bluuebunny/crossref_metadata_2025 huggingface dataset:
Transport models and intelligent transportation system to support urban evacuation planning process
Authors: Giovanna Chilà , Giuseppe Musolino , Antonio Polimeni , Corrado Rindone , Francesco Russo , Antonino Vitetta
Published: April 2016

This study focuses on risk management and specifically the exposure component. The exposure may be reduced by means of evacuation. This measure allows people and goods to be rescued from the area where the calamitous effects are announced. In the past years, many models have been proposed to simulate and design transport system under evacuation conditions. It must be underlined that the models applied to ordinary conditions cannot be directly applied to evacuation conditions due to very strong differences in demand, supply and interaction. Other models have been developed for emergency conditions. Nevertheless they consider only specific aspects and do not provide a comprehensive framework. This study presents the main quantitative results of a long‐lasting research project for which a unifying approach for the simulation and design of a transportation system under evacuation conditions is adopted. In this project, an intelligent transportation system (ITS) is implemented to monitor real evacuation tests in a town where an emergency event has been simulated and experimented. In this study, a general methodology is reported with the description of the main models and procedures. Models are calibrated and validated by means of observed data obtained from ITS.
Equivalent circuit of a reconfigurable triple‐slot reflectarray cell
Authors: Nadaud Kevin , Gillard Raphaël , Fourn Erwan , Gundel Hartmut W.
Published: April 2016

This study presents an equivalent model for a multiple‐resonance reflectarray cell. It allows predicting the different phase‐states of the cell from only a very few full‐wave simulations. Demonstrations are first given for a passive cell where different geometrical parameters are varied. Then, the approach is generalised to a reconfigurable cell. Finally, a canonical reflectarray with a steered beam has been synthesised in order to illustrate the capabilities of the proposed equivalent circuit.
Propagation of electromagnetic waves guided by perfectly conducting model of a tape helix supported by dielectric rods
Authors: Naveen Babu Gnanamoorthi , Stanislaus Richards Joe
Published: April 2016

The homogeneous boundary value problem existing in the electromagnetic wave propagation in a dielectric‐loaded perfectly conducting tape helix with infinitesimal tape thickness is investigated in this study. The ill‐posed boundary value problem is regularised using the mollification method. The homogeneous boundary value problem is solved for the dielectric loaded perfectly conducting tape helix taking into account the exact boundary conditions for the perfectly conducting dielectric loaded tape helix. The solved approximate dispersion equation takes the form of the solvability condition for an infinite system of linear homogeneous equations namely, the determinant of the infinite order coefficient matrix is zero. For the numerical computation of the dispersion equation, all the entries of the symmetrically truncated version of the coefficient matrix are estimated by summing an adequate number of the rapidly converging series for them. The tape‐current distribution is estimated from the null‐space vector of the truncated coefficient matrix corresponding to a specified root of the dispersion equation. The numerical results suggest that the propagation characteristic computed by the anisotropically conducting model (that neglects the component of the tape‐current density perpendicular to the winding direction) is only an abstinent approximation to consider for moderately wide tapes.
W band axially displaced monopulse dual‐reflector antenna for inter‐satellite communications
Authors: Wang Yanxun , Dou Wenbin , Bi Bo
Published: April 2016

An axially displaced monopulse dual‐reflector antenna operating at W band is proposed in this study. The antenna configuration consists of a hyperboloid as the subreflector, a combination of series of paraboloids with different focal length as the main reflector and a low‐loss sum‐and‐difference network, which is based on waveguide magic Ts and bent waveguides. Compared with traditional dual‐reflector antenna, axial size and weight of this novel antenna can be reduced to a certain extent. Measured results show that the gain is 40.1 dBi, the sidelobe is <−19.7 dB and the null‐depth is <−27.7 dB at the central frequency. The radiation patterns remain almost the same in the bandwidth. It is demonstrated that this antenna exhibits good radiation performances and is suitable for inter‐satellite systems.
Generalised interval‐based analysis tool for pattern distortions in reflector antennas with bump‐like surface deformations
Authors: Anselmi Nicola , Salucci Marco , Rocca Paolo , Massa Andrea
Published: April 2016

The prediction of the effects on the power pattern of bump‐like distortions in the surface of reflector antennas is addressed. The expressions of the upper and the lower bounds of the power pattern radiated by the deformed reflector are analytically derived by means of the interval analysis as a function of the uncertainty on the bump depth. A set of representative numerical results is reported and discussed to validate the effectiveness and the reliability of the proposed approach also in comparison with state‐of‐the‐art methods and commercial software based on statistical methods and physical optics, respectively.
Enhancing the performance of EBG resonator antennas by individually truncating the superstructure layers
Authors: Hashmi Raheel M. , Esselle Karu P.
Published: April 2016

