Synthesis of new polymeric hindered amine light stabilizers: Performance evaluation in styrenic polymers

Polymeric hindered amine light stabilizers (HALSs), in which the HALS functionality was attached to the terminal isocyanate chain end of poly(styryl‐co‐styryl isocyanate), were synthesized by a two‐step process. First, cinnamoyl azide was prepared and copolymerized with styrene by a free‐radical copolymerization method. Polymeric low‐molecular‐weight and high‐molecular‐weight 2,2,6,6‐tetramethyl‐4‐pipridinol‐graft‐poly(styryl‐co‐styryl isocyanate) and 4‐amino‐2,2,6,6‐tetramethyl piperidine‐graft‐poly(styryl‐co‐styryl isocyanate) were synthesized by a grafting method. The photodegradation and stabilization of different grades of high‐impact polystyrene (HIPS) were studied at 55°C in air at different time intervals, and the photostabilizing efficiency of polymeric HALSs was compared with conventional light stabilizers, such as 2,2,6,6‐tetramethyl‐4‐pipridinol and bis(2,2,6,6‐tetramethyl‐4‐piperidinyl)sebacate. Polymeric HALSs showed significant improvements in the photostabilization of HIPS. The solubility and diffusion coefficient of polymeric HALSs were studied. The morphological changes in HIPS caused by photooxidation were also studied. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1126–1138, 2003     

Influence of processing on stability,microstructure and thermoelectric properties of Ca3Co4 − xO9 + δ

Due to high figure of merit, Ca₃Co_4 ? xO_9 + δ (CCO) has potential as p-type material for high-temperature thermoelectrics. Here, the influence of processing including solid state sintering, spark plasma sintering and post-calcination on stability, microstructure and thermoelectric properties is reported. By a new post-calcination approach, single-phase materials were obtained from precursors to final dense ceramics in one step. The highest zT of 0.11 was recorded at 800 °C for CCO with 98 and 72% relative densities. In situ high-temperature X-ray diffraction in air and oxygen revealed a higher stability of CCO in oxygen (～970 °C) than in air (～930 °C), with formation of Ca₃Co₂O₆ which also showed high stability in oxygen, even at 1125 °C. Since achievement of phase pure high density CCO by post-calcination method in air is challenging, the phase stability of CCO in oxygen is important for understanding and further improvement of the method.     

Ge-Rich (70%) SiGe Nanowire MOSFET Fabricated Using Pattern-Dependent Ge-Condensation Technique

A top-down approach of forming SiGe-nanowire (SGNW) MOSFET, with Ge concentration modulated along the source/drain (Si_0.7Ge_0.3) to channel (Si_0.3Ge_0.7) regions, is presented. Fabricated by utilizing a pattern-size-dependent Ge-condensation technique, the SGNW heterostructure PMOS device exhibits 4.5times enhancement in the drive current and transconductance (G_m) as compared to the homojunction planar device (Si_0.7Ge_0.3). This large enhancement can be attributed to several factors including Omega-gated nanowire structure, enhanced hole injection efficiency (due to valence band offset), and improved hole mobility (due to compressive strain and Ge enrichment in the nanowire channel).     

Barium ferrite: Preparation by liquid mix technique and its characterization

Barium ferrite has been prepared by a novel non-conventional preparation method known as the liquid mix technique which involves the preparation of citrates of the metals concerned. The decomposition of the citrates indicated a gradual transition from an amorphous material to a crystalline phase leading to the formation of barium ferrite at 600° C as indicated by the X-ray diffraction and Mössbauer measurements. Submicrometre-sized particles of the ferrite could be obtained directly on decomposition of the citrates, thus avoiding the milling or grinding operations normally employed to reduce the particles to the size required for obtaining good magnetic properties. The best properties (coercivity and remanence) were obtained for the ferrite sintered around 990° C.     

