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Stability in energy for the Newmark beta-family of time integration operators for nonlinear material problems is examined. It is shown that the necessary and sufficient conditions for unconditional stability are equivalent to those predicted by Fourier methods for linear problems.
Contact-impact problems involving finite deformation axisymmetric membranes are solved by the finite element method with explicit time integration. The formulation of the membrane element and the contact constraint conditions are discussed. The hyperelastic, compressible Blatz and Ko material is used to model the material properties of the membrane. Two example problems are presented.
Basic calculations are presented for evaluating the feasibility of a scanning microwave radiometer system for mapping the thickness of lake ice. An analytical model for the apparent brightness temperature as a function of ice thickness has been developed, and elaborated to include such variables as galactic and atmospheric noise, aspect angle, polarization, temperature gradient in the ice, the presence of transition layers such as snow, slush, and water, increased loss due to air inclusions in the ice layer, and the presence of multiple ice thicknesses within the antenna footprint. It was found that brightness temperature measurements at six or seven frequencies in the range of 0.4 to 0.7 GHz were required to obtain unambiquous thickness estimates. A number of data processing methods were examined. The effects of antenna beamwidth, scanning rate, receiver bandwidth, noise figure, and integration time were studied.
The data base and techniques developed for Skylab experiment ED76 were used to process and analyze data from 54 solid dielectric track recorders. The processing of mica and cellulose nitrate for neutron and proton detectors is described. The measured time integrated fission rates for seven detectors is given.
Equations are derived by using branched trajectory optimization techniques and the maximum principle to maximize the payload capability of a reusable tug/expendable kickstage vehicle configuration for planetary missions. The two stages and the payload are launched into a low earth orbit by a single space shuttle. The analysis includes correction for precession of the orbit. This correction is done by the tug. The tug propels the payload and the kickstage to an energy beyond earth escape and returns within a specified time to the precessed orbit. After separating from the tug, the kickstage accelerates the payload to the required injection conditions. Planetary injection conditions are specified by the mission energy and a fixed declination and right ascension of the outgoing asymptote. The multipoint boundary value problem resulting from the analysis is solved by a Newton-Raphson iteration technique. Partial derivatives of the boundary conditions are obtained by perturbing the initial conditions one at a time, integrating the trajectory and adjoint equations, and observing the changes in boundary conditions. Maximum payload capability is derived for two typical mission energies. In addition, the variations of several mission and stage parameters are also examined.
The case of a cold gas in the absence of external force fields is considered. Since the only energy involved is kinetic energy, the total kinetic action (i.e., the space-time integral of the kinetic energy density) should serve as the total free-energy functional in this case, and as such should be a local minimum for all possible fluctuations about stable flow. This conjecture is tested by calculating explicit, manifestly covariant expressions for the first and second variations of the total kinetic action in the context of Lagrangian kinematics. The general question of the correlation between physical stability and the convexity of any action integral that can be interpreted as the total free-energy functional of the flow is discussed and illustrated for the cases of rectillinear and rotating shearing flows.
The paper describes a computer-operated image-scanning and data-collection system for the magnetograph at the Mt. Wilson 150-foot Tower telescope. The system is based on a minicomputer with a 32K word core memory and a generalized interface unit for controlling image motion, a keyboard, and an associated television screen. Operation of the solar image guider and the data-collection assembly is outlined along with the observation and data-reduction procedures. Advantages of the system include the ability to move the image in almost any conceivable fashion, a wide choice of integration times, and increased accuracy in magnetic and Doppler calibrations as well as in setting of the magnetic zero level.
The effects of forward flight on the turbulence characteristics of a jet in a co-flowing stream have been determined for a 2.22 inch circular jet in a 36 inch free jet wind tunnel. The nozzle exit velocity was 400 ft/sec, and the tunnel velocity was set at 0, 40, 120 and 200 ft/sec. Measurements of flow properties including mean velocity, turbulence intensity and spectra, convection velocity, integral length scale, and convected integral time scale were carried out using two linearized hot wires. Results were used to predict changes due to flight in the jet acoustic sources. The noise reductions for a cold jet with a velocity of 1000 ft/sec, due to the change in acoustic sources in flight, agreed well at all angles with measured noise reductions.
Temperature sensitivity degradation due to antenna losses is recognized as a hindrance to extension of available remote-sensing radiometry techniques to larger systems for enhanced spatial resolution. The use of large antennas is also complicated by difficulties with bandwidth and integration time. Advantages of introducing active devices at the subarray level, with distributed Dicke switching or correlation detection, are examined, and their possible contribution to the design of effective imaging microwave radiometers for remote sensing of geophysical parameters (sea state, distribution of sea ice, cloud types and their distributions, soil moisture) is assessed.
