Showing papers by "Wright-Patterson Air Force Base published in 1976"
TL;DR: The Halpin-Tsai equations are based upon the self-consistent micromechanics method developed by Hill as discussed by the authors. But they are not suitable for semi-crystalline polymers.
Abstract: The Halpin-Tsai equations are based upon the “self-consistent micromechanics method” developed by Hill. Hermans employed this model to obtain a solution in terms of Hill's “reduced moduli”. Halpin and Tsai have reduced Hermans' solution to a simpler analytical form and extended its use for a variety of filament geometries. The development of these micromechanic's relationships, which form the operational bases for the coniposite analogy of Halpin and Kardos for semi-crystalline polymers, are reviewed herein.
2,609 citations
TL;DR: In this article, the energy levels of the nonzero angular momentum states of the static screened Coulomb potential were calculated using variational trail functions, and it was shown that Hulth-en-like trial functions provide better variational energies and wave functions with fewer parameters than hydrogenic or Slater-type functions for screened-coulomb and similar potentials.
Abstract: Using solutions to a Hulth\`en-like effective potential as variational trail functions we have calculated the energy levels of the nonzero angular momentum states of the static screened Coulomb potential. Our one-parameter results for the $2p$, $3p$, $3d$, $4p$, $4d$, and $4f$ levels are in excellent agreement with earlier, more elaborate calculations. We have also calculated spontaneous emission transition probabilities between several pairs of states and find that our results compare favorably with previous calculations. We conclude that Hulth\`en-like trial functions provide better variational energies and wave functions with fewer parameters than hydrogenic or Slater-type functions for screened Coulomb and similar potentials.
550 citations
TL;DR: In this article, a limited memory algorithm is developed for adaptive correction of the a priori statistics which are intended to compensate for time-varying model errors, which provides improved state estimates at little computational expense when applied to an orbit determination problem for a near-earth satellite with significant modeling errors.
Abstract: Sequential estimators are derived for suboptimal adaptive estimation of the unknown a priori state and observation noise statistics simultaneously with the system state. First- and second-order moments of the noise processes are estimated based on state and observation noise samples generated in the Kalman filter algorithm. A limited memory algorithm is developed for adaptive correction of the a priori statistics which are intended to compensate for time-varying model errors. The algorithm provides improved state estimates at little computational expense when applied to an orbit determination problem for a near-earth satellite with significant modeling errors.
528 citations
TL;DR: In this paper, a two-phase research project investigated the effects of job enrichment and goal setting on worker productivity and satisfaction in a well-controlled, simulated job environment and found that people with unenriched jobs worked under the enrichment conditions and people originally without goals were assigned goals.
Abstract: : A two phase research project investigated the effects of job enrichment and goal setting on worker productivity and satisfaction in a well-controlled, simulated job environment. In the first phase, two conditions of goal setting (assigned goals versus no goals) and two conditions of job enrichment (enriched versus unenriched) were established, producing four experimental conditions. In the second phase (after 2 days work) people with unenriched jobs worked under the enrichment conditions and people originally without goals were assigned goals. Results are discussed in terms of the current theoretical approaches for understanding employee motivation on the job.
184 citations
TL;DR: In this paper, the isothermal oxidation behavior of commercial hot-pressed Si3N4 was evaluated for temperatures from 1300° to 1500°C Multiphase scales were formed, consisting mainly of α-cristobalite and enstatite A large increase in reaction rate above 1450°C is believed to be caused by melting in the scale and the consequent increase in the rate of oxygen transport.
Abstract: The isothermal oxidation behavior of commercial hot-pressed Si3N4 was evaluated for temperatures from 1300° to 1500°C Multiphase scales were formed, consisting mainly of α-cristobalite and enstatite A large increase in reaction rate above 1450°C is believed to be caused by melting in the scale and the consequent increase in the rate of oxygen transport No oxygen pressure dependence was observed at 1400°C over the oxygen pressure range 10-9 atm to 600 torr However, a small decrease in the kinetics was observed when measurements were made in reduced total pressures of oxygen as compared to O2/N2mixtures at a constant total pressure
110 citations
107 citations
TL;DR: In this article, the exciton binding energy was determined to be (4.20 \ifmmode\pm\times\else\texttimes\fi{} 0.10}^{\ensuremath{-}3}$ eV.
