707 research outputs found
Diamond wire cutting of cast iron
Diamond wire has been the standard industrial practice in stone excavation for over three decades now. Today new applications in the construction and controlled demolition industry are emerging, which involve the cutting of metals and sometimes diamond wire seems the only viable solution. Diamond tool life cutting metals is about one order of magnitude lower than stone, so a better knowledge of this process is of direct industrial interest. In this paper we report the main results of experimental tests for a cylindrical and a tapered electroplated diamond bead cutting cast iron UNI G250. Experimental data to estimate the optimal process parameters and predict tool life are reported and an experimental model is presented. In addition a new tool wear criterion and a new standardized testing method for diamond bead cutting of cast iron and to compare the performance of different diamond bead ..
VHE observations of the gamma-ray binary system LS 5039 with H.E.S.S
LS 5039 is a gamma-ray binary system observed in a broad energy range, from
radio to TeV energies. The binary system exhibits both flux and spectral
modulation as a function of its orbital period. The X-ray and very-high-energy
(VHE, E > 100 GeV) gamma-ray fluxes display a maximum/minimum at
inferior/superior conjunction, with spectra becoming respectively
harder/softer, a behaviour that is completely reversed in the high-energy
domain (HE, 0.1 < E < 100 GeV). The HE spectrum cuts off at a few GeV, with a
new hard component emerging at E > 10 GeV that is compatible with the
low-energy tail of the TeV emission. The low 10 - 100 GeV flux, however, makes
the HE and VHE components difficult to reconcile with a scenario including
emission from only a single particle population. We report on new observations
of LS 5039 conducted with the High Energy Stereoscopic System (H.E.S.S.)
telescopes from 2006 to 2015. This new data set enables for an
unprecedentedly-deep phase-folded coverage of the source at TeV energies, as
well as an extension of the VHE spectral range down to ~120 GeV, which makes LS
5039 the first gamma-ray binary system in which a spectral overlap between
satellite and ground-based gamma-ray observatories is obtained.Comment: Proceeding for ICRC 201
H.E.S.S. observations of PSR B1259-63 during its 2014 periastron passage
An extended observation campaign of the gamma-ray binary system PSR
B125963 has been conducted with the H.E.S.S. (High Energy Stereoscopic
System) II 5-telescope array during the system's periastron passage in 2014. We
report on the outcome of this campaign, which consists of more than 85 h of
data covering both pre- and post-periastron orbital phases. The lower energy
threshold of the H.E.S.S. II array allows very-high-energy (VHE; GeV) gamma-ray emission from PSR B125963 to be studied for the first
time down to 200 GeV. The new dataset partly overlaps with and extends in phase
previous H.E.S.S. campaigns on this source in 2004, 2007 and 2011, allowing for
a detailed long-term characterisation of the flux level at VHEs. In addition,
the 2014 campaign reported here includes VHE observations during the exact
periastron time, , as well as data taken simultaneously to the
gamma-ray flare detected with the Fermi-LAT. Our results will be discussed in a
multiwavelength context, thanks to the dense broad-band monitoring campaign
conducted on the system during this last periastron passage.Comment: 8 pages, 5 figures. In Proceedings of the 34th International Cosmic
Ray Conference (ICRC2015), The Hague, The Netherland
Comparing extrapolations of the coronal magnetic field structure at 2.5 solar radii with multi-viewpoint coronagraphic observations
The magnetic field shapes the structure of the solar corona but we still know
little about the interrelationships between the coronal magnetic field
configurations and the resulting quasi-stationary structures observed in
coronagraphic images (as streamers, plumes, coronal holes). One way to obtain
information on the large-scale structure of the coronal magnetic field is to
extrapolate it from photospheric data and compare the results with
coronagraphic images. Our aim is to verify if this comparison can be a fast
method to check systematically the reliability of the many methods available to
reconstruct the coronal magnetic field. Coronal fields are usually extrapolated
from photospheric measurements typically in a region close to the central
meridian on the solar disk and then compared with coronagraphic images at the
limbs, acquired at least 7 days before or after to account for solar rotation,
implicitly assuming that no significant changes occurred in the corona during
that period. In this work, we combine images from three coronagraphs
(SOHO/LASCO-C2 and the two STEREO/SECCHI-COR1) observing the Sun from different
viewing angles to build Carrington maps covering the entire corona to reduce
the effect of temporal evolution to ~ 5 days. We then compare the position of
the observed streamers in these Carrington maps with that of the neutral lines
obtained from four different magnetic field extrapolations, to evaluate the
performances of the latter in the solar corona. Our results show that the
location of coronal streamers can provide important indications to discriminate
between different magnetic field extrapolations.Comment: Accepted by A&A the 20th of May, 201
Measurement of 1323 and 1487 keV resonances in 15N({\alpha}, {\gamma})19F with the recoil separator ERNA
The origin of fluorine is a widely debated issue. Nevertheless, the
^{15}N({\alpha},{\gamma})^{19}F reaction is a common feature among the various
production channels so far proposed. Its reaction rate at relevant temperatures
is determined by a number of narrow resonances together with the DC component
and the tails of the two broad resonances at E_{c.m.} = 1323 and 1487 keV.
