Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “cD”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

A search for neutral hydrogen in D and cD galaxies

Recent X-ray spectroscopic results suggest that 2-3 solar masses/yr of cooling gas may be falling into M87 and as much as 300 solar masses/yr into giant galaxies in rich clusters. The eventual fate of the gas in the radiatively accreting flow is an open question. In an attempt to set some bounds on the evolution of the gas, a sensitive search was performed for H I in a sample of eight D and cD galaxies in rich and poor clusters. Null detections in all cases set upper limits of (4-20) x 10 to the 8th solar masses of H I in the giant galaxies. Possible reasons for these nondetections and alternative evolutionary fates for the accreting gas are discussed.

Burns, J. O.↗
NASA NTRS1981

Defect chemistry and characterization of (Hg, Cd)Te

Single crystal samples of phosphorus doped Hg sub 0.8 Cd sub 0.2 Te were anneald at temperatures varying from 450 C to 600 C in various Hg atmospheres. The samples were quenched to room temperature from the annealing temperatures. Hall effect and mobility measurements were performed at 77 K on all these samples. The results indicate the crystals to be p type for a total phosphorus concentration of 10 to the 19th power/cu cm in all the samples. The hole concentration at 77 K increases with increasing Hg pressures at 450 C and 500 C contrary to the observation in undoped crystals. Also, at low Hg pressures the concentration of holes in the phosphorus doped crystals is lower than in the undoped crystals. The hole concentration in all the samples is lower than the intrinsic carrier concentration at the annealing temperatures. The hole mobility in the doped crystals is similar to that in the undoped crystals. A defect model according to which phosphorus behaves as a single acceptor interstitially, occupying Te lattice sites while it acts as a single donor occupying Hg lattice sites was established. Equilibrum constants established for the incorporation of all the phosphorus species explain the experimental results

Vydyanath, H. R.↗
NASA NTRS1982

Defect chemistry and characterization of Hg sub 1x Cd sub x Te

Single crystal samples of undoped and doped Hg sub 1-x Cd sub x Te were annealed at varying temperatures and partial pressures of Hg. Hall effect and mobility measurements were carried out on these samples after quenching to room temperature. Based on the variation of the carrier concentration and the carrier mobility as a function of the partial pressure of Hg temperature, and dopant concentration, defect models were established for the doped and the undoped crystals. These models indicate that the native acceptor defects in both Hg0.8Cd0.2Te and Hg0.6Cd0.4Te doubly ionized and the native donor defects are negligible in concentration, implying that p to n conversion in these alloys occurs due only to residual donors. Incorporation mechanism of copper, indium, iodine, and phosphorus were investigated. A large concentration of indium is found to be paired with the native acceptor defects. Results on crystals doped with phosphorus indicate that phosphorus behaves amphoterically, acting as a donor on Hg lattice sites and as an acceptor intersitially on Te lattice sites. A majority of the phosphorus is found to be present as neutral species formed from the pairing reaction between phosphorus on Hg lattice sites and phosphorus in interstitial sites. Equilibrium constants for the intrinsic excitation reaction, as well as for the incorporation of the different dopants and the native acceptor defects were established.

Vydyanath, H. R.↗
NASA NTRS1982

Performance of a 2D-CD nonaxisymmetric exhaust nozzle on a turbojet engine at altitude

Baseline thrust and cooling data obtained with a 2D-CD versatile research exhaust nozzle mounted on a turbojet engine in an altitude chamber are presented. The tests covered a range of nozzle pressure ratios, nozzle pressure ratios, nozzle throat areas, and internal expansion area ratios. The thrust data obtained show good agreement with theory and scale model results after correcting the data for leakage and bypass cooling flows. Additional work is needed to improve predictability of cooling performance.

Straight, D. M.↗
NASA NTRS1982

Directional solidification and characterization of Hg(1-x)Cd(x)Te alloys

A series of Hg(1-x)Cd(x)Te alloy crystals was grown by high temperature gradient directional solidification at furnace translation rates ranging from 0.068 to 1.12 microns/s. For several ingots, the measured longitudinal compositional profiles were fitted to theoretical profiles to estimate the magnitude of D, the liquid HgTe-CdTe interdiffusion coefficient. The best-fit value of D was about 550,000 sq cm/s. The majority of the ingots showed significant radial compositional variations along the growth axis. These variations are attributed, at least in part, to fluid flows ahead of the growth interface. The results are discussed in terms of the heat transfer characteristics of the alloy/ampule/furnace system, and on the effects of these characteristics on the shape and stability of the growth interface in a 1-g environment.

