Homogene Al-Verteilung in synthetisch hergestellten Al-Goethiten

Goethit (α-FeOOH) ist eines der häufigsten Eisenoxide in Böden der gemäßigten Breiten, das sich vor allem durch die Verwitterung von eisenreichem Ausgangsgestein bildet. In Abhängigkeit der pedogenen Bildungsbedingungen kann es hierbei zum Einbau von Metallkationen in die Gitterstruktur kommen. Am häufigsten lässt sich der Austausch von Fe3+ durch Al3+detektieren, wobei im Allgemeinen davon ausgegangen wird, dass der Einbau durch isomorphen Ersatz erfolgt. Neuere Studien legen jedoch nahe, dass auch die Bildung von separaten Al-reichen Phasen an und innerhalb der Goethit-Struktur möglich sind (1). Für die Untersuchungen wurden Al-Goethite mit Al-Gehalten zwischen 0.1 und 7 % synthetisch hergestellt und mittels Infrarotspektroskopie (FTIR), Röntgendiffraktometrie (XRD) und Mößbauerspektroskopie mineralogisch charakterisiert. Um vorhandene Al-Akkumulationsbereiche auf dem Goethit zu visualisieren, wurde je 0.1 mg Probe auf Graphitträger aufgebracht und mittels Sekundärionen-Massenspektrometrie (NanoSIMS), Energiedispersiver Röntgenspektroskopie (EDX) und Rasterelektronenmikroskopie untersucht. Die Verwendung von NanoSIMS ermöglicht uns hierbei die Al-Verteilung mit einer hohen räumlichen Auflösung von ~ 100 nm darzustellen, wohingegen die Auflösung von EDX-Aufnahmen auf ~ 1 µm begrenzt ist. Durch die Gegenüberstellung beider bildgebender Verfahren ist darüber hinaus ein direkter Vergleich hinsichtlich der detektierbaren Al-Verteilung möglich. Die Auswertung der XRD- und FTIR-Spektren zeigt, dass es mit ansteigendem Al-Gehalt zu Gitterdefekten innerhalb der Goethit-Struktur kommt, wobei das Fehlen von separaten Al-Phasen in den Spektren als erste Hinweise für eine homogene Al-Verteilung angesehen werden kann. Zudem wird deutlich, dass vor allem bei niedrigen Al-Konzentrationen und der Untersuchung von Einzelmineralen, NanoSIMS-Aufnahmen gegenüber EDX-Aufnahmen vorzuziehen sind. Auf Grund der hohen räumlichen Auflösung und niedrigen Nachweisgrenze des NanoSIMS konnten wir auch für geringe Al-Gehalte die homogene räumliche Verteilung von Al nachweisen. Die Kombination von spektroskopischen und bildgebenden Verfahren ermöglicht somit die Schlussfolgerung, dass innerhalb des untersuchten Konzentrationsbereiches Al homogen in die Goethit-Struktur eingebaut ist

Size and Shape Distributions of Primary Crystallites in Titania Aggregates

The primary crystallite size of titania powder relates to its properties in a number of applications. Transmission electron microscopy was used in this interlaboratory comparison (ILC) to measure primary crystallite size and shape distributions for a commercial aggregated titania powder. Data of four size descriptors and two shape descriptors were evaluated across nine laboratories. Data repeatability and reproducibility was evaluated by analysis of variance. One-third of the laboratory pairs had similar size descriptor data, but 83% of the pairs had similar aspect ratio data. Scale descriptor distributions were generally unimodal and were well-described by lognormal reference models. Shape descriptor distributions were multi-modal but data visualization plots demonstrated that the Weibull distribution was preferred to the normal distribution. For the equivalent circular diameter size descriptor, measurement uncertainties of the lognormal distribution scale and width parameters were 9.5% and 22%, respectively. For the aspect ratio shape descriptor, the measurement uncertainties of the Weibull distribution scale and width parameters were 7.0% and 26%, respectively. Both measurement uncertainty estimates and data visualizations should be used to analyze size and shape distributions of particles on the nanoscale

Lunar Exploration Orbiter (LEO): Providing a Globally Covered, Highly Resolved, Integrated Geological, Geochemical and Gephysical Data Base of the Moon

