Physical Modeling of the Atmospheric Boundary Layer in the University of New Hampshire’s Flow Physics Facility

The atmospheric boundary layer is the lowest part of the atmosphere, and is defined by a region from the surface of the earth to approximately 500-1000m altitude in which air velocity changes from zero at the surface to the velocity of the wind at a certain altitude. The type of atmospheric boundary layer is characterized by the terrain it encounters, varying from open sea and mud flats to suburban areas and city centers with high- and low-rise buildings. The goal of this project is to generate different types of atmospheric boundary layers for scale model testing in the UNH Flow Physics Facility (FPF).The project began with the analysis of smooth wall (baseline) data previously recorded in the FPF. Several arrays of roughness elements were designed to simulate varying roughness lengths experienced by atmospheric boundary layers and tested in the FPF. The resulting velocity profiles in the boundary layer were measured using hot wire anemometry and pitot static tubes. These measured velocity profiles (mean and turbulence) and velocity spectra were compared to atmospheric boundary layers using ASCE Standards (ASCE/SEI 49-12). This application can then be used in the future for wind engineering studies, such as the structural analysis of buildings

Sleepless in school? The social dimensions of young people's bedtime rest and routines

There are increasing concerns that social pressures, such as family changes and social media, are ‘invading’ the sanctuary of the bedroom with the result that students arrive at school tired and stressed. This paper seeks to examine whether these concerns are justified and contribute to the growing literature on the social dimensions of sleep through examining the rest and routines of two cohorts of young people aged 12–13 and 14–15 years old. Our research indicates that, in general, most young people have ‘reasonable’ amounts of sleep and routines. But, a significant proportion does go to school tired, with apparent negative consequences for their well-being. The paper examines some of the within-cohort variations, in particular, the significance of volume of sleep, routines and engagement with social media and how these may reflect the material and cultural circumstances of the young people. The paper concludes by arguing for more research on the complex social causes and consequences of sleep deprivation among today’s youth

Dark matter density profiles from the Jeans equation

We make a simple analytical study of radial profiles of dark matter structures, with special attention to the question of the central radial density profile. We let our theoretical assumptions be guided by results from numerical simulations, and show that at any radius where both the radial density profile, rho, and the phase-space-like density profile, rho/sigma^epsilon, are exact power laws, the only allowed density slopes in agreement with the spherical symmetric and isotropic Jeans equation are in the range 1< beta <3, where beta = - dln(rho)/dln(r). We also allow for a radial variation of these power laws, as well as anisotropy, and show how this allows for more shallow central slopes.Comment: 4 pages, no figures, minor typos correcte

The phase-space distribution of infalling dark matter subhalos

We use high-resolution numerical simulations to study the physical properties of subhalos when they merge into their host halos. An improved algorithm is used to identify the subhalos. We then examine their spatial and velocity distributions in spherical and triaxial halo models. We find that the accretion of satellites preferentially occurs along the major axis and perpendicular to the spin axis of the host halo. Furthermore, the massive subhalos show a stronger preference to be accreted along the major axis of the host halo than the low-mass ones. Approximate fitting formulae are provided for the physical properties of subhalos. Combined with analytical and semi-analytic techniques, these empirical formulae provide a useful basis for studying the subsequent evolution of subhalos and satellite galaxies in their hosts. Future studies should however account for satellites that may not be undergoing the first infall in their evolution.Comment: revised version in press in MN with added material and references, 21 pages and 25 figure

Major Mergers of Galaxy Haloes: Cuspy or Cored Inner Density Profile?

We present the results from a series of collisionless N-body simulations of major mergers of galaxy dark matter haloes with density profiles having either inner cusps or cores. Our simulations range from 2x10^5 to 10^7 particles, allowing us to probe the phase-space distribution of dark matter particles in the innermost regions (less than 0.005 virial radii) of cold dark matter haloes, a subject of much recent debate. We find that a major merger of two cored haloes yields a cored halo and does not result in a cuspy profile seen in many cosmological simulations. This result is unchanged if we consider mergers with parent mass ratios of 3:1 instead of 1:1. Mergers of a cuspy halo with either a cored halo or a second cuspy halo of equal mass, on the other hand, produce cuspy haloes with a slightly reduced inner logarithmic slope. Cuspy haloes, once formed, therefore appear resilient to major mergers. We find the velocity structure of the remnants to be mildly anisotropic, with a Maxwellian velocity distribution near the centre but not in the outer portions of the final haloes. Violent relaxation is effective only during the early phase of mergers, with phase mixing likely to be the dominant relaxation process at late times.Comment: MNRAS (in press). 15 pages, 16 figures; minor changes, one additional figure, updated reference

