ANÁLISE DOS POLUENTES ATMOSFÉRICOS NO2 E O3 VIA AMOSTRADORES PASSIVOS DE BAIXO CUSTO

<p><em>O uso de equipamentos que monitorem a concentração de poluentes pode contribuir para prevenção de possíveis danos à saúde humana. Ess</em><em>e trabalho consiste no desenvolvimento de amostradores passivos de baixo custo para a determinação dos poluentes NO₂ e O₃ no campus Alto Paraopeba, através da análise fatorial e superfície de resposta. Os amostradores foram construídos em placas de Petri com filtros de papel contendo diferentes soluções absorvedoras para cada tipo de gás monitorado. Os amostradores de NO₂ foram expostos no refeitório da Universidade e os amostradores de O₃ foram expostos na sala de máquinas fotocopiadoras. Nos amostradores foram usadas diferentes quantidades de solução absorvedora e, também, diferentes tempos de exposição. Os resultados mostraram que a melhor condição para o NO₂ foi obtida com 4,6 mL de solução absorvedora e no tempo de 68 horas de exposição. Nessas condições, a concentração de NO₂ no Restaurante Universitário foi de 10,5 µg/m³. Para o ozônio, as concentrações variaram entre 4,2 µg/m³ e 40 µg/m³, e a melhor condição (3 mL de solução absorvedora e tempo de 77 horas) está localizada no ponto sela e não na região ótima do gráfico. Isso ocorre devido ao fato do ozônio se decompor rapidamente a oxigênio.</em> <em>Os amostradores passivos apresentaram resultados satisfatórios e recomenda-se seu uso como uma alternativa de baixo custo para o monitoramento de NO₂ e O₃ no Restaurante Universitário e sala de Fotocopiadoras. </em></p><p><em>ABSTRACT</em></p><em>The use of equipment that monitors the concentration of pollutants can contribute to the prevention of possible damages to human health. This work is to develop inexpensive passive samplers for the determination of NO₂ and O₃ pollution in the campus Alto Paraopeba beyond the optimization of analytical methods by software that provides a complete environment for data analysis; by factor analysis and response surface generated by it. The samplers were constructed on Petri dishes with paper filter containing different absorbing solutions according to each monitored gas. The samplers were exposed to NO₂ at university restaurant and others samplers were exposed to O₃ at the photocopier room of the campus. In samplers were used different amounts of absorber solution and also different exposure times. The results showed that the best condition for NO₂ was obtained with 4.6 mL of absorbing solution in time of 68 hours exposure. Under these conditions, the concentration of NO₂ in the university restaurant was 10.5 µg/m³. For ozone, the concentrations ranged from 4.2 µg/m³ and 40 µg/m³, and the best condition (3 mL absorbing solution and time of 77 hours) is located at saddle point and not at the optimal region of the graph. This is because ozone has rapidly decomposes to oxygen. Passive samplers presented satisfactory results and it is recommended to use them as a low cost alternative for the monitoring of NO₂ and O₃ in the University Restaurant and Photocopiers room.</em>

A pragmatic approach towards designing a second shutdown system for Tehran research reactor

One second shutdown system is proposed for the Tehran Research Reactor to achieve the goal of higher safety in compliance with current operational requirements and regulations and improve the overall reliability of the reactor shutdown system. The proposed second shutdown system is a diverse, independent shutdown system compared to the existing rod based one that intends to achieve and maintain sub-criticality condition with an enough shutdown margin in many of abnormal situations. It is designed as much as practical based on neutron absorber solution injection into the existing core while the changes and interferences with the existing core structure are kept to a minimum. Core neutronic calculations were performed using MCNPX 2.6.0 and MTR_PC package for the current operational core equipped with the second shutdown system, and one experiment was conducted in the Tehran Research Reactor to test the neutronic calculations. A good agreement was seen between theoretical results and experimental ones. In addition, capability of the second shutdown system in the case of occurrence of design basis accident in the Tehran Research Reactor is demonstrated using PARET program.

Comparison of Carbon-Based Nano Materials as Conductive Fillers for Single Layer Microwave Absorber

In this paper, we have studied the permittivities of E-glass fabric/epoxy composite laminates containing three different types of carbon-based nano conductive fillers such as carbon black (CB), carbon nano fiber (CNF) and multi-wall carbon nano tube (MWNT). The measurements were performed for permittivities at the frequency band of 0.5 GHz ~ 18.0 GHz using a vector network analyzer with a 7 mm coaxial air line. The experimental results show that the complex permittivities of the composites depend strongly on the natures and concentrations of the conductive fillers. The real and imaginary parts of the complex permittivities of the composites were proportional to the filler concentrations. But, depending on the types of fillers and frequency band, the increasing rates of the real and imaginary parts with respect to the filler concentrations were all different. At the frequency of 10 GHz, the rates in the CNF filled composite and the MWNT filled composite were much larger then those of the CB filled composite. Between the CNF filled composite and MWNT filled composite, however, the former showed a little higher increasing rates than the other. These different rates can have great effect on the thickness in designing the single layer microwave absorbers. The effect of the different rates was examined by using Cole-Cole plots; the plot is composed of a single layer absorber solution line and permittivity lines of these three types of composites.

Dithering of absorbers for efficient finite‐difference modeling of viscoelastic wave propagation

Viscoelastic modeling traditionally uses multiple relaxation mechanisms (absorbers) per wave type in each cell of the numerical grid. We show that one absorber per cell suffices when the absorbers of different relaxation frequencies and absorption strengths are dithered in a supercell, i.e., a very small area of several nearby cells. The relaxation frequencies used in a supercell can be preselected to cover the bandwidth required in the modeling and distributed locally in a random manner to minimize numerical scattering. The absorption strengths, however, must be found iteratively to yield an average absorption that matches the desired medium over the bandwidth. We have tested the dithered‐absorber method for modeling a variety of 2-D media using a staggered‐grid finite‐difference scheme. For a uniform medium, our result agrees well with the exact analytic solution. For inhomogeneous models, the dithered‐absorber solution agrees well with the finite‐difference solution computed with five absorbers per cell. The computer time and memory requirements of the dithered‐absorber method are only ≈60% and ≈40% of those with five absorbers per cell. In all cases, random numerical scattering is very small—typically less than similar types of error because of model discretization.

Gas Chromatographic Determination of Micro Amounts of Cyanide Residues in Wines, Distilled Liquors, and Other Alcoholic Beverages

A gas chromatographic method for the determination of cyanide residues in alcoholic beverages has been developed from procedures previously reported for application to water samples. Quantitatively isolating HCN from alcoholic beverages presented difficulties not encountered with aqueous solutions, particularly in the presence of SO2 in the sample. HCN was liberated from the acidified sample by heating at 70°C, flushed into an NaOH absorber solution, converted to cyanogen bromide (CNBr), extracted into diisopropyl ether, chromatographed on a Porapak Q column, and detected by an electron capture detector. SO2 that is present in most wines interfered with the bromination step and caused low recoveries. This interference was eliminated by initially converting any cyanide present in the sample to the stable mercuric cyanide salt and then purging the acidified sample solution of all SO2. The Hg(CN)2 present was then dissociated by adding KI and the analysis proceeded as previously described. Mean recoveries of 80–97 % were obtained for 2–20 μg cyanide from replicate analyses of spiked samples of distilled liquors free of SO2. The relative standard deviations ranged from 6.1 to 11.1%. Mean recoveries of 65 to 91% were obtained in the same range of cyanide from replicate analyses of spiked wine samples known to contain SO2, with relative standard deviations ranging from 0.8 to 10.2%. The limit of detection was 0.2 μg HCN.