Odd-Parity Bipolar Spherical Harmonics

Bipolar spherical harmonics (BiPoSHs) provide a general formalism for quantifying departures in the cosmic microwave background (CMB) from statistical isotropy (SI) and from Gaussianity. However, prior work has focused only on BiPoSHs with even parity. Here we show that there is another set of BiPoSHs with odd parity, and we explore their cosmological applications. We describe systematic artifacts in a CMB map that could be sought by measurement of these odd-parity BiPoSH modes. These BiPoSH modes may also be produced cosmologically through lensing by gravitational waves (GWs), among other sources. We derive expressions for the BiPoSH modes induced by the weak lensing of both scalar and tensor perturbations. We then investigate the possibility of detecting parity-breaking physics, such as chiral GWs, by cross-correlating opposite parity BiPoSH modes with multipole moments of the CMB polarization. We find that the expected signal-to-noise of such a detection is modest.Comment: 19 pages, 4 figures, Accepted to PR

Astrometric Effects of a Stochastic Gravitational Wave Background

A stochastic gravitational wave background causes the apparent positions of distant sources to fluctuate, with angular deflections of order the characteristic strain amplitude of the gravitational waves. These fluctuations may be detectable with high precision astrometry, as first suggested by Braginsky et al. in 1990. Several researchers have made order of magnitude estimates of the upper limits obtainable on the gravitational wave spectrum \Omega_gw(f), at frequencies of order f ~ 1 yr^-1, both for the future space-based optical interferometry missions GAIA and SIM, and for VLBI interferometry in radio wavelengths with the SKA. For GAIA, tracking N ~ 10^6 quasars over a time of T ~ 1 yr with an angular accuracy of \Delta \theta ~ 10 \mu as would yield a sensitivity level of \Omega_gw ~ (\Delta \theta)^2/(N T^2 H_0^2) ~ 10^-6, which would be comparable with pulsar timing. In this paper we take a first step toward firming up these estimates by computing in detail the statistical properties of the angular deflections caused by a stochastic background. We compute analytically the two point correlation function of the deflections on the sphere, and the spectrum as a function of frequency and angular scale. The fluctuations are concentrated at low frequencies (for a scale invariant stochastic background), and at large angular scales, starting with the quadrupole. The magnetic-type and electric-type pieces of the fluctuations have equal amounts of power.Comment: 23 pages, 2 figures, references added and minor text correction

Angular momentum evolution in dark-matter haloes

We have analysed high-resolution N-body simulations of dark-matter (DM) haloes, focusing specifically on the evolution of angular momentum. We find that not only is individual particle angular momentum not conserved, but the angular momentum of radial shells also varies over the age of the Universe by up to factors of a few. We find that torques from external structure are the most likely cause for this distribution shift. Since the model of adiabatic contraction that is often applied to model the effects of galaxy evolution on the DM density profile in a halo assumes angular momentum conservation, this variation implies that there is a fundamental limit on the possible accuracy of the adiabatic contraction model in modelling the response of DM haloes to the growth of galaxies

The Role of Ram Pressure Stripping in the Quenching of Cluster Star Formation

Recent observations of galaxy clusters have shown that environmental effects apparently associated with the cluster begin to lower the star formation rates of galaxies at distances as great as three times the cluster virial radius. These observations may indicate preprocessing of cluster galaxies in groups or in the cluster core for galaxies on highly elliptical orbits, but may also imply that the environmental effects due to the cluster are directly affecting galaxies on their first infall. To explore these issues, we investigate different models of ram pressure stripping as it acts on satellite galaxies in clusters, and compare to observations of the radial star formation gradient in clusters. We calculate the location of the accretion shock around model clusters, and use this as the radius of onset of ram pressure stripping in the GALFORM semi-analytic model of galaxy formation. Comparison of the results of our model, and previously considered, simpler ram pressure models, with recent observations indicates that current data is unable to strongly discriminate between models of ram pressure stripping due to the complex interplay of preprocessing effects at work. However, future observations of a larger sample of clusters will likely be able to place stronger constraints on the process of ram pressure stripping and its role in shaping radial trends in and around clusters.Comment: 10 pages, 4 figures, published in the Astrophysical Journa

