bluuebunny/crossref_metadata_2025 huggingface dataset:
Low‐loss and polarisation‐insensitive interlayer coupler on three‐dimensional SiOx‐waveguide platform
Authors: Hiraki T. , Tsuchizawa T. , Nishi H. , Yamamoto T. , Yamada K.
Published: December 2014

A low‐loss and polarisation‐insensitive vertical directional coupler that connects vertically stacked SiOx waveguides is reported. The fabrication process features the low‐temperature formation of an SiOx film to prevent thermal damage to the lower layer waveguides. Experimental results showed interlayer coupling losses of <0.1 dB in both transverse‐electric and transverse‐magnetic modes.
Performance of Archimedean spiral antenna backed by FSS reflector
Authors: Mohamad S. , Cahill R. , Fusco V.
Published: December 2014

The use of a backing cavity composed of a frequency selective surface (FSS) above a metal plate as a means to suppress the back lobe radiation and increase the gain of an Archimedean spiral antenna that operates from 3 to 10 GHz is investigated. The FSS is designed to reflect signals in the upper band (7–10 GHz) with a loss of <0.25 dB, and allow transmission in the lower band (3–6 GHz). Good impedance match and bidirectional to unidirectional beam transformation is obtained when the FSS and metal plate are inserted at a distance λ/4 below the spiral at the centre of the upper and lower bands, respectively. Simulated and measured radiation patterns are employed to show the performance enhancement, which is attributed to the FSS reflector.
Span power management scheme for rapid lightpath provisioning in multi‐core fibre networks
Authors: Chatterjee Bijoy Chand , Jayabal Yamini , Yamanaka Naoaki , Okamoto Satoru , Fumagalli Andrea , Oki Eiji
Published: December 2014

The activation time when creating lightpaths is adversely affected by the time optical amplifiers require to adjust the newly added signal power. This shortcoming is particularly true with multi‐core erbium‐doped amplifiers. A fibre span power management scheme is proposed based on the use of dummy wavelength signals, whose function is to alleviate this shortcoming and shorten the required lightpath activation time. An analytical model is developed to estimate the effectiveness of the proposed scheme in achieving this goal.
Broad beamwidth stacked patch antenna with wide circularly polarised bandwidth
Authors: Jiang Hao , Xue Zhenghui , Li Weiming , Ren Wu
Published: December 2014

A broad beamwidth stacked patch antenna with wide circularly polarised (CP) bandwidth is presented. The proposed antenna consists of a stacked structure with a rectangular shell under its ground structure to obtain CP characteristics and wide beamwidth. The radiation quality is excellent over the entire upper hemisphere. The 3 dB beamwidth of the proposed antenna on 2.4 GHz is larger than 140°. Moreover, the CP bandwidth, determined from the 3 dB axial ratio, is found to be about 240 MHz. CP bandwidth of 10.2% and the impedance bandwidth of 52.8% centred on 2.4 GHz are obtained. The proposed antenna is a good candidate for wide angle scanning phased arrays.
Automatic LC network tuner based on negative resistances
Authors: Silva P.M. , Rottava R. , de Sousa F.R.
Published: December 2014

A novel technique to tune an inductor–capacitor (LC) network based on a receiving signal frequency is proposed. The method consists of using a negative resistor to artificially increase the quality factor of the LC circuit to reduce the decision range of the voltage detector. This approach allows the use of low complexity algorithms that converge in a few steps. The technique was validated through a demonstrator for radiofrequency identification tags in production line testing, with satisfactory results. The designed negative resistor maintained a constant resistance for a large range of input signals.
Class AB tunable active inductor
Authors: Pantoli L. , Stornelli V. , Leuzzi G.
Published: December 2014

A class AB active inductor with high linearity, including a minimum number of components, is presented. Class AB operation is absent from the literature on the design of active inductors but is addressed in this reported work. Circuit details are given. A prototype board on a TLX8 substrate has been fabricated and tested showing the circuit feasibility for use in many commercial market applications, as integrated circuits, or discrete filters and oscillators.
Single‐ended structure sense‐amplifier‐based flip‐flop for low‐power systems
Authors: Lin Jin‐Fa , Hwang Yin‐Tsung , Wong Chen‐Syuan , Sheu Ming‐Hwa
Published: December 2014

A novel low‐power sense‐amplifier‐based flip‐flop (FF) is presented. Using a simplified single‐ended pass transistor‐based latch design, the loading of the sense amplifier is greatly alleviated, which facilitates a size reduced sense‐amplifier design as well. These factors improve the power consumption and the delay of the FF design substantially and the performance claims are verified through extensive post‐layout simulations.
Place recognition for visual loop‐closures using similarities of object graphs
Authors: Oh J.H. , Jeon J.D. , Lee B.H.
Published: December 2014

