Femtosecond laser ablation-ICP-mass spectrometry analysis of a heavy metallic matrix : determination of platinum group metals and gold in lead fire-assay buttons as a case study

Owing to the shorter time interval during which energy is delivered to the sample material, femtosecond (fs) laser ablation is preferable over nanosecond laser ablation for metallic samples. In this project, the influence of various laser parameters-beam diameter, repetition rate and laser fluence-on the ablation of Pb as a heavy metallic matrix using an infrared (lambda = 795 nm) fs-LA system (150 fs pulse duration) was studied. The merits of Ar and He as carrier gases were compared and as He did not provide a substantial improvement in the limits of detection, while deposition of sample material on the window of the ablation chamber was more pronounced, Ar was selected for all further measurements. The effect on the ICP caused by the introduction of various amounts of sample aerosol was studied by monitoring the signal intensity for Ar-38(+). It was shown that maximizing the amount of sample ablated and thus, the amount of sample aerosol introduced into the ICP, did not result in maximum sensitivity, which was rather obtained under 'compromise' conditions. Subsequently, femtosecond LA-quadrupole-based ICP-mass spectrometry (ICP-MS) was used for the determination of traces of the platinum group metals (PGMs) Rh, Pd, Ru, Ir and Pt and of Au in Pb buttons obtained by fire assay of platiniferous ore reference materials. The signal of Pb-204(+) was used as an internal reference, correcting for variations in the laser ablation and transport efficiencies and in the instrument's sensitivity. The spectral interferences established for some of the target nuclides due to the occurrence of Pb2+ ions were successfully overcome by pressurizing the reaction cell with NH3. Quantification versus a calibration curve constructed on the basis of the results obtained for matrix-matched standards (>99% Pb) provided excellent accuracy, superior to those obtained using nanosecond LA-ICP-MS. Also the limits of detection were improved by a factor ranging between 3 and 10 and are <0.010 mu g g(-1) for the most important PGMs (Rh, Pd, Pt) and Au. Several measures, such as the use of a large ablation cell and housing up to 10 Pb buttons, were taken to increase the sample throughput. In the same context, day-to-day reproducibility of the calibration curve was also examined. When recording a 'fresh' calibration curve every day, the average bias between the experimental results and the corresponding reference values was established to be <2.5% for every target element. When using one calibration curve during three consecutive days, the bias still remains <10%, while the sample throughput is increased and analysis of several tens of buttons per day is feasible (10-15 min total analysis time per sample)

08422 Abstracts Collection -- Computer Vision in Camera Networks for Analyzing Complex Dynamic Natural Scenes

From 12.10. to 15.10.2008, the Dagstuhl Event 08422 was held in Schloss Dagstuhl~--~Leibniz Center for Informatics. During the seminar, several participants presented their current research, and ongoing work and open problems were discussed. Abstracts of the presentations given during the seminar as well as abstracts of seminar results and ideas are put together in this paper. The first section describes the seminar topics and goals in general. Links to extended abstracts or full papers are provided, if available

Universal Image Statistics as a Basis for Esthetic Perception

In the last decades many neuroscientists have started to investigate the perception of nature and art by the human visual system. Natural scenes lead to an esthetically pleasing perception, therefore scientists have begun to research the reasons to understand the processing principles of the human visual system

Beschäftigungszuschuss im SGB II: Ein neues Instrument als Ultima Ratio

Mit dem Beschäftigungszuschuss (BEZ) nach § 16e SGB II wurde im Jahr 2007 erstmals in der aktiven Arbeitsmarktpolitik ein Instrument für Langzeitarbeitslose eingeführt, das die unbefristete Förderung einer sozialversicherungspflichtigen Beschäftigung vorsieht. Daher kommt der Teilnehmerauswahl hier noch mehr als bei anderen arbeitsmarktpolitischen Instrumenten eine besondere Bedeutung zu. Das IAB hat gemeinsam mit Kooperationspartnern im Auftrag des BMAS untersucht, welche Personen bis Ende 2008 für die Förderung mit dem BEZ ausgewählt wurden

Prefrontal control over motor cortex cycles at beta-frequency during movement inhibition

A fully adapted behavior requires maximum efficiency to inhibit processes in the motor domain [ 1 ]. Although a number of cortical and subcortical brain regions have been implicated, converging evidence suggests that activation of right inferior frontal gyrus (r-IFG) and right presupplementary motor area (r-preSMA) is crucial for successful response inhibition [ 2, 3 ]. However, it is still unknown how these prefrontal areas convey the necessary signal to the primary motor cortex (M1), the cortical site where the final motor plan eventually has to be inhibited or executed. On the basis of the widely accepted view that brain oscillations are fundamental for communication between neuronal network elements [ 4–6 ], one would predict that the transmission of these inhibitory signals within the prefrontal-central networks (i.e., r-IFG/M1 and/or r-preSMA/M1) is realized in rapid, periodic bursts coinciding with oscillatory brain activity at a distinct frequency. However, the dynamics of corticocortical effective connectivity has never been directly tested on such timescales. By using double-coil transcranial magnetic stimulation (TMS) and electroencephalography (EEG) [ 7, 8 ], we assessed instantaneous prefrontal-to-motor cortex connectivity in a Go/NoGo paradigm as a function of delay from (Go/NoGo) cue onset. In NoGo trials only, the effects of a conditioning prefrontal TMS pulse on motor cortex excitability cycled at beta frequency, coinciding with a frontocentral beta signature in EEG. This establishes, for the first time, a tight link between effective cortical connectivity and related cortical oscillatory activity, leading to the conclusion that endogenous (top-down) inhibitory motor signals are transmitted in beta bursts in large-scale cortical networks for inhibitory motor control

Kurz vor der Reform: Arbeitsmarktinstrumente auf dem Prüfstand

Eine der wichtigsten Aufgaben der aktiven Arbeitsmarktpolitik ist es, die Integration Arbeitsloser in das Erwerbsleben zu unterstützen. Um das Instrumentarium dafür sachgerecht auszugestalten, müssen Qualität und Wirkung der einzelnen Bausteine bekannt sein. Das IAB hat im Januar 2011 gemeinsam mit dem BMAS die bisher vorliegenden wissenschaftlichen Befunde zu den Instrumenten der Arbeitsmarktpolitik systematisch aufgearbeitet und im 'Sachstandsbericht der Evaluation der Instrumente' zusammengefasst. Dieser IAB-Kurzbericht stellt die - nach Instrumentengruppen gegliederten - zentralen Befunde des Sachstandsberichts und die daraus folgenden Empfehlungen vor. Er gibt damit einen kompakten Überblick über die Ergebnisse von Evaluationsprojekten in Deutschland