Biomedical subjects

T Schätz

Publications and source records attributed to T Schätz.

5 recordsLinked to original sources

PubMed2003

Quantum information processing with trapped ions.

Experiments directed towards the development of a quantum computer based on trapped atomic ions are described briefly. We discuss the implementation of single-qubit operations and gates between qubits. A geometric phase gate between two ion qubits is described. Limitations of the trapped-ion method such as those caused by Stark shifts and spontaneous emission are addressed. Finally, we describe a strategy to realize a large-scale device.

Journal Article↗

PubMed2002

Three-dimensional crystalline ion beams.

We report on the experimental realization of two- and three-dimensional crystalline ion beams in the rf quadrupole storage ring PALLAS (LMU, Munich). At a beam energy around 1 eV the phase transition to the Coulomb ordered state is identified by a sudden decrease of the spatial width and of the velocity spread of the beam. The focusing conditions required to attain crystalline beams up to structures of helices surrounding a string are systematically investigated and related to the situation in typical heavy ion storage rings.

Journal Article↗

PubMed2001

Crystalline ion beams.

By freezing out the motion between particles in a high-energy storage ring, it should be possible to create threads of ions, offering research opportunities beyond the realm of standard accelerator physics. The usual heating due to intra-beam collisions should completely vanish, giving rise to a state of unprecedented brilliance. Despite a continuous improvement of beam cooling techniques, such as electron cooling and laser cooling, the ultimate goal of beam crystallization has not yet been reached in high-energy storage rings. Electron-cooled dilute beams of highly charged ions show liquid-like order with unique applications. An experiment using laser cooling suggested a reduction of intra-beam heating, although the results were ambiguous. Here we demonstrate the crystallization of laser-cooled Mg+ beams circulating in the radiofrequency quadrupole storage ring PALLAS at a velocity of 2,800 m s-1, which corresponds to a beam energy of 1 eV. A sudden collapse of the transverse beam size and the low longitudinal velocity spread clearly indicate the phase transition. The continuous ring-shaped crystalline beam shows exceptional stability, surviving for more than 3,000 revolutions without cooling.

Journal Article↗

PubMed1997

Structural analysis of mouse rDNA: coincidence between nuclease hypersensitive sites, DNA curvature and regulatory elements in the intergenic spacer.

We have analyzed the chromatin structure of mouse ribosomal RNA genes (rDNA) by partial digestion of genomic DNA with micrococcal nuclease (MNase), DNase I and identified hypersensitive sites by indirect end-labeling. This analysis has revealed defined regions of nuclease hypersensitivity in the intergenic spacer which in turn coincide with regulatory elements. Hypersensitive sites map to the transcription initiation site, the enhancer repeats, the spacer promoter and two sequence elements which coincide with amplification-promoting sequences. Analysis of the DNA curvature by computer modeling uncovered a striking correlation between sequence-directed structural features of regulatory regions and the position of nuclease hypersensitive sites. Moreover, we demonstrate that nucleosomes are specifically positioned upstream and downstream of the transcription start site. In vitro studies using chromatin assembled in the presence of Drosophila embryo extracts show that binding of the transcription termination factor TTF-I to the upstream terminator mediates this specific nucleosome positioning at the rDNA promoter in an ATP- dependent fashion.

3T3 Cells↗

PubMed1997

Curvature and sequence analysis of eukaryotic promoters.

We have calculated the curvature of 504 eukaryotic promoters predicted by the bent A-tract model of Bolshoy et al. (Proc. Natl. Acad. Sci. USA, 88(6), pp. 2312-16) and the bent non-A-tract models of Calladine et al. (J. Mol. Biol., 201, pp. 127-37) and Satchwell et al. (J. Mol. Biol., 191, pp. 659-75) and found in each case a correlation between TBP binding sites and DNA curvature. Characterizing the TBP binding sites revealed that in addition to the classical TATA box (TATAAA) five more elements occur significantly often in the promoters, nearly all of them being one point mutations of the classical TATA box element. Separate curvature calculations for promoters with canonical and non-canonical TATA boxes have shown that in both cases the strong curvature of the helix axes in the domain of the binding sites is maintained (classical TBP binding sites: + 64-135%, non-classical TBP binding sites: + 27-49%). These results support the proposition that beside DNA flexibility and DNA-protein interactions intrinsic curvature of DNA is one further important criterion for the recognition of different DNA elements by TBP.

Animals↗