Parton Energy Loss in Two-Stream Plasma System

The energy loss of a fast parton scattering elastically in a weakly coupled quark-gluon plasma is formulated as an initial value problem. The approach is designed to study an unstable plasma, but it also reproduces the well known result of energy loss in an equilibrium plasma. A two-stream system, which is unstable due to longitudinal chromoelectric modes, is discussed here some detail. In particular, a strong time and directional dependence of the energy loss is demonstrated.Comment: 6 pages; presented by K. Deja at the conference Strangeness in Quark Matter, Cracow, Poland, September 18-24, 201

What’s the Difference: A Study of the Nature and Extent of Racism in Rugby League

At the start of the 1993/4 season the Commission for Racial Equality (CRE) and the Professional Footballers' Association launched the 'Let's Kick Racism Out of Football' campaign which subsequently gained the support of the Football Association, the FA Premier, the Endsleigh League and the Football Trust (CRE/PFA, 1994). That campaign led to discussions between the Rugby Football League (RFL), Leeds City Council and the Commission for Racial Equality (CRE) with a view to taking action to address racism in rugby league. Some sports though have become renowned as being sites for racialist confrontations, most notably football, as recorded in Hill's (1989) account of John Barnes' experiences and Holland's (1994) work on the terraces at Newcastle, Leeds and Bolton. General impressions suggested that the position in rugby league was not as bad as in football, but racist abuse and occasional incidents of banana throwing and monkey chants have all been recorded at rugby league matches. Concern about racism at matches has also been expressed recently in the letters pages of the rugby league press and players have talked about their own experiences on television. Since we live in a racist society it would be remarkable if there was no evidence of racism in sport. Nonetheless, as the National Governing Body of the sport, the RFL recognised that this was not a reason for taking no action if it were demonstrated that there are cases of racism in rugby league. However, before embarking on direct action it was decided that information was needed on the nature and extent of racism within the game. To that end Leeds Metropolitan University was asked to survey attitudes and it was agreed that this investigation should have three main components: a) the attitudes of the clubs b) the attitudes of (black and white) players c) the attitudes of spectators At this stage we have been concerned only with the professional game, thou

KMS conditions for 4-point Green functions at finite temperature

We study the 4-point function in the Keldysh formalism of the closed time path formulation of real time finite temperature field theory. We derive the KMS conditions for these functions and discuss the number of 4-point functions that are independent. We define a set of `physical' functions which are linear combinations of the usual Keldysh functions. We show that these functions satisfy simple KMS conditions. In addition, we consider a set of integral equations which represent a resummation of ladder graphs. We show that these integral equations decouple when one uses the physical functions that we have defined. We discuss the generalization of these results to QED.Comment: 17 pages in Revtex with 2 figure

Small expendable deployer system measurement analysis

The first on-orbit experiment of the Small Expendable Deployer System (SEDS) for tethered satellites will collect telemetry data for tether length, rate of deployment, and tether tension. The post-flight analysis will use this data to reconstruct the deployment history and determine dynamic characteristics such as tether shape and payload position. Linearized observability analysis has determined that these measurements are adequate to define states for a two-mass tether model, and two state estimators were written

Kalman estimation for SEDS measurements

The first on-orbit experiment of the Small Expendable Deployer System (SEDS) for tethered satellites will collect telemetry data for tethered length, rate of deployment, and tether tension. The post-flight analysis will use this data to reconstruct the deployment history and determine payload position and tether shape. Two Kalman estimator algorithms were written, and output using simulated measurement data was compared. Both estimators exhibited the same estimated state histories, indicating that numerical instability in the traditional algorithm was not the cause of filter divergence. Estimation of acceleration biases was added, which reduced the error but did not correct the divergence. An add-a-bead estimator that adds lumped masses as the tether is deployed was written, which provides a state model that matches the BEADSIM simulation providing the true measurements and states. This twenty-one bead estimator produced state histories similar to those of the two-bead estimator, indicating that the filter divergence was not caused by a reduced-order model. The noise models used to date are relatively simple and may be the source of estimator divergence. The investigation of colored noise models, cross-correlated measurement and process covariances, and noise-adaptive filter techniques is recommended

Building complex simulations rapidly using MATRIX(x): The Space Station redesign

MSFC's quick response to the Space Station redesign effort last year required the development of a computer simulation to model the attitude and station-keeping dynamics of a complex body with rotating solar arrays in orbit around the Earth. The simulation was written using a rapid-prototyping graphical simulation and design tool called MATRIX(x) and provided the capability to quickly remodel complex configuration changes by icon manipulation using a mouse. The simulation determines time-dependent inertia properties, and models forces and torques from gravity-gradient, solar radiation, and aerodynamic disturbances. Surface models are easily built from a selection of beams, plates, tetrahedrons, and cylinders. An optimization scheme was written to determine the torque equilibrium attitudes that balance gravity-gradient and aerodynamic torques over an orbit, and propellant-usage estimates were determined. The simulation has been adapted to model the attitude dynamics for small spacecraft

Ward Identities in Non-equilibrium QED

We verify the QED Ward identity for the two- and three -point functions at non-equilibrium in the HTL limit. We use the Keldysh formalism of real time finite temperature field theory. We obtain an identity of the same form as the Ward identity for a set of one loop self-energy and one loop three-point vertex diagrams which are constructed from HTL effective propagators and vertices.Comment: 19 pages, RevTex, 4 PostScript figures, revised version to be published in Phys. Rev.

Multi-sensor Testing for Automated Rendezvous and Docking

During the past two years, many sensors have been tested in an open-loop fashion in the Marshall Space Flight Center (MSFC) Flight Robotics Laboratory (FRL) to both determine their suitability for use in Automated Rendezvous and Docking (AR&D) systems and to ensure the test facility is prepared for future multi-sensor testing. The primary focus of this work was in support of the CEV AR&D system, because the AR&D sensor technology area was identified as one of the top risks in the program. In 2006, four different sensors were tested individually or in a pair in the MSFC FRL. In 2007, four sensors, two each of two different types, were tested simultaneously. In each set of tests, the target was moved through a series of pre-planned trajectories while the sensor tracked it. In addition, a laser tracker "truth" sensor also measured the target motion. The tests demonstrated the functionality of testing four sensors simultaneously as well as the capabilities (both good and bad) of all of the different sensors tested. This paper outlines the test setup and conditions, briefly describes the facility, summarizes the earlier results of the individual sensor tests, and describes in some detail the results of the four-sensor testing. Post-test analysis includes data fusion by minimum variance estimation and sequential Kalman filtering. This Sensor Technology Project work was funded by NASA's Exploration Technology Development Program

Solving Cubic Equations Using Direct Factoring in Complex Field

Cardano’s Method is not easily understood by undergraduate students. In this research project, we developed a method that students can understand without advanced mathematics skills. The method we developed only need to use the skills of factoring polynomials in complex field and finding cubic roots of a complex number.The procedures we developed are as following:1) Write cubic equation in the form of A3 + B3 + C3 – 3ABC = 0, where A is a function of x, B and C are complex numbers.2) Solve the quadratic equation Z2 – (B3 + C3)Z + B3 C3 = 0, which gives B and C.3) Factor equation of (1) into (A + B + C)(A +Bw + Cw2)(A +Bw2+Cw) = 0, where w is a complex rootof 1.4) Solve equations A+B+C = 0, A+Bω+Cω2 = 0, and A+Bω2+Cω =