Martian meteorite launch: high-speed ejecta from small craters

We performed high-resolution computer simulations of impacts into homogeneous and layered martian terrain analogs to try to account for the ages and characteristics of the martian meteorite collection found on Earth. We found that craters as small as approximately 3 kilometers can eject approximately 10(7) decimeter-sized fragments from Mars, which is enough to expect those fragments to appear in the terrestrial collection. This minimum crater diameter is at least four times smaller than previous estimates and depends on the physical composition of the target material. Terrain covered by a weak layer such as an impact-generated regolith requires larger, therefore rarer, impacts to eject meteorites. Because older terrain is more likely to be mantled with such material, we estimate that the martian meteorites will be biased toward younger ages, which is consistent with the meteorite collection.     

Hemodynamic signals correlate tightly with synchronized gamma oscillations

Functional imaging methods monitor neural activity by measuring hemodynamic signals. These are more closely related to local field potentials (LFPs) than to action potentials. We simultaneously recorded electrical and hemodynamic responses in the cat visual cortex. Increasing stimulus strength enhanced spiking activity, high-frequency LFP oscillations, and hemodynamic responses. With constant stimulus intensity, the hemodynamic response fluctuated; these fluctuations were only loosely related to action potential frequency but tightly correlated to the power of LFP oscillations in the gamma range. These oscillations increase with the synchrony of synaptic events, which suggests a close correlation between hemodynamic responses and neuronal synchronization.     

A new population of very high energy gamma-ray sources in the Milky Way

Very high energy gamma-rays probe the long-standing mystery of the origin of cosmic rays. Produced in the interactions of accelerated particles in astrophysical objects, they can be used to image cosmic particle accelerators. A first sensitive survey of the inner part of the Milky Way with the High Energy Stereoscopic System (HESS) reveals a population of eight previously unknown firmly detected sources of very high energy gamma-rays. At least two have no known radio or x-ray counterpart and may be representative of a new class of "dark" nucleonic cosmic ray sources.     

Effect of Acid Aluminous Soil on Photosynthetic Parameters of Potato (Solanum tuberosum L.)

Potato is grown worldwide, in some cases in very acid soils. Aluminum (Al) is a major limiting factor for crop productivity in acid soils. Al toxicity was studied mainly on plant roots, while less attention was given to its effects on leaves. Al tolerance observed in solution cultures has rarely been correlated with Al tolerance in acid soils. Al tolerance was assessed in 12 potato cultivars grown in nutrient solutions containing 0, 25, and 50 μmol Al L^?1 by its relative root elongation (RRE). The effect of acid soil with high level of exchangeable Al on leaf mineral content, chlorophyll content, net photosynthetic rate, transpiration rate, stomatal conductance, intercellular CO₂ concentration, water use efficiency (WUE), and light use efficiency (LUE) was studied on cultivars, with the greatest differences in RRE (cv. Tresor, 63.1 and 42.5% and cv. Canberra, 23.3 and 19.2%, for the 25 and 50 μmol Al L^?1 treatments, respectively), grown for 49 days after planting (DAP) in acid and limed soil. Growth in acid soil significantly reduced concentrations of nitrogen (?18.51%) and magnesium (?27.17%) in the leaves in cv. Canberra and concentrations of potassium and copper in both cultivars. Canberra grown in acid soil showed a significant decrease in chlorophyll content and photosynthetic rate, from 28 to 49 DAP, and in transpiration rate and LUE when averaged across all measurements, while cv. Tresor was not affected. Physiological disorders observed on leaves of plants grown in acid soil can be correlated with the differences in Al tolerance observed in nutrient solutions.     

Modelling macronutrients in shelf sea sediments: fitting model output to experimental data using a genetic algorithm

Purpose

Diagenetic modelling, the mathematical simulation of the breakdown of sedimentary organic matter and subsequent fate of associated nutrients, has progressed to a point where complex, non-steady state environments can be accurately modelled. A genetic algorithm has never been used in conjunction with an early diagenetic model, and so we aim to discover whether this method is viable to determining a set of realistic model parameters, which itself is often a difficult task.

Materials and methods

A range of sensitivity analyses were conducted to establish the parameters for which the model was most sensitive before a micro-genetic algorithm (μGA) was used to fit an output from a previously published diagenetic model (OMEXDIA) to observational data, taken at the North Dogger site from a series of cruises in the North Sea. Profiles of carbon, oxygen, nitrate and ammonia were considered. The method allows a set of parameters to be determined in a manner analogous to natural selection. Each iteration of the genetic algorithm within each experiment decreases the variance between the observed profiles and those calculated by OMEXDIA.

