656 research outputs found
Laser ion acceleration using a solid target coupled with a low density layer
We investigate by particle-in-cell simulations in two and three dimensions
the laser-plasma interaction and the proton acceleration in multilayer targets
where a low density "near-critical" layer of a few micron thickness is added on
the illuminated side of a thin, high density layer. This target design can be
obtained by depositing a "foam" layer on a thin metallic foil. The presence of
the near-critical plasma strongly increases both the conversion efficiency and
the energy of electrons and leads to enhanced acceleration of proton from a
rear side layer via the Target Normal Sheath Acceleration mechanism. The
electrons of the foam are strongly accelerated in the forward direction and
propagate on the rear side of the target building up a high electric field with
a relatively flat longitudinal profile. In these conditions the maximum proton
energy is up to three times higher than in the case of the bare solid target.Comment: 9 pages, 11 figures. Submitted to Physical Review
Coefficient of thermal expansion of nanostructured tungsten based coatings assessed by thermally induced substrate curvature method
The in plane coefficient of thermal expansion (CTE) and the residual stress
of nanostructured W based coatings are extensively investigated. The CTE and
the residual stresses are derived by means of an optimized ad-hoc developed
experimental setup based on the detection of the substrate curvature by a laser
system. The nanostructured coatings are deposited by Pulsed Laser Deposition.
Thanks to its versatility, nanocrystalline W metallic coatings,
ultra-nano-crystalline pure W and W-Tantalum coatings and amorphous-like W
coatings are obtained. The correlation between the nanostructure, the residual
stress and the CTE of the coatings are thus elucidated. We find that all the
samples show a compressive state of stress that decreases as the structure goes
from columnar nanocrystalline to amorphous-like. The CTE of all the coatings is
higher than the one of the corresponding bulk W form. In particular, as the
grain size shrinks, the CTE increases from 5.1 10 K for
nanocrystalline W to 6.6 10 K in the ultra-nano-crystalline
region. When dealing with amorphous W, the further increase of the CTE is
attributed to a higher porosity degree of the samples. The CTE trend is also
investigated as function of materials stiffness. In this case, as W coatings
become softer, the easier they thermally expand.Comment: The research leading to these results has also received funding from
the European Research Council Consolidator Grant ENSURE (ERC-2014-CoG No.
647554
Thermomechanical properties of amorphous metallic tungsten-oxygen and tungsten-oxide coatings
In this work, we investigate the correlation between morphology, composition,
and the mechanical properties of metallic amorphous tungsten-oxygen and
amorphous tungsten-oxide films deposited by Pulsed Laser Deposition. This
correlation is investigated by the combined use of Brillouin Spectroscopy and
the substrate curvature method. The stiffness of the films is strongly affected
by both the oxygen content and the mass density. The elastic moduli show a
decreasing trend as the mass density decreases and the oxygen-tungsten ratio
increases. A plateaux region is detected in correspondence of the transition
between metallic and oxide films. The compressive residual stresses, moderate
stiffness and high local ductility that characterize compact amorphous
tungsten-oxide films make them promising for applications involving thermal or
mechanical loads. The coefficient of thermal expansion is quite high (i.e. 8.9
10 K), being strictly correlated to the amorphous
structure and stoichiometry of the films. Under thermal treatments they show a
quite low relaxation temperature (i.e. 450 K). They crystallize into the
monoclinic phase of WO starting from 670 K, inducing an increase
by about 70\% of material stiffness.Comment: The research leading to these results has also received funding from
the European Research Council Consolidator Grant ENSURE (ERC-2014-CoG No.
647554). The views and opinions expressed herein do not necessarily reflect
those of the European Commissio
Wavelet entropy and fractional Brownian motion time series
We study the functional link between the Hurst parameter and the Normalized
Total Wavelet Entropy when analyzing fractional Brownian motion (fBm) time
series--these series are synthetically generated. Both quantifiers are mainly
used to identify fractional Brownian motion processes (Fractals 12 (2004) 223).
