bluuebunny/crossref_metadata_2025 huggingface dataset:
Estimating supercapacitor performance for embedded applications using fractional‐order models
Authors: Freeborn T.J.
Published: July 2016

Commercially available supercapacitors currently require designers to experimentally characterise devices before integration for their specific applications. In this work a simple fractional‐order equivalent model for a supercapacitor is used to derive the design equation to estimate the discharge time due to a constant current. This model is shown to capture the transient discharging behaviour in the voltage range of interest (5–3 V) typical of many embedded systems. Experimental results using Kemet FT0H105ZF supercapacitors (1 F rating) as a secondary power supply for an Arduino Uno system are presented to highlight the application of this model and equations to a ubiquitous embedded system.
Interference‐aware frequency hopping for Bluetooth in crowded Wi‐Fi networks
Authors: So J. , Kim Y.
Published: July 2016

A new interference‐aware frequency hopping (IAFH) scheme for Bluetooth to mitigate the interference from Wi‐Fi networks is proposed. The conventional adaptive frequency hopping (AFH) scheme classifies channels into ‘good’ or ‘bad’ according to the predefined threshold and uses good channels with a uniform hop probability. Unlike the conventional AFH scheme, the proposed IAFH dynamically classifies channels into ‘good’ or ‘bad’ according to the observed interference levels and uses good channels with non‐uniform hop probabilities. The simulation results demonstrate that the proposed IAFH scheme significantly outperforms the conventional AFH scheme.
Automatic epilepsy detection from EEG introducing a new edge weight method in the complex network
Authors: Supriya S. , Siuly S. , Zhang Y.
Published: July 2016

Automatic diagnosis of epilepsy using electroencephalogram (EEG) signals is a hot topic in medical community as traditional diagnosis relies on tedious visual screening by highly trained clinicians from lengthy EEG recording. Hence, a new methodology to automatically detect epilepsy from EEG signals considering complex network as the principal dynamics of the epileptic EEG signals can be perfectly described by complex network is introduced. A novel edge weight method for visibility graph in the complex network for detection of epilepsy syndrome is presented. The effect of new edge weights for one key characteristic (such as, average weighted degree) of complex network is investigated. Finally, the extracted feature set is evaluated by two popular machine learning classifiers: support vector machine (SVM) with several kernel functions and linear discriminant analysis. The experimental results on Bonn University datasets show that the proposed approach is able to characterise the epilepsy from EEG signals generating up to 100% classification performance by SVM with polynomial kernel.
Filtering push–pull power amplifier based on novel impedance transformers
Authors: Zhang Bo , Dong Gaoya , Wu Yongle , Yu Cuiping , Liu Yuanan
Published: July 2016

A novel filtering push–pull power amplifier (PPPA), based on unbalanced‐to‐balanced impedance transformers, is presented for the first time. This novel impedance transformer can not only simplify the PPPA topology and miniaturise the overall circuit size, but also provide the bandpass filtering response and improve the second harmonic suppression performance. The proposed impedance transformers, which are constructed by two different C‐type line resonators, can provide good impedance matching performance under the odd‐mode excitation, while achieve high common mode suppression under the even‐mode excitation. Finally, a PPPA is designed and fabricated with the centre frequency of 2.45 GHz and bandwidth of 200 MHz for WLAN application. Moreover, detailed explanation and measured results are demonstrated for verification.
Adaptive fuzzy memory fault‐tolerant control of non‐linear systems with partially known time‐varying delays
Authors: Zhai Ding , An Liwei , Dong Jiuxiang , Zhang Qingling
Published: July 2016

This studies the fuzzy‐approximation‐based adaptive memory fault‐tolerant control problem for a class of non‐linear time‐delay systems with non‐affine non‐linear delayed faults. The main advantages of the developed scheme are as follows: first, based on the partial information of time‐varying delays, the unknown delay terms are approximated by combing fuzzy logic systems and adaptive mechanisms, and then, based on the obtained delay estimates, a memory controller is constructed, which removes the restriction on delays and time‐delay functions due to the Krasovskii function in the existing results; second, non‐affine non‐linear delayed faults are initially considered, and this new technique combing the property of hyperbolic tangent function, implicit function theorem and mean value theorem is adopted to circumvent the algebraic loop problems in controller design. It is proved that the proposed controller can ensure that the closed‐loop system is semi‐globally bounded, and all entire state tracking errors converge to a priori known accuracy. Finally, a simulation example is included for validating the advantages of the proposed approach.
Output feedback control for singular Markovian jump systems with uncertain transition rates
Authors: Chen Jian , Lin Chong , Chen Bing , Wang Qing‐Guo
Published: July 2016

