Smoothed Particle Hydrodynamics simulations of the core-degenerate scenario for Type Ia supernovae

The core-degenerate (CD) scenario for type Ia supernovae (SN Ia) involves the merger of the hot core of an asymptotic giant branch (AGB) star and a white dwarf, and might contribute a non-negligible fraction of all thermonuclear supernovae. Despite its potential interest, very few studies, and based on only crude simplifications, have been devoted to investigate this possible scenario, compared with the large efforts invested to study some other scenarios. Here we perform the first three-dimensional simulations of the merger phase, and find that this process can lead to the formation of a massive white dwarf, as required by this scenario. We consider two situations, according to the mass of the circumbinary disk formed around the system during the final stages of the common envelope phase. If the disk is massive enough, the stars merge on a highly eccentric orbit. Otherwise, the merger occurs after the circumbinary disk has been ejected and gravitational wave radiation has brought the stars close to the Roche lobe radius on a nearly circular orbit. Not surprisingly, the overall characteristics of the merger remnants are similar to those found for the double-degenerate (DD) scenario, independently of the very different core temperature and of the orbits of the merging stars. They consist of a central massive white dwarf, surrounded by a hot, rapidly rotating corona and a thick debris region.Comment: 17 pages, 10 figures. Accepted for publication in MNRA

Adapting the revised prenatal coping inventory (NuPCI) for use in a Spanish population

Objective: To adapt the Revised Prenatal Coping Inventory (NuPCI) for the evaluation of prenatal stress coping strategies utilised by Spanish women. Methods: A cross-sectional study was performed to evaluate the psychometric properties of NuPCI adapted for a Spanish population. Two hundred and sixty one puerperium women completed the NuPCI at the time of discharge after childbirth. Instrument construct validity was evaluated using subscale item correlations. Internal consistency was assessed using Cronbach’s a test. Results: Items from each subscale (Preparation, Avoidance and Spiritual – Positive Coping) were significantly correlated with the global result (p¿¿0.7). The most frequently used coping strategy was Preparation and the least used was Avoidance. Utilisation of the coping strategies with Preparation decreased with increasing parity (p¿=¿.002) and greater prenatal stress was associated with increased use of the Avoidance coping strategy (p¿<¿.001). Conclusions: The NuPCI adapted for Spanish women demonstrates good psychometric properties for evaluating the three types of prenatal stress coping strategies: Preparation, Avoidance and Spiritual – Positive Coping. Results were similar to those presented by the instrument in its English language version

An upper limit to the secular variation of the gravitational constant from white dwarf stars

A variation of the gravitational constant over cosmological ages modifies the main sequence lifetimes and white dwarf cooling ages. Using an state-of-the-art stellar evolutionary code we compute the effects of a secularly varying G on the main sequence ages and, employing white dwarf cooling ages computed taking into account the effects of a running G, we place constraints on the rate of variation of Newton's constant. This is done using the white dwarf luminosity function and the distance of the well studied open Galactic cluster NGC 6791. We derive an upper bound G'/G ~ -1.8 10^{-12} 1/yr. This upper limit for the secular variation of the gravitational constant compares favorably with those obtained using other stellar evolutionary properties, and can be easily improved if deep images of the cluster allow to obtain an improved white dwarf luminosity function.Comment: 15 pages, 4 figures, accepted for publication in JCA

Finding Exogenous Variables in Data with Many More Variables than Observations

Many statistical methods have been proposed to estimate causal models in classical situations with fewer variables than observations (p<n, p: the number of variables and n: the number of observations). However, modern datasets including gene expression data need high-dimensional causal modeling in challenging situations with orders of magnitude more variables than observations (p>>n). In this paper, we propose a method to find exogenous variables in a linear non-Gaussian causal model, which requires much smaller sample sizes than conventional methods and works even when p>>n. The key idea is to identify which variables are exogenous based on non-Gaussianity instead of estimating the entire structure of the model. Exogenous variables work as triggers that activate a causal chain in the model, and their identification leads to more efficient experimental designs and better understanding of the causal mechanism. We present experiments with artificial data and real-world gene expression data to evaluate the method.Comment: A revised version of this was published in Proc. ICANN201

Evidence for a merger of binary white dwarfs: the case of GD 362

GD 362 is a massive white dwarf with a spectrum suggesting a H-rich atmosphere which also shows very high abundances of Ca, Mg, Fe and other metals. However, for pure H-atmospheres the diffusion timescales are so short that very extreme assumptions have to be made to account for the observed abundances of metals. The most favored hypothesis is that the metals are accreted from either a dusty disk or from an asteroid belt. Here we propose that the envelope of GD 362 is dominated by He, which at these effective temperatures is almost completely invisible in the spectrum. This assumption strongly alleviates the problem, since the diffusion timescales are much larger for He-dominated atmospheres. We also propose that the He-dominated atmosphere of GD 362 is likely to be the result of the merger of a binary white dwarf.Comment: 4 pages, 3 figures. Accepted for publication in Astrophysical Journal Letter

