Status of the DOE/NASA critical gas turbine research and technology project

Activities performed in order to provide an R&T data base for utility gas turbine systems burning coal-derived fuels are described. Experiments were run to determine the corrosivity effects of trace metal contaminants (and potential fuel additives) on gas turbine materials and these results were correlated in a corrosion-life prediction model. Actual fuels were burned in a burner rig hot corrosion test to verify the model. A deposition prediction model was assembled and compared with results of actual coal-derived fuel deposition tests. Thermal barrier coatings were tested to determine their potential for protecting gas turbine hardware from the corrosive contaminants. Several coatings were identified with significantly improved spallation-resistance (and, hence, corrosion resistance)

The Akulov-Volkov Lagrangian, Symmetry Currents and Spontaneously Broken Extended Supersymmetry

A generalization of the Akulov-Volkov effective Lagrangian governing the self interactions of the Nambu-Goldstone fermions associated with spontaneously broken extended supersymmetry as well as their coupling to matter is presented and scrutinized. The resulting currents associated with R-symmetry, supersymmetry and space-time translations are constructed and seen to form a supermultiplet structure.Comment: 17 pages, LaTeX; Title, abstract and introduction changes, references adde

Potential benefits of a ceramic thermal barrier coating on large power generation gas turbine

Thermal barrier coating design option offers benefit in terms of reduced electricity costs when used in utility gas turbines. Options considered include: increased firing temperature, increased component life, reduced cooling air requirements, and increased corrosion resistance (resulting in increased tolerance for dirty fuels). Performance and cost data were obtained. Simple, recuperated and combined cycle applications were considered, and distillate and residual fuels were assumed. The results indicate that thermal barrier coatings could produce large electricity cost savings if these coatings permit turbine operation with residual fuels at distillate-rated firing temperatures. The results also show that increased turbine inlet temperature can result in substantial savings in fuel and capital costs

The nature of 1WGA J1958.2+3232: a new intermediate polar

We present low and intermediate resolution spectroscopy of the optical counterpart to the recently discovered pulsating X-ray source 1WGA J1958.2+3232. The presence of strong HI , HeI and HeII emission lines together with the absence of absorption features rules out the possibility that the object is a massive star, as had recently been suggested. The observed X-ray and optical characteristics are consistent with the object being an intermediate polar. The double-peaked structure of the emission lines indicates that an accretion disc is present

Heat transport in the XXZXXZ spin chain: from ballistic to diffusive regimes and dephasing enhancement

In this work we study the heat transport in an XXZ spin-1/2 Heisenberg chain with homogeneous magnetic field, incoherently driven out of equilibrium by reservoirs at the boundaries. We focus on the effect of bulk dephasing (energy-dissipative) processes in different parameter regimes of the system. The non-equilibrium steady state of the chain is obtained by simulating its evolution under the corresponding Lindblad master equation, using the time evolving block decimation method. In the absence of dephasing, the heat transport is ballistic for weak interactions, while being diffusive in the strongly-interacting regime, as evidenced by the heat-current scaling with the system size. When bulk dephasing takes place in the system, diffusive transport is induced in the weakly-interacting regime, with the heat current monotonically decreasing with the dephasing rate. In contrast, in the strongly-interacting regime, the heat current can be significantly enhanced by dephasing for systems of small size

On Local Dilatation Invariance

The relationship between local Weyl scaling invariant models and local dilatation invariant actions is critically scrutinized. While actions invariant under local Weyl scalings can be constructed in a straightforward manner, actions invariant under local dilatation transformations can only be achieved in a very restrictive case. The invariant couplings of matter fields to an Abelian vector field carrying a non-trivial scaling weight can be easily built, but an invariant Abelian vector kinetic term can only be realized when the local scale symmetry is spontaneously broken.Comment: 3 page

Nuclear rocket propulsion. NASA plans and progress, FY 1991

NASA has initiated planning for a technology development project for nuclear rocket propulsion systems for space explorer initiative (SEI) human and robotic missions to the moon and Mars. An interagency project is underway that includes the Department of Energy National Laboratories for nuclear technology development. The activities of the project planning team in FY 1990 and 1991 are summarized. The progress to date is discussed, and the project plan is reviewed. Critical technology issues were identified and include: (1) nuclear fuel temperature, life, and reliability; (2) nuclear system ground test; (3) safety; (4) autonomous system operation and health monitoring; and (5) minimum mass and high specific impulse

Heteroduplex analysis of tra delta f' plasmids and the mechanism of their formation

Four tra delta FargG+ plasmids, derived from matings between Hfr AB312 and a recA recipient, have been shown to have deletions of at least 50% of the F genome, including the region in which the tra genes map. The mutant plasmids do contain the F genes required for plasmid maintenance. Correlations can be made between, on the one hand, the F genes present on the tradelta F' plasmids and the F genes transferred early by an Hfr donor, and, on the other hand, the F genes deleted from the tradelta F' plasmids and the F genes transferred late by an Hfr donor. A biased representation of proximally and distally transferred chromosomal markers among the tradelta F' elements was also demonstrated. Taken Taken together, the asymmetrical representation of Hfr genes and the cis dominance of the Tra phenotype of these mutants can best be explained by the hypothesis that the tradelta F' plasmids are formed by repliconation of the transferred exogenote in a recA recipient

A representative sample of Be Stars I: Sample Selection, Spectral Classification and Rotational Velocities

We present a sample of 58 Be stars containing objects of spectral types O9 to B8.5 and luminosity classes III to V. We have obtained 3670 - 5070 Angstrom spectra of the sample which are used to derive spectral types and rotational velocities. We discuss the distribution of spectral types and rotational velocities obtained and conclude that there are no significant selection effects in our sample.Comment: 10 Pages, 9 Figures, Accepted for publication in A&A