One Relator Quotients of Graph Products

In this paper, we generalise Magnus' Freiheitssatz and solution to the word problem for one-relator groups by considering one relator quotients of certain classes of right-angled Artin groups and graph products of locally indicable polycyclic groups

Periodic elements of the free idempotent generated semigroup on a biordered set

We show that every periodic element of the free idempotent generated semigroup on an arbitrary biordered set belongs to a subgroup of the semigroup

Physical activity and academic achievement in children: A historical perspective

AbstractAs the focus on academic achievement has increased, physical activity (PA) opportunities in schools have decreased in the United States. In an attempt to discover how the decline in PA may affect academic achievement, researchers have been studying the effects of PA on cognition and academic achievement in children for more than 50 years. This review takes a historical perspective on the science of PA and academic achievement prior to and during the past 5 years. A total of 125 published articles were included and reviewed. Fifty-three of these articles were published in the past 5 years. In recent years, the overall quality of the studies has increased, but the results continue to be inconsistent. Many use cross-sectional designs and the methods vary substantially. The majority of conclusions show a positive effect of PA on constructs related to academic achievement. Future studies should use strong study designs to examine the types and doses of PA needed to produce improvements in academic achievement

Dynamical Diffraction Theory for Wave Packet Propagation in Deformed Crystals

We develop a theory for the trajectory of an x ray in the presence of a crystal deformation. A set of equations of motion for an x-ray wave packet including the dynamical diffraction is derived, taking into account the Berry phase as a correction to geometrical optics. The trajectory of the wave packet has a shift of the center position due to a crystal deformation. Remarkably, in the vicinity of the Bragg condition, the shift is enhanced by a factor $\omega /\Delta \omega$ ($\omega$: frequency of an x ray, $\Delta\omega$: gap frequency induced by the Bragg reflection). Comparison with the conventional dynamical diffraction theory is also made.Comment: 4 pages, 2 figures. Title change

Largeness and SQ-universality of cyclically presented groups

Largeness, SQ-universality, and the existence of free subgroups of rank 2 are measures of the complexity of a finitely presented group. We obtain conditions under which a cyclically presented group possesses one or more of these properties. We apply our results to a class of groups introduced by Prishchepov which contains, amongst others, the various generalizations of Fibonacci groups introduced by Campbell and Robertson

High-pressure behavior of superconducting boron-doped diamond

This work investigates the high-pressure structure of freestanding superconducting ($T_{c}$ = 4.3\,K) boron doped diamond (BDD) and how it affects the electronic and vibrational properties using Raman spectroscopy and x-ray diffraction in the 0-30\,GPa range. High-pressure Raman scattering experiments revealed an abrupt change in the linear pressure coefficients and the grain boundary components undergo an irreversible phase change at 14\,GPa. We show that the blue shift in the pressure-dependent vibrational modes correlates with the negative pressure coefficient of $T_{c}$ in BDD. The analysis of x-ray diffraction data determines the equation of state of the BDD film, revealing a high bulk modulus of $B_{0}$=510$\pm$28\,GPa. The comparative analysis of high-pressure data clarified that the sp$^{2}$ carbons in the grain boundaries transform into hexagonal diamond.Comment: 7 pages, 4 figure

Physical activity behaviours of highly active preschoolers

Background: Understanding the physical activity behaviour of young children who are highly active mayprovide important guidance for promoting physical activity in preschools.Objectives: The objective of this study was to describe the movement characteristics of high-active (HA)children during attendance at preschools.Methods: Children in 20 preschools (n = 231) wore accelerometers and were classified into tertiles ofmoderate-to-vigorous physical activity. Children's movement characteristics were observed using the Observational System for Recording Physical Activity in Children – Preschool Version. Mixed-model analyses compared movement types between HA children and lower-active (LA) children during the total school day.Results: HA (n = 77) children were observed to be more active than LA children (n = 154) indoors(P < 0.001), but no differences were observed outdoors. HA children were more frequently observed running, crawling, climbing, jumping, skipping, swinging and throwing across the total school day than LA children. Outdoors, HA children participated in more swinging and throwing and less jumping or skipping than LA children. Indoors, HA children spent more time pulling, pushing and running, and less time walking than LA children.Conclusions: HA children have unique activity patterns. Further interventions to increase physical activity of all preschoolers should increase the time spent outside and include varied activity types throughout the entire school day