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Search Results: 1 - 10 of 6733 matches for " Tom Weier "
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How to circumvent the size limitation of liquid metal batteries due to the Tayler instability
Frank Stefani,Tom Weier,Thomas Gundrum,Gunter Gerbeth
Physics , 2010, DOI: 10.1016/j.enconman.2011.03.003
Abstract: Recently, a new type of battery has been proposed that relies on the principle of self-assembling of a liquid metalloid positive electrode, a liquid electrolyte, and a liquid metal negative electrode. While this configuration has been claimed to allow arbitrary up-scaling, there is a size limitation of such a system due to a current-driven kink-type instability that is known as the Tayler instability. We characterize this instability in large-scale self-assembled liquid metal batteries and discuss various technical means how it can be avoided.
The Tayler instability at low magnetic Prandtl numbers: between chiral symmetry breaking and helicity oscillations
Norbert Weber,Vladimir Galindo,Frank Stefani,Tom Weier
Physics , 2015,
Abstract: The Tayler instability is a kink-type, current driven instability that plays an important role in plasma physics but might also be relevant in liquid metal applications with high electrical currents. In the framework of the Tayler-Spruit dynamo model of stellar magnetic field generation, the question of spontaneous helical (chiral) symmetry breaking during the saturation of the Tayler instability has received considerable interest. Focusing on fluids with low magnetic Prandtl numbers, for which the quasistatic approximation can be applied, we utilize an integro-differential equation approach in order to investigate the saturation mechanism of the Tayler instability. Both the exponential growth phase and the saturated phase are analyzed in terms of the action of the alpha and beta effects of mean-field magnetohydrodynamics. In the exponential growth phase we always find a spontaneous chiral symmetry breaking which, however, disappears in the saturated phase. For higher degrees of supercriticality, we observe helicity oscillations in the saturated regime. For Lundquist numbers in the order of one we also obtain chiral symmetry breaking of the saturated magnetic field.
Numerical simulation of the Tayler instability in liquid metals
Norbert Weber,Vladimir Galindo,Frank Stefani,Tom Weier,Thomas Wondrak
Physics , 2012, DOI: 10.1088/1367-2630/15/4/043034
Abstract: The electrical current through an incompressible, viscous and resistive liquid conductor produces an azimuthal magnetic field that becomes unstable when the corresponding Hartmann number exceeds a critical value in the order of 20. This Tayler instability, which is not only discussed as a key ingredient of a non-linear stellar dynamo model (Tayler-Spruit dynamo), but also as a limiting factor for the maximum size of large liquid metal batteries, was recently observed experimentally in a column of a liquid metal (Seilmayer et al., Phys. Rev. Lett. 108, 244501, 2012}. On the basis of an integro-differential equation approach, we have developed a fully three-dimensional numerical code, and have utilized it for the simulation of the Tayler instability at typical viscosities and resistivities of liquid metals. The resulting growth rates are in good agreement with the experimental data. We illustrate the capabilities of the code for the detailed simulation of liquid metal battery problems in realistic geometries.
Current-driven flow instabilities in large-scale liquid metal batteries, and how to tame them
Norbert Weber,Vladimir Galindo,Frank Stefani,Tom Weier
Physics , 2013,
Abstract: The use of liquid metal batteries is considered as one promising option for electric grid stabilisation. While large versions of such batteries are preferred in view of the economies of scale, they are susceptible to various magnetohydrodynamic instabilities which imply a risk of short-circuiting the battery due to the triggered fluid flow. Here we focus on the current driven Tayler instability and give critical electrical currents for its onset as well as numerical estimates for the appearing flow structures and speeds. Scaling laws for different materials, battery sizes and geometries are found. We further discuss and compare various means for preventing the instability.
Experimental evidence for Tayler instability in a liquid metal column
Martin Seilmayer,Frank Stefani,Thomas Gundrum,Tom Weier,Gunter Gerbeth,Marcus Gellert,Guenther Ruediger
Physics , 2011, DOI: 10.1103/PhysRevLett.108.244501
Abstract: In the current-driven, kink-type Tayler instability (TI) a sufficiently strong azimuthal magnetic field becomes unstable against non-axisymmetric perturbations. The TI has been discussed as a possible ingredient of the solar dynamo mechanism and a source of the helical structures in cosmic jets. It is also considered as a size limiting factor for liquid metal batteries. We report on a liquid metal TI experiment using a cylindrical column of the eutectic alloy GaInSn to which electrical currents of up to 8 kA are applied. We present results of external magnetic field measurements that indicate the occurrence of the TI in good agreement with numerical predictions. The interference of TI with the competing large scale convection, resulting from Joule heating, is also discussed.
