bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimisation of energy efficiency based on average driving behaviour and driver's preferences for automated driving
Authors: Themann Philipp , Bock Julian , Eckstein Lutz
Published: July 2014

The implementation of anticipating driving styles in adaptive cruise control systems promises to considerably reduce fuel consumption of vehicles. As drivers have to accept the optimised driving styles of such systems, which implement longitudinally automated driving, the optimisation results should not deviate strongly from the average driving behaviour. This work presents an approach to the optimisation of the vehicle's longitudinal dynamics, which is based on a predicted average driving profile. The proposed approach ensures that the optimisation results meet the expectations of drivers by directly accounting for driver's preferences on weighting up travel time against fuel consumption relative to the average driving profile. Based on human decision finding, rational and intuitive planning decisions are modelled in a cost function and represent optimisation constraints. The approach generally includes information from vehicle‐to‐vehicle and vehicle‐to‐infrastructure communication (V2X), which is an extension to the state‐of‐the‐art. This study describes the optimisation approach and presents a method to determine suitable optimisation parameters in order to consider driver's preferences. The optimisation approach is applied in a simulated test drive and improvements in fuel economy are analysed. Finally, the authors sketch a reference system architecture to prove the feasibility of the presented approach.
Improving short‐term traffic forecasts: to combine models or not to combine?
Authors: Tselentis Dimitrios I. , Vlahogianni Eleni I. , Karlaftis Matthew G.
Published: July 2014

This study compares the performance of statistical and Bayesian combination models with classical single time series models for short‐term traffic forecasting. Combinations are based on fractionally integrated autoregressive time series models of travel speed with exogenous variables that consider speed's spatio‐temporal evolution, and volume and weather conditions. Several statistical hypotheses on the effectiveness of combinations compared to the single models are also tested. Results show that, in the specific application, linear regression combination techniques may provide more accurate forecasts than Bayesian combination models. Moreover, combining models with different degrees of spatio‐temporal complexity and exogeneities is most likely to be the best choice in terms of accuracy. Moreover, the risk of combining forecasts is lower than the risk of choosing a single model with increased spatio‐temporal complexity.
Wideband transmission line model for Archimedean spiral slot structures
Authors: Ruyle Jessica E. , Bernhard Jennifer T.
Published: July 2014

Spiral slot structures appear in a variety of microwave applications such as circuit elements, transmission lines and broadband antennas. However, design methodologies for these structures that are accurate above the first resonance involve multi‐line transmission line models – requiring difficult to compute multi‐line characteristics. This study presents the methodology for a transmission line model for an Archimedean spiral slot structure that uses singly‐coupled line characteristics, which can be found analytically, to approximate the multi‐line transmission line. With this model, the first resonance and many higher‐order resonant frequencies of the spiral structure are well predicted, enabling multi‐frequency use of the spiral slot. The results of the model compare well with full‐wave simulations and are validated with measurements.
Comments on ‘circular polariser for use in a gyro‐travelling wave amplifier’
Authors: Tikhov Yuri
Published: July 2014

It is shown that sine‐corrugated polariser proposed in above paper as a priori superior design in high‐power handling over broadband frequency range in fact needs more convincing substantiation.
Fast handover control scheme for multi‐node using the group‐based approach
Authors: Chiang Meng‐Shu , Huang Chung‐Ming , Tuan Dao Duy
Published: July 2014

The fast handover Mobile IPv6 (FMIPv6) offers a handover preparation mechanism for a mobile node (MN) to reduce the handover latency over wireless network. However, FMIPv6 mainly deals with one MN instead of multiple MNs. In the wireless network, a group of MNs may move from the same previous network to the next network. In this paper, a group‐based fast handover (GB‐FH) control scheme is proposed to resolve the aforementioned problem. For the proposed GB‐FH scheme, one MN initiates a handover preparation and other neighboring MNs can join the handover preparation using the “hitch‐and‐ride” concept, which means that when one MN is preparing for a handover, its neighbours can join the on‐going handover preparation. Through the use of the shared invocation of the handover preparation procedure, (1) the handover preparation delay and handover latency can be reduced for about 20% and 8% respectively comparing with FMIPv6, (2) handover control messages can be reduced for about 57% comparing with FMIPv6 and (3) the contention of the wireless channel for multiple MNs can be improved due to the use of fewer control messages.
High‐performance Brillouin distributed temperature sensor using Fourier wavelet regularised deconvolution algorithm
Authors: Pradhan Himansu Shekhar , Sahu Prasant Kumar
Published: July 2014

In this study, the authors presented a distributed optical fibre temperature sensor whose performance is improved using the optimisation techniques and Fourier wavelet regularised deconvolution (ForWaRD) method. As the input power launched into the sensing fibre is critical, the authors have considered both conventional optimisation technique and evolutionary optimisation techniques namely: genetic algorithm, differential evolution algorithm and particle swarm optimisation algorithm to increase the stimulated Brillouin scattering (SBS) threshold power. Using the optimised value of the parameters and employing evolutionary computing techniques, the proposed 50 km long temperature sensing system offers a 4.7 dB improvement in SBS threshold power over the design of experiment based system. It is being verified that power of the backscattered signals approximately are the convolution of the input pulsed power and corresponding backscatter optical fibre impulse responses. The Fourier wavelet regularised deconvolution (ForWaRD) method is employed to improve the spatial resolution of the proposed sensing system without reducing the pulse width of the input pulse. Employing ForWaRD technique a 10 m better spatial resolution observed as compared with the Fourier deconvolution technique. The proposed 50 km long temperature sensing system exhibits a temperature resolution of 1.85 K because of suppression of SBS threshold and noise reduction.
Theoretical modelling of mercury cadmium telluride mid‐wave detector for high temperature operation
Authors: Martyniuk Piotr , Gawron Waldemar , Stanaszek Dariusz , Pusz Wioletta , Rogalski Antoni
Published: July 2014

