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Search Results: 1 - 10 of 118052 matches for " T Steinmetz "
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Numerical simulation of transient electro-quasistatic fields using advanced subspace projection techniques
T. Steinmetz,G. Wimmer,M. Clemens
Advances in Radio Science : Kleinheubacher Berichte , 2006,
Abstract: The transient simulation of electro-quasistatic fields requires a formulation that takes both dielectric effects as well as nonlinear conductive effects into account. The successive solution of large linear systems of equations with similar or even identical system matrices has to be performed repeatedly if this formulation is discretized by the Finite-Element method and an Implicit-Runge-Kutta method, respectively. The solution processes can be accelerated by using subspace recycling techniques and subspace projection extrapolation techniques. Numerical results for three-dimensional high-voltage applications are presented and the efficiency of these techniques is shown.
Tsunami early warning and decision support
T. Steinmetz,U. Raape,S. Te?mann,C. Strobl
Natural Hazards and Earth System Sciences (NHESS) & Discussions (NHESSD) , 2010, DOI: 10.5194/nhess-10-1839-2010
Abstract: An innovative newly developed modular and standards based Decision Support System (DSS) is presented which forms part of the German Indonesian Tsunami Early Warning System (GITEWS). The GITEWS project stems from the effort to implement an effective and efficient Tsunami Early Warning and Mitigation System for the coast of Indonesia facing the Sunda Arc along the islands of Sumatra, Java and Bali. The geological setting along an active continental margin which is very close to densely populated areas is a particularly difficult one to cope with, because potential tsunamis' travel times are thus inherently short. National policies require an initial warning to be issued within the first five minutes after an earthquake has occurred. There is an urgent requirement for an end-to-end solution where the decision support takes the entire warning chain into account. The system of choice is based on pre-computed scenario simulations and rule-based decision support which is delivered to the decision maker through a sophisticated graphical user interface (GUI) using information fusion and fast information aggregation to create situational awareness in the shortest time possible. The system also contains risk and vulnerability information which was designed with the far end of the warning chain in mind – it enables the decision maker to base his acceptance (or refusal) of the supported decision also on regionally differentiated risk and vulnerability information (see Strunz et al., 2010). While the system strives to provide a warning as quickly as possible, it is not in its proper responsibility to send and disseminate the warning to the recipients. The DSS only broadcasts its messages to a dissemination system (and possibly any other dissemination system) which is operated under the responsibility of BMKG – the meteorological, climatological and geophysical service of Indonesia – which also hosts the tsunami early warning center. The system is to be seen as one step towards the development of a "system of systems" enabling all countries around the Indian Ocean to have such early warning systems in place. It is within the responsibility of the UNESCO Intergovernmental Oceonographic Commission (IOC) and in particular its Intergovernmental Coordinating Group (ICG) to coordinate and give recommendations for such a development. Therefore the Decision Support System presented here is designed to be modular, extensible and interoperable (Raape et al., 2010).
A Laser Frequency Comb System for Absolute Calibration of the VTT Echelle Spectrograph
H. -P. Doerr,T. Steinmetz,R. Holzwarth,T. Kentischer und W. Schmidt
Physics , 2012, DOI: 10.1007/s11207-012-9960-5
Abstract: A wavelength calibration system based on a laser frequency comb (LFC) was developed in a co-operation between the Kiepenheuer-Institut f\"ur Sonnenphysik, Freiburg, Germany and the Max-Planck-Institut f\"ur Quantenoptik, Garching, Germany for permanent installation at the German Vacuum Tower Telescope (VTT) on Tenerife, Canary Islands. The system was installed successfully in October 2011. By simultaneously recording the spectra from the Sun and the LFC, for each exposure a calibration curve can be derived from the known frequencies of the comb modes that is suitable for absolute calibration at the meters per second level. We briefly summarize some topics in solar physics that benefit from absolute spectroscopy and point out the advantages of LFC compared to traditional calibration techniques. We also sketch the basic setup of the VTT calibration system and its integration with the existing echelle spectrograph.
Transporting, splitting and merging of atomic ensembles in a chip trap
P. Hommelhoff,W. H?nsel,T. Steinmetz,T. W. H?nsch,J. Reichel
Physics , 2004, DOI: 10.1088/1367-2630/7/1/003
Abstract: We present a toolbox for cold atom manipulation with time-dependent magnetic fields generated by an atom chip. Wire layouts, detailed experimental procedures and results are presented for the following experiments: Use of a magnetic conveyor belt for positioning of cold atoms and Bose-Einstein condensates with a resolution of two nanometers; splitting of thermal clouds and BECs in adjustable magnetic double well potentials; controlled splitting of a cold reservoir. The devices that enable these manipulations can be combined with each other. We demonstrate this by combining reservoir splitter and conveyor belt to obtain a cold atom dispenser. We discuss the importance of these devices for quantum information processing, atom interferometry and Josephson junction physics on the chip. For all devices, absorption-image video sequences are provided to demonstrate their time-dependent behaviour.
