Variation of the gradient and balmer discontinuity during the eclipse of the variable RW Tauri: Comparison between observations and theory

For the first time after Barbier and Chalonge's (1938, 1941) pioneering works, the variations of b andD during the eclipse of a variable (RT Tau), have been observed. The observations have been performed at the Observatories of Jungfraujoch and Haute Provence with the photoelectric system in seven colors of Geneva (Golay, 1964; Hauck, 1968). The comparison between the observed curves ofD and the theoretical ones, provides the limb darkening coefficients; the same comparison between the observed b (reddened) and theoretical ones (not reddened) together with that ofD, points out some anomalies of the variable RW Tau.

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Sommario Per la prima volta, dopo i primi lavori di Barbier e Chalonge (1938, 1941), sono state osservate le variazioni di b eD durante l'eclisse di una variabile (RW Tau). Le osservazioni sono state fatte agli Osservatori della Jungfraujoch e di Haute Provence col sistema fotoelettrico in sette colori di Ginevra (Golay, 1964; Hauck, 1968). Il confronto fra le curve osservate e teoriche diD, fornisce i coefficienti di oscuramento al bordo; lo stesso confronto fra i b osservati (arrossati) e quelli teorici (non arrossati) unitamente a quello delleD mette in evidenza alcune anomalie della variabile RW Tau.

     

A statistical estimator of the spatial distribution of the water-table altitude

An algorithm was designed to statistically estimate the areal distribution of water-table altitude. The altitude of the water table was bounded below by the minimum water-table surface and above by the land surface. Using lake elevations and stream stages, and interpolating between lakes and streams, the minimum water-table surface was generated. A multiple linear regression among the minimum water-table altitude, the differerence between land-surface and minimum water-table altitudes, and the water-level measurements from surficial aquifier system wells resulted in a consistently high correlation for all groups of physiographic regions in Florida. A simple linear regression between land-surface and water-level measurements resulted in a root-mean-square residual of 4.23 m, with residuals ranging from -8.78 to 41.54 m. A simple linear regression between the minimum water table and the water-level measurements resulted in a root-mean-square residual of 1.45 m, with residuals ranging from -7.39 to 4.10 m. The application of the multiple linear regression presented herein resulted in a root-mean-square residual of 1.05 m, with residuals ranging from -5.24 to 5.63 m. Results from complete and partial F tests rejected the hypothesis of eliminating any of the regressors in the multiple linear regression presented in this study.     

Analysis of seismic dynamical systems

A procedure is presented for the analysis of complex stationary time series for which the Fourier power spectra reveals broadband noise or broadened pulses. We first determine the Hurst exponent from which we may know whether the time series under study is mainly random or if the data points present correlations. If the data are correlated, a chaotic analysis will reveal whether they may be interpreted as a low dimensional nonlinear system (defined by a low correlation dimension and a finite and positive Kolmogorov entropy and largest positive Lyapunov exponent) or as a stochastic process. We have studied three kind of temporal series: inter-event time series of infrasonic pulses recorded at Stromboli volcano, and, S-coda waves and microseisms, that have been recorded at the eastern Pyrenees. Results show that microseisms and Coda waves can be modeled as a low dimensional deterministic system, Correlation dimensions 2.3, 3.2, respectively. At the contrary infrasonic has resulted stochastic. This chaotic character can be attributed to the medium properties. Coda waves with scattering through a fractal distribution of scatters or to multiple reflection inside resonators (for example sedimentary basins) and microseisms as a propagation of wave guide of variable cross section which have the same temporal characteristics as a nonlinear forced oscillator.     

Entropy‐based equation to assess hillslope sediment production

A new equation to assess hillslope sediment production, based on physical and probabilistic approaches, is presented. The equation, which allows the computation of the delivery ratio for every event, considers the physical variables of travel distance, stream power, settling velocity and gross erosion. The probability density function that arises from the new formulation is solved using the principle of maximum entropy. Based on data from five watersheds in both tropical and temperate zones, the new delivery parameter K_v is calibrated and associated with vegetation cover and conservation practice. The proposed equation is rationally based in relation to parameter K_v. The entropy‐based equation was applied to assess sediment yield in two other experimental watersheds, showing good predictability for the set (mean absolute error of 20·8%). No systematic error was found in the analysed data. The entropy‐based equation showed good predictability for long‐term sets of data and for high‐erosivity events, but did not perform well for the low‐erosivity ones. Copyright © 2007 John Wiley & Sons, Ltd.     

Extreme temperature scenarios in Mexicali,Mexico under climate change conditions

Extreme weather events can have severe consequences for the population and the environment. Therefore, in this study a temporal trend of annual temperatures was built with a time series from 1950 to 2010 for Mexicali, Mexico, and estimates of 5- to 100-year return periods are provided by modeling of summer maximum and winter minimum temperatures. A non-parametric Kendall’s tau test and the Sen’s slope estimator were used to compute trends. The generalized extreme value (GEV) distribution was applied to the approximation of block maxima and the generalized Pareto distribution (GPD) to values over a predetermined threshold. Due to the non-stationary characteristic of the series of temperature values, the temporal trend was included as a covariable in the location parameter and substantial improvements were observed, particularly with the extreme minimum temperature, compared to that obtained with the GEV with no covariable and with the GPD. A positive and significant statistically trend in both summer maximum temperature and winter minimum temperature was found. By the end of 21st century the extreme maximum temperature could be 2 to 3 °C higher than current, and the winter could be less severe, as the probabilistic model suggests increases of 7 to 9 °C in the extreme minimum temperature with respect to the base period. The foreseeable consequences on Mexicali city are discussed.     

