bluuebunny/crossref_metadata_2025 huggingface dataset:
Cascading of diode bypassed transistor‐voltage‐source units in multilevel inverters
Authors: Al‐Judi Arif , Nowicki Edwin
Published: May 2013

Multilevel inverters are gaining interest in industry, especially for renewable energy sources, as a means to reduce output distortion and also reduce electromagnetic interference effects. However, multilevel inverters have a high‐transistor component count. In order to reduce the number of power transistors within a multilevel inverter, a bypass diode technique is suggested for two multilevel inverter topologies. In the first inverter configuration, referred to here as the diode‐bypassed multilevel dc‐link inverter, one H‐bridge is required for the entire single‐phase system, with one transistor and one bypass diode needed for each voltage source used in the inverter. Each voltage source contributes in supplying power to the load in both the positive and negative half cycles of the output waveform. In the second configuration, referred to here as the diode‐bypassed neutral point inverter, one transistor and one bypass diode is required for each voltage source, plus two additional transistors for the entire single‐phase inverter system. For this configuration, each dc source contributes only to one half‐cycle of the output waveform, either positive or negative. For both configurations, it is possible to ensure even power distribution among all the voltage sources (or compensate for imbalance in the state of charge of the dc sources). Experimental results suggest the feasibility of constructing the proposed inverter topologies and simulations provide preliminary power‐efficiency data.
Formulation of line‐to‐line voltage total harmonic distortion of two‐level inverter with low switching frequency
Authors: Vadizadeh Hadi , Farokhniah Naeem , Toodeji Hamidreza , Kavousi Ayoub
Published: May 2013

THD is the most common criterion to determine the harmonic content of each waveform. Conventional methods, which are usually used, result in approximate answers due to their inability to take all harmonic orders into account. This paper focuses on the three‐phase two‐level inverter and proposes two methods, founded on the basic definition of THD, to calculate its line voltage THD, precisely. The first method considers stepped essence of line voltage and the second uses its Fourier coefficients. By proposed methods, all harmonic orders of two‐level inverter with any switching angles, named n‐degree of freedom, are considered. Another feature of the introduced methods is deriving analytical formulas for line voltage THD. This helps some switching strategies like THD Minimisation (THDM) to get rid of heuristic methods, which find those switching angles that globally minimise THD. Superiority of the proposed methods for one and two degrees of freedom is verified by both numeric and graphic results, simulated in MATLAB. The comparison table is only used for higher degrees of freedom, because of impossibility of plotting n‐dimensional space. Finally, experimental results for two sets of switching angles are compared with the results of proposed methods to evaluate the accuracy of introduced methods.
Analysis and improvement of performance in LCL filter‐based PWM rectifier/inverter application using hybrid damping approach
Authors: Mukherjee Nilanjan , De Dipankar
Published: May 2013

A hybrid passive‐active damping solution with improved system stability margin and enhanced dynamic performance is proposed for high power grid interactive converters. In grid connected active rectifier/inverter application, line side LCL filter improves the high frequency attenuation and makes the converter compatible with the stringent grid power quality regulations. Passive damping though offers a simple and reliable solution but it reduces overall converter efficiency. Active damping solutions do not increase the system losses but can guarantee the stable operation up to a certain speed of dynamic response which is limited by the maximum bandwidth of the current controller. This paper examines this limit and introduces a concept of hybrid passive‐active damping solution with improved stability margin and high dynamic performance for line side LCL filter based active rectifier/inverter applications. A detailed design, analysis of the hybrid approach and trade‐off between system losses and dynamic performance in grid connected applications are reported. Simulation and experimental results from a 10 kVA prototype demonstrate the effectiveness of the proposed solution. An analytical study on system stability and dynamic response with the variations of various controller and passive filter parameters is presented.
Improved power quality converter for direct torque control‐based induction motor drives
Authors: Madishetti Sandeep , Bhuvaneswari G. , Singh Bhim
Published: May 2013

This study presents the performance of a direct torque control (DTC)‐based induction motor drive (IMD) with improved power quality converter at the front end. It is designed, modelled, simulated in MATLAB/simulink platform and implemented in hardware using a digital signal processor (DSP). An improved power quality converter known as Vienna rectifier is used in the system to mitigate the power quality problems at the utility interface in the DTC‐IMD. The proposed Vienna rectifier is a three switch converter to improve the power quality in terms of reduced total harmonic distortion of ac mains current, power factor correction and dc‐link voltage regulation. The performance of the proposed system is validated experimentally using a DSP. The performance of the system is tested for step change in input reference speed and the load torque and it is found that the power quality indices conform to IEEE‐519 standard under all operating conditions.
Research of a novel temperature adaptive gate driver for power metal‐oxide semiconductor
Authors: Hua‐long Zhuang , Guo‐huan Hua , Shen Xu , Wei‐feng Sun , Zhi‐qun Li
Published: May 2013

