bluuebunny/crossref_metadata_2025 huggingface dataset:
Symmetric and asymmetric transformer based cascaded multilevel inverter with minimum number of components
Authors: Farakhor Amir , Reza Ahrabi Rouzbeh , Ardi Hossein , Najafi Ravadanegh Sajad
Published: March 2015

In this study, a novel transformer based cascaded multilevel inverter is presented. The proposed inverter can operate in both symmetric and asymmetric topologies. The presented inverter benefits from the advantages such as reduced number of power switches and reduced total peak inverse voltage of the switching components. The numbers of insulated gate driver circuits are also decreased with respect to the power switches. Furthermore, the presented topology requires just a single DC source. In addition, the numbers of on‐state switches in the current paths are reduced. Therefore the voltage drops across the switches are mitigated and as a result the efficiency of the presented inverter is improved. The mentioned advantages cause the implementation cost to be reduced. The operation of the converter is discussed thoroughly for both symmetric and asymmetric operations. The feasibility of the presented inverter topology is validated using the simulation results. Experimental results under 1.5 kW are also added to justify the theoretical analyses.
Simplified multi‐modular shunt active power filter system and its modelling
Authors: Wang Yifan , Xu Qunwei , Chen Guozhu
Published: March 2015

To meet the requirement of large capacity for harmonic suppression and reactive power compensation, modular shunt active power filter (SAPF) system is attractive for its high‐reliability and flexibility. However, a unique physical address is needed for each module in traditional SAPFs. If a module fails, the faulted module should be substituted by another one with the same physical address. Therefore it is hard to realise modularisation, and the cost of the system is high. In addition, in such a system, a single SAPF generally adopts the topology with LCL filter and are coupled because of grid impedance. Generally, this coupling is not taken into account when designing the control laws. In consequence, depending on the number of paralleled SAPFs and the grid impedance, the paralleled SAPFs do not behave as expected. In this study, a simplified N + 1 redundant SAPF system and its control strategy are presented. The SAPFs are modelled as a multivariable system. The analysis carried out enables to obtain an equivalent SAPF that describes the totality of paralleled SAPFs. The coupling effect is described and the control law design of paralleled SAPFs with LCL filters is clarified. The validity of the simplified N + 1 SAPF system and the efficiency of the control strategies are demonstrated by prototype experiments.
Comparison of models of fuel cells based on experimental data for the design of power electronics systems
Authors: Boscaino Valeria , Capponi Giuseppe , Miceli Rosario , Ricco Galluzzo Guiseppe , Rizzo Renato
Published: March 2015

Fuel cells have a key role in the potential provision of combined generation of heat and power. Sophisticated power management algorithms have been developed to reduce hydrogen consumption. An accurate analysis of the interaction between the fuel cell system and the front‐end power converter is fundamental to achieving high performances. Accurate modelling of the entire system is required, especially the primary energy source, including the auxiliary components. Fuel cell modelling techniques have been presented extensively in the literature. Models are usually oriented to give technical insight concerning the fuel cell systems. The importance of fuel cell modelling in the design and control of front‐end power converters seldom has been addressed, and this has led to highly complex model structures and the need to assume the values of several parameters that cannot be measured easily in a power electronics laboratory. Such models are not well suited for designing renewable energy systems. Hence, semi‐empirical models oriented to the design of power systems are presented and compared. Both white‐box and black‐box modelling approaches are presented, and both models were tested on a 5‐kW commercial fuel cell system provided by Nuvera. Both modelling approaches were validated comparing the simulation and experimental results.
Simplified distribution grid model for power quality studies in the presence of photovoltaic generators
Authors: Patsalides Minas , Efthymiou Venizelos , Stavrou Andreas , Georghiou George Elia
Published: March 2015

Renewable energy sources are expected to have a considerable share in the global energy mix over the next years and consequently further research is required to enhance the planning strategies, modify prudently the existing standards and set quality levels on delivered power in order to accommodate the penetration of these technologies. Depending on the distribution grid dynamics and the load demand, the amplitude of voltage may vary significantly, and therefore proper simulation models are required for performing dedicated studies. In this study, a simplified and accurate model representing the distribution grid dynamics is introduced for power quality studies in the presence of distributed photovoltaic (PV) generators. The proposed simplified distribution grid model (SDGM) is validated using measurements and it is then used along with a verified PV system model to estimate the voltage variation and PV capacity of the distribution grid under investigation. Moreover, a sensitivity analysis is performed by varying the parameters of the SDGM to assess how the PV capacity is altered. As a last step, common voltage regulation schemes are analysed through the use of the proposed model, validating operational modes that can accommodate high distributed PV capacities.
Sparse‐reconstruction‐based direction of arrival, polarisation and power estimation using a cross‐dipole array
Authors: Tian Ye , Sun Xiaoying , Zhao Shishun
Published: March 2015

