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Selective Laser Melting Manufacturing of Microwave Waveguide Devices
No full textAdditive manufacturing technologies are currently envisaged to boost the development of a next generation of microwave and millimeter-wave devices intended for, among others, satellite telecommunications, navigation, imaging, radio-astronomy, and cosmology. Due to their excellent electromagnetic and mechanical properties, all-metal waveguide components are key building blocks of several radio frequency (RF) systems used in these application domains. This article reports on the prospects originating from the application of all-metal 3D printing to the manufacturing of high-performance microwave waveguide devices. The technology investigated is the selective laser melting process, where a laser beam is used to fuse metal powder particles spread over a building platform. The complete parts are built by overlapping several constant-thickness layers. An overview on process parameters, material properties, and design rules is reported for this technology. The electromagnetic properties of test samples built in Al and Ti alloys have been experimentally characterized. A robust design of Ku/K-band filters aimed at satellite telecommunications has been implemented in several prototypes manufactured in Al. The corresponding measured performance confirm the applicability of the laser selective melting process to the intended application
Fe-N/C catalysts for oxygen reduction reaction supported on different carbonaceous materials. Performance in acidic and alkaline direct alcohol fuel cells
No full textFour carbonaceous materials (acetylene black, multi-walled carbon nanotubes, and two carbon materials synthesized by hard-template method) were used as a support to synthesize four Fe-N/C non-noble metal (NNM) catalysts for oxygen reduction reaction (ORR) by impregnation with a FeIII-1,10-phenanthroline complex and subsequent pyrolysis in inert atmosphere. The catalysts were characterized by N2 physisorption, XPS, Raman and TGA, and their ORR activity was measured by rotating disk electrode (RDE) in both acidic and alkaline conditions. The catalysts were tested in an acidic direct methanol fuel cell (DMFC) and in an alkaline direct ethanol fuel cell (DEFC). Due to the slower ORR kinetics at low pH, the features of the carbon support have an important influence on the performance in acidic DMFC. Conversely, the enhanced ORR kinetics at high pH, makes the influence of the C-support less evident in alkaline DEFC. Moreover, the short-term durability test in DMFC for our best Fe-N/C catalysts showed better results compared to Pt/C benchmark catalyst. The durability in alkaline DEFC is poor, even though the initial performance can be partially recovered after purge-drying and reactivation
Interdigitated crystalline MMT-MCA in polyamide 6
No full textPolyamide 6 (PA6) was flame retarded by using interdigitated crystalline montmorillonite-melamine cyanurate (MMT-MCA). Its morphologies were assessed by using X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM), thermal stability by thermogravimetric analysis (TGA), fire retardancy by limiting oxygen index (LOI), vertical burning testing (UL-94), and cone calorimeter (CONE) tests and mechanical properties by stress strain tests. The results indicated that the interdigitated crystalline MMT-MCA was homogeneously nano-dispersed as MMT and MCA in PA6 due to a p-p stacking exfoliation mechanism. Compared with PA6/MCA and PA6/OMMT/MCA, PA6/MMT-MCA shows enhanced thermal stability and fire retardancy. With 8 wt% total loading of MMT- MCA, the sample of PA6/MMT-MCA reached UL-94 V-0 rating (3.2 mm). The MMT-MCA can also enhance the mechanical properties of PA6
INTRODUCING CORE-SHELL TECHNOLOGY FOR CONFORMANCE CONTROL
No full textReservoir heterogeneities can severely affect the effectiveness of waterflooding because displacing fluids tend to flow along high-permeability paths and prematurely breakthrough at producing wells. A Proof-of-Concept (PoC) study is presented while discussing the experimental results of a research on "core-shell" technology to improve waterflooding in heterogeneous oil reservoirs. The proposed methodology consists in injecting a water dispersion of nanocapsules after the reservoir has been extensively flushed with water. The nanocapsules are made of a "core" (either polymeric or siliceous materials), protected by a "shell" that can release its content at an appropriate time, which activates through gelation or aggregation thus plugging the high permeability paths. Additional flooding with water provides recovery of bypassed oil. The initial conceptual screening of possible materials was followed by extensive batch and column lab tests. Then, 3D dynamic simulations at reservoir scale were performed to compensate for the temporary lack of pilot tests and/or field applications
LCA evaluation for the hydrogen production from biogas through the innovative BioRobur project concept
No full textBioRobur is a project aimed to produce hydrogen from biogas through an auto-thermal reforming (ATR) process, in which innovative catalytic systems are used to promote the ATR reactions involved in the process for the conversion of biogas into syngas. A detailed LCA study of hydrogen production from biogas ATR using the BioRobur technology has been performed. LCA analysis has been also conducted for other two conventional processes for the production of hydrogen from biogas: the steam reforming and water hydrolysis (a biogas-fueled Internal Combustion engine (ICE) followed by an Electrolyser). A comparison between these technologies has been made from both the environmental and the energetic viewpoints. The LCA has demonstrated that BioRobur is the most environmentally friendly of considered processes. Moreover, the ICE plus Electrolyser has resulted to be the because of the very large amount of biogas needed for the least efficient process, due to the low conversion yield of biogas into energy of the ICE
