Coupling of energy conversion systems and wellbore heat exchanger in a very deep oil well

The conventional geothermal power plants use the reinjection wells mostly to avoid the depletion of the geothermal reservoir gathering in the underground of the produced brine. Nevertheless, reinjection operations entail high economic costs and some risks. An alternative is the extraction of the heat without geothermal fluids production, the wellbore heat exchanger. The goal of the present paper is the analysis of the power production of the wellbore heat exchanger (WBHX) in time and the comparison between two different conversion systems of the thermal energy into electrical: the organic ranking cycle (ORC) plant and the Stirling motor. The selected case study is the oil field of Villafortuna Trecate, a medium enthalpy geothermal resource. The simulation results show a substantial decrease of the wellhead temperature in the first 6 months. After 1 year, the thermal power extracted with the WBHX is greater than 1.3 MW. The design parameters are 20 m3/h for the flow rate, outlet temperature 100.38 °C and the inlet temperature is 40 °C. The R-C318 has been selected as working fluid in the ORC plant: the net electrical power is 121 kW. The air is the working fluid in the Stirling motor: the evaluated net electrical power is 152 kW. The Stirling engine has an efficiency greater than 41 % compared to a system ORC

Sviluppo, Deployment e Validazione Sperimentale di Architetture Distribuite di Machine Learning su Piattaforma fog05

Ultimamente sta crescendo sempre di più l'interesse riguardo al fog computing e alle possibilità che offre, tra cui la capacità di poter fruire di una capacità computazionale considerevole anche nei nodi più vicini all’utente finale: questo permetterebbe di migliorare diversi parametri di qualità di un servizio come la latenza nella sua fornitura e il costo richiesto per le comunicazioni. In questa tesi, sfruttando le considerazioni sopra, abbiamo creato e testato due architetture di machine learning distribuito e poi le abbiamo utilizzate per fornire un servizio di predizione (legato al condition monitoring) che migliorasse la soluzione cloud relativamente ai parametri citati prima. Poi, è stata utilizzata la piattaforma fog05, un tool che permette la gestione efficiente delle varie risorse presenti in una rete, per eseguire il deployment delle architetture sopra. Gli obiettivi erano due: validare le architetture in termini di accuratezza e velocità di convergenza e confermare la capacità di fog05 di gestire deployment complessi come quelli necessari nel nostro caso. Innanzitutto, sono state scelte le architetture: per una, ci siamo basati sul concetto di gossip learning, per l'altra, sul federated learning. Poi, queste architetture sono state implementate attraverso Keras e ne è stato testato il funzionamento: è emerso chiaramente come, in casi d'uso come quello in esame, gli approcci distribuiti riescano a fornire performance di poco inferiori a una soluzione centralizzata. Infine, è stato eseguito con successo il deployment delle architetture utilizzando fog05, incapsulando le funzionalità di quest'ultimo dentro un orchestratore creato ad-hoc al fine di gestire nella maniera più automatizzata e resiliente possibile la fornitura del servizio offerto dalle architetture sopra

X-ray Emission from an Asymmetric Blast Wave and a Massive White Dwarf in the Gamma-ray Emitting Nova V407 Cyg

Classical nova events in symbiotic stars, although rare, offer a unique opportunity to probe the interaction between ejecta and a dense environment in stellar explosions. In this work, we use X-ray data obtained with Swift and Suzaku during the recent classical nova outburst in V407 Cyg to explore such an interaction. We find evidence of both equilibrium and non-equilibrium ionization plasmas at the time of peak X-ray brightness, indicating a strong asymmetry in the density of the emitting region. Comparing a simple model to the data, we find that the X-ray evolution is broadly consistent with nova ejecta driving a forward shock into the dense wind of the Mira companion. We detect a highly absorbed soft X-ray component in the spectrum during the first 50 days of the outburst that is consistent with supersoft emission from the nuclear burning white dwarf. The high temperature and short turn off time of this emission component, in addition to the observed breaks in the optical and UV lightcurves, indicate that the white dwarf in the binary is extremely massive. Finally, we explore the connections between the X-ray and GeV gamma-ray evolution, and propose that the gamma ray turn-off is due to the stalling of the forward shock as the ejecta reach the red giant surface.Comment: Accepted for publication in ApJ. 17 pages, 9 figure