Results and discussion

Despite some of the observed profiles, particularly for carbon, showing unusual patterns, the genetic algorithm was able to generate a set of parameters which was able to fit the observations. The genetic algorithm can therefore help to determine the values of other parameters used in the model, for which observational values are difficult to measure (e.g. the flux of organic matter to the sediment from the overlying water column and the rates of degradation of organic matter). We also show that the values of the parameters determined by the μGA technique are able to be used in a potentially temporally predictive manner.

Conclusions

The μGA used is a viable method to fit carbon and nutrient sedimentary profiles observed in complex, dynamic shelf sea systems, despite OMEXDIA originally being designed for a different sedimentary environment. The results therefore show that this novel use of a genetic algorithm is a suitable method for both model calibration and validation and that the technique may help in explaining processes which are poorly understood.     

Reduced tillage effects on physical properties of silt loam soils growing root crops

In the scope of the increasing concern for soil conservation, reduced tillage (RT) agriculture is growing more important in today's agriculture in Western Europe. However, crop rotations often include beets and potatoes, crops that are generally assumed to be less suitable under RT agriculture because they result in a high disturbance of the soil at the formation of the ridges and at harvest. Therefore, the short- and long-term effect of RT agriculture on bulk density (BD), water retention curve (WRC), aggregate stability and field-saturated hydraulic conductivity of silt loam soils with crop rotations including root crops was evaluated. Ten fields at seven locations representing the important RT types, applied for a different number of years, and eight fields under conventional tillage (CT) agriculture with similar soil type and crop rotation were selected. At each location, BD of the 5–10 cm layer was mostly lower in the RT fields (1.42 ± 0.05 Mg m⁻³ [average with standard deviation]) compared to the CT fields (1.44 ± 0.09 Mg m⁻³) and the water content at saturation was mostly higher (0.394 ± 0.027 m³ m⁻³ and 0.382 ± 0.021 m³ m⁻³ for RT and CT fields, respectively). No differences in BD (1.53 ± 0.03 Mg m⁻³) or WRC could be found in the 25–30 cm soil layer when comparing the RT with the CT fields. The stability index of the 0–10 cm layer measured by ‘dry and wet sieving’ [De Leenheer, L., De Boodt, M., 1959. Determination of aggregate stability by the change in mean weight diameter. Mededelingen van landbouwhogeschool en de opzoekingstations van de staat te Gent 24, 290–300] was 40% higher under RT than CT agriculture. The mean weight diameter (MWD) [Le Bissonnais, Y., 1996. Aggregate stability and assessment of soil crustability and erodibility: I. Theory and methodology. Eur. J. Soil Sci. 47, 425–437] was significantly higher even after short-term RT compared to CT agriculture. The MWD after a heavy shower, a slow wetting of the soil and stirring the soil after prewetting was 19%, 38% and 34% higher for RT than CT fields, respectively. The field-saturated hydraulic conductivity tended to be higher under RT compared to the CT fields. Despite the high disturbance of the soil every 2 or 3 years of crop rotations including sugar beets or potatoes, RT agriculture had a positive effect on the investigated physical soil properties.     

Comparison of milk fatty acid profiles measured on Kouri cows near Lake Chad and on dairy cattle as reported by meta-analytical data

Kouri (Bos taurus) is a breed aboriginal from Lake Chad and threatened with extinction. This study aimed to compare milk fatty acid profiles measured on Kouri cows and on high-yielding dairy cattle in Europe and elsewhere as reported by meta-analytical data (22 experimentations). Milk samples were collected from 14 Kouri dairy cows in dry season (March to June) and fatty acids (FA) were determined by gas chromatography. Overall, 32 FA have been identified. Kouri showed lower values (P < 0.001) in the sum of saturated FA (SFA, ?10.9 pts), cis-9, cis-12 18:2 (?1.00 pt) (P < 0.01, higher values (P < 0.001) in the sum of monounsaturated FA (MUFA, +15.3 pts), C18:0) (+3.5 pts), cis-9, trans-11 C18:2-CLA (+1.00 pts), trans-11 18:1 (+1.4 pts) and (P < 0.01) in cis-9, C18:1 (+3.00 pts) acids. The differences between the milk FA profile of the Kouri cows and that obtained from meta-analytical data could be the possible consequence of the use of particular lake pastures by Kouri cows.