395 research outputs found
A role of Schmidt-Lanterman Incisures for sustaining Schwann cell function in Charcot-Marie-Tooth Disease type 1A
No full textA role of Schmidt-Lanterman Incisures for sustaining Schwann cell function in Charcot-Marie-Tooth Disease type 1A
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Science of the Total Environment
No full textRecently, the subsoils of ephemeral stream(arroyos) floodplains in the northern Chihuahuan Desert were discovered to contain large naturally occurring NO3− reservoirs (floodplain:~38,000 kg NO3-N/ha; background:~60 kg NO3-N/ha). These reservoirs may be mobilized through land use change or natural stream channel migration which makes differentiating between anthropogenic and natural groundwaterNO3−sources challenging. In this study, the fate and sources of NO3− were investigated in an area with multiple NO3− sources such as accidental sewer line releases and sewage lagoons aswell as natural reservoirs of subsoil NO3−. To differentiate sources, this study used a large suite of geochemical tools including δ15N[NO3], δ18O[NO3], δ15N[N2], δ13C[DIC], 14C, tritium (3H), dissolved gas concentrations, major ion chemistry, and contaminants of emerging concern (CEC) including artificial sweeteners. NO3− at sites with the highest concentrations (25 to 229 mg/L NO3-N) were determined to be largely sourced from naturally occurring subsoil NO3− based on δ15N[NO3] (\u3c8 ‰) and mass ratios of Cl−/Br− (〈100) and NO3−/Cl− (\u3e1.5). Anthropogenic NO3− was deciphered using mass ratios of Cl−/Br− (\u3e120) and NO3−/Cl− (\u3c1), δ15N[NO3] (\u3e8‰), and CEC detections. Nitrogen isotope analyses indicated that denitrification is fairly limited in the field area. CEC were detected at 67 % of sites including 3H dead sites (\u3c1 pCi/L) with low percent modern carbon-14 (PMC; \u3c30 %). Local supply wells are 3H dead with low PMC; as 3H does not re-equilibrate and 14C is very slow to re-equilibrate during recirculation through infrastructure, sites with low PMC, 3H \u3c 1 pCi/L, and CEC detections were interpreted as locations with substantial anthropogenic groundwater recharge. Neotame was used to identify locations of very recent (\u3c15 years before present) or ongoing wastewater influxes to the aquifer. This work shows the important influence of naturally occurring subsoil NO3− reservoirs on groundwater in arid regions and the major contribution of artificial recharge
Author Correction: The NLR gene family: from discovery to present day
No full textAuthor Correction: The NLR gene family: from discovery to present da
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Geochemical evolution of uraniferous soda lakes in Eastern Mongolia
No full textExtremely high concentrations of U were discovered in hypersaline soda lakes in eastern Mongolia. The lakes are small, shallow (<1km², <1m), and terminal with variable salinity. The origin and fate of U in these lakes was investigated using geochemical analyses and modeling, using samples collected from lakes and lake pore waters, wells and a stream. Samples were analyzed for Sr and U isotopes, cations, trace metals, anions, total inorganic carbon (TIC), and unstable field parameters. A representative groundwater in the field area is dilute and alkaline, with pH=7.9, 10 mmol L⁻¹ of TIC and 5 mmol L⁻¹ Cl⁻. In contrast, a representative lake water is pH(similar to)10 with TIC and Cl⁻ each more than 1000 mmol L⁻¹. Uranium concentrations in lake waters range from 0.24 to more than 62.5 (Greek small letter mu)mol L⁻¹, possibly making these lakes the highest naturally occurring U concentrations ever reported in a natural water. Groundwater concentrations of U range from 0.03 and 0.43 (Greek small letter mu)mol L⁻¹. The U is natural and derived from groundwater discharging to stable closed basin lakes. Waters are concentrated by evaporation and U(VI) is chelated by CO₃⁻² to form the highly soluble UO₂(CO₃)₃⁻⁴. Two sets of well waters with corresponding lake discharge waters were analyzed for U isotopes. Unnatural concentrations of ²³⁵U were tested for, the presence of which would indicate fallout-derived U. The average of four samples was ²³⁸U/²³⁵U=136(plus or minus)2 indicating that the U is naturally derived. (Greek small letter delta)²³⁴U between one well and its corresponding discharge lake had similar (Greek small letter delta)²³⁴U values ([Greek small letter delta]²³⁴U=837.6- 858.5). The other sample pair however, revealed significant differences between the well and its discharge lake ([Greek small letter delta] ²³⁴U=303.6-1530). This suggests nuclide recoil is significantly enriching one of the lakes with ²³⁴U beyond secular equilibrium during alpha-decay of ²³⁸U in lake sediments or along the groundwater flow path. Modeled evaporation of lakes demonstrates that a U-mineral phase is likely to precipitate during evaporation. Strontium isotopes varied in groundwaters between ⁸⁷Sr/⁸⁶Sr= 0.706192-0.709776 and in lakes ⁸⁷Sr/⁸⁶Sr=0.708702-0.709432. Cretaceous mafic rocks likely account for low ⁸⁷Sr/⁸⁶Sr values while Cretaceous alkaline rhyolites account for the high ⁸⁷Sr/⁸⁶Sr values. High concentrations of U, Na, Cl⁻, and K correlate to radiogenic Sr in lake waters indicating that U is sourced from local Cretaceous alkaline rhyolites.Earth and Planetary Science