Measurement through the direct detection of the 19F recoil ions with the
European Recoil separator for Nuclear Astrophysics (ERNA) were performed. The
reaction was initiated by a 15N beam impinging onto a 4He windowless gas
target. The observed yield of the resonances at Ec.m. = 1323 and 1487 keV is
used to determine their widths in the {\alpha} and {\gamma} channels. We show
that a direct measurement of the cross section of the
^{15}N({\alpha},{\gamma})^{19}F reaction can be successfully obtained with the
Recoil Separator ERNA, and the widths {\Gamma}_{\gamma} and {\Gamma}_{\alpha}
of the two broad resonances have been determined. While a fair agreement is
found with earlier determination of the widths of the 1487 keV resonance, a
significant difference is found for the 1323 keV resonance {\Gamma}_{\alpha} .
The revision of the widths of the two more relevant broad resonances in the
15N({\alpha},{\gamma})19F reaction presented in this work is the first step
toward a more firm determination of the reaction rate. At present, the residual
uncertainty at the temperatures of the ^{19}F stellar nucleosynthesis is
dominated by the uncertainties affecting the Direct Capture component and the
364 keV narrow resonance, both so far investigated only through indirect
experiments.Comment: 8 pages, 11 figures. Accepted for publication in PR
Updates on the PeNCIL project
By comparing measured and expected polarization in the HI Lyα 121.6 nm coronal emission line it is possible to infer the magnetic ïŹeld in the solar corona. PeNCIL is the ideal device to perform such a measurement. It is a light transmitting polarimeter optimized at 121.6 nm, completely free of mechanical moving parts, thought as part of an internally occulted coronagraph to be ïŹown aboard a future small solar mission. Its optical components are in de Senarmont conïŹguration: a ïŹxed MgF2 quarter wave retarder, a nano-wire grid polarizer (nano-WGP) and a MgF2 variable retarder modulated through a calibrated piezo-clamp (PCVR). The nano-WGP and the PCVR represent a ïŹrst-ever achievement in the history of technology development for VUV. The nano-WGP fabrication is at the edge of the current nanotechnology since the pitch between wires shall be 40 nm. The PCVR is based on a MgF 2 parallelepipedic sample refractive index variations as produced by a piezo-electric clamp. This work addresses the status of the project with particular emphasis on the design and manufacturing of the nano-WGP and the PCVR
Metrology on-board PROBA-3: The Shadow Position Sensor (SPS) subsystem
PROBA-3 is an ESA Mission whose aim is to demonstrate the in-orbit Formation Flying and attitude control capabilities of its two satellites by means of closed-loop, on-board metrology. The two small spacecraft will form a giant externally occulted coronagraph that will observe in visible polarized light the inner part of the solar corona. The SPS subsystem is composed of eight sensors that will measure, with the required sensitivity and dynamic range, the penumbra light intensity around the coronagraph instrument entrance pupil
Gender differences in post-stroke functional outcome at discharge from an intensive rehabilitation hospital
Toward a reassessment of the 19F(p,âα0)16O reaction rate at astrophysical temperatures
AbstractThe 19F(p,âα0)16O reaction at low energies plays an important role in fundamental physics. In particular in nuclear astrophysics it represents, together with the 19F(p,âÎł)20Ne reaction, the crossing point between the CNO and the NeNa cycles in stars. Further, in hydrogen-rich stellar environments, it is the most important fluorine destruction channel. In this paper we report new measurements on the 19F(p,âα0)16O reaction at deeply sub-Coulomb energies (0.2â0.6 MeV), a region where, despite the key role of this reaction, very few and old data are reported. The deduced astrophysical S-factor is â1.5â2 times larger than currently adopted extrapolations with possibly important astrophysical consequences
Comparison between Ischemic and Hemorrhagic Strokes in Functional Outcome at Discharge from an Intensive Rehabilitation Hospital
Comparison studies on recovery outcomes in ischemic (IS) and hemorrhagic strokes (HS) have yielded mixed results. In this retrospective observational study of consecutive IS and HS patients, we aimed at evaluating functional outcomes at discharge from an intensive rehabilitation hospital, comparing IS vs. HS, analyzing possible predictors. Modified Rankin Scale (mRS) at discharge was the main outcome. Out of the 229 patients included (mean age 72.9 ± 13.9 years, 48% males), 81 had HS (35%). Compared with IS (n = 148), HS patients were significantly younger (75 ± 12.5 vs. 68.8 ± 15.4 years, p = 0.002), required longer hospitalizations both in acute (23.9 ± 36.7 vs. 35.2 ± 29.9 days, p = 0.019) and rehabilitation hospitals (41.5 ± 31.8 vs. 77.2 ± 51.6 days, p = 0.001), and had more severe initial clinical deficit (mean number of neurological impairments: 2.0 ± 1.1 vs. 2.6 ± 1.4, p = 0.001) and mRS scores at admission (p = 0.046). At discharge, functional status change, expressed as mRS, was not significantly different between IS and HS (F = 0.01, p = 0.902), nor was the discharge destination (p = 0.428). Age and clinical severity were predictors of functional outcome in both stroke types. On admission in an intensive rehabilitation hospital, HS patients presented a worse functional and clinical status compared to IS. Despite this initial gap, the two stroke types showed an overlapped trajectory of functional recovery, with age and initial stroke severity as the main prognostic factors
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