Natural cementation affects the properties of soils, the interpretation of in situ and laboratory test results, and the selection of criteria for geotechnical design. In this paper, published experimental studies are reviewed, a microscale analysis is presented of the effect of cementation on small-strain stiffness for distinct stress-cementation histories, and the effect of cementation on small-strain velocity and damping is experimentally studied. Observations include the prevailing effects of cementation over effective stress, the coexistence of frictional and viscous losses, and the effects of decementation when the medium is unloaded from the level of confinement prevailing during cementation.Key words: wave velocity, seismic response, stiffness, damping, sampling effects, loading history.

The practice of soil improvement has received renewed attention in the last two decades. As a result, existing methods were improved and new ones developed. This paper presents a knowledge-based decision support system for the selection of soil improvement methods, Improve. The system uses a knowledge representation structure based on "windows" together with a best-first search algorithm. In this context, windows are mathematical representations of the restrictions to the values variables can take, combining the knowledge and its uncertainty in a unique entity. This form of knowledge representation has many advantages and allows for procedures not available in other systems, such as the development of composite solutions, the use of different evaluation functions, the search for lacunae, and the case-based representation of knowledge.

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ABSTRACT.One of the inversion schemes most employed in seismic tomography processing is least squares and derived algorithms, using as input data the vector of first arrivals. A division of the whole space between sources and receivers is performed, constructing a pixel model with its elements of the same size. Spatial coverage is defined, then, as the sum of traveled length by all rays through every pixel that conform the medium considered. It is related, therefore, with the source-receiver's distribution and the form of the domain among them. In cross-hole array, rays do not evenly sample the properties of the medium, leading to non-uniform spatial coverage. It is known that this affects the inversion process. The purpose of this paper, then, was to study the problem of spatial coverage uniformity to obtain travel path matrices leading to inversion algorithms with better convergence. The medium was divided in elements of different size but with an even spatial coverage (named as 'ipixels'), and then it was explored how this improved the inversion process. A theoretical model was implemented with added noise to emulate real data; and then the vector of measured times was generated with known velocity distribution. Afterwards an inversion method using minimum length solution was performed to test the two domain divisions. The results showed that the fact of using ipixels not only improved the inversion scheme used in all cases; but in addition allowed to get convergence where it was impossible to do using pixels; particularly through the method considered. This is a direct result of the improvement of condition number of the associated matrices.Keywords: seismic tomography, cross-hole, spatial coverage, pixel, ipixel. RESUMEN.Uno de los esquemas de inversión más empleados en el procesamiento de datos de tomografía sísmica es el de mínimos cuadrados y algoritmos relacionados, utilizando el vector de primeros arribos como datos de entrada. Se lleva a cabo una división del dominio completo entre emisores y receptores, con el objeto de diseñar un modelo de píxeles del mismo tamaño. Se define la cobertura espacial como la suma de los tiempos de viaje de todos los rayos en cada uno de los píxeles que conforman el medio. Por lo tanto este parámetro está relacionado con la distribución emisor-receptor y con la forma del dominio entre los mismos. En el dispositivo cross-hole los rayos no muestrean de igual forma al medio, conduciendo a una cobertura espacial no uniforme. Se sabe que este inconveniente afecta el proceso de inversión. El propósito de este artículo fué el de estudiar el problema de la uniformidad de la cobertura espacial a fin de lograr matrices de tiempo de viaje que conduzcan a algoritmos de inversión con mejor convergencia. El medio se dividió en elementos de diferente tamaño pero con cobertura espacial uniforme (denominados 'ipixels'). Se implementó un modelo teórico con ruido a fin de simular datos reales; y el vector de tiempos se calculó con una distribución conocida de velocidades. Luego se probó la...

The Cuba Company was the largest single foreign investment in Cuba during the first two decades of the twentieth century and remained one of the largest corporations. This article presents a detailed history of the commercial networks forged between political officials and North American and Cuban businessmen through the development of the company. These networks proved crucial to the success of the Cuba Company and subsequently shaped the development of the new Cuban Republic.