10,647 research outputs found
Cosmic rays in magnetized intracluster plasma
Recent results are reported on Magnetic Fields in Clusters of Galaxies,
Diffuse Radio Emission, and Radio - X-ray connection in Radio Halos.Comment: 2 pages, 1 figure, Invited talk at the JD15 "Magnetic Fields in
Diffuse Media", IAU XXVII General Assembly, Rio de Janeir
Large scale GW calculations
We present GW calculations of molecules, ordered and disordered solids and
interfaces, which employ an efficient contour deformation technique for
frequency integration, and do not require the explicit evaluation of virtual
electronic states, nor the inversion of dielectric matrices. We also present a
parallel implementation of the algorithm which takes advantage of separable
expressions of both the single particle Green's function and the screened
Coulomb interaction. The method can be used starting from density functional
theory calculations performed with semi-local or hybrid functionals. We applied
the newly developed technique to GW calculations of systems of unprecedented
size, including water/semiconductor interfaces with thousands of electrons
Comparative analysis of the diffuse radio emission in the galaxy clusters A1835, A2029, and Ophiuchus
We recently performed a study of a sample of relaxed, cooling core galaxy
clusters with deep Very Large Array observations at 1.4 GHz. We find that in
the central regions of A1835, A2029, and Ophiuchus the dominant radio galaxy is
surrounded by a diffuse low-brightness radio emission that takes the form of a
mini-halo. Here we present the results of the analysis of the extended diffuse
radio emission in these mini-halos. In order to investigate the morphological
properties of the diffuse radio emission in clusters of galaxies we propose to
fit their azimuthally averaged brightness profile with an exponential,
obtaining the central brightness and the e-folding radius from which the radio
emissivity can be calculated. We investigate the radio properties of the
mini-halos in A1835, A2029, and Ophiuchus in comparison with the radio
properties of a representative sample of mini-halos and halos already known in
the literature. We find that radio halos can have quite different length-scales
but their emissivity is remarkably similar from one halo to the other. In
contrast, mini-halos span a wide range of radio emissivity. Some of them, like
the Perseus mini-halos, are characterized by a radio emissivity which is more
than 100 times greater than that of radio halos. On the other hand, the new
mini-halos in cooling core clusters analyzed in this work, namely A2029,
Ophiuchus, and A1835, have a radio emissivity which is much more typical of
halos in merging clusters rather than similar to that of the other mini-halos
previously known.Comment: 17 pages, 11 figures, A&A in press. For a version with high quality
figures, see http://erg.ca.astro.it/preprints/mini_halo_2
Design of defect spins in piezoelectric aluminum nitride for solid-state hybrid quantum technologies
Spin defects in wide-band gap semiconductors are promising systems for the
realization of quantum bits, or qubits, in solid-state environments. To date,
defect qubits have only been realized in materials with strong covalent bonds.
Here, we introduce a strain-driven scheme to rationally design defect spins in
functional ionic crystals, which may operate as potential qubits. In
particular, using a combination of state-of-the-art ab-initio calculations
based on hybrid density functional and many-body perturbation theory, we
predicted that the negatively charged nitrogen vacancy center in piezoelectric
aluminum nitride exhibits spin-triplet ground states under realistic uni- and
bi-axial strain conditions; such states may be harnessed for the realization of
qubits. The strain-driven strategy adopted here can be readily extended to a
wide range of point defects in other wide-band gap semiconductors, paving the
way to controlling the spin properties of defects in ionic systems for
potential spintronic technologies.Comment: In press. 32 pages, 4 figures, 3 tables, Scientific Reports 201
A giant radio halo in the low luminosity X-ray cluster Abell 523
Radio halos are extended and diffuse non-thermal radio sources present at the
cluster center, not obviously associated with any individual galaxy. A strong
correlation has been found between the cluster X-ray luminosity and the halo
radio power. We observe and analyze the diffuse radio emission present in the
complex merging structure Abell 523, classified as a low luminosity X-ray
cluster, to discuss its properties in the context of the halo total radio power
versus X-ray luminosity correlation. We reduced VLA archive observations at 1.4
GHz to derive a deep radio image of the diffuse emission, and compared radio,
optical, and X-ray data. Low-resolution VLA images detect a giant radio halo
associated with a complex merging region. The properties of this new halo agree
with those of radio halos in general discussed in the literature, but its radio
power is about a factor of ten higher than expected on the basis of the cluster
X-ray luminosity. Our study of this giant radio source demonstrates that radio
halos can also be present in clusters with a low X-ray luminosity. Only a few
similar cases have so far been found . This result suggests that this source
represent a new class of objects, that cannot be explained by classical radio
halo models. We suggest that the particle reacceleration related to merging
processes is very efficient and/or the X-ray luminosity is not a good indicator
of the past merging activity of a cluster.Comment: 5 pages, 6 figures, Astronomy and Astrophysics Letter in pres
Role of surface states in the Casimir force between semiconducting films
We present results of first principle calculations of the Casimir force
between Si films of nanometric size, which show that it depends significantly
upon the configuration of the surface atoms, and give evidence of the
importance of surface states.Comment: to be published on J.Phys.
Comparison of average larval fish vertical distributions among species exhibiting different transport pathways on the southeast United States continental shelf
Water currents are vertically structured in many marine systems and as a result, vertical movements by fish larvae and zooplankton affect horizontal transport (Power, 1984).
In estuaries, the vertical movements of larvae with tidal periods can result in their retention or ingress (Fortier
and Leggett, 1983; Rijnsdorp et al., 1985; Cronin and Forward, 1986; Forward et al., 1999). On the continental
shelf, the vertical movements of organisms interact daily and ontogenetically with depth-varying currents to affect horizontal transport (Pillar et al., 1989; Barange and Pillar, 1992; Cowen et al., 1993, 2000; Batchelder et al., 2002)
Carrier multiplication between interacting nanocrystals for fostering silicon-based photovoltaics
Being a source of clean and renewable energy, the possibility to convert
solar radiation in electric current with high efficiency is one of the most
important topics of modern scientific research. Currently the exploitation of
interaction between nanocrystals seems to be a promising route to foster the
establishment of third generation photovoltaics. Here we adopt a fully
ab-initio scheme to estimate the role of nanoparticle interplay on the carrier
multiplication dynamics of interacting silicon nanocrystals. Energy and charge
transfer-based carrier multiplication events are studied as a function of
nanocrystal separation showing benefits induced by the wavefunction sharing
regime. We prove the relevance of these recombinative mechanisms for
photovoltaic applications in the case of silicon nanocrystals arranged in dense
arrays, quantifying at an atomistic scale which conditions maximize the
outcome.Comment: Supplementary materials are freely available onlin
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