bluuebunny/crossref_metadata_2025 huggingface dataset:
PKC-β Exacerbates in vitro Brain Barrier Damage in Hyperglycemic Settings via Regulation of RhoA/Rho-kinase/MLC2 Pathway
Authors: Srivastava Kirtiman , Shao Beili , Bayraktutan Ulvi
Published: August 2013

Stroke patients with hyperglycemia (HG) develop higher volumes of brain edema emerging from disruption of blood–brain barrier (BBB). This study explored whether inductions of protein kinase C- β (PKC- β) and RhoA/Rho-kinase/myosin-regulatory light chain-2 (MLC2) pathway may account for HG-induced barrier damage using an in vitro model of human BBB comprising human brain microvascular endothelial cells (HBMEC) and astrocytes. Hyperglycemia (25 mmol/L D-glucose) markedly increased RhoA/Rho-kinase protein expressions (in-cell westerns), MLC2 phosphorylation (immunoblotting), and PKC- β (PepTag assay) and RhoA (Rhotekin-binding assay) activities in HBMEC while concurrently reducing the expression of tight junction protein occludin. Hyperglycemia-evoked in vitro barrier dysfunction, confirmed by decreases in transendothelial electrical resistance and concomitant increases in paracellular flux of Evan's blue-labeled albumin, was accompanied by malformations of actin cytoskeleton and tight junctions. Suppression of RhoA and Rho-kinase activities by anti-RhoA immunoglobulin G (IgG) electroporation and Y-27632, respectively prevented morphologic changes and restored plasma membrane localization of occludin. Normalization of glucose levels and silencing PKC- β activity neutralized the effects of HG on occludin and RhoA/Rho-kinase/MLC2 expression, localization, and activity and consequently improved in vitro barrier integrity and function. These results suggest that HG-induced exacerbation of the BBB breakdown after an ischemic stroke is mediated in large part by activation of PKC- β.
Differential lung NK cell responses in avian influenza virus infected chickens correlate with pathogenicity
Authors: Jansen Christine A. , de Geus Eveline D. , van Haarlem Daphne A. , van de Haar Peter M. , Löndt Brandon Z. , Graham Simon P. , Göbel Thomas W. , van Eden Willem , Brookes Sharon M. , Vervelde Lonneke
Published: August 2013

Infection of chickens with low pathogenicity avian influenza (LPAI) virus results in mild clinical signs while infection with highly pathogenic avian influenza (HPAI) viruses causes death of the birds within 36–48 hours. Since natural killer (NK) cells have been shown to play an important role in influenza-specific immunity, we hypothesise that NK cells are involved in this difference in pathogenicity. To investigate this, the role of chicken NK-cells in LPAI virus infection was studied. Next activation of lung NK cells upon HPAI virus infection was analysed. Infection with a H9N2 LPAI virus resulted in the presence of viral RNA in the lungs which coincided with enhanced activation of lung NK cells. The presence of H5N1 viruses, measured by detection of viral RNA, did not induce activation of lung NK cells. This suggests that decreased NK-cell activation may be one of the mechanisms associated with the enhanced pathogenicity of H5N1 viruses.
The maize leaf lipidome shows multilevel genetic control and high predictive value for agronomic traits
Authors: Riedelsheimer Christian , Brotman Yariv , Méret Michaël , Melchinger Albrecht E. , Willmitzer Lothar
Published: August 2013

Although the plant lipidome show an enormous level of structural and functional diversity, our knowledge about its genetic control and its connection to whole-plant phenotypes is very limited. Here, we profiled 563 lipid species with UPLC-FT-MS in 289 field-grown inbred lines genotyped with 56,110 SNPs. Genome-wide association study identified 174 associations for 76 lipids explaining up to 31.4% of the genetic variance (P-value 8.4 × 10−18). Candidate genes were found for lipid synthesis, breakdown, transfer and protection against peroxidation. The detected SNP-lipid associations could be grouped into associations with 1) individual lipids, 2) lipids from one biochemical class and 3) lipids from several classes, suggesting a multilevel genetic control architecture. We further found a strong connection between the lipidome and agronomic traits in field-evaluated hybrid progeny. A cross-validated prediction model yielded correlations of up to 0.78 suggesting that the lipidome accurately predicts agronomic traits relevant in hybrid maize breeding.
Origin of the Chemical and Kinetic Stability of Graphene Oxide
Authors: Zhou Si , Bongiorno Angelo
Published: August 2013

At moderate temperatures (≤ 70°C), thermal reduction of graphene oxide is inefficient and after its synthesis the material enters in a metastable state. Here,first-principlesand statistical calculations are used to investigate both the low-temperature processes leading to decomposition of graphene oxide and the role of ageing on the structure and stability of this material. Our study shows that the key factor underlying the stability of graphene oxide is the tendency of the oxygen functionalities to agglomerate and form highly oxidized domains surrounded by areas of pristine graphene. Within the agglomerates of functional groups, the primary decomposition reactions are hindered by both geometrical and energetic factors. The number of reacting sites is reduced by the occurrence of local order in the oxidized domains and due to the close packing of the oxygen functionalities, the decomposition reactions become – on average – endothermic by more than 0.6 eV.
Sliding mode control for stochastic Markovian jumping systems with incomplete transition rate
Authors: Chen Bei , Niu Yugang , Zou Yuanyuan
Published: August 2013

