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Results from mean flow field surveys are reported. Flow fluctuation amplitude measurements and acoustic measurements are presented. The organized structure was characterized in terms of axial flow and radial flow.
The tectonic, igneous and metallogenic features of South America are discussed in terms of the crustal deformation associated with stresses due to mantle convection as inferred from the high degree harmonics in the geopotential field. The application of Runcorn's model for the laminar viscous flows in the upper mantle to satellite and gravity data results in a convection pattern which reveals the ascending flows between the descending Nazca plate and the overlying South American plate as well as segments of the descending Nazca plate beneath South America. The arc volcanism in South America is shown apparently to be related to the upwelling of high-temperature material induced by the subduction of the Nazca plate, with the South American basin systems associated with downwelling mantle flows. The resulting tensional stress fields are shown to be regions of structural kinship characterized by major concentrations of ore deposits and related to the cordillera, shield and igneous systems and the upward Andean movements. It is suggested that the upwelling convection flows in the upper mantle, coupled with crustal tension, have provided an uplift mechanism which has forced the hydrothermal systems in the basement rocks to the surface.
A study is presented of the possibility of using the acoustic radiation emitted from turbulent combustion zones to characterize the structure, mechanics and properties of turbulent combustion. Theoretical consideration is given to the acoustic characteristics of a nonpremixed open turbulent jet flame and the response of the acoustic spectrum to changes in combustion conditions. Experimental observations made of the acoustic emissions from a laboratory burner that establishes turbulent flames at the exit of a fully developed pipe flow as well as two commercial burners using methane, ethane and propane fuels are then presented which reveal changes in the acoustic amplitudes in three high-frequency bands associated with changes in the air-fuel ratio. Results suggest a means for combustion diagnostics and demonstrate the possibility of using acoustic measurements in investigations of combustion zone processes.
Detailed photographic surface photometry is presented of the nine first brightest galaxies in poor clusters suspected of being cD galaxies. The surface photometry is put on an absolute scale, using multiaperture photoelectric photometry. Oemler (1976) and de Vaucouleurs (1948) laws are fitted to the profiles to derive structural parameters, and the structural properties of the galaxies are compared with those of the cD galaxies in rich clusters studied by Oemler (1976) and those of normal ellipticals studied by Kormendy (1977). It is found that (1) the profiles of first brightest galaxies are well fitted by an r to the 1/4 power law over a range of more than nine magnitudes and down to the faintest light levels observed and (2) structural parameters characterizing only the central part of first brightest galaxies in poor and rich clusters, and excluding the envelope component in the case of rich clusters, smoothly extend properties exhibited by normal ellipticals. These observations are consistent with the idea that the central part of first brightest galaxies in both poor and rich clusters is made up by the mergers of smaller galaxies.
Serial minimum-shift keyed (MSK) modulation, a technique for generating and detecting MSK using series filtering, is ideally suited for high data rate applications provided the required conversion and matched filters can be closely approximated. Low-pass implementations of these filters as parallel inphase- and quadrature-mixer structures are characterized in this paper in terms of signal-to-noise ratio (SNR) degradation from ideal and envelope deviation. Several hardware implementation techniques utilizing microwave devices or lumped elements are presented. Optimization of parameter values results in realizations whose SNR degradation is less than 0.5 dB at error probabilities of .000001.
Graph theory is used to obtain numerical solutions to eigenvalue problems of large space structures (LSS) characterized by a state vector of large dimensions. The LSS are considered as large, flexible systems requiring both orientation and surface shape control. Graphic interpretation of the determinant of a matrix is employed to reduce a higher dimensional matrix into combinations of smaller dimensional sub-matrices. The reduction is implemented by means of a Boolean equivalent of the original matrices formulated to obtain smaller dimensional equivalents of the original numerical matrix. Computation time becomes less and more accurate solutions are possible. An example is provided in the form of a free-free square plate. Linearized system equations and numerical values of a stiffness matrix are presented, featuring a state vector with 16 components.
To effectively assess the Pogo stability of the space shuttle vehicle, it was necessary to characterize the structural, propellant, and propulsion dynamics subsystems. Extensive analyses and comprehensive testing programs were established early in the project as an implementation of management philosophy of Pogo prevention for space shuttle. The role of the space shuttle main engine (SSMF) in the Pogo prevention plans, the results obtained from engine ground testing with analysis, and measured data from STS-1 flight are discussed.
Poly(arylene ether sulfones) comprise a class of materials known as engineering thermoplastics which have a variety of important applications. These polymers are tough, rigid materials with good mechanical properties over a wide temperature range, and they are processed by conventional methods into products typically having excellent hydrolytic, thermal, oxidative and dimensional stability. Wholly aromatic random copolymers of hydroquinone and biphenol with 4.4 prime dichlorodiphenyl sulfone were synthesized via mechanical nucleophilic displacement. Their structures were characterized and mechanical behavior studied. These tough, ductile copolymers show excellent radiation resistance to electron beam treatment and retain much of the mechanical properties up to at least 700 Mrads under argon.
The implications and accuracy of anomaly maps produced using Magsat data on the scalar and vector magnetic field of the earth are discussed. Comparisons have been made between the satellite maps and aeromagnetic survey maps, showing smoother data from the satellite maps and larger anomalies in the aircraft data. The maps are being applied to characterize the structure and tectonics of the underlying regions. Investigations are still needed regarding the directions of magnetization within the crust and to generate further correlations between anomaly features and large scale geological structures. Furthermore, an increased data base is recommended for the Pacific Ocean basin in order to develop a better starting model for Pacific tectonic movements. The Pacific basin was large farther backwards in time and subduction zones surround the basin, thereby causing difficulties for describing the complex break-up scenario for Gondwanaland.
