900 research outputs found
Revealing the magnetic field in a distant galaxy cluster: discovery of the complex radio emission from MACS J0717.5 +3745
Aims. To study at multiple frequencies the radio emission arising from the
massive galaxy cluster MACS J0717.5+3745 (z=0.55). Known to be an extremely
complex cluster merger, the system is uniquely suited for an investigation of
the phenomena at work in the intra-cluster medium (ICM) during cluster
collisions. Methods. We use multi-frequency and multi-resolution data obtained
with the Very Large Array radio telescope, and X-ray features revealed by
Chandra, to probe the non-thermal and thermal components of the ICM, their
relations and interactions. Results. The cluster shows highly complex radio
emission. A bright, giant radio halo is detected at frequencies as high as 4.8
GHz. MACS J0717.5+3745 is the most distant cluster currently known to host a
radio halo. This radio halo is also the most powerful ever observed, and the
second case for which polarized radio emission has been detected, indicating
that the magnetic field is ordered on large scales.Comment: 14 pages, 13 figures, Astronomy and Astrophysics, accepte
Point-of-Care Ultrasound Assessment of Tropical Infectious Diseases—A Review of Applications and Perspectives
The development of good quality and affordable ultrasound machines has led to the establishment and implementation of numerous point-of-care ultrasound (POCUS) protocols in various medical disciplines. POCUS for major infectious diseases endemic in tropical regions has received less attention, despite its likely even more pronounced benefit for populations with limited access to imaging infrastructure. Focused assessment with sonography for HIV-associated TB (FASH) and echinococcosis (FASE) are the only two POCUS protocols for tropical infectious diseases, which have been formally investigated and which have been implemented in routine patient care today. This review collates the available evidence for FASH and FASE, and discusses sonographic experiences reported for urinary and intestinal schistosomiasis, lymphatic filariasis, viral hemorrhagic fevers, amebic liver abscess, and visceral leishmaniasis. Potential POCUS protocols are suggested and technical as well as training aspects in the context of resource-limited settings are reviewed. Using the focused approach for tropical infectious diseases will make ultrasound diagnosis available to patients who would otherwise have very limited or no access to medical imaging
A search for steep spectrum radio relics and halos with the GMRT
Context: Diffuse radio emission, in the form of radio halos and relics,
traces regions in clusters with shocks or turbulence, probably produced by
cluster mergers. Some models of diffuse radio emission in clusters indicate
that virtually all clusters should contain diffuse radio sources with a steep
spectrum. External accretion shocks associated with filamentary structures of
galaxies could also accelerate electrons to relativistic energies and hence
produce diffuse synchrotron emitting regions. Here we report on Giant Metrewave
Radio Telescope (GMRT) observations of a sample of steep spectrum sources from
the 74 MHz VLSS survey. These sources are diffuse and not associated with
nearby galaxies.
Aims: The main aim of the observations is to search for diffuse radio
emission associated with galaxy clusters or the cosmic web.
Methods: We carried out GMRT 610 MHz continuum observations of unidentified
diffuse steep spectrum sources.
Results: We have constructed a sample of diffuse steep spectrum sources,
selected from the 74 MHz VLSS survey. We identified eight diffuse radio sources
probably all located in clusters. We found five radio relics, one cluster with
a giant radio halo and a radio relic, and one radio mini-halo. By complementing
our observations with measurements from the literature we find correlations
between the physical size of relics and the spectral index, in the sense that
smaller relics have steeper spectra. Furthermore, larger relics are mostly
located in the outskirts of clusters while smaller relics are located closer to
the cluster center.Comment: 20 pages, 26 figures, accepted for publication in A&A on October 7,
200
Clusters of galaxies : observational properties of the diffuse radio emission
Clusters of galaxies, as the largest virialized systems in the Universe, are
ideal laboratories to study the formation and evolution of cosmic
structures...(abridged)... Most of the detailed knowledge of galaxy clusters
has been obtained in recent years from the study of ICM through X-ray
Astronomy. At the same time, radio observations have proved that the ICM is
mixed with non-thermal components, i.e. highly relativistic particles and
large-scale magnetic fields, detected through their synchrotron emission. The
knowledge of the properties of these non-thermal ICM components has increased
significantly, owing to sensitive radio images and to the development of
theoretical models. Diffuse synchrotron radio emission in the central and
peripheral cluster regions has been found in many clusters. Moreover
large-scale magnetic fields appear to be present in all galaxy clusters, as
derived from Rotation Measure (RM) studies. Non-thermal components are linked
to the cluster X-ray properties, and to the cluster evolutionary stage, and are
crucial for a comprehensive physical description of the intracluster medium.
