Institut für Physik und Astronomie
Refine
Year of publication
Document Type
- Article (4113)
- Doctoral Thesis (774)
- Postprint (126)
- Monograph/Edited Volume (120)
- Other (83)
- Review (35)
- Habilitation Thesis (24)
- Preprint (24)
- Master's Thesis (10)
- Conference Proceeding (6)
Is part of the Bibliography
- yes (5318) (remove)
Keywords
- diffusion (58)
- stars: massive (56)
- gamma rays: general (47)
- anomalous diffusion (45)
- stars: early-type (45)
- cosmic rays (43)
- stars: winds, outflows (42)
- Magellanic Clouds (39)
- radiation mechanisms: non-thermal (38)
- X-rays: stars (37)
Institute
- Institut für Physik und Astronomie (5318)
- Extern (61)
- Institut für Chemie (19)
- Interdisziplinäres Zentrum für Dynamik komplexer Systeme (18)
- Institut für Geowissenschaften (10)
- Mathematisch-Naturwissenschaftliche Fakultät (7)
- Potsdam Institute for Climate Impact Research (PIK) e. V. (7)
- Department Psychologie (6)
- Institut für Biochemie und Biologie (4)
- Zentrum für Lehrerbildung und Bildungsforschung (ZeLB) (4)
- Institut für Informatik und Computational Science (2)
- Institut für Mathematik (2)
- Department Erziehungswissenschaft (1)
- Department Linguistik (1)
- Department Sport- und Gesundheitswissenschaften (1)
- Institut für Ernährungswissenschaft (1)
- Institut für Romanistik (1)
- Institut für Umweltwissenschaften und Geographie (1)
- Strukturbereich Bildungswissenschaften (1)
- Wirtschaftswissenschaften (1)
Concerns have been raised that anthropogenic climate change could lead to large-scale singular climate events, i.e., abrupt nonlinear climate changes with repercussions on regional to global scales. One central goal of this thesis is the development of models of two representative components of the climate system that could exhibit singular behavior: the Atlantic thermohaline circulation (THC) and the Indian monsoon. These models are conceived so as to fulfill the main requirements of integrated assessment modeling, i.e., reliability, computational efficiency, transparency and flexibility. The model of the THC is an interhemispheric four-box model calibrated against data generated with a coupled climate model of intermediate complexity. It is designed to be driven by global mean temperature change which is translated into regional fluxes of heat and freshwater through a linear down-scaling procedure. Results of a large number of transient climate change simulations indicate that the reduced-form THC model is able to emulate key features of the behavior of comprehensive climate models such as the sensitivity of the THC to the amount, regional distribution and rate of change in the heat and freshwater fluxes. The Indian monsoon is described by a novel one-dimensional box model of the tropical atmosphere. It includes representations of the radiative and surface fluxes, the hydrological cycle and surface hydrology. Despite its high degree of idealization, the model satisfactorily captures relevant aspects of the observed monsoon dynamics, such as the annual course of precipitation and the onset and withdrawal of the summer monsoon. Also, the model exhibits the sensitivity to changes in greenhouse gas and sulfate aerosol concentrations that are known from comprehensive models. A simplified version of the monsoon model is employed for the identification of changes in the qualitative system behavior against changes in boundary conditions. The most notable result is that under summer conditions a saddle-node bifurcation occurs at critical values of the planetary albedo or insolation. Furthermore, the system exhibits two stable equilibria: besides the wet summer monsoon, a stable state exists which is characterized by a weak hydrological cycle. These results are remarkable insofar, as they indicate that anthropogenic perturbations of the planetary albedo such as sulfur emissions and/or land-use changes could destabilize the Indian summer monsoon. The reduced-form THC model is employed in an exemplary integrated assessment application. Drawing on the conceptual and methodological framework of the tolerable windows approach, emissions corridors (i.e., admissible ranges of CO2- emissions) are derived that limit the risk of a THC collapse while considering expectations about the socio-economically acceptable pace of emissions reductions. Results indicate, for example, a large dependency of the width of the emissions corridor on climate and hydrological sensitivity: for low values of climate and/or hydrological sensitivity, the corridor boundaries are far from being transgressed by any plausible emissions scenario for the 21st century. In contrast, for high values of both quantities low non-intervention scenarios leave the corridor already in the early decades of the 21st century. This implies that if the risk of a THC collapse is to be kept low, business-as-usual paths would need to be abandoned within the next two decades. All in all, this thesis highlights the value of reduced-form modeling by presenting a number of applications of this class of models, ranging from sensitivity and bifurcation analysis to integrated assessment. The results achieved and conclusions drawn provide a useful contribution to the scientific and policy debate about the consequences of anthropogenic climate change and the long-term goals of climate protection. --- Anmerkung: Die Autorin ist Trägerin des von der Mathematisch-Naturwissenschaftlichen Fakultät der Universität Potsdam vergebenen Michelson-Preises für die beste Promotion des Jahres 2003/2004.
In-plane strain and shape analysis of Si/SiGe nanostructures by grazing incidence diffraction
(2000)
We consider networks of chaotic maps with different network topologies. In each case, they are coupled in such a way as to generate synchronized chaotic solutions. By using the methods of control of chaos we are controlling a single map into a predetermined trajectory. We analyze the reaction of the network to such a control. Specifically we show that a line of one-dimensional logistic maps that are unidirectionally coupled can be controlled from the first oscillator whereas a ring of diffusively coupled maps cannot be controlled for more than 5 maps. We show that rings with more elements can be controlled if every third map is controlled. The dependence of unidirectionally coupled maps on noise is studied. The noise level leads to a finite synchronization lengths for which maps can be controlled by a single location. A two-dimensional lattice is also studied. (C) 2005 American Institute of Physics