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Results for “RESONANCE EFFECT”

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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1971

Vibration-rotation double resonance effects in symmetrical top molecules.

Rotational transitions in symmetrical top molecules in the wavelength regions of 1-3 mm are sufficiently strong to be observed directly on an oscilloscope. Changes in the vibrational level populations induced by laser radiations affect the intensity of the rotational transitions. Observation of the microwave lines under the influence of chopped laser radiation shows a variety of interesting and potentially informative effects. At pressures above a few tenths of a torr the effect of laser radiation is to reduce the microwave response. This is true for all microwave lines at all those laser frequencies which are absorbed by the gas, and this effect is roughly proportional to the absorption coefficient. The rise and decay times of this effect increase with pressure and the the linear dimensions of the absorption cell. At low pressures the microwave response may increase, decrease, or remain unaffected depending on the observed microwave transitions and the specific laser line applied to the gas.

Marantz, H.↗
NASA NTRS1973

Effects of resonant tesseral gravity coefficients on Viking-type orbits.

A special perturbation technique has been developed for the long-period and secular motion of a Viking-type orbiter. The technique uses a method of singly averaging the perturbations over the mean anomaly to determine changes in orbital elements due to atmospheric drag, solar radiation pressure, solar gravity, and the asymmetrical Mars gravitational field. The technique has been specialized to treat resonant tesseral gravity effects resulting from the commensurability of the satellite orbit period with the rotational period of the primary. Results are presented which indicate that orbiter lifetimes can be significantly reduced by resonant tesserals for orbits near the critical inclination. Conversely, it is shown that lifetimes can be extended via capture in resonant orbits which are stable against small drag forces.

Compton, H. R.↗
NASA NTRS2005

Instrumentation for Sensitive Gas Measurements

An improved instrument for optical absorption spectroscopy utilizes off-axis paths in an optical cavity in order to increase detection sensitivity while suppressing resonance effects. The instrument is well suited for use in either cavity ring-down spectroscopy (CRDS) [in which one pulses an incident light beam and measures the rate of decay of light in the cavity] or integrated cavity output spectroscopy (ICOS) [in which one uses a continuous-wave incident light beam and measures the power of light in the cavity as a function of wavelength]. Typically, in optical absorption spectroscopy, one seeks to measure absorption of a beam of light in a substance (usually a gas or liquid) in a sample cell. In CRDS or ICOS, the sample cell is placed in (or consists of) an optical cavity, so that one can utilize multiple reflections of the beam to increase the effective optical path length through the absorbing substance and thereby increase the sensitivity for measuring absorption. If an absorbing substance is not present in the optical cavity, one can utilize the multiple passes of the light beam to increase the sensitivity for measuring absorption and scattering by components of the optical cavity itself. It is desirable to suppress the effects of resonances in the cavity in order to make the spectral response of the cavity itself as nearly constant as possible over the entire wavelength range of interest. In the present instrument, the desired flattening of the spectral response is accomplished by utilizing an off-axis beam geometry to effectively decrease the frequency interval between longitudinal electromagnetic modes of the cavity, such that the resulting transmission spectrum of the cavity is nearly continuous: in other words, the cavity becomes a broad-band optical device.

OKeefe, Anthony↗
NASA NTRS1993

Remote measurement of planetary magnetic fields by the Hanle effect

Resonance fluorescence lines in the spectra of planetary atmospheres are polarized. They will be depolarized by magnetic fields in the scattering medium (Hanle effect). The amount of depolarization was calculated for some atomic (FeI, CaI) lines and some molecular lines (NO gamma bands) seen in the Earth's day glow spectra. The results are presented and the potential advantages of LIDAR measurements for obtaining atmospheric magnetic fields are discussed. The depolarization of Na and Ca lines are suitable for measuring magnetic fields in and near Io.

Kumar, C. K.↗
NASA NTRS1992

Diode-laser frequency stabilization based on the resonant Faraday effect

The authors present the results of a method for frequency stabilizing laser diodes based on the resonant Faraday effects. A Faraday cell in conjunction with a polarizer crossed with respect to the polarization of the laser diode comprises the intracavity frequency selective element. In this arrangement, a laser pull-in range of 9 A was measured, and the laser operated at a single frequency with a linewidth less than 6 MHz.

Wanninger, P.↗
NASA NTRS2003

Effect of Resonator Axis Skew on Normal Incidence Impedance

High by-pass turbofan engines have fewer fan blades and lower rotation speeds than their predecessors. Consequently, the noise suppression at the low frequency end of the noise spectra has become an increasing concern. This has led to a renewed emphasis on improving noise suppression efficiency of passive, duct liner treatments at the lower frequencies. For a variety of reasons, passive liners are comprised of locally-reacting, resonant absorbers. One reason for this design choice is to satisfy operational and economic requirements. The simplest liner design consists of a single layer of honeycomb core sandwiched between a porous facesheet and an impervious backing plate. These resonant absorbing structures are integrated into the nacelle wall and are very ef- ficient over a limited bandwidth centered on their resonance frequency. Increased noise suppression bandwidth and greater suppression at lower frequencies is typically achieved for conventional liners by increasing the liner depth and incorporating thin porous septa into the honeycomb core. However, constraints on liner depth in modern high by-pass engine nacelles severely limit the suppression bandwidth extension to lower frequencies. Also, current honeycomb core liners may not be suitable for irregular geometric volumes heretofore not considered. It is of interest, therefore, to find ways to circumvent liner depth restrictions and resonator cavity shape constraints. One way to increase effective liner depth is to skew the honeycomb core axis relative to the porous facesheet surface. Other possibilities are to alter resonator cavity shape, e.g. high aspect ratio, narrow channels that possibly include right angle bends, 180. channel fold-backs, and splayed channel walls to conform to irregular geometric constraints. These possibilities constitute the practical motivation for expanding impedance modeling capability to include unconventional resonator orientations and shapes. The work reported in this paper is in the nature of a progress report and is limited to examining the implications of resonator axis skew on the composite normal incidence impedance of an array of resonator channels. Specifically, experimental results are compared with a modified impedance prediction model for highaspect- ratio, rectangular, resonator channels with varying amounts of skew relative to the incident particle velocity. It is shown that for resonator channel widths of 1 to 2 mm, aspect ratios of 25 to 50, and skew angles of zero to sixty degrees, the surface impedance of test models can be predicted with good accuracy. Predicted resistances and reactances are particularly well correlated through the first resonance and first anti-resonance for all six test models investigated. Beyond the first anti-resonance, the impedance prediction model loses the ability to predict details of resistance and reactance but still predicts the mean trends very well.

Parrott, Tony L.↗
NASA NTRS1992

Partially coherent scattering in stellar chromospheres. I - Effects on resonance line thermalization

The conditions necessary for partially coherent scattering to influence the thermalization depth are investigated, and the effects of partial redistribution in homogeneous slab atmospheres are approximated using several common resonance lines as examples. For electron densities above 10 exp 10/cu cm, it is concluded that even when coherent scattering dominates the escape process, the thermalization depths of the strongest resonance lines of H, Ca II, and Mg II agree roughly with the Doppler diffusion in frequency. No elastic scattering effects on the thermalization of Mg II h and k and Ca II H and K are found. At lower densities, such as for giant star chromospheres and QSO models, the results deviate strongly from the Doppler complete redistribution case.

Gayley, Kenneth G.↗