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Some comments on mechanical fatigue characterization of steel rails in Standards
No full textCurrent Standards and recommendations on characterization of steel materials for rail production define tests for material supplying. As reported in technical literature, fatigue is the phenomenon which represent one of the main cause of rail damage and failure. Experimental testing of fatigue characterization according to Standards on different samples and with different surface roughness values, satisfying the Standard requirements, are performed. The results are then presented and discussed. Some nomenclature ambiguities are pointed out, which can lead to different loading conditions for fatigue testing
CMC hypersurfaces with canonical principal direction in space forms
No full textA hypersurface of the space form has a canonical principal direction (CPD) relative to the closed and conformal vector field of if the projection of to is a principal direction of . We show that CPD hypersurfaces with constant mean curvature are foliated by isoparametric hypersurfaces. In particular, we show that a CPD surface with constant mean curvature of space form M is invariant by the flow of a Killing vector field whose action is polar on M. As consequence we show that a compact CPD minimal surface of the sphere S^3 is a Clifford torus. Finally, we consider the case when a CPD Euclidean hypersurface has zero Gauss-Kronecker curvature
Power amplifier MMICs for 15 GHz microwave links in 0.25 μm GaN technology
No full textThis paper presents three power amplifiers designed for 15 GHz microwave radio application employing GaN 0.25 μm technology. The first design is a 3W combined power amplifier, the second is a 7-15 GHz dual-band 3W combined power amplifier, and the third is a 4W Doherty power amplifier. Advantages and limitations of GaN 0.25 μm technology applied to the three different design solutions for this specific application are discussed, presenting and comparing the measurement results obtained on the developed amplifiers
Le regge dei Savoia-Carignano (1831-1861). Prima dell'Italia, dopo i Savoia
No full textIl saggio focalizza il sistema di residenze messo in atto durante il periodo di regno di Carlo Alberto (1831-1849) attraverso l'apporto di figure come Pelagio Palagi ed Erenest Melano e con interventi che aggiornano e incrementano residenze già esistenti (castello di Racconigi) o che realizzano ex-novo siti reali come quello di Pollenzo, in un contesto che spazia dal Neoclassico al Neogotico
ANOVA and other statistical tools for bearing damage detection
No full textThe aim of the paper is to exhaustively exploit and test some statistical tools, such as ANOVA and Linear Discriminant Analysis, to investigate a massive amounts of data collected over a rig available @DIRG Lab, specifically conceived to test high speed aeronautical bearings; the rig permits the control of rotational speed (6000 - 30000 RPM), radial load (0 to 1800 N) and temperature, and allows monitoring vibrations by means of 4 tri-axial accelerometers. Fifteen different damages have been realised on the bearing but, for simplicity, this papers only treats those cases where simple identification methods have failed or not demonstrated to be fully affordable. The damages have been inferred on rolls or on the internal ring, with different severities, which are reported as a function of their extension, i.e. 150, 250, 450 μm. A total number of 17 combinations of load and speed have been analysed per each damaged bearing. Although ANOVA rigorously applies when some conditions are respected on the probability distribution of the responses, such as Independence of observations, Normality (normal distribution of the residuals) and Homoscedasticity (homogeneity of variances - equal variances), the paper exploits the robustness of the technique even when data do not fully fall into the requisites. Analyses are focused on the best features to be taken into account, trying to seek for the most informative, but also trying to extract a "best choice" for the acceleration direction and the most informative point to be monitored over the simple structure. Wanting to focus on the classification of the single observation, Linear Discriminant Analysis has been tested, demonstrating to be quite effective as the number of misclassification is not very high, (at least considering the widest damages). All these classifications have unfortunately the limit of requiring labelled examples. Acquisitions in un- damaged and damaged conditions are in fact essential to guarantee their applicability, which is quite often impossible for real industrial plants. The target can be anyway reached by adopting distances from un-damaged conditions which, conversely, must be known as a reference. Advantages of the statistical methods are quickness, simplicity and full independence from human interaction
Gassino Torinese e Sewing a small town. Un borgo italiano tra i tanti per la costruzione di un modello didattico d'architettura e di ricerca progettuale applicata di respiro internazionale
No full textIl Tempo come fattore strutturante dello Spazio architettonico. La «quarta dimensione» della «memoria»
No full textAdvanced High Efficiency and Broadband Power Amplifiers Based on GaN HEMT for Wireless Applications