This study reports on photoelectrical performance: detectivity and response time of mid‐wave infrared (MWIR) (111) mercury cadmium telluride (MCT/HgCdTe) detectors under high operating temperature (HOT) conditions. The detector structure was simulated with the numerical platform APSYS by Crosslight Inc. A detailed analysis of the detectivity and response time as a function of device architecture and applied bias was performed to optimise the working conditions. The detectivity and time response of the MWIR HgCdTe detector with 50% cut‐off wavelength of λc ≃ 5.3 μm at T = 200 K were estimated to be D* = 2.6 × 1011 cm Hz1/2 /W and τs ≃ 1650 ps, respectively, for V = 200 mV with a series resistance, RSeries = 380 Ω. Reducing the series resistance limits the response time to the τs ≃ 500 ps range.
DSP‐based resolver‐to‐digital conversion system designed in time domain
Authors: Hou Chung‐Chuan , Chiang Ying‐Hsuan , Lo Chi‐Pong
Published: July 2014

Resolver is an absolute angle measurement and is mounted on the motor shaft to acquire the motor's absolute angular position. This study presents an equivalent circuit of the resolver neglected rotational back electromotive force. The transfer function of the resolver is derived from the equivalent circuit. The frequency response of the resolver is measured by a dynamic signal analyser to obtain the adequate frequency of resolver's reference signal. Furthermore, a digital signal processor (DSP)‐based resolver‐to‐digital conversion system is designed in time domain. A pulse signal generated by the DSP is utilised as a reference signal coupled into the resolver's rotor winding and provides primary excitation. The sine and cosine modulated output signals are sampled by the analogue‐to‐digital converter of the DSP within 1 μs. The sampled frequency of outputs signals are the same frequency as the pulse signal. The angular position is derived by the inverse tangent of the quotient of the demodulated sine and cosine samples. Test results are presented to validate the performances of the proposed scheme.
Analysis, design and performance of a soft‐switching single‐phase inverter
Authors: Wang Chien‐Ming , Lin Chang‐Hua , Lin Hsin‐Yi , Hsu Shih‐Yung
Published: July 2014

A soft‐switching pulse‐width modulation (PWM) single‐phase inverter using a voltage clamp soft‐switching step‐up/down dc link is proposed in this study. The proposed voltage clamp soft‐switching step‐up/down DC link not only provides the switches in the section of conventional PWM buck inverter operate at zero‐voltage‐switching (ZVS), but it has a step‐up/down input voltage function and the switches in itself also operate at ZVS. Thus, except for the switch in the section of ZVS‐PWM auxiliary circuit, all power semiconductor devices in proposed inverter operate at ZVS turn‐on and turn‐off. The switch in the section of ZVS‐PWM auxiliary circuit operates at zero‐current‐switching (ZCS) turn‐on and turn‐off. Besides operating at constant frequency, the proposed inverter has no voltage stress and current stress on the main switch compared to the hard switching inverter counterpart. Auxiliary components rated at very small current are used. The principle of operation, theoretical analysis and experimental results of the proposed soft‐switching inverter, rated 1 kW and operated at 40 kHz, are provided in this study to verify the performance.
Analysis and design of repetitive controller based on regeneration spectrum and sensitivity function in active power filter system
Authors: Sun Jianjun , Gong Jinwu , Chen Baifeng , Zha Xiaoming
Published: July 2014

Conventional repetitive controller can hardly obtain a fast dynamic response. In order to achieve a faster dynamic performance, an improved repetitive controller is proposed in this study. The controller adds a proportional link in parallel with the original repetitive control loop. Based on the regeneration spectrum theory and the sensitivity function, the stability, steady‐state error and convergence of the control system are analysed. A parameter design method is also developed. The feasibility of the controller is shown in simulations and verified by the experimental works. The simulation and experiment results confirm that the improved repetitive controller and the parameter design method are effective in the active power filter design.
Control of wheel motors for the provision of traction and steering of railway vehicles
Authors: Mei T.X. , Qu Kewang , Li Hong
Published: July 2014

This study presents the development of a control system for permanent magnet motors embedded in railway wheels for integrated traction and steering of rail vehicles. The overall control scheme and the control strategies for the provision of traction and wheelset steering are presented, but a main focus of this study will be concerned with the development of a new sensor‐less position detection technique that overcomes the difficulties of position detection at zero and very low speed using the back‐emf‐based methods. The new technique does not require the injection of high frequency harmonics, and detects the motor position from simple measurements of the neutral point voltage of the motor influenced by the variation of inductances with respect to rotor position. Both theoretical development and experimental verifications are provided.
An Innovative subarray partitioning method for clutter suppression by space‐time adaptive processing based on the ant colony optimisation
Authors: Xiong Zi‐Yuan , Xu Zhen‐Hai , Wu Jia‐Ni , Xiao Shun‐Ping
Published: July 2014