The German initiative for the Lunar Exploration Orbiter (LEO) originated from the national conference “Exploration of our Solar System”, held in Dresden in November 2006. Major result of this conference was that the Moon is of high interest for the scientific community for various reasons, it is affordable to perform an orbiting mission to Moon and it insures technological and scientific progress necessary to assist further exploration activities of our Solar System. Based on scientific proposals elaborated by 50 German scientists in January 2007, a preliminary payload of 12 instruments was defined. Further analysis were initated by DLR in the frame of two industry contracts, to perform a phase-zero mission definition. The Moon, our next neighbour in the Solar System is the first choice to learn, how to work and live without the chance of immediate support from earth and to get prepared for further and farther exploration missions. We have to improve our scientific knowledge base with respect to the Moon applying modern and state of the art research tools and methods. LEO is planed to be launched in 2012 and shall orbit the Moon for about four years in a low altitude orbit

Farmland biodiversity and agricultural management on 237 farms in 13 European and two African regions

Farmland is a major land cover type in Europe and Africa and provides habitat for numerous species. The severe decline in farmland biodiversity of the last decades has been attributed to changes in farming practices, and organic and low-input farming are assumed to mitigate detrimental effects of agricultural intensification on biodiversity. Since the farm enterprise is the primary unit of agricultural decision making, management-related effects at the field scale need to be assessed at the farm level. Therefore, in this study, data were collected on habitat characteristics, vascular plant, earthworm, spider, and bee communities and on the corresponding agricultural management in 237 farms in 13 European and two African regions. In 15 environmental and agricultural homogeneous regions, 6–20 farms with the same farm type (e.g., arable crops, grassland, or specific permanent crops) were selected. If available, an equal number of organic and non-organic farms were randomly selected. Alternatively, farms were sampled along a gradient of management intensity. For all selected farms, the entire farmed area was mapped, which resulted in total in the mapping of 11 338 units attributed to 194 standardized habitat types, provided together with additional descriptors. On each farm, one site per available habitat type was randomly selected for species diversity investigations. Species were sampled on 2115 sites and identified to the species level by expert taxonomists. Species lists and abundance estimates are provided for each site and sampling date (one date for plants and earthworms, three dates for spiders and bees). In addition, farmers provided information about their management practices in face-to-face interviews following a standardized questionnaire. Farm management indicators for each farm are available (e.g., nitrogen input, pesticide applications, or energy input). Analyses revealed a positive effect of unproductive areas and a negative effect of intensive management on biodiversity. Communities of the four taxonomic groups strongly differed in their response to habitat characteristics, agricultural management, and regional circumstances. The data has potential for further insights into interactions of farmland biodiversity and agricultural management at site, farm, and regional scale

Changes in feeding selectivity of freshwater invertebrates across a natural thermal gradient

Environmental warming places physiological constraints on organisms, which may be mitigated by their feeding behavior. Theory predicts that consumers should increase their feeding selectivity for more energetically valuable resources in warmer environments to offset the disproportionate increase in metabolic demand relative to ingestion rate. This may also result in a change in feeding strategy or a shift towards a more specialist diet. This study used a natural warming experiment to investigate temperature effects on the feeding selectivity of three freshwater invertebrate grazers: the snail Radix balthica, the blackfly larva Simulium aureum, and the midgefly larva Eukiefferiella minor. Chesson’s Selectivity Index was used to compare the proportional abundance of diatom species in the guts of each invertebrate species with corresponding rock biofilms sampled from streams of different temperature. The snails became more selective in warmer streams, choosing high profile epilithic diatoms over other guilds and feeding on a lower diversity of diatom species. The blackfly larvae appeared to switch from active collector gathering of sessile high profile diatoms to more passive filter feeding of motile diatoms in warmer streams. No changes in selectivity were observed for the midgefly larvae, whose diet was representative of resource availability in the environment. These results suggest that key primary consumers in freshwater streams, which constitute a major portion of invertebrate biomass, can change their feeding behavior in warmer waters in a range of different ways. These patterns could potentially lead to fundamental changes in the flow of energy through freshwater food webs

The genetic architecture of the human cerebral cortex

The cerebral cortex underlies our complex cognitive capabilities, yet little is known about the specific genetic loci that influence human cortical structure. To identify genetic variants that affect cortical structure, we conducted a genome-wide association meta-analysis of brain magnetic resonance imaging data from 51,665 individuals. We analyzed the surface area and average thickness of the whole cortex and 34 regions with known functional specializations. We identified 199 significant loci and found significant enrichment for loci influencing total surface area within regulatory elements that are active during prenatal cortical development, supporting the radial unit hypothesis. Loci that affect regional surface area cluster near genes in Wnt signaling pathways, which influence progenitor expansion and areal identity. Variation in cortical structure is genetically correlated with cognitive function, Parkinson's disease, insomnia, depression, neuroticism, and attention deficit hyperactivity disorder

