Dynamic model development and control for multiple‐output flyback converters in DCM and CCM

Multiple‐output flyback converters are widely used in switching power supplies due to their low component count and cost‐effective structure. The main problem of this structure is how to balance output voltages in different load conditions. This paper proposes a new approach for single‐input multiple‐output flyback converters operating in DCM and CCM by a small‐signal averaged model. The averaged model is derived by presenting the piecewise‐linear waveform for the inductor currents inside the converter. In DCM, the magnetizing current and currents through the output windings reach zero when the switch is turned off. In CCM, the magnetizing current of the converter is continuous over a switching interval and this possibility exists that only some of the output diodes completely conduct when the switch is off. The proposed model of the converter can be used in a wide range of operations within identical and non‐identical loading conditions. Using a laboratory prototype, several case studies and input‐to‐output transfer functions are considered to verify the proposed model. The controller design is performed for the both CCM and DCM, and then dynamic characteristics of the overall system are evaluated.     

A reconfigurable real-time neuromorphic hardware for spiking winner-take-all network

The central nervous system receives a vast amount of sensory inputs, and it should be able to discriminate and recognize different kinds of multisensory information. Winner-take-all (WTA) consists of a simple recurrent neural network carrying out discrimination of input signals through competition. This paper presents a real-time scalable digital hardware implementation of the spiking WTA network. The need for concurrent computing, real-time performance, proper accuracy, and the reconfigurable device has led to the field-programmable gate array (FPGA) as the target hardware platform. A set of techniques is employed to lessen memory and resource usage. The proposed architecture consists of multiprocessing elements, which share hardware resources between a specific number of neurons. We introduce a novel connectivity array for neurons (dedicated to the WTA network) to cut down memory usage. Also, a multiplier-less method in the neuron model and a novel tree adder in the synapse processing unit are designed to improve computational efficiency. The proposed network simulates 4,500 neurons in real time on a Xilinx Artix-7 FPGA, while a scalable architecture facilitates the implementation of up to 20,000 neurons on this device. The pipeline structure can guarantee real-time performance for large-scale networks. Based on simulation and physical synthesis results, the presented network mimics biological WTA dynamics and consumes efficient hardware resources.     

Production and Characterization of Gelatin Spherical Particles Formed via Electrospraying and Encapsulated with Polyphenolic Antioxidants from <Emphasis Type="Italic">Momordica charantia</Emphasis>

This study dealt with the production and characterization of gelatin nanospheres and encapsulation with Momordica charantia, commonly known as bitter gourd fruit vegetable extract (BGE). The impact of encapsulation and increasing the encapsulate loading on various physiochemical characteristics of gelatin polymeric entities as well as antioxidative attributes of BGE was studied. Nanospheres were formed via an electrospraying process conducted at 20 kV, 0.5 mL/h, and 10 cm of voltage, flow rate, and emitter/collector distance, respectively. The spherical beads were encapsulated with BGE at 5 to 15% (w/w%) loading rate. Morphological analysis through scanning electron microscopy (SEM) and atomic force microscopy (AFM) demonstrated that nanospheres could be successfully produced. Furthermore, nanosphere encapsulation of the extract was demonstrated in transmission electron microscope (TEM) micrographs. Spectroscopic analysis indicated no chemical interactions between core and wall materials. The thermal stability of encapsulated nanoparticles slightly increased and the glass transition temperature (T_g) disappeared due to increased crystallinity. Thermogravimetric graphs of encapsulated spherical beads, at all core loadings, showed an additional phase ranging from 138 to 249 °C, overlapping with the BGE’s main TGA degradation phase. The presence of this phase, which was absent from empty bead thermograms, confirmed encapsulation occurrence during electrospraying process. Furthermore, an average of 80% of antioxidative content and potency of the extract was conserved during the encapsulation process. Moreover, phenolic content and antioxidative activity of the encapsulated extract showed higher stability than extracts while stored at refrigerated and ambient conditions.     