As an effective reduced‐dimension space‐time adaptive processing (STAP) approach, subarray technique is widely used in practice. It is known that, the choice of subarray layout has a strong impact on the performance of subarray level signal processing algorithms. However, the design of subarray partitioning is a difficult problem both in theory and practice. It is extremely valuable to do some research on subarray partition for the huge array radar, especially for those airborne and spaceborne radars with restrict constraint on the cost and space. For these radars, the clutter suppression is an important metric. In this study, the clutter suppressing method by STAP at subarray level is analysed, and the corresponding design of subarray partition is studied. At first, applying the graph theory, a subarray partition strategy is abstracted into a path inside a directed acyclic graph structure. Then, a method based on the ant colony optimisation method is proposed to optimise subarray partition for clutter suppression in STAP. By properly designing the initial and heuristic information, the new method is relatively robust and the complexity is fairly low. Numerical results are presented to verify the effectiveness of the proposed method.
Three‐dimensional electrical capacitance tomography reconstruction by the Landweber iterative algorithm with fuzzy thresholding
Authors: Yan Hua , Wang Yi Fan , Zhou Ying Gang
Published: July 2014

The image reconstruction for electrical capacitance tomography is a non‐linear, underdetermined and ill‐posed inverse problem. It is difficult to obtain a reconstructed image with high quality, especially in the case of three‐dimensional (3D) reconstruction. An iterative image reconstruction algorithm with fuzzy thresholding is proposed in this study. The threshold value in each iteration is generated by minimising the measure of fuzziness of current reconstructed image. The algorithm proposed is tested by the noise‐free and the noise‐contaminated capacitance data. Extensive computer simulations demonstrate that the fuzzy thresholding can reduce low grey‐level artefacts effectively. As a result, the spatial error, volume error, permittivity error and scattered artefacts of the reconstructed image are reduced obviously; not only that, the number of iterations needed to obtain a good reconstruction result is decreased greatly. The result of 3D reconstruction of a H‐shape object verifies the effectiveness of the fuzzy thresholding further.
Alternative formulation of the Kalman filter for correlated process and observation noise
Authors: Chang Guobin
Published: July 2014

The Kalman filter for linear system with cross‐correlated process and observation noises at the same epoch is revisited. As the process noise is correlated with the observation noise, the probability of the former conditioned on the latter should have a higher concentration than its original probability, implying that the conditional one becomes more accurate. Inspired by this, an alternative formulation of the filter is derived that the conditional process noise rather than the original one is used in the prediction step. The conditional mean and covariance are derived in two different ways, that is, through state augmentation and conditionally Gaussian distribution. It is also proved that the proposed formulation is theoretically equivalent to the two available frameworks. However, this formulation has the merit of explaining why the estimate is improved taking the cross‐correlation into account, that is, the a posteriori covariance of the process noise is reduced compared to the original one implying that the process model becomes more accurate. A simple but illustrative example is simulated and the efficacy of the proposed framework is validated.
Flaw detection and measurement for mobile display
Authors: Wang Yao‐Chin , Lin Bor‐Shyh
Published: July 2014

With advanced small‐pixel and high‐resolution mobile displays, the display are obtaining smaller pixel size and higher resolution on thin‐film‐transistor (TFT) array process. This study proposed the flaw detection and measurement in small pixel design mobile displays based on oxide‐semiconductor‐based TFT liquid crystal displays. The measurement is with respect to electrical‐physic characterisation metrics and observer studies. Studies resulted in small‐sized pixel TFT array between the flaw detection performance and maker preference approaches. Detection performance factors provided information on the differences among small pixel design for advanced mobile display technologies. The results of the detection performance and preference study showed that the application for advanced mobile display panels. It also shown that critical pixel defect played an important role than previously seen in non‐small pixel TFT array panels for managing process yield. The method of voltage imaging for detection, developed in this study provides an initial insight into the high resolution of small‐sized pixel designs for advanced mobile displays with precision and diagnostic images in portable devices.
Modelling and calibration of microthermal sensor for underwater wall shear stress measurement
Authors: Li Xiaoying , Li Yanbing , Ma Binghe , Wang Leitao
Published: July 2014

To measure underwater wall shear stress, a calibration method for a microthermal sensor is studied. In CC (constant current) mode, a mathematical model which quantitatively describes the relationship between the output of the thermal sensor and the wall shear stress is presented. A well‐characterised water tunnel was set up to provide a series of known wall shear stresses in the range of 0–5 Pa. Calibration results prove the proposed model and characterise the thermal sensor precisely. The consistency of the parameters indicates that the performance of the thermal sensor keeps stable in water while driven by electricity. The R ‐squares in all calibrations exceed 0.995. The deviations between the predicted and the generated wall shear stress are about 5%.
Synthesis and characterisation of modified carbon nanotubes with potassium salts of the monosubstituted Keggin polyoxometalates
Authors: Bamoharram Fatemeh F. , Poorzaki Maryam , Morsali Ali , Beiramabadi S. , Ahmadpour Ali , M Heravi Majid , Ayati Ali
Published: July 2014