The role of superstructure finiteness in improving the peak directivity and the directivity bandwidth (DBW) of electromagnetic band gap (EBG) resonator antennas (ERAs) is studied. Simple one‐ and two‐layer superstructures consisting of unprinted dielectric slabs are used for this purpose. In the latter case, each dielectric slab is truncated individually to improve the ERA performance. Initially, existing analytical models that only take into account the reflection characteristics of the superstructure are used to predict the peak obtainable directivity and the directivity bandwidth. Detailed numerical studies are then conducted to observe the validity of these analytical predictions and to study the ERA performance for various finite sizes of the superstructure. It is found that DBW as well as the peak directivity of the antenna is strongly influenced by the size of the superstructure. Moreover, in case of two‐layer superstructures, carefully designing each layer to have a different finite size improved the DBW product of an ERA by more than 65%. Experimental results of three ERA prototypes are presented to validate the trends observed in the numerical findings.
Performance improvement by transmit diversity technique for implant ultra‐wideband communication
Authors: Shimizu Yuto , Furukawa Tomofumi , Anzai Daisuke , Wang Jianqing
Published: April 2016

In implant body area networks (BANs), an ultra‐wideband (UWB) technology is a promising candidate to accomuplish high data rate. However, due to its frequency, the UWB signals suffer from large attenuation in the implant communication link. This fact suggests the difficulty on achieving reliable communication. For achieving reliable communication, it is well known that a spatial diversity technique is efficient. In this study, the authors pay attention to the fact that it is possible to further miniaturise the UWB antenna due to its very high frequency. Then, the authors aim to develop a transmit polarisation diversity antenna for implant UWB communications, and apply the developed transmit diversity system to a UWB‐impulse radio (UWB‐IR) scheme and a multiband‐orthogonal frequency division multiplexing (MB‐OFDM) scheme, respectively. For evaluating the proposed system, the authors first analyse the propagation characteristics in the implant UWB channel, using the finite difference time domain numerical analysis technique. Then, the authors evaluate and discuss the communication performances of the both modulation schemes for the transmit polarisation diversity. As a result, at a communication distance of 7 cm, the throughputs have accomplished to 300 Mbps for the MB‐OFDM scheme and 30 Mbps for UWB‐IR scheme, respectively.
Instantaneous power variance and radio frequency to dc conversion efficiency of wireless power transfer systems
Authors: Blanco Javier , Bolos Ferran , Georgiadis Apostolos
Published: April 2016

This study compares the maximum rectifier radio frequency (RF)–dc conversion efficiency for various input signals with random modulation. The instantaneous power variance (IPV) is proposed as an easy to compute parameter to classify the effect of modulation on the obtained rectifier efficiency. A prototype ultra high frequency (UHF) rectifier is used to simulate as well as measure the performance of randomly modulated signals with binary phase‐shift keying (BPSK), quadrature phase‐shift keying (QPSK), 8 phase‐shift keying (PSK) and 64 quadrature amplitude modulation (QAM) modulations. In addition to considering different modulation formats, the roll‐off factor of the baseband filter is also varied due to the fact that it has a strong impact on the time‐varying nature of the signal envelope. For the given rectifier, it is shown that the peak RF–dc conversion efficiency versus the output load is shifted to larger load values for signals with higher IPV. Furthermore, by comparing signals with different time‐varying envelope characteristics, it is shown that IPV represents a more accurate signal characteristic than peak‐to‐average power ratio in terms of properly characterising the effect of modulation on the rectifier efficiency.
Design of continuous‐mode GaN power amplifier with compact fundamental impedance solutions on package plane
Authors: Pang Jingzhou , He Songbai , Dai Zhijiang , Huang Chaoyi , Peng Jun , You Fei
Published: April 2016

A novel methodology for designing broadband Class‐J power amplifiers (PAs) with compact fundamental impedances on the package plane is presented. A simple transistor model with knee voltage region is built to predict efficiency performance and clipping waveforms caused by the clipping effects. To realise the proposed impedance solutions, a broadband matching network is presented based on the shot‐stepped Chebyshev impedance transformer. A broadband Gallium Nitride (GaN) PA is designed using this method and achieve a very wide operation band from 0.8 to 3.6 GHz. More than 10 dB gain, 55.8–74.1% drain efficiency and around −30 dBc adjacent channel power ratio are measured without linearisation throughout the entire band. At 33 dBm average output power level, an average power‐added efficiency of 27% and adjacent power leakage ratio of −46.3 dBc is obtained with 9 dB peak‐to‐average power ratio 20 MHz long‐term evolution test signals at 2.4 GHz.
Ka‐band doherty power amplifier with 26.9 dBm output power, 42% peak PAE and 32% back‐off PAE using GaAs PHEMTS
Authors: Curtis Jeffery , Pham Anh‐Vu , Aryanfar Farshid
Published: April 2016

The authors present the design and development of a two stage Doherty power amplifier (DPA) in the Ka‐band. The amplifier is fabricated in a 0.15‐µm gallium arsenide (GaAs) pseudomorphic high electron mobility transistor (pHEMT) process. The DPA has a centre frequency of 26.6 GHz, a measured small signal gain of 10.5 dB, output power at 1‐dB compression point (P1 dB) of 26.9 dBm, maximum power added efficiency (PAE) of 42%, and PAE of 32% at 6 dB back‐off power. To the best of the author's knowledge, this DPA is the first millimetre‐wave (mm‐wave) power amplifier to achieve a record 32% PAE at 6‐dB back‐off power from 26.9 dBm at Ka‐band.
Simulation of orbital angular momentum radio communication systems based on partial aperture sampling receiving scheme
Authors: Hu Yiping , Zheng Shilie , Zhang Zhuofan , Chi Hao , Jin Xiaofeng , Zhang Xianmin
Published: April 2016

