Bifurcation control in a delayed two-neuron fractional network

The issue of bifurcation control for a delayed fractional network involving two neurons is concerned. Delay-dependent stability conditions and the bifurcation point are established by discussing the associated characteristic equation of the proposed network. Then, a delayed feedback controller is firstly designed to stabilize the Hopf bifurcation, and desirable dynamics is achieved. It is indicated that the designed controller is extremely effective which can postpone the onset of bifurcation by carefully selecting the feedback gain. Finally, simulation results are given to verify the efficiency of the theoretical results.     

Reduction of EMI in AC Drives Through Dithering Within Limited Switching Frequency Range

In this paper, a method is presented to reduce electromagnetic (EM) emissions in AC drives. This method is applicable to many AC drives. It is proposed to dither the switching frequency of the power devices of an inverter in a pseudorandom way to spread out the emitted RF energy over a larger frequency range. The proposed method requires only software changes. Practical constraints to implement the frequency dithering approach are discussed. Simulation and measurement results show an improvement of more than 10 dB. The proposed method also converts specific spikes in the long-wave range from narrowband to broadband noise, which results in less stringent EM emission requirements for many applications.     

Optimization approaches and climates investigations in NZEB—A review

The conception of net zero energy buildings (NZEB) has been introduced to limit energy consumption and pollution emissions in buildings. Classification of NZEB is based on renewable energy (RE) supply options, energy measurement process, RE-sources location, and balances whether are energetic or exergetic. In general, it is traditionally agreed that there are three main steps to reach the NZEB performance, starting through the use of passive strategies, energy efficient technologies, and then RE generation systems. Then, these three steps could be accompanied with the smart integration of advanced efficient energy technologies. A state of the art shows that the main ZEB studies are related to: energy savings, reduce electric bills, energy independence, pollution reduction, and occupants comfort, in addition, others are more interested in the aesthetic aspect by combining modern technologies with innovations to achieve high energy and sustainability performance. Building optimization is a promising technique to evaluate NZEB design choices; it has been adopted to choose the perfect solution to reach the zero energy performance through the optimization of an objective function related to energy (thermal loads, RE generation, energy savings) and/or environment (CO₂ emissions) and/or economy (life-cycle cost (LCC), net-present value (NPV), investment cost). This paper starts by presenting the global energetic and pollution challenges the world faces. Moreover, it shows, to the best to the author’s knowledge, the existing NZEB definitions and the corresponding case studies investigated in 8 different climatic zones (humid continental, humid subtropical, Mediterranean, moderate continental, moderate continental, marine west coast, tropical, semi-arid and hot), the paper also focus on the importance to treat each climate separately. Even in the same country, two or more climates may co-exist. NZEBs drawbacks are also presented. Furthermore, different optimization problems are reviewed in the last section. Building energy optimization methods are employed to obtain the ideal solution for specific objective functions which are either related to energy, and/or environment and/or economy. Optimization variables are distributed between passive and/or RE generation systems. Finally, a table summarizing the most commonly used electric and thermal RE applications which yield to the zero energy balance in each climate, as well as three flowcharts are presented to summarize the whole three-stage procedure, to reach NZEB, starting from building designing, passing through the optimization procedure, and lastly categorizing the zero energy balance.     

Experimental analysis of a DC bucking motor blockinggeomagnetically induced currents

An experimental study investigates the performance of a DC bucking motor for the blocking of geomagnetically induced currents (GICs) within a 3 kVA/416 V three-phase distribution feeder. This blocking method consists of connecting a separately excited DC motor between neutral and ground of a Y-grounded transformer consisting of a bank of three single-phase transformers. Losses and currents of the transformer and the blocking device are measured at no-load, rated-load, unbalanced-load and line-to-neutral short circuit conditions without and with GICs. Thereafter, the DC, AC and total λ-i characteristics of one single-phase transformer of the above-mentioned transformer bank are simultaneously measured using an arbitrary waveform generator, a power amplifier and a digital data acquisition network. These λ-i characteristics (where the DC bias current is a parameter) are then used to model a single-phase transformer under DC bias current conditions (e.g., assumed GICs) and to calculate voltages and currents of a single-phase transformer when subjected to GICs. The simulated signals are then compared with measured time functions     

Early dropout prediction using data mining: a case study with high school students

Early prediction of school dropout is a serious problem in education, but it is not an easy issue to resolve. On the one hand, there are many factors that can influence student retention. On the other hand, the traditional classification approach used to solve this problem normally has to be implemented at the end of the course to gather maximum information in order to achieve the highest accuracy. In this paper, we propose a methodology and a specific classification algorithm to discover comprehensible prediction models of student dropout as soon as possible. We used data gathered from 419 high schools students in Mexico. We carried out several experiments to predict dropout at different steps of the course, to select the best indicators of dropout and to compare our proposed algorithm versus some classical and imbalanced well‐known classification algorithms. Results show that our algorithm was capable of predicting student dropout within the first 4–6 weeks of the course and trustworthy enough to be used in an early warning system.     

Step‐up/step‐down DC‐DC converter with near zero input/output current ripples

A novel single switch two diode wide conversion ratio step down/up converter is presented. The proposed converter is derived from the conventional single‐ended primary inductor converter (SEPIC) topology, and it can operate as a capacitor‐diode voltage multiplier, which offers simple structure, reduced electromagnetic interference (EMI), and reduced semiconductor voltage stress. The main advantages of the proposed converter are the continuous input/output current, higher voltage conversion ratio, and near‐zero input and output current ripples compared with the conventional SEPIC converter. The absence of both a transformer and an extreme duty cycle permits the proposed converter to operate at high switching frequencies. Hence, the overall advantages will be: higher efficiency, reduced size and weight, simpler structure and control. The theoretical analysis results obtained with the proposed structure are compared with the conventional SEPIC topology. The performance of the proposed converter is verified through computer simulations and experimental results. Copyright © 2012 John Wiley & Sons, Ltd.     

Soil management enhancing hydrocarbon biodegradation in the polluted Kuwaiti desert

Oil-polluted Kuwaiti desert samples, exposed to the open air, were subjected to specific types of management, once every 2 weeks, throughout a year; control samples were not treated. The total amounts of extractable alkanes from the control samples remained fairly constant during the dry hot months, but decreased during the rainy months reaching, after 1 year, slightly more than one-half of the amount at zero time. This result demonstrates the self-cleaning of the Kuwaiti desert and the essential role of moisture in this process. Out of the eight types of management studied, the repeated fertilization of the polluted sample with 3% KNO3 solution was most efficient, reducing the extractable alkanes after 1 year to about one-third of zero reading. Repeated fertilization with treated sewage effluent was inhibitory to alkane biodegradation, probably because of increasing soil acidity. The latter inhibitory effect was annulled by liming. Repeated irrigation with 3% NaCl solution was inhibitory, but 1% NaCl solution slightly promoted alkane biodegradation. The various samples contained 10(10)-10(11) oil-utilizing bacteria/g soil, predominantly Bacillus, Pseudomonas, Rhodococcus and Streptomyces. Oil-utilizing fungi were much less frequent and were predominantly Aspergillus and Penicillium species. The microbial numbers varied not only according to the type of soil management but also to the season.