219 research outputs found
Non-thermal radiation from molecular clouds illuminated by cosmic rays from nearby supernova remnants
Molecular clouds are expected to emit non-thermal radiation due to cosmic ray
interactions in the dense magnetized gas. Such emission is amplified if a cloud
is located close to an accelerator of cosmic rays and if cosmic rays can leave
the accelerator and diffusively reach the cloud. We consider the situation in
which a molecular cloud is located in the proximity of a supernova remnant
which is accelerating cosmic rays and gradually releasing them into the
interstellar medium. We calculate the multiwavelength spectrum from radio to
gamma rays which emerges from the cloud as the result of cosmic ray
interactions. The total energy output is dominated by the gamma ray emission,
which can exceed the emission from other bands by an order of magnitude or
more. This suggests that some of the unidentified TeV sources detected so far,
with no obvious or very weak counterpart in other wavelengths, might be
associated with clouds illuminated by cosmic rays coming from a nearby source.Comment: 4 pages, 3 figures, proceedings of the "4th Heidelberg International
Symposium on High Energy Gamma-Ray Astronomy" July 7-11, 2008, Heidelberg,
German
On the gamma-ray emission of W44 and its surroundings
We present the analysis of 9.7 years Fermi-LAT data of the middle-aged
supernova remnant W44 and the massive molecular gas complex that surrounds it.
We derived a high-quality spectral energy distribution of gamma-radiation of
the shell over three decades. The very hard spectrum below 1 GeV supports the
earlier claims regarding the hadronic origin of radiation. We also confirm the
presence of two extended -ray structures located at two opposite edges
of the remnant along its major axis. Based on the high-resolution gas maps, we
demonstrate that the gamma-ray structures are caused by the enhanced cosmic-ray
density rather than the gradient of the gas distribution. We argue that the
revealed cosmic-ray "clouds" suggest an anisotropic character of the escape of
high-energy particles from the shell along the magnetic field of the remnant
Probing the Cosmic Ray density in the inner Galaxy
The galactic diffuse -ray emission, as seen by Fermi Large Area
Telescope (LAT), shows a sharp peak in the region around 4 kpc from the
Galactic center, which can be interpreted either as due to an enhanced density
of cosmic-ray accelerators or to a modification of the particle diffusion in
that region. Observations of -rays originating in molecular clouds are
a unique tool to infer the cosmic-ray density point by point, in distant
regions of the Galaxy. We report here the analysis of 11 yr Fermi-LAT data,
obtained in the direction of nine molecular clouds located in the 1.5--4.5 kpc
region. The cosmic-ray density measured at the locations of these clouds is
compatible with the locally measured one. We demonstrate that the cosmic-ray
density gradient inferred from the diffuse gamma-ray emission is the result of
the presence of cosmic-ray accelerators rather than a global change of the sea
of Galactic cosmic rays due to their propagation
Probing the Galactic cosmic ray flux with submillimeter and gamma ray data
The study of Galactic diffuse radiation combined with the knowledge
of the distribution of the molecular hydrogen in the Galaxy offers a unique
tool to probe the cosmic ray flux in the Galaxy. A methodology to study the
level of the cosmic ray "sea" and to unveil target-accelerator systems in the
Galaxy, which makes use of the data from the high resolution survey of the
Galactic molecular clouds performed with the NANTEN telescope and of the data
from gamma-ray instruments, has been developed. Some predictions concerning the
level of the cosmic ray "sea" and the -ray emission close to cosmic ray
sources for instruments such as Fermi and Cherenkov Telescope Array are
presented.Comment: Proceedings of the 4th Heidelberg International Symposium on High
Energy Gamma-Ray Astronom
Molecular Clouds as Cosmic Ray Laboratories
We will here discuss how the gamma-ray emission from molecular clouds can be
used to probe the cosmic ray flux in distant regions of the Galaxy and to
constrain the highly unknown cosmic ray diffusion coefficient. In particular we
will discuss the GeV to TeV emission from runaway cosmic rays penetrating
molecular clouds close to young and old supernova remnants and in molecular
clouds illuminated by the background cosmic ray flux.Comment: to appear on Proceedings of 25th Texas Symposium on Relativistic
Astrophysic
Form and function of the mantle edge in Protobranchia (Mollusca: Bivalvia)
We analyzed, by optical and transmission electron microscopy, the morphology and function of the mantle edge, including the formation of the periostracum, of ten species of protobranchs. Five species from the order Nuculida, four species from the order Nuculanida and one species from the order Solemyida were studied. A second outer fold, which seems to function as a template for the internal marginal crenulations of the valves, is present in the crenulated species of Nucula. The minute non-crenulated Ennucula aegeensis shows the glandular basal cells displaced toward the periostracal groove, resembling a minute additional fold between the outer and middle folds. Intense secretion of glycocalyx, together with active uptake of particles, have been observed in the inner epithelium of the middle mantle fold and the whole epithelium of the inner mantle fold in all the studied species. Contrary to the rest of the bivalves, all the protobranchs analyzed have two basal cells involved in the formation of the external nanometric pellicle of the periostracum, a character that would support the monophyly of protobranchs. A three-layered pattern is the general rule for the periostracum in protobranchs, like for other bivalves. The presence of pouches of translucent layer inside the tanned dark layer under periostracal folds is characteristic of the species with a folded periostracum; its function is unclear but could give flexibility to the periostracum. The non-nacreous internal shell layer and the presence of translucent pouches under periostracal folds in Sarepta speciosa resemble those found in nuculanids. However, the free periostracum is rather similar to those of N. hanleyi and E. aegeensis, with a continuous vesicular layer. All the latter supports the inclusion of Sarepta in the order Nuculanida but could indicate either a basal lineage or that the translucent vesicular layer is an adaptive trait.This research was funded by the projects CGL2017-85118-P and PID2020-116660GB-I00 of the Spanish Ministry of Economy, Industry and Competitiveness. Funding for open access charge has been provided by the University of Málaga/CBUA
A light-controlled resistive switching memory
Sketch of the configuration of a light-controlled resistive switching memory. Light enters through the Al 2O 3 uncovered surface and reaches the optically active p-Si substrate, where carriers are photogenerated and subsequently injected in the Al 2O 3 layer when a suitable voltage pulse is applied. The resistance of the Al 2O 3 can be switched between different non-volatile states, depending on the applied voltage pulse and on the illumination conditions.Fil: Ungureanu, Mariana. CIC nanoGUNE Consolider; EspañaFil: Zazpe, Raul. CIC nanoGUNE Consolider; EspañaFil: Golmar, Federico. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Nacional de Tecnología Industrial; Argentina. CIC nanoGUNE Consolider; EspañaFil: Stoliar, Pablo Alberto. Comisión Nacional de Energía Atómica; Argentina. CIC nanoGUNE Consolider; EspañaFil: Llopis, Roger. CIC nanoGUNE Consolider; EspañaFil: Casanova, Felix. CIC nanoGUNE Consolider; España. Basque Foundation for Science; EspañaFil: Hueso, Luis E.. CIC nanoGUNE Consolider; España. Basque Foundation for Science; Españ
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