Digital FM - Tutorial.
Digital FM techniques, signal spectral properties, discrimination detection, phenomenological model, etc
Salz, J.↗
SEARCH · Engineering Papers
Results for “Phenomenological Models”
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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Coercive force of thin magnetic films
Phenomenological model aids in understanding the mechanisms responsible for the easy-axis coercive force in thin magnetic films of NiFe, MnBi, and gadolinium iron garnet.
Baldwin, J. A.↗
The physical theory of one dimensional galactic cosmic-ray propagation in the atmosphere
An analytical theory of atmospheric cosmic-ray propagation is developed based on a phenomenological model of hadron-nucleus collisions. This model correctly predicts the sea level cosmic-ray nucleon, pion and muon spectra, the cosmic-ray ionization profile in the atmosphere, and neutron flux and density profiles in the atmosphere. It is concluded that the large scale properties of atmospheric cosmic-rays can be accurately predicted on the basis of a nucleonic cascade with all secondaries mediated by pion production. Implications for energy independence of cross sections, the recent 70 GeV results from Serpukhov, and nucleonic relaxation rates in the atmosphere are discussed.
Obrien, K.↗
Fourier plane filters
An electrically addressed liquid crystal Fourier plane filter capable of real time optical image processing is described. The filter consists of two parts: a wedge filter having forty 9 deg segments and a ring filter having twenty concentric rings in a one inch diameter active area. Transmission of the filter in the off (transparent) state exceeds fifty percent. By using polarizing optics, contrast as high as 10,000:1 can be achieved at voltages compatible with FET switching technology. A phenomenological model for the dynamic scattering is presented for this special case. The filter is designed to be operated from a computer and is addressed by a seven bit binary word which includes an on or off command and selects any one of the twenty rings or twenty wedge pairs. The overall system uses addressable latches so that once an element is in a specified state, it will remain there until a change of state command is received. The drive for the liquid crystal filter is ? 30 V peak at 30 Hz to 70 Hz. These parameters give a rise time for the scattering of 20 msec and a decay time of 80 to 100 msec.
Oliver, D. S.↗
Substorms in space - The correlation between ground and satellite observations of the magnetic field
Several of the events criticized by Akasofu (1972) are reexamined. It is concluded that there is no simple one-to-one relationship between polar magnetic substorms and magnetospheric substorms as defined by midlatitude magnetograms. It appears that in some cases polar magnetic substorms occur during the growth phase of a magnetospheric substorm. Magnetospheric observations are more systematically organized by midlatitude onsets than by auroral zone onsets. The determination of onset times is discussed together with the determination of substorm similarity, the phenomenological model of magnetic variations during magnetospheric substorms, the event of February 25, 1967, and the complex event of February 13, 1968.
Mcpherron, R. L.↗
Solar wind and substorm-related changes in the lobes of the geomagnetic tail
The relationship of the geomagnetic tail lobe energy density to solar wind dynamic pressure, the north-south component of the interplanetary magnetic field, and substorm expansion onsets is investigated. Enhanced lobe energy densities are observed to follow both southward turnings of the interplanetary magnetic field and solar wind dynamic pressure increases. An empirical relationship is developed relating the tail lobe magnetic energy density to the solar wind dynamic pressure by using data obtained when the interplanetary field was northward. Localized, off-center, or multiple-onset substorm expansion phases are shown to have little effect on the lobe magnetic field. A positive correlation is found between magnetosphere-wide substorm expansions and decreases in the lobe energy density. The positive correlation of the energy density with both the solar wind dynamic pressure and a southward interplanetary magnetic field and the positive correlation between magnetospheric substorm activity and lobe energy density decreases are demonstrated to be consistent with a phenomenological model of substorm behavior.
