arXiv subjects

C. Frajuca

Publications and source records attributed to C. Frajuca.

7 recordsLinked to original sources

arXiv2023

The Design Strain Sensitivity of the Schenberg Spherical Resonant Antenna for Gravitational Waves

The main purpose of this study is to review the Schenberg resonant antenna transfer function and to recalculate the antenna design strain sensitivity for gravitational waves. We consider the spherical antenna with six transducers in the semi dodecahedral configuration. When coupled to the antenna, the transducer-sphere system will work as a mass-spring system with three masses. The first one is the antenna effective mass for each quadrupole mode, the second one is the mass of the mechanical structure of the transducer first mechanical mode and the third one is the effective mass of the transducer membrane that makes one of the transducer microwave cavity walls. All the calculations are done for the degenerate (all the sphere quadrupole mode frequencies equal) and non-degenerate sphere cases. We have come to the conclusion that the 'ultimate' sensitivity of an advanced version of Schenberg antenna (aSchenberg) is around the standard quantum limit (although the parametric transducers used could, in principle, surpass this limit). However, this sensitivity, in the frequency range where Schenberg operates, has already been achieved by the two aLIGOs in the O3 run, therefore, the only reasonable justification for remounting the Schenberg antenna and trying to place it in the sensitivity of the standard quantum limit would be to detect gravitational waves with another physical principle, different from the one used by laser interferometers. This other physical principle would be the absorption of the gravitational wave energy by a resonant mass like Schenberg.

astro-ph.IM↗

arXiv2019

The Laser Gravitational Compass

Using the observational properties of Einstein's gravitational field it is shown that a minimum of four non-coplanar mass probes are necessary for the Michelson and Morley interferometer to detect gravitational waves within the context of General Relativity. With fewer probes, some alternative theories of gravitation can also explain the observations. The conversion of the existing gravitational wave detectors to four probes is also suggested.

gr-qc↗

arXiv2019

$α$-cluster structure above double-shell closures and $α$-decay of $^{104}$Te

An analysis of the $α$ + core properties of $^{104}$Te along with a global discussion on the $α$-cluster structure above the double-shell closures is presented from the viewpoint of the local potential model. The $α$ + core interaction is described by a nuclear potential of (1 + Gaussian)$\times$(W.S. + W.S.$^3$) shape with two free parameters, which has been successfully tested in nuclei of different mass regions. The model produces $Q_α$ values and $α$-decay half-lives for $^{104}$Te in agreement with the 2018 experimental data of Auranen et al. in the energy range $5.13 \; \mathrm{MeV} < Q_α < 5.3 \; \mathrm{MeV}$ using an $α$ preformation factor $P_α = 1$. The comparison of the calculated reduced $α$-widths for the ground state bands of $^{104}$Te, $^{94}$Mo and $^{212}$Po indicates that $^{104}$Te has an $α$-cluster degree significantly higher than $^{94}$Mo and much higher than $^{212}$Po. These results point to $^{104}$Te as a preferential nucleus for $α$-clustering in the $N,Z = 50$ region and corroborate the statement on the superallowed $α$-decay in $^{104}$Te.

nucl-th↗

arXiv2018

Relating Braking Indices of Young Pulsars to the Dynamics of Superfluid Cores

Pulsars are stars that emit electromagnetic radiation in well-defined time intervals. The frequency of such pulses decays with time as is quantified by the {\it braking index} ($n$). In the canonical model $n = 3$ for all pulsars, but observational data show that $n \neq 3$, indicating a limitation of the model. In this work we present a new approach to study the frequency decay of the rotation of a pulsar, based on an adaptation of the canonical one. We consider the pulsar a star that rotates in vacuum and has a strong magnetic field but, differently from the canonical model, we assume that its moment of inertia changes in time due to a uniform variation of a displacement parameter in time. We found that the braking index results smaller than the canonical value as a consequence of an increase in the star's displacement parameter, whose variation is small enough to allow plausible physical considerations that can be applied to a more complex model for pulsars in the future. In particular, this variation is of the order of neutron vortices' creep in rotating superfluids. When applied to pulsar data our model yielded values for the stars' braking indices close to the observational ones. The application of this approach to a more complex star model, where pulsars are assumed to have superfluid interiors, is the next step in probing it. We hypothesize that the slow expansion of the displacement parameter might mimic the motion of core superfluid neutron vortices in realistic models.

astro-ph.HE↗

arXiv2016

Geometrical Aspects of Venus Transit

We obtained two astronomical values, the Earth-Venus distance and Venus diameter, by means of a geometrical treatment of photos taken of Venus transit in June of 2012. Here we presented the static and translational modelsthat were elaborated taking into account the Earth and Venus orbital movements. An additional correction was also added by considering the Earth rotation movement. The results obtained were compared with the values of reference from literature, showing very good concordance.

physics.gen-ph↗

arXiv2016

Braking indices of pulsars obtained in the presence of an effective force

Braking indices of pulsars present a scientific challenge as their theoretical calculation is still an open problem. In this paper we report results of a study regarding such calculation which adapts the canonical model (which admits that pulsars are rotating magnetic dipoles) basically by introducing a compensating component in the energy conservation equation of the system. This component would correspond to an effective force that varies with the first power of the tangential velocity of the pulsar's crust. We test the proposed model using data available and predict braking indices values for different stars. We comment on the high braking index recently measured of the pulsar J1640-4631.

astro-ph.HE↗

arXiv2005

Can lightning be a noise source for a spherical gravitational wave antenna?

The detection of gravitational waves is a very active research field at the moment. In Brazil the gravitational wave detector is called Mario SCHENBERG. Due to its high sensitivity it is necessary to model mathematically all known noise sources so that digital filters can be developed that maximize the signal-to-noise ratio. One of the noise sources that must be considered are the disturbances caused by electromagnetic pulses due to lightning close to the experiment. Such disturbances may influence the vibrations of the antenna's normal modes and mask possible gravitational wave signals. In this work we model the interaction between lightning and SCHENBERG antenna and calculate the intensity of the noise due to a close lightning stroke in the detected signal. We find that the noise generated does not disturb the experiment significantly.

gr-qc↗