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Numerical Studies on the Influence of Cavity Thermal Expansion on the Performance of a High-Power Gyrotron
No full textAn iterative procedure is described, which models the influence of the thermal expansion of the gyrotron cavity on the expected gyrotron performance. It is a multiphysics simulation method, which involves electrodynamic, thermal-hydraulic, and thermo-mechanical simulations. The method is applied to the first European 170-GHz, 1-MW continuous wave prototype gyrotron for the ITER. According to the simulations, a performance reduction of 15% is expected at nominal operating parameters, because of the thermal expansion of the cavity. Alternative operating points to mitigate this effect are proposed and numerically validated. The numerical results are discussed in light of experimental findings
A parametric study of Limit Cycle Oscillation of a bladed disk caused by flutter and friction at the blade root joints
No full textSpeeding Up the Internet: Regulation and Investment in the European Fiber Optic Infrastructure
No full textIn this paper, we study how the coexistence of access regulations for legacy (copper) and fiber networks shapes the incentives to invest in fiber-based network infrastructures. To this end, we first develop a theoretical model that extends the existing literature by, among other things, considering alternative firms with proprietary legacy network (e.g., cable operators) and the presence of asymmetric mandated access to networks. In the empirical part, we test the theoretical predictions using a novel panel data from 27 EU member states pertaining to the last decade. Our main finding is that, in line with the theoretical results, stricter access regulations (i.e., a decrease in access price to legacy network and the adoption of fiber regulation) decrease the incumbent operators' fiber investments. The estimated magnitude of these effects is economically significant. On the other hand, cable operators, who are responsible for the largest share of investments in fiber, are not affected by access regulation. Our paper thus provides policy insights for the on-going revision of the EU regulation framework for the electronic communications industry
Microcantilever resonator arrays for immunodetection of B-lactoglobulin milk allergen
No full textThe incidence of allergic disease is globally increasing so much that food allergy is actually considered as one of the main diseases of civilization, as well as among the major costs for healthcare worldwide. In such a scenario, the recent legislations introduced from European Union to protect consumers drastically drive the need for rapid, sensitive, and robust techniques to detect allergens within foodstuffs. We here report on an innovative immunorecognition method for β-lactoglobulin milk allergen detection, based on microcantilever resonator arrays, a promising class of biosensors. An original sandwich assay that uses the same polyclonal antibody as capture and secondary immunorecognition agent was proposed to overcome the low affinity of the simple direct method. The developed immunoassay showed better Limit Of Detection (LOD) and Limit Of Quantification (LOQ) than commercial ELISA plates, even after an aging of four months. To our knowledge, this work represents the first example in the literature of successfully immunodetection of milk allergens in low concentrations by microcantilever resonator arrays, thus opening new perspectives on alternative diagnostic tools for milk allergens screening tests
Towards solid batteries operating at ambient temperature: composite polymer electrolytes based on LLZO in a cross-linked PEO matrix
No full textPossible concerns about the safety of rechargeable lithium metal batteries has postponed their introduction into the smart electronics or automotive industries and have promoted advances in the field of non-flammable solid electrolytes. Among the oxide ceramic super lithium ion conductors, garnet-type Li7La3Zr2O12 (LLZO) has recently attracted much attention because of its relatively high ionic conductivity at room temperature (>10-4 S cm-1), negligible electronic conductivity and absence of harmful decomposition products upon contact with atmospheric moisture. Anyway, processing LLZO in pellets by sintering, results in brittle and more or less porous electrolytes, which often display poor interfacial contact with Li metal electrodes. Moreover, there are some reports of lithium dendrite growth and instability towards the cathode material - especially while processing of the electrode at high temperature - referred to cells assembled with this electrolyte family. To circumvent these problems, recent efforts have been dedicated to the formulation of composite hybrid polymer electrolytes (CPEs), where the ceramic material is embedded in a polymeric matrix. As compared to the pristine components, CPEs are stiff while preserving flexibility, are easily processed, and can be conceived to attain improved ionic conductivity and interfacial contact with the electrodes. In this work, a polymer based matrix containing poly(ethylene oxide) (PEO), lithium bis (trifluoromethylsulphonyl)imide (LiTFSI), tetra(ethylene glycol dimethyl ether) (G4) and a photoinitiator was added with LLZO particles, thoroughly mixed, formed into a film and cross-linked under UV radiation to obtain a composite hybrid electrolyte. This easy procedure allows obtaining self-standing CPEs with desirable properties of flexibility, shape retention upon thermal stress, improved interfacial contact with the electrodes and ionic conductivity suitable for practical application. Lab-scale lithium metal cells assembled with the CPEs and lithium iron phosphate (LFP) cathodes demonstrated specific capacities up to 125 mAh g-1 at 1C rate and could work for hundreds of cycles at ambient temperature
