Wessling (Hungary)

During laser synthesis of colloids, cavitation bubbles with lifetimes in the microsecond-scale form and shield the laser pulse leading to a decrease in nanoparticle output. A second type of productivity-limiting bubble that severely affects the productivity of the process is often neglected. With lifetimes from milliseconds to seconds, these persistent bubbles are systematically studied in this work by quantifying their composition, amount, size and dwell time in liquids with different viscosities and by relating the results to the nanoparticle productivities. It is found that during synthesis in water, water splitting occurs leading to persistent bubbles consisting of hydrogen and oxygen. In glycols, hydrogen and molecular carbon species containing microbubbles are formed. These persistent microbubbles shield up to 65% of the incoming laser beam depending on the liquid as well as the laser fluence and require attention by means of reducing their dwell time in the ablation zone and enhancing the nanoparticle output by liquid flow. The highest productivities and monodisperse quality are achieved in liquids with the lowest viscosities.

ABSTRACTSolid-state urea clathrate formation (SSUCF) as a chemical separation method prior to stable carbon isotope fingerprinting of diesel fuel contaminations was studied. The stable carbon isotope ratios (δ13C) of n-alkanes in diesel fuel can be used to trace the origin of a contamination. The accurate measurement of the stable isotopic composition of individual compounds requires baseline separation from any other co-eluting compounds. For this purpose silica gel column chromatography (SGCC) and SSUCF were applied. Detailed optimisation of SSUCF was performed: different activators, clathrate formation temperatures, activator volumes, clathrate formation times and sample capacity were investigated. The main benefits of the developed method are reduced clathrate formation time and increased recoveries for lower molecular weight n-alkanes. The recoveries of the developed SSUCF method ranged between 63 and 100% for C10–C24 n-alkanes with relative standard deviation no more than 7%. The precision of the gas chromatography-isotope ratio mass spectrometry measurement was acceptable with a standard deviation of the δ13C values ranging between 0.08 and 0.15‰. The absence of isotopic fractionation was also investigated.The robustness of the method was tested within a model experiment. Nine different water samples including distilled water, tap water, river water, industrial wastewaters and groundwater samples were spiked with the same diesel fuel. The water samples were extracted with n-hexane and after purification with both SGCC and SSUCF n-alkanes were measured. The δ13C values of n-alkanes were found to be similar for all samples. The importance of sample purification prior to compound-specific isotope analysis (CSIA) was also demonstrated within this model experiment by analysing samples from different stages of the sample preparation.Our results show that the proposed method can remarkably improve the precision of compound-specific stable carbon isotope analysis of n-alkanes originating from diesel contamination of the aquatic environment.

Currently the European satellites ERS-2 and ENVISAT are flying on the same orbit with a time separation of 30 minutes. In this presentation pairs of the respective synthetic aperture radar data are analyzed with respect to different atmospheric and oceanic processes. The presented results were obtained in the framework of the ESA AO project COTAR. The tandem configuration exists since the launch of ENVISAT in 2002. In the presentation an overview will be given of the available image pairs acquired over the ocean on a global scale. Combinations of ERS-2 SAR data with both image mode and wide swath mode scenes provided by the ENVISAT ASAR are considered. The two SAR images enable the analysis of the change of radar cross section within half an hour. This temporal separation is very interesting for oceanographic applications because there are many processes like atmospheric fronts, convective cells, ocean tides, etc., which are detectable on this time scale. In the presentation tandem pairs acquired over the research platform FINO west of the island Borkum in the North Sea will be presented. The area is of high practical interest because of the planned Offshore Windpark Borkum West. The platform provides wind measurements at different heights and additional oceanic information to support the planning activities for this windpark. The dynamics of atmospheric structures is analysed. It is well known that the near surface wind field is a dominating factor for the normalized radar cross section of the sea surface. For this reason SAR scenes are well suited to study atmospheric effects with high spatial resolution. It is shown that the use of tandem pairs enables the study of processes like the propagation of an atmospheric fronts or the evolution of convective cells. Both effects are illustrated with different examples using additional information from in situ measurements. Furthermore existing techniques for the estimation of the wind field in 10 m height from SAR data are applied to both images. The evolution of the spatial structure of both wind speed and wind direction is analysed. The observations are related to some theoretical issues like, e.g., the Taylor hypothesis. Particular emphasize is put on the connection between the spatial and the temporal structure of the wind field. This topic is of high practical relevance, e.g., in the context of offshore windenergy exploitation. Additional applications like ship tracking, oil spill detection and the study of ocean wave field dynamics are briefly discussed as well.

