Asteroseismology of solar-type stars García, Rafael A.; Ballot, Jérôme
Living reviews in solar physics,
09/2019, Letnik:
16, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Until the last few decades, investigations of stellar interiors had been restricted to theoretical studies only constrained by observations of their global properties and external characteristics. ...However, in the last 30 years the field has been revolutionized by the ability to perform seismic investigations of stellar interiors. This revolution begun with the Sun, where helioseismology has been yielding information competing with what can be inferred about the Earth’s interior from geoseismology. The last two decades have witnessed the advent of asteroseismology of solar-like stars, thanks to a dramatic development of new observing facilities providing the first reliable results on the interiors of distant stars. The coming years will see a huge development in this field. In this review we focus on solar-type stars, i.e., cool main-sequence stars where oscillations are stochastically excited by surface convection. After a short introduction and a historical overview of the discipline, we review the observational techniques generally used, and we describe the theory behind stellar oscillations in cool main-sequence stars. We continue with a complete description of the normal mode analyses through which it is possible to extract the physical information about the structure and dynamics of the stars. We then summarize the lessons that we have learned and discuss unsolved issues and questions that are still unanswered.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Free radicals generated within subcellular compartments damage macromolecules which lead to severe structural changes and functional alterations of cellular organelles. A manifestation of free ...radical injury to biological membranes is the process of lipid peroxidation, an autooxidative chain reaction in which polyunsaturated fatty acids in the membrane are the substrate. There is considerable evidence that damage to polyunsaturated fatty acids tends to reduce membrane fluidity. However, adequate levels of fluidity are essential for the proper functioning of biological membranes. Thus, there is considerable interest in antioxidant molecules which are able to stabilize membranes because of their protective effects against lipid peroxidation. Melatonin is an indoleamine that modulates a wide variety of endocrine, neural and immune functions. Over the last two decades, intensive research has proven this molecule, as well as its metabolites, to possess substantial antioxidant activity. In addition to their ability to scavenge several reactive oxygen and nitrogen species, melatonin increases the activity of the glutathione redox enzymes, that is, glutathione peroxidase and reductase, as well as other antioxidant enzymes. These beneficial effects of melatonin are more significant because of its small molecular size and its amphipathic behaviour, which facilitates ease of melatonin penetration into every subcellular compartment. In the present work, we review the current information related to the beneficial effects of melatonin in maintaining the fluidity of biological membranes against free radical attack, and further, we discuss its implications for ageing and disease.
Fatigue is one of the most prevalent symptoms among cancer patients. Specifically, in metastatic castration-resistant prostate cancer (mCRPC) patients, fatigue is the most common adverse event ...associated with current treatments. The purpose of this study is to describe the prevalence of fatigue and its impact on quality of life (QoL) in patients with CRPC in routine clinical practice.
This was a cross-sectional, multicentre study. Male chemo-naïve adults with high-risk non-metastatic (M0) CRPC and metastatic (M1) CRPC (mCRPC) were eligible. Fatigue was measured using the Brief Fatigue Inventory (BFI) and QoL was assessed using the Functional Assessment of Cancer Therapy questionnaire for patients with prostate cancer (FACT-P) and the FACT-General (FACT-G) questionnaire. Data were analysed using Mann-Whitney or Kruskal-Wallis tests (non-parametric distribution), a T-test or an ANOVA (parametric distribution) and the Fisher or chi-squared tests (categorical variables).
A total of 235 eligible patients were included in the study (74 31.5% with M0; and 161 68.5% with M1). Fatigue was present in 74%, with 38.5% of patients reporting moderate-to-severe fatigue. Mean FACT-G and FACT-P overall scores were 77.6 ± 16.3 and 108.7 ± 21.4, respectively, with no differences between the CRPC M0 and CRPC M1 subgroups. Fatigue intensity was associated with decreased FACT-G/P scores, with no differences between groups. Among 151 mCRPC patients with available treatment data, those treated with abiraterone-prednisone ≥3 months showed a significant reduction in fatigue intensity (p = 0.043) and interference (p = 0.04) compared to those on traditional hormone therapy (HT). Patients on abiraterone-prednisone ≥3 months showed significantly better FACT-G/P scores than patients on HT (p = 0.046 and 0.018, respectively).
Our data show a high prevalence and intensity of fatigue and its impact on QoL in chemo-naïve CRPC patients. There is an association between greater fatigue and less QoL, irrespective of the presence or absence of metastasis. Chemo-naïve mCRPC patients receiving more than 3 months of abiraterone acetate plus prednisone showed an improvement of fatigue and QoL when compared to those on traditional HT.
Not applicable since it is not an interventional study.
ABSTRACT
We explore the production and escape of ionizing photons in young galaxies by investigating the ultraviolet and optical emission-line properties of models of ionization-bounded and ...density-bounded H ii regions, active-galactic-nucleus (AGN) narrow-line regions, and radiative shocks computed all using the same physically consistent description of element abundances and depletion on to dust grains down to very low metallicities. We compare these models with a reference sample of metal-poor star-forming galaxies and Lyman-continuum (LyC) leakers at various redshifts, which allows the simultaneous exploration of more spectral diagnostics than typically available at once for individual subsamples. We confirm that current single- and binary-star population synthesis models do not produce hard-enough radiation to account for the high-ionization emission of the most metal-poor galaxies. Introducing either an AGN or radiative-shock component brings models into agreement with observations. A published model including X-ray binaries is an attractive alternative to reproduce the observed rise in He iiλ4686/H β ratio with decreasing oxygen abundance in metal-poor star-forming galaxies, but not the high observed He iiλ4686/Hβ ratios of galaxies with large EW(Hβ). A source of harder ionizing radiation appears to be required in these extreme objects, such as an AGN or radiative-shock component, perhaps linked to an initial-mass-function bias towards massive stars at low metallicity. This would also account for the surprisingly high O i/O iii ratios of confirmed LyC leakers relative to ionization-bounded models. We find no simple by-eye diagnostic of the nature of ionizing sources and the escape of LyC photon, which require proper simultaneous fits of several lines to be discriminated against.
