924 research outputs found
Merging clusters of galaxies observed with XMM-Newton
We present results from the XMM-Newton observations of our ongoing program on
merging clusters. To date three clusters have been observed, covering the
temporal sequence from early to late stage mergers: A1750, A2065 and A3921.
Using spatially-resolved spectroscopy of discrete regions, hardness ratio and
temperature maps, we show that all three clusters display a complex temperature
structure. In the case of A1750, a double cluster, we argue that the observed
temperature structure is not only related to the ongoing merger but also to
previous merger events. A2065 seems an excellent example of a `compact merger',
i.e. when the centres of the two clusters have just started to interact,
producing a shock in the ICM. Using comparisons with numerical simulations and
complementary optical data, the highly complex temperature structure evident in
A3921 is interpreted as an off-axis merger between two unequal mass components.
These results illustrate the complex physics of merger events. The relaxation
time can be larger than the typical time between merger events, so that the
present day morphology of clusters depends not only on on-going interaction but
also on the more ancient formation history.Comment: 10 pages, 3 figures. Use elsart.cls. Accepted for publication in
Advances in Space Research. A version with full resolution figures can be
found at http://www.star.bris.ac.uk/elena/cospar_3clusters.pd
Aircraft control via variable cant-angle winglets
Copyright @ 2008 American Institute of Aeronautics and AstronauticsThis paper investigates a novel method for the control of "morphing" aircraft. The concept consists of a pair of winglets; with adjustable cant angle, independently actuated and mounted at the tips of a baseline flying wing. The general philosophy behind the concept was that for specific flight conditions such as a coordinated turn, the use of two control devices would be sufficient for adequate control. Computations with a vortex lattice model and subsequent wind-tunnel tests demonstrate the viability of the concept, with individual and/or dual winglet deflection producing multi-axis coupled control moments. Comparisons between the experimental and computational results showed reasonable to good agreement, with the major discrepancies thought to be due to wind-tunnel model aeroelastic effects.This work has been supported by a Marie Curie excellence research grant funded by the European Commission
A2163: Merger events in the hottest Abell galaxy cluster II. Subcluster accretion with galaxy-gas separation
Located at z = 0.203, A2163 is a rich galaxy cluster with an intra-cluster
medium (ICM) that exhibits extraordinary properties, including an exceptionally
high X-ray luminosity, average temperature, and a powerful and extended radio
halo. The irregular and complex morphology of its gas and galaxy structure
suggests that this cluster has recently undergone major merger events that
involve two or more cluster components. In this paper, we study the gas
structure and dynamics by means of spectral-imaging analysis of X-ray data
obtained from XMM-Newton and Chandra observations. From the evidence of a cold
front, we infer the westward motion of a cool core across the E-W elongated
atmosphere of the main cluster A2163-A. Located close to a galaxy over-density,
this gas 'bullet' appears to have been spatially separated from its galaxy (and
presumably dark matter component) as a result of high-velocity accretion.
From gas brightness and temperature profile analysis performed in two
opposite regions of the main cluster, we show that the ICM has been
adiabatically compressed behind the crossing 'bullet' possibly because of shock
heating, leading to a strong departure of the ICM from hydrostatic equilibrium
in this region. Assuming that the mass estimated from the Yx proxy best
indicates the overall mass of the system and that the western cluster sector is
in approximate hydrostatic equilibrium before subcluster accretion, we infer a
merger scenario between two subunits of mass ratio 1:4, leading to a present
total system mass of M500 . The exceptional
properties of A2163 present various similarities with those of 1E0657-56, the
so-called 'bullet-cluster'. These similarities are likely to be related to a
comparable merger scenario.Comment: A&A, in pres
Particle dynamics in a non-flaring solar active region model
The aim of this work is to investigate and characterise particle behaviour in a (observationally-driven) 3D MHD model of the solar atmosphere above a slowly evolving, non-flaring active region. We use a relativistic guiding-centre particle code to investigate particle acceleration in a single snapshot of the 3D MHD simulation. Despite the lack of flare-like behaviour in the active region, direct acceleration of electrons and protons to non-thermal energies (≲ 42 MeV) was found, yielding spectra with high-energy tails which conform to a power law. Examples of particle dynamics, including particle trapping caused by local electric rather than magnetic field effects, are observed and discussed, together with implications for future experiments which simulate non-flaring active region heating and reconnection.Publisher PDFPeer reviewe
Axisymmetric solitary waves on the surface of a ferrofluid
We report the first observation of axisymmetric solitary waves on the surface
of a cylindrical magnetic fluid layer surrounding a current-carrying metallic
tube. According to the ratio between the magnetic and capillary forces, both
elevation and depression solitary waves are observed with profiles in good
agreement with theoretical predictions based on the magnetic analogue of the
Korteweg-deVries equation. We also report the first measurements of the
velocity and the dispersion relation of axisymmetric linear waves propagating
on the cylindrical ferrofluid layer that are found in good agreement with
theoretical predictions.Comment: to be published in Phys. Rev. Let
Stress fluctuation, crack renucleation and toughening in layered materials
It has been established that contrast in the elastic properties can lead to enhancement of fracture toughness in heterogeneous materials. Focussing on layered materials as a model system, we show that this enhancement is a result of two distinct phenomena – first, fluctuations in stress leading to regions where the stress intensity at the crack is considerably smaller than that of the macroscopically applied value; and second, the lack of stress intensity when a crack is at a compliant to stiff interface thereby requiring renucleation. Using theoretical, computational and experimental methods, we study two geometries – a layered material and a layered material with a narrow channel – to separate the two phenomena. The stress fluctuation is present in both, but renucleation is present only in the layered medium. We provide quantitative estimates for the enhanced toughness
Coronal bright point statistics I. Lifetime, shape, and coronal co-rotation
Context. The corona of the Sun is the part of the solar atmosphere with
temperatures of over one million Kelvin, which needs to be heated internally in
order to exist. This heating mechanism remains a mystery; we see large
magnetically active regions in the photosphere lead to strong extreme UV (EUV)
emission in the corona. On much smaller scales (on the order of tens of Mm),
there are bipolar and multipolar regions that can be associated with evenly
sized coronal bright points (CBPs). Aims. Our aim was to study the properties
of CBPs in a statistical sense and to use continuous data from the SDO
spacecraft, which makes it possible to track CBPs over their whole lifetime.
