3,499 research outputs found
Study of a high spatial resolution 10B-based thermal neutron detector for application in neutron reflectometry: the Multi-Blade prototype
Although for large area detectors it is crucial to find an alternative to
detect thermal neutrons because of the 3He shortage, this is not the case for
small area detectors. Neutron scattering science is still growing its
instruments' power and the neutron flux a detector must tolerate is increasing.
For small area detectors the main effort is to expand the detectors'
performances. At Institut Laue-Langevin (ILL) we developed the Multi-Blade
detector which wants to increase the spatial resolution of 3He-based detectors
for high flux applications. We developed a high spatial resolution prototype
suitable for neutron reflectometry instruments. It exploits solid 10B-films
employed in a proportional gas chamber. Two prototypes have been constructed at
ILL and the results obtained on our monochromatic test beam line are presented
here
Some Restrictions Abroad Affecting Corporations
A neutron detector concept based on solid layers of boron carbide enriched in 1 B has been in development for the last few years as an alternative for He-3 by collaboration between the ILL, ESS and Linkoping University. This Multi-Grid detector uses layers of aluminum substrates coated with (B4C)-B-10 on both sides that are traversed by the incoming neutrons. Detection is achieved using a gas counter readout principle. By segmenting the substrate and using multiple anode wires, the detector is made inherently position sensitive. This development is aimed primarily at neutron scattering instruments with large detector areas, such as time-of-flight chopper spectrometers. The most recent prototype has been built to be interchangeable with the He-3 detectors of IN6 at ILL. The 1 B detector has an active area of 32 x 48 cm(2). It was installed at the IN6 instrument and operated for several weeks, collecting data in parallel with the regularly scheduled experiments, thus providing the first side-by-side comparison with the conventional He-3 detectors. Results include an efficiency comparison, assessment of the in-detector scattering contribution, sensitivity to gamma-rays and the signal-to-noise ratio in time-of-flight spectra. The good expected performance has been confirmed with the exception of an unexpected background count rate. This has been identified as natural alpha activity in aluminum. New convertor substrates are under study to eliminate this source of background
Indirect exchange in GaMnAs bilayers via spin-polarized inhomogeneous hole gas: Monte Carlo simulation
The magnetic order resulting from an indirect exchange between magnetic
moments provided by spin-polarized hole gas in the metallic phase of a GaMnAs
double layer structure is studied via Monte Carlo simulation. The coupling
mechanism involves a perturbative calculation in second order of the
interaction between the magnetic moments and carriers (holes). We take into
account a possible polarization of the hole gas due to the existence of an
average magnetization in the magnetic layers, establishing, in this way, a
self-consistency between the magnetic order and the electronic structure. That
interaction leads to an internal ferromagnetic order inside each layer, and a
parallel arrangement between their magnetizations, even in the case of thin
layers. This fact is analyzed in terms of the inter- and intra-layer
interactions.Comment: 17 pages and 14 figure
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Basic Psychological Need Satisfaction, Recovery State, and Recovery Timing
This study aimed to provide insight into recovery from work-related load effects by examining (1) whether basic psychological need satisfaction (BPN satisfaction) during non-work days facilitates recovery; (2) whether the effect of BPN satisfaction is stronger in case of an unfavorable initial recovery state; and (3) whether the association between BPN satisfaction and recovery is stronger on non-work weekend days compared to nonwork weekdays. Data were collected across seven consecutive days from 205 employees (39% shift workers). Fatigue and depressed mood were assessed as indicators of (failed) recovery. Multilevel analyses revealed that BPN satisfaction during non-work days was related to improved recovery state. This association was stronger if employees had experienced elevated fatigue on the preceding day, and on non-work weekend days compared to non-work weekdays
Spin diffusion in doped semiconductors
The behavior of spin diffusion in doped semiconductors is shown to be
qualitatively different than in undoped (intrinsic) ones. Whereas a spin packet
in an intrinsic semiconductor must be a multiple-band disturbance, involving
inhomogeneous distributions of both electrons and holes, in a doped
semiconductor a single-band disturbance is possible. For n-doped nonmagnetic
semiconductors the enhancement of diffusion due to a degenerate electron sea in
the conduction band is much larger for these single-band spin packets than for
charge packets, and can exceed an order of magnitude at low temperatures even
for equilibrium dopings as small as 10^16 cm^-3. In n-doped ferromagnetic and
semimagnetic semiconductors the motion of spin packets polarized antiparallel
to the equilibrium carrier spin polarization is predicted to be an order of