No full textIn advanced wireless communication systems, a rapid increase in the mobile data traffic and broad information bandwidth requirement can lead to the use of complex spectrally efficient modulation schemes such as orthogonal frequency-division multiplexing (OFDM). Generally, complex non-constant envelope modulated signals have very high peak-to-average ratios (PAPR). Doherty Power Amplifier (DPA) is the most commonly used power amplifier (PA) architecture for meeting high efficiency requirement in advanced communication systems, in the presence of high PAPR signals. However, limited bandwidth of the conventional DPA is often identified as a bottleneck for widespread deployment in base-station application for multi-standard communication signals. The research in this thesis focuses on the development of new designs to overcome the bandwidth limitations of a conventional PA. In particular, the bandwidth limitation factors of a conventional DPA architecture are studied. Moreover, a novel design technique is proposed for DPA's bandwidth extension. In the first PA design, limited bandwidth and linearity problems are addressed simultaneously. For this purpose, a new Class-AB PA with extended bandwidth and improved linearity is presented for LTE 5 W pico-cell base-station over a frequency range of 1.9-2.5 GHz. A two-tone load/source-pull and bias point optimization techniques are used to extract the sweet spots for optimum efficiency and linearity from the 6 W Cree GaN HEMT device for the whole frequency band. The realized prototype presented saturated PAE higher than 60%, a power gain of 13 dB and an average output power of 36.5 dBm over the desired bandwidth. The proposed PA is also characterized by QAM-256 and LTE input communication signals for linearity characterization. Measured ACPRs are lower than -40 dBc for an input power of 17 dBm. The documented results indicate that the proposed Class-AB architecture is suitable for pico-cell base-station application. In the second PA design, an inherent bandwidth limitation of Class-F power amplifier forced by the improper load harmonics terminations at multiple harmonics is investigated and analyzed. It is demonstrated that the impedance tuning of the second and third harmonics at the drain terminal of a transistor is crucial to achieve a broadband performance. The effect of harmonics terminations on power amplifier's bandwidth up to fourth harmonics is investigated. The implemented broadband Class-F PA achieved maximum saturated drain efficiency 60-77%, and 10 W output power throughout (1.1-2.1 GHz) band. The simulated and measured results verify that the presented Class-F PA is suitable for a high-efficiency system application in wireless communications over a wide range of frequencies. In the third PA design, a single- and dual-input DPA for LTE application in the 3.5 GHz frequency band are presented and compared. The main goal of this study is to improve the performance of gallium-nitride (GaN) Doherty transmitters over a wide bandwidth in the 3.5 GHz frequency band. For this purpose, the linearity-efficiency trade-off for the two proposed architectures is discussed in detail. Simulated results demonstrate that the single- and dual-input DPA exhibited a peak drain efficiency (DE) of 72.4% and 77%, respectively. Both the circuits showed saturated output power more than 42.9 dBm throughout the designed band. Saturated efficiency, gain and bandwidth of dual-input DPA are higher than that of the single-input DPA. On the other side, dual-input DPA linearity is worse as compared to the single-input DPA. In the last PA design, a novel design methodology for ultra-wide band DPA is presented. The bandwidth limitation factors of the conventional Doherty amplifier are discussed on the ground of broadband matching with impedance variation. To extend the DPA bandwidth, three different methods are used such as post-matching, low impedance transformation ratio and the optimization of offset line for wide bandwidth in the proposed design. The proposed Doherty power amplifier was designed and realized based on two 10 W GaN HEMT devices from Cree Inc. The measured results exhibited 42-57% of efficiency at the 6-dB back-off and saturated output power ranges from 41.5 to 43.1 dBm in the frequency range of 1.15 to 2.35 GHz (68.5% fractional bandwidth). Moreover, less than -25 dBc ACPRs are measured at 42 dBm peak output power throughout the designed band. In a nutshell, all power amplifiers presented in this thesis are suitable for wideband operation and their performances are satisfying the required operational standard. Therefore, this thesis has a significant contribution in the domain of high efficiency and broadband power amplifiers
Experimental validation of a massive educational service in a blended learning environment
No full textNew information and communication technologies offer today many opportunities to improve the quality of educational services in universities and in particular they allow to design and implement innovative learning models. This paper describes and validates our university blended learning model, and specifically the massive educational video service that we offer to our students since 2010. In these years, we have gathered a huge amount of detailed data about the students' access to the service, and the paper describes a number of analyses that we carried out with these data. The common goal was to find out experimentally whether the main objectives of the educational video service we had in our mind when we designed it, namely appreciation, effectiveness and flexibility, were reflected by the users' behavior. We analyzed how many students used the service, for how many courses, and how many videos they accessed within a course (appreciation of the service). We analyzed the correlation between the use of the service and the performance of the students in terms of successful examination rate and average mark (effectiveness of the service). Finally, by using data mining techniques we profiled users according to their behavior while accessing the educational video service. We found out six different patterns that reflect different uses of the services matching different learning goals (flexibility of the service). The results of these analyses show the quality of the proposed blended learning model and the coherency of its implementation with respect to the design goals