Lehoczky, S. L.↗
NASA NTRS1982

Electrical characterization of Hg(1-x)Cd(x)Te alloys

Theoretical models are described for calculations of charge-carrier concentrations, Fermi energy, and conduction electron mobility as functions of x, temperature, and ionized and neutral defect concentrations of Hg(1-x)Cd(x)Te alloys. Measurements are reported of electron concentration and electron mobility from 5-300 K for alloys with x values of between 0.17 and 0.30. The electrical data are in reasonable agreement with theory, and were analyzed to obtain estimates of donor and acceptor state concentrations. The electron mobilities are calculated in terms of a microscopic theory of electrical conduction derived from the solution of the Boltzmann equation for the perturbed steady-state electron distribution function, and they show that longitudinal optical-phonon and charged and neutral defect scattering are the dominant mobility-limiting mechanisms.

Lehoczky, S. L.↗
NASA NTRS1983

Measured thermal diffusivity of Hg(1-x)Cd(x)Te solids and melts

The thermal diffusivity of Hg(1-x)Cd(x)Te melts is found to rise rapidly with temperature to values characteristic of metals. Solid and melt diffusivities for values of x from 0 to 0.3 and over a temperature range from 150 to 900 C have been determined by the laser flash method of Parker, Taylor, and Cowan. The diffusivity decreases from a maximum at x = 0 in both the solid and the liquid, with the values observed at x = 0.3 being about 40 percent of those for x = 0. The solid diffusivity for x = 0 is 1.7 sq mm/s at 150 C, decreasing to 0.7 sq mm/s at the melting point. The x = 0 liquid diffusivity increases from 0.7 sq mm/s at the melting point to 3.5 sq mm/s at 900 C.

Holland, L. R.↗
NASA NTRS1983

Liquidus temperatures of Hg-rich Hg-Cd-Te alloys

Measurements are made of the liquidus temperatures for ten (Hg/1-x/Cd)Te/1-y/ compositions in which x ranges from 0.091 to 0.401 and y ranges from 0.544 to 0.952. It is found that for metal-rich melts with the same x value, the liquidus temperature increases with y when y is in the range 0.5-0.7. This behavior is explained by the higher degree of association between Cd and Te than between Hg and Te in the melts. It is noted that recent calculated values of the liquidus isotherms by Tung et al. (1982) are in fair to good agreement with the experimental results obtained here.

Szofran, F. R.↗
NASA NTRS1984

Design, development, performance, and reconditioning of Ni-Cd batteries using polyropylene separators

A performance assessment is made for the Viking Mars Lander Program's sealed, sterilizable, 8-ampere hour Ni-Cd batteries, which use a nonwoven polypropylene separator material. Attention is given to separator wettability, the optimization of electrolyte quantity, and the reduction of plate carbonate, in view of thermal considerations and other environmental design and test requirements generated by mission characteristics. Life data based on mission experience identify, in addition to performance and degradation behavior, a series of shallow discharge reconditioning cycles and an intensive program of deep discharge reconditioning.

Britting, A. O., Jr.↗
NASA NTRS1984

Static internal performance evaluation of several thrust reversing concepts for 2D-CD nozzles

Recent performance testing of the two-dimensional convergent-divergent (2D-CD) nozzle has established the concept as a viable alternative to the axisymmetric nozzle for advanced technology aircraft. This type of exhaust system also offers potential integration and performance advantages in the areas of thrust reversing and vectoring over axi-symmetric nozzles. These advantages include the practical integration of thrust reversers which operate not only to reduce landing roll but also operate in-flight for enhanced maneuvering and thrust spoiling. To date there is a very limited data base available from which criteria can be developed for the design and evaluation of this type of thrust reverser system. For this reason, a static scale model test was conducted in which five different thrust reverser designs were evaluated. Each of the five models had varying performance/integration requirements which dictated the five different designs. Some of the parameters investigated in this test included; variable angle external cascade vanes, fixed angle internal cascade vanes, variable position inner doors, external slider doors and internal slider valves. In addition, normal force and yawing moment generation was investigated using the thrust reverser system. Selected results from this test will be presented and discussed in this paper.