The incoherent orbital angular momentum (OAM) radio waves can be used to transmit different information on the same frequency and have a great potential in wireless communication system. However, it needs a large aperture size to receive and demultiplex the orthogonal OAM waves due to the amplitude null in the beam centre and the beam divergence. An improved receiving scheme named partial aperture sampling receiving (PASR) is proposed to solve this problem. The theoretical analysis of PASR is first presented and simulations of OAM radio communication link are carried on to evaluate the performance of PASR. The effects of some non‐ideal receiver conditions, e.g. radial deviation and angular deviation on the PASR scheme and the superiority of PASR are explored. These simulated results will give a helpful guide on the manipulation of practical OAM‐based wireless communication systems.
High‐performance unified power quality conditioner using command generator tracker‐based direct adaptive control strategy
Authors: Patjoshi Rajesh Kumar , Mahapatra Kamalakanta
Published: April 2016

This study proposes a command generator tracker‐based direct adaptive control technique (CGT‐DAC) in a three‐phase three‐wire unified power quality conditioner (UPQC). This proposed CGT‐DAC improves the PQ issues such as current and voltage harmonics, sag/swell and voltage unbalance in the power system distribution network. CGT is a model reference control law for a linear time‐invariant system with known coefficients and is formulated for the generation of reference signals for both shunt and series inverter. Furthermore, CGT can adaptively regulate the DC‐link capacitor voltage without utilising additional controller. Moreover, DAC is designed to track a linear reference model to reduce the tracking error between model reference output and measured signal to be controlled. Therefore, the proposed CGT‐DAC approach provides more robustness, flexibility and adaptability in all operating conditions of the power system over a conventional proportional–integral (PI) controller. This proposed control strategy of UPQC is validated through MATLAB/SIMULINK followed by the experimental system of real‐time‐hardware‐in the loop‐based OPAL‐RT system and adequate results are reported after a comparative assessment with the conventional PI‐controller.
Buck‐boost‐flyback integrated converter with single switch to achieve high voltage gain for PV or fuel‐cell applications
Authors: Shen Chih‐Lung , Chiu Po‐Chieh
Published: April 2016

This study presents a buck‐boost‐flyback integrated converter (BBFIC), which can step up the voltage of photovoltaic (PV) module or fuel cell to a much higher level for grid‐tied applications. The converter combines two buck‐boost converters and one flyback converter into a single‐stage structure with single power switch. In the power stage, an inductor and a coupled inductor are adopted to feature buck‐boost and flyback behaviours, and three capacitors are connected in series to stack up output voltage. Even though it possesses the characteristics of buck‐boost and flyback converters, the problem of reversed voltage polarity is avoided and the energy stored in leakage inductor can be recycled without additional active clamp circuits. The structure of BBFIC can be easily expanded to obtain an extra‐high voltage gain by stacking buck‐boost cells or flyback cells. Voltage gain derivation and theoretical analysis are detailed in this study. Simulations and practical results measured from a prototype have validated the proposed BBFIC.
Modelling of lithium‐titanate battery with ambient temperature effect for charger design
Authors: Low Wen Yao , Abdul Aziz Mohd Junaidi , Idris Nik Rumzi Nik
Published: April 2016

Lithium‐titanate battery is a new generation of lithium‐ion battery that offers an outstandingly fast charging capability. Its charging profile forms the basis for an efficient battery charger design for the battery. As a remedial solution, this study proposes a mathematical model to capture the charging profiles of the lithium‐titanate battery at different charging rates and ambient temperatures. In this aspect, the charging characteristic of lithium‐titanate battery is represented by a transfer function, which is applicable for small‐signal analysis and large‐signal simulation of battery charger design. The methodology of battery modelling is solely based on the constant‐current charging profiles of a battery. Enhanced charging curve normalisation method is applied to obtain the charging characteristic of battery. A novel temperature‐based equation is developed to represent the normalised charging curves at different ambient temperatures. Then, a transfer function‐based model is developed to simulate the charging profiles of battery. The developed model is validated through experimental studies. Comparison of experimental and simulation results shows that the developed model is able to capture the charging behaviour of a lithium‐titanate battery for various charging rates and temperatures.
Grid‐tied photovoltaic system based on PSO MPPT technique with active power line conditioning
Authors: de Oliveira Fernando M. , Oliveira da Silva Sérgio A. , Durand Fábio R. , Sampaio Leonardo P. , Bacon Vinícius D. , Campanhol Leonardo B.G.
Published: April 2016

This study presents a single‐phase grid‐tied photovoltaic (PV) system based on a global maximum power point tracking (MPPT) technique, which is performed by means of the particle swarm optimisation (PSO) method. The PSO‐based MPPT technique is employed to solve problems related to mismatching phenomena, such as partial shading, in which the PV arrays are commonly submitted. Considering the search of the global maximum power point under partial shading, the effectiveness of the PSO‐based MPPT technique is highlighted when compared with the well‐known perturb and observe MPPT technique, since both the mentioned MPPT techniques are used to determine the dc‐bus voltage reference to ensure a proper grid‐tied inverter operation. A current generator algorithm based on a synchronous reference frame is proposed, which operates in conjunction with a dc‐bus controller and MPPT algorithms, computing the reference current of the grid‐tied inverter. In addition, the current generator controls the energy processed by the PV system to avoid over power rating of the grid‐tied inverter, since the active power injection into the grid, reactive power compensation and harmonic currents suppression are carried out simultaneously. The performance and feasibility of the grid‐tied PV system are evaluated by means of simulation and experimental results.
Power flow and transmission loss analysis of modular multi‐level converter based multi‐terminal high‐voltage DC systems
Authors: Zhang Yuanze , Ravishankar Jayashri , Fletcher John
Published: April 2016

