Yearbook 2007

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New phenomena in strongly correlated electron systems

Max Planck Institute for Chemical Physics of Solids Wirth, Steffen; Singh, Surjeet; Capan, Cigdem (Louisiana State University, Baton Rouge, USA); Nicklas, Michael; DiTusa, John F. (Louisiana State University, Baton Rouge, USA); Fisk, Zachary (University of California, Irvine, USA); Steglich, Frank
Strong electronic correlations in solids may result in fascinating, yet often not fully understood phenomena. The latter include unconventional superconductivity and quantum criticality in heavy fermion metals. Here, magnetotransport measurements may shed light on the impact of antiferromagnetic spin fluctuations on these phenomena. Nonetheless, further detailed experimental and theoretical investigations are required for a more complete comprehension within this emerging field of solid state physics. more

Matter Distribution Maps reveal Cosmic Scaffolding

Max Planck Institute for Extraterrestrial Physics Finoguenov, Alexis; Böhringer, Hans; Guzzo, Luigi; Hasinger, Günther
The formation of the large-scale structure of the Universe is essentially determined by the Dark Matter, which constitutes the dominating part of the matter density of the Universe. The visible matter then follows these structures and gives only an indirect picture of the cosmic matter distribution. The COSMOS survey succeeded to provide most detailed picture of the Dark Matter in a sky region with a size of 1.6 square degrees. For the first time the scaffolding of the matter distribution with angular resolution on the sky as well as in depth is seen. It shows a loose network of filaments which intersect in massive structures identified with the locations of galaxy clusters. This overall structure is in good agreement with computer simulations of structure formation models. more
Plasmas are regarded as the most disordered state of matter, so it came as a major surprise when in 1994 MPE scientists discovered that under special conditions plasmas can become liquids and may even spontaneously crystallise. These so-called “Complex Plasmas” have unusual properties. They belong to the class of “soft matter” and make it possible, for the first time, to research condensed matter states at the most elementary (individual particle) level at all relevant length and time scales – including the limits and onset of cooperative phenomena. more
The identity of dark matter is one of the greatest puzzles of our Universe. Its solution may be associated with supersymmetry which is a fundamental space-time symmetry that has not been verified experimentally so far. In many supersymmetric extensions of the Standard Model of particle physics, the lightest supersymmetric particle cannot decay and is hence a promising dark matter candidate. The lightest neutralino, which appears already in the minimal supersymmetric model, can be identified as such a candidate in indirect and direct dark matter searches and at future colliders. As the superpartner of the graviton, the gravitino is another candidate for the lightest superparticle that provides a compelling explanation of dark matter. While it will neither be detected in indirect or direct searches nor be produced directly at accelerators, the analysis of late-decaying charged particles can allow for an experimental identification of the gravitino at future accelerators. In this way, the upcoming experiments at the CERN Large Hadron Collider may become a key to the understanding of our Universe. more

The ATLAS experiment

Max Planck Institute for Physics Andricek, L., Bangert, A., Barillari, T., Benekos, N., Beimforde, M., Bethke, S., Dedes, G., Dubbert, J., Ehrich, Th., Ghodbane, N., Giovannini, P., Göttfert, T., Groh, M., Härtel, R., Horvat, S., Jantsch. A., Kaiser, St., Kiryunin, A., Kluth, S.,; Kortner, O., Kotov, S., Kroha, H., Legger, F., Löben, J.v., Macchilo, A. Moordieck-Möck, S., Moser, H.-G., Menke, S., Nisius, R., Oberlack, H., D'Orazio, A., Patarai, S., Pospelov, G., Potrap, I., Rauter, E., Rebuzzi, D., Richter, R., Richter, R.H.,; Salihagic, D., Schacht, P., Schieck, J., von der Schmitt, H., Stonjek, S., Valderanis, Ch., Yuan, J. Zhuang, X., Zhuravlov, V.
Atlas is one of two general-purpose detectors designed to exploit the full discovery potential of proton-proton collisions at 14 TeV center-of-mass energy of the Large Hadron Collider at CERN/Geneva. High luminosity as well as high energy are the outstanding requirements to study rare processes. In consequence, the detector has to cope with rather difficult design goals. The origin of mass in the standard model, and thus the search for the Higgs boson, is the most prominent issue in particle physics. A major focus is also the super-symmetric extension of the standard model, manifested in a symmetry between fermions and bosons. The institute is involved in the design, construction and integration of major parts of the detector. With the start of data-taking foreseen for 2008, the preparation of the analysis program is an important focus in the ongoing activities of the institute. more
To make the proteins in all of our cells, the genetic information that is stored in DNA is first copied to mRNA and then translated to the polypeptide chain. RNA polymerase II is responsible fort the first step, and it proceeds in a discontinuous fashion with about half of its time spent in pauses. Experimental and theoretical studies on single molecules of RNAP II identify a pause state that proceeds as a random walk, which can generate pauses of durations that bridge scales of time. more

Neutrino Spectroscopy with Borexino: First Direct Measurement of the solar 7Be Neutrino Flux

