Versatile directional searches for gravitational waves with Pulsar Timing Arrays

By regularly monitoring the most stable millisecond pulsars over many years, pulsar timing arrays (PTAs) are positioned to detect and study correlations in the timing behaviour of those pulsars. Gravitational waves (GWs) from supermassive black hole binaries (SMBHBs) are an exciting potentially detectable source of such correlations. We describe a straightforward technique by which a PTA can be ‘phased-up’ to form time series of the two polarization modes of GWs coming from a particular direction of the sky. Our technique requires no assumptions regarding the time-domain behaviour of a GW signal. This method has already been used to place stringent bounds on GWs from individual SMBHBs in circular orbits. Here, we describe the methodology and demonstrate the versatility of the technique in searches for a wide variety of GW signals including bursts with unmodelled waveforms. Using the first six years of data from the Parkes Pulsar Timing Array, we conduct an all-sky search for a detectable excess of GW power from any direction. For the lines of sight to several nearby massive galaxy clusters, we carry out a more detailed search for GW bursts with memory, which are distinct signatures of SMBHB mergers. In all cases, we find that the data are consistent with noise

Viewing A Local Flora Digitally

In a world of increasing ‘plant blindness,’ many people, including university students, lack the background to recognize the native flora of a region. However, the availability of digital teaching and learning resources such as Moodle’s H5P activities increases the usefulness of online learning for even such experiential topics as field botany. Viewing local flora digitally is a project to create an online resource that will outline the recognition characters of the most species-rich families found in the Interior of BC, as well as many of the most common flowering plant species. The objective of this project was threefold: (1) to build a digital resource, available to both future TRU students and the greater community, (2) foster our own knowledge and appreciation of the Kamloops flora, and (3) develop the skills to build digital education resources. By working collaboratively, we were able to cover 21 of the most species-rich flowering plant families. For each flowering plant family included, this resource has outlined the recognition characters, unique features, and provided local examples of the family. Information was incorporated into interactive H5P activities and summative quizzes that serve to engage the student and reinforce the content. The activities and quizzes built in Moodle have the potential to be transferred to a more public domain, through platforms such as WordPress. The events of the last year have shown the importance of online teaching and learning resources. Not only has this project allowed us to develop the necessary vocabulary and skills to recognize our local flora but has allowed us to contribute to a resource that can be used by future students and the public. The development of accessible science helps not only the university but the community in which TRU resides

Periodically-dressed Bose-Einstein condensates: a superfluid with an anisotropic and variable critical velocity

Two intersecting laser beams can produce a spatially-periodic coupling between two components of an atomic gas and thereby modify the dispersion relation of the gas according to a dressed-state formalism. Properties of a Bose-Einstein condensate of such a gas are strongly affected by this modification. A Bogoliubov transformation is presented which accounts for interparticle interactions to obtain the quasiparticle excitation spectrum in such a condensate. The Landau critical velocity is found to be anisotropic and can be widely tuned by varying properties of the dressing laser beams.Comment: 5 pages, 4 figure

Vortex Nucleation in a Stirred Bose-Einstein Condensate

We studied the nucleation of vortices in a Bose-Einstein condensate stirred by a laser beam. We observed the vortex cores using time-of-flight absorption imaging. By varying the size of the stirrer, we observed either discrete resonances or a broad response as a function of the frequency of the stirrer's motion. Stirring beams small compared to the condensate size generated vortices below the critical rotation frequency for the nucleation of surface modes, suggesting a local mechanism of generation. In addition, we observed the centrifugal distortion of the condensate due to the rotating vortex lattice and found evidence for bent vortices

Comparison of theoretical and absolute experimental fully differential cross sections for ion-atom impact ionization

We report fully differential cross section (FDCS) calculations and absolute measurements for ion-atom impact ionization. Using the COLTRIMS (cold target recoil ion momentum spectroscopy) method we have obtained absolute FDCS both in the scattering plane as well as out of the scattering plane for 100 MeV amu(- 1) C6+ ionization of helium FDCS results are presented for different projectile scattering angles and ejected electron energies. The measurements are compared with a theoretical calculation employing an asymptotically exact three body final state wavefunction that contains all active two particle subsystem interactions to infinite order in perturbation theory. For the active electron a Hartree-Fock (HF) bound state wavefunction is used for the initial state and numerical continuum state eigenfunctions of a HF potential for the ion are used for the final state In the scattering plane these theoretical results are in very good agreement with experiment for small and intermediate momentum transfer. However some significant discrepancies are found for large momentum transfer and outside the scattering plane. These discrepancies disappear upon comparison with successively less differential cross sections

Mortality impact of AIDS in Abidjan, 1986-1992

To quantify the mortality impact of AIDS in the city of Abidjan (Côte d'Ivoire) by a full scale analysis of mortality trends before and after the onset of the epidemic. Data on deaths registered in the 10 vital registration centers of the city between 1973 and 1992, and data on causes of deaths in the four public hospitals were coded and investigated. Data on deaths were compared with census data in order to compute death rates. Life tables were computed for each of the 20 years of the study. The trends in death rates were analysed during the 10 years before the onset of the AIDS epidemic (1973-1982) and compared with the changing death rates in the following 10 years (1983-1992). Deaths attributable to AIDS were defined as those in excess of the original trends. The evolution in the number of deaths in the hospital allowed an analysis by cause of death. There was a marked increase in death rates starting in 1986, date of the first diagnosed AIDS cases in the city. This increase was significant for both sexes, but more pronounced among men. It was concentrated primarily among young adults (aged 25-44 years) and among older children (aged 5-14 years), and most of it was considered to be attributable to AIDS and related infections, tuberculosis in particular. When data were cumulated from 1986 to 1992, approximately 25000 persons were estimated to have died of AIDS. The high number of AIDS deaths estimated in Abidjan underlines the heavy toll already paid by african populations, and calls for intensive action. (Résumé d'auteur

Three-Dimensional Imaging of Atomic Four-Body Processes

To understand the physical processes that occur in nature we need to obtain a solid concept about the 'fundamental' forces acting between pairs of elementary particles. It is also necessary to describe the temporal and spatial evolution of many mutually interacting particles under the influence of these forces. This latter step, known as the few-body problem, remains an important unsolved problem in physics. Experiments involving atomic collisions represent a useful testing ground for studying the few-body problem. For the single ionization of a helium atom by charged particle impact, kinematically complete experiments have been performed since 1969 (ref. 7). The theoretical analysis of such experiments was thought to yield a complete picture of the basic features of the collision process, at least for large collision energies. These conclusions are, however, almost exclusively based on studies of restricted electron-emission geometries. Here, we report three-dimensional images of the complete electron emission pattern for the single ionization of helium by the impact of C6+ ions of energy 100 MeV per a.m.u. (a four-body system) and observe features that have not been predicted by any published theoretical model. We propose a higher-order ionization mechanism, involving the interaction between the projectile and the target nucleus, to explain these features