Мобильные установки для ручной и механизированной лазерной сварки и обработки металлов (Обзор)

Представлен обзор мобильных установок для ручной и механизированной лазерной сварки и обработки конструкционных металлов. Даны описания и краткие технические характеристики установки для очистки металлических поверхностей от краски и других загрязнений, переносных аппаратов для механизированной лазерной сварки стыковых и нахлесточных соединений, установки дл лазерной обработки и наплавки.The paper presents a review of mobile units for manual and mechanized laser welding and treatment of metals. Description and brief specification of a unit for cleaning metallic surfaces from paint and other contamination, portable units for mechanized laser welding of butt and overlap joints and of a laser surfacing unit are given

La sédimentation lacustre indicateur de changements des paléoenvironnements au cours des 30 000 dernières années (Carajas, Amazonie, Brésil)

Les résultats de l'analyse par spectrométrie infrarouge des échantillons de deux carottes prélevées dans deux dépressions marécageuses de la Serra Sul dos Carajas (Amazonie Orientale), mettent en évidence cinq grandes étapes paléohydrologiques au cours des 30 000 dernières années. La comparaison avec les résultats de la palynologie permet de mieux comprendre l'impact de changements climatiques brefs sur les paléoenvironnements. (Résumé d'auteur

Impact of pre-Columbian 'geoglyph' builders on Amazonian forests

Over 450 pre-Columbian (pre-AD1492) geometric ditched enclosures ('geoglyphs') occupy ca. 13,000 km2 of Acre state, Brazil, representing a key discovery of Amazonian archaeology. These huge earthworks were concealed for centuries under terra firme (upland interfluvial) rainforest, directly challenging the 'pristine' status of this ecosystem and its perceived vulnerability to human impacts. We reconstruct the environmental context of geoglyph construction and the nature, extent and legacy of associated human impacts. We show that bamboo forest dominated the region for ≥6000 y and that only small, temporary clearings were made to build the geoglyphs; however, construction occurred within anthropogenic forest that had been actively managed for millennia. In the absence of widespread deforestation, exploitation of forest products shaped a largely forested landscape that survived intact until the late 20th century

The origin and composition of carbonatite-derived carbonate-bearing fluorapatite deposits

Carbonate-bearing fluorapatite rocks occur at over 30 globally distributed carbonatite complexes and represent a substantial potential supply of phosphorus for the fertiliser industry. However, the process(es) involved in forming carbonate-bearing fluorapatite at some carbonatites remain equivocal, with both hydrothermal and weathering mechanisms inferred. In this contribution, we compare the paragenesis and trace element contents of carbonate-bearing fluorapatite rocks from the Kovdor, Sokli, Bukusu, Catalão I and Glenover carbonatites in order to further understand their origin, as well as to comment upon the concentration of elements that may be deleterious to fertiliser production. The paragenesis of apatite from each deposit is broadly equivalent, comprising residual magmatic grains overgrown by several different stages of carbonate-bearing fluorapatite. The first forms epitactic overgrowths on residual magmatic grains, followed by the formation of massive apatite which, in turn, is cross-cut by late euhedral and colloform apatite generations. Compositionally, the paragenetic sequence corresponds to a substantial decrease in the concentration of rare earth elements (REE), Sr, Na and Th, with an increase in U and Cd. The carbonate-bearing fluorapatite exhibits a negative Ce anomaly, attributed to oxic conditions in a surficial environment and, in combination with the textural and compositional commonality, supports a weathering origin for these rocks. Carbonate-bearing fluorapatite has Th contents which are several orders of magnitude lower than magmatic apatite grains, potentially making such apatite a more environmentally attractive feedstock for the fertiliser industry. Uranium and cadmium contents are higher in carbonate-bearing fluorapatite than magmatic carbonatite apatite, but are much lower than most marine phosphorites

Journal of Geochemical Exploration

Texto completo. Acesso restrito. p. 133-147Geochemical and petrological studies were carried out in two Brazilian tropical areas. At the Cu prospect of ‘Chapada Grande’, under a wet savanna climate, the upper part of a lateritic profile with a partially eroded Fe crust was investigated. In the ‘Vale do Paramirim’, under a dry savanna climate, in an area of Pb-Zn-(Cu) anomalies, lateritic soils with an underlying stone-line change laterally into sandy leached soils. In both cases, there exists a good lithodependence upon the fresh parent rock of all the weathered material. At Chapada, there is a strong bonding between Fe-oxyhydroxides and Cu. In soils above the crust, Fe-oxyhydroxides are mainly in the coarse granulometric fraction (>1 mm) in the form of Fe nodules whereas, in slopes soils without underlying crus, Fe-oxyhydroxides are mainly in the fine fraction (<105 μm). In the Vale do Paramirim, the lateral leaching of Fe and clays is accompanied by a strong diminution of the Pb-Zn-Cu content of the surface horizons and by an alteration of the correlations between these elements. In lateritic soils Cu and Zn are correlated but both elements present a very weak correlation with Pb; on the other hand, in sandy soils the correlation between the three elements are identically weak. With respect to geochemical prospecting, the study shows that sampling and data interpretation methods might be adapted to the soil type in the prospected environment. In both cases, the grouping of the data by classes of soils defined according to surface features (such as colour or the presence of coarse particules) is highly recommended before any statistical treatment is undertaken.Salvado