The static output feedback stabilisation problems for singular Markovian jump system are studied. Transition rates are assumed to be generally uncertain, namely, they could be unknown or only their estimate values are known. A criterion on the existence of an output feedback controller is established in terms of bilinear matrix inequalities (BMIs) to guarantee the closed‐loop systems are stochastically admissible. To solve the BMIs in the criteria, the other criterion is presented by using a less conservative linearisation method, and an algorithm is proposed to solve the related conditions. Finally, three numerical examples are given to show the effectiveness of their methods.
Taguchi robust optimum design for reducing the cogging torque of EPS motors considering magnetic unbalance caused by manufacturing tolerances of PM
Authors: Kim Kyu‐Seob , Jung Kyung‐Tae , Kim Ji‐Min , Hong Jung‐Pyo , Kim Sung‐Il
Published: July 2016

Electric machines are widely used across a variety of applications. In particular, the cogging torque of a permanent magnet (PM) synchronous motor is a significantly important characteristic in the application of electric power steering (EPS) systems. Accordingly, various optimal design methods are adopted to reduce the cogging torque for an EPS motor. However, in most cases, the measured cogging torque of the EPS motor is much greater than finite element method result, because the additional cogging torque harmonic components are generated by manufacturing tolerances. Especially, the specific harmonic components are produced due to magnetic unbalance by the asymmetry of motor shape which is caused by the tolerances in motor cores or PMs. These components are not eliminated by applying a skew. Thus, in order to reduce the effect of the tolerances, a robust design is needed. In this study, the effect of PM tolerances is studied, and Taguchi robust design is performed to enhance the motor quality regardless of the tolerances.
Electromagnetic vibration and noise analysis of permanent magnet synchronous motor with different slot‐pole combinations
Authors: Lin Fu , Zuo Shuguang , Wu Xudong
Published: July 2016

This study first employs Maxwell stress tensor method to derive the spatial and temporal distribution characteristics of radial force which induces the electromagnetic vibration and noise. 2D fast Fourier transform is adopted to obtain the frequency components of radial force with specifically spatial harmonic order and force harmonics in six motors with different slot‐pole combinations are compared. Then, a multiphysics model for electromagnetic vibration and noise prediction considering the non‐uniformly distributed force on the teeth surface is established. Mode superposition method and boundary element method are, respectively, used to calculate the stator vibration and noise. The vibration and noise level in motors with different slot‐pole combinations are compared and the corresponding field harmonic sources of noise peaks are located based on 2D decomposing of radial force. Finally, the noise level under different rotational speed and current is discussed. It is mainly concluded that the lowest spatial order force dominates the vibration and noise performance. The noise level under different rotational speed and current depends on the amplitude and frequency of the lowest order force which is the closest to the frequency of the stator mode with the same spatial order.
Adaptive Mho relay for synchronous generator loss‐of‐excitation protection: a capability curve limit‐based approach
Authors: Morais Adriano P. , Bretas Arturo S. , Meyn Sean , Cardoso Ghendy
Published: July 2016

Loss‐of‐excitation (LOE) relays work under pre‐defined operating characteristics. If an abnormal condition should arise, such operating characteristics might not be suitable for current system conditions. In this study, an adaptive real‐time data‐based analytical methodology is proposed for improving LOE protection performance. The core idea is to generate in real time an adaptive operating characteristic for the Mho relay, based on the well know Berdy's method. The adaptive Mho operating characteristic is derived through the proposed methodology using the generator capability curve. Validation is obtained through comparative simulation test cases using DigSilent Power Factory® program. Test case results show that the proposed protection adaptive analytical methodology displays secure and effective high speed LOE detection, indicating potential for real‐life applications.
AC flashover characteristics of insulators under haze–fog environment
Authors: Guo Yujun , Jiang Xingliang , Liu Yang , Meng Zhigao , Li Zhenyu
Published: July 2016

The occurrence of large‐scale haze–fog weather in some developing countries brings a new threat to the safe operation of outdoor insulation. In order to study the effect of the haze–fog on the flashover performance of insulators and the flashover mechanism, kieselguhr, calcium sulphate (CaSO­4) and ammonium sulphate ((NH4)2SO4) in different particle sizes were mixed with ultrasonic fog to simulate the haze–fog environment and quantitative ac flashover experiments on the standard suspension porcelain insulator were carried out. The test results indicate that the flashover voltage is related with the pollution degree, particle component, particle size and fog‐water conductivity, and may decrease by more than 20% under haze–fog environment. The effect of salt aerosols on flashover voltage is determined by the solubility and larger than that of non‐soluble mineral aerosols or organic carbon aerosols. The flashover voltage increases with the increase of the particle size, but decreases with the increase of fog‐water conductivity. The flashover of insulator under haze–fog condition is a special kind of pollution flashover in essence.
Simple median‐based EP PP scheme for enhancement of reconstructed Bayer colour filter array images
Authors: Yang Yi‐Hong , Wang Peng‐Hua , Chen Po‐Ning
Published: July 2016

