2,702 research outputs found
Magnesium diboride superconductors for magnet applications
With the discovery of its superconducting properties in 2001, MgB2 is the latest superconductor for use in large scale applications such as superconducting magnets.\ud
Compared to other metallic superconductors like Nb-Ti and Nb3Sn, it has the\ud
advantage of a higher Tc (40 K), which enables magnets to operate at higher temperatures (» 20 K) and cuts down cooling costs. Compared to high-Tc conductors such as YBa2Cu3Ox and Bi2Sr2Ca2Cu3Ox on the other hand, it is a relatively simple compound and therefore easier to synthesise. Together with the abundance of magnesium and boron, this causes its presently estimated cost-to-performance ratio to be a factor of » 100 lower than that of high-Tc conductors
Spectral and polarization study of the double relics in Abell 3376 using the GMRT and the VLA
Double radio relics in galaxy clusters are rare phenomena that trace shocks
in the outskirts of merging galaxy clusters. We have carried out a spectral and
polarization study of the spectacular double relics in the galaxy cluster A3376
using the Giant Metrewave Radio Telescope at 150 and 325 MHz and the Very Large
Array at 1400 MHz. The polarization study at 1400 MHz reveals a high degree of
polarization (~30%) and aligned magnetic field vectors (not corrected for
Faraday rotation) in the eastern relic. A highly polarized (>60%) filamentary
radio source of size ~300 kpc near the eastern relic and north of the bent-jet
radio galaxy is detected for the first time. The western relic is less
polarized and does not show aligned magnetic field vectors. The distribution of
spectral indices between 325 and 1400 MHz over the radio relics show steepening
from the outer to the inner edges of the relics. The spectral indices of the
eastern and the western relics imply Mach numbers in the range 2.2 to 3.3.
Remarkable features such as the inward filament extending from the eastern
relic, the highly polarized filament, the complex polarization properties of
the western relic and the separation of the BCG from the ICM by a distance >900
kpc are noticed in the cluster. A comparison with simulated cluster mergers is
required to understand the complex properties of the double relics in the
context of the merger in A3376. An upper limit (log(P(1.4GHz) W/Hz < 23.0) on
the strength of a Mpc size radio halo in A3376 is estimated.Comment: 9 pages, 4 figures, accepted for publication in MNRA
Monetary and Fiscal Policy Design under EMU: A Dynamic Game Approach
This paper analyzes the problem of designing macroeconomic stabilization policies within the European Monetary Union (EMU) as a dynamic game between a centralized monetary authority, the European Central Bank (ECB), and national fiscal policy makers. Non-cooperative feedback Nash equilibrium and cooperative Nash bargaining solutions are determined under various assumptions about r ationing regimes in goods and labor markets and structural characteristics of the economies involved.
XMM-Newton observations of the merging galaxy cluster CIZA J2242.8+5301
We studied the intracluster medium of the galaxy cluster CIZA J2242.8+5301
using deep XMM-Newton observations. The cluster hosts a remarkable 2-Mpc long,
~50-kpc wide radio relic that has been nicknamed the "Sausage". A smaller, more
irregular counter-relic is also present, along with a faint giant radio halo.
We analysed the distribution of the ICM physical properties, and searched for
shocks by trying to identify density and temperature discontinuities. East of
the southern relic, we find evidence of shock compression corresponding to a
Mach number of 1.3, and speculate that the shock extends beyond the length of
the radio structure. The ICM temperature increases at the northern relic. More
puzzling, we find a "wall" of hot gas east of the cluster centre. A partial
elliptical ring of hot plasma appears to be present around the merger. While
radio observations and numerical simulations predict a simple merger geometry,
the X-ray results point towards a more complex merger scenario.Comment: Extensively revised and expanded, with 18 pages and 17 figure
Why are central radio relics so rare?
In this paper we address the question why cluster radio relics that are
connected to shock acceleration, so-called radio gischt, have preferentially
been found in the outskirts of galaxy clusters. By identifying merger shock
waves in cosmological grid simulations, we explore several prescriptions for
relating the energy dissipated in shocks to the energy emitted in the radio
band. None of the investigated models produce detectable radio relics within
100-200 kpc from the cluster centre. All models cause > 50 per cent of the
detectable relic emission at projected distances > 800 kpc. Central radio
relics caused by shocks that propagate along the line-of-sight are rare events
for simple geometrical reasons, and they have a low surface brightness making
them elusive for current instruments. Our simulations show that the radial
distribution of observed relics can be explained by the radial trend of
dissipated kinetic energy in shocks, that increases with distance from the
cluster centre up until half of the virial radius.Comment: 6 pages, 4 figures. MNRAS accepte
Diffuse radio emission in the merging cluster MACS J0717.5+3745: the discovery of the most powerful radio halo
Hierarchical models of structure formation predict that galaxy clusters grow
via mergers of smaller clusters and galaxy groups, as well as through
continuous accretion of gas. MACS J0717.5+3745 is an X-ray luminous and complex
merging cluster, located at a redshift of 0.55. Here we present Giant Metrewave
Radio Telescope (GMRT) radio observations at 610 MHz of this cluster. The main
aim of the observations is to search for diffuse radio emission within the
galaxy cluster MACS J0717.5+3745 related to the ongoing merger. These GMRT
observations are complemented by Very Large Array (VLA) archival observations
at 1.4, 4.9 and 8.5 GHz. We have discovered a radio halo in the cluster MACS
J0717.5+3745 with a size of about 1.2 Mpc. The radio power P_1.4 GHz is 5 x
10^25 W/Hz, which makes it the most powerful radio halo known till date. A 700
kpc radio structure, which we classify as a radio relic, is located in between
the merging substructures of the system. The location of this relic roughly
coincides with regions of the intra-cluster medium (ICM) that have a
significant enhancement in temperature as shown by Chandra. The major axis of
the relic is also roughly perpendicular to the merger axis. This shows that the
relic might be the result of a merger-related shock wave, where particles are
accelerated via the diffuse shock acceleration (DSA) mechanism. Alternatively,
the relic might trace an accretion shock of a large-scale galaxy filament to
the south-west. The global spectral index of radio emission within the cluster
is found to be -1.24 +/-0.05 between 4.9 GHz and 610 MHz. We derive a value of
5.8 microGauss for the equipartition magnetic field strength at the location of
the radio halo. [abridged].Comment: 8 pages, 9 figures, accepted for publication in A&A on August 3, 200
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