Development of the package-reactor (2) -core characteristics-

A new small reactor concept named the Package-Reactor has been jointly developed by Hitachi, Ltd. and Mitsubishi Heavy Industries, Ltd. The reactor technology was built from that of conventional LWRs. The reactor core consists of 12 cassettes containing fuel rods with a similar design to that of PWR fuel rods. Each cassette has about a 0.4 m outer diameter and they are fixed with about 0.5 m pitch to each other in the atmospheric pressure condition. A tube-type control cluster was developed. It can decrease the rise of reactivity for the one-rod-stuck condition. An advanced cassette design was studied in which the down-comer is placed at the center of the fuel region. This concept, which improves neutron economics and the cold shutdown margin, will increase the marketability of the Package-Reactor. An operation period of more than 8 years can be achieved with UO₂ fuel enrichment of 5.0wt%.     

Kinetics of thermal degradation and thermo-oxidative degradation of conductive styrene-butadiene rubber-carbon black composites

The kinetics of the thermal degradation and thermo-oxidative degradation of conductive styrene-butadiene rubber (SBR)-carbon black composites were investigated using thermogravimetric analysis both in nitrogen and oxygen atmospheres. Experiments were carried out at heating rates of 5, 10, 15 and 20 °C/min in both the atmospheres. Friedman method, Kissinger method, Flynn–Wall–Ozawa method and Coats–Redfern method have been used to determine the activation energies of degradation. The invariant kinetic parameters using the IKP method were also determined. The results showed that the thermal stability of the composites in pure nitrogen is higher than that in air atmosphere and the increase in filler loading was found to increase the thermal stability in nitrogen atmosphere. The probable degradation mechanisms of the polymer in both the atmospheres were evaluated based on Fourier Transform Infra Red Spectroscopy (FT-IR) studies.     

Effect of temperature,pressure, and composition on DC resistivity and AC conductivity of conductive styrene–butadiene rubber–particulate metal alloy nanocomposites

Conductive nanocomposites were prepared using styrene butadiene rubber as the polymer matrix and nanosized powder of copper–nickel (Cu–Ni) alloy as the filler. The filler loading was varied from 0 to 40 phr. The electrical conductivity of filled polymer composites is due to the formation of some continuous conductive networks in the polymer matrix. Atomic force microscopy was used to determine the particle size of the nanofiller and its nature of dispersion in the rubber matrix. The DC volume resistivity was measured against the loading of the nanofiller to check the percolation limit. The effect of temperature, applied pressure, time duration under constant compressive stress on the DC resistivity and AC conductivity of the composites with different filler loading were investigated. The change in DC resistivity and AC conductivity against temperature of these composites exhibited positive coefficient of temperature. With the change in applied pressure and time duration under constant compressive stress the DC resistivity undergoes an exponential decrease. The effect of AC field frequency on the AC conductivity was investigated. POLYM. COMPOS. 28:696–704, 2007. © 2007 Society of Plastics Engineers     

Investigation of Stress and Temperature Effect on the Longitudinal Ultrasonic Waves in Polymers

This work aims at establishing the effect of stress and temperature on the velocity of ultrasonic longitudinal waves in typical engineering polymers, and evaluating the potential of ultrasonic stress measurement in the evaluation of residual stresses in polymer parts. In order to estimate the effect of material morphology, two amorphous and two semicrystalline polymers have been considered. A series of tests are implemented, to determine the acoustoelastic constants and temperature constant of materials, by using the designed transducer fixtures for in situ measurement of longitudinal wave velocity. As expected, the velocity changes linearly with stress and temperature, and the temperature effect is as important as the acoustoelastic effect. It shows that this kind of nondestructive method is a valuable quantitative tool to estimate the residual stress in polymer products, but the material temperature influence must be considered during the estimation.     

Thermally stable electromagnetic interference shielding material from polysulfone nanocomposites: Comparison on carbon nanotube and nanofiber reinforcement

The present investigation aims to develop thermally stable electromagnetic interference shielding materials from polysulfone (PSU) nanocomposites filled with multiwall carbon nanotubes (MWCNT) or carbon nanofibers (CNF). The effect of filler type and their structural features such as aspect ratio (length/diameter) and wall integrity on the different properties of nanocomposites has been investigated. Nanocomposite filled with MWCNT/CNF exhibits higher thermal stability compared with the neat PSU matrix. The onset degradation temperature of PSU at 532°C enhances to 537 and 538°C at 3 wt% MWCNT and 3 wt% CNF loading, respectively. CNFs filled nanocomposite shows higher electromagnetic interference shielding effectiveness (EMISE) compared with MWCNT filled one at the same filler loading. Compared with MWCNT, CNF imparts lower electrical percolation threshold. Nanocomposite filled with MWCNTs possesses percolation threshold at 1.5 wt%, whereas nanocomposite filled with CNFs possesses the same at 0.9 wt%. The EMISE of 20–45 dB are obtained from only 1 mm thick CNF filled nanocomposites from the filler loading 3 to 10 wt%. This value of EMISE above 40 dB suggests that the prepared nanocomposite can be used as an effective lightweight EMI shielding material for high frequency (8.2–12.4 GHz) applications, where high thermal stability is required. POLYM. COMPOS. 36:566–575, 2015. © 2014 Society of Plastics Engineers     

