Stellar Collisions and the Interior Structure of Blue Stragglers

Collisions of main sequence stars occur frequently in dense star clusters. In open and globular clusters, these collisions produce merger remnants that may be observed as blue stragglers. Detailed theoretical models of this process require lengthy hydrodynamic computations in three dimensions. However, a less computationally expensive approach, which we present here, is to approximate the merger process (including shock heating, hydrodynamic mixing, mass ejection, and angular momentum transfer) with simple algorithms based on conservation laws and a basic qualitative understanding of the hydrodynamics. These algorithms have been fine tuned through comparisons with the results of our previous hydrodynamic simulations. We find that the thermodynamic and chemical composition profiles of our simple models agree very well with those from recent SPH (smoothed particle hydrodynamics) calculations of stellar collisions, and the subsequent stellar evolution of our simple models also matches closely that of the more accurate hydrodynamic models. Our algorithms have been implemented in an easy to use software package, which we are making publicly available (see http://vassun.vassar.edu/~lombardi/mmas/). This software could be used in combination with realistic dynamical simulations of star clusters that must take into account stellar collisions.Comment: This revised version has 37 pages, 13 figures, 4 tables; submitted to ApJ; for associated software package, see http://vassun.vassar.edu/~lombardi/mmas/ This revised version presents additional comparisons with SPH results and slightly improved merger recipe

Individual differences and strategies for human reasoning

Theories of human reasoning have tended to assume cognitive universality, i. e. that all individuals reason in basically the same way. However, some research (e. g. that of Ford. 1995) has found evidence of individual differences in the strategies people use for syllogistic reasoning. This thesis presents a series of experiments which aimed to identify individual differences in strategies for human reasoning and investigate their nature and aetiology. Experiment 1 successfully replicated and extended Ford (1995) and provided further evidence that most individuals prefer to reason with either verbal-propositional or visuo-spatial representations. Data from verbal and written protocols showed that verbal reasoners tended to use a method of substitution whereby they obtain a value for the common term from one premise and then simply substitute it in the other premise to obtain a conclusion. Spatial reasoners, on the other hand, presented protocols which resembled Euler circles and described the syllogistic premises in terms of sets and subsets. Experiment 2 provided some further qualitative evidence about the nature of such strategies, especially the verbal reasoners, showing that within strategy variations occurred. Experiment 3 extended this line of research, identifying a strong association between verbal and spatial strategies for syllogistic reasoning and abstract and concrete strategies for transitive inference (the latter having originally been identified by Egan and Grimes- Farrow, 1982). Experiments 1-3 also showed that inter-strategic differences in accuracy are generally not observed, hence, reasoners present an outward appearance of ubiquity despite underlying differences in reasoning processes. Experiments 5 and 6 investigated individual differences in cognitive factors which may underpin strategy preference. Whilst no apparent effects of verbal and spatial ability or cognitive style were found, reasoners did appear to draw differentially on the verbal and spatial components of working memory. Confirmatory factor analysis showed that whilst verbal reasoners draw primarily on the verbal memory resource, spatial reasoners draw both on this and on spatial resource. Overall, these findings have important implications for theories of human reasoning, which need to take into account possible individual differences in strategies if they are to present a truly comprehensive account of how people reason.Economic and Social Research Counci

Emotional hypervigilance: development of a new questionnaire and examining the importance to posttraumatic quality of life.

Objective: Hypervigilance is a symptom of posttraumatic stress disorder usually defined in terms of behaviours such as environment scanning and planning escape routes. The objective of Study 1 was to develop a new measure to assess the extent to which individuals employ a specifically emotional form of hypervigilance. The aim of Study 2 was to investigate whether emotional hypervigilance is associated with posttraumatic quality of life in addition to the known effects of symptoms and experiential avoidance. Method: Study 1 presents the development and initial testing (N = 275) of the Emotional Vigilance and Awareness Questionnaire (EVAQ). In Study 2, a non-clinical sample (N = 162) completed an online survey comprising the EVAQ, measures of posttraumatic symptoms (PTS), posttraumatic quality of life (PTQ) and experiential avoidance.Results: In Study 1, factor analyses resulted in a 12-item scale which showed good psychometric properties in unifactorial and three factorial forms. Subscales reflected vigilance to Emotion Change (EC), Emotion Awareness (EA) and conscious Emotion Monitoring (EM). The EVAQ showed incremental validity against the Brief Hypervigilance Questionnaire and positive associations with established measures of low mood and negative affect. In Study 2, EVAQ scores showed significant associations with experiential avoidance and PTQ. Conclusions: The EVAQ is a valid and reliable new measure for assessing hypervigilance and hyperawareness of emotion, an overlooked factor in posttraumatic symptomology, particularly when considered as a unifactorial construct. The EVAQ may be useful in research and therapeutic settings with individuals who disengage with distressing emotions and present avoidant behaviour

Maternal mental health and breastfeeding duration: the role of optimism and coping strategies.

