A static compensator model for use with electromagnetic transientssimulation programs

A static VAr compensator (SVC) model based on state variable techniques is presented. This model is capable of being interfaced to a parent (or host) electromagnetic transients program, and, in particular a stable method of interfacing to the EMTDC program is described. The model is primarily that of a thyristor-controlled reactor. (TCR) and a thyristor-switched capacitor (TSC). Capacitor switchings within the TSC have been handled in a novel way to simplify storage and computation time requirements. During thyristor switching, the child SVC model is capable of using a smaller timestep than the one used by the parent electromagnetic transients program; after the switching, the SVC model is capable of reverting back to a (larger) timestep compatible with the one used by the parent program. Other features considered include the modeling of a phase-locked-loop-based, valve firing system. An application of this model to the simulation of a SVC controlling the AC voltage of the inverter bus of a back-to-back HVDC (high-voltage direct current) tie is presented     

Synthesis of butadiene-acroleine block polymers

Summary From GPC and ¹H NMR results, we have shown that block polymers built with acroleine and butadiene units can be synthesized. Moreover, the cross-linkage ability of the acroleine blocks in these products under UV irradiation has been checked. This is very interesting for an industrial application. Indeed, homopolyacroleines can be used as a photopolymer layer to prepare negative or positive printing plates.     

The nanophthalmic macula

AIMS: To define an unusual macular appearance found in association with nanophthalmos. METHODS: A case review. RESULTS: Seven children (aged 8 months to 17 years) with nanophthalmos were examined. They all exhibited the same clinical findings of an unusual yellow macula appearance with retinal folds and crowded optic discs. Visual electrophysiology performed in four cases was normal. CONCLUSION: A distinctive yellow macular pigmentation with associated chorioretinal folds and crowded optic discs is present in nanophthalmos. It is proposed that the retinal folds are due to a disparity between scleral and retinal growth while the macula discoloration is due to a congenital abnormality in arrangement or position of the luteal pigment and is not degenerative. Included in this case series is the second case in the literature of nanophthalmos associated with Kenny's syndrome. Inheritance of nanophthalmos appears to be autosomal recessive.     

Control sensitivity indices for stability analysis of HVDC systems

This paper presents a new concept called the “Control Sensitivity Index” or CSI, for the stability analysis of HVDC converters connected to weak AC systems. The CSI for a particular control mode can be defined as the ratio of incremental changes in the two system variables that are most relevant to that control mode. The index provides valuable information on the stability of the system and, unlike other approaches, aids in the design of the controller. It also plays an important role in defining nonlinear gains for the controller. This paper offers a generalized formulation of CSI and demonstrates its application through an analysis of the CSI for three modes of HVDC control. The conclusions drawn from the analysis are confirmed by a detailed electromagnetic transients simulation of the AC/DC system. The paper concludes that the CSI can be used to improve the controller design and, for an inverter in a weak AC system, the conventional voltage control mode is more stable than the conventional γ control mode     

Effect of Ice-Induced Cross-Polarization on Digital Earth- Space Links

Among the techniques proposed to increase the capacity of the allocated frequency bands, reuse of the same channel twice with orthogonal polarizations seems to be very promising. However, imperfect isolation between the two orthogonal channels, arising, for example, from nonspherical scatterers encountered by the transmitted waves during propagation, is likely to limit the possibilities of this frequency reuse technique. While rain-induced cross-polarization is relatively well understood, the impact of cross-polarization coupling due to ice crystals on communication systems has to be thoroughly investigated. In this paper a statistical analysis of depolarization events observed at 20 GHz from the linearly polarized beacon of ATS-6 is carried out. It shows that ice depolarization events occur as frequently and are as significant as rain depolarization events, and also that ice crystals are typically canted withinpm10degof the vertical. From the results obtained, the effect of ice cross-polarization on a dual-polarized microwave link utilizingM-ary PSK transmission is investigated. These results point out the necessity of implementing cross-polarization cancellation devices.     