Rowe, R. K.↗
NASA NTRS1984

Further comments on segregation during Bridgman growth of Cd(x)Hg(1-x)Te

The authors comment on recent papers published by Capper et al. (1983) and Jones et al. (1983) which report and discuss the variation of composition with axial position in Bridgman-grown Cd(x)Hg(1-x)Te alloys. The validity of a diffusion-controlled model for non-mixing growth conditions is particularly noted.

Lehoczky, S. L.↗
NASA NTRS1986

Sputtering and native oxide formation on (110) surfaces of Cd(1-x)Mn(x)Te

Native oxides on the surface of Cd(1-x)Mn(x)Te (X between 0 and 0.7) have been analyzed on the basis of X-ray photoemission spectroscopy measurements. Depth profile analysis revealed a significant increase in the thickness at higher Mn concentrations and a strong Mn segregation to the surface, respectively. Sputter-induced damage on cleaved (110)-oriented surfaces was analyzed by photoreflectance and photoluminescence measurements. The damage was found to be larger on CdTe than on the alloy. Thermal annealing showed nearly complete restoration for the surface of the alloy, while CdTe revealed irreversible modifications in the near-surface regime upon sputtering and post annealing.

Neff, H.↗
NASA NTRS1986

An advanced Ni-Cd battery cell design

The evolution of an advanced Ni-Cd space battery cell design continues to prove very promising. High oxygen/hydrogen gas recombination rates (currently up to a C/5 charge rate) and increased electrolyte activation level tolerance (currently up to 5.6 grams Ah of positive capacity) were demonstrated by test. A superior performance, extended life battery cell offering advantages should soon be available for mission applications

Miller, L.↗
NASA NTRS1986

Modeling Ni-Cd performance. Planned alterations to the Goddard battery model

The Goddard Space Flight Center (GSFC) currently has a preliminary computer model to simulate a Nickel Cadmium (Ni-Cd) performance. The basic methodology of the model was described in the paper entitled Fundamental Algorithms of the Goddard Battery Model. At present, the model is undergoing alterations to increase its efficiency, accuracy, and generality. A review of the present battery model is given, and the planned charges of the model are described.

Jagielski, J. M.↗
NASA NTRS1986

Heat capacity, enthalpy of mixing, and thermal conductivity of Hg(1-x)Cd(x)Te pseudobinary melts

Heat capacity and enthalpy of mixing of Hg(1-x)Cd(x)Te pseudobinary melts were calculated assuming an associated solution model for the liquid phase. The thermal conductivity of the pseudobinary melts for x = 0, 0.05, 0.1, and 0.2 was then calculated from the heat capacity values and the experimental values of thermal diffusivity and density for these melts. The thermal conductivity for the pseudobinary solid solution is also discussed.

Su, Ching-Hua↗
NASA NTRS1987

A thermodynamic model of the Hg(0.8)Cd(0.2)Te-iodine transport system. I - Te-saturated source material. II - Source material composition within the homogeneity range

A thermochemical analysis of the Hg(0.8)Cd(0.2)Te-iodine vapor transport system is presented, and theoretical calculations of diffusion-controlled mass transport rates are made. The predicted mass fluxes are compared with experimental data obtained from transport experiments under vertical, stabilizing conditions reported earlier and with results of additional transport experiments conducted during the present study. Experimental mass transport rate studies of the transport system for fixed amount of excess Hg as a function of transport agent pressure are presented. The mass fluxes are determined for the vertical, stabilizing orientation of the density gradient relative to the gravitational vector. In order to compare experimental mass transport rates with computed values, the thermochemical analysis is extended to take the formation of Hg vacancies in the above compound into account along with their effect on the partial pressure of the system.

Chandra, D.↗
NASA NTRS1987

Test summary for advanced H2 cycle NI-CD cell

To improve operational tolerances and mass, the H2 gas recombination design provisions of the Ni-H2 system were incorporated into the sealed Ni-Cd system. Produced is a cell design capable of operating on the H2 cycle versus the normal O2 cycle. Three test cells have now completed approximately 4,330 LEO (90 minute) cycles at 20 percent depth of discharge (DOD). Performance remains stable although one cell exhibited a temporary pressure anomaly.

Miller, Lee↗