Microstructural, mechanical and mass transport properties of isotropic and capillary alginate gels

Macroscopically homogeneous and inhomogeneous calcium alginate gels are formed via internal or external addition of various amounts of calcium to an alginate solution. The externally formed gels contain parallel aligned capillary structures. The mechanical and mass transport properties and the microstructure of the differently set gels were characterized by rheological measurements, fluorescence recovery after photobleaching (FRAP) and transmission electron microscopy (TEM). TEM images show a zone of distorted anisotropic gel structure in the vicinity of the capillaries as well as indications of a lower degree of void connectivity. The diffusion rates of dextran at large distances from the capillaries were fast and capillary gels showed a plastic behaviour in comparison to the internally set gels. The results presented show large functional differences between the internally and externally set gels, which cannot be explained by the presence of capillaries alone

Psychological Distress in Erectile Dysfunction : The Moderating Role of Attachment

Introduction: In clinical consultations, men with erectile dysfunction do not always express personal, sexual, and interpersonal concerns. Aim: We explore whether the attenuated impact of erectile dysfunction may be explained by a regulation of negative affect that causes activation of the attachment system. Methods: The study sample consisted of 69 men diagnosed with erectile dysfunction, mean (SD) age 56 (10.83) years. Participants completed self-reported questionnaires to assess erectile dysfunction severity, attachment style, sexual satisfaction, relationship satisfaction, and psychological symptoms. Main Outcome Measure: The moderating role of attachment between erectile dysfunction and sexual satisfaction, relationship satisfaction, and psychological distress was evaluated using multiple linear regression and moderation analysis. Results: All men in the sample had high attachment avoidance, distributed between the dismissive-avoidant (69.6%) and fearful-avoidant (30.4%) substyles, but low levels of psychological symptoms. Despite their erectile dysfunction, 27 patients (39.1%) rated their sexual life as satisfactory, and 46 (66.7%) rated their relationship with their partner as satisfactory. Men with fearful-avoidant attachment reported feeling more sexual desire and less sexual satisfaction than men with dismissive-avoidant attachment. Multiple linear regression analysis showed that sexual satisfaction variance was explained by erectile dysfunction severity, attachment anxiety, and relationship satisfaction scores. Moderation analysis showed that attachment anxiety, but not relationship satisfaction, moderated the impact of erectile dysfunction on sexual satisfaction. Conclusion: The avoidance dimension of attachment, which tends to be high in patients with erectile dysfunction, involves deactivation of the sexual system in an effort to minimize the emotional distress associated with erectile dysfunction, which damages sexual and relationship intimacy and delays the decision to obtain professional help. The presence of high attachment avoidance and the moderating value of attachment anxiety allow us to propose specific treatments for these men. Maestre-Lorén F, Castillo-Garayoa JA, López-i-Martín X, et al. Psychological Distress in Erectile Dysfunction: The Moderating Role of Attachment. Sex Med 2021;9:100436

The evolution of white dwarfs with a varying gravitational constant

Within the theoretical framework of some modern unification theories the constants of nature are functions of cosmological time. White dwarfs offer the possibility of testing a possible variation of G and, thus, to place constraints to these theories. We present full white dwarf evolutionary calculations in the case that G decreases with time. White dwarf evolution is computed in a self-consistent way, including the most up-to-date physical inputs, non-gray model atmospheres and a detailed core chemical composition that results from the calculation of the full evolution of progenitor stars. We find that the mechanical structure and the energy balance of white dwarfs are strongly modified by the presence of a varying G. In particular, for certain values of the rate of change of G, the evolution of cool white dwarfs is markedly affected. The impact of a varying G is more notorious in the case of more massive white dwarfs. In view of the recent results reporting that a very accurate white dwarf cooling age can be derived for the old and metal-rich open cluster NGC 6791, our study suggests that this cluster could be a potential target to constrain or detect a ypothetical secular variation of G.Comment: 5 pages, 4 figures, accepted for publication in A&

A white dwarf cooling age of 8 Gyr for NGC 6791 from physical separation processes

NGC 6791 is a well studied open cluster1 that it is so close to us that can be imaged down to very faint luminosities. The main sequence turn-off age (~8 Gyr) and the age derived from the termination of the white dwarf cooling sequence (~6 Gyr) are significantly different. One possible explanation is that as white dwarfs cool, one of the ashes of helium burning, 22Ne, sinks in the deep interior of these stars. At lower temperatures, white dwarfs are expected to crystallise and phase separation of the main constituents of the core of a typical white dwarf, 12C and 16O, is expected to occur. This sequence of events is expected to introduce significant delays in the cooling times, but has not hitherto been proven. Here we report that, as theoretically anticipated, physical separation processes occur in the cores of white dwarfs, solving the age discrepancy for NGC 6791.Comment: 3 pages, 2 figures, published in Natur