A new method for object‐based place recognition, where objects are used as a key intermediate representation of places, is proposed. Places are represented by object graphs and recognised from similarity scores between the generated graphs. An iterative Hungarian method is proposed for aligning graphs, where node and edge differences are used for measuring the similarity. The proposed technique robustly detects places without false positives, as it considers both the appearance and geometric information of places. Experiments are performed with mobile robots in indoor environments verified the effectiveness of the proposed method.
Ferrite core non‐linearity in coils for magnetic neurostimulation
Authors: RamRakhyani Anil Kumar , Lazzi Gianluca
Published: December 2014

The need to correctly predict the voltage across terminals of mm‐sized coils, with ferrite core, to be employed for magnetic stimulation of the peripheral neural system is the motivation for this work. In such applications, which rely on a capacitive discharge on the coil to realise a transient voltage curve of duration and strength suitable for neural stimulation, the correct modelling of the non‐linearity of the ferrite core is critical. A demonstration of how a finite‐difference model of the considered coils, which include a model of the current‐controlled inductance in the coil, can be used to correctly predict the time‐domain voltage waveforms across the terminals of a test coil is presented. Five coils of different dimensions, loaded with ferrite cores, have been fabricated and tested: the measured magnitude and width of the induced pulse are within 10% of simulated values.
Joint resource allocation with subcarrier pairing in cooperative OFDM DF multi‐relay networks
Authors: Li Xueyi , Zhang Qi , Zhang Guangchi , Cui Miao , Yang Liang , Qin Jiayin
Published: December 2014

For conventional subcarrier pairing scheme in cooperative orthogonal frequency division multiplexing decode‐and‐forward multi‐relay networks, to avoid interference, each subcarrier pair (SP) is assigned to a single relay. Over a specific subcarrier, the destination receives signals transmitted from the relay. In this study, to better exploit the degrees of spatial freedom, the authors propose to assign each SP to multiple relays. Thus, over a specific subcarrier, the destination receives signals transmitted from multiple relays. Under the total network power constraint, to maximise the sum transmission rate, they propose a joint resource allocation scheme, in which they jointly optimised the four types of resources: assisting relays selection, transmission mode selection, subcarrier pairing and power allocation. They further propose a suboptimal algorithm which can significantly reduce the computational complexity of the aforementioned optimal allocation scheme with sacrificing little on the performance. It is shown from simulation results that the author's proposed schemes have significant performance improvement over the resource allocation schemes in the literature.
Non‐singular fixed‐time terminal sliding mode control of non‐linear systems
Authors: Zuo Zongyu
Published: December 2014

This study addresses a fixed‐time terminal sliding‐mode control methodology for a class of second‐order non‐linear systems in the presence of matched uncertainties and perturbations. A newly defined non‐singular terminal sliding surface is constructed and a guaranteed closed‐loop convergence time independent of initial states is derived based on the phase plane analysis and Lyapunov tools. The simulation results of a single inverted pendulum in the end are included to show the effectiveness of the proposed methodology.
Consensus in second‐order multi‐agent systems via impulsive control using position‐only information with heterogeneous delays
Authors: Wang Yan‐Wu , Yi Jing‐Wen
Published: December 2014

This study investigates the consensus problem of second‐order multi‐agent systems (MASs) via impulsive control using position‐only information with communication delays. The communication delays between any two distinct agents are different which can be larger than one impulsive period. A distributed impulsive consensus protocol is designed, in which only the delayed sampled relative positions to neighbours and the relative position to the last sampling state are utilised. By introducing some virtual subgraphs and performing three steps of model transformation, the consensus problem of original continuous‐time system is converted to the stability problem of a discrete‐time expanded error system. Some necessary and sufficient criteria are derived to grantee the dynamic average‐consensus of the MAS. Furthermore, a special case, that is, the delays less than one impulsive period, is discussed, and the bounds of impulsive periods for the dynamic average‐consensus are obtained in explicit expressions for both the undirected and directed communication graphs, respectively. Two numerical simulation examples are given to illustrate the effectiveness of theoretical results.
Multi‐consensus for second‐order multi‐agent systems based on sampled position information
Authors: Chen Jie , Guan Zhi‐Hong , He Ding‐Xin , Chi Ming , Cheng Xin‐Ming
Published: December 2014

In this study, the multi‐consensus problem is investigated for second‐order multi‐agent systems with only sampled position information. By matrix theory and algebraic graph, the multi‐consensus and multi‐tracking can be achieved if the gains and sampling period satisfy a range. Simulations are provided to verify the effectiveness of the results.
Integrated multi‐agent system framework: decentralised search, tasking and tracking
Authors: Meng Wei , He Zhirong , Teo Rodney , Su Rong , Xie Lihua
Published: December 2014