A kpc-scale X-ray jet in the BL Lac source S5 2007+777

X-ray jets in AGN are commonly observed in FRII and FRI radio-galaxies, but rarely in BL Lacs, most probably due to their orientation close to the line of sight and the ensuing foreshortening effects. Only three BL Lacs are known so far to contain a kpc-scale X-ray jet. In this paper, we present the evidence for the existence of a fourth extended X-ray jet in the classical radio-selected source S5 2007+777, which for its hybrid FRI/II radio morphology has been classified as a HYMOR (HYbrid MOrphology Radio source). Our Chandra ACIS-S observations of this source revealed an X-ray counterpart to the 19"-long radio jet. Interestingly, the X-ray properties of the kpc-scale jet in S5 2007+777 are very similar to those observed in FRII jets. First, the X-ray morphology closely mirrors the radio one, with the X-rays being concentrated in the discrete radio knots. Second, the X-ray continuum of the jet/brightest knot is described by a very hard power law, with photon index Gamma_x~1, although the uncertainties are large. Third, the optical upper limit from archival HST data implies a concave radio-to-X-ray SED. If the X-ray emission is attributed to IC/CMB with equipartition, strong beaming (delta=13) is required, implying a very large scale (Mpc) jet. The beaming requirement can be somewhat relaxed assuming a magnetic field lower than equipartition. Alternatively, synchrotron emission from a second population of very high-energy electrons is viable. Comparison to other HYMOR jets detected with Chandra is discussed, as well as general implications for the origin of the FRI/II division.Comment: Accepted for publication in ApJ, 19 pages, 3 figure

Credit rationing and firm size

This paper examines the likelihood of credit rationing faced by firms of different size. Contrary to common thought, several recent contributions on this topic argue that, when rationing credit, size alone is not a sufficient condition for discriminating between firms. We show that this result can be predicted using a framework based on the Stiglitz-Weiss model. In particular, in an environment of asymmetric information, we highlight how the likelihood of credit rationing depends upon the shape of the distribution function of project returns, especially its asymmetry and Kurtosis. Our empirical results do not support the hypothesis that small firms face more credit rationing than larger firms

Structural analysis of the double-walled copper-steel cryogenic chamber of the ASTAROTH experiment

This document describes the verification process of structural performance of the double- walled copper-steel cryogenic chamber of the ASTAROTH (All Sensitive crysTal ARray with lOw THreshold) experiment and the evaluation of the stresses generated near the thermal bridge connecting the inner and outer wall. The chamber consists of an external AISI 316L stainless steel dewar and an inner double-walled OF (Oxygen Free) copper dewar connected to an AISI 316L stainless steel flanged collar. The results showed that close to the thermal bridge (copper-steel junction) the stresses slightly exceed the YS of copper at the estimated operating temperature (localised strain-hardening condition). On the other hand, the safety coefficient respect to fracture is well above one for both materials. This condition, together with the fact that limited cooling cycles are expected during the operating life of the system, leads to the assumption that a progressive material hardening will occur in this area, thus locally raising the YS limit

