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At least 1,459 records · Page 81
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NASA NTRS1984

Study to eliminate ground resonance using active controls

The effectiveness of active control blade feathering in increasing rotor body damping and the possibility to eliminate ground resonance instabilities were investigated. An analytical model representing rotor flapping and lead-lag degrees of freedom and body pitch, roll, longitudinal and lateral motion is developed. Active control blade feathering is implemented as state variable feedback through a conventional swashplate. The influence of various feedback states, feedback gain, and weighting between the cyclic controls is studied through stability and response analyses. It is shown that blade cyclic inplane motion, roll rate and roll acceleration feedback can add considerable damping to the system and eliminate ground resonance instabilities, which the feedback phase is also a powerful parameter, if chosen properly, it maximizes augmentation of the inherent regressing lag mode damping. It is shown that rotor configuration parameters, like blade root hinge offset, flapping stiffness, and precone considerably influence the control effectiveness. It is found that active control is particularly powerful for hingeless and bearingless rotor systems.

Straub, F. K.↗
NASA NTRS1985

Arrangement for damping the resonance in a laser diode

An arrangement for damping the resonance in a laser diode is described. This arrangement includes an additional layer which together with the conventional laser diode form a structure (35) of a bipolar transistor. Therein, the additional layer serves as the collector, the cladding layer next to it as the base, and the active region and the other cladding layer as the emitter. A capacitor is connected across the base and the collector. It is chosen so that at any frequency above a certain selected frequency which is far below the resonance frequency the capacitor impedance is very low, effectively shorting the base to the collector.

Katz, J.↗
NASA NTRS1984

Alfvenic resonances on solar spicules

It is suggested that twisting and heating of solar spicules can be produced by Alfven waves which enter the spicule from below. The spicule is treated as a region of constant Alfven speed which is bounded above by a region of much higher Alfven speed (the corona) and below by a region of exponentially increasing Alfven speed (the photosphere and chromosphere). It is shown how the spicule can act as a resonant cavity. The transmission of the waves into the cavity is analytically determined to be enhanced at certain resonant frequencies. With reasonable spicule parameters, and assuming the spicule damping to be moderately large, it is found that twisting velocities of approximately 20-30 km/s can be induced on the spicule. It is suggested that the Alfven waves are dissipated via a turbulent cascade of their energy to higher wavenumbers. It is shown that the waves can thereby heat the spicules to the observed temperatures. It is further suggested that the continued input of energy can explain why H-alpha spicules fade, since the predicted heating rate is sufficient to heat the spicules to temperatures at which the hydrogen is fully ionized; thus H-alpha spicules may evolve into EUV spicules.

Sterling, A. C.↗
NASA NTRS1984

Approximate analysis for resonance of an incompressible shear layer plus edges

A method for approximately analyzing the feedback between downstream and upstream edges in incompressible shear flow is described. The shear flow is modeled by a vortex sheet. Equations for resonance eigenvalues are derived. After the reduction of growth rate by finite shear layer thickness is allowed for, agreement is found between calculated resonances and those that have been observed experimentally.

Durbin, P. A.↗
NASA NTRS1985

Beam-driven ion cyclotron harmonic resonances in the terrestrial foreshock

A terrestrial upstream wave event which demonstrates multiple, ion cyclotron harmonic resonances between the interplanetary wave population and an observed proton beam is analyzed. The techniques and parameters employed in the data analysis are discussed, including the use of differential and band-pass filters. An upstream wave event demonstrating multiple harmonic waves is examined, and the instability analysis relevant to the ion beam observations thought to be responsible for that event is discussed. It is shown that an observed bi-Maxwellian ion beam is capable of generating right and left-hand polarized waves through ion cyclotron harmonic resonance.