Mitigating the Exploitation of U.S. Borders by Jihadists and Criminal Organizations
Todd Steinmetz
Journal of Strategic Security , 2011,
Abstract: Following the events of September 11, 2001, the U.S. Government began improving security in large population centers and near potential highvalue terrorist targets. Included in these efforts was the development of a more robust border security program, with an emphasis on reducing the threat of terrorist infiltration at America's borders. However, nearly a decade after 9/11, terrorism and organized crime continue to pose significant threats to the United States. As many of these threats emanate from other nations, improved border security helps mitigate these threats. This article summarizes known terrorist activity along the U.S. northern and southern borders, and highlights the threat of organized crime in the southwest border region. Furthermore, it analyzes current border security efforts and identifies key deficiencies in the system. Finally, it provides a tool kit for future border security endeavors that center on developing a larger but more coordinated and nimble border security force, driven by intelligence, and supported by proven technologies and tactical infrastructure.
Photoionization Effects During Galaxy Formation
Matthias Steinmetz
Physics , 1995, DOI: 10.1111/j.1749-6632.1995.tb17624.x
Abstract: SPH hydrodynamical simulations of the formation of galaxies are presented including the effects of an UV background radiation field. Based on a talk presented at the 17th Texas Symposium on Relativistic Astrophysics held in Munich, December 1994.
The relation between QSO absorption systems and high redshift galaxies
Matthias Steinmetz
Physics , 1997,
Abstract: The relation between high redshift galaxies and QSO absorption systems is discussed in the context of hierarchical galaxy formation. It is demonstrated that imprints of the reionization history of the universe are detectable in the $b$-parameter distribution of the \Lya forest at redshifts two to four, favoring models in which hydrogen and helium are reionized simultaneously at or before redshift five by a quasar-like spectrum of UV photons. Hydrodynamical simulations including star formation, feedback due to supernovae and chemical enrichment are also presented. Energy feedback in form of kinetic energy can give rise to an efficient transport of metals out to distances of a few hundred kpc. The observational signature of this metal transport mechanism compared to simple homogeneous enrichment models is discussed. Finally, it is shown that present day $L^*$ galaxies typically have several progenitors at $z\approx3$ spread over a few hundred kpc. These progenitors are closely associated with damped \Lya and Ly-limit systems, and have velocity dispersions, luminosities and colors comparable to U-dropout galaxies at $z\approx 3$.
GRAPESPH: Cosmological SPH simulations with the special purpose hardware GRAPE
Matthias Steinmetz
Physics , 1995, DOI: 10.1093/mnras/278.4.1005
Abstract: A combined N--body/SPH code is presented which benefits from the high speed of the special purpose hardware GRAPE (GRAvity PipE). Besides gravitational forces, GRAPE also returns the list of neighbours and can, therefore, be used to speed up the hydrodynamical part, too. After the interaction list has been passed, density, pressure forces, propagation and interpolation of particles etc. are calculated on the front end, a 50 MHz SUN SPARC 10. In order to combine SPH and GRAPE, possible limitations due to the hardware design of GRAPE are carefully analyzed and modifications compared to current SPH codes are discussed. The resulting code, GRAPESPH, is similarly flexible as TREESPH. It seems especially well suited to investigate the formation of individual objects in a large scale structure environment, like eg. galaxies or clusters. The total performance is at least half as good as treesph on a CRAY and for most applications it seems to be even better. The CPU time per time step is only slightly dependent on the clustering state. GRAPESPH, therefore, provides a very attractive alternative to the use of supercomputers in cosmology.
Simulating Galaxy Formation
Matthias Steinmetz
Physics , 1995,
Abstract: A review on numerical simulations of galaxy formation is given. Different numerical methods to solve collisionless and gas dynamical systems are outlined and one particular simulation technique, Smoothed Particle Hydrodynamics, is discussed in some detail. After a short discussion of the most relevant physical processes which affect the dynamics of the gas, the success and shortcomings of state of the art simulations are discussed via the example of the formation of disk galaxies.
Numerical Simulations of Galaxy Formation
Matthias Steinmetz
Physics , 1996,
Abstract: An overview over the current status of modeling galaxies by means of numerical simulations is given. After a short description of how galaxies form in hierarchically clustering scenarios, success and failures of current simulations are demonstrated using three different applications: the morphology of present day galaxies; the appearance of high redshift galaxies; and the nature of the Ly-alpha forest and metal absorption lines. It is shown that current simulations can qualitatively account for many observed features of galaxies. However, the objects which form in these simulations suffer from a strong overcooling problem. Star formation and feedback processes are likely to be indispensable ingredients for a realistic description even of the most basic parameters of a galaxy. The progenitors of todays galaxies are expected to be highly irregular and concentrated, as supported by recent observations. Though they exhibit a velocity dispersion similar to present day L > L^* galaxies, they may be much less massive. The filamentary distribution of the gas provides a natural explanation for Ly-alpha and metal absorption systems. Furthermore, numerical simulations can be used to avoid misinterpretations of observed data and are able to alleviate some apparent contradictions in the size estimates of Ly-alpha absorption systems.
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