Forces between Alumina Surfaces in Salt Solutions: Non-DLVO Forces and the Implications for Colloidal Processing

Direct measurements of the forces between basal (0001) surfaces of sapphire in salt solutions are presented. The measurements reveal the presence of forces in addition to those described by classical DLVO theory. At pH 7.2 in 0.01 M NaBr solution, we find an additional short-range oscillatory force with periodicity approximately equal to twice the diameter of a water molecule. At pH 3 we find an additional strong, short-range, monotonic, repulsive force and a long-range attractive force over a range of NaBr concentrations from 0.001 M to 0.1 M . Both monotonic forces are approximately exponential, with decay lengths of 0.55 and 12 nm, respectively. The short-range force is analogous to hydration forces previously measured on negatively charged surfaces. This force would provide plasticity to alumina slurries and is suggested to be the force responsible for the anomalous viscosity and consolidation behavior of alumina slurries at high salt concentrations.     

Variation of the partial thermodynamic properties of oxygen with composition in YBa2Cu3O7−δ

The variation of equilibrium oxygen potential with oxygen concentration inYBa ₂Cu₃O₇-δhas been measured in the temperature range of 773 to 1223 K. For temperatures up to 1073 K, the oxygen content of theYBa ₂Cu₃O₇-δsample, held in a stabilized-zirconia crucible, was altered by coulometric titration. The compound was in contact with the electrolyte, permitting direct exchange of oxygen ions. For measurements above 1073 K, the oxide was contained in a magnesia crucible placed inside a closed silica tube. The oxygen potential in the gas phase above the 123 compound was controlled and measured by a solid-state cell based on yttria-stabilized zirconia, which served both as a pump and sensor. Pure oxygen at a pressure of 1.01 × 10⁵ Pa was used as the reference electrode. The oxygen pressure over the sample was varied from 10^-1 to 10⁵ Pa. The oxygen concentrations of the sample equilibrated with pure oxygen at 1.01 × 10⁵ Pa at different temperatures were determined after quenching in liquid nitrogen by hydrogen reduction at 1223 K. The plot of chemical potential of oxygen as a function of oxygen non-stoichiometry shows an inflexion at δ ∼ 0.375 at 873 K. Data at 773 K indicate tendency for phase separation at lower temperatures. The partial enthalpy and entropy of oxygen derived from the temperature dependence of electromotive force (emf ) exhibit variation with composition. The partial enthalpy for °= 0.3, 0.4, and 0.5 also appears to be temperature dependent. The results are discussed in comparison with the data reported in the literature. An expression for the integral free energy of formation of YBa₂Cu₃O_6.5 is evaluated based on measurements reported in the literature. By integration of the partial Gibbs’ energy of oxygen obtained in this study, the variation of integral property with oxygen concentration is obtained at 873 K.     

Characterization of polyurethane foams from soybean oil

Modified soy‐based vegetable oil polyols were successfully incorporated as a replacement for conventional polyols to produce flexible slabstock polyurethane foams. The oil was characterized for its hydroxyl value and fatty acid composition. The modified oils had higher hydroxyl values and lower unsaturated acids than regular unmodified oils. Three different modified polyols were used to investigate the reactivity with isocyanates. The effects on the foaming reaction of two different isocyanates, namely TDI and MDI, were investigated. The reactions were also carried out with a mixture of polyols containing synthetic polyols and vegetable oil‐based polyols to delineate the effect of each component. FTIR technique was used to identify the sequence of chemical reactions during the foaming process. The effect of water levels and isocyanate content on the kinetics of the foaming reaction was investigated. Information regarding the formation of hard and soft segments with the varying compositions was obtained. As the water content increased, the amount of the hard segment and urea formation increased in both soy oil polyols and synthetic polyols. Increased synthetic polyols in the mixture increased the rate of reaction and phase mixing due to the availability of primary hydroxyl groups. Scanning electron microscopy (SEM) and small‐angle X‐ray scattering (SAXS) were used to probe the morphology. As the water content increased, the cell size increased. At lower water content a more uniform cell structure was evident and at higher water levels hard domain size increased. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3097–3107, 2002     

Nontuberculous mycobacterial infection of the central nervous system in patients with AIDS

Infections due to nontuberculous mycobacteria (NTM) are especially common in patients with AIDS. Meningitis due to NTM, however, is rare. A search for CSF cultures positive for NTM over the past 11 years at our hospital yielded 16 cases. Of these, 15 were caused by Mycobacterium avium-intracellular (MAI), and one was caused by M fortuitum. All patients with MAI infection had widespread dissemination and at least one risk factor for AIDS. Clinical features included weight loss, altered mentation, and seizures. Analysis of cerebrospinal fluid revealed a mildly elevated leukocyte count with lymphocyte predominance and normal protein and glucose values. All direct smears were negative for acid-fast bacilli. In-hospital mortality was 67%. The patient with infection due to M fortuitum had a preexisting diagnosis of AIDS and had a right upper lobe pneumonia and headaches. Cranial CT showed an enlarged infundibulum of the pituitary gland. Results of CSF analysis were essentially normal, and direct smears were negative. He left the hospital against medical advice. Our study indicates that the finding of MAI in the CSF in patients with AIDS is associated with an in-house mortality of 67% indicating a very poor prognosis.     

Reliability analysis of a complex system with a deteriorating standby unit under common-cause failure and critical human error

This paper presents a stochastic model representing two units and one as a standby unit with critical human error and common cause failure. The deteriorating effect of the standby unit on the system is studied. Repair times of the failed system are arbitrarily distributed while all other transition time distributions are negative exponential. The analysis is carried out using supplementary variable techniques and various measures of system effectiveness such as pointwise availability, steady-state availability, MTTF and variance of the time to failure of the system are obtained.     

Creating a bifunctional protein by insertion of beta-lactamase into the maltodextrin-binding protein

Hybrid proteins were generated by inserting the penicillin-hydrolyzing enzyme, TEM beta-lactamase (Bla), into the maltodextrin-binding protein (MalE). The inserted Bla was functionally accommodated by MalE when it was placed within permissive sites. The maltose binding and penicillinase activities of purified hybrids were indistinguishable from those of the wild-type MalE and Bla proteins. Moreover, these hybrids displayed an additional unexpected property: maltose stabilized the active site of inserted Bla.     

Inert-gas extrusion of rigid PVC foam

A novel approach to the extrusion of high-density, rigid PVC foam uses commercial RPVC compounds with inert-gas physical blowing agents (carbon dioxide and argon). The process was developed on a segmented single-screw extruder with L/D of 40. On-line monitoring of process variables was also carried out. This technique provides an alternative to conventional processing methods using chemical blowing agents.