Max Planck Institute for Nuclear Physics Schönert, Stefan; Oberauer, Lothar (TU München); Göger-Neff, Marianne (TU München)
The Borexino experiment for the measurement of low-energy neutrinos started data taking on May 15, 2007. After only two months of measuring time, the Borexino collaboration for the first time succeeded to unambiguously identify in real time neutrinos which are released in the electron capture of 7Be in the core of the Sun and thereby to verify independently neutrino oscillations. Besides this, also neutrinos from the Earth’s interior and from far distant nuclear reactors generate signals in Borexino. more

Relativistic Quantum Dynamics in Ultra-Strong Laser Fields

Max Planck Institute for Nuclear Physics Müller, Carsten; Bauer, Dieter; Hatsagortsyan, Karen Z.; Feuerstein, Bernold; Keitel, Christoph H.
Charged particles driven by ultra-strong laser fields can be accelerated up to relativistic energies. The energy can be released in atomic collisions in form of X-rays with laser quality. This opens a way towards future radiation sources and open questions in nuclear and particle physics. The following article reports on recent theoretical studies in this research field. more
The transcription of chromosomal DNA into messenger RNA (mRNA) is a central process of eukaryotic gene expression. Shortly after initiation, transcription is paused by inhibition of the positive transcription elongation factor P-TEFb. This arrest acts as a control step before productive elongation of mature mRNA molecules takes place. P-TEFb is regulated by the protein Hexim1 and the small nuclear RNA 7SK. Scientists from MPI of Molecular Physiology in Dortmund have analysed the interaction between P-TEFb and its regulatory factors on a molecular level and shown, how the HIV Tat protein relieves this arrest to stimulate gene expression and production of viral proteins. more
Plants synthesize a vast array of secondary compounds derived from phenylalanine, which fulfill defense functions against unfavorable environmental conditions. To understand the basis for this chemical diversity, the mechanism of substrate selection was unraveled for a key enzyme of phenylpropanoid metabolism. This knowledge may provide strategies of engineering natural product pathways aiming at targeted modifications of plant properties. more
Cultivated barley ranks number four among the world cereals. Barley emerged about 10000 years ago from wild barley species. At the institute, the genetic diversity among cultivated and wild barley varieties is studied with novel genome research tools. The new results are exploited, on one hand, to support modern plant breeding. On the other hand, the data assist in unravelling the molecular regulation of growth and development in crop plants. more
Frost is an important factor limiting geographical distribution and agricultural productivity of plants. Temperate zone plants can adapt to low growth temperatures and thereby increase in freezing tolerance. The analysis of populations of the model plant species Arabidopsis thaliana derived from natural habitats with different climatic conditions shows the complexity of the cold acclimation response both on the physiological and the molecular level. more
We describe experiments on photoionisation of a free cluster jet with synchrotron radiation. Electron spectroscopy allows to map changes of the electronic structure upon condensation of monomers to clusters. Energy remaining in the cluster after photoionization can be released via emission of a secondary electron, which proceeds by an ultrafast energy transfer between neighbouring atoms or molecules within the cluster. more

Physics of fast particles in fusion plasmas

Max Planck Institute for Plasma Physics Guenter, Sibylle; Lauber, Philipp; Strumberger, Erika
The efficiency of a future fusion power plant depends on the confinement of the fusion products, i.e. the helium nuclei, in the magnetic configuration. Therefore, the investigation of the transport properties of this super-thermal particle population is of great scientific interest and will be one of main research areas at the international fusion experiment ITER. Especially large-scale internal and external magnetic perturbations and instabilities driven by the energetic particles can contribute critically to this transport. more
Biological membranes, flexible bilayers composed of lipid molecules, form the outer envelope of every living cell. Many of its important properties rest on principles that can be understood using methods from soft matter physics. For instance, adhering proteins can interact with each other after imprinting a local membrane curvature, as has recently been demonstrated in computer simulations. more
Quantum mechanical molecular dynamics simulations and solid state NMR spectroscopy reveal structural and dynamical properties of polymeric membrane materials of modern fuel cells. The atomistic resolution allows to model the proton transport along the fluctuating hydrogen bond network. The results support the design of improved materials for proton conducting polymers, yielding significant efficiency improvements in future generations of fuel cells. more
The restless legs syndrome (RLS) is a common neurological disorder. Since the first description a large genetic contribution in the aetiology was suspected. For the first time genetic risk variants for RLS have been identified performing a genome wide association study by genotyping 500 000 common genetic variants. More than 1600 patients with RLS and 2600 controls of the general population have participated in this study. The identified genes MEIS1, BTBD9, and LBXCOR1 are know as control factors in embryonic development. Their role in the adult brain is still unknown. more
In speaking and language understanding, word information is retrieved from memory and combined into larger units (unification). Unification operations take place in parallel at the semantic, syntactic and phonological levels of processing. A new framework is proposed that connects psycholinguistic models to a neurobiological account of language. According to this proposal the left inferior frontal gyrus (LIFG) plays an important role in unification. Research in other domains of cognition indicates that left prefrontal cortex has the right neurobiological characteristics for its involvement in the unification for language. A psycholinguistic perspective is provided on the nature of unification and the role of LIFG. more
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