Showing papers by "Missouri University of Science and Technology published in 1994"

Impact on Laminated Composites: Recent Advances

Abstract: Impact damage in structures made out of composite materials is a major concern since such damage can be introduced during the life of the structure, and its mechanical properties can be drastically reduced as a result. In a previous review of the literature on impact on composite materials, this author considered 285 published before 1989. In this article over 300 articles most of which appeared after 1989 are reviewed. These figures indicate that this is a very active area of research, and the present paper seeks to present a comprehensive view of the latest developments. Taken together, these two reviews present a comprehensive view of the state of knowledge in the area. Most the current research effort is focused on low velocity impact damage and, in particular, the damage predictions and the evaluation and prediction of residual properties of damaged laminates. A significant number of papers deal with ballistic impacts on laminated composites and the use of composite materials in designing light armor.

Simulation of communication systems

Abstract: When both a complex system and a complex channel model are encountered, the result is typically a design or analysis problem that cannot be solved using traditional (pencil and paper) mathematical analysis. Computer-aided techniques, which usually involve some level of numerical simulation, can be a very valuable tool in these situations. The purpose of this article is to provide a tutorial review of some of the basic techniques of communication system simulation. The authors consider the basic techniques used to represent signals, generate signals, and model linear systems, nonlinear systems, and time-varying systems within a simulation. They consider the important problem of using a simulation to estimate the performance of a communication system. >

Use of a macrocyclic antibiotic, rifamycin B, and indirect detection for the resolution of racemic amino alcohols by CE.

Abstract: Ansamycins are a very specific class of macrocyclic antibiotics of which the rifamycins are among the better known members. Rifamycins bind to and inhibit DNA polymerase. Rifamycin B (the most easily obtained ansamycin) is negatively charged and is shown to associate with and enantioselectively resolve several chiral amino alcohols including terbutaline, isoproterenol, bamethan, metaproterenol, synephrine, metanephrine, salbutamol, epinephrine, norphenylephrine, ephedrine, psi-ephedrine, octopamine, norepinephrine, normetanephrine, metoprolol, alprenolol, atenolol, and oxprenolol. A description of the structure and properties of rifamycins, in general, and rifamycin B, in particular, is given. The complexation and chiral recognition of the aforementioned racemic compounds by rifamycin B is afforded by multiple interactions of which charge-charge, hydrogen-bonding, and hydrophobic inclusion interactions most likely dominate in hydroorganic solvents. The effect of various experimental factors on enantiomeric resolution is discussed in terms of optimizing the CE separations. Since most chiral antibiotic macrocycles are ionizable, somewhat flexible, and contain hydrophobic and hydrophilic moieties, they tend to be significantly affected by variations in the solution environment.

Low-Energy Electrons and Their Dynamical Correlation with Recoil Ions for Single Ionization of Helium by Fast, Heavy-Ion Impact.

Abstract: Helium single ionization by 3.6 meV/u Ni[sup 24+] impact was explored in a kinematically complete experiment by combining a high-resolution recoil-ion momentum spectrometer with a novel 4[pi] low-energy electron analyzer. More than 90% of the soft electrons'' ([ital E][sub [ital e]][approx lt]50 eV) are ejected in the forward direction in agreement with classical-trajectory Monte Carlo predictions. The electron longitudinal momentum is not balanced by the longitudinal momentum change of the projectile but mainly by the backwards recoiling He[sup 1+] ion. Energy losses of the 0.2 GeV projectiles as small as [Delta][ital E][sub [ital P]]/[ital E][sub [ital P]]=3.4[times]10[sup [minus]7] are observable.

Use of a Macrocyclic Antibiotic as the Chiral Selector for Enantiomeric Separations by TLC

Abstract: The macrocyclic antibiotic, vancomycin, was used as a chiral mobile phase additive for the thin layer chromatographic (TLC) resolution of 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (AQC) derivatized amino acids, racemic drugs and dansyl-amino acids. Excellent separations were achieved for most of these compounds in the reversed phase mode. Both the nature of the stationary phase and the composition of the mobile phase strongly influenced enantiomeric resolution. The best results were obtained using diphenyl stationary phases. Acetonitrile was the organic modifier that produced the most effective separations with the shortest development times. It is highly likely that macrocyclic antibiotics will play a major role in future enantiomeric separations.