This study investigates the problem of sliding mode control for a class of stochastic Markovian jumping systems with partially known transition rate. A key feature in this work is to relax the requirement that all the elements in transition rate matrix are known, which does not always hold in actual applications. The finite set of modes is firstly divided into two parts, respectively, with known transitions rate and unknown one. Then, the sliding mode controller is designed to cope with the effect of partially known transition rate, in which two different robust terms are proposed, respectively, for the known and unknown modes. It is shown that both the reachability and asymptotic stability of sliding mode dynamics can be ensured by the present method, despite the partially known transition rate. Finally, numerical simulation results are given.
Sensor fault detection, isolation and system reconfiguration based on extended Kalman filter for induction motor drives
Authors: Zhang Xinan , Foo Gilbert , Don Vilathgamuwa Mahinda , Tseng King Jet , Bhangu Bikramjit Singh , Gajanayake Chandana
Published: August 2013

Induction motors (IMs) have been extensively used in industrial applications because of their inexpensiveness, ruggedness and reliability. Generally, to improve the performance of IM drives, one position sensor, one DC‐link voltage sensor and at least two AC current sensors are necessary. However, failure of any of these sensors can cause degraded system performance or even instability. Consequently, it is very important to develop a sensor fault resilient control system for IMs drives so that continuous and normal operation is maintained even in cases of sensor faults. This study proposes a compact and robust sensor fault detection, isolation and system reconfiguration algorithm based on extended Kalman filter and reduced number of adaptive observers. A comprehensive set of experimental results are provided to verify the effectiveness of the proposed algorithm.
Anisotropic properties of non‐oriented steel sheets
Authors: Chwastek Krzysztof
Published: August 2013

Even the so‐called non‐oriented steels used in electrical engineering reveal anisotropy of their magnetic properties. Anisotropy may have a substantial impact on the performance of magnetic circuits; therefore it is necessary to take this phenomenon into account already at the design stage. A simple formula useful for the description of magnetisation curves in two principal directions is proposed. The B(H) dependencies for other directions are determined using a model based on coenergy concept. The worst magnetic properties are obtained for the samples cut at approximately 60 degrees. The presented description may be useful for prediction of rotational loss in ferromagnetic sheets used as core material in electric machines.
Approximate model and low‐order harmonic reduction for high‐voltage direct current tap based on series single‐phase modular multilevel converter
Authors: Hao Quanrui , Li Guo‐Jie , Ooi Boon‐Teck
Published: August 2013

The series single‐phase modular multilevel converter (SSP–MMC) is investigated as one option for high‐voltage direct current tap aimed to reduce the number of switching devices by one‐third. First an approximation method is applied to calculate the sub‐module capacitor voltage of the proposed SSP–MMC. Based on that, the approximate equivalent circuits for ac and dc sides are both presented to demonstrate the mechanism of the second and third harmonics. Then the methods to reduce the second and third harmonics are proposed as parts of the overall control loop. Simulation results obtained in power system computer aided design (PSCAD) are provided to validate the brief equivalent models and the second and third harmonic reduction methods.
Three‐phase power flow calculations by direct ZLOOP method for microgrids with electric vehicle charging demands
Authors: Yang Nien‐Che
Published: August 2013

A three‐phase power flow solution approach for microgrids with electric vehicle (EV) demands is proposed in this study. Based on the loop frame of reference, a direct iterative approach is adopted. Most of microgrids are essentially unbalanced; hence, the proposed approach is developed based on true phase (a‐b‐c) frame, rather than the sequence‐component frame. Based on the true phase frame, the total dimension of the performance equations of the network is the minimum required to represent the microgrid system. The mathematical component models, such as feeders, capacitors/reactors, transformers, automatic voltage regulators, loads, distributed energy resource units and EV demands can easily be involved in the proposed approach. To examine the validity of the proposed algorithm, four IEEE sample systems and a practical Taiwan Power Company distribution system are used as benchmarks for comparisons. The test results show that the proposed approach is accurate, efficient and robust with minimum memory requirements for three‐phase power flow studies.
Loss‐of‐field detection in synchronous generators using decision tree technique
Authors: Amraee Turaj
Published: August 2013

A loss‐of‐field (LOF) detection scheme is proposed based on the decision tree (DT) technique. The proposed method is a response‐based scheme. Instead of direct detection of LOF the proposed scheme provide the LOF protection based on simple measurements at generator terminal. The trajectories of generator terminal voltage and generated active and reactive powers are used as new features in LOF detection. The proposed DT‐based technique is robust and adaptive and keeps its performance under different fault scenarios. This scheme automatically adapts to favourable conditions near decision boundary and detects relevant features by the concept of information gain. The proposed method is simulated for a dynamic system under various fault conditions and the results are compared with a multilayer perceptron network classifier for various classification features.
Vibration sensitivity reduction of two microwave oscillators using inter‐injection locking technique
Authors: Modarresi Mohammad Reza , Banai Ali , Farzaneh Forouhar
Published: August 2013