Furthermore, we tested various rotation-speed profiles for CBPs in order to
find out if the lower corona is co-rotating with the photosphere. Then we
compiled a database with about 346 CBPs together with information of their
sizes, shapes, appearance and disappearance, and their visibility in the EUV
channels of the AIA instrument. We want to verify our methods with similar
previous studies. Methods. We used the high-cadence data of the largest
continuous SDO observation interval in 2015 to employ an automated tracking
algorithm for CBPs. Some of the information (e.g., the total lifetime, the
characteristic shape, and the magnetic polarities below the CBPs) still
requires human interaction. Results. In this work we present statistics on
fundamental properties of CBPs along with some comparison tables that relate,
for example, the CBP lifetime with their shape. CBPs that are visible in all
AIA channels simultaneously seem to be brighter in total and also have a
stronger heating, and hence a higher total radiation flux. We compared the EUV
emission visibility in different AIA channels with the CBP's shape and
lifetime. ... (full version see pdf)Comment: 8 pages, 11 figures, 3 table, publishe
Longitudinal analysis of safety and medication adherence of patients in the Fingolimod patient support program: a real-world observational study.
The Fingolimod Patient Support Program (F-PSP) is an interprofessional specialty pharmacy service designed to ensure responsible use of fingolimod by promoting patient safety and medication adherence. This study aims to evaluate the safety and medication adherence of patients who joined the F-PSP between 2013 and 2016. Sociodemographic and medical characteristics, patient safety data (patient-reported symptoms, discontinuations due to adverse events (AEs), repeated first-dose monitoring), and medication adherence (implementation, persistence, reasons for discontinuation, influence of covariates, barriers and facilitators) were described. Sixty-seven patients joined the F-PSP. Patients reported a high frequency of symptoms. Due to AEs, 7 patients discontinued fingolimod, 3 took therapeutic breaks, and 1 reduced the regimen temporarily. Three patients repeated the first-dose monitoring. Patients had a high medication adherence over the 18-month analysis period: implementation decreased from 98.8 to 93.7%, and fingolimod persistence was 83.2% at 18 months. The patients' level of education, professional situation, and living with child(ren) influenced implementation. Patients reported more facilitators of medication adherence than barriers. The F-PSP seems valuable for supporting individual patients (ensuring responsible use of fingolimod and inviting patients for shared-decision making) and public health (indirectly gathering real-world evidence)
Merging history of three bimodal clusters
We present a combined X-ray and optical analysis of three bimodal galaxy
clusters selected as merging candidates at z ~ 0.1. These targets are part of
MUSIC (MUlti--Wavelength Sample of Interacting Clusters), which is a general
project designed to study the physics of merging clusters by means of
multi-wavelength observations. Observations include spectro-imaging with
XMM-Newton EPIC camera, multi-object spectroscopy (260 new redshifts), and
wide-field imaging at the ESO 3.6m and 2.2m telescopes. We build a global
picture of these clusters using X-ray luminosity and temperature maps together
with galaxy density and velocity distributions. Idealized numerical simulations
were used to constrain the merging scenario for each system. We show that A2933
is very likely an equal-mass advanced pre-merger ~ 200 Myr before the core
collapse, while A2440 and A2384 are post-merger systems ~ 450 Myr and ~1.5 Gyr
after core collapse, respectively). In the case of A2384, we detect a
spectacular filament of galaxies and gas spreading over more than 1 h^{-1} Mpc,
which we infer to have been stripped during the previous collision. The
analysis of the MUSIC sample allows us to outline some general properties of
merging clusters: a strong luminosity segregation of galaxies in recent
post-mergers; the existence of preferential axes --corresponding to the merging
directions-- along which the BCGs and structures on various scales are aligned;
the concomitance, in most major merger cases, of secondary merging or accretion
events, with groups infalling onto the main cluster, and in some cases the
evidence of previous merging episodes in one of the main components. These
results are in good agreement with the hierarchical scenario of structure
formation, in which clusters are expected to form by successive merging events,
and matter is accreted along large--scale filaments
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