In this study, the median‐based edge‐preserving (EP) modification is revisited and has been shown to improve effectively the quality of a reconstructed Bayer colour filter array image in terms of the composite peak signal‐to‐noise ratio (CPSNR) performance index. Along this research direction, the authors propose an EP‐modified signal‐correlation‐based (SCB) post‐processing (PP), called EP‐SCB, as an enhancement to any existing interpolation method. The Bayer image reconstruction system they consider thus consists of two operational phases. The first phase performs an initial estimation of the missing red, green and blue colours by using an existing interpolation method, whereas the second phase applies EP‐SCB PP. Since a certain class of images may not fulfil the premise of having small variations in local colour difference, which is assumed by SCB‐type interpolation, thereby resulting in a deterioration in CPSNR after EP‐SCB PP, a threshold test on local variance ratio is also devised to conditionally switch off the second phase. Experimental results show that the EP‐SCB PP with variance‐ratio test gives a worst average CPSNR than the original interpolation methods tested in none of the Kodak and IMAX image groups experimented.
Dispersion HIE‐FDTD method for simulating graphene‐based absorber
Authors: Xu Ning , Chen Juan , Wang Jianguo , Qin Xijia , Shi Jiepei
Published: July 2016

A dispersion hybrid implicit–explicit finite‐difference time‐domain (HIE‐FDTD) method is proposed for simulating the graphene‐based absorber at terahertz frequencies. The surface conductivity of the graphene derived from the Kubo formula is incorporated into the conventional HIE‐FDTD algorithm by using the auxiliary differential equation technique. The time step size of this method is not related with the fine cells inside the graphene layer. The simulation result of the infinite graphene sheet shows that the dispersion HIE‐FDTD method has high computational accuracy and the computational time is greatly reduced compared with the dispersion FDTD method. By using the dispersion HIE‐FDTD method, it is validated that the graphene sheet can be used as a broadband absorber.
Performance comparison of 60 GHz printed patch antennas with different geometrical shapes using miniature hybrid microwave integrated circuits technology
Authors: Hannachi Chaouki , Tatu Serioja Ovidiu
Published: July 2016

This study presents a comparative study of several printed antennas having different shapes of the patch (rectangular, square, triangular, trapezoidal, circular, elliptical, and annular ring), suitable for 60 GHz wireless applications. All these microstrip patch antennas have been designed and fabricated on a very thin ceramic substrate to enable a high level of integration with other integrated circuits including passive circuits (such as power dividers, hybrid couplers, and passive filters), and active circuits (such as low noise amplifier (LNA), radio frequency (RF) mixers, and frequency multipliers). In that event, all of those circuits will be incorporated on a single and very small planar substrate to reduce overall size, and to avoid lossy millimetre‐wave connectors. To analyse and compare the performances, advanced design system of Keysight Technologies was used for circuits design and simulation. This comparison is based on the obtained results particularly in radiation characteristics and inputs return loss, by determining the main associated parameters such as the bandwidth, voltage standing wave ratio, gain, directivity, efficiency, and cross‐polarisation level. This comparative study would be very helpful for RF design engineers to select suitable antenna geometry while designing microstrip patch antenna arrays at 60 GHz millimetre‐wave band.
Receiving antenna mode of troposcatter passive ranging based on the signal group delay
Authors: Wang Zhuang , Wang Mengnan , Wang Qi , Cheng Zhu , Zhang Xueting
Published: July 2016

The beyond‐line‐of‐sight (BLOS) ranging of radiation sources can be realised through the troposcatter propagation of electromagnetic signals. Present troposcatter ranging systems are based on multi‐station cross localisation theory wherein synchronisation and data fusion of all stations are not tractable. The troposcatter signal group delay properties provide a new ranging mechanism that can be realised through a single station conveniently and inexpensively. However, for radiation sources with multibeams, e.g. frequency‐scanned radar, which forms several sub‐beams with different elevation angles in the vertical direction, the scattering signal of sub‐beams with high elevation angles has overall hysteresis compared to lower ones. This effect is called group delay between sub‐beams. In this study, a one‐to‐one correspondence between group delay and target distance is derived to a closed‐form expression with target and receiver antenna parameters. Furthermore, a group‐delay‐based passive ranging mechanism is proposed for exploiting this correspondence to increase the range of the BLOS target. Then two indicators for evaluation, ranging resolution and delay‐measure requirement, are proposed for investigating ranging performance under the receiving antenna mode with different elevation angles, vertical beamwidths and erection heights. Results show the ranging resolution is ∼0.1–0.3 μs/300 km and delay‐measure requirement is ∼0.002–0.033 μs for the given parameters.
TSO experience with voltage control from wind power plants
Authors: Langlois Charles‐Éric
Published: July 2016

