132 research outputs found
Domain Decomposition Methods in Optimal Flow Control for High Performance Computing
This thesis is concerned with linear and non-linear optimal flow control problems which are modeled by systems of partial differential equations. The numerical treatment of such problems, especially in the context of flow problems, is often very expensive and challenging. To tackle this complexity, we present parallel approaches based on non-overlapping domain decomposition methods that exploit the computational power provided by modern high performance computing technologies
Position-sensitive ion detection in precision Penning trap mass spectrometry
A commercial, position-sensitive ion detector was used for the first time for
the time-of-flight ion-cyclotron resonance detection technique in Penning trap
mass spectrometry. In this work, the characteristics of the detector and its
implementation in a Penning trap mass spectrometer will be presented. In
addition, simulations and experimental studies concerning the observation of
ions ejected from a Penning trap are described. This will allow for a precise
monitoring of the state of ion motion in the trap.Comment: 20 pages, 13 figure
Temporal resolution deficits in the visual fields of MS patients
AbstractWe assessed the relationship between temporal resolution and MS-induced neuropathy. A diagnostic strategy comprising assessments of temporal resolution at 16 points in the extra-foveal visual field up to 12° from the fovea was first compared with foveal temporal resolution and with a standard VEP procedure in the same MS patients. At the group level, foveal temporal resolution was less sensitive to demyelination than the 16-point diagnostic strategy, the detection rate of which was comparable to that of the VEP procedure. Cross-sensitivity of the VEP and the 16-point diagnostic procedure was low. Subsequently, the average severity of MS-induced temporal resolution deficits was studied at three retinal loci of the same size but different eccentricities. Foveal deficits were not significantly greater than more peripheral deficits within the central 12°
Mass measurements of very neutron-deficient Mo and Tc isotopes and their impact on rp process nucleosynthesis
The masses of ten proton-rich nuclides, including the N=Z+1 nuclides 85-Mo
and 87-Tc, were measured with the Penning trap mass spectrometer SHIPTRAP.
Compared to the Atomic Mass Evaluation 2003 a systematic shift of the mass
surface by up to 1.6 MeV is observed causing significant abundance changes of
the ashes of astrophysical X-ray bursts. Surprisingly low alpha-separation
energies for neutron-deficient Mo and Tc are found, making the formation of a
ZrNb cycle in the rp process possible. Such a cycle would impose an upper
temperature limit for the synthesis of elements beyond Nb in the rp process.Comment: Link to online abstract:
http://link.aps.org/doi/10.1103/PhysRevLett.106.12250
TRIGA-SPEC: A setup for mass spectrometry and laser spectroscopy at the research reactor TRIGA Mainz
The research reactor TRIGA Mainz is an ideal facility to provide neutron-rich
nuclides with production rates sufficiently large for mass spectrometric and
laser spectroscopic studies. Within the TRIGA-SPEC project, a Penning trap as
well as a beam line for collinear laser spectroscopy are being installed.
Several new developments will ensure high sensitivity of the trap setup
enabling mass measurements even on a single ion. Besides neutron-rich fission
products produced in the reactor, also heavy nuclides such as 235-U or 252-Cf
can be investigated for the first time with an off-line ion source. The data
provided by the mass measurements will be of interest for astrophysical
calculations on the rapid neutron-capture process as well as for tests of mass
models in the heavy-mass region. The laser spectroscopic measurements will
yield model-independent information on nuclear ground-state properties such as
nuclear moments and charge radii of neutron-rich nuclei of refractory elements
far from stability. This publication describes the experimental setup as well
as its present status.Comment: 20 pages, 17 figure
Calibration of the ISOLDE acceleration voltage using a high-precision voltage divider and applying collinear fast beam laser spectroscopy
A high-voltage divider with accuracy at the ppm level and collinear laser
spectroscopy were used to calibrate the highvoltage installation at the
radioactive ion beam facility ISOLDE at CERN. The accurate knowledge of this
voltage is particularly important for collinear laser spectroscopy
measurements. Beam velocity measurements using frequencycomb based collinear
laser spectroscopy agree with the new calibration. Applying this, one obtains
consistent results for isotope shifts of stable magnesium isotopes measured
using collinear spectroscopy and laser spectroscopy on laser-cooled ions in a
trap. The long-term stability and the transient behavior during recovery from a
voltage dropout were investigated for the different power supplies currently
applied at ISOLDE.Comment: 13 pages, 6 figure
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