Transmitting boundaries: A comparison

The use of discrete models for the dynamic analysis of a contiuum requires the existence of a finite domain with well defined boundaries. When these boundaries do not exist naturally but have to be artificially imposed it may be necessary to apply appropriate conditions on forces or displacements at the boundary nodes to reproduce the physical behaviour of the actual problem. In the solution of soil structure interaction problems these conditions are simulated through the use of transmitting boundaries. In this paper several of these boundaries are evaluated comparing the results they produce in the amplification of seismic motions, the determination of foundation stiffnesses and the structural response. The distance of the boundaries to the zone of interest, the level of excitation (influencing the amount of internal soil damping), the geometry of the problem (finite soil layer versus a half-space) and the relative frequency of the structure with respect to the soil and the specified motion are all parameters which must be taken into account for this evaluation.     

Stratigraphie séquentielle du Carbonifère inférieur du Haut Atlas central et des Jebilet (Maroc): un exemple de bassins à turbidites contrôlées par la tectonique

Marine deposits of Visean age are well exposed in the Marrakesh area. Two third order sequences are identified in the central High Atlas and Jebilet: SA, which is of Middle Visean age (CM); SB of Upper Visean age (Cf6αβγ); and a complex with olistoliths of Upper Visean-Lower Namurian age (Cf6δ-Cf7). The SA and SIB sequences consist of a relative low-lying system tract with turbidites, a retrograde transgressive system tract and a prograde high-lying system tract. The relative low level comprises a turbiditic fan fed by tectonic uplift, which does not strictly coincide with eustatic processes. The transgressive system tract retrogrades firstly on the slope during tectonic reactivation with slumps, channels and silty levees, secondly on the shelf edge with a mixture of turbiditic and storm deposits and finally on the shelf with storm deposits and reef building. The high level system tract progrades on the shelf by a delta fan. This model is similar to sequences described in Spain and Italy by Mutti (1992), where tectonism is dominant.Nevertheless, eustasy, as described by Vail et al. (1977) played a part, since the same sequences are found in the chart of Ross and Ross (1987): S1, which of Middle Visean age (Cf5) and S2 which is of Upper Visean age (Cf6αβγ). Only the comparison between regional sequences described in Morocco and the sequences of the European platform allow tectonics and eustasy to be taken into consideration.     

Combating Desertification,is it always possible? The case of small Egyptian farmers

This paper briefly presents the current state of land degradation in Egypt and then discusses the socio-economical and institutional aspects that are relevant to the problem and have bearings on possibilities of sustaining agricultural development efforts.     

ON MOBILE ELEMENT TRANSPORT IN HEATED ABEE

Seven trace elements (Ag, Co, Cs, Ga, In, Te, Tl) are either completely retained or are lost to the same extent in Abee samples heated at 700 °C for one week at 10^?5-10^?3 atm Ne or in 10^?5 atm H₂. Bi and Se are lost significantly more easily and Zn is better retained in samples heated in Ne than in H₂. Zn retention varies inversely with ambient Ne pressure. Mobile element transport seems unaffected by physical interactions in the gas phase but may reflect solid-state surface effects. During week-long heating at low pressures (initially ～ 10^?5 atm H₂) S is mobilized only at 1000 °C while C contents decrease progressively from 600–1000 °C. Apparent activation energies for C are 60 kcal/mole below 700 °C and 16 kcal/mole above this temperature suggesting diffusive loss from different hosts and/or processes over different temperature intervals. In E4–6 chondrites C and S contents largely reflect nebular fractionation and condensation processes.     

Hydrocarbon-generating potential of the Eocene Thebes Formation,Gulf of Suez: 1D basin modeling as a supplementary tool for source rock evaluation

The present work provides high-resolution modeling of the thermal maturation of the Eocene Thebes Formation using a multi-1D approach. The model focuses not solely on the thermal maturity but also on timing of hydrocarbon generation (primary generation and secondary cracking), adsorption by organic matter, and expulsion. The time-lapse conceptual model was developed using well log data, geochemical analyses, and composite logs. The stratigraphic sequence of the Belayim Marine oil field was subdivided into a time series based on the tectonic framework of the Gulf of Suez. An elevated basal heat flow has been assigned throughout the rifting phases and basin evolution. The simulation developed for seven wells reveals variations in burial, thermal history, and accordingly the thermal maturity. The predicted thermal maturity ranges from immature to mature with a different tendency to generate hydrocarbons (both primary generation of oil and/or gas secondary cracking) dependent on kerogen type, basin development, and burial history. Hydrocarbon generation (oil) starts after the Messinian Time Event during the deposition of the Post-Zeit Formation. Hydrocarbon generation was related to burial rather than basin evolution for the 113-M-27, BM-23, BM-65, and BM-70 wells. Conversely, generation correlated principally to basin development particularly Messinian Time Event for the 113-M-34 well. Expulsion occurred subsequent to generation of thermogenic gas (secondary cracking of generated oil). It is not possible to investigate the relationship between the production index and thermal maturity as a consequence of expulsion that reduced the S1 values. The different levels of thermal maturity (potential, active, and effective source rock) allow for the differentiation of regions of potential hydrocarbon accumulation that were charged from the Thebes Formation.