Driving power metal‐oxide semiconductor field‐effect transistor at high frequency may induce significant switching losses, which have a great proportion in total power losses. Especially in the case of higher temperature, switching losses increased tangibly. A novel temperature adaptive gate driver with low power consumption in a high‐temperature environment is proposed for switched‐mode power supply by the temperature compensation technique. It has been realised to decrease the switching losses in wide scope temperature, and cannot sacrifice performance of the electromagnetic interferences, by regulating di/dt and dv/dt of switching curve in high temperature. A 0.25 μm, 40 V bipolar‐CMOS‐DMOS (BCD) process technology is utilised and experimental circuits and results are then presented. Compared with the conventional gate driver, the turn‐on loss and turn‐off loss of the temperature adaptive gate driver can be reduced, respectively, by 17% and 22%. At present, it has been used in an AC–DC converter to improve work efficiency.
Analysis of a novel resonant converter with series connected transformers
Authors: Chien Chang‐Hung , Wang Yeong‐Her , Lin Bor‐Ren
Published: May 2013

A novel zero‐voltage switching (ZVS) DC/DC converter with series connected transformers for high input voltage application is presented. Two series half‐bridge legs and two split capacitors are adopted in order to limit the voltage stress of active switches at Vin/2. Two resonant converter modules are used to reduce current stress on active switches and rectifier diodes. Based on the series resonant tank, the active switches are turned on at ZVS and rectifier diodes are turned off at zero‐current switching. Thus, the switching loss of active switches and reverse recovery problem of rectifier diodes are reduced. The secondary windings are connected in series to ensure that the primary winding currents are balanced. Finally, experiments are provided to verify the effectiveness of the proposed converter.
Composite observer‐based control algorithm for distribution static compensator in four‐wire supply system
Authors: Singh Bhim , Raj Arya Sabha
Published: May 2013

This study presents an implementation of composite observer‐based control algorithm in three‐leg voltage source inverter (VSI)‐based distribution static compensator (DSTATCOM) in four‐wire power distribution network. This control algorithm is used for extraction of load fundamental current components of polluted load currents. These components of load currents are used for estimation of reference source currents to generate the gating pulses of insulated gate bipolar transistors used in VSI of DSTATCOM. This control algorithm is implemented for mitigation of power quality problems such as reactive power compensation, harmonic elimination and load balancing under linear/non‐linear loads. The performance of DSTATCOM is found quite satisfactory for these unbalanced loads.
Analysis of an interleaved zero‐voltage switching/zero current switching resonant converter with duty cycle control
Authors: Lin Bor‐Ren , Cheng Po‐Jen
Published: May 2013

An interleaved series resonant converter with fixed frequency pulse‐width modulation (PWM) is presented to achieve load current sharing, ripple current cancelation, zero‐voltage switching (ZVS) for power switches and zero‐current switching (ZCS) for rectifier diodes. Two three‐level DC converters with clamped diodes and flying capacitor are adopted to share load current. The voltage stress of power switches is clamped at one‐half of DC bus voltage. The interleaved PWM scheme is used to control two converters in order to reduce the output current ripple and size of output capacitor. The series resonant tank in three‐level PWM converter is adopted to realise ZVS turn‐on for all power switches andZCS for rectifier diodes. Thus, the switching losses of active switches are reduced and the reverse recovery losses of rectifier diodes are eliminated. The fixed frequency PWM operation is adopted to regulate output voltage, so that the drawback of a wide range of switching frequency in the conventional series resonant converters is overcome. Finally, experiments based on a scale‐down prototype are provided to verify the effectiveness of the proposed converter.
Control and quantification of kinetic energy released by wind farms during power system frequency drops
Authors: Attya Ayman Bakry Taha , Hartkopf Thomas
Published: May 2013

High wind energy penetration levels in modern power systems draw attention towards wind farms expected role during frequency drops. Wind farms positive contribution required by system operators basically depends on the amount of kinetic energy stored in wind turbines rotating parts and how to manage it during frequency deviations elimination. This study presents an algorithm to estimate and control the quantity of extractable kinetic energy stored in a wind farm during frequency drops. Moreover, it manages stored kinetic energy release within a given time span to achieve positive participation in frequency drops clearance. The proposed method is based on tuning the tip speed ratio before and during the frequency drop according to several factors. The recovery time required by the wind turbine to retain its normal speed is also a function of several parameters including turbine inertia and the incoming wind speed. The proposed algorithm's impact on power system frequency is analysed by assessing the expected enhancement in frequency deviation. A hypothetical grid is considered as the benchmark including detailed modelling for wind speeds, wind turbine and wind farm to improve the creditability of the obtained results. Presented research work outcomes highlight the impact of wind farms replacement for conventional generators. Executed simulations proved that applying the proposed algorithm neutralises wind energy penetration influence on system frequency response, even more, it causes solid improvements unless the incident wind speed is too slow or the frequency drop is too high. Simulation environments are MATLAB and Simulink.
Residual doping concentration estimation in a separation by IMplanted OXygen film using current measurements
Authors: Ravariu Cristian
Published: May 2013

In situ measurements of static characteristics for an ad‐hoc silicon‐on‐insulator (SOI) device represent an important method for SOI technologies characterisation. The Separation by IMplanted OXygen (SIMOX) technique is based on oxygen ions implantation into Si‐film. After annealing, an increased doping concentration was reported, because of the residual oxygen clusters within the film, giving rise to oxygen thermal donors. Therefore this study offers an original algorithm for doping concentration estimation in these SOI films. A specific device used for in situ electrical characterisation of SOI wafers is the pseudo‐metal oxide semiconductor (MOS) transistor. In this study, the doping concentrations extraction is based on graphical solution of a non‐linear equation and third‐order derivative zeroing of the measured static characteristics. In this scope, experimental curves ID–VG, in inversion and accumulation were experimentally measured for a pseudo‐MOS transistor made in SIMOX technology. In this situation, the threshold and flat‐band voltage are extracted, free of classical conventions. The extracted doping concentration in film is roughly 5.8 × 1015 cm− 3; also the conductivity is changed from p to n in film, as the literature predicted.
Genetic algorithm‐optimised charge simulation method for electric field modelling of plate‐type electrostatic separators
Authors: Abouelsaad Mohamed M. , Abouelatta Mohamed A. , Salama Abd‐Elhadi R.
Published: May 2013