The results of an analysis effort performed to demonstrate the feasibility of employing approximate dynamical models and frequency shaped cost functional control law desgin techniques for helicopter vibration suppression are presented. Both fixed gain and adaptive control designs based on linear second order dynamical models were implemented in a detailed Rotor Systems Research Aircraft (RSRA) simulation to validate these active vibration suppression control laws. Approximate models of fuselage flexibility were included in the RSRA simulation in order to more accurately characterize the structural dynamics. The results for both the fixed gain and adaptive approaches are promising and provide a foundation for pursuing further validation in more extensive simulation studies and in wind tunnel and/or flight tests.
A microcrack process zone is frequently suggested to accompany macrofractures in rock and play an important role in the resistance to fracture propagation. Attenuation of surface waves propagating through mode I fractures in wedge-loaded double-cantilever beam specimens of Westerly granite has been recorded in an attempt to characterize the structure of the fracture process zone. The ultrasonic measurements do not support the generally accepted model of a macroscopic fracture that incrementally propagates with the accompaniment of a cloud of microcracks. Instead, fractures in Westerly granite appear to form as gradually separating surfaces within a zone having a width of a few millimeters and a length of several tens of millimeters. A fracture process zone of this size would necessitate the use of meter-sized specimens in order for linear elastic fracture mechanics to be applicable.
An understanding of the response of composite laminates to foreign object impact is of fundamental importance to the design and the accurate evaluation of aircraft and aerospace structures. A characterization of the basic deformation response of the system is needed for the accurate and consistent modeling of the damage caused by the impact. The response to low velocity impact of foreign objects (less than 10 m/sec at 10 J of impact energy or less) is of particular interest because it corresponds to tool drop problems. An investigation of the vibration response of a simple square beam was conducted, taking into account both sharp initial velocity pulse conditions and simulated impact conditions. Attention is given to nonlinear beam theory, boundary conditions and materials modeling, initial conditions and impact modeling, and a solution of the obtained system of partial differential equations by the finite difference approach.
AlGaAs-GaAs heteroface space concentrator solar cells have been fabricated by metalorganic chemical vapor deposition. AMO efficiencies as high as 21.1% have been observed both for p-n and np structures under concentration (90 to 100X) at 25 C. Both cell structures are characterized by high quantum efficiencies and their performances are close to those predicted by a realistic computer model. In agreement with the computer model, the n-p cell exhibits a higher short-circuit current density.
A simultaneous campaign of balloon and radar measurements took place on March 14 to 16, 1984, above the Arecibo 430-MHz radar. This radar was operating with a vertical resolution of 150 m following two antenna beam directions: 15 deg. from the zenith, respectively, in the N-S and E-W directions. The main results concerning the comparison between the flight and simultaneous radar measurements obtained on March 15, 1984 are analyzed. The radar return power profile (S/N ratio in dB) exhibits maxima which are generally well correlated with step-like structures in the potential temperature profile. These structures are generally considered as the consequence of the mixing processes induced by the turbulence. A good correlation appears in the altitude range 12.5 to 19 km between wind shears induced by a wave structure observed in the meridional wind and the radar echo power maxima. This wave structure is characterized by a vertical wavelength of about 2.5 km, and a period in the range 30 to 40 hours. These characteristics are deduced from the twice daily rawinsonde data launched from the San Juan Airport by the National Weather Service. These results pointed out an example of the interaction between wave and turbulence in the upper troposphere and lower stratosphere. Turbulent layers are observed at locations where wind shears related to an internal inertia-gravity wave are maxima.
It is suggested that the quasi-static evolution of coronal magnetic structures is characterized by a cascade of magnetic energy to smaller length scales. This cascade process takes place on a time scale t sub b determined entirely by the photospheric motions. The Ohmic heating rate E sub H in the statistically stationary state was estimated using observational data on the diffusivity of photospheric motions; E sub H turned out to be too small by a factor of 40 when compared with observed coronal energy losses. However, given the fact that the theoretical estimate is based on a rather uncertain extrapolation to the diffusive regime, current heating cannot be ruled out as a viable mechanism of coronal heating.
The objective of this research was to test vibration suppression (settling time and jitter) of a large space structure (LSS) characterized by low frequency high global vibration modes. Five percent passive damping in a large truss was analyzed, tested and correlated. A representative system article re-target analysis shows that modest levels of passive damping dramatically reduce the control energy required. LSS must incorporate passive damping from the outset. The LSS system performance will not be met by either active or passive damping alone.
A study on the field-induced surface-charge region in 3C silicon carbide (SiC) using 1 MHz capacitance-voltage (C-V) measurements at room temperature is here reported. A double column mercury probe was used on oxidized SiC substrates to form metal-oxide-semiconductor (MOS) structures. These structures were characterized in terms of the substrate doping profile, effective fixed oxide charge, and interface trap density. A distinctive feature of the MOS C-V curves from accumulation to inversion is that after going into deep depletion the capacitance rises to its equilibrium inversion level during the voltage sweep. Capacitance transient measurements indicate that the minority-carrier generation occurs at the SiO2/SiC interface.
The microstructure of extruded rods of iron-rich FeAl(B2-structure), as characterized by TEM, SEM, optical microscopy and x-ray diffractometry, consisted of elongated grains with a 111-line fibre texture containing a high dislocation density. Numerous oxide particles were found, mostly in lines which reflected the matrix flow during extrusion. In addition, some large inclusions were present. Tensile testing of annealed, relatively dislocation-free specimens as a function of increasing temperature found increasing ductility up to 900K, above which a ductility drop occurred accompanied by a change in fracture mode, from transgranular cleavage to intergranular fracture. The yield strength, which was independent of temperature up to 800K (at about 500MPa), also decreased rapidly as diffusion became more important. The predominant slip vector changed from 111-line to 100-line around 700K.