Structure and stability of the compressible Stuart vortex

The structure and two- and three-dimensional stability properties of a linear array of compressible Stuart vortices (CSV; Stuart 1967; Meiron et al. 2000) are investigated both analytically and numerically. The CSV is a family of steady, homentropic, two-dimensional solutions to the compressible Euler equations, parameterized by the free-stream Mach number M_∞, and the mass flux _ inside a single vortex core. Known solutions have 0 < M_∞ < 1. To investigate the normal-mode stability of the generally spatially non-uniform CSV solutions, the linear partial-differential equations describing the time evolution of small perturbations to the CSV base state are solved numerically using a normal-mode analysis in conjunction with a spectral method. The effect of increasing M_∞ on the two main classes of instabilities found by Pierrehumbert & Widnall (1982) for the incompressible limit M_∞ → 0 is studied. It is found that both two- and three-dimensional subharmonic instabilities cease to promote pairing events even at moderate M_∞. The fundamental mode becomes dominant at higher Mach numbers, although it ceases to peak strongly at a single spanwise wavenumber. We also find, over the range of ε investigated, a new instability corresponding to an instability on a parallel shear layer. The significance of these instabilities to experimental observations of growth in the compressible mixing layer is discussed. In an Appendix, we study the CSV equations when ε is small and M_∞ is finite using a perturbation expansion in powers of ε. An eigenvalue determining the structure of the perturbed vorticity and density fields is obtained from a singular Sturm–Liouville problem for the stream-function perturbation at O(ε). The resulting small-amplitude steady CSV solutions are shown to represent a bifurcation from the neutral point in the stability of a parallel shear layer with a tanh-velocity profile in a compressible inviscid perfect gas at uniform temperature

Smooth transonic flow in an array of counter-rotating vortices

Numerical solutions to the steady two-dimensional compressible Euler equations corresponding to a compressible analogue of the Mallier & Maslowe (Phys. Fluids, vol. A 5, 1993, p. 1074) vortex are presented. The steady compressible Euler equations are derived for homentropic flow and solved using a spectral method. A solution branch is parameterized by the inverse of the sound speed at infinity, $c_{\infty}^{-1}$, and the mass flow rate between adjacent vortex cores of the corresponding incompressible solution, $\epsilon$. For certain values of the mass flux, the solution branches followed numerically were found to terminate at a finite value of $c_{\infty}^{-1}$. Along these branches numerical evidence for the existence of extensive regions of smooth steady transonic flow, with local Mach numbers as large as 1.276, is presented

Potential influences on suicide prevalence in comparisons of UK post-industrial cities

No abstract available

The regional geopolitics of the strait of Gibraltar

Security of passage of the Strait of Gibraltar is an imperative for the world community. To achieve this, there must be stability on the northern and southern shores of the Strait. Peace in the region is currently threatened by the "creeping jurisdiction" which both Spain and Morocco wish to exert over the waters of the Strait. Other factors which threaten stability are the historical rivalry which exists between Spain and the Islamic southern shore; the legacy of disputed sovereignty in the Crown Colony of Gibraltar and the Spanish Plazas in North Africa; the economic divide betwen the EC and Maghreb along the Strait axis; and the possible threat of militant Islam. Contentions also exist between Morocco and Algeria, eg the Western Saharan War. The re-establishment of a strong "power hierarchy" in the area must be supported by such international instruments as the UN Convention on the Law of the Sea (1982). The Crown Colony and the Spanish Plazas must be decolonized once Spain is firmly integrated into the EC and NATO, and once Morocco has reached a level of economic and political development that is condusive to closer ties with Western institutions

Brand Community, Loyalty and Promise in myfootballclub.co.uk

Purpose The primary purpose of this paper is to link the notions of brand community, loyalty and promise as a reminder to marketers of the importance to brands of keeping their commercial promises to brand community members. Design/methodology/approach The paper reports on a questionnaire survey (n=500) of members of a sport brand community as part of an investigation into the relationship between brand community and brand loyalty. Findings Brand loyalty was predicted by age, frequency of attendance, motivations for joining the brand community and the degree to which expectations built by the brand promise are met. Research limitations/implications In common with many inquiries in the area of brand community, this is a single case study. It is primarily a cross-sectional study, with a minor longitudinal element. Practical implications Branding practitioners and consultants with responsibility for brand community management issues need to balance the consumer-to-consumer dimensions of community with a careful understanding and operationalisation of the brand promise. Originality/value (mandatory): This is the first paper to integrate the constructs of brand community and brand loyalty with that of brand promise

Trajectory generation for road vehicle obstacle avoidance using convex optimization

This paper presents a method for trajectory generation using convex optimization to find a feasible, obstacle-free path for a road vehicle. Consideration of vehicle rotation is shown to be necessary if the trajectory is to avoid obstacles specified in a fixed Earth axis system. The paper establishes that, despite the presence of significant non-linearities, it is possible to articulate the obstacle avoidance problem in a tractable convex form using multiple optimization passes. Finally, it is shown by simulation that an optimal trajectory that accounts for the vehicle’s changing velocity throughout the manoeuvre is superior to a previous analytical method that assumes constant speed

A survey of antibodies to pestivirus in sheep in the Republic of Ireland

<p/> <p>Sera from 1,448 adult ewes in 91 flocks, representing all 26 counties in the Republic of Ireland, were examined for pestivirus antibodies using a commercially available ELISA which detected IgG₁antibody to border disease virus. Eighty-one sheep (5.6%) in 42 flocks (46.0%) were antibody-positive. Within infected flocks, the mean seroprevalence level was 11.4% with a range of 6.3% to 30.0%. The highest antibody prevalence was detected in sheep from central lowland counties of Ireland. Comparative neutralisation testing of 42 ELISA-positive sera detected geometric mean antibody titres of 136 to the NADL strain of bovine viral diarrhoea virus (BVDV), 92 to the Moredun strain of border disease virus and 21 to the 137/4 strain of border disease virus. These results suggest that BVDV may be the major ruminant pestivirus infecting sheep in Ireland. Although there are high numbers of infected flocks, many sheep within such flocks remain antibody-negative and are at risk of giving birth to lambs with congenital border disease.</p

GravEn: Software for the simulation of gravitational wave detector network response

Physically motivated gravitational wave signals are needed in order to study the behaviour and efficacy of different data analysis methods seeking their detection. GravEn, short for Gravitational-wave Engine, is a MATLAB software package that simulates the sampled response of a gravitational wave detector to incident gravitational waves. Incident waves can be specified in a data file or chosen from among a group of pre-programmed types commonly used for establishing the detection efficiency of analysis methods used for LIGO data analysis. Every aspect of a desired signal can be specified, such as start time of the simulation (including inter-sample start times), wave amplitude, source orientation to line of sight, location of the source in the sky, etc. Supported interferometric detectors include LIGO, GEO, Virgo and TAMA.Comment: 10 Pages, 3 Figures, Presented at the 10th Gravitational Wave Data Analysis Workshop (GWDAW-10), 14-17 December 2005 at the University of Texas, Brownsvill