Yearbook 2004

The notion of multiplicative order is very old and has interested mathematicians since the days of Fermat. It plays a role in different branches of mathematics. We will give a short overview of the history of research in this area up to recent work concerning the distribution of the order over residue classes. more

The theory of dynamical systems provides powerful methods for studying diverse problems from planetary orbits to number theory. Recent work by Einsiedler, Katok and Lindenstrauss used methods from dynamical systems to make significant progress on a classical conjecture in number theory. more

We investigate the formation of structure in coupled dynamical systems. Although the individual elements may possess complex dynamics of their own, the system can globally synchronize. This is even possible when the activities between elements are transmitted with temporal delays, that is, when the system does no longer have an intrinsic notion of simultaneity. For suitable parameter constellations, it can also be observed that the restriction of the individual degrees of freedom of the participating elements caused by the coupling leads to the emergence of global dynamical patterns on a longer time scale. This suggests a new mathematical approach to the formation of structure in coupled systems. more

In addition to neurons the brain contains several types of glial cells. While neurons are responsible for fast signal transmission and processing, the functional roles of glial cells have largely remained elusive, in part because methods to investigate these cells in the intact brain were lacking. The development of novel staining methods and in vivo application of two-photon fluorescence microscopy has now enabled to visualize glial cells with high spatial and temporal resolution in the intact neocortex and to study their behavior. Using this combined approach, wave-like oscillations of the intracellular calcium concentration were resolved in the network of astrocytes. These waves might be involved in long-range signaling in the neocortex. In addition, microglial cells, the defense cells of the brain, were found to be not at rest in the healthy brain; they continually survey the surrounding parenchyma with their motile processes showing an astonishingly high level of structural plasticity that far exceeds what is known from other cell types. Moreover, microglial cells took immediate protective actions upon rupture of a blood vessel by targeting and shielding the injured site with their processes. These new results highlight the importance of glial cells as fundamental elements of the brain, both under normal physiological conditions as well as following brain damage such as for example caused by a stroke. more

OLITA, the Outpatient Longterm Intensive Therapy for Alcoholics, was developed as a comprehensive research project in 1993. This paper reports on the results of the OLITA project and its future perspectives. In summer 2003, the monocentric pilot study in Göttingen was completed successfully after ten years and the enrollment of 180 patients. More than 50% of the patients remained abstinent during a follow-up of up to seven years after termination of therapy. The unemployment rate declined from 58% to 22%, comorbid psychiatric disorders decreased from 60% to 13%. An ongoing video-based prospective longitudinal study investigates the therapeutic processes associated with this success. At present, a multicenter trial for the translation of OLITA using the franchising approach is initiated. more

Molecular Imaging enables a non-invasive assessment of the dynamics of disease-specific molecular events in the living organism in vivo. Various imaging modalities including positron emission tomography (PET), magnetic resonance imaging (MRI), and optical imaging are being used to assess a variety of molecular mechanisms, such as gene expression, transcriptional regulation and signal transduction. In brain tumors the imaging targets are endogenous genes as markers for the proliferative activity of the tumor, exogenously introduced genes as markers for the effectiveness of gene therapeutic strategies, and signal transduction and transcriptional regulatory pathways for the improved understanding of glioma development. The most important application of molecular imaging is in translational research, where new forms of molecular targeted therapies should be implemented in clinical application. more

Since begin of the industrial revolution levels of the greenhouse gases carbon dioxide, methane and nitrous oxide have risen dramatically. Fossil fuel combustion, increasingly intensive agriculture and an expanding global human population have been the primary causes for this rapid increase. The same increases in fossil fuel burning and biofuel use have also led to an increase in the emissions of sulphur dioxide, soot and particulate organic matter which form aerosol (=suspended particulate matter) in the atmosphere. Most aerosols cool the atmosphere by increasing Earth's reflectivity, but aerosols containing soot warm it by absorbing sunlight. Cleaner fuel technologies are today leading to a reduction in sulphate emissions. Unlike carbon dioxide and sulphur dioxide emissions, soot emissions are largest in developing countries and are still increasing. According to future emission scenarios, the most polluted regions in the first part of the 21th century will be found at lower latitudes whilst aerosol emissions have decreased in North America and Europe. The most notable climate response as calculated by the MPI Earth-System Model to this latitudinal shift in atmospheric aerosol load is a mitigated surface warming and a wetter soil in highly polluted regions and a pronounced warming and drying in regions where the aerosol load is decreasing. more