Abstract: The exciton energy spectrum in GaAs has been studied by photoluminescence and reflection. The photoluminescence was excited using a krypton laser (6471 \AA{}). We observed for the first time the spectra for the excited states of the free exciton in GaAs and also the spectra for the ground states in zero field and in the field range from 12 to 40 kG. The value for the exciton binding energy was determined to be (4.20 \ifmmode\pm\else\textpm\fi{} 0.3) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}3}$ eV from which the band-gap energy of 1.5195 \ifmmode\pm\else\textpm\fi{} 0.0005 eV has been deduced. The values for the Zeeman splitting factors for electron ($g$ factor) and hole ($\ensuremath{\kappa}$ parameter) were deduced from these measurements to be ${g}_{c}=\ensuremath{-}0.50\ifmmode\pm\else\textpm\fi{}0.05$ and $\ensuremath{\kappa}=1.0\ifmmode\pm\else\textpm\fi{}0.2$, respectively. A phenomenological description for the free-exciton energy spectrum in the intermediate-field regime is used to explain the experimental measurements.
104 citations
TL;DR: In this paper, twelve different combinations of hot die forging and heat treatment, in the α+β and β phase regions, were investigated, and the resulting heat treated forgings were classified into four distinct categories based on their microstructural appearance.
Abstract: To establish correlations between microstructure and mechanical properties for the Till alloy, twelve different combinations of hot die forging and heat treatment, in the α+β and β phase regions, were investigated. The resulting heat treated forgings were classified into four distinct categories based on their microstructural appearance. The room temperature tensile, post-creep tensile, fracture toughness and fatigue crack propagation properties were measured along with creep and low cycle fatigue at 566°C. The creep, tensile, fatigue crack propagation and fracture toughness properties, grouped in a manner similar to the microstructural categories. The fracture appearance and behavior of the cracks during propagation in fatigue and in fracture toughness tests were examined, and correlations with the microstructure discussed. In the case of the fully transformed acicular microstructure, it was found that the size and the orientation of colonies of similarly aligned α needles are dominant factors in the crack behavior.
100 citations
TL;DR: In this paper, the effect of microstructure on the notch fatigue properties of Ti-6A1-4V was investigated and it was found that the fatigue performance of the alloy varied significantly as the micro-structure was altered by heat treatment.
Abstract: The effect of microstructure on the notch fatigue properties of Ti-6A1-4V was investigated. Specimens with five distinctly different microstructures were tested and subsequently examined in detail. It was found that the notch fatigue performance of the alloy varied significantly as the microstructure was altered by heat treatment. The best high cycle fatigue strength was found in specimens heat treated above the beta transus temperature, containing an almost totally transformed acicular alpha structure. The fatigue performance of specimens with this microstructure appeared to be controlled by the size of the nucleated crack. It is suggested that at low stress levels the nucleated crack is limited in size to the width of a single alpha needle, while at high stresses the nucleated crack may be as large as an entire colony of similarly aligned alpha needles.
97 citations
01 Jun 1976
TL;DR: In this paper, the fine features of the Auger valence band spectra of TiO and TiO 2 have been related to transitions arising from oxygen 2s and titanium 3d, 4s molecular orbitals.
Abstract: The fine features of the Auger valence band spectra of TiO and TiO 2 have been related to transitions arising from oxygen 2s and titanium 3d, 4s molecular orbitals. The Auger bands investigated include the L III , M 1 N 1 , L III M 1 M 4,5 , L III M 2,3 N 1 , and L III M 2,3 , M 4,5 transitions. The N ( E ) valence band spectra have been unfolded and the resulting components correlated with X-ray emission data and a molecular orbital (MO) model. Differences in spectral shapes are shown to be linked with differences in the density of state of oxygen—titanium molecular orbitals.
96 citations
TL;DR: In this paper, the role of Y2O3 in the hot-pressing of Si3N4 was discussed in terms of its role in a liquid-phase sintering process which incorporates dissolution and precipitation of Si 3N4 at the solid-liquid interface.
Abstract: Examination of compositions in the system Si3N4-Y2O3-SiO2 using sintered samples revealed the existence of two regions of melting and three silicon yttrium oxynitride phases. The regions of melting occur at ∼1600° C at high SiO2 concentrations (∼13 mol% Si3N4 + 19 mol% Y2O3 + 68 mol% SiO2) and at 1650° C at high Y2O3 concentrations (25 mol % Si3N4 + 75 mol % Y2O3). Two ternary phases 4Y2O3 ·SiO2 ·Si3N4 and 10Y2O3 ·9SiO2 ·Si3N4 and one binary phase Si3N4 ·Y2O3 were observed. The 4Y2O3 ·SiO2 ·Si3N4 phase has a monoclinic structure (a= 11.038 A, b=10.076 A, c=7.552 A, β=108° 40′) and appears to be isostructural with silicates of the wohlerite cuspidine series. The 10Y2O3 ·9SiO2 ·Si3N4 phase has a hexagonal unit cell (a=7.598 A c=4.908 A). Features of the Si3N4-Y2O3-SiO2 systems are discussed in terms of the role of Y2O3 in the hot-pressing of Si3N4, and it is suggested that Y2O3 promotes a liquid-phase sintering process which incorporates dissolution and precipitation of Si3N4 at the solid-liquid interface.
