On the Poincare Gauge Theory of Gravitation

We present a compact, self-contained review of the conventional gauge theoretical approach to gravitation based on the local Poincare group of symmetry transformations. The covariant field equations, Bianchi identities and conservation laws for angular momentum and energy-momentum are obtained.Comment: v2: minor changes, references added; 18 pages, no figure

The extended uncertainty principle inspires the R\'{e}nyi entropy

We use the extended uncertainty principle (EUP) in order to obtain the R\'{e}nyi entropy for a black hole (BH). The result implies that the non-extensivity parameter, appeared in the R\'{e}nyi entropy formalism, may be evaluated from the considerations which lead to EUP. It is also shown that, for excited BHs, the R\'{e}nyi entropy is a function of the BH principal quantum number, i.e. the BH quantum excited state. Temperature and heat capacity of the excited BHs are also investigated addressing two phases while only one of them can be stable. At this situation, whereas entropy is vanished, temperature may take a non-zero positive minimum value, depending on the value of the non-extensivity parameter. The evaporation time of excited BH has also been studied

Alcune note sulla geografia umana della Provincia Sardinia

Abstract - The recent discovery of some epigraphic artefacts in the countryside of Barumini and Siddi (Sardinia, Italy) is an opportunity to reflect on the Romanization of Sardinia. The new interpretation of CIL X, 7840 from Vallermosa, where the Fifenses are mentioned, and the identification of a new populus, the Barsanes (vel Barsani), allow us to put forward the proposal of a new cartography of Roman Sardinia. The epitaph of a colonus suggests an opportunity of going deeply into the question of Marmilla agrarian organization in the Roman age ---- [ITALIANO] Sommario - Il recente rinvenimento di alcuni manufatti epigrafici in agro di Siddi e Barumini sono l’occasione per una riflessione sulla romanizzazione della Sardegna. La rilettura di CIL X, 7840 da Vallermosa in cui vengono menzionati i Fifenses e l’individuazione di un nuovo populus, i Barsanes (vel Barsani) consentono di poter avanzare la proposta di una nuova cartografia su cui discutere. L’iscrizione di un colonus suggerisce lo spunto per un approfondimento dell’organizzazione agraria della Marmilla in età romana

A precise response function for the magnetic component of Gravitational Waves in Scalar-Tensor Gravity

The important issue of the magnetic component of gravitational waves (GWs) has been considered in various papers in the literature. From such analyses, it resulted that such a magnetic component becomes particularly important in the high frequency portion of the frequency range of ground based interferometers for GWs which arises from standard General Theory of Relativity (GTR). Recently, such a magnetic component has been extended to GWs arising from Scalar-Tensor Gravity (STG) too. After a review of some important issues on GWs in STG, in this paper we re-analyse the magnetic component in the framework of STG from a different point of view, by correcting an error in a previous paper and by releasing a more precise response function. In this way, we also show that if one neglects the magnetic contribution considering only the low-frequency approximation of the electric contribution, an important part of the signal could be, in principle, lost. The determination of a more precise response function for the magnetic contribution is important also in the framework of the possibility to distinguish other gravitational theories from GTR. At the end of the paper an expansion of the main results is also shown in order to recall the presence of the magnetic component in GRT too.Comment: Accepted for publication in Physical Review D, to be published during 2011. 36 pages, in this second version typos have been corrected and references have been update

CFD-3D and 1D modeling of fuel cell powertrain for a hydrogen vehicle

As it is known the transport sector represents a major contributor to climate change. In particular, private transport contributes to the degradation of the air quality inside the cities or the residential areas. To address this issue, a progressive reduction of the use of fossil fuels as a primary energy source for these vehicles and the promotion of cleaner powertrain alternatives is in order. This study focuses on designing a fuel cell powertrain for a hydrogen-powered passenger car using numerical modeling. To this purpose, we initially modeled a base fuel cell and optimized its performance by using various materials for the bipolar plates and adjusting the platinum loading between the anode and cathode. Then, a preliminary design of the new powertrain has been proposed in order to achieve a nominal power of 100 kW and it has been tested on a WLTP 3b homologation cycle. Finally, we have been able to numerically estimate the behavior of the three main feeding line: hydrogen line, air line and cooling line. In conclusion, the obtained results demonstrate how numerical modelling can be successfully used in the design of complex systems such as those related to alternative energy. This work also provides a solid basis for the future development of increasingly efficient and environmentally friendly hydrogen vehicles

Behavior of Some Earth Dams on Liquefiable Soil

The 1977 March 4 Vrancea earthquake emphasized several zones with liquefiable materials on Romanian territory. Some earth dams of such zones, placed to over 200 km from the earthquake epicenter were damaged. Important hydropower works are at present in different design or construction stages in such area, comprising long earth dams. The Seismic analysis procedure applied to their design was based on the finite element method. Some characteristic cross - sections of the earth dams in different versions have been studied. The analysed sections had different shapes (with and without stabilizing benches downstream) and included different zoning of the materials (sand fine sand and free draining materials). The analyses pointed out the importance of the drainage blanket at the base of the dam for the increase of the liquefaction strength capacity of the soil - structure system. Some improvement works in certain zones of the foundation soil resulted as being necessary

Three-Dimensional CFD Simulation of a Proton Exchange Membrane Electrolysis Cell

The energy shift towards carbon-free solutions is creating an ever-growing engineering interest in electrolytic cells, i.e., devices to produce hydrogen from water-splitting reactions. Among the available technologies, Proton Exchange Membrane (PEM) electrolysis is the most promising candidate for coping with the intermittency of renewable energy sources, thanks to the short transient period granted by the solid thin electrolyte. The well-known principle of PEM electrolysers is still unsupported by advanced engineering practices, such as the use of multidimensional simulations able to elucidate the interacting fluid dynamics, electrochemistry, and heat transport. A methodology for PEM electrolysis simulation is therefore needed. In this study, a model for the multidimensional simulation of PEM electrolysers is presented and validated against a recent literature case. The study analyses the impact of temperature and gas phase distribution on the cell performance, providing valuable insights into the understanding of the physical phenomena occurring inside the cell at the basis of the formation rate of hydrogen and oxygen. The simulations regard two temperature levels (333 K and 353 K) and the complete polarization curve is numerically predicted, allowing the analysis of the overpotentials break-up and the multi-phase flow in the PEM cell. An in-house developed model for macro-homogeneous catalyst layers is applied to PEM electrolysis, allowing independent analysis of overpotentials, investigation into their dependency on temperature and analysis of the cathodic gas–liquid stratification. The study validates a comprehensive multi-dimensional model for PEM electrolysis, relevantly proposing a methodology for the ever-growing urgency for engineering optimization of such devices