A multi-array competitive immunoassay for the detection of broad-range molecular size organic compounds relevant for astrobiology

We have developed antibodies and a multi-array competitive immunoassay (MACIA) for the detection of a wide range of molecular size compounds, from single aromatic ring derivatives or polycyclic aromatic hydrocarbons (PAHs), through small peptides, proteins or whole cells (spores). Multiple microarrays containing target molecules are used simultaneously to run several competitive immunoassays. The sensitivity of the MACIA for small organic compounds like naphthalene, 4-phenilphenol or 4-tertbutilphenol is in the range of 100–500 ppb (ng ml⁻¹), for others like the insecticide terbutryn it is at the ppt (ng l⁻¹) level, while for small peptides, as well as for more complex molecules like the protein thioredoxin, the sensitivity is approximately 1–2 ppb, or 10⁴–10⁵ spores of Bacillus subtilis per milliliter. For organic compounds, a water–methanol solution was used in order to achieve a better dissolution of the organics without compromising the antibody–antigen interaction. The above-mentioned compounds were detected by MACIA in water–(10%) methanol extracts from spiked pyrite and hematite-containing rock powder samples, as well as from a spiked-sand sample subjected to organic extraction with dichloromethane–methanol (1/1).     

Heat flow, lenticulae spacing, and possibility of convection in the ice shell of europa

Two opposing models to explain the geological features observed on Europa’s surface have been proposed. The thin-shell model states that the ice shell is only a few kilometers thick, transfers heat by conduction only, and can become locally thinner until it exposes an underlying ocean on the satellite’s surface. According to the thick-shell model, the ice shell may be several tens of kilometers thick and have a lower convective layer, above which there is a cold stagnant lid that dissipates heat by conduction. Whichever the case, from magnetic data there is strong support for the presence of a layer of salty liquid water under the ice. The present study was performed to examine whether the possibility of convection is theoretically consistent with surface heat flows of ∼100-200 mW m⁻², deduced from a thin brittle lithosphere, and with the typical spacing of 15-23 km proposed for the features usually known as lenticulae. It was obtained that under Europa’s ice shell conditions convection could occur and also account for high heat flows due to tidal heating of the convective (nearly isothermal) interior, but only if the dominant water ice rheology is superplastic flow (with activation energy of 49 kJ mol⁻¹; this is the rheology thought dominant in the warm interior of the ice shell). In this case the ice shell would be ∼15-50 km thick. Furthermore, in this scenario explaining the origin of the lenticulae related to convective processes requires ice grain size close to 1 mm and ice thickness around 15-20 km.     

Possibility of Convection for Diffusion (Newtonian) Viscosity in the Ice Shell of Europa?

Recent investigations into convection in Europa’s ice shell have been based on non-Newtonian (stress-dependent) or Newtonian (stress-independent) viscosity for water ice. However, despite the wide use of Newtonian convection, experimentally observed water ice flow is non-Newtonian, and analysis of stability against convection of the ice shell using updated flow laws has been only performed for non-Newtonian rheologies. Here we use the flow law proposed for diffusion creep to analyze the possibility of the onset of convection for Newtonian viscosity in relation to the thermal state of Europa. Our findings indicate that for diffusion creep convection might have started, but that significantly lower heat flows (and equivalently higher shell thicknesses) and/or grain sizes are required than for superplastic flow, which is the most probable flow mechanism if the ice shell is convective.     

The slow rotation of 253 Mathilde

CCD photometry of the NEAR mission fly-by target 253 Mathilde is presented. Measurements taken during 52 nights of observations, from February to June 1995, allow a rotation period of 17.406±0.010 days and a lightcurve amplitude of 0.45±0.02 mag to be determined. A B-V color index of 0.67±0.02 and a V-R of 0.35±0.02 are measured, which are compatible with C-type membership. The determination of the phase relation results in H = 10.28±0.03 and G = 0.12±0.06. Indications that the lightcurve is not strictly singly-periodic are found. A power-spectrum analysis detects a secondary frequency f₂ = 0.0322±0.0010 d⁻¹, which is interpreted as evidence for a complex rotation state.     

