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Search Results: 1 - 10 of 3065 matches for " Guido Rizzi "
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Space geometry of rotating platforms: an operational approach
Guido Rizzi,Matteo Luca Ruggiero
Physics , 2002, DOI: 10.1023/A:1020427318877
Abstract: We study the space geometry of a rotating disk both from a theoretical and operational approach, in particular we give a precise definition of the space of the disk, which is not clearly defined in the literature. To this end we define an extended 3-space, which we call relative space: it is recognized as the only space having an actual physical meaning from an operational point of view, and it is identified as the 'physical space of the rotating platform'. Then, the geometry of the space of the disk turns out to be non Euclidean, according to the early Einstein's intuition; in particular the Born metric is recovered, in a clear and self consistent context. Furthermore, the relativistic kinematics reveals to be self consistent, and able to solve the Ehrenfest's paradox without any need of dynamical considerations or ad hoc assumptions.
The Sagnac Phase Shift suggested by the Aharonov-Bohm effect for relativistic matter beams
Guido Rizzi,Matteo Luca Ruggiero
Physics , 2003, DOI: 10.1023/A:1026053828421
Abstract: The phase shift due to the Sagnac Effect, for relativistic matter beams counter-propagating in a rotating interferometer, is deduced on the bases of a a formal analogy with the the Aharonov-Bohm effect. A procedure outlined by Sakurai, in which non relativistic quantum mechanics and newtonian physics appear together with some intrinsically relativistic elements, is generalized to a fully relativistic context, using the Cattaneo's splitting technique. This approach leads to an exact derivation, in a self-consistently relativistic way, of the Sagnac effect. Sakurai's result is recovered in the first order approximation.
The relativistic Sagnac Effect: two derivations
Guido Rizzi,Matteo Luca Ruggiero
Physics , 2003,
Abstract: The phase shift due to the Sagnac Effect, for relativistic matter and electromagnetic beams, counter-propagating in a rotating interferometer, is deduced using two different approaches. From one hand, we show that the relativistic law of velocity addition leads to the well known Sagnac time difference, which is the same independently of the physical nature of the interfering beams, evidencing in this way the universality of the effect. Another derivation is based on a formal analogy with the phase shift induced by the magnetic potential for charged particles travelling in a region where a constant vector potential is present: this is the so called Aharonov-Bohm effect. Both derivations are carried out in a fully relativistic context, using a suitable 1+3 splitting that allows us to recognize and define the space where electromagnetic and matter waves propagate: this is an extended 3-space, which we call "relative space". It is recognized as the only space having an actual physical meaning from an operational point of view, and it is identified as the 'physical space of the rotating platform': the geometry of this space turns out to be non Euclidean, according to Einstein's early intuition.
A direct kinematical derivation of the relativistic Sagnac effect for light or matter beams
Guido Rizzi,Matteo Luca Ruggiero
Physics , 2003, DOI: 10.1023/A:1027345505786
Abstract: The Sagnac time delay and the corresponding Sagnac phase shift, for relativistic matter and electromagnetic beams counter-propagating in a rotating interferometer, are deduced on the ground of relativistic kinematics. This purely kinematical approach allows to explain the ''universality'' of the effect, namely the fact that the Sagnac time difference does not depend on the physical nature of the interfering beams. The only prime requirement is that the counter-propagating beams have the same velocity with respect to any Einstein synchronized local co-moving inertial frame.