This study is concerned with integrated target search, tasking and tracking using multiple fixed‐wing unmanned air vehicles (UAVs). The problem is to design control logic and optimise flight paths for UAVs. The fixed‐wing UAVs are required to cooperatively search the potential targets in the area of operation (AO) and keep monitoring and tracking the found targets according to a certain predefined minimal revisit time. Each UAV can only communicate with its neighbours and also flight autonomy is designed for individual UAVs. High level control logic based on finite state automaton model, integrating the four modes of operations, that is, take‐off mode, fly‐to‐AO mode, search mode and tracking mode, is developed. For the target search, an improved decentralised coverage based algorithm is designed for fixed‐wing UAVs. Task assignment is developed based on contract net protocol. For the target tracking, the optimal paths are derived for the UAVs to continuously monitoring multiple static targets. The developed integrated multi‐agent system is evaluated by a hybrid three‐dimensional simulation system using a real miniature fixed‐wing UAV dynamic model.
Power allocation scheme for distributed filtering over wireless sensor networks
Authors: Yang Wen , Shi Hongbo
Published: December 2014

In this work, distributed filtering over wireless sensor networks with limited energy is considered, where each sensor sends its local state estimate to its adjacent sensors through an unreliable wireless channel, which introduces random data packet drops. The packet drop rate depends on the power allocated by the sensor under an energy constraint. Several offline power scheduling strategies are introduced to distribute the power of sensors. A sufficient condition is provided to guarantee the convergence of network estimation error covariance. Further, an online power scheduling strategy is proposed, where each sensor utilises its real‐time information to distribute energy for communications. The filtering performance of different power scheduling strategies are compared to show the influence of power distributed scheme on the expected state estimation error covariance.
Modified switching‐table strategy for reduction of current harmonics in direct torque controlled dual‐three‐phase permanent magnet synchronous machine drives
Authors: Hoang Khoa Dang , Ren Yuan , Zhu Zi‐Qiang , Foster Martin
Published: December 2014

The switching‐table‐based direct torque control (ST‐DTC) strategies of dual‐three‐phase permanent magnet synchronous machine (PMSM) drives are investigated in this study. Owing to its inherited advantage of suppression of sixth harmonic torque pulsation, dual‐three‐phase machine has attracted more and more interests among various sorts of multiphase machines. However, unexpected stator harmonic currents are often observed in the classical ST‐DTC strategy for dual‐three‐phase PMSM drives, which cause large losses and decrease the efficiency of the drive system. An optimised ST‐DTC strategy which consists a two‐step process to determinate the most appropriate inverter voltage vector is proposed to reduce the stator harmonic currents. The merits of the classical DTC, that is, simple structure and good dynamic performance, are still preserved. The experimental results verify that the proposed method can significantly reduce the current harmonics.
3D permeance model of induction machines taking into account saturation effects and its connection with stator current and shaft speed spectra
Authors: Martinez Javier , Belahcen Anouar , Arkkio Antero
Published: December 2014

This study presents a 3D‐permeance model of induction machines that reproduces the axial evolution of the air‐gap flux for skewed rotors. This evolution is presented using the terminology of axial magnetic modes. These axial waves are the result of the interaction between the rotor slot harmonics permeance series and the space harmonic index related to the magneto‐motive force generated by the skewed rotor cage. Wavelength of this axial mode is compared with the results of a validated multi‐slice finite element model. Axial wave modes in the slice model were processed using estimation techniques giving an excellent matching with the results of the permeance model. Experimental validation has been indirectly carried out comparing different spectral components for both skewed and non‐skewed identical motors and comparing their magnitudes. Differences in the magnitude are associated with the existence of axial modes that change the total flux contained in the air gap of the motor. This study mainly focuses on the study of saturation harmonic.
Rotor design to improve dynamic performance of axial flux hysteresis motors
Authors: Modarres Mohammad , Kwon Byung‐Il
Published: December 2014

In high‐speed axial flux hysteresis motors (AFHMs), the hysteresis ring and the hysteresis ring holder have the main roles of producing hysteresis torque in steady state and eddy current torque at sub‐synchronous speed, respectively. In conventional AFHM, and especially in the high‐speed AFHM types, the hysteresis ring holder is placed between the hysteresis ring and stator to produce more eddy current torque at the time of starting. Since the minimum magnetic air gap can cause better motor performance, the previous research exchanges the hysteresis ring place and its holder. However, it has worst motor dynamic response as a result. To cope with these issues, a new model is proposed in this study. A thin copper piece is attached at the bottom of the hysteresis ring to improve the eddy current torque and consequently motor dynamic response. Then finite element analysis is done in order to acquire the accurate copper thickness and investigate the new proposed AFHM. Furthermore, experimental setups are provided and AFHM results in all cases are measured. The obtained test and simulation results show that the new proposed model make a better dynamic performance for the AFHM.
Investigation of fault‐tolerant capability of five‐phase doubly salient electromagnetic generator
Authors: Zhao Yao , Wang Huizhen , Xiao Lan
Published: December 2014

