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At least 73 records · Page 4

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NASA NTRS1973

Plate motion and the secular shift of the mean pole

The global plate motion indicates that changes in the products of inertia of the earth due to tectonic plate movement may provide a secular shift of the mean pole. A mathematical procedure for calculating this shift based on the plate theory is presented. Explicit expressions were obtained for the dependence of the secular polar shift on the dimensions and locations of the plate boundaries. Numerical results show that the secular motion of the mean pole is 0.0002 sec/year in the direction of 67 W. Hence, it is deduced that the influence of the plate motion on the secular polar shift may account for 10% of the observed value.

Liu, H.↗

NASA NTRS1973

The second-order gravitational red shift

The direct measurement of the nonlinear term of the gravitational field equations by using very stable clocks is discussed along with measuring the perhelion advance of a planet or satellite. These are considered measurements of the second-order gravitational red shift. The exact expression for the frequency shift of light in a gravitational field is derived. Other topics discussed include: The Doppler-cancelling technique; the second-order red shift in a spherically symmetric gravitational field; finite signal transit time; and the reality and interpretation of coordinates in the second-order red shift experiment.

Jaffe, J.↗

NASA NTRS1974

Anthropometric changes and fluid shifts

Several observations of body size, shape, posture, and configuration were made to document changes resulting from direct effects of weightlessness during the Skylab 4 mission. After the crewmen were placed in orbit, a number of anatomical and anthropometric changes occurred including a straightening of the thoracolumbar spine, a general decrease in truncal girth, and an increase in height. By the time of the earliest in-flight measurement on mission day 3, all crewmen had lost more than two liters of extravascular fluid from the calf and thigh. The puffy facies, the bird legs effect, the engorgement of upper body veins, and the reduced volume of lower body veins were all documented with photographs. Center-of-mass measurements confirmed a fluid shift cephalad. This shift remained throughout the mission until recovery, when a sharp reversal occurred; a major portion of the reversal was completed in a few hours. The anatomical changes are of considerable scientific interest and of import to the human factors design engineer, but the shifts of blood and extravascular fluid are of more consequence. It is hypothesized that the driving force for the fluid shift is the intrinsic and unopposed lower limb elasticity that forces venous blood and then other fluid cephalad.

Thornton, W. E.↗

NASA NTRS1978

Measurements of pressure-induced shifts in the 1-0 and 2-0 bands of HF and in the 2-0 bands of HCl-35 and HCl-37

Fourier absorption spectra of HCl and HF measured at room temperature and low pressures were found to indicate pressure-induced shifts of the spectral lines at gas pressures of only 10 torr. Self-induced shifts were determined for the HF 2-0 band and for the HCl-35 and HCl-37 2-0 bands, and shift oscillations in the 2-0 bands due to near-resonant dipole-dipole interactions between the two gases were also evaluated. Separate measurements of pressure-induced shifts in the HF 1-0 and 2-0 bands and in both isotopic HCl bands were obtained using argon, neon, nitrogen, and CO2 separately as the perturbing gases.

Guelachvili, G.↗

NASA NTRS1979

Vibrational dependence of pressure induced spectral linewidths and line shifts - Application of the infinite order sudden scattering approximation

The infinite order sudden (IOS) approximation to molecular rotation is applied to simplify the theory of linewidths and shifts in vibration-rotation spectra. This approximation is expected to be most accurate for hard, short-range collisions and is therefore complementary to Anderson theory which is best for weak, glancing collisions. The IOS approximation predicts identical linewidths and shifts for P- and R-branch transitions with the same line number. It also predicts zero line shifts for pure rotational spectra. The dependence of linewidths and shifts on vibrational band is seen to be due mainly to variation in diagonal vibrational matrix elements of the intermolecular potential. Calculations are performed for the 0-0, 0-1, and 0-2 bands of CO perturbed by He, using a theoretical interaction potential with no semiempirical or adjustable parameters; results are in satisfactory accord with experimental data.

Green, S.↗

NASA NTRS1981

Equatorward shift of the cusp during magnetospheric substorms

The equatorward shift of the midday part of the auroral oval (the cusp region) during the expansion phase of magnetospheric substorms is reexamined. A magnetospheric model developed by Akasofu and Corrick (1980) is used, which is constructed by using the earth's dipole field, an image dipole field of the earth and 40 bisected circular loops. A new dayside current system represented by six current loops separated by 15 deg in longitude, each carrying 100 KA, is added to this model. For a total current of .6 MA, the latitude of the cusp shifts equatorward by 1.8 deg; for a current of 1.8 MA, the cusp location shifts by more than 5 deg. Thus, the magnetic field of an enhanced dynamo current is the dayside boundary layer and of the connected circuit can account for the observed equatorward shift of the cusp region.

