Advanced control of grid-connected inverters for proton exchange membrane fuel cell system

Voltage support is one of the most important issues for operating grid-connected inverters under grid faults. Many control strategies have been addressed in literature, but most of them focus on the voltage support control without considering issues of power quality due to voltage harmonics. In order to sort out the drawback, a novel advanced control strategy is presented in this paper. It is able to provide the voltage support function. Meanwhile, the power quality is improved by regulating the control coefficients. The time-domain simulation and experimental results are provided to evaluate the conventional and proposed control strategies. The results show that the total harmonic distortion of PCC voltage can be reduced from 9.35% to 2.88% with the proposed solution. Meanwhile, the voltage support is also achieved, which verify the effectiveness of the proposed solution.     

Risk factors analysis: Work-related musculoskeletal disorders among male traffic policemen using high-powered motorcycles

IntroductionThe occupational safety and health issues for police riders and other professional riders are often related to ergonomic hazards and risks. The purpose of this research was to identify the factors that contribute to the health effects in developing work-related musculoskeletal disorders (WMSDs) among male traffic policemen using high-powered motorcycles.Materials and methodsA cross-sectional study was conducted using 137 police riders. A set of questionnaires including the Standardised Nordic Questionnaire (SNQ) and human vibration meter (Svantek 106) was used in this study.ResultsThe prevalence of WMSDs was 67.9%. Multiple logistic regression analysis revealed that the duration of riding a motorcycle (OR = 0.175, 95% CI:0.052, 0.581), years of service (OR = 0.152, 95% CI: 0.040, 0.567), and hand-arm vibration, HAV (OR = 3.053, 95% CI: 1.126, 8.280) were significant risk factors for the prevalence of WMSDs.DiscussionThe majority of riders reported symptoms of WMSDs within the past 12 months. Riding duration, years of service, and hand-arm vibration (HAV) were found to be the most important risk factors for WMSDs in this rider group. The results highlight that in the context of ergonomic interaction, high-powered motorcycles and the police riders are not a good fit. Hence, further study is needed to improve the safety and health of the police riders.     

Behavioral Intrusion Prediction Model on Bayesian Network over Healthcare Infrastructure

Due to polymorphic nature of malware attack, a signature-based analysis is no longer sufficient to solve polymorphic and stealth nature of malware attacks. On the other hand, state-of-the-art methods like deep learning require labelled dataset as a target to train a supervised model. This is unlikely to be the case in production network as the dataset is unstructured and has no label. Hence an unsupervised learning is recommended. Behavioral study is one of the techniques to elicit traffic pattern. However, studies have shown that existing behavioral intrusion detection model had a few issues which had been parameterized into its common characteristics, namely lack of prior information (p (θ)), and reduced parameters (θ). Therefore, this study aims to utilize the previously built Feature Selection Model subsequently to design a Predictive Analytics Model based on Bayesian Network used to improve the analysis prediction. Feature Selection Model is used to learn significant label as a target and Bayesian Network is a sophisticated probabilistic approach to predict intrusion. Finally, the results are extended to evaluate detection, accuracy and false alarm rate of the model against the subject matter expert model, Support Vector Machine (SVM), k nearest neighbor (k-NN) using simulated and ground-truth dataset. The ground-truth dataset from the production traffic of one of the largest healthcare provider in Malaysia is used to promote realism on the real use case scenario. Results have shown that the proposed model consistently outperformed other models.     

The stability of electrical characteristics of Ti/n-Si/Ag,Ti/n-Si/Cu and Ti/n-Si/AgCu diodes prepared under the same conditions with respect to increasing aging time

The purpose of this study is to fabricate Ti/n-Si/Ag, Ti/n-Si/Cu and Ti/n-Si/AgCu Schottky type diodes and to investigate the effects of aging time on the diode parameters such as ideality factor, barrier height, series resistance, interface state density and rectification ratio. High purity titanium (Ti) metal was deposited on the back side of the n-Si semiconductor and then the Ti/n-Si junction was annealed at 420 °C in nitrogen atmosphere. This junction showed ohmic behavior. To fabricate rectifier contacts, Ag, Cu metals and AgCu alloy have been evaporated on the other polished surface of n-Si with Ti ohmic contact. Ag and Cu ratios in the AgCu alloy which are used in the process of preparing the Schottky contact were taken in equal weights. Thus, Ti/n-Si/Ag, Ti/n-Si/Cu and Ti/n-Si/AgCu Schottky type diodes were prepared under the same conditions. The current-voltage (I-V) characterization of Ti/n-Si/Ag, Ti/n-Si/Cu and Ti/n-Si/AgCu diodes were immediately made at room temperature in dark conditions. To investigate the effect of aging time, the I-V measurements of the diodes have been repeated after 1, 7, 15, 30 and 90 days. Characteristic parameters of the diode were calculated from the I-V measurements which are taken with respect to aging time. The results were compared. From these results, it can clearly be seen that the electrical characteristics of diode which is made from AgCu alloy are more stable than other two diodes.     