Phase noise is one of the most important specifications of microwave oscillators. External factors such as mechanical vibrations increase the phase noise of the oscillator. A novel technique is introduced to reduce vibration‐induced phase noise using inter‐injection locking of two coupled oscillators. Two similar oscillators with equal free running frequencies are chosen and are subjected to sinusoidal vibration. The mechanical configuration is such that vibration sensitivity vector increases the frequency of one oscillator and decreases the other one's frequency of oscillation. Coupling these two oscillators using inter‐injection locking, the common after‐lock frequencies of both oscillators would be equal to the free running frequency of oscillation; as such the influence of vibration on the oscillators is reduced. Experimental measurements are carried out to confirm the proposed technique.
Multiple‐input DC/DC converter topology for hybrid energy system
Authors: Kumar Lalit , Jain Shailendra
Published: August 2013

In this study, a multiple‐input non‐isolated DC/DC converter topology is presented. The proposed multiple‐input DC/DC converter is proficient for energy diversification from renewable and storage energy sources individually or simultaneously. It can be operated in buck, boost and buck–boost modes of operation with the capability of bidirectional power flow to achieve desired voltage level on either side. The development of small‐signal modelling based on state‐space averaging has been discussed. In addition, a power management control scheme for the proposed converter has also been presented. The proposed concept has been investigated through simulation using the MATLAB/Simulink environment and validated experimentally on a laboratory prototype using dSPACE 1103 real time digital controller.
Space vector‐based three‐level discontinuous pulse‐width modulation algorithm
Authors: Beig Abdul Rahiman , Kanukollu Saikrishna , Dekka Apparao
Published: August 2013

Discontinuous pulse‐width modulation (PWM) techniques result in reduced power loss in voltage source inverters. This study presents the space vector approach to the three‐level discontinuous PWM technique. The switching sequences for four basic types of discontinuous PWM and the implementation are presented. An improved discontinuous PWM algorithm is presented for low modulation index region. All these algorithms are verified experimentally and the results are presented. The performance of discontinuous PWM algorithms is compared with that of conventional space vector‐based PWM algorithms.
Comparative study of multilevel inverters under unbalanced voltage in a single DC link
Authors: Maswood Ali I. , Gabriel Ooi H. P. , Al Ammar Essam
Published: August 2013

This study explores the feasibility of an AC/DC/AC drive with near unity power factor front‐end rectifier and five‐level rear‐end multilevel inverter topology with a focus on achieving lower voltage total harmonic distortion and higher energy efficiency. The unity PF front‐end rectifier in this AC/DC/AC drive may cause unbalanced voltage in the DC bus capacitors leading to high voltage distortion on the output AC voltage of a rear‐end multilevel inverter. Based on the analysis, modelling and experimental results, rear‐end multilevel flying‐capacitor inverter with unity PF front‐end rectifier in an AC/DC/AC power drive is proposed which is able to provide better DC voltage balancing when compared to diode‐clamped topology. Having no diode components being used in this multilevel inverter, the flying‐capacitor topology produces lesser commutation losses. Furthermore, rear‐end multilevel flying‐capacitor topology offers better efficiency and good quality output voltage without any bulky and expensive LC filter and even without any additional DC voltage balancing circuitry. The analytical performance of the drive is verified on a 1.3 kW laboratory prototype.
Thirteen‐level cascaded H‐bridge inverter operated by Generic phase shifted pulse‐width modulation
Authors: Rabinovici Raul , Baimel Dmitry , Tomasik Jacek , Zuckerberger Adrian
Published: August 2013

The study proposes a new Generic phase shifted (PS) pulse‐width modulation (PWM) approach. Four Generic PS PWM algorithms are proposed. The important advantage of the proposed approach is that it can be easily implemented with multilevel inverters of any topology. The first method produces the 13‐level PS PWM signal from six 3‐level phase disposition (PD) PWM signals whose carrier signals are PS from each other by the time interval of 1/(6fcarrier). The second method produces the 13‐level PWM signal also from six 3‐level PD PWM signals, whereas their modulation and the carrier signals are both PS by the time interval of Tmodulation/(6 × 5), where Tmodulation is the modulation cycle time interval. The third method produces the 13‐level PWM signal from three 5‐level PD PWM signals, whereas their carrier signals are PS from each other by the time interval of 1/(3fcarrier). The fourth method produces the 13‐level PS PWM signal from three 5‐level PD PWM signals, whereas their modulation and carrier signals are both PS by the time interval of Tmodulation/(3 × 5). The proposed methods are analysed and compared one to the other and to the conventional PD PWM method. The analysis is validated by extensive simulation results.
Design and implementation of a low cost, high yield dielectric barrier discharge ozone generator based on the single switch resonant converter
Authors: Salam Zainal , Facta Mochammad , Amjad Muhammad , Buntat Zolkafle
Published: August 2013

