Spin-orbit transitions in α\alpha and γ\gamma-CoV2_{2}O6_{6}

$\gamma$-triclinic and $\alpha$-monoclinic polymorphs of CoV$_{2}$O$_{6}$ are two of the few known transition metal ion based materials that display stepped $1/3$ magnetization plateaus at low temperatures. Neutron diffraction [M. Markkula et al. Phys. Rev. B 86, 134401 (2012)], x-ray dichroism [N. Hollmann et al. Phys. Rev. B 89, 201101(R) (2014)], and dielectric measurements [K. Singh et al. J. Mater. Chem. 22, 6436 (2012)] have shown a coupling between orbital, magnetic and structural orders in CoV$_{2}$O$_{6}$. We apply neutron inelastic scattering to investigate this coupling by measuring the spin-orbit transitions in both $\alpha$ and $\gamma$ polymorphs. We find the spin-exchange and anisotropy in monoclinic $\alpha$-CoV$_{2}$O$_{6}$ to be weak in comparison with the spin-orbit coupling $\lambda$ and estimate an upper limit of $|J/\lambda| \sim$ 0.05. However, the spin exchange is larger in the triclinic polymorph and we suggest the excitations are predominately two dimensional. The local compression of the octahedra surrounding the Co$^{2+}$ ion results in a direct coupling between higher energy orbital levels, the magnetic ground state, and elastic strain. CoV$_{2}$O$_{6}$ is therefore an example where the local distortion along with the spin-orbit coupling provides a means of intertwining structural and magnetic properties. We finish the paper by investigating the low-energy magnetic fluctuations within the ground state doublet and report a magnetic excitation that is independent of the local crystalline electric field. We characterize the temperature and momentum dependence of these excitations and discuss possible connections to the magnetization plateaus.Comment: (15 pages, 10 figures

Superconductivity with hard-core repulsion: BCS-Bose crossover and s-/d-wave competition

We consider fermions on a 2D lattice interacting repulsively on the same site and attractively on the nearest neighbor sites. The model is relevant, for instance, to study the competition between antiferromagnetism and superconductivity in a Kondo lattice. We first solve the two-body problem to show that in the dilute and strong coupling limit the s-wave Bose condensed state is always the ground state. We then consider the many-body problem and treat it at mean-field level by solving exactly the usual gap equation. This guarantees that the superconducting wave-function correctly vanishes when the two fermions (with antiparallel spin) sit on the same site. This fact has important consequences on the superconducting state that are somewhat unusual. In particular this implies a radial node-line for the gap function. When a next neighbor hopping t' is present we find that the s-wave state may develop nodes on the Fermi surface.Comment: 10 pages, 9 fig

Modelling of the Complex CASSOWARY/SLUGS Gravitational Lenses

We present the first high-resolution images of CSWA 31, a gravitational lens system observed as part of the SLUGS (Sloan Lenses Unravelled by Gemini Studies) program. These systems exhibit complex image structure with the potential to strongly constrain the mass distribution of the massive lens galaxies, as well as the complex morphology of the sources. In this paper, we describe the strategy used to reconstruct the unlensed source profile and the lens galaxy mass profiles. We introduce a prior distribution over multi-wavelength sources that is realistic as a representation of our knowledge about the surface brightness profiles of galaxies and groups of galaxies. To carry out the inference computationally, we use Diffusive Nested Sampling, an efficient variant of Nested Sampling that uses Markov Chain Monte Carlo (MCMC) to sample the complex posterior distributions and compute the normalising constant. We demonstrate the efficacy of this approach with the reconstruction of the group-group gravitational lens system CSWA 31, finding the source to be composed of five merging spiral galaxies magnified by a factor of 13.Comment: Accepted for publication in MNRA

Evaluated kinetic and photochemical data for atmospheric chemistry: Volume IV – gas phase reactions of organic halogen species

This article, the fourth in the series, presents kinetic and photochemical data sheets evaluated by the IUPAC Subcommittee on Gas Kinetic Data Evaluation for Atmospheric Chemistry. It covers the gas phase and photochemical reactions of organic halogen species, which were last published in 1997, and were updated on the IUPAC website in 2006/07. The article consists of a summary sheet, containing the recommended kinetic parameters for the evaluated reactions, and four appendices containing the data sheets, which provide information upon which the recommendations are made

BCS to Bose Crossover in Anisotropic Superconductors

In this work we use functional integral techniques to examine the nearest neighbour attractive Hubbard model on a quasi-2D lattice. It is a simple phenomenological model for the high-Tc cuprates that allows both extended (non-local) s- and d-wave singlet superconductivity as well as mixed symmetry states. The Hartree-Gor'kov mean field theory of the model has a finite temperature phase diagram which shows a transition from pure s-wave to pure d-wave superconductivity, via a mixed symmetry s+id state, as a function of doping. Including Gaussian fluctuations we examine the crossover from weak-coupling BCS superconductivity to the strong-coupling Bose-Einstein condensation of composite s- or d-wave bosons and comment on the origin and symmetry of the pseudogap.Comment: 20 pages inc. 13 figure