Successful infection by the corn pathogen Ustilago maydis is accompanied by a number of morphological transitions that resemble simple developmental programs. Prerequisite for plant penetration is the formation of an infectious filament that exhibits polar tip growth and forms empty sections at its distal pole. In order to investigate the impact of RNA-binding proteins on such developmental processes, members of this protein class were identified according to sequence similarities with well characterized RNA-binding domains. Out of 94, 25 candidates were chosen and respective gene deletion strains were constructed and tested for pathogenic development. The loss of Rrm4, a protein with three N-terminal RNA recognition motifs (RRM) and a C-terminal protein interaction domain, resulted in reduced filamentation and virulence. Further analysis revealed that deletion strains form shorter, bipolar growing filaments. Subcellular localisation in vivo showed that Rrm4 forms particles that move bi-directionally along microtubules. Further mutational analysis of the various protein domains revealed that the N-terminal RNA contact regions RRM1 and RRM2 are most likely necessary to contact cargo whereas the C-terminal protein interaction domain is crucial for particle formation. These results indicate that Rrm4-containing particles transport RNA from the nucleus to the cell poles and that this process is important for unipolar tip growth of the infectious hyphae. A role for long distance transport of RNA along microtubules has already been implicated for embryo development and neuronal signal transmission. Our results obtained in U. maydis constitute the first example for long distance RNA transport in microorganisms indicating that the basic concept is evolutionarily more conserved than previously anticipated. more

Bacterial cells communicate extensively with each other using intercellular signaling molecules. In most cases these signals are small diffusible molecules and part of a communication system that helps the bacteria to assess population size. Analyses of the formation of the magnificently shaped, multicellular, spore-filled fruiting bodies in Myxococcus xanthus revealed a unique intercellular communication system in which the signaling molecule is a 17 kDa, non-diffusible, cell surface-associated protein. This signaling molecule is tailored to guide the slow moving cells of M. xanthus into the fruiting bodies and to coordinate temporally and spatially the two morphogenetic events, aggregation and sporulation, during fruiting body formation. more

Research interests of the Microbial Habitat Group include exchange processes between marine sediments and the overlying water, the in situ quantification of transport and reaction in sediments as well as experimental studies on the influence of currents, waves, and pressure gradients on the biological and biogeochemical sedimentary processes. A special focus lies on microbial and geochemical processes in permeable sediments and other types of ocean margin systems, especially reduced and chemosynthetic habitats. more

Modern spin-electronics defines high requirements for the design and fabrication of new materials. Dilute magnetic semiconductors take an important position among the materials that can fulfill these requirements. Here we report on the results of some of our first-principles studies on these materials. We show that partially filled electronic bands play an important role in the magnetism of these systems. The long-range exchange interaction appears as a compromise between the delocalization of the hole states from the 3d impurities and the strength of the 3d-hole interaction. The properties of this compromise depend strongly on the system studied and can be determined only within the framework of the realistic first-principles density-functional-theory calculations more

The "Cytoskeleton" group focuses on the structure, self-assembly, and dynamics of protein fibers in cells, in particular on microtubules and their associated proteins which are responsible for cell movement, cell division, cell differentiation, or intracellular transport. One of the microtubule associated proteins, the tau protein, forms typical aggregates in nerve cells affected by Alzheimer's disease. Recent findings reveal a linkage between tau's multiple functions and the cellular transport system which could prove essential for the aetiology of Alzheimer's disease. more