Interconnected voltage‐source converter based multi‐terminal high‐voltage DC (HVDC) systems provide better system redundancy, higher flexibility and capability of exchanging power between multiple areas. Recent developments in modular multi‐level converter technology makes multi‐terminal HVDC (MTDC) transmission more promising than before. This study provides an in‐depth analysis of the power flow and transmission loss for MTDC systems with different grid topologies. A voltage–power droop control based algorithm is applied to solve the power flow problems. The main contribution of this study is the novel way of determining and calculating the transmission line losses for different MTDC network topology configurations. Three MTDC system topologies are investigated. Simulated case studies are used to observe the system power flow and transmission losses for all three topologies.
Nested array receiver with time‐delayers for joint target range and angle estimation
Authors: Wang Wen‐Qin , Zhu Chenglong
Published: April 2016

Phased‐array provides range‐independent beampattern and consequently it cannot detect/suppress range‐dependent targets/interferences. Moreover, an M‐element phased‐array can resolve at most M − 1 targets simultaneously. This study proposes a nested array receiver using diverse time‐delayers (DTDs) for jointly estimating the range and angle of targets. The essence is to construct a new array structure by systematically nesting two uniform linear arrays through DTDs instead of phase controlling in traditional nested array technique. Using the second‐order statistics of the received data, an M‐element array can resolve O(M2) targets. Moreover, the nested DTD receiver design is exploited for minimum variance distortionless response beamforming and direction finding. The improvements offered by the proposed method, as compared with basic DTD receivers, are demonstrated by examining the output signal‐to‐interference‐plus‐noise ratio, the probability of detection and the Cramér–Rao lower bounds for estimating the range and angle of targets.
Range‐spread target detection based on the matched ambiguity function
Authors: Zuo Lei , Li Ming , Liu Zheng , Cao Runqing
Published: April 2016

In this study, the authors deal with the problem of detecting a range‐spread target with a high velocity. First, they prove that the mixer output consists of several sinusoidal signals. Then, the matched signal of a noisy mixer output is defined in terms of the energy concentration of the noisy high‐resolution range profile (HRRP). Consequently, the matched ambiguity function (MAF) of a noisy mixer output is obtained. Based on the MAF, a range‐spread target detector, referred to as MAF‐detector (MAF‐D), is proposed. The MAF‐D uses a single noisy HRRP and thus can detect the target with a high translational velocity and a high rotational velocity. Experimental results, conducted by the recorded radar data, show that the proposed detector outperforms the conventional detectors.
Multi‐target multi‐scan smoothing in clutter
Authors: Kim Tae Han , Song Taek Lyul
Published: April 2016

The multi‐target multi‐scan smoothing algorithm, which is an extended version of the smoothing integrated track splitting (sITS) algorithm, is presented in this study. The differences between the sITS and the proposed algorithms are that the (iterative) joint integrated track splitting (ITS) algorithm is applied and joint data association probabilities are used for the backward ITS update. A comparative assessment of the smoothing/non‐smoothing and single‐target/multi‐target data association algorithm is carried out to verify the false track discrimination, trajectory estimation and track retention performances.
Location aware sensor routing protocol for mobile wireless sensor networks
Authors: Hayes Tom , Ali Falah H.
Published: April 2016

Location aware sensor routing (LASeR) protocol is a novel solution to the challenges of routing in mobile wireless sensor networks (MWSNs). It addresses the high reliability and low latency requirements of emerging applications. The protocol uses location information to maintain a gradient field even in highly mobile environments, whilst reducing the routing overhead. This allows the protocol to utilise a blind forwarding technique to propagate packets towards the sink. The protocol inherently utilises multiple paths simultaneously to create route diversity and increase its robustness. LASeR is designed for use in a high variety of MWSN applications with autonomous land, sea or air vehicles. Analytical expressions are derived and evaluated against the simulations. Extensive modelling and simulation of the proposed routing protocol has shown it to be highly adaptable and robust. It is compared with the recent MWSN proactive highly ambulatory sensor routing protocol, the high performance mobility adaptive cross‐layer routing protocol, as well as ad‐hoc on‐demand distance vector and optimised link state routing. Protocols are evaluated on packet delivery ratio, end‐to‐end delay, overhead, throughput and energy consumption. The results highlight both the high performance of LASeR in various challenging environments and its superiority over the state‐of‐the‐art.
Facile and eco‐friendly fabrication of Cu2O truncated octahedral crystallites with enhanced antibacterial performance against Escherichia coli and Staphylococcus aureus
Authors: Yang Chunmei , Li Qing , Lin Hua , Li Yuan , Xie Guomeng
Published: April 2016

