88 research outputs found
Theory of Stellar Oscillations
In recent years, astronomers have witnessed major progresses in the field of
stellar physics. This was made possible thanks to the combination of a solid
theoretical understanding of the phenomena of stellar pulsations and the
availability of a tremendous amount of exquisite space-based asteroseismic
data. In this context, this chapter reviews the basic theory of stellar
pulsations, considering small, adiabatic perturbations to a static, spherically
symmetric equilibrium. It starts with a brief discussion of the solar
oscillation spectrum, followed by the setting of the theoretical problem,
including the presentation of the equations of hydrodynamics, their
perturbation, and a discussion of the functional form of the solutions.
Emphasis is put on the physical properties of the different types of modes, in
particular acoustic (p-) and gravity (g-) modes and their propagation cavities.
The surface (f-) mode solutions are also discussed. While not attempting to be
comprehensive, it is hoped that the summary presented in this chapter addresses
the most important theoretical aspects that are required for a solid start in
stellar pulsations research.Comment: Lecture presented at the IVth Azores International Advanced School in
Space Sciences on "Asteroseismology and Exoplanets: Listening to the Stars
and Searching for New Worlds" (arXiv:1709.00645), which took place in Horta,
Azores Islands, Portugal in July 201
Toward an internally consistent astronomical distance scale
Accurate astronomical distance determination is crucial for all fields in
astrophysics, from Galactic to cosmological scales. Despite, or perhaps because
of, significant efforts to determine accurate distances, using a wide range of
methods, tracers, and techniques, an internally consistent astronomical
distance framework has not yet been established. We review current efforts to
homogenize the Local Group's distance framework, with particular emphasis on
the potential of RR Lyrae stars as distance indicators, and attempt to extend
this in an internally consistent manner to cosmological distances. Calibration
based on Type Ia supernovae and distance determinations based on gravitational
lensing represent particularly promising approaches. We provide a positive
outlook to improvements to the status quo expected from future surveys,
missions, and facilities. Astronomical distance determination has clearly
reached maturity and near-consistency.Comment: Review article, 59 pages (4 figures); Space Science Reviews, in press
(chapter 8 of a special collection resulting from the May 2016 ISSI-BJ
workshop on Astronomical Distance Determination in the Space Age
Floristic overview of the epiphytic bryophytes of terra firme forests across the Amazon basin
Sources and rates of potassium for sweet orange production
Fruit yield and quality of citrus trees (Citrus spp.) is markedly affected by potassium (K) fertilization. Potassium chloride is the major source of K, even though other sources are also available for agricultural use when crops are sensitive to chloride or where potential for accumulation of salts in soils exists. Only few studies addressed the effect of K sources on yield and quality of citrus fruits. Therefore, the present study was conducted to evaluate K2SO4 and KCl fertilizer sources at 0, 100, 200, and 300 kg ha-1 per year K2O on fruit yield and quality of 'PĂŞra' and 'Valencia' sweet orange trees in the field. The experiments were carried out in a 4 Ă— 2 factorial design under randomized complete blocks, with four replicates from 2001 to 2004. Fruit yield increased with increased K fertilization. Nutrient rate for maximum economic yield of 'PĂŞra' was 200 kg ha-1 of K2O and for 'Valencia', 270 kg ha-1 of K2O. Differences were attributed to higher production and K exportation by fruits of 'Valencia'. Fruit mass also increased with increased K fertilization what decreased total soluble solids in juice, and which correlated with leaf K concentrations for 'Valencia' (r = 0.76; p < 0.05). Leaf Ca, Mg and B concentrations decreased with K rates. Additionally, leaf Cl increased up to 440 mg kg-1 with KCl rates, even though no negative effects occurred either on fruit yield or quality of trees
Bio-analytical Assay Methods used in Therapeutic Drug Monitoring of Antiretroviral Drugs-A Review
Thermal Evolution and Magnetic Field Generation in Terrestrial Planets and Satellites
Cohort Profile: Pregnancy And Childhood Epigenetics (PACE) Consortium.
Development Psychopathology in context: famil
Evaluation of Double Sampling Estimators of Subalpine Herbage Production
Electronic capacitance metering, relative and dry weight estimations, and canopy cover estimation of herbaceous standing crops were statistically evaluated with respect to sampling costs, precisions, and the vegetal and environmental factors which affected their double-sampling correlations. Twenty-four factors were investigated using stepwise regression analysis. Minimum sampling costs were achieved when the double-sampling estimator technique was compatible with the characteristics of the sampling site. Relative and dry weight estimations were found to be consistently precise estimators in meadow, aspen, fir, and spruce-fir, and spruce-fir vegetation types. Both were successfully used by workers with no prior experience or training. The sampling techniques were capable of providing, at equal sampling cost, up to a 4-fold increase in sample size over that of clipping along, depending on the vegetation type
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