Voltages across diametrically opposite contact pairs on the outer surface of superconducting Nb tubes are found to depend dramatically upon the spatial configuration of the voltage-measuring leads relative to the positions of the moving magnetic flux lines. Experiments have been conducted to study these voltages for different wall thicknesses and for a variety of arrangements of the leads when flux in the hole and the wall of the Nb tube is made to exit or enter, completely or partially, by applying heat at a narrow strip along its length. Using the critical-state concept, a model for the change of flux and the resulting electric fields in the Nb tube on application of a heat pulse is presented. The resulting time-dependent and time-integrated voltages are calculated in excellent quantitative agreement with the experimental results. These results show that the flux-flow voltages across two contact points on a superconductor arise from the generation of an induced electric field over a chosen path in the superconductor between the contact points and from a change of magnetic flux through the surface bounded by the measuring leads and the chosen path in the superconductor.
The applicability of a high resolution infrared heterodyne radiometer for atmospheric temperature profiling is considered. Upwelling radiation at the 754.321/cm and the 945.976/cm rotational-vibrational lines of CO2 are monitored by a six IF channel infrared heterodyne radiometer with spectral specificity between 0.002 and 0.012/cm. Computer simulated retrievals have been carried out which indicate a maximum temperature inaccuracy of 3.5 K for vertical profiles between ground level and 50 km and a system integration time of 8 seconds.
The paper reports measurements of the time integrated spectral intensity near 34 nm of a BRV (Balloffet-Romand-Vodar) source of emission continuum. The transmittance profile of the combined filters is presented and the percent efficiency (electrons per photon) of the calibration system is given as a function of wavelength. It is noted that the BRV source provides an excellent emission continuum for XUV spectroscopy.
It is shown that Earl's (1973) eigenvalue sum for the cosmic-ray spatial diffusion coefficient parallel to the mean magnetic field is precisely equivalent to the time integral of the particle-velocity correlation function parallel to the mean field. A derivation due to Kubo (1957) is applied to cosmic-ray pitch-angle scattering, and it is proven that all nine components of the cosmic-ray diffusion tensor can be expressed as integrals over the velocity correlation function. A pitch-angle correlation function is derived, and the effect of long-wavelength turbulence on the velocity correlation function and spatial diffusion coefficients is examined. Application of the velocity-correlation method to a realistic case involving both pitch-angle scattering and appreciable fluctuation in the direction of the local field indicates that long-wavelength turbulence in the local field reduces the parallel diffusion coefficient and places an upper limit on the ratio of the perpendicular to parallel diffusion coefficients.
Hard X-ray measurements of six gamma-ray bursts observed by detectors on the OGO-5 and OSO-6 satellites during the period Oct. 1969 to Apr. 1971 are presented. Spectra for five of the six bursts were determined using measurements from both satellites in order to reduce ambiguities due to uncertain source locations. A significant fraction, 20 to 60%, of the energy of the bursts fall in the hard X-ray range (20 to 130 keV). The time-integrated spectra were fitted by power-law, exponential, and thermal bremsstrahlung functions. They are consistent with power-laws which steepen at energies approx. above 150 keV, as reported earlier for two other bursts. Evidence for spectral variability from event to event in the hard X-ray region is presented. The hard X-ray spectra of the gamma-ray bursts differ from those of the recently discovered 1 to 15 keV bursts.
The SMM gamma ray experiment and the important scientific capabilities of the instrument are discussed. The flare size detectable as a function of spectrum integration time was studied. A preliminary estimate indicates that a solar gamma ray line at 4.4 MeV one-fifth the intensity of that believed to have been emitted on 4 August 1972 can be detected in approximately 1000 sec with a confidence level of 99%.
The effects of the transmission media - the earth's troposphere and ionosphere, and the solar wind - on precise Doppler tracking are discussed. The charged particle effects can be largely removed by dual frequency observations; however there are limitations to these corrections (besides system noise and/or finite integration times) including the effects of magnetic fields, diffraction, and differential refraction, all of which must be carefully evaluated. The earth's troposphere can contribute an error of delta f/f approximately 10 to the minus 14th power.
Hard X-ray measurements of six gamma-ray bursts observed during the period from October 1969 to April 1971 are presented. The measurements were made with detectors on the OGO-5 and OSO-6 satellites. Spectra for five of the six bursts have been determined using measurements from both satellites in order to reduce ambiguities due to uncertain source locations. A significant fraction, about 20-60%, of the energy of the bursts falls in the hard X-ray range (20-130 keV). The time-integrated spectra have been fitted by power-law, exponential, and thermal-bremsstrahlung functions. They are consistent with power laws which steepen at energies of at least 150 keV, as reported earlier for two other bursts. Evidence for spectral variability from event to event in the hard X-ray region is presented. For a power-law representation, the power-law index has values ranging from approximately unity to 2.5. The hard X-ray spectra of the gamma-ray bursts differ significantly from those of the recently discovered 1-15-keV X-ray bursts.
Exact analytical solutions are presented for the standard time-independent spherically symmetric convection-diffusion-adiabatic deceleration equation governing the transport of cosmic rays in the interplanetary medium for the case in which particles are produced with spherical symmetry at the sun. It is assumed that the solar-wind speed is constant and radial, and that the spatial diffusion coefficient has a power-law dependence on momentum. The Green's function describing the modulation of a monoenergetic production of particles is presented. The solutions provide a useful basis for the study of time-integrated properties of energetic solar-flare particle spectra.