An Acetic Acid‐Based Extraction Protocol for the Recovery of U,Th and Pb from Calcium Carbonates for U‐(Th)‐Pb Geochronology

A new method for the simultaneous recovery of U, Th and Pb from ca. 0.5 g calcium carbonate samples for the purpose of U‐(Th)‐Pb geochronometry is presented. The protocol employs ion‐exchange chromatography. Standard anion exchange resin (AG 1‐X8 100–200 mesh) was used as the static phase, and 90% acetic acid was used as the mobile phase to elute the unwanted matrix components; dilute nitric acid was used to elute the U, Th and Pb. Blanks of 1.8 pg Th, 6.4 pg Pb and 8.4 pg U were obtained. The protocol was evaluated by determining the isotopic composition of U‐Th‐Pb separates obtained from an in‐house reference material (prepared from a natural speleothem) by MC‐ICP‐MS. An independently dated speleothem was also reanalysed. Based on these tests, the extraction protocol had an acceptable blank and produced a Pb separate sufficiently free of matrix‐induced instrumental biases to be appropriate for U‐Th‐Pb chronology.     

Low‐Resolution Modeling of Dense Drainage Networks in Confining Layers

Groundwater‐surface water (GW‐SW) interaction in numerical groundwater flow models is generally simulated using a Cauchy boundary condition, which relates the flow between the surface water and the groundwater to the product of the head difference between the node and the surface water level, and a coefficient, often referred to as the “conductance.” Previous studies have shown that in models with a low grid resolution, the resistance to GW‐SW interaction below the surface water bed should often be accounted for in the parameterization of the conductance, in addition to the resistance across the surface water bed. Three conductance expressions that take this resistance into account were investigated: two that were presented by Mehl and Hill (2010) and the one that was presented by De Lange (1999). Their accuracy in low‐resolution models regarding salt and water fluxes to a dense drainage network in a confined aquifer system was determined. For a wide range of hydrogeological conditions, the influence of (1) variable groundwater density; (2) vertical grid discretization; and (3) simulation of both ditches and tile drains in a single model cell was investigated. The results indicate that the conductance expression of De Lange (1999) should be used in similar hydrogeological conditions as considered in this paper, as it is better taking into account the resistance to flow below the surface water bed. For the cases that were considered, the influence of variable groundwater density and vertical grid discretization on the accuracy of the conductance expression of De Lange (1999) is small.     

Deuterated hydrogen molecule and search for early structure-formation signatures in the Universe

Possible detection of signatures of structure formation at the end of the 'dark age' epoch  ( z ∼ 40–20)  is examined. We discuss the spectral–spatial fluctuations in the cosmic microwave background radiation (CMBR) temperature produced by elastic resonant scattering of CMBR photons on deuterated hydrogen (HD) molecules located in protostructures moving with peculiar velocity. Detailed chemical kinematic evolution of HD molecules in the expanding homogeneous medium is calculated. Then, the HD abundances are linked to protostructures at their maximum expansion, whose properties are estimated by using the top-hat spherical approach and the Λ cold dark matter (ΛCDM) cosmology. We find that the optical depths in the HD three lowest pure rotational lines for high-peak protohaloes at their maximum expansion are much higher than those in LiH molecule. The corresponding spectral–spatial fluctuation amplitudes, however, are probably too weak to be detected by current and forthcoming millimetre telescope facilities. We extend our estimates of spectral–spatial fluctuations to gas clouds inside collapsed CDM haloes by using results from a crude model of HD production in these clouds. The fluctuations for the highest peak CDM haloes at redshifts ∼20–30 could be detected in the future. Observations will be important to test model predictions of early structure formation in the Universe.     

