Asteroseismology of red giants & galactic archaeology

Red-giant stars are low- to intermediate-mass ($M \lesssim 10$~M$_{\odot}$) stars that have exhausted hydrogen in the core. These extended, cool and hence red stars are key targets for stellar evolution studies as well as galactic studies for several reasons: a) many stars go through a red-giant phase; b) red giants are intrinsically bright; c) large stellar internal structure changes as well as changes in surface chemical abundances take place over relatively short time; d) red-giant stars exhibit global intrinsic oscillations. Due to their large number and intrinsic brightness it is possible to observe many of these stars up to large distances. Furthermore, the global intrinsic oscillations provide a means to discern red-giant stars in the pre-helium core burning from the ones in the helium core burning phase and provide an estimate of stellar ages, a key ingredient for galactic studies. In this lecture I will first discuss some physical phenomena that play a role in red-giant stars and several phases of red-giant evolution. Then, I will provide some details about asteroseismology -- the study of the internal structure of stars through their intrinsic oscillations -- of red-giant stars. I will conclude by discussing galactic archaeology -- the study of the formation and evolution of the Milky Way by reconstructing its past from its current constituents -- and the role red-giant stars can play in that.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

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

Statins in the chemoprevention of colorectal cancer in established animal models of sporadic and colitis-associated cancer

Despite the availability of effective surveillance for colorectal cancer with colonoscopy, chemoprevention might be an acceptable alternative. Statins are potent inhibitors of cholesterol biosynthesis. In clinical trials, statins have been found to be beneficial in the primary and secondary prevention of coronary heart disease. However, the overall benefits observed with statins appear to be greater than what might be expected from changes in lipid levels alone, suggesting effects beyond cholesterol lowering. This systematic review aimed to gather information on the possible chemopreventive role of statins in preventing carcinogenesis and tumor promotion by a diverse array of mechanisms in both sporadic and colitis-associated cancer in animal models. The MEDLINE database was thoroughly searched using the following 'statin, HMG-CoA reductase inhibitor, colon cancer, mice, rats, chemoprevention, colitis-associated cancer'. Additional articles were gathered and evaluated. There are a lot of clinical studies and meta-analyses, as well as a plethora of basic research studies implementing cancer cell lines and animal models, on the chemopreventive role of statins in colorectal cancer (CRC). However, data derived from clinical studies are inconclusive, yet they show a tendency toward a beneficial role of statins against CRC pathogenesis. Thus, more research on the molecular pathways of CRC tumorigenesis as related to statins is warranted to uncover new mechanisms and compare the effect of statins on both sporadic and colitis-associated cancer in animal models. Basic science results could fuel exclusive colitis-associated cancer clinical trials to study the chemopreventive effects of statins and to differentiate between their effects on the two types of CRCs in humans. © 2016 Wolters Kluwer Health, Inc. All rights reserved

Interactions between parasitism and milk production - Mastitis in sheep

The present review discusses interactions and focuses in the direct effects of parasites in production of milk and development of mastitis in ewes. In most relevant published studies, a clear reduction in milk yield of ewes affected with parasites has been recorded. This reduction in milk yield has been quantified to average 22% among the relevant studies. Nematode parasitism can also cause shorter persistency of lactation, whilst the situation regarding potential effects on milk composition is not clear. Moreover, in field and experimental studies trichostrongylid intestinal infections have been documented to increase risk of mastitis in affected ewes; among parasitic species, the effect was associated primarily with Teladorsagia spp. infection. Trematode infection has also been found to increase risk for mastitis development at the early stage of lactation period. Research supports that effective parasite control will enable sheep to fully express their genetic potential and benefit for increased milk yield and effective udder health management schemes. © 2019 Elsevier B.V

On the impact of the structural surface effect on global stellar properties and asteroseismic analyses

In a series of papers, we have recently demonstrated that it is possible to construct stellar structure models that robustly mimic the stratification of multidimensional radiative magnetohydrodynamic simulations at every time-step of the computed evolution. The resulting models offer a more realistic depiction of the near-surface layers of stars with convective envelopes than parametrizations, such as mixing length theory, do. In this paper, we explore how this model improvement impacts on seismic and non-seismic properties of stellar models across the Hertzsprung-Russell diagram. We show that the improved description of the outer boundary layers alters the predicted global stellar properties at different evolutionary stages. In a hare and hound exercise, we show that this plays a key role for asteroseismic analyses, as it, for instance, often shifts the inferred stellar age estimates by more than 10 per cent. Improper boundary conditions may thus introduce systematic errors that exceed the required accuracy of the PLATO space mission. Moreover, we discuss different approaches for computing stellar oscillation frequencies. We demonstrate that the so-called gas \u3931 approximation performs reasonably well for all main-sequence stars. Using a Monte Carlo approach, we show that the model frequencies of our hybrid solar models are consistent with observations within the uncertainties of the global solar parameters when using the so-called reduced \u3931 approximation

