403 research outputs found
Fog-Driven Context-Aware Architecture for Node Discovery and Energy Saving Strategy for Internet of Things Environments
The consolidation of the Fog Computing paradigm and the ever-increasing diffusion of Internet of Things (IoT) and smart objects are paving the way toward new integrated solutions to efficiently provide services via short-mid range wireless connectivity. Being the most of the nodes mobile, the node discovery process assumes a crucial role for service seekers and providers, especially in IoT-fog environments where most of the devices run on battery. This paper proposes an original model and a fog-driven architecture for efficient node discovery in IoT environments. Our novel architecture exploits the location awareness provided by the fog paradigm to significantly reduce the power drain of the default baseline IoT discovery process. To this purpose, we propose a deterministic and competitive adaptive strategy to dynamically adjust our energy-saving techniques by deciding when to switch BLE interfaces ON/OFF based on the expected frequency of node approaching. Finally, the paper presents a thorough performance assessment that confirms the applicability of the proposed solution in several different applications scenarios. This evaluation aims also to highlight the impact of the nodes' dynamic arrival on discovery process performance
Radiative acceleration and transient, radiation-induced electric fields
The radiative acceleration of particles and the electrostatic potential
fields that arise in low density plasmas hit by radiation produced by a
transient, compact source are investigated. We calculate the dynamical
evolution and asymptotic energy of the charged particles accelerated by the
photons and the radiation-induced electric double layer in the full
relativistic, Klein-Nishina regime. For fluxes in excess of , the radiative force on a diluted plasma
(n\la 10^{11} cm) is so strong that electrons are accelerated rapidly
to relativistic speeds while ions lag behind owing to their larger inertia. The
ions are later effectively accelerated by the strong radiation-induced double
layer electric field up to Lorentz factors , attainable in the
case of negligible Compton drag. The asymptotic energies achieved by both ions
and electrons are larger by a factor 2--4 with respect to what one could
naively expect assuming that the electron-ion assembly is a rigidly coupled
system. The regime we investigate may be relevant within the framework of giant
flares from soft gamma-repeaters.Comment: 14 pages, 7 figures, ApJ, in press (tentatively scheduled for the v.
592, 2003 issue
Triple-negative breast carcinomas of low malignant potential: review on diagnostic criteria and differential diagnoses
Triple-negative breast carcinomas constitute a wide spectrum of lesions, mostly being highly aggressive. Nevertheless, some special histologic subtypes can have low malignant potential. The purpose of the present paper is to review diagnostic criteria and prognostic parameters of breast neoplasms of special histotypes. Specifically, adenoid cystic carcinoma, adenomyoepithelioma, acinic cell carcinoma, mucoepidermoid carcinoma, tall cell carcinoma with reverse polarity, and secretory carcinoma will be discussed. For each tumour, definition and morphological and molecular features, together with prognostic parameters, will be presented. Paradigmatic cases will be illustrated
An active state of the BL Lac Object Markarian 421 detected by INTEGRAL in April 2013
Multiwavelength variability of blazars offers indirect insight into their
powerful engines and on the mechanisms through which energy is propagated from
the centre down the jet. The BL Lac object Mkn 421 is a TeV emitter, a bright
blazar at all wavelengths, and therefore an excellent target for variability
studies. Mkn 421 was observed by INTEGRAL and Fermi-LAT in an active state on
16-21 April 2013. Well sampled optical, soft, and hard X-ray light curves show
the presence of two flares. The average flux in the 20-100 keV range is 9.1e-11
erg/s/cm2 (~4.5 mCrab) and the nuclear average apparent magnitude, corrected
for Galactic extinction, is V ~12.2. In the time-resolved X-ray spectra (3.5-60
keV), which are described by broken power laws and, marginally better, by
log-parabolic laws, we see a hardening that correlates with flux increase, as
expected in refreshed energy injections in a population of electrons that later
cool via synchrotron radiation. The hardness ratios between the JEM-X fluxes in
two different bands and between the JEM-X and IBIS/ISGRI fluxes confirm this
trend. During the observation, the variability level increases monotonically
from the optical to the hard X-rays, while the large LAT errors do not allow a
significant assessment of the MeV-GeV variability. The cross-correlation
analysis during the onset of the most prominent flare suggests a monotonically
increasing delay of the lower frequency emission with respect to that at higher
frequency, with a maximum time-lag of about 70 minutes, that is however not
well constrained. The spectral energy distributions from the optical to the TeV
domain are satisfactorily described by homogeneous models of blazar emission
based on synchrotron radiation and synchrotron self-Compton scattering, except
in the state corresponding to the LAT softest spectrum and highest flux.Comment: 11 pages, 6 figures, in press in A&
Global e-VLBI observations of the gamma-ray narrow line Seyfert 1 PMN J0948+0022
There is growing evidence of relativistic jets in radio-loud narrow-line
Seyfert 1 (RL-NLS1) galaxies. We constrain the observational properties of the
radio emission in the first RL-NLS1 galaxy ever detected in gamma-rays, PMN
J0948+0022, i.e., its flux density and structure in total intensity and in
polarization, its compactness, and variability. We performed three real-time
e-VLBI observations of PMN J0948+0022 at 22 GHz, using a global array including
telescopes in Europe, East Asia, and Australia. These are the first e-VLBI
science observations ever carried out with a global array, reaching a maximum
baseline length of 12458 km. The observations were part of a large
multiwavelength campaign in 2009. The source is detected at all three epochs.
The structure is dominated by a bright component, more compact than 55
microarcsec, with a fainter component at a position angle theta~ 35deg.
Relativistic beaming is required by the observed brightness temperature of
3.4x10^11 K. Polarization is detected at a level of about 1%. The parameters
derived by the VLBI observations, in addition to the broad-band properties,
confirm that PMN J0948+0022 is similar to flat spectrum radio quasars. Global
e-VLBI is a reliable and promising technique for future studies.Comment: Accepted for publication as a Letter in Astronomy and Astrophysic
Infrared to X-ray observations of PKS 2155-304 in a low state
AIMS: Our goal is to understand the nature of blazars and the mechanisms for
the generation of high-energy gamma-rays, through the investigation of the
prototypical blazar PKS 2155-304, which shows complex behaviour. METHODS: We
analyze simultaneous infrared-to-X-ray observations obtained with XMM-Newton
and REM on November 7, 2006, when the source was in a low X-ray state. We
perform a comparative analysis of these results with those obtained from
previous observations in different brightness states. RESULTS: We found that
the peak of the synchrotron emission moved from ultraviolet to optical
wavelengths and the X-ray spectrum is best fit with a broken power law model
with Gamma_2 ~ 2.4 harder than Gamma_1 ~ 2.6 and a break at about 3.5 keV. This
suggests that the soft X-rays (E < 3.5 keV) are related to the high-energy tail
of the synchrotron emission, while the hard X-rays (E > 3.5 keV) are from the
energy region between the synchrotron and inverse-Compton humps. The different
variability at energies below and above the break strengthens this hypothesis.
Our results also stress the importance of monitoring this source at both low
and high energies to better characterize its variability behaviour.Comment: 5 pages, 3 figures. A&A Letters, Accepted for publicatio
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