This work proposes a low cost ozone generator which is capable of producing high ozone yield. Its dielectric barrier discharge planar‐shaped chamber is constructed using common materials; the electrodes are made of aluminium mesh and copper plate, whereas muscovite mica is used as the dielectric. The availability of thin mica sheet (< 1 mm) allows for the lowering of the initiation voltage without the use of discharge gas. The chamber is fed by a high‐voltage power supply that utilises the single switch resonant converter topology with ferrite transformer. To validate the idea, an experimental prototype ozone generator is designed and constructed. The generator is fed by a low‐voltage DC power supply (8–17 V) and does not require water or air‐cooling for its chamber. Despite its small footprint, the maximum achievable ozone yield is 120 g/kWh at 2.0 l/min, with measured efficiency of 75%. Finally, the performance of the proposed generator is critically evaluated in comparison with several important works in the same area.
Novel three‐phase asymmetrical cascaded multilevel voltage source inverter
Authors: Belkamel Hamza , Mekhilef Saad , Masaoud Ammar , Abdel Naeim Mohsen
Published: August 2013

Series connection of power cells in asymmetrical cascaded configurations helps to cancel redundant output levels and maximise the number of different levels generated by the inverter. A new configuration of three‐phase multilevel asymmetrical cascaded voltage source inverter is presented. This structure consists of series‐connected sub‐multilevel inverters blocks. The number of utilised switches, insulated gate driver circuits, voltage standing on switches, installation area and cost are considerably reduced. Cascaded‐cell DC voltages in each inverter leg form an arithmetic sequence with common difference of E. With the selected inverter DC sources, high‐frequency pulse‐width modulation (PWM) control methods can be effectively applied without loss of modularity. Low‐frequency and sinusoidal PWM techniques were successfully applied. Hence, high flexibility in the modulation of the proposed inverter is demonstrated. The prototype of the suggested inverter was manufactured and the obtained simulation and hardware results ensured the feasibility of the configuration, and the compatibility of both modulation techniques was accurately noted. Lastly, the semiconductor losses in the converter were calculated using simulation models. Based on the analysis of the total power losses, the proposed inverter provided high efficiency at different operating conditions.
Active anti‐islanding detection based on pulse current injection for distributed generation systems
Authors: Hou Chung‐Chuan , Chen Yu‐Chun
Published: August 2013

This study proposes an active anti‐islanding detection using an adjustable pulse current for distributed generation systems. The pulse current injection is utilised to find out difference voltage response between utility systems and islanding operation systems within 2.8 ms, which is faster than conventional current injection methods. Furthermore, the power line communication is utilised to keep islanding detection system with accuracy. Finally, the performances of the proposed scheme are validated by simulation and test results.
Reciprocal effects of the distorted wind turbine source and the shunt active power filter: full compensation of unbalance and harmonics under ‘capacitive non‐linear load’ condition
Authors: Rahmani Bijan , Tavakoli Bina Mohammad
Published: August 2013

Available compensating algorithms for shunt active power filters (SAPFs) and unified power quality conditioner perform somehow improperly in practice under certain circumstances. Typical examples could be any distorted ‘non‐linear loads’ showing low impedances at certain frequencies; also, there are technological limitations for the SAPF in modulating switching frequencies, including microcontroller processing speed, the employed control and modulation techniques, delays and so on. This study proposes an advanced universal power quality conditioning system (AUPQS) to fine tune the available solutions for generating purely sinusoidal wind turbine‐end currents under both distorted‐unbalanced load‐terminal voltages and non‐linear load conditions (capacitive loads leave much worse consequences than those of the inductive). It is shown that both series and SAPF are capable of full compensation of microgrid by the SAPF using the advanced generalised theory of instantaneous power. Meanwhile, the resultant source currents could be somehow non‐sinusoidal. However, the proposed AUPQS will be able to fully eliminate the consequence of voltage asymmetry and unbalanced waveforms on the SAPF, generated because of the wind turbine operation by performing certain corrections on these solutions. Moreover, an independent single‐phase rectifier is proposed at the load‐end to regulate DC‐link voltage. Effectiveness of the proposed AUPQS is confirmed by Simulink simulations.
Modelling and industrial application of series hybrid active power filter
Authors: Jianben Liu , Shaojun Dai , Qiaofu Chen , Kun Tao
Published: August 2013

In the series hybrid active power filter (SHAPF) based on fundamental magnetic flux compensation (FMFC), the harmonic voltage across the magnetising inductance of the series transformer will disturb the inverter output current and worsen the filtering effect of the SHAPF. However, this influence caused by harmonic voltage was ignored in the previous research. Therefore there is blindness and casualness in the parameter selection of the SHAPF based on FMFC. Taking a 10 kV, 1 MVA industrial application of the SHAPF in a manufacture factory in Guangdong Province as an example, this study establishes the accurate global mathematical model of the SHAPF. Furthermore, based on the proposed global mathematical model, the series transformer parameters are analysed in detail to show its influence on the filtering performance of the SHAPF. This mathematical model can be used as foundations of the parameter selection of the SHAPF. Finally, an engineering prototype is manufactured and applied. The practical experimental results verify the theoretical analysis.
A novel approach of space vector modulation for cycloinverter using genetic algorithm
Authors: Agarwal Preeti , Agarwal Vineeta
Published: August 2013

