2,136 research outputs found
Evolution of a beam dynamics model for the transport lines in a proton therapy facility
Despite the fact that the first-order beam dynamics models allow an
approximated evaluation of the beam properties, their contribution is essential
during the conceptual design of an accelerator or beamline. However, during the
commissioning some of their limitations appear in the comparison against
measurements. The extension of the linear model to higher order effects is,
therefore, demanded. In this paper, the effects of particle-matter interaction
have been included in the model of the transport lines in the proton therapy
facility at the Paul Scherrer Institut (PSI) in Switzerland. To improve the
performance of the facility, a more precise model was required and has been
developed with the multi-particle open source beam dynamics code called OPAL
(Object oriented Particle Accelerator Library). In OPAL, the Monte Carlo
simulations of Coulomb scattering and energy loss are performed seamless with
the particle tracking. Beside the linear optics, the influence of the passive
elements (e.g. degrader, collimators, scattering foils and air gaps) on the
beam emittance and energy spread can be analysed in the new model. This allows
for a significantly improved precision in the prediction of beam transmission
and beam properties. The accuracy of the OPAL model has been confirmed by
numerous measurements.Comment: 17 pages, 19 figure
Size and Causes of the Occupational Gender Wage-gap in the Netherlands
Research from the United States consistently shows that female-dominated occupations generally yield lower wages than male-dominated occupations. Using detailed occupational data, this study analyses the size andcauses of this occupational genderwage-gap in the Dutch labourmarket using multi-levelmodelling techniques.The analyses showthat bothmen andwomen earn lowerwages if they are employed in female-dominated occupations. This especially indicates the signi¢cance of gender inWestern labour markets, since overall levels of wage inequality are relatively small in the Netherlands compared to, for example, the United Kingdom and the United States. Di¡erences in required responsibility are particularly important in accounting for this occupational wage-gap. Nonetheless, we find large wage penalties for working in a female-dominated instead of a maledominated occupation for occupations that require high levels of education, skills, and responsibility.
Acrylamide: Increased concentrations in homemade food and first evidence of its variable absorption from food, variable metabolism and placental and breast milk transfer in humans
We have developed a liquid chromatography/mass spectrometry (LC-MS/MS) assay to determine acrylamide in various body fluids. The assay also allows the reliable quantitation of acrylamide in food. In a total of 11 healthy male and female subjects, we were able to show that acrylamide from food given to humans is in fact absorbed from the gut. The half-lives determined in two male subjects were 2.2 and 7 h. Acrylamide was found in human breast milk and penetrated the human placenta (n = 3). The variability of acrylamide concentrations found in this investigation is most likely caused by variable intersubject bioavailability and metabolism. This may be an important indication that the assessment of the risk from acrylamide for the individual may be very difficult without knowing the concentrations of acrylamide in the body. This should be considered in the design of any risk assessment study or post hoc analysis of earlier studies. At this time, we suggest that pregnant women and breast-feeding mothers avoid acrylamide-containing food. Copyright (C) 2002 S. Karger AG, Basel
Dielectronic recombination data for astrophysical applications: Plasma rate-coefficients for Fe^q+ (q=7-10, 13-22) and Ni^25+ ions from storage-ring experiments
This review summarizes the present status of an ongoing experimental effort
to provide reliable rate coefficients for dielectronic recombination of highly
charged iron ions for the modeling of astrophysical and other plasmas. The
experimental work has been carried out over more than a decade at the heavy-ion
storage-ring TSR of the Max-Planck-Institute for Nuclear Physics in Heidelberg,
Germany. The experimental and data reduction procedures are outlined. The role
of previously disregarded processes such as fine-structure core excitations and
trielectronic recombination is highlighted. Plasma rate coefficients for