Westwards component of ice surface velocity on the Greenland Ice Sheet measured in spring/summer 2012
No full textIce surface motion was recorded by five dual-frequency Leica SR520 GPS receivers deployed on poles drilled 2 m into the ice surface, within 700 m of Moulin L41A at 66.97N -49.27E. GPS data were post-processed kinematically (King, 2004, http://dx.doi.org/10.3189/172756504781829747) with Track v.1.27 software (Chen, 1998, Ph.D. thesis, Cambridge MA, USA) against bedrock-mounted reference stations using a precise ephemeris from the International GNSS Service )Dow et al., 2009, http://dx.doi.org/10.1007/s00190-008-0300-3). Reference stations were located 1 km from the terminus of Russell Glacier and at Kellyville, giving baseline lengths less than 41 km. Due to gaps in the time series caused by power outage, we averaged the horizontal velocities recorded at the five stations with the fewest gaps to give a single record. Positions were recorded at 30 s intervals; 1-hr means were then smoothed using a 5-point binomial filter. Since there was generally little difference in velocity between the stakes, the mean velocity across the network gives a better indication of the seasonal pattern of ice motion with fewer gaps than in the individual records. Velocities are centred differences of hourly displacements. GPS stakes required periodic re-drilling as they gradually melted out
Single photon extraction for FACT's SiPMs allows for novel IACT event representation
No full textImaging Atmospheric Cherenkov Telescopes provide large gamma-ray collection areas > 104 m2 and successfully probe the high energetic gamma-ray sky by observing extensive air-showers during the night. The First G-APD Cherenkov Telescope (FACT) explores silicon based photoelectric converters (called G-APDs or SiPMs) which provide more observation time with strong moonlight, a more stable photon gain over years of observations, and mechanically simpler imaging cameras. So far, the signal extraction methods used for FACT originate from sensors with no intrinsic quantized responses like photomultiplier tubes. This standard signal extraction is successfully used for the long time monitoring of the gamma-ray flux of bright blazars. However, we now challenge our classic signal extraction and explore single photon extraction methods to take advantage of the highly stable and quantized single photon responses of FACT’s SiPM sensors. Instead of having one main pulse with one arrival time and one photon equivalent extracted for each pixel, we extract the arrival times of all individual photons in a pixel’s time line which opens up a new dimension in time for representing extensive air-showers with an IACT.S. A. Mueller, J. Adam, M. L. Ahnen, D. Baack, M. Balbo, A. Biland, M. Blank, T. Bretz, K. Bruegge, J. Buss, A. Dmytriiev, D. Dorner, S. Einecke, D. Elsaesser, C. Hempfling, T. Herbst, D. Hildebrand, L. Kortmann, L. Linhoff, M. Mahlke, K. Mannheim, D. Neise, A. Neronov, M. Noethe, J. Oberkirch, A. Paravac, F. Pauss, W. Rhode, B. Schleicher, F. Schulz, A. Shukla, V. Sliusar, F. Temme, J. Thaele, R. Walte
Ice ablation record from the Greenland Ice Sheet measured in spring/summer 2012
No full textSurface ablation rates were measured daily using changes in ice surface height at five ablation stakes arranged in a cross configuration at ~2 m separation. The stakes were located in the supraglacial hydrological catchment feeding Moulin L41A. The stakes were installed in holes deeper than the length of the stake (so each measurement of ice surface height was made from the ice surface down to the top of the stake) to avoid the problem of enhanced surface melting caused by solar radiation absorbed by the stake. All ablation measurements were carried out by the same observer to ensure consistency for example in the interpretation of the level of a rough ice surface. A full description was provided by Chandler et al. (2015) at https://doi.org/10.5194/tc-9-487-2015
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