Integrating lysimeter drainage and eddy covariance flux measurements in a groundwater recharge model

Abstract

Field-scale water balance is difficult to characterize because controls exerted by soils and vegetation are mostly inferred from local-scale measurements with relatively small support volumes. Eddy covariance flux and lysimeters have been used to infer and evaluate field-scale water balances because they have larger footprint areas than local soil moisture measurements. This study quantifies heterogeneity of soil deep drainage (D) in four 12.5-m² repacked lysimeters, compares evapotranspiration from eddy covariance (ET_EC) and mass balance residuals of lysimeters (ETwb_Lys), and models D to estimate groundwater recharge. Variation in measured D was attributed to redirection of snowmelt infiltration and differences in lysimeter hydraulic properties caused by surface soil treatment. During the growing seasons of 2010, 2011 and 2012, ETwb_Lys (278, 289 and 269 mm, respectively) was in good agreement with ET_EC (298, 301 and 335 mm). Annual recharge estimated from modelled D was 486, 624 and 613 mm for three calendar years 2010, 2011 and 2012, respectively. In summary, lysimeter D and ET_EC can be integrated to estimate and model groundwater recharge.

Editor D. Koutsoyiannis     

DEVEX-disdrometer evaluation experiment: Basic results and implications for hydrologic studies

Increasing our understanding of the small scale variability of drop size distributions (DSD), and therefore of several bulk characteristics of rainfall processes, has major implications for our interpretation of the remote sensing based estimates of precipitation and its uncertainty. During the spring and summer of 2002 the authors conducted the DEVEX experiment (disdrometer evaluation experiment) to compare measurements of natural rain made with three different types of disdrometers collocated at the Iowa City Municipal Airport in Iowa City, Iowa in the Midwestern United States. This paper focuses on the evaluation of the instruments rather than analysis of the hydrometeorological aspects of the observed events. The comparison demonstrates discrepancies between instruments. The authors discuss the systematic and random effects in terms of rainfall quantities, drop size distribution properties, and the observed drop size vs. velocity relationships. Since the instruments were collocated, the effects of the natural variability of rain are reduced some with time integration, isolating the instrumental differences. The authors discuss the status of DSD measurement technologies and the implications for a range of hydrologic applications from remote sensing of rainfall to atmospheric deposition to soil erosion and sediment transport in the environment. The data set collected during the DEVEX experiment is made available to the research community.     

Prestack shot-gather depth migration by a rigid flow of Gaussian wave packets

We introduce a new method for prestack depth migration of seismic common-shot gathers. The computational procedure follows standard steps of the reverse-time migration, i.e., downward continuation of the source and the receiver wavefields, followed by application of an imaging condition (e.g. zero-lag cross-correlation of these fields). In our method we first find a sparse data representation with a small number of Gaussian wave packets. We then approximate the downward wavefield propagation (for the source and the receiver fields) by a rigid flow of these wave packets along seismic rays. In this case, the wave packets are simply translated and rotated according to the ray geometry. One advantage of using Gaussian wave packets is that analytic formulas can be used for translation, rotation, and the application of the cross-correlation imaging condition. Moreover, they allow more sparse representations than competing methods. Finally we formulate a computationally and memory efficient migration procedure, as only few rays have to be traced, and since it is cheap to compute the cross-correlation for the intersecting rays.     

Traces of structural H2O molecules in baryte

The infrared (IR) spectra of gem-quality baryte crystals from different occurrences are characterized by relatively weak but strongly pleochroic absorption bands at 3,280, 3,220, 3,155, and 3,115 cm⁻¹. These bands are assigned to anti-symmetric and symmetric OH stretching vibrations of two types of H₂O molecules localized on vacant Ba sites. The H–H axis of the H₂O I molecule is slightly tilted from the a-axis direction, its twofold axis being nearly parallel to the b-axis, thus defining the plane of the H₂O molecule practically parallel to (001). The H₂O II molecule has its H–H axis parallel to the b-axis direction, with its plane lying approximately parallel to (101). The values of the total water contents of the baryte crystals, calculated on the basis of IR spectroscopic data, are ranging from about 1.7–3.8 wt.ppm. The possible presence of H₃O⁺ ions is also discussed.     

