Aside from its significance in establishing the impact-mass extinction paradigm, the Chicxulub crater will probably come to exemplify the structure of large complex craters. Much of Chicxulub’s structure may be ‘mapped’ by tying its gravity expression to seismic-reflection profiles revealing an ∼180 km diameter for the now-buried crater. The distribution of karst topography aids in outlining the peripheral crater structure as also revealed by the horizontal gradient of the gravity anomaly. The fracturing inferred to control groundwater flow is apparently related to subsidence of the crater fill. Modelling the crater’s gravity expression based on a schematic structural model reveals that the crater fill is also responsible for the majority of the negative anomaly. The crater’s melt sheet and central structural uplift are the other significant contributors to its gravity expression. The Chicxulub impact released ∼1.2 × 10 ³¹ ergs based on the observed collapsed disruption cavity of ∼86 km diameter reconstructed to an apparent disruption cavity ( D _ad ) of ∼94 km diameter (equivalent to the excavation cavity) and an apparent transient cavity ( D _at ) of ∼80 km diameter. This impact energy, together with the observed ∼2 × 10 ¹¹ g global Ir fluence in the Cretaceous-Tertiary (K-T) fireball layer indicates that the impactor was a comet estimated as massing ∼1.8 × 10 ¹⁸ g of ∼16.5 km diameter assuming a 0.6 gcm ⁻³ density. Dust-induced darkness and cold, wind, giant waves, thermal pulses from the impact fireball and re-entering ejecta, acid rain, ozone-layer depletion, cooling from stratospheric aerosols, H ₂ O greenhouse, CO ₂ greenhouse, poisons and mutagens, and oscillatory climate have been proposed as deleterious environmental effects of the Chicxulub impact with durations ranging from a few minutes to a million years. This succession of effects defines a temperature curve that is characteristic of large impacts. Although some patterns may be recognized in the K-T extinctions, and the survivorship rules changed across the boundary, relating specific environmental effects to species’ extinctions is not yet possible. Geochemical records across the boundary support the occurrence a prompt thermal pulse, acid rain and a ∼5000 year-long greenhouse. The period of extinctions seems to extend into the earliest Tertiary.

Electrical Capacitance Tomography (ECT) is a novel technology that can deal with the complexity of two-phase gas-oil flow measurement by explicitly deriving the component distributions on two adjacent planes along a pipeline. One of its most promising applications is the visualization of gas-oil flows. ECT offers some advantages over other tomography modalities, such as no radiation, rapid response, low-cost, being non-intrusive and non-invasive, and the ability to withstand high temperature and high pressure. The linear back-projection (LBP) algorithm is one of the most popular methods employed to perform image reconstruction in ECT. Despite its relatively poor accuracy, it is a simple and fast procedure capable of real-time operation in many applications, and it has remained a very popular choice. However, since it was first reported it has lacked a clear formal support in the context of this application. Its only justification has been that it was an adaptation of a method normally used in linear X-ray medical tomography, and the fact that it actually does produce useful (albeit only 'qualitative') images. In this paper, one illustrative way of interpreting LBP is presented. It is shown how LBP is actually based on the linearisation of a normalised form of the forward problem. More specifically, the normalised forward problem is approximated by means of a series of hyper-planes. Thereconstruction matrix used in LBP is found to be a ‘weighted’ transpose of the linear operator (matrix) that defines the linearised normalised forward problem. The rows of this latter matrix contain the information of the sensitivity maps used in LBP. La Tomografía de Capacitancia Eléctrica (TCE) es una nueva tecnología capaz de lidiar con la complejidad de la medición de flujos bifásicos de gas-aceite, derivando la distribución de componentes en dos planos adyacentes a lo largo de un ducto. Una de sus aplicaciones más prometedoras es la visualización de flujos de gas y aceite. TCE ofrece algunas ventajas sobre otras modalidades tomográficas: no hay radiación, una respuesta rápida, bajo costo, es una técnica no intrusiva y no invasiva, y la posibilidad de operar con altas temperaturas y altas presiones. El método denominado "linear back-projection (LBP)" es una de las técnicas más populares que se emplean en la reconstrucción de imágenes a partir de datos de tomografía de capacitancia eléctrica. A pesar de su pobre exactitud, es un procedimiento simple y rápido capaz de operar en tiempo real en muchas aplicaciones y ha permanecido como una opción muy popular. Sin embargo, desde que fue propuesto por vez primera ha carecido de un suporte formal, en el contexto de esta aplicación. Su única justificación radica en que es una adaptación de un método comúnmente empleado en la tomografía médica de rayos X, así como en el hecho de que produce imágenes útiles (aunque sólo "cualitativamente" buenas). En este trabajo se presenta una forma ilustrativa de interpretar el método LBP. Se muestra cómo el método LBP está basado en la linealización de una forma normalizada del problema directo. Más específicamente, el problema directo normalizado se aproxima mediante una serie de hiperplanos. La matriz de reconstrucción utilizada en el método LBP resulta ser una transpuesta "ponderada" del operador lineal (matriz) que define el problema directo normalizado. Los renglones de esta última matriz contienen la información de los mapas de sensitividades empleados en el método LBP.