Assessment of magnetite as a magnetic tracer for sediments in the study of ephemeral gully erosion: Conditioning factors of magnetic susceptibility

In gully erosion, the detached soil can be transported over long distances along the landscape. The eroded material can be redistributed and/or deposited on the soil surface along the landscape and then eventually be buried by newly eroded and deposited sediment. There can be significant variability of the soil conditions (e.g., texture and moisture content) over which the eroded material travels. The eroded material can be detected through the use of magnetic tracers attached to or mixed with the eroded soil. In this study we evaluated the degree to which the magnetic signal of the magnetite is conditioned by (i) burial depth of tracer, (ii) condition of soil covering the tracer and (iii) tracer concentration. In the laboratory containers were filled with a specific soil. In the filling process, a 0.5-cm layer of a soil–magnetite mixture was interspersed in the soil profile at a certain depth. Experiments encompassed three different soil–tracer concentrations (1000:1, 200:1, 100:1), four burial depths of tracer (0 cm, 3 cm, 5 cm and 10 cm from soil surface), and two different soils. In each case, the magnetic susceptibility was measured with a susceptometer. Experiments were repeated with different soil moisture contents. If the tracer is located under the soil surface, a minimum soil–tracer concentration of 200:1 is required for its correct detection. The intensity of the magnetic signal decreases dramatically with the vertical distance of the tracer from the soil surface. The maximum detection depth for the tracer's magnetic signal is strongly dependent on the natural magnetic susceptibility of the soil, which masks the tracer's signal. Variation in soil moisture content does not significantly affect the magnetic signal. For extensive field studies, the soil–tracer volume to be handled would be very high and therefore, it is necessary to explore new tracer application techniques.     

UAV RGB,thermal infrared and multispectral imagery used to investigate the control of terrain on the spatial distribution of dryland biocrust

Biocrusts (topsoil communities formed by mosses, lichens, bacteria, fungi, algae, and cyanobacteria) are a key biotic component of dryland ecosystems. Whilst climate patterns control the distribution of biocrusts in drylands worldwide, terrain and soil attributes can influence biocrust distribution at landscape scale. Multi-source unmanned aerial vehicle (UAV) imagery was used to map and study biocrust ecology in a typical dryland ecosystem in central Spain. Red, green and blue (RGB) imagery was processed using structure-from-motion techniques to map terrain attributes related to microclimate and terrain stability. Multispectral imagery was used to produce accurate maps (accuracy > 80%) of dryland ecosystem components (vegetation, bare soil and biocrust composition). Finally, thermal infrared (TIR) and multispectral imagery was used to calculate the apparent thermal inertia (ATI) of soil and to evaluate how ATI was related to soil moisture (r² = 0.83). The relationship between soil properties and UAV-derived variables was first evaluated at the field plot level. Then, the maps obtained were used to explore the relationship between biocrusts and terrain attributes at ecosystem level through a redundancy analysis. The most significant variables that explain biocrust distribution are: ATI (34.4% of variance, F = 130.75; p < 0.001), Elevation (25.8%, F = 97.6; p < 0.001), and potential solar incoming radiation (PSIR) (52.9%, F = 200.1; p < 0.001). Differences were found between areas dominated by lichens and mosses. Lichen-dominated biocrusts were associated with areas with high slopes and low values of ATI, with soil characterized by a higher amount of soluble salts, and lower amount of organic carbon, total phosphorus (P_tot) and total nitrogen (N_tot). Biocrust-forming mosses dominated lower and moister areas, characterized by gentler slopes and higher values of ATI with soils with higher contents of organic carbon, P_tot and N_tot. This study shows the potential to use UAVs to improve our understanding of drylands and to evaluate the control that the terrain has on biocrust distribution.     

Population of a spatio-temporal knowledge base for jurisdictional domains

Jurisdictional domains are legal divisions of the Earth’s surface frequently used in classification and search systems for location-based queries. However, there are few compilations of jurisdictional domains that include their evolution. One of the causes is the complexity of their generation. As an advance in this area, this paper describes a process that facilitates the creation of knowledge bases containing the evolution of jurisdictional domains. As application example, this paper presents the creation of a jurisdictional knowledge base of Spain with its evolution between 1830 and 2011.     

The contribution of benthic macrofauna to the nutrient filter in coastal lagoons

Human activities in coastal areas have increased the occurrence of eutrophication events, especially in vulnerable ecosystems such as coastal lagoons. Although we have a general knowledge of the consequences of eutrophication in these ecosystems, some efforts need to be made to understand biotic feedbacks that could modify the response of the environment to nutrient enrichment. The plant-mediated 'coastal filter' is one of the main factors that determine lagoonal efficiency in processing excess nutrients. In this context, the present paper examined the relative contribution of benthic macrofauna to the 'coastal filter' of a Mediterranean lagoon. The analysis of macrofaunal assemblages in the Mar Menor lagoon led to a clear differentiation between shallow areas of net nutrient recycling and exportation and deeper areas of net retention. These differences enhance nutrient removal from the water column, thus increasing the ecosystem's resistance to eutrophication.     