Truncated octahedral cuprous oxide (Cu2O) crystallites with highly uniform morphologies and sizes ranging from 2.4–2.5 µm were prepared by using a green and convenient approach and their antibacterial activities were studied. They were obtained through the chemical reduction of copper chloride by glucose in the presence of sodium hydroxide and polyethylene glycol at room temperature for 2 h. X‐ray powder diffraction, energy dispersive spectrometer, scanning electron microscopy, and transmission electron microscopy as well as high‐resolution transmission electron microscopy (HRTEM) were used to characterise the obtained products. Structural analysis revealed that these truncated octahedral crystallites were composed of eight {111} faces and six {200} faces. The effects of time, temperature and polyethylene glycol on the formation of truncated octahedral cuprous oxide were investigated. The possible growth process and mechanism of truncated octahedral cuprous oxide were proposed. The antibacterial activities of truncated octahedral Cu2O were also explored. They exhibited significant antimicrobial activity against both gram‐negative and gram‐positive bacteria. The result of antibacterial study revealed that the prepared Cu2O can be a promising candidate for wide range of bio‐medical applications.
Resistivity and optical transmittance dependence on length and diameter of nanowires in silver nanowire layers in application to transparent conductive coatings
Authors: Anoshkin Ilya V. , Nefedova Irina I. , Nefedov Igor S. , Lioubtchenko Dmitri V. , Nasibulin Albert G. , Räisänen Antti V.
Published: April 2016

Optical absorption spectra and electrical conductivity of silver nanowires with mean diameters of 56, 73, and 106 nm and mean length of 10.4, 12.6, and 32.0 µm, respectively have been experimentally studied. The size dependent effective permittivity of silver nanowire layers is calculated using mixing equations as for anisotropic materials according to the Maxwell‐Garnett theory. The absorption spectra peak positions of nanowires with various diameters are interpreted according to the theoretical calculations based on the Mie theory, which allow to predict dependence of the optical properties on the nanowire diameter. The sheet resistance measurements show that 13–15 Ω/sq at the level of 80–90% transmittance at 550 nm wavelength can be achieved.
Grain refining performance of Al–Ti(C0.7, N0.3) master alloy and its effect on mechanical properties for commercial pure aluminium
Authors: An Xuguang , Liu Ying , Ye Jinwen , Wang Linzhi
Published: April 2016

A new Al–4.2 wt.% Ti(C0.7, N0.3) master alloy with a uniform microstructure was successfully prepared by casting method. Grain refining test indicates that Al–4.2 wt.% Ti(C0.7, N0.3) master alloy exhibits an excellent grain refining performance on commercial pure aluminium and the average grain size of pure Al can be effectively refined to 130 µm from about 3000 µm after adding 0.1 wt.% Ti(C0.7, N0.3) particles by Al–4.2 wt.% Ti(C0.7, N0.3) master alloy. The tensile strength and elongation are increased by about 20.5% from 55 to 66.3 and 14.9% from 39 to 44.8 due to the grain refinement by adding Al–4.2 wt.% Ti(C0.7, N0.3) master alloy. Compared with Al–5Ti–1B master alloy, Al–4.2 wt.% Ti(C0.7, N0.3) master alloy has a slightly better ability in improving the mechanical properties of pure aluminium due to the better grain refining performance.
Numerical study of turbulence-influence mechanism on arc characteristics in an air direct current circuit breaker
Authors: Wu Mingliang , Yang Fei , Rong Mingzhe , Wu Yi , Qi Yang , Cui Yufei , Liu Zirui , Guo Anxiang
Published: April 2016

This paper focuses on the numerical investigation of arc characteristics in an air direct current circuit breaker (air DCCB). Using magneto-hydrodynamics (MHD) theory, 3D laminar model and turbulence model are constructed and calculated. The standard k-epsilon model is utilized to consider the turbulence effect in the arc chamber of the DCCB. Several important phenomena are found: the arc column in the turbulence-model case is more extensive, moves much more slowly than the counterpart in the laminar-model case, and shows stagnation at the entrance of the chamber, unlike in the laminar-model case. Moreover, the arc voltage in the turbulence-model case is much lower than in the laminar-model case. However, the results in the turbulence-model case show a much better agreement with the results of the breaking experiments under DC condition than in the laminar-model case, which is contradictory to the previous conclusions from the arc researches of both the low-voltage circuit breaker and the sulfur hexafluoride (SF6) nozzle. First, in the previous air-arc research of the low-voltage circuit breaker, it is assumed that the air plasma inside the chamber is in the state of laminar, and the laminar-model application gives quite satisfactory results compared with the experiments, while in this paper, the laminar-model application works badly. Second, the turbulence-model application in the arc research of the SF6-nozzle performs much better and gives higher arc voltage than the laminar-model application does, whereas in this paper, the turbulence-model application predicts lower arc voltage than the laminar-model application does. Based on the analysis of simulation results in detail, the mechanism of the above phenomena is revealed. The transport coefficients are strongly changed by turbulence, which will enhance the arc diffusion and make the arc volume much larger. Consequently, the arc appearance and the distribution of Lorentz force in the turbulence-model case substantially differ from the arc appearance and the distribution of Lorentz force in the laminar-model case. Thus, the moving process of the arc in the turbulence-model case is slowed down and slower than in the laminar-model case. Moreover, the more extensive arc column in the turbulence-model case reduces the total arc resistance, which results in a lower arc voltage, more consistent with the experimental results than the arc voltage in the laminar-model case. Therefore, the air plasma inside this air DCCB is believed to be in the turbulence state, and the turbulence model is more suitable than the laminar model for the arc simulation of this kind of air DCCB.
The ionization energy of C2
Authors: Krechkivska O. , Bacskay G. B. , Welsh B. A. , Nauta K. , Kable S. H. , Stanton J. F. , Schmidt T. W.
Published: April 2016