Book reviews

Astrophysics and Space Science -     

Physics of solar prominences

Summary Conclusion This colloquium on solar prominences - the first ever held - has shown that a major part of activity in prominence research in recent years concentrated on both observation and computation of the magnetic conditions which were found to play a crucial role for the development and the maintainance of prominences. Remarkable progress was made in fine-scale measurements of photospheric magnetic fields around filaments and in internal field measurements in prominences. In addition, important information on the structure of the magnetic fields in the chromosphere adjacent to the filaments may be derived from high resolution photographs of the H fine structure around filaments which have become available recently; unfortunately, an unambiguous determination of the vector field in the chromosphere is not yet possible.It is quite clear, now, that stable filaments extend along neutral lines which divide regions of opposite longitudinal magnetic fields. Different types of neutral lines are possible, depending on the history and relationship of the opposite field regions. There is convincing evidence that the magnetic field in the neighbouring chromosphere may run nearly parallel to the filament axis and that there are two field components in stable prominences: an axial field dominant in the lower parts and a transverse field dominant in the higher parts.Methods for the computation of possible prominence field configurations from measured longitudinal photospheric fields were developed in recent years. In a number of cases (e.g. for loop prominences) the observed configuration could be perfectly represented by a force-free or even a potential field; poor agreement was found between computed and measured field strengths in quiescent prominences. In order to reconcile both of them it is necessary to assume electric currents. Unambiguous solutions will not be found until measurements of the vector field in the photosphere and in the prominences are available.The two-dimensional Kippenhahn-Schlüter model is still considered a useful tool for the study of prominence support and stability. However, a more refined model taking into account both field components and considering also thermal stability conditions is available now. It was proposed that quiescent prominences may form in magnetically neutral sheets in the corona where fields of opposite directions meet.As for the problem of the origin of the dense prominence material there are still two opposite processes under discussion. The injection of material from below, which was mainly applied to loop prominences, has recently been considered also a possible mechanism for the formation of quiescent prominences. On the other hand, the main objections against the condensation mechanism could be removed: it was shown that (1) sufficient material is available in the surrounding corona, and that (2) coronal matter can be condensed to prominence densities and cooled to prominence temperatures in a sufficiently short time.The energy balance in prominences is largely dependent on their fine structure. It seems that a much better radiative loss function for optically thin matter is now available. The problem of the heat conduction can only be treated properly if the field configuration is known. Very little is known on the heating of the corona and the prominence in a complicated field configuration. For the optically thick prominences the energy balance becomes a complicated radiative transfer problem.Still little is known on the first days of prominence development and on the mechanism of first formation which, both, are crucial for the unterstanding of the prominence phenomenon. As a first important step, it was shown in high resolution H photographs that the chromospheric fine structure becomes aligned along the direction of the neutral line already before first filament appearance. More H studies and magnetic field measurements are badly needed.Recent studies have shown that even in stable prominences strong small-scale internal rotational or helical motions exist; they are not yet understood. On the other hand, no generally agreed interpretation of large-scale motions of prominences seems to exist. A first attempt to explain the ascendance of prominences, the Disparitions Brusques, as the result of a kink instability was made recently.New opportunities in prominence research are offered by the study of invisible radiations: X-rays and meterwaves provide important information, not available otherwise, on physical conditions in the coronal surroundings of prominences; EUV observations will provide data on the thin transition layer between the cool prominence and the hot coronal plasma.Mitt. aus dem Fraunhofer Institut No. 111.     

On the gravitation absorption hypothesis

Summary It is recommended that the data from measurements with supraconducting gravity meters be also analysed with regard to verifying the gravitation absorption hypothesis. Based on theoretical data from a3-year period, the spectrum of the assumed effect of shielding the gravitational influence of the Sun by the Earth's body on the value of the acceleration of gravity has been calculated for the tidal station Brussels (Figs 2a–e).

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