A novel combination of genetic algorithms (GAs) and the charge simulation method (CSM) is proposed for enhancing the computation precision of electric fields associated with plate‐type electrostatic separators; a new recycling technology of electrical and electronics waste. An algorithm is developed to, automatically, arrive at optimal arrangement of the simulating charges and their locations in order to eliminate dependency on user judgment and experience. Accurate results for electric field computation, compared with earlier published techniques, are realised for several design parameters of the separator. Experiments carried out for determination of detachment fields of small metallic particles (steel spheres of radius 0.501 mm) confirmed validity of the numerical simulation. The present work shows that the coupled GA–CSM algorithm can be an efficient and flexible design tool for accurate field computation of electrostatic separation equipment.
Calibration and operation of a fibre Bragg grating temperature sensing system in a grid‐connected hydrogenerator
Authors: Werneck Marcelo Martins , Allil Regina Célia da Silva Barros , Ribeiro Bessie A.
Published: May 2013

There have been many applications of fibre Bragg grating (FBG) in temperature measurements; however, there are no studies concerned with their application, uncertainty and repeatability as temperature sensor in the electric power industry. This study describes the research, construction, calibration and operation of an FBG‐based temperature system performing a continuous monitoring of temperature inside a fully operational and connected‐to‐the‐grid hydroelectric generator. The FBGs were calibrated for quantification of parameters such as uncertainty, sensitivity, linearity and error. The plot of calibrating temperature against measured temperature presented a one‐to‐one fitting accuracy to the third decimal place, uncertainty errors smaller than 1°C and a correlation coefficient R2 = 0.99996, demonstrating good linearity and accuracy of FBG sensors for temperature measurements. After being deployed for 2.5 years, the system has proved itself to be capable of reliably and accurately measuring and monitoring temperatures inside the generator, even taking into consideration the harsh environment. Results showed that the optical system provides a better electromagnetic interference immunity when compared with conventional temperature sensors. With this system in operation, a huge amount of installation and maintenance costs could be avoided with the replacement of many kilometres of electric wires by a few optical cables.
Control of a class of non‐linear uncertain chaotic systems via an optimal Type‐2 fuzzy proportional integral derivative controller
Authors: Khooban Mohammad Hassan , Alfi Alireza , Abadi Davood Nazari Maryam
Published: May 2013

This study deals with the problem of controlling a class of uncertain non‐linear systems in the presence of external disturbances. To achieve this goal, a novel optimal Type‐2 fuzzy proportional integral derivative (OT2FPID) controller is introduced. In the proposed controller, a novel heuristic algorithm namely particle swarm optimisation with random inertia weight (RNW–PSO) is employed. To achieve an optimal performance, the parameters of the proposed controller as well as the input and output membership functions are optimised simultaneously by RNW–PSO. To evaluate the performance of the proposed controller, the results are compared with those obtained by optimal H∞ adaptive proportional integral derivative controller, which is the latest research in the problem in hand. Simulation results show the effectiveness of the OT2FPID controller.
Study on transfection of bone morphogenetic protein‐2 gene into rabbit bone marrow stromal cells and composition to nanohydroxyapatite for constructing tissue engineered bones
Authors: Li Wencui , Liu Lijun , Zhu Weimin , Wang Daping , Zeng Yanjun
Published: May 2013

A study is presented on effects of the adenovirus‐mediated human bone morphogenetic protein‐2 (Ad‐BMP‐2) expression vector's transfection into rabbit bone marrow stromal cells (rBMSCs) and the subsequent composition to nanohydroxyapatite (Nano‐HA) for the construction of biomimetic artificial bone in vitro. The adenovirus vector was constructed by Gateway TM technology, and the rBMSCs transfected by Ad‐BMP‐2 were cultured in vitro. Immunohistochemistry, reverse transcriptase‐polymerase chain reaction and Western blot were used to detect the bone morphogenetic protein‐2 (BMP‐2) expression. After culture for 48 h, the transfected cells were seeded onto the Nano‐HA scaffold. Scanning electron microscopy (SEM) was used to observe the growth and attachment of cells on the composite scaffold on the third and fifth days. After transfection, the hBMP‐2 gene showed high expressions in mRNA and protein levels. SEM revealed even distribution and fine adherence of the cells in the composite scaffold. The Western blot showed high expression of BMP‐2 in the transfected and compound cells. The target cells that were transfected with the adenovirus vector that contained the genes, were bonded to the Nano‐HA scaffold, and therefore the cell carrier complexes became stable and effectively secreted growth factors, and the biomimetic artificial bones were successfully constructed in vitro.
Repositioning technique in nanowire manipulation by oscillating gripper
Authors: Toku Yuhki , Kobayashi Kohtaro , Muraoka Mikio
Published: May 2013

