Selective decay by Casimir dissipation in fluids

The problem of parameterizing the interactions of larger scales and smaller scales in fluid flows is addressed by considering a property of two-dimensional incompressible turbulence. The property we consider is selective decay, in which a Casimir of the ideal formulation (enstrophy in 2D flows, helicity in 3D flows) decays in time, while the energy stays essentially constant. This paper introduces a mechanism that produces selective decay by enforcing Casimir dissipation in fluid dynamics. This mechanism turns out to be related in certain cases to the numerical method of anticipated vorticity discussed in \cite{SaBa1981,SaBa1985}. Several examples are given and a general theory of selective decay is developed that uses the Lie-Poisson structure of the ideal theory. A scale-selection operator allows the resulting modifications of the fluid motion equations to be interpreted in several examples as parameterizing the nonlinear, dynamical interactions between disparate scales. The type of modified fluid equation systems derived here may be useful in modelling turbulent geophysical flows where it is computationally prohibitive to rely on the slower, indirect effects of a realistic viscosity, such as in large-scale, coherent, oceanic flows interacting with much smaller eddies

Integrability of one degree of freedom symplectic maps with polar singularities

In this paper, we treat symplectic difference equations with one degree of freedom. For such cases, we resolve the relation between that the dynamics on the two dimensional phase space is reduced to on one dimensional level sets by a conserved quantity and that the dynamics is integrable, under some assumptions. The process which we introduce is related to interval exchange transformations.Comment: 10 pages, 2 figure

Severe health and social care issues among British migrants who retire to Spain

In recent years, there has been a growth in academic interest in international retirement migration in Europe, particularly north-south retirement migration to destinations like Spain. In this paper we focus on those members of the British community who have lived in Spain for a considerable time and for whom familial, social and institutional ties with Britain are weak or disrupted. Age Concern España was established by members of the British community to provide information and services on healthcare, benefits and local services in Spain. Four indicative case studies of those requesting assistance and classified as being of ‘serious need’ are presented. They illustrate the ways in which happy and fulfilling lives in Spain were abruptly changed as the person’s resources (bodily, economic, social and skills) for independent living diminished, and in which institutions and friendship networks played a key role in supporting life. The paper is the product of collaboration between researchers and practitioners in Spain and the UK, and brings together previous research with new qualitative case studies. Whilst policy-makers, practitioners and gerontologists have an increasing awareness of the needs of older migrants and the challenges they pose for public policy, particularly for health and social care systems in Spain, there have been little sustained analysis and cross-country debate

B-52 control configured vehicles: Flight test results

Recently completed B-52 Control Configured Vehicles (CCV) flight testing is summarized, and results are compared to analytical predictions. Results are presented for five CCV system concepts: ride control, maneuver load control, flutter mode control, augmented stability, and fatigue reduction. Test results confirm analytical predictions and show that CCV system concepts achieve performance goals when operated individually or collectively

Link Invariants for Flows in Higher Dimensions

Linking numbers in higher dimensions and their generalization including gauge fields are studied in the context of BF theories. The linking numbers associated to $n$-manifolds with smooth flows generated by divergence-free p-vector fields, endowed with an invariant flow measure are computed in different cases. They constitute invariants of smooth dynamical systems (for non-singular flows) and generalizes previous results for the 3-dimensional case. In particular, they generalizes to higher dimensions the Arnold's asymptotic Hopf invariant for the three-dimensional case. This invariant is generalized by a twisting with a non-abelian gauge connection. The computation of the asymptotic Jones-Witten invariants for flows is naturally extended to dimension n=2p+1. Finally we give a possible interpretation and implementation of these issues in the context of string theory.Comment: 21+1 pages, LaTeX, no figure

On the MHD load and the MHD metage

In analogy with the load and the metage in hydrodynamics, we define magnetohydrodynamic load and magnetohydrodynamic metage in the case of magnetofluids. They can be used to write the magnetic field in MHD in Clebsch's form. We show how these two concepts can be utilised to derive the magnetic analogue of the Ertel's theorem and also, how in the presence of non-trivial topology of the magnetic field in the magnetofluid one may associate the linking number of the magnetic field lines with the invariant MHD loads. The paper illustrates that the symmetry translation of the MHD metage in the corresponding label space generates the conservation of cross helicity.Comment: Some issues in the paper are yet to be addressed. Constructive critisicms are most welcom

On Koopman-von Neumann Waves II

In this paper we continue the study, started in [1], of the operatorial formulation of classical mechanics given by Koopman and von Neumann (KvN) in the Thirties. In particular we show that the introduction of the KvN Hilbert space of complex and square integrable "wave functions" requires an enlargement of the set of the observables of ordinary classical mechanics. The possible role and the meaning of these extra observables is briefly indicated in this work. We also analyze the similarities and differences between non selective measurements and two-slit experiments in classical and quantum mechanics.Comment: 18+1 pages, 1 figure, misprints fixe

High momentum lepton pairs from jet-plasma interactions

We discuss the emission of high momentum lepton pairs (p_T>4 GeV) with low invariant masses (M << p_T) in central Au+Au collisions at RHIC (\sqrt{s_{NN}}=200 GeV). The spectra of dileptons produced through interactions of quark and antiquark jets with the quark-gluon plasma (QGP) have been calculated. Annihilation and Compton scattering processes, as well as processes benefitting from collinear enhancement, including Landau-Pomeranchuk-Migdal (LPM) effects, are calculated and convolved with a one dimensional hydrodynamic expansion. The jet-induced contributions are compared to thermal dilepton emission and Drell-Yan processes, and are found to dominate around p_T=4 GeV.Comment: Parallel talk given at QM2006, Shanghai November 2006. 4 pages, 3 figure

Lunar elemental analysis obtained from the Apollo gamma-ray and X-ray remote sensing experiment

Gamma-ray and X-ray spectrometers carried in the service modules of the Apollo 15 and Apollo 16 spacecraft were employed for compositional mapping of the lunar surface. The measurements involved the observation of the intensity and characteristic energy distribution of gamma rays and X-rays emitted from the lunar surface. A large-scale compositional map of over 10 percent of the lunar surface was obtained from an analysis of the observed spectra. The objective of the X-ray experiment was to measure the K spectral lines from Mg, Al, and Si. Spectra were obtained and the data were reduced to Al/Si and Mg/Si intensity ratios and ultimately to chemical ratios. Analyses of the results have indicated (1) that the Al/Si ratios are highest in the lunar highlands and considerably lower in the maria, and (2) that the Mg/Si concentrations generally show the opposite relationship. The objective of the gamma-ray experiment was to measure the natural and cosmic-ray-induced activity emission spectrum. At this time, the elemental abundances for Th, U, K, Fe, Ti, Si, and O have been determined over a number of major lunar regions. Regions of relatively high natural radioactivity were found in the Mare Imbrium and Oceanus Procellarum regions

Pseudo-boundaries in discontinuous 2-dimensional maps

It is known that Kolmogorov-Arnold-Moser boundaries appear in sufficiently smooth 2-dimensional area-preserving maps. When such boundaries are destroyed, they become pseudo-boundaries. We show that pseudo-boundaries can also be found in discontinuous maps. The origin of these pseudo-boundaries are groups of chains of islands which separate parts of the phase space and need to be crossed in order to move between the different sub-spaces. Trajectories, however, do not easily cross these chains, but tend to propagate along them. This type of behavior is demonstrated using a ``generalized'' Fermi map.Comment: 4 pages, 4 figures, Revtex, epsf, submitted to Physical Review E (as a brief report