Hydrological response of a dryland ephemeral river to southern African climatic variability during the last millennium

A long-term flood record from the Buffels River, the largest ephemeral river of NW South Africa (9250 km²), was reconstructed based on interpretation of palaeoflood, documentary and instrumental rainfall data. Palaeoflood data were obtained at three study reaches, with preserved sedimentary evidence indicating at least 25 large floods during the last 700 yr. Geochronological control for the palaeoflood record was provided by radiocarbon and optically stimulated luminescence (OSL) dating. Annual resolution was obtained since the 19th century using the overlapping documentary and instrumental records. Large floods coincided in the past within three main hydroclimatic settings: (1) periods of regular large flood occurrence (1 large flood/~30 yr) under wetter and cooler prevailing climatic conditions (AD 1600–1800), (2) decreasing occurrence of large floods (1 large flood/~100 yr) during warmer conditions (e.g., AD 1425–1600 and after 1925), and (3) periods of high frequency of large floods (~ 4–5 large floods in 20–30 yr) coinciding with wetter conditions of decadal duration, namely at AD 1390–1425, 1800–1825 and 1915–1925. These decadal-scale periods of the highest flood frequency seem to correspond in time with changes in atmospheric circulation patterns, as inferred when comparing their onset and distribution with temperature proxies in southern Africa.     

Petrophysical properties, composition and deterioration of the Calatorao biogenic stone: case of the sculptures masonry of the Valley of the Fallen (Madrid, Spain)

The huge sculptures placed outdoors in the Valley of the Fallen Memorial Park (El Escorial, Madrid) made with blocks of Black-Limestone from Calatorao-Zaragoza, Spain (BLCZ) and disposed on a concrete core exhibit weathering traces, flaking, saline efflorescence and falling fragments, currently represent a danger for visitors. Frost action is important in the Valley of the Fallen by the large number of freeze–thaw cycles produced during Sculptures‘live under a temperate Mediterranean climate with severe seasonality. The formation of fissures facilitates the water transport within the rock and the salt- and ice-induced deterioration. Temperate climates with frequent freezing and thawing cycles can be the most effective drivers of the visible physical weathering. In order to propose a suitable weathering model, collected black-limestones from sculptures and Calatorao quarries were analyzed by optical microscopy, environmental scanning electron microscopy with energy dispersive spectrometry (ESEM-EDS), inductively coupled mass spectrometry (ICP-MS) and X-ray diffraction. Mercury intrusion porosimetry (MIP), nitrogen absorption and helium pycnometry techniques were used for pore analyses of the BLCZ micro-blocks (10 × 10 × 10 cm) described in terms of pore size distribution, pore volume and specific surface area. The appreciable amount of organic matter was isolated by solvent extraction, acid treatment, flotation and perborate degradation followed by Gas Chromatography–Mass Spectrometry (GC–MS), Analytical Pyrolysis (Py-GC/MS), Fourier Transformed Infrared Spectroscopy and Raman techniques. Both weathered and fresh BLCZ samples contained more than 90 % calcite shells with circa 10 % of pyrite (fresh samples) or iron hydroxides (weathered samples), quartz grains, claystone and fossil organic matter consisting of a condensed matrix with polyalkyl chains and polycyclic methoxyl-lacking aromatic structures. The petrophysical analyses revealed volumes of pores, sized <0.025 μm obtained by N₂ adsorption, of 3.18 × 10^?3 cm³ g^?1 while the measured porosity by MIP in the pore range from 0.005 to 200 μm was 3.30 × 10^?3 cm³ g^?1. These data could be explained by the existence of clay minerals and organic matter in the pore system less than 50 nm of diameter. Concerning BLCZ deterioration it was found that the porous framework of BLCZ was filled with sulphates formed from artificial cement observed in the sculptures inside trough a testing hole and from its intrinsic pyrite. The results suggested that although biological processes were not major agents in rock deterioration, there was also weak compatibility between sculptures‘constituents, (limestone, concrete and oxidized iron clamps) which under, continental Mediterranean conditions, were continuously releasing weathering compounds accelerating disruption of the cut-stone sculptures.