Silver-Palladium Thick-Film Conductors

Abstract: The trends in integrated circuit packaging technology are toward high speed, high density, reliability, and low cost These demand the improvement of material formulations and processing technology Among the thick-film materials systems, conductor materials generally represent an important and the most expensive element Therefore, attention has been centered on the performance of the fired metal film and its cost Silver and palladium (Ag/Pd) conductors are important components of thick-film paste technology Thick-film Ag/Pd conductors find applications in many aspects of electronics and electronic packaging, such as hybrid microcircuits, multichip modules, packaging for integrated microcircuits, and in passive electronic components such as multilayer capacitors, varistors, and inductors In this paper, the performance and properties of fired Ag/Pd films are discussed through their physical and chemical aspects The final film properties are correlated to a number of factors, including thermodynamics and kinetics of Pd oxidation during burnout and firing; chemical and physical reaction of the Ag/Pd with the ceramic substrate, organic vehicle, and solder; Ag diffusion and migration; inorganic and organic additives; powders characteristics; and paste properties

A magnetic neutron diffraction, and Moessbauer spectral study of the Nd2Fe(17-x)Al(x) solid solutions

Abstract: The magnetic properties of a series of Nd2Fe17−xAlx solid solutions, with x equal to 2.04, 4.01, 5.97, 7.94, and 9.06, have been studied by magnetic measurements, neutron diffraction, and Mossbauer spectroscopy. Magnetization studies indicate that the Curie temperature increases from 330 K in Nd2Fe17 to a maximum of ∼470 K at an x of 3.5. The compounds crystallize in the Th2Zn17 structure with lattice parameters and unit cell volumes which increase linearly with increasing aluminum content. The neutron diffraction results indicate that aluminum atoms are excluded from the 9d site, prefer the 18h site at low aluminum content, and prefer the 6c and 18f sites at high aluminum content. At 10 K the magnetic moments of the iron and neodymium atoms are collinear and take up a basal orientation at all aluminum contents. The moments decrease with increasing aluminum content and the magnetic moments per unit cell at 10 K are in excellent agreement with the 4.2 K saturation magnetization values. At 295 K the Nd2Fe17...

Electrodeposited Defect Chemistry Superlattices

Abstract: Nanometer-scale layered structures based on thallium(III) oxide were electrodeposited in a beaker at room temperature by pulsing the applied potential during deposition. The conducting metal oxide samples were superlattices, with layers as thin as 6.7 nanometers. The defect chemistry was a function of the applied overpotential: High overpotentials favored oxygen vacancies, whereas low overpotentials favored cation interstitials. The transition from one defect chemistry to another in this nonequilibrium process occurred in the same potential range (100 to 120 millivolts) in which the rate of the back electron transfer reaction became significant. The epitaxial structures have the high carrier density and low electronic dimensionality of high transition temperature superconductors.

Role of crude oil in the genesis of Mississippi Valley-type deposits. Evidence from the Cincinnati arch

Abstract: Mississippi Valley-type (MVT) sulfide minerals and oil from deposits along the Cincinnati arch have almost identical [delta][sup 34]S values (-9% to +9% for MVT sulfides, -12% to +9% for oils). These values are very similar to those for MVT sulfides and oil in the Illinois-Kentucky district and support their proposed inclusion in a regional hydrothermal system. Many MVT deposits with low [delta][sup 34]S values are closely associated with oil, whereas MVT deposits with high [delta][sup 34]S values often contain bitumen. Reduced sulfur in MVT deposits with high [delta][sup 34]S values probably came from thermochemical sulfate reduction, whereas that in MVT deposits with low [delta][sup 34]S values probably came from oil and related organic matter. Oil-related sulfur could have been derived from oil fields or disseminated oil and other organic matter in regional wallrocks. 44 refs., 3 figs., 2 tabs.

Thermal Conductivity of a Particulate Diamond-reinforced Cordierite Matrix Composite

Abstract: The effect of 15 vol% particulate diamond reinforcement on the thermal conductivity of a cordierite matrix was studied as a function of diamond particle size from room temperature to 700°C. The thermal conductivity was found to increase with increasing particle size to a maximum increase of about 75% for a mean particle size of 50 μ. The particle size effect was found to be more pronounced at the lower temperatures than at the higher temperatures. The observed effect of particle size and temperature was attributed to the existence of an interfacial thermal barrier, possibly resulting from interfacial phonon scattering, with a positive temperature dependence of the interfacial thermal conductance. The magnitude of this conductance suggested strong adhesion between the diamond and cordierite.

