Optimization of heat transfer and pressure drop in a tube with loose-fit perforated twisted tapes by Taguchi method and grey relational analysis

Journal of Thermal Analysis and Calorimetry - This work introduces the determination of the optimum values of the design parameters in a tube with loose-fit perforated twisted tapes. The effects of...     

Fast switching anisotropic networks obtained by in situ photopolymerization of liquid crystal molecules

Lightly cross-linked anisotropic networks with uniaxial and π/2 twisted orientations were produced by photopolymerization of monotropic mixtures containing liquid crystal mono and diacrylates. In this way the polymer backbone was immobilized and became decoupled from the motion of the mesogenic side groups. The networks showed very good reversibility and even after becoming isotropic, upon cooling, the initial orientation was recovered. In the same way, in the presence of electric fields the mesogenic groups could be reoriented in the direction of the electric field, reverting back to the initial orientation on removal of the field at a rate comparable with those observed in the monomeric state. Combining viscoelastic measurements with the dielectric behaviour of the monomeric liquid crystal and the anisotropic network, a comparison between the internal and bulk rotational viscosities was also made.     

Dielectric relaxation of liquid crystal molecules in anisotropic confinements

Abstract

The dielectric relaxation of the liquid crystal 4-n-pentyl-4′-cyanobiphenyl (K15) in the presence of an anisotropic network has been studied. Anisotropic networks containing K15 molecules were prepared by in situ polymerisation of liquid-crystalline diacrylate molecules in a mixture containing K15. By changing the network concentration, the effect of the network molecules on the behaviour of the K15 molecules, which were not chemically attached to the network, was investigated. With increasing network concentration it was found that the mean relaxation times of K15 molecules shifted to lower temperatures and that their distribution became broader. The activation energy associated with the relaxation, however, remained almost constant before showing some increase at high network concentrations.     

Liquid crystals: first active organics in electronics

A Commentary on the paper “Anisotropic gels and plasticized networks formed by liquid crystal molecules”, by R. A. M. Hikmet. First published in Liquid Crystals, 9, 405–416 (1991).     

Performing thermodynamic analysis by simulating the general characteristics of the two-spool turbojet engine suitable for drone and UAV propulsion

Journal of Thermal Analysis and Calorimetry - This study presents determining performance parameters as well as thermodynamic analysis through certain design parameters of a two-spool turbojet...     

Synthesis and photopolymerization of cholesteric liquid crystalline diacrylates

The synthesis of chiral liquid crystalline diacrylates is described. By mixing one of them with non-chiral liquid crystalline diacrylates. cholesteric phases are obtained of which the wavelength of reflection can be chosen by the composition of the mixture. After isothermal photopolymerization of the mixture a crosslinked network is obtained with thermally stable properties.     

Poly(p‐phenylene methylene)‐based block copolymers by mechanistic transformation

The synthesis of poly(p‐phenylene methylene) (PPM)‐based block copolymers such as poly(p‐phenylene methylene)‐b‐poly(ε‐caprolactone) and poly(p‐phenylene methylene)‐b‐polytetrahydrofuran by mechanistic transformation was described. First, precursor PPM was synthesized by acid‐catalyzed polymerization of tribenzylborate at 16 °C. Then, this polymer was used as macroinitiators in either ring‐opening polymerization of ε‐caprolactone or cationic ring‐opening polymerization of tetrahydrofuran to yield respective block copolymers. The structures of the prepolymer and block copolymers were characterized by GPC and ¹H NMR investigations. The composition of block copolymers as determined by ¹H NMR and TGA analysis was found to be in very good agreement. The thermal behavior and surface morphology of the copolymers were also investigated, respectively, by differential scanning calorimetry and atomic force microscopy measurements, and the contribution of the major soft segment has been observed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Ultrasonically-aided extrusion of blends of two thermotropic LCPs

Ultrasonically-aided extrusion of two thermotropic LCPs based on 6-oxy-2-naphthoyl and p-oxybenzoyl moieties (LCP1), and p-oxybenzoyl, terephthaloyl and hydroquinone moieties (LCP2) and their blends that are partially miscible was investigated. Ultrasonic treatment induced structural changes in the components, leading to improved mechanical properties of LCP1 moldings, and degradation of LCP2. Also, the ultrasonic treatment was found to further improve the partial miscibility of the blends. Although LCP1 and LCP2 behaved differently under ultrasonic treatment, synergistic effects on fibrillation and mechanical properties of blends were observed in injection moldings. Mechanical properties of melt spun fibers of blends lied between those of the components. Lack of synergism in mechanical properties of fibers was primarily attributed to saturation of LCP2 orientation at low draw down ratios in fiber spinning.     

Outpatient appointment scheduling in presence of seasonal walk-ins

This study investigates appointment systems (AS), as combinations of access rules and appointment-scheduling rules, explicitly designed for dealing with walk-in seasonality. In terms of ‘access rules’, strategies are tested for adjusting capacity through intra-week, or monthly seasonality of walk-ins, or their combined effects. In terms of ‘appointment rules’, strategies are tested to determine which particular slots to double-book or leave open in cases where seasonal walk-in rates exceed or fall short of the overall yearly rate. In that regard, this study integrates capacity and appointment decisions, which are usually addressed in an isolated manner in previous studies. Simulation optimization is used to derive heuristic solutions to the appointment-scheduling problem, and the findings are compared in terms of in-clinic measures of patient wait time, physician idle time and overtime. The goal is to provide practical guidelines for healthcare practitioners on how to best design their AS when seasonal walk-ins exist.     

Oscillating oxygen evolution at Ta anodes

Anodic Ta oxide films are said to inhibit oxygen evolution. In industry, however, large amounts of gas are evolved during the anodization of tantalum anodes for electrolytic capacitor fabrication. We quantified the oxygen by fluorescence quenching in a flow-through cuvette and found that 4% of the anodic charge are consumed for oxygen evolution. In wires or sheets, this oxygen is removed by diffusion without bubble formation and, thus, not recognized. Due to the large inner area of the sintered Ta anodes, the oxygen evolution causes strong oscillations of the current density and bubble formation. The amount of oxygen is proportional to the oxide amount formed in parallel. This is explained by a model where mobile ions during oxide growth form interband states which allow electron tunneling. Accordingly, stationary no oxygen evolution is observed.