Sublimation-driven evolution of the local radius and the moment of inertia of a long-period comet

In this paper we intend to analyze how the sublimation of ice from cometary nuclei affects changes of the moments of inertia. Our aim is to show general trends for different orientations of cometary nucleus’ rotation axis. Thus we apply numerical model of a hypothetical homogeneous and initially spherical nucleus composed of water ice and dust. As an example we present simulations for a model comet of the orbital elements and the nucleus size the same as determined for C/1995 O1 Hale-Bopp, a widely analyzed long-period comet. We calculated water production from the nucleus and changes of the shape (initially spherical) and of the moment of inertia versus time. Simulations are performed for the full range (0–90°) of inclinations I of the rotation axis. The second paramater related to the orientation of the rotation axis is the argument Φ (0–360°). The heat conductivity of the nucleus spans over the vast range, 0.04–4 W m⁻¹ K⁻1.     

Surface evolution of salt‐encrusted playas under extreme and continued dryness

Miocene continental saltpans are scattered in the Central Valley of the Atacama Desert, one of the driest regions on Earth. These evaporitic deposits are hydrologically inactive, and are detached from groundwater brines or aquifers. The surface of the saltpans, also known as salars, comprises desiccation polygons, commonly with nodular salt structures along their sides. The morphology and bulk mineralogy of salt polygons differs between and within salars, and the shape and internal structure of salt nodules varies between different polygon types. Based on field observation, and mineralogy and crystallography data, we generated a conceptual model for the genesis and evolution of these surface features, whereby rare rainfall events are responsible for the transformation of desiccation salt polygons and the initial formation of salt nodules along polygon borders. In addition, frequent, but less intense, deliquescence events further drive the evolution of salt nodules, resulting in a characteristic internal structure that includes laminations, and changes in porosity and crystal morphologies. As a result, and despite the extreme dryness, the surfaces of fossil salars are dynamic on timescales of several years to decades, in response to daily cycles in atmospheric moisture, and also to rare and meager rainfall events. We propose that fossil salars in the Atacama Desert represent an end stage in the evolution of evaporitic deposits under extreme and prolonged dryness. Copyright © 2015 John Wiley & Sons, Ltd.     

Sensitivity of Simulated Hyporheic Exchange to River Bathymetry: The Steinlach River Test Site

This study determines the aspects of river bathymetry that have the greatest influence on the predictive biases when simulating hyporheic exchange. To investigate this, we build a highly parameterized HydroGeoSphere model of the Steinlach River Test Site in southwest Germany as a reference. This model is then modified with simpler bathymetries, evaluating the changes to hyporheic exchange fluxes and transit time distributions. Results indicate that simulating hyporheic exchange with a high-resolution detailed bathymetry using a three-dimensional fully coupled model leads to nested multiscale hyporheic exchange systems. A poorly resolved bathymetry will underestimate the small-scale hyporheic exchange, biasing the simulated hyporheic exchange towards larger scales, thus leading to overestimates of hyporheic exchange residence times. This can lead to gross biases in the estimation of a catchment's capacity to attenuate pollutants when extrapolated to account for all meanders along an entire river within a watershed. The detailed river slope alone is not enough to accurately simulate the locations and magnitudes of losing and gaining river reaches. Thus, local bedforms in terms of bathymetric highs and lows within the river are required. Bathymetry surveying campaigns can be more effective by prioritizing bathymetry measurements along the thalweg and gegenweg of a meandering channel. We define the gegenweg as the line that connects the shallowest points in successive cross-sections along a river opposite to the thalweg under average flow conditions. Incorporating local bedforms will likely capture the nested nature of hyporheic exchange, leading to more physically meaningful simulations of hyporheic exchange fluxes and transit times.     

The effects of mafic-felsic magma interaction on magma diversity: insights from an early Paleozoic hornblendite-quartz monzonite suite in the South China block

Mineralogy and Petrology - Understanding the mechanisms responsible for the interplay between mafic and felsic magmas is the key to retrieving information on their sources, and characterizing the...     

