The hp-adaptive FEM based on continuous Sobolev embeddings: isotropic refinements

The aim of this paper is to present a new class of smoothness testing strategies in the context of hp-adaptive refinements based on continuous Sobolev embeddings. In addition to deriving a modified form of the 1d smoothness indicators introduced in [26], they will be extended and applied to a higher dimensional framework. A few numerical experiments in the context of the hp-adaptive FEM for a linear elliptic PDE will be performed.

Effects of sample mass and macrofossil type on radiocarbon dating of arctic and boreal lake sediments

Dating lake sediments by accelerator mass spectrometry (AMS) 14C analysis of terrestrial plant macrofossils overcomes one of the main problems associated with dating bulk sediment samples, i.e., the presence of old organic matter. Even so, many AMS dates from arctic and boreal sites appear to misrepresent the age of the sediment. To understand the nature of these apparent dating anomalies better, we conducted a series of 14C dating experiments using samples from Alaskan and Siberian lake-sediment cores. First, to test whether our analytical procedures introduced a sample-mass bias, we obtained 14C dates for different-sized pieces of single woody macrofossils. In these sample-mass experiments, statistically equivalent ages were found for samples as small as 0.05 mg C. Secondly, to assess whether macrofossil type influenced dating results, we conducted sample-type experiments in which 14C dates were obtained for different macrofossil types sieved from the same depth in the sediment. We dated materials from multiple levels in sediment cores from Upper Capsule Lake (North Slope, northern Alaska) and Grizzly Lake (Copper River Basin, southern Alaska) and from single depths in other records from northern Alaska. In several of the experiments there were significant discrepancies between dates for different plant tissues, and in most cases wood and charcoal were older than other macrofossil types, usually by several hundred years. This pattern suggests that 14C dates for woody macrofossils may misrepresent the age of the sediment by centuries, perhaps because of their longer terrestrial residence time and the potential in-built age of longlived plants. This study identifies why some 14C dates appear to be inconsistent with the overall age-depth trend of a lake-sediment record, and it may guide the selection of 14C samples in future studies.

Development of a method for fast and automatic radiocarbon measurement of aerosol samples by online coupling of an elemental analyzer with a MICADAS AMS

A fast and automatic method for radiocarbon analysis of aerosol samples is presented. This type of analysis requires high number of sample measurements of low carbon masses, but accepts precisions lower than for carbon dating analysis. The method is based on online Trapping CO2 and coupling an elemental analyzer with a MICADAS AMS by means of a gas interface. It gives similar results to a previously validated reference method for the same set of samples. This method is fast and automatic and typically provides uncertainties of 1.5–5% for representative aerosol samples. It proves to be robust and reliable and allows for overnight and unattended measurements. A constant and cross contamination correction is included, which indicates a constant contamination of 1.4 ± 0.2 μg C with 70 ± 7 pMC and a cross contamination of (0.2 ± 0.1)% from the previous sample. A Real-time online coupling version of the method was also investigated. It shows promising results for standard materials with slightly higher uncertainties than the Trapping online approach.

THEODORE, a two-step heating system for the EC/OC determination of radiocarbon (14C) in the environment

Measurements of 14C in the organic carbon (OC) and elemental carbon (EC) fractions, respectively, of fine aerosol particles bear the potential to apportion anthropogenic and biogenic emission sources. For this purpose, the system THEODORE (two-step heating system for the EC/OC determination of radiocarbon in the environment) was developed. In this device, OC and EC are transformed into carbon dioxide in a stream of oxygen at 340 and 650 �C, respectively, and reduced to filamentous carbon. This is the target material for subsequent accelerator mass spectrometry (AMS) 14C measurements, which were performed on sub-milligram carbon samples at the PSI/ETH compact 500 kV AMS system. Quality assurance measurements of SRM 1649a, Urban Dust, yielded a fraction of modern fM in total carbon (TC) of 0.522 ±0.018 (n ¼ 5, 95% confidence level) in agreement with reported values. The results for OC and EC are 0.70± 0.05 (n ¼ 3) and 0.066 ± 0.020 (n ¼ 4), respectively.

129I/127I ratios and 129I concentrations in a recent sea sediment core and in rainwater from Sevilla (Spain) by AMS

In spite of the environmental relevance of 129I, there is still a scarcity of data about its presence in the different natural compartments. In this work, results are presented on the concentration of 129I in rainwater samples taken in Sevilla (southwestern Spain) and in a sediment core taken near the Ringhals coast (Sweden). Typical concentrations of 108 and 109129I at/l are found in rainwater samples, similar to other values in literature. In the case of the sediment core, our results clearly show the impact of anthropogenic sources, with concentrations in the order of 1013129I at./kg and isotopic ratios 129I/127I in the order of 10−8 in the higher layers.

High-resolution AMS (super 14) C dating of post-bomb peat archives of atmospheric pollutants.

Peat deposits in Greenland and Denmark were investigated to show that high-resolution dating of these archives of atmospheric deposition can be provided for the last 50 years by radiocarbon dating using the atmospheric bomb pulse. (super 14) C was determined in macrofossils from sequential one cm slices using accelerator mass spectrometry (AMS). Values were calibrated with a general-purpose curve derived from annually averaged atmospheric (super 14) CO (sub 2) values in the northernmost northern hemisphere (NNH, 30 degrees -90 degrees N). We present a through review of (super 14) C bomb-pulse data from the NNH including our own measurements made in tree rings and seeds from Arizona as well as other previously published data. We show that our general-purpose calibration curve is valid for the whole NNH producing accurate dates within 1-2 years. In consequence, (super 14) C AMS can precisely date individual points in recent peat deposits within the range of the bomb-pulse (from the mid-1950s on). Comparing the (super 14) C AMS results with the customary dating method for recent peat profiles by (super 210) Pb, we show that the use of (super 137) Cs to validate and correct (super 210) Pb dates proves to be more problematic than previously supposed. As a unique example of our technique, we show how this chronometer can be applied to identify temporal changes in Hg concentrations from Danish and Greenland peat cores.

Characterization of the Axial Jet Separator with a CO2/Helium Mixture: Toward GC-AMS Hyphenation

Development of interfaces for sample introduction from high pressures is important for real-time online hyphenation of chromatographic and other separation devices with mass spectrometry (MS) or accelerator mass spectrometry (AMS). Momentum separators can reduce unwanted low-density gases and introduce the analyte into the vacuum. In this work, the axial jet separator, a new momentum interface, is characterized by theory and empirical optimization. The mathematical model describes the different axial penetration of the components of a jetgas mixture and explains the empirical results for injections of CO2 in helium into MS and AMS instruments. We show that the performance of the new interface is sensitive to the nozzle size, showing good qualitative agreement with the mathematical model. Smaller nozzle sizes are more preferable due to their higher inflow capacity. The CO2 transmission efficiency of the interface into a MS instrument is ~14% (CO2/helium separation factor of 2.7). The interface receives and delivers flows of ~17.5 mL/min and ~0.9 mL/min, respectively. For the interfaced AMS instrument, the ionization and overall efficiencies are 0.7-3% and 0.1-0.4%, respectively, for CO2 amounts of 4-0.6 µg C, which is only slightly lower compared to conventional systems using intermediate trapping. The ionization efficiency depends on to the carbon mass flow in the injected pulse and is suppressed at high CO2 flows. Relative to a conventional jet separator, the transmission efficiency of the axial jet separator is lower, but its performance is less sensitive to misalignments.