Caan, M. N.↗
Critical problems in establishing the morphology of substorms in space
A phenomenological model of the magnetospheric substorm has been developed which divides the substorm into three phases: a growth phase, an expansion phase, and a recovery phase. Current research is reviewed in the light of criticism of this model. The most important inadequacies of the model concern the fact that the tail lobe and the plasma sheet do not always react as single entities as previously supposed. Further research is needed on the problems of substorm variability, errors in onset time, the number of distinct spatial regions, and the dependence of magnetic activity on past history.
Mcpherron, R. L.↗
Coronal holes and high-speed wind streams
Coronal holes, regions of unusually low density and low temperature in the solar corona, are identified as Bartel's M regions, i.e., sources of high-speed wind streams that produce recurrent geomagnetic variations. Throughout the Skylab period the polar caps of the sun were coronal holes, and at lower latitudes the most persistent and recurrent holes were equatorial extensions of the polar caps. The holes rotated 'rigidly' at the equatorial synodic rate. They formed in regions of unipolar photospheric magnetic field, and their internal magnetic fields diverged rapidly with increasing distance from the sun. The geometry of the magnetic field in the inner corona seems to control both the physical properties of the holes and the global distribution of high-speed wind streams in the heliosphere. Phenomenological models for the birth and decay of coronal holes have been proposed.
Zirker, J. B.↗
Linear and nonlinear interactions between the earth tide and a tectonically stressed earth
In the vincinity of earthquake focal regions, conditions may not be equal. Crustal rocks stressed to more than approximately 0.6 of their failure strength exhibit material properties over and above that of linear elasticity. Interactions between the earth tide and crustal rocks that are under high tectonic stress are discussed in terms of simple phenomenological models. In particular, the difference between a nonlinear elastic model of dilatancy and a dilatancy model that exhibits hysteresis is noted. It is concluded that the small changes in stress produced by the earth tide act as a probe of the properties of crustal rocks. Observations of earth tide tilts and strains in such high stress zones may, therefore, provide keys to the constitutive properties and the tectonic stress rate tensor of these zones.
Beaumont, C.↗
The use of ground magnetograms to time the onset of magnetospheric substorms
A critical review of magnetospheric substorm timing techniques is presented. Attention is given to substorm timing with auroral zone magnetograms, substorm onset timing with midlatitude magnetograms, multiple onset substorms, and a phenomenological model for multiple onset substorms. Emphasis is placed on some pitfalls that have led some investigators to err in substorm onset determinations. In particular, multiple onset substorms appear to account for many of the reported discrepancies in substorm timing. It is suggested that present idealized models of substorm morphology must be modified to include the multiple onset substorms.
Mcpherron, R. L.↗
Strongly turbulent stabilization of electron beam-plasma interactions
The stabilization of electron beam interactions due to strongly turbulent nonlinearities is studied analytically and numerically for a wide range of plasma parameters. A fluid mode coupling code is described in which the effects of electron and ion Landau damping and linear growth due to the energetic electron beam are included in a phenomenological manner. Stabilization of the instability is found to occur when the amplitudes of the unstable modes exceed the threshold of the oscillating two-stream instability. The coordinate space structure of the turbulent spectrum which results clearly shows that soliton-like structures are formed by this process. Phenomenological models of both the initial stabilization and the asymptotic states are developed. Scaling laws between the beam-plasma growth rate and the fluctuations in the fields and plasma density are found in both cases, and shown to be in good agreement with the results of the simulation.
Freund, H. P.↗
Ion and advanced electric thruster research
A phenomenological model of the orificed, hollow cathode based on the field enhanced, thermionic mechanism of electron emission is presented. High frequency oscillations associated with the orificed, hollow cathode are shown to be a consequence of current flow through the cathode orifice. A procedure for Langmuir probing of the hollow cathode discharge and analyzing the resulting probe characteristics is discussed. The results of sputter yield measurements made for molybdenum, tantalum, type 304 stainless steel and copper surfaces being bombarded by low energy argon or mercury ions are also given. The effects of nitrogen and alternated copper layers on the sputter yields of molybdenum, tantalum and 304 stainless steel are also discussed. A dynamic model of electrothermal rocket and ramjet thrusters is developed. The gross performance of these devices is compared to that of an electromagnetic gun for the case of a high acceleration, Earth launch mission. The theoretical performance of electrothermal rockets and ramjets is shown to be comparable to that of the electromagnetic gun.
