Showing papers by "Missouri University of Science and Technology published in 1977"

A Finite-Element Approach for Nonlinear Panel Flutter

Abstract: A finite-element approach has been developed for determining nonlinear flutter characteristics of twodimensional panels, based on aerodynamic forces from quasi-steady aerodynamic theory. The stiffness equations of motion, iterative solution procedure, and convergence characteristics are presented. Comparisons are made with linear flutter and large amplitude vibration results and demonstrate that good accuracy is obtained. Nonlinear flutter results are presented; effects of aerodynamic damping, boundary support conditions, and initial in-plane forces are included.

Studies of vibrational surface modes in ionic crystals. I. Detailed shell-model studies for the unrelaxed (001) face of seven crystals having the rocksalt structure

Abstract: We present a comprehensive, unified account of the lattice dynamics of unrelaxed (001) faces of seven crystals having the rocksalt structure, three of which have an absolute gap between the acoustical and optical bulk bands (RbF, RbCl, and NaI) and four of which have overlap between these bulk bands (NaF, NaCl, LiF, and MgO). The results are obtained from calculations of the normal modes of a thin crystal film in which the ionic interactions are described by the rigid-shell model. An outline of the formulation of the shell model for the film is given, and the rapid convergence of surface-phonon frequencies with increasing film thickness is demonstrated. Surface- and pseudosurface-phonon dispersion curves and bulk bands are displayed in the form of the dispersion curves of a 15-layer film over the two-dimensional surface Brillouin zone. The surface-excess phonon density of states ${f}^{s}(\ensuremath{\omega})$ is given, and its peaks and valleys are correlated with features in the film dispersion curves. The domains of existence and the vibrational character of the more prominent surface-phonon bands are discussed. We establish the relation between the surface modes of the lattice models and the macroscopic surface waves of the dielectric and elastic continuum theories (Fuchs-Kliewer and Rayleigh waves, respectively). Comparison with experiments is made; the agreement with low-energy atom scattering from single-crystal surfaces of LiF and with inelastic neutron scattering from microcrystallite samples of MgO is particularly notable, although the latter comparison also displays some significant discrepancies.

Sodium Diffusion in Glass: I, Single‐Alkali Silicate

Abstract: The isotope effect for 22Na/24Na diffusion was measured for three 25-mol% alkali-silicate glasses. A multiple diffusion mechanism wherein the Na ions diffuse both singly (vacancy mechanism) and in pairs (interstitialcy mechanism) provided the best agreement with the experimental data. According to this tentative model, diffusion by Na ion pairs predominates at low temperatures, and the fraction of Na ions diffusing singly increases with increasing temperature. In the glasses investigated, nearly all of the Na ions diffuse singly in the vicinity of the transformation range.

Evaluation of organic additives for use in zinc electrowinning

Abstract: Organic additives are used extensively in zinc electrowinning to assist in controlling the process. A cyclic voltammetry technique has been developed to provide a rapid, quantitative evaluation of the effectiveness of selected organic additives in minimizing the deleterious effects that impurities, such as antimony, have on zinc deposition. Results have indicated that animal glues are more effective than the other organic additives tested, which included several gums, enzymes, and amino acids, in relation to the current efficiency of zinc production. Of the various animal glues compared in this research, the most effective appeared to have average molecular weights in the 25,000 to 30,000 range. The effects of certain process variables on the test results have also been evaluated; these included the acid concentration of the zinc sulfate solution and the cathode preparation.

Uniformly Most Powerful Unbiased Tests on the Scale Parameter of a Gamma Distribution With a Nuisance Shape Parameter

Abstract: Conditional tests on the scale parameter of the gamma distribution with an unknown nuisance shape parameter are considered. Such tests, based upon the conditional distribution of the sample mean x (or equivalently Wi , = x/x) given the geometric mean x, are uniformly most powerful unbiased tests. Percentage points of the conditional distribution are tabulated for small sample sizes and an asymptotic normal approximation is also obtained.

Effect of Stiffening on Sound Transmission into a Cylindrical Shell in Flight

Abstract: Theme I the context of airborne-noise transmission through an aircraft fuselage, a mathematical model is presented for sound transmission into a stiffened cylindrical shell. The stiffening effect of the ring frames and stringers is approximated by a "smeared" stiffener theory which includes the eccentricity of the stiffeners. Numerical results are presented for a typical narrow-bodied jet in cruising flight.

