The impact of chemical differentiation of white dwarfs on thermonuclear supernovae

Gravitational settling of 22Ne in cooling white dwarfs can affect the outcome of thermonuclear supernovae. We investigate how the supernova energetics and nucleosynthesis are in turn influenced by this process. We use realistic chemical profiles derived from state-of-the-art white dwarf cooling sequences. The cooling sequences provide a link between the white dwarf chemical structure and the age of the supernova progenitor system. The cooling sequence of a 1 M_sun white dwarf was computed until freezing using an up-to-date stellar evolutionary code. We computed explosions of both Chandrasekhar mass and sub-Chandrasekhar mass white dwarfs, assuming spherical symmetry and neglecting convective mixing during the pre-supernova carbon simmering phase to maximize the effects of chemical separation. Neither gravitational settling of 22Ne nor chemical differentiation of 12C and 16O have an appreciable impact on the properties of Type Ia supernovae, unless there is a direct dependence of the flame properties (density of transition from deflagration to detonation) on the chemical composition. At a fixed transition density, the maximum variation in the supernova magnitude obtained from progenitors of different ages is ~0.06 magnitudes, and even assuming an unrealistically large diffusion coefficient of 22Ne it would be less than ~0.09 mag. However, if the transition density depends on the chemical composition (all other things being equal) the oldest SNIa can be as much as 0.4 magnitudes brighter than the youngest ones (in our models the age difference is 7.4 Gyr). In addition, our results show that 22Ne sedimentation cannot be invoked to account for the formation of a central core of stable neutron-rich Fe-group nuclei in the ejecta of sub-Chandrasekhar models, as required by observations of Type Ia supernovae.Comment: 8 pages, 8 figures, 3 tables, accepted for Astronomy and Astrophysics. Revised version with corrected typo

Are interventions effective at improving driving in older drivers?: A systematic review

Background With the aging of the population, the number of older drivers is on the rise. This poses significant challenges for public health initiatives, as older drivers have a relatively higher risk for collisions. While many studies focus on developing screening tools to identify medically at-risk drivers, little research has been done to develop training programs or interventions to promote, maintain or enhance driving-related abilities among healthy individuals. The purpose of this systematic review is to synopsize the current literature on interventions that are tailored to improve driving in older healthy individuals by working on components of safe driving such as: self-awareness, knowledge, behaviour, skills and/or reducing crash/collision rates in healthy older drivers. Methods Relevant databases such as Scopus and PubMed databases were selected and searched for primary articles published in between January 2007 and December 2017. Articles were identified using MeSH search terms: ("safety" OR "education" OR "training" OR "driving" OR "simulator" OR "program" OR "countermeasures") AND ("older drivers" OR "senior drivers" OR "aged drivers" OR "elderly drivers"). All retrieved abstracts were reviewed, and full texts printed if deemed relevant. Results Twenty-five (25) articles were classified according to: 1) Classroom settings; 2) Computer-based training for cognitive or visual processing; 3) Physical training; 4) In-simulator training; 5) On-road training; and 6) Mixed interventions. Results show that different types of approaches have been successful in improving specific driving skills and/or behaviours. However, there are clear discrepancies on how driving performance/behaviours are evaluated between studies, both in terms of methods or dependent variables, it is therefore difficult to make direct comparisons between these studies. Conclusions This review identified strong study projects, effective at improving older drivers' performance and thus allowed to highlight potential interventions that can b- (undefined

The soluble transferrin receptor as a marker of iron homeostasis in normal subjects and in HFE-related hemochromatosis