In this study, a manipulation device is developed that is able to pick up and reposition a nanomaterial. In the device, the gripper, composed of two silicon microcantilevers, is actuated by XYZ stages on a rotational stage and has eight degrees of freedom. One of the microcantilevers can be vibrated at a resonant frequency by an acoustic oscillator mounted on the gripper base. We successfully picked up a copper (II) oxide NW grown on a substrate and then repositioned the NW. During the picking‐up process, the NW was statically bent to break at the root by the gripper motion, or cyclically bent using the acoustic oscillator to induce a fatigue fracture. During the repositioning process, natural adhesion between the NW and the gripping surface often presented a challenge when removing the NW. This difficulty was overcome by vibrating the gripping surface, which resulted in the reduction of the adhesion effects. The mechanism of the reduction of the adhesion effects is discussed concerning the relationship between the adhesion energy and the peeling force acting on the NW. Another technique of repositioning using an inertia force generated by the oscillator is also discussed.
Evolutionary algorithm and parameters extraction for dye‐sensitised solar cells one‐diode equivalent circuit model
Authors: Peng Wei , Zeng Yun , Gong Hao , Leng Yong‐qing , Yan Yong‐hong , Hu Wei
Published: May 2013

With the aim of improving energy conversion efficiency of dye‐sensitised solar cells (DSCs), three evolutionary algorithms (EAs), namely genetic algorithm, particle swarm optimisation (PSO) and differential evolution, are investigated the first time to extract the DSCs parameters based on the single‐diode photovoltaic (PV) equivalent circuit model. By comparing the accuracy, calculation speed and anti‐noise ability of the three EA techniques, PSO shows the highest accuracy and the best anti‐noise property. To evaluate the parameters, especially the series‐internal resistance (Rs) that is important for DSCs energy conversion efficiency, a batch of DSCs devices were made and the Rs obtained by changing the series resistance value connected with the DSCs. The two methods give the Rs approximately equal value, and almost same current–voltage figures based on PSO simulation with measured characteristics, which prove PSO is an efficient computational method and can be used to extract the parameters for the DSCs PV model.
Chloroform‐sensing properties of plasmonic nanostructures using poly(methyl methacrylate) transduction layer
Authors: Ma Wenying , Luo Ji , Ling Weiwei , Wang Weimin
Published: May 2013

The design and development of a sensitive, fast and selective chloroform vapour sensor based on a poly(methyl methacrylate) (PMMA) transduction layer and a plasmonic nanostructures transducer is presented. The PMMA layer swelled when it was in exposure to the vapours, which would in turn bring in an extinction efficiency change in the localised surface plasmon resonance (LSPR) spectrum for triangular silver nanoprisms. The LSPR spectral response to chloroform and other vapours was measured by a UV–vis spectrometer in real time. Experiment results showed that the PMMA–LSPR sensor indicated a sensitivity of 4.76 × 10−5 ppm−1 and a detection limit of 21 ppm. A fast, stable and reversible response was observed during positive and negative test cycles upon variations of the environment in the gas cell between clean air and saturated chloroform contained air. The PMMA–LSPR sensor also showed good selectivity of chloroform when it was exposed to vapours with different functional groups. It has been demonstrated that plasmonic nanostructures coated with PMMA transduction films can be applied to chloroform sensing and vapour classifying applications.
Rayleigh‐instability‐driven dewetting of thin Au and Ag films on indium–tin‐oxide surface under nanosecond laser irradiations
Authors: Ruffino Francesco , Carria Egidio , Kimiagar Salimeh , Crupi Isodiana , Grimaldi Maria Grazia
Published: May 2013

Investigations have been carried out on laser‐beam‐induced nanoparticle (NP) formation in thin (5 nm) Au and Ag films on indium–tin‐oxide substrate. After the irradiation the films were observed to break‐up into NPs through a dewetting mechanism. This mechanism was investigated as a Rayleigh‐instability‐driven process. In fact, for each used laser fluence, the resulting Au and Ag NPs' mean size and surface‐to‐surface mean distance were quantified and correlated between them in the framework of the Rayleigh‐instability theory showing an excellent agreement.
Synthesis, microstructure and magnetic properties of Heusler Co2FeSn nanoparticles
Authors: Li Tao , Duan Jihong , Yang Chunkui , Kou Xinli
Published: May 2013

Heusler Co2FeSn nanoparticles in a B 2‐type cubic structure were synthesised for the first time using a simple solution reduction method. X‐ray diffraction, a scanning electron microscope, an energy dispersive spectrometer and a vibrating sample magnetometer were used to characterise the synthesised products. The crystal structure and composition of the samples vary with the concentration of potassium hydroxide, synthesis temperature and reaction time. Magnetic measurement reveals that the obtained Co2FeSn nanoparticles are soft magnetic at room temperature. The Co2FeSn nanoparticles synthesised in this work are magnetically superior and economically feasible for spintronic applications.
Non‐local modelling on the buckling of a weakened nanobeam
Authors: Zhang Yongqiang , Pang Miao , Chen Weiqiu
Published: May 2013

In the framework of the theory of non‐local elasticity, a model on the buckling of a weakened nanobeam subjected to constant axial load is presented. Based on this model, the characteristic equation for a simply supported weakened nanobeam is obtained, through which the value of buckling load can be determined. The influences of small length scale and weakened junction on the buckling load are discussed. It is shown that the buckling load is dependent upon the scale coefficient, junction stiffness and junction location.
Uncertainty quantification in MD simulations of concentration driven ionic flow through a silica nanopore. I. Sensitivity to physical parameters of the pore
Authors: Rizzi F. , Jones R. E. , Debusschere B. J. , Knio O. M.
Published: May 2013