Strengthening impact assessment: a call for integration and focus

We suggest that the impact assessment community has lost its way based on our observation that impact assessment is under attack because of a perceived lack of efficiency. Specifically, we contend that the proliferation of different impact assessment types creates separate silos of expertise and feeds arguments for not only a lack of efficiency but also a lack of effectiveness of the process through excessive specialisation and a lack of interdisciplinary practice. We propose that the solution is a return to the basics of impact assessment with a call for increased integration around the goal of sustainable development and focus through better scoping. We rehearse and rebut counter arguments covering silo-based expertise, advocacy, democracy, sustainability understanding and communication. We call on the impact assessment community to rise to the challenge of increasing integration and focus, and to engage in the debate about the means of strengthening impact assessment

Cosmological distance indicators

We review three distance measurement techniques beyond the local universe: (1) gravitational lens time delays, (2) baryon acoustic oscillation (BAO), and (3) HI intensity mapping. We describe the principles and theory behind each method, the ingredients needed for measuring such distances, the current observational results, and future prospects. Time delays from strongly lensed quasars currently provide constraints on $H_0$ with < 4% uncertainty, and with 1% within reach from ongoing surveys and efforts. Recent exciting discoveries of strongly lensed supernovae hold great promise for time-delay cosmography. BAO features have been detected in redshift surveys up to z <~ 0.8 with galaxies and z ~ 2 with Ly-$\alpha$ forest, providing precise distance measurements and $H_0$ with < 2% uncertainty in flat $\Lambda$CDM. Future BAO surveys will probe the distance scale with percent-level precision. HI intensity mapping has great potential to map BAO distances at z ~ 0.8 and beyond with precisions of a few percent. The next years ahead will be exciting as various cosmological probes reach 1% uncertainty in determining $H_0$, to assess the current tension in $H_0$ measurements that could indicate new physics.Comment: Review article accepted for publication in Space Science Reviews (Springer), 45 pages, 10 figures. Chapter of a special collection resulting from the May 2016 ISSI-BJ workshop on Astronomical Distance Determination in the Space Ag

Gravitational Lensing at Millimeter Wavelengths

With today's millimeter and submillimeter instruments observers use gravitational lensing mostly as a tool to boost the sensitivity when observing distant objects. This is evident through the dominance of gravitationally lensed objects among those detected in CO rotational lines at z>1. It is also evident in the use of lensing magnification by galaxy clusters in order to reach faint submm/mm continuum sources. There are, however, a few cases where millimeter lines have been directly involved in understanding lensing configurations. Future mm/submm instruments, such as the ALMA interferometer, will have both the sensitivity and the angular resolution to allow detailed observations of gravitational lenses. The almost constant sensitivity to dust emission over the redshift range z=1-10 means that the likelihood for strong lensing of dust continuum sources is much higher than for optically selected sources. A large number of new strong lenses are therefore likely to be discovered with ALMA, allowing a direct assessment of cosmological parameters through lens statistics. Combined with an angular resolution <0.1", ALMA will also be efficient for probing the gravitational potential of galaxy clusters, where we will be able to study both the sources and the lenses themselves, free of obscuration and extinction corrections, derive rotation curves for the lenses, their orientation and, thus, greatly constrain lens models.Comment: 69 pages, Review on quasar lensing. Part of a LNP Topical Volume on "Dark matter and gravitational lensing", eds. F. Courbin, D. Minniti. To be published by Springer-Verlag 2002. Paper with full resolution figures can be found at ftp://oden.oso.chalmers.se/pub/tommy/mmviews.ps.g

A review of early influences on physical activity and sedentary behaviors of preschool‐age children in high‐income countries

Purpose: Promoting physical activity (PA) is a key component of preventing and controlling childhood obesity. Despite well‐documented benefits of PA, globally, rates of PA among young children have declined over the past decades, and most children are not accruing sufficient PA daily. Helping children develop the foundation for PA habits early in life is critical for the promotion of health in childhood and prevention of chronic diseases later in life, and will ultimately promote longer and healthier lives for individuals and the general population. The purpose of this review is to provide a synthesis of current evidence on influences on PA and sedentary behaviors of preschool‐age children in high‐income countries. Design and Methods: A systematic review of three databases was performed. Studies conducted in high‐income countries and published from 2000 onward that addressed influences on PA and sedentary behaviors of preschool‐age children were identified and reviewed. Additionally, reference lists of identified articles and relevant published reviews were reviewed. Studies that met the following inclusion criteria were considered: (a) sample included preschoolers (age ≤5 years); (b) PA and/or sedentary behaviors or factors associated with PA and/or sedentary behaviors was assessed; (c) published in English; (d) used either quantitative or qualitative methods; and (e) conducted in a high‐income country. Data were extracted from selected studies to identify influences on PA and sedentary behaviors of preschool‐age children and organized using the social–ecological model according to multiple levels of influence. Results: Results from included studies identify multiple factors that influence PA and sedentary behaviors of young children in high‐income countries at the various levels of the social–ecological model including intrapersonal, interpersonal, environmental, organizational, and policy. Practice Implications: Given pediatric nurses’ role as primary care providers, and their frequent and continued contact with parents and their children throughout childhood through well‐child visits, immunization, and minor acute illnesses, they are well positioned to promote and support the development of early healthful PA habits of children starting in early childhood