Background and Objectives. The soluble transferrin receptor (sTfR) is a clinical marker of erythropoietic activity, also used in the diagnosis of iron deficiency. In the present paper we explore the meaning of this parameter in normal physiological conditions of iron homeostasis and in the setting of iron overload due to hereditary hemochromatosis (HH). Design and Methods. Reference values for sTfR were established in a population of 42 apparently healthy subjects, analyzed in relation to other hematologic parameters, namely, hemoglobin (Hb), mean corpuscular volume (MCV), transferrin saturation (TfSat) and serum ferritin. The same analysis was done in a group of 45 patients with HH who were homozygous for the C282Y mutation of HFE and had a wide range of TfSat values. In addition, individual serial profiles were analyzed in three patients. Results. In normal subjects circulating sTfR correlated significantly with the TfSat level, reflecting the systemic effect of iron availability on the erythropoietic activity in a normal physiological steady state. A TfSat of 25% appeared as a threshold value, below which there was a progressive increase in sTfR; this increase in sTfR occurred concomitantly with a decrease in Hb, MCV and serum ferritin. In HH patients the up-regulation of sTfR started at TfSat values as high as 50%. Interpretation and Conclusions. The fact that sTfR up-regulation started at higher TfSat values in HH patients suggests that the recognition of systemic iron available for erythropoiesis is altered in this condition. Based on these results, a new hypothesis is advanced, proposing that the HFE protein in involved as a sensor of systemic iron availability, via the soluble transferrin receptor

Differential Behavior Between Isolated and Aggregated Rabbit Auricular Chondrocytes on Plastic Surfaces

A knowledge of the behavior of chondrocytes in culture is relevant for tissue engineering. Chondrocytes dedifferentiate to a fibroblast-like phenotype on plastic surfaces. Dedifferentiation is reversible if these cells are then cultured in suspension. In this report a description is given of how when chondrocyte aggregates formed in suspension are next seeded on plastic, most of them attach as round or polygonal cells. This morphological differentiation, with synthesis of type II collagen, is stable for long culture periods. This simple method can be of use as a model for studies of chondrocyte behavior on plastic. The results indicate that in addition to culture conditions, such as cell isolation method or cell density, chondrocyte behavior on plastic depends on the presence of aggregates

Bubble and Dew Point Calculations in Multicomponent and Multireactive Mixtures

Bubble and dew point calculations are useful in chemical engineering and play an important role in the study of separation equipments for non-reactive and reactive mixtures. To the best of the authors’s knowledge, few methods have been proposed for these calculations in systems with several chemical reactions. The objective of this paper is to introduce new conditions for performing bubble and dew point calculations in reactive mixtures. We have developed these conditions based on the application of transformed variables of Ung and Doherty (1995). Using these transformed variables, the solution space is restricted to compositions that are already at chemical equilibrium and by consequence the problem dimension is also reduced. The reliability and efficiency of three equation-solving methods are tested and compared using our equilibrium conditions: a) a simultaneous equation-solving approach using Newton method (SESN), b) an equation-decoupling approach using successive substitution method (EDSS) and c) an optimization approach using the stochastic optimization method Simulated Annealing(OSA). Our results indicated that even for simple reactive systems, bubble and dew point calculations are challenging for classical equation-solving methods and require robust strategies. We conclude that OSA and EDSS methods are reliable to locate bubble and dew points in reactive systems. EDSS is more efficient than OSA; however, OSA does not need initial guesses and is more suitable for difficult problems

Effects of Extracellular Matrix on the Morphology and Behaviour of Rabbit Auricular Chondrocytes in Culture

Isolated chondrocytes dedifferentiate to a fibroblast-like shape on plastic substrata and proliferate extensively, but rarely form nodules. However, when dissociation is not complete and some cartilage remnants are included in the culture, proliferation decreases and cells grow in a reticular pattern with numerous nodules, which occasionally form small cartilage-like fragments. In an attempt to reproduce this stable chondrogenic state, we added a cartilage protein extract, a sugar extract, and hyaluronan to the medium of previously dedifferentiated chondrocytes. When protein extract was added, many cartilaginous nodules appeared. Hyaluronan produced changes in cell phenotype and behaviour, but not nodule formation. Protein extract has positive effects on the differentiation of previously proliferated chondrocytes and permits nodule formation and the extensive production of type-II collagen. A comparison with incompletely dissociated chondrocyte cultures suggests that the presence of some living cells anchored to their natural extracellular matrix provides some important additional factors for the phenotypical stability of chondrocytes on plastic surfaces. In order to elucidate if it is possible that the incidence of apoptosis is related to the results, we also characterized the molecular traits of apoptosis