Density Profile Asymptotes at the Centre of Dark Matter Halos

For the spherical symmetric case, all quantities describing the relaxed dark matter halo can be expressed as functions of the gravitational potential $\Phi$. Decomposing the radial velocity dispersion $\sigma_r$ with respect to $\Phi$ at very large and very small radial distances the possible asymptotic behavior for the density and velocity profiles can be obtained. If reasonable boundary conditions are posed such as a finite halo mass and force-free halo centre the asymptotic density profiles at the centre should be much less steep than the profiles obtained within numerical simulations. In particular cases profiles like Plummer's model are obtained. The reasons of that seeming discrepancy with respect to the results of N-body simulations are discussed.Comment: Accepted for publication in Astronomy & Astrophysics, LaTeX, 7 pages, 2 figure

Beyond ‘peer pressure’: rethinking drug use and ‘youth culture’

The study of drug use by young people in the West has been transformed over the last decade by the development of sociological approaches to drug use which take serious account of the cultural context in which young people encounter drugs. One consequence is that the notion of ‘peer pressure’, as the primary articulation of the engagement between youth culture and drug use, has been displaced by that of ‘normalisation’, which envisages ‘recreational’ drug use as one expression of consumer-based youth cultural lifestyles. In stark contrast, academic discussion of drug use in Russia remains primarily concerned with the prevalence and health consequences of (intravenous) drug use while explanations of rising rates of drug use focus on structural factors related to the expansion of drugs supply and, to a lesser extent, post-Soviet social and economic dislocation. In this article, original empirical research in Russia is used to develop an understanding of young people's drug use that synthesises structural and cultural explanations of it. It does this by situating young people's narratives of their drugs choices in the context of local drugs markets and broader socio-economic processes. However, it attempts to go beyond seeing structural location as simply a ‘constraint’ on individual choice by adopting an understanding of ‘youth culture’ as a range of youth cultural practices and formations that simultaneously embody, reproduce and negotiate the structural locations of their subjects

Power spectrum for the small-scale Universe

The first objects to arise in a cold dark matter universe present a daunting challenge for models of structure formation. In the ultra small-scale limit, CDM structures form nearly simultaneously across a wide range of scales. Hierarchical clustering no longer provides a guiding principle for theoretical analyses and the computation time required to carry out credible simulations becomes prohibitively high. To gain insight into this problem, we perform high-resolution (N=720^3 - 1584^3) simulations of an Einstein-de Sitter cosmology where the initial power spectrum is P(k) propto k^n, with -2.5 < n < -1. Self-similar scaling is established for n=-1 and n=-2 more convincingly than in previous, lower-resolution simulations and for the first time, self-similar scaling is established for an n=-2.25 simulation. However, finite box-size effects induce departures from self-similar scaling in our n=-2.5 simulation. We compare our results with the predictions for the power spectrum from (one-loop) perturbation theory and demonstrate that the renormalization group approach suggested by McDonald improves perturbation theory's ability to predict the power spectrum in the quasilinear regime. In the nonlinear regime, our power spectra differ significantly from the widely used fitting formulae of Peacock & Dodds and Smith et al. and a new fitting formula is presented. Implications of our results for the stable clustering hypothesis vs. halo model debate are discussed. Our power spectra are inconsistent with predictions of the stable clustering hypothesis in the high-k limit and lend credence to the halo model. Nevertheless, the fitting formula advocated in this paper is purely empirical and not derived from a specific formulation of the halo model.Comment: 30 pages including 10 figures; accepted for publication in MNRA

China and the South : objectives, actors and interactions

China has stepped up its engagement of developing countries through both bilateral interactions and the establishment of more formal multilateral fora. To achieve this, China's leaders have established a clear state policy designed to secure much needed resources and to establish an identity as a new and different type of ‘great power’. China has also become a proactive provider of development aid which, when combined with other forms of economic engagement, have raised concerns in the West that China is undermining the promotion of a liberal global order. But we need to take care in considering who, or what, is driving Chinese policy. The institutional weakness of the Ministry of Foreign Affairs means that commercial and financial agencies have dominated the agenda; major state owned enterprises and increasingly large numbers of small, often private enterprises are pursuing their own commercial agendas overseas, which are often not controlled by Beijing. The result is a patchwork of different types of relationships with developing countries, more often driven by the commercial concerns of economic actors than by a coherent diplomatic strategy