Three optimizations for Assume–Guarantee reasoning with L<Superscript>*</Superscript>

The learning-based automated Assume–Guarantee reasoning paradigm has been applied in the last few years for the compositional verification of concurrent systems. Specifically, L^* has been used for learning the assumption, based on strings derived from counterexamples, which are given to it by a model-checker that attempts to verify the Assume–Guarantee rules. We suggest three optimizations to this paradigm. First, we derive from each counterexample multiple strings to L^*, rather than a single one as in previous approaches. This small improvement saves candidate queries and hence model-checking runs. Second, we observe that in existing instances of this paradigm, the learning algorithm is coupled weakly with the teacher. Thus, the learner completely ignores the details of the internal structure of the system and specification being verified, which are available already to the teacher. We suggest an optimization that uses this information in order to avoid many unnecessary membership queries (it reduces the number of such queries by more than an order of magnitude). Finally, we develop a method for minimizing the alphabet used by the assumption, which reduces the size of the assumption and the number of queries required to construct it. We present these three optimizations in the context of verifying trace containment for concurrent systems composed of finite state machines. We have implemented our approach in the ComFoRT tool, and experimented with real-life examples. Our results exhibit an average speedup of between 4 to 11 times, depending on the Assume–Guarantee rule used and the set of activated optimizations. This research was supported by the Predictable Assembly from Certifiable Components (PACC) initiative at the Software Engineering Institute, Pittsburgh.     

Semiconducting behaviour and pressure dependence of electrical resistivity in tin monoselenide single crystals grown by a modified direct vapour transport technique

Tin monoselenide single crystals were grown successfully by a modified direct vapour transport technique. The crystals were found to be semiconducting in nature. The influence of pressure on the electrical resistivity of the crystals grown was studied and the results explained on the basis of a transition from a predominantly two-dimensional material to a more three-dimensional one.     

Dielectric behaviour of styrene-methyl methacrylate copolymer foams at microwave frequencies

Ambient dielectric effects were studied by the short-circuited waveguide method at 9.375 GHz microwave frequency in foams from copolymers of styrene and methyl methacrylate of varying compositions, generated under identical conditions of solvent-nonsolvent ratio, impregnation time and steaming period. The results were correlated with foam-density, porosity and composition and were interpreted in terms of dipole-dipole interactions and the applicability of Wiener's inequalities, logarithmic law of Lichtenecker and Rother with an empirical factor of 0.64 in the index based on the additive law of mixtures and the Böttcher-Bruggeman's relation. Scanning electron micrography on copper-coated fractured surfaces of the samples was done in order to examine the degree of foamability, cell-size distribution and the mechanism of failure. Microhardness, compressive and flexural strength were also measured. Loss characteristics were similarly ascribed to copolymer foamability and dipoleorientability. A prudent choice in the monomer reactivity ratio might therefore yield an optimum reinforcement and a proper dielectric requirement suitable for electronic and radar device constructions.     

Mechanical,thermal, and rheological behavior of ethylene methyl acrylate‐MWNT nanocomposites

Mechanical, thermal, and rheological properties of ethylene methyl acrylate (EMA) composites reinforced with multiwalled carbon nanotubes (MWNTs) have been reported here. Morphological analyses revealed that MWNTs are more uniformly dispersed in EMA upto 3.5 wt% MWNTs loading. Uniform dispersion of MWNTs in EMA matrix leads to decreased crystallinity and increased crystallite size. These are reflected in the mechanical and thermal properties of the composites. The storage moduli of the composites significantly increase by the incorporation of MWNTs, particularly at higher temperatures. The nanocomposites register a slightly higher viscosity than that of neat EMA depending on the contents of MWNTs. Storage modulus (in dynamic shear) increases especially at higher frequency levels due to increased polymer–filler interactions. Dynamic and steady shear rheological properties register a good correlation in regard to the viscous versus elastic response of the nanocomposites. The morphology correlates well with the dynamic rheological characteristics of these nanocomposites. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Characterization of CdSe thin films deposited by chemical bath solutions containing triethanolamine

Cadmium selenide (CdSe) thin films were prepared by chemical bath deposition on glass substrates at different temperatures beginning at room temperature (25 °C) upto 80 °C from an aqueous alkaline medium using a precursor solution containing cadmium acetate, 2,2′,2′′-nitrilotriethanol (triethanolamine), ammonia and sodium selenosulphate. The pH of bath was kept constant around 10.50±0.10. Energy dispersive analysis of X-rays confirmed that the films are nearly stoichiometric in composition. The structural and surface morphological properties have been studied by X-ray diffraction, Scanning electron microscopy and Atomic force microscope techniques. X-ray diffraction study reveals a cubic structure with preferential orientation along (111) direction. The dependency of structural parameters such as crystallite size, strain and dislocation density with different bath temperatures for CdSe thin films are calculated. X-ray peak broadening was used to evaluate the crystallite size and lattice strain by the Williamson–Hall plots. Optical properties are studied by photoluminescence spectra which shows blue shift in peak position and reduction in luminescence intensity were observed for films deposited at different bath temperatures.