Recent observations in bridge deck aeroelasticity

The Deer Isle Bridge, opened for traffic about the same time as the old Tacoma Narrows Bridge, has a deck section shape which resembles that of the ill fated bridge. Because of the Tacoma Narrows experience, various structural stiffening systems were added to the Deer Isle Bridge to alleviate the type of wind response that destroyed its contemporary. In addition, the Deer Isle Bridge deck is also provided with open-grate vents to improve its aerodynamics. The Deer Isle Bridge remained active under wind even with these modifications, though an earlier study has confirmed the efficacy of the structural modifications in stiffening the bridge. It has been the subject of an extensive field survey by the Federal Highway Administration for the last several years. The present paper summarizes the results of a wind tunnel investigation of a two-dimensional scale model of the Deer Isle Bridge deck, new techniques used in the experiments and the conclusions drawn therefrom on the aeroelasticity of these bluff sections. This forms a part of a comprehensive study centered on the field experiments on the Deer Isle Bridge.     

Facile microwave-assisted synthesized reduced graphene oxide/tin oxide nanocomposite and using as anode material of microbial fuel cell to improve power generation

A new nanocomposite material was fabricated by a facile and reliable method for microbial fuel cell (MFC) anode. Tin oxide (SnO₂) nanoparticles were anchored on the surface of reduced graphene oxide (RGO/SnO₂) in two steps. The hydrothermal method was used for the modification of GO and then microwave-assisted method was used for coating of SnO₂ on the modified GO. Nanohybrids of RGO/SnO₂ achieved a maximum power density of 1624 mW m⁻², when used as the MFC anode. The obtained power density was 2.8 and 4.8 times larger than that of RGO coated and bare anodes, respectively. The electrodes were characterized by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The electrochemical characteristics were also studied by cyclic voltammetry (CV), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). The high conductivity and large specific surface of the nanocomposite were greatly improved the bacterial biofilm formation and increased the electron transfer. The results demonstrate that the RGO/SnO₂ nanocomposite was advantageous material for the modification of anode and enhanced electricity generation of MFC.     

Sorbent enhanced hydrogen production from steam gasification of coal integrated with CO2 capture

In this work, CO₂ capture and H₂ production during the steam gasification of coal integrated with CO₂ capture sorbent were investigated using a horizontal fixed bed reactor at atmospheric pressure. Four different temperatures (650, 675, 700, and 750 °C) and three sorbent-to-carbon ratios ([Ca]/[C] = 0, 1, 2) were studied. In the absence of sorbent, the maximum molar fraction of H₂ (64.6%) and conversion of coal (71.3%) were exhibited at the highest temperature (750 °C). The experimental results verified that the presence of sorbent in the steam gasification of coal enhanced the molar fraction of H₂ to more than 80%, with almost all CO₂ was fixed into the sorbent structure, and carbon monoxide (CO) was converted to H₂ and CO₂ through the water gas shift reaction. The steam gasification of coal integrated with CO₂ capture largely depended on the reaction temperature and exhibited optimal conditions at 675 °C. The maximum molar fraction of H₂ (81.7%) and minimum CO₂ concentration (almost 0%) were obtained at 675 °C and a sorbent-to-carbon ratio of 2.     

Performance of two immobilized lipases for interesterification between canola oil and fully-hydrogenated canola oil under supercritical carbon dioxide

The performance and stability of Lipozyme RM IM and TL IM for the interesterification between canola oil and fully-hydrogenated canola oil (FHCO) in the presence of SCCO₂ were studied using a high pressure batch stirred reactor at 65 °C/17.5 MPa. The influence of exposure time (4, 8, and 12 h) in SCCO₂ and pressurization/depressurization cycles of up to 12 times on the enzyme's resultant activity were studied. There was no significant difference (p > 0.05) in the performance of the two enzymes over reaction time, reaching a constant degree of interesterification of about 23% after 2 h. Although FE-SEM images illustrated some morphological changes on the surface of the enzymes after 4 cycles of 7 h each, similar degrees of interesterification were achieved after each cycle. However, the amount of reaction intermediates decreased by 50–60% in the product obtained by using SCCO₂-treated enzymes after 12 pressurization/depressurization cycles compared to untreated enzymes, while there were no significant changes in the conformational and morphological structure of the treated enzymes based on FTIR and FE-SEM analysis. Findings enhance our understanding of enzymatic conversions of lipids under high pressure CO₂, targeting production of base-stock for zero-trans margarines.     

