681 research outputs found
Electromagnetic wave absorption and structural properties of wide-band absorber made of graphene-printed glass-fibre composite
Lightweight composites combining electromagnetic wave absorption and excellent mechanical properties are required in spacecraft and aircraft. A one- dimensional metamaterial absorber consisting of a stack of glass fibre/epoxy layers and graphene nanoplatelets/epoxy films was proposed and fabricated through a facile air-spraying based printing technology and a liquid resin infusion method. The production process allows an optimum dispersion of graphene nanoplatelets, promoting adhesion and mechanical integration of the glass fibre/epoxy layers with the graphene nanoplatelets/epoxy films. According to experimental results, the proposed wide-band absorber provides a reflection coefficient lower than â10 dB in the range 8.5â16.7 GHz and an improvement of flexural modulus of more than 15%, with a total thickness of âŒ1 mm. Outstanding electromagnetic wave absorption and mechanical performance make the proposed absorber more competitive in aeronautical and aerospace applications
Pressure tensor in the presence of velocity shear: stationary solutions and self-consistent equilibria
Observations and numerical simulations of laboratory and space plasmas in
almost collisionless regimes reveal anisotropic and non-gyrotropic particle
distribution functions. We investigate how such states can persist in the
presence of a sheared flow. We focus our attention on the pressure tensor
equation in a magnetized plasma and derive analytical self-consistent plasma
equilibria which exhibit a novel asymmetry with respect to the magnetic field
direction. These results are relevant for investigating, within fluid models
that retain the full pressure tensor dynamics, plasma configurations where a
background shear flow is present.Comment: 13 pages, 7 figure
Workersâ exposure assessment during the production of graphene nanoplatelets in r&d laboratory
Widespread production and use of engineered nanomaterials in industrial and research settings raise concerns about their health impact in the workplace. In the last years, graphene-based nanomaterials have gained particular interest in many application fields. Among them, graphene nanoplatelets (GNPs) showed superior electrical, optical and thermal properties, low-cost and availability. Few and conflicting results have been reported about toxicity and potential effects on workersâ health, during the production and handling of these nanostructures. Due to this lack of knowledge, systematic approaches are needed to assess risks and quantify workersâ exposure to GNPs. This work applies a multi-metric approach to assess workersâ exposure during the production of GNPs, based on the Organization for Economic Cooperation and Development (OECD) methodology by integrating real-time measurements and personal sampling. In particular, we analyzed the particle number concentration, the average diameter and the lung deposited surface area of airborne nanoparticles during the production process conducted by thermal exfoliation in two different ways, compared to the background. These results have been integrated by electron microscopic and spectroscopic analysis on the filters sampled by personal impactors. The study identifies the process phases potentially at risk for workers and reports quantitative information about the parameters that may influence the exposure in order to propose recommendations for a safer design of GNPs production process
Electrocatalytic properties of Pd-based nano-structured material for application in fuel cells
Fuel cells, especially low temperature fuel cells, are clean-energy devices that have high potentiality for use in electric power production and non-polluting vehicles. Platinum is commonly used as electrocatalysts in fuel cell electrodes, because of its excellent electrocatalytic activity and chemical stability. But, because of its high cost and limited resources, its use represents a bottleneck for large-scale application and commercialization of fuel cells. Palladium could be a good substitute for Pt, because of its similar chemical and physical properties, lower cost and higher abundance. Main challenges concern the development of Pd-based materials with high catalytic activity and durability at a reduced cost (i.e. metal content). Crucial technological issue is the optimization of the active surface of the catalysts, by the control of the morphology, shape and dispersion of the metal particles. The talk will describe the main results of the research activity carried out during the second year of the Italia-USA Bilateral Project in ENEA, concerning the fabrication and characterization of different kinds of nanostructured Pd-based electrocatalysts, by using both electrochemical and vacuum thin film deposition techniques
Search for Neutron Flux Generation in a Plasma Discharge Electrolytic Cell
Following some recent unexpected hints of neutron production in setups like
high-voltage atmospheric discharges and plasma discharges in electrolytic
cells, we present a measurement of the neutron flux in a configuration similar
to the latter. We use two different types of neutron detectors,
poly-allyl-diglicol-carbonate (PADC, aka CR-39) tracers and Indium disks. At
95% C.L. we provide an upper limit of 1.5 neutrons cm^-2 s^-1 for the thermal
neutron flux at ~5 cm from the center of the cell. Allowing for a higher energy
neutron component the largest allowed flux is 64 neutrons cm^-2 s^-1. This
upper limit is two orders of magnitude smaller than what previously claimed in
an electrolytic cell plasma discharge experiment. Furthermore the behavior of
the CR-39 is discussed to point our possible sources of spurious signals.Comment: 4 pages, 3 figure
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Variational techniques for a one-dimensional energy balance model
A one-dimensional climate energy balance model (1D EBM) is a simplified climate model for the zonally averaged global temperature profile, based on the Earth's energy budget. We examine a class of 1D EBMs which emerges as the parabolic equation corresponding to the EulerâLagrange equations of an associated variational problem, covering spatially inhomogeneous models such as with latitude-dependent albedo. Sufficient conditions are provided for the existence of at least three steady-state solutions in the form of two local minima and one saddle, that is, of coexisting âcoldâ, âwarmâ and unstable âintermediateâ climates. We also give an interpretation of minimizers as âtypicalâ or âlikelyâ solutions of time-dependent and stochastic 1D EBMs.
We then examine connections between the value function, which represents the minimum value (across all temperature profiles) of the objective functional, regarded as a function of greenhouse gas concentration, and the global mean temperature (also as a function of greenhouse gas concentration, i.e. the bifurcation diagram).
Specifically, the global mean temperature varies continuously as long as there is a unique minimizing temperature profile, but coexisting minimizers must have different global mean temperatures. Furthermore, global mean temperature is non-decreasing with respect to greenhouse gas concentration, and its jumps must necessarily be upward.
Applicability of our findings to more general spatially heterogeneous reactionâdiffusion models is also discussed, as are physical interpretations of our results
DiagnĂłstico mediante PCR-duplex de la nueva variante RHDVb del virus de la enfermedad hemorrĂĄgica en conejos
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