The aim of this work is understand the differences in the information obtained
from them, if any.Comment: 10 pages, 2 figures, submitted to Physica A for considering its
publicatio
Electron heating in subpicosecond laser interaction with overdense and near-critical plasmas
n this work we investigate electron heating induced by intense laser interaction with micrometric flat solid
foils in the context of laser-driven ion acceleration. We propose a simple law to predict the electron temperature in
a wider range of laser parameters with respect to commonly used existing models. An extensive two-dimensional
(2D) and 3D numerical campaign shows that electron heating is due to the combined actions of j×B
and Brunel effect. Electron temperature can be well described with a simple function of pulse intensity and angle of incidence,
with parameters dependent on pulse polarization. We then combine our model for the electron temperature with
an existing model for laser-ion acceleration, using recent experimental results as a benchmark. We also discuss
an exploratory attempt to model electron temperature for multilayered foam-attached targets, which have been
proven recently to be an attractive target concept for laser-driven ion acceleration
Numerical investigation of non-linear inverse Compton scattering in double-layer targets
Non-linear inverse Compton scattering (NICS) is of significance in laser-plasma physics and for application-relevant laser-driven photon sources. Given this interest, we investigated this synchrotron-like photon emission in a promising configuration achieved when an ultra-intense laser pulse interacts with a double-layer target (DLT). Numerical simulations with two-dimensional particle-in-cell codes and analytical estimates are used for this purpose. The properties of NICS are shown to be governed by the processes characterizing laser interaction with the near-critical and solid layers composing the DLT. In particular, electron acceleration, laser focusing in the low-density layer, and pulse reflection on the solid layer determine the radiated power, the emitted spectrum, and the angular properties of emitted photons. Analytical estimates, supported by simulations, show that quantum effects are relevant at laser intensities as small as similar to 1 0 21 W/cm(2) Target and laser parameters affect the NICS competition with bremsstrahlung and the conversion efficiency and average energy of emitted photons. Therefore, DLT properties could be exploited to tune and enhance photon emission in experiments and future applications
LDL receptor expression on T lymphocytes in old patients with Down syndrome
BACKGROUND: In Down syndrome patients several metabolic abnormalities have been reported, some involving the lipid metabolism. The level of LDL in plasma is the major determinant of the risk of vascular disease. There appear to be no studies on the LDL receptor in Down syndrome patients. METHODS: Flow cytometric methods for measuring the LDL receptor in peripheral blood mononuclear cells (PBMC) can identify patients with hypercholesterolemia. We applied this method in 19 old patients with Down syndrome and 23 healthy controls. RESULTS: Down syndrome patients had high levels of triglycerides and low levels of HDL, and high levels of CRP. We also found a down-regulation of LDL receptor expression. CONCLUSIONS: Down syndrome patients show no increase in the frequency of cardiovascular disease. The low incidence in cardiovascular disease despite the low level of HDL, high levels of CRP and reduction of LDL receptor expression lead to the conclusion that either these are not risk factors in these patients or that other risks factors – not yet identified – are considerably lower
PMUTs Arrays for Structural Health Monitoring of Bolted-Joints
Micro-electro-mechanical systems (MEMS) have enabled new techniques for the miniaturization of sensors suitable for Structural Health Monitoring (SHM) applications. In this study, MEMS-based sensors, specifically Piezoelectric Micromachined Ultrasonic Transducers (PMUT), are used to evaluate and monitor the pre-tensioning of a bolted joint structural system. For bolted joints to function properly, it is essential to maintain a suitable level of pre-tensioning. In this work, an array of PMUTs attached to the head and to the end of a bolt, serve as transmitter and receiver, respectively, in a pitch-catch Ultrasonic Testing (UT) scenario. The primary objective is to detect the Change in Time of Flight (CTOF) of the acoustic wave generated by the PMUT array and propagating along the bolt’s axis between a non-loaded bolt and a bolt in service. To model the pre-tensioning of bolted joints and the transmission of the acoustic wave to and from a group of PMUTs through the bolt, a set of numerical models is created. The CTOF is found to be linearly related to the amount of pre-tensioning. The numerical model is validated through comparisons with the results of a preliminary experimental campaign
Laser-driven production with advanced targets of Copper-64 for medical applications
Radionuclides are of paramount importance in nuclear medicine both for clinical uses and radiopharmaceutical production. Among the others, nuclides suitable for theranostics like Copper-64 are particularly attractive since they can play both a diagnostic and therapeutic role. In the last years, the growing demand for these nuclides stimulated the research of new solutions, along with cyclotrons already in use, for their production. In this respect, a promising alternative is laser-driven proton accelerators based on the interaction of superintense laser pulses with target materials. Because of their potential compactness and flexibility, they are under investigation for several applications ranging from materials science to nuclear medicine. Moreover, the use of advanced Double-Layer targets (DLTs) was identified as a viable route to increase the number and energy of the accelerated protons to satisfy the requirements of demanding applications. In this contribution, we numerically investigate the use of DLT-based laser-driven sources for Copper-64 production. We show that activities relevant to pre-clinical studies can be achieved with an existing 150 TW laser and DLTs. Moreover, we extend the discussion by considering a broad range of laser systems by exploiting a theoretical model. Our results can guide the choice of laser and target parameters for future experimental investigations
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