A new topology of five‐phase fault‐tolerant doubly salient electromagnetic generator (FTDSEG) is proposed for high reliability applications in this paper. The analysis of no‐load and loading operations shows the potential fault‐tolerance capability. On the basis of comparative analysis on structure characteristics between five‐phase non‐FTDSEG (NFTDSEG) and five‐phase FTDSEG, the variation of rotor pole number from NFTDSEG to FTDSEG is revealed. Meanwhile, the flux linkage and electromotive forces (EMFs) of five‐phase NFTDSEG and five‐phase FTDSEG are investigated with finite element method and five faults of five‐phase FTDSEG are analysed in detail. Especially when single phase short‐circuit fault happens, the magnetic field of the motor, flux linkage of short‐circuit phase and short‐circuit currents without load are investigated in four different short‐circuit moments and the fault is in consideration of armature winding resistance. The ultimate variation trend of flux linkage is irrelevant to moment when the short‐circuit fault happens. The flux linkage and EMF of short‐circuit phase are also analysed. The laws of fault operating influence on external and power characteristics of FTDSEG are researched in five faults with different exciting currents. The fault‐tolerant ability of five‐phase FTDSEG has been demonstrated by the experimental results.
Control strategy for permanent magnet synchronous motor with contra‐rotating rotors under unbalanced loads condition
Authors: Cheng Shuangyin , Luo Derong , Huang Shoudao , Chen Zhe , Huang Keyuan
Published: December 2014

This study presents an investigation into the control of an axial‐flux permanent magnet synchronous machine (PMSM) with contra‐rotating rotors fed by a single inverter, which corresponds to two PMSM connected in series. In this study, the mathematic model of the PMSM with contra‐rotating rotors is developed and the instability of the system with unbalanced loads is analysed. Based on the analysis, a control strategy which can keep synchronism of the two rotors under varying load is implemented. In addition, a method for starting the motor reliably is proposed, which is applicable to ship or under water vehicle propulsions. The control strategy is implemented on a DSP 28335 processor featured hardware platform and is tested on a 1.2 kW prototype machine. Experimental results validate the correctness of the analysis and control strategy.
Hybrid method of moments – induced EMF method for analysing multi‐element planar inverted F antenna arrays
Authors: Nikolopoulos Christos D. , Capsalis Christos N.
Published: December 2014

Multi‐element planar inverted F antenna (PIFA) phase array characteristics are investigated, using a hybrid method of moments (MoM) – induced electro‐motive force (EMF) method. First the MoM is used to study the dependence of mutual impedance between two array elements with respect to the distance between them. Then a general rule on the relationship between mutual impedance and distance is developed. Using this relation the induced EMF method is then employed in order to obtain the characteristics of a phased array with PIFA elements independently of the number of elements and the geometry of the array. Simulation results are presented in 1.8 GHz frequency bands and the accuracy of the proposed method is found satisfactory, while all the advantages of simplicity of the induced EMF method are exploited. Phased arrays are used in smart antennas which can also be adaptive, the proposed method can be used for real time calculation of the excitation coefficients in comparison with the calculation from a time consuming simulation program that is not realistic.
Fast surrogate‐assisted simulation‐driven optimisation of add‐drop resonators for integrated photonic circuits
Authors: Koziel Slawomir , Ogurtsov Stanislav
Published: December 2014

Computationally feasible and efficient simulation‐driven optimisation of add‐drop resonators for integrated photonic circuits is discussed. The approach exploits modelling of critical features of the otherwise highly non‐linear responses, and almost linear dependence of these features on designable parameters. This, as well as a suitable formulation of the objective function and embedding the optimisation process in the trust‐region framework, allows us to greatly reduce the computational effort in terms of the number of full‐wave simulations of the photonic component of interest necessary to find its optimised design. Operation and efficiency of the proposed technique is demonstrated using the example of a 6‐µm high index contrast add‐drop microring resonator.
Comparison of heterogeneous network rain fade simulation tools: global integrated network SIMulator and MultiEXCELL
Authors: Paulson Kevin Scott , Luini Lorenzo , Chinda Ibrahim Denis , Basarudin Hafiz
Published: December 2014

Two heterogeneous network simulation tools are compared and tested against measured data from terrestrial and Earth‐space microwave links. Both global integrated network SIMulator (GINSIM) and MultiEXCELL are able to produce joint distributions of rain fade time‐series for arbitrary networks of microwave telecommunications links. The tools are fundamentally different in that GINSIM has, as its input, time‐series of composite rain rate maps produced by networks of meteorological radars and can produce time‐series of joint rain fade. MultiEXCELL uses the rain rate distribution as an input to constrain distributions of parameters of simulated rain cells. This study tests the simulators by comparing a range of annual fade statistics produced by simulation with data measured on experimental links. Link fade data were measured on two, Ka band, Earth‐space links and a convergent 38 GHz terrestrial link near Chilbolton in southern England; and a further Earth‐space link located in Dundee, Scotland. Both GINSIM and MultiEXCELL are shown to be able to predict joint fade distributions and diversity gain, for the satellite and terrestrial links, to useful accuracy. Differences in performance are analysed, leading to suggested development routes for both systems.
Group‐based cognitive radio network formation without common channels
Authors: Li Xiukui , Zekavat Seyed A. (Reza)
Published: December 2014

