Showing papers by "Wright-Patterson Air Force Base published in 1970"

Shear Deformation in Heterogeneous Anisotropic Plates

Abstract: : A bending theory for anisotropic laminated plates developed by Yang, Norris,and Stavsky is investigated. The theory includes shear deformation and rotary inertia in the same manner as Mindlin's theory for isotropic homogeneous plates. The governing equations reveal that unsymmetrically laminated plates display the same bending-extensional coupling phenomenon found in classical laminated plate theory based on the Kirchhoff assumptions. Solutions are presented for bending under transverse load and for flexural vibration frequencies of symmetrical and nonsymmetrical laminates. Good agreement is observed in numerical results for plate bending as compared to exact solutions obtained from classical elasticity theory. For certain fiber reinforced composite materials, radical departure from classical laminated plate theory is indicated. (Author-PL)

Interlaminar Stresses in Composite Laminates Under Uniform Axial Extension

Abstract: The response of a finite-width composite laminate under uniform axial strain is treated through the application of classical elasticity theory. Finite-difference solution techniques are employed to obtain solutions for stresses and displacements throughout the region. Results for material properties typical of a high modulus graphite-epoxy composite material system are presented which explain the mechanism of shear transfer within a symmetric laminate. In addition, results of this work are compared to those given in a recent approximate formulation.

Spin Exchange in Excitons, the Quasicubic Model and Deformation Potentials in II-VI Compounds

Abstract: The effect of the spin-exchange interaction between electron and hole is investigated for the case of excitons originating from one of the $p$-like valence bands and an $s$-like conduction band, as is the case for IIb-VIb compounds. A general exciton matrix is constructed, starting from the work of Pikus. It includes spin-orbit, crystal-field, spin-exchange, and deformation-potential interactions. Use of this matrix then allows a theoretical fit to our experimental data which describes the shift of exciton levels under uniaxial pressure in ZnO, CdS, and CdSe. This fit results in the determination of six deformation potentials, two spin-orbit parameters, the crystal-field parameter, and the exchange parameter. The general theory, when adapted to the zinc-blende structure, allows us to fit our data on cubic ZnS and ZnSe, resulting in a determination of two deformation potentials and the spin-exchange parameter for each compound.

Crystal Structure of Monoclinic Hafnia and Comparison with Monoclinic Zirconia

Abstract: The crystal structure of monoclinic HfO2 was determined using Weissenberg techniques. Data were obtained from a needlelike single crystal which was grown from a lithium molybdate melt. The crystal was rotated about the α axis, and reflection data were obtained for nine levels. A three-dimensional least-squares refinement confirms that monoclinic hafnia is isomorphous with monoclinic zirconia. The atomic coordinates in the structures agree within one standard deviation. Thus, the fractional coordinates for the metal atom differ by less than 0.0005 and those for the oxygen atoms by no more than 0.01. Whereas three of the seven Hf–O distances are larger than the corresponding Zr–O distances, the average value is approximately 0.01 A smaller. The average metal-metal distance is approximately 0.02 A less in HfO2 than in ZrO2.

Electronic Core Levels of Zinc Chalcogenides

Abstract: X-ray-induced photoemission studies were used to determine the energy levels of core electrons in ZnO, ZnS, ZnSe, and ZnTe. The investigated energy range extends from the Fermi level to about 1200 eV below the valence band. The observed Auger transitions in these compounds are in good agreement with the measured energy levels. Some of the uncertainties in using this technique for the study of electron energy levels in semiconducting or insulating crystals were investigated and are discussed. The measured energy levels are compared with published experimental data for the respective pure elements. Comparison is also made with energy values predicted by several different types of theoretical calculations. Significant conclusions are: (i) The location of the Zn $3d$ level in the zinc chalcogenides has been unambiguously determined and (ii) the discrepancy between our measured values and the theoretically determined energy values is angular momentum dependent.

