New phase-coherent measurements of pulsar braking indices

Pulsar braking indices offer insight into the physics that underlies pulsar spin-down. Only five braking indices have been measured via phase-coherent timing; all measured values are less than 3, the value expected from magnetic dipole radiation. Here we present new measurements for three of the five pulsar braking indices, obtained with phase-coherent timing for PSRs J1846-0258 (n=2.65±0.01), B1509-58 (n=2.839±0.001) and B0540-69 (n=2.140±0.009). We discuss the implications of these results and possible physical explanations for them.      

Optimal sequencing for a multipurpose water supply system

The optimal sequencing of a multipurpose water supply system in the Hajduhátság region of Hungary is determined by dynamic programming. The goal function minimizes the present value of capital costs, operation costs, and economic losses due to water shortages. Future water requirements are considered to be random variables because of natural and forecasting uncertainties. The nonlinear optimization problem at each stage is equivalent to a readily solved game theoretical problem, the solution of which is straightforward. Sensitivity analysis performed with respect to economic losses, water requirements and discount rate, showed that optimal development and sequencing depend largely on the economic losses and the discount rate.     

Prediction of local ore recoveries and ore-waste ratios at the silver bell uranium mine

Geostatistical estimation techniques were customized to allow forecasting of production figures at the Silver Bell uranium mine (Uravan District).Surface drill hole data were used to provide a block model of kriged estimators of average uranium grades. Figures for recoverable ore grade and the ore-waste ratio are then deduced from regressive curves previously obtained from underground information and production data. Cross-validations of the entire model were performed and were found positive.     

Seasonal temperatures for the past ∼400 years reconstructed from diatom and chironomid assemblages in a high-altitude lake (Lej da la Tscheppa,Switzerland)

We analysed a 42 cm long sediment record from Lej da la Tscheppa, a high-altitude lake (2,616 m a.s.l.) in the Upper Engadine valley (Switzerland) for subfossil diatoms, chironomids and pollen. The chronology of the top 21 cm of the record was established using ²¹⁰Pb analysis using a constant-rate-of-supply model, and validated with ¹³⁷Cs measurements and the content of spheroidal carbonaceous particles. A tentative chronology for the lower part of the core was obtained through extrapolation of the sedimentation rates in the uppermost part of the record. Pollen assemblages in the record reflect regional changes in forestation and land-use patterns in the Upper Engadine valley and show no evidence of significant local human activity in the lake’s catchment. Diatom assemblages record a distinct increase in planktonic taxa since the early 19th century, suggesting a decrease in the duration of ice-cover. In contrast, chironomid assemblages remained stable during a large part of the record. We applied an established chironomid-based July air temperature transfer function and a newly developed diatom-based spring air temperature transfer function to reconstruct past seasonal air temperature changes at Lej da la Tscheppa. The reconstructions indicate a diatom-inferred warming trend in spring temperatures during the past ca. 400 years, whereas chironomid-inferred summer temperatures suggest a slight cooling trend. These biota-based reconstructions are in good agreement with the centennial-scale temperature trend in an independent reconstruction of regional temperatures in the Upper Engadine region based on instrumental records and documentary proxy evidence from the Alps. Our results suggest that, in high-altitude lakes, independent chironomid- and diatom-based seasonal temperature reconstruction is possible and can be successfully used to track seasonal temperature trends.     

Monitoring the decrease of lake Chad from space

Observations from space of the open water areas within Lake Chad are presented. They complement andsustain the earlier study of Mohler et al. (1989), which demonstrates a decrease of about 90 percent in surface between 1966 and 1986. Further, Meteosat images were processed to obtain weekly maps of albedo following the scheme of Mousssu et al. (1989). The analysis of these maps throughout the year reveals the functioning of the lake as well as the large variability of the open water areas during a year.     

Which variables are essential for renewable energies?

ABSTRACT

Essential Variables are defined as a minimal set of variables that explain the state of the system. They are crucial for predicting its developments, and support metrics that measure its evolution. The variables should be relevant to meet requirements of stakeholders and be technically and economically feasible for systematic observation. A definition of Essential Renewable Energies Variables is proposed linked with their identification in several domains in renewable energy using a bottom-up and user-driven approach, and spanning over several years of documented interaction with stakeholders. Lists of variables are proposed in hydropower, solar, wind, and marine energies. It does not comprise the variables relating to social and economic aspects supporting decision making in investment nor those relating to civil engineering that are needed to erect a plant or farm.     