Multi-Color Spectral Transcript Analysis (SPECTRA) for Phenotypic Characterization of Tumor Cells
Joanne H. Hsu,Jingly F. Weier,Heinz-Ulrich G. Weier,Yuko Ito
Biomolecules , 2013, DOI: 10.3390/biom3010180
Abstract: Many human tumors show significant changes in their signal transduction pathways and, thus, the way the cells interact with their environment. Often caused by chromosomal rearrangements, including gene amplifications, translocations or deletions, the altered levels of gene expression may provide a tumor-specific signature that can be exploited for diagnostic or therapeutic purposes. We investigated the utility of multiplexed fluorescence in situ hybridization (FISH) using non-isotopically labeled cDNA probes detected by Spectral Imaging as a sensitive and rapid procedure to measure tumor-specific gene expression signatures. We used a commercially available system to acquire and analyze multicolor FISH images. Initial investigations used panels of fluorescent calibration standards to evaluate the system. These experiments were followed by hybridization of five-to-six differently labeled cDNA probes, which target the transcripts of tyrosine kinase genes known to be differently expressed in normal cells and tumors of the breast or thyroid gland. The relatively simple, yet efficient, molecular cytogenetic method presented here may find many applications in characterization of solid tumors or disseminated tumor cells. Addressing tumor heterogeneity by means of multi-parameter single cell analyses is expected to enable a wide range of investigations in the areas of tumor stem cells, tumor clonality and disease progression.
VR Based Visualization and Exploration of Plant Biological Data
Wolfram Schoor,Felix Bollenbeck,Thomas Seidl,Diana Weier
Journal of Virtual Reality and Broadcasting , 2010,
Abstract: This paper investigates the use of virtual reality (VR) technologies to facilitate the analysis of plant biological data in distinctive steps in the application pipeline. Reconstructed three-dimensional biological models (primary polygonal models) transferred to a virtual environment support scientists' collaborative exploration of biological datasets so that they obtain accurate analysis results and uncover information hidden in the data. Examples of the use of virtual reality in practice are provided and a complementary user study was performed.
The influence of current collectors on Tayler instability and electro-vortex flows in liquid metal batteries
N. Weber,V. Galindo,J. Priede,F. Stefani,T. Weier
Physics , 2014, DOI: 10.1063/1.4905325
Abstract: The Tayler instability is a kink-type flow instability which occurs when the electrical current through a conducting fluid exceeds a certain critical value. Originally studied in the astrophysical context, the instability was recently shown to be also a limiting factor for the upward scalability of liquid metal batteries. In this paper, we continue our efforts to simulate this instability for liquid metals within the framework of an integro-differential equation approach. The original solver is enhanced by multi-domain support with Dirichlet-Neumann partitioning for the static boundaries. Particular focus is laid on the detailed influence of the axial electrical boundary conditions on the characteristic features of the Tayler instability, and, secondly, on the occurrence of electro-vortex flows and their relevance for liquid metal batteries.
Synchronized helicity oscillations: a link between planetary tides and the solar cycle?
F. Stefani,A. Giesecke,N. Weber,T. Weier
Physics , 2015,
Abstract: Recent years have seen an increased interest in the question whether the gravitational action of planets could have an influence on the solar dynamo. Without discussing the observational validity of the claimed correlations, we ask for a possible physical mechanism which might link the weak planetary forces with solar dynamo action. We focus on the helicity oscillations which were recently found in simulations of the current-driven, kink-type Tayler instability which is characterized by an m=1 azimuthal dependence. We show how these helicity oscillations can be resonantly excited by some m=2 perturbation that reflects a tidal oscillation. Specifically, we speculate that the 11.07 years tidal oscillation induced by the Venus-Earth-Jupiter system may lead to a 1:1 resonant excitation of the oscillation of the alpha effect. Finally, in the framework of a reduced, zero-dimensional alpha-Omega dynamo model we recover a 22.14 years cycle of the solar dynamo.
Validation of DNA probes for molecular cytogenetics by mapping onto immobilized circular DNA
Karin M Greulich-Bode, Mei Wang, Andreas P Rhein, Jingly F Weier, Heinz-Ulli G Weier
Molecular Cytogenetics , 2008, DOI: 10.1186/1755-8166-1-28
Abstract: We describe a sensitive approach to quality control probe clones suspected of carrying deletions or for measuring clone overlap with near kilobase resolution. The method takes advantage of the fact that P1/PAC/BAC's can be isolated as circular DNA molecules, stretched out on glass slides and fine-mapped by multicolor hybridization with smaller probe molecules. Two examples demonstrate the application of this technique: mapping of a gene-specific ~6 kb plasmid onto an unusually small, ~55 kb circular P1 molecule and the determination of the extent of overlap between P1 molecules homologous to the human NF-κB2 locus.The relatively simple method presented here does not require specialized equipment and may thus find widespread applications in DNA probe preparation and characterization, the assembly of physical maps for model organisms or in studies on gene rearrangements.Fluorescence in situ hybridization (FISH) has established itself in recent years as an independent method in high-resolution physical map assembly, often providing information that complements PCR-based STS contents mapping [1-5]. Initial characterization of clones by hybridization of non-isotopically labeled probes to metaphase chromosomes allows estimates of probe position within a 10–20 Mbp interval, often detecting clones that are chimeric or contain regions duplicated in the genome [6]. There is, however, a need to thoroughly characterize DNA probes for molecular cytogenetic studies, detect rearrangements within the probe such as deletions, duplications or inversions and anchor probes in a high resolution physical map.Chromatin released from somatic cells by chemical or mechanical treatment provides a template onto which cloned DNA probes can be mapped to determine overlap or physical distance with even higher resolution [7-16]. The application of such techniques for the assembly of high-resolution physical maps, however, is quite inefficient because the genomic templates contain mostly non-target
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