959 research outputs found
Synchronization Gauges and the Principles of Special Relativity
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.Comment: 56 pages, 3 eps figures, invited paper; to appear in Foundations of
Physics (Special Issue to honor Prof. Franco Selleri on his 70th birthday
Corona poling for polarization of nanofibrous mats: advantages and open issues
This paper deals with the polarization process of piezoelectric nanofibrous mats of PVdF-TrFE by using a corona discharge process. With respect to traditional contact poling this process reduces the electrical breakdown risk which could easily occur when a highly porous mat is placed between two solid electrodes. Different set-up configurations were investigated by varying the applied voltage and the distance between the needle and the sample. The polarized nanofibers show a piezoelectric strain coefficients (mathrmd_33) comparable with the values of a commercial stiff film
Investigation on Harmonic Tuning for Active Ku-Band Rectangular Dielectric Resonator Antennas
A slot-coupled rectangular dielectric resonator antenna (DRA) operating in the 14–14.5 GHz frequency band is investigated as a possible radiating element for an active integrated antenna of a transmitting phased array. The effectiveness of the resonator shape factor on achieving harmonic tuning is addressed. Simulation results show that the DRA shape factor can be used to provide a fine tuning of the DRA input impedance both at the fundamental frequency and its first harmonics, so synthesizing the proper load for the optimization of the microwave amplifier power-added efficiency (PAE)
Michael Faraday e James Clerk Maxwell: i giorni fiorentini [Michael Faraday and James Clerk Maxwell: The Florentine days]
Does Clauser-Horne-Shimony-Holt Correlation or Freedman-Clauser Correlation lead to the largest violation of Bell's Inequality?
An inequality is deduced from Einstein's locality and a supplementary
assumption. This inequality defines an experiment which can actually be
performed with present technology to test local realism. Quantum mechanics
violate this inequality a factor of 1.5. In contrast, quantum mechanics
violates previous inequalities (for example, Clauser-Horne-Shimony-Holt
inequality of 1969, Freedman-Clauser inequality of 1972, Clauser-Horne
inequality of 1974) by a factor of . Thus the magnitude of violation
of the inequality derived in this paper is approximately larger than
the magnitude of violation of previous inequalities. This result can be
particularly important for the experimental test of locality.Comment: 15 pages, LaTeX file, no figure
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