Stochastic analysis of natural gas consumption in residential and commercial buildings

Consumer consumption characteristic is an important asset for safe design and management of gas distribution networks. Different characteristics of natural gas consumption in residential and commercial buildings are studied from statistical and stochastic points of view. The technique is applied during 2008 and 2009 to a densely populated district in Tehran, Iran, with relatively large number of buildings (67,655 residential and 13,286 commercial buildings). There are different trends in the histograms of gas consumption, but there is a general trend in diagrams of probability index (the probability of gas consumption exceeding a specific value) and their regressions. The most frequent amount of gas consumption for all 45-day periods is 100 m³ as compared with the annual average of 320 m³ for residential buildings. The latter reduces to 80 m³ for the averaged periodic consumption per unit in a building. Also it seems that the most frequent amount of periodic gas consumption of residential buildings is about 31% of their respective annual average during the warm months of the year, and 150% during the cold months. Periodic consumptions less than 1500 m³ and average consumptions less than 1400 m³ are more probable in residential buildings, which are larger than that of commercial ones, but this trend reverses at higher consumption values. If actual consumption is normalized by the average consumption, the number of units in the building or the floor area, the probability index of commercial buildings is generally higher than residential ones. The binomial distribution is analytically used to predict the probability of average gas consumption exceeding 320 and 2000 m³ in two example cases of 500 and 1000 buildings.     

Concentration‐dependent minority carrier lifetime in an In0.53Ga0.47As interdigitated lateral PIN photodiode model based on spin‐on chemical fabrication methodology

The fitted parameters for the analytic function used to specify the doping dependence of minority carrier lifetimes for In_0.53Ga_0.47As (InGaAs) is described in this paper. This model together with other carrier models was used to develop an interdigitated lateral PIN photodiode utilizing InGaAs as the absorbing layer. We propose the usage of spin‐on chemicals such as spin‐on dopants and spin‐on glass to form the p+ wells, n+ wells and the surface passivation layer of the device hence providing a cheap and easy solution versus the conventional epitaxial growth methodology. The modeled device achieved dark currents of 0.21 nA and capacitance of 2.87 nF at an operating voltage of 5 V. Optical illumination at a wavelength of 1550 nm and power of 10 W/cm² enabled the device to achieve responsivity of 0.56 A/W and external quantum efficiency of 44%. The −3 dB frequency response of the device was at 8.93 GHz and signal‐to‐noise ratio is 36 dB. The developed device shows close correlation with experimentally developed devices developed using other fabrication methodologies. The results of this work would be useful in the thorough development of InGaAs‐based devices based on spin‐on chemical fabrication methodology using commercial device simulation packages. Copyright © 2010 John Wiley & Sons, Ltd.     

Use of needle track detection to quantify the displacement of stranded seeds following prostate brachytherapy

We aim to compute the movement of permanent stranded implant brachytherapy radioactive sources (seeds) in the prostate from the planned seed distribution to the intraoperative fluoroscopic distribution, and then to the postimplant computed tomography (CT) distribution. We present a novel approach to matching the seeds in these distributions to the plan by grouping the seeds into needle tracks. First, we identify the implantation axis using a sample consensus algorithm. Then, we use a network flow algorithm to group seeds into their needle tracks. Finally, we match the needles from the three stages using both their transverse plane location and the number of seeds per needle. We validated our approach on eight clinical prostate brachytherapy cases, having a total of 871 brachytherapy seeds distributed in 193 needles. For the intraoperative and postimplant data, 99.31% and 99.41% of the seeds were correctly assigned, respectively. For both the preplan to fluoroscopic and fluoroscopic to CT registrations, 100% of the needles were correctly matched. We show that there is an average intraoperative seed displacement of 4.94±2.42 mm and a further 2.97±1.81 mm of postimplant movement. This information reveals several directional trends and can be used for quality control, treatment planning, and intraoperative dosimetry that fuses ultrasound and fluoroscopy.