1,320 research outputs found
Ipopv2: Photoionization of Ni XIV -- a test case
Several years ago, M. Asplund and coauthors (2004) proposed a revision of the
Solar composition. The use of this new prescription for Solar abundances in
standard stellar models generated a strong disagreement between the predictions
and the observations of Solar observables. Many claimed that the Standard Solar
Model (SSM) was faulty, and more specifically the opacities used in such
models. As a result, activities around the stellar opacities were boosted. New
experiments (J. Bailey at Sandia on Z-Pinch, The OPAC consortium at LULI200) to
measure directly absorbtion coefficients have been realized or are underway.
Several theoretical groups (CEA-OPAS, Los Alamos Nat. Lab., CEA-SCORCG, The
Opacity Project - The Iron Project (IPOPv2)) have started new sets of
calculations using different approaches and codes. While the new results seem
to confirm the good quality of the opacities used in SSM, it remains important
to improve and complement the data currently available. We present recent
results in the case of the photoionization cross sections for Ni XIV (Ni13+ )
from IPOPv2 and possible implications on stellar modelling.Comment: 10 pages, 3 figures, Conf. on New Advances in Stellar Physics: From
Microscopic to Macroscopic Processe
Thermal denaturation of fluctuating finite DNA chains: the role of bending rigidity in bubble nucleation
Statistical DNA models available in the literature are often effective models
where the base-pair state only (unbroken or broken) is considered. Because of a
decrease by a factor of 30 of the effective bending rigidity of a sequence of
broken bonds, or bubble, compared to the double stranded state, the inclusion
of the molecular conformational degrees of freedom in a more general mesoscopic
model is needed. In this paper we do so by presenting a 1D Ising model, which
describes the internal base pair states, coupled to a discrete worm like chain
model describing the chain configurations [J. Palmeri, M. Manghi, and N.
Destainville, Phys. Rev. Lett. 99, 088103 (2007)]. This coupled model is
exactly solved using a transfer matrix technique that presents an analogy with
the path integral treatment of a quantum two-state diatomic molecule. When the
chain fluctuations are integrated out, the denaturation transition temperature
and width emerge naturally as an explicit function of the model parameters of a
well defined Hamiltonian, revealing that the transition is driven by the
difference in bending (entropy dominated) free energy between bubble and
double-stranded segments. The calculated melting curve (fraction of open base
pairs) is in good agreement with the experimental melting profile of
polydA-polydT. The predicted variation of the mean-square-radius as a function
of temperature leads to a coherent novel explanation for the experimentally
observed thermal viscosity transition. Finally, the influence of the DNA strand
length is studied in detail, underlining the importance of finite size effects,
even for DNA made of several thousand base pairs.Comment: Latex, 28 pages pdf, 9 figure
Ionic Capillary Evaporation in Weakly Charged Nanopores
Using a variational field theory, we show that an electrolyte confined to a
neutral cylindrical nanopore traversing a low dielectric membrane exhibits a
first-order ionic liquid-vapor pseudo-phase-transition from an
ionic-penetration "liquid" phase to an ionic-exclusion "vapor" phase,
controlled by nanopore-modified ionic correlations and dielectric repulsion.
For weakly charged nanopores, this pseudotransition survives and may shed light
on the mechanism behind the rapid switching of nanopore conductivity observed
in experiments.Comment: This version is accepted for publication in PR
Updated opacities from the opacity project
Using the code autostructure, extensive calculations of inner-shell atomic data have been made for the chemical elements He, C, N, O, Ne, Na, Mg, Al, Si, S, Ar, Ca, Cr, Mn, Fe and Ni. The results are used to obtain updated opacities from the Opacity Project (OP). A number of other improvements on earlier work have also been included. Rosseland-mean opacities from the OP are compared with those from OPAL. Differences of 5-10 per cent occur. The OP gives the 'Z-bump', at log(T) 5.2, to be shifted to slightly higher temperatures. The opacities from the OP, as functions of temperature and density, are smoother than those from OPAL. The accuracy of the integrations used to obtain mean opacities can depend on the frequency mesh used. Tests involving variation of the numbers of frequency points show that for typical chemical mixtures the OP integrations are numerically correct to within 0.1 per cent. The accuracy of the interpolations used to obtain mean opacities for any required values of temperature and density depends on the temperature-density meshes used. Extensive tests show that, for all cases of practical interest, the OP interpolations give results correct to better than 1 per cent. Prior to a number of recent investigations which have indicated a need for downward revisions in the solar abundances of oxygen and other elements, there was good agreement between properties of the Sun deduced from helioseismology and from stellar evolution models calculated using OPAL opacities. The revisions destroy that agreement. In a recent paper, Bahcall et al. argue that the agreement would be restored if opacities for the regions of the Sun with 2 × 106T 5 × 106 K (0.7-0.4 R) were larger than those given by OPAL by about 10 per cent. In the region concerned, the present results from the OP do not differ from those of OPAL by more than 2.5 per cent
