457 research outputs found
Ab initio melting curve of molybdenum by the phase coexistence method
We report ab initio calculations of the melting curve of molybdenum for the
pressure range 0-400 GPa. The calculations employ density functional theory
(DFT) with the Perdew-Burke-Ernzerhof exchange-correlation functional in the
projector augmented wave (PAW) implementation. We present tests showing that
these techniques accurately reproduce experimental data on low-temperature
b.c.c. Mo, and that PAW agrees closely with results from the full-potential
linearized augmented plane-wave implementation. The work attempts to overcome
the uncertainties inherent in earlier DFT calculations of the melting curve of
Mo, by using the ``reference coexistence'' technique to determine the melting
curve. In this technique, an empirical reference model (here, the embedded-atom
model) is accurately fitted to DFT molecular dynamics data on the liquid and
the high-temperature solid, the melting curve of the reference model is
determined by simulations of coexisting solid and liquid, and the ab initio
melting curve is obtained by applying free-energy corrections. Our calculated
melting curve agrees well with experiment at ambient pressure and is consistent
with shock data at high pressure, but does not agree with the high pressure
melting curve deduced from static compression experiments. Calculated results
for the radial distribution function show that the short-range atomic order of
the liquid is very similar to that of the high-T solid, with a slight decrease
of coordination number on passing from solid to liquid. The electronic
densities of states in the two phases show only small differences. The results
do not support a recent theory according to which very low dTm/dP values are
expected for b.c.c. transition metals because of electron redistribution
between s-p and d states.Comment: 27 pages, 10 figures. to be published in Journal of Chemical Physic
The effects of a revised Be e-capture rate on solar neutrino fluxes
The electron-capture rate on Be is the main production channel for Li
in several astrophysical environments. Theoretical evaluations have to account
for not only the nuclear interaction, but also the processes in the plasma
where Be ions and electrons interact. In the past decades several estimates
were presented, pointing out that the theoretical uncertainty in the rate is in
general of few percents. In the framework of fundamental solar physics, we
consider here a recent evaluation for the Be+e rate, not used up to now
in the estimate of neutrino fluxes. We analysed the effects of the new
assumptions on Standard Solar Models (SSMs) and compared the results obtained
by adopting the revised Be+e rate to those obtained by the one reported
in a widely used compilation of reaction rates (ADE11). We found that new SSMs
yield a maximum difference in the efficiency of the Be channel of about
-4\% with respect to what is obtained with the previously adopted rate. This
fact affects the production of neutrinos from B, increasing the relative
flux up to a maximum of 2.7\%. Negligible variations are found for the physical
and chemical properties of the computed solar models. The agreement with the
SNO measurements of the neutral current component of the B neutrino flux is
improved.Comment: 7 pages, 3 figures, 4 tables. Accepted for the publication on A&
Meta-analysis of cancer incidence in children born after assisted reproductive technologies
A meta-analysis was performed on 11 cohort studies of Assisted Reproductive Technologies (ART) and subsequent childhood cancer, published up to February 2005, which reported comparable, nonoverlapping data, and then restricted to eight studies which presented a similar research design. The overall Standardised Incidence Ratio was 1.33 (95% CI 0.62–2.85), and 0.77 (95% CI 0.41–1.42) when the analysis was restricted to eight studies. No evidence of publication bias was observed for the overall analysis. The data are consistent with a lack of increase in risk of childhood cancer, though the amount of data on ART and cancer is still limited; larger multicentric studies as well as a pooled analysis on the available data are warranted
Gas adsorption and dynamics in Pillared Graphene Frameworks
We thank prof. Marco Frasconi for advice on the kind of moieties to be used as pillars. N.M.P. is supported by the European Research Council PoC 2015 “Silkene” No. 693670, by the European Commission H2020 under the Graphene Flagship Core 1 No. 696656 (WP14 “Polymer Nanocomposites”) and under the Fet Proactive “Neurofibres” No. 732344. S.T and G.G. acknowledge funding from previous WP14 “Polymer Nanocomposites” grant. Access to computing and storage facilities owned by parties and projects contributing to the Czech National Grid Infrastructure MetaCentrum provided under the programme “Projects of Large Research, Development, and Innovations Infrastructures” (CESNET LM2015042), is greatly appreciated (https://www.metacentrum.cz/en/)
Theoretical estimate of the half-life for the radioactive Cs and Cs in astrophysical scenarios
We analyze the CsBa and
CsBa decays, which are crucial
production channels for Ba isotopes in Asymptotic Giant Branch (AGB) stars. We
reckon, from relativistic quantum mechanis, the effects of multichannel
scattering onto weak decays, including nuclear and electronic excited states
(ES) populated above 10 keV, for both parent and daughter nuclei. We
find increases in the half-lives for K (by more than a factor 3 for
Cs) as compared to previous works based on systematics. We also discuss
our method in view of these previous calculations. An important impact on
half-lives comes from nuclear ES decays, while including electronic
temperatures yields further increases of about 20\% at energies 10-30 keV,
typical of AGB stars of moderate mass (). Despite
properly considering these effects, the new rates remain sensitively lower than
the TY values, implying longer half-lives at least above 8-9 keV. Our rate
predictions are in substantial accord with recent results based on the shell
model, and strongly modify branching ratios along the -process path
previously adopted. With our new rate, nucleosynthesis models well account for
the isotopic admixtures of Ba in presolar SiC grains and in the Sun.Comment: 15 pages, 3 figures, 5 tables. Accepted for publication in Ap
Computational methods for 2D materials modelling
Materials with thickness ranging from a few nanometers to a single atomic
layer present unprecedented opportunities to investigate new phases of matter
constrained to the two-dimensional plane.Particle-particle Coulomb interaction
is dramatically affected and shaped by the dimensionality reduction, driving
well-established solid state theoretical approaches to their limit of
applicability. Methodological developments in theoretical modelling and
computational algorithms, in close interaction with experiments, led to the
discovery of the extraordinary properties of two-dimensional materials, such as
high carrier mobility, Dirac cone dispersion and bright exciton luminescence,
and inspired new device design paradigms. This review aims to describe the
computational techniques used to simulate and predict the optical, electronic
and mechanical properties of two-dimensional materials, and to interpret
experimental observations. In particular, we discuss in detail the particular
challenges arising in the simulation of two-dimensional constrained fermions,
and we offer our perspective on the future directions in this field.Comment: This submission does not include the third party cited figure
Knowledge and Prevention Practices Before Breast Cancer Diagnosis in a Cross-Sectional Study Among Survivors: Impact on Patients\u27 Involvement in the Decision Making Process
Disparities exist in breast cancer knowledge and education, which tend to influence symptom interpretation and decision to seek screening/care. The present project describes a cohort of women\u27s experiences, knowledge, and health behavior prior to and after a diagnosis of breast cancer. It also studies how knowledge and demographic factors are associated with level of involvement participants had in the treatment of their breast cancer. Women \u3e 18 years who have been diagnosed and treated for breast cancer within 10 years were recruited in Pittsburgh, PA, through the Healthy People Cohort Registry, a database of volunteers from the community, and Brooklyn, NY, through the American Cancer Society breast cancer survivor database. Subsequent to institutional ethics approval, a questionnaire was administered by mail and through an electronic interactive format. The study included 124 breast cancer survivors, one-quarter of whom were of African ancestry. Roughly half of the women indicated that their overall knowledge of breast cancer was limited before diagnosis; no significant association between overall knowledge before diagnosis and stage at diagnosis or an active role of the patient in treatment choices was observed. Two-third of the women reported using personal research on internet, books, and other media to increase knowledge on breast cancer after diagnosis; the improvement of knowledge was associated with an active role in therapy choice. White women\u27s self report of breast cancer knowledge prior to diagnosis was higher than that of women of African origin (p = 0.03); the latter experienced more delays in getting results about the diagnosis (p = 0.002), in starting treatment (p = 0.03), and in having treatment available at local facilities (p = 0.007) than white women. White women were more likely to improve their knowledge through their own research (p = 0.08) and through the contribution of their physician (p = 0.06) than women of African origin.There is still a need for addressing breast cancer knowledge among black women, and improvement in physician emotional support and in their contribution to the patient\u27s knowledge is necessary. These efforts may have a positive impact on breast cancer knowledge among black women in the US
Lack of access to medical care during Hurricane Sandy and mental health symptoms
© 2018 The Authors Destruction caused by natural disasters compromises medical providers’ and hospitals’ abilities to administer care. Hurricane Sandy was particularly devastating, resulting in massive disruptions of medical care in the region. This study aimed to determine whether a lack of access to medical care during Hurricane Sandy was associated with posttraumatic stress disorder (PTSD) symptoms and other mental health/substance abuse outcomes. A secondary aim was to examine whether having a chronic illness moderates those associations. Self-reported medical access and mental health symptomatology were obtained from New York City and Long Island residents (n = 1669) following Hurricane Sandy under the Leaders in Gathering Hope Together project (10/23/2013–2/25/2015) and Project Restoration (6/5/2014–8/9/2016). Multivariable logistic regressions were utilized to determine the relationship between lack of access to medical care and mental health outcomes. Of the 1669 participants, 994 (59.57%) were female, 866 (51.89%) were white, and the mean age was 46.22 (SD = 19.2) years old. Those without access to medical care had significantly higher odds of showing symptoms of PTSD (AOR = 2.71, CI = [1.77–4.16]), as well as depression (AOR = 1.94, CI = [1.29–2.92]) and anxiety (AOR = 1.61, CI = [1.08–2.39]) compared to those with access. Lack of access to care was associated with a 2.12 point increase in perceived stress scale score (SE = 0.63). The interaction between having a chronic illness and lack of access to medical care was not significantly associated with any outcomes. The findings emphasize the importance of making medical care more accessible to patients, both chronically and acutely ill, during natural disasters to benefit their physical as well as their mental health
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