Evolutionary and pulsational properties of white dwarf stars

Abridged. White dwarf stars are the final evolutionary stage of the vast majority of stars, including our Sun. The study of white dwarfs has potential applications to different fields of astrophysics. In particular, they can be used as independent reliable cosmic clocks, and can also provide valuable information about the fundamental parameters of a wide variety of stellar populations, like our Galaxy and open and globular clusters. In addition, the high densities and temperatures characterizing white dwarfs allow to use these stars as cosmic laboratories for studying physical processes under extreme conditions that cannot be achieved in terrestrial laboratories. They can be used to constrain fundamental properties of elementary particles such as axions and neutrinos, and to study problems related to the variation of fundamental constants. In this work, we review the essentials of the physics of white dwarf stars. Special emphasis is placed on the physical processes that lead to the formation of white dwarfs as well as on the different energy sources and processes responsible for chemical abundance changes that occur along their evolution. Moreover, in the course of their lives, white dwarfs cross different pulsational instability strips. The existence of these instability strips provides astronomers with an unique opportunity to peer into their internal structure that would otherwise remain hidden from observers. We will show that this allows to measure with unprecedented precision the stellar masses and to infer their envelope thicknesses, to probe the core chemical stratification, and to detect rotation rates and magnetic fields. Consequently, in this work, we also review the pulsational properties of white dwarfs and the most recent applications of white dwarf asteroseismology.Comment: 85 pages, 28 figures. To be published in The Astronomy and Astrophysics Revie

Post-Covid-19 Irritable Bowel Syndrome

Objectives The long-term consequences of COVID-19 infection on the gastrointestinal tract remain unclear. Here, we aimed to evaluate the prevalence of gastrointestinal symptoms and post-COVID-19 disorders of gut-brain interaction after hospitalisation for SARS-CoV-2 infection. Design GI-COVID-19 is a prospective, multicentre, controlled study. Patients with and without COVID-19 diagnosis were evaluated on hospital admission and after 1, 6 and 12 months post hospitalisation. Gastrointestinal symptoms, anxiety and depression were assessed using validated questionnaires. Results The study included 2183 hospitalised patients. The primary analysis included a total of 883 patients (614 patients with COVID-19 and 269 controls) due to the exclusion of patients with pre-existing gastrointestinal symptoms and/or surgery. At enrolment, gastrointestinal symptoms were more frequent among patients with COVID-19 than in the control group (59.3% vs 39.7%, p < 0.001). At the 12-month follow-up, constipation and hard stools were significantly more prevalent in controls than in patients with COVID-19 (16% vs 9.6%, p=0.019 and 17.7% vs 10.9%, p=0.011, respectively). Compared with controls, patients with COVID-19 reported higher rates of irritable bowel syndrome (IBS) according to Rome IV criteria: 0.5% versus 3.2%, p=0.045. Factors significantly associated with IBS diagnosis included history of allergies, chronic intake of proton pump inhibitors and presence of dyspnoea. At the 6-month follow-up, the rate of patients with COVID-19 fulfilling the criteria for depression was higher than among controls. Conclusion Compared with controls, hospitalised patients with COVID-19 had fewer problems of constipation and hard stools at 12 months after acute infection. Patients with COVID-19 had significantly higher rates of IBS than controls

Psychological and Clinical Factors Mediate Post-COVID-19 Irritable Bowel Syndrome

Background: Exposure to COVID-19 has been shown previously to be associated with a higher risk for irritable bowel syndrome (IBS). This study aimed to better explain this relationship using mediation analysis. Methods: This post hoc analysis of a multicenter cohort study includes 623 patients with and without COVID-19 infection. All participants completed the ROME IV criteria, gastrointestinal symptom rating scale (GSRS), and hospital anxiety and depression scale (HADS) over 1 year. Mediation analysis utilized the PROCESS macro and Baron and Kenny's method for parametric and nonparametric mediating variables, respectively. Key results: The impact of COVID-19 on the development of post-COVID-19 IBS is completely mediated by dyspnea at baseline (adjusted OR = 3.561, p = 0.012), severity of acid regurgitation at 1 month [indirect effect, log-odds metric = 0.090, 95% CI (0.006-0.180)], hunger pains at 1 [indirect effect, log-odds metric = 0.094, 95% CI (0.024-0.178)], and 6 months [indirect effect, log-odds metric = 0.074, 95% CI (0.003-0.150)], depression at 6 [indirect effect, log-odds metric = 0.106, 95% CI (0.009-0.225)] and 12 months [indirect effect, log-odds metric = 0.146, 95% CI (0.016-0.311)] as well as borborygmus [indirect effect, log-odds metric = 0.095, 95% CI (0.009-0.203)], abdominal distention [indirect effect, log-odds metric = 0.162, 95% CI (0.047-0.303)], and increased flatus [indirect effect, log-odds metric = 0.110, 95% CI (0.005-0.234)] at 12 months. Conclusions and inferences: Our findings provide evidence for psychological and clinical mediators between COVID-19 and post-COVID-19 IBS, which may be promising targets for interventions tailored for treating or preventing depression. The presence of specific GI symptoms at COVID-19 onset and their persistence should increase awareness of a potential new onset of IBS diagnosis.

