Influence of annealing temperature on the structural and anti-corrosion characteristics of sol–gel derived,spin-coated thin films

Recently, an aqueous particulate sol–gel process using metallic chloride precursors was introduced to synthesize zirconium titanate. In this paper, the effect of annealing temperature on the structural and corrosion protection characteristics of spin-coated thin films obtained from this sol–gel system was investigated. Based on scanning electron microscopy, transmission electron microscopy, atomic force microscopy, and spectroscopic reflectometry studies, it was found that the flatness and thickness of the thin films were decreased by increasing the annealing temperature. Also, the corrosion protection of stainless steel AISI 316L provided by the prepared coatings, as analyzed by electrochemical potentiodynamic polarization experiments in a simulated body fluid, was improved in this order: 500 °C-annealed sample<900 °C-annealed sample<700 °C-annealed sample, attributed to a compromise between the defect density and the adhesion of the films to the substrate.     

A New Approach for Error Rate Analysis of Wide-Band DSSS-CDMA System with Imperfect Synchronization Under Jamming Attacks

Most of the researches on error rate analysis of direct sequence spread spectrum (DSSS-CDMA) systems assume that the synchronization is perfect. However, in practice, the synchronization is often imperfect due to various effects of channel parameters such as noise and fading. The degree of imperfection further increases due to jamming attacks. The present study, therefore, derives new expressions to compute the probability of error in DSSS-CDMA systems under imperfect synchronisation. It is assumed that the channel is wideband and is subjected to various jamming attacks. A new parameter, called as probability of successful synchronization, was introduced which includes the effects of both the probability of false alarm and detection under fast and slow jammers. Monte Carlo simulations were conducted in MATLAB to establish the validity of the derived mathematical expressions.

     

70—THE MECHANICS OF SELF-PLYING STRUCTURES. PART II: MULTIFILAMENT STRANDS

Analyses of the mechanics of self-plying structures are presented for multi-filament component strands, and an account is given of the experimental verification of theoretical predictions, made by means of the use of nylon multifilament model yarns.     

Incorporating Economy and Long-term Inflow Forecasting Uncertainty into Decision-making for Agricultural Water Allocation during Droughts

Optimizing water allocations for the agricultural sector, the main water consumer, at the beginning of a period of drought is essential. However, long-term inflow forecasting, with its high uncertainty, is a necessary component of the allocation process. This paper presents a methodology that combines this uncertainty with economic factors to determine water allocation. The following models were developed and linked: optimization of agricultural water allocation under water scarcity, long-term flow forecast and quantification of forecast uncertainties. The approach coordinates economic values of water with system operational requirements. The Zayandeh Rud dam and irrigation system was selected to explore the methodology of this research.     

Design of X‐band Moreno cross‐guide coupler based on superformula curves

This article deals with the design of Moreno cross‐guide couplers based on supershapes for X‐band applications. Crossed‐waveguide couplers are mainly used due to their compact structures. In these couplers, cross‐aperture structures are usually employed to offer flat coupling and high isolation. In the present article, the possible shapes for apertures and metal inserts that can be derived by the superfomula curves are explored and the effects of variations of superformula parameters are investigated on the performance of Moreno coupler. Finally, the proposed Moreno coupler is validated through fabrication and measurement. The experimental validation shows an excellent agreement with the simulated results. In the frequency range from 8 to 12.5 GHz, the measured coupling value changes from 18.8 to 20.8 dB and the directivity is better than 38 dB and 29 dB from 8 to 11 GHz and 11 to 12.5 GHz, respectively. The results are valuable for the design and evaluation of broadband high directive waveguide couplers.     

Velocity‐free attitude stabilization with inertial vector measurements

This paper deals with the attitude stabilization problem of a rigid body, where neither the angular velocity nor the attitude is used in the feedback; only body‐referenced vector measurements are needed. The proposed control scheme is based on an angular velocity observer‐like system relying solely on vector measurements. The proposed controller ensures almost global asymptotic stability and provides some interesting performance properties through an appropriate tuning of the control gains. The performance and effectiveness of the proposed control scheme are illustrated via simulation results where the control gains are adjusted using a nonlinear optimization. Copyright © 2015 John Wiley & Sons, Ltd.     

Ultra clean coal production by microwave irradiation pretreatment and sequential leaching with HF followed by HNO3

The goal of this project was to develop and test an innovative coal cleaning process to reduce the ash content of coal and produce ultra clean coal (UCC). Coal samples that were prepared from concentrates of Iran's Zirab and Tabas coal preparation plants were found to have initial ash contents of 8.31 and 10.36%, respectively. These coals were demineralized with the combination of microwave irradiation pretreatment and dual acid leaching processes with HF followed by HNO₃ in a batch reactor. For samples that were microwaved and leached with HF, the reduction in ash ranged from 22 to 76% and from 22 to 82% for Zirab and Tabas coal samples, respectively, depending on leaching conditions. Microwave irradiation pretreatment had a positive effect on demineralization with HF, especially for the coarse size fractions. For the fine size fractions, reduced leaching times were found to enhance the effect of microwave irradiation. The microwave-irradiated, HF-leached product was leached further using a 1.4 M HNO₃ solution at a leaching temperature of 65 °C to remove fluoride sediments and pyritic sulfur. The ash content of the Zirab coal was reduced from 2.57 to 0.69% by leaching with the HNO₃ solution for 1 h. The ash content of the Tabas coal was reduced from 2.44 to 0.39% by leaching with the HNO₃ solution for 3 h. The results show that microwave irradiation can be considered as a pretreatment process in the chemical leaching of coal to produce UCC.