TL;DR: In this article, the authors give a review of the literature on complex multivariate distributions and some new results on these distributions are also given, and discuss the applications of the complex multiivariate distributions in the area of the inference on multiple time series.
TL;DR: In this article, a series of pin bearing tests has been conducted to examine the effect of temperature and moisture on the strength of graphite/epoxy laminates, and it is apparent from the test results that no interaction between temperature and humidity can be found.
Abstract: A series of pin bearing tests has been conducted to examine the effect of temperature and moisture on the strength of graphite/epoxy laminates. Three laminate orientations [OZ/±45] 1$’ [902 /:t45] 2$ and [0/90/:t45] 2$ were studied under room temperature and 260°F. Wet specimens with 1.5% of moisture content by weight were also tested under the above temperatures. Based on the experimental results under the conditions tested, a number of conclusions can be drawn. The pin bearing strength at the 260°F-wet condition was 40% less than the strength at room temperature-dry in all three orientations. It is apparent from the test results that no interaction between temperature and moisture on the strength degradation can be
TL;DR: A new group of materials called the silicon lanthanide oxynitrides has been prepared by the reaction between Si3N4 and several oxides of the lanthanides series as mentioned in this paper.
Abstract: A new group of materials called the silicon lanthanide oxynitrides has been prepared by the reaction between Si3N4 and several oxides of the lanthanide series (La2O3, Sm2O3, Dy2O3, Er2O3, and Yb2O3). These oxides formed compounds of the type Si3N4 · R2O3 and R4Si2O7N2 (R being lanthanide). In addition La2O3 and Yb2O3 formed the compounds 2Si3N4 · La2O3 and Yb2Si3O5N2, respectively. Certain similarities in the unit cells of these compounds have been noted, and their structures are discussed in terms of similarity to known minerals. It is suggested that this group of materials contains a large number of compounds.
TL;DR: Inelastic electron tunneling spectroscopy (IETS) has been used extensively in analytical chemistry and surface interactions as discussed by the authors. But the application of IETS to analytical chemistry has not been discussed.
Abstract: The technique of inelastic electron tunneling spectroscopy (IETS) is reviewed. The physical principles involved, the theoretical status, and the experimental techniques necessary to obtain tunneling spectra are presented. The details of sample preparation and the necessary measuring circuits are discussed thoroughly. The application of IETS to analytical chemistry and surface interactions is illustrated through a review of the spectra that have been obtained from 1966 to the present.
TL;DR: In this article, the drift velocity of electrons in mixtures containing a molecular gas in a rare-gas diluent has been calculated as a function of the electric field to neutral number density and of molecular-gas concentration using a numerical solution of the Boltzmann transport equation.
Abstract: The drift velocity of electrons in mixtures containing a molecular gas in a rare-gas diluent has been calculated as a function of $\frac{E}{N}$ (ratio of the electric field to neutral number density) and of molecular-gas concentration using a numerical solution of the Boltzmann transport equation. The results agree well with available experimental data where gas purity was strictly controlled. In argon, it is shown that very small amounts of a molecular additive can drastically alter the behavior of the electron drift velocity. The curves exhibit a local maximum with respect to $\frac{E}{N}$ and an absolute maximum with respect to molecular concentration. A useful formula for the mobility has been derived, which explains the peculiar behavior of the electron drift velocity in these gas mixtures.
TL;DR: Two experiments employing the release from PI method were conducted to determine whether degree of release could be predicted by the amount of denotative attribute overlap between the control and experimental groups, but was less successful in the second unless a connotative attribute is also introduced.
Abstract: Two experiments employing the release from PI method were conducted to determine whether degree of release could be predicted by the amount of denotative attribute overlap between the control and experimental groups. This theory was very appropriate for predicting the results of the first experiment, but was less successful in the second unless a connotative attribute is also introduced. It is suggested that this class of attribute should be included in semantic memory conceptualization.
TL;DR: In this paper, the authors investigated the expansion anisotropy of the hafnium titanate phase in the 0 to 60 mol percent TiO/sub 2/ region using x-ray diffraction analysis, differential thermal analysis, melting point studies, and dilatometry.