Long-Term Impact of COVID-19 on Disorders of Gut–Brain Interaction: Incidence, Symptom Burden, and Psychological Comorbidities

Background: The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has highlighted the potential exacerbation of gastrointestinal symptoms in patients with disorders of gut-brain interaction (DGBIs). However, the distinct symptom trajectories and psychological burden in patients with post-COVID-19 DGBIs compared with patients with pre-existing irritable bowel syndrome (IBS)/functional dyspepsia (FD) and non-DGBI controls remain poorly understood. Objectives: To examine the long-term gastrointestinal symptom progression and psychological comorbidities in patients with post-COVID-19 DGBI, patients with pre-existing IBS/FD and non-DGBI controls. Methods: This post hoc analysis of a prospective multicenter cohort study reviewed patient charts for demographic data and medical history. Participants completed the Gastrointestinal Symptom Rating Scale at four time points: baseline, 1, 6, and 12&nbsp;months, and the Hospital Anxiety and Depression Scale at 6 and 12&nbsp;months. The cohort was divided into three groups: (1) post-COVID-19 DGBIs (2) non-DGBI, and (3) pre-existing IBS/FD, with the post-COVID-19 DGBIs group compared to the latter two control groups. Results: Among 599 eligible patients, 27 (4.5%) were identified as post-COVID-19 DGBI. This group experienced worsening abdominal pain, hunger pain, heartburn, and acid regurgitation, unlike symptom improvement or stability in non-DGBI controls (p&nbsp;&lt;&nbsp;0.001 for all symptoms, except hunger pain, p&nbsp;=&nbsp;0.001). While patients with pre-existing IBS/FD improved in most gastrointestinal symptoms but worsened in constipation and incomplete evacuation, patients with post-COVID-19 DGBI exhibited consistent symptom deterioration across multiple gastrointestinal domains. Anxiety and depression remained unchanged in patients with post-COVID-19 DGBI, contrasting with significant reductions in controls (non-DGBI: p&nbsp;=&nbsp;0.003 and p&nbsp;=&nbsp;0.057; pre-existing IBS/FD: p&nbsp;=&nbsp;0.019 and p&nbsp;=&nbsp;0.007, respectively). Conclusions: COVID-19 infection is associated with the development of newly diagnosed DGBIs and distinct symptom trajectories when compared with patients with pre-existing IBS/FD. Patients with post-COVID-19 DGBI experience progressive gastrointestinal symptom deterioration and persistent psychological distress, underscoring the need for tailored management strategies for this unique subgroup

TARJETA POSTAL NAVIDEÑA [Material gráfico]

ITALIACopia digital. Madrid : Ministerio de Educación, Cultura y Deporte, 201

Molecular and Pathological characterization of a non-aganglionic congenital megacolon in the rabbit

Congenital megacolon (CM) is a severe colonic dysfunction usually associated with an underlying aganglionosis of the enteric nervous system (ENS). CM unrelated to aganglionosis may also occur with a largely unknown pathogenesis. Aim: to characterize a new, non-rodent natural model of non-aganglionic congenital megacolon. The CM phenotype is related to an incomplete dominant allele at the English spotting locus (En) and appears only in homozygous En/En animals. Methods: An F1 population of 80 animals was created crossing En/en rabbits. En/En rabbits (almost completely with a white fur due to the absence of melanocytes in the skin) and littermate controls (en/en) (normally coloured) have been monitored since birth up to severe deterioration of En/En animals with the CM phenotype. Cecum and ascending colon of controls (n=4) and CM (n=6) were processed for quantitative double label immunohistochemistry (using antibodies for structural and neurochemical markers of the ENS: Hu, substance P [SP] and neural nitric oxide synthase [nNOS]) and electron microscopy analysis. DNA was extracted from blood samples collected from all F1 animals and used for candidate gene analysis. Results: Compared to controls (en/en), En/En rabbits were subvital showing feeding abnormalities, reduced body weight and a massive colonic distension predominant in the cecum and ascending colon. Genetic tests confirmed the effects and segregation of the En alleles in the F1 population. Sequencing and genotyping of identified single nucleotide polymorphisms (SNP) in a few candidate genes showed complete co-segregation of a SNP in the KIT gene with the coat colour effects of the English spotting locus (LOD = 37.93; \uf071 = 0.00). Quantitative gene expression in colon and cecum specimens showed that the level of Kit gene in En/En rabbits was only 5-10% vs that of en/en rabbits. Morphometric data on whole mounts of cecum and ascending colon showed a decreased number of Hu- and SP-immunoreactive (IR) neurons in En/En vs. en/en rabbits (950\uf0b1110 vs 1440\uf0b1120 and 76\uf0b114 vs 160\uf0b124, respectively; P<0.05). Although not statistically significant, nNOS-IR neurons were less abundant in En/En vs en/en. Compared to en/en, electron microscopy analysis of En/En tissues showed neuronal (rough endoplasmic reticulum with dilated cisternae, chaotically arranged cytoskeleton and nerve endings with empty synaptic vesicles) and interstitial cells of Cajal (ICC) (few cells with immature or altered features) abnormalities, particularly in the ascending colon. Conclusions: Combined neuronal and ICC network alterations underlie this non-aganglionic model of CM. Kit mutations may account for ICC abnormalities. The present findings can help understanding neuro-muscular changes occurring in human non-aganglionic C

Prospect for VLBI network extension: the first results of an Ad-hoc S2 array experiments

The Canadian S2 system gives a chance for Russian and some other radio telescopes in the world to be involved into international VLBI programs. Brief descriptions of previous S2 experiments and future possibilities axe presented