The objective of this research is to develop a mathematical model that accurately estimates the opacity of sulfur dioxide in a carbon dioxide atmosphere under conditions characteristic of the Venus troposphere based on extensive laboratory measurements. High precision measurements of the millimeter-wavelength properties of sulfur dioxide are being conducted under multiple pressure and temperatures. These measurements are being conducted in both W-band and F-band (2-3 and 3-4 millimeter-wavelengths). The results of this research will significantly improve the understanding of the millimeter-wavelength emission spectrum of Venus and possibly determine the source of variations in the Venus millimeter-wavelength emissions.

We developed radiative transfer models to reproduce Titan’s visible and near infrared spectra, to determine the effects of the haze, and retrieve the methane abundances during Titan’s current southern summer. With ground-based high resolution spectra of CH3D absorption at 1.6 μm, we measured the global CH₃D abundance. Combined with observations of 8.6 μm emission of CH₃D and CH₄ that indicate their relative abundances, we thus determined the global CH₄ abundance. We expanded on these ground-based measurements, with improved radiative transfer models based on the Huygens DISR models, and spectra which resolve the spatial variation of the CH₃D lines. The profiles of CH3D thus obtained revealed that the methane abundance on the lowest 10 km of Titan’s atmosphere does not vary by more than 20% over 32°S-32°N. With the extensive coverage of Cassini VIMS observations at 0.35-1.6 μm, we determined the latitudinal variation of the methane at 20-50 km and of the haze. We find an ambiguity between the methane and haze abundances, so their gradients become coupled. At the lower limit of the methane gradient, the spectral variation observed can be reproduced with no methane change, and a haze density increase of 60% between 20°S and 10°S. The largest methane variation allowed by the data, derived assuming no haze variation with latitude, is a drop of 60% over latitudes 27°S to 19°N. Our analysis indicates that the latitudinal variations in Titan’s visible to near-IR albedo, the North/South Asymmetry, result primarily from variations in the thickness of the haze above 80 km altitude. The range of methane latitudinal variations allowed between 27°S to 19°N indicates temperature variations of no more than 1.5 K at 20-30 km, altitudes where the Huygens profile is saturated.

Advanced research in Controlled/Modified Atmosphere storage systems has shown that open channels of different lengths and cross sectional areas, connected to an air tight storage chamber, are able to maintain variable stable gas concentrations which could be near optimal concentrations for CA/MA storage of various commodities. / This study was geared towards assessing the suitability of the diffusion channels in maintaining a desired gas concentration for CA storage of spinach. Initially, the respiratory behaviour of spinach was studied in gas sealed chambers (replicated four times) stored at four different temperatures, 2$ sp circ$C, 8$ sp circ$C, 15$ sp circ$C and 23$ sp circ$C. The respiration rate of spinach was 20 mgCO$ sb2$/kg.h, 66 mgCO$ sb2$/kg.h, 163 mgCO$ sb2$/kg.h and 271 mgCO$ sb2$/kg.h for 2$ sp circ$C, 8$ sp circ$C, 15$ sp circ$C and 23$ sp circ$C, respectively. A model was developed based on principles of enzymatic kinetics which could reliably predict the respiration rate of spinach at any given storage temperature. / Two other sets of experiments were carried in a cold room set at 2$ sp circ$C. (Abstract shortened by UMI.)

The combined effect of films of various gas barrier properties, various gas packaging atmospheres (air, vacuum and gas packaging, oxygen absorbents) and storage temperatures (4 and 12$ sp circ$C) were investigated on the color stability and shelf-life of fresh beef. Meat color was described by reflectance measurements and by reading the color coordinates L* (lightness), a* (redness), b* (yellowness), C* (chroma) and h (hue angle) in the CIE-LAB system. All packaged beef was regarded as unacceptable when reflectance differences values at 630 and 580 nm i.e., due to oxymyoglobin (MbO$ sb2)$ were $ sim$30-35. Based on these standards, aerobic packaging of beef in polyvinylchloride (PVC) film had a shelf-life of $ sim$5 d and 1 d at 4 and 12$ sp circ$C respectively. Beef packaged in both low gas-moisture barrier films resulted in black discoloration after only 2 d at 4$ sp circ$C due to increased moisture loss. Longer extensions in both color and microbial shelf-life of fresh beef were possible by packaging products under modified atmospheres using high gas barrier Cryovac$ sp circler$ bags. Both vacuum packaging (VP) and vacuum skin packaging (VSP) resulted in a shelf-life of $ sim$35 d at 4$ sp circ$C. Gas packaging using high levels of CO$ sb2$ (100%) in conjunction with Ageless-SS$ sp circler$ oxygen absorbent, delayed discoloration for $ sim$42 d at 4$ sp circ$C. (Abstract shortened by UMI.)

No description available.