SPARC endogenous level, rather than fibroblast-produced SPARC or stroma reorganization induced by SPARC, is responsible for melanoma cell growth

SPARC (secreted protein acidic and rich in cysteine) is a matricellular protein whose overexpression in malignant or tumor-stromal cells is often associated with increased aggressiveness and bad prognosis in a wide range of human cancer types, particularly melanoma. We established the impact that changes in the level of SPARC produced by malignant cells and neighboring stromal cells have on melanoma growth. Melanoma cell growth in monolayer was only slightly affected by changes in SPARC levels. However, melanoma growth in spheroids was strongly inhibited upon SPARC hyperexpression and conversely enhanced when SPARC expression was downregulated. Interestingly, SPARC overexpression in neighboring fibroblasts had no effect on spheroid growth irrespective of SPARC levels expressed by the melanoma cells, themselves. Downregulation of SPARC expression in melanoma cells induced their rejection in vivo through a mechanism mediated exclusively by host polymorphonuclear cells. On the other hand, SPARC hyperexpression enhanced vascular density, collagen deposition, and fibroblast recruitment in the surrounding stroma without affecting melanoma growth. In agreement with the in vitro data, overexpression of SPARC in co-injected fibroblasts did not affect melanoma growth in vivo. All the data indicate that melanoma growth is not subject to regulation by exogenous SPARC, nor by stromal organization, but only by SPARC levels produced by the malignant cells themselves.Facultad de Ciencias Veterinaria

Mineralogia dos filões aplito-pegmatíticos litiníferos da região de Segura

Na região de Segura, os filões aplito-pegmatíticos litiníferos Variscos intruíram o Complexo Xisto-Grauváquico, Câmbrico. Osfilões pegmatíticos são do tipo REL-Li e incluem-se na família dos pegmatitos LCT. A ocorrência de lepidolite, montebrasite, microlite, cassiterite e minerais do grupo da columbite primários sugerem um elevado grau de diferenciação nestes filões. A montebrasite primária é heterogénea e a lacroixite secundária ocorre nas suas zonas enriquecidas em Na. A cassietrite é zonada com alternância de zonas escuras e zonas claras e possui Mn > Fe, o que é raro. As zonas escuras são fortemente pleocróicas, com zonamento oscilatório, e possuem teores mais elevados de Nb e Ta do que as zonas claras. As inclusões de moscovite, apatite, ferrotapiolite, ixiolite e microlite foram encontradas em ambas as zonas de cassiterite, mas as exsoluções de ferrocolumbite, ferrocolumbite manganífera e manganocolumbite ocorrem nas zonas escuras

Gibbs Energy Minimization Using Simulated Annealing for Two-phase Equilibrium Calculations in Reactive Systems

Phase equilibrium calculations in systems subject to chemical reactions are involved in the design, synthesis and optimization of reactive separation processes. Until now, several methods have been developed to perform simultaneously physical and chemical equilibrium calculations. However, published methods may face numerical difficulties such as variable initialization dependence, divergence and convergence to trivial solutions or unstable equilibrium states. Besides, these methods generally use conventional composition variables and reactions extents as unknowns which directly affect the numerical implementation, reliability and efficiency of solving strategies. The objective of this work is to introduce and test an alternative approach to perform Gibbs energy minimization in phase equilibrium problems for reactive systems. Specifically, we have employed the transformed composition variables of Ung and Doherty and the stochastic optimization method Simulated Annealing for two-phase equilibrium calculations in reacting systems. Performance of this strategy has been tested using several benchmark problems and results show that proposed approach is generally suitable for the global minimization of transformed Gibbs energy in reactive systems with two-phase equilibrium