Modern wind power plants (WPPs) are equipped with sophisticated controllers that allow various schemes to be used by manufacturers to meet grid code requirements. This includes active and reactive power controls as well as voltage control. Voltage control can be achieved in a number of different ways to satisfy the different grid codes, but also the project specific needs. Hydro‐Québec TransÉnergie (HQT) has performed numerous dynamic studies related to the integration of WPPs and optimisation of their control schemes including voltage control. This study presents the HQT experience with various voltage control issues including tuning of the WPP controller and study cases of angle and voltage stability issues.
Improving supervised wind power forecasting models using extended numerical weather variables and unlabelled data
Authors: Fang Shengchen , Chiang Hsiao‐Dong
Published: July 2016

A variety of supervised forecasting models using numerical weather prediction data have been utilised for short‐term wind power forecasting. These forecasting models only use meteorological variables of the target wind farm as essential features. This study proposes a novel method to improve existing supervised forecasting models such as support vector machines, artificial neural networks, and Gaussian processes (GPs) for higher forecasting accuracy. The proposed method develops a data‐driven feature extraction procedure to utilise unlabelled numerical weather data, and the feature extraction procedure transforms extended numerical weather variables into supplementary input features which then can be used for supervised forecasting models. The only modification to an existing supervised forecasting model is the addition of these supplementary input features, and thus does not alter the training algorithm of the supervised forecasting model. For illustrative purposes, the GP is used as the supervised forecasting model to be improved. Numerical evaluation of the proposed method was performed on a subset of data provided in the 2012 Global Energy Forecasting Competition (GEF 2012). Evaluation results reveal that the proposed method achieves higher forecasting accuracy for all wind farms.
Observation and analysis of atmospheric rainfall based on the very high frequency radar
Authors: Qing Haiyin , Chu Yenhsyang , Zhao Zhengyu , Su Chinglun , Zhou Chen , Zhang Yuannong
Published: July 2016

Very high frequency (VHF) radar can not only get higher resolution atmospheric three‐dimensional (3D) wind fields, but also observe complex atmospheric echoes in the rainfall environment. This paper uses Chung‐Li VHF Radar with five beams to observe the frontal rainfall and explore the physical process of atmospheric rainfall. The observed results indicate: 1) the height of bright band is at about 3.5 km with the thickness about 0.5 km and is lower about 0.5 km than the zero isotherm observed by the radiosonde. 2) When the strong updraft exists, the rainfall echoes will weaken and the bright band will be indistinct; when the downdraught exists, the rainfall echoes will strengthen and the bright band will be distinct. 3) The thickness of melting layer is about 1 km, the velocity of rainfall particles in the melting layer is smaller than that below it but spectral width is the opposite. The aspect sensitivity calculated from five beams shows that the radar rainfall echoes mainly come from the anisotropic scattering below the melting layer but isotropic scattering in the melting layer.
Real‐time fault analysis of transmission lines using wavelet multi‐resolution analysis based frequency‐domain approach
Authors: Ananthan Sundaravaradan Navalpakkam , Padmanabhan Rajaraman , Meyur Rounak , Mallikarjuna Balimidi , Reddy Maddikara Jaya Bharata , Mohanta Dusmanta Kumar
Published: July 2016

In a power system, transmission lines are prone to faults of different nature, which challenge the system stability and reliability. Thus system performance analysis under such fault conditions has drawn attention of researchers. Particularly, the advent of fast and efficient data acquisition using higher sampling rates combined with high speed digital signal processors has paved the way for efficient digital real‐time simulations. Though sustained efforts have been made by different researchers to develop some good real‐time digital simulators, this study is an attempt to implement a laboratory prototype model of a 20 V, 200 km transmission line, representing a 400 kV extra‐high voltage transmission line, so as to improve the real time performance. In addition, efficient National Instruments based data acquisition system in conjunction with LabVIEW has been incorporated to acquire the best possible representative data with commensurate characterisation and transmission with fidelity. The unique contributions of this real‐time fault analysis laboratory hybrid model are accurate fault detection and classification using a frequency‐domain approach having immunity to fault impedance and fault inception angle, which affect the time‐domain analyses severely. It is also equipped with visual displays so that even non‐experts can use it for planning and decision‐making purposes.
Partial discharge pattern recognition method based on variable predictive model‐based class discriminate and partial least squares regression
Authors: Zhu Yongli , Jia Yafei , Wang Liuwang
Published: July 2016

