436 research outputs found
The application of the adiabatic compression scenario to the radio relic in the galaxy cluster Abell 3411-3412
Although radio relics are understood to originate in intracluster shock waves
resulting from merger shocks, the most widely used model for describing this
(re-)acceleration process at shock fronts, the diffusive shock acceleration
(DSA) model, has several challenges, including the fact that it is inefficient
at low shock Mach numbers. In light of these challenges, it is worthwhile to
consider alternative mechanisms. One possibility is the adiabatic compression
by a shock wave of a residual fossil electron population which has been left
over from a radio galaxy jet. This paper applies this model to the relic hosted
in the merging galaxy cluster Abell 3411-3412, where a radio bridge between the
relic and a radio galaxy has been observed, with the aim to reproduce the
spatial structure of the spectral index of the relic. Four scenarios are
presented, in which different effects are investigated, such as effects behind
the shock front and different shock strengths. The results show that the
adiabatic compression model can reproduce the observed spectral indices across
the relic for a shock Mach number that is lower than the value required by the
DSA-type modelling of this relic and is in accordance with the values derived
from X-ray observations, if other mechanisms, such as an expansion phase or
post-shock turbulence, are effective behind the shock front.Comment: 10 pages, 1 figure, accepted for publication in MNRA
The 5th edition of the Roma-BZCAT. A short presentation
The 5th edition of the Roma-BZCAT Multifrequency Catalogue of Blazars is
available in a printed version and online at the ASDC website
(http://www.asdc.asi.it/bzcat); it is also in the NED database. It presents
several relevant changes with respect to the past editions which are briefly
described in this paper.Comment: 5 pages, 3 figures. Accepted for publication in Astrophysics and
Space Scienc
Performance analysis of a common-rail Diesel engine fuelled with different blends of waste cooking oil and gasoil
An experimental campaign was performed to study the behavior of a common-rail Diesel engine in automotive configuration when it is fuelled with blends of Diesel fuel (DF) and waste cooking oil (WCO). In particular the tested fuels are: B20 blend, composed of 20% WCO and 80% DF; B50, composed of 50% WCO and 50% DF; WCO 100% and 100% DF.
In order to fuel the engine with fuel having a similar viscosity, this quantity, together with density, has been meas-ured at temperature ranging from rom to about 80 °C. According to these measurements, before fuelling the engine B20 was heated up to 35 °C and B50 to 75 °C.
An in-house software was developed to acquire the data elaborated by the electronic control unit.
Results show the trend in torque and global efficiency at different gas pedal position (gpp) and different engine speed. The experiments show that larger discrepancies are measured at smaller gpp values, while at larger ones dif-ferences become smaller. A similar trend is noticed for engine global efficiency
Thermo-economic assessment of a olive pomace gasifier for cogeneration applications
A thermo-economic analysis of a combined heat and power (CHP) plant fed by syngas produced through the gasification of dry olive pomace is presented. The plant is composed by a 800 kWtdowndraft gasifier, a gas clean-up system, a 200 kWemicroturbine (MGT) and a heat recovery system to cogenerate hot water. Surplus heat is used to dry olive pomace from 50% to 17% wb moisture content. The plant is modeled in ASPEN Plus. Real data from experimental tests are used to calibrate the gasifier model, while the technical specification and performance of the CHP plant are collected from commercial plants in operation and data from manufacturers. Mass and energy balances are reported throughout the paper. The thermodynamic simulation of the biomass gasifier coupled to the MGT, the thermal and electrical conversion efficiency and temperature of cogenerated heat available are also presented. A thermo-economic assessment is then proposed, to investigate the economic profitability of this small scale CHP plant in the Italian energy policy scenario and considering the subsidies available for renewable electricity in the form of feed-in tariffs. For this purpose, the case study of base load CHP plant operation and heat supplied to different typologies of energy end user is assumed. The results allow quantifying the most influencing economic and technical factors that affect the performance and profitability of such investment and the bottlenecks that should be faced to facilitate a broader implementation of such CHP schemes for on site generation
Relativistic inverse Compton scattering of photons from the early universe
Electrons at relativistic speeds, diffusing in magnetic fields, cause copious
emission at radio frequencies in both clusters of galaxies and radio galaxies,
through the non-thermal radiation emission called synchrotron. However, the
total power radiated through this mechanism is ill constrained, as the lower
limit of the electron energy distribution, or low-energy cutoffs, for radio
emission in galaxy clusters and radio galaxies have not yet been determined.