A novel approach has been made to calculate the switching angles for space vector modulation (SVM) technique, which is applied in a cycloinverter to generate high‐frequency power output. The turn‐on and turn‐off times of SVM pattern are evaluated in such a way that the total harmonic distortion (THD) is minimised and the output voltage of cycloinverter approaches as close as possible to desired sinusoidal waveform. To accomplish this optimisation task, genetic algorithms (GAs) is used and THD is adopted in the proposed objective function. The lowest fitness value of this objective function decides the correct value of the switching angles. The switching strategy for the cycloinverter is presented on MATLAB‐based time‐domain simulations. Simulation results show that the proposed approach with GAs, is superior to the conventional SVM. The output waveforms and their spectrum are presented to show effectiveness of the proposed scheme. Simulated results are also validated with the experimental results.
A novel heuristic optimisation algorithm for automated design of resonant compensators for shunt active filters
Authors: Lenwari Wanchak , Okaeme Nnamdi
Published: August 2013

This study presents the automated control design for shunt active filters using a novel heuristic optimisation algorithm. The hybrid bacterial foraging optimisation algorithm is specifically developed for the automated optimisation of the modified resonant compensator for the compensation of all main harmonics, 5th, 7th, 11th and 13th. The compensator is based on the sinusoidal internal model principle providing excellent improvement in control accuracy and performance for harmonic signals. The compensator is implemented in a single rotating reference frame fixed to the supply voltage vector. The automated design procedure and a novel optimisation algorithm are presented in detail. Experimental results demonstrate the effectiveness of the proposed control design and the accuracy of current tracking performance.
Comprehensive steady‐state analytical model of a three‐phase diode rectifier connected to a constant DC voltage source
Authors: Di Gerlando Antonino , Foglia Giovanni Maria , Iacchetti Matteo F. , Perini Roberto
Published: August 2013

This study deals with the analytical modelling of the steady‐state operation of a three‐phase diode rectifier whose dc bus is connected to a constant voltage source. Such a system exhibits several operation modes that are fully investigated. Analytical expressions of the boundaries of each mode as well as the average dc and the rms ac currents are deduced as a function of the ac and dc parameters, including voltage drops across diodes. They allow us to evaluate the power delivered to the dc bus as well as the efficiency of the conversion in each mode of operation. These results can also be extended to practical rectifiers with bulk dc capacitors and allow for performing parametric analyses and optimisation in the design of drives or permanent magnet synchronous generators directly connected to a diode rectifier. The theoretical results are validated by experimental tests.
Experimental verification of Hopf bifurcation in pulse‐width modulated inverter fed cage induction motor drive system
Authors: Deivasundari ParvathyShankar , Uma Govindarajan , Santhi Rajendran
Published: August 2013

Bifurcation theory deals with the change of qualitative behaviour in a parameter space of dynamical systems. This study investigates the bifurcation phenomenon of an industrial drive having typically constant speed requirement for which pulse‐width modulated inverter fed cage induction motor (IM) is a good choice. The focus is on bifurcation analysis of the stator voltage controlled IM drive, with a particular emphasis on the dynamics and stability under variations of load torque and proportional integral controller gain. Extensive computer simulations are performed to capture the system's dynamic behaviour and demarcate the bifurcation boundaries. Trajectory and Poincaré section before and after the bifurcation are shown. The detailed mathematical model of the closed‐loop system is derived and is used to analyse the observed bifurcation phenomena. The describing equations reveal that the system loses stability via supercritical Hopf bifurcation. Experimental results are also provided to confirm the theoretical analysis.
High‐efficiency dual‐input converter with high‐voltage gain and internal charge function
Authors: Wai Rong‐Jong , Hong Lian‐Sheng
Published: August 2013

In this study, a high‐efficiency dual‐input converter with an internal charge circuit is developed. The proposed coupled‐inductor‐based converter can boost the voltages of two input power sources with different low‐voltage levels to a controllable high‐voltage DC bus. The high‐voltage DC bus can be taken as the main power for a high‐voltage DC load or the front terminal of a DC–AC inverter. The charge circuit inside the proposed dual‐input converter can provide the redundant energy from the major source for the auxiliary power source (e.g. battery module) to save the manufacturing cost. According to the operation of power management, the operational states of the proposed dual‐input converter can be divided into three situations including a standalone power‐supply state, a charge state and a unify power‐supply state. The techniques of voltage clamping and soft switching are employed in this converter, and the corresponding device specifications are adequately performed. Thus, the goal of high‐efficiency dual‐input power conversion with high‐voltage gain can be achieved. Some experimental results via a 1.5 kW‐level prototype are given to verify the effectiveness of the proposed dual‐input converter in practical applications.
Digital current control of a three‐phase four‐leg voltage source inverter by using p–q–r theory
Authors: Ozdemir Ayhan , Ozdemir Zekeriya
Published: August 2013

In this study, balanced/unbalanced linear/non‐linear current control in three‐phase four‐leg voltage source inverter (VSI) is carried out by using modified p–q–r method instead of the classical p–q–r method, digital proportional integral derivative (PID) control rule and three‐dimensional (3D) space vector pulse width modulation (3D SVPWM). For this purpose, three‐phase four‐leg power inverter and PWM signal generation circuits are designed and modelled separately. Even if the power source voltage is unsymmetrical, the proposed modified p–q–r method leads to measurement and to generating the instantaneous harmonic and reactive components of load current accurately. The performance of the classical p–q–r theory under non‐ideal mains voltages is improved and the accuracy of the proposed modified p–q–r theory is demonstrated both through simulation and real‐time application. Each phase of the three‐phase four‐leg VSI modelled directly in abc reference frame is decoupled from each other This simplifies the digital PID controller design significantly. Modelling of the whole system, modified p–q–r measurement and digital PID design steps are given in detail. Real‐time experimental results for the designed three‐phase four‐leg VSI in stand‐alone mode are compared with the simulation results.
Estimation of multi‐conductor powerline cable parameters for the modelling of transfer characteristics
Authors: Wang Linyu , Avolio Gustavo , Deconinck Geert , Van Lil Emmanuel , Lei Lai Loi
Published: August 2013

