2,525 research outputs found
MACHe3, a prototype for non-baryonic dark matter search: KeV event detection and multicell correlation
Superfluid He3 at ultra-low temperatures (100 microKelvins) is a sensitive
medium for the bolometric detection of particles. MACHe3 (MAtrix of Cells of
Helium 3) is a project for non-baryonic dark matter search using He3 as a
sensitive medium. Simulations made on a high granularity detector show a very
good rejection to background signals. A multicell prototype including 3
bolometers has been developed to allow correlations between the cells for
background event discrimination. One of the cells contains a low activity Co57
source providing conversion electrons of 7.3 and 13.6 keV to confirm the
detection of low energy events. First results on the multicell prototype are
presented. A detection threshold of 1 keV has been achieved. The detection of
low energy conversion electrons coming from the Co57 source is highlighted as
well as the cosmic muon spectrum measurement. The possibility to reject
background events by using the correlation among the cells is demonstrated from
the simultaneous detection of muons in different cells
Inelastic Diffraction and Spectroscopy of Very Weakly Bound Clusters
We study the coherent inelastic diffraction of very weakly bound two body
clusters from a material transmission grating. We show that internal
transitions of the clusters can lead to new separate peaks in the diffraction
pattern whose angular positions determine the excitation energies. Using a
quantum mechanical approach to few body scattering theory we determine the
relative peak intensities for the diffraction of the van der Waals dimers
(D_2)_2 and H_2-D_2. Based on the results for these realistic examples we
discuss the possible applications and experimental challenges of this coherent
inelastic diffraction technique.Comment: 15 pages + 5 figures. J. Phys. B (in press
Food consumption of the invasive amphipod Dikerogammarus villosus in field mesocosms and its effects on leaf decomposition and periphyton
Diffractive triangulation of radiative point sources
We describe a general method to determine the location of a point source of waves relative to a twodimensional
single-crystalline active pixel detector. Based on the inherent structural sensitivity of
crystalline sensor materials, characteristic detector diffraction patterns can be used to triangulate the
location of a wave emitter. The principle described here can be applied to various types of waves,
provided that the detector elements are suitably structured. As a prototypical practical application of
the general detection principle, a digital hybrid pixel detector is used to localize a source of electrons
for Kikuchi diffraction pattern measurements in the scanning electron microscope. This approach
provides a promising alternative method to calibrate Kikuchi patterns for accurate measurements of
microstructural crystal orientations, strains, and phase distributions
Stabilized high-power laser system for the gravitational wave detector advanced LIGO
An ultra-stable, high-power cw Nd:YAG laser system, developed for the ground-based gravitational wave detector Advanced LIGO (Laser Interferometer Gravitational-Wave Observatory), was comprehensively characterized. Laser power, frequency, beam pointing and beam quality were simultaneously stabilized using different active and passive schemes. The output beam, the performance of the stabilization, and the cross-coupling between different stabilization feedback control loops were characterized and found to fulfill most design requirements. The employed stabilization schemes and the achieved performance are of relevance to many high-precision optical experiments
Elementary excitations, exchange interaction and spin-Peierls transition in CuGeO
The microscopic description of the spin-Peierls transition in pure and doped
CuGeO_3 is developed taking into account realistic details of crystal
structure. It it shown that the presence of side-groups (here Ge) strongly
influences superexchange along Cu-O-Cu path, making it antiferromagnetic.
Nearest-neighbour and next-nearest neighbour exchange constants and
are calculated. Si doping effectively segments the CuO_2-chains
leading to or even slightly ferromagnetic. Strong
sensitivity of the exchange constants to Cu-O-Cu and (Cu-O-Cu)-Ge angles may be
responsible for the spin-Peierls transition itself (``bond-bending mechanism''
of the transition). The nature of excitations in the isolated and coupled
spin-Peierls chains is studied and it is shown that topological excitations
(solitons) play crucial role. Such solitons appear in particular in doped
systems (Cu_{1-x}Zn_xGeO_3, CuGe_{1-x}Si_xO_3) which can explain the
phase diagram.Comment: 7 pages, revtex, 7 Postscript figure
Adolescent Perceptions of Injury and Pressures of Returning to Sport: A Retrospective Qualitative Analysis
The increase in sport participation among adolescents has led to the rise in sport-related injuries, many of which have unique characteristics based on the patient, their perceptions, and the pressures faced when returning to sport. The purpose of this study was to identify the underlying factors that contributed to adolescents’ perceptions of injury and the various pressures they experienced when returning to sport. Two themes emerged from the study: support and fear. Support was provided to participants through development, care, and the environment. Fear was the factor that affected the participant in their return to sport, which came in the form of worry and doubt
Studie: Verteilte Publikationserstellung mit Microsoft Word und den Microsoft SharePoint Services
Scientific cruise report of the arctic expedition ARK-XX/3 of RV Polarstern in 2004: Fram Strait, Yermak Plateau and East Greenland Continental Margin
An analysis method for time ordered data processing of Dark Matter experiments
The analysis of the time ordered data of Dark Matter experiments is becoming
more and more challenging with the increase of sensitivity in the ongoing and
forthcoming projects. Combined with the well-known level of background events,
this leads to a rather high level of pile-up in the data. Ionization,
scintillation as well as bolometric signals present common features in their
acquisition timeline: low frequency baselines, random gaussian noise, parasitic
noise and signal characterized by well-defined peaks. In particular, in the
case of long-lasting signals such as bolometric ones, the pile-up of events may
lead to an inaccurate reconstruction of the physical signal (misidentification
as well as fake events). We present a general method to detect and extract
signals in noisy data with a high pile-up rate and qe show that events from few
keV to hundreds of keV can be reconstructed in time ordered data presenting a
high pile-up rate. This method is based on an iterative detection and fitting
procedure combined with prior wavelet-based denoising of the data and baseline
subtraction. {We have tested this method on simulated data of the MACHe3
prototype experiment and shown that the iterative fitting procedure allows us
to recover the lowest energy events, of the order of a few keV, in the presence
of background signals from a few to hundreds of keV. Finally we applied this
method to the recent MACHe3 data to successfully measure the spectrum of
conversion electrons from Co57 source and also the spectrum of the background
cosmic muons
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