Resonant two-photon threshold ionization spectroscopy is employed to determine the ionization energy of C2 to 5 meV precision, about two orders of magnitude more precise than the previously accepted value. Through exploration of the ionization threshold after pumping the 0–3 band of the newly discovered 43Πg←a3Πu band system of C2, the ionization energy of the lowest rovibronic level of the a3Πu state was determined to be 11.791(5) eV. Accounting for spin-orbit and rotational effects, we calculate that the ionization energy of the forbidden origin of the a3Πu state is 11.790(5) eV, in excellent agreement with quantum thermochemical calculations which give 11.788(10) eV. The experimentally derived ionization energy of X1Σg+ state C2 is 11.866(5) eV.
Electronic structure and thermoelectric properties of half-Heusler compounds with eight electron valence count—KScX (X = C and Ge)
Authors: Ciftci Yasemin O. , Mahanti Subhendra D.
Published: April 2016

Electronic band structure and structural properties of two representative half-Heusler (HH) compounds with 8 electron valence count (VC), KScC and KScGe, have been studied using first principles methods within density functional theory and generalized gradient approximation. These systems differ from the well studied class of HH compounds like ZrNiSn and ZrCoSb which have VC = 18 because of the absence of d electrons of the transition metal atoms Ni and Co. Electronic transport properties such as Seebeck coefficient (S), electrical conductivity (σ), electronic thermal conductivity (κe) (the latter two scaled by electronic relaxation time), and the power factor (S2σ) have been calculated using semi-classical Boltzmann transport theory within constant relaxation time approximation. Both the compounds are direct band gap semiconductors with band extrema at the X point. Their electronic structures show a mixture of heavy and light bands near the valance band maximum and highly anisotropic conduction and valence bands near the band extrema, desirable features of good thermoelectric. Optimal p- or n-type doping concentrations have been estimated based on thermopower and maximum power factors. The optimum room temperature values of S are ∼1.5 times larger than that of the best room temperature thermoelectric Bi2Te3. We also discuss the impact of the band structure on deviations from Weidemann-Franz law as one tunes the chemical potential across the band gap.
Composite vibrational spectroscopy of the group 12 difluorides: ZnF2, CdF2, and HgF2
Authors: Solomonik Victor G. , Smirnov Alexander N. , Navarkin Ilya S.
Published: April 2016

The vibrational spectra of group 12 difluorides, MF2 (M = Zn, Cd, Hg), were investigated via coupled cluster singles, doubles, and perturbative triples, CCSD(T), including core correlation, with a series of correlation consistent basis sets ranging in size from triple-zeta through quintuple-zeta quality, which were then extrapolated to the complete basis set (CBS) limit using a variety of extrapolation procedures. The explicitly correlated coupled cluster method, CCSD(T)-F12b, was employed as well. Although exhibiting quite different convergence behavior, the F12b method yielded the CBS limit estimates closely matching more computationally expensive conventional CBS extrapolations. The convergence with respect to basis set size was examined for the contributions entering into composite vibrational spectroscopy, including those from higher-order correlation accounted for through the CCSDT(Q) level of theory, second-order spin-orbit coupling effects assessed within four-component and two-component relativistic formalisms, and vibrational anharmonicity evaluated via a perturbative treatment. Overall, the composite results are in excellent agreement with available experimental values, except for the CdF2 bond-stretching frequencies compared to spectral assignments proposed in a matrix isolation infrared and Raman study of cadmium difluoride vapor species [Loewenschuss et al., J. Chem. Phys. 50, 2502 (1969); Givan and Loewenschuss, J. Chem. Phys. 72, 3809 (1980)]. These assignments are called into question in the light of the composite results.
Coherent electron-spin-resonance manipulation of three individual spins in a triple quantum dot
Authors: Noiri A. , Yoneda J. , Nakajima T. , Otsuka T. , Delbecq M. R. , Takeda K. , Amaha S. , Allison G. , Ludwig A. , Wieck A. D. , Tarucha S.
Published: April 2016

Quantum dot arrays provide a promising platform for quantum information processing. For universal quantum simulation and computation, one central issue is to demonstrate the exhaustive controllability of quantum states. Here, we report the addressable manipulation of three single electron spins in a triple quantum dot using a technique combining electron-spin-resonance and a micro-magnet. The micro-magnet makes the local Zeeman field difference between neighboring spins much larger than the nuclear field fluctuation, which ensures the addressable driving of electron-spin-resonance by shifting the resonance condition for each spin. We observe distinct coherent Rabi oscillations for three spins in a semiconductor triple quantum dot with up to 25 MHz spin rotation frequencies. This individual manipulation over three spins enables us to arbitrarily change the magnetic spin quantum number of the three spin system, and thus to operate a triple-dot device as a three-qubit system in combination with the existing technique of exchange operations among three spins.
Mechanical properties of low- and high-k dielectric thin films: A surface Brillouin light scattering study
Authors: Zizka J. , King S. , Every A. G. , Sooryakumar R.
Published: April 2016

