance approach and new adulterant routinely quantified (Aminopyrine)

From a set of 159 samples seized by Brazilian Federal police between 2010 to 2013 in the Federal District, the major component chemical profiling routine analyses revealed the presence of cocaine with purity range of 5.5 to 99.9% (mean 69.8%). Most cocaine base samples show moderately and not oxidized levels, whereas cocaine hydrochloride samples exhibit moderate to high oxidation degrees. More than 40% of the analyzed samples did not have any adulterant. Phenacetin was the most abundant adulterant (24% average purity). Aminopyrine, a new adulterant, was identified and quantified only in cocaine base samples, mainly as a trace adulterant but also as a major compound. In most samples adulterated with aminopyrine, phenacetin was also identified as a major adulterant, suggesting a possible association of the two pharmaceuticals in the cutting process. Aminopyrine was not detected in 2010 seizures, but became a common adulterant throughout the years of 2011 to 2013. A mass balance approach analysis also established that adulterants are responsible for only 12% of the mass of all seizures (i.e., 84 kg), whereas 77% (i.e., 553 kg) is due to alkaloids (cocaine and cis/trans-cinnamoylcocaine), contributing to provide forensic intelligence information to police investigators

Sources, background and enrichment of lead and other elements: Lower Guadiana River

The lower sector of the Guadiana River Basin, located in southern Portugal and Spain, hosts soils and plants with elevated Pb, Cu and As near former and current mining sites. Two geogenic and two anthropogenic sources of Pb were identified where elevated concentrations are mostly related to the occurrence of sulphide-rich ore deposits, Volcanic Sedimentary formations and mining. These were generally reflected by the multiple regression analysis (MRA) and confirmed by isotope determinations. Nevertheless, caution was needed in interpreting statistical and isotopic results; therefore the combination of both techniques was important. Elements, such as Ca, Na, Cu and As, show enrichment in soil developed on shale, sandstone and conglomerate of Upper Devonian age belonging to the Phyllite-Quartzite Group. Lead exhibits an enrichment in soil developed on felsic volcanic rocks from the Volcanic Sedimentary Complex (VSC) of Upper Devonian-Lower Carboniferous age, which has been identified by the relationship between topsoil median values of different lithologies and grand subsoil median values. In the same soil, Fe, As, Co, Ni and Cr are depleted. Translocation of Pb to the aerial parts of plants is insignificant in all three plant species studied and analysed (Cistus ladanifer L., Thymus vulgaris, Lavandula luisieri). High Pb concentrations in soil, where Cistus ladanifer L. developed, the only representative number of species analysed, do not correspond generally to elevated Pb contents in plants, except near mine sites, where lower pH of soil, increases Pb bioavailability. The different statistical methodologies combined with Pb isotopic studies were successfully applied in the identification of Pb sources in soil and Cistus ladanifer L. plant of the Lower sector of Guadiana River basin. Therefore, rocks, mineralisations, subsoil, topsoil and plant processes were successfully integrated to understand the migration of Pb into the food chai