Optical photonic crystals synthesized from colloidal systems ofpolystyrene spheres and nanocrystalline titania

We have developed a novel ceramic processing technique to fabricate photonic crystals (PCs) with close-packed lattices of air pores in a dielectric background. The ordering of colloidal spheres and incorporation of the titania is performed simultaneously, in contrast to other approaches. Excellent ordering of the lattice of air pores is achieved over domains extending over 100 μ. The PCs exhibit a uniform color and a corresponding sharp peak in the reflectivity at the wavelength of the first stopband. The position of the reflectivity peak scales very well with the size of the air pores, providing strong evidence for photonic crystal effects     

Inverse Face‐Centered Cubic Thin Film Photonic Crystals

Recent work on a technique for fabricating inverse fcc photonic crystals from a colloidal system of monodisperse microspheres and titania nanoparticles is described. The technique can be used to produce photonic crystals with other background materials that are available as nanoparticles. The Figure shows the Moiré pattern of a typical photonic crystal sample.     

Integrating code generation and peephole optimization

Summary Peephole optimization when integrated with automatic code generation into a uniform framework has significant advantages in the specification and implementation of efficient compiler back-ends. Attribute grammars provide a framework for expression of machine-specific code optimizations. We present a grammar-driven peephole optimization algorithm that is particularly well suited to attributed-parsing code generators. Integration via semantic attributes corrects interrelated phase-ordering problems and produces a faster and smaller compiler back-end.     

Visible Frequency Thin Film Photonic Crystals from Colloidal Systems of Nanocrystalline Titania and Polystyrene Microspheres

This work describes a simple and novel ceramic processing technique to form periodic ordered structures in ceramic materials with a uniform pore size distribution. This material shows photonic gaps at visible/near-IR wavelengths. Monodisperse colloidal polystyrene microspheres are self-organized into a crystalline structure of close-packed spheres in a suspension of nanocrystalline titania. The nanoparticle titania fills the intersphere region simultaneously during colloidal crystallization. Removal of the polystyrene microspheres by calcination at a temperature of 520°C results in a periodic porous structure with a high refractive index background material. Crystals having ordered regions, a few millimeters across with typical grain sizes of 50–70 μm, are grown as thin films on substrates including glass and silicon. Optical reflectivity measurements indicate peaks at the stop band wavelengths that scale with the pore size. Visual inspection and optical microscopy reveal uniform colored regions for crystals with periodicity comparable to visible wavelengths. Despite the presence of cracks resulting from drying and heat treatment as well as numerous grain boundaries, optical characterization clearly demonstrates a photonic band gap. Reflectance peaks due to a pseudogap can be shifted by application of high pressure. In the following sections we will describe the experimental procedure and discuss optical reflectance and transmission measurements that can reveal information about the crystals, namely, the lattice constant, the refractive index, and the filling fraction of the background material.     

Flat-sheet and hollow fiber membrane bioreactors: A study of the kinetics and active site conformational changes of immobilized papain including sorption studies of reaction constituents

Papain, a sulfhydryl protease has been immobilized on flat-sheet modified polysulfone membranes and hydroxyethyl cellulose coated polyethersulfone hollow fibers. Amidase activity of the enzyme in solution on the membranes has been assayed. Immobilized papain on the modified polysulfone membrane and the hollow fibers retains 12% and 25% of its activity (with 1 mmol dm^?3 substrate) in solution, respectively. Loading experiments revealed decreased activity on the modified polysulfone membrane with increased enzyme loading. Adsorption experiments for the reaction product, p-nitroaniline, have been performed and an attempt has been made to correct for this in activity calculations. Apparent Michaelis–Menten parameters were determined for the modified polysulfone and hollow fibers with both K_m and V_max being lower in the immobilized cases. Electron paramagnetic resonance study of the changes in active site conformation of an enzyme on a hollow fiber membrane are reported for the first time. Experiments using the sulfhydryl-specific (1-oxyl-2,2,5,5-teetrahyl-Δ³-pyrroline-3-methyl)methanethiolsulfonate spin label depicted the presence of two subpopulations of immobilized papain on the hollow fibers, one of them active and one denatured.     

Dynamic Thermal Buckling of Functionally Graded Spherical Caps

In the present work, dynamic buckling behavior of clamped functionally graded spherical caps suddenly exposed to a thermal field is studied using the finite-element procedure. The material properties are graded in the thickness direction. The temperature load corresponding to a sudden jump in the maximum average displacement in the time history of the shell structure is taken as the dynamic buckling temperature. Numerical study is carried out to highlight the influences of shell geometries and material gradient index on the critical buckling temperature.     

Synthesis and characterization of LiMgyMn2-yO4 cathode materials by a modified Pechini process for lithium batteries

Abstract. Cubic spinels of composition, LiMg_yMn_2-yO₄, with y = 0.0, 0.05, 0.1, 0.15 and 0.2, were synthesized by a modified Pechini process using polyethylene glycol and citric acid. The phase formation and/or crystallization of the precursors were studied by thermal analysis. Products were characterized by X-ray diffraction and SEM analysis. Coin cells were fabricated with lithium as the anode and LiMg_yMn_2-yO₄ as the cathode in an electrolyte of 1 M LiPF₆ in a 1: 1 (v/v) mixture of EC and DEC. The charge-discharge studies were performed and the results were compared with materials prepared by a solid state thermal method.     

The Model Repository of the Models of Infectious Disease Agent Study

The model repository (MREP) is a relational database management system (RDBMS) developed under the auspices of models of infectious disease agent study (MIDAS). The purpose of the MREP is to organize and catalog the models, results, and suggestions for using the MIDAS and to store them in a way to allow users to run models from an access-controlled disease MREP. The MREP contains source and object code of disease models developed by infectious disease modelers and tested in a production environment. Different versions of models used to describe various aspects of the same disease are housed in the repository. Models are linked to their developers and different versions of the codes are tied to Subversion, a version control tool. An additional element of the MREP will be to house, manage, and control access to a disease model results warehouse, which consists of output generated by the models contained in the MREP. The result tables and files are linked to the version of the model and the input parameters that collectively generated the results. The result tables are warehoused in a relational database that permits them to be easily identified, categorized, and downloaded.