5.5-7.5 MeV Proton generation by a moderate intensity ultra-short laser interaction with H2O nano-wire targets

We report on the first generation of 5.5-7.5 MeV protons by a moderate intensity short-pulse laser (4.5 \times 1017 W/cm^2, 50 fsec) interacting with H2O nano-wires (snow) deposited on a Sapphire substrate. In this setup, the laser intensity is locally enhanced by the tip of the snow nano-wire, leading to high spatial gradients. Accordingly, the plasma near the tip is subject to enhanced ponderomotive potential, and confined charge separation is obtained. Electrostatic fields of extremely high intensities are produced over the short scale length, and protons are accelerated to MeV-level energies.Comment: submitted to PRL, under press embargo. 6 figure

Foliar nutrient uptake from dust sustains plant nutrition

Mineral nutrient uptake from soil through the roots is considered the main nutrition pathway for vascular terrestrial plants. Recently, desert dust was discovered as an alternative nutrient source to plants through direct uptake from dust deposited on their foliage. Here we study the uptake of nutrients from freshly deposited desert and volcanic dusts by chickpea plants under ambient and future elevated levels of atmospheric CO2 through the roots and directly through the foliage. We find that within weeks, chickpea plants acquire phosphorus (P) from dust only through foliar uptake under ambient conditions and P, iron (Fe), and nickel (Ni) under elevated CO2 conditions, significantly increasing their growth. Using an additional chickpea variety with contrasting leaf properties, we show that the foliar nutrient uptake pathway from dust is facilitated by leaf surface chemical and physiological traits, such as low pH and trichome densities. We analyzed Nd radiogenic isotopes extracted from plant tissues after dust application to assess the contribution of mineral nutrients that were acquired through the foliage. Our results suggest that foliar mineral nutrient uptake from dust is an important pathway that may play an even bigger role in an elevated-CO2 world.</p

Neutron Capture on the s-Process Branching Point 171^{171}Tm via Time-of-Flight and Activation

The neutron capture cross sections of several unstable nuclides acting as branching points in the s process are crucial for stellar nucleosynthesis studies. The unstable $^{171}$Tm(t$_{1/2}$=1.92 yr) is part of the branching around mass A∼170 but its neutron capture cross section as a function of the neutron energy is not known to date. In this work, following the production for the first time of more than 5 mg of $^{171}$Tm at the high-flux reactor Institut Laue-Langevin in France, a sample was produced at the Paul Scherrer Institute in Switzerland. Two complementary experiments were carried out at the neutron time-of-flight facility (n_TOF) at CERN in Switzerland and at the SARAF liquid lithium target facility at Soreq Nuclear Research Center in Israel by time of flight and activation, respectively. The result of the time-of-flight experiment consists of the first ever set of resonance parameters and the corresponding average resonance parameters, allowing us to make an estimation of the Maxwellian-averaged cross sections (MACS) by extrapolation. The activation measurement provides a direct and more precise measurement of the MACS at 30 keV: 384(40) mb, with which the estimation from the n_TOF data agree at the limit of 1 standard deviation. This value is 2.6 times lower than the JEFF-3.3 and ENDF/B-VIII evaluations, 25% lower than that of the Bao et al. compilation, and 1.6 times larger than the value recommended in the KADoNiS (v1) database, based on the only previous experiment. Our result affects the nucleosynthesis at the A∼170 branching, namely, the $^{171}$Yb abundance increases in the material lost by asymptotic giant branch stars, providing a better match to the available pre-solar SiC grain measurements compared to the calculations based on the current JEFF-3.3 model-based evaluation

Elemental and isotopic composition of surface soils from key Saharan dust sources

Saharan dust contains significant amount of P, an important macronutrient to all living organisms, which has been shown to exert large effects on nearby and remote ecosystems located across the dust transport pathways. The biological effect of Saharan dust depends on the amount and nature of the P speciation of the dust. However, thus far relatively small numbers of samples from potential source areas (PSA) has been analyzed. Here we report the P speciation (resin-P, HCl-P, Fe-bound-P and organic-P), the δ18OP values, the elemental composition, and the 87Sr/86Sr and 143Nd/144Nd of the fine fraction and bulk soil from 5 important PSAs across Northern Africa. We found the HCl-P concentrations between different source areas were relatively constrained but that these concentrations were higher in the fine fraction, which here is used a surrogate for dust. The δ18OP values for soils from sand dunes varied from 15.0 to 21.4‰, which is in the range of phosphate minerals from sedimentary origin. The δ18OP values of soils from dry lakes were significantly higher (24.0–28.5‰), probably since their P is derived from fossilized plankton that lived in the lake as it dried up. The 87Sr/86Sr and εNd values ranged from 0.7219 to 0.7276 and − 12.7 to − 14.0 in eastern samples and from 0.7146 to 0.7185 and − 11.9 to − 13.4 in western samples, suggesting a different source for the siliciclastic material of eastern and western samples. Our analysis indicates that the δ18OP values are decoupled from the Sr and Nd isotopic systems. Together, the new chemical and isotope data are specific for different PSAs and thus are used for source apportionment purposes. Such data can be used to provide more accurate estimates of the flux of potentially bioavailable P to marine and terrestrial ecosystems. These estimates can be used in global climate models to determine the magnitude and distribution of P control on carbon uptake

North Atlantic controlled depositional cycles in MIS 5e layered sediments from the deep Dead Sea basin

AbstractThe drilled Inter-Continental Drilling Project core at the deeps of the Dead Sea reveals thick sequences of halite deposits from the last interglacial period, reflecting prevailing arid conditions in the lake’s watershed. Here, we examine sequences of intercalating evaporates (halite or gypsum) and fine-detritus laminae and apply petrographic, micro-X-ray fluorescence, and statistical tools to establish in high-temporal resolution the hydroclimatic controls on the sedimentation in the last interglacial Dead Sea. The time series of the thickness of the best-recovered core sections of the layered halite, detritus, and gypsum reveals periodicities of ~11, 7–8, and 4–5 yr, pointing to a North Atlantic control and possibly solar influence on the hydrology of the Dead Sea watershed during the regionally arid period of the last interglacial period. Similar periodicities were detected in the last glacial and modern sedimentary sequences of the Dead Sea and other archives of the central Levant, indicating a persistent impact of the solar cycles on regional hydrology, possibly through the effects of the North Atlantic Oscillation.</jats:p