2,590 research outputs found
Breaking the mass / anisotropy degeneracy in the Coma cluster
We provide the first direct lifting of the mass/anisotropy degeneracy for a
cluster of galaxies, by jointly fitting the line of sight velocity dispersion
and kurtosis profiles of the Coma cluster, assuming an NFW tracer density
profile, a generalized-NFW dark matter profile and a constant anisotropy
profile. We find that the orbits in Coma must be quasi-isotropic, and find a
mass consistent with previous analyses, but a concentration parameter 50%
higher than expected in cosmological N-body simulations. We then test the
accuracy of our method on realistic non-spherical systems with substructure and
streaming motions, by applying it to the ten most massive structures in a
cosmological N-body simulation. We find that our method yields fairly accurate
results on average (within 20%), although with a wide variation (factor 1.7 at
1 sigma) for the concentration parameter, with decreased accuracy and
efficiency when the projected mean velocity is not constant with radius.Comment: 5 pages, oral presentation at IAU Colloquium 195, Outskirts of Galaxy
Clusters: intense life in the suburbs, ed. A. Diaferi
Three-particle correlations in QCD parton showers
Three-particle correlations in quark and gluon jets are computed for the
first time in perturbative QCD. We give results in the double logarithmic
approximation and the modified leading logarithmic approximation. In both
resummation schemes, we use the formalism of the generating functional and
solve the evolution equations analytically from the steepest descent evaluation
of the one-particle distribution. We thus provide a further test of the local
parton hadron duality and make predictions for the LHC.Comment: 9 pages and 5 figures. Version published by Physical Review D with
reference: Phys. Rev. D 84, 034015 (2011). Two more figures and one section
adde
Recent ASDEX Upgrade research in support of ITER and DEMO
Recent experiments on the ASDEX Upgrade tokamak aim at improving the physics base for ITER and DEMO to aid the machine
design and prepare efficient operation. Type I edge localized mode (ELM) mitigation using resonant magnetic perturbations
(RMPs) has been shown at low pedestal collisionality (
Μ
â
ped
<
0
.
4
)
. In contrast to the previous high
Μ
â
regime, suppression only
occurs in a narrow RMP spectral window, indicating a resonant process, and a concomitant confinement drop is observed due
to a reduction of pedestal top density and electron temperature. Strong evidence is found for the ion heat flux to be the decisive
element for the LâH power threshold. A physics based scaling of the density at which the minimum
P
LH
occurs indicates that
ITER could take advantage of it to initiate H-mode at lower density than that of the final
Q
=
10 operational point. Core density
fluctuation measurements resolved in radius and wave number show that an increase of
R/L
T
e
introduced by off-axis electron
cyclotron resonance heating (ECRH) mainly increases the large scale fluctuations. The radial variation of the fluctuation level
is in agreement with simulations using the GENE code. Fast particles are shown to undergo classical slowing down in the
absence of large scale magnetohydrodynamic (MHD) events and for low heating power, but show signs of anomalous radial
redistribution at large heating power, consistent with a broadened off-axis neutral beam current drive current profile under these
conditions. Neoclassical tearing mode (NTM) suppression experiments using electron cyclotron current drive (ECCD) with
feedback controlled deposition have allowed to test several control strategies for ITER, including automated control of (3,2) and
(2,1) NTMs during a single discharge. Disruption mitigation studies using massive gas injection (MGI) can show an increased
fuelling efficiency with high field side injection, but a saturation of the fuelling efficiency is observed at high injected mass as
needed for runaway electron suppression. Large locked modes can significantly decrease the fuelling efficiency and increase
the asymmetry of radiated power during MGI mitigation. Concerning power exhaust, the partially detached ITER divertor
scenario has been demonstrated at
P
sep
/R
=
10 MW m
â
1
in ASDEX Upgrade, with a peak time averaged target load around
5MWm
â
2
, well consistent with the component limits for ITER. Developing this towards DEMO, full detachment was achieved
at
P
sep
/R
=
7MWm
â
1
and stationary discharges with core radiation fraction of the order of DEMO requirements (70% instead
of the 30% needed for ITER) were demonstrated. Finally, it remains difficult to establish the standard ITER
Q
=
10 scenario at
low
q
95
=
3 in the all-tungsten (all-W) ASDEX Upgrade due to the observed poor confinement at low
ÎČ
N
. This is mainly due to
a degraded pedestal performance and hence investigations at shifting the operational point to higher
ÎČ
N
by lowering the current
have been started. At higher
q
95
, pedestal performance can be recovered by seeding N
2
as well as CD
4
, which is interpreted as
improved pedestal stability due to the decrease of bootstrap current with increasing
Z
eff
. Concerning advanced scenarios, the
upgrade of ECRH power has allowed experiments with central ctr-ECCD to modify the
q
-profile in improved H-mode scenarios,
showing an increase in confinement at still good MHD stability with flat elevated
q
-profiles at values between 1.5 and 2.European Commission (EUROfusion 633053
Comment on "Theory of tailoring sonic devices: Diffraction dominates over refraction"
Recently N. Garcia et al. (Phys. Rev. E 67, 046606 (2003)) theoretically
studied several acoustic devices with dimensions on de order of several
wavelenghts. The authors discussed on experimental results previously reported
by several of us (F. Cervera et al., Phys. Rev. Lett. 88, 023902 (2002)). They
concluded that diffraction and not refraction is the ominating mechanism that
explain the focusing effects observed in those experiments. In this Comment we
reexamined their calculations and discussed why some of their interpretations
of our results are misleading.Comment: 2 pages, 2 figures, a comment on an articl
Development and initial validation of a sensory threshold examination protocol (STEP) for phenotyping canine pain syndromes
Objective
To study feasibility and test-retest repeatability of a sensory threshold examination protocol (STEP) and report quantitative sensory threshold distributions in healthy dogs.
