455 research outputs found
Galactic Globular Cluster Stars: from Theory to Observation
We use evolutionary calculations presented in a recent paper (Cassisi et al.
1998) to predict B,V,I magnitudes for stars in galactic globulars. The effect
of the adopted mixing length on stellar magnitudes and colors is discussed,
showing that the uncertainty on such a theoretical parameter prevents the use
of MS stars as bona fide theoretical standard candles. However, comparison with
Hipparcos data for field subdwarfs discloses a substantial agreement between
theory and observation. Present predictions concerning the magnitude of TO and
of HB stars are compared with similar results appeared in the recent
literature. We present and discuss a theoretical calibration of the difference
in magnitude between HB and TO as evaluated with or without element
sedimentation. Finally we use theoretical HB magnitudes to best fit the CM
diagram of M68 and M5, taken as representative of metal poor and intermediate
metallicity galactic globulars, deriving an age of 111.0 Gyr and
101.0 Gyr, respectively, for the adopted chemical compositions, plus an
additional uncertainty of 1.4 Gyr if the uncertainty on the chemical
composition is taken into account. This result is discussed on the basis of
current evaluations concerning cluster ages and distance moduli.Comment: 8 pages, 13 postscript figures, 6 postscript tables To be published
on Astronomy & Astrophysics Supplement Serie
Helioseismic constraints to the central solar temperature and neutrino fluxes
The central solar temperature T and its uncertainties are calculated in helioseismologically-constrained solar models. From the best fit to the convective radius, density at the convective radius and seismically determined helium abundance the central temperature is found to be T=1.58x10^7 K, in excellent agreement with Standard Solar Models. Conservatively, we estimate that the accuracy of this determination is Delta T/T=1.4 %, better than that in SSM. Neutrino fluxes are calculated. The lower limit to the boron neutrino flux, obtained with maximum reduction factors from all sources of uncertainties, is 2 sigma higher than the flux measured recently by SuperKamiokande
Bayesian inference of solar and stellar magnetic fields in the weak-field approximation
The weak-field approximation is one of the simplest models that allows us to
relate the observed polarization induced by the Zeeman effect with the magnetic
field vector present on the plasma of interest. It is usually applied for
diagnosing magnetic fields in the solar and stellar atmospheres. A fully
Bayesian approach to the inference of magnetic properties in unresolved
structures is presented. The analytical expression for the marginal posterior
distribution is obtained, from which we can obtain statistically relevant
information about the model parameters. The role of a-priori information is
discussed and a hierarchical procedure is presented that gives robust results
that are almost insensitive to the precise election of the prior. The strength
of the formalism is demonstrated through an application to IMaX data. Bayesian
methods can optimally exploit data from filter-polarimeters given the scarcity
of spectral information as compared with spectro-polarimeters. The effect of
noise and how it degrades our ability to extract information from the Stokes
profiles is analyzed in detail.Comment: 16 pages, 5 figures, accepted for publication in Ap
Single mode terahertz quantum cascade amplifier
A terahertz (THz) optical amplifier based on a 2.9 THz quantum cascade laser (QCL) structure has been demonstrated. By depositing an antireflective coating on the QCL facet, the laser mirror losses are enhanced to fully suppress the lasing action, creating a THz quantum cascade (QC) amplifier. Terahertz radiation amplification has been obtained, by coupling a separate multi-mode THz QCL of the same active region design to the QC amplifier. A bare cavity gain is achieved and shows excellent agreement with the lasing spectrum from the original QCL without the antireflective coating. Furthermore, a maximum optical gain of âŒ30âdB with single-mode radiation output is demonstrated
Single mode terahertz quantum cascade amplifier
A terahertz (THz) optical amplifier based on a 2.9 THz quantum cascade laser (QCL) structure has been demonstrated. By depositing an antireflective coating on the QCL facet, the laser mirror losses are enhanced to fully suppress the lasing action, creating a THz quantum cascade (QC) amplifier. Terahertz radiation amplification has been obtained, by coupling a separate multi-mode THz QCL of the same active region design to the QC amplifier. A bare cavity gain is achieved and shows excellent agreement with the lasing spectrum from the original QCL without the antireflective coating. Furthermore, a maximum optical gain of âŒ30âdB with single-mode radiation output is demonstrated
Helioseismology and standard solar models
We present a systematical analysis of uncertainties in the helioseismological
determination of quantities characterizing the solar structure. We discuss the
effect of errors on the measured frequencies, the residual solar model
dependence and the uncertainties of the inversion method. We find
Y_{ph}=0.238-0.259, and
gr/cm^3 (the index b refers to the bottom of the convective envelope). In the
interval , the quantity U=P/\rho is determined with and
accuracy of \permille or better. The predictions of a few recent solar
model calculations are compared with helioseismological results.Comment: 16 pages, 4 tables and 5 ps figures, uses tighten.sty, aps.sty and
revtex.st
Superparamagnetic iron oxide nanoparticles for magnetic hyperthermia: recent advancements, molecular effects, and future directions in the omics era
Superparamagnetic iron oxide nanoparticles (SPIONs) have attracted attention in the biomedical field thanks to their ability to prompt hyperthermia in response to an alternated magnetic field. Hyperthermia is well known for inducing cell death, in particular in tumour cells, which seem to have a higher sensitivity to temperature increases. For this reason, hyperthermia has been recommended as a therapeutic tool against cancer. Despite the potentialities of this approach, little is still known about the effects provoked by magnetic hyperthermia at the molecular level, and about the particular cell death mechanisms that are activated. Nevertheless, in-depth knowledge of this aspect would allow improvement of therapeutic outcomes and favour clinical translation. Moreover, in the last few decades, a lot of effort has been put into finding an effective delivery strategy that could improve SPION biodistribution and localisation at the action site. The aim of this review is to provide a general outline of magnetic hyperthermia, focusing on iron oxide nanoparticles and their interactions with magnetic fields, as well as on new strategies to efficiently deliver them to the target site, and on recent in vitro and in vivo studies proposing possible cell death pathways activated by the treatment. We will also cover their current clinical status, and discuss the contributions of omics in understanding molecular interactions between iron oxide nanoparticles and the biological environment
Scattering polarization of hydrogen lines in the presence of turbulent electric fields
We study the broadband polarization of hydrogen lines produced by scattering
of radiation, in the presence of isotropic electric fields. In this paper, we
focus on two distinct problems: a) the possibility of detecting the presence of
turbulent electric fields by polarimetric methods, and b) the influence of such
fields on the polarization due to a macroscopic, deterministic magnetic field.
We found that isotropic electric fields decrease the degree of linear
polarization in the scattered radiation, with respect to the zero-field case.
On the other hand, a distribution of isotropic electric fields superimposed
onto a deterministic magnetic field can generate a significant increase of the
degree of magnetic-induced, net circular polarization. This phenomenon has
important implications for the diagnostics of magnetic fields in plasmas using
hydrogen lines, because of the ubiquitous presence of the Holtsmark,
microscopic electric field from neighbouring ions. In particular, previous
solar magnetographic studies of the Balmer lines of hydrogen may need to be
revised because they neglected the effect of turbulent electric fields on the
polarization signals. In this work, we give explicit results for the
Lyman-alpha and Balmer-alpha lines.Comment: 15 pages, 6 figure
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