Probing Brownstein-Moffat Gravity via Numerical Simulations

In the standard scenario of the Newtonian gravity, a late-type galaxy (i.e., a spiral galaxy) is well described by a disk and a bulge embedded in a halo mainly composed by dark matter. In Brownstein-Moffat gravity, there is a claim that late-type galaxy systems would not need to have halos, avoiding as a result the dark matter problem, i.e., a modified gravity (non-Newtonian) would account for the galactic structure with no need of dark matter. In the present paper, we probe this claim via numerical simulations. Instead of using a "static galaxy," where the centrifugal equilibrium is usually adopted, we probe the Brownstein-Moffat gravity dynamically via numerical $N$-body simulations.Comment: 33 pages and 14 figures - To appear in The Astrophysical Journa

Noncommutative Einstein-AdS Gravity in three Dimensions

We present a Lorentzian version of three-dimensional noncommutative Einstein-AdS gravity by making use of the Chern-Simons formulation of pure gravity in 2+1 dimensions. The deformed action contains a real, symmetric metric and a real, antisymmetric tensor that vanishes in the commutative limit. These fields are coupled to two abelian gauge fields. We find that this theory of gravity is invariant under a class of transformations that reduce to standard diffeomorphisms once the noncommutativity parameter is set to zero.Comment: 11 pages, LaTeX, minor errors corrected, references adde

Applying MOG to lensing: Einstein rings, Abell 520 and the Bullet Cluster

We investigate gravitational lensing in the context of the MOG modified theory of gravity. Using a formulation of the theory with no adjustable or fitted parameters, we present the MOG equations of motion for slow, nonrelativistic test particles and for ultrarelativistic test particles, such as rays of light. We demonstrate how the MOG prediction for the bending of light can be applied to astronomical observations. Our investigation first focuses on a small set of strong lensing observations where the properties of the lensing objects are found to be consistent with the predictions of the theory. We also present an analysis of the colliding clusters 1E0657-558 (known also as the Bullet Cluster) and Abell 520; in both cases, the predictions of the MOG theory are in good agreement with observation.Comment: 14 pages, 2 figures; final proof before publicatio

Bimetric Gravity Theory, Varying Speed of Light and the Dimming of Supernovae

In the bimetric scalar-tensor gravitational theory there are two frames associated with the two metrics {\hat g}_{\mu\nu} and g_{\mu\nu}, which are linked by the gradients of a scalar field \phi. The choice of a comoving frame for the metric {\hat g}_{\mu\nu} or g_{\mu\nu} has fundamental consequences for local observers in either metric spacetimes, while maintaining diffeomorphism invariance. When the metric g_{\mu\nu} is chosen to be associated with comoving coordinates, then the speed of light varies in the frame with the metric {\hat g}_{\mu\nu}. Observers in this frame see the dimming of supernovae because of the increase of the luminosity distance versus red shift, due to an increasing speed of light in the early universe. Moreover, in this frame the scalar field \phi describes a dark energy component in the Friedmann equation for the cosmic scale without acceleration. If we choose {\hat g}_{\mu\nu} to be associated with comoving coordinates, then an observer in the g_{\mu\nu} metric frame will observe the universe to be accelerating and the supernovae will appear to be farther away. The theory predicts that the gravitational constant G can vary in spacetime, while the fine-structure constant \alpha=e^2/\hbar c does not vary. The problem of cosmological horizons as viewed in the two frames is discussed.Comment: 22 pages, Latex file. No figures. Corrected typos. Added reference. Further references added. Further corrections. To be published in Int. J. Mod. Phys. D, 200

Full-coverage film cooling: 3-dimensional measurements of turbulence structure and prediction of recovery region hydrodynamics

Hydrodynamic measurements were made with a triaxial hot-wire in the full-coverage region and the recovery region following an array of injection holes inclined downstream, at 30 degrees to the surface. The data were taken under isothermal conditions at ambient temperature and pressure for two blowing ratios: M = 0.9 and M = 0.4. Profiles of the three main velocity components and the six Reynolds stresses were obtained at several spanwise positions at each of the five locations down the test plate. A one-equation model of turbulence (using turbulent kinetic energy with an algebraic mixing length) was used in a two-dimensional computer program to predict the mean velocity and turbulent kinetic energy profiles in the recovery region. A new real-time hotwire scheme was developed to make measurements in the three-dimensional turbulent boundary layer over the full-coverage surface

Introduction of a Mobile Device Based Tertiary Survey Application Reduces Missed Injuries: A Multi-Center Prospective Study

Missed injuries in trauma patients are a significant source of preventable morbidity. The tertiary survey is a head-to-toe physical exam performed within 24 hours of admission to identify any injuries which may have been missed during initial assessment and resuscitation. The Physician Assist Trauma Software (PATS) is an electronic program designed to guide users through a thorough tertiary survey and document the results. This thesis project was designed to study the impact of implementing this novel mobile device based electronic tertiary survey program on missed injuries. The first phase of this study involved quantifying and characterizing the missed injury rate at two distinct pilot sites. The second phase compared missed injury rates before and after implementation of the PATS program. Completion rates before and after implementation were also compared as a measure of feasibility. The implementation of the PATS program significantly decreased missed injury rates and improved documentation compliance at both sites. The third phase focused on user-level feasibility by surveying the pre- and post-PATS practitioners responsible for completing the tertiary survey. Overall, users found the PATS program useful, time-saving, and effective. The PATS program appears to be an effective and feasible way to reduce missed injuries and improve documentation in trauma