On the impact of the structural surface effect on global stellar properties and asteroseismic analyses

editorial reviewedIn a series of papers, we have recently demonstrated that it is possible to construct stellar structure models that robustly mimic the stratification of multidimensional radiative magnetohydrodynamic simulations at every time-step of the computed evolution. The resulting models offer a more realistic depiction of the near-surface layers of stars with convective envelopes than parametrizations, such as mixing length theory, do. In this paper, we explore how this model improvement impacts on seismic and non-seismic properties of stellar models across the Hertzsprung-Russell diagram. We show that the improved description of the outer boundary layers alters the predicted global stellar properties at different evolutionary stages. In a hare and hound exercise, we show that this plays a key role for asteroseismic analyses, as it, for instance, often shifts the inferred stellar age estimates by more than 10 per cent. Improper boundary conditions may thus introduce systematic errors that exceed the required accuracy of the PLATO space mission. Moreover, we discuss different approaches for computing stellar oscillation frequencies. We demonstrate that the so-called gas Γ1 approximation performs reasonably well for all main-sequence stars. Using a Monte Carlo approach, we show that the model frequencies of our hybrid solar models are consistent with observations within the uncertainties of the global solar parameters when using the so-called reduced Γ1 approximation. © 2020 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society

Platelet depletion/transfusion as a lethal factor in a colitis-associated cancer mouse model

Background/Aim: TLR-4 Knock-out (KO) mice are protected from colitis-associated cancer in the established AOM/DSS mouse model. The aim of this study was to assess whether the TLR4 KO mice would still be protected from carcinogenesis after platelet depletion and transfusion with TLR4 wild-type platelets. Materials and Methods: Thirty-two female C57BL6 mice were divided into 6 groups. Among the three groups that received Azoxymethane/Dextran Sulfate Sodium (AOM/DSS), one group included TLR4KO mice, which were depleted of their platelets and were then transfused with platelets from TLR4 wild-type mice. The other two groups included wild-type and TLR-4KO mice that only received AOM/DSS. Results: All 6 animals in the KO group that underwent platelet depletion/transfusion succumbed. Three of them died before the administration of DSS and three in the week following DSS administration. In contrast, mice in the other two groups experienced less weight loss and only 1 mouse died in each of them. Conclusion: Platelet depletion/transfusion was detrimental in TLR-4 transgenic mice that received AOM/DSS. © 2019 International Institute of Anticancer Research. All rights reserved

The interplay between innate immunity (TLR-4) and sCD40L in the context of an animal model of colitis-associated cancer

Background/Aim: Several studies have found elevated soluble CD40 Ligand (sCD40L) in the serum of patients with malignancies as well as those with inflammatory bowel disease (IBD). Our goal was to determine the possible causal role of sCD40L in colitis-associated colorectal cancer (CAC) by using the well-established azoxymethane/dextran sulfate sodium (AOM/DSS) protocol. Materials and methods: Twelve wild type (WT) and twelve TLR4 knock out (KO) female C57BL6 mice were divided into 4 experimental groups. Six WT and six TLR4 KO mice were treated with a single intraperitoneal dose (10 mg/kg of body weight) of AOM followed by three 7-day cycles of oral 2.5% DSS. The other two groups included 6 WT and 6 TLR4 KO mice that received only water and served as the control groups. The mice were sacrificed after 84 days. Results: All mice in the AOM/DSS WT group developed CAC while all mice from the AOM/DSS TLR4 KO group were protected from CAC. We measured the serum and pathologic tissue levels of sCD40L with quantitative sandwich enzyme-linked immunoassay (ELISA) and found that serum sCD40L was significantly higher in wild-type mice that developed CAC compared to their healthy counterparts (wild-type and TLR-4 KO controls). In comparison, serum sCD40L levels were comparable between TLR-4 KO mice, which are protected from developing CAC, and their healthy counterparts (wild-type and TLR-4 KO controls). Of note, tissue levels of sCD40L were not affected by the development of CAC. Conclusion: Our findings point to the presence of an axis between TLR-4 and sCD40L, which may lead to decreased immunosurveillance and the subsequent development of colitis-associated cancer. © 2020 International Institute of Anticancer Research. All rights reserved