Subsolidus Equilibria and Stabilization of Tetragonal ZrO2 in the System ZrO2‐Al2O3‐SiO2

Abstract: The irreversible reaction between zircon and alumina to form mullite and zirconia was observed to proceed very slowly at 1480°C, confirming the existence of a stable join between mullite and zirconia in addition to the join between mullite and zircon. Attempts to determine equilibrium assemblages in powder samples of several combinations of the constituents at 1300° and 1400°C were unsuccessful. Metastable tetragonal ZrO2 was observed in fired powder samples containing kaolinite, in fired zircon-alumina samples, and in calcined gels prepared from zirconyl nitrate, aluminum nitrate, and colloidal silica in water. Tetragonal ZrO2 was the dominant crystalline phase in gels fired for 24 h at 800°, 950°, and 1100°C; the thermal stability of the phase was enhanced by Al2O3 and by SiO2, but most effectively by mixtures of the two. Line broadening measurements and electron microscope observation indicate that the tetragonal ZrO2, with apparent crystallite sizes between 0.009 and 0.1 μm, develops as an intergrowth with, and is stabilized by, the amorphous matrix of Al2O3 and SiO2.

Sodium Diffusion in Glass: II, Mixed Na-K Silicate Glasses

Abstract: The isotope effect for 22Na/24Na diffusion was used to investigate the sodium ion transport mechanism in mixed Na-K silicate glasses. A combined vacancy-interstitialcy mechanism provided the best agreement with the experimental 22Na/24Na isotope effect data. At low temperatures sodium diffusion occurs predominantly by 2-atom interstitialcy jumps, but with increasing temperature an increasing fraction of the ions diffuse by a single-atom vacancy mechanism.

Analysis of combined forced and free convection across a horizontal cylinder

Abstract: A new analysis is performed to study the flow and heat transfer characteristics of laminar combined forced and free convection about a horizontal cylinder. The transformed conservation equations of the nonsimilar boundary layers are solved by a finite difference method. Numerical results for gases having a Prandtl number of 0.7 are presented for buoyancy parameters which cover the entire domain of the mixed convection, ranging from pure forced convection to pure free convection. It is found that both the local wall shear and the local heat transfer rate (1) increase with increasing buoyancy force for assisting flow, (2) decrease with increasing buoyancy force for opposing flow, and (3) depend very strongly on the variation of the local free stream velocity, particularly for small to moderate buoyancy forces. With regard to the heat transfer results, the buoyancy force effects on forced convection are found to be important for Gr/Re2 ≥ 1.93 and ≤ –1.60, respectively for assisting and opposing flows, whereas the inertia force effects on free convection become significant for Re2/Gr ≥ 0.012. On a fait une nouvelle analyse des caracteristiques d'ecoulement et de transfert de la chaleur d'une convection laminaire forcee ou libre autour d'un cylindre horizontal. On a resolu, par une methode de differences finies, les equations de conservation transformees de couches-limites non semblables. On presente les resultats numeriques dans le cas de gaz dont le nombre de Prandtl est 0.7 et pour des parametres qui embrassent le domaine entier de la convection mixte, lequel comprend la convection pure (forcee et libre). On a constate que le cisaillement a la paroi locale et le taux de transfert local de la chaleur (1) s'accroissaient lorsque la force de flottement augmentait pour un courant aidant, (2) decroissaient lorsque la force de flottement augmentait pour un courant contraire et (3) dependaient considerablement de la variation de la vitesse locale du courant libre, surtout dans le cas de forces de flottement allant de faibles a moderes. En ce qui a trait aux resultats du transfert de la chaleur, les effets des forces de flottement sur la convection forcee se sont averes importants pour Gr/Re2 ≥ 1.93 et ≤ 1.60, dans le cas des courants aidant et contraire respectivement, tandis que les effets de la force d'inertie sur la convection libre se sont averes importants pour Re2/Gr ≤ 0.012.

Optimization of prism coupling efficiency for surface electromagnetic wave excitation in the infrared

Abstract: The ir SEW coupling efficiency of a BaF2 prism has been determined for various gap heights and internal angle configurations, utilizing the two prism coupling technique and a CO2 laser. Samples consisted of W foil and Ni, Pt, and Cu films deposited on glass substrates by electron beam deposition and vacuum evaporation. Optimum prism coupling gap heights were found to occur for each metal. It was determined that selection of the proper internal prism angle increases coupling efficiency by a factor of 3 over the coupling efficiency of the right angle prism.