Nutrire Roma: il ruolo dell’agricoltura urbana nel fenomeno urbano

Scopo di questa nota è di esaminare i caratteri e le dinamiche che connotano l’agricoltura urbana nel caso di Roma. Il contributo sintetizza in chiave evolutiva i fatti stilizzati del rapporto tra città e campagna, successivamente si indaga il contesto produttivo agricolo al fine di proporre una tassonomia dei tipi di agricoltura urbana. Il tentativo che qui si propone è una preliminare lettura dell’agricoltura urbana attraverso un sistema di criteri per la classificazione della distribuzione funzionale e relazionale del primario in aree metropolitane. Tali categorie interpretative tentano di ricostruire le relazioni causali che traducono i modelli produttivi agricoli (caratteristiche strutturali, ordinamenti, forme giuridiche, forme d’uso delle risorse naturali, collocazione), in specifiche forme spaziali e funzionali nella dimensione urbana – fisica e sociale -. Sul piano teorico tale lettura s’inserisce nel paradigma coevolutivo e guarda al paesaggio come il risultato delle interazioni tra il sistema ambientale e l’agire dell’uomo che abita e utilizza il territorio (Marino e Cavallo, 2009). Una sintesi tipologica definitiva sembra ancora un obiettivo da raggiungere, sicuramente questo è il primo passo verso la costruzione di una griglia interpretativa e di un vocabolario tipologico da mettere poi a sistema con i dati morfologici e quelli di uso del suolo.The aim of this paper is to examine the characteristics and the dynamics that characterize urban agriculture in the case of Rome. We summarize in an evolutionary approach the stylized facts of the relationship between town and country, then we investigate the context of agricultural production in order to propose a taxonomy of the types of urban agriculture. The effort proposed here is a preliminary analysis of urban agriculture through a system of criteria for the classification of the distribution of the functional and relational features of agricultural activities in metropolitan areas. These interpretative categories attempt to reconstruct the causal relationships that translate agricultural production models (farms’ data, legal forms, use of natural resources, localization), in specific forms in the spatial and functional urban dimension - physical and social - . On the theoretical level this analysis is embedded in the co-evolutionary paradigm and looks to the landscape as the result of interactions between the environmental system and the action of human who lives and uses the territory (Marino and Cavallo, 2009). This typization ultimately still seems a goal to achieve, this is the first step towards the construction of an interpretative and vocabulary typological then be systematize with the morphological data and those of land use.Peer Reviewe

Particle motion in a rotating dust spacetime: the Bonnor solution

We investigate the geometrical properties, spectral classification, geodesics, and causal structure of the Bonnor's spacetime [Journal of Physics A Math. Gen., \textbf{10}, 1673 (1977)], i.e., a stationary axisymmetric solution with a rotating dust as a source. This spacetime has a directional singularity at the origin of the coordinates (related to the diverging vorticity field of the fluid there), which is surrounded by a toroidal region where closed timelike curves (CTCs) are allowed, leading to chronology violations. We use the effective potential approach to provide a classification of the different kind of orbits on the symmetry plane as well as to study the motion parallel to the symmetry axis. In the former case we find that as a general feature test particles released from a fixed space point and directed towards the singularity are repelled and scattered back as soon as they approach the CTC boundary, without reaching the central singularity.Comment: 11 pages, 5 figures (10 eps files

Fast Ultrahigh-Density Writing of Low Conductivity Patterns on Semiconducting Polymers

The exceptional interest in improving the limitations of data storage, molecular electronics, and optoelectronics has promoted the development of an ever increasing number of techniques used to pattern polymers at micro and nanoscale. Most of them rely on Atomic Force Microscopy to thermally or electrostatically induce mass transport, thereby creating topographic features. Here we show that the mechanical interaction of the tip of the Atomic Force Microscope with the surface of a class of conjugate polymers produces a local increase of molecular disorder, inducing a localized lowering of the semiconductor conductivity, not associated to detectable modifications in the surface topography. This phenomenon allows for the swift production of low conductivity patterns on the polymer surface at an unprecedented speed exceeding 20 $\mu m s^{-1}$; paths have a resolution in the order of the tip size (20 nm) and are detected by a Conducting-Atomic Force Microscopy tip in the conductivity maps.Comment: 22 pages, 6 figures, published in Nature Communications as Article (8 pages