This lower limit, parametrized by the lower limit of the electron momentum -
pmin - is critical for estimating the energetics of non-thermal electrons
produced by cluster mergers or injected by radio galaxy jets, which impacts the
formation of large-scale structure in the universe, as well as the evolution of
local structures inside galaxy clusters. The total pressure due to the
relativistic, non-thermal population of electrons is critically dependent on
pmin, making the measurement of this non-thermal pressure a promising technique
to estimate the electron low-energy cutoff. We present here the first
unambiguous detection of this pressure for a non-thermal population of
electrons in a radio galaxy jet/lobe, located at a significant distance away
from the center of the Bullet cluster of galaxies.Comment: 5 pages, 2 figures, submitted to Scientific Report
Neurovisual training (TRIGRAM) in young patients with visual-perceptive dyslexia
Dyslexia is a language-based learning disability. Although this condition is characterized by anatomical malformation of the brain, it seems that the typical reading pattern of dyslexic may be also related to more complex sensory deficits. Among them, visual- perceptive deficits have been described in a subtype of dyslexia, called visual-perceptive dyslexia. The distinctive feature of a patient suffering from visual-perceptive dyslexia form is marked by effortlessly recognize the characteristics of each individual stimulus.
The Tetra protocol is a visual-perceptual evaluation protocol that was introduced for the diagnostic phase and the rehabilitation of visual-perceptive dyslexia. The diagnostic tests include: the eidomorphometry test, designed to evaluate the perception of spatial relationships; the contrast sensitivity threshold test, especially at low spatial frequencies; and the REPORT TEST words, to assess the speed and the reading efficiency. In addition, the rehabilitation phase is carried out with the visual neuro-enhancement program TRIGRAM, a visual training proposal designed to reduce the lateral masking phenomenon in visual-perceptive dyslexic.
Thus, in this study we used the diagnostic tests of TETRA® Protocol to determine presence of visual-perceptual abnormalities in children with dyslexia. Proven time the presence of these visual-perceptual alterations, the patients were also subjected to the rehabilitation sessions of TRIGRAM, in order to investigate whether this visual training may improve the pattern of reading. At the end of the program (t1) and after three months (t2), the same subjects underwent the same diagnostic tests of TETRA® Protocol to evaluate and confirm the results obtained during rehabilitation program.
The results showed a significant increase in contrast sensitivity at low and high spatial frequencies. Moreover, the same improvements in the visual system's ability to discriminate the contours of an object within the field of view, have been maintained three months after the end of treatment. We also observed a significant improvement in the perception of spatial relationships, with reduction of SRA value.
In conclusion, this study demonstrates that the visual rehabilitation training (TRIGRAM) is able to improve the perception of spatial relationships, and increase contrast sensitivity in young patients affected by "visual dyslexia". Nonetheless, these data need to be confirmed in larger cohort of subjects in order to establish whether these effects can also increase lexical ability (increased reading speed and reduce errors during the lexical task)
Probing the nature of Dark Matter with the SKA
Dark Matter (DM) is a fundamental ingredient of our Universe and of structure
formation, and yet its nature is elusive to astrophysical probes. Information
on the nature and physical properties of the WIMP (neutralino) DM (the leading
candidate for a cosmologically relevant DM) can be obtained by studying the
astrophysical signals of their annihilation/decay. Among the various e.m.
signals, secondary electrons produced by neutralino annihilation generate
synchrotron emission in the magnetized atmosphere of galaxy clusters and
galaxies which could be observed as a diffuse radio emission (halo or haze)
centered on the DM halo. A deep search for DM radio emission with SKA in local
dwarf galaxies, galaxy regions with low star formation and galaxy clusters
(with offset DM-baryonic distribution, like e.g. the Bullet cluster) can be
very effective in constraining the neutralino mass, composition and
annihilation cross-section. For the case of a dwarf galaxy, like e.g. Draco,
the constraints on the DM annihilation cross-section obtainable with SKA1-MID
will be at least a factor more stringent than the limits obtained
by Fermi-LAT in the -rays. These limits scale with the value of the B
field, and the SKA will have the capability to determine simultaneously both
the magnetic field in the DM-dominated structures and the DM particle
properties. The optimal frequency band for detecting the DM-induced radio
emission is around GHz, with the SKA1-MID Band 1 and 4 important to
probe the synchrotron spectral curvature at low- (sensitive to DM
composition) and at high- (sensitive to DM mass).Comment: 10 pages, 5 figures, to appear as part of 'Cosmic Magnetism' in
proceedings of 'Advancing Astrophysics with the Square Kilometre Array'
PoS(AASKA14)10
- …