A novel hybrid of potassium salts of the monosubstituted Keggin polyoxometalates/carbon nanotube nanocomposite is synthesised. Multiwalled carbon nanotubes (MWCNTs) were synthesised by the catalytic chemical vapour deposition method. The characterisation of the materials by Fourier transform infrared spectroscopy, and transmission electron microscopy, shows that the functionalisation of MWCNTs by potassium salts of the monosubstituted Keggin polyoxometalates was successfully achieved via the impregnation method in both endohedral and exohedral forms. Theoretical studies for the covalent conjugation of Keggin polyoxometalates to carbon nanotubes, showed that the functionalisation of MWCNTs by some groups such as COOH and OH is required.
Short-interval multi-laser Thomson scattering measurements of hydrogen pellet ablation in LHD
Authors: Yasuhara R. , Sakamoto R. , Yamada I. , Motojima G. , Hayashi H.
Published: July 2014

Thomson scattering forms an important aspect of measuring the electron density and temperature profiles of plasmas. In this study, we demonstrate Thomson scattering measurements obtained over a short interval (<1 ms) by using an event triggering system with a multi-laser configuration. We attempt to use our system to obtain the electron temperature and density profiles before and immediately after pellet injection into the large helical device. The obtained profiles exhibit dramatic changes after pellet injection as per our shot-by-shot measurements. We believe that this measurement technique will contribute towards a better understanding of the physics of the pellet deposition.
Spectra generated by a confined softcore Coulomb potential
Authors: Hall Richard L. , Saad Nasser
Published: July 2014

Analytic and approximate solutions for the energy eigenvalues generated by a confined softcore Coulomb potentials of the form a/(r + β) in d > 1 dimensions are constructed. The confinement is effected by linear and harmonic-oscillator potential terms, and also through “hard confinement” by means of an impenetrable spherical box. A byproduct of this work is the construction of polynomial solutions for a number of linear differential equations with polynomial coefficients, along with the necessary and sufficient conditions for the existence of such solutions. Very accurate approximate solutions for the general problem with arbitrary potential parameters are found by use of the asymptotic iteration method.
High repetition rate laser-induced breakdown spectroscopy using acousto-optically gated detection
Authors: Pořízka Pavel , Klessen Benjamin , Kaiser Jozef , Gornushkin Igor , Panne Ulrich , Riedel Jens
Published: July 2014

This contribution introduces a new type of setup for fast sample analysis using laser-induced breakdown spectroscopy (LIBS). The novel design combines a high repetition rate laser (up to 50 kHz) as excitation source and an acousto-optical modulator (AOM) as a fast switch for temporally gating the detection of the emitted light. The plasma radiation is led through the active medium of the AOM where it is diffracted on the transient ultrasonic Bragg grid. The diffracted radiation is detected by a compact Czerny-Turner spectrometer equipped with a CCD line detector. Utilizing the new combination of high repetition rate lasers and AOM gated detection, rapid measurements with total integration times of only 10 ms resulted in a limit of detection (LOD) of 0.13 wt.% for magnesium in aluminum alloys. This short integration time corresponds to 100 analyses/s. Temporal gating of LIP radiation results in improved LODs and consecutively higher sensitivity of the LIBS setup. Therefore, an AOM could be beneficially utilized to temporally detect plasmas induced by high repetition rate lasers. The AOM in combination with miniaturized Czerny-Turner spectrometers equipped with CCD line detectors and small footprint diode pumped solid state lasers results in temporally gateable compact LIBS setups.
Dual-angle, self-calibrating Thomson scattering measurements in RFX-MOD
Authors: Giudicotti L. , Pasqualotto R. , Fassina A.
Published: July 2014

In the multipoint Thomson scattering (TS) system of the RFX-MOD experiment the signals from a few spatial positions can be observed simultaneously under two different scattering angles. In addition the detection system uses optical multiplexing by signal delays in fiber optic cables of different length so that the two sets of TS signals can be observed by the same polychromator. Owing to the dependence of the TS spectrum on the scattering angle, it was then possible to implement self-calibrating TS measurements in which the electron temperature Te, the electron density ne and the relative calibration coefficients of spectral channels sensitivity Ci were simultaneously determined by a suitable analysis of the two sets of TS data collected at the two angles. The analysis has shown that, in spite of the small difference in the spectra obtained at the two angles, reliable values of the relative calibration coefficients can be determined by the analysis of good S/N dual‑angle spectra recorded in a few tens of plasma shots. This analysis suggests that in RFX-MOD the calibration of the entire set of TS polychromators by means of the similar, dual-laser (Nd:YAG/Nd:YLF) TS technique, should be feasible.
Keto-enol tautomerization and intermolecular proton transfer in photoionized cyclopentanone dimer in the gas phase
Authors: Ghosh Arup K. , Chatterjee Piyali , Chakraborty Tapas
Published: July 2014