Fabrication, characterization, and enzymatic activity of encapsulated fungal protease--fatty lipid biocomposite films

Encapsulation of an aspartic protease from the fungus Aspergillus saitoi (F-prot) in thermally evaporated fatty acid films by a simple beaker-based immersion technique under enzyme-friendly conditions is described. The approach is based on diffusion of the enzyme from aqueous solution, driven primarily by attractive electrostatic interaction between charged groups on the enzyme surface and ionized lipid molecules in the film. The encapsulated enzyme molecules could be "pumped out" of the biocomposite film into solution by modulating the electrostatic interaction between the enzyme and fatty acid molecules via solution pH variation. The kinetics of F-prot diffusion into the acid films was followed using quartz crystal microgravimetry measurements while the secondary and tertiary structure of the enzyme in the lipid matrix was studied using Fourier transform infrared (FT-IR) and fluorescence spectroscopies. FT-IR and fluorescence measurements indicated little perturbation to the native structure of the enzyme. A chemical analysis of the F-prot-fatty acid biocomposite film was also performed using X-ray photoelectron spectroscopy. The encapsulated F-prot molecules showed catalytic activity (as estimated by reaction with hemoglobin) comparable to free enzyme molecules in solution, indicating facile access of biological analytes/reactants in solution to the enzyme molecules. The advantages/disadvantages of this approach vis-à-vis methods currently used for encapsulation of biomolecules are briefly discussed.     

Defect‐Related Optical Behavior in Surface Modified TiO2 Nanostructures

The surface modification of TiO₂ nanostructures to incorporate nitrogen and form visible light absorbing titanium oxynitride centers is studied. Anatase TiO₂ structures in the 5–20 nm range, formed by a wet chemical technique, were surface modified and the nitridation of the highly reactive TiO₂ nanocolloid surface, as determined by X‐ray photoelectron spectroscopy (XPS) studies, is achieved by a quick and simple treatment in alkyl ammonium compounds. The nitriding process was also simultaneously accompanied by metal seeding resulting in a metal coating layer on the TiO₂ structures. The structure of the resultant titanium oxynitride nanostructures remains anatase. These freshly prepared samples exhibited a strong emission near 560 nm (2.21 eV), which red‐shifted to 660 nm (1.88 eV) and dropped in intensity with aging in the atmosphere. This behavior was also evident in some of the combined nitrogen doped and metal seeded TiO₂ nanocolloids. Electron spin resonance (ESR) performed on these samples identified a resonance at g = 2.0035, which increased significantly with nitridation. The resonance is attributed to an oxygen hole center created near the surface of the nanocolloid, which correlates well with the observed optical activity.     

Anionic graft copolymers. I. Poly(vinyl chloride)-g-polystyrene. Preparation and characterization

Graft copolymers of PVC-g-PS of controlled branching were prepared by carbanionic deactivation. The reaction products were characterized mainly by GPC. It appears that secondary reactions affect the efficiency of the grafting, chiefly at low ratios of polystyrene to poly(vinyl chloride). Techniques of grafting and analyses are discussed.     

A chemically driven visible laser transition using fastnear-resonant energy transfer

Evidence is obtained which demonstrates the potential for developing purely chemical visible lasers based on rapid near-resonant energy transfer from metastable excited triplet states of germanium and silicon monoxide (a³Σ⁺,b ³Π) to select metal atoms. In this study, the Group IIIA metal atoms were chosen as the energy receptors for the energy transfer-pump sequence. Excited triplet states were generated from the Ge-O₃, Ge-N₂, Si-N₂O, and Si-NO₂ reactions; the bulk of the experimental results was obtained with a germanium-based system. The energy stored in the long-lived triplet states is transferred to pump X²P_1/2 thallium, indium, and gallium atoms to their lowest lying ² S_1/2 states. The authors observe a system of temporal behavior which suggests the creation of a population inversion producing a gain condition and forming the basis for full cavity oscillation on the Tl 7²S_1/2-6P _3/2 transition at 535 nm