Publications (21)83.94 Total impact
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Article: Vesta's shape and morphology.
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ABSTRACT: Vesta's surface is characterized by abundant impact craters, some with preserved ejecta blankets, large troughs extending around the equatorial region, enigmatic dark material, and widespread mass wasting, but as yet an absence of volcanic features. Abundant steep slopes indicate that impact-generated surface regolith is underlain by bedrock. Dawn observations confirm the large impact basin (Rheasilvia) at Vesta's south pole and reveal evidence for an earlier, underlying large basin (Veneneia). Vesta's geology displays morphological features characteristic of the Moon and terrestrial planets as well as those of other asteroids, underscoring Vesta's unique role as a transitional solar system body.Science 05/2012; 336(6082):687-90. · 31.20 Impact Factor -
Article: Vesta’s Shape and Morphology
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ABSTRACT: Vesta’s surface is characterized by abundant impact craters, some with preserved ejecta blankets, large troughs extending around the equatorial region, enigmatic dark material, and widespread mass wasting, but as yet an absence of volcanic features. Abundant steep slopes indicate that impact-generated surface regolith is underlain by bedrock. Dawn observations confirm the large impact basin (Rheasilvia) at Vesta’s south pole and reveal evidence for an earlier, underlying large basin (Veneneia). Vesta’s geology displays morphological features characteristic of the Moon and terrestrial planets as well as those of other asteroids, underscoring Vesta’s unique role as a transitional solar system body.Science 05/2012; 336(6082):687-690. · 31.20 Impact Factor -
Conference Proceeding: Mapping Vesta: First Results from Dawn's Survey Orbit
EPSC-DPS Joint Meeting 2011; 10/2011 -
Article: Chronology and Cratering at Vesta: First Results from Dawn's Survey Orbit
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ABSTRACT: In early August 2011 the Dawn spacecraft enters its Survey Orbit about Vesta to start a one year long mapping mission utilizing four science experiments. We will present our methods and results of preliminary age determinations of some of the major surface units of Vesta based on imaging data of the Framing Camera Experiment.09/2011; -1:501. -
Article: MAGIC discovery of VHE Emission from the FSRQ PKS 1222+21
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ABSTRACT: Very High Energy (VHE) gamma-ray emission from the flat spectrum radio quasar (FSRQ) PKS 1222+21 (4C 21.35, z=0.432) was detected with the MAGIC Cherenkov telescopes during a short observation (~0.5 hr) performed on 2010 June 17. The MAGIC detection coincides with high energy MeV/GeV gamma-ray activity measured by the Large Area Telescope (LAT) on board the Fermi satellite. The VHE spectrum measured by MAGIC extends from about 70 GeV up to at least 400 GeV and can be well described by a power law dN/dE \propto E^-Gamma with a photon index Gamma= 3.75+/-0.27stat +/-0.2syst. The averaged integral flux above 100 GeV is (4.56+/-0.46)x10^(-10) cm^-2 s^-1 (~1 Crab Nebula flux). The VHE flux measured by MAGIC varies significantly within the 30 min exposure implying a flux doubling time of about 10 min. The VHE and MeV/GeV spectra, corrected for the absorption by the extragalactic background light (EBL), can be described by a single power law with photon index 2.72+/-0.34 between 3 GeV and 400 GeV, and is consistent with emission belonging to a single component in the jet. The absence of a spectral cutoff constrains the gamma-ray emission region outside the Broad Line Region, which would otherwise absorb the VHE gamma-rays. Together with the detected fast variability, this challenges present emission models from jets in FSRQ. Moreover, the combined Fermi/LAT and MAGIC spectral data yield constraints on the density of the Extragalactic Background Light in the UV-optical to near-infrared range that are compatible with recent models.01/2011; -
Article: The MAGIC Telescope for Gamma-Ray Astronomy above 30 GeV
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ABSTRACT: The MAGIC telescope, presently at its commissioning phase, will become fully operative by the end of 2003. Placed at the Roque de los Muchachos Observatory (ORM) on the island of La Palma, MAGIC is the largest among new generation ground-based gamma ray telescopes, and will reach an energy threshold as low as 30 GeV. The range of the electromagnetic spectrum between 10 and 250 GeV remains to date mostly unexplored. Observations in this energy region are expected to provide key data for the understanding of a wide variety of astrophysical phenomena belonging to the so-called "non thermal Universe", like the processes in the nuclei of active galaxies, the radiation mechanisms of pulsars and supernova remnants, and the enigmatic gamma-ray bursts. An overview of the telescope and its physics goals is presented.Chinese Journal of Astronomy and Astrophysics 04/2009; 3(S1):531. · 0.89 Impact Factor -