To form cognitive radio nodes into a wireless ad‐hoc network, generally, globally or locally common channels are assumed to be available or some channels are dynamically selected as locally common ones. However, a cognitive radio node is not licensed to any channel for communication. With dynamic channel availability, neither locally nor globally common channels could be assumed available. Therefore, in this study, a new approach for cognitive radio network formation is presented that is not constrained by the availability of common channels. The proposed approach is based on the ‘group’ concept. Activated cognitive radio nodes form multiple ‘groups’ according to some criteria. Each group consists of a head node, some gateway nodes and ordinary nodes. During sensing phase, nodes sense channels and negotiate the channel and time slot assignment; thus, during data transmitting phase, each node is able to communicate with its different neighbour nodes in assigned channels during given time slots. Hence, nodes can be connected together to form a network without common channels and the network connectivity is improved. This study presents the network forming process including neighbour node detection, node communication, group formation, time slot assignment, channel assignment and medium access control protocol. Finally, simulations are conducted to investigate the network connectivity.
Minimum‐costs of multiple unicasts wireless networks with inter‐session network coding
Authors: Mei Zhonghui , Yang Zhen
Published: December 2014

A multiple unicasts wireless network where multiple paths are available for each unicast is considered. To minimise the total network cost which is defined as the number of transmissions to support the given data flows of the network, general network coding (GNC) and active general network coding (AGNC) are employed. AGNC can exploit more network coding opportunities than GNC by allowing some additional information which is transmitted to recover the native flows from the network coded ones. The overall network cost minimisation problem can be decomposed into two sub‐problems: source traffic splitting which can be resolved by potential game theory and network coding traffic adjusting which can be resolved by project gradient algorithm. Simulation results demonstrate that both of AGNC and GNC outperform the conventional scheme which does not adopt network coding. In addition, Better performance can be achieved by AGNC in contrast with GNC.
Universal lighting control of unknown connected light emitting diode arrays via a T–S fuzzy model‐based approach
Authors: Chiu Chian‐Song , Shen Chih‐Teng , Hsieh Guan‐Chyun
Published: December 2014

This study presents a universal lighting driver for unknown connected light emitting diode (LED) arrays by using a single‐ended primary inductor converter (SEPIC) DC/DC converter and a T–S fuzzy model‐based current controller. Driving and lighting an LED array with unknown series and parallel connection is a significant research for universal adaptable applications. To this end, the input voltage of the LED array is up/down adjusted by the SEPIC DC/DC converter, whereas exact LED lighting current control is realised by the proposed T–S fuzzy parallel distributed integral compensation control method. For easier implementation, a linear‐simplified fuzzy observer is introduced under output feedback. Asymptotic convergence is guaranteed by strict stability analysis and linear matrix inequality gain design. Moreover, the fuzzy lighting current controller does not require the electrical model and arrangement of the LED array. In addition, even if we take uncertainty, disturbance and rapidly changing reference current into consideration, the high robustness and transient response performance are still assured via robust gain design. Finally, the satisfactory performance is shown from experimental results.
Performance evaluation of three‐phase, neutral‐point clamped bi‐directional rectifier for supply and load perturbations
Authors: Langer Nitin , Bhat Abdul Hamid
Published: December 2014

In this study, an improved performance three‐phase neutral‐point clamped bidirectional rectifier with modified control scheme is proposed. The proposed control strategy takes into consideration the amount/degree of deviation of source voltage from desired rated value during supply perturbation and accordingly modifies the reference current template for each phase individually which is termed as compensated reference current. In other words, magnitude, shape and phase of compensated reference current waveform for each phase are different depending on amount of deviation of that phase. A complete mathematical model of rectifier using pulse width modulation technique is developed. The performance of the converter is evaluated in terms of near unity input power factor, low input current total harmonic distortion, reduced ripple factor of the regulated DC output voltage and particularly the neutral‐point voltage balance under different load conditions both for rectification and inversion modes of operation. It is shown that the three‐level AC to DC converter with the proposed control scheme displays better performance under source voltage perturbations such as voltage sag, swell, unbalance, harmonics, frequency variations as well as phase angle deviations which are regularly encountered in practical environment.
Multilevel voltage source inverter with optimised usage of bidirectional switches
Authors: Jamaludin Jafferi , Rahim Nasrudin Abd. , Ping Hew Wooi
Published: December 2014

