1,721,031 research outputs found
Optical Design of a 500 x PV Solar Concentrator with 1 Degree Field of View
No full textIn this paper we present our first results regarding the development of a Concentrating Photovoltaic (CPV) systems based on a classical Cassegrain optical design and a beam homogenizer. The system is characterized by a geometrical concentration factor (Cgeo) of around 500X. The optical design has been developed in order to obtain a 10 mm wide square image. Particular attention has been devoted to the homogenizer and to its building materials in order to reduce the cost and the thermal effects caused by concentrated radiation. Moreover the optical design has been specifically chosen to produce a Sun square image that optimizes the pv cell coupling. The field of view (FOV) of the designed concentrator is of +/- 0.5 degrees. The primary mirror has a 220 mm wide square aperture and a focal length of 80 mm (f/0.4). The secondary mirror is hyperbolic with a magnification of 6X that lead to a 4 mm diameter Sun image. In order to obtain a 10 mm wide square image, we used a total internal reflection (TIR) homogenizer. In this way the focal plane may host a typical commercial triple junction PV receiver assembly with a 10 mm squared active area. Cells of different sizes may be easily fitted by changing the exit side dimension of the homogenizer. The optical design has been optimized and it is ready for the test and optical characterization
Influence of material and manufacturing technology on the failure behavior of composite laminate bonded joints
Full text linkThe purpose of this work is to evaluate the influence of co-lamination vs. co-bonding on the failure behavior, and namely the fracture toughness, of carbon fibre reinforced (CFR) composite laminate joints in order to assess comparatively their performance. Since the strength of the laminate and ply texture are parameters affecting the strength of the joint, the comparison is extended to two different types of CFR pre-preg fibers, a satin T1100 with 2573 Nanoalloy® epoxy resin supplied by Toray and a twill T700 with ER450 toughened epoxy resin supplied by CIT, Toray group, representative of two different fields of application, racing and automotive, respectively
Sistema di misura ottico non a contatto per tumori sottocutanei nei topi
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Magnetic analysis of MnAs films grown on GaAs and Si substrates for potential spintronics and magnetocaloric applications
No full textWe present a magnetic characterisation of MnAs films grown by MOVPE on semiconductor substrates, for comparing the effect of thickness and substrate on their magnetic and magneto-thermal properties, with particular focus on the nature of the magneto-structural transition between the ferromagnetic hexagonal α-phase and the paramagnetic orthorhombic β-phase. The nature of this transformation depends on the presence of strain and turns out to be of second-order type for epitaxial-crystalline MnAs/(0 0 1)GaAs films and closer to a first-order type for polycrystalline MnAs/SiO2/Si films. The magnetocaloric effect at the transition has been estimated for thin film samples, resulting appreciably lower than that of bulk MnAs. © 2009 Elsevier B.V. All rights reserved
Thermal Testing of Bonded Joints for a Hyper Hemispheric Panoramic Camera
No full textIn any space mission, observation of the surrounding scenario is one of the most important activities. Through high-performance imaging systems, space instruments allow the acquisition of new information about the observed environment and improve scientific studies. However, traditional cameras by which space instruments are typically equipped, show a limited field of view, requiring the presence of actuators coupled with moving elements to acquire the entire scenario. Indeed, moving elements increase the risk of failure, especially in the space environment, which is characterized by very harsh conditions, and where any maintenance is critical or impossible. Hyper-hemispheric panoramic cameras provide a compact solution to this issue because, thanks to their large field of view, they can acquire the surrounding scenario with a single image acquisition. Within the framework of this research, the validation of the thermo-mechanical design of the catadiopter, one of the main optics of the Hyper Hemispheric camera, was performed in the expected working temperature range from - 120 °C to 100 °C. Some mockups representative of the connection area between the mechanics and the optics were manufactured and tested with thermal cycling to assess the baseline holding strategy, which requires gluing of materials with different Coefficients of Thermal Expansion. The activity allowed the validation of the selected composite adapters (Torlon 7130) to be used as intermediate material between the optics and the holder
Comparison of tensile strength and fracture toughness of co-bonded and cold-bonded carbon fiber laminate-aluminum adhesive joints
Full text linkThe purpose of this work is to compare the co-bonding vs. cold-bonding route on the adhesive joint performance of a CFRP (Carbon Fiber Reinforced Polymer) laminate–aluminum connection. In particular, the overlap shear, tensile strength and Mode I and Mode II fracture toughness will be evaluated. The adhesives for co-bonding and cold-bonding are, respectively, a thermosetting modified epoxy, unsupported structural film and a two-component epoxy adhesive, chosen as representative of applications in the high-performance/race car field. The emerging trend is that, in tensile e Mode I fracture tests, the failure path is predominantly in the composite. Mode II fracture tests instead resulted in a cohesive fracture, meaning that, under pure shear loading, the weakest link may not be the composite. The lap-shear tests are placed midway (cohesive failure for co-bonding and composite delamination for cold-bonding, respectively), probably due to the different peel stress values related to the different adhesive Young’s modulus. The exploitation of the full capacity of the adhesive joint, hence the possibility of highlighting better, different performances of co-bonding vs. cold-bonding, would require consistent improvement of the out-of-plane strength of the CFRP laminate and/or to someway redistribute the peel stress on the bondline
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Comparison of tensile strength and fracture toughness under mode I and II loading of co-cured and co-bonded CFRP joints
Full text linkCarbon-Fiber Reinforced Polymer (CFRP) parts are joined mainly using adhesive bonding because, differently from fastening, additional parts (hence weight saving) and through holes (that are always detrimental for the strength due to the possibility of developing damage into the composite) are not necessary. Additionally, it allows for large connection areas, thus distributing stresses better than fastened connections. However, since CFRP can be joined by co-curing, the choice of bonding has to be evaluated as an alternative by a trade-off in terms of strength and durability, compared to cost and manufacturing time and complexity. In this work, a comparison between co-cured and co-bonded CFRP is done with respect to tensile strength and mode I and mode II fracture toughness, in order to understand whether cobonding guarantees the same performance of a co-cured composite par
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