Elevation effects on rainfall: A stochastic model

The variation in point precipitation with elevation is investigated using an event-based stochastic model of thunderstorm rainfall and empirical data. Parameters of the model correspond to the number of events per unit of time and the depth of rainfall per event. An increase in precipitation with elevation may be due to an increase in the number of events, in the amount of rainfall per event or to some combination of both possibilities. The distribution of the number of events per season is assumed to be a Poisson variate while the distribution of point rainfall depths may be taken as geometric. The summation of a random number of random variables is used to represent seasonal point precipitation. Assuming that the two parameters of the model increase linearly with elevation, then total seasonal rainfall increases as a quadratic polynomial with elevation. The use of the model allows one to obtain the return period of storm rainfall of a given magnitude despite a short historical record. An independent set of data was used to verify the procedure.     

Continental drift: What driving mechanism?

A subducting oceanic lithospheric slab acts as an efficient heat sink which strongly influences the convection pattern in the neighbouring sub-continental mantle. Laboratory convection experiments show that this thermal coupling induces a roll about 5 times broader than deep underneath the continental lithosphere. The experiments are performed in a tank with imposed top and bottom temperature, and with, in addition, one cooled side wall. The convective pattern is observed by differential interferometry. For upper mantle convection one predicts rolls extending 3000 to 4000 km into the continental domain, parallel to the active margin. We show that, for Gondwana prior to the break-up, this simple convection pattern can explain the tensional state of the crust leading to the emission of flood basalts (Karroo, Parana and Antarctica). The thermal and mechanical effect of the large roll also provides a mechanism for the break-up itself and subsequent drift of the continental fragments. This motion of the continental plate leads finally to the closure of existing marginal basins along the Pacific coast of Gondwana. The laboratory experiments throw some light into another phenomenon of possible geodynamical relevance: within the large convection roll a smaller scale circulation is observed in the form of diapiric upwelling produced by thermal instabilities in the boundary layer. This dynamics may apply to hot spot volcanicity.

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Zusammenfassung Die subduzierte ozeanische Lithosphäre beeinflußt die Konvektion unterhalb der kontinentalen Lithosphäre, weil sie die Rolle einer Wärmepumpe spielt. Experimentelle Versuche zeigen, daß diese thermische Kopplung flache Konvektionsrollen im kontinentalen Mantel erzeugt, mit horizontalen Dimensionen zwischen 3000 und 4000 km. Diese flachen Zellen werden als Ursache der Dehnungstektonik in Gondwana vorgeschlagen (Karroo, Parana, Antarktika). Ihre thermische und mechanische Wirkung führt letztlich zum Zerbrechen des Superkontinents. Die Versuche im Laboratorium zeigen auch Instabilitäten kleinerer Dimensionen, welche thermische Diapire erzeugen, ähnlich den sogenannten hot spots.

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Résumé La lithosphere océanique en subduction constitue un puits de chaleur qui influence la convection dans le manteau sous-continental voisin. Des expériences de laboratoire montrent que ce refroidissement latéral crèe des rouleaux convectifs sous la lithosphere continentale de 3000 à 4000 km d'extension horizontale pour une convection limitée au manteau supérieur. Appliqué au Gondwana, ceci explique la tectonique en extension accompagnée d'épanchements basaltiques (Karroo, Parana, Antarctique) précédant l'ouverture Atlantique et Indienne. Cette ouverture est elle-même provoquée par l'action thermique et mécanique des grands rouleaux convectifs. Les expériences de laboratoire font également apparaître des instabilités à petite échelle, semblables aux diapirs que l'on pense être à l'origine du volcanisme intraplaque.

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, .. . , 3000 4000 , (Karoo, , ). . , , .. (Hot spots) .

     

Oxygen self-diffusion in forsterite: Implications for the high-temperature creep mechanism

The diffusivity of¹⁸O in forsterite Mg₂SiO₄ has been measured in the temperature range 1150–1600°C. The activation energy of oxygen self-diffusion in this silicate is found to equal0.32 ± 0.04MJ/mol(77 ± 10kcal/mol), and there is no dependence of the diffusivity upon the oxygen partial pressure surrounding the samples. The diffusion profiles were analysed either with an ion probe or by means of the¹⁸O(p, α)¹⁵N nuclear reaction. The latter method made use of a resonance in the nuclear cross-section in the case of diffusion profiles shorter than 100 nm (1000Å); for diffusion profiles up to 4 μm the same reaction was used, but in a non-resonant mode. New data on creep in forsterite and natural olivine are also given, including the influence of the oxygen partial pressurep_O2 which is zero for forsterite and proportional to(p_O2)¹⁶ for natural olivine. From this set of data we infer the possible relationship between diffusion and creep for these materials. This relationship may be more complicated than that predicted by simple climb mechanism.