Constraints to the Masses of Brown Dwarf Candidates from the Lithium Test

We present intermediate dispersion (0.7-2.2 \AA ~pix$^{-1}$) optical spectroscopic observations aimed at applying the ``Lithium Test'' to a sample of ten brown dwarf candidates located in the general field, two in young open clusters, and two in close binaries. We find evidence for strong Li depletion in all of them, and thus infer lower mass limits of 0.065~M$_\odot$, depending only slightly ($\pm$0.005~M$_\odot$) on the interior models. None of the field brown dwarf candidates in our sample appears to be a very young (age $<$~10$^8$~yr) substellar object. For one of the faintest proper motion Pleiades members known (V=20.7) the Li test implies a mass greater than $\sim$0.08~M$_\odot$, and therefore it is not a brown dwarf. From our spectra we estimate spectral types for some objects and present measurements of Halpha emission strengths and radial velocities. Finally, we compare the positions in the H-R diagram of our sample of brown dwarf candidates with the theoretical region where Li is expected to be preserved (Substellar Lithium Region). We find that certain combinations of temperature calibrations and evolutionary tracks are consistent with the constraints imposed by the observed Li depletion in brown dwarf candidates, while others are not.Comment: 20 pp.; 4 figs, available under request; plain LaTeX, ApJ in press, OACatania-94-00

Color identification testing device

Testing device, which determines ability of a technician to identify color-coded electric wires, is superior to standard color blindness tests. It tests speed of wire selection, detects partial color blindness, allows rapid testing, and may be administered by a color blind person

Power cepstrum technique with application to model helicopter acoustic data

The application of the power cepstrum to measured helicopter-rotor acoustic data is investigated. A previously applied correction to the reconstructed spectrum is shown to be incorrect. For an exact echoed signal, the amplitude of the cepstrum echo spike at the delay time is linearly related to the echo relative amplitude in the time domain. If the measured spectrum is not entirely from the source signal, the cepstrum will not yield the desired echo characteristics and a cepstral aliasing may occur because of the effective sample rate in the frequency domain. The spectral analysis bandwidth must be less than one-half the echo ripple frequency or cepstral aliasing can occur. The power cepstrum editing technique is a useful tool for removing some of the contamination because of acoustic reflections from measured rotor acoustic spectra. The cepstrum editing yields an improved estimate of the free field spectrum, but the correction process is limited by the lack of accurate knowledge of the echo transfer function. An alternate procedure, which does not require cepstral editing, is proposed which allows the complete correction of a contaminated spectrum through use of both the transfer function and delay time of the echo process

The nature of operating flight loads and their effect on propulsion system structures

Past diagnostics studies revealed the primary causes of performance deterioration of high by-pass turbofan engines to be flight loads, erosion, and thermal distortion. The various types of airplane loads that are imposed on the engine throughout the lifetime of an airplane are examined. These include flight loads from gusts and maneuvers and ground loads from takeoff, landing, and taxi conditions. Clarification is made in definitions of the airframer's limit and ultimate design loads and the engine manufacturer's operating design loads. Finally, the influence of these loads on the propulsion system structures is discussed

DSN human factors project

The project plan was to hold focus groups to identify the factors influencing the ease of use characteristics of software and to bond the problem. A questionnaire survey was conducted to evaluate those factors which were more appropriately measured with that method. The performance oriented factors were analyzed and relationships hypothesized. The hypotheses were put to test in the experimental phase of the project. In summary, the initial analysis indicates that there is an initial performance effect favoring computer controlled dialogue but the advantage fades fast as operators become experienced. The user documentation style is seen to have a significant effect on performance. The menu and prompt command formats are preferred by inexperienced operators. The short form mnemonic is least favored. There is no clear best command format but the short form mnemonic is clearly the worst

B747/JT9D flight loads and their effect on engine running clearances and performance deterioration; BCAC NAIL/P and WA JT9D engine diagnostics programs

Flight loads on the 747 propulsion system and resulting JT9D blade to outer airseal running clearances during representative acceptance flight and revenue flight sequences were measured. The resulting rub induced clearance changes, and engine performance changes were then analyzed to validate and refine the JT9D-7A short term performance deterioration model