Star Formation Around Supergiant Shells in the LMC

We examine the recent star formation associated with four supergiant shells (SGSs) in the Large Magellanic Cloud (LMC): LMC 1, 4, 5, and 6, which have been shown to have simple expanding-shell structures. H II regions and OB associations are used to infer star formation in the last few Myr, while massive young stellar objects (YSOs) reveal the current ongoing star formation. Distributions of ionized, H I, and molecular components of the interstellar gas are compared with the sites of recent and current star formation to determine whether triggering has taken place. We find that a great majority of the current star formation has occurred in gravitationally unstable regions, and that evidence of triggered star formation is prevalent at both large and local scales.Comment: 12 pages, 4 figures, accepted for publication in the Astronomical Journal, improved image quality of figure

Modeling and Simulation of a Pneumatically-Actuated Rescue Robot

Presented at the 52nd National Conference on Fluid Power, Las Vegas, NV, USA, March 23-25, 2011.A four-legged pneumatically actuated search and rescue robot is presented as a system with potentially enhanced versatility relative to existing rescue robots. The usage of fluid powered actuation, combined with tele-operation of the robot via an operator workstation, enables the twelve degree of freedom robot to better manipulate large objects. A simulation is developed to enable ease of design variation and implementation testing in difficult virtual terrains. The simulation consists of an actuator model, modeled in Simulink, which is interfaced with an open-source dynamic simulation. The simulation calculates the robot dynamics based on actuator inputs. Where previous research has focused on the development of simulation kinematics and simple actuator models, this paper discusses development of a friction model for improved fidelity of the simulator, as well as implementation and verification in the dynamic model. The balance between model performance and the level of realism required for system development is found and discussed

User Interface with Multisensory Feedback for Fluid Powered Rescue Robot

Presented at the 6th FPNI – PhD Symposium, June 15-19 2010, West Lafayette, Indiana.A semi-autonomously controlled fluid-powered legged search and rescue robot is proposed as a solution to the ever-increasing demand for more versatile rescue robot technology. The success of such a robot is dependent on the existence of a user interface that optimizes the balance between user and machine decisions and provides the operator with the appropriate amount of information to soundly make such decisions. The system design, consisting of a simulation/physical robot, on-board computer, and operator interface are described. Aspects of the relation between operator input and robot motion are discussed, such as the influence of feedback on operator actions or the integration of input into semi-autonomous gaits. The basis for tests seeking to optimize the interface design is established

Changing knowledge, attitudes and behaviours towards cytomegalovirus in pregnancy through film-based antenatal education: a feasibility randomised controlled trial of a digital educational intervention

Background Congenital cytomegalovirus (CMV) is the most common congenital infection globally, however information about CMV is not routinely included in antenatal education in the United Kingdom. This feasibility study aimed to gather the essential data needed to design and power a large randomised controlled trial (RCT) to investigate the efficacy of a digital intervention in reducing the risk of CMV acquisition in pregnancy. In order to do this, we carried out a single-centre RCT, which explored the knowledge, attitudes and risk reduction behaviours in women in the intervention and treatment as usual groups, pre- and post-intervention. Methods CMV seronegative women living with a child less than four years old, receiving antenatal care at a single UK tertiary centre, were randomised to the digital intervention or ‘treatment as usual’ groups. Participants completed questionnaires before the digital intervention and after and at 34 gestational weeks, and responses within groups and between groups were compared using tailored randomisation tests. CMV serology was tested in the first trimester and at the end of pregnancy. Results Of the 878 women screened, 865 samples were analysed with 43% (n = 372) being CMV seronegative and therefore eligible to take part in the RCT; of these, 103 (27.7%) women were enrolled and 87 (84%) of these completed the study. Most participants (n = 66; 64%) were unfamiliar with CMV at enrolment, however at 34 gestational weeks, women in the intervention group (n = 51) were more knowledgeable about CMV compared to the treatment as usual group (n = 52) and reported engaging in activities that may increase the risk of CMV transmission less frequently. The digital intervention was highly acceptable to pregnant women. Overall, four participants seroconverted over the course of the study: two from each study group. Conclusions A large multi-centre RCT investigating the efficacy of a CMV digital intervention is feasible in the United Kingdom; this study has generated essential data upon which to power such a study. This single-centre feasibility RCT demonstrates that a digital educational intervention is associated with increase in knowledge about CMV and can result in behaviour change which may reduce the risk of CMV acquisition in pregnancy