This study demonstrates how the multiple parameters can be exactly obtained in sparse signal reconstruction framework using a cross‐dipole array. Instead of using subspace‐based methods, first direction of arrival (DOA) estimation of all sources is obtained, by solving a weighted ‘group lasso’ problem in second‐order statistics domain. Then a truncated ℓ1‐function is utilised to approximate ℓ0‐norm, and an unbiased estimator is successively proposed to obtain the polarisation and power estimation. A statistical technique is introduced to select the regularisation parameter properly. Compared with the estimation of signal parameters via rotational invariance techniques‐based algorithm, the proposed algorithm can provide improved resolution and estimation accuracy. Furthermore, the proposed algorithm can identify two sources with the same DOA successfully, provided that the polarisation parameters are different.
Two‐step estimator for moving‐emitter geolocation using time difference of arrival/frequency‐difference of arrival measurements
Authors: Kim Yong‐Hee , Kim Dong‐Gyu , Kim Hyoung‐Nam
Published: March 2015

This study presents a two‐step least‐squares approach for estimating the position and velocity of a moving emitter using time difference of arrival (TDOA) and frequency‐difference of arrival (FDOA) measurements in a two‐dimensional scenario. The proposed method first estimates the emitter position based on the asymptotes of TDOA hyperbolae and then linearises the non‐linear equations of FDOAs using the estimate of the emitter position obtained in the first stage. Although the proposed method has lower performance than other methods in terms of estimation accuracy, it provides a closed‐form solution without geometric constraints of sensor placement and an initial guess of emitter parameters. Since many methods derive the estimates of position and velocity with iterative numerical techniques, the proposed method can be a good alternative to set the initial guess under conditions of low measurement error. Simulation results are included to validate the algorithm, and its performance is compared with the Cramer–Rao lower bound.
Numerical simulation of a grounding grid buried in horizontal multilayered earth based on ‘T’ typical basic elements in the frequency domain
Authors: Li Zhong‐Xin , Yin Yu , Zhang Cui‐Xia , Zhang Liu‐Chun
Published: March 2015

In this study, the authors propose a new mathematical model that allows the accurate computation of currents flowing through a substation's grounding grid buried in horizontal multilayered earth, which is a hybrid of Galerkin's method of moment and the conventional nodal analysis method based on ‘T’ typical basic elements. The dynamic state complex image method and the closed form of Green's function of a horizontal dipole or monopole in the earth model are introduced into this mathematical model to enhance its efficiency. In addition, an analytical formula for mutual induction and impedance coefficient calculations are used to accelerate the application of this method. Finally, some numerical results related to a practical grounding problem are discussed and some conclusions are given.
Design of booster shed parameters for post insulators under heavy icing conditions using geometric modelling and the Taguchi method
Authors: Ale‐Emran Sayyed Mahdi , Farzaneh Masoud
Published: March 2015

A generic design approach is presented to optimise the parameters of booster sheds (BSs) installed on post station insulators in heavy icing conditions. This approach is based on geometric modelling and Taguchi method and it allows to improve the electrical performance of the insulators. It deals with geometrical parameters of BSs including their number, inclination angle and diameter. Numerical analyses using geometric modelling, MATLAB programming and Minitab software were carried out in this study. The presented approach seems to be a good alternative to experimental measurements which are costly and difficult to perform. This investigation shows that the optimised value of BS inclination angle is equal to the upper shed angle of the insulator. Moreover, it indicates that generally the maximum feasible values for the diameter and number of BSs are the best options.
Distribution and influence factors of electric field in high‐voltage power capacitor
Authors: Liang Yanping , Wang Dongmei , Liu Daihong
Published: March 2015

Power capacitor works in series or parallel acts as a role of reactive power compensation and filtration in high‐voltage power transmission. Once one capacitor is damaged, the whole unit even the entire system would fail to work. The breakdown parts of power capacitor component are generally occurred in the area where the electric field intensity is concentrated, so the electric field distribution of component needs to be calculated accurately. In this study, according to the inner structure of power capacitor component, the numerical simulation of inner electric field is carried on, and the electric field distribution characteristics are obtained. The factors that affect the electric field, such as, the medium material, electrode thickness and medium thickness are researched. Specially, the electric field distribution at component edge is given, and the relationship between voltage and medium breakdown field intensity is discussed. The results provide a theoretical basis for the design and operation of power capacitor.
Assessment of flow instabilities in in‐vitro stenotic arteriovenous grafts using an equivalent astable multivibrator
Authors: Chen Wei‐Ling , Lin Yu‐Hsuan , Kan Chung‐Dann , Yu Fan‐Ming , Lin Chia‐Hung
Published: March 2015

In clinical examinations, narrowed vessel accesses will produce unsteady flow and cause changes in blood flow volume. These phenomena result in pressure, velocity and flow resistance increases and induce stress on vessel walls. The vessel wall vibrates and squeezes the low axial blood flow, a lumped resistor (R) representing resistance to blood flow. The compliance is a pressure against blood volume relationship, a lumped capacitor (C) representing the compliance capacity of the blood vessel. Vibration phenomena results on the elastic vessel wall because of transverse vibration pressure. Turbulent and instability flow will induce simple harmonic motions, and the rise time, amplitude and pulse duration of transverse vibrations are determined by the flow resistances and vessel compliances. Hence, an astable multivibrator as detection model employs time constant, τ = (R × C), to evaluate the flow instability and the dysfunction risk in in‐vitro arteriovenous grafts (AVGs). Experimental results show the time constants have linear regression with a positive correlation as the degree of stenosis increases. Positive pole values, s = (−1/τ), are used to validate that the AVG be unstable because the force responses will continuously grow with time because of vibration increases. For comparison with the computerised analysis and auscultation method, in‐vivo examinations of the proposed equivalent model can be further carried out for screening of AVG dysfunction.
Effect of the grounding system on the lightning current profile along a tall structure
Authors: Rameli Norhidayu , Ab‐Kadir Mohd Zainal Abidin , Izadi Mahdi , Gomes Chandima , Azis Norhafiz
Published: March 2015