Article: Discovery of very high energy gamma-rays from the flat spectrum radio quasar 3C 279 with the MAGIC telescope
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ABSTRACT: 3C 279 is one of the best studied flat spectrum radio quasars located at a comparatively large redshift of z = 0.536. Observations in the very high energy band of such distant sources were impossible until recently due to the expected steep energy spectrum and the strong gamma-ray attenuation by the extragalactic background light photon field, which conspire to make the source visible only with a low energy threshold. Here the detection of a significant gamma-ray signal from 3C 279 at very high energies (E > 75 GeV) during a flare in early 2006 is reported. Implications of its energy spectrum on the current understanding of the extragalactic background light and very high energy gamma-ray emission mechanism models are discussed.02/2009; -
Article: An AGN Observation Catalogue for the MAGIC Cherenkov Telescope
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ABSTRACT: The 17m diameter MAGIC telescope will become operational in mid-2003. Active Galactic Nuclei (AGN) known to be T eV γ -ray emitters will be observed by the telescope in its initial phase. But, due to the high sensitivity measuring fluxes and low Energy Threshold, MAGIC will be able to observe very high redshifted AGNs which have remained undetected by the present Cherenkov telescopes. The EGRET AGNs and Constamante-Ghisellini T eV BL Lacs candidates are taken as a reference to perform a study of source observability by evaluating their fluxes at the MAGIC energy detection range.06/2003; 5:2555. -
Article: A new class of potent hypolipemic agents raising high-density lipoproteins. Synthesis, reactions and pharmacological properties
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ABSTRACT: A series of thiazolo[3,2-c]pyrimidin-5,7-diones has been synthesized. Results from in vivo evaluations in rats have shown that many of these compounds produce a pronounced increase of HDL cholesterol and a marked decrease of LDL and VLDL cholesterol. The most potent compound 17 (30 mg/kg/d per os over 7 d in male rats) led to the following changes: HDL cholesterol +101%, LDL cholesterol −40%, and VLDL cholesterol −98%. These effects may result in antiatherosclerotic properties in these compounds. The preparation of 7-amino-2,3-dihydrothiazolo[3,2-a]pyrimidin-5-ones and 5-amino-2,3-dihydrothiazolo[3,2-a] pyrimidin-7-ones is described.European Journal of Medicinal Chemistry. 29(11):819-829. -
Article: In situ high-voltage electron microscope deformation study of a two-phase (α2 + γ) Ti-Al alloy
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ABSTRACT: In situ straining experiments in a high-voltage electron microscope have been performed on two-phase Ti-47at.%Al-2at.Cr-0.2at.%Si at room temperature and at 900 K, Two microstructures were investigated which were produced by thermomechanical treatments: a so-called near-gamma and a nearly lamellar microstructure. The processes controlling the motion of individual dislocations in the γ phase are very similar in both materials. At room temperature, ordinary dislocations and superdislocations show a jerky motion which is impeded by localized obstacles and jogs. At high temperature, the dislocations are smoothly bent or arranged in preferred orientations and move in a viscous way. This mode of motions as well as the nonplanar arrangement of dislocations point to the action of climb as an essential process during the high-temperature deformation of Ti-Al. These observations are very similar to those on Al-rich single phase TiAl investigated earlier. The considerably higher flow stress of the two-phase alloys is an effect of their particular microstructures, i.e. of grain boundaries and lamella interfaces.Materials Science and Engineering: A. 233:15-25. -
Article: Diffractive determination of thermo-elastic single crystal constants using polycrystalline samples. I. Thermal expansion of γ-TiAl from 300 to 900K
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ABSTRACT: Thermo-elastic properties of structural materials at operating temperatures can be investigated by energy-dispersive high-resolution neutron diffraction on polycrystalline specimens in order to extract the single crystal tensors of thermal expansion (second rank) and stiffness and compliance (fourth rank). In this paper the characteristic features of the diffractive scheme are explained and the relations for the step given. Single-phase γ-Ti54Al was used as a pilot material. The feasibility of the method could be shown. Qualitative agreement with recent single crystal measurements up to 750 K is achieved.Intermetallics 7:251-258. · 1.65 Impact Factor -
Article: A multifunctional energy-storage system with high-power lead–acid batteries
