Phenomenological model for symmetry breaking in chaotic system

We assume that the energy spectrum of a chaotic system undergoing symmetry breaking transitions can be represented as a superposition of independent level sequences, one increasing on the expense of the others. The relation between the fractional level densities of the sequences and the symmetry breaking interaction is deduced by comparing the asymptotic expression of the level-number variance with the corresponding expression obtained using the perturbation theory. This relation is supported by a comparison with previous numerical calculations. The predictions of the model for the nearest-neighbor-spacing distribution and the spectral rigidity are in agreement with the results of an acoustic resonance experiment.Comment: accepted for publication in Physical Review

Hybrid membrane/PSA processes for CO2/N-2 separation

New integrated schemes combining membrane permeation and pressure swing adsorption (PSA) have been developed for gas separation. By using the membrane as a pre-bulk separation unit and coupling it to the intrinsically dynamic periodic operation of the PSA, the separation performance of the hybrid scheme is enhanced with respect to that of die two stand-alone units. Instead of constant-composition regular feed, the PSA is fed with a mixture which is progressively enriched in the more adsorbed component during the pressurization and high-pressure adsorption steps of the cycle. This results in sharper concentration fronts. The hybrid scheme detailed here has been applied successfully to the bulk separation of an 30:70 mol% CO2/N-2 mixture over activated carbon. Process performance is reported in terms of product recovery and purity at cyclic steady state. Numerical simulations were validated by experimental work on a composite membrane and a laboratory-scale PSA unit. For the examples studied, product purity and recovery for the hybrid process were increased by 23% and 58% for CO2, and by 14% and 5% for N-2, compared to an equivalent stand-alone PSA.publishersversionpublishe

Determination of tetracycline and its major degradation products by liquid chromatography with fluorescence detection

A liquid chromatographic method of tetracycline and its major degradation products on a C8-reversed phase column with acidic mobile phase and fluorescence detection is described. The quantification limit, measured as the amount of sample that gave a signal ten times the peak-to-peak noise of the baseline, was: 0.25 ng for tetracycline (TC) and epitetracycline (ETC), 25 ng for and 4-epianhydrotetracycline (EATC) and 50 ng for anhydrotetracycline (ATC) of injected standard. By means of this liquid chromatography (LC) assay TC, ETC, EATC and ATC as main degradation products of tetracycline, can be separated and determined with good sensitivity and specificity within 15 min.http://www.sciencedirect.com/science/article/B6TGX-43HVHWC-1D/1/9763379e028400de01242a673bd4528

Influência da verticalização na temperatura do ar e tetos verdes para mitigar o efeito térmico na grande Belém.

A capital do Estado do Pará vem mudando a sua paisagem urbanística com a intensificação de edifícios de grande porte. Em Belém, sensações de desconforto térmico são frequentemente associadas ao processo de verticalização e diminuição de suas áreas verdes. Objetivou-se com este trabalho avaliar evidências desses efeitos usando séries históricas de 44 anos de temperatura do ar e dados disponibilizados na literatura sobre a evolução do número de pavimentos de 1878 a 2009. Os resultados indicaram que as temperaturas mínimas se elevaram nos últimos 16 anos, expressas em termos de anomalias quentes, a partir de 1995. A redução das amplitudes térmicas é explicada, cerca de 93%, pela verticalização urbana, indicando a necessidade de estratégias mitigadoras dos efeitos de bolsões de calor, principalmente nos bairros mais verticalizados. A proposta de uso de tetos verdes visa atenuar o aquecimento, ainda que em edifícios altos a relação de área de cobertura pela área envoltória seja mínima, sendo o mais indicado as fachadas verdes. Porém o uso de tetos vegetados não deixa de representar uma ação significativa para potencializar as reduções de ganhos de calor por opaco, redesenhando por meio de uma arquitetura bioclimática a paisagem urbana da grande Belém.PIBIC-2011

THERMODYNAMIC AND THERMOPHYSICAL ASSESSMENT OF HYDROCARBONS APPLICATION IN HOUSEHOULD REFRIGERATOR

The research efforts and development in the refrigeration and air conditioning sector applied to the use of natural refrigeration fluids is not associated only with the need to preserve the environment alone, but has great importance with regard to the latent need for energy efficient equipment. With this perspective, the present study deals with the thermodynamic evaluation of the use of hydrocarbons refrigerants in household refrigeration systems that utilize HFC134a as a working fluid. A theoretical-computational analysis was developed for R134a, propane (R290) and the selected mixtures (R290/R600a 60%/40%, R290/R600a/R134a 40%/30%/30% and R600a/R290 50%/50%) in the standard refrigeration cycle ASHRAE, using the thermodynamic and thermophysical properties provided by the REFPROP 6.0 software. The results of computational simulations between the fluids were compared to find the evidence of the best alternative to HFC134a. In this sense, it was observed that the hydrocarbons reduced the levels of pressure on the condenser and evaporator, along with smaller compression tasks necessary in the system, owing to the thermo-physical properties privileged in these fluids. The use of these fluids is also proportionate to lower temperatures of compressor discharge, increasing the life of this highly valuable component of the system