Akasofu, S.-I.↗

NASA NTRS1982

Fluid shifts and erythropoiesis - Relevance to the 'anemia' of space flight

To model the fluid shifts thought to occur in man during space flight, cephalic fluid shifts have been induced in man subjected to horizontal or headdown bedrest, in squirrel monkeys exposed to lower body positive pressure, and in rats subjected to antiorthostatic hypokinesia. The influence on erythropoiesis of such fluid redistribution has been studied. Only in man did a cephalic fluid shift consistently and significantly lead to a plasma volume reduction and an increased hematocrit. Although there was evidence for erythrosuppression and the subjects were 'anemic' at the end of the study, serum erythropoietin titers remained normal throughout bedrest. The erythrosuppression probably did not arise due to the increased hematocrit but may have been related to P50 shifts or the loss of body weight. Each model appeared to reproduce different parts of man's physiological response to weightlessness and promises to be useful in unraveling the etiology of the 'anemia' of space flight.

Dunn, C. D. R.↗

NASA NTRS1985

Geometric basis for the far red shift

An alternative explanation is offered for the redshift (an abrupt change in the ratio of scattering to absorption in the radiance spectra of heading canopies of such crops as wheat and grain sorghum). The shift occurs abruptly at wavelengths near the red-infrared boundary towards the longer wavelengths. The new explanation, following that of Collins (1978) and Schutt et al. (1984), is based on one particular architectural change that occurs in any heading plant canopy. Specifically, the newly extended heads alter the interaction between light and the established foliage. The heads reduce the amount of sunlight striking the topmost leaves which are generally comparatively good specular reflectors. The heads also reduce the ability to observe the specularly reflecting leaves. The reduction in the amplitude of the radiance (due to decreased specularly reflected light) at heading appears to be a shift in the wavelength of the red edge. It is proposed that vertical (amplitude) shifts - due to changes in the amount of specularly reflected light as a function of heading - have been misinterpreted as horizontal (wavelength) shifts due in part to the characteristic shape of the radiance curve at the red edge.

Vanderbilt, V. C.↗

NASA NTRS1985

Phase shifting two coupled circadian pacemakers - Implications for jet lag

Two Van der Pol oscillators with reciprocal linear velocity coupling are utilized to model the response of the human circadian timing system to abrupt displacements of the environmental time cues (zeitgebers). The core temperature rhythm and sleep-wake cycle simulated by the model are examined. The relationship between the masking of circadian rhythms by environmental variables and behavioral and physiological events and the rates of resynchronization is studied. The effects of zeitgeber phase shifts and zeitgeber strength on the resynchronization rates are analyzed. The influence of intrinsic pacemakers periods and coupling strength on resynchronization are investigated. The simulated data reveal that: resynchronization after a time zone shift depends on the magnitude of the shift; the time of day of the shift has little influence on resynchronization; the strength of zeitgebers affects the rate and direction of the resynchronization; the intrinsic pacemaker periods have a significant effect on resynchronization; and increasing the coupling between the oscillators results in an increase in the rate of resynchronization. The model data are compared to transmeridian flight studies data and similar resynchronization patterns are observed.

Gander, P. H.↗

NASA NTRS1987

Photoemission studies of core level shifts in HgCdTe, CdMnTe, and HgZnTe

The results of photoemission studies of core level shifts in the Hg(1-x)Cd(x)Te, Cd(1-x)Mn(x)Te, and Hg(1-x)Zn(x)Te alloys are discussed. In Hg(0.7)Cd(0.3)Te, the Hg 5d level is found to shift to lower binding energy by 0.1 eV, and the Cd 4d level to shift to higher binding energy by 0.25 eV upon alloying (relative to their binaries). The Born-Haber cycle is used to determine core level binding energies relative to the valence-band maximum in the context of tight-binding theory, and calculated core level shifts upon alloying in HgCdTe are shown to be too small to account for the observed values. A natural valence-band offset between HgTe and CdTe of 0.35 eV is found.

Shih, C. K.↗

NASA NTRS1988

Air-broadened Lorentz halfwidths and pressure-induced line shifts in the nu(4) band of C-13H4

Air-broadened halfwidths and pressure-induced line shifts in the nu(4) fundamental of C-13H4 were determined from spectra recorded at room temperature and at 0.01/cm resolution using a Fourier transform spectrometer. Halfwidths and pressure shifts were determined for over 180 transitions belonging to J-double prime values of less than or = to 16. Comparisons of air-broadened halfwidths and pressure-induced line shifts made for identical transitions in the nu(4) bands of C-12H4 and C-13H4 have shown that C-13H4 air-broadened halfwidths are about 5 percent smaller than the corresponding C-12H4 halfwidths, and the pressure shifts for C-13H4 lines are about 5-15 percent larger than those for C-12H4.

Devi, V. Malathy↗

NASA NTRS1989

Water-vapor line broadening and shifting by air, nitrogen, oxygen, and argon in the 720-nm wavelength region

High-resolution spectroscopic measurements of H2O vapor in the 720-nm wavelength region were conducted to investigate the broadening and shifting of H2O lines by air, nitrogen, oxygen, and argon over a wide range of pressures and temperatures. For each of the buffer gases under study, a linear relationship was found between the widths and the shifts, with the broader lines having the smaller pressure shifts. The pressure shifts measured compared favorably with theoretical values reported by Bykov et al. (1988). The temperature-dependence exponents for air-broadening were found to be J-dependent, with the lower-J lines having the higher exponents.