A Quantitative Comparison of Opacities Calculated Using the Distorted- Wave and -Matrix Methods
The present debate on the reliability of astrophysical opacities has reached
a new climax with the recent measurements of Fe opacities on the Z-machine at
the Sandia National Laboratory \citep{Bailey2015}. To understand the
differences between theoretical results, on the one hand, and experiments on
the other, as well as the differences among the various theoretical results,
detailed comparisons are needed. Many ingredients are involved in the
calculation of opacities; deconstructing the whole process and comparing the
differences at each step are necessary to quantify their importance and impact
on the final results. We present here such a comparison using the two main
approaches to calculate the required atomic data, the -Matrix and
distorted-wave methods, as well as sets of configurations and coupling schemes
to quantify the effects on the opacities for the and ions.Comment: 10 pages, 2 figure
Nitrogen K-shell photoabsorption
Reliable atomic data have been computed for the spectral modeling of the
nitrogen K lines, which may lead to useful astrophysical diagnostics. Data sets
comprise valence and K-vacancy level energies, wavelengths, Einstein
-coefficients, radiative and Auger widths and K-edge photoionization cross
sections. An important issue is the lack of measurements which are usually
employed to fine-tune calculations so as to attain spectroscopic accuracy. In
order to estimate data quality, several atomic structure codes are used and
extensive comparisons with previous theoretical data have been carried out. In
the calculation of K photoabsorption with the Breit--Pauli -matrix method,
both radiation and Auger damping, which cause the smearing of the K edge, are
taken into account. This work is part of a wider project to compute atomic data
in the X-ray regime to be included in the database of the popular {\sc xstar}
modeling code
Evaluation of the burden of HPV-related hospitalizations as a useful tool to increase awareness: 2007–2017 data from the sicilian hospital discharge records
In light of the implementation of human papillomavirus (HPV) prevention strategies, epidemiological studies in different geographical areas are required in order to assess the impact of HPV-related diseases. The purpose of the present study was to describe the burden of HPV-related hospitalizations in Sicily. A retrospective observational study estimated 43,531 hospitalizations attributable to HPV from 2007 to 2017. During the observed period, there was a decrease for all HPV-related conditions with a higher reduction, among neoplasms, for cervical cancer (annual percent change (APC) = −9.9%, p < 0.001). The median age for cervical cancer was 45 years old, with an increasing value from 43 to 47 years (p < 0.001). The age classes with greater decreases in hospital admissions for invasive cancers were women aged 35 years or more (APC range from −5.5 to −9.86) and 25–34 years old (APC = −11.87, p < 0.001) for women with cervical carcinoma in situ. After ten years for vaccine introduction and sixteen years for cervical cancer screening availability, a relatively large decrease in hospital admissions for cervical cancer and other HPV-related diseases in Sicily was observed. Some clinical characteristics of hospitalization, such as increasing age, are suggestive clues for the impact of preventive strategies, but further research is needed to confirm this relationship
Decay Properties of K-Vacancy States in Fe X-Fe XVII
We report extensive calculations of the decay properties of fine-structure
K-vacancy levels in Fe X-Fe XVII. A large set of level energies, wavelengths,
radiative and Auger rates, and fluorescence yields has been computed using
three different standard atomic codes, namely Cowan's HFR, AUTOSTRUCTURE and
the Breit-Pauli R-matrix package. This multi-code approach is used to the study
the effects of core relaxation, configuration interaction and the Breit
interaction, and enables the estimate of statistical accuracy ratings. The
K-alpha and KLL Auger widths have been found to be nearly independent of both
the outer-electron configuration and electron occupancy keeping a constant
ratio of 1.53+/-0.06. By comparing with previous theoretical and measured
wavelengths, the accuracy of the present set is determined to be within 2 mA.
Also, the good agreement found between the different radiative and Auger data
sets that have been computed allow us to propose with confidence an accuracy
rating of 20% for the line fluorescence yields greater than 0.01. Emission and
absorption spectral features are predicted finding good correlation with
measurements in both laboratory and astrophysical plasmas.Comment: 13 pages, 4 figures. Submitted to A&A. Electronic Table 3-4 available
at http://lheawww.gsfc.nasa.gov/users/palmeri/patrick.htm
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