Both the feature extraction method and pattern recognition method are of great importance to assess the health condition of a power transformer. Since the partial discharge (PD) signals of the transformer are non‐stationary and non‐linear, and the existing pattern recognition methods fail to capitalise on the inter‐relations between the extracted features of the signals, a novel pattern recognition method, namely variable predictive model based class discrimination (VPMCD) is introduced for the PD pattern recognition in this research. However, the parameters of VPMCD are estimated by using least squares (LS) regression which is sensitive to multiple correlations between independent variables. Fortunately, partial LS (PLS) regression is usable even if features are highly correlated or the number of trained samples is very small. It is novelly adopted to overcome the defects of LS regression. Therefore, an automatic PD source classifier based on PLS and VPMCD, i.e. PLS‐VPMCD, is put forward in this study. PD signal features from either pulse shape characterisations or phase‐resolved PD are extracted. Then, the features are used as the input vectors of PLS‐VPMCD classifier. PD signals sampled from four artificial defect models are adopted for the algorithms testing. Compared with the original VPMCD and back propagation recognition methods, PLS‐VPMCD has much higher recognition accuracy.
Free chattering hybrid sliding mode control for a class of non‐linear systems: electric vehicles as a case study
Authors: Khooban Mohammad Hassan , Niknam Taher , Blaabjerg Frede , Dehghani Moslem
Published: July 2016

In current study, in order to find the control of general uncertain nonlinear systems, a new optimal hybrid control approach called Optimal General Type II Fuzzy Sliding Mode (OGT2FSM) is presented. In order to estimate unknown nonlinear activities in monitoring dynamic uncertainties, the benefits of general type‐2 fuzzy logic systems (GT2FLS) is utilized by the suggested controller. The suggested controller not only warranties the constancy and hardiness against uncertainties of the lumped resulted by external disturbances and un‐modeled dynamics, but also considerably decreases the control chattering inherent in traditional sliding mode control. Moreover, the Modified Backtracking Search Algorithm (MBSA), which is a new heuristic algorithm, is used in the offered controller. A comparison is performed between the results of current study and the results of some of the most recent studies on the same topic, which are an Adaptive Interval Type‐2 Fuzzy Logic Controller (AGT2FLC) and Conventional Sliding Mode Controller (CSMC), to assess the efficiency of the suggested controller. The suggested control scheme is finally used to the Electric Vehicles type as a case study. Results of simulation confirm the good performance the suggested controller.
Identification of interharmonics using disperse energy distribution algorithm for flicker troubleshooting
Authors: Lin Hsiung Cheng
Published: July 2016

It is well known that interharmonics close to the fundamental or harmonics may cause significant flicker. Although International Electrotechnical Commission (IEC) standard is adopted for interharmonic measurement, the interharmonic frequencies may not be obtained accurately under this framework. Based on the frequency resolution at 5 Hz recommended by IEC, this study develops a dispersed energy distribution (DED) algorithm to measure those interharmonics that may cause flicker due to a low frequency fluctuation phenomenon. The relation between the frequency and dispersed leakage from discrete Fourier transform is induced, and the mathematical model is thus established to find the interharmonic frequency. However, the dispersed energy can be collected to retrieve its original amplitude. The performance results based on the periodically varying load verify that the proposed scheme can achieve reliable, rapid and accurate outcome.
Health index calculation for power transformers using technical and economical parameters
Authors: Zeinoddini‐Meymand Hamed , Vahidi Behrooz
Published: July 2016

In this study technical diagnostic tests and economical lifetime assessment of transformers are investigated to evaluate the overall health condition of working transformers. Two artificial intelligence models including artificial neural network and adaptive neuro‐fuzzy inference system models are presented to determine the health index for transformers. The technical and economical parameters are used as input parameters to develop the models. Technical parameters are extracted from oil characteristics and dissolved gas analysis of different transformers. Economical parameters are constructed with transformer capital investments, maintenance and operating costs. The models are developed using 226 experimental field datasets of transformers technical and economical parameters. The models are trained using 80% of the experimental datasets. The remaining 20% is used to evaluate the performance and applicability of the models. The results prove that the models can be used to determine the health condition of transformers with high accuracy.
Highly compression‐tolerant folded carbon nanotube/paper as solid‐state supercapacitor electrode
Authors: Song Yu , Cheng Xiaoliang , Chen Haotian , Han Mengdi , Chen Xuexian , Huang Jiahuan , Su Zongming , Zhang Haixia
Published: July 2016

