The efficiency of the conversion of solar energy into wind energy by means of Hadley cells

Summary In the present paper, we apply endoreversible thermodynamics in order to calculate the upper bound for the fraction of solar energy absorbed by the Earth, that can be converted into the mechanical energy present in the atmosphere. We assume the presence of six Hadley cells in the Earth's wind system and find an upper limit of 1.17%. For Mars we assume a single Hadley cell and find an upper limit of 0.87%.With 10 Figures     

Ground deformations in collapsed caldera structures

A method is presented to analyze the effect of stress-strain discontinuities on the ground deformations generated by a pressure source. This is meant to simulate the effects due to caldera structures, likely to present fractured zones at the borders of the collapsed area. A method originally developed by Crouch (1976) to solve plane-strain problems has been used to simulate deformation curves for several source and discontinuity geometries. The main result is that the location of the discontinuities controls the extension of the deformed zone, and always reduces it with respect to a continuous medium. With respect to a homogeneous medium the presence of lateral discontinuities also acts towards lowering the overpressure required to produce a given amount of deformation. These results indicate that, when analyzing ground deformations in calderas, the use of classical methods involving continuous media should be avoided, or at least taken with caution. These methods, in fact, assume that the extension of the deformed zone is only linked to the source depth.Some examples of ground deformations in active calderas have been analyzed in the framework of the results obtained from theoretical modeling. Four calderas recently affected by ground deformations have been considered: Rabaul (New Guinea), Campi Flegrei (Italy), Long Valley and Yellowstone (U.S.A.). The effects of collapsed structures on the deformation field are possibly evidenced for all the four calderas. At Rabaul and Campi Flegrei, the fracture systems mainly affecting the ground deformations probably represent younger, innermost collapses and are well evidenced by seismicity studies. Ground deformations are here concentrated in an area much smaller than the one enclosed by geologically visible caldera rims. In particular, at Rabaul, the effect of the innermost collapse can explain the high concentration of the uplift in the period 1971–1985, previously modeled by a very shallow source (1–3 km) in terms of overpressure in the main magma chamber, probably located at 4–5 km of depth.     

Estimates of site seismicity rates using ill-defined macroseismic data

A new approach to the problem of site seismic hazard analysis is proposed, based on intensity data affected by uncertainties. This approach takes into account the ordinal and discrete character of intensities, trying to avoid misleading results due to the assumption that intensity can be treated as a real number (continuous distribution estimators, attenuation relationships, etc.). The proposed formulation is based on the use of a distribution function describing, for each earthquake, the probability that site seismic effects can be described by each possible intensity value. In order to obtain site hazard estimates where local data are lacking, the dependence of this distribution function with the distance from the macroseismic epicenter and with epicentral intensity is examined. A methodology has been developed for the purpose of combining such probabilities and estimating site seismicity rates which takes into account the effect of uncertainties involved in this kind of analysis. An application of this approach is described and discussed.     

Derivation of vegetative variables from a landsat tm image for modelling soil erosion

A study was carried out to assess the potential use of satellite thematic mapper (TM) images to produce maps of vegetation-related variables for erosion modelling. In a Mediterranean study area in southern France the (semi-)natural vegetation was described at 33 field plots using four quantitative methods: the Fosberg structural classification system, the cover and management factor of the Universal Soil Loss Equation, the leaf area index and the total percentage cover. After radiometric correction of the image, the spectral TM bands were processed following three different methods. Each method aimed at combining the data of the six spectral TM bands into a single band in such a way that the resulting image displayed optimal information on green vegetation cover. The algorithms used comprise the normalized difference vegetation index, the conventional ‘tasselled cap’ transformation and a locally tuned tasselled cap transformation. Only slight differences were found between the different methods to calculate spectral vegetation indices for this particular case. Furthermore, the correlations between the field variables and image-derived spectral indices are generally small. The largest correlations were found for the normalized vegetation index and the leaf area index (r + 0·71) and for the normalized vegetation index and Fosberg's structural vegetation classes (r + 0·76). However, Fosberg's method results in very general classes, which are of little use for soil erosion models. Furthermore, the spectral indices appeared to be sensitive for the vitality of the vegetation. Consequently, an area covered by a sensed, senescent vegetation will not yield a large value for the spectral index, but its soil is protected against splash erosion. This might lead to a misinterpretation of the soil protective cover when satellite images are used. A final conclusion is that a balance has to be found between the more accurate, but time-consuming field surveys to gather information on erosion-controlling factors and a certain loss of accuracy associated with the use of quick and easy remote sensing methods.     