Electron Energy-Loss and Ultraviolet-Reflectivity Spectra of Crystalline ZnO

Abstract: A comparison between the ultraviolet-reflectivity spectrum and the characteristic energy-loss spectrum of ZnO has been carried out. Reflectivity measurements made over an energy range of band gap to 22 eV yielded a spectrum with structure at 3.34, 5.0, 7.3, and 8.4 eV, and in the region 11-15 eV. Energy-loss measurements made over the energy range of band gap to 50 eV using 10-keV electrons exhibited peaks at 3.82, 5.47, 9.56, 13.5, 18.8, and 35.5 eV. The dominant peak in this spectrum is that at 18.8 eV and has been associated with a plasmon excitation. The samples in both cases were hexagonal ZnO platelets at room temperature. A dispersion analysis has been performed on the reflectivity data yielding the optical constants $n$, $k$, ${\ensuremath{\epsilon}}_{1}$, ${\ensuremath{\epsilon}}_{2}$, the effective number of free electrons ${n}_{\mathrm{eff}}$, the effective dielectric constant ${\ensuremath{\epsilon}}_{0\mathrm{eff}}$, and the imaginary part of ${\ensuremath{\epsilon}}^{\ensuremath{-}1}$. The energy-loss function has been calculated and found to compare well with the energy-loss spectrum obtained from the electron-transmission measurements.

Auger-Electron Spectroscopy of Transition Metals

Abstract: The Auger-electron spectra in the intermediate- and low-energy range (0-1 keV) for many of the transition metals of periods 4-6 (specifically, Sc, Ti, V, Cr, Fe, Co, Y, Zr, Nb, Mo, Ru, Rh, La, Hf, Ta, W, Re, Ir, Pt, and Au) have been measured. In general, the spectra from elements in the same period of the Periodic Table are similar, the main difference being the energy at which the Auger electrons appear. The main transitions observed from period-4 elements are of the $\mathrm{LMM}$ type. For period-5 elements, the Auger transitions involve $\mathrm{MNN}$ levels, and for the period-6 elements, the transitions are of the $\mathrm{NNN}$ (Coster-Kronig) type.

Preparation and Characterization of Alkoxy-Derived SrZrO3 and SrTiO3

Abstract: High-purity strontium, zirconium, and titanium alkoxides were synthesized and characterized as precursors for complex oxides. Simultaneous hydrolytic decomposition either of strontium and zirconium alkoxides or of strontium and titanium alkoxides was used to obtain nearly stoichiometric, ideally mixed SrZrO3 or SrTiO3 powders of high surface activity. As-prepared helium-dried SrTiO3 is crystalline before calcination. An ultraviolet radiation technique demonstrates the nucleation and growth of SrZrO3 crystallites in the calcination temperature range to 350°C. The experimental results are supported by ir, TGA, and X-ray diffraction data. The high degree of control over purity, mixing uniformity, and crystallite size demonstrates the value of the alkoxide precursor approach for the solution of reproducibility problems encountered in the synthesis of electrical-quality ceramics.

Gravimetric Determination of Defect Concentrations in NiO

Abstract: Thermogravimetric measurements were made on NiO from 800° to 1100°C over the oxygen pressure range 10−1 to 10−4 atm. On the basis of complementary conductivity measurements showing a P(O2)1/5 oxygen pressure dependence, it is proposed that the predominant defects are described by an electroneutrality condition involving doubly ionized metal vacancies, impurities, and electron holes, 2[V”M]=[FM]+p. It is shown that for this defect model, the weight change relative to a low oxygen pressure reference weight is a measure of the effective vacancy concentration, defined as [V”M]eff≡[V”M]-≡[FM], and therefore has the same oxygen pressure dependence as the electron hole concentration followed in the conductivity measurements. The expression [V”M]eff=0.168 P(O2)1/5 exp (−0.86±0.15/kT) is derived to express the effective vacancy concentration in NiO. The probable effective impurity content of the specimens used is calculated.