Abstract: The system HfO/sub 2/-TiO/sub 2/ was investigated in the 0 to 60 mol percent TiO/sub 2/ region using x-ray diffraction analysis, differential thermal analysis, melting-point studies, and dilatometry. For samples quenched from 1500 and 1250/sup 0/C, single-phase HfTiO/sub 4/ is present from approximately 36 to 53 percent TiO/sub 2/, with HfO/sub 2/ coexisting as a second phase below 36 percent TiO/sub 2/ and TiO/sub 2/ coexisting as a second phase above 53 percent TiO/sub 2/. Room-temperature lattice parameters of the hafnium titanate phase decreased linearly with composition for samples quenched from 1500/sup 0/C and furnace-cooled from 1600/sup 0/C. High-temperature lattice parameter studies confirmed the expansion anisotropy of the hafnium titanate phase in the single-phase region. Linear thermal-expansion measurements revealed very low coefficients (less than 1 x 10/sup -6///sup 0/C) for compositions in the 30 to 40 percent TiO/sub 2/ range and relatively high coefficients (approximately 4 x 10/sup -6///sup 0/C) for the 25, 45, 50, and 60 mol percent TiO/sub 2/ compositions. The low expansion was attributed to microcracking. 5 fig.
TL;DR: In this article, the authors investigated the effect of realistic temperatures and pressures on ejector performance and found that mass entrainment performance usually decreased with increasing primary pressure although an aeroacoustic interaction reversed the trend over small intervals.
Abstract: Attention has recently been given to the use of thrust augmenting ejectors in the wings of V/STOL aircraft. Laboratory experiments using low temperature and pressure primary air have measured high-performance levels with well-designed ejectors. The present experiments were motivated by aircraft designers' questions regarding the effects of realistic temperatures and pressures on ejector performance. The simplest geometry was used: a convergent nozzle issuing into an axisymmetric duct that entrained from and exhausted to ambient conditions. The length of the ejector was varied from 12 to 0.75 diam. Primary temperatures and pressures spanned the intervals 60 to 1000°F and 10 to 80 psig. In support of existing theory, the mass entrainment performance usually decreased with increasing primary pressure although an aeroacoustic interaction reversed the trend over small intervals. Increasing the primary temperature decreased the performance of long ejectors but had little effect on the performance of short ejectors. The results are interpreted in terms of measurements of the pressure along the wall of the mixing duct and total pressure and temperature profiles acquired at the exhaust plane of the ejector.
TL;DR: It is shown that the existing model structure is overparameterized and can be simplified by modifying some of the original assumptions and recommendations for further simplification in the human operator model structure are made.
TL;DR: In this article, the potential energy curves along the diffusion path due to all ions other than conducting species are simulated by (Vo/2) (1-cos(2πx/a)), where a is the lattice constant.
Abstract: Three one-dimensional models, interstitialcy-like, vacancy-like, and interstitial-like, are constructed to study general properties of superionic conductors. Potential energy curves along the diffusion path due to all ions other than conducting species are simulated by (Vo/2) (1-cos(2πx/a)), where a is the lattice constant. By considering only the Coulomb and repulsive potentials among conducting ions, the activation energies, Ea, are calculated as functions of Vo. It is shown that due to local correlated motions of conducting ions, the values of Ea are much smaller than those of Vo. For instance, for the interstitialcy-like mechanism, Ea changes from 0.02 eV to only 0.4 eV while Vo changes from 0.8 eV to 3.2 eV. For the vacancy-like mechanism, Ea is less than 0.2 eV for Vo below 0.9 eV, and is less than 0.05 eV for Vo less than 0.4 eV. Other properties such as attempt frequency, conductivity, ion distribution, and diffuse X-ray scattering pattern are discussed. The correspondences between the models and actual superionic conductors, such as β-alumina, β″-alumina, and α-AgI are also discussed. Comments on existing theories of superionic conductors are presented.
TL;DR: In this paper, the diffusion equation when the diffusion coefficient varies with time is considered and a transformation is proposed to deal with the time-dependent diffusion coefficient. But this transformation requires a large adjustment in the time scale.
Abstract: This paper concerns the diffusion equation when the diffusion co efficient varies with time. It has been agreed that the sorption of moisture in composites is described by the diffusion equation and that the diffusion coefficient is highly sensitive to temperature. When the temperature varies with time, as during a "thermal spike", the diffusion coefficient becomes time dependent.It is shown in this paper that the above time-variation can be treated simply and efficiently with the aid of a simple transformation. This trans formation permits the utilization of all the available solutions, that were based on a time-independent diffusion coefficient, upon a simple and easy adjustment in the time-scale.