In this article, uncertainty quantification is applied to molecular dynamics (MD) simulations of concentration driven ionic flow through a silica nanopore. We consider a silica pore model connecting two reservoirs containing a solution of sodium (Na+) and chloride (Cl−) ions in water. An ad hoc concentration control algorithm is developed to simulate a concentration driven counter flow of ions through the pore, with the ionic flux being the main observable extracted from the MD system. We explore the sensitivity of the system to two physical parameters of the pore, namely, the pore diameter and the gating charge. First we conduct a quantitative analysis of the impact of the pore diameter on the ionic flux, and interpret the results in terms of the interplay between size effects and ion mobility. Second, we analyze the effect of gating charge by treating the charge density over the pore surface as an uncertain parameter in a forward propagation study. Polynomial chaos expansions and Bayesian inference are exploited to isolate the effect of intrinsic noise and quantify the impact of parametric uncertainty on the MD predictions. We highlight the challenges arising from the heterogeneous nature of the system, given the several components involved, and from the substantial effect of the intrinsic thermal noise.
On the relationship between the classical Dicke-Jaynes-Cummings-Gaudin model and the nonlinear Schrödinger equation
Authors: Du Dianlou , Geng Xue
Published: May 2013

In this paper, the relationship between the classical Dicke-Jaynes-Cummings-Gaudin (DJCG) model and the nonlinear Schrödinger (NLS) equation is studied. It is shown that the classical DJCG model is equivalent to a stationary NLS equation. Moreover, the standard NLS equation can be solved by the classical DJCG model and a suitably chosen higher order flow. Further, it is also shown that classical DJCG model can be transformed into the classical Gaudin spin model in an external magnetic field through a deformation of Lax matrix. Finally, the separated variables are constructed on the common level sets of Casimir functions and the generalized action-angle coordinates are introduced via the Hamilton-Jacobi equation.
Shunting inhibitory cellular neural networks with chaotic external inputs
Authors: Akhmet M. U. , Fen M. O.
Published: May 2013

Taking advantage of external inputs, it is shown that shunting inhibitory cellular neural networks behave chaotically. The analysis is based on the Li-Yorke definition of chaos. Appropriate illustrations which support the theoretical results are depicted.
Electron microscopy investigations of purity of AlN interlayer in AlxGa1−xN/GaN heterostructures grown by plasma assisted molecular beam epitaxy
Authors: Sridhara Rao D. V. , Jain Anubha , Lamba Sushil , Muraleedharan K. , Muralidharan R.
Published: May 2013

The electron microscopy was used to characterize the AlN interlayer in AlxGa1−xN/AlN/GaN heterostructures grown by plasma assisted molecular beam epitaxy (PAMBE). We show that the AlN interlayer grown by PAMBE is without gallium and oxygen incorporation and the interfaces are coherent. The AlN interlayer has the ABAB stacking of lattice planes as expected for the wurtzite phase. High purity of AlN interlayer with the ABAB stacking leads to larger conduction band offset along with stronger polarization effects. Our studies show that the origin of lower sheet resistance obtained by PAMBE is the purity of AlN interlayer.
Principal physical properties of GaN/AlN multiquantum well systems determined by density functional theory calculations
Authors: Strak Pawel , Kempisty Pawel , Ptasinska Maria , Krukowski Stanislaw
Published: May 2013

A critical comparison of three polarization based approaches with the fields in AlN/GaN multiple quantum wells (MQWs) systems proved that they give identical results. The direct density functional theory (DFT) results, i.e., the fields, are in qualitative agreement with data obtained within the polarization theory. The results of DFT calculations of an AlN/GaN MQW system were used in the projection method to obtain a spatial distribution of the bands in the structure with atomic resolution. In parallel, the plane averaged and c-smoothed potential profiles obtained from the solution of the Poisson equation were used to determine the electric field in the multiquantum well structures and the magnitude of dipole layers at the AlN/GaN heterostructures. The dipole layers cause potential jumps of about 2.4 V that seriously affects the band offsets. The presence of the dipole layer is in good agreement with the potential measurements by electron holography. It was shown that the wells of the width up to 4 Ga layers behave as potential minima, but the wider layers behave as standard quantum wells. The barriers up to 3 Al layers do not localize the carriers. It is shown that the Quantum Confined Stark Effect causes a huge decrease of their energies and oscillator strengths of the optical transitions, especially for wider structures. For wider wells, the strengths fall much faster for perpendicular polarization which indicates the important role of the anisotropic band offsets. A direct simulation shows that the band offset for the valence band crystal field split off hole states, i.e., pz states are different from heavy and light hole (i.e., p⊥=px⊗py) states being equal to valence band offset (VBO)⊥=0.85 eV and rough estimate of VBOII≅0.5 eV, respectively. These values are in good agreement with the recently reported measurement of AlN/GaN offsets.
Mechanical stress influence on electronic transport in low-k SiOC dielectric single damascene capacitor
Authors: Yang Ya-Liang , Young Tai-Fa , Chang Ting-Chang , Shen Fu-Yen , Hsu Jia-Haw , Tsai Tsung-Ming , Chang Kuan-Chang , Chen Hisn-Lu
Published: May 2013

