1,721,007 research outputs found
Bar, fast food e tavole calde: nomi e funzioni dei locali di ristoro nelle città romane dell’Impero
No full textLe città di Pompei, Ercolano e Ostia costituiscono una notevole fonte di dati per quanto riguarda la vita quotidiana e commerciale di alcune botteghe, che avevano non solo la possibilità di vendere cibi e bevande calde e di mettere a disposizione dei clienti una serie di spazi in cui pranzare, ma anche di alloggiare con carri e animali: questo lavoro risulta essere un tentativo per mettere in relazione le testimonianze archeologiche rinvenute con le definizioni fornite dalle fonti e, allo stesso tempo, per creare una classificazione tipologica di tali locali sulla base degli arredi interni, delle dimensioni e della collocazione nel contesto urbano
The POG technique for Modelling Multi-phase Permanent Magnet Synchronous Motors
No full textIn the paper the Power-Oriented Graphs (POG) technique is used for modelling n-phase permanent magnet synchronous motors. The POG technique is a graphical modelling technique which uses only two basic blocks (the elaboration and connection blocks) for modelling physical systems. Its main characteristics are the following: it keeps a direct correspondence between pairs of system variables and real power flows; the POG blocks represent real parts of the system; it is suitable for representing physical systems both in scalar and vectorial fashion; the POG schemes can be easily transformed, both graphically and mathematically; the POG schemes are simple, modular, easy to use and suitable for education. The POG model of the considered electrical motor shows very well, from a ``power'' point of view, its internal structure: the electric part of the motor interacts with the mechanical part by means of a ``connection'' block which neither store nor dissipate energy. The dynamic model of the motor is as general as possible and it considers an arbitrary odd number of phases and an arbitrary number of harmonics of the rotor flux waveform. Generalized orthonormal transformations allow to write the dynamic equations of the system in a very compact way. The model is finally implemented with Matlab/Simulink software. The Simulink structure of the motor clearly reflects its POG representation. Simulation results are then presented to validate the machine model
Multi-phase Synchronous Motors: POG Modeling and Optimal Shaping of the Rotor Flux
No full textIn the paper the Power-Oriented Graphs (POG) technique is used for modelling m-phase permanent magnet synchronous motors and a study on the rotor flux is given. The POG model of the considered electrical motor shows its internal structure from a ``power'' point of view. The dynamic model of the motor is as general as possible and it considers an arbitrary odd number of phases. Generalized orthonormal transformations allow to write the dynamic equations of the system in a very compact form. The rotor flux is analyzed, in particular in order to minimize currents needed for the torque generation. An optimal shape for the rotor flux is presented. The model is finally implemented in Matlab/Simulink and some simulations are carried out
CORONAE, STEPHANAI E DIADEMATA. MANUFATTI PER IL CAPO E SIMBOLI DEL POTERE FEMMINILE (DA LIVIA A ELIA ARIADNE)
No full textCoronae, stephanai e diademata sono gli attributi più evidenti nella ritrattistica femminile di età imperiale e si configurano non solo come gioielli, ma anche come veicolo di informazioni. Obiettivo del presente lavoro è dimostrare come tali manufatti siano significativi indizi del rango e della posizione delle donne della famiglia imperiale, poiché legati al titolo di Augusta e alla legittimazione del potere grazie al ruolo delle donne come madri. Attraverso lo studio di un campione di ritratti pertinenti alla statuaria, alla glittica e alla numismatica, si propone una tipologia degli attributi e si affronta la loro analisi in relazione ai singoli soggetti, alle diverse dinastie e ai contesti in cui sono utilizzati. La ricerca ha sviluppo diacronico e copre il periodo compreso fra Livia ed Elia Ariadne.Coronae, stephanai and diademata are the clearest feautures in Roman female portraiture and they emerge not only as jewels, but also as a way to convey information. Aim of this work is to demonstrate how these artifacts are substantial clues to understand roles and positions of the female part of Roman Imperial families, since they are connected to the title of Augusta and to the dynastic legitimacy, thanks to female role as mothers of emperors. A catalogue of portraits from statuary, glyptic and numismatic leads to a tipology of these objects and to their analysis regarding single persons, dynasties and backgrounds. The study goes from Livia to Aelia Ariadne
Qualitative graphical representation of Nyquist plots
