1,773 research outputs found
Beta asymmetry parameter in the decay of 114In
The beta asymmetry parameter A for the pure Gamow-Teller decay of 114In is
reported. The low temperature nuclear orientation method was combined with a
GEANT4 based simulation code allowing for the first time to address in detail
the effects of scattering and of the magnetic field. The result, A = -0.994 +/-
0.010stat +/- 0.010syst, constitutes the most accurate value for the asymmetry
parameter of a nuclear beta transition to date. The value is in agreement with
the Standard Model prediction of A = -1 and provides new limits on tensor type
charged weak currents.Comment: 11 pages, 2 figures; additional information was added on systematic
effects, the magnetic field map and the calculation of the Qcos(theta) value
Performance of Geant4 in simulating semiconductor particle detector response in the energy range below 1 MeV
Geant4 simulations play a crucial role in the analysis and interpretation of
experiments providing low energy precision tests of the Standard Model. This
paper focuses on the accuracy of the description of the electron processes in
the energy range between 100 and 1000 keV. The effect of the different
simulation parameters and multiple scattering models on the backscattering
coefficients is investigated. Simulations of the response of HPGe and
passivated implanted planar Si detectors to \beta{} particles are compared to
experimental results. An overall good agreement is found between Geant4
simulations and experimental data
Living on the edge: Space use of Eurasian red squirrels in marginal high-elevation habitat.
In marginal habitats located at the edge of a species\u2019 range, environmental conditions are frequently
extreme and individuals may be subject to different selective pressures compared to central populations.
These so-called edge or marginal populations tend to have lower densities and reproductive rates than
populations located in more suitable habitats, but little is known about local adaptations in spacing
behavior. We studied space use and social organization in a population of Eurasian red squirrels (Sciurus
vulgaris) in a high-elevation marginal habitat of dwarf mountain pine (Pinus mugo) and compared it with
spacing patterns in high-quality Scots pine (Pinus sylvestris) forest at lower-elevation. Home ranges and
core areas were larger in the marginal habitat. In both habitats, males used larger home ranges than
females, but sex differences in core area size were significant only in the edge population. Patterns of
core area overlap were similar in both habitats with intra-sexual territoriality among adult females and
higher degrees of inter-sexual overlap, typical for the species throughout its range. However, low
densities in the edge population resulted in higher female by males overlap in spring-summer, suggesting
males increased home ranges and core areas during mating season to augment access to estrus
females. Thus, in the marginal habitat, with low food abundance and low population densities, linked
with extreme winter conditions, squirrels, especially males, used large home ranges. Finally, squirrels
responded more strongly to variation in food availability (inverse relation between home range size and
seed abundance), and even to fluctuations in density (inverse relation between core area size and density
of animals of the same sex), in the marginal than in the high-quality habitat, suggesting high behavioral
plasticity to respond to the ecological constraints in marginal habitats
Ion cyclotron resonance heating scenarios for DEMO
International audienceThe present paper offers an overview of the potential of ion cyclotron resonance heating (ICRH) or radio frequency (RF) heating for the DEMO machine. It is found that various suitable heating schemes are available. Similar to ITER and in view of the limited bandwidth of about 10M Hz that can be achieved to ensure optimal functioning of the launcher, it is proposed to make core second harmonic tritium heating the key ion heating scheme, assisted by fundamental cyclotron heating 3 He in the early phase of the discharge; for the present design of DEMO-with a static magnetic field strength of B o = 5.855T-that places the T and 3 He layers in the core for f = 60M Hz and suggests to center the bandwidth around that main operating frequency. In line with earlier studies for hot, dense plasmas in large-size magnetic confinement machines it is shown that good single pass absorption is achieved but that the size as well as operating density and temperature of the machine cause the electrons to absorb a non-negligible fraction of the power away from the core when core ion heating is aimed at. Current drive and alternative heating options are briefly discussed and a dedicated computation is done for the traveling wave antenna, proposed for DEMO in view of its compatibility with substantial antenna-plasma distances. The various tasks that ICRH can fulfill are briefly listed. Finally, the impact of transport and the sensitivity of the obtained results to changes in the machine parameters is commented on
Nutcrackers become choosy seed harvesters in a mast-crop year.
