9,946 research outputs found
Coupling JOREK and STARWALL for Non-linear Resistive-wall Simulations
The implementation of a resistive-wall extension to the non-linear MHD-code
JOREK via a coupling to the vacuum-field code STARWALL is presented along with
first applications and benchmark results. Also, non-linear saturation in the
presence of a resistive wall is demonstrated. After completion of the ongoing
verification process, this code extension will allow to perform non-linear
simulations of MHD instabilities in the presence of three-dimensional resistive
walls with holes for limited and X-point plasmas.Comment: Contribution for "Theory Of Fusion Plasmas, Joint Varenna - Lausanne
International Workshop, Villa Monastero, Varenna, Italy (27.-31.8.2012)",
accepted for publication in Journal of Physics Conference Serie
Magnetic field stabilization system for atomic physics experiments
Atomic physics experiments commonly use millitesla-scale magnetic fields to
provide a quantization axis. As atomic transition frequencies depend on the
amplitude of this field, many experiments require a stable absolute field. Most
setups use electromagnets, which require a power supply stability not usually
met by commercially available units. We demonstrate stabilization of a field of
14.6 mT to 4.3 nT rms noise (0.29 ppm), compared to noise of 100 nT
without any stabilization. The rms noise is measured using a field-dependent
hyperfine transition in a single Ca ion held in a Paul trap at the
centre of the magnetic field coils. For the Ca "atomic clock" qubit
transition at 14.6 mT, which depends on the field only in second order, this
would yield a projected coherence time of many hours. Our system consists of a
feedback loop and a feedforward circuit that control the current through the
field coils and could easily be adapted to other field amplitudes, making it
suitable for other applications such as neutral atom traps.Comment: 6 pages, 5 figure
Two-dimensional streptavidin crystals on giant lipid bilayer vesicles
Streptavidin was crystallized on giant bilayer vesicles (20-60 mum) in sucrose solution at various pH values. The streptavidin-coated vesicles exhibited unique roughened spherical and prolate ellipsoidal shapes, illustrating resistance to curvature of the two-dimensional crystals. Studies indicated that the spheroids and prolate ellipsoids correspond to different crystal morphologies. Through confocal microscopy, the various crystal morphologies on vesicle surfaces were observed under different solution conditions. Unlike two-dimensional (2D) streptavidin crystals grown in ionic buffer that assume the P1, P2, and C222 lattices at pH 4, 5.5, and 7, respectively (Wang et al. Langmuir 1999, 15, 154 1), crystals grown in sucrose with no added salt show only the lowest density C222 lattice due to strong electrostatic interactions
Gauss sum factorization with cold atoms
We report the first implementation of a Gauss sum factorization algorithm by
an internal state Ramsey interferometer using cold atoms. A sequence of
appropriately designed light pulses interacts with an ensemble of cold rubidium
atoms. The final population in the involved atomic levels determines a Gauss
sum. With this technique we factor the number N=263193.Comment: 4 pages, 5 figure
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