1,301 research outputs found
Radiation studies for GaAs in the ATLAS Inner Detector
We estimate the hardness factors and the equivalent 1 MeV neutron fluences
for hadrons fluences expected at the GaAs positions wheels in the ATLAS Inner
Detector. On this basis the degradation of the GaAs particle detectors made
from different substrates as a function of years LHC operation is predicted.Comment: 11 pages, 6 Postscript figures, uses elsart.cls, submitted to Nucl.
Inst. and Met
Three-dimensional stability of Burgers vortices
Burgers vortices are explicit stationary solutions of the Navier-Stokes
equations which are often used to describe the vortex tubes observed in
numerical simulations of three-dimensional turbulence. In this model, the
velocity field is a two-dimensional perturbation of a linear straining flow
with axial symmetry. The only free parameter is the Reynolds number , where is the total circulation of the vortex and is
the kinematic viscosity. The purpose of this paper is to show that Burgers
vortex is asymptotically stable with respect to general three-dimensional
perturbations, for all values of the Reynolds number. This definitive result
subsumes earlier studies by various authors, which were either restricted to
small Reynolds numbers or to two-dimensional perturbations. Our proof relies on
the crucial observation that the linearized operator at Burgers vortex has a
simple and very specific dependence upon the axial variable. This allows to
reduce the full linearized equations to a vectorial two-dimensional problem,
which can be treated using an extension of the techniques developped in earlier
works. Although Burgers vortices are found to be stable for all Reynolds
numbers, the proof indicates that perturbations may undergo an important
transient amplification if is large, a phenomenon that was indeed observed
in numerical simulations.Comment: 31 pages, no figur
Mid-infrared interferometry with K band fringe-tracking I. The VLTI MIDI+FSU experiment
Context: A turbulent atmosphere causes atmospheric piston variations leading
to rapid changes in the optical path difference of an interferometer, which
causes correlated flux losses. This leads to decreased sensitivity and accuracy
in the correlated flux measurement. Aims: To stabilize the N band
interferometric signal in MIDI (MID-infrared Interferometric instrument), we
use an external fringe tracker working in K band, the so-called FSU-A (fringe
sensor unit) of the PRIMA (Phase-Referenced Imaging and Micro-arcsecond
Astrometry) facility at VLTI. We present measurements obtained using the newly
commissioned and publicly offered MIDI+FSU-A mode. A first characterization of
the fringe-tracking performance and resulting gains in the N band are
presented. In addition, we demonstrate the possibility of using the FSU-A to
measure visibilities in the K band. Methods: We analyzed FSU-A fringe track
data of 43 individual observations covering different baselines and object K
band magnitudes with respect to the fringe-tracking performance. The N band
group delay and phase delay values could be predicted by computing the relative
change in the differential water vapor column density from FSU-A data.
Visibility measurements in the K band were carried out using a scanning mode of
the FSU-A. Results: Using the FSU-A K band group delay and phase delay
measurements, we were able to predict the corresponding N band values with high
accuracy with residuals of less than 1 micrometer. This allows the coherent
integration of the MIDI fringes of faint or resolved N band targets,
respectively. With that method we could decrease the detection limit of
correlated fluxes of MIDI down to 0.5 Jy (vs. 5 Jy without FSU-A) and 0.05 Jy
(vs. 0.2 Jy without FSU-A) using the ATs and UTs, respectively. The K band
visibilities could be measured with a precision down to ~2%.Comment: 11 pages, 13 figures, Accepted for publication in A&
ESC NN-Potentials in Momentum Space. II. Meson-Pair Exchange Potentials
The partial wave projection of the Nijmegen soft-core potential model for
Meson-Pair-Exchange (MPE) for NN-scattering in momentum space is presented.
Here, nucleon-nucleon momentum space MPE-potentials are NN-interactions where
either one or both nucleons contains a meson-pair vertex. Dynamically, the
meson-pair vertices can be viewed as describing in an effective way (part of)
the effects of heavy-meson exchange and meson-nucleon resonances. From the
point of view of ``duality,'' these two kinds of contribution are roughly
equivalent. Part of the MPE-vertices can be found in the chiral-invariant
phenomenological Lagrangians that have a basis in spontaneous broken chiral
symmetry. It is shown that the MPE-interactions are a very important component
of the nuclear force, which indeed enables a very succesful description of the
low and medium energy NN-data. Here we present a precise fit to the NN-data
with the extended-soft-core (ESC) model containing OBE-, PS-PS-, and
MPE-potentials. An excellent description of the NN-data for
MeV is presented and discussed. Phase shifts are given and a is reached.Comment: 27 pages, 5 PostScript figures, revtex
AC-coupled GaAs microstrip detectors with a new type of integrated bias resistors
Full size single-sided GaAs microstrip detectors with integrated coupling
capacitors and bias resistors have been fabricated on 3'' substrate wafers.
PECVD deposited SiO_2 and SiO_2/Si_3N_4 layers were used to provide coupling
capacitaces of 32.5 pF/cm and 61.6 pF/cm, respectively. The resistors are made
of sputtered CERMET using simple lift of technique. The sheet resistivity of 78
kOhm/sq. and the thermal coefficient of resistance of less than 4x10^-3 /
degree C satisfy the demands of small area biasing resistors, working on a wide
temperature range.Comment: 20 pages, 9 figures, to be published in NIM
Growth and shape of indium islands on molybdenum at micro-roughened spots created by femtosecond laser pulses
Indium islands on molybdenum coated glass can be grown in ordered arrays by surface structuring using a femtosecond laser. The effect of varying the molybdenum coated glass substrate temperature and the indium deposition rate on island areal density, volume and geometry is investigated and evaluated in a physical vapor deposition (PVD) process. The joined impact of growth conditions and spacing of the femtosecond laser structured spots on the arrangement and morphology of indium islands is demonstrated. The results yield a deeper understanding of the island growth and its precise adjustment to industrial requirements, which is indispensable for a technological application of such structures at a high throughput, for instance as precursors for the preparation of Cu(In,Ga)Se2 micro concentrator solar cells
Regularly arranged indium islands on glass/molybdenum substrates upon femtosecond laser and physical vapor deposition processing
A bottom-up approach is presented for the production of arrays of indium
islands on a molybdenum layer on glass, which can serve as micro-sized
precursors for indium compounds such as copper-indium-gallium-diselenide used
in photovoltaics. Femtosecond laser ablation of glass and a subsequent
deposition of a molybdenumfilm or direct laser processing of the
molybdenumfilm both allow the preferential nucleation and growth of indium
islands at the predefined locations in a following indium-based physical vapor
deposition(PVD) process. A proper choice of laser and deposition parameters
ensures the controlled growth of indium islands exclusively at the laser
ablated spots. Based on a statistical analysis, these results are compared to
the non-structured molybdenumsurface, leading to randomly grown indium islands
after PVD
Pionic Deuterium
The strong interaction shift and broadening in pionic deuterium have been
remeasured with high statistics by means of the (3p-1s) X-ray transition using
the cyclotron trap and a high-resolution crystal spectrometer. Preliminary
results are (-2325+/-31) meV (repulsive) for the shift and (1171+23/-49} meV
for the width, which yields precise values for the pion-deuteron scattering
length and the threshold parameter for pion production.Comment: Conf. Proc. Few Body 19 (FB19), August 31 - September 5, 2009, Bonn,
Germany 9 pages, 13 figure
- …