This study presents a multilevel voltage source inverter that has been designed to reduce circuit complexity by optimising the use of bidirectional switches. The proposed inverter is built by adding an auxiliary circuit comprising an arrangement of bidirectional switches to the three‐phase, six‐switch, full‐bridge configuration. Several bidirectional switches are made to function in the optimised mode in which their operations are divided among the three phases. The presence of the optimised mode considerably reduces the number of power switches as the number of levels in the line‐to‐line voltage waveform increases. A novel modulation scheme based on space vector concept with virtual vectors utilisation has also been developed. A detailed study of the proposed inverter is described through the example of a five‐level structure. The performance of the proposed inverter is analysed through MATLAB/SIMULINK simulation and verified via the practical tests conducted on a laboratory prototype with a DSP‐based controller. A comparison is also made against classical multilevel inverters to complete the analysis.
Analysis of voltage source converter‐based high‐voltage direct current under DC line‐to‐earth fault
Authors: Rafferty John , Xu Lie , Morrow John
Published: December 2014

DC line faults on high‐voltage direct current (HVDC) systems utilising voltage source converters (VSCs) are a major issue for multi‐terminal HVDC systems in which complete isolation of the faulted system is not a viable option. Of these faults, single line‐to‐earth faults are the most common fault scenario. To better understand the system under such faults, this study analyses the behaviour of HVDC systems based on both conventional two‐level converter and multilevel modular converter technology, experiencing a permanent line‐to‐earth fault. Operation of the proposed system under two different earthing configurations of converter side AC transformer earthed with converter unearthed, and both converter and AC transformer unearthed, was analysed and simulated, with particular attention paid to the converter operation. It was observed that the development of potential earth loops within the system as a result of DC line‐to‐earth faults leads to substantial overcurrent and results in oscillations depending on the earthing configuration.
Extended configuration of dual active bridge DC–DC converter with reduced number of switches
Authors: Sedaghati Farzad , Hosseini Seyed Hossein , Sabahi Mehran , Gharehpetian Gevork B.
Published: December 2014

Dual active bridge (DAB) DC–DC converter is one of the most famous DC–DC converters for medium and high‐power applications. This study presents an extended configuration of DAB DC–DC converter, which uses circuit elements with low power ratings. The main merits of the proposed configuration are its bidirectional power flow, fewer numbers of switches without imposing any limitation on the transferred power rating and zero voltage switching (ZVS) characteristics. The operation principle of the converter is presented, and ZVS analysis is described in detail. Furthermore, the steady‐state and dynamic operation models of the proposed converter are derived. A comparison between the extended DAB converter and conventional modular DAB converter is performed to verify the advantages and disadvantages of the proposed topology. The design considerations of high‐frequency transformers and required external inductors are presented. Finally, measurement and simulation results are presented to verify the operation principle of the proposed converter and its dynamic performance.
System strength considerations in a converter dominated power system
Authors: Urdal Helge , Ierna Richard , Zhu Jiebei , Ivanov Chavdar , Dahresobh Amir , Rostom Djaved
Published: December 2014

The drive towards renewable energy sources (RES) is dramatically changing the dynamic electrical characteristics of Generators, which are traditionally the dominant dynamic component in Power Systems. Non‐synchronous generation (NSG) approaching or even exceeding control area demand is now happening on a rapidly expanding scale. The study identifies from National Grid's perspective as Great Britain transmission system operator, the key challenges during periods of operation with high proportion of RES relative to demand. It raises some major questions. What determines system strength in an HVAC system largely without synchronous generators and what is adequate for stability? What levels of %NSG can be expected in the future energy scenarios? What are the financial consequences of constraining RES production if the technical capabilities create an upper limit of %NSG which the system can be operated at? The study finally proposes closer collaboration across the industry to find the optimal missing solutions.
Distributed demand‐side management optimisation for multi‐residential users with energy production and storage strategies
Authors: Manasseh Emmanuel Chifuel , Ohno Shuichi , Yamamoto Toru , Mvuma Aloys
Published: December 2014

This study considers load control in a multi‐residential setup where energy scheduler (ES) devices installed in smart meters are employed for demand‐side management (DSM). Several residential end‐users share the same energy source and each residential user has non‐adjustable loads and adjustable loads. In addition, residential users may have storage devices and renewable energy sources such as wind turbines or solar as well as dispatchable generators. The ES devices exchange information automatically by executing an iterative distributed algorithm to locate the optimal energy schedule for each end‐user. This will reduce the total energy cost and the peak‐to‐average ratio (PAR) in energy demand in the electric power distribution. Users possessing storage devices and dispatchable generators strategically utilise their resources to minimise the total energy cost together with the PAR. Simulation results are provided to evaluate the performance of the proposed game theoretic‐based distributed DSM technique.
Dynamic pricing based on a cloud computing framework to support the integration of renewable energy sources
Authors: Thankappan Nair Rajeev , Sankar Ashok
Published: December 2014

