1,721,146 research outputs found
Il Principio Antropico fra il dominio della scienza e quello della filosofia
No full textViene ripresa la rassegna storica fatta da Barrow e Tipler sull'origine del principio Antropico e sulle sue varie formulazioni. La loro analisi critica porta ad una rifocalizzazione del Principio cercando di tenere distinto l'ambito della Scienza da quello della Trascendenza
Gravitomagnetic resonance in the field of a gravitational wave
Full text linkUsing the construction of the Fermi frame, the field of a gravitational wave can be described in terms of gravitoelectromagnetic fields that are transverse to the propagation direction and orthogonal to each other. In particular, the gravitomagnetic field acts on spinning particles and we show that, due to the action of the gravitational-wave field, a new phenomenon - which we call gravitomagnetic resonance - may appear. We give both a classical and a quantum description of this phenomenon and suggest that it can be used as the basis for a new type of gravitational-wave detectors. Our results highlight the effectiveness of collective spin excitations, e.g., spin waves in magnetized materials, in detecting high-frequency gravitational waves. Here we suggest that, when gravitational waves induce a precession of the electron spin, power is released in the ferromagnetic resonant mode endowed with quadrupole symmetry of a magnetized sphere. This offers a possible path to the detection of the gravitomagnetic effects of a gravitational wave
Inflation in the Scaling Limit
No full textWe investigate the stochastic dynamics of the inflaton for a wide class of potentials leading either to chaotic or to power-law inflation. At late times the system enters a scaling regime where macroscopic order sets in: the field distribution sharply peaks around the classical slow-rollover configuration and curvature perturbations originate with a non-Gaussian scale-invariant statistics
Non-Gaussian Perturbations from Inflationary Dynamics
No full textThe dynamics of the scalar field driving inflation can be described as a Brownian motion under the influence of a classical force arising from its self-interactions. Fluctuations of the inflaton on large scales give rise to density perturbations. If the inflaton potential is not too flat, as in models of nonexponential inflation, these perturbations can be non-Gaussian. In a power-law inflation with an exponential potential non-Gaussian scale-invariant adiabatic perturbations are rapidly produced
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Quadrupole effects on the motion of extended bodies in Schwarzschild spacetime
No full textThe motion of an extended body up to the quadrupolar structure is studied in the Schwarzschild background following Dixon's model and within certain restrictions (constant frame components for the spin and the quadrupole tensor, center of mass moving along a circular orbit, etc). We find a number of interesting situations in which deviations from the geodesic motion, due to the internal structure of the particle, can originate measurable effects. However, the standard clock effect for a pair of co/counter-rotating bodies spinning up/down is not modified by the quadrupolar structure of the particle. © 2008 IOP Publishing Ltd
Quadrupole effects on the motion of extended bodies in Kerr spacetime
No full textThe motion of a body endowed with a dipolar as well as a quadrupolar structure is investigated in the Kerr background according to the Dixon model, extending a previous analysis done in the Schwarzschild background. The full set of evolution equations is solved under the simplifying assumptions of constant frame components for both the spin and the quadrupole tensors and that the center of mass moves along an equatorial circular orbit, the total 4-momentum of the body being aligned with it. We find that the motion deviates from the geodesic one due to the internal structure of the body, leading to measurable effects. Corrections to the geodesic value of the orbital period of a close binary system orbiting the galactic center are discussed assuming that the galactic center is a Kerr supermassive black hole
Cavity magnon polariton based precision magnetometry
No full textA photon-magnon hybrid system can be realized by coupling the electron spin resonance of a magnetic material to a microwave cavity mode. The quasiparticles associated with the system dynamics are the cavity magnon polaritons, which arise from the mixing of strongly coupled magnons and photons. We illustrate how these particles can be used to probe the magnetization of a sample with a remarkable sensitivity, devising suitable spin-magnetometers, which ultimately can be used to directly assess oscillating magnetic fields. Specifically, the capability of cavity magnon polaritons of converting magnetic excitations to electromagnetic ones allows for translating to magnetism the quantum-limited sensitivity achieved by state-of-the-art microwave detectors. Here, we employ hybrid systems composed of microwave cavities and ferrimagnetic spheres to experimentally implement two types of novel spin-magnetometer
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