Investigation on bio-derived hydrogel electrolytes for dye-sensitized solar cells
No full textDye-sensitized solar cells (DSSCs) with water-based electrolytes are considered as one of the possible breakthrough towards DSSCs large-scale diffusion. If opportunely developed and optimized, aqueous solar cells can be considered a truly low impact photovoltaic device and no toxic components. Moreover, the possibility of gelling the electrolyte into a polymeric matrix can reduce the leakage outside the device, thus increasing the long-term stability. Above all, bio-derived polymers appear promising being renewable and easy available with low cost. In this contribution, the investigation on bio-derived hydrogel electrolytes for dye-sensitized solar cells is proposed. Moreover, the use of design of experiments (DoE) is demonstrated to be a useful chemometric technique for the concurrent investigation of a series of experimental factors that directly influence the photovoltaic performances of solar cells. Results obtained enlighten that a solid mathematical-statistical approach is fundamental to support the researchers and effectively drive the experiments towards the achievements of optimal operating conditions for aqueous solar cells
Evaluation of the charge transfer kinetics of spin-coated BiVO4 thin films for sun-driven water photoelectrolysis
No full texttThe present research work focuses on bismuth vanadate (BiVO4) thin films deposited on FTO-coated glasselectrodes through the spin-coating technique, and discusses the influence of different film morphologies(dense and porous) on the physicochemical properties and photoelectrochemical (PEC) performance ofthe as-prepared photoanodes, for the water splitting reaction. The surface recombination phenomenon,which is one of the main issues of BiVO4, has been quantified by means of two distinct approaches: tran-sient photocurrent measurements and electrochemical impedance spectroscopy (EIS). This phenomenonhas resulted to be higher in the porous material, thus a poorer performance has been observed than inthe dense material. In order to increase the BiVO4efficiency, a cobalt phosphate (CoPi) catalyst has beenphoto-electrodeposited onto the best BiVO4electrode, employing an optimized technique and a pho-tocurrent of up to 3 mA/cm2at 1.23 V vs. RHE under neutral pH and 1 sun irradiation (100 mW/cm2)has been achieved. The charge transfer kinetics of the BiVO4photoanodes, with and without CoPi, hasalso been quantified. The beneficial effect of this water oxidation catalyst, as well as the influence of thepreparation method on the uniformity of the film and on its actual performance, is discussed in view ofits prospective application in a real PEC device
Mechanical characterization of glass-ceramic scaffolds at multiple characteristic lengths through nanoindentation
No full textThe mechanical behaviour of implantable scaffolds is of relevant interest in all applications which require load-bearing capability. This study aims at establishing a quantitative relationship between the mechanical properties of glass-ceramic scaffolds for bone repair and the nano/micro-scale properties of their constituent materials. A nanoindentation study is carried out spanning different penetration depth on bulk (pore-free) glass-ceramic samples and on the walls of porous scaffolds. Micro-tomographical investigations allow assessing small-scale porosity of the scaffold walls. A simple homogenization model is used to establish the relationship between the elastic modulus of the bulk material and that of the micro-porous walls of the scaffolds. The elastic modulus of scaffold walls was found to be approximately 50%lower than that of the bulk glass-ceramic. The properties estimated experimentally on the walls of the scaffolds are quantitatively consistent with the analytical predictions provided by the homogenization model and the micro-porosity measured through tomographical analyse
A comparative study of two SOFC based cogeneration systems fed by municipal solid waste by means of either the gasifier or digester
No full textExploiting Spectrum Sensing Data for Key Management
No full textIn cognitive radio networks, secondary users (SUs) communicate on unused spectrum slots in the frequency bands assigned to primary users (PUs). Like any other wireless communication system, cognitive radio networks are ex- posed to physical layer attacks. In particular, we focus on two common at- tacks, namely, spectrum sensing data falsification and eavesdropping. Such attacks can be counteracted by using symmetric key algorithms, which how- ever require a complex key management scheme. In this paper we propose a novel algorithm that significantly reduces the complexity of the management of symmetric link keys by leveraging spectrum sensing data that is available to all nodes. In our algorithm, it is assumed that a primary secret key is pre-distributed to the legitimate SUs, which is needed every number of de- tection cycles. With the aid of the information provided in the primary key, our algorithm manipulates the collected samples so that a segment of the estimated sensing statistic at the two legitimate SUs can be used as a seed to generate a common symmetric link key. The link key is then employed to encrypt the transmitted data. Our algorithm exhibits very good performance in terms of bit mismatch rate (BMR) between two link keys generated at the two legitimate SUs. In addition, our solution is robust against the difference in the received signal to noise ratio between two legitimate SUs thus making it suitable for practical scenarios. Furthermore, our algorithm exploits the decision statistic that SUs use for spectrum sensing, hence, it does require neither extra processing nor extra time, allowing the SUs to quickly and securely tab into empty spectrum slots