We report chemical abundances obtained by Sloan Digital Sky Survey (SDSS)-III/Apache Point Observatory Galactic Evolution Experiment for giant stars in five globular clusters located within 2.2 kpc ...of the Galactic Centre. We detect the presence of multiple stellar populations in four of those clusters (NGC 6553, NGC 6528, Terzan 5 and Palomar 6) and find strong evidence for their presence in NGC 6522. All clusters with a large enough sample present a significant spread in the abundances of N, C, Na and Al, with the usual correlations and anticorrelations between various abundances seen in other globular clusters. Our results provide important quantitative constraints on theoretical models for self-enrichment of globular clusters, by testing their predictions for the dependence of yields of elements such as Na, N, C and Al on metallicity. They also confirm that, under the assumption that field N-rich stars originate from globular cluster destruction, they can be used as tracers of their parental systems in the high-metallicity regime.
Ageing is a complex process, induced by multifaceted interaction of genetic, epigenetic, and environmental factors. It is manifested by a decline in the physiological functions of organisms and ...associated to the development of age-related chronic diseases and cancer development. It is considered that ageing follows a strictly-regulated program, in which some signaling pathways critically contribute to the establishment and maintenance of the aged state. Chronic inflammation is a major mechanism that promotes the biological ageing process and comorbidity, with the transcription factor NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells) as a crucial mediator of inflammatory responses. This, together with the finding that the activation or inhibition of NF-κB can induce or reverse respectively the main features of aged organisms, has brought it under consideration as a key transcription factor that acts as a driver of ageing. In this review, we focused on the data obtained entirely through the generation of knockout and transgenic mouse models of either protein involved in the NF-κB signaling pathway that have provided relevant information about the intricate processes or molecular mechanisms that control ageing. We have reviewed the relationship of NF-κB and premature ageing; the development of cancer associated with ageing and the implication of NF-κB activation in the development of age-related diseases, some of which greatly increase the risk of developing cancer.
We derive age constraints for 1639 red giants in the APOKASC sample for which seismic parameters from Kepler, as well as effective temperatures, metallicities and α/Fe values from APOGEE DR12 (Apache ...Point Observatory Galactic Evolution Experiment Data Release 12) are available. We investigate the relation between age and chemical abundances for these stars, using a simple and robust approach to obtain ages. We first derive stellar masses using standard seismic scaling relations, then determine the maximum possible age for each star as function of its mass and metallicity, independently of its evolutionary stage. While the overall trend between maximum age and chemical abundances is a declining fraction of young stars with increasing α/Fe, at least 14 out of 241 stars with α/Fe >0.13 are younger than 6 Gyr. Five stars with α/Fe ≥0.2 have ages below 4 Gyr. We examine the effect of modifications in the standard seismic scaling relations, as well as the effect of very low helium fractions, but these changes are not enough to make these stars as old as usually expected for α-rich stars (i.e. ages greater than 8–9 Gyr). Such unusual α-rich young stars have also been detected by other surveys, but defy simple explanations in a galaxy evolution context.
The use of reclaimed water to irrigate agricultural crops has increased in recent years as a consequence of water shortage constituting a potential risk for human health. The main objective of this ...study was to evaluate the impact on the soil-plant system and determining the accumulation of carbamazepine (CBZ), diclofenac (DCF), ketoprofen (KTP) and naproxen (NPX) in the edible part of lettuce under commonly used agricultural practices in commercial production. For this purpose, red oak baby lettuce (Lactuca sativa L.) was irrigated with reclaimed water fortified with different concentrations of pharmaceuticals. The study was carried out in two different scenarios: soil and tray. The tray experiments were conducted with substrate and took place at three different seasons of the year. Lettuce tissue sampled from these experiments were analysed 3 times during the lettuce growing cycle (first, second and third harvest). The practices of first harvest regrowth were also evaluated. For all experiments, CBZ showed the highest accumulation in lettuce leaves of the pharmaceuticals tested, showing a correlation between irrigation exposure time and pharmaceutical uptake. Unexpectedly, DCF was the compound with the highest uptake levels after regrowth practices. Results suggested that pharmaceuticals uptake could be directly associated with the irrigation method and possible accumulation in soil and substrates, while concentration of pharmaceuticals in substrates were 10 times higher. Based on the concentration values detected in lettuce leaves, the risk assessment suggests that no compounds imply any risk to human health, except CBZ for those on vegetarian diets in the tray scenario. Although commercial agricultural practices are usually not considered with regards to risk reduction, in this experiment we demonstrated that climatic conditions are a key factor in pharmaceuticals uptake and different agricultural practices (soil cropping and drip irrigation) can limit the presence of pharmaceutical compounds in crops.
Display omitted
•A correlation between irrigation exposure time and pharmaceutical uptake.•The uptake of pharmaceuticals is directly associated with the irrigation method and the possible accumulation in soils and substrates.•The pharmaceutical concentration in substrate were 10 times higher than in soil.•The consumption of lettuce grown in trays may pose a health risk regarding carbamazepine for vegetarians.•Climatic conditions and different agricultural practices are a key factor in pharmaceuticals uptake.
PDF
