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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 1,531 records · Page 85
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NASA NTRS1985

The effect of line damping, magneto-optics and parasitic light on the derivation of sunspot vector magnetic fields

The least square fitting of Stokes observations of sunspots using a Milne-Eddington-Unno model appears to lead, in many circumstances, to various inconsistencies such as anomalously large doppler widths and, hence, small magnetic fields which are significantly below those inferred solely from the Zeeman splitting in the intensity profile. It is found that the introduction of additional physics into the model such as the inclusion of damping wings and magneto-optic birefrigence significantly improves the fit to Stokes parameters. Model fits excluding the intensity profile, i.e., of both magnitude as well as spectral shape of the polarization parameters alone, suggest that parasitic light in the intensity profile may also be a source of inconsistencies. The consequences of the physical changes on the vector properties of the field derived from the Fe I lambda 6173 line for the 17 November 1975 spot as well as on the thermodynamic state are discussed. A Doppler width delta lambda (D) - 25mA is bound to be consistent with a low spot temperature and microturbulence, and a damping constant of a = 0.2.

Skumanich, A.↗
NASA NTRS1985

The energy spectra of solar flare electrons

A survey of 50 electron energy spectra from .1 to 100 MeV originating from solar flares was made by the combination of data from two spectrometers onboard the International Sun Earth Explorer-3 spacecraft. The observed spectral shapes of flare events can be divided into two classes through the criteria of fit to an acceleration model. This standard two step acceleration model, which fits the spectral shape of the first class of flares, involves an impulsive step that accelerates particles up to 100 keV and a second step that further accelerates these particles up to 100 MeV by a single shock. This fit fails for the second class of flares that can be characterized as having excessively hard spectra above 1 MeV relative to the predictions of the model. Correlations with soft X-ray and meter radio observations imply that the acceleration of the high energy particles in the second class of flares is dominated by the impulsive phase of the flares.

Evenson, P. A.↗
NASA NTRS1985

Images of the earth's aurora and geocorona from the Dynamics Explorer mission

Several series of auroral and geocoronal images from th Dynamics Explorer Mission are presented and analyzed. It is found that the motion of the transpolar arc of a theta aurora is correlated with the y-component of the IMF; the arc motion is in the general direction of the y-component. In addition, a sequence of global images of a small auroral substorm shows the initial development of intense luminosities in a relatively small spatial region or 'bright spot' in the premidnight sector of the auroral oval and a subsequent appearance of an expanding area of lesser intensities at low latitudes and contiguous to the midnight boundary of the bright spot. Finally, a series of images of the geocorona in scattered solar Ly-alpha emissions is used to obtain a best-fit spherical model of atomic hydrogen densities in the earth's exosphere; a Chamberlain model provides an adequate fit to radial distances of 4.5 earth-radii, beyond which an exponential fit is used. The geocoronal tail is detected as an asymmetric increase in scattered Ly-alpha intensities in the antisolar direction.

Frank, L. A.↗
NASA NTRS1986

Ultrasonic Inspection Near Small Bores

Portable ultrasonic probe makes it possible to inspect for hidden cracks near insides of narrow tubes. Using pulse-echo technique, instrument detects cracks as small as 0.015-in. (0.38-mm) deep. Used for nondestructive inspection of other hard-to-reach places where conventional large transducers will not fit or where difficult to apply coupling liquid for contact ultrasonic testing. Inspects bore of tubelike fitting. Instrument makes it unnecessary to disassemble fitting to check for cracks. Precise orientation of transducer with respect to part not necessary for detecting cracks.

Parent, R. G.↗
NASA NTRS1986

A SIRTF interdiciplinary scientist proposal

Segal's chronometric cosmology provides an adequate fit to the radio source counts only for an unrealistic choice of spectral index. Since the typical observed spectral index of 0.75 gives a completely unacceptable X squared = 136 with 24 (or fewer) degrees of freedom, it is concluded that the actual Universe does not fit the chronometric model. Counts of ultraviolet excess quasistellar objects also show a steep N(S) curve that the chronometric cosmology cannot explain. Claims to the contrary by Segal, Loncaric, and Segal (1980) and Segal and Nicoll (1986) depend on a seemingly innocuous assumption that in fact destroys the power of the N(S) test. Even though the chronometric model gives a better fit that other non-evolving models it must be ruled out along with all non-evolving cosmologies.

Wright, E. L.↗
NASA NTRS1986

The structure of high-temperature flare plasma. II Comparison with observations

In Emslie, (1985) scaling law's which relate peak loop temperature to injected nonthermal electron flux in electron-heated models of the flare corona are derived. These predicted relationships are compared with recent coordinated observations in hard X-rays and soft X-rays. Satisfactory agreement is found for large events, while for smaller events the plasma electron temperature determined by soft X-ray spectral fitting is too high. A possible resolution of this apparent discrepancy through careful examination of the method used to determine the temperature of the soft X-ray emitting plasma is discussed. It is concluded that temperatures determined by spectral fitting over a series of lines are not necessarily representative of the true temperature of the plasma, since the fitting technique is plagued by the same difficulties as a more straightforward technique involving a single spectral line or portion of continuum (Craig and Brown, 1976). The differences between actual and derived temperatures are sufficiently large to remove the above discrepancy between observations and modeling of electron-heated coronae.