Integration of renewable energy sources into the electric grid in the domestic sector results in bidirectional energy flow from the supply side of the consumer to the grid. Traditional pricing methods are difficult to implement in such a situation of bidirectional energy flow and they face operational challenges on the application of price‐based demand side management programme because of the intermittent characteristics of renewable energy sources. In this study, a dynamic pricing method using real‐time data based on a cloud computing framework is proposed to address the aforementioned issues. The case study indicates that the dynamic pricing captures the variation of energy flow in the household. The dynamic renewable factor introduced in the model supports consumer oriented pricing. A new method is presented in this study to determine the appropriate level of photovoltaic (PV) penetration in the distribution system based on voltage stability aspect. The load flow study result for the electric grid in Kerala, India, indicates that the overvoltage caused by various PV penetration levels up to 33% is within the voltage limits defined for distribution feeders. The result justifies the selected level of penetration.
Stochastic channel model for simulation of mobile ad hoc networks
Authors: Eriksson Gunnar , Fors Karina , Wiklundh Kia , Sterner Ulf
Published: December 2014

Channel models, applicable to mobile ad hoc network (MANET) simulations, need to be both accurate and computationally efficient. It has been shown that inaccuracies in the channel model can seriously affect various network performance measures. It is essential that the model gives realistic time and spatial variability as the terminals move. Furthermore, the frequency selective effects from multipath propagation must be realistically modelled, so that the effects of different signalling bandwidths are captured correctly. However, to meet the necessary low‐complexity constraints current commonly used channel models for network simulations are very simplified. In this study, the authors propose a model structure that is able to capture the essence of the channel characteristics, and to cope with the constraint of low computational complexity. The model describes the channel time and frequency variability between nodes in a MANET. It models the large‐ and small‐scale fading, where the correlation between the fading parameters as well as the spatial correlation is considered. Furthermore, the study presents parameters for the proposed model based on wideband peer‐to‐peer channel measurements in an urban environment at 300 MHz. When analysing the link and network performance, they show that the proposed channel model describes the channel dynamics appropriately.
Pre‐coder design over two‐symbol extension for K ‐user cyclic interference channels
Authors: Chae Hyukjin , Jang Jinyoung , Kim Dongku
Published: December 2014

The authors consider K ‐user cyclic single‐input–single‐output (SISO) interference channel (IC) where each receiver is interfered with from only one neighbouring transmitter. In the K ‐user cyclic SISO IC, K /2 sum degrees of freedom can be achieved when two‐symbol extension is applied even without channel state information at the transmitter. They derive an approximation of the ergodic sum rate as a function of pre‐coders and propose designs of pre‐coders to maximise the ergodic sum rate.
Influence of ion dose on nanostructure morphology and electrical properties of nitrogen implanted‐annealed copper
Authors: Kazemeini‐Asl Anousheh , Larijani Majdid M. , Fathollahi Vahid
Published: December 2014

Cu thin films sputter‐coated on single crystals of silicon were implanted with 30 keV nitrogen ions under various doses from 1.9 × 1017 to 5.7 × 1017 ions/cm2. The prepared samples were subsequently annealed in nitrogen atmosphere. The grazing incidence X‐ray diffraction analysis revealed that in addition to the crystalline copper nitride phase, copper azides were developed by nitrogen ion implantation. With an increase of the implantation dose to 2.3 × 1018 ions/cm2, much of the Cu film was transformed to the crystalline Cu3N phase. Furthermore, the effect of nitrogen ion implantation on Cu thin films under various doses was investigated. The structural properties, morphology and sheet resistance of samples were investigated by grazing incidence X‐ray diffraction, atomic force microscopy, field emission scanning electron microscopy and four‐point probe techniques, respectively. In addition, the dependence of resistivity of the implanted samples on the implantation dose as well as structural properties is discussed.
Free‐standing aluminium nanowire arrays for high‐transmission plasmonic colour filters
Authors: Honma Hiroaki , Takahashi Kazuhiro , Fukuhara Masashi , Ishida Makoto , Sawada Kazuaki
Published: December 2014

Presented is a fabrication process for the transmission of red–green–blue (RGB) colour filters based on surface plasmons (SPs) using aluminium (Al) nanowire arrays patterned through electron‐beam lithography and the lift‐off technique. An array of Al nanowires was deployed over a through hole formed by sacrificial silicon etching. The period of the Al nanowire arrays is the dominant structural parameter in determining the transmission peak position of SPs for a given material configuration. The Al nanowire arrays are designed with the same Al wire width under the assumption of operation using a microelectromechanical systems (MEMS) comb‐drive actuator for the realisation of an RGB tunable colour filter. The peak wavelength of the transmitted light was red‐shifted by increasing the period of the Al nanowire arrays from 450 to 600 nm, and RGB colours were demonstrated. A black pixel was produced using the 400 nm pitch Al nanowire array. The maximum measured transmittance of the peak wavelength was 56%. In addition, the number of nanowires sufficient for low‐power operation by a MEMS comb‐drive actuator was investigated and sufficient transmission light intensity was obtained from the pixel size of 10 µm2, including 20 Al nanowires.
An automatic tool to analyze and cluster macromolecular conformations based on self-organizing maps
Authors: Bouvier Guillaume , Desdouits Nathan , Ferber Mathias , Blondel Arnaud , Nilges Michael
Published: December 2014