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ABSTRACT: A multifunctional energy storage system is presented which is used to improve the utilization of renewable energy supplies. This system includes three different functions: (i) uninterruptible power supply (UPS); (ii) improvement of power quality; (iii) peak-load shaving. The UPS application has a long tradition and is used whenever a reliable power supply is needed. Additionally, nowadays, there is a growing demand for high quality power arising from an increase of system perturbation of electric grids. Peak-load shaving means in this case the use of renewable energy stored in a battery for high peak-load periods. For such a multifunctional application large lead–acid batteries with high power and good charge acceptance, as well as good cycle life are needed. OCSM batteries as with positive tubular plates and negative copper grids have been used successfully for a multitude of utility applications. This paper gives two examples where multifunctional energy storage systems have started operation recently in Germany. One system was installed in combination with a 1 MW solar plant in Herne and another one was installed in combination with a 2 MW wind farm in Bocholt. At each place, a 1.2 MW h (1 h-rate) lead–acid battery has been installed. The batteries consist of OCSM cells with the standard design but modified according to the special demand of a multifunctional application.Journal of Power Sources 78:156-163. · 4.95 Impact Factor -
Article: Effect of compression on the behaviour of lead-acid batteries
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ABSTRACT: Mechanical pressure applied to the plate group is known to increase the cycle life of lead-acid batteries. However, the mechanism of the active material stabilisation process is not completely understood yet. The evolution of mechanical pressure in a lead-acid battery during a cycle and through cycle life is also a topic with still many open questions. Additionally, the separation systems available today are not able to exert high compression on the electrode plates: glass mats crush when compressed too much and the gel design does not allow any significant pressure generation at all. Daramic have developed the new acid jellying separator (AJS) allowing the application of mechanical pressure on the plate group. This paper reports on 1.The capacity evolution during cycling for cells with different separation systems namely AGM, gel and AJS, under a variety of initial compression levels.2.The evolution of mechanical pressure on the cell walls during a cycle and through cycle life for different separation systems, and initial compression levels.3.The condition of the active materials at the end of life for cells cycled under compression.4.The effect of the addition of phosphoric acid to the electrolyte.5.The effect of the application of mechanical pressure on the corrosion of pure lead based on cyclic voltammetry measurements under compression.The results of these studies are presented together with some conclusions about the mechanism and effect of compression on a VRLA battery.Journal of Power Sources 95:85-96. · 4.95 Impact Factor -
Article: Extending cycle life of lead-acid batteries: a new separation system allows the application of pressure on the plate group
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ABSTRACT: Since 1983, it has been claimed that pressure applied on a lead-acid battery increases its cycle life. But until now, the use of pressure in production batteries was limited by the mechanical properties of the conventional separation systems (absorptive glass mat (AGM), and gel) which cannot withstand mechanical pressure. In 1997, Daramic developed the new acid jellying separator (AJS) with the aim of combining the advantages of both conventional separation systems and to allow the application of lasting plate group pressure. The new separation system was evaluated and much information was gained on the effect of pressure in a lead-acid battery, e.g. on the evolution of the mechanical pressure during one cycle and during cycle life.Journal of Power Sources 105(2):114-119. · 4.95 Impact Factor -
Article: X-ray standing waves and scanning electron microscopy — Energy dispersive X-ray emission spectroscopy study of gold nanoparticles
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ABSTRACT: A systematic characterization of mono-disperse nanoparticles with nominal diameters of 25 nm, 46 nm, 73 nm, 100 nm, 115 nm, and 250 nm was performed using X-ray standing waves (XSW). The samples were prepared on Si-wafer pieces and analyzed at DELTA synchrotron facility at beamline BL8 under grazing incidence geometry of the primary radiation. Additionally, SEM-EDX inspections of single particles as well as population-density checks were conducted. Particles with smaller diameters were able be characterized by XSW while the larger ones were not completely covered by the interference field produced by the provided 15 keV monochromatic radiation of BL8. The results of the measurements were compared with those of numerical simulations. The extension of the interference field perpendicular to the Si-wafer reflector was determined to be 83 nm ± 4 nm.Spectrochimica Acta Part B Atomic Spectroscopy 65(5):409-414. · 2.88 Impact Factor -
Article: M87