Black spot development or "melanosis" is a common defect in fresh shrimp which results in product being devalued and rejected by consumers. Currently, sulfiting agents are used to control melanosis in shrimp. However, with increasing regulatory and consumer concerns about the safety of sulphites as a method of melanosis control, the shrimp processing industry is actively seeking alternative methods to control melanosis on, and extend the shelf life of, fresh shrimp. One method which has the potential to fulfill both objectives is glucose oxidase (GOX)/glucose dipping solutions in conjunction with Modified Atmosphere Packaging (MAP). / Preliminary studies have shown that black spot development can be controlled for 14 days at 4$ sp circ$C in white shrimp (Pandalus occidentalis) and pink shrimp (Pandalus borealis) using GOX/glucose or GOX/glucose/ascorbic acid in conjunction with gas packaging (60% CO$ sb2$: 40% N$ sb2$). This dipping/packaging treatment also improves the physical, chemical and microbiological changes in white shrimp compared to samples dipped only in water and air packaged. This study has shown that the combined use of two or more "barriers" can be used to extend the shelf life of, and control melanosis on, fresh shrimp. This novel process of "dipping" shrimp in GOX/glucose solutions in conjunction with MAP will have a significant effect in the area of shrimp hygiene and will have the potential to minimize shrimp spoilage incurred through melanosis.

Stellar model atmospheres are a fundamental tool for our understanding of stars. Because the chemical composition of stars cannot be measured directly, the inferred stellar parameters are model dependent. In recent years great progress has been made in the modeling of stellar atmospheres, allowing the relaxation of simplifying assumptions made in previous models. The use of new 3D model atmospheres to infer the solar chemical composition has resulted in a decrease of the solar metallicity. This result has caused some controversy and is being challenged. The main aim of this thesis is to ascertain if the new models of stellar atmospheres are realistic and can be trusted to derive the chemical composition of stars in general, and the Sun in particular. Other objectives also include the study of line formation in the Sun at high spatial resolution, and possible implications in the modeling. The Sun is the ideal test-bench for detailed analyses of stellar atmospheres. With the solar surface being resolved in great detail and at different viewing angles, a wealth of information can be gathered that allows for very robust tests of atmosphere models. The testing detailed here addresses several fronts. On one hand, the model�s temperature structure is directly tested with the classical tests of continuum centre-to-limb variations and absolute fluxes. On the other hand, the line formation is tested at different viewing angles and high spatial and spectral resolution. Here the main focus is on oxygen lines, as oxygen has an important contribution for the total solar metallicity. However, other lines are also tested. High quality data were specifically obtained for these line formation tests, using the Swedish 1-m Solar Telescope. For the temperature structure tests we find a surprisingly good agreement between the 3D model and the observations, surpassing even semi-empirical models. The solar 1D non-LTE models have a very similar behaviour to 1D LTE models, confirming that LTE is a good approximation in the solar photosphere. The 3D theoretical model performs consistently better than its 1D counterparts. The oxygen line formation tests are carried out in great detail, with a careful wavelength calibration, revised atomic data, and allowing for departures from LTE. Again we find a reassuring agreement between the 3D model predictions and the observations, both for the centre-to-limb variation of the lines and the line formation at high spatial resolution. The observations at different viewing angles also allowed the empirical determination of the role of hydrogen collisions with oxygen, important when deriving the oxygen abundance. The tests undertaken here show that the 3D model atmospheres are indeed very realistic. Their predicted temperature structure and velocity fields compare very favourably with observations of the Sun. Together with previous tests, this indicates they can be relied upon to derive the chemical composition of the Sun and similar late-type stars.

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Observations of exoplanet transit spectra are essential to understanding the physics and chemistry of distant worlds. The effects of opacity sources and many physical processes combine to set the shape of a transit spectrum. Two such key processes-refraction and cloud and/or haze forward-scattering-have seen substantial recent study. However, models of these processes are typically complex, which prevents their incorporation into observational analyses and standard transit spectrum tools. In this work, we develop analytic expressions that allow for the efficient parameterization of forward-scattering and refraction effects in transit spectra. We derive an effective slant optical depth that includes a correction for forward-scattered light, and present an analytic form of this correction. We validate our correction against a full-physics transit spectrum model that includes scattering, and we explore the extent to which the omission of forward-scattering effects may bias models. Also, we verify a common analytic expression for the location of a refractive boundary, which we express in terms of the maximum pressure probed in a transit spectrum. This expression is designed to be easily incorporated into existing tools, and we discuss how the detection of a refractive boundary could help indicate the background atmospheric composition by constraining the bulk refractivity of the atmosphere. Finally, we show that opacity from Rayleigh scattering and collision-induced absorption will outweigh the effects of refraction for Jupiter-like atmospheres whose equilibrium temperatures are above 400-500 K.

Made available in DSpace on 2014-10-09T12:37:09Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:08:54Z (GMT). No. of bitstreams: 1 04604.pdf: 1479024 bytes, checksum: 7c6ae155b3f6a993e0067537881b8a01 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP