RESUMO

Land surface temperature (LST) seems to be related to the temperature of shallow aquifers and the unsaturated zone thickness (∆Zuz). That relationship is valid when the study area fulfils certain characteristics: a) there should be no downward moisture fluxes in an unsaturated zone, b) the soil composition in terms of both, the different horizon materials and their corresponding thermal and hydraulic properties, must be as homogeneous and isotropic as possible, c) flat and regular topography, and d) steady state groundwater temperature with a spatially homogeneous temperature distribution. A night time Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) image and temperature field measurements are used to test the validity of the relationship between LST and ∆Zuz at the Pampa del Tamarugal, which is located in the Atacama Desert (Chile) and meets the above required conditions. The results indicate that there is a relation between the land surface temperature and the unsaturated zone thickness in the study area. Moreover, the field measurements of soil temperature indicate that shallow aquifers dampen both the daily and the seasonal amplitude of the temperature oscillation generated by the local climate conditions. Despite empirically observing the relationship between the LST and ∆Zuz in the study zone, such a relationship cannot be applied to directly estimate ∆Zuz using temperatures from nighttime thermal satellite images. To this end, it is necessary to consider the soil thermal properties, the soil surface roughness and the unseen water and moisture fluxes (e.g., capillarity and evaporation) that typically occur in the subsurface.

RESUMO

Seabird excrements (guano) have been preserved in the arid climate of Northern Chile since at least the Pliocene. The deposits of marine organic material in coastal areas potentially open a window into the present and past composition of the coastal ocean and its food web. We use the stable isotope composition of nitrogen and carbon as well as element contents to compare the principal prey of the birds, the Peruvian anchovy, with the composition of modern guano. We also investigate the impact of diagenetic changes on the isotopic composition and elemental contents of the pure ornithogenic sediments, starting with modern stratified deposits and extending to fossil guano. Where possible, 14C systematics is used for age information. The nitrogen and carbon isotopic composition of the marine prey (Peruvian anchovy) of the birds is complex as it shows strong systematic variations with latitude. The detailed study of a modern profile that represents a few years of guano deposition up to present reveals systematic changes in nitrogen and carbon isotopic composition towards heavier values that increase with age, i.e. depth. Only the uppermost, youngest layers of modern guano show compositional affinity to the prey of the birds. In the profile, the simultaneous loss of nitrogen and carbon occurs by degassing, and non-volatile elements like phosphorous and calcium are passively enriched in the residual guano. Fossil guano deposits are very low in nitrogen and low in carbon contents, and show very heavy nitrogen isotopic compositions. One result of the study is that the use of guano for tracing nitrogen and carbon isotopic and elemental composition in the marine food web of the birds is restricted to fresh material. Despite systematic changes during diagenesis, there is little promise to retrieve reliable values of marine nitrogen and carbon signatures from older guano. However, the changes in isotopic composition from primary marine nitrogen isotopic signatures towards very heavy values generate a compositionally unique material. These compositions trace the presence of guano in natural ecosystems and its use as fertilizer in present and past agriculture.

Assuntos

RESUMO

Laguna Tuyajto is a small, shallow saline water lake in the Andean Altiplano of northern Chile. In the eastern side it is fed by springs that discharge groundwater of the nearby volcanic aquifers. The area is arid: rainfall does not exceed 200mm/year in the rainiest parts. The stable isotopic content of spring water shows that the recharge is originated mainly from winter rain, snow melt, and to a lesser extent from some short and intense sporadic rainfall events. Most of the spring water outflowing in the northern side of Laguna Tuyajto is recharged in the Tuyajto volcano. Most of the spring water in the eastern side and groundwater are recharged at higher elevations, in the rims of the nearby endorheic basins of Pampa Colorada and Pampa Las Tecas to the East. The presence of tritium in some deep wells in Pampa Colorada and Pampa Las Tecas indicates recent recharge. Gas emission in recent volcanoes increase the sulfate content of atmospheric deposition and this is reflected in local groundwater. The chemical composition and concentration of spring waters are the result of meteoric water evapo-concentration, water-rock interaction, and mainly the dissolution of old and buried evaporitic deposits. Groundwater flow is mostly shallow due to a low permeability ignimbrite layer of regional extent, which also hinders brine spreading below and around the lake. High deep temperatures near the recent Tuyajto volcano explain the high dissolved silica contents and the δ(18)O shift to heavier values found in some of the spring waters. Laguna Tuyajto is a terminal lake where salts cumulate, mostly halite, but some brine transfer to the Salar de Aguas Calientes-3 cannot be excluded. The hydrogeological behavior of Laguna Tuyajto constitutes a model to understand the functioning of many other similar basins in other areas in the Andean Altiplano.

RESUMO

OBJECTIVE: The current cervical disc arthroplasty is limited by postoperative facet joint arthritis, heterotopic ossification and segmental kyphosis. The total Frisbee disc, which has an upper convex/concave non-spherical surface and a lower flat sliding surface, is a new approach for improved outcomes. Prior to clinical application, safety and suitability tests are required. METHODS: The Frisbee is the first 3rd generation disc according to a new classification of total disc because it can precisely mimic the segmental ROM, including the soft limitation of axial rotation. The ISO 18192-1 test was carried out to determine the rate of wear debris. A FE model was used to assess the safety of prosthetic components. In the sagittal plane several variables to determine the most favorable lordotic angle were evaluated. RESULTS: Two angled prosthetic plates are safer than one sliding angled core to prevent the displacement. The lordosis of 7° of the Frisbee leads to kyphosis of no more than 2° without reduction of the ROM. The wear rate of the Frisbee is five times smaller compared to an FDA-approved disc with a spherical sliding surface. CONCLUSIONS: Based on the test results, the clinical application of Frisbee can now be studied. The postoperative kyphosis observed with other devices is not an issue with the Frisbee design. Physiological ROM is combined with the significant reduction of wear debris. For these reasons the Frisbee has the potential to provide a better balanced segmental loading reducing the degeneration of the joint surface and heterotopic ossification. .

OBJETIVO: A atual artroplastia de disco cervical é limitada pela artrite facetária pós-operatória, pela ossificação heterotópica e pela cifose segmentar. O disco Frisbee total, que tem face superior não-esférica convexo-côncava e face inferior plana e deslizante, é uma nova modalidade para melhores resultados. Antes da aplicação clínica, são necessários testes de segurança e adequação. MÉTODOS: O Frisbee é o primeiro disco de 3ª geração, de acordo com uma nova classificação de disco total, pois pode imitar precisamente a AM segmentar, incluindo a limitação suave da rotação axial. O teste ISO 18192-1 foi realizado para determinar a taxa de resíduos de desgaste. Um modelo de FE foi utilizado para avaliar a segurança dos componentes protéticos. No plano sagital, foram avaliadas diversas variáveis para determinar o ângulo de lordose mais favorável. RESULTADOS: Duas placas protéticas anguladas são mais seguras para evitar o deslocamento do que um núcleo angulado deslizante. A lordose de 7° do Frisbee leva a uma cifose de não mais de 2°, sem redução da AM. A taxa de desgaste do Frisbee é cinco vezes menor em comparação com um disco aprovado pela FDA, com superfície de deslizamento esférica. CONCLUSÕES: Com base nos resultados dos testes, a aplicação clínica do Frisbee pode, agora, ser estudada. A cifose pós-operatória, observada com outras próteses não constitui problema com o desenho do Frisbee. A AM fisiológica é combinada com a redução significativa dos detritos de desgaste. Por essas razões o Frisbee tem o potencial de fornecer uma carga segmentar mais equilibrada, reduzindo a degeneração da face articular e a ossi...

OBJETIVO: La actual artroplastia de disco cervical es limitada por la artritis facetaria posoperatoria, por la osificación heterotópica y por la cifosis segmentaria. El disco Frisbee total, que tiene faz superior no esférica, convexo-cóncava e faz interior plana y deslizante, es una nueva modalidad para mejores resultados. Antes de la aplicación clínica, se necesita de pruebas de seguridad y adecuación. MÉTODOS: El Frisbee es el primer disco de la tercera generación, de acuerdo con una nueva clasificación de disco total, pues puede imitar, con precisión, la AM segmentaria, incluyendo la limitación suave de la rotación axial. La prueba ISO 18192-1 fue realizada para determinar la tasa de residuos de desgaste. Un modelo de FE fue utilizado para evaluar la seguridad de los componentes protéticos. En el plano sagital, se evaluaron diversas variables para determinar el ángulo más favorable de lordosis. RESULTADOS: Dos placas protéticas anguladas son más seguras, para evitar el desplazamiento, que un núcleo angulado deslizante. La lordosis de 7mo del Frisbee lleva a una cifosis de no más de 2do, sin reducción de la AM. La tasa de desgaste del Frisbee es cinco veces menor en comparación con un disco aprobado por la FDA, con superficie esférica de deslizamiento. CONCLUSIONES: Con base en los resultados de las pruebas, la aplicación clínica del Frisbee puede ser estudiada en la actualidad. La cifosis posoperatoria, observada con otras prótesis, no es un problema con el diseño del Frisbee. La AM fisiológica se combina con la reducción significativa de los detritos de desgaste. Por esas razones, el Frisbee tiene el potencial para suministrar una carga segmentaria más equilibrada, reduciendo la degeneración de la fase articular y la osificación heterotópica. .

Assuntos