1,721,019 research outputs found
Untersuchungen an einem Eisbohrkern vom Grenzgletscher in Bezug auf Raumladungssignal, pH-Wert, Leitfähigkeit, Stratigraphie und Totalgasgehalt ; Die Analyse der 14C-Messungen von absolut datierten Baumringproben
No full text"Verglichen mit dem, was ich sagen möchte, ist die Wahrheit ein Gerücht"
No full textNachwort zur Textsammlung von Res Flückige
The Record of Gases and Reactive Species in Ice Cores, and Problems of Interpretation
No full textSince the start of the ice core drilling some 30 years ago, a whole zoo of species and parameter have been measured and reported in the literature. Those records per se are of minor relevance. Of great interest is the link to the corresponding atmospheric concentrations, which are related to basic parameter of the Earth System
Seasonal Variations in Hydrogen Peroxide in Polar Ice Cores
No full textHydrogen peroxide is present in polar snow and ice in remarkably high concentrations. With values up to 300 ppb, H2O2 is one of the most concentrated impurities in polar ice. We present a continuous H2O2 firn record from Siple Station (Antarctica); it covers the last 83 years with a resolution of 10–20 samples per year. A very strong seasonality is present in this record. This seasonality is also observed in a Greenland ice core from Dye 3, where we have continuously measured the top 10 m with the same resolution. The maximum concentrations correspond to summer snow layers and can exceed winter snow concentrations by a factor of 10. This property makes H2O2 a useful tracer for dating suitable cores by counting annual layers. The different steps needed to relate the atmospheric to the ice–core H2O2 concentration are discussed. As with isotopic tracers, diffusion in the firn smooths the original H2O2 concentration profile.</jats:p
Secular non-random variations of cosmogenic carbon-14 in the terrestrial atmosphere
No full textThe time dependence of the14C content of bristlecone pine wood samples dated by their tree rings and grown during the last 8000 years was examined. The14C values as measured by the La Jolla Radiocarbon Laboratory were used for the investigation.
Two different smoothing techniques were used for constructing values for equal time intervals. In this manner the introduction of regularities, that could have resulted from applied mathematical techniques, could be excluded.
There is good evidence for non-random features in the power spectrum, in particular for a 200-year periodicity.
The regularities in the power spectrum are further indications supporting the assumption that the14C variations reflect a property of the sun
A miniDOAS instrument optimised for ammonia field measurements
No full textWe present a differential optical absorption spectroscopy (DOAS) instrument, called "miniDOAS", optimised for optical open-path field-measurements of ambient ammonia (NH3) alongside nitrogen oxide (NO) and sulfur dioxide (SO2). The instrument is a further development of the miniDOAS presented by Volten et al. (2012). We use a temperature-controlled spectrometer, a deuterium light source and a modified optical arrangement. The system was set up in a robust, field-deployable, temperature-regulated housing. For the evaluation of light spectra we use a new high-pass filter routine based upon robust baseline extraction with local regression. Multiple linear regression including terms of an autoregressive-moving-average model is used to determine concentrations. For NH3 the random uncertainty is about 1.4% of the concentration, and not better than 0.2 mu g m(-3). Potential biases for the slope of the calibration are given by the precision of the differential absorption cross sections (+/- 3 %) and for the offset by the precision of the estimation of concentration offsets (c(ref)) introduced by the reference spectrum I-ref. Comparisons of miniDOAS measurements to those by NH3 acid trap devices showed good agreement. The miniDOAS can be flexibly used for a wide range of field trials, such as micrometeorological NH3 flux measurements with approaches based upon horizontal or vertical concentration differences. Results from such applications covering concentration dynamics of less than one up to several hundreds of mu g m(-3) are presented
Reduced nitrogen released by agriculture: emission quantification by advanced methodology
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Radon-222 monitoring of soil diffusivity
Full text linkThe temporal evolution of activity profiles of the radon isotope 222Rn in the top 50 cm of soil is used to quantify diffusive gas transport in the air-filled pore space. Air is continuously collected from gas-permeable, hydrophobic membrane tubes placed at various depths under the surface and circulated through a high-sensitivity Rn detector. With a micro-processor controlled inlet system an automatic monitoring of several levels is possible for extended periods of time with a typical time resolution of one hour. In addition, a new dynamic approach to measure the in-situ soil diffusivity Ds (m²/s) around the subsurface tubes is presented where the recovery from air injection is evaluated every 3 hours. Within a test period of 3 weeks Ds dropped from 10−6 m²/s to 3 10−7 m²/s at a depth of z=50 cm due to increasing water content of the soil
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