540 research outputs found
Events in the life of a cocoon surrounding a light, collapsar jet
According to the collapsar model, gamma-ray bursts are thought to be produced
in shocks that occur after the relativistic jet has broken free from the
stellar envelope. If the mass density of the collimated outflow is less than
that of the stellar envelope, the jet will then be surrounded by a cocoon of
relativistic plasma. This material would itself be able to escape along the
direction of least resistance, which is likely to be the rotation axis of the
stellar progenitor, and accelerate in approximately the same way as an
impulsive fireball. We discuss how the properties of the stellar envelope have
a decisive effect on the appearance of a cocoon propagating through it. The
relativistic material that accumulated in the cocoon would have enough kinetic
energy to substantially alter the structure of the relativistic outflow, if not
in fact provide much of the observed explosive power. Shock waves within this
plasma can produce gamma-ray and X-ray transients, in addition to the standard
afterglow emission that would arise from the deceleration shock of the cocoon
fireball.Comment: 16 pages, 5 figures, slightly revised version, accepted for
publication in MNRA
The Phenolic Quality of Red Grapes at Delivery: Objective Evaluation with Colour Measurements
The current research evaluated the possibility of the real time (before crushing) measurement of the phenolic quality index of red grapes to define the true quality of the raw material destined for the production of wine or juice. The measurement procedure involved the use of a spectrometer and the acquisition of a reflectance spectral signal via optical fibres immersed directly in the sample to be analysed. The measurements were done on the same juice (grape must) used for refractometry analysis of the sugars. It was established that it was possible to objectively classify the red grape cultivars tested on the basis of their anthocyanin and total polyphenol content. The experiments done in the winery and laboratory demonstrate a positive correlation between the colour of the must sampled from the grape at delivery and the total polyphenols in that grape. The colorimetric parameter can be acquired instantly and the data used in real time to improve the management of the winemaking process and to pay for the grapes on the basis of their phenolic quality
The Accretion Rates and Spectral Energy Distributions of BL Lacertae Objects
We investigate the relationship between accretion rates and the spectral
energy distributions (SEDs) of BL Lac objects, using a sample of objects for
which published information on the host galaxies, emission-line luminosities,
and peak frequencies and luminosities of their SEDs are available. The sample
is composed of 43 BL Lac objects which have a relatively continuous
distribution of peak frequencies. Under the assumption that the observed
emission lines are photoionized by the central accretion disk, we use the line
luminosities to estimate the accretion luminosities and hence accretion rates.
We find that low frequency-peaked BL Lac objects (LBLs) span a wide range of
accretion rates, whereas high frequency-peaked BL Lac objects (HBLs) cover a
more restricted range of lower values. There appears to be a continuous
distribution of accretion rates between the two subclasses of BL Lac objects.
We find that the peak frequency of the SED, \pknu, correlates with the
accretion rate, approximately with the form \pknu\propto \Lambda^{-3} in HBLs
and \pknu \propto \Lambda^{-0.25} in LBLs, where . The peak luminosity of the SED is also correlated with .