Grossmann, Benoist E.↗

NASA NTRS1991

Wavelength shifts in fluorescence maxima of stressed and non-stressed Norway spruce needles over the growing season

Laboratory fluorescence measurements of first and third year metal stressed and non stressed Norway spruce needles collected in May, Jul. Sep. and Nov. display significant wavelength shifts in the intensity maxima in the blue, green, red, and near infrared spectral regions, with the largest shifts occurring in the blue spectral region for both first and third year needles from Nov. Smaller, but the otherwise significant shifts also take place in the blue spectral region for first year needles from Sep. in the red spectral region for third year neddles from May, Jul. and Sep. and in the near infrared spectral region for first and third year needles from Jul. and Sep. Wavelength shifts in needle fluorescence maxima over the growing season are greatest in the blue and to a lesser extent, greenspectral regions from Sep. to Nov. but are also significant in the red and near infrared spectral regions from Jul. to Sep. and Sep. to Nov., and in the near infrared spectral region also from May to Jul.

Banninger, Cliff↗

NASA NTRS1992

A source mechanism producing HF-induced plasma lines (HFPLS) with up-shifted frequencies

Attention is given to a nonlinear scattering process analyzed as a source mechanism producing the frequency up-shifted HFPLs observed in the Arecibo ionospheric heating experiments. A physical picture is offered to explain how Langmuir waves with frequencies greater than the HF heater wave frequency can be produced in the heating experiments and be detected by incoherent radars as frequency up-shifted HFPLs. Since the considered scattering process occurs in a region near the reflection height, it explains why the frequency up-shifted HFPLs should originate from the altitude near the reflection height as observed. The theory also shows that the amount of frequency up-shift is inversely proportional to the frequency of the HF heater and increases linearly with the electron temperature. The quantitative analysis of the theory shows a good agreement with the experimental results.

Kuo, S. P.↗

NASA NTRS1992

Phase shift of TE and TM modes in an optical fiber due to axial strain (exact solution)

Axial strain may be determined by monitoring the phase shift of modes of a variety of optical fiber sensors. In this paper, the exact solution of a circular optical fiber is used to calculate the phase shift of the TE and TM modes. Whenever an optical fiber is stressed, the optical path length, the index of refraction, and the propagation constants of each fiber mode change. In consequence, the modal phase term, beta(ln)z, of the fields is shifted by an amount Delta phi. In certain cases, it is desirable to control the phase shift term in order to make the fiber either more or less sensitive to certain kinds of strain. It is shown that it can be accomplished by choosing appropriate fiber parameters.

Egalon, Claudio O.↗

NASA NTRS1992

Solar Doppler-shift measurements in the Ne VII 465 A emission line

Using a Dopplergram obtained with the Naval Research Laboratory extreme ultraviolet spectrograph on Skylab, we have searched for Doppler shifts in the Ne VII 465 A emission line, which is formed at a temperature of about 500,000 K. In the quiet sun we find no measurable average Doppler shift to a measurement accuracy of +/- 18 km/s. Small regions of the quiet sun do, however, display measurable Doppler shifts. In active regions, we measure Doppler shifts indicating downflow velocities of up to 70 km/s.

Mariska, John T.↗

NASA NTRS1993

Confirmation of solar cycle-dependent intermediate-degree p-mode frequency shifts

Results of intercomparisons of seven different sets of frequencies of intermediate-degree p-modes obtained at several different locations between 1981 and 1989 are presented. It is shown that the frequency shifts exhibited by all of these intermediate-degree p-modes are consistent with the intermediate-degree frequency shifts presented by Libbrecht and Woodward (1990) and also with the low-degree frequency shifts presented by Elsworth et al. (1990). It is also shown that these frequency shifts correlate with solar cycle-dependent changes in sunspot number, area, and irradiance. Unbinned and binned differences between 1984 Mount Wilson Observatory and revised 1981 South Pole frequencies are illustrated.

Rhodes, Edward J., Jr.↗

NASA NTRS1993

The gust-front detection and wind-shift algorithms for the Terminal Doppler Weather Radar system

The Federal Aviation Administration's (FAA) Terminal Doppler Weather Radar (TDWR) system was primarily designed to address the operational needs of pilots in the avoidance of low-altitude wind shears upon takeoff and landing at airports. One of the primary methods of wind-shear detection for the TDWR system is the gust-front detection algorithm. The algorithm is designed to detect gust fronts that produce a wind-shear hazard and/or sustained wind shifts. It serves the hazard warning function by providing an estimate of the wind-speed gain for aircraft penetrating the gust front. The gust-front detection and wind-shift algorithms together serve a planning function by providing forecasted gust-front locations and estimates of the horizontal wind vector behind the front, respectively. This information is used by air traffic managers to determine arrival and departure runway configurations and aircraft movements to minimize the impact of wind shifts on airport capacity. This paper describes the gust-front detection and wind-shift algorithms to be fielded in the initial TDWR systems. Results of a quantitative performance evaluation using Doppler radar data collected during TDWR operational demonstrations at the Denver, Kansas City, and Orlando airports are presented. The algorithms were found to be operationally useful by the FAA airport controllers and supervisors.

Hermes, Laurie G.↗