HOT: Hold your own tools for AR-based constructive art
No full textUsing digital instruments to support artistic expression and creativity is a hot topic. In this work, we focused on the design of a suitable interface for Augmented Reality-based constructive art on handheld devices. Issues to be faced encompassed how to give artists sense of spatial dimensions, how to provide them with different tools for realizing artworks, and how much moving away from ``the real'' and going towards ``the virtual''. Through a touch-capable device, such as a smartphone or a tablet, we offer artists a clean workspace, where they can decide when to introduce artworks and tools. In fact, besides exploiting the multi-touch functionality and the gyroscopes/accelerometers to manipulate artworks in six degrees of freedom (6DOF), the proposed solution exploits a set of printed markers that can be brought into the camera's field of view to make specific virtual tools appear in the augmented scene. With such tools, artists can decide to control, e.g., manipulation speed, scale factor, scene parameters, etc., thus complementing functionalities that can be accessed via the device's screen
A Stochastic Programming Approach for the Traveling Purchaser Problem
No full textThe deterministic Traveling Purchaser Problem (TPP) aims at selecting a subset of suppliers, offering products at different prices and quantities, so to satisfy a products demand while minimizing traveling and purchasing costs. In this paper, we study a variant of the TPP where both the available quantities and the purchasing prices are uncertain. This more challenging version of the problem, named TPP under uncertainty, allows the purchaser to protect himself against risks of insufficient demand fulfillment and to exploit the benefits of buying at lower price levels. We introduce a two-stage Stochastic Programming formulation of the problem and we present a tailored solution approach based on a Branch-and-Cut method and on a heuristic approach to find initial solutions. Extensive computational experiments show efficiency of the proposed approach in finding the optimal solution of the deterministic equivalent proble
Absolute frequency measurement of the ^1\textS_0 - ^3\textP_0 transition of 171Yb
No full textWe report the absolute frequency measurement of the unperturbed transition 1S0 -3P0 at 578 nm in 171Yb realized in an optical lattice frequency standard relative to a cryogenic caesium fountain. The measurement result is 518 295 836 590 863.59(31) Hz with a relative standard uncertainty of 5.9×10−16. This value is in agreement with the ytterbium frequency recommended as a secondary representation of the second in the International System of Units
Internationalization of SMEs and Organizational Factors in Emerging Economies: High –Tech Industry of Iran
No full textSMEs as an engine of growth play an important role in emerging economies for poverty reduction, the role which has attracted the attention of scholars in recent years. This study explores the effect of firm characteristics, resources and top management team (TMT) characteristics on the internationalization of SMEs. According to our conceptual model, we assumed that firm resources mediate the link between international performance of SMEs and characteristics of firms and of TMT. To test our model, we asked top managers of international SMEs in Iran ICT sector to fill in a questionnaire. The data was analyzed through structural equation modeling which leads us to codifying a causal model accordingly. The findings show a direct and indirect positive effect of TMT characteristics on internationalization of SMEs, however, it indicates that indirect effect of firm characteristics is not significant. Finally, a set of guidelines are proposed for internationalization of SMEs in emerging economie
Back-propagation neural networks and generalized linear mixed models to investigate vehicular flow and weather data relationships with crash severity in urban road segments
No full textThe paper deals with the identification of variables and models that can explain why a certain severity level (SL) may be expected in the event of a certain type of crash at a specific point of an urban road network. Two official crash records, a weather database, a traffic data source, and information on the characteristics of the investigated urban road segments of Turin (Italy) for the seven years from 2006 to 2012 were used. Examination of the full database of 47,592 crash events, including property damage only crashes, reveals 9,785 injury crashes occurring along road segments only. Of these, 1,621 were found to be associated with a dataset of traffic flows aggregated in 5 minutes for the 35 minutes across each crash event, and to weather data recorded by the official weather station of Turin. Two different approaches, a back-propagation neural network model and a generalized linear mixed model were used. Results show the impact of flow and other variables on the SL that may characterize a crash; differences in the significant variables and performance of the two modelling approaches are also commented on in the manuscript