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ABSTRACT: From January until April 2008 the MAGIC Telescope has been monitoring the radio galaxy M87 during several nights. A significant and variable signal has been detected. Following an agreement between the HESS/MAGIC/VERITAS Cherenkov Telescopes, additional observations have been triggered. We will give a short overview of the results from the campaign in January and February.-1:28. -
Conference Proceeding: Lunar geological structure catalog for Dawn
EGU General Assembly 2011; -
Article: Numerical simulation of pore space clogging in geothermal reservoirs by precipitation of anhydrite
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ABSTRACT: Anhydrite cementation in hydrothermal reservoirs can decrease porosity and permeability significantly. In these cases, the amount of hot water produced by hydrothermal heat mining installations is far too low for an economical use of the resource. We study two such cases in the North German sedimentary basin where a secondary anhydrite cementation drastically reduced the original high permeability of a Rhaetian sandstone reservoir. Core-flooding experiments under reservoir conditions indicate that in contrast to the instant dissolution of anhydrite in saline reservoirs, the nucleation probability of anhydrite and the speed of epitaxy on anhydrite crystals ( and , respectively) are very low. We performed numerical simulations of reactive flow on the local and regional scale in order to understand the apparent conflict between constricted nucleation, observed in laboratory experiments, and a complete filling of the pore space by anhydrite cementation found in core samples from boreholes at Neuruppin and Allermöhe. A highly resolved cylindrical reservoir model was used to simulate a chemical stimulation of the Allermöhe reservoir, i.e. the forced increase in porosity and permeability around the borehole in response to the injection of cold brines. Studying the dissolution process for different brine temperatures and salinities, we found that an injection of cold, highly saline brines will break through a cemented barrier of a radius of 5 m around the borehole after 10 days of stimulation. An additional study of the combined effect of hydraulic fracturing and chemical stimulation showed that both types of borehole stimulation increase the permeability by approximately the same amount if dissolution can act directly on the fracture walls. On the reservoir scale, numerical simulations indicate that strata-bound convective flow in the Rhaetian reservoir, driven by temperature differences due to the topography of the aquifer, is insufficient to explain the observed high degree of cementation. However, it can be shown that Ca2+ and dissolved in the reservoir brine are forced to precipitate around the fracture zone, if additional hot fluids flow up along faults, heat up the aquifer, and mix with the colder reservoir brine.International Journal of Rock Mechanics and Mining Sciences 42:1070-1081. · 1.27 Impact Factor -
Conference Proceeding: Lunar volcanic feature catalog for Dawn
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ABSTRACT: Except for a number of low-resolution full-globe images obtained by the Hubble Space Telescope the surface of Vesta remains largely unknown. New image data from NASA’s Dawn mission that will arrive at asteroid Vesta in July 2011 for a 9 month systematic mapping phase to investigate Vesta’s geology [1]. This proposal of lunar analogues relies on medium to lowresolution image data from the Clementine and Lunar Orbiter missions as well as high-resolution image data obtained from the Lunar Reconnaissance Orbiter (LRO), Chandrayaan-1 and Kaguya camera experiments that are comparable to the expected Dawn instrument resolutions.EPSC-DPS Joint Meeting 2011; -
Conference Proceeding: Mapping Vesta: First Results from Dawn’s Survey Orbit
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ABSTRACT: The geologic objectives of the Dawn Mission [1] are to derive Vesta’s shape, map the surface geology, understand the geological context and contribute to the determination of the asteroids’ origin and evolution.Geomorphology and distribution of surface features will provide evidence for impact cratering, tectonic activity, volcanism, and regolith processes. Spectral measurements of the surface will provide evidence of the compositional characteristics of geological units. Age information, as derived from crater sizefrequency distributions, provides the stratigraphic context for the structural and compositional mapping results, thus revealing the geologic history of Vesta. We present here the first results of the Dawn mission from data collected during the approach to Vesta, and its first discrete orbit phase – the Survey Orbit, which lasts 21 days after the spacecraft had established a circular polar orbit at a radius of ~3000 km with a beta angle of 10°-15°.EPSC-DPS Joint Meeting 2011;
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Institutions
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2009
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Max-Planck-Institut für Physik
München, Bavaria, Germany
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