Linearized gravity and gauge conditions

In this paper we consider the field equations for linearized gravity and other integer spin fields on the Kerr spacetime, and more generally on spacetimes of Petrov type D. We give a derivation, using the GHP formalism, of decoupled field equations for the linearized Weyl scalars for all spin weights and identify the gauge source functions occuring in these. For the spin weight 0 Weyl scalar, imposing a generalized harmonic coordinate gauge yields a generalization of the Regge-Wheeler equation. Specializing to the Schwarzschild case, we derive the gauge invariant Regge-Wheeler and Zerilli equation directly from the equation for the spin 0 scalar.Comment: 24 pages, corresponds to published versio

Laboratory Experiments, Numerical Simulations, and Astronomical Observations of Deflected Supersonic Jets: Application to HH 110

Collimated supersonic flows in laboratory experiments behave in a similar manner to astrophysical jets provided that radiation, viscosity, and thermal conductivity are unimportant in the laboratory jets, and that the experimental and astrophysical jets share similar dimensionless parameters such as the Mach number and the ratio of the density between the jet and the ambient medium. Laboratory jets can be studied for a variety of initial conditions, arbitrary viewing angles, and different times, attributes especially helpful for interpreting astronomical images where the viewing angle and initial conditions are fixed and the time domain is limited. Experiments are also a powerful way to test numerical fluid codes in a parameter range where the codes must perform well. In this paper we combine images from a series of laboratory experiments of deflected supersonic jets with numerical simulations and new spectral observations of an astrophysical example, the young stellar jet HH 110. The experiments provide key insights into how deflected jets evolve in 3-D, particularly within working surfaces where multiple subsonic shells and filaments form, and along the interface where shocked jet material penetrates into and destroys the obstacle along its path. The experiments also underscore the importance of the viewing angle in determining what an observer will see. The simulations match the experiments so well that we can use the simulated velocity maps to compare the dynamics in the experiment with those implied by the astronomical spectra. The experiments support a model where the observed shock structures in HH 110 form as a result of a pulsed driving source rather than from weak shocks that may arise in the supersonic shear layer between the Mach disk and bow shock of the jet's working surface.Comment: Full resolution figures available at http://sparky.rice.edu/~hartigan/pub.html To appear in Ap

Observation of Wigner cusps in a metallic carbon nanotube

Previous gate-dependent conductance measurements of metallic carbon nanotubes have revealed unexplainable conductance suppressions, occurring at two different gate voltages. These were previously attributed to the gate-dependency of contact resistance. Our gate-dependent conductivity measurements on a metallic nanotube with known chirality show that these bimodal conductance suppressions are the manifestations of Wigner cusps, often seen in atomic and nuclear physics experiments.Comment: 6 pages, 3 figure

A Semi-Lagrangian scheme for a modified version of the Hughes model for pedestrian flow

In this paper we present a Semi-Lagrangian scheme for a regularized version of the Hughes model for pedestrian flow. Hughes originally proposed a coupled nonlinear PDE system describing the evolution of a large pedestrian group trying to exit a domain as fast as possible. The original model corresponds to a system of a conservation law for the pedestrian density and an Eikonal equation to determine the weighted distance to the exit. We consider this model in presence of small diffusion and discuss the numerical analysis of the proposed Semi-Lagrangian scheme. Furthermore we illustrate the effect of small diffusion on the exit time with various numerical experiments

Dual, orthogonal, backlit pinhole radiography in OMEGA experiments

Backlit pinhole radiography used with ungated film as a detector creates x-ray radiographs with increased resolution and contrast. Current hydrodynamics experiments on the OMEGA Laser use a three-dimensional sinusoidal pattern as a seed perturbation for the study of instabilities. The structure of this perturbation makes it highly desirable to obtain two simultaneous orthogonal backlighting views. We accomplished this using two backlit pinholes each mounted 12 mm12mm from the target. The pinholes, of varying size and shape, were centered on 5 mm5mm square foils of 50 μm50μm thick Ta. The backlighting is by KK-alpha emission from a 500 μm500μm square Ti or Sc foil mounted 500 μm500μm from the Ta on a plastic substrate. Four laser beams overfill the metal foil, so that the expanding plastic provides radial tamping of the expanding metal plasma. The resulting x-rays pass through the target onto (ungated) direct exposure film (DEF). Interference between the two views is reduced by using a nose cone in front of the DEF, typically with a 9 mm9mm Ta aperture and with magnets to deflect electrons. Comparison of varying types of pinholes and film exposures will be presented from recent experiments as well as an analysis of the background noise created using this experimental technique.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87894/2/10E327_1.pd

Post-traumatic stress disorder following childbirth: an update of current issues and recommendations for future research

Objective: This paper aimed to report the current status of research in the field of post-traumatic stress disorder following childbirth (PTSD FC), and to update the findings of an earlier 2008 paper. Background: A group of international researchers, clinicians and service users met in 2006 to establish the state of clinical and academic knowledge relating to PTSD FC. A paper identified four key areas of research knowledge at that time. Methods: Fourteen clinicians and researchers met in Oxford, UK to update the previously published paper relating to PTSD FC. The first part of the meeting focused on updating the four key areas identified previously, and the second part on discussing new and emerging areas of research within the field. Results: A number of advances have been made in research within the area of PTSD FC. Prevalence is well established within mothers, several intervention studies have been published, and there is growing interest in new areas: staff and pathways; prevention and early intervention; impact on families and children; special populations; and post-traumatic growth. Conclusion: Despite progress, significant gaps remain within the PTSD FC knowledge base. Further research continues to be needed across all areas identified in 2006, and five areas were identified which can be seen as ‘new and emerging’. All of these new areas require further extensive research. Relatively little is still known about PTSD FC

X-ray Induced Pinhole Closure in Point Projection X-ray Radiography

In pinhole-assisted point-projection x-ray radiography (or ''backlighting''), pinholes are placed between the sample of interest and an x-ray source (or ''backlighter'') to effectively limit the source size and hence improve the spatial resolution of the system. Pinholes are generally placed close to such x-ray backlighters to increase the field-of-view, leading to possible vaporization and pinhole closure due to x-ray driven ablation, thereby potentially limiting the usefulness of this method. An experimental study and modeling of time-dependent closure and resolution is presented. The pinhole closure timescale is studied for various pinhole sizes, pinhole to backlighter separations and filtering conditions. In addition the time-dependent resolution is extracted from one-dimensional wire imaging prior to pinhole closure. Cylindrical hydrodynamic modeling of the pinhole closure shows reasonable agreement with data, giving us a predictive capability for pinhole closure in future experiments