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Mok's characteristic varieties and the normal holonomy group
No full textIn this paper we complete the study of the normal holonomy groups of complex submanifolds (non nec. complete) of Cn or CPn. We show that irreducible but non transitive normal holonomies are exactly the Hermitian s-representations of [CD09, Table 1] (see Corollary 1.1). For each one of them we construct a non necessarily complete complex submanifold whose normal holonomy is the prescribed s-representation. We also show that if the submanifold has irreducible non transitive normal holonomy then it is an open subset of the smooth part of one of the characteristic varieties studied by N. Mok in his work about rigidity of locally symmetric spaces. Finally, we prove that if the action of the normal holonomy group of a projective submanifold is reducible then the submanifold is an open subset of the smooth part of a so called join, i.e. the union of the lines joining two projective submanifolds
Analysis of the DC performance of the ITER CSI coil using the 4C code
No full textThe DC performance of the ITER Central Solenoid Insert (CSI) coil, a single layer solenoid wound using the same Nb3Sn conductor that will be adopted for the 3L module of ITER CS, was measured during the 2015 test campaign in different magnetic field and current operating conditions, before and after electromagnetic and thermal cycles, as well as before and after quench tests. The 4C thermal-hydraulic code is applied here to the analysis of the CSI performance: first, the free parameters of the model are calibrated; then, the model is validated against measurements not used for its calibration. The model is then used to compute the current sharing temperature, to be compared with the measured jacket temperature, and to assess the performance after quench tests
Non-monotonic dependence of the current density on the thickness of the photoactive layer
No full textWe have developed a mathematical model able to predict the dependence of the current density, j0, in the dc limit, on the thickness of a photoactive semiconductor layer, d, in contact with an electrolyte. The model considers the application of an external bias. The theoretical analysis has been done by means of a diffusive model, where the excess of charges moves by diffusion in the presence of a generation term, due to the incident light, and a recombination term, proportional to the excess of charge carriers. We show that a non-monotonic dependence of j0 vs. d is expected. For small d, the photocurrent density is proportional to d and the proportionality constant is related to both the attenuation of the light in the photoactive semiconductor layer and to the applied potential. In the opposite limit of large d, the current tends to a constant value that is dependent on both the light intensity and the applied bias. Our theoretical predictions are in qualitative agreement with the experimental data reported in literature for BiVO4 films. © 2017 Elsevier B.V
Life Cycle Assessment (LCA) of biogas-fed Solid Oxide Fuel Cell (SOFC) plant
No full textThe Life Cycle Assessment (LCA) of biogas-fed Solid Oxide Fuel Cell (SOFC) integrated with a CO2 recovery system is presented in this work. The goal of the work is to evaluate the environmental performance of an SOFC fueled with sewage biogas and to compare it with traditional technologies (internal combustion engines and microturbines) using the same fuel. CO2 recovery is performed through a tubular photobioreactor, fixing the recovered carbon in the form of a micro-algae. The analysis takes into account both the biogas production line (anaerobic digester) and its exploitation into the fuel cell (i.e., the power generator). Results show that the SOFC manufacturing activity is highly intensive since it requires a large amount of use of electricity. During operation, instead, the highest burden is associated with the fuel production. We analyzed two scenarios for biogas operation underlining the benefits of introducing sludge pre-thickening before the anaerobic digestion process. The use of a sludge pre-thickening system can reduce the inlet flow of natural gas into the plant, thus affecting the fuel chain contribution and reducing the overall impact. The photobioreactor results in consuming more energy than what it produces (looking at the operation phase only; the manufacturing phase was not even included) and being responsible for more carbon emissions than the amount fixed in algae. On the other side, data for the photobioreactor system were based on a real system at the proof-of-concept level. Therefore significant improvements are expected for an industrial-size system. Finally, the SOFC environmental burdens have been compared with main competitors in the same field (internal combustion engines and microturbines), showing the superior environmental performance. The proposed energy system is thus an interesting choice for cleaner energy production
Enforcement of dynamic HTTP policies on resource-constrained residential gateways
No full textGiven that nowadays users access content mostly through mobile apps and web services, both based on HTTP, several filtering applications, such as parental control, malware detection, and corporate policy enforcement, require inspecting Universal Resource Locators (URLs) contained in HTTP requests. Currently, such filtering is most commonly performed in end devices or in middleboxes. Filtering applications running on end devices are less resource intensive because they operate only on traffic from a single user and possibly leverage a hook at the HTTP level to access protocol data, but it is left to the user whether to execute them. On the other hand, middleboxes present the challenge of ensuring that they lay on the path of all the traffic from any relevant device. Residential gateways seem to be the ideal place where to implement traffic filtering because they forward all traffic generated by the hosts on home(-office) networks. However, these devices usually have very limited computation and memory resources, while URL-based filtering is quite demanding. In fact existing approaches rely on a large database of rules coupled with either deep packet inspection or transparent proxying for URL extraction. This paper introduces U-Filter, a URL filtering solution based on a distributed architecture where a lightweight, efficient URL extraction and policy enforcement component runs on residential gateways, delegating to a remote policy server the resource intensive task of verifying policy compliance. Thanks to the lightweight communication between the two components and the very limited resource requirements of the local module, U-Filter (i) can be deployed on resource-limited devices such as residential gateways, and (ii) has almost no impact on the performance of the device, as well as on the users' browsing experience, as demonstrated by the experiments presented in the paper
Occupational exposure to vibrations: some considerations with reference to the recently issued regulations
No full textRemote monitoring of the Comba Citrin landslide using discontinuous GBInSAR campaigns
No full textThis paper describes the use of the discontinuous Ground-Based Interferometric Synthetic Aperture Radar technique (GBInSAR) to monitor the displacement of the Comba Citrin landslide in the North Western Italian Alps. Two GBInSAR surveys were carried out respectively during the summer and the fall of 2015 separated by a temporal baseline of 63 days. For each GBInSAR survey, which lasted respectively 166.2 h (6 dd, 22 h, 12′) and 238.3 h (9 dd, 22 h, 18′), two sets of 139 and 275 SAR images were acquired. After the selection of a specific stack of Persistent Scatterers, the SAR images of each survey were analyzed separately and in combination with the images of the other survey to detect the possible displacements occurred both in every single survey as well as in the elapsed time between the two different campaigns. The displacement maps showed that two different sectors of the monitored slope were affected by millimetres to centimetres movements during the monitoring period. The results obtained for the Comba Citrin landslide show that the discontinuous GBInSAR can be reliably adopted to monitor the displacement of landslides moving at an average rate of few centimetres per year
Sol-gel chemistry, templating and spin-coating deposition: A combined approach to control in a simple way the porosity of inorganic thin films/coatings
No full textPorous materials are powerful functional devices that can find applications in many fields, from nanotechnology to biomedicine, from catalysis to membrane separation. In general, porous materials can be processed in various forms, but a rising interest is growing around inorganic thin films and coatings, due to the increased number of applications based on their use. Among the different strategies proposed till now for preparing inorganic porous thin layers/coatings, a simple and versatile route consists in the combined use of sol-gel chemistry, templating, and spin-coating deposition. Therefore, in order to provide a helpful toolbox for users, an extended discussion around the physico-chemical principles behind each of these steps is here reported, also highlighting the advantages and disadvantages of each procedure, together with critical points
