Selective CO oxidation over promoted Au/γ-Al2O3 catalysts in the presence of CO2 and H2O in the feed

In this work, the effect of promoter type (Mg, Mn, Ce, Co, Fe and Ni) on selective CO oxidation performance of Au/γ-Al₂O₃ was studied with the realistic feed stream containing CO₂ and H₂O. The effects of Au loading, promoter loading, reaction temperature and the feed composition were also investigated. It was found that MgO was the best promoter in the presence of CO₂ and H₂O, and 1.25 wt.% Mg was sufficient for promotion. The CO conversion decreased with the addition of CO₂ while the presence of H₂O had some positive effects.     

A novel indicator system for catalytic spectrophotometric determination and speciation of inorganic selenium species (Se(Ⅳ), Se(Ⅵ)) at trace levels in natural lake and river water samples

A novel catalytic kinetic method is proposed for the determination of Se(Ⅳ), Se(Ⅵ), and total inorganic selenium in water based on the catalytic effect of Se(Ⅳ) on the reduction of Celestine blue by sodium sulfide at pH 7.0 phosphate buffer. The fixed-time method was adopted for the determination and speciation of inorganic selenium. Under the optimum conditions, the two calibration graphs are linear with a good correlation coefficient in the range 2-20 and 20-200 μg·L-1 of Se(Ⅳ) for the fixed-time method a...     

A novel material for lightweight concrete production

This paper presents the results of an experimental study on the effects of using recycled waste expanded polystyrene foam (EPS), as a potential aggregate in lightweight concrete. In this study, thermally modified waste EPS foams have been used as aggregate. Modified waste expanded polystyrene aggregates (MEPS) were obtained by heat treatment method by keeping waste EPS foams in a hot air oven at 130 °C for 15 min. Effects of MEPS aggregate on several properties of concrete were investigated. For this purpose, six series of concrete samples were prepared. MEPS aggregate was used as a replacement of natural aggregate, at the levels of 0%, 25%, 50%, 75%, and 100% by volume. The density of MEPS is much less than that of natural aggregate; MEPS concrete becomes a lightweight concrete with a density of about 900–1700 kg/m³. The 28-d compressive strengths of MEPS concrete range from 12.58 MPa to 23.34 MPa, which satisfies the strength requirement of semi-structural lightweight concrete.     

A deep learning approach with Bayesian optimization and ensemble classifiers for detecting denial of service attacks

Detecting malicious behavior is important for preventing security threats in a computer network. Denial of Service (DoS) is among the popular cyber attacks targeted at web sites of high‐profile organizations and can potentially have high economic and time costs. In this paper, several machine learning methods including ensemble models and autoencoder‐based deep learning classifiers are compared and tuned using Bayesian optimization. The autoencoder framework enables to extract new features by mapping the original input to a new space. The methods are trained and tested both for binary and multi‐class classification on Digiturk and Labris datasets, which were introduced recently for detecting various types of DDoS attacks. The best performing methods are found to be ensembles though deep learning classifiers achieved comparable level of accuracy.     

Enhancing community of inquiry and reflective thinking skills of undergraduates through using learning analytics-based process feedback

This research aims to investigate into the effect of using learning analytics (LA)-based process feedback on students' perceptions of community of inquiry (teaching, social and cognitive presence) and their reflective thinking skills. By using a mixed-method research approach (QUAN + qual), this study was conducted as an experimental design with the pretest–posttest control group. A total of 104 university students who were randomly assigned to the experiment group (EG) and control group (CG) were recruited in this study. The procedure was conducted within the scope of the computing course based on the flipped classroom (FC) model. While the participants in the EG received LA-based process feedback which shows their LA results in a weekly manner, those in the CG did not get any LA-based process feedback. The data were collected through the Community of Inquiry Scale, the Reflective Thinking Scale and a semi-structured student opinion form. The findings indicated that sending feedback including the students' LA results had a statistically significant effect on the students' perceptions of community of inquiry and reflective thinking skills. Based on the findings of the study, several recommendations for teachers, instructional designers and researchers have been made.     

Ferromagnetic Resonance Study of Fe/Cu Multilayer Thin Film

Fe/Cu/Fe multilayer thin film was grown on Si (100) substrate by using magnetron sputtering technique at room temperature. Dynamic and static magnetisations of the film have been investigated using ferromagnetic resonance (FMR) and vibrating sample magnetometer (VSM) techniques in the temperature range of 10–300 K. From the room-temperature in-plane FMR measurements, a growth-induced uniaxial magnetic anisotropy was observed. Out-of-plane FMR measurements exhibited a large magnetic anisotropy due to a large saturation magnetisation of Fe. A computer code was written to simulate the experimental FMR data and to obtain the magnetic parameters of the Fe/Cu/Fe multilayer thin film. g value, effective magnetisation, uniaxial anisotropy field and perpendicular anisotropy constant from the fitting of the angular dependence of the resonance field at both the in-plane and out-of plane geometries were determined. The exchange bias effect was observed from the low-temperature VSM measurements. The saturation magnetisation and coercive field decrease with increasing temperature due to the increase of the thermal fluctuations.     