Chemical changes in fluid composition due to CO2 injection in the Altmark gas field: preliminary results from batch experiments

Dissolution?Cprecipitation phenomena induced by CO₂ injection to Altmark Permian sandstone were observed through laboratory experiments carried out under simulated reservoir conditions (125?°C and 50 bars of pressure). The rock sample was collected from the Altmark gas reservoir, which is being considered for enhanced gas recovery. Two sets of experiments were performed with pulverized rock samples in a closed batch reactor with either pure water (run 1) or 3?M aqueous NaCl solution (run 2) and reacted with injected CO₂ for 3, 5, and 9?days. The liquid samples were analyzed by inductively coupled plasma optical emission spectroscopy and total reflection X-ray fluorescence, where the latter proved to be a feasible alternative to conventional analytical techniques, especially since only small sample volumes (about 10???l) are needed. Chemical analysis for both fluids (water and NaCl brine) indicated a significant dissolution of calcite and anhydrite in the solution, which might be a crucial process during CO₂ injection. The brine solution enhanced the dissolution of calcite and anhydrite compared to pure water at the beginning of the reaction. Moreover, the progressive higher Si⁴⁺/Al³⁺ molar ratios (in average by a factor of 3) in the brine experiments indicated quartz dissolution. Thermodynamic calculations of mineral saturation indices highlighted the dissolution of the Ca-bearing minerals, which was in agreement with experimental results. Modeling enabled an evaluation of the dissolution processes of minerals in a low-salinity region, yet hindrances to model more saline conditions emphasize the need for further laboratory studies in order to parameterize models for deep aquifer conditions.     

Methodology to evaluate the renewal period of carbonate aquifers: a key tool for their management in arid and semiarid regions,with the example of Becerrero aquifer,Spain

A methodological procedure is proposed for determining the renewal period (RP), which expresses the ratio of total storage to recharge of carbonate aquifers, and it was applied to the overexploited moderate-size Becerrero carbonate aquifer (southern Spain). To this end, geological and subsurface data—time domain electromagnetic (TEM) soundings and borehole logs—were integrated to construct a three-dimensional (3D) geological model of the aquifer. The interconnected porosity was estimated by analyzing 73 rock samples. The resulting 3D geometrical model makes it possible to quantify the fractions of the aquifer having a confined or unconfined behaviour. Based on the total storage capacity (179?·?10⁶–514?·?10⁶ m³) and available aquifer recharge estimation (4.8?·?10⁶–6.4?·?10⁶ m³/year), an RP between 37 and 106 years is obtained. In view of the RP, an exploitation rate slightly lower than the average recharge of the system is recommended, so that the piezometric level will be stable but below the discharge head that is produced through the springs in natural conditions. The proposed methodology to obtain an aquifer RP and the management strategies designed accordingly are of broad interest, especially for carbonate aquifers, which are abundant in arid and semiarid regions.     

Microbial diversity in waters,sediments and microbial mats evaluated using fatty acid-based methods

The review summarises recent advances towards a greater comprehensive assessment of microbial diversity in aquatic environments using the fatty acid methyl esters and phospholipid fatty acids approaches. These methods are commonly used in microbial ecology because they do not require the culturing of micro-organisms, are quantitative and reproducible and provide valuable information regarding the structure of entire microbial communities. Because some fatty acids are associated with taxonomic and functional groups of micro-organisms, they allow particular groups of micro-organisms to be distinguished. The integration of fatty acid-based methods with stable isotopes, RNA and DNA analyses enhances our knowledge of the role of micro-organisms in global nutrient cycles, functional activity and phylogenetic lineages within microbial communities. Additionally, the analysis of fatty acid profiles enables the shifts in the microbial diversity in pristine and contaminated environments to be monitored. The main objective of this review is to present the use of lipid-based approaches for the characterisation of microbial communities in water columns, sediments and biomats.     

Weiwoboidae fam.nov.of 'Higher' Fulgoroidea (Hemiptera:Fulgoromorpha) from the Eocene Deposits of Yunnan,China

<正>A new family of so-called‘higher' planthoppers,Weiwoboidae fam.nov.,from the Lower Eocene of Yunnan is described.A new monotypic genus,Weiwoboa gen.nov.,with Weiwoboa meridiana sp.nov.is also described and illustrated.The characters of tegmen venation of the new family,its evolution,and supposed relationships are briefly discussed.     

Microelectrona cladara gen.et sp.nov.:A New Protodikraneurini from the Eocene Baltic Amber(Hemiptera:Cicadomorpha:Cicadellidae:Typhlocybinae)

<正>A new genus Microelectrona gen.nov.and species Microelectrona cladara sp.nov.of the extinct tribe Protodikraneurini of the leafhoppers(Cicadeilidae:Typhlocybinae) from the Eocene Baltic amber is described. The piece of amber containing leafhopper inclusion is broken,unveiling some of the morphological structures,and enabling their studies using scanning electron microscopy.