Time-of-flight mass spectra of cyclopentanone and its clusters cooled in a supersonic jet expansion have been measured following 4-, 3-, and 2-photon ionizations by the 2nd, 3rd, and 4th harmonic wavelengths, respectively, of a Q-switched Nd:YAG laser. The mass spectra reveal signatures of energetically favored keto to enol tautomerization of the molecular ion leading to intermolecular proton transfer, and this observation is found sharply dependent on the ionization wavelengths used. Electronic structure calculation predicts that in spite of the energetic preference, keto-enol conversion barrier of isolated molecular ion is high. However, the barrier is significantly reduced in a CH⋯O hydrogen-bonded dimer of the molecule. The transition states associated with tautomeric conversion of both cyclopentanone monomer and dimer cations have been identified by means of intrinsic reaction co-ordinate calculation. In a supersonic jet expansion, although a weakly bound dimer is readily generated, the corresponding cation and also the protonated counterpart are observed only for ionization by 532 nm. For other two ionization wavelengths, these species do not register in the mass spectra, where the competing reaction channels via α-cleavage of the ring become dominant. In contrast to the report of a recent study, we notice that the intact molecular ion largely survives fragmentations when ionized from the 2-photon resonant 3p Rydberg state as intermediate using nanosecond laser pulses, and the corresponding resonant 3-photon ionization spectrum has been recorded probing the intact molecular ion.
Hydration shell effects in the relaxation dynamics of photoexcited Fe-II complexes in water
Authors: Nalbach P. , Achner A. J. A. , Frey M. , Grosser M. , Bressler C. , Thorwart M.
Published: July 2014

We study the relaxation dynamics of photoexcited Fe-II complexes dissolved in water and identify the relaxation pathway which the molecular complex follows in presence of a hydration shell of bound water at the interface between the complex and the solvent. Starting from a low-spin state, the photoexcited complex can reach the high-spin state via a cascade of different possible transitions involving electronic as well as vibrational relaxation processes. By numerically exact path integral calculations for the relaxational dynamics of a continuous solvent model, we find that the vibrational life times of the intermittent states are of the order of a few ps. Since the electronic rearrangement in the complex occurs on the time scale of about 100 fs, we find that the complex first rearranges itself in a high-spin and highly excited vibrational state, before it relaxes its energy to the solvent via vibrational relaxation transitions. By this, the relaxation pathway can be clearly identified. We find that the life time of the vibrational states increases with the size of the complex (within a spherical model), but decreases with the thickness of the hydration shell, indicating that the hydration shell acts as an additional source of fluctuations.
Time-resolved measurements of the hot-electron population in ignition-scale experiments on the National Ignition Facility (invited)
Authors: Hohenberger M. , Albert F. , Palmer N. E. , Lee J. J. , Döppner T. , Divol L. , Dewald E. L. , Bachmann B. , MacPhee A. G. , LaCaille G. , Bradley D. K. , Stoeckl C.
Published: July 2014

In laser-driven inertial confinement fusion, hot electrons can preheat the fuel and prevent fusion-pellet compression to ignition conditions. Measuring the hot-electron population is key to designing an optimized ignition platform. The hot electrons in these high-intensity, laser-driven experiments, created via laser-plasma interactions, can be inferred from the bremsstrahlung generated by hot electrons interacting with the target. At the National Ignition Facility (NIF) [G. H. Miller, E. I. Moses, and C. R. Wuest, Opt. Eng. 43, 2841 (2004)], the filter-fluorescer x-ray (FFLEX) diagnostic–a multichannel, hard x-ray spectrometer operating in the 20–500 keV range–has been upgraded to provide fully time-resolved, absolute measurements of the bremsstrahlung spectrum with ∼300 ps resolution. Initial time-resolved data exhibited significant background and low signal-to-noise ratio, leading to a redesign of the FFLEX housing and enhanced shielding around the detector. The FFLEX x-ray sensitivity was characterized with an absolutely calibrated, energy-dispersive high-purity germanium detector using the high-energy x-ray source at NSTec Livermore Operations over a range of K-shell fluorescence energies up to 111 keV (U Kβ). The detectors impulse response function was measured in situ on NIF short-pulse (∼90 ps) experiments, and in off-line tests.
Prospects for measuring the fuel ion ratio in burning ITER plasmas using a DT neutron emission spectrometer
Authors: Hellesen C. , Skiba M. , Dzysiuk N. , Weiszflog M. , Hjalmarsson A. , Ericsson G. , Conroy S. , Andersson-Sundén E. , Eriksson J. , Binda F.
Published: July 2014

The fuel ion ratio nt/nd is an essential parameter for plasma control in fusion reactor relevant applications, since maximum fusion power is attained when equal amounts of tritium (T) and deuterium (D) are present in the plasma, i.e., nt/nd = 1.0. For neutral beam heated plasmas, this parameter can be measured using a single neutron spectrometer, as has been shown for tritium concentrations up to 90%, using data obtained with the MPR (Magnetic Proton Recoil) spectrometer during a DT experimental campaign at the Joint European Torus in 1997. In this paper, we evaluate the demands that a DT spectrometer has to fulfill to be able to determine nt/nd with a relative error below 20%, as is required for such measurements at ITER. The assessment shows that a back-scattering time-of-flight design is a promising concept for spectroscopy of 14 MeV DT emission neutrons.
Unsteady vortex lattice method coupled with a linear aeroelastic model for horizontal axis wind turbine
Authors: Jeon Minu , Lee Seunghoon , Lee Soogab
Published: July 2014