The behaviour of a lightning current traversing along a tall structure is influenced by the factor of the ground reflection coefficient parameter. This parameter is widely assumed to be constant in the analysis of lightning current along at all structure. However, in reality, the ground reflection depends on the relationship between the tower and ground impedances which results in multiple values for the ground reflection coefficient. These values are determined by the ground impedance, whereby the grounding electrode arrangement and soil resistivity play key roles. Hence, this study evaluates the effect of the grounding system on the lightning current profile along a tall structure. The lightning current along a tall structure is simulated by the implementation of a distributed source representation model. The results indicate that a multiple ground reflection coefficient is generated for different types of grounding electrode arrangements and soil resistivity values. The grounding electrode arrangement in horizontal, grid or circular forms provides at least a reduction of 30% reflected current along a tall structure for a high soil resistivity. Hence, this result may provide a general guide for telecommunication (TM) engineers to consider the condition of soil resistivity and the grounding system before installing a TM tower.
Adaptive soil model for real‐time thermal rating of underground power cables
Authors: Diaz‐Aguiló Marc , de León Francisco
Published: March 2015

This study presents a validated adaptive method intended for real‐time thermal rating (RTTR) of underground power cables. The accuracy of the RTTR algorithm, when producing emergency ratings or predictive calculations, strongly depends on the following parameters (which have large uncertainties): correct soil modelling, the proper determination of the soil properties and the accurate estimation of the ambient temperature. To remove the uncertainties, this study uses a novel approach to the modelling of the soil that allows the implementation of an extended Kalman filter to estimate robustly the properties of the soil and the ambient temperature in real‐time with the data obtained from cable temperature sensors. These estimation techniques have been validated for several cable installations and the accuracy of emergency current calculations has been assessed by comparing the calculated results with finite element method simulations. In the context of smart grid applications, the possibility of adapting the estimation models in real time with the new obtained measurements is a key aspect to assure robustness and accuracy of the power system operation and control.
Adaptive central difference filter for non‐linear state estimation
Authors: Das Manasi , Dey Aritro , Sadhu Smita , Ghoshal Tapan Kumar
Published: March 2015

A new algorithm for adaptive non‐linear filter suitable for signal models with unknown measurement noise covariance is presented here. The proposed adaptive filter is based on numerically efficient central difference algorithm which is potentially suitable for on board implementation. Unlike some competing adaptation scheme the proposed method guarantees positive definiteness of the estimated covariance matrix and avoids consequent singularity. Superiority of the proposed filter in comparison with non‐adaptive central difference filter (CDF), an adaptive unscented Kalman filter and also another CDF based adaptive filter with alternative adaptation scheme has been demonstrated by Monte Carlo simulations. The signal models used are a well‐known reentry ballistic target tracking problem and a high dimensional, relatively complex spacecraft attitude determination problem. The algorithm has provisions for (i) iterative refinement, (ii) modulating the degree of adaptation and also (iii) for incorporating tradeoff mechanisms between computational load and estimation error.
Hartley transform and the use of the Whitened Hartley spectrum as a tool for phase spectral processing
Authors: Paraskevas Ioannis , Barbarosou Maria , Chilton Edward
Published: March 2015

The Hartley transform is a mathematical transformation which is closely related to the better known Fourier transform. The properties that differentiate the Hartley Transform from its Fourier counterpart are that the forward and the inverse transforms are identical and also that the Hartley transform of a real signal is a real function of frequency. The Whitened Hartley spectrum, which stems from the Hartley transform, is a bounded function that encapsulates the phase content of a signal. The Whitened Hartley spectrum, unlike the Fourier phase spectrum, is a function that does not suffer from discontinuities or wrapping ambiguities. An overview on how the Whitened Hartley spectrum encapsulates the phase content of a signal more efficiently compared with its Fourier counterpart as well as the reason that phase unwrapping is not necessary for the Whitened Hartley spectrum, are provided in this study. Moreover, in this study, the product–convolution relationship, the time‐shift property and the power spectral density function of the Hartley transform are presented. Finally, a short‐time analysis of the Whitened Hartley spectrum as well as the considerations related to the estimation of the phase spectral content of a signal via the Hartley transform, are elaborated.
Bipolar latch with compensated keep‐alive current
Authors: Gustat Hans
Published: March 2015

