410 research outputs found
Non equilibrium effects in fragmentation
We study, using molecular dynamics techniques, how boundary conditions affect
the process of fragmentation of finite, highly excited, Lennard-Jones systems.
We analyze the behavior of the caloric curves (CC), the associated thermal
response functions (TRF) and cluster mass distributions for constrained and
unconstrained hot drops. It is shown that the resulting CC's for the
constrained case differ from the one in the unconstrained case, mainly in the
presence of a ``vapor branch''. This branch is absent in the free expanding
case even at high energies . This effect is traced to the role played by the
collective expansion motion. On the other hand, we found that the recently
proposed characteristic features of a first order phase transition taking place
in a finite isolated system, i.e. abnormally large kinetic energy fluctuations
and a negative branch in the TRF, are present for the constrained (dilute) as
well the unconstrained case. The microscopic origin of this behavior is also
analyzed.Comment: 21 pages, 11 figure
Near-infrared interferometric observation of the Herbig Ae star HD144432 with VLTI/AMBER
We study the sub-AU-scale circumstellar environment of the Herbig Ae star
HD144432 with near-infrared (NIR) VLTI/AMBER observations to investigate the
structure of its inner dust disk. The interferometric observations were carried
out with the AMBER instrument in the H and K band. We interpret the measured H-
and K-band visibilities, the near- and mid-infrared visibilities from the
literature, and the SED of HD144432 by using geometric ring models and
ring-shaped temperature-gradient disk models with power-law temperature
distributions. We derived a K-band ring-fit radius of 0.17 \pm 0.01 AU and an
H-band radius of 0.18 \pm 0.01 AU (for a distance of 145 pc). This measured
K-band radius of \sim0.17 AU lies in the range between the dust sublimation
radius of \sim0.13 AU (predicted for a dust sublimation temperature of 1500 K
and gray dust) and the prediction of models including backwarming (\sim0.27
AU). We found that an additional extended halo component is required in both
the geometric and temperature-gradient modeling. In the best temperature-
gradient model, the disk consists of two components. The inner part of the disk
is a thin ring with an inner radius of \sim0.21 AU, a temperature of \sim1600
K, and a ring thickness \sim0.02 AU. The outer part extends from \sim1 AU to
\sim10 AU with an inner temperature of \sim400 K. We find that the disk is
nearly face-on with an inclination angle of < 28 degree. Our
temperature-gradient modeling suggests that the NIR excess is dominated by
emission from a narrow, bright rim located at the dust sublimation radius,
while an extended halo component contributes \sim6% to the total flux at 2
{\mu}m. The MIR model emission has a two-component structure with \sim20% flux
from the inner ring and the rest from the outer part. This two-component
structure suggests a disk gap, which is possibly caused by the shadow of a
puffed-up inner rim.Comment: 7 pages, 5 figures, accepted by A&
Urea-Doped Calcium Phosphate Nanoparticles as Sustainable Nitrogen Nanofertilizers for Viticulture: Implications on Yield and Quality of Pinot Gris Grapevines
In recent years, the application of nanotechnology for the development of new âsmart
fertilizersâ is regarded as one of the most promising solutions for boosting a more sustainable and
modern grapevine cultivation. Despite showing interesting potential benefits over conventional fertilization practices, the use of nanofertilizers in viticulture is still underexplored. In this work, we
investigated the effectiveness of non-toxic calcium phosphate nanoparticles (Ca3(PO4)2ânH2O)
doped with urea (U-ACP) as a nitrogen source for grapevine fertilization. Plant tests were performed for two years (2019â2020) on potted adult Pinot gris cv. vines grown under semi-controlled
conditions. Four fertilization treatments were compared: N1: commercial granular fertilization (45
kg N haâ1); N2: U-ACP applied in fertigation (36 kg N haâ1); N3: foliar application of U-ACP (36 kg
N haâ1); C: control, receiving no N fertilization. Plant nitrogen status (SPAD), yield parameters as
well as those of berry quality were analyzed. Results here presented clearly show the capability of
vine plants to recognize and use the nitrogen supplied with U-ACP nanoparticles either when applied foliarly or to the soil. Moreover, all of the qualiâquantitative parameters measured in vine