Optical simulations for fire detectors

In this paper, we present the method for optical simulation that we have successfully applied to new designs of fire detectors, with a focus on optical scattering smoke detectors. Our simulation is based on a commercially available software tool for non-sequential ray-tracing and on measurements of the differential scattering cross-section of test fire aerosols. With optical simulation, we succeeded in predicting the main characteristics of an optical scattering smoke detector, the zero-smoke signal and the response signal to test fires with sufficient precision.     

Ag-doped TiO2 photocatalysts with effective charge transfer for highly efficient hydrogen production through water splitting

The development of efficient metal doped semiconductors for solar energy harvesting to produce hydrogen has attracted significant attention. Herein, the H₂ generation over Ag-doped TiO₂ photocatalyst, synthesized using a simple and cost-effective method based on chemical reduction, was reported. The Ag/TiO₂ exhibited an absorption peak in the visible region and the reduction of the bandgap to 2.5 eV due to surface plasmonic resonance (SPR). X-ray photoelectron spectroscopy revealed the presence of oxygen vacancies and 11% of Ag in Ti–Ag–O phase. The effect of reaction time and photocatalyst loading in the absence and presence of sacrificial reagents (alcohols and sulfur) on water splitting was studied and compared the activity of Ag/TiO₂ with that of bare TiO₂. The H₂ production rate of 23.5 mmol g⁻¹ h⁻¹ (with an apparent quantum yield of 19%), over 1.5Ag/TiO₂, was the highest ever reported so far. The observed higher activity could mainly be attributed to the existence of oxygen vacancies and the Ti–Ag–O phase. The photocatalyst was stable for three consecutive cycles in both the presence and absence of sacrificial reagents. This study offers new insights into the rational design of metal-support hybrid structures for hydrogen production through photocatalytic water splitting.     

Opposite effects of self-growth amorphous carbon and carbon nanotubes on the reforming of toluene with Ni/α-Al2O3 for hydrogen production

Ni-based catalysts are prone to be deactivated by carbon deposition. This study aims to investigate the influence mechanism of different types of carbon deposition on the activity of Ni/α-Al₂O₃ catalyst at various steam-to-carbon (S/C) ratios during steam reforming of toluene for hydrogen production. At a low S/C ratio of 1, the catalytic activity of Ni/α-Al₂O₃ was inhibited due to the covering and blocking of Ni active sites by the formation of amorphous carbon on the Ni surface. While at a high S/C ratio of 3, more than 80 wt% of carbon deposition was found to be self-growth carbon nanotubes (CNTs) with an average diameter of around 15 nm. The activity of Ni/α-Al₂O₃ in steam reforming of toluene was unusually promoted, which can be attributed to the tip-growth mechanism of CNTs, whereby the Ni particles migrated to the tip or the surface of CNTs, resulting in the improved active site dispersion.     

Surface characterization of carbon fibres and interfacial properties of carbon fibre composites

The surface characteristics of carbon fibres treated by electrochemical oxidation have been determined, and the effect of these properties on the interfacial adhesive strength (interlaminar shear strength (ILSS) and transverse flexural strength) of epoxy-matrix composites investigated. The surface properties of the carbon fibres were dependent on the nature of the electrolyte used during the electrochemical oxidative treatment. Use of a basic electrolyte resulted in an improvement of composite ILSS and transverse flexural strength due to an increase in the number of surface functional groups. On the other hand, using an acid electrolyte resulted in the ILSS increasing with the number of surface functional groups, while the transverse flexural strength decreased for composites in which the carbon fibres had a high surface oxygen content. It is concluded that the weak boundary layer derived from fissures on the surface of carbon fibres treated in an acid electrolyte decreased the transverse flexural strength.     

Conductivity enhancement by controlled percolation of inorganic salt in multiphase hexanoyl chitosan/polystyrene polymer blends

Hexanoyl chitosan and polystyrene blends are immiscible by the elucidation of the glass transition temperature (T_g) as well as the viscometric and morphological analyses. Selective localization of the lithium salt in hexanoyl chitosan phase as the percolation pathway enhanced the conductivity in the blends as compared to the neat hexanoyl chitosan. The ionic conductivity of a polymer electrolyte is described by σ = enμ. Thus, estimation of charge carrier density (n) and mobility (μ) is important in order to assess the performance. In this work, these parameters are calculated using impedance spectroscopy and FTIR.