Processing and microstructure of particle stabilized silica foams

Silica foams containing ~ 85% porosity and with different shapes and sizes have been prepared by air entrainment in suspensions of hydrophobized silica + alumina (5 wt.%) powder mixture in aqueous solution of isopropanol and binders, followed by casting, drying and sintering. The silica powder with surfaces modified by presence of long chain amphiphilic molecules has been used successfully for stabilization of air bubbles in suspensions, so that their disproportionation and collapse could not be observed even after 4 weeks. Microstructural examination using optical and scanning electron microscopy as well as measurements by mercury porosimetry has shown trimodal pore size distribution with fine (4–10 μm), medium (50–100 μm) and coarse (~ 680 μm) pores.     

Phase Transformation Introduced by Mechanical and Chemical Surface Preparations of Tetragonal Zirconia Polycrystals

Cutting of Y₂O₃-doped TZP rods by a low-speed diamond saw introduces an unidentified, metastable phase X (x -ZrO₂) coexisting with the tetragonal ( t -ZrO₂) and the monoclinic ( m -ZrO₂) phases initially present in the sample. Further mechanical deformation of the cut surface by indentation or polishing sustains the x -ZrO₂. Chemical etching removes the x -ZrO₂ and increases the m -ZrO₂content.     

Vascular reaction following intramedullary nailing of the tibia in dogs

We have reinvestigated radioiodinated plasminogen as an agent for localizing preformed thrombi. Canine plasminogen was isolated from fresh plasma by the affinity chromatography technique on a lysine-sepharose 4B column and tagged with I-123 or I-131, at less than one iodine atom per molecule of enzyme, by the conventional ICI method. When injected into dogs more than 2 days after thrombus induction, radioiodinated plasminogen produced thrombus-to-blood activity ratios of 7.8 +/- 2.4. Thrombi as old as 6 days can be visualized in 80% of the cases. Both the weight of the thrombus and the thrombus-to-blood ratio are more variable for 1-day-old thrombi; this may be associated with plasminogen release accompanying thrombus retraction. The results suggest that radioiodinated plasminogen has potential as an imaging agent for pre-existing thrombi.     

Development and comparison of models for light-pulse transport through scattering-absorbing media

We examine the transport of short light pulses through scattering-absorbing media through different approximate mathematical models. It is demonstrated that the predicted optical signal characteristics are significantly influenced by the various models considered, such as P(N) expansion, two-flux, and discrete ordinates. The effective propagation speed of the scattered radiation, the predicted magnitudes of the transmitted and backscattered fluxes, and the temporal shape and spread of the optical signals are functions of the models used to represent the intensity distributions. A computationally intensive direct numerical integration scheme that does not utilize approximations is also implemented for comparison. Results of some of the models asymptotically approach those of direct numerical simulation if the order of approximation is increased. In this study therefore we identify the importance of model selection in analyzing short-pulse laser applications such as optical tomography and remote sensing and highlight the parameters, such as wave speed, that must be examined before a model is adopted for analysis.     

Effect of ash on maximum thickness of plastic layer of coals

A study of the effect of ash yield on the maximum thickness of the plastic layer (MTPL) of some coking coals (as measured by the Sapozhnikov plastometer) has revealed that with an increase in the former the latter in general decre?es. A rectilinear relation approximately exists between the ash percentage (dry basis) and log MTPL values of coals. For the samples studied, a multiple correlation incorporating the rank factor was found to be unnecessary. Higher Fe₂O₃ and SO₃ contents from the coal were found to be associated with higher MTPL values.     

Apparent solubility of drugs in partially crystalline systems

Using several griseofulvin samples, representing different solid-state structures, the solubility behavior of drugs in both one-state (totally ordered, semiordered or disordered) and two-state systems was studied. Special attention was directed towards the surface structure of the particles. The partially crystalline samples were obtained by milling the raw material (crystalline standard) or storing the quenched sample (amorphous standard). The solid-state structure of the materials was studied using x-ray diffraction (XRD), differential scanning calorimetry (DSC), isothermal microcalorimetry (IMC), and scanning electron microscopy (SEM). The saturation concentration of the materials was studied in suspensions containing different dispersion concentrations of drug after centrifugation and filtration, using spectrophotometry. In all cases these dispersion concentrations exceeded the solubility of the drug. The solubilities were plotted vs. dispersion concentrations for each sample. Several solubility plateaus were found. The lowest and highest solubility plateaus corresponded to the solubilities of crystalline and amorphous standards. These plateaus were reached at 8 and 44 µg/mL for crystalline and amorphous griseofulvin standards, respectively. An intermediate plateau served as an indication of the existence of a totally semiordered structure. This was reached at 19 µg/mL for griseofulvin. Any deviation from these plateaus was suggested to be indicative of the existence of heterogeneity on the surface structure, which in most cases could be described as a two state system. In such cases, the apparent solubility was a function of dispersion concentration, until at very high dispersion concentrations (4000-20,000 µg/mL) the saturation concentration of the totally disordered (44 µg/mL) or semiordered (19 µg/mL) one-state phase was reached. No reduction in these values was observed during storage for 50 days. It is thus concluded that, in partially crystalline systems, the saturation concentration is an interfacial phenomenon, which depends on the amount, reactivity, and solid-state structure of the exposed solid surfaces in equilibrium with the solution. A simplified solubility model is proposed to qualitatively describe the relationship between established apparent solubilities (saturation concentrations) and different combinations of solid-state structures.     

The design of low noise digital filters with controlled dynamic range

A novel digital filter structure, that allows proper positioning of the zeros of the noise transfer functions to reduce the output roundoff noise, is introduced. Relations between zero locations, roundoff noise and dynamic range are derived and are then utilized in an heuristic optimization method for synthesizing a low noise scaled digital filter structure. Illustrative examples supporting the proposed approach are included.