As an efficient seed-disperser, Eurasian nutcrackers (Nucifraga caryocatactes) generally consume and hoard mature, edible pine seeds for future use. In 2009, when the Arolla pine, Pinus. cembra, produced a mast-crop, we investigated cones discarded
by nutcrackers. Most cones were only partly eaten and some mature seeds remained in the distal part. This was in contrast to years of lower seed production when nearly all seeds were harvested from the majority of cones. To determine
whether nutcracker cone-discarding behaviour maximised intake rate, seed kernels and the aborted seeds rate were measured from the different cone parts. In 2009, seeds from cone-tops were on average 17% lighter than in the base and middle sections, and the proportion of aborted seeds in the top part was 81% higher than in the other sections. There was no difference in seed mass and proportion of aborted seeds in cone-tops of intact cones and cones handled by nutcrackers. Regarding each cone as a patch, cone discarding behaviour can be considered as an optimal cone-leaving rule, maximising rate of energy-intake, supporting the Marginal Value Theorem. Hence, we suggest that increased food abundance leads to more selective seed harvesting in nutcrackers
Estimating offspring production using capture-mark-recapture and genetic methods in red squirrels.
Reproductive rate is a key demographic
parameter of life history and population ecology.
In traditional population-ecology studies of small
mammals, this and other vital rates are inferred from
capture-mark-recapture (CMR) data. However, CMR
assumes that immigrants at first capture can be distinguished
from unmarked locally born offspring, an
assumption not always met. We verified CMR estimates
of locally born red squirrel (Sciurus vulgaris) offspring as
a measure of reproductive rate, with candidate offspring
(CO)\u2013candidate parent (mothers, CPs) assignment by
CERVUS, using ten DNA microsatellite loci. Seventytwo
of 122 candidate offspring (59%) were assigned to
52 of 125 CPs in six populations. Estimates of mean
litter size were 1.5 young (range 1\u20133). The 50 CO (41%)
not assigned to a reproducing female in the study site
were considered immigrants. Parentage assignment also
provided evidence of dispersal between two of our sites.
Overall, CMR and CERVUS agreed in 77% of cases.
Considering only the 55 juveniles determined as locally
born by CMR, 50 (91%) were also assigned as local
offspring with CERVUS. The main discrepancy between
the two methods was that 22 subadult squirrels classified
immigrants by CMR, were assigned by CERVUS to
females which had reproduced in our sites. It is concluded
that although in our study system agreement
between CMR and CERVUS in determining local offspring
was high, using genetic parentage assignment
helped to correctly classify some subadults, considered
immigrants by CMR, as locally born. Hence, in largescale
demographic studies, combining CMR with parentage
assignment will allow more precise estimates of
reproduction and dispersal
Ion cyclotron wall conditioning experiments on Tore Supra in presence of the toroidal magnetic field
Wall conditioning techniques applicable in the presence of the high toroidal magnetic field will be required for the operation of ITER for tritium removal, isotopic ratio control and recovery to normal operation after disruptions. Recently ion cyclotron wall conditioning (ICWC) experiments have been carried out on Tore Supra in order to assess the efficiency of this technique in ITER relevant conditions. The ICRF discharges were operated in He/H-2 Mixtures at the Tore Supra nominal field (3.8 T) and a RF frequency of 48 MHz, i.e. within the ITER operational space. RF pulses of 60 s (max.) were applied using a standard Tore Supra two-strap resonant double loop antenna in ICWC mode, operated either in pi or 0-phasing with a noticeable improvement of the RF coupling in the latter case. In order to assess the efficiency of the technique for the control of isotopic ratio the wall was first preloaded using a D-2 glow discharge. After 15 minutes of ICWC in He/H-2 gas mixtures the isotopic ratio was altered from 4% to 50% at the price of an important H implantation into the walls. An overall analysis comparing plasma production and the conditioning efficiency as a function of discharge parameters is given
The half-life of Fr in Si and Au at 4K and at mK temperatures
The half-life of the decaying nucleus Fr was determined in
different environments, i.e. embedded in Si at 4 K, and embedded in Au at 4 K
and about 20 mK. No differences in half-life for these different conditions
were observed within 0.1%. Furthermore, we quote a new value for the absolute
half-life of Fr of t = 286.1(10) s, which is of comparable
precision to the most precise value available in literature
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