Crossovers from parity conserving to directed percolation universality

The crossover behavior of various models exhibiting phase transition to absorbing phase with parity conserving class has been investigated by numerical simulations and cluster mean-field method. In case of models exhibiting Z_2 symmetric absorbing phases (the NEKIMCA and Grassberger's A stochastic cellular automaton) the introduction of an external symmetry breaking field causes a crossover to kink parity conserving models characterized by dynamical scaling of the directed percolation (DP) and the crossover exponent: 1/\phi ~ 0.53(2). In case an even offspringed branching and annihilating random walk model (dual to NEKIMCA) the introduction of spontaneous particle decay destroys the parity conservation and results in a crossover to the DP class characterized by the crossover exponent: 1/\phi\simeq 0.205(5). The two different kinds of crossover operators can't be mapped onto each other and the resulting models show a diversity within the DP universality class in one dimension. These 'sub-classes' differ in cluster scaling exponents.Comment: 6 pages, 6 figures, accepted version in PR

Geometrical organization of solutions to random linear Boolean equations

The random XORSAT problem deals with large random linear systems of Boolean variables. The difficulty of such problems is controlled by the ratio of number of equations to number of variables. It is known that in some range of values of this parameter, the space of solutions breaks into many disconnected clusters. Here we study precisely the corresponding geometrical organization. In particular, the distribution of distances between these clusters is computed by the cavity method. This allows to study the `x-satisfiability' threshold, the critical density of equations where there exist two solutions at a given distance.Comment: 20 page

Is Understanding Reducible?

Despite playing an important role in epistemology, philosophy of science, and more recently in moral philosophy and aesthetics, the nature of understanding is still much contested. One attractive framework attempts to reduce understanding to other familiar epistemic states. This paper explores and develops a methodology for testing such reductionist theories before offering a counterexample to a recently defended variant on which understanding reduces to what an agent knows

The orientability of spacetime

Contrary to established beliefs, spacetime may not be time-orientable. By considering an experimental test of time-orientability it is shown that a failure of time-orientability of a spacetime region would be indistinguishable from a particle-antiparticle annihilation event

The role of school enjoyment and connectedness in the association between depressive and externalising symptoms and academic attainment:Findings from a UK prospective cohort study

BACKGROUND: Previous research on the relationship between children's depressive and externalising symptoms, experience of school, and academic attainment is inconclusive. The aims of this study were (i) to test bidirectional associations between children's school experience and depressive and externalising symptoms at age 10-11 and 13-14, (ii) to ascertain whether school experience age 13-14 is associated with academic attainment age 16, and (iii) to test whether school experience mediates the relationship between depressive or externalising symptoms and attainment. METHODS: Data was used from the Avon Longitudinal Study of Parents and Children (n=6,409). A cross-lagged model was used to investigate bidirectional associations between school experience (enjoyment and connectedness) and depression and externalising at age 10-11 and 13-14. The same framework was used to test if school experience aged 13-14 mediated associations of depressive and externalising symptoms with later attainment. RESULTS: Depressive and externalising symptoms at 10-11 were negatively associated with school connectedness (depressive: standardised β=-0.06, CI: -0.11, 0.01; externalizing: β=-0.13, CI: -0.17, -0.08), and school enjoyment at 13-14 (depressive β=-0.04, -0.08, 0.03; externalising: β=-0.08, CI: -0.13, -0.03). School enjoyment at 13-14 was positively associated with attainment at 16 (β=0.10, CI: 0.04, 0.15), and partially mediated associations between depressive and externalising symptoms at 10-11 and attainment at 16 (depressive: proportion mediated 2.2%, CI: -1.5, 5.9; externalising: proportion mediated; 4.7%, CI: 0.7, 10.1,). LIMITATIONS: Results may be subject to residual confounding. CONCLUSIONS: School enjoyment is a potentially modifiable risk factor that may affect educational attainment of adolescents with depressive or externalising symptoms

A Formal Apology for Metaphysics

There is an old meta-philosophical worry: very roughly, metaphysical theories have no observational consequences and so the study of metaphysics has no value. The worry has been around in some form since the rise of logical positivism in the early twentieth century but has seen a bit of a renaissance recently. In this paper, I provide an apology for metaphysics in the face of this kind of concern. The core of the argument is this: pure mathematics detaches from science in much the same manner as metaphysics and yet it is valuable nonetheless. The source of value enjoyed by pure mathematics extends to metaphysics as well. Accordingly, if one denies that metaphysics has value, then one is forced to deny that pure mathematics has value. The argument places an added burden on the sceptic of metaphysics. If one truly believes that metaphysics is worthless (as some philosophers do), then one must give up on pure mathematics as well

Geometry of tropical moduli spaces and linkage of graphs

We prove the following "linkage" theorem: two p-regular graphs of the same genus can be obtained from one another by a finite alternating sequence of one-edge-contractions; moreover this preserves 3-edge-connectivity. We use the linkage theorem to prove that various moduli spaces of tropical curves are connected through codimension one.Comment: Final version incorporating the referees correction

How Mistimed and Unwanted Pregnancies Affect Timing of Antenatal Care Initiation in three Districts in Tanzania

Early antenatal care (ANC) initiation is a doorway to early detection and management of potential complications associated with pregnancy. Although the literature reports various factors associated with ANC initiation such as parity and age, pregnancy intentions is yet to be recognized as a possible predictor of timing of ANC initiation. Data originate from a cross-sectional household survey on health behaviour and service utilization patterns. The survey was conducted in 2011 in Rufiji, Kilombero and Ulanga districts in Tanzania on 910 women of reproductive age who had given birth in the past two years. ANC initiation was considered to be early only if it occurred in the first trimester of pregnancy gestation. A recently completed pregnancy was defined as mistimed if a woman wanted it later, and if she did not want it at all the pregnancy was termed as unwanted. Chisquare was used to test for associations and multinomial logistic regression was conducted to examine how mistimed and unwanted pregnancies affect timing of ANC initiation. Although 49.3% of the women intended to become pregnant, 50.7% (34.9% mistimed and 15.8% unwanted) became pregnant unintentionally. While ANC initiation in the 1st trimester was 18.5%, so was 71.7% and 9.9% in the 2nd and 3rd trimesters respectively. Multivariate analysis revealed that ANC initiation in the 2nd trimester was 1.68 (95% CI 1.10‒2.58) and 2.00 (95% CI 1.05‒3.82) times more likely for mistimed and unwanted pregnancies respectively compared to intended pregnancies. These estimates rose to 2.81 (95% CI 1.41‒5.59) and 4.10 (95% CI 1.68‒10.00) respectively in the 3rd trimester. We controlled for gravidity, age, education, household wealth, marital status, religion, district of residence and travel time to a health facility. Late ANC initiation is a significant maternal and child health consequence of mistimed and unwanted pregnancies in Tanzania. Women should be empowered to delay or avoid pregnancies whenever they need to do so. Appropriate counseling to women, especially those who happen to conceive unintentionally is needed to minimize the possibility of delaying ANC initiation.\u