Emslie, A. G.↗
NASA NTRS1986

On the analytical determination of relaxation modulus of viscoelastic materials by Prony's interpolation method

A computer implementation to Prony's curve fitting by exponential functions is presented. The method, although more than one hundred years old, has not been utilized to its fullest capabilities due to the restriction that the time range must be given in equal increments in order to obtain the best curve fit for a given set of data. The procedure used in this paper utilizes the 3-dimensional capabilities of the Interactive Graphics Design System (I.G.D.S.) in order to obtain the equal time increments. The resultant information is then input into a computer program that solves directly for the exponential constants yielding the best curve fit. Once the exponential constants are known, a simple least squares solution can be applied to obtain the final form of the equation.

Rodriguez, Pedro I.↗
NASA NTRS1986

The energy distributions of B supergiants in the Large Magellanic Cloud

It is shown that line-blanketed, LTE, plane-parallel model atmosphere calculations provide excellent fits to the ultraviolet-through-visual energy distributions of B supergiants in the Large Magellanic Cloud. The models were computed using Kurucz's (1979) ATLAS atmosphere program, but with lower gravities than were contained in Kurucz's published model grid. The ultraviolet continua of low gravity stars are found to be sensitive to changes in temperature and gravity. Measurements of Teff and log g for ten LMC B supergiants from model atmosphere fits to the energy distributions yield estimates of their radii, luminosities, and masses. Model atmosphere fits suggest that the late B supergiants have significantly lower masses than the earlier B types of the same luminosity, contrary to stellar evolution theory which predicts that B supergiants are in a post-core hydrogen burning phase and should evolve very quickly and at essentially constant mass.

Fitzpatrick, Edward L.↗
NASA NTRS1986

Self indexing latch system

A self-latching jaw assembly is described which includes a pair of jaws for latching a fitting of an associated structure such as the keel fitting of a space telescope. The jaw assembly automatically locates the fitting received on a positioning pedestal and latches it in its original location on the pedestal without need of precision alignment. The first jaw is actuated and moved to the right whereupon a reciprocating plunger, extended from the nose of the jaw senses the hub of the spool. A jaw position responsive switch is then actuated to terminate the drive motor of the jaw. The astronaut will then actuate the drive motor of the jaw and the jaw will move to the left, whereupon the standoff will engage the face of the jaw in a latching position. In the latching position, the noses of the jaws will be under the flanges of the spool.

John C Gibson↗
NASA NTRS1987

Tube coupling device

A first annular ring of a tube coupling device has a keyed opening sized to fit around the nut region of a male coupling, and a second annular ring has a keyed opening sized to fit around the nut of a female coupling. Each ring has mating ratchet teeth and these rings are biased together, thereby engaging these teeth and preventing rotation of these rings. This in turn prevents the rotation of the male nut region with respect to the female nut. For tube-to-bulkhead locking, one facet of one ring is notched, and a pin is pressed into an opening in the bulkhead. This pin is sized to fit within one of the notches in the ring, thereby preventing rotation of this ring with respect to the bulkhead.

Myers, William N.↗
NASA NTRS1986

Steady surficial core motions - An alternate method

A new method for deriving steady surficial core motions from geomagnetic field models is presented and applied. The original method determines the steady velocity field at the top of a frozen-flux core which best fits, in both the spatial and temporal linear least squares sense, a model of the large scale geomagnetic secular variation (SV) at the base of a source-free mantle (Voorhies, 1986). New method is based upon the same physical assumptions, but fits SV at earth's surface instead of the core-mantle boundary (CMB). The newly derived flow differs somewhat from prior solutions, and shows but slight westward drift; however, other key global properties are virtually unchanged. Over a 15 year interval the new method provides a better fit to the time-varying geomagnetic field at earth's surface than does the old.

Voorhies, Coerte V.↗
NASA NTRS1987

Low-mass, pre-main-sequence stars - The infrared emission from circumstellar dust

Models for the dust shells around the low-mass, premain sequence stars IRS 1 and IRS 2 embedded in the Serpens molecular cloud are calculated which accurately fit the stars' observed near-IR fluxes. The far-IR fluxes are predicted, and the model parameters are adjusted to provide a best fit to the observed near-IR spectra. Best fit models are obtained for protostar masses of 2.97 and 2.14 solar masses, an accretion rate of about 10 to the -7th solar masses/yr, and inner shell radii of 9.6 x 10 to the 12th and 4.6 x 10 to the 12th cm, respectively, for IRS 1 and 2. The calculated spectra of the dust shells alone peak at about 2 microns and have no other broad continuum maxima longward of 2-3 microns. The empirical technique of Churchwell and Koornneef (1986) for estimating the mean temperature, radius, and luminosity of circumstellar dust shells by using H and K fluxes gives values in reasonably good agreement with the model calculations.