Background/AimsMental health can influence the likelihood that a woman will initiate and continue breastfeeding behaviour that is associated with improved infant and maternal health. Mental health outcomes are associated with variables such as optimism and coping. The aim of this study was to explore the relationship between coping, optimism and mental health, and their impact on breastfeeding duration.MethodsA total of 612 women who had breastfed completed an online questionnaire comprising the hospital anxiety and depression scale, cognitive emotional regulation questionnaire, brief coping orientation to problems experienced inventory and life orientation test. Data were analysed using correlations, ordinal linear regression and mediation analysis.ResultsThere was a direct relationship between breastfeeding duration and depression but no direct relationship between duration and anxiety. A mediation analysis showed no mediating between breastfeeding duration and depression. Optimism did mediate the relationship between anxiety and duration, with optimism being associated with reduced anxiety and increased duration.ConclusionsThe findings highlight the importance of support for mothers while breastfeeding to improve mental health outcomes and foster coping strategies, such as optimism

An Analytic Model for Blue Straggler Formation in Globular Clusters

We present an analytic model for blue straggler formation in globular clusters. We assume that blue stragglers are formed only through stellar collisions and binary star evolution, and compare our predictions to observed blue straggler numbers taken from the catalogue of Leigh, Sills & Knigge (2011). We can summarize our key results as follows: (1) Binary star evolution consistently dominates blue straggler production in all our best-fitting models. (2) In order to account for the observed sub-linear dependence of blue straggler numbers on the core masses (Knigge, Leigh & Sills 2009), the core binary fraction must be inversely proportional to the total cluster luminosity and should always exceed at least a few percent. (3) In at least some clusters, blue straggler formation must be enhanced by dynamical encounters (either via direct collisions or by stimulating mass-transfer to occur by altering the distribution of binary orbital parameters) relative to what is expected by assuming a simple population of binaries evolving in isolation. (4) The agreement between the predictions of our model and the observations can be improved by including blue stragglers that form outside the core but later migrate in due to dynamical friction. (5) Longer blue straggler lifetimes are preferred in models that include blue stragglers formed outside the core since this increases the fraction that will have sufficient time to migrate in via dynamical friction.Comment: 11 pages, 4 figures, accepted for publication in MNRA

#Disgusted: Identifying potential sub-factors of Moral Disgust through Reflexive Thematic Analysis of Tweets

Social media provides an untapped resource for exploring Moral Disgust. We therefore drew on ‘tweets’ about Moral Disgust (k=526) to better conceptualise the situations, people, and concepts users found Disgusting. Our Reflexive Thematic Analysis identified two themes and accompanying subthemes: Hierarchical Disgust and Third-Party Disgust. Hierarchical Disgust was constructed from expressions of Disgust directed to power structures, abuses of power, and leaders, whereas Third-Party Disgust comprised expressions directed at negative outcomes for others, often in the form of discrimination or harm. Both themes served as a form of group protection through out-group distancing and normative in-group policing. Importantly, this research extends classic Disgust literature (e.g., Tybur et al., 2013), presenting a novel approach to naturalistic data collection and providing future researchers with an approach to study other emotions, beliefs, and subjects that are expressed online

Motivating Emotional Intelligence: A Reinforcement Sensitivity Theory (RST) Perspective

Trait emotional intelligence (trait EI) is generally associated with positive outcomes and can inform clinical and social interventions. We investigated the sub-factors of trait EI: Wellbeing, Self-control, Emotionality, and Sociability, in the context of the Reinforcement Sensitivity Theory (RST) of motivation. In Study 1, participants (N = 247) completed Carver and White’s (1994) BIS/BAS scales and a measure of trait EI. All EI sub-factors were positively associated with BAS Drive and negatively with BIS. Study 2 (N = 382) employed a new questionnaire based on revised RST (Corr & Cooper, 2016). All trait EI factors were positively associated with BAS Goal-Drive Persistence and Reward Interest, and negatively with the BIS. Self-control showed negative associations with BAS Impulsivity and was the only factor not to correlate with BAS Reward Reactivity. Results suggest that high trait EI individuals are goal driven, sensitive to reward and lower in avoidance motivation and negative emotion. This motivational basis to trait EI further explicates its structure

The ATLAS3D project - XXVII : Cold gas and the colours and ages of early-type galaxies

Date of Acceptance: 16/12/2013We present a study of the cold gas contents of the ATLAS3D early-type galaxies, in the context of their optical colours, near-ultraviolet colours and Hβ absorption line strengths. Early-type (elliptical and lenticular) galaxies are not as gas poor as previously thought, and at least 40 per cent of local early-type galaxies are now known to contain molecular and/or atomic gas. This cold gas offers the opportunity to study recent galaxy evolution through the processes of cold gas acquisition, consumption (star formation) and removal. Molecular and atomic gas detection rates range from 10 to 34 per cent in red sequence early-type galaxies, depending on how the red sequence is defined, and from 50 to 70 per cent in blue early-type galaxies. Notably, massive red sequence early-type galaxies (stellar masses >5 × 1010 M⊙, derived from dynamical models) are found to have H I masses up to M(H I)/M* ∼ 0.06 and H2 masses up to M(H2)/M* ∼ 0.01. Some 20 per cent of all massive early-type galaxies may have retained atomic and/or molecular gas through their transition to the red sequence. However, kinematic and metallicity signatures of external gas accretion (either from satellite galaxies or the intergalactic medium) are also common, particularly at stellar masses ≤5 × 1010 M⊙, where such signatures are found in ∼50 per cent of H2-rich early-type galaxies. Our data are thus consistent with a scenario in which fast rotator early-type galaxies are quenched former spiral galaxies which have undergone some bulge growth processes, and in addition, some of them also experience cold gas accretion which can initiate a period of modest star formation activity. We discuss implications for the interpretation of colour–magnitude diagramsPeer reviewedFinal Accepted Versio