1,119 research outputs found
On the occurrence and detectability of Bose-Einstein condensation in helium white dwarfs
It has been recently proposed that helium white dwarfs may provide promising
conditions for the occurrence of the Bose-Einstein condensation. The argument
supporting this expectation is that in some conditions attained in the core of
these objects, the typical De Broglie wavelength associated with helium nuclei
is of the order of the mean distance between neighboring nuclei. In these
conditions the system should depart from classical behavior showing quantum
effects. As helium nuclei are bosons, they are expected to condense.
In order to explore the possibility of detecting the Bose-Einstein
condensation in the evolution of helium white dwarfs we have computed a set of
models for a variety of stellar masses and values of the condensation
temperature. We do not perform a detailed treatment of the condensation process
but mimic it by suppressing the nuclei contribution to the equation of state by
applying an adequate function. As the cooling of white dwarfs depends on
average properties of the whole stellar interior, this procedure should be
suitable for exploring the departure of the cooling process from that predicted
by the standard treatment.
We find that the Bose-Einstein condensation has noticeable, but not dramatic
effects on the cooling process only for the most massive white dwarfs
compatible with a helium dominated interior (\approx 0.50 M_\odot) and very low
luminosities (say, Log(L/L_\odot) < -4.0). These facts lead us to conclude that
it seems extremely difficult to find observable signals of the Bose-Einstein
condensation.
Recently, it has been suggested that the population of helium white dwarfs
detected in the globular cluster NGC 6397 is a good candidate for detecting
signals of the Bose-Einstein condensation. We find that these stars have masses
too low and are too bright to have an already condensed interior.Comment: 13 pages, 3 figures, 2 tables, accepted for publication in the
Journal of Cosmology and Astroparticle Physics (JCAP
An evolutionary model for the gamma-ray system PSR J1311-3430 and its companion
The most recent member of the millisecond pulsar with very low-mass
companions and short orbital periods class, PSR J1311-3430 (Pletsch et al.
2012) is a remarkable object in various senses. Besides being the first
discovered in gamma-rays, its measured features include the very low or absent
hydrogen content. We show in this Letter that this important piece of
information leads to a very restricted range of initial periods for a given
donor mass. For that purpose, we calculate in detail the evolution of the
binary system self-consistently, including mass transfer and evaporation,
finding the features of the new evolutionary path leading to the observed
configuration. It is also important to remark that the detailed evolutionary
history of the system naturally leads to a high final pulsar mass, as it seems
to be demanded by observations.Comment: 5 pages, 5 figures, 1 table. Accepted for publication in MNRAS
Letter
Effect of Scatterering on Coherent Anti-Stokes Raman Scattering (CARS) signals
We develop a computational framework to examine the factors responsible for
scattering-induced distortions of coherent anti-Stokes Raman scattering (CARS)
signals in turbid samples. We apply the Huygens-Fresnel Wave-based Electric
Field Superposition (HF-WEFS) method combined with the radiating dipole
approximation to compute the effects of scattering-induced distortions of focal
excitation fields on the far-field CARS signal. We analyze the effect of
spherical scatterers, placed in the vicinity of the focal volume, on the CARS
signal emitted by different objects (2{\mu}m diameter solid sphere, 2{\mu}m
diameter myelin cylinder and 2{\mu}m diameter myelin tube). We find that
distortions in the CARS signals arise not only from attenuation of the focal
field but also from scattering-induced changes in the spatial phase that
modifies the angular distribution of the CARS emission. Our simulations further
show that CARS signal attenuation can be minimized by using a high numerical
aperture condenser. Moreover, unlike the CARS intensity image, CARS images
formed by taking the ratio of CARS signals obtained using x- and y-polarized
input fields is relatively insensitive to the effects of spherical scatterers.
Our computational framework provide a mechanistic approach to characterizing
scattering-induced distortions in coherent imaging of turbid media and may
inspire bottom-up approaches for adaptive optical methods for image correction.Comment: 15 pages, 7 figure
The evolutionary status of the white dwarf companion of the binary pulsar PSR J1713+0747
Splaver and coworkers have measured the masses of the white dwarf and the neutron star components of the PSR J1713+0747 binary system pair by Shapiro Delay. We attempt to find the original configuration of this system performing a set of binary evolution calculations to simultaneously account for the masses of both stars and the orbital period. We considered initial masses of 1.5 and 1.4 \msun for the normal (donor) and the neutron star, respectively. We assumed two metallicity values (Z = 0.010 and 0.020), and an initial orbital period near 3 days. We assume that the neutron star is only able to retain \lesssim 0.10 of the matter transferred by the donor star. Calculations were performed employing our binary hydro code that handles the mass transfer rate in a fully implicit way together with state-of-the-art physical ingredients, diffusion and a non-grey atmospheres. We compare the structure of the resulting white dwarfs with the characteristic age of PSR J1713+0747 finding a nice agreement with observations by Lundgren et al. especially for the case of a donor star with Z= 0.010. This result indicates that the evolution of this kind of binary system is well understood. The models predict that, due to diffusion, the atmosphere of the white dwarf is an almost hydrogen-pure one. We find that such structures are unable to account for the colours measured by Lundgren et al. within their error bars. Thus, some discrepances in the white dwarf emergent radiation remain to be explained
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Dynamic neural network architectures for on field stochastic calibration of indicative low cost air quality sensing systems
In the last few years, the interest in the development of new pervasive or mobile implementations of air quality multisensor devices has significantly grown. New application opportunities appeared together with new challenges due to limitations in dealing with rapid pollutants concentrations transients both for static and mobile deployments. In this work, we propose a Dynamic Neural Network (DNN) approach to the stochastic prediction of air pollutants concentrations by means of chemical multisensor devices. DNN architectures have been devised and tested in order to tackle the cross sensitivities issues and sensors inherent dynamic limitations. Testing have been performed using an on-field recorded dataset from a pervasive deployment in Cambridge (UK), encompassing several weeks. The results obtained with the dynamic model are compared with the response of the static neural network and the performance analysis indicates the capability of the on-field dynamic multivariate calibration to ameliorate the static calibration approach performance in this real world air quality monitoring scenario. Interestingly, results analysis also suggests that the improvements are more significant when pollutants concentration changes more rapidly.This work has been supported by an STSM (Short Term Scientific Mission) grant from COST Action TD1105 EuNetAir
Association between alleles of the waxy gene and traits of grain quality in Philippine Seed Board rice varieties
The association between alleles of the Waxy gene, defined by the number of CT repeats on exon 1, and traits of grain quality was carried out using 47 Philippine Seed Board rice varieties. The major alleles of the Waxy gene in the set of 47 were (CT), (CT) (CT)and (CT)20. Varieties were divided into four clusters based on the metric of each trait of grain quality. (CT) (27-32% amylose content (AC)) and (CT) (22-30% AC) were mainly in clusters 3 and 4 (hard texture), and (CT) (20-24% AC) and (CT) (18- 27% AC) were exclusively in grain quality cluster 1 (soft texture) and 2 (medium texture). (CT) associated negatively with AC in this set. Only six (CT) and one (CT) rices were in cluster 4 (high-AC low-GT) and had high RVA consistency (final viscosity - trough viscosity) > 200 RVU. (CT) seemed to be the preferred source of low-intermediate AC in the Philippine rice breeding program, followed by (CT)
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