Study design
Prospective, observational, cohort study.
Animals
Twenty-five healthy client-owned dogs.
Methods
Tactile sensitivity (TST) (von Frey filaments), mechanical thresholds (MT with 2, 4 and 8 mm probes), heat thresholds (HT) and responsiveness to cold stimulus (CT at 0 °C) were quantitatively assessed for five body areas (BA: tibias, humeri, neck, thoracolumbar region and abdomen) in a randomized order on three different occasions. Linear Mixed Model and Generalised Linear Mixed models were used to evaluate the effects of body weight category, age, sex, BA, occasion, feasibility score and investigator experience. Test-retest repeatability was evaluated with the Intra-class Correlation Coefficient (ICC).
Results
The STEP lasted 90 minutes without side effects. The BA affected most tests (p = 0.001). Higher thresholds and longer cold latencies were scored in the neck (p = 0.024) compared to other BAs. Weight category affected all thresholds (p = 0.037). Small dogs had lower MT (~1.4 N mean difference) and HT (1.1 0C mean difference) than other dogs (p = 0.029). Young dogs had higher HT than adults (2.2 0C mean difference) (p = 0.035). Gender also affected TST, MT and HT (p < 0.05) (females versus males: TST OR= 0.5, MT= 1.3 N mean difference, HT= 2.2 0C mean difference). Repeatability was substantial to moderate for all tests, but poor for TST. There was no difference in thresholds between occasions, except for CT. Test-retest repeatability was slightly better with the 2 mm MT probe compared to other diameters and improved with operator experience.
Conclusions
and clinical relevance The STEP was feasible, well tolerated and showed substantial test-retest repeatability in healthy dogs. Further validation is needed in dogs suffering pain
Overview of ASDEX Upgrade results
The ASDEX Upgrade (AUG) programme is directed towards physics input to critical
elements of the ITER design and the preparation of ITER operation, as well as addressing
physics issues for a future DEMO design. Since 2015, AUG is equipped with a new pair of
3-strap ICRF antennas, which were designed for a reduction of tungsten release during ICRF
operation. As predicted, a factor two reduction on the ICRF-induced W plasma content could
be achieved by the reduction of the sheath voltage at the antenna limiters via the compensation
of the image currents of the central and side straps in the antenna frame. There are two main
operational scenario lines in AUG. Experiments with low collisionality, which comprise
current drive, ELM mitigation/suppression and fast ion physics, are mainly done with freshly
boronized walls to reduce the tungsten influx at these high edge temperature conditions. Full
ELM suppression and non-inductive operation up to a plasma current of Ip = 0.8 MA could
be obtained at low plasma density. Plasma exhaust is studied under conditions of high neutral
divertor pressure and separatrix electron density, where a fresh boronization is not required.
Substantial progress could be achieved for the understanding of the confinement degradation
by strong D puffing and the improvement with nitrogen or carbon seeding. Inward/outward
shifts of the electron density profile relative to the temperature profile effect the edge stability
via the pressure profile changes and lead to improved/decreased pedestal performance.
Seeding and D gas puffing are found to effect the core fueling via changes in a region of high
density on the high field side (HFSHD).
The integration of all above mentioned operational scenarios will be feasible and
naturally obtained in a large device where the edge is more opaque for neutrals and higher
plasma temperatures provide a lower collisionality. The combination of exhaust control
with pellet fueling has been successfully demonstrated. High divertor enrichment values of
nitrogen EN 10 have been obtained during pellet injection, which is a prerequisite for the
simultaneous achievement of good core plasma purity and high divertor radiation levels.
Impurity accumulation observed in the all-metal AUG device caused by the strong neoclassical
inward transport of tungsten in the pedestal is expected to be relieved by the higher
neoclassical temperature screening in larger devices.European Commission (EUROfusion 633053
A heavy quark effective field lagrangian keeping particle and antiparticle mixed sectors
We derive a tree-level heavy quark effective Lagrangian keeping
particle-antiparticle mixed sectors allowing for heavy quark-antiquark pair
annihilation and creation. However, when removing the unwanted degrees of
freedom from the effective Lagrangian one has to be careful in using the
classical equations of motion obeyed by the effective fields in order to get a
convergent expansion on the reciprocal of the heavy quark mass. Then the
application of the effective theory to such hard processes should be sensible
for special kinematic regimes as for example heavy quark pair production near
threshold.Comment: LaTeX, 14 pages, 1 EPS figure
- âŠ