They play an important role in the cluster formation and evolution. We review
here the observational properties of diffuse non-thermal sources detected in
galaxy clusters: halos, relics and mini-halos. We discuss their classification
and properties. We report published results up to date and obtain and discuss
statistical properties. We present the properties of large-scale magnetic
fields in clusters and in even larger structures: filaments connecting galaxy
clusters. We summarize the current models of the origin of these cluster
components, and outline the improvements that are expected in this area from
future developments thanks to the new generation of radio telescopes.Comment: Accepted for the publication in The Astronomy and Astrophysics
Review. 58 pages, 26 figure
Teacher resilience in adverse contexts: issues of professionalism and professional identity
Teacher resilience is a construct that is relative, developmental and dynamic; it is socially constructed and depends on personal and professional dispositions. Issues of commitment, professionalism, and professional identity, for instance, need to be taken into account if teacher resilience is to be fully understood. In this chapter I draw upon a larger piece of research aimed at investigating teachers’ work and lives in challenging circumstances. Data were collected through a national survey (n=2702 teachers), focus group (n=99 teachers) and interviews to 11 school principals. Findings suggest the connection between teacher commitment and resilience which are associated with issues of school culture and leadership, a sense of vocation, and teachers’ beliefs and professional values. Factors and sources of teacher motivation and resilience are also identified within a context marked by teacher intensification, lack of trust, worsening of teaching conditions, lower social and economic status and legislative “tsunami”. The chapter ends with the discussion of the importance of relationships in the teaching profession and issues of motivation and professionalism which entails given ways of being and feeling as a teacher.Financial Support by CIEC (Research Centre on Child Studies, IE, UMinho; FCT R&D unit 317, Portugal) by the Strategic Project UID/CED/00317/2013, with financial support of National Funds through the FCT (Foundation for Science and Technology) and co-financed by European Regional Development Funds (FEDER) through the COMPETE 2020 - Competitiveness and Internationalization Operational Program (POCI) with the reference POCI-01-0145-FEDER-00756
The role of the axial substituent in subphthalocyanine acceptors for bulk-heterojunction solar cells
Four hexachlorosubphthalocyanines SubPcCl6‐X bearing different axial substituents (X) have been synthesized for use as novel electron acceptors in solution‐processed bulk‐heterojunction organic solar cells. Subphthalocyanines are aromatic chromophoric molecules with cone‐shaped structure, good solution processability, intense optical absorption in the visible spectral region, appropriate electron mobilities, and tunable energy levels. Solar cells with subphthalocyanines as the electron acceptor and PTB7‐Th as the electron donor exhibit a power conversion efficiency up to 4 % and an external quantum efficiency approaching 60 % due to significant contributions from both the electron donor and the electron acceptor to the photocurrent, indicating a promising prospect of non‐fullerene acceptors based on subphthalocyanines and structurally related systems.The work was performed in the framework of the Mujulima (EU-FP7, No. 604148) and TripleSolar (ERC Adv Grant No. 339031) projects, and received funding from the Ministry of Education, Culture and Science, The Netherlands (Gravity program 024.001.035). We are also grateful to MINECO, Spain (CTQ2014-52869-P) and the Comunidad de Madrid, Spain (FOTOCARBON, S2013/MIT-2841)
Early Diagnosis, Treatment and Follow-Up of Cystic Echinococcosis in Remote Rural Areas in Patagonia: Impact of Ultrasound Training of Non-Specialists
Cystic echinococcosis (CE) is an important and widespread disease that affects sheep, cattle, and humans living in areas where sheep and cattle are raised. CE is highly endemic in rural sections of Rio Negro, Argentina, where our group is based. However, it requires continuous monitoring of both populations with human disease best assessed by means of ultrasound (US) screening. This is challenging in remote rural areas due to the shortage of imaging specialists. To overcome this hurdle, we set up a two-day training program of Focused Assessment with Sonography for Echinococcosis (FASE) on CE for family medicine practitioners with no previous experience in US. After the course, they were equipped with portable US scanners and dispatched to remote rural areas in Rio Negro where they screened patients, located and staged the cysts and decided on the treatment with the help of surgeons and radiologists in local tertiary care centers
Relics as probes of galaxy cluster mergers
Galaxy clusters grow by mergers with other clusters and galaxy groups. These
mergers create shocks within the intracluster medium (ICM). It is proposed that
within the shocks particles can be accelerated to extreme energies. In the
presence of a magnetic field these particles should then form large regions
emitting synchrotron radiation, creating so-called radio relics. An example of
a cluster with relics is CIZA J2242.8+5301. Here we present hydrodynamical
simulations of idealized binary cluster collisions with the aim of constraining
the merger scenario for this cluster. We conclude that by using the location,
size and width of double radio relics we can set constraints on the mass
ratios, impact parameters, timescales, and viewing geometries of binary cluster
merger events.Comment: Accepted for publication in special issue of Journal of Astrophysics
and Astronomy: conference proceedings of "Diffuse Relativistic Plasmas"
conference, Bangalore, 1-4 March 2011, 4 pages, 2 figure
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