Aromatic liquid crystalline copolyesters with low Tm and high Tg: Synthesis,characterization, and properties

In this study, a series of aromatic copolyesters P‐BPAx with lower melting temperature and higher glass transition temperature derived from hydroxybenzoic acid (HBA), 6‐hydroxy‐2‐naphthoic acid (HNA), bisphenol A (BPA) and terephthalic acid (TA) were synthesized via melt polymerization. The copolyesters were characterized by FTIR, solid state ¹³C NMR, DSC, TGA, polarized optical microscopy, X‐ray diffraction, and rheometry measurements. With addition of BPA, the resulting copolyester's melting temperature decreased from 260 to 221°C and its glass transition temperature increased from 70 to 135°C, compared with the parent copolyester P‐HBA70 (HBA/HNA copolymer). With exception of copolyester P‐BPA5.0 (225–280°C), the copolyesters could maintain liquid crystalline behavior in a broad temperature range from 230°C to higher than 410°C. The ability to form nematic liquid crystalline phase disappeared when BPA concentration became higher than 15 mol %. X‐ray diffraction analysis showed crystallinity decreased as the BPA content increased. A slightly distorted O" and a substantially distorted O′ orthorhombic phase was observed for P‐BPA2.5. Upon annealing at 220°C, the O" phase disappeared and the O′ phase became stronger gradually. Rheology study data showed the ability to process the copolyesters improved in those compositions containing <2.5 mol % BPA. Continuing to increase concentrations of BPA, they became intractable. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40487.     

Effect of spatial variability on arma modelling of ground motion

The Autoregressive-Moving Average (ARMA) process is an efficient method for describing ground motion through a small number of parameters. By relating these parameters to physical variables, it is possible to reasonably predict the ground motion of a site where no strong motion data has been recorded. In this paper, the effects of spatial variability on modelling strong ground motion with ARMA processes are investigated. The cross-correlation between variance stabilized series is analyzed for sites located in Mexico City. Also, the correlation and distribution of modelling parameters in the Smart-1 dense array is investigated.     

Performance of energy-efficient rice mills

ABSTRACT

This study reports the energy-efficient performance of three different brands of rice polisher machines operating at different rice mills. The observations of feed screws, sieves and cams have been recorded and we have analysed the chemical composition, microstructure, hardness of cams of different rice mills and given solutions for the performance enhancement of cams. Our objective is to enhance the production of rice variety with quality characteristics and general appearance as required by the consumers.     

Molecular mechanism of temporal physico/chemical changes that take place during imidization of polyamic acid: Coupled real-time rheo-optical and IR dichroism measurements

Multiple overlapping physical and chemical changes often take place during casting/drying and imidization from PMDA-ODA polyamic acid precursors from cast solutions. To shed light into details of these complex phenomena, we designed a unique real time measurement system that combines true stress, true strain, in-plane birefringence and temperature with polarized ultra-rapid scan FT-IR spectrometry (URS-FT-IR). At the early stages of heating (21°C–130 °C), initially isotropic solution cast film was observed to develop stress and birefringence as the solvent decomplexed and evaporated without showing any imidization as it was held in uniaxially constrained state. At a temperature around 130 °C, the onset of imidization reaction was detected while the stress went through a maximum. Beyond this stage, the evaporation of bound solvent and chemical conversion was observed to take place simultaneously and this is accompanied by a steady increase in birefringence. As the majority of the bound solvent evaporated, the stress and birefringence values started leveling off at long times.     

A novel differential evolution application to short-term electrical power generation scheduling

This paper proposes a new way of applying a differential evolution algorithm to short-term electrical power generation scheduling. Traditionally, the problem is divided into two subproblems. An evolutionary algorithm, which works with binary decision variables, is applied to the first subproblem to find a low cost scheduling of power generators, satisfying some operational constraints. Then, the lambda-iteration method, is used to calculate the power generated by the online generators. In this study, the problem is treated as a whole for the first time in literature and an application of a real-valued differential evolution algorithm is proposed. This approach eliminates the use of an iterative local search technique such as lambda-iteration in all solution evaluations. Through comparisons with results from literature, it is shown that the proposed method achieves a similar solution quality to existing methods, without needing the time consuming lambda-iteration step. Finally, the new approach is applied to real-world data from the Turkish interconnected power network.     

An improved tank in series model for PEMFC

This study presents an improved Tank in Series Reactor (TSR) Proton Exchange Membrane (PEM) fuel cell model with mass and energy balance equations accounting for evaporation and condensation in cathode channels. The TSR model includes the modified charge balance equation suitable for potentiostatic fuel cell operation mode. Polarization curves calculated with the improved model agree with experimental data from the literature. The developed TSR model is able to predict the limiting two-dimensional profiles in PEMFC. Simulation results illustrate the influence of co-current and counter current mode on PEM fuel cell performance.     

Toward Sustainable Water Management in the Southeastern Anatolia Project (GAP)

Being the largest and the most comprehensive regional development effort ever undertaken in Turkey, the Southeastern Anatolia Project (GAP) will constitute the primary driving force for the socioeconomic development of the region and consequently of Turkey. Owing to its multipurpose nature, GAP necessitates, on the one hand, discreet conduct in meeting the demands on time so as to spur the rapid development of the region through prudent management of water, and on the other hand, careful consideration, for the sake of sustainable development, of imminent as well as long-term environmental impacts in order for the project to be viable. An integrated basin-wide approach leading to, among other things, quantity and quality management, prioritybased allocation, conservation, conjunctive use of various resources of water, maintenance of facilities as well as inter- and intra-institutional arrangements, has been adopted from the outset, and is being revised and improved in as profound a way as possible as the project progresses.     

On line measurement of crystallinity of nylon 6 nanocomposites by laser Raman spectroscopy and neural networks

A neural network is trained to estimate the unknown crystallinity and temperature of Nylon 6 and its nanocomposites while the material is undergoing cooling at a fixed rate. The innovation of the work is that the full spectrum captured by the laser Raman spectroscope is used to train a neural network for estimation of crystallinity and temperature. The small‐angle light scattering (SALS) and differential scanning calorimetry (DSC) data were used to provide the training examples for the neural network. Results indicate that the neural network can provide reliable estimates of the crystallinity and temperature provided that there is a sufficient number of training data available. Neural network methodology is also efficient in establishing the crystallization–temperature relationship as a function of cooling rate and demonstrates the heterogeneous nucleation effect of nanoclay in the nylon 6 matrix. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 474–483, 2004     

Performance analysis of a hybrid DS/SFH CDMA system usinganalytical and measured pico cellular channels

This paper presents the throughput and delay analysis of a packet-switched code division multiple access (CDMA) network based on the hybrid direct sequence (DS)/slow frequency hopping (SFH) spread-spectrum multiple access (SS MA) technique with Q-, B-, and D-PSK modulation using analytical and measured pico cellular channels. The performance of the hybrid DS/SFH, DS, and SFH multiple access techniques have been compared in a pico cellular personal communications network (PCN) environment. Multipath and multiple access interference are considered. The performance is evaluated for a given delay spread and a fixed bandwidth. The effects of forward error correction (FEC) coding and diversity techniques, such as selection diversity and maximal ratio combining on the performance, are also investigated