Energy-Band Structure of BeS, BeSe, and BeTe

Abstract: A first-principles self-consistent orthogonalized-plane-wave energy-band calculation has been performed for cubic BeS, BeSe, and BeTe using a nonrelativistic formalism and Slater's free-electron-exchange approximation. These are the first energy-band solutions reported for these compounds. No experimental data are available concerning the energy bands or optical properties of these semiconducting compounds. The imaginary part of the dielectric constants, spin-orbit splittings, effective masses, and x-ray form factors (Fourier transforms of the electron charge density) have been calculated.

Thermal degradation of polymers with phenylene units in the chain. IV. Aromatic polyamides and polyimides

Abstract: The breakdown mechanism of an aromatic polyamide and four polyimides has been studied under vacuum in the temperature range of 375–620°C, by using techniques described earlier, involving collection and analysis of volatile products as well as analyses of residues at different temperatures. The decomposition of the polyamide up to 375°C yielded predominantly carbon dioxide, while between 375 and 450°C about equal amounts of carbon dioxide and carbon monoxide formed. Hydrogen is the major product between 450 and 550°C, along with hydrogen cyanide, methane, and carbon monoxide. The major reaction at the lower temperatures seems to be the cleavage of the linkage between the carbonyl group and the ring, with subsequent formation of a carbodiimide linkage via isocyanate intermediates, and liberation of carbon dioxide. Alternatively, cleavage between the carboxyl and the NH-group leads to the formation of carbon monoxide. Carbon dioxide and carbon monoxide are also the major volatile decomposition products of the polyimides at the lower temperatures. The primary cleavage reaction is believed to be the rupture of the imide ring between a carbonyl and nitrogen, with subsequent formation of isocyanate groups. The latter react with each other to form carbodiimide linkages and carbon dioxide, while the remaining benzoyl radical is the source for carbon monoxide.

A Survey of the Mechanical Characteristics of Skin and Tissue in Response to Vibratory Stimulation

Abstract: The possibility that the mechanical characteristics of skin and tissues may influence physiological and psychophysical measurements of tactile sensitivity is considered. A survey of selected literature indicating how certain mechanical characteristics of skin and tissue vary as a function of changes in variables known to influence physiological and psychophysical measurements of the tactile system is presented. Finally, certain physiological and psychophysical studies in which the physical properties of the area stimulated may have influenced the results are mentioned.

Excitation of Forbidden Lines in Gaseous Nebulae. II. Calculations for 3p q Ions

Abstract: The formulation for electron collisions with ions in configurations 1s 2 2s 2 2p 2 and 1s 2 2s 2 2p 6 3s 2 3q q has been given in paper I of the present series (Saraph, Seaton & Shemming 1969). The present paper gives results of numerical calculations for 3p q ions, made in the distorted wave approximation. Collision strengths are obtained for all inelastic transitions in the configurations 1s 2 2s 2 2p 6 3s 2 3p q , q = 1 to 5. Calculations are made for three different energies and for values of the residual change z in the range z = 1 to z = 15. Results may be interpolated for all members of the isoelectronic sequences up to nickel.

Buckling and Postbuckling Behavior of Composite Cylindrical Shells under Axial Compression

Abstract: A theoretical analysis of the buckling and postbuckling equilibrium behavior of a fiber reinforced cylindrical shell under uniform axial compression is presented. The investigation also includes some data on the effect of initial imperfections on the buckling behavior of fiber reinforced cylindrical shells, von Karman-Donnell large displacement equations and the principle of stationary potential energy are applied to study the postbuckling behavior. The results are given for various fiber orientations in the three-layer shell having a radius-to-thickness ratio of 166.77, consisting of either glass-epoxy or boron-epoxy composites. The cases when the stiffness coupling matrix is not equal to zero and the coupling matrix is set equal to zero are considered. It is shown that the latter simplifying assumption gives unconservative buckling and postbuckling loads. From the results of the effect of initial imperfections on the buckling behavior, it is seen that the boron-epoxy composite shells are less imperfection sensitive than glass-epoxy composite shells. This investigation shows that, in general, composite shells are less imperfection sensitive than isotropic shells.