Smith, C. W.↗
NASA NTRS1985

Absolute response and noise equivalent power of cyclotron resonance-assisted InSb detectors at submillimeter wavelengths

Spectra are presented of the responsivity and noise equivalent power (NEP) of liquid-helium-cooled InSb detectors as a function of magnetic field in the range 20-110 per cm. The measurements are all made using a Fourier transform spectrometer with thermal sources. The results show a discernable peak in the detector response at the conduction electron cyclotron resonance (CCR) frequency for magnetic fields as low as 3 kG. The magnitude of responsivity at the resonance peaks is roughly constant with magnetic field and is comparable to the low-frequency hot-electron bolometer response. The NEP at the peaks is found to be comparable to the best long wavelength results previously reported. For example, NEP = 4.5 x 10 to the 13th W/(square root of Hz) at 4.2 K, 6 kG, and 40 per cm was measured. The InSb CCR will provide a much improved detector for laboratory spectroscopy, as compared with hot electron bolometers, in the 20-100 per cm range.

Brown, E. R.↗
NASA NTRS1986

A 25-kW Series-Resonant Power Converter

Prototype exhibited efficiency of 93.9 percent. 25-kW resonant dc/dc power converter designed, developed, fabricated, and tested, using Westinghouse D7ST transistors as high-power switches. D7ST transistor characterized for use as switch in series-resonant converters, and refined base-drive circuit developed. Technical base includes advanced switching magnetic, and filter components, mathematical circuit models, control philosophies, and switch-drive strategies. Power-system benefits such as lower losses when used for high-voltage distribution, and reduced magnetics and filter mass realized.

Frye, R. J.↗
NASA NTRS1985

The design of a small linear-resonant, split Stirling cryogenic refrigerator compressor

The development of a small linear-resonant compressor for use in a 1/4-watt, 78K, split Stirling cryogenic refrigerator is discussed. The compressor contains the following special features: (1) a permanent-magnet linear motor; (2) resonant dynamics; (3) dynamic balancing; and (4) a close-clearance seal between the compressor piston and cylinder. This paper describes the design of the compressor, and presents component test data and system test data for the compressor driving a 1/4-watt expander.

Ackermann, R. A.↗
NASA NTRS1986

Theoretical studies of Resonance Enhance Stimulated Raman Scattering (RESRS) of frequency doubled Alexandrite laser wavelengths in cesium vapor

It is well known that the presence of a real atomic level which is nearly resonant with the pump field can greatly enhance the Raman emission cross section. In order to accurately calculate the Raman gain in systems where resonance enhancement plays a dominant role, expressions for the pump and signal susceptibilities must be derived. These expressions should be valid for arbitrary field strengths in order to allow for pump and signal saturation. In addition, the theory should allow for arbitrary longitudinal and transverse relaxation rates. This latter point is extremely vital for three level atomic systems such as the alkali earth metals since they do not have population reservoirs and can have widely varying spontaneous lifetimes on the three pertinent transitions. Moreover, the dephasing rates are strong functions of electron states and are therefore also different for the three coupled pairs of levels. These considerations are not as important when molecular systems are concerned since the large reservoir of rotational states serve to produce essentially equal longitudinal recovery rates for the population of the three levels. The three level system with three arbitrary longitudinal and transverse relaxation rates was solved. There is no need for setting either pair of rates equal and the expressions are valid for arbitrarily strong fields.

Lawandy, N. M.↗
NASA NTRS1985

Microstrip termination effects on dielectric resonator filters

Dielectric resonator filters coupled to microstrip lines appear to answer the requirements of high performance and small size and weight that must be satisfied for use in satellite-based radiometers. The open-circuit and short-circuit types of coupling dielectric resonators to microstrip lines were compared with respect to radiation losses at various frequencies. The filters were fabricated from 1.6 mm Duroid board. The termination impedances for the microstrip lines were measured using a calibrated HP 8510 network analyzer. The values for radiation resistance obtained experimentally for both types of coupling agreed well with the values calculated from the Lewin theory (1960). It was found that the use of short-circuit coupling results in significantly reduced radiation resistance compared to the use of open-circuit lines. Improvement increases with increased frequency.

Trew, R. J.↗
NASA NTRS1985

Observations of the right-hand resonant ion beam instability in the distant plasma sheet boundary layer

Examples of the onset of a resonant ion beam instability are illustrated on the basis of ISEE 3 observations of 66 large amplitude wave events at the plasma sheet boundary layer. Analysis of the observational data showed that the observed wave and ion beam parameters were, in general, in agreement with linear theoretical predictions of resonant ion beam instability. The distribution of ion energies at the onset of the instability is given in a table.