Undications of current action in late Jurassic limestones,radiolarian limestones,saccocoma limestones and associated rocks from the subbetic of SE Spain

In the Vélez Blanco region (province of Almeia), filament limestones occur associated with pellet limestones, crinoidal limestones, radiolarian limestones, Saccocoma limestones and tintinnid limestones. These predominantly Late Jurassic rocks are underlain by Middle Jurassic oolitic limestones and overlain by Cretaceous pelagic limestones and marls.A distinction can be made between long and short filaments. The former are interpreted as undamaged valves, the latter as shell fragments of the pelagic pelecypod Bositra buchi. Bositra valves and fragments have been sorted by weak current (and/or wave) action.In the Saccocoma limestones, evidence for similar sorting of Saccocoma debris has been found.The radiolarian limestones represent a low-energy basin environment, but are not comparable with recent deep-sea radiolarian oozes.Nodular limestone intercalations and hiatuses represent a current- (and/or wave-) swept environment.The occurrence of filament-rich and Radiolaria-bearing, but benthos-poor, intervals within the oolitic limestone indicates that the deposition of such rocks can take place at moderate sea depths.     

Bioaccumulation factors of chlorinated hydrocarbons between mussels and seawater

The bioaccumulation of PCB and DDT compounds by mussels, Mytilus spp., from ambient seawater was determined by measuring concentrations of these chlorinated hydrocarbons in both mussels and seawater at four sites on the Mediterranean coast of France and two sites in California. Bioaccumulation factors were found to vary over an order of magnitude. Ratios of the concentrations of PCB in mussels, consisting predominantly of pentachloro-and hexachlorobiphenyls, to concentrations in ambient seawater ranged between 69 000 and 690 000; the corresponding ratios of concentrations of p,p′-DDE or p,p′-DDT ranged from 40 000 to 690 000. Although mussels appear to be appropriate and convenient indicator organisms of local chlorinated hydrocarbon contamination levels, the factors contributing to this variance must be determined before mussels are widely used in global monitoring programmes.     

Formation of artifacts in sediments upon freeze-drying

Comparison of the analytical data on the alkenes extracted from both dried and wet Messel shale sediment points to the formation of artifacts, presumably as a result of clay-catalyzed dehydration reactions.     

The Oklo natural reactor: Cumulative fission yields and retentivity of the symmetric mass region fission products

Solid source mass spectrometry has been used to determine the relative cumulative fission yields of five elements in three samples of uranium ore from reactor zones in the Oklo mine site. Eighteen fission chains covering the mass range from105 ≤ A ≤ 130 have been measured for Pd, Ag, Cd, Sn and Te. These measurements have enabled a number of nuclear parameters to be calculated including the relative proportions of²³⁵U,²³⁸U and²³⁹Pu involved in the fission process.The concentration of the five elements in the Oklo samples have also been measured using the stable isotope dilution technique. These values have then been compared to the estimates of the amount of these elements produced by fission under the conditions that are appropriate to the three samples. This procedure enables the retentivity of the elements in the reactor zones to be evaluated. Our work confirms the fact that Pd and Te are retained almost in their entirety in the samples, whereas the other three elements have been partially lost from the reactor site. Almost all the Cd fission products have been lost, and more than 50% of the Ag and Sn fission-produced material has been removed.