Wilbur, P. J.↗
Variable N-type negative resistance in an injection-gated double-injection diode
Double-injection (DI) switching devices consist of p+ and n+ contacts (for hole and electron injection, respectively), separated by a near intrinsic semiconductor region containing deep traps. Under proper conditions, these devices exhibit S-type differential negative resistance (DNR) similar to silicon-controlled rectifiers. With the added influence of a p+ gate appropriately placed between the anode (p+) and cathode (n+), the current-voltage characteristic of the device has been manipulated for the first time to exhibit a variable N-type DNR. The anode current and the anode-to-cathode voltage levels at which this N-type DNR is observed can be varied by changing the gate-to-cathode bias. In essence, the classical S-type DI diode can be electronically transformed into an N-type diode. A first-order phenomenological model is proposed for the N-type DNR.
Kapoor, A. K.↗
Statistical fatigue of unnotched composite laminates
A general analytical, phenomenological model is developed for characterizing fatigue damage accumulation in unnotched composite laminates, and experimental results are used to evaluate the model. The fatigue model, which is developed for various types of cyclic loadings, is based on the assumption that the residual strength reduction is a monotonically decreasing function of the fatigue life. Parameters are determined from baseline test data consisting of one set of residual strength data, one set of static strength data, and one set of constant amplitude fatigue life data. Once the parameters are determined, the model is able to predict: (1) the statistical distribution of the fatigue life, and the residual strength under constant and variable amplitude loads, and (2) the effect of periodic proof tests, without any additional experimental data. Experimental test results show that predictions made from the present model agree quite well with the experimental results. The model is also applicable to fatigue of bonded or bolted composite joints.
Yang, J. N.↗
The submillimeter wavelength spectrum of methanol
Observations and assignments of some of the absorption lines in methanol from 200 to 850 GHz are reported. A simple phenomenological model is described which allows interpretation of spectra and prediction of new lines with little computational effort.
Pickett, H. M.↗
Fokker-Planck response of stochastic satellites
The present investigation is concerned with the effects of stochastic geometry and random environmental torques on the pointing accuracy of spinning and three-axis stabilized satellites. The study of pointing accuracies requires a knowledge of the rates of error growth over and above any criteria for the asymptotic stability of the satellites. For this reason the investigation is oriented toward the determination of the statistical properties of the responses of the satellites. The geometries of the satellites are considered stochastic so as to have a phenomenological model of the motions of the flexible structural elements of the satellites. A widely used method of solving stochastic equations is the Fokker-Planck approach where the equations are assumed to define a Markoff process and the transition probability densities of the responses are computed directly as a function of time. The Fokker-Planck formulation is used to analyze the response vector of a rigid satellite.
Huang, T. C.↗
Dynamics of interfacial pattern formation
A phenomenological model of dendritic solidification incorporating interfacial kinetics, crystalline anisotropy, and a local approximation for the dynamics of the thermal diffusion field is proposed. The preliminary results are in qualitative agreement with natural dendrite-like pattern formation.
Ben-Jacob, E.↗
Thrust for interorbital propulsion - A question of lifetime
The most promising operational window for the use of magnetoplasmadynamic (MPD) thrusters is identified to be at megawatt power levels for orbital maneuvering. For such applications, the operation of a steady-state MPD thruster system imposes stringent requirements on the lifetime of thruster surfaces which will erode due to interactions with the plasma working fluid. Basic erosion mechanisms are presented and the problems associated with measuring the erosion rates are discussed. An experimental approach that would allow the development of a phenomenological model for erosion is proposed.
Gabriel, S. B.↗