Computer-assisted tomography for studies of an Albaqualf

Na busca de técnicas mais apuradas para a determinação e avaliação de parâmetros físicos do solo com aplicabilidade em várzeas, vem se destacando a tomografia computadorizada, por medir a densidade e a umidade com boa sensibilidade e alta resolução espacial. O presente trabalho teve como objetivo descrever aspectos e procedimentos da calibração de um minitomógrafo de raios-X e gama para estudo da densidade e umidade de um Planossolo no Rio Grande do Sul, bem como estabelecer parâmetros estatísticos para sua adequada utilização. A calibração do minitomógrafo foi obtida pela regressão linear entre as unidades tomográficas (UT), apresentadas pelo programa de reconstrução de imagem, e os coeficientes de atenuação linear (µl, cm-1), medidos por transmissão direta de raios gama, em amostras dos horizontes A e B do Planossolo, água destilada, benzina e alumínio. Para as medidas de transmissão direta de radiação utilizaram-se recipientes com água destilada, benzina, solo e Al, obtendo-se as seguintes fórmulas para o cálculo da densidade do solo no horizonte A: Ds = [(UT/986,16)-(0,200xq)]/0,267; e no horizonte B: Ds = [(UT/986,16)-(0,200xq)]/0,297, em que UT é o valor médio de UT em cada linha e q é a umidade volumétrica da amostra de solo, em m3 m-3. Com as configurações obtidas, verificou-se variabilidade média de 2,74% e 0,73%, respectivamente, em termos de homogeneidade e repetibilidade. Os erros atribuídos ao equipamento são de 0,051 e 0,046 Mg m-3, respectivamente, nos horizontes A e B, revelando precisão e adaptabilidade no emprego da técnica em estudos do Planossolo._________________________________________________________________________________ ABSTRACT: In order to find better techniques to evaluate the soil physical parameters applied to lowland soils, the computerized tomography has been used to measure soil density and water content with accuracy and high spatial resolution. This work was carried out in order to describe features and calibration procedures of a computerized minitomographer using X-ray and gama-rays as sources of radiation and to establish suitable statistical parameters on the study of soil bulk density and water content in a Planosol (Albaqualf) from Rio Grande do Sul State, Brazil. The minitomographer calibration was obtained from the linear regression equation among the tomography's unities (TU) presented by the image reconstruction program and the linear attenuation coefficient (µl, cm-1), by the measurement of direct transmission of g-rays as source of radiation in soil samples from A and B horizons, distilled water, benzin and aluminum. In order to get measures of the direct radiation transmission, containers with distilled water, benzin, soil and aluminum were used to obtain the following equations to calculate soil bulk density in the A horizon: Ds = [(TU/986.16)-(0.200xq)]/0.267 and in the B horizon: Ds = [(TU/986.16)-(0.200xq)]/0.297, where TU is the mean value in the line and q is the soil volumetric water content (m3 m-3). The obtained configurations allowed to attain average variabilities of 2.74% and 0.73% for homogeneity and repeatability, respectively. The expected errors related to the equipment are 0.051 and 0.046 Mg m-3, to the A and B horizons, respectively. The results showed the technique accuracy and adaptability in the studies of the physical characteristics of a Planosol

A Pre-Landing Assessment of Regolith Properties at the InSight Landing Site

This article discusses relevant physical properties of the regolith at the Mars InSight landing site as understood prior to landing of the spacecraft. InSight will land in the northern lowland plains of Mars, close to the equator, where the regolith is estimated to be ≥3--5 m thick. These investigations of physical properties have relied on data collected from Mars orbital measurements, previously collected lander and rover data, results of studies of data and samples from Apollo lunar missions, laboratory measurements on regolith simulants, and theoretical studies. The investigations include changes in properties with depth and temperature. Mechanical properties investigated include density, grain-size distribution, cohesion, and angle of internal friction. Thermophysical properties include thermal inertia, surface emissivity and albedo, thermal conductivity and diffusivity, and specific heat. Regolith elastic properties not only include parameters that control seismic wave velocities in the immediate vicinity of the Insight lander but also coupling of the lander and other potential noise sources to the InSight broadband seismometer. The related properties include Poisson’s ratio, P- and S-wave velocities, Young’s modulus, and seismic attenuation. Finally, mass diffusivity was investigated to estimate gas movements in the regolith driven by atmospheric pressure changes. Physical properties presented here are all to some degree speculative. However, they form a basis for interpretation of the early data to be returned from the InSight mission.Additional co-authors: Nick Teanby and Sharon Keda

Gas Sorption in Clay Mineral Systems

Abstract--Sorption isotherms for four gases (N2, A, Kr and CO2) , commonly used in specific surface area and pore structure measurements, have been accurately determined on a number of clay mineral and oxide systems. Specific surface areas obtained by application of the BET theory to these isotherms illustrate the extent o which the apparent cross-sectional reas for these sorbed gases vary with surface structure, ex-changeable cation and microporosity. V-n plots for nitrogen adsorption on these materials using nitrogen adsorption on crystalline materials of large crystal size as a standard isotherm provide appreciable ranges of linearity in each case. The specific surface areas obtained from these straight line plots agree well with the corresponding BET values. The linearity of these plots for illite clays indicates the absence of capillary condensation and that adsorption in slit-shaped pores takes place largely by the formation of physically adsorbed layers on the surfaces. Much larger BET specific surface areas were obtained from carbon dioxide sorption at 196K on goethite, hematite and gibbsite than from nitrogen, argon and krypton sorption at 78"K. It is suggested that enhanced sorption of CO2 into microporous regions of the oxides, inaccessible to the other gases, occurs in a similar fashion to that frequently observed for coal and charcoal materials. V-n plots for CO2 sorption in these materials using that for an illite clay as a standard isotherm, support his conclusion. Considerably ower BET specific surface areas were obtained for CO 2 sorption on kaolinite than were obtained for nitrogen, argon and krypton sorption. The shape of the V-n plots for CO., sorption on kao-linite compared with illite suggest hat an initial specific adsorption of CO2 on the kaolinite is followed by a change in state with the completion of this layer, allowing normal multilayer formation to proceed