38,164 research outputs found
Pushing up the daisies
When components of an interacting dynamical system (such as organs within an organism, or daisies within the Daisyworld model) have a limited range of viability to changes in some essential variable, intuition suggests that increasing any individual range of viability will also increase viability in the context of the whole system. We show circumstances in which the reverse is true
Average degree conditions forcing a minor
Mader first proved that high average degree forces a given graph as a minor.
Often motivated by Hadwiger's Conjecture, much research has focused on the
average degree required to force a complete graph as a minor. Subsequently,
various authors have consider the average degree required to force an arbitrary
graph as a minor. Here, we strengthen (under certain conditions) a recent
result by Reed and Wood, giving better bounds on the average degree required to
force an -minor when is a sparse graph with many high degree vertices.
This solves an open problem of Reed and Wood, and also generalises (to within a
constant factor) known results when is an unbalanced complete bipartite
graph
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Mediated intimacy: Sex advice in media culture
The bold argument of Mediated Intimacy (Barker et al., 2018)1 is that media of various kinds play an increasingly important role in shaping people’s knowledge, desires, practices and expectations about intimate relationships. While arguments rage about the nature and content of sex and relationship education in schools, it is becoming clear that more and more of us – young and old – look not to formal education, or even to our friends, for information about sex, but to the media (Albury, 2016; Attwood et al., 2015). This is not simply a matter of media ‘advice’ in the form of self-help books, magazine problem pages, or online ‘agony’ columns – though these are all proliferating and are discussed at length in the book. It is also about the wider cultural habitat of images, ideas and discourses about intimacy that circulate through and across media: the ‘happy endings’ of romantic comedies; the ‘money shots’ of pornography; the celebrity gossip about who is seeing whom, who is ‘cheating’, and who is looking ‘hot’; the lifestyle TV about ‘embarrassing bodies’ or being ‘undateable’; the newspaper features on how to have a ‘good’ divorce or ‘ten things never to say on a first date’; the new apps that incite us to quantify and rate our sex lives, and so forth. These constitute the ‘taken for granted’ of everyday understandings of intimacy, and they are at the heart of Mediated Intimacy
Fitting multilevel multivariate models with missing data in responses and covariates that may include interactions and non-linear terms
The paper extends existing models for multilevel multivariate data with mixed response types to handle quite general types and patterns of missing data values in a wide range of multilevel generalized linear models. It proposes an efficient Bayesian modelling approach that allows missing values in covariates, including models where there are interactions or other functions of covariates such as polynomials. The procedure can also be used to produce multiply imputed complete data sets. A simulation study is presented as well as the analysis of a longitudinal data set. The paper also shows how existing multiprocess models for handling endogeneity can be extended by the framework proposed
Dissociation dynamics of fluorinated ethene cations:\ud from time bombs on a molecular level to double-regime dissociators\ud
The dissociative photoionization mechanism of internal energy selected CHF, 1,1-CHF, CHF and CF cations have been studied in the 13−20 eV photon energy range using imaging photoelectron photoion coincidence spectroscopy. Five predominant channels have been found; HF loss, statistical and non-statistical F loss, cleavage of the C–C bond post H or F-atom migration, and cleavage of the C=C bond. By modelling the breakdown diagrams and ion time-of-flight distributions using statistical theory, experimental 0 K appearance energies, E, of the daughter ions have been determined. Both CHF and 1,1-CHF are veritable time bombs with respect to dissociation via HF loss, where slow dissociation over a reverse barrier is followed by an explosion with large kinetic energy release. The first dissociative ionization pathway for CHF and CF involves an atom migration across the C=C bond, giving CF–CHF and CF–CF, respectively, which then dissociate to form CHF and CF. The nature of the F-loss pathway has been found to be bimodal for CHF and 1,1-CHF, switching from statistical to non-statistical behaviour as the photon energy increases. The dissociative ionization of CF is found to be comprised of two regimes. At high internal energies, a long-lived excited electronic state is formed, which loses an F atom in a non-statistical process and undergoes statistical redistribution of energy among the nuclear degrees of freedom. This is followed by a subsequent dissociation. In other words only the ground electronic state phase space stays inaccessible. The accurate E of CF and CF formation from CF together with the now well established ∆Hº of CF yield self-consistent enthalpies of formation for the CF, CF, CF, and CF species
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