Yearbook 2005

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Filled Skutterudites – Physics and Chemistry of Iron-Antimonides of Alkali, Alkaline-Earth, and Rare-Earth Metals

Max Planck Institute for Chemical Physics of Solids Leithe-Jasper, Andreas; Schnelle, Walter; Rosner, Helge; Wirth, Steffen; Sichelschmidt, Jörg; Baenitz, Michael; Gippius, Andrei (Moscow State University, Moskau, Russland); Rabis, Annegrit; Raychaudhuri, Pratap (Tata Institute of Fundamental Research, Mumbai, Indien); Sheet, Goutam (Tata Institute of Fundamental Research, Mumbai, Indien); Burkhardt, Ulrich; Borrmann, Horst; Ramlau, Reiner; Mydosh, John A.; Steglich, Frank; Grin, Juri
Novel ternary intermetallic compounds of iron and antimony with a crystal structure containing large cavities, which can be filled by an electropositive element, show unusual magnetic and thermal properties. A study of the chemical bonding and of the structure-properties relationship is presented. more
Hubble Space Telescope observations reveal that the Andromeda galaxy harbours a central supermassive black hole of 140 million solar masses. The new data exclude astrophysical alternatives to a black hole. The black hole is surrounded by a tiny disk of young stars whose origin remains enigmatic. more

Gamma Astronomy with the MAGIC Telescope

Max Planck Institute for Physics Bartko, H.; Bock, R. K.; Coarasa, J. A.; Garczarczyk, M.; Goebel, F.; Hayashida, M.; Hose, J.; Liebing, P.; Lorenz, E.; Majumdar, P.; Mase, K.; Mazin, D.; Mirzoyan, R.; Mizobuchi, S.; Otte, N.; Paneque, D.; Rudert, A.; Sawallisch, P.; Shinozaki, K.; Stipp, A.-L.; Teshima, M.; Tonello, N.; Wagner, R. M.; Wittek, W.
The MAGIC (Major Atmospheric Gamma-ray Imaging Cherenkov) telescope is a new imaging Cherenkov telescope on the Canary island La Palma. Its purpose is the ground-based detection of high energy cosmic gamma radiation. MAGIC aims to cover the unexplored part of the electromagnetic spectrum between 30 and 300 GeV. Important objects of observation are Active Galactic Nuclei (AGN), supernova remnants, neutron stars and black holes. Further research topics are the nature of the mysterious gamma ray bursts and the search for dark matter particles. more
Paper and pencil are no longer adequate for the prediction of measurements at high-energy colliders, such as the Large Hadron Collider currently under construction at CERN. These predictions are essential for testing the present theories of elementary particles, i.e. the fundamental laws of nature, yet their computation without automated steps is quite involved and error-prone. This article introduces the necessary computational methods and shows their implementation in a computer program on the example of the FeynArts, FormCalc, and LoopTools packages, which are being developed at the MPI. With the automation thus achieved, results can be obtained in minutes that were previously in the domain of man-years. more

Ultracold plasmas and Rydberg gases

Max Planck Institute for the Physics of Complex Systems Pattard, Thomas; Pohl, Thomas; Ates, Cenap; Rost, Jan-Michael
Ultracold plasmas and Rydberg gases give rise to a number of interesting questions based on the unusual properties of these systems. Extremely low temperatures on the one hand, and high electronic excitation together with negligible translational excitation on the other, call for a symbiosis of ideas and concepts from different fields of physics. more
It might be only a coincidence that mankind did not yet perturb the climate system even more than it seems to be the case anyway. The coincidence might be the mostly man-made formation of atmospheric sulfuric acid which forms climate-active aerosol particles. Recent work of the Max Planck Institute for Nuclear Physics has led to new insights in the formation of these aerosol particles. The work comprises process studies in the laboratory as well as atmospheric measurements of aerosol precursors (trace gases, ions, and molecular clusters) [1]. more
The dust detector CDA (Cosmic Dust Analyser) instrument on board the Cassini/Huygens spacecraft started to detect Saturnian dust particles already half a year before the spacecraft started its exploration of the Saturnian system. The sensor registered short collimated streams of nanometre-sized dust particles which were expelled from the inner Saturnian system into the interplanetary space. Based on the dynamical properties of the stream particles, Saturn's A ring was found to be one of the particle sources. This discovery offered the unexpected opportunity to analyze material of Saturn's main ring in situ which is not accessible otherwise. Observations during a close Cassini fly-by of the icy moon Enceladus gave strong indication for ice volcanism. This discovery eventually explained why this moon is effectively replenishing Saturn's vast E-ring with fresh dust particles. more