Synchronization Gauges and the Principles of Special Relativity
Guido Rizzi,Matteo Luca Ruggiero,Alessio Serafini
Physics , 2004, DOI: 10.1007/s10701-004-1624-3
Abstract: The axiomatic bases of Special Relativity Theory (SRT) are thoroughly re-examined from an operational point of view, with particular emphasis on the status of Einstein synchronization in the light of the possibility of arbitrary synchronization procedures in inertial reference frames. Once correctly and explicitly phrased, the principles of SRT allow for a wide range of `theories' that differ from the standard SRT only for the difference in the chosen synchronization procedures, but are wholly equivalent to SRT in predicting empirical facts. This results in the introduction, in the full background of SRT, of a suitable synchronization gauge. A complete hierarchy of synchronization gauges is introduced and elucidated, ranging from the useful Selleri synchronization gauge (which should lead, according to Selleri, to a multiplicity of theories alternative to SRT) to the more general Mansouri-Sexl synchronization gauge and, finally, to the even more general Anderson-Vetharaniam-Stedman's synchronization gauge. It is showed that all these gauges do not challenge the SRT, as claimed by Selleri, but simply lead to a number of formalisms which leave the geometrical structure of Minkowski spacetime unchanged. Several aspects of fundamental and applied interest related to the conventional aspect of the synchronization choice are discussed, encompassing the issue of the one-way velocity of light on inertial and rotating reference frames, the GPS's working, and the recasting of Maxwell equations in generic synchronizations. Finally, it is showed how the gauge freedom introduced in SRT can be exploited in order to give a clear explanation of the Sagnac effect for counter-propagating matter beams.
Building pattern recognition applications with the SPARE library
Lorenzo Livi,Guido Del Vescovo,Antonello Rizzi,Fabio Massimo Frattale Mascioli
Computer Science , 2014,
Abstract: This paper presents the SPARE C++ library, an open source software tool conceived to build pattern recognition and soft computing systems. The library follows the requirement of the generality: most of the implemented algorithms are able to process user-defined input data types transparently, such as labeled graphs and sequences of objects, as well as standard numeric vectors. Here we present a high-level picture of the SPARE library characteristics, focusing instead on the specific practical possibility of constructing pattern recognition systems for different input data types. In particular, as a proof of concept, we discuss two application instances involving clustering of real-valued multidimensional sequences and classification of labeled graphs.
A instabilidade contínua na Guiné-Bissau
Kamilla Rizzi
Meridiano 47 : Boletim de Análise de Conjuntura em Rela??es Internacionais , 2010,
Abstract: Pouco mais de um ano após os assassinatos políticos que chocaram a comunidade internacional, uma nova tentativa de golpe militar ocorreu na Guiné-Bissau, em 1o de abril passado. A contínua instabilidade política guineense vem desde a independência, em 1973.
Comunicación mediática y consenso democrático. Una investigación sobre las transformaciones de la obligación política
Lino Rizzi
Revista mexicana de ciencias políticas y sociales , 2003,
Abstract: En este artículo, el autor realiza un análisis filosófico-político de la disociación entre la noción política de ciudadanía y la comunicación mediática, con el propósito de comprender el estatus político del derecho a la expresión pública. En el trabajo se sostiene que la comunicación ya no es más un acto político y por ello ya no conserva la característica imprescindible llamada performabilidad, que abarca la polémica, la visibilidad, la accesibilidad, la posibilidad de preguntar, de replicar y de discutir. En este tenor, el autor destaca que mientras en las constituciones la definición de ciudadanía está anclada a un carácter asociativo y discursivo, los nuevos medios de comunicación hacen posible la desarticulación de la implicación antropológica necesaria en el acto comunicativo; esto porque tal parece que la reunión pública ya no es una necesidad humana para realizar el intercambio de ideas y para formar y conformar las opiniones, pues los medios de comunicación están invadiendo este espacio. Como consecuencia, existe una contradicción entre el sistema democrático y las prácticas de comunicación sin participación pública.
The Meaning of Bell's Theorem
Anthony Rizzi
Physics , 2003,
Abstract: The import of Bell's Theorem is elucidated. The theorem's proof is illustrated both heuristically and in mathematical detail in a pedagogical fashion. In the same fashion, it is shown that the proof is correct mathematically, but it doesn't require, as is usually thought, one to abandon locality or realism.
Angular and Linear Momentum in General Relativity: Their Geometric Structure and Interrelation
Anthony Rizzi
Physics , 2002,
Abstract: Generalized definitions for angular and linear momentum are given and shown to reduce to the ADM (at spatial infinity) definitions and the definitions at null infinity in the appropriate limit. These definitions are used to express angular momentum in terms of linear momentum. The formalism allows one to see the connection with the classical and special relativitistic notions of momenta. Further, the techniques elucidate, for the first time, the geometric nature of these conserved quantities. The boosted Schwarzschild solution is used to illustrate some aspects. The definitions are useful and give insight in the region far from all masses where gravity waves are detected.
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