The modelling of transfer characteristics of low‐voltage power distribution networks for Power Line Communications requires the knowledge of the electrical parameters of the cables comprising these networks. In this study, a method is developed for characterising the power line cable parameters. In complement to many existing approaches, the authors estimate the cable parameters from a limited set of measurements. Measurement results can take into account fabrication tolerances, bending of the cables etc., which help to obtain more accurate results. A multi‐conductor powerline cable has multiple, coupled propagation modes with corresponding primary parameters. Based on multi‐conductor transmission line theory, the authors propose a practical measurement approach to derive the parameters separately. A previous analysis was made for four‐conductor powerline cable. Here, it will also be generalised for three‐conductor cables. With the parameters, the transfer function of the same kind of cable can be obtained easily. The approach is validated by comparing the deduced transfer function of a power line cable with the directly measured one.
Anharmonic theoretical simulations of infrared spectra of halogenated organic compounds
Authors: Carnimeo Ivan , Puzzarini Cristina , Tasinato Nicola , Stoppa Paolo , Charmet Andrea Pietropolli , Biczysko Malgorzata , Cappelli Chiara , Barone Vincenzo
Published: August 2013

The recent implementation of the computation of infrared (IR) intensities beyond the double-harmonic approximation [J. Bloino and V. Barone, J. Chem. Phys. 136, 124108 (2012)]10.1063/1.3695210 paved the route to routine calculations of infrared spectra for a wide set of molecular systems. Halogenated organic compounds represent an interesting class of molecules, from both an atmospheric and computational point of view, due to the peculiar chemical features related to the halogen atoms. In this work, we simulate the IR spectra of eight halogenated molecules (CH2F2, CHBrF2, CH2DBr, CF3Br, CH2CHF, CF2CFCl, cis-CHFCHBr, cis-CHFCHI), using two common hybrid and double-hybrid density functionals in conjunction with both double- and triple-ζ quality basis sets (SNSD and cc-pVTZ) as well as employing the coupled-cluster theory with basis sets of at least triple-ζ quality. Finally, we compare our results with available experimental spectra, with the aim of checking the accuracy and the performances of the computational approaches.
Tempered random attractors for parabolic equations in weighted spaces
Authors: Bates Peter W. , Lu Kening , Wang Bixiang
Published: August 2013

This paper deals with the asymptotic behavior of solutions of parabolic equations on unbounded domains which contain stochastic terms as well as non-autonomous deterministic terms. We define a continuous random dynamical system for the equations in weighted Sobolev spaces that allow functions to have certain polynomial growth rate at infinity and hence include all bounded solutions. We prove pullback asymptotic compactness of solutions as well as the existence and uniqueness of tempered random attractors in the weighted spaces. The structures of the tempered attractors are fully characterized by tempered complete solutions. In the case where the non-autonomous deterministic terms are periodic in time, we show that the tempered random attractors are also periodic in time. To overcome the difficulty of non-compactness of Sobolev embeddings on unbounded domains, the idea of uniform pathwise estimates on the tails of solutions is employed to show asymptotic compactness.
Random loop representations for quantum spin systems
Authors: Ueltschi Daniel
Published: August 2013

We describe random loop models and their relations to a family of quantum spin systems on finite graphs. The family includes spin \documentclass[12pt]{minimal}\begin{document}$\frac{1}{2}$\end{document}12 Heisenberg models with possibly anisotropic spin interactions and certain spin 1 models with SU(2)-invariance. Quantum spin correlations are given by loop correlations. Decay of correlations is proved in 2D-like graphs, and occurrence of macroscopic loops is proved in the cubic lattice in dimensions 3 and higher. As a consequence, a magnetic long-range order is rigorously established for the spin 1 model, thus confirming the presence of a nematic phase.
Ozone and carbon trioxide synthesis by low energy ion implantation onto solid carbon dioxide and implications to astrochemistry
Authors: Sivaraman Bhalamurugan , Raja Sekhar B. N. , Fulvio Daniele , Hunniford Adam , McCullough Bob , Palumbo Maria Elisabetta , Mason Nigel
Published: August 2013

Ion implantation experiments were carried out on amorphous (30 K) and crystalline (80 K) solid CO2 using both reactive (D+, H+) and non-reactive (He+) ions, simulating different irradiation environments on satellite and dust grain surfaces. Such ion irradiation synthesized several new species in the ice including ozone (O3), carbon trioxide (CO3), and carbon monoxide (CO) the main dissociation product of carbon dioxide. The yield of these products was found to be strongly dependent upon the ion used for irradiation and the sample temperature. Ion implantation changes the chemical composition of the ice with recorded infrared spectra clearly showing the coexistence of D3h and C2v isomers of CO3, for the first time, in ion irradiated CO2 ice.
Extending molecular simulation time scales: Parallel in time integrations for high-level quantum chemistry and complex force representations
Authors: Bylaska Eric J. , Weare Jonathan Q. , Weare John H.
Published: August 2013