TL;DR: A resizing algorithm is developed that employs a uniform-flutter-velocity-derivative optimality criterion for flutter- critical elements and the fully-stressed-design criterion for strength-critical elements.
Abstract: Several methods for sizing the finite elements of an aircraft structural idealization to achieve minimum-weight design under combined strength and flutter-speed requirements are developed and evaluated. Two basic categories are considered: methods based on a combination of energy principles and optimality criteria; and procedures employing numerical-search techniques. Drawing upon the experience gained from studies of both of these basic methods, a resizing algorithm is developed that employs a uniform-flutter-velocity-derivative optimality criterion for flutter-critical elements and the fully-stressed-design criterion for strength-critical elements. The final result is a practical, automated approach for dealing with large-scale idealizations having both structural and mass-balance design variables.
TL;DR: A series of novel AB monomers such as 2-[p-carboxyphenyl]-5,6-diaminobenzimidazole hydrochloride have been synthesized as mentioned in this paper.
Abstract: A series of novel AB monomers such as 2-[p-carboxyphenyl]-5,6-diaminobenzimidazole hydrochloride have been synthesized. In addition, a new aromatic monomer, 1,3-diamino-4,6-bis(p-toluenesulfonamido)benzene has been prepared in high purity and substituted for 1,2,4,5-tetraaminobenzene in a polymerization with terephthalic acid. Homopolymerization of the AB monomers, and polycondensation of monomer with terephthalic acid in polyphosphoric acid, produced the rod-like para-oriented polymer, poly[1,7-dihydrobenzo(1,2-d: 4,5-d)diimidazole-2,6-diyl-1,4-phenylene]. The yellow polymer was completely soluble in methanesulfonic acid (MSA) and PPA, exhibiting intrinsic viscosities as high as 5 dl/g in MSA, and a blue opalescence in solution. Polymerization at temperatures above 225°C caused crystallization and subsequent precipitation to occur. Polymer thus obtained was completely insoluble in MSA and possessed a high degree of crystallinity as demonstrated by x-ray analysis.
TL;DR: In this paper, the authors used a knowledge of the aperture fields to predict the pattern using aperture integration and diffraction theory, and verified the assumptions made concerning the aperture field were verified by probing the internal fields and aperture fields of an X band corrugated horn.
Abstract: The corrugated horn has been established as an antenna with low sidelobes and backlobes, rotationally symmetric patterns (for square pyramidal and conical horn shapes), and broad-band performance [1]-[9]. These properties make this horn useful for many applications. Previous studies have used conventional aperture integration techniques to evaluate the patterns of the corrugated horn. In general, the near axis E -plane radiation pattern of a pyramidal corrugated horn may be adequately predicted from standard analysis established for the H -plane patterns of conventional horn geometries [3]. This method, however, fails to predict the far-out sidelobe and backlobe radiation levels. The work presented here uses a knowledge of the aperture fields to predict the pattern using aperture integration and diffraction theory. The assumptions made concerning the aperture fields were verified by probing the internal fields and aperture fields of an X band corrugated horn. The results of this field probing are contained in the Appendix. The method of solution used in this paper parallels that used in previous publications [10]-[12]. Specifically, the pattern in the main beam region is computed using conventional aperture integration procedures, the contribution of the H -plane edges is found using a slope diffraction analysis, and the contribution of the E -plane edges is found by use of duality.
TL;DR: The past five years have seen significant changes in the Air Force philosophy and approach in achieving structural safety and durability in military aircraft as mentioned in this paper, motivated by problems of high cost, late system development programs, with a high level of in-service structural maintenance and modification costs (poor durability) and, in some cases, less than desired fracture resistance (poor damage tolerance/safety).
Abstract: The past five years have seen significant changes in the Air Force philosophy and approach in achieving structural safety and durability in military aircraft. These changes have been motivated by problems of high cost, late system development programs, with a high level of in-service structural maintenance and modification costs (poor durability) and, in some cases, less than desired fracture resistance (poor damage tolerance/safety). The problem area has been attacked along a number of avenues; one major thrust has been a thorough examination and revision of the structural design and test specifications, the MIL-A-8860 series. In this paper, certain aspects of the overall problem are discussed; an overview of the pre-1969/70 Air Force approach is presented, along with its short-comings; and, finally, significant aspects of current policy are listed, giving comparisons with the old requirements.
TL;DR: In this article, the preparation of acetyldi-t-butyl-silane with functional groups on silicon was described, and α-ethoxyvinyllithium was treated with a halosilane to give an α-silyl enol ether, which was then hydrolyzed under mild conditions to give the corresponding acetylsilane.