Surface Brillouin light scattering measurements are used to determine the elastic constants of nano-porous low-k SiOC:H (165 nm) and high-k HfO2 (25 nm) as well as BN:H (100 nm) films grown on Si substrates. In addition, the study investigates the mechanical properties of ultra-thin (25 nm) blanket TiN cap layers often used as hard masks for patterning, and their effects on the underlying low-k dielectrics that support a high level of interconnected porosity. Depending on the relative material properties of individual component layers, the acoustic modes manifest as confined, propagating, or damped resonances in the light scattering spectra, thereby enabling the mechanical properties of the ultra-thin films to be determined.
Silicon based near infrared photodetector using self-assembled organic crystalline nano-pillars
Authors: Ajiki Yoshiharu , Kan Tetsuo , Yahiro Masayuki , Hamada Akiko , Adachi Junji , Adachi Chihaya , Matsumoto Kiyoshi , Shimoyama Isao
Published: April 2016

We propose a silicon (Si) based near-infrared photodetector using self-assembled organic crystalline nano-pillars, which were formed on an n-type Si substrate and were covered with an Au thin-film. These structures act as antennas for near-infrared light, resulting in an enhancement of the light absorption on the Au film. Because the Schottky junction is formed between the Au/n-type Si, the electron excited by the absorbed light can be detected as photocurrent. The optical measurement revealed that the nano-pillar structures enhanced the responsivity for the near-infrared light by 89 (14.5 mA/W) and 16 (0.433 mA/W) times compared with those of the photodetector without nano-pillars at the wavelengths of 1.2 and 1.3 μm, respectively. Moreover, no polarization dependency of the responsivity was observed, and the acceptable incident angle ranged from 0° to 30°. These broad responses were likely to be due to the organic nano-pillar structures' having variation in their orientation, which is advantageous for near-infrared detector uses.
Note: Evaluation of slurry particle size analyzers for chemical mechanical planarization process
Authors: Jang Sunjae , Kulkarni Atul , Qin Hongyi , Kim Taesung
Published: April 2016

In the chemical mechanical planarization (CMP) process, slurry particle size is important because large particles can cause defects. Hence, selection of an appropriate particle measuring system is necessary in the CMP process. In this study, a scanning mobility particle sizer (SMPS) and dynamic light scattering (DLS) were compared for particle size distribution (PSD) measurements. In addition, the actual particle size and shape were confirmed by transmission electron microscope (TEM) results. SMPS classifies the particle size according to the electrical mobility, and measures the particle concentration (single particle measurement). On the other hand, the DLS measures the particle size distribution by analyzing scattered light from multiple particles (multiple particle measurement). For the slurry particles selected for evaluation, it is observed that SMPS shows bi-modal particle sizes 30 nm and 80 nm, which closely matches with the TEM measurements, whereas DLS shows only single mode distribution in the range of 90 nm to 100 nm and showing incapability of measuring small particles. Hence, SMPS can be a better choice for the evaluation of CMP slurry particle size and concentration measurements.
Guiding 2.94 μm using low-loss microstructured antiresonant triangular-core fibers
Authors: Chen Yang , Saleh Mohammed F. , Joly Nicolas Y. , Biancalana Fabio
Published: April 2016

We introduce a new simple design of hollow-core microstructured fiber targeted to guide mid-infrared light at a wavelength of 2.94 μm. The fiber has a triangular-core supported via silica-glass webs enclosed by a large hollow capillary tube. The fiber specific dimensions are determined by the anti-resonant guiding mechanism. For a triangular-core with side length 100 μm, the fiber has a minimum transmission loss 0.08 ± 0.005 dB/m and dispersion 2.3 ps/km/nm at the operational wavelength of 2.94 μm.
Shock wave induced martensitic transformations and morphology changes in Fe-Pd ferromagnetic shape memory alloy thin films
Authors: Bischoff A. J. , Arabi-Hashemi A. , Ehrhardt M. , Lorenz P. , Zimmer K. , Mayr S. G.
Published: April 2016

Combining experimental methods and classical molecular dynamics (MD) computer simulations, we explore the martensitic transformation in Fe70Pd30 ferromagnetic shape memory alloy thin films induced by laser shock peening. X-ray diffraction and scanning electron microscope measurements at shock wave pressures of up to 2.5 GPa reveal formation of martensitic variants with preferred orientation of the shorter c-axis of the tetragonal unit cell perpendicular to the surface plane. Moreover, consequential merging of growth islands on the film surface is observed. MD simulations unveil the underlying physics that are characterized by an austenite-martensite transformation with a preferential alignment of the c-axis along the propagation direction of the shock wave, resulting in flattening and in-plane expansion of surface features.
p-BaSi2/n-Si heterojunction solar cells with conversion efficiency reaching 9.0%
Authors: Tsukahara Daichi , Yachi Suguru , Takeuchi Hiroki , Takabe Ryota , Du Weijie , Baba Masakazu , Li Yunpeng , Toko Kaoru , Usami Noritaka , Suemasu Takashi
Published: April 2016

p-BaSi2/n-Si heterojunction solar cells consisting of a 20 nm thick B-doped p-BaSi2 epitaxial layer (p = 2.2 × 1018 cm−3) on n-Si(111) (ρ = 1–4 Ω cm) were formed by molecular beam epitaxy. The separation of photogenerated minority carriers is promoted at the heterointerface in this structure. Under AM1.5 illumination, the conversion efficiency η reached 9.0%, which is the highest ever reported for solar cells with semiconducting silicides. An open-circuit voltage of 0.46 V, a short-circuit current density of 31.9 mA/cm2, and a fill factor of 0.60 were obtained. These results demonstrate the high potential of BaSi2 for solar cell applications.
Study on statistical breakdown delay time in argon gas using a W-band millimeter-wave gyrotron
Authors: Kim Dongsung , Kim Sung Gug , Sawant Ashwini , Yu Dongho , Choe MunSeok , Choi EunMi
Published: April 2016