An original highly compression‐tolerant folded carbon nanotube (CNT)/paper electrode, which could be assembled into compressible solid‐state supercapacitor with polyvinyl alcohol/phosphoric acid gel electrolyte, is designed. It is worth mentioning that both the compression‐tolerant ability of the folded structure and the strain ability of the CNT electrode are conducive to achieving the compressible supercapacitor. Such device could withstand pressure and shape‐changing, which has great potential to be used in various environments. This compressible solid‐state supercapacitor also owns the maximum specific capacitance of 11.07 mF/cm2, and capacitance retention retains more than 90% after 100 cycling times. Furthermore, the stability performance of the device is also discussed which is almost steady under 50% strain state. When two devices are connected in serial and fully charged, this power unit could light up a red light emitting diode continuously even under the compression state. Therefore, this device performs as a promising candidate to be compatible with other compression‐tolerant electronics and enlightens a broad field of compressible energy storage and self‐powered systems.
Non‐destructive production of natural environment‐adaptive super‐hydrophobic hierarchical ceramic surface on a steel substrate
Authors: Shan Wen , Yang Guan‐Jun , Li Cheng‐Xin , Fang Baizeng , Li Chang‐Jiu
Published: July 2016

A super‐hydrophobic ceramic surface with excellent adaptability to the natural environment was developed on a metal substrate through a facile electrophoretic deposition approach. Alumina, as a demonstrating low cost ceramic material, was electrophoretically deposited on a steel surface to form a hierarchical surface structure. After the treatment with stearic acid, the as‐fabricated surface exhibits a high water contact angle and very low sliding angle, revealing a super hydrophobicity. Furthermore, the surface can maintain the super hydrophobicity with liquids of different pH values, performing good natural environment adaptability.
A study on the high-order mode oscillation in a four-cavity intense relativistic klystron amplifier
Authors: Liu Ying-Hui , Niu Xin-Jian , Jia Nan , Li Zheng-Hong , Wang Hui , Cheng Hui , Yang Xiao-Chuan , Duan Yaoyong
Published: July 2016

The high-order mode oscillation is studied in designing a four-cavity intense relativistic klystron amplifier. The reason for the oscillation caused by high-order modes and a method to suppress these kinds of spurious modes are found through theoretical analyses and the study on the influence of major parameters of a high frequency structure (such as the oscillation frequency of cavities, the cavity Q value, the length of drift tube section, and the characteristic impedance). Based on much simulation, a four-cavity intense relativistic klystron amplifier with a superior performance has been designed, built, and tested. An output power of 2.22 GW corresponding to 27.4% efficiency and 61 dB gain has been obtained. Moreover, the high-order mode oscillation is suppressed effectively, and an output power of 1.95 GW corresponding to 26% efficiency and 62 dB gain has been obtained in our laboratory.
High-speed stimulated Brillouin scattering spectroscopy at 780 nm
Authors: Remer Itay , Bilenca Alberto
Published: July 2016

We demonstrate a high-speed stimulated Brillouin scattering (SBS) spectroscopy system that is able to acquire stimulated Brillouin gain point-spectra in water samples and Intralipid tissue phantoms over 2 GHz within 10 ms and 100 ms, respectively, showing a 10-100 fold increase in acquisition rates over current frequency-domain SBS spectrometers. This improvement was accomplished by integrating an ultra-narrowband hot rubidium-85 vapor notch filter in a simplified frequency-domain SBS spectrometer comprising nearly counter-propagating continuous-wave pump-probe light at 780 nm and conventional single-modulation lock-in detection. The optical notch filter significantly suppressed stray pump light, enabling detection of stimulated Brillouin gain spectra with substantially improved acquisition times at adequate signal-to-noise ratios (∼25 dB in water samples and ∼15 dB in tissue phantoms). These results represent an important step towards the use of SBS spectroscopy for high-speed measurements of Brillouin gain resonances in scattering and non-scattering samples.
Ablation and transmission of thin solid targets irradiated by intense extreme ultraviolet laser radiation
Authors: Aslanyan V. , Kuznetsov I. , Bravo H. , Woolston M. R. , Rossall A. K. , Menoni C. S. , Rocca J. J. , Tallents G. J.
Published: July 2016

The interaction of an extreme ultraviolet (EUV) laser beam with a parylene foil was studied by experiments and simulation. A single EUV laser pulse of nanosecond duration focused to an intensity of 3 × 1010 W cm−2 perforated micrometer thick targets. The same laser pulse was simultaneously used to diagnose the interaction by a transmission measurement. A combination of 2-dimensional radiation-hydrodynamic and diffraction calculations was used to model the ablation, leading to good agreement with experiment. This theoretical approach allows predictive modelling of the interaction with matter of intense EUV beams over a broad range of parameters.
High resolution kilometric range optical telemetry in air by radio frequency phase measurement
Authors: Guillory Joffray , Šmíd Radek , García-Márquez Jorge , Truong Daniel , Alexandre Christophe , Wallerand Jean-Pierre
Published: July 2016