Tsurutani, B. T.↗
NASA NTRS1985

X-ray resonance scattering in a spherically symmetric coronal model

In the solar corona the opacities of some of the prominent X-ray emission lines are on the order of tau of about I over typical coronal path lengths. A particular solution of the radiative transfer problem involving an extended, spherically symmetric coronal shell radiating isotropic, homogeneous emission in which single-scattering also takes place is presented and discussed. Within the context of this simplified model, it is found that scattered radiation is an important contribution to the total emergent resonance line flux and that for the He-like family of resonance (r), intercombination (i), and forbidden (f) lines, the ratio G = (f + i)/r would decrease as a function of optical depth for disk-center emission in an extended spherically symmetric corona.

Haisch, B. M.↗
NASA NTRS1985

Projection and quasi-projection operators for electron impact resonances on many-electron atomic targets

A framework is established for deriving true projection operators in electron resonance calculations involving many electron targets (ions and atoms). The analytical approach is based on Feshbach's formalism the true and quasi-projection operators (QPO) one-electron systems. In the case of QPOs, the formalism is explicitly generalized to treat autoionization states lying in the region of inelastic scattering. In order to illustrate the analytical method, a recent calculation of the lowest 2P0 resonance in He is described. The application of the modified Feshbach formalism to calculation of nonresonant phase shifts in many electron systems is also discussed.

Temkin, A.↗
NASA NTRS1985

Evolution of the Janus-Epimetheus coorbital resonance due to torques from Saturn's rings

The effects of the gravitational interactions between Saturn's rings and the coorbital satellites, Janus and Epimetheus, on the 1:1 horseshoe resonance between these moons is examined. It is shown that the 7:6 resonance of these moons, which presumably maintains the sharp outer edge of the A ring, leads to a rapid tightening of the coorbital lock. The results lead to the prediction that the orbital configuration might evolve from the current horseshoe-type lock to one of tadpole orbits around a single Lagrangian point in about 20 myr.

Lissauer, J. J.↗
NASA NTRS1985

State-plane analysis of parallel resonant converter

A method for analyzing the complex operation of a parallel resonant converter is developed, utilizing graphical state-plane techniques. The comprehensive mode analysis uncovers, for the first time, the presence of other complex modes besides the continuous conduction mode and the discontinuous conduction mode and determines their theoretical boundaries. Based on the insight gained from the analysis, a novel, high-frequency resonant buck converter is proposed. The voltage conversion ratio of the new converter is almost independent of load.

Oruganti, R.↗
NASA NTRS1986

Resonant electron diffusion as a saturation process of the synchrotron maser instability

The theory of resonant electron diffusion as an effective saturation process of the auroral kilometric radiation has been formulated. The auroral kilometric radiation is assumed to be amplified by the synchrotron maser instability that is driven by an electron distribution of the loss-cone type. The calculated intensity of the saturated radiation is found to have a significantly lower value in comparison with that caused by the quasi-linear diffusion process as an alternative saturation process. This indicates that resonant electron diffusion dominates over quasi-linear diffusion in saturating the synchrotron maser instability.

Lee, M. C.↗
NASA NTRS1985

A solid state tunable laser for resonance measurements of atmospheric sodium

The measurement of wave dynamics in the upper mesosphere using a solid-state laser to excite the resonance fluorescence line of sodium is examined. Two Nd:YAG lasers are employed to produce the sodium resonance line. The method involves mixing the 1064 nm radiation with that from a second Nd:YAG operating at 1319 nm in a nonlinear infrared crystal to directly produce 589 nm radiation by sum frequency generation. The use of the transmitter to measure the sodium layer from the Space Shuttle Platform is proposed. A diagram of the laser transmitter is presented.

Philbrick, C. R.↗
NASA NTRS1986

Heating of the solar corona by the resonant absorption of Alfven waves

An improved method for calculating the resonance absorption heating rate is discussed and the results are compared with observations in the solar corona. The primary conclusion to be drawn from these calculations is that to the level of the approximation adopted, the observations of the heating rate and nonthermal line broadening in the solar corona are consistent with heating by the resonance absorption mechanism.

Davila, Joseph M.↗