No full textIn this paper, the procedure for manually drawing the Nyquist plot of a generic transfer function is revised and, in particular, two novel parameters (ΔτΔτ, ΔpΔp), which allow to simplify this process, are presented. Thanks to these parameters, the analysis of the frequency response at low and high frequencies is considerably enhanced, with a very little effort. These parameters allow to predict initial and final directions of the polar curve in the vicinity of initial and final points and consequently the sectors of the complex plane where the plot starts/ends. In many cases it is possible to obtain a qualitative Nyquist plot, able to correctly predict the stability properties of the closed-loop system, by simply joining the initial and final tracts found with the proposed procedure. Moreover, the analysis based on these parameters can aid to correctly interpret the plots obtained with computer programs which often, in particular when poles at the origin are present, hide the behavior of the frequency response in the area close to the origin of the complex plane
Dynamic Behavior of Multi-phase Asynchronous Motors
No full textThe goal of this paper is the analysis of the dynamic behavior of a multi-phase asynchronous motor. The Power-Oriented Graphs technique has been used for modeling the system and a very simple and compact model has been obtained. The steady-state equations of the system have been studied finding remarkable relations between the motor voltage and current vectors. The eigenvalues of the electrical part of the motor have been mathematically expressed as function of thesystem parameters. Some simulations have been presented to validatethe effectiveness of the model
Real and complex models of multi-phase permanent magnet synchronous motors
No full textThis paper deals with the modelling of multi-phase permanent magnet synchronous machines (PMSM) with an arbitrary number of phases and arbitrary shape of the rotor flux. The aim of the paper is to propose new dynamic models for the multi-phase electrical machines based on the use of real and complex state space transformations which are invariant with respect to power. The dynamic models of the motor are obtained using a Lagrangian approach in the frame of the power-oriented graphs technique. The obtained dynamic models can directly be implemented in Simulink whatever the number of phase is. The state space transformations presented in the paper (both real and complex) are compared to the main other transformations know in the literature. Some simulation results are finally presented
Extended and reduced POG dynamic model of an automatic corking machine for threaded plastic caps
No full textThe aim of this work is to show how the modeling of an
electromechanical system can be addressed using the energy-based graphical modeling technique named “Power-Oriented Graphs” (POG). Differences and analogies of POG against Bond Graphs modeling technique are discussed. The paper presents the POG dynamic model of an automatic corking machine for threaded plastic caps: the system is composed by two electric motors moving a ball screw/spline that realizes the linear/rotary motion necessary to screw a plastic cap on a bottle. First an extended POG model is presented, together with
the equivalent Bond Graph model, then some proper congruent state space transformations and a POG-based graphical method are introduced to transform and reduce the system dynamic model. Simulation and experimental results are finally presented and compared
Open and closed logarithmic Nyquist plots
No full textThe Nyquist plot is a fundamental tool in the investigation of the stability of control systems. Usually Nyquist polar diagrams are plotted in a linear scale and often, in particular when poles at the origin are present, the diagrams need different levels of magnification in order to inspect the behavior of the frequency response in the areas very close to or very far from the origin of the complex plane. In this paper a new logarithmic Nyquist plot is proposed where the amplitude is in a logarithmic scale and the diagram is entirely contained and shown in a circle of finite radius. This method does not need to zoom in or zoom out the plot. All the considerations made by Nyquist stability criterion can be done with this plot which maintains all the properties of polar plots such as gain and phase margins, intersection points with the real axis, encirclements of the critical point. The design of first order lead and lag compensators can be done on this diagram in a simple way. The proposed new Nyquist plot is implemented in a Matlab function available to users
Energetic Model of the Tire-Ground Interaction and Comparison with LuGre Friction Model
No full textIn this paper the energetic dynamic model of the tire-ground interaction in a vehicle is presented and a comparison with the LuGre friction model is given. The Power-Oriented Graphs (POG) technique is exploited for both representing and analyzing the two dynamic systems. In particular the LuGre model is analyzed showing some drawbacks and a modified model is proposed in order to guarantee dissipativity. Simulation results end the paper comparing the two dynamic models of the tire-ground interaction
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