Wolfire, Mark G.↗
NASA NTRS1987

Comparing the jerk with other global models of the geomagnetic field from 1960 to 1978

About 3300 satellite values of geomagnetic intensity and about 700 observatory values of annual mean magnetic vector components from 1960 to 1978 were fitted by three global models of the geomagnetic field B. Each model includes a spatially constant external field whose time dependence is a constant plus another constant times the Dst index, and each model accepts a time-independent station correction at each observatory. The time dependence of the internal Gauss coefficients is either cubic, quintic, or biquadratic (two independent quadratics, one before and one after January 1, 1970); and g1(0) also has an induced term proportional to the Dst index. The rms residual of the data fit is the same for the cubic and biquadratic models and insignificantly smaller for the quintic model. The quintic and biquadratic models have 1164 adjustable parameters, and the cubic has 1038. At a high level of significance the parameters of the best fitting biquadratic rule out a physical model for the magnetic impulse of 1969 in which the level surfaces of electrical conductivity in the lower mantle are approximately spherical, and the radial magnetic field at the core-mantle boundary goes from one quadratic time dependence to another in a year or less.

Backus, G. E.↗
NASA NTRS1987

Full potential integral solution for transonic flows with and without embedded Euler domains

Two methods are presented to solve for the transonic airfoil flow problems. The first method is based on the integral equation solution of the full-potential equation in terms of the velocity field, and a Shock Capturing-Shock Fitting (SCSF) scheme has been developed. The SCSF-scheme consists of a shock-capturing part and a shock-fitting part in which shock panels are introduced at the shock location. The sock panels are fitted and crossed by using the Rankine-Hugoniot relations. The second method is based on coupling the integral equation of the full-potential equation with the pseudo time integration of Euler equations in a small embedded region around the shock. The integral solution provides the initial and boundary conditions for the Euler domain. This scheme is named as the Integral Equation-Embedded Euler (IEEE) scheme. The two methods are applied to NACA 0012 and NACA 64A010A over a wide range of Mach numbers, and the reults are in good agreement with the experimental data and other computational results. The schemes converge within a number of iterations which is one-order of magnitude less than the finite-difference schemes.

Kandil, Osama A.↗
NASA NTRS1987

Ca + HF - The anatomy of a chemical insertion reaction

A comprehensive first-principles theoretical investigation of the gas phase reaction Ca + HF - CaF + H is reported. Ab initio potential energy calculations are first discussed, along with characteristics of the computed potential energy surface. Next, the fitting of the computed potential energy points to a suitable analytical functional form is described, and maps of the fitted potential surface are displayed. The methodology and results of a classical trajectory calculation utilizing the fitted potential surface are presented. Finally, the significance of the trajectory study results is discussed, and generalizations concerning dynamical aspects of Ca + HF scattering are drawn.

Jaffe, R. L.↗
NASA NTRS1987

Characterization of fault recovery through fault injection on FTMP

The development of fault-injection procedures and statistical analysis techniques to characterize the fault recovery of fault-tolerant systems is described. Pin-level fault-injection was conducted on a fault-tolerant microprocessor computer in order to generate data to assess the utility of current fault-injection sampling methods. The validity of common reliability-modeling assumptions concerning the statistical distribution of recovery times is investigated. A multiple comparison analysis for detecting behavior variations, and a distribution fitting for determining the best fit for the data were conducted. It is observed that the detection behavior is not homogeneous across all data sets, and that none of the factors under experimental control can account for the observed groupings of behavior. It is determined that no single distribution fits all the data sets, and that stratified random sampling and statistically robust parameter-estimation techniques are required to characterize fault detection time.

Finelli, George B.↗
NASA NTRS1987

Temperature dependence (4K to 300K) of the electrical resistivity of methane grown carbon fibers

Experimental measurements of the electrical resistivity vs temperature of methane vapor grown carbon fibers are presented. The fibers are heat treated from 1100 C (as-grown) to 3000 C. Data are fit to a standard two band model, which yields values for boundary scattering limited electron mobility, in-plane mean free path, energy band overlap, and total carrier density. The data are also fit to an ellipsoidal band model, where data fits yield effective masses, band overlap, Fermi velocity, phonon contributions to scattering, and ionized impurity scattering rates.

Woollam, John A.↗
NASA NTRS1988

Estimation of time- and state-dependent delays and other parameters in functional differential equations

A parameter estimation algorithm is developed which can be used to estimate unknown time- or state-dependent delays and other parameters (e.g., initial condition) appearing within a nonlinear nonautonomous functional differential equation. The original infinite dimensional differential equation is approximated using linear splines, which are allowed to move with the variable delay. The variable delays are approximated using linear splines as well. The approximation scheme produces a system of ordinary differential equations with nice computational properties. The unknown parameters are estimated within the approximating systems by minimizing a least-squares fit-to-data criterion. Convergence theorems are proved for time-dependent delays and state-dependent delays within two classes, which say essentially that fitting the data by using approximations will, in the limit, provide a fit to the data using the original system. Numerical test examples are presented which illustrate the method for all types of delay.

Murphy, K. A.↗