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This paper illustrates a formulation of a continuous state space model in dq frame of the Thyristor Controlled Reactor (TCR), which can be used for stability studies by eigenvalue analysis. Differently from the previous approaches, this model is just addressed to reproduce the operation of the non-linear part of the TCR system, without considering shunted capacitor or control system, thus obtaining a characterization of the TCR independent from the application. A typical problem of the continuous models in dq frame of the TCR system is the presence of an un-damped homogenous current component in the solution, which is inconsistent with the real operation; the proposed model solves this problem improving the accuracy. The model performance has been also evaluated in the frequency domain comparing the obtained results with a numerical simulation of the TCR implemented by PSIM program.

This paper presents a multidisciplinary methodology to estimate the underground heat-exchange potential for Borehole Heat Exchangers (BHEs) coupled with Ground Source Heat Pumps (GSHPs) over wide areas. The proposed methodology was tested in four sites in western Sicily (southern Italy) where the shortage of subsurface geological data, in addition to the undefined authorization processes for this kind of system, is probably the main barrier to planning and exploiting geothermal heat for heating and cooling purposes. Reliable high-resolution 3D geological and petrophysical models were built based on the integration of airborne electromagnetic data and laboratory measurements of the thermal properties of rock samples. A GIS-based procedure was applied to assess the geothermal heat-exchange potential using 3D models of thermal conductivity as the main input. The results of the analyses are represented by thematic maps of the underground heat exchange potential for BHEs coupled with GSHPs. The study areas show a generally high suitability for the use of this technology and several municipalities in the area could take advantage of the resulting maps for energy planning.

Nb electrodissolution is studied in solutions of alkali metal hydroxides MOH (M=Li, Na, K, Rb and Cs). The j– E curves show in all cases a dissolution/passivation peak followed by a current plateau. The current shows a marked dependence on the cation M: the peak current density jpk goes through a maximum for M=K and the plateau current density jpl increases monotonically with the atomic number of M. Electrochemical impedance spectroscopy indicates that in the plateau region, a similar barrier oxide is present over the metal substrate in all solutions. XPS analyses show that polarisation causes, in certain cases, formation of a porous film of alkali metal niobates or mixed oxides, probably by a mechanism of dissolution/precipitation. It is proposed that the peak current is controlled by both the solution basicity and the solubility of this layer, whereas the dependence of the plateau current on M reflects the variations in solution basicity and in the specific ability of the metal cations to promote dissolution of the barrier oxide.

For the design of ground-source heat-pump systems, the local subsoil is an invariant factor. To improve the evaluation of the local heat exchange capability, significant efforts recently have been devoted to identifying the ground thermal conductivity vertical profile. In recent years, an innovative method using hybrid optic fiber cables inserted into the ground has been developed. The technique relies on copper wires that thermally stimulate the ground. Optical fibers measure the temperature variation over time all along the cable at a high spatial and temporal resolution. In this work, the hybrid cable was grouted into a 125-m well located in the Po Plain in Northern Italy. The provided core defined the geological environment as a continuous succession of unconsolidated alluvial deposits of very limited thickness, grouped in 15 different granulometric units. Three enhanced thermal response test (ETRT) data sets were acquired in different seasons; for 5 days of heating followed by 5 days of recovery, the soil temperature was recorded continuously along the well, with a spatial resolution of 1 m. A new approach using a multiple linear regression is proposed to analyze the data sets to distinguish the thermal conductivity of each individual granulometric unit. The obtained thermal conductivity values were compared and discussed considering the standard thermal response test outputs and the thermal conductivity data obtained from direct measurements performed on the cores. The analytical method's reliability stands due to the high repeatability of the obtained results, despite the increased complexity of the treated geological setting.

The existing building stock requires substantial interventions to meet the energy performance criteria imposed by the current standards. The installation of a new insulating layer into the building envelope is the most common energy retrofit measure. This strategy is usually focused only on steady state thermal conditions while it influences also the transient thermal behavior. However the on - site characterization of the building dynamic behavior is partially or totally neglected, due to the lack of a feasible investigation procedure. This may lead to a negative thermal performance of the building, paving the way to litigations between the contractor and the tenants. A novel measurement technique, based on infrared thermography, is proposed to investigate the dynamic behavior of the wall. Several wall samples are tested in laboratory with an experimental layout that resembled an outdoor installation, where a sinusoidal thermal stimulus is imposed on the back of the specimen. The surface temperature evolution over time is recorded with an infrared camera both on the front and on the back surfaces of the specimen, in order to measure the time-shift on a broad wall area. A key aspect of the proposed experimental procedure is that it could be applied to the on-site building survey, significantly improving the evaluation of the actual energy performance of the building. The obtained results are compared with a mathematical model showing good agreement.

p-Type Co(3)O(4) nanostructured films are synthesized by a plasma-assisted process and tested in the photocatalytic production of H(2) from water/ethanol solutions under both near-UV and solar irradiation. It is demonstrated that the introduction of fluorine into p-type Co(3)O(4) results in a remarkable performance improvement with respect to the corresponding undoped oxide, highlighting F-doped Co(3)O(4) films as highly promising systems for hydrogen generation. Notably, the obtained yields were among the best ever reported for similar semiconductor-based photocatalytic processes.

A series of samples are collected from the catholyte solution of a vanadium redox flow battery (VRFB) at different values of state of charge (SoC)/state of discharge (SoD). The samples are analyzed by means of Raman spectroscopy to identify: (i) the species present into the catholyte; and (ii) how the composition of the catholyte is modulated along the charge and discharge processes of the VRFB. Raman results reveal that the most abundant species in the catholye are VO2+ and VO2 +; they are coordinated by HSO4 - and SO4 2- ligands. During the charge process of the VRFB the equilibrium between the vanadium species is shifted towards the formation of an ensemble of V(V) complexes. Instead, during discharge a family of V(IV) species is obtained. The formation of concatenated HV2O5 - and H3V2O7 - species in the catholyte is revealed, which indicates that side electrochemical reactions occur during the charge and discharge processes of a VRFB. The presence of these side reactions plays a crucial role in the modulation of the Coulombic efficiency of the VRFB. This work highlights the complexity of the chemical situation at a VRFB cathode, and the great importance to understand/control such chemical situation to improve the performance of VRFBs in the scenario of electrochemical energy storage field

ZnO nanorod assemblies were grown by plasma-enhanced chemical vapor deposition on polycrystalline Al2O3 at 200-300 C, resulting in urchin-like 1-D ZnO NR arrays with a strong c-axis orientation. Their outstanding gas sensing responses and very low detection limits highlight the potential of the present systems in the production of high efficiency chemical sensors for a variety of applications.