plants fed with nanoparticles were perfectly comparable to those of plants grown in conventional
condition, despite the restrained dosage of nitrogen applied with the nanoparticles. Therefore, these
results provide both clear evidence of the efficacy of U-ACP nanoparticles as a nitrogen source and
the basis for the development of alternative nitrogen fertilization strategies, optimizing the dosage/benefit ratio and being particularly interesting in a context of a more sustainable and modern
viticulture.PSR 2014/2020 Regione Autonoma Friuli Venezia GiuliaâMisure 16.1.1, DGR 1313/2018, DC 398/AGFOR 2020âGESOVIT PROJECTFondazione Cariplo, Italy, Grant n. 2016-0648, project: Romancing the stone: size controlled HYdroxyaPATItes for sustainable Agriculture (HYPATIA
The major upgrade of the MAGIC telescopes, Part II: A performance study using observations of the Crab Nebula
MAGIC is a system of two Imaging Atmospheric Cherenkov Telescopes located in
the Canary island of La Palma, Spain. During summer 2011 and 2012 it underwent
a series of upgrades, involving the exchange of the MAGIC-I camera and its
trigger system, as well as the upgrade of the readout system of both
telescopes. We use observations of the Crab Nebula taken at low and medium
zenith angles to assess the key performance parameters of the MAGIC stereo
system. For low zenith angle observations, the standard trigger threshold of
the MAGIC telescopes is ~50GeV. The integral sensitivity for point-like sources
with Crab Nebula-like spectrum above 220GeV is (0.66+/-0.03)% of Crab Nebula
flux in 50 h of observations. The angular resolution, defined as the sigma of a
2-dimensional Gaussian distribution, at those energies is < 0.07 degree, while
the energy resolution is 16%. We also re-evaluate the effect of the systematic
uncertainty on the data taken with the MAGIC telescopes after the upgrade. We
estimate that the systematic uncertainties can be divided in the following
components: < 15% in energy scale, 11-18% in flux normalization and +/-0.15 for
the energy spectrum power-law slope.Comment: 21 pages, 25 figures, accepted for publication in Astroparticle
Physic
Multi-Wavelength Observations of the Blazar 1ES 1011+496 in Spring 2008
The BL Lac object 1ES 1011+496 was discovered at Very High Energy gamma-rays
by MAGIC in spring 2007. Before that the source was little studied in different
wavelengths. Therefore a multi-wavelength (MWL) campaign was organized in
spring 2008. Along MAGIC, the MWL campaign included the Metsahovi radio
observatory, Bell and KVA optical telescopes and the Swift and AGILE
satellites. MAGIC observations span from March to May, 2008 for a total of 27.9
hours, of which 19.4 hours remained after quality cuts. The light curve showed
no significant variability. The differential VHE spectrum could be described
with a power-law function. Both results were similar to those obtained during
the discovery. Swift XRT observations revealed an X-ray flare, characterized by
a harder when brighter trend, as is typical for high synchrotron peak BL Lac
objects (HBL). Strong optical variability was found during the campaign, but no
conclusion on the connection between the optical and VHE gamma-ray bands could
be drawn. The contemporaneous SED shows a synchrotron dominated source, unlike
concluded in previous work based on nonsimultaneous data, and is well described
by a standard one zone synchrotron self Compton model. We also performed a
study on the source classification. While the optical and X-ray data taken
during our campaign show typical characteristics of an HBL, we suggest, based
on archival data, that 1ES 1011+496 is actually a borderline case between
intermediate and high synchrotron peak frequency BL Lac objects.Comment: 13 pages, accepted for publication in MNRA
Probing the very-high-energy gamma-ray spectral curvature in the blazar PG 1553+113 with the MAGIC telescopes
PG 1553+113 is a very-high-energy (VHE, ) -ray
emitter classified as a BL Lac object. Its redshift is constrained by
intergalactic absorption lines in the range . The MAGIC telescopes
have monitored the source's activity since 2005. In early 2012, PG 1553+113 was
found in a high-state, and later, in April of the same year, the source reached
its highest VHE flux state detected so far. Simultaneous observations carried
out in X-rays during 2012 April show similar flaring behaviour. In contrast,
the -ray flux at observed by Fermi-LAT is
compatible with steady emission. In this paper, a detailed study of the flaring