Parallel in time simulation algorithms are presented and applied to conventional molecular dynamics (MD) and ab initio molecular dynamics (AIMD) models of realistic complexity. Assuming that a forward time integrator, f (e.g., Verlet algorithm), is available to propagate the system from time ti (trajectory positions and velocities xi = (ri, vi)) to time ti + 1 (xi + 1) by xi + 1 = fi(xi), the dynamics problem spanning an interval from t0…tM can be transformed into a root finding problem, F(X) = [xi − f(x(i − 1)]i = 1, M = 0, for the trajectory variables. The root finding problem is solved using a variety of root finding techniques, including quasi-Newton and preconditioned quasi-Newton schemes that are all unconditionally convergent. The algorithms are parallelized by assigning a processor to each time-step entry in the columns of F(X). The relation of this approach to other recently proposed parallel in time methods is discussed, and the effectiveness of various approaches to solving the root finding problem is tested. We demonstrate that more efficient dynamical models based on simplified interactions or coarsening time-steps provide preconditioners for the root finding problem. However, for MD and AIMD simulations, such preconditioners are not required to obtain reasonable convergence and their cost must be considered in the performance of the algorithm. The parallel in time algorithms developed are tested by applying them to MD and AIMD simulations of size and complexity similar to those encountered in present day applications. These include a 1000 Si atom MD simulation using Stillinger-Weber potentials, and a HCl + 4H2O AIMD simulation at the MP2 level. The maximum speedup (\documentclass[12pt]{minimal}\begin{document}$\frac{serial\, execution\, time}{parallel\, execution\, time}$\end{document}serialexecutiontimeparallelexecutiontime) obtained by parallelizing the Stillinger-Weber MD simulation was nearly 3.0. For the AIMD MP2 simulations, the algorithms achieved speedups of up to 14.3. The parallel in time algorithms can be implemented in a distributed computing environment using very slow transmission control protocol/Internet protocol networks. Scripts written in Python that make calls to a precompiled quantum chemistry package (NWChem) are demonstrated to provide an actual speedup of 8.2 for a 2.5 ps AIMD simulation of HCl + 4H2O at the MP2/6-31G* level. Implemented in this way these algorithms can be used for long time high-level AIMD simulations at a modest cost using machines connected by very slow networks such as WiFi, or in different time zones connected by the Internet. The algorithms can also be used with programs that are already parallel. Using these algorithms, we are able to reduce the cost of a MP2/6-311++G(2d,2p) simulation that had reached its maximum possible speedup in the parallelization of the electronic structure calculation from 32 s/time step to 6.9 s/time step.
The quantum nature of the OH stretching mode in ice and water probed by neutron scattering experiments
Authors: Senesi Roberto , Flammini Davide , Kolesnikov Alexander I. , Murray Éamonn D. , Galli Giulia , Andreani Carla
Published: August 2013

The OH stretching vibrational spectrum of water was measured in a wide range of temperatures across the triple point, 269 K <T < 296 K, using Inelastic Neutron Scattering (INS). The hydrogen projected density of states and the proton mean kinetic energy, ⟨EK⟩OH, were determined for the first time within the framework of a harmonic description of the proton dynamics. We found that in the liquid the value of ⟨EK⟩OH is nearly constant as a function of T, indicating that quantum effects on the OH stretching frequency are weakly dependent on temperature. In the case of ice, ab initio electronic structure calculations, using non-local van der Waals functionals, provided ⟨EK⟩OH values in agreement with INS experiments. We also found that the ratio of the stretching (⟨EK⟩OH) to the total (⟨EK⟩exp) kinetic energy, obtained from the present measurements, increases in going from ice, where hydrogen bonding is the strongest, to the liquid at ambient conditions and then to the vapour phase, where hydrogen bonding is the weakest. The same ratio was also derived from the combination of previous deep inelastic neutron scattering data, which does not rely upon the harmonic approximation, and the present measurements. We found that the ratio of stretching to the total kinetic energy shows a minimum in the metastable liquid phase. This finding suggests that the strength of intermolecular interactions increases in the supercooled phase, with respect to that in ice, contrary to the accepted view that supercooled water exhibits weaker hydrogen bonding than ice.
Experimental evidence of the quantum point contact theory in the conduction mechanism of bipolar HfO2-based resistive random access memories
Authors: Prócel L. M. , Trojman L. , Moreno J. , Crupi F. , Maccaronio V. , Degraeve R. , Goux L. , Simoen E.
Published: August 2013

