1,264 research outputs found
Cosmic rays and Radio Halos in galaxy clusters : new constraints from radio observations
Clusters of galaxies are sites of acceleration of charged particles and
sources of non-thermal radiation. We report on new constraints on the
population of cosmic rays in the Intra Cluster Medium (ICM) obtained via radio
observations of a fairly large sample of massive, X-ray luminous, galaxy
clusters in the redshift interval 0.2--0.4. The bulk of the observed galaxy
clusters does not show any hint of Mpc scale synchrotron radio emission at the
cluster center (Radio Halo). We obtained solid upper limits to the diffuse
radio emission and discuss their implications for the models for the origin of
Radio Halos. Our measurements allow us to derive also a limit to the content of
cosmic ray protons in the ICM. Assuming spectral indices of these protons delta
=2.1-2.4 and microG level magnetic fields, as from Rotation Measures, these
limits are one order of magnitude deeper than present EGRET upper limits, while
they are less stringent for steeper spectra and lower magnetic fields.Comment: 14 pages, 5 figures, ApJ Letter, accepte
Chandra detection of the radio and optical double hot spot of 3C 351
In this letter we report a Chandra X-ray detection of the double northern hot
spot of the radio quasar 3C 351. The hot spot has also been observed in the
optical with the Hubble Space Telescope (R-band) and with the 3.5m. Telescopio
Nazionale Galileo (B-band). The radio-to-optical and X-ray spectra are
interpreted as the results of the synchrotron and synchrotron-self-Compton
(SSC) mechanisms, respectively, with hot-spot magnetic field strengths ~3 times
smaller than the equipartition values. In the framework of shock acceleration
theory, we show that the requirement for such a relatively small field strength
is in agreement with the fitted synchrotron spectral models and with the sizes
of the hot spots. Finally, we show that the combination of a lower magnetic
field strength with the high frequencies of the synchrotron cut-off in the
fitted synchrotron spectra provides strong evidence for electron acceleration
in the hot spots.Comment: 16 pag. + 2 .PS figures (fig.2 color), ApJ Letter in pres
The number of stimulus-onset asynchronies affects the perception of the sound-induced flash illusion in young and older adults
The sound-induced flash illusion is a multisensory illusion occurring when one flash is presented with two beeps and perceived as two flashes. Younger individuals are largely susceptible to the illusion when the stimulus onset asynchrony between the first and the second beep falls within the temporal window of integration, but the susceptibility falls dramatically outside of this short temporal range. Older individuals, in particular older adults prone to falling and/or mild cognitive impairment, show an extended susceptibility to the illusion. This suggests that they have inefficient multisensory integration, particularly in the temporal domain. In the present study, we investigated the reliability of the illusion across younger and older people, guided by the hypothesis that the experimental context, i.e., exposure to a wider or smaller number of stimulus onset asynchronies, would modify the intra-personal susceptibility to the illusion at shorter asynchronies vs. longer asynchronies, likely due to the gathering of model evidence based on Bayesian inference. We tested 22 young adults and 29 older adults and verified these hypotheses. Both groups showed higher susceptibility to the illusion when exposed to a smaller range of asynchronies, but only for longer ones, not within the 100 ms window. We discuss the theoretical implications in terms of online perceptual learning and practical implications in terms of standardisation of the experimental context when attempting to find normative values
Analysis of a bakery production system using discrete simulation
The main objective of this study is to analyse different production scenarios of a company, and propose improvements with the use of discrete event simulation. We use a simulation tool, SIMIO software, to reproduce the existing production layout of the company. Our purpose is to gather relevant information about the actual production system behaviour, and to find strategies to increase the production level to meet the market demand.