Radiative lifetime of the A 2 Δ state of CH

Abstract: The lifetime of various rotational levels of the v′ = 0 and 1 vibrational states of the A2Δ state of CH are reported. The lifetimes for the various levels were nearly constant with the rotational quantum number N′. For the v′ = 0 level it was 508 ± 25 ns and for the v′ = 1 level, it was 514 ± 33 ns. The bandhead lifetime was 500 ns and these lifetimes are very close to the bandhead lifetime.

Suggested Chemistry of Zinc Oxychloride Cements

Abstract: Solutions of ZnCl2 were prepared from ZnCl2·nH2O and by reaction of zinc metal with HCl. Specific gravities and pH values were determined as a function of composition. A ternary phase, 4ZnO·ZnCl2·5H2O, was precipitated when the ZnCl2 solutions were diluted to a pH of 5.48 ± 0.05. Mixtures of ZnO with ZnCl, and HCI solutions were equilibrated in sealed containers and analyzed by X-ray diffraction. The resulting phase diagram shows 2 ternary phases, 4ZnO·ZnCl2·5H2O (4·1·5) and ZnO·ZnCl2·2H2O (1.1.2), both of which are soluble to the extent of < 1 wt% in ZnCl2 solutions. Thermogravimetric data indicate that the 1.1.2 phase loses half the constituent H2O at ∼230°C and the remainder, with ZnCl2, at higher temperatures. The 4.1.5 phase dissociates to ZnO and 1.1.2 at ∼160°C. The system ZnCl2-H2O is not binary, but is a section through the ternary system ZnO-HCl-H2O, with the solubility curve of the 4.1.5 phase intersecting the ZnCl2-H2O section in dilute solutions.

Synthesis of heat exchange networks by mixed integer optimization

Abstract: Process synthesis involves manipulation of the process arrangement, while studying the variables of each arrangement, to arrive at the optimal process. If each process arrangement is treated as a discrete variable, process synthesis becomes a mixed integer optimization problem. This paper examines the synthesis of heat exchanger networks using the adaptive random search procedure, which can be used to search continuous and discrete independent variables simultaneously. The means of handling the heat exchanger arrangement as a discrete variable is discussed, and the incorporation of various synthesis heuristics is presented. The results of synthesis of 2 × 2, 2 × 3, and 3 × 3 networks are presented and compared with other methods of synthesis.

Aitken nuclei measurements in the lower stratosphere

Abstract: A report is presented on Aitken nuclei (AN) measurements between 6 km and 19 km with the new Stratospheric Aitken Nuclei Detection System (SANDS) which was installed in the nose section of the WB-57F aircraft. Measurements were made between 48°N and 9°S latitudes over the U.S.A., Gulf of Mexico, Central and South America between March, 1974, and February, 1975. Evaluation of 18 flights led to the following conclusion: The vertical profiles of AN concentration are similar to those found by Junge et al. (1961). However, the AN concentrations at altitudes above 17 km are higher by several tens of AN cm -3 . Horizontal flights showed a low AN concentration above 18 km over the tropical regions (below 20 AN cm -3 ), and an influence of the Rocky Mountains and the Andes Mountains on the AN measurements at 18 km altitude. Usually, several km above the tropopause, a negative correlation between AN, and ozone concentration was found. DOI: 10.1111/j.2153-3490.1977.tb00715.x

Positron lifetime as a function of grain size

Abstract: Published data on positron annihilation lifetime in copper as a function of grain size have been analyzed to show that there is a linear relationship between the internal grain boundary surface area, per unit volume,S v, and the positron lifetime, τ. The analysis indicates that grain boundaries are important in the trapping of positrons. It is suggested that the slope of the resulting straight line,dS v/dτ, can be used to determine the annihilation rate of the grain boundaries.

Inferential procedures for the truncated exponential distribution

Abstract: Suppose that X1,X2,…,Xn are independent and identically distributed with density , 0≤x≤t and that inferences about θ are to be made. The exact distribution of is known but is quite complicated and so an approximation to its distribution is needed. It is shown here that the beta approximation for the density of (nt)−1U obtained by equating the first two moments performs better, for moderate n, than the normal approximation given by the central limit theorem and is asymptotically equivalent to it. The use of this approximation in making inferences in some life testing situations is discussed via an example.

On sliding block coding for transmission of a source over a stationary nonanticipatory channel

Abstract: It is shown that the capacity Cb of a stationary nonanticipatory channel with respect to block coding is at least as great as the capacity Cs of the channel with respect to sliding block coding. For several types of stationary nonanticipatory channels (namely, ergodic channels, channels with additive random noise, and averaged channels whose components are discrete memoryless channels), it is shown that Cb = Cs, thereby generalizing a result of Gray and Ornstein for the discrete memoryless channel.