1,720,988 research outputs found
Fundamental times, lengths and physical constants: Some unknown contributions by Ettore Majorana
No full textWe review the introduction in physics of the concepts of an elementary space length and of a fundamental time scale, analyzing some related unknown contributions by Ettore Majorana. In particular, we discuss the quasi-Coulombian scattering in presence of a finite length scale, as well as the introduction of an intrinsic (universal) time delay in the expressions for the retarded electromagnetic potentials. Finally, we also review a special model considered by Majorana in order to deduce the value of the elementary charge, in such a way anticipating key ideas later introduced in quantum electrodynamics. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei
CPT-VIOLATING NEUTRINO OSCILLATIONS
No full textWe propose a simple phenomenological model predicting, through Lorentz symmetry breaking, a CPT-violating asymmetry between particle and antiparticle states in neutrino oscillations involving sterile neutrinos. Such a model is able to explain the apparently observed anomalous excess of low-energy upsilon(e-)like events, reported by the MiniBooNE collaboration, as well as the non-observation of the corresponding anomalous excess of upsilon(e-)like events. The present model leads to very specific physical predictions in the neutrino oscillations scenario, and account for the observed anomalies in terms of only one CPT-Lorentz violation parameter of the order of the Grand-Unification energy scale
Black hole dynamical evolution in a Lorentz-violating spacetime
No full textWe consider the black hole dynamical evolution in the framework of a Lorentz-violating spacetime endowed with a Schwarzchild-like momentum-dependent metric. Large deviations from the Hawking-Bekenstein predictions are obtained, depending on the values of the Lorentz-violating parameter lambda introduced. A nontrivial evolution comes out, following mainly from the existence of a nonvanishing minimum mass: for large Lorentz violations, most of the black hole evaporation takes place in the initial stage, which is then followed by a stationary stage (whose duration depends on the value of lambda) where the mass does not change appreciably. Furthermore, for the final stage of evolution, our model predicts a sweet slow death of the black hole, whose "slowness'' again depends on lambda, in contrast with the violent final explosion predicted by the standard theory
Magnetic properties of two-phase superconductors
No full textWe have recently proposed a theoretical model for superconductors endowed with two distinct superconducting phases, described by two scalar order parameters which condensate at different critical temperatures. On analyzing the magnetic behavior of such systems, we have found some observable differences with respect to the case of ordinary Ginzburg-Landau superconductors. In particular, at low temperature the London penetration length is strongly reduced and the Ginzburg-Landau parameter K becomes a function of temperature. By contrast, in the temperature region between the two-phase transitions K is constant and the system is a type-I or a type-II superconductor depending on the ratio between the critical temperatures. (c) 2008 Elsevier B.V. All rights reserved
Describing Sr2RuO4 superconductivity in a generalized Ginzburg-Landau theory
No full textWe propose a simple explanation of unconventional thermodynamical and magnetic properties observed for Sr2RuO4. Actually, our two-phase model of superconductivity, based on a straight generalization of the Ginzburg-Landau theory, does predict two jumps in the heat capacity as well as a double curve for the dependence of the critical temperature on an external magnetic field. Such theoretical previsions well agree with the currently available experimental data for Sr2RuO4. (C) 2009 Elsevier B.V. All rights reserved
A generalization of the Ginzburg-Landau theory to p-wave superconductors
No full textWe succeed in building up a straightforward theoretical model for spin-triplet p-wave superconductors, by introducing a second-order parameter and a nonlinear interaction between the two mean fields in the Ginzburg Landau theory. Such interaction breaks the isotropy of the original medium and allows pairs of electrons to arrange into S = 1 Cooper pairs. The present model predicts a thermodynamical and magnetic behavior analogous to that observed in conventional s-wave superconductors
A new dielectric effect in viscous liquids
No full textAn accurate experimental and theoretical study has been performed about a phenomenon, not previously reported in the literature, occurring in highly viscous liquids: the formation of a definite pipe structure induced by the passage of a heavy body, this structure lasting for quite a long time. A very rich phenomenology (including mechanical, optical and structural effects) associated with the formation of the pipe has been observed in different liquids. Actually, the peculiar dynamical evolution of that structure does not appear as a trivial manifestation of standard relaxation or spurious effects. In particular, we have revealed different time scales during the evolution of the pipe and a non-monotonous decrease of the persistence time with decreasing viscosity (with the appearance of at least two different maxima). We put forward a microscopic model, consistent with the experimental data, where the pipe behaves as a “dielectric shell” whose time evolution is described through a simple thermodynamical approach, predicting several properties effectively observed. © EDP Sciences 2013
Second discontinuity in the specific heat of two-phase superconductors
No full textThe recently proposed theoretical model of superconductors endowed with two distinct superconducting phases and critical temperatures is further analyzed by introducing two distinct order parameters, described by two scalar fields which condensate at different temperatures. We find some deviations in basic thermodynamical quantities with respect to the Ginzburg-Landau one-phase superconductors. In particular, in contrast to the usual case where only one jump in specific heat takes place at the normal-superconductor transition temperature, we actually predict an additional discontinuity for C-V when passing from a superconducting phase to the other one. (c) 2007 Elsevier B.V. All rights reserved
High sensitivity measurements of thermal properties of textile fabrics
No full textA new testing apparatus is proposed to measure the thermal properties of fabrics made from polymeric materials. The calibration of the apparatus and the data acquisition procedure are considered in detail in order to measure thermal conductivity, resistance, absorption and diffusivity constants of the tested fabric samples. Differences between dry and wet fabrics have been carefully detected and analyzed. We have developed a new measurement protocol, the ThermoTex protocol, which agrees with the UNI EN 31092 standard and entails accurate quantification of the experimental errors according to a standard statistical analysis, thus allowing a rigorous investigation of the physical behavior of the phenomena involved. As a consequence, our equipment exhibits great potential for optimizing the thermal comfort of fabrics, according to the market demand, thanks to the possible development of a predictive phenomenological theory of the effects involved. © 2013 Elsevier Ltd. All rights reserved
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