Chemical synthesis of monomeric self-sealant type esters Status report

Synthesis of alkyl esters of alpha-cyanosorbic acid for self-sealing polymerizatio

Measurement of vortex velocities over a wide range of vortex age, downstream distance and free stream velocity

A wind tunnel test was conducted to obtain vortex velocity signatures over a wide parameter range encompassing the data conditions of several previous researchers while maintaining a common instrumentation and test facility. The generating wing panel was configured with both a revolved airfoil tip shape and a square tip shape and had a semispan aspect of 4.05/1.0 with a 121.9 cm span. Free stream velocity was varied from 6.1 m/sec to 76.2 m/sec and the vortex core velocities were measured at locations 3, 6, 12, 24 and 48 chordlengths downstream of the wing trailing edge, yielding vortex ages up to 2.0 seconds. Wing pitch angles of 6, 8, 9 and 12 deg were investigated. Detailed surface pressure distributions and wing force measurements were obtained for each wing tip configuration. Correlation with vortex velocity data taken in previous experiments is good. During the rollup process, vortex core parameters appear to be dependent primarily on vortex age. Trending in the plateau and decay regions is more complex and the machanisms appear to be more unstable

Nonperiodic Optical Flickering In Hz Herculis

NASA NGR 44-012-209NSF GP-25901, GP-41796Astronom

Feasibility of Fireball Trail Detection Using Ground-Based GPS Receivers

The feasibility of using GPS data to detect fireballs is analyzed by first modeling the fireball’s trail diffusion and plasma chemistry to get a resulting ion density profile of the trail over time. The signal perturbation caused by the fireball trail is simulated for a ground receiver using an analytic solution for diffraction from a Gaussian lens. Five cases were modeled with varying initial peak ion densities and altitudes taken from fireball and reentry vehicle data. This paper shows that it is feasible to detect a fireball trail using GPS if the fireball has a sufficiently high initial ion density, above approximately 1018 m-3, and occurs at an altitude above approximately 75 km. For the five cases the amplitude scintillation index, S4, and phase scintillation index, σɸ , values of the signal for the last detectable ion density profile were calculated

Self-consistent modelling of the polar thermosphere and ionosphere to magnetospheric convection and precipitation (invited review)

It has recently been demonstrated that the dramatic effects of plasma precipitation and convection on the composition and dynamics of the polar thermosphere and ionosphere include a number of strong interactive, or feedback, processes. To aid the evaluation of these feedback processes, a joint three dimensional time dependent global model of the Earth's thermosphere and ionosphere was developed in a collaboration between University College London and Sheffield University. This model includes self consistent coupling between the thermosphere and the ionosphere in the polar regions. Some of the major features in the polar ionosphere, which the initial simulations indicate are due to the strong coupling of ions and neutrals in the presence of strong electric fields and energetic electron precipitation are reviewed. The model is also able to simulate seasonal and Universal time variations in the polar thermosphere and ionospheric regions which are due to the variations of solar photoionization in specific geomagnetic regions such as the cusp and polar cap

Policy Driven Management for Distributed Systems

Separating management policy from the automated managers which interpret the policy facilitates the dynamic change of behavior of a distributed management system. This permits it to adapt to evolutionary changes in the system being managed and to new application requirements. Changing the behavior of automated managers can be achieved by changing the policy without having to reimplement them—this permits the reuse of the managers in different environments. It is also useful to have a clear specification of the policy applying to human managers in an enterprise. This paper describes the work on policy which has come out of two related ESPRIT funded projects, SysMan and IDSM. Two classes of policy are elaborated—authorization policies define what a manager is permitted to do and obligation policies define what a manager must do. Policies are specified as objects which define a relationship between subjects (managers) and targets (managed objects). Domains are used to group the objects to which a policy applies. Policy objects also have attributes specifying the action to be performed and constraints limiting the applicability of the policy. We show how a number of example policies can be modeled using these objects and briefly mention issues relating to policy hierarchy and conflicts between overlapping policies. © 1994, Plenum Publishing Corporation. All rights reserved.Accepted versio

Exhaust emission reduction for intermittent combustion aircraft engines

Three concepts for optimizing the performance, increasing the fuel economy, and reducing exhaust emission of the piston aircraft engine were investigated. High energy-multiple spark discharge and spark plug tip penetration, ultrasonic fuel vaporization, and variable valve timing were evaluated individually. Ultrasonic fuel vaporization did not demonstrate sufficient improvement in distribution to offset the performance loss caused by the additional manifold restriction. High energy ignition and revised spark plug tip location provided no change in performance or emissions. Variable valve timing provided some performance benefit; however, even greater performance improvement was obtained through induction system tuning which could be accomplished with far less complexity

Results of the pretest analysis of the Apollo SM-LM RCS engine when operated at severe off-limits test conditions

Pretest analyses of Apollo SM-LM RCS engine to predict component failure effects on engine performanc