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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.

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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Signal sequence detection given noisy, common background image sets.

The optimum processing (likelihood functional) is found for a set of M images, each the sum of a member of a signal sequence due to an object to be detected and its parameters estimated, a sample function of a noise field, and a sample function of a common background field. The noise fields are independent, zero mean, white Gaussian fields, all independent of the background field. The latter is assumed to be either (1) completely unknown or of known mean and covariance functions with (2) a certain fluctuation property or (3) Gaussian. Three equivalent forms of the optimum processing are found: (1) a summation of generalized matched filterings of the images, (2) a summation of matched filtering of certain generalized differences of the images, and (3) a summation of 'estimator-correlator' type filterings. The detection performance and optimum signal/image selection under the Neyman-Pearson criterion is given, and is shown that optimum processor and signal design can completely eliminate any effect of the background on detectability.

Harger, R. O.↗
NASA NTRS1973

Scientific considerations for a common Saturn/Uranus atmospheric entry probe.

Development of a scientific rationale for an atmospheric probe designed to be capable of entry into either Saturn or Uranus. The effects of the NASA Monograph model atmospheres (SP 8091 and SP 8103) on the entry and descent trajectory specify instrument sampling design. The cool model atmospheres require descents to the vicinity of 20 bars to satisfy the objectives while about 4 bars is sufficient for the warm models. The measurement performance for a descent sampling time of 44 minutes shows that the atmosphere can be reconstructed from measured data. The required total probe entry weight is 103 kg, of which about 15 kg is for the science instruments. The descent data rate varies from 32 to 51 bps, depending upon the mode of transmitting preentry data. The resulting common probe can be redirected in flight between Saturn and Uranus.

Ledbetter, K. W.↗
NASA NTRS1973

Characteristics of tracks of ions of 14 less than or equal to Z less than or equal to 36 in common rock silicates.

Identification of heavy ion tracks in minerals by measurements of track etch rates and total etchable track lengths were irradiated with beams of Si, Cl, Ti, Fe, Zn, and Kr at energies up to 10.35 MeV/nucleon. Nine minerals commonly used to study fossil cosmic ray tracks in meteorites and lunar samples. From measurements of etched track length as a function of residual range, response curves for various minerals were determined as a function of ionization rate, using the expression previously derived by Price et al. (1968). These curves increase smoothly with ionization rate instead of rising abruptly at some critical value as was previously thought. It is shown that the track etch rate concept accounts qualitatively for total etchable track length distributions, but that the positions of the peaks of different elements in these histograms occur at shorter lengths for fossil tracks than for fresh tracks. Annealing data indicate that, at maximum lunar surface temperatures, tracks in olivine, orthopyroxenes, and feldspars may be significantly shortened, whereas tracks in clinopyroxenes will not be affected.

Price, P. B.↗
NASA NTRS1974

A comparison of several computational techniques for solving some common aeronomic problems

Several numerical integration techniques for solving common aeronomic problems involving species rate equations are compared for speed and accuracy. A newer technique that defines families of species that are nearly conserved is found to be superior to an iterative technique when both methods are applied to simple test problems. The 'conservation' technique is also found to be more economical than the more complex Gear (1969) integration scheme for comparable accuracy.

Turco, R. P.↗
NASA NTRS1975

Common antenna preamplifier-isolator for VLF-LF receivers

A modified high impedance preamplifier circuit which provides outputs to drive an Omega-VLF receiver and an ADF-LF receiver from a common antenna on general aviation aircraft is reported. The preamplifier was evaluated with fixed ground station receivers and results show the burn out problem of the first stage MOSFET during very close lightning discharges was eliminated.

Burhans, R. W.↗
NASA NTRS1975

Resonance line transfer with partial redistribution. IV - A generalized formulation for lines with common upper states. V - The solar Ca II lines

A generalized formulation is given for treating partial redistribution effects in transfer problems in resonance lines with common upper states. The formulation allows explicitly for the possibility that several spectral lines may arise in transitions from a given upper level to several sharp lower levels, including, for example, the ground state and metastable states. Line profiles for the Ca II H and K lines have been calculated, accounting for the partial frequency coherence of scattered photons. These profiles are compared with calculations made with identical atomic and atmospheric models but assuming complete redistribution. Very significant differences between the profiles obtained using these two different physical descriptions of the scattering process are found, and it is now apparent that the assumption of complete redistribution is a serious oversimplification of the actual physical situation. The results question the validity of equating brightness temperatures observed at K(sub 1) in stellar spectra with minimum temperatures in stellar chromospheres; it appears likely that such a procedure will systematically underestimate the value of T-min.

Milkey, R. W.↗