The Biosynthesis of Phenazines

Max Planck Institute of Molecular Physiology Ahuja, Ekta G.; Bayer, Peter; Blankenfeldt, Wulf; Janning, Petra; Herde, Petra; Mavrodi, Dmitri V.; Thomashow, Linda S.
Phenazines are nitrogen-containing aromatic compounds with antibiotic properties that many bacteria synthesize and secrete into their environment to defend themselves against other competing microorganisms. Phenazine biosynthesis branches off the shikimate pathway but details remain elusive. Scientists from the MPI for molecular physiology have demonstrated that PhzF, a conserved enzyme of the bacterial phenazine biosynthesis operon, isomerises 2,3-dihydro-3-hydroxo anthranilic acid to a ketone. This product dimerises and subsequently undergoes several oxidation and a decarboxylation reaction to yield phenazine-1-carboxylic acid, the end product of the pathway. Using an approach that involves structural and biochemical methods, scientists in Dortmund have obtained evidence for the catalytic role of each of the enzymes of the phz-operon and are able to generate an almost complete structural and mechanistic picture of this interesting pathway. more
For the development of small molecules for chemical biology and medicinal chemistry research relevance in nature is the decisive criterion. For the identification of biologically relevant and prevalidated starting points in vast structural space for compound collection development structural similarities in the ligand sensing cores of proteins and in their natural ligands, i. e the small natural products emerging by biosynthesis, are identified. This analysis is used for similarity clustering of proteins and structural classification of natural products. This approach at the MPI for Molecular Physiology leads to hypothesis-generating tools setting the starting points for chemical genomics research, i. e. the identification and use of small molecules to elucidate the biological function of protein families. more
Plant mutants that lack the so-called Mlo protein are highly resistant against powdery mildew fungi. It is assumed that the fungus exploits presence of this protein to suppress plant defense mechanisms. more
The roxy1 mutant from Arabidopsis thaliana initiates a reduced number of petal primordia and exhibits abnormalities during further petal development. The defects are restricted to the second whorl of the flower and independent of the organ identity. ROXY1 is predominantly expressed in tissues that give rise to new flower organs, including petal precursor cells and petal primordia. Glutaredoxins (GRXs) are small, ubiquitous oxidoreductases that have been intensively studied in E. coli, yeast and humans and oxidize or reduce conserved, cysteine containing motifs. They are involved in a large variety of cellular processes and exert a crucial function in the response to oxidative stress. Our data demonstrate that, unexpectedly, a plant glutaredoxin is involved in flower development, likely by mediating posttranslational modifications and thus affecting the activity of target proteins required for normal petal organ initiation and morphogenesis. Surprisingly, ROXY1 belongs to a novel subgroup, the CC-type, being specific for land plants. The existence of large CC-type subfamilies in angiosperms supports the assumption that their capability to posttranslationally modify target protein activity has been integrated into crucial plant specific processes coinciding with the development of complex flowers. Further analysis of ROXY1 and other CC-type members aims for an understanding of their biochemical properties, the identification of target proteins and unraveling the intriguing connection between redox regulation and flower development. more
Gene silencing is frequently observed in transgenic plants. A molecular genetic approach was taken to show that gene silencing was triggered if the transcript level of the introduced transgenes surpassed a gene-specific threshold. more
In the Materials Science Department of IPP processes of the plasma surface interaction in fusion devices are investigated. In this article, experiments in the device MAJESTIX are reported. This device is devoted to the investigation of microscopic processes relevant to the interaction of hydrogen, hydrocarbon radicals, and ions with carbon surfaces. These processes are of particular importance in plasma surface interaction in fusion devices. more
Stellarators are characterised by a complex three-dimensional structure, distinguishing them from other toroidal magnetic confinement concepts. The investigation of instabilities, especially micro instabilities, and their development into turbulence is not well understood for stellarators. It is particularly interesting if turbulence in stellarators is different from those in other confinement configurations and if a manipulation by optimisation of the magnetic structure is possible. In the following, numerical simulations of the ion-temperature driven instability in the plasma core and of turbulence in the plasma edge for Wendelstein 7-X will be presented. more
The smallest functional units of organisms and soft materials have dimensions between 1 and 10 nm and are not usually repeated periodically in space. By site-directed spin labelling and modern electron spin resonance experiments it is possible to elucidate functionally important aspects of such complex structures. more
The first experimental results for up-conversion photoluminescence excited by using ultra low (~10 W/cm2) intensity non-coherent light in solution of diphenylanthracene blended with platinum octaethyl porphyrin are presented. The crucial advantage of this bi-molecular up-conversion process is the inherent independence from the coherence properties of the excitation light. more
Modern high-throughput and ultra high-throughput genetic approaches allow the identification of predictors of individual response to treatment with anti-depressants. The herein drafted studies exemplify that large cohorts of well phenotyped individuals are vital to the success of genetic analyses. more
This study focuses on the earliest perception and processing of input in an unknown second language. Scientists of the MPI for Psycholinguistics examine the effect of length of exposure, item frequency, and gestural deictic links between sound and context for word recognition and lexical learning in adults. more
Research on language production explores our ability to translate our thoughts into spoken words. The focus of interest is on the interplay between cognitive representations and processes, which together allow us to speak in a seemingly effortless way. The research described here addresses the semantic, syntactic, and phonological processes involved in speaking. Furthermore, it seeks to specify how these processes are linked to other, closely related cognitive functions. more
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