On the Propagation of a Shear Band in a Steel Tube

Abstract: Marchand and Duffy tested thin-walled steel tubes in a split Hopkinson torsion bar at a nominal strain-rate of approximately 1,600/s and could not determine conclusively whether a shear band initiating at a point in the tube propagated around the circumference in one direction or in both directions. They estimated the speed of propagation to be 520 m/s in the former case and 260 m/s in the latter. Here, the authors simulate their test numerically, and find that the shear band propagates in both directions around the circumference of the tube. When the tube is twisted at a nominal strain-rate of 5,000/s, the band speed varies from 180 m/s at the site of the initiation to approximately 1,000 m/s at the nearly diametrically opposite point. The band speed increases with an increase in the nominal strain-rate. The material defect is modeled by assuming that a small region near the center of the tubular surface is made of a material weaker than that of the rest of the tube.

Color and Selected Properties of PbO─BiO1.5─GaO1.5 Glasses

Abstract: The density; molar volume; thermal expansion coefficient; dissolution rate in water, HC1, and NaOH; glass transition and crystallization temperatures; and the absorption edge in the ultraviolet-visible and infrared were measured for PbO─BiO1.5─GaO1.5 glasses. The range of compositions investigated was xPbO (100 −(x + y))BiO1.5. yGaO1.5 for x between 20 and 60 cat% and y of 20, 25, 30, and 35 cat%. The glass-forming tendency increased with increased GaO1.5 and decreased with increased PbO or BiO1.5. The compositional dependence of these properties was consistent with the weight, size, charge, and bond strength of the cations. The Ga3 + ions in these glasses are believed to act primarily as network-forming cations, whereas the majority of the Bi3+ and Pb2+ ions behave as network-modifying cations. It is suggested that a small friction of the lead ions are present as Pb4+. Depending upon melting conditions, these glasses ranged in color from brown to yellow. Various attempts, including containerless melting, were made to obtain colorless glasses, but no conditions were found which totally eliminated the color. The least color (pale yellow) was obtained when the glasses were melted in an air or nitrogen atmosphere in an alumina or gold crucible.

Dynamic in-plane racking tests of curtain wall glass elements

Abstract: Attention has been paid recently to the potentially serious life safety and economic loss issues related to the seismic performance of ‘architectural,’ or ‘non-structural’ building elements such as glass lites in curtain wall systems. In response, a pilot study was undertaken at the University of Missouri-Rolla to investigate the dynamic racking performance of a 15·6 × 12·0 ft (4·56 × 3·68 m) section of curtain wall containing three 5 × 6 ft (1·52 × 1·84 m) glass panels. The curtain wall system was a ‘wide mullion’ design that had generous 1 in (25 mm) clearances between glass edges and the aluminium glazing pocket. Dynamic racking tests were performed totally in plane; no out-of-plane or torsional motions were included. Various types of glass specimens were tested, including annealed, heat-strengthened and fully tempered glass in monolithic and laminated configurations. Dry glazed and two-side structural silicone curtain walls were tested. Test results for dry glazed specimens showed that annealed and heat-strengthened laminated glass experienced no fallout whatsoever. By contrast, annealed monolithic glass experienced frequent fallout in both small and large shards. Fully tempered monolithic glass experienced dicing, which resulted in occasional fallout of entire glass lites. Loss of rigidity in fully tempered laminated glass (when both glass plies were broken) occasionally caused entire lites to fall out. Polyester film (not anchored to the mullions) was applied to annealed monolithic glass; it prevented small shards from falling out, but sometimes contributed to entire lite fallout after the onset of severe glass cracking. Annealed laminated glass units with two-side structural silicone glazing exhibited only very minor glass damage and no glass fallout.

Mixed Convection from a Vertical Plate in Porous Media with Surface Injection or Suction

Abstract: The problem of mixed convection along an isothermal vertical plate in porous media with uniform surface injection or suction is studied. The analysis deals with the entire regime of mixed convection by introducing a single parameter X= [1+ (Rax / Pex )1/2]-1 where X= 1 corresponds to pure forced convection and x = 0 to pure free convection. This x parameter describes both buoyancy and forced flow effects. The nonsimilar variable ξ=(ϑ0x /α) (pex 1/2 + Rax 1/2)-1 represents the effect of injection (ϑ0> 0 or ξ> 0) or suction (ϑ< 0 or xi < 0) at the wall. The transformed nonlinear system of equations involving these parameters is solved using a finite difference method. Results are presented for temperature and velocity profiles, local wall shear stress, and local Nusselt number for the buoyancy assisting flow condition. It is found that suction increases, whereas injection decreases, the rate of heat transfer at the wall. Correlation equations are given for the local and average Nusselt numbers.