A permanent current in addition to the main clocked current is sometimes used to increase the maximum clock rate of a bipolar latch. Although it speeds up the activation of a clocked differential stage, it deteriorates the latch function by the additional current in the inactive phase of each differential stage. Thus, a keep‐alive current must be kept small with respect to the main clocked current. In this Letter, a compensation technique is shown avoiding the erroneous output of a keep‐alive current. It still speeds up the activation of the main transistor pair, but results in a constant symmetric offset without affecting the differential value of the output voltage. In simulations of flip‐flops and clocked comparators, this compensated keep‐alive current has a much larger effect on the maximum clock rate than the uncompensated keep‐alive current used so far.
Azo-Compound-Mediated Cyanoalkylation of Alkenes by Copper Catalysis: General Access to Cyano-Substituted Oxindoles
Authors: Tang Shi , Zhou Dong , Li Zhi-Hao , Fu Mei-Jun , Jie Li , Sheng Rui-Long , Li Shu-Hua
Published: March 2015

A practical and highly efficient azo-compound-mediated/ promoted radical cyanoalkylation of activated alkenes by copper catalysis was developed, which allowed for general synthesis of oxindoles bearing various nitrile moieties, especially the rarely reported 3° nitrile moiety via cascade radical addition/C(sp2)–H cyclization. This protocol demonstrates that DIAD served for a new promoter instead of usual Ag salts or bases in the C(sp3)–H functionalization of acetonitrile for the first time. The use of readily available AIBN and beyond as the radical sources, and inexpensive copper as the catalyst, as well as the simplicity of operation and handling, make this protocol an attractive access to therapeutically important cyano-substituted oxindoles.
Cross Sections for Electron Collisions with Carbon Monoxide
Authors: Itikawa Yukikazu
Published: March 2015

Cross section data are collected and reviewed for electron collisions with carbon monoxide. Collision processes included are total scattering, elastic scattering, momentum transfer, excitations of rotational, vibrational and electronic states, ionization, and dissociation. For each process, recommended values of the cross sections are presented, when possible. The literature has been surveyed through to the end of 2013.
Impact of environmentally induced fluctuations on quantum mechanically mixed electronic and vibrational pigment states in photosynthetic energy transfer and 2D electronic spectra
Authors: Fujihashi Yuta , Fleming Graham R. , Ishizaki Akihito
Published: March 2015

Recently, nuclear vibrational contribution signatures in two-dimensional (2D) electronic spectroscopy have attracted considerable interest, in particular as regards interpretation of the oscillatory transients observed in light-harvesting complexes. These transients have dephasing times that persist for much longer than theoretically predicted electronic coherence lifetime. As a plausible explanation for this long-lived spectral beating in 2D electronic spectra, quantum-mechanically mixed electronic and vibrational states (vibronic excitons) were proposed by Christensson et al. [J. Phys. Chem. B 116, 7449 (2012)] and have since been explored. In this work, we address a dimer which produces little beating of electronic origin in the absence of vibronic contributions, and examine the impact of protein-induced fluctuations upon electronic-vibrational quantum mixtures by calculating the electronic energy transfer dynamics and 2D electronic spectra in a numerically accurate manner. It is found that, at cryogenic temperatures, the electronic-vibrational quantum mixtures are rather robust, even under the influence of the fluctuations and despite the small Huang-Rhys factors of the Franck-Condon active vibrational modes. This results in long-lasting beating behavior of vibrational origin in the 2D electronic spectra. At physiological temperatures, however, the fluctuations eradicate the mixing, and hence, the beating in the 2D spectra disappears. Further, it is demonstrated that such electronic-vibrational quantum mixtures do not necessarily play a significant role in electronic energy transfer dynamics, despite contributing to the enhancement of long-lived quantum beating in 2D electronic spectra, contrary to speculations in recent publications.
Method for collecting thermocouple data via secured shell over a wireless local area network in real time
Authors: Arnold F. , DeMallie I. , Florence L. , Kashinski D. O.
Published: March 2015

This manuscript addresses the design, hardware details, construction, and programming of an apparatus allowing an experimenter to monitor and record high-temperature thermocouple measurements of dynamic systems in real time. The apparatus uses wireless network technology to bridge the gap between a dynamic (moving) sample frame and the static laboratory frame. Our design is a custom solution applied to samples that rotate through large angular displacements where hard-wired and typical slip-ring solutions are not practical because of noise considerations. The apparatus consists of a Raspberry PI mini-Linux computer, an Arduino micro-controller, an Ocean Controls thermocouple multiplexer shield, and k-type thermocouples.
Mixing and chemical reaction at high Schmidt number near turbulent/nonturbulent interface in planar liquid jet
Authors: Watanabe T. , Naito T. , Sakai Y. , Nagata K. , Ito Y.
Published: March 2015

This study investigates the mixing of reactive species at a high Schmidt number (Sc ≈ 600) near the turbulent/nonturbulent (T/NT) interface in a planar liquid jet with a chemical reaction A + B → R. Reactants A and B are supplied from the jet and ambient flows, respectively. An I-type hot-film probe and optical fiber probe are used for the simultaneous measurements of the streamwise velocity, mixture fraction, and concentrations of all reactive species and for detecting the T/NT interface. Statistics conditioned on the time elapsed after interface detection are analyzed. The conditional mean mixture fraction and concentrations change sharply near the interface. The widths of these changes are independent of the chemical species. The conditional statistics reveal the dependence of the chemical reaction on the interface orientation. The segregation intensity near the interface shows that the mixing state of the two reactants also depends on the interface orientation. However, the large reaction rate near the interface is related to the large concentration of reactant A rather than the mixing state, because reactant A supplied from the jet tends to be deficient near the interface. Near the interface where the reaction rate is large, the concentration of the chemical product is also large. The difference in the product concentration between the different interface orientations is larger for the infinitely fast reaction (as investigated by using the equilibrium limit) than the finite Damköhler number case, and the dependence of the chemical reaction on the interface orientation is expected to be significant for a fast chemical reaction.
Regulating block copolymer phases via selective homopolymers
Authors: Yang Shuang , Lei Zhen , Hu Nan , Chen Er-Qiang , Shi An-Chang
Published: March 2015