In February 2007 the German TerraSAR-X satellite will be launched and the TerraSAR-X mission will enter its approximately 5 months commissioning phase. At that time, the challenging developments on both sides, the advanced high- resolution multi-mode SAR instrument on the one hand and the corresponding sophisticated TerraSAR-X ground segment on the other hand will prove correct interaction and functioning. Screening and processing of the SAR data is the task of the DLR developed TerraSAR Multi Mode SAR Processor TMSP. Preceded by data reception, transcription including decryption and followed by archiving, cataloguing and product delivery, processing of the data by the TMSP is the central part of the SAR data workflow implemented in the Payload Ground Segment PGS. Space and ground segment have been subject to intense complete system testing on ground. Here, the compatibility of SAR instrument commanding, SAR instrument operations and subsequent SAR data processing has been successfully proven for the various acquisition modes of the sensor. Compliance of specified and measured product performance has been investigated as far as possible utilizing simulated point target SAR data. However, the real challenge will be the screening and SAR processing of TerraSAR-X data acquired in orbit and linked down to the receiving station. Therefore, the complete reception and processing chain will be properly tuned and adjusted to the properties of the received TerraSAR-X payload data. The TMSP algorithms have to be configured, e.g. thresholds for calibration pulse analysis, estimation window sizes for SAR data analysis, parameterization of estimation algorithms. Also the configuration of product variants with respect to resolution and radiometric quality will be checked and refined. This paper presents the very first experiences in reception, transcription, screening and processing of TerraSAR-X data with respect to performance, throughput and quality. During the TMSP checkout phase the compatibility of instrument commanding and SAR processing have to be verified and the accordance of SAR performance prediction and the obtained product performance and quality have to be investigated. First characteristics of the SAR data with respect to raw data statistics, calibration pulse analysis and Doppler centroid measurements will be shown. As far as available examples of SAR image products featuring the different image modes, Stripmap, ScanSAR and Spotlight at different incidence angles and polarizations will be displayed and a first estimate of product performance parameters will be given.

New observations taken in aircraft wakes, including the DLR ATTAS, provide strong constraints on models of aircraft plume aerosols. Using a comprehensive microphysics code, we have performed sensitivity studies to identify the key microphysical mechanisms acting in such plumes. Analysis of these simulations reveals that the largest volatile plume particles—those most likely to contribute to the background abundance of condensation nuclei—are dominated by ion‐mode particles when chemiions are included. Moreover, such modeling demonstrates that standard treatments of plume microphysics—in the absence of chemiions—fails to explain field measurements. The principal factor controlling the population of ultrafine plume particles is the number of chemiions emitted by the aircraft engines. Since the ions are a byproduct of the combustion itself, and their abundance in the exhaust stream is controlled by ion‐ion recombination, the initial ion concentrations—and so the eventual emission indices for ion‐mode particles—are expected to be relatively invariant. Our results indicate that reductions in fuel sulfur content, while not likely to lower the total number of volatile particles emitted, would decrease the size of the ion‐mode particles in fresh aircraft wakes, reducing their atmospheric lifetimes and potential environmental effects.

The discovery of Comet IRAS–Araki–Alcock provided the first opportunity for studying a comet at a distance of 4.5 × 106 km from the Earth, thus allowing a spatial resolution of ∼20 km to be achieved. Photographic and spectroscopic plates obtained on 9.9 UT May 1983 using the 90-cm Schmidt and the 182-cm Coper-nicus telescopes at the Asiago Observatory have revealed new fundamental discoveries. The photometric data system (PDS)-elaborated Schmidt plates show that the inner coma of the comet is directed towards the Sun with an inclination of ∼30°, a phenomenon probably due to the rotation of the nucleus. On the spectroscopic plates taken with the grating spectrograph in the spectral range 3,800–8,500 A with a resolution of 6 A, 450 lines can be distinguished, although 90 lines are still unidentified. After detailed analysis, we have identified the molecules HCO and H2S+ which have never before been observed in the visible part of the spectrum of any astronomical object. We suspect that H2CO, DCO, S2 and NH4 are also present. We report here only the preliminary results from our spectroscopic data.