We have developed an optical Absolute Distance Meter (ADM) based on the measurement of the phase accumulated by a Radio Frequency wave during its propagation in the air by a laser beam. In this article, the ADM principle will be described and the main results will be presented. In particular, we will emphasize how the choice of an appropriate photodetector can significantly improve the telemeter performances by minimizing the amplitude to phase conversion. Our prototype, tested in the field, has proven its efficiency with a resolution better than 15 μm for a measurement time of 10 ms and distances up to 1.2 km.
Multimode resistive switching in nanoscale hafnium oxide stack as studied by atomic force microscopy
Authors: Hou Y. , Celano U. , Goux L. , Liu L. , Degraeve R. , Cheng Y. , Kang J. , Jurczak M. , Vandervorst W.
Published: July 2016

The nanoscale resistive switching in hafnium oxide stack is investigated by the conductive atomic force microscopy (C-AFM). The initial oxide stack is insulating and electrical stress from the C-AFM tip induces nanometric conductive filaments. Multimode resistive switching can be observed in consecutive operation cycles at one spot. The different modes are interpreted in the framework of a low defect quantum point contact theory. The model implies that the optimization of the conductive filament active region is crucial for the future application of nanoscale resistive switching devices.
Initial instability of round liquid jet at subcritical and supercritical environments
Authors: Muthukumaran C. K. , Vaidyanathan Aravind
Published: July 2016

In the present experimental work, the behavior of laminar liquid jet in its own vapor as well as supercritical fluid environment is conducted. Also the study of liquid jet injection into nitrogen (N2) environment is carried out at supercritical conditions. It is expected that the injected liquid jet would undergo thermodynamic transition to the chamber condition and this would alter the behavior of the injected jet. Moreover at such conditions there is a strong dependence between thermodynamic and fluid dynamic processes. Thus the thermodynamic transition has its effect on the initial instability as well as the breakup nature of the injected liquid jet. In the present study, the interfacial disturbance wavelength, breakup characteristics, and mixing behavior are analysed for the fluoroketone liquid jet that is injected into N2 environment as well as into its own vapor at subcritical to supercritical conditions. It is observed that at subcritical chamber conditions, the injected liquid jet exhibits classical liquid jet characteristics with Rayleigh breakup at lower Weber number and Taylor breakup at higher Weber number for both N2 and its own environment. At supercritical chamber conditions with its own environment, the injected liquid jet undergoes sudden thermodynamic transition to chamber conditions and single phase mixing characteristics is observed. However, the supercritical chamber conditions with N2 as ambient fluid does not have significant effect on the thermodynamic transition of the injected liquid jet.
On the third critical speed for rotating Bose-Einstein condensates
Authors: Correggi M. , Dimonte D.
Published: July 2016

We study a two-dimensional rotating Bose-Einstein condensate confined by an anharmonic trap in the framework of the Gross-Pitaevskii theory. We consider a rapid rotation regime close to the transition to a giant vortex state. It was proven in Correggi et al. [J. Math. Phys. 53, 095203 (2012)] that such a transition occurs when the angular velocity is of order ε−4, with ε−2 denoting the coefficient of the nonlinear term in the Gross-Pitaevskii functional and ε ≪ 1 (Thomas-Fermi regime). In this paper, we identify a finite value Ωc such that if Ω = Ω0/ε4 with Ω0 > Ωc, the condensate is in the giant vortex phase. Under the same condition, we prove a refined energy asymptotics and an estimate of the winding number of any Gross-Pitaevskii minimizer.
The electronic spectrum of cryogenic ruthenium-tris-bipyridine dications in vacuo
Authors: Xu Shuang , Smith James E. T. , Weber J. Mathias
Published: July 2016

We report the electronic spectrum of the prototypical ruthenium coordination complex Ru(bpy)32+ (bpy = 2, 2′-bipyridine) by messenger tagging with N2 in a cryogenic ion trap and photodissociation spectroscopy of mass selected Ru(bpy)32+ ⋅ N2 ions. We observe individual electronic bands and groups of bands with unprecedented detail, particularly in the usually unresolved metal-to-ligand charge transfer region of the spectrum. By comparing our experimental results with time-dependent density functional theory, both with and without spin-orbit interaction [Heully et al., J. Chem. Phys. 131, 184308 (2009)], we are able to assign the spectrum of the isolated ion.
Effect of water polyamorphism on the molecular vibrations of glycerol in its glassy aqueous solutions
Authors: Suzuki Yoshiharu , Mishima Osamu
Published: July 2016

A glassy dilute glycerol-water solution undergoes a mutual polyamorphic transition relating to the transition between high- and low-density amorphous ices of solvent water. The polyamorphic transition behavior depends on the glycerol concentration, indicating that the glycerol affects the water polyamorphism. Here, we used the glassy dilute glycerol-water solution of the solute molar fraction of 0.07 and examined the effect of the polyamorphic change in solvent water on the molecular vibrations of glycerol via Raman spectroscopy. It is found that the molecular vibration of glycerol in high-density liquid like solvent water is different from that in the low-density liquid like solvent water and that the change in the molecular vibration of glycerol is synchronized with the polyamorphic transition of solvent water. The dynamical change of the solute molecule relates to the polyamorphic state of solvent water. This result suggests that the polyamorphic fluctuation of water structure emanated from the presumed liquid-liquid critical point plays an important role for the function of aqueous solution under an ambient condition such as the conformational stability of solute, the functional expression of solute, and so on.
Drift-wave transport in the velocity shear layer
Authors: Rosalem K. C. , Roberto M. , Caldas I. L.
Published: July 2016