The phase behavior of strongly segregated AB diblock copolymer and selective C homopolymer blends is examined theoretically using a combination of strong stretching theory (SST) and self-consistent field theory (SCFT). The C-homopolymer is immiscible with the B-blocks but strongly attractive with the A-blocks. The effect of homopolymer content on the order-order phase transitions is analyzed. It is observed that, for AB diblock copolymers with majority A-blocks, the addition of the C-homopolymers results in lamellar to cylindrical to spherical phase transitions because of the A/C complexation. For diblock copolymers with minor A-blocks, adding C-homopolymers leads to transitions from spherical or cylindrical morphology with A-rich core to lamellae to inverted cylindrical and spherical morphologies with B-rich core. The results from analytical SST and numerical SCFT are in good agreement within most regions of the phase diagram. But the deviation becomes more obvious when the composition of A-blocks is too small and the content of added C-homopolymers is large enough, where the SCFT predicts a narrow co-existence region between different ordered phases. Furthermore, it is found that the phase behavior of the system is insensitive to the molecular weight of C-homopolymer.
Formation of large-scale structures with sharp density gradient through Rayleigh-Taylor growth in a two-dimensional slab under the two-fluid and finite Larmor radius effects
Authors: Goto R. , Miura H. , Ito A. , Sato M. , Hatori T.
Published: March 2015

Two-fluid and the finite Larmor effects on linear and nonlinear growth of the Rayleigh-Taylor instability in a two-dimensional slab are studied numerically with special attention to high-wave-number dynamics and nonlinear structure formation at a low β-value. The two effects stabilize the unstable high wave number modes for a certain range of the β-value. In nonlinear simulations, the absence of the high wave number modes in the linear stage leads to the formation of the density field structure much larger than that in the single-fluid magnetohydrodynamic simulation, together with a sharp density gradient as well as a large velocity difference. The formation of the sharp velocity difference leads to a subsequent Kelvin-Helmholtz-type instability only when both the two-fluid and finite Larmor radius terms are incorporated, whereas it is not observed otherwise. It is shown that the emergence of the secondary instability can modify the outline of the turbulent structures associated with the primary Rayleigh-Taylor instability.
The hyperfine structure in the rotational spectra of D217O and HD17O: Confirmation of the absolute nuclear magnetic shielding scale for oxygen
Authors: Puzzarini Cristina , Cazzoli Gabriele , Harding Michael E. , Vázquez Juana , Gauss Jürgen
Published: March 2015

Guided by theoretical predictions, the hyperfine structures of the rotational spectra of mono- and bideuterated-water containing 17O have been experimentally investigated. To reach sub-Doppler resolution, required to resolve the hyperfine structure due to deuterium quadrupole coupling as well as to spin-rotation (SR) and dipolar spin-spin couplings, the Lamb-dip technique has been employed. The experimental investigation and in particular, the spectral analysis have been supported by high-level quantum-chemical computations employing coupled-cluster techniques and, for the first time, a complete experimental determination of the hyperfine parameters involved was possible. The experimentally determined 17O spin-rotation constants of D217O and HD17O were used to derive the paramagnetic part of the corresponding nuclear magnetic shielding constants. Together with the computed diamagnetic contributions as well as the vibrational and temperature corrections, the latter constants have been employed to confirm the oxygen nuclear magnetic shielding scale, recently established on the basis of spin-rotation data for H217O [Puzzarini et al., J. Chem. Phys. 131, 234304 (2009)].
Benchmarking DFT and semiempirical methods on structures and lattice energies for ten ice polymorphs
Authors: Brandenburg Jan Gerit , Maas Tilo , Grimme Stefan
Published: March 2015

Water in different phases under various external conditions is very important in bio-chemical systems and for material science at surfaces. Density functional theory methods and approximations thereof have to be tested system specifically to benchmark their accuracy regarding computed structures and interaction energies. In this study, we present and test a set of ten ice polymorphs in comparison to experimental data with mass densities ranging from 0.9 to 1.5 g/cm3 and including explicit corrections for zero-point vibrational and thermal effects. London dispersion inclusive density functionals at the generalized gradient approximation (GGA), meta-GGA, and hybrid level as well as alternative low-cost molecular orbital methods are considered. The widely used functional of Perdew, Burke and Ernzerhof (PBE) systematically overbinds and overall provides inconsistent results. All other tested methods yield reasonable to very good accuracy. BLYP-D3atm gives excellent results with mean absolute errors for the lattice energy below 1 kcal/mol (7% relative deviation). The corresponding optimized structures are very accurate with mean absolute relative deviations (MARDs) from the reference unit cell volume below 1%. The impact of Axilrod-Teller-Muto (atm) type three-body dispersion and of non-local Fock exchange is small but on average their inclusion improves the results. While the density functional tight-binding model DFTB3-D3 performs well for low density phases, it does not yield good high density structures. As low-cost alternative for structure related problems, we recommend the recently introduced minimal basis Hartree-Fock method HF-3c with a MARD of about 3%.
A novel design of Rogowski coil for measurement of nanosecond-risetime high-level pulsed current
Authors: Han Ruo-Yu , Ding Wei-Dong , Wu Jia-Wei , Zhou Hai-Bin , Jing Yan , Liu Qiao-Jue , Chao You-Chuang , Qiu Ai-Ci
Published: March 2015

