6,882 research outputs found
Solar radius and luminosity variations induced by the internal dynamo magnetic fields
Although the occurrence of solar irradiance variations induced by magnetic
surface features (e.g., sunspots, faculae, magnetic network) is generally
accepted, the existence of intrinsic luminosity changes due to the internal
magnetic fields is still controversial. This additional contribution is
expected to be accompanied by radius variations, and to be potentially
significant for the climate of the Earth. We aim to constrain theoretically the
radius and luminosity variations of the Sun that are due to the effect of the
variable magnetic fields in its interior associated with the dynamo cycle. We
have extended a one-dimensional stellar evolution code to include several
effects of the magnetic fields on the interior structure. We investigate
different magnetic configurations, based on both observational constraints and
on the output of state-of-the-art mean field dynamo models. We explore both
step-like and simply periodic time dependences of the magnetic field peak
strength. We find that the luminosity and radius variations are in anti-phase
and in phase, respectively, with the magnetic field strength. For peak magnetic
field strengths of the order of tens of kilogauss, luminosity variations
ranging between 10^{-6} and 10^{-3} (in modulus) and radius variations between
10^{-6} and 10^{-5} are obtained. Modest but significant radius variations (up
to 10^{-5} in relative terms) are obtained for magnetic fields of realistic
strength and geometry, providing a potentially observable signature of the
intrinsic variations. Establishing their existence in addition to the accepted
surface effects would have very important implications for the understanding of
solar-induced long-term trends on climate.Comment: 18 pages, 7 figures; accepted for publication in Astronomische
Nachrichte
The Association between Knowledge and Attitude, in Reproductive Health and Sexual Behavior in Female Adolescents, Banda Aceh
Background: More than a quarter of the world’s population is between the ages of 10 and 24, with 86% living in less developed countries. These young people are tomorrow’s parents. Reproductive health is important for adolescents. The reproductive and sexual health decisions they make today will affect the health and well-being of their communities and of their countries for decades to come. Lack of knowledge about reproductive health in adolescents can make them easily influenced by misinformation that is harmful to their reproductive health. This study aimed to determine the association between knowledge, attitude, and healthy sexual behavior among female high school students in Banda Aceh.
Subjects and Method: This was a cross-sectional study conducted at senior high school 8, Banda Aceh, Indonesia, in March 2012. A sample of 145 female students was selected for this study by stratified random sampling. The dependent variable was healthy sexual behavior. The independent variables were knowledge and attitude about reproductive health. The data were collected by questionnaire and analyzed by Chi-square test.
Results: 58.62% female students had good knowledge and 65.52% had positive attitude. Healthy sexual behavior increased with good knowledge (OR=1.76; 95% CI= 0.51 to 0.67; p= 0.147) and positive attitude about reproductive health (OR= 2.00; 95% CI= 0.58 to 0.73; p= 0.078).
Conclusion: Healthy sexual behavior is associated with knowledge and attitude about reproductive health. Therefore, health education plays an important role in increasing their knowledge and behavior of young people in order to maintain good reproductive health.
Keywords: sexual behaviour, attitude, knowledge, reproductive health, female adolescent
Superbubbles
Individual massive stars with M sub bol -6 have huge stellar winds that create interstellar bubbles. Stars with masses greater than 8 solar mass are considered supernova progenitors. These massive stars are numerous in OB associations where few supernova remnants are detected. Model calculations describing the evolution of an association show: that large, hot cavities are formed by pushing the ambient gas into neutral shells; that the shell radii change with galactocentric radius; that only thirty percent of the interstellar medium is in the form of supercavities; and that a consequence is that only a small fraction of supernovae form supernova remnants
The hunt for the Milky Way's accreted disc
The Milky Way is expected to host an accreted disc of stars and dark matter.
This forms as massive >1:10 mergers are preferentially dragged towards the disc
plane by dynamical friction and then tidally shredded. The accreted disc likely
contributes only a tiny fraction of the Milky Way's thin and thick stellar
disc. However, it is interesting because: (i) its associated `dark disc' has
important implications for experiments hoping to detect a dark matter particle
in the laboratory; and (ii) the presence or absence of such a disc constrains
the merger history of our Galaxy. In this work, we develop a chemo-dynamical
template to hunt for the accreted disc. We apply our template to the
high-resolution spectroscopic sample from Ruchti et al. (2011), finding at
present no evidence for accreted stars. Our results are consistent with a
quiescent Milky Way with no >1:10 mergers since the disc formed and a
correspondingly light `dark disc'. However, we caution that while our method
can robustly identify accreted stars, our incomplete stellar sample makes it
more challenging to definitively rule them out. Larger unbiased stellar samples
will be required for this.Comment: 14 pages; 8 figures; 1 table. Accepted for publication in MNRA
Estimation of C II and C II* column densities along Galactic sight-lines
We present interstellar C II (1334.5323 \AA) and C II* (1335.7077 \AA) column
density measurements along 14 Galactic sight-lines. These sight-lines sample a
variety of Galactic disk environments and include paths that range nearly two
orders of magnitude in average hydrogen densities () along the lines of
sight. Five of the sight-lines show super-Solar gas phase abundances of carbon.
Our results show that the excess carbon along these sight-lines may result from
different mechanisms taking place in the regions associated with these stars.Comment: 9 pages, 3 figures; Accepted for publication in BAS
Determinants of the intention to use performance-enhancing substances among Portuguese gym users
The present study examined the determinants of the intentions to use prohibited performance- enhancing substances (PES) and the hypothesis of gender and PES use influencing Theory of Planned Behavior (TPB) variables. A TPB approach was used. A convenience sample of Portuguese gym users (n = 453) completed an anonymous web-based survey. Variance-based structural equation modeling, multigroup analysis strategy, latent mean analysis approach and one-way ANOVA analysis were used. The findings showed that, at structural level, results support the TPB framework in terms of characterizing and predicting intentions to PES use in the gym users sample, and that subjective norms were the strongest predictor of PES use intentions. Female and male differed in intentions to use PES, subjective norms and beliefs. However, the predictive model in study remains invariable in both groups. Concerning PES use, results showed the existence of a significant difference, regarding all the TPB´s constructs of the PES users and nonusers’ groups, and that the predictive capacity of each predictor was different for each group. Psychological strategies should be based on subjective norms, alongside beliefs and attitudes towards PES use, since these variables influence the intention to use PES in that particular population
Diffusion on non exactly decimable tree-like fractals
We calculate the spectral dimension of a wide class of tree-like fractals by
solving the random walk problem through a new analytical technique, based on
invariance under generalized cutting-decimation transformations. These fractals
are generalizations of the NTD lattices and they are characterized by non
integer spectral dimension equal or greater then 2, non anomalous diffusion
laws, dynamical dimension splitting and absence of phase transitions for spin
models.Comment: 5 pages Latex, 3 figures (figures are poscript files
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