The effects of thermal treatment on the austenitic grain size and mechanical properties of 18 Pct Ni maraging steels

Abstract: A technique has been developed for controlling the austenitic grain size of 18 pct Ni maraging steels by thermal treatment alone. This treatment has been applied to two different grades, 250 and 300, of maraging steel, and a large grain size, ASTM 2, was reduced to ASTM 7 in both cases. The process of grain size refinement requires thermal cycling from a temperature belowM f to a temperature considerably above the austenitizing temperature. The minimum austenitic grain size attainable depends on the prior strain in the material as well as the thermal treatment. While significant grain size refinement can be attained by one cycle to the proper temperature, the attainment of the minimum uniform grain size requires several cycles. The effects of austenitic grain size on tensile properties have been investigated both at room temperature and at elevated temperatures. The prior austenitic grain size has a small but measurable effect on the mechanical behavior of aged material at room temperature. The austenitic grain size has a significant effect on the ultimate tensile strength at 1600°F.

Ladder polymers from tetraaminodiquinoxalpyrene

Abstract: A new fused aromatic heterocyclic tetraamine 2,3,11,12-tetraaminodiquinoxal [2,3-e,2′,3′-1] pyrene has been prepared and polymerized with 1,4,5,8-naphthalenetetracarboxylic acid and pyromellitic dianhydride. The resulting ladder polymers with inherent viscosities ranging from 0.5 to 1.0 dl/g in methanesulfonic acid exhibited thermal stabilities near 600°C in nitrogen and near 450°C in air.

A theory of pattern perception based on human physiology.

Abstract: The gross connectivity, patterns of information pathways in the primate and human visual systems, when examined by an information processing engineer, bear a curious resemblance to the two-dimensional-pattern optical computers which he builds himself in an attempt to achieve pattern recognition. The portions of the visual system inferior to the primary visual cortex are essentially a topologically accurate homeo-morphic mapping of the retinal image, at least in the vicinity of the fovea. Analysis of the topological aspects of the visual scene and hence ‘ Pattern Recognition ’ must therefore take place in the primary visual cortex and successive cortical areas We have previously reported how intra- and inter-cortical connectivity could support a combined memory and computation scheme capable of performing pattern recognition by a variation of two-dimensional cross correlation. This paper is a report of an extension of the previous model enabling it to perform pattern recognition by computing the two-dimens...

A review of para-foil applications

Abstract: and agree well with the semiempirical expression previously determined. Most encouraging results were obtained from an experiment performed on the elliptical airfoil of 18% thickness ratio with dual symmetrical jets. These results indicate that the leading-edge jet does not disturb the flow and actually furnishes some additional reaction force to the lift. Hence, the important application of the elliptical airfoil (or oval airfoil) with dual jets to the retreating blade of a helicopter rotor is evident. Furthermore, the results of aerodynamic response measurements of the model to cyclic changes in the blowing jet are surprisingly encouraging. The cyclic valve was tested at frequencies equivalent to twice that of the rotational speed of a conventional helicopter blade, and the response of the lift was found to be excellent with negligible delay. The response of the drag as well as the chordwise pressure distribution to the cyclic changes in the blowing jet were also found to be very good. These results clearly indicate that the periodic variation of lift on the airfoil can be fulfilled by cyclic variation of the jet momentum; hence, the circulation control problem is reduced to simply the problem of pressure control inside the model.

Exciton—LO-Phonon Interaction and the Anti-Stokes Emission Line in CdS

Abstract: Phonon interaction with the ${I}_{1}$ (4888-\AA{}) emission line in CdS (exciton bound to a neutral acceptor site) has often been observed. For the first time the optical frequency anti-Stokes transition, involving the collapse of a bound exciton, has been observed in the emission from selected platelets at 1.2\ifmmode^\circ\else\textdegree\fi{}K. Since the thermally excited phonon field at this temperature is negligible, the observation of anti-Stokes emission directly supports the conclusion that LO phonons are generated to a nonthermal level of distribution as the excitons decay.