magnitude faster than for parallel polarized spin packets. These results are
reversed for p-doped semiconductors.Comment: 8 pages, 4 figure
Temperature-dependent magnetization in diluted magnetic semiconductors
We calculate magnetization in magnetically doped semiconductors assuming a
local exchange model of carrier-mediated ferromagnetic mechanism and using a
number of complementary theoretical approaches. In general, we find that the
results of our mean-field calculations, particularly the dynamical mean field
theory results, give excellent qualitative agreement with the experimentally
observed magnetization in systems with itinerant charge carriers, such as
Ga_{1-x}Mn_xAs with 0.03 < x < 0.07, whereas our percolation-theory-based
calculations agree well with the existing data in strongly insulating
materials, such as Ge_{1-x}Mn_x. We comment on the issue of non-mean-field like
magnetization curves and on the observed incomplete saturation magnetization
values in diluted magnetic semiconductors from our theoretical perspective. In
agreement with experimental observations, we find the carrier density to be the
crucial parameter determining the magnetization behavior. Our calculated
dependence of magnetization on external magnetic field is also in excellent
agreement with the existing experimental data.Comment: 17 pages, 15 figure
Altered microbial community structure and metabolism in cow's milk allergic mice treated with oral immunotherapy and fructo-oligosaccharides
Previously, we showed enhanced efficacy of oral immunotherapy (OIT) using fructo-oligosaccharides (FOS, prebiotics) added to the diet of cow's milk allergic mice indicated by a reduction in clinical symptoms and mast cell degranulation. Prebiotics are fermented by gut bacteria, affecting both bacterial composition and availability of metabolites (i.e. short-chain fatty acids (SCFA)). It is thus far unknown which microbial alterations are involved in successful outcomes of OIT with prebiotic supplementation for the treatment of food allergy. To explore potential changes in the microbiota composition and availability of SCFA induced by OIT+FOS. C3H/HeOuJ mice were sensitised and received OIT with or without a FOS supplemented diet. After three weeks, faecal samples were collected to analyse gut microbiota composition using 16S rRNA sequencing. SCFA concentrations were determined in cecum content. FOS supplementation in sensitised mice changed the overall microbial community structure in faecal samples compared to sensitised mice fed the control diet (P=0.03). In contrast, a high level of resemblance in bacterial community structure was observed between the non-sensitised control mice and the OIT+FOS treated mice. OIT mice showed an increased relative abundance of the dysbiosis-associated phylum Proteobacteria compared to the OIT+FOS mice. FOS supplementation increased the relative abundance of genus Allobaculum (Firmicutes), putative butyrate-producing bacteria. OIT+FOS reduced the abundances of the genera's unclassified Rikenellaceae (Bacteroidetes, putative pro-inflammatory bacteria) and unclassified Clostridiales (Firmicutes) compared to sensitised controls and increased the abundance of Lactobacillus (Firmicutes, putative beneficial bacteria) compared to FOS. OIT+FOS mice had increased butyric acid and propionic acid concentrations. OIT+FOS induced a microbial profile closely linked to non-allergic mice and increased concentrations of butyric acid and propionic acid. Future research should confirm whether there is a causal relationship between microbial modulation and the reduction in acute allergic symptoms induced by OIT+FOS
A theory of ferromagnetism in planar heterostructures of (Mn,III)-V semiconductors
A density functional theory of ferromagnetism in heterostructures of compound
semiconductors doped with magnetic impurities is presented. The variable
functions in the density functional theory are the charge and spin densities of
the itinerant carriers and the charge and localized spins of the impurities.
The theory is applied to study the Curie temperature of planar heterostructures
of III-V semiconductors doped with manganese atoms. The mean-field,
virtual-crystal and effective-mass approximations are adopted to calculate the
electronic structure, including the spin-orbit interaction, and the magnetic
susceptibilities, leading to the Curie temperature. By means of these results,
we attempt to understand the observed dependence of the Curie temperature of
planar -doped ferromagnetic structures on variation of their
properties. We predict a large increase of the Curie Temperature by additional
confinement of the holes in a -doped layer of Mn by a quantum well.Comment: 8 pages, 7 figure
The H1 Forward Proton Spectrometer at HERA
The forward proton spectrometer is part of the H1 detector at the HERA
collider. Protons with energies above 500 GeV and polar angles below 1 mrad can
be detected by this spectrometer. The main detector components are
scintillating fiber detectors read out by position-sensitive photo-multipliers.
These detectors are housed in so-called Roman Pots which allow them to be moved
close to the circulating proton beam. Four Roman Pot stations are located at
distances between 60 m and 90 m from the interaction point.Comment: 20 pages, 10 figures, submitted to Nucl.Instr.and Method
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