The quantum point contact (QPC) model for dielectric breakdown is used to explain the electron transport mechanism in HfO2-based resistive random access memories (ReRAM) with TiN(30 nm)\HfO2(5 nm)\Hf(10 nm)\TiN(30 nm) stacks. Based on experimental I-V characteristics of bipolar HfO2-based ReRAM, we extracted QPC model parameters related to the conduction mechanism in several devices in order to make a statistical study. In addition, we investigated the temperature effect on the conduction mechanism and compared it with the QPC model. Based on these experimental results, we show that the QPC model agrees well with the conduction behavior of HfO2-based ReRAM memory cells.
A high-energy electron scattering study of the electronic structure and elemental composition of O-implanted Ta films used for the fabrication of memristor devices
Authors: Vos M. , Grande P. L. , Nandi S. K. , Venkatachalam D. K. , Elliman R. G.
Published: August 2013

High-energy electron scattering is used to investigate Ta films implanted with 10 keV O ions. These films are of interest as they have been used for the fabrication of memristors. High-energy electron scattering is used with incoming electron energies ranging from 5 to 40 keV. The inelastic mean free path, and hence the probing depth, is at these energies of the same order as the range of the implanted ions. At the same time, we can distinguish the mass of the atom that scattered the electron elastically, due to the dependence of the recoil energy on the mass of the scatterer. This allows us to determine quantitatively the atomic composition near the surface from the signal of electrons that have scattered elastically but not inelastically. Electrons that have scattered inelastically as well as elastically provide us with information on the possible electronic excitations. Their signal is used to monitor the presence of the Ta2O5 phase near the surface (characterised by a significant band gap of ≃4.5 eV), and estimate at what depth below the surface pure Ta metal is present. In this way, we obtain a fairly detailed picture of the elemental composition and electronic properties of these films.
External quantum efficiency enhancement in organic photovoltaic devices employing dual organic anode interfacial layers
Authors: Fleetham Tyler , O'Brien Barry , Mudrick John P. , Xue Jiangeng , Li Jian
Published: August 2013

We demonstrate the use of a dual anode interfacial layer of poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) and tetracene for efficient small molecule organic solar cells. These layers provided a multifaceted improvement on device performance by enhancing absorption in the donor layer, serving as an exciton blocking layer at the anode interface, providing a low resistance anode contact, and serving as a templating layer for increased crystallinity in the donor layer. Palladium phthalocyanine/C60 planar heterojunction devices fabricated on top of the dual layers of PEDOT:PSS and tetracene demonstrates 85% enhancement in the donor contribution to external quantum efficiency and yielded a maximum power conversion efficiency of 3.66%.
Gibbs energies, enthalpies, and entropies of water and lysozyme at the inner edge of excess hydration
Authors: Sirotkin Vladimir A. , Khadiullina Aigul V.
Published: August 2013

The aim of this study is to simultaneously monitor the excess partial Gibbs energies, enthalpies, and entropies of water and white egg lysozyme and demonstrate how these quantities correlate with the coverage of the protein macromolecules by water molecules. Isothermal calorimetry and water sorption measurements were applied to characterize the hydration dependencies of the excess thermodynamic functions. The excess partial quantities are found to be sensitive to changes in the water and protein states. At the lowest water weight fractions (w1), changes in the excess functions are primarily attributable to the addition of water. The transition of lysozyme from a glassy (rigid) to a flexible (elastic) state is accompanied by significant changes in the excess partial quantities. When the charged groups on the protein are covered, this transition occurs at w1 = 0.05; when the coverage of both polar and weakly interacting surface elements is complete, the excess partial quantities become hydrated at w1 > 0.5. At the highest water content, water addition has no significant effect on the excess quantities. At w1 > 0.5, changes in the excess functions solely reflect changes in the state of the protein.
Statistical physics of self-replication
Authors: England Jeremy L.
Published: August 2013

Self-replication is a capacity common to every species of living thing, and simple physical intuition dictates that such a process must invariably be fueled by the production of entropy. Here, we undertake to make this intuition rigorous and quantitative by deriving a lower bound for the amount of heat that is produced during a process of self-replication in a system coupled to a thermal bath. We find that the minimum value for the physically allowed rate of heat production is determined by the growth rate, internal entropy, and durability of the replicator, and we discuss the implications of this finding for bacterial cell division, as well as for the pre-biotic emergence of self-replicating nucleic acids.
The multi-scattering model for calculations of positron spatial distribution in the multilayer stacks, useful for conventional positron measurements
Authors: Dryzek Jerzy , Siemek Krzysztof
Published: August 2013

The spatial distribution of positrons emitted from radioactive isotopes into stacks or layered samples is a subject of the presented report. It was found that Monte Carlo (MC) simulations using GEANT4 code are not able to describe correctly the experimental data of the positron fractions in stacks. The mathematical model was proposed for calculations of the implantation profile or positron fractions in separated layers or foils being components of a stack. The model takes into account only two processes, i.e., the positron absorption and backscattering at interfaces. The mathematical formulas were applied in the computer program called LYS-1 (layers profile analysis). The theoretical predictions of the model were in the good agreement with the results of the MC simulations for the semi infinite sample. The experimental verifications of the model were performed on the symmetrical and non-symmetrical stacks of different foils. The good agreement between the experimental and calculated fractions of positrons in components of a stack was achieved. Also the experimental implantation profile obtained using the depth scanning of positron implantation technique is very well described by the theoretical profile obtained within the proposed model. The LYS-1 program allows us also to calculate the fraction of positrons which annihilate in the source, which can be useful in the positron spectroscopy.