Particle drift driven by electrostatic wave fluctuations is numerically computed to describe the transport in a gradient velocity layer at the tokamak plasma edge. We consider an equilibrium plasma in large aspect ratio approximation with E×B flow and specified toroidal plasma velocity, electric field, and magnetic field profiles. A symplectic map, previously derived for infinite coherent time modes, is used to describe the transport dependence on the electric, magnetic, and plasma velocity shears. We also show that resonant perturbations and their correspondent islands in the Poincaré maps are much affected by the toroidal velocity profiles. Moreover, shearless transport barriers, identified by extremum values of the perturbed rotation number profiles of the invariant curves, allow chaotic trajectories trapped into the plasma. We investigate the influence of the toroidal plasma velocity profile on these shearless transport barriers.
Research Update: Cu–S based synthetic minerals as efficient thermoelectric materials at medium temperatures
Authors: Suekuni Koichiro , Takabatake Toshiro
Published: July 2016

Synthetic minerals and related systems based on Cu–S are attractive thermoelectric (TE) materials because of their environmentally benign characters and high figures of merit at around 700 K. This overview features the current examples including kesterite, binary copper sulfides, tetrahedrite, colusite, and chalcopyrite, with emphasis on their crystal structures and TE properties. This survey highlights the superior electronic properties in the p-type materials as well as the close relationship between crystal structures and thermophysical properties. We discuss the mechanisms of high power factor and low lattice thermal conductivity, approaching higher TE performances for the Cu–S based materials.
Highly accurate thickness measurement of multi-layered automotive paints using terahertz technology
Authors: Krimi Soufiene , Klier Jens , Jonuscheit Joachim , von Freymann Georg , Urbansky Ralph , Beigang René
Published: July 2016

In this contribution, we present a highly accurate approach for thickness measurements of multi-layered automotive paints using terahertz time domain spectroscopy in reflection geometry. The proposed method combines the benefits of a model-based material parameters extraction method to calibrate the paint coatings, a generalized Rouard's method to simulate the terahertz radiation behavior within arbitrary thin films, and the robustness of a powerful evolutionary optimization algorithm to increase the sensitivity of the minimum thickness measurement limit. Within the framework of this work, a self-calibration model is introduced, which takes into consideration the real industrial challenges such as the effect of wet-on-wet spray in the painting process.
Monopoles, instantons, and the Helmholtz equation
Authors: Franchetti Guido , Maldonado Rafael
Published: July 2016

In this work we study the dimensional reduction of smooth circle invariant Yang-Mills instantons defined on 4-manifolds which asymptotically become circle fibrations over hyperbolic 3-space. A suitable choice of the 4-manifold metric within a specific conformal class gives rise to singular and smooth hyperbolic monopoles. A large class of monopoles is obtained if the conformal factor satisfies the Helmholtz equation on hyperbolic 3-space. We describe simple configurations and relate our results to the Jackiw-Nohl-Rebbi construction, for which we provide a geometric interpretation.
Schottky diodes from 2D germanane
Authors: Sahoo Nanda Gopal , Esteves Richard J , Punetha Vinay Deep , Pestov Dmitry , Arachchige Indika U. , McLeskey James T.
Published: July 2016

We report on the fabrication and characterization of a Schottky diode made using 2D germanane (hydrogenated germanene). When compared to germanium, the 2D structure has higher electron mobility, an optimal band-gap, and exceptional stability making germanane an outstanding candidate for a variety of opto-electronic devices. One-atom-thick sheets of hydrogenated puckered germanium atoms have been synthesized from a CaGe2 framework via intercalation and characterized by XRD, Raman, and FTIR techniques. The material was then used to fabricate Schottky diodes by suspending the germanane in benzonitrile and drop-casting it onto interdigitated metal electrodes. The devices demonstrate significant rectifying behavior and the outstanding potential of this material.
Tuning optical and three photon absorption properties in graphene oxide-polyvinyl alcohol free standing films
Authors: Karthikeyan B. , Udayabhaskar R. , Hariharan S.
Published: July 2016

We report the optical and nonlinear optical properties of graphene oxide (GO)-polyvinyl alcohol (PVA) free standing films. The composite polymer films were prepared in ex-situ method. The variation in optical absorption spectra and optical constants with the amount of GO loading was noteworthy from the optