Process and waveguide parameter relationships for the design of planar silver ion-exchanged glass waveguides

In this paper the experimental results of diffusion studies and modal characterization of Ag⁺-Na⁺exchanged glass waveguides are presented. Empirical relations between the process and the device parameters are derived and subsequently used to formulate a systematic procedure for fabricating single- and multimode waveguides.     

EVALUATION AND MODELING OF TWO-STAGE OSMO-CONVECTIVE DRYING OF APPLE SLICES

Two-stage drying kinetics of cylindrical pieces of apples were evaluated by subjecting test samples first to various osmotic treatments and then to convective air drying to complete the drying process. Osmotic drying was carried out with cut apple cylinders of three different sizes (12, 17 and 20 mm diameter), all with a length to diameter ratio of 1 : 1, in a well agitated large tank containing the osmotic solution at the desired temperature. Solution to fruit volume ratio was kept greater than 60. After the osmotic treatment, apple slices were further dried in a cabinet drier at an average temperature 58°C. A central composite rotatable design (CCRD) with five levels of sucrose concentrations (34-63°Brix) and five temperatures (34-66°C) was used for osmotic treatment. Half-drying time and solids gain time were used as measures of rate of drying and associated diffusion coefficients for moisture loss and solids gain were evaluated. Half-drying time decreased with an increase in temperature or concentration, or a decrease in sample size. Diffusion coefficients were lower for smaller samples, and were higher for migration of moisture as compared to solids. For a given level of moisture removal, air drying times were shorter than osmotic drying times. Composite models were developed to describe the effect of process variables and particle size on the drying behavior of apple slices.     

FT-IR studies on the evolution of different phases and their interaction in ferric molybdate—molybdenum trioxide catalysts

Two samples of Fe–Mo catalysts have been prepared from ferric nitrate and ammonium paramolybdate, one following a conventional procedure and the other by a new precipitation procedure in a buffer medium. The evolution of different Fe–Mo phases, from the fresh precipitate to the aged and then to the calcined state, has been followed by FT-IR spectroscopy. All the spectral vibrations have been related to different coordination spheres of Mo and Fe ions in the samples and a comparison with a commercial catalyst of similar composition has been made. The new preparation procedure leads to small, uniform (0·3 μm size) particles and a homogeneous morphology of phases as seen by scanning electron microscopy. Additionally, a higher surface area (10·3 m² g^?1), lower bulk density (0·66 g cm^?3), a methanol conversion efficiency of > 90% and an HCHO selectivity of 95% distinguish this sample from the conventionally prepared one. Better thermal stability of this sample is inferred from the IR spectral and XRD analyses of the heat-treated (up to 800°C) samples and is related to the interaction between Fe₂(MoO₄)₃ and MoO₃ phases.     

Moisture Diffusion Inside Paper Materials in the Hygroscopic Range and Characteristics of Diffusivity Parameters

Some current models for moisture diffusion in paper in the hygroscopic range are analyzed. In general, two types of diffusion models can be recognized. Models of the first type treat paper as a homogeneous medium with moisture flux that is proportional to the gradient in moisture content. Although useful in some instances this approach fails frequently because it homogenizes the internal dynamics and relaxation processes occurring within the paper material. Recent studies have shown that a subtler approach which treats paper as a composite of fibers and void spaces is more successful at describing moisture transport dynamics. A review of these studies along with a generalization of this approach to three dimensions is considered here. The parameters appearing in such models can be identified with the physical processes of diffusion through the void space and through the fiber matrix. Diffusivities in these individual phases are supplemented by a local kinetic coefficient representing moisture flux interchange between the void and fiber phases. When the local moisture exchange coefficient takes on large values, the fibers and the void spaces are at local equilibrium with no net exchange of moisture. Under such conditions, the model reduces to the simpler Fickian diffusion model with nonlinear moisture diffusivity equivalent to earlier models.     

Purification and crystallization of the oxygenase component of naphthalene dioxygenase in native and selenomethionine-derivatized forms

A new procedure was developed for the purification of the terminal oxygenase component (ISPNAP) of naphthalene dioxygenase. From a five liter culture of Escherichia coli JM109(DE3)(pDTG121), 91 mg of pure protein were obtained with a specific activity of 2.48 mumol/ min/mg protein. ISPNAP was crystallized in the rhombohedral space group R32 with cell dimensions of a = b = 179.2 A; c = 322.5 A in the hexagonal setting. The crystals are brown, indicating the presence of an intact Rieske iron-sulfur center. Problems with non-isomorphism between native data sets necessitated the preparation of a selenomethionine-substituted protein. Complete replacement of methionine with selenomethionine was achieved and the purified protein had a specific activity almost identical to native ISPNAP. Crystals from this preparation belong to the same space group and have similar cell dimensions to native ISPNAP.     

A profilometric study of levelling in electroplating

The levelling power of a plating bath is usually assessed from measurements of surface roughness (R _a or r.m.s.) before and after plating. The availability of new parameters for surface characterization now permits a better understanding of the role played by surface microgeometry in levelling. This paper explores the possibility of using these parameters for finding a reliable representation of levelling for quantitative assessment. A new measure based on the profile length parameter is suggested.     

Bioceramics composition modulate resorption of human osteoclasts

Biomaterials used in bone regeneration are designed to be gradually resorbed by the osteoclast and replaced by new bone formed through osteoblastic activity. The aim of the present study is to analyze the role of osteoclasts in the resorption process. The attachment of human osteoclasts and the appearance of their resorption lacunae, when cultured on either the resorbable crystalline, calcium orthophosphate materials or on the long-term stable bioceramic material was investigated. The resorbable materials contain Ca₁₀[K,Na](PO₄)₇ (AW-Si) and Ca₂KNa(PO₄)₂ (GB14, GB9 & D9/25) as their main crystal phases, however they differ in their total solubility. These differences result from small variations in the composition. The long-term stable material consist of about 30% fluorapatite beside calcium zirconium phosphate (Ca₅(PO₄)3F + CaZr₄(PO₄)₆) and shows a very small solubility. AW-Si has an alkali containing crystalline phase, Ca₁₀[K,Na](PO₄). While GB14, GB9 and D9/25 contain the crystalline phase Ca₂KNa(PO₄)₂ with small additions of crystalline and amorphous diphosphates and/or magnesium potassium phosphate (GB14). D9/25 and AW-Si is less soluble compared to GB14, and GB9 among the resorbable materials. Resorbable and long-term stable materials vary in their chemical compositions, solubility, and surface morphology. Osteoclasts modified the surface in their attempts to resorb the materials irrespective of the differences in their physical and chemical properties. The depth and morphology of the resorption imprints were different depending on the type of material. These changes in the surface structure created by osteoclasts are likely to affect the way osteoblasts interact with the materials and how bone is subsequently formed.