Many aerodynamic phenomena on wind turbines are extremely complicated, such as the ground boundary layer effects, directional and spatial variations in wind shear, unsteady yaw effects, and unsteady aerodynamics due to the platform motion of offshore floating wind turbines. Thus, it is unclear whether prediction of the aerodynamic load of a turbine using conventional blade element momentum theory is accurate. On the other hand, this method does not consider unsteady wake effect behind the rotor, the unsteady vortex lattice method can treat non-uniform flow effects derived from the trailing wake from the turbine. Moreover, the aeroelasticity of wind turbines is significant because of the recent scaling up of the turbine size. This induces unsteady aerodynamic phenomena because of fluctuations in the geometrical relative velocity and induced velocity. In the present work, we developed a fully coupled simulation code and analyzed the unsteady aerodynamics of wind turbines by substituting aerodynamic model from FAST's AeroDyn to the vortex lattice method. The developed code was validated with unsteady aerodynamic experimental Phase VI data from the National Renewable Energy Laboratory. Finally, the results show that the developed coupled code yields accurate values and good performance in the unsteady yaw case.
Strain-balanced Si/SiGe type-II superlattices for near-infrared photodetection
Authors: Ali Dyan , Richardson Christopher J. K.
Published: July 2014

Strain balanced silicon-silicon germanium type-II superlattice p-i-n photodetectors grown on a silicon germanium relaxed buffer layer are shown to exhibit an absorption band that extends beyond 0.7 eV (λ = 1.77 μm) with dark current densities of 27 μA cm−2. Simulations of the absorption edge, which are based on x-ray diffraction characterization, low observed dark current densities, and low dislocation densities, are consistent with fully strained heterostructures. Potential applications for devices made from this heterostructure design could include integrated silicon detectors, or low-noise absorption regions for infrared-extended silicon based avalanche photodiodes.
Penetrative imaging of sub-surface microstructures with a near-field microwave microscope
Authors: Sun Weiqiang , Yang Yong , Wu Zhe , Feng Tao , Zhuang Qianwei , Peng Lian-Mao , Xu Shengyong , Ong Chong Kim
Published: July 2014

Microwaves have the capability of penetrating through materials with low permittivity. By means of a near-field scanning microwave microscope system, we obtained two-dimensional maps of the incident microwave's reflection coefficient intensity and frequency shift, which correspond well to the spatial distribution and electrical conductance of fluids and metallic thin film structures hidden underneath 15–170 μm thick dielectric covers. The lateral resolution and sensitivity to conductivity for the target samples were found closely related to the thickness of the cover layer. The technique offers a real-time, in-situ, and a non-invasive approach to monitor the local chemical reactions, the motion of fluids, and the distribution or concentrations of ions or bio-materials in lab-on-a-chip systems. This technique also has the potential to be developed for the detection of live cells and tissues.
Structural, optical, and electrical properties of strained La-doped SrTiO3 films
Authors: Choi Miri , Posadas Agham B. , Rodriguez Cesar A. , O'Hara Andrew , Seinige Heidi , Kellock Andrew J. , Frank Martin M. , Tsoi Maxim , Zollner Stefan , Narayanan Vijay , Demkov Alexander A.
Published: July 2014

The structural, optical, and room-temperature electrical properties of strained La-doped SrTiO3 epitaxial thin films are investigated. Conductive La-doped SrTiO3 thin films with concentration varying from 5 to 25% are grown by molecular beam epitaxy on four different substrates: LaAlO3, (LaAlO3)0.3(Sr2AlTaO6)0.7, SrTiO3, and DyScO3, which result in lattice mismatch strain ranging from −2.9% to +1.1%. We compare the effect of La concentration and strain on the structural and optical properties, and measure their effect on the electrical resistivity and mobility at room temperature. Room temperature resistivities ranging from ∼10−2 to 10−5 Ω cm are obtained depending on strain and La concentration. The room temperature mobility decreases with increasing strain regardless of the sign of the strain. The observed Drude peak and Burstein-Moss shift from spectroscopic ellipsometry clearly confirm that the La addition creates a high density of free carriers in SrTiO3. First principles calculations were performed to help understand the effect of La-doping on the density of states effective mass as well as the conductivity and DC relaxation time.
Structural, optical, and magnetic properties of highly-resistive Sm-implanted GaN thin films
Authors: Lo Fang-Yuh , Huang Cheng-De , Chou Kai-Chieh , Guo Jhong-Yu , Liu Hsiang-Lin , Ney Verena , Ney Andreas , Shvarkov Stepan , Pezzagna Sébastien , Reuter Dirk , Chia Chi-Ta , Chern Ming-Yau , Wieck Andreas D. , Massies Jean
Published: July 2014

Samarium ions of 200 keV in energy were implanted into highly-resistive molecular-beam-epitaxy grown GaN thin films with a focused-ion-beam implanter at room temperature. The implantation doses range from 1 × 1014 to 1 × 1016 cm−2. Structural properties studied by x-ray diffraction and Raman-scattering spectroscopy revealed Sm incorporation into GaN matrix without secondary phase. The optical measurements showed that the band gap and optical constants changed very slightly by the implantation. Photoluminescence measurements showed emission spectra similar to p-type GaN for all samples. Magnetic investigations with a superconducting quantum interference device identified magnetic ordering for Sm dose of and above 1 × 1015 cm−2 before thermal annealing, while ferromagnetism was only observed after thermal annealing from the sample with highest Sm dose. The long-range magnetic ordering can be attributed to interaction of Sm ions through the implantation-induced Ga vacancy.
Investigation of in-plane- and z-polarized intersubband transitions in pyramid-shaped InAs/GaAs quantum dots coupled to wetting layer: Size and shape matter
Authors: Sabaeian Mohammad , Shahzadeh Mohammadreza
Published: July 2014