Semi fractal three leaf clover‐shaped CPW antenna for triple band operation

This article presents a unique and compact coplanar waveguide (CPW) antenna that exhibits triband operation with circular polarization. The single antenna was designed to operate simultaneously in the following bands: WiMAX (3.3–3.6 GHz), wireless local area network (WLAN) (5.15–5.825 GHz), ITS (5.795–6.400 GHz), and ITU‐R (7.725–8.5 GHz). The realization of the triband antenna was achieved by using two semi fractal ring patches resembling the shape of a three leaf clover, and by introducing a pair of symmetrical L‐shaped slits in its ground plane. The antenna's physical parameters were investigated to fully understand their affect on the antenna's performance. The salient parameters obtained from this analysis enabled the optimization of the antenna's overall characteristics. The design concept was confirmed by fabricating the antenna prototype and measuring its characteristics. The proposed antenna has dimensions of 20 × 20 × 1 mm³. Measured results show the antenna exhibits circular polarization in WiMAX and ITU‐R bands, and linear polarization in the WLAN band. The antenna radiates omnidirectionally in the H‐plane, and approximately bidirectionally in the E‐plane. In addition, the antenna presents stable gain over the triband. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:413–418, 2015.     

Mobile robot localization based on PSO estimator

Localization is fundamental to autonomous operation of the mobile robot. A particle filter (PF) is widely used in mobile robot localization. However, the robot localization based PF has several limitations, such as sample impoverishment and a degeneracy problem, which reduce significantly its performance. Evolutionary algorithms, and more specifically their optimization capabilities, can be used in order to overcome PF based on localization weaknesses. In this paper, mobile robot localization based on a particle swarm optimization (PSO) estimator is proposed. In the proposed method, the robot localization converts dynamic optimization to find the best robot pose estimate, recursively. Unlike the localization based on PF, the resampling step is not required in the proposed method. Moreover, it does not require noise distribution. It searches stochastically along the state space for the best robot pose estimate. The results show that the proposed method is effective in terms of accuracy, consistency, and computational cost compared with localization based on PF and EKF.     

Metamaterial‐based antennas for integration in UWB transceivers and portable microwave handsets

Two planar antennas based on metamaterial unit‐cells are designed, fabricated, and tested. The unit‐cell configuration consists of H‐shaped or T‐shaped slits and a grounded spiral. The slits essentially behave as series left‐handed capacitance and the spiral as a shunt left‐handed inductance. The unit‐cell was modeled and optimized using commercial 3D full‐wave electromagnetic simulation tools. Both antennas employ two unit‐cells, which are constructed on the Rogers RO4003 substrate with thickness of 0.8 mm and ε_r = 3.38. The size of H‐shaped and T‐shaped unit cell antennas are 0.06λ₀ × 0.02λ₀ × 0.003λ₀ and 0.05λ₀ × 0.02λ₀ × 0.002λ₀, respectively, where λ₀ is the free–space wavelength. The measurements confirm the H–shaped and T–shaped unit‐cell antennas operate across 1.2–6.7 GHz and 1.1–6.85 GHz, respectively, for voltage standing wave ratio (VSWR) < 2, which correspond to fractional bandwidth of ～140% and ～ 145%, respectively. The H‐shaped unit‐cell antenna has gain and efficiency of 2–6.8 dBi and 50–86%, respectively, over its operational range. The T‐shaped unit‐cell antenna exhibits gain and efficiency of 2–7.1 dBi and 48–91%, respectively. The proposed antennas have specifications applicable for integration in UWB wireless communication systems and microwave portable devices. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:88–96, 2016.     

The effects of different cement dosages, slumps and pumice aggregate ratios on the compressive strength and densities of concrete

Compressive strengths of concretes made up of mixtures of pumice aggregate (PA) and normal aggregate were measured. To determine the effect of PA ratio, different cement dosage and slumps on the compressive strength of concrete, (1) 25%, 50%, 75% and 100% pumice ratios were used instead of normal aggregate by volume, (2) 200, 250, 350, 400 and 500 kg/m³ cement dosages were used and (3) 3±1, 5±1 and 7±1 cm slumps were also used in this study.The analysis of the test results leads to the conclusion that PA decreased the density of concretes up to 41.5% and reductions occurred due to the increase of the PA ratio in the mixes. With the increase of cement dosage in the mixes, both density and compressive strength of concretes increased up to 3.2% and 265%, respectively, when compared to the control sample that contain 200 kg/m³ cement dosage. The effect of the slump on the density and compressive strength was varied. Elasticity moduli were decreased with an increase of PA ratio and increased with an increase of cement dosage. Water absorption improved with an increase of cement content.