In pulsed power systems, pulsed currents with risetimes from nanosecond to microsecond can be effectively measured by self-integrating Rogowski coils. Appropriate design of the structure and the integrating resistor is crucial to the high-frequency response of a coil. In this paper, several novel designs of Rogowski coil’s integrating resistors were proposed and tested. Experimental results showed that the optimized coil could response square waves with fronts of ∼1.5 ns and had a sensitivity of ∼0.75 V/kA. The maximal peak current was designed as 100 kA.
Internal stress distribution for generating closure domains in laser-irradiated Fe–3%Si(110) steels
Authors: Iwata Keiji , Imafuku Muneyuki , Suzuki Tamaki , Shobu Takahisa , Orihara Hideto , Sakai Yusuke , Akita Koichi , Ohya Shin-Ichi , Ishiyama Kazushi
Published: March 2015

Internal stress distribution for generating closure domains occurring in laser-irradiated Fe–3%Si(110) steels was investigated using high-energy X-ray analysis and domain theory based on the variational principle. The measured triaxial stresses inside the specimen were compressive and the stress in the rolling direction became more dominant than stresses in the other directions. The calculations based on the variational principle of magnetic energy for closure domains showed that the measured triaxial stresses made the closure domains more stable than the basic domain without closure domains. The experimental and calculation results reveal that the laser-introduced internal stresses result in the occurrence of the closure domains.
Temperature and non-linear response of cantilever-type mechanical oscillators used in atomic force microscopes with interferometric detection
Authors: Fläschner G. , Ruschmeier K. , Schwarz A. , Bakhtiari M. R. , Thorwart M. , Wiesendanger R.
Published: March 2015

The sensitivity of atomic force microscopes is fundamentally limited by the cantilever temperature, which can be, in principle, determined by measuring its thermal spectrum and applying the equipartition theorem. However, the mechanical response can be affected by the light field inside the cavity of a Fabry-Perot interferometer due to light absorption, radiation pressure, photothermal forces, and laser noise. By evaluating the optomechanical Hamiltonian, we are able to explain the peculiar distance dependence of the mechanical quality factor as well as the appearance of thermal spectra with symmetrical Lorentzian as well as asymmetrical Fano line shapes. Our results can be applied to any type of mechanical oscillator in an interferometer-based detection system.
X-ray magnetic circular dichroism study of epitaxial magnetite ultrathin film on MgO(100)
Authors: Liu W. Q. , Song M. Y. , Maltby N. J. , Li S. P. , Lin J. G. , Samant M. G. , Parkin S. S. P. , Bencok P. , Steadman Paul , Dobrynin Alexey , Xu Y. B. , Zhang R.
Published: March 2015

The spin and orbital magnetic moments of the Fe3O4 epitaxial ultrathin film synthesized by plasma assisted simultaneous oxidization on MgO(100) have been studied with X-ray magnetic circular dichroism. The ultrathin film retains a rather large total magnetic moment, i.e., (2.73 ± 0.15) μB/f.u., which is ∼70% of that for the bulk-like Fe3O4. A significant unquenched orbital moment up to 0.54 ± 0.05 μB/f.u. was observed, which could come from the symmetry breaking at the Fe3O4/MgO interface. Such sizable orbital moment will add capacities to the Fe3O4-based spintronics devices in the magnetization reversal by the electric field.
Modulation of the magnetic/conductive dead layer at the manganites-SrTiO3 interface
Authors: Gao W. W. , Hu F. X. , Shen B. G. , Sun J. R.
Published: March 2015

We presented a systematic study on the transport properties of the La0.67A0.33MnO3 (LAMO) (A = Ba, Ca) and La0.67Ca0.33MnO3/LaMnO3 (LCMO/LMO) films with the LAMO layer of the thickness from 0 to 50 nm and a fixed LMO thickness of 3 nm. An interface layer with degenerated magnetic and conductive properties has been observed. It is interesting that the dead layer in LBMO is much thinner than that in LCMO. The thickness for the dead layer is, deduced from the conductivity-film thickness relation at 5 K, ∼6 nm for LCMO and ∼3 nm for LBMO, essentially weakly dependent of magnetic field. After introducing the LMO buffer layer, the magnetic field dependence is considerably enhanced; a simple estimate indicates that a field of 5 T depresses the layer thickness from ∼6 nm to ∼3 nm. It indicates that the LMO layer enhances the sensitivity of trapped charge carriers at the interface to magnetic field, thus activates the dead layer.
Phase evolution and magnetic properties of HoIn3−xCox
Authors: Chen Songlin , Guo Yongquan , He Qiang
Published: March 2015

The phase evolution of HoIn3−xCox exhibits the phase transformations from the original HoIn3 with cubic structure to the intermediated HoCo2In with orthorhombic structure and to the final HoCo3 with rhombohedral structure. The corresponding magnetic states are found to closely associate with the structural phase transformation of HoIn3−xCox.With increasing Co contents, HoIn3−xCox are paramagnetic in region of x < 0.6, mixture of paramagnetic and ferromagnetic in range of 0.6 < x < 1.8, and ferromagnetic in range of 3 > x > 2.4 at room temperature, respectively. The field dependence of magnetization curves follows an equation of M=Ms(1−aH)+χH, where Ms and χ are corresponding to the saturation moment and susceptibility; a is a parameter related to the external field. The fitting results show that the susceptibility increases with increasing Co contents and Ms depends upon the Co content as well. It implies that the evolution of magnetic phases in HoIn3−xCox might originate from the change of exchange interaction from the one between the isolated Co spins and the surrounding conduction electrons in Co-poor regime to the one between Co-Co pairs mediated by the conduction electrons in Co-rich regime.
Conditions for supersonic bent Marshak waves
Authors: Xu Qiang , Ren Xiao-dong , Li Jing , Dan Jia-kun , Wang Kun-lun , Zhou Shao-tong
Published: March 2015

Supersonic radiation diffusion approximation is an useful method to study the radiation transportation. Considering the 2-d Marshak theory, and an invariable source temperature, conditions for supersonic radiation diffusion are proved to be coincident with that for radiant flux domination in the early time when εxf/L≪1. However, they are even tighter than conditions for radiant flux domination in the late time when εxf/L≫1, and can be expressed as M>4(1+ε/3)/3 and τ>1. A large Mach number requires the high temperature, while the large optical depth requires the low temperature. Only when the source temperature is in a proper region the supersonic diffusion conditions can be satisfied. Assuming a power-low (in temperature and density) opacity and internal energy, for a given density, the supersonic diffusion regions are given theoretically. The 2-d Marshak theory is proved to be able to bound the supersonic diffusion conditions in both high and low temperature regions, however, the 1-d theory only bounds it in low temperature region. Taking SiO2 and the Au, for example, these supersonic regions are shown numerically.
Incorporating semiconducting single-walled carbon nanotubes as efficient charge extractors in organic solar cells
Authors: Abeygunasekara Waranatha L. , Hiralal Pritesh , Samaranayake Lilantha , Chien Chih-Tao , Kumar Abhishek , Flewitt Andrew J. , Karunaratne Veranja , Amaratunga Gehan A. J.
Published: March 2015

We report on the improvement of power conversion efficiency (PCE) of PTB7/PC70BM solar cells by the addition of small quantities (0.02%–0.04%) of pristine single-walled carbon nanotubes (SWNTs) in the active-layer. SWNTs and purified semiconducting SWNTs (S-SWNTs) were added in quantities, which is 2 orders of magnitude lower than previously reported value and resulted in a reduction in the series resistance of the solar cell with minor changes on the shunt resistance. On addition of purified S-SWNT, the PCE of air measured devices enhanced by 29% from 4.9% to 6.3%, with short-circuit current density (Jsc) improving from 12.1 mA/cm2 to 14.4 mA/cm2 and a fill factor improvement from 54% to 61%. In addition, the role of processing additive N-Methyl-2-pyrrolidone, which acts as a SWNT dispersant, is also investigated. A single diode model of a solar cell is used to extract the cell parameters and understand the effect of SWNTs. Based on experimental data and it's fitting to the single diode model, we propose that S-SWNT improve the transport and extraction of photogenerated charges within the solar cell device.
Maze solving automatons for self-healing of open interconnects: Modular add-on for circuit boards
Authors: Nair Aswathi , Raghunandan Karthik , Yaswant Vaddi , Pillai Sreelal S. , Sambandan Sanjiv
Published: March 2015

We present the circuit board integration of a self-healing mechanism to repair open faults. The electric field driven mechanism physically restores fractured interconnects in electronic circuits and has the ability to solve mazes. The repair is performed by conductive particles dispersed in an insulating fluid. We demonstrate the integration of the healing module onto printed circuit boards and the ability of maze solving. We model and perform experiments on the influence of the geometry of conductive particles as well as the terminal impedances of the route on the healing efficiency. The typical heal rate is 10 μm/s with healed route having mean resistance of 8 kΩ across a 200 micron gap and depending on the materials and concentrations used.
Abnormal electric-field-induced light scattering in Pb(Mg1/3Nb2/3)O3-PbTiO3 transparent ceramics
Authors: Zhou Yibo , Zhao Wei , Ruan Wei , Zeng Jiangtao , Zheng Liaoying , Cheng Jian , Li Guorong
Published: March 2015

We present a strong electric-field-induced light scattering phenomenon in relaxor ferroelectrics 75Pb(Mg1/3Nb2/3)-25PbTiO3 transparent ceramics under a weak threshold electric field, which is attributed to the abrupt growth of polar nanoregions above the threshold field with a significant change of local crystal symmetry, dielectric, and Raman response. These results provide further understanding on the electric field-induced domain behaviors and peculiar properties in relaxor ferroelectrics.
Photogating of mono- and few-layer MoS2
Authors: Miller Bastian , Parzinger Eric , Vernickel Anna , Holleitner Alexander W. , Wurstbauer Ursula
Published: March 2015

We describe a photogating effect in mono- and few-layer MoS2, which allows the control of the charge carrier density by almost two orders of magnitude without electrical contacts. Our Raman studies are consistent with physisorbed environmental molecules, which effectively deplete the intrinsically n-doped charge carrier system via charge transfer and which can be gradually removed by the exposure to light. This photogating process is reversible and precisely tunable by the light intensity. The photogating efficiency is quantified by comparison with measurements on electrostatically gated MoS2.
Titanium dioxide/silicon hole-blocking selective contact to enable double-heterojunction crystalline silicon-based solar cell
Authors: Nagamatsu Ken A. , Avasthi Sushobhan , Sahasrabudhe Girija , Man Gabriel , Jhaveri Janam , Berg Alexander H. , Schwartz Jeffrey , Kahn Antoine , Wagner Sigurd , Sturm James C.
Published: March 2015

In this work, we use an electron-selective titanium dioxide (TiO2) heterojunction contact to silicon to block minority carrier holes in the silicon from recombining at the cathode contact of a silicon-based photovoltaic device. We present four pieces of evidence demonstrating the beneficial effect of adding the TiO2 hole-blocking layer: reduced dark current, increased open circuit voltage (VOC), increased quantum efficiency at longer wavelengths, and increased stored minority carrier charge under forward bias. The importance of a low rate of recombination of minority carriers at the Si/TiO2 interface for effective blocking of minority carriers is quantitatively described. The anode is made of a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) heterojunction to silicon which forms a hole selective contact, so that the entire device is made at a maximum temperature of 100 °C, with no doping gradients or junctions in the silicon. A low rate of recombination of minority carriers at the Si/TiO2 interface is crucial for effective blocking of minority carriers. Such a pair of complementary carrier-selective heterojunctions offers a path towards high-efficiency silicon solar cells using relatively simple and near-room temperature fabrication techniques.
Effect of direct current sputtering power on the behavior of amorphous indium-gallium-zinc-oxide thin-film transistors under negative bias illumination stress: A combination of experimental analyses and device simulation
Authors: Jang Jun Tae , Park Jozeph , Ahn Byung Du , Kim Dong Myong , Choi Sung-Jin , Kim Hyun-Suk , Kim Dae Hwan
Published: March 2015

The effect of direct current sputtering power of indium-gallium-zinc-oxide (IGZO) on the performance and stability of the corresponding thin-film transistor devices was studied. The field effect mobility increases as the IGZO sputter power increases, at the expense of device reliability under negative bias illumination stress (NBIS). Device simulation based on the extracted sub-gap density of states indicates that the field effect mobility is improved as a result of the number of acceptor-like states decreasing. The degradation by NBIS is suggested to be induced by the formation of peroxides in IGZO rather than charge trapping.
Sensitivity of optical mass sensor enhanced by optomechanical coupling
Authors: He Yong
Published: March 2015

Optical mass sensors based on cavity optomechanics employ radiation pressure force to drive mechanical resonator whose mechanical susceptibility can be described by nonlinear optical transmission spectrum. In this paper, we present an optical mass sensor based on a two-cavity optomechanical system where the mechanical damping rate can be decreased by adjusting a pump power so that the mass sensitivity which depends on the mechanical quality factor has been enhanced greatly. Compared with that of an optical mass sensor based on single-cavity optomechanics, the mass sensitivity of the optical mass sensor is improved by three orders of magnitude. This is an approach to enhance the mass sensitivity by means of optomechanical coupling, which is suitable for all mass sensor based on cavity optomechanics. Finally, we illustrate the accurate measurement for the mass of a few chromosomes, which can be achieved based on the current experimental conditions.
Evidence for phase transitions and pseudospin phonon coupling in K0.9(NH4)0.1H2AsO4
Authors: Kumar Pradeep , Ramesh K. P. , Muthu D. V. S.
Published: March 2015

This work reports a detailed temperature dependent Raman study on the mixed crystals of K0.9(NH4)0.1H2AsO4 (KADA) from 5K to 300K in the spectral range of 60-1200cm−1, covering tetragonal to orthorhombic structural phase transition accompanied by paraelectric to ferroelectric transition at Tc* ∼ 60K. Multiple phase transitions below transition temperature (Tc* ∼ 60K) are marked by the appearance of new modes, splitting of existing ones as well as anomalies in the self-energy parameters (i.e. mode frequencies and damping coefficient) of the phonon modes. Temperature independent behaviour of damping coefficient and abrupt jump in the mode frequency of some of the internal vibrations of AsO4 tetrahedra as well as external vibrations clearly signal long range ferroelectric ordering and proton ordering below Tc*. In addition, we observed that temperature dependence of many prominent phonon modes diverges significantly from their normal anharmonic behaviour below Tc* suggesting potential coupling between pseudospins and phonons.