We fabricate a SiOC comb structure capacitor device, and apply mechanical stress into samples by bending. From I-V fitting, we obtain the energy barrier lowering β, and conclude that the electron transport in single damascene capacitor is due to Poole-Frenkel emission. Tension yields a decrease of energy barrier in the single damascene dielectric layer and an increase of leakage current compared to the unstressed sample. In contrast, compression stress yields the energy barrier increase and the leakage current decrease. The variation of leakage current is originated from the energy barrier change induced by mechanical stress.
Solitonic Dirac fermion wave guide networks on topological insulator surfaces
Authors: Hammer René , Ertler Christian , Pötz Walter
Published: May 2013

Magnetic texturing on the surface of a topological insulator allows the design of wave guide networks and beam splitters for domain-wall Dirac fermions. Guided by simple analytic arguments, we model a Dirac domain-wall fermion interferometer consisting of two parallel pathways imprinted by solitonic ferromagnetic texturing. A specially developed staggered-grid leap-frog discretization scheme in 2 + 1 dimensions with absorbing boundary conditions is employed to study the interferometer in an open device geometry. Its net transmission can be tuned from constructive to destructive interference, either by variation of the magnetization texture (effective path length) or an applied gate bias (wavelength). Possible ways to observe and utilize this effect are discussed.
DropBot: An open-source digital microfluidic control system with precise control of electrostatic driving force and instantaneous drop velocity measurement
Authors: Fobel Ryan , Fobel Christian , Wheeler Aaron R.
Published: May 2013

We introduce DropBot: an open-source instrument for digital microfluidics (http://microfluidics.utoronto.ca/dropbot). DropBot features two key functionalities for digital microfluidics: (1) real-time monitoring of instantaneous drop velocity (which we propose is a proxy for resistive forces), and (2) application of constant electrostatic driving forces through compensation for amplifier-loading and device capacitance. We anticipate that this system will enhance insight into failure modes and lead to new strategies for improved device reliability, and will be useful for the growing number of users who are adopting digital microfluidics for automated, miniaturized laboratory operation.
Controlling magnetism of multiferroic (Bi0.9La0.1)2FeCrO6 thin films by epitaxial and crystallographic orientation strain
Authors: Khare Amit , Singh Abhishek , Prabhu S. S. , Rana D. S.
Published: May 2013

Effects of the tensile and compressive epitaxial strain and the crystallographic orientations on the structural and magnetic properties of (Bi0.9La0.1)2FeCrO6 (BLFCO) films were studied. The BLFCO (001) films (30 nm and 70 nm) were deposited on various single crystal substrates having lattice mismatch with the film in the range of −4.16% to +7.2%. We find that a pronounced ferromagnetic order manifests in the coherently strained films compared to that in the partially strained films. The saturation magnetic moment exhibits dissimilar effects on the type of the lattice mismatch: the coherent tensile strain is less favorable than the coherent compressive strain for the magnetic order in these films. We further establish that the ferromagnetic order exhibits maximum magnetic moment for (111)-oriented and minimum for (110)-oriented coherently strained BLFCO epitaxial films.
Ultra-thin free-standing single crystalline silicon membranes with strain control
Authors: Shchepetov A. , Prunnila M. , Alzina F. , Schneider L. , Cuffe J. , Jiang H. , Kauppinen E. I. , Sotomayor Torres C. M. , Ahopelto J.
Published: May 2013

We report on fabrication and characterization of ultra-thin suspended single crystalline flat silicon membranes with thickness down to 6 nm. We have developed a method to control the strain in the membranes by adding a strain compensating frame on the silicon membrane perimeter to avoid buckling after the release. We show that by changing the properties of the frame the strain of the membrane can be tuned in controlled manner. Consequently, both the mechanical properties and the band structure can be engineered, and the resulting membranes provide a unique laboratory to study low-dimensional electronic, photonic, and phononic phenomena.
Sub-picosecond and nanometer scale dynamics of aluminum target surface heated by ultrashort laser pulse
Authors: Deneuville F. , Chimier B. , Descamps D. , Dorchies F. , Hulin S. , Petit S. , Peyrusse O. , Santos J. J. , Fourment C.
Published: May 2013

The possibility of measuring surface hydrodynamics at picosecond and nanometer scales by using a time resolved optical interfero-polarimeter is demonstrated. This method is applied to observe the surface position of aluminum target heated by ultrashort laser pulse. Numerical simulations of the surface relaxation during a few tens of picoseconds after irradiation are in very good agreement with the measurements. Results show the important contribution of oxide layer in the surface dynamic evolution and the great accuracy of our experimental method.
Direct folding simulation of a long helix in explicit water
Authors: Gao Ya , Lu Xiaoliang , Duan Lili , Zhang Dawei , Mei Ye , Zhang John Z. H.
Published: May 2013

A recently proposed Polarizable Hydrogen Bond (PHB) method has been employed to simulate the folding of a 53 amino acid helix (PDB ID 2KHK) in explicit water. Under PHB simulation, starting from a fully extended structure, the peptide folds into the native state as confirmed by measured time evolutions of radius of gyration, root mean square deviation (RMSD), and native hydrogen bond. Free energy and cluster analysis show that the folded helix is thermally stable under the PHB model. Comparison of simulation results under, respectively, PHB and standard nonpolarizable force field demonstrates that polarization is critical for stable folding of this long α-helix.
A thermal logic device based on fluid-solid interfaces
Authors: Murad Sohail , Puri Ishwar K.
Published: May 2013