In this study, we investigated plasma initiation delay times for argon volume breakdown at the W-band frequency regime. The threshold electric field is defined as the minimum electric field amplitude needed for plasma breakdown at various pressures. The measured statistical delay time showed an excellent agreement with the theoretical Gaussian distribution and the theoretically estimated formative delay time. Also, we demonstrated that the normalized effective electric field as a function of the product of pressure and formative time shows an outstanding agreement to that of 1D particle-in-cell simulation coupled with a Monte Carlo collision model [H. C. Kim and J. P. Verboncoeur, Phys. Plasmas 13, 123506 (2006)].
High temperature and low pressure chemical vapor deposition of silicon nitride on AlGaN: Band offsets and passivation studies
Authors: Reddy Pramod , Washiyama Shun , Kaess Felix , Hayden Breckenridge M. , Hernandez-Balderrama Luis H. , Haidet Brian B. , Alden Dorian , Franke Alexander , Sarkar Biplab , Kohn Erhard , Collazo Ramon , Sitar Zlatko
Published: April 2016

In this work, we employed X-ray photoelectron spectroscopy to determine the band offsets and interface Fermi level at the heterojunction formed by stoichiometric silicon nitride deposited on AlxGa1-xN (of varying Al composition “x”) via low pressure chemical vapor deposition. Silicon nitride is found to form a type II staggered band alignment with AlGaN for all Al compositions (0 ≤ x ≤ 1) and present an electron barrier into AlGaN even at higher Al compositions, where Eg(AlGaN) > Eg(Si3N4). Further, no band bending is observed in AlGaN for x ≤ 0.6 and a reduced band bending (by ∼1 eV in comparison to that at free surface) is observed for x > 0.6. The Fermi level in silicon nitride is found to be at 3 eV with respect to its valence band, which is likely due to silicon (≡Si0/−1) dangling bonds. The presence of band bending for x > 0.6 is seen as a likely consequence of Fermi level alignment at Si3N4/AlGaN hetero-interface and not due to interface states. Photoelectron spectroscopy results are corroborated by current-voltage-temperature and capacitance-voltage measurements. A shift in the interface Fermi level (before band bending at equilibrium) from the conduction band in Si3N4/n-GaN to the valence band in Si3N4/p-GaN is observed, which strongly indicates a reduction in mid-gap interface states. Hence, stoichiometric silicon nitride is found to be a feasible passivation and dielectric insulation material for AlGaN at any composition.
The electro-mechanical responses of suspended graphene ribbons for electrostatic discharge applications
Authors: Zhang Wei , Ma Rui , Chen Qi , Xia Ming , Ng Jimmy , Wang Albert , Xie Ya-Hong
Published: April 2016

This work presents a suspended graphene ribbon device for electrostatic discharge (ESD) applications. The device structure was proposed and fabricated after careful design considerations. Compared to the conventional ESD devices such as diodes, bipolar junction transistors, and metal-oxide-semiconductor field effect transistors, the proposed device structure is believed to render several advantages including zero leakage, low parasitic effects, fast response, and high critical current density. A process flow was developed for higher yield and reliability of the suspended graphene ribbons. Direct current (DC) and transmission-line pulse (TLP) measurements were carried out to investigate the switching behavior of the device, which is crucial for ESD operation. DC measurements with a different configuration were used to assess the mechanical shape evolution of the graphene ribbon upon biasing. Finite Element Simulations were conducted and agreed well with the experimental results. Furthermore, the current carrying capability of non-suspended graphene ribbons was tested using TLP. It was found that the critical current density of graphene is higher than that of copper wires widely used as interconnects in integrated circuits (ICs).
A two-magnet strategy for improved mixing and capture from biofluids
Authors: Scherr Thomas F. , Ryskoski Hayley B. , Doyle Andrew B. , Haselton Frederick R.
Published: April 2016

Magnetic beads are a popular method for concentrating biomolecules from solution and have been more recently used in multistep pre-arrayed microfluidic cartridges. Typical processing strategies rely on a single magnet, resulting in a tight cluster of beads and requiring long incubation times to achieve high capture efficiencies, especially in highly viscous patient samples. This report describes a two-magnet strategy to improve the interaction of the bead surface with the surrounding fluid inside of a pre-arrayed, self-contained assay-in-a-tube. In the two-magnet system, target biomarker capture occurs at a rate three times faster than the single-magnet system. In clinically relevant biomatrices, we find a 2.5-fold improvement in biomarker capture at lower sample viscosities with the two-magnet system. In addition, we observe a 20% increase in the amount of protein captured at high viscosity for the two-magnet configuration relative to the single magnet approach. The two-magnet approach offers a means to achieve higher biomolecule extraction yields and shorter assay times in magnetic capture assays and in self-contained processor designs.