Raman and infrared study of 100 MeV swift Ag heavy ion irradiation effects in CaSO4·2H2O single crystals

The modifications of calcium sulphate (CaSO₄·2H₂O) single crystals are investigated by means of Raman and Fourier transform infrared spectroscopy (FT-IR) using 100 MeV Ag⁸⁺ ions in the fluence range 1 × 10¹¹ to 5 × 10¹³ ions/cm². It is observed that the intensities of the Raman modes decrease with increase in ion fluence. We determined damage cross-section (σ) for all the Raman active modes and found to be different for different Raman modes. Further, FT-IR studies have been carried out to confirm surface amorphisation for a fluence of 1 × 10¹³ ions/cm². It is observed that the absorption peaks at 1132–1156 cm⁻¹ corresponds to ν₃(SO₄²⁻) mode. The decrease in Raman peaks intensity with ion fluence is attributed to degradation of ν₃(SO₄²⁻) modes present on the surface of the sample.     

Influence of adjuncts as a debittering aids in encountering the bitterness developed in cheese slurry during accelerated ripening

An attempt was made to accelerate the flavour development in cheese base with the help of exogenous proteolytic and lipolytic enzymes (1:1 proportion, each at the rate of 0.025% by weight of cheese‐base) and ripening at elevated temperatures (i.e. 20 ± 1 °C) for up to 12 days. To counter the bitterness developed, adjunct cultures were used: viable or attenuated (freeze‐shocked or heat shocked). Study of biochemical characteristics, electrophoretic pattern and sensory evaluation of the product were carried out. An acceptable enzyme‐modified, lightly salted cheese base was obtained using 0.025% each of proteolytic and lipolytic enzymes, along with 5% starter culture and adjuncts followed by ripening up to 12 days. Freeze‐shocked adjunct Lactobacillus helveticus produced enzyme‐modified cheese base with no detectable bitterness. The usage of exogenous enzymes, temperature of ripening, ripening period and interactions amongst these parameters had significant (P < 0.01) influence on all of the biochemical characteristics monitored.     

Modified friction factor correlation for CICC’s based on a porous media analogy

The first cool-down of the EDIPO (European DIPOle) test facility is foreseen to take place in 2011 by means of the existing 1.2 kW cryoplant at EPFL-CRPP Villigen. In this work, the thermo-hydraulic analysis of the EDIPO cool-down is performed in order both to assess the its duration and to optimize the procedure. The cool-down is driven by the helium flowing in both the outer cooling channel and in the windings connected hydraulically in parallel. We take into account limitations due to the pressure drop in the cooling circuit and the refrigerator capacity as well as heat conduction in the iron yoke. Two schemes of the hydraulic cooling circuit in the EDIPO windings are studied (coils connected in series and coils connected in parallel). The analysis is performed by means of an analytical model complemented by and numerical model. The results indicate that the cool-down to 5 K can be achieved in about 12 days.     

Synthesis,characterization and application of biopolymer-ionic liquid composite membranes

Biopolymer composite membranes based on chitosan doped with an ionic liquid (IL) 1-ethyl 3-methylimidazolium thiocyanate (EMImSCN) have been developed and characterized. The doped ionic liquid films show remarkable enhancement in ionic conductivity (σ). The Fourier transform infrared (FTIR) spectroscopy, atomic force microscopy (AFM) and X-ray diffraction studies (XRD) affirmed the composite nature, good incorporation of ionic liquid and reduction in crystallinity of films, respectively. The interaction between ionic liquid, chitosan and iodide polymer electrolyte matrix was evaluated by cyclic voltammetry. The fabricated dye sensitized solar cell (DSSC) using this new biopolymer electrolyte membranes shows promising performance.     

Scheduling UET-UCT tasks: branch-and-bound search in the priority space

The paper is concerned with the problem of scheduling partially ordered unit execution time tasks on parallel processors with unit communication delays and release times. Two criteria are considered, the maximum lateness and its particular case, the makespan. This problem plays an important role in scheduling theory and was originally inspired by the applications to multi-processor computer systems. It is well known that for both criteria the problem is NP-hard in the strong sense. The paper presents an implementation of the branch-and-bound method which does not partition the feasible region explicitly. The theoretical results are complemented by computational experiments.