Thermal rectification requires that thermal conductivity not be a separable function of position and temperature. Investigators have considered inhomogeneous solids to design thermal rectifiers but manipulations of solid lattices are energy intensive. We propose a thermal logic device based on asymmetric solid-fluid resistances that couples two fluid reservoirs separated by solid-fluid interfaces. It is the thermal analog of a three terminal transistor, the hot reservoir being the emitter, the cold reservoir the output, and smaller input reservoirs as the base. Changing the input temperature alters the transport factor and the flux gain as does the base current in a transistor.
Optimized inverted polymer solar cells incorporating Cs2CO3-doped C60 as electron transport layer
Authors: Barbot A. , Lucas B. , Di Bin C. , Ratier B. , Aldissi M.
Published: May 2013

An efficient charge transfer between co-sublimed cesium carbonate (Cs2CO3) and fullerene C60 provides an n-type material exhibiting an electrical conductivity above 1 S/cm. This type of doped layers can be used in organic optoelectronic devices to reduce ohmic losses at organic-electrode interfaces. We report here an analysis of inverted polymer-based solar cells incorporating Cs2CO3 doped C60 as electron transport layer (ETL). The optimization of both dopant concentration and thickness resulted in a maximum efficiency of 3.79% compared to 3% for similar devices using undoped C60 as ETL and 2.13% for devices without any ETL.
Polymer–nanocrystal hybrid photodetectors with planar heterojunctions designed strategically to yield a high photoconductive gain
Authors: Kyu An Tae , Eon Park Chan , Sung Chung Dae
Published: May 2013

We demonstrate an approach to enhancing the photoresponsivity of a polymer photodetector (PPD). Both conventional bulk heterojunction (BHJ) and planar heterojunction (PHJ) PPDs were fabricated considering that the interface between a CdSe nanocrystal and a polymer can create photoconductive gain. A systematic study of the illumination wavelength and light power dependence of the photocurrent gain, combined with the charge carrier transport analysis, suggested that the PHJ-PPD could yield a higher hole mobility than could be achieved in a BHJ-PPD without compromising on the selective electron trapping effects. The optimized PHJ-PPD led to a photoconductive detectivity of 1.3 × 1010 cm Hz1/2/W.
Topography-guided spreading and drying of 6,13-bis(triisopropylsilylethynyl)-pentacene solution on a polymer insulator for the field-effect mobility enhancement
Authors: Keum Chang-Min , Bae Jin-Hyuk , Kim Min-Hoi , Park Hea-Lim , Payne Marcia M. , Anthony John E. , Lee Sin-Doo
Published: May 2013

We report on the enhancement of the field-effect mobility of solution-processed 6,13-bis(triisopropylsilylethynyl)-pentacene (TIPS-pentacene) by unidirectional topography (UT) of an inkjet-printed polymer insulator. The UT leads to anisotropic spreading and drying of the TIPS-pentacene droplet and enables to spontaneously develop the ordered structures during the solvent evaporation. The mobility of the UT-dictated TIPS-pentacene film (0.202 ± 0.012 cm2/Vs) is found to increase by more than a factor of two compared to that of the isotropic case (0.090 ± 0.032 cm2/Vs). The structural arrangement of the TIPS-pentacene molecules in relation to the mobility enhancement is described within an anisotropic wetting formalism. Our UT-based approach to the mobility enhancement is easily applicable to different classes of soluble organic field-effect transistors by adjusting the geometrical parameters such as the height, the width, and the periodicity of the UT of an inkjet-printed insulator.
Ultra-smooth epitaxial Ge grown on Si(001) utilizing a thin C-doped Ge buffer layer
Authors: Mantey J. , Hsu W. , James J. , Onyegam E. U. , Guchhait S. , Banerjee S. K.
Published: May 2013

Here, we present work on epitaxial Ge films grown on a thin buffer layer of C doped Ge (Ge:C). The growth rate of Ge:C is found to slow over time and is thus unsuitable for thick (>20 nm) layers. We demonstrate Ge films from 10 nm to >150 nm are possible by growing pure Ge on a thin Ge:C buffer. It is shown that this stack yields exceedingly low roughness levels (comparable to bulk Si wafers) and contains fewer defects and higher Hall mobility compared to traditional heteroepitaxial Ge. The addition of C at the interface helps reduce strain by its smaller atomic radius and its ability to pin defects within the thin buffer layer that do not thread to the top Ge layer.
Hysteresis mechanism and control in pentacene organic field-effect transistors with polymer dielectric
Authors: Huang Wei , Shi Wei , Han Shijiao , Yu Junsheng
Published: May 2013

Hysteresis mechanism of pentacene organic field-effect transistors (OFETs) with polyvinyl alcohol (PVA) and/or polymethyl methacrylate (PMMA) dielectrics is studied. Through analyzing the electrical characteristics of OFETs with various PVA/PMMA arrangements, it shows that charge, which is trapped in PVA bulk and at the interface of pentacene/PVA, is one of the origins of hysteresis. The results also show that memory window is proportional to both trap amount in PVA and charge density at the gate/PVA or PVA/pentacene interfaces. Hence, the controllable memory window of around 0 ∼ 10 V can be realized by controlling the thickness and combination of triple-layer polymer dielectrics.
Skin prick test reactivity to foods in adult Malaysians with rhinitis
Authors: Gendeh Balwant Singh , Murad Shahnaz , Razi Azizah Mohd , Abdullah Nasaruddin , Mohamed Abdullah Sani , Kadir Khalid Abdul
Published: May 2013