Motivation: Sampling the conformational space of biological macromolecules generates large sets of data with considerable complexity. Data-mining techniques, such as clustering, can extract meaningful information. Among them, the self-organizing maps (SOMs) algorithm has shown great promise; in particular since its computation time rises only linearly with the size of the data set. Whereas SOMs are generally used with few neurons, we investigate here their behavior with large numbers of neurons.

Results: We present here a python library implementing the full SOM analysis workflow. Large SOMs can readily be applied on heavy data sets. Coupled with visualization tools they have very interesting properties. Descriptors for each conformation of a trajectory are calculated and mapped onto a 3D landscape, the U-matrix, reporting the distance between neighboring neurons. To delineate clusters, we developed the flooding algorithm, which hierarchically identifies local basins of the U-matrix from the global minimum to the maximum.

Availability and implementation: The python implementation of the SOM library is freely available on github: https://github.com/bougui505/SOM.

Contact:  michael.nilges@pasteur.fr or guillaume.bouvier@pasteur.fr

Supplementary information:  Supplementary data are available at Bioinformatics online.
Modified screening and ranking algorithm for copy number variation detection
Authors: Xiao Feifei , Min Xiaoyi , Zhang Heping
Published: December 2014

Motivation: Copy number variation (CNV) is a type of structural variation, usually defined as genomic segments that are 1 kb or larger, which present variable copy numbers when compared with a reference genome. The screening and ranking algorithm (SaRa) was recently proposed as an efficient approach for multiple change-points detection, which can be applied to CNV detection. However, some practical issues arise from application of SaRa to single nucleotide polymorphism data.

Results: In this study, we propose a modified SaRa on CNV detection to address these issues. First, we use the quantile normalization on the original intensities to guarantee that the normal mean model-based SaRa is a robust method. Second, a novel normal mixture model coupled with a modified Bayesian information criterion is proposed for candidate change-point selection and further clustering the potential CNV segments to copy number states. Simulations revealed that the modified SaRa became a robust method for identifying change-points and achieved better performance than the circular binary segmentation (CBS) method. By applying the modified SaRa to real data from the HapMap project, we illustrated its performance on detecting CNV segments. In conclusion, our modified SaRa method improves SaRa theoretically and numerically, for identifying CNVs with high-throughput genotyping data.

Availability and Implementation: The modSaRa package is implemented in R program and freely available at http://c2s2.yale.edu/software/modSaRa.

Supplementary information:  Supplementary data are available at Bioinformatics online.
Long-term studies of Crozet Island killer whales are fundamental to understanding the economic and demographic consequences of their depredation behaviour on the Patagonian toothfish fishery
Authors: Guinet Christophe , Tixier Paul , Gasco Nicolas , Duhamel Guy
Published: December 2014

This paper provides a synthesis of results obtained as part of a long-term collaborative study involving biologists, fishers, and resource managers—centring on the occurrence of killer whales in the Crozet Archipelago before and after the implementation of a demersal longline fishery for Patagonian toothfish. Depredation behaviour was reported as soon as the fishery was initiated, with dramatic effects on both the demographic trajectories of the killer whales and on the amount of fish lost by the fishers. Killer whales interacting with the fishery exhibited very high mortality rates when illegal fishing took place, while killer whales not interacting were unaffected. However, after illegal fishing ended, killer whales interacting with the fishery exhibited both higher fecundity and survival rates compared with killer whales not interacting. Since whales typically removed fish entirely from the hooks, an adapted methodology that did not rely on determining the number of damaged fish was developed to estimate depredation rates. In the Crozet EEZ over a 10-year period, 33.9% of the total amount of Patagonian toothfish caught, representing a total of 28 million €, was estimated to be lost due to the combined effects of killer whale and sperm whale depredation. In an effort to reduce depredation losses, modifications to fishing methods, such as changing the fishing season, changing fishing areas when exposed to depredation and changing longline length and hauling speed were successfully tested. Acoustic deterrent devices were ineffective in deterring killer whales from depredating longlines. Alternative fishing gears, such as fish pots, were also tested. However, while providing encouraging results regarding the suppression of depredation and seabird bycatch, fish pots were not efficient enough to sustain an economically viable fishery. In conclusion, we discuss how the findings of this comprehensive study can be used elsewhere in fisheries confronted with depredation.