Based on initial simulation model, some production scenarios were developed involving the production of different
products. The analysis of the developed models highlighted the need for improvements. Among the obtained
results, the creation of different mixed production scenarios allowed to increase the production level while maintaining
the current existing resources. The results of this work can be easily implemented in the company in
order to increase the production level without increasing costs since they do not involve the purchase of new
equipment. In conclusion, this study highlighted the ability of the simulation technique to analyse manufacturing
processes throughout the creation of different scenarios providing insights on the production process improving
the companies’ productive performanceinfo:eu-repo/semantics/publishedVersio
The resolved fraction of the Cosmic X-ray Background
We present the X-ray source number counts in two energy bands (0.5-2 and 2-10
keV) from a very large source sample: we combine data of six different surveys,
both shallow wide field and deep pencil beam, performed with three different
satellites (ROSAT, Chandra and XMM-Newton). The sample covers with good
statistics the largest possible flux range so far: [2.4*10^-17 - 10^-11] cgs in
the soft band and [2.1*10^-16 - 8*10^{-12}]cgs in the hard band. Integrating
the flux distributions over this range and taking into account the (small)
contribution of the brightest sources we derive the flux density generated by
discrete sources in both bands. After a critical review of the literature
values of the total Cosmic X--Ray Background (CXB) we conclude that, with the
present data, the 94.3%, and 88.8% of the soft and hard CXB can be ascribed to
discrete source emission. If we extrapolate the analytical form of the Log
N--Log S distribution beyond the flux limit of our catalog in the soft band we
find that the flux from discrete sources at ~3*10^-18 cgs is consistent with
the entire CXB, whereas in the hard band it accounts for only 93% of the total
CXB at most, hinting for a faint and obscured population to arise at even
fainter fluxes.Comment: Accepted for publication in Ap
Imaging-SIMS (Secondary Ion Mass Spectroscopy) Studies of Advanced Materials
This article describes the application of scanning ion microprobe (SIM) microanalysis for the characterization of advanced engineered materials. In conjunction with secondary ion mass spectrometry (SIMS), scanning ion microprobes can image elemental distributions over surfaces with high lateral resolution (50-100 nm). With this technique, most elements, including isotopes, can be detected with good sensitivity. The principles and instrumentation associated with the SIM/SIMS technique are briefly described and ongoing developments are outlined. The analytical capabilities of the technique are illustrated by case studies of aluminum-lithium alloys, zinc oxide varistors, aluminum matrix composites, and photographic materials
The contribution of Quasars to the Far Infrared Background
Recent observational results obtained with SCUBA, COBE and ISO have greatly
improved our knowledge of the infrared and sub-mm background radiation. These
limits become constraining given the realization that most AGNs are heavily
obscured and must reradiate strongly in the IR/sub-mm. Here we predict the
contribution of AGNs to the IR/sub-mm background, starting from measurements of
the hard X-ray background. We show that an application of what we know of AGN
Spectral Energy Distributions (SEDs) and the IR background requires that a
significant fraction of the 10-150 micron background comes from AGNs. This
conclusion can only be avoided if obscured AGNs are intrinsically brighter in
the X-rays (with respect to the optical-UV) than unobscured AGNs, contrary to
``unified schemes'' for AGNs, or have a dust to gas ratio much lower (< 0.1)
than Galactic. We show that these results are rather robust and not strongly
dependent on the details of the modeling.Comment: 13 pages, 1 figure, Astrophysical Journal, in pres
Analysis and optimisation of a production line using discrete simulation
This study presents a simulation-based procedure to analyse a production line of a metalworking company. We use a simulation tool, ProModel R software, to reproduce the existing production line layout of the company best-selling product which represents about 70% of the total sales. Our purpose is to get information about the existing system behaviour, and to find strategies to increase actual production level to meet the market’s demand. Based on an initial simulation model, different production scenarios were proposed and results have shown that it is possible to increase the production level allowing to meet the increasing demand for
the product. The following changes in the production system were considered: (i) the use of intermediate stock of work-in-process items, (ii) the introduction of new equipment, and (iii) a mixed strategy where the introduction of new equipment is combined with the use of intermediate stock of work-in-process items. In summary, this research exhibits the flexibility of the simulation technique to address manufacturing problems throughout the creation of different scenarios providing some of the behaviour of the systems allowing the anticipation of final outputs.info:eu-repo/semantics/publishedVersio
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