The aim of the study was to determine the incidence of food and house dust mite (HDM) allergy in patients with nasal congestion and rhinorrhea attending the Otorhinolaryngology Clinic, National University of Malaysia, Kuala Lumpur. This was a prospective matched, controlled study of patients skin prick tested with commercial food and common aeroallergens. The participants were 148 Malaysian adults with symptoms of nasal congestion and rhinorrhea and 113 adult Malaysian control subjects without rhinitis symptoms. The skin prick test (SPT) was used to evaluate 11 foods common to the Malaysian diet and 3 HDM inhalants. Forty‐eight percent of the patients with rhinitis had positive SPT results to foods, compared with 4.4% of control subjects (P < 0.05). The most commonly implicated foods were shrimp (48%) and rice (30%), which are common in the Malaysian diet. Seventy‐two percent of rhinitis patients had positive SPT results to HDM, compared with 22.2% of control subjects (P < 0.05). Patients with rhinitis also had significantly more gastrointestinal problems than control subjects (P < 0.05). The incidences of HDM and food allergy are significantly greater in Malaysian adults with rhinitis symptoms than in control subjects without rhinitis. The effect of avoidance or immunotherapy awaits further study.
Cost‐effective management of benign positional vertigo using canalith repositioning
Authors: Li John C. , Li Celeste J. , Epley John , Weinberg Lynn
Published: May 2013

OBJECTIVE

The misdiagnosis and inappropriate treatment of benign positional vertigo have resulted in significant costs to the medical system. In the current medical‐economic climate, there is an increased emphasis on cost control. Recent studies have shown that the canalith repositioning procedure (CRP) is effective; the next step is to show the impact of CRP in cost‐effective management of benign positional vertigo.

METHODS

Forty‐six of 100 patients who underwent CRP for benign positional vertigo responded to a survey regarding the financial impact of their disease. They were asked to subjectively estimate the sum of all disease‐related expenses. Objective substantiation of this number was estimated by tabulating physician data, laboratory data, and failed treatment costs.

RESULTS

The subjective figure totaled $2684.74 per individual. Summation of the tangible objective figures yielded $2009.63 per patient, corroborating the subjective figure.

CONCLUSIONS

Because CRP is a relatively simple procedure that can obviate many wasted expenses in most patients, we believe that it is very cost‐effective and should be incorporated into routine practice.
Preapplication of mitomycin C for enhanced patency of myringotomy
Authors: Estrem Scott A. , Baker Terry J.
Published: May 2013

OBJECTIVES

Ventilation tubes are the mainstay of surgical treatment for eustachian tube dysfunction and have been used successfully for many years. Certain disadvantages of ventilation tubes, however, have prompted research into alternative techniques including laser myringotomy. We investigated the use of KTP laser myringotomy in conjunction with topical mitomycin C to delay healing and prolong the patency of the myringotomy.

METHODS

Twenty myringotomies were created in 10 Sprague‐Dawley rats. A solution of mitomycin C was applied to the intact tympanic membrane for 15 minutes. The solution was then suctioned free, and a myringotomy was created with a KTP laser. Fifty‐three rats with saline application serving as controls from a previous study were used to allow statistical assessment.

RESULTS

The myringotomies remained open for a median of 9.5 weeks. Control myringotomies, which received saline solution instead of mitomycin C, healed within a median of 1.5 weeks. The difference was statistically significant at P < 0.0001. No complications were noted.

CONCLUSION

Topically administered mitomycin C before laser myringotomy is effective in prolonging the patency of laser myringotomies in rats. The patency rate is similar to that achieved in experiments in which topical mitomycin C is placed into the myringotomy site created by the laser.
Octreotide scintigraphy for the detection of paragangliomas
Authors: Telischi Fred F. , Bustillo Andres , Whiteman Michelle L. H. , Serafini Aldo N. , Reisberg Michael J. , Gomez‐Marin Orlando , Civantos Francisco J. , Balkany Thomas J.
Published: May 2013

Paragangliomas are neuroendocrine tumors located primarily in the head and neck region, but they can also occur at other sites. Confirming the preoperative diagnosis and detecting synchronous tumors may be difficult in some patients. Octreotide is a somatostatin analog that, when coupled to a radioisotope, produces a scintigraphic image of tumors expressing somatostatin type 2 receptors. Paragangliomas, like many neuroendocrine tumors, have been found to have a high density of somatostatin type 2 receptors on the cell surface. This study compared the results of preoperative octreotide scintigraphy with the histopathology in 21 patients who underwent surgery for presumed head and neck paragangliomas. Octreotide scan findings were positive in 16 patients with paragangliomas and negative in 3 patients with other pathology. One false‐positive and 1 false‐negative result were obtained. Thus, this test had an accuracy of 90%, a sensitivity of 94%, and a specificity of 75%. Previously unidentified synchronous tumors were identified in 5 patients. On the basis of this series of patients, octreotide scintigraphy appears to be a reliable test to detect paragangliomas and may be quite helpful in preoperative planning.