These results suggest that the accretion rate influences the shape of the SED
in BL Lac objects. They also support models which couple the jet and the
accretion disk. We present a physical scenario to account for the empirical
trends.Comment: 6 pages in emulateapj.sty, 3 figures 1 table. The Astrophysical
Journal (in press
High power ultrasound treatment of crushed grapes: beyond the extraction phenomena
The treatment of white and red crushed grapes by high power ultrasounds (US) represents an emerging technology in winemaking. In 2019, it was officially recognized by OIV through the resolution n°616-2019, and it was also approved by European Union in January 2022. The US effect on extraction mechanisms was widely studied, but more researches are needed to better understand the ultrasound effect on some specific classes of grape compounds. This research aimed to highlight at laboratory scale some specific effects of ultrasounds on some key compounds of white and red grapes. The samples were sonicated at different frequency (20-30 kHz), time (1-10 min), and power (30-90%) technological conditions used in maceration, to obtain valuable information on potential technological transferability. Valuable results were obtained regarding the release of thiols from their precursors, and the reactivity changes of unstable proteins of white wines. The experimental trails on red grape varieties allowed a maintenance of free anthocyanins and no degradative effects were highlighted. Significant and valuable effects were determined also on the tannin polymerization, with an astringency decrease. The sonication treatment of crushed grapes showed several chemical effects that contribute to decreasing the winemaking inputs and preserving the wine quality. The process conditions must be managed related to grape variety and ripeness for a precision winemakin
Study to optimize the effectiveness of Copper treatments for a low impact viticulture
Among all pathologies that afflict grapevine, Downy Mildew (DM) is the most important. Generally controlled
by using Copper (Cu), recently European Commission confirmed its usage but limiting the maximum amount to 28 Kg
per hectare in 7 years (Reg. EU 2018/1981). Anyway, in the grape growing context it is difficult to reduce the use of Cu
and generally chemicals, due to climate conditions, as well as climate changing. For this instance, Cu treatments have to
be improved. Hence, the aims of this work were to determine the possibility to reduce Cu using and evaluating the
variation of Cu cladding on grapevine leaves and grapes, in relation to the phytoiatric status. The efficacy level of the Cu
protection given to DM and the correlation among them was also assessed. Five organic vineyards located in
north-eastern of Italy were selected as experimental sites. Leaves and grapes were sampled during vegetative season
and analysed for determining the quantity of elemental Cu by the use of ICP AES. Spreading of DM in vineyards was
evaluated as well and the correlation between DM and Cu quantity on leaves and grapes was determined. First results
indicate that the mean level of Cu applied by farmers (range: 3.77 to 8.88 ”g/cm
2 of Cu on leaves) during vegetative
season is not enough to have an optimal protection against DM (diffusion on grapes and leaves: 40 to 50%), although at
the maximum amount of Cu, the plant protection effect was quite good. Thus, Cu treatments have to be pondered on the
basis of meteorological data and previous infection of DM, so that it will be possible to determine the right quantity of Cu
to be applied in correlation to DM presence and weather. As future goals, data will be correlated with image analysis, in
order to quickly study the best conditions for Cu application directly on field and having back a real time information of
Cu cladding and risk classes of DM infection. In this way, it is possible to reduce inputs in plant defence and then
guarantee a quality and sustainable production of grapes, wines and must
Gamma-ray Spectral Evolution of NGC1275 Observed with Fermi-LAT
We report on a detailed investigation of the high-energy gamma-ray emission
from NGC\,1275, a well-known radio galaxy hosted by a giant elliptical located
at the center of the nearby Perseus cluster. With the increased photon
statistics, the center of the gamma-ray emitting region is now measured to be
separated by only 0.46' from the nucleus of NGC1275, well within the 95%
confidence error circle with radius ~1.5'. Early Fermi-LAT observations
revealed a significant decade-timescale brightening of NGC1275 at GeV photon
energies, with a flux about seven times higher than the one implied by the
upper limit from previous EGRET observations. With the accumulation of one-year
of Fermi-LAT all-sky-survey exposure, we now detect flux and spectral
variations of this source on month timescales, as reported in this paper. The
average >100 MeV gamma-ray spectrum of NGC1275 shows a possible deviation from
a simple power-law shape, indicating a spectral cut-off around an observed
photon energy of E = 42.2+-19.6 GeV, with an average flux of F = (2.31+-0.13) X
10^{-7} ph/cm^2/s and a power-law photon index, Gamma = 2.13+-0.02. The largest
gamma-ray flaring event was observed in April--May 2009 and was accompanied by
significant spectral variability above E > 1-2 GeV. The gamma-ray activity of
NGC1275 during this flare can be described by a hysteresis behavior in the flux
versus photon index plane. The highest energy photon associated with the
gamma-ray source was detected at the very end of the observation, with the
observed energy of E = 67.4GeV and an angular separation of about 2.4' from the
nucleus. In this paper we present the details of the Fermi-LAT data analysis,
and briefly discuss the implications of the observed gamma-ray spectral
evolution of NGC1275 in the context of gamma-ray blazar sources in general.Comment: 20 pages, 6 figures, accepted for publication in the Ap
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