In this work, the effects of the shape and size on the intersubband electronic and optical properties of three-dimensional self-assembled pyramid-shaped InAs/GaAs quantum dots (QDs) were investigated in detail. More precisely, in-plane- and z-polarized transitions dipole moment (TDM), oscillator strength (OS), and absorption coefficients of P-to-S, WL-to-P, and WL-to-S transitions were studied as a function of the QD height. The P-to-S TDM showed to be strong and purely in-plane-polarized transition dominating two others. However, the TDMs and OSs of WL-to-P and WL-to-S transitions which are in-plane- and z-polarized transitions, respectively, showed a competition behavior for short and tall QDs. The former dominates for short QDs, and the latter for tall QDs. The physical reasons behind these interesting phenomena were also explained using the probability of finding the carriers in the pyramid region attached to the WL. The theoretical results are in good agreement with experimental data reported for short QDs [Appl. Phys. Lett. 82, 630 (2003)].
On the nature of the Mn-related states in the band structure of (Ga,Mn)As alloys via probing the E1 and E1 + Δ1 optical transitions
Authors: Gluba L. , Yastrubchak O. , Sęk G. , Rudno-Rudziński W. , Sadowski J. , Kulik M. , Rzodkiewicz W. , Rawski M. , Andrearczyk T. , Misiewicz J. , Wosinski T. , Żuk J.
Published: July 2014

The dilute (Ga,Mn)As became a model ferromagnetic semiconductor, however there is still a disagreement on the source of its magnetism. In this paper, we verify the ellipsometric results and compare them with more precise photoreflectance method, which gives an important insight into the interaction of the Mn-related states with the ones of GaAs valence band. No spectral shifts observed for the E1 and E1 + Δ1 interband transitions in highly doped and annealed (Ga,Mn)As epitaxial layers indicate that the coupling between a detached Mn impurity band and the valence band does not occur. Our findings are supported by the characterizations of the (Ga,Mn)As epitaxial layers with the high resolution transmission electron microscopy and magnetization measurements.
The particle valve: On-demand particle trapping, filtering, and release from a microfabricated polydimethylsiloxane membrane using surface acoustic waves
Authors: Collins David J. , Alan Tuncay , Neild Adrian
Published: July 2014

We introduce a surface acoustic wave (SAW) based method for acoustically controlled concentration, capture, release, and sorting of particles in a microfluidic system. This method is power efficient by the nature of its design: the vertical direction of a traveling acoustic wave, in which the majority of the energy at the SAW-water interface is directed, is used to concentrate particles behind a microfabricated polydimethylsiloxane membrane extending partially into a channel. Sorting is also demonstrated with this concentration shown to be size-dependent. Low-power, miniature SAW devices, using methods such as the one demonstrated here, are well placed for future integration into point-of-care diagnostic systems.
A tunable hemispherical platform for non-stretching curved flexible electronics and optoelectronics
Authors: Zhuang Jinda , Ju Y. Sungtaek
Published: July 2014

One major challenge in incorporating flexible electronics or optoelectronics on curved surfaces is the requirement of significant stretchability. We report a tunable platform for incorporating flexible and yet non-stretching device layers on a hemisphere. In this configuration, an array of planar petals contractively maps onto the surface of an inflatable hemisphere through elastocapillary interactions mediated by an interface liquid. A mechanical model is developed to elucidate the dependence of the conformality of the petal structures on their elastic modulus and thickness and the liquid surface tension. The modeling results are validated against experimental results obtained using petal structures of different thicknesses, restoring elastic spring elements of different spring constants, and liquids with different surface tension coefficients. Our platform will enable facile integration of non-stretching electronic and optoelectronic components prepared using established planar fabrication techniques on tunable hemispherical surfaces.
Engineering spectrum and dispersion with filters for high-sensitivity radio frequency detections
Authors: Shen Chao , Chen Zhe , Shao Yongzhi , Wang Pingshan
Published: July 2014

We demonstrate that engineering spectrum and dispersion with filters are an effective approach to boost sensor sensitivities for various radio-frequency (RF) sensing applications. A low-pass filter with a ∼2 GHz cutoff frequency and a band-pass filter with a ∼3 GHz center frequency are designed and incorporated into an interferometer to achieve ultra-high sensitivity RF detections. Compared with coplanar waveguides, the filters have up to 10-times longer group delays and 9-times stronger localized RF E-fields. Thus, the interactions between RF fields and material-under-test, which is a slab of polydimethylsiloxane in this work, are significantly enhanced. The interferometer sensitivities are boosted by up to 11 times for operating frequency shifts and 25 dB for magnitude change at frequencies up to 12 GHz.
Volmer–Weber InAs quantum dot formation on InP (113)B substrates under the surfactant effect of Sb
Authors: Zhao Yu , Mauger Samuel J. C. , Bertru Nicolas , Folliot Hervé , Rohel Tony , Koenraad Paul M.
Published: July 2014

We report on Sb surfactant growth of InAs nanostructures on GaAs0.51Sb0.49 layers deposited on InP (001) and on (113)B oriented substrates. On the (001) orientation, the presence of Sb significantly favors the two-dimensional growth regime. Even after the deposition of 5 mono-layers of InAs, the epitaxial film remains flat and InAs/GaAs0.51Sb0.49 type-II quantum wells are achieved. On (113)B substrates, same growth runs resulted in formation of high density InAs islands. Microscopic studies show that wetting layer is missing on (113)B substrates, and thus, a Volmer-Weber growth mode is concluded. These different behaviors are attributed to the surface energy changes induced by Sb atoms on surface.
Gain and tuning characteristics of mid-infrared InSb quantum dot diode lasers
Authors: Lu Q. , Zhuang Q. , Hayton J. , Yin M. , Krier A.
Published: July 2014