Mineralogy and geochemistry of El Dorado epithermal gold deposit, El Sauce district, central-northern Chile

Summary The El Dorado Au-Cu deposit is located in an extensive intra-caldera zone of hydrothermal alteration affecting Upper Cretaceous andesites of the Los Elquinos Formation at La Serena (≈ 29°47′S Lat., 70°43′W Long., Chile). Quartz-sulfide veins of economic potential are hosted by N25W and N20E fault structures associated with quartz-illite alteration (+supergene kaolinite). The main ore minerals in the deposit are pyrite, chalcopyrite ± fahlore (As/(As + Sb): 0.06−0.98), with electrum, sphalerite, galena, bournonite-seligmanite (As/(As + Sb): 0.21−0.31), marcasite, pyrrhotite being accessory phases. Electrum, with an Ag content between 32 and 37 at.%, occurs interstitial to pyrite aggregates or along pyrite fractures. Pyrite commonly exhibits chemical zonation with some zones up to 1.96 at.% As. Electron probe microanalyses of pyrite indicate that As-rich zones do not exhibit detectable Au values. Fluid inclusion microthermometry shows homogenization temperatures between 130 and 352 °C and salinities between 1.6 and 6.9 wt.% NaCl eq. Isotope data for quartz, ankerite and phyllosilicates and estimated temperatures show that δ¹⁸O and δD for the hydrothermal fluids were between 3 and 10‰ and between −95 and −75‰, respectively. These results suggest the mineralizing fluids were a mixture of meteoric and magmatic waters. An epithermal intermediate-sulfidation model is proposed for the formation of the El Dorado deposit. Author’s present address: J. Carrillo-Rosúa, Dpto. de Didáctica de las Ciencias Experimentales, Universidad de Granada, Campus de Cartuja, 18071, Granada, Spain     

Spatio-temporal characteristics of small-scale wave–current ripples on the Ameland ebb-tidal delta

Ebb-tidal deltas are highly dynamic environments affected by both waves and currents that approach the coast under various angles. Among other bedforms of various scales, these hydrodynamics create small-scale bedforms (ripples), which increase the bed roughness and will therefore affect hydrodynamics and sediment transport. In morphodynamic models, sediment transport predictions depend on the roughness height, but the accuracy of these predictors has not been tested for field conditions with strongly mixed (wave–current dominated) forcing. In this study, small-scale bedforms were observed in the field with a 3D Profiling Sonar at five locations on the Ameland ebb-tidal delta, the Netherlands. Hydrodynamic conditions ranged from wave dominated to current dominated, but were mixed most of the time. Small-scale ripples were found on all studied parts of the delta, superimposed on megaripples. Even though a large range of hydrodynamic conditions was encountered, the spatio-temporal variations in small-scale ripple dimensions were relatively small (height 0.015 m, length 0.11 m). Also, the ripples were always highly three-dimensional. These small dimensions are probably caused by the fact that the bed consists of relatively fine sediment. Five bedform height predictors were tested, but they all overestimated the ripple heights, partly because they were not created for small grain sizes. Furthermore, the predictors all have a strong dependence on wave- and current-related velocities, whereas the ripple heights measured here were only related to the near-bed orbital velocity. Therefore, ripple heights and lengths in wave–current-dominated, fine-grained coastal areas ( mm) may be best estimated by constant values rather than values dependent on the hydrodynamics. In the case of the Ameland ebb-tidal delta, these values were found to be m and m. ©2019 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.     

Lucinid clam influence on the biogeochemistry of the seagrass<Emphasis Type="Italic">Thalassia testudinum</Emphasis> sediments

Lucinid bivalves dominate the infauna of tropical seagrass sediments. While the effect of seagrass on lucinids has been studied, the reverse effect has largely been ignored. Lucinids can alter porewater chemistry (i.e., increase porewater nutrients by suspension feeding and decrease porewater sulfides by oxygen introduction and bacterial oxidation), which can potentially change seagrass productivity and growth morphology. To observe correlations between porewater chemistry and lucinid presence, a field survey and laboratory microcosm experiment were conducted. Survey sampling sites with lucinids had significantly lower sulfide and higher ammonium concentrations than sampling sites without lucinids. There was no difference in phosphate concentration among sampling sites. Both lucinid species used in the microcosm experiment (Ctena orbiculata andLucinesca nassula) significantly lowered sulfide concentrations in the sediment porewater. Microcosm and field survey results were incorporated into a sulfide budget. In seagrass sediments, lucinids remove 2–16% of the total sulfide produced. Sulfide is a major stressor to both plants and animals in Florida Bay sediments; this removal may be important to maintaining seagrass productivity and health. Oxygen introduction into sediments byC. orbiculata was estimated in a dye experiment.C. orbiculata were added to small tubes containing sieved mud and incubated in a bath of seawater with a Rhodamine WT. Rhodamine WT accumulation in the sediment was measured. A first order estimate showed that oxygen introduction can account for less than 5% ofC. orbiculata sulfide removal.