Axial motion and scalar transport in stretched spiral vortices

We consider the dynamics of axial velocity and of scalar transport in the stretched-spiral vortex model of turbulent fine scales. A large-time asymptotic solution to the scalar advection-diffusion equation, with an azimuthal swirling velocity field provided by the stretched spiral vortex, is used together with appropriate stretching transformations to determine the evolution of both the axial velocity and a passive scalar. This allows calculation of the shell-integrated three-dimensional spectra of these quantities for the spiral-vortex flow. The dominant term in the velocity (energy) spectrum contributed by the axial velocity is found to be produced by the stirring of the initial distribution of axial velocity by the axisymmetric component of the azimuthal velocity. This gives a k(-7/3) spectrum at large wave numbers, compared to the k(-5/3) component for the azimuthal velocity itself. The spectrum of a passive scalar being mixed by the vortex velocity field is the sum of two power laws. The first is a k(-1) Batchelor spectrum for wave numbers up to the inverse Batchelor scale. This is produced by the axisymmetric component of the axial vorticity but is independent of the detailed radial velocity profile. The second is a k(-5/3) Obukov-Corrsin spectrum for wave numbers less than the inverse Kolmogorov scale. This is generated by the nonaxisymmetric axial vorticity and depends on initial correlations between this vorticity and the initial scalar field. The one-dimensional scalar spectrum for the composite model is in satisfactory agreement with experimental measurement

Topics on urban planning annotated bibliography

Urban planning and development - bibliography and abstract

A Quantum Adiabatic Evolution Algorithm Applied to Random Instances of an NP-Complete Problem

A quantum system will stay near its instantaneous ground state if the Hamiltonian that governs its evolution varies slowly enough. This quantum adiabatic behavior is the basis of a new class of algorithms for quantum computing. We test one such algorithm by applying it to randomly generated, hard, instances of an NP-complete problem. For the small examples that we can simulate, the quantum adiabatic algorithm works well, and provides evidence that quantum computers (if large ones can be built) may be able to outperform ordinary computers on hard sets of instances of NP-complete problems.Comment: 15 pages, 6 figures, email correspondence to [email protected] ; a shorter version of this article appeared in the April 20, 2001 issue of Science; see http://www.sciencemag.org/cgi/content/full/292/5516/47

A new view on the ISM of galaxies: far-infrared and submillimetre spectroscopy with Herschel

The FIR/submm window is amongst the least explored spectral regions of the electromagnetic spectrum. It is, however, a key to study the general properties of the interstellar medium of galaxies, as it contains important spectral line diagnostics from the neutral, ionized and molecular ISM. The Herschel Space Observatory, successfully launched on 14 May 2009, is the first observatory to cover the entire FIR/submm range between 57 and 672 mum. We discuss the main results from the ISO era on FIR spectroscopy of galaxies and the enormous science potential of the Herschel mission through a presentation of its spectroscopic extragalactic key programs.Comment: 10 pages, 4 figures, accepted for publication in New Astronomy Review

Distribution of an Exotic Pest, \u3ci\u3eAgromyza Frontella\u3c/i\u3e (Diptera: Agromyzidae), in Manitoba, Canada.

Agromyza frontella is an exotic alfalfa pest from Europe that was first detected in North America in 1968 and has since spread westward into Ontario and the north central United States. Informal surveys had detected A. frontella in Manitoba, but its distribution throughout this province was unknown. In 1998 we collected alfalfa stems to detect plant damage and sweep samples to detect adult A. frontella and the parasitoid Dacnusa dryas throughout the alfalfa growing region of Manitoba. In south central Manitoba, 100% of stems were damaged by A. frontella, and\u3e 100 adults/10 sweeps were recorded at several sites. In west central Manitoba, no plants were damaged and \u3c 10 adults/10 sweeps were observed. We believe this region to be near the western edge of A. frontella distribution. The most important introduced parasitoid of A. frontella, D. dryas, was not detected which suggests that D. dryas has not invaded Manitoba

Memory and rejuvenation in a spin glass

The temperature dependence of the magnetisation of a Cu(Mn) spin glass ($T_g$ $\approx$ 57 K) has been investigated using weak probing magnetic fields ($H$ = 0.5 or 0 Oe) and specific thermal protocols. The behaviour of the zero-field cooled, thermoremanent and isothermal remanent magnetisation on (re-)cooling the system from a temperature (40 K) where the system has been aged is investigated. It is observed that the measured magnetisation is formed by two parts: (i) a temperature- and observation time-dependent thermally activated relaxational part governed by the age- and temperature-dependent response function and the (latest) field change made at a lower temperature, superposed on (ii) a weakly temperature-dependent frozen-in part. Interestingly we observe that the spin configuration that is imprinted during an elongated halt in the cooling, if it is accompanied by a field induced magnetisation, also includes a unidirectional excess magnetisation that is recovered on returning to the ageing temperature.Comment: EPL style; 7 pages, 5 figure

Memory and superposition in a spin glass

Non-equilibrium dynamics in a Ag(Mn) spin glass are investigated by measurements of the temperature dependence of the remanent magnetisation. Using specific cooling protocols before recording the thermo- or isothermal remanent magnetisations on re-heating, it is found that the measured curves effectively disclose non-equilibrium spin glass characteristics such as ageing and memory phenomena as well as an extended validity of the superposition principle for the relaxation. The usefulness of this "simple" dc-method is discussed, as well as its applicability to other disordered magnetic systems.Comment: REVTeX style; 8 pages, 4 figure

Nonspinning searches for spinning binaries in ground-based detector data: Amplitude and mismatch predictions in the constant precession cone approximation

Current searches for compact binary mergers by ground-based gravitational-wave detectors assume for simplicity the two bodies are not spinning. If the binary contains compact objects with significant spin, then this can reduce the sensitivity of these searches, particularly for black hole--neutron star binaries. In this paper we investigate the effect of neglecting precession on the sensitivity of searches for spinning binaries using non-spinning waveform models. We demonstrate that in the sensitive band of Advanced LIGO, the angle between the binary's orbital angular momentum and its total angular momentum is approximately constant. Under this \emph{constant precession cone} approximation, we show that the gravitational-wave phasing is modulated in two ways: a secular increase of the gravitational-wave phase due to precession and an oscillation around this secular increase. We show that this secular evolution occurs in precisely three ways, corresponding to physically different apparent evolutions of the binary's precession about the line of sight. We estimate the best possible fitting factor between \emph{any} non-precessing template model and a single precessing signal, in the limit of a constant precession cone. Our closed form estimate of the fitting-factor depends only the geometry of the in-band precession cone; it does not depend explicitly on binary parameters, detector response, or details of either signal model. The precessing black hole--neutron star waveforms least accurately matched by nonspinning waveforms correspond to viewing geometries where the precession cone sweeps the orbital plane repeatedly across the line of sight, in an unfavorable polarization alignment