There have been relatively few reports of lasing from InSb quantum dots (QDs). In this work, type II InSb/InAs QD laser diodes emitting in the mid-infrared at 3.1 μm have been demonstrated and characterized. The gain was determined to be 2.9 cm−1 per QD layer, and the waveguide loss was ∼15 cm−1 at 4 K. Spontaneous emission measurements below threshold revealed a blue shift of the peak wavelength with increasing current, indicating filling of ground state heavy hole levels in the QDs. The characteristic temperature, T0 = 101 K below 50 K, but decreased to 48 K at higher temperatures. The emission wavelength of these lasers showed first a blue shift followed by a red shift with increasing temperature. A hybrid structure was used to fabricate the laser by combining a liquid phase epitaxy grown p-InAs0.61Sb0.13P0.26 lower cladding layer and an upper n+ InAs plasmon cladding layer which resulted in a maximum operating temperature (Tmax) of 120 K in pulsed mode, which is the highest reported to date.
Synthesis and Characterization of Cerium Tetraphenylporphyrin Nitrate and Molecular Recognition for NO
Authors: Xu Qiu-xia , Zhang Jian-bin , Zhao Tian-xiang , Lan Gong-jia , Wei Xiong-hui
Published: July 2014

Cerium (III) tetraphenylporphyrin nitrate Ce(TPP)NO3 was synthesized by using mesotetraphenylporphyrin (TPP) and Ce(NO3)·6H2O in mixture solution of CHCl3 and C2H5OH (V :V =1:1). The complex was characterized by UV-Vis, FT-IR, conventional fluorescence, MALDI-TOF-MS, and 1H NMR spectral techniques. The structure of complex was proposed viaSpectral analyses, in which tetraphenylporphyrin was coordinated to a cerium ion in a tetradentate fashion, while one nitrate was coordinated to the same cerium ion. After bubbling NO to the solution of Ce(TPP)NO3 in CH2Cl2, spectral analyses suggested that Ce(TPP)NO3 could interact with NO to form a novel complex of Ce(TPP)(NO)NO3, and NO was coordinated to the center cerium ion. When nitrogen was poured into the Ce(TPP)(NO)(NO3) solution, the complex could be reduced to Ce(TPP)NO3.
Interaction in Binary Mixtures of Gemini Surfactant G12-6-12 and CTAB by NMR
Authors: Zhang Jin-zhi , Xie Li , Chai Shi-gan , Zou Qi-chao
Published: July 2014

The interaction between N, N′-bis(dimethyldodecyl)-1,6-hexanediammoniumdibromide (G12-6-12) and cetyltrimethylammonium bromide (CTAB) in D2O aqueous medium has been investigated by NMR at 298 K. The measured critical micelle concentration (cmc) of G12-6-12 and CTAB are about 0.773 and 0.668 mmol/L, respectively. The cmc* (cmc of mixture) values are less than CMC* (cmc of ideally mixed solution) in the mixed system, and the interaction parameter βM<0 at different molar fractions α of G12-6-12 in the mixed systems, but just when α≤0.3, cmc* values are much smaller than CMC*, and βM satisfies the relation of ∣βM∣>∣ln(cmc1/cmc2)∣ (cmc1: cmc of pure G12-6-12 and cmc2: cmc of pure CTAB). The results indicate that there exists synergism between G12-6-12 and CTAB, and they can form mixed micelles, which is further proven by 2D NOESY and self-diffusion coefficient D experiments. There are intermolecular cross peaks between G12-6-12 and CTAB in 2D NOESY, and the radius of micelles in mixed solution is bigger than that in G12-6-12 pure solution in D experiments, indicating there are mixed micelles. However, when α>0.3, we find that cmc*≈CMC*, βM≈0, obviously, the two surfactants are almost ideal mixing fitting the pseudo-phase separation model and regular solution theory.
Preparation of TiO2 Nanocrystals/Graphene Composite and Its Photocatalytic Performance
Authors: Deng Ling-juan , Gu Yuan-zi , Xu Wei-xia , Ma Zhan-ying
Published: July 2014

TiO2 nanocrystals/graphene (TiO2/GR) composite are prepared by combining flocculation and hydrothermal reduction technology using graphite oxide and TiO2 colloid as precursors. The obtained materials are examined by scanning electron microscopy, transition electron microscopy, X-ray diffraction, N2 adsorption desorption, and ultraviolet-visible diffuse spectroscopy. The results suggest that the presence of TiO2 nanocrystals with diameter of about 15 nm prevents GR nanosheets from agglomeration. Owing to the uniform distribution of TiO2 nanocrystals on the GR nanosheets, TiO2/GR composite exhibits stronger light absorption in the visible region, higher adsorption capacity to methylene blue and higher efficiency of charge separation and transportation compared with pure TiO2. Moreover, the TiO2/GR composite with a GR content of 30% shows higher photocatalytic removal efficiency of MB from water than that of pure TiO2 and commercial P25 under both UV and sunlight irradiation.