Selection of functional and operational requirements for the new 13-m DLR Ka-band ground station in Weilheim

Currently, there are several commercial satellite missions worldwide which provide high rate communication services at Ka-band frequencies (18-40 GHz) to various ground-based users. Moreover, commercial geostationary satellite missions slowly begin to use Ka-band frequencies for LEOP (Launch and Early Orbit Phase), TT&C (Telemetry, Tracking and Command) and payload data operations. One of such satellites is ViaSat-1, which is planned for the launch in 2011. At the same time, due to lack of millimeter wave and high data rate systems, future deep space and near-Earth missions are not in a position to downlink scientific data in a full capacity, which limits mission objectives and possible data return. High data return can only be implemented employing higher frequency bands, e.g. Ka-band. Putting in service higher frequencies allows several advantages. For example, Ka-band brings up to 600% link advantage over X-band. In this concern, the Ka-band antenna is an inevitable part of the modern ground station complex, which allows higher data throughput. Today ESA and NASA have already upgraded their Deep Space ground stations to provide Ka-band capability. There are several projects and potential missions which will require Ka-band support in Europe: H2SAT, EDRS, future L2 (Lagrange) and lunar programs, to name a few. These will include IOT (In-Orbit Testing), TT&C services and potentially LEOP. Having this in mind, GSOC has already started the development of a new full-motion 13-m Ka-band ground station, which will simultaneously enable the missions support and research of a new frequency band, including the design of a high data rate modems, rain attenuation models and Fade Mitigation Techniques. Due to the small wavelength (10-15 mm) of Ka-band signal, the requirements for such ground stations (for front- and back end) in terms of pointing accuracy, acceleration and velocity limits, Doppler shift compensation and the requirements to the specific hardware are very challenging compared to traditional S/X/Ku-band ground stations. This paper describes the most critical requirements partially based on CCSDS recommendations and the needs of future national and European space missions. The following problems have been addressed: frequency selection; pointing accuracy; angular velocity and acceleration, Doppler shift compensation, rain fade mitigation and link budget

X-SAR/SRTM Instrument Phase Error Calibration

Before starting the operational processing of all the acquired X-SAR interferometric SAR data from the SRTM mission, the calibration of deterministic phase errors as far as possible is necessary. Besides the phase errors caused by the shuttle and mast dynamic variations and the position and attitude inaccuracy, there are phase errors originating from the radar instrument itself that may be compensated. Temperature variations and radar parameter changes like gain settings are the major contributors to these phase errors. During the mission we monitored and recorded telemetry data indicating periodic temperature variation along with the orbit, during a data-take and from mission day one to the end. Temperature variations in microwave devices and cables cause a phase variation, which contributes to the overall phase error and degrades the accuracy of the interferometric height measurement. The phase errors have been measured directly, like for the long mast cables, or derived from the calibration tone phase analysis or simply by correcting the known phase to temperature characterization values of the microwave parts with the measured mission temperature data. The lessons learned from that mission and the results of the analysis and the improvement of the height accuracy is presented in this paper

Performance of the Shuttle Radar Topography Mission, X-Band Radar System

Abstract-- The German contribution to the Shuttle Radar Topography Mission (SRTM) is an X-band SAR Interferometer. In 1994 successfully flown flight hardware from the Shuttle radar lab is reused and modified to form a single pass interferometer. The original system is used as the prime channel with the radar transmitter and the channel one receiver. The secondary receive only channel is a new design with an electronically steering antenna beam using existing spare parts like the antenna panels for the 6 meter long array. The steering capability became necessary to compensate for the mast dynamics to keep the prime and secondary antenna beams aligned in azimuth. The performance degradation by using only half of the antenna length compared to the prime channel is recovered by using better low noise amplifiers and by avoiding long corporate feed networks. To optimize the radar parameters special developed software tools are used. Based on a low-resolution backscatter and height map from the Earth, the gain settings and the receiver window presettings are calculated and monitored real-time. This paper describes the X-SAR instrument monitoring concept and reports about the performance, the experience and results from the SRTM mission early this year