dielectronic recombination of Fe^q+ ions (q=7-10, 13-22) and Ni^25+ are
presented graphically and in a simple parameterized form allowing for easy use
in plasma modeling codes. It is concluded that storage-ring experiments are
presently the only source for reliable low-temperature dielectronic
recombination rate-coefficients of complex ions.Comment: submitted for publication in the International Review of Atomic and
Molecular Physics, 8 figures, 3 tables, 68 reference
Enhanced dielectronic recombination of lithium-like Ti19+ ions in external ExB fields
Dielectronic recombination(DR) of lithium-like Ti19+(1s2 2s) ions via 2s->2p
core excitations has been measured at the Heidelberg heavy ion storage ring
TSR. We find that not only external electric fields (0 <= Ey <= 280 V/cm) but
also crossed magnetic fields (30 mT <= Bz <= 80 mT) influence the DR via high-n
(2p_j nl)-Rydberg resonances. This result confirms our previous finding for
isoelectronic Cl14+ ions [Bartsch T et al, PRL 82, 3779 (1999)] that
experimentally established the sensitivity of DR to ExB fields. In the present
investigation the larger 2p_{1/2}-2p_{3/2} fine structure splitting of Ti19+
allowed us to study separately the influence of external fields via the two
series of Rydberg DR resonances attached to the 2s -> 2p_{1/2} and 2s ->
2p_{3/2} excitations of the Li-like core, extracting initial slopes and
saturation fields of the enhancement. We find that for Ey > 80 V/cm the field
induced enhancement is about 1.8 times stronger for the 2p_{3/2} series than
for the 2p_{1/2} series.Comment: 10 pages, 3 figures, to be published in Journal of Physics B, see
also http://www.strz.uni-giessen.de/~k
Interference effects in the photorecombination of argonlike Sc3+ ions: Storage-ring experiment and theory
Absolute total electron-ion recombination rate coefficients of argonlike
Sc3+(3s2 3p6) ions have been measured for relative energies between electrons
and ions ranging from 0 to 45 eV. This energy range comprises all dielectronic
recombination resonances attached to 3p -> 3d and 3p -> 4s excitations. A broad
resonance with an experimental width of 0.89 +- 0.07 eV due to the 3p5 3d2 2F
intermediate state is found at 12.31 +- 0.03 eV with a small experimental
evidence for an asymmetric line shape. From R-Matrix and perturbative
calculations we infer that the asymmetric line shape may not only be due to
quantum mechanical interference between direct and resonant recombination
channels as predicted by Gorczyca et al. [Phys. Rev. A 56, 4742 (1997)], but
may partly also be due to the interaction with an adjacent overlapping DR
resonance of the same symmetry. The overall agreement between theory and
experiment is poor. Differences between our experimental and our theoretical
resonance positions are as large as 1.4 eV. This illustrates the difficulty to
accurately describe the structure of an atomic system with an open 3d-shell
with state-of-the-art theoretical methods. Furthermore, we find that a
relativistic theoretical treatment of the system under study is mandatory since
the existence of experimentally observed strong 3p5 3d2 2D and 3p5 3d 4s 2D
resonances can only be explained when calculations beyond LS-coupling are
carried out.Comment: 11 pages, 7 figures, 3 tables, Phys. Rev. A (in print), see also:
http://www.strz.uni-giessen.de/~k
Optimizing propagating spin wave spectroscopy
The frequency difference between two oppositely propagating spin waves can be
used to probe several interesting magnetic properties, such as the
Dzyaloshinkii-Moriya interaction (DMI). Propagating spin wave spectroscopy is a
technique that is very sensitive to this frequency difference. Here we show
several elements that are important to optimize devices for such a measurement.
We demonstrate that for wide magnetic strips there is a need for de-embedding.
Additionally, for these wide strips there is a large parasitic antenna-antenna
coupling that obfuscates any spin wave transmission signal, which is remedied
by moving to smaller strips. The conventional antenna design excites spin waves
with two different wave vectors. As the magnetic layers become thinner, the
resulting resonances move closer together and become very difficult to
disentangle. In the last part we therefore propose and verify a new antenna
design that excites spin waves with only one wave vector. We suggest to use
this antenna design to measure the DMI in thin magnetic layers.Comment: 12 pages, 4 figure
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