state is presented. The VHE spectrum shows clear curvature, being well fitted
either by a power law with an exponential cut-off or by a log-parabola. A
simple power-law fit hypothesis for the observed shape of the PG 1553+113 VHE
-ray spectrum is rejected with a high significance (fit probability
P=2.6 ). The observed curvature is compatible with the
extragalactic background light (EBL) imprint predicted by current generation
EBL models assuming a redshift . New constraints on the redshift are
derived from the VHE spectrum. These constraints are compatible with previous
limits and suggest that the source is most likely located around the optical
lower limit, , based on the detection of Ly absorption. Finally,
we find that the synchrotron self-Compton (SSC) model gives a satisfactory
description of the observed multi-wavelength spectral energy distribution
during the flare.Comment: 13 pages, 7 figures, accepted for publication in MNRA
Discovery of VHE Gamma Radiation from IC443 with the MAGIC Telescope
We report the detection of a new source of very high energy (VHE, E_gamma >=
100GeV) gamma-ray emission located close to the Galactic Plane, MAGIC
J0616+225, which is spatially coincident with SNR IC443. The observations were
carried out with the MAGIC telescope in the periods December 2005 - January
2006 and December 2006 - January 2007. Here we present results from this
source, leading to a VHE gamma-ray signal with a statistical significance of
5.7 sigma in the 2006/7 data and a measured differential gamma-ray flux
consistent with a power law, described as dN_gamma/(dA dt dE) = (1.0 +/-
0.2)*10^(-11)(E/0.4 TeV)^(-3.1 +/- 0.3) cm^(-2)s^(-1)TeV^(-1). We briefly
discuss the observational technique used and the procedure implemented for the
data analysis. The results are put in the perspective of the multiwavelength
emission and the molecular environment found in the region of IC443.Comment: Accepted by ApJ Letter
Constraints on the steady and pulsed very high energy gamma-ray emission from observations of PSR B1951+32/CTB 80 with the MAGIC Telescope
We report on very high energy gamma-observations with the MAGIC Telescope of
the pulsar PSR B1951+32 and its associated nebula, CTB 80. Our data constrain
the cutoff energy of the pulsar to be less than 32 GeV, assuming the pulsed
gamma-ray emission to be exponentially cut off. The upper limit on the flux of
pulsed gamma-ray emission above 75 GeV is 4.3*10^-11 photons cm^-2 sec^-1, and
the upper limit on the flux of steady emission above 140 GeV is 1.5*10^-11
photons cm^-2 sec^-1. We discuss our results in the framework of recent model
predictions and other studies.Comment: 7 pages, 7 figures, replaced with published versio
MAGIC upper limits on the very high energy emission from GRBs
The fast repositioning system of the MAGIC Telescope has allowed during its
first data cycle, between 2005 and the beginning of year 2006, observing nine
different GRBs as possible sources of very high energy gammas. These
observations were triggered by alerts from Swift, HETE-II, and Integral; they
started as fast as possible after the alerts and lasted for several minutes,
with an energy threshold varying between 80 and 200 GeV, depending upon the
zenith angle of the burst. No evidence for gamma signals was found, and upper
limits for the flux were derived for all events, using the standard analysis
chain of MAGIC. For the bursts with measured redshift, the upper limits are
compatible with a power law extrapolation, when the intrinsic fluxes are
evaluated taking into account the attenuation due to the scattering in the
Metagalactic Radiation Field (MRF).Comment: 25 pages, 9 figures, final version accepted by ApJ. Changet title to
"MAGIC upped limits on the VERY high energy emission from GRBs", re-organized
chapter with description of observation, removed non necessaries figures,
added plot of effective area depending on zenith angle, added an appendix
explaining the upper limit calculation, added some reference
First bounds on the very high energy gamma-ray emission from Arp 220
Using the Major Atmospheric Gamma Imaging Cherenkov Telescope (MAGIC), we
have observed the nearest ultra-luminous infrared galaxy Arp 220 for about 15
hours. No significant signal was detected within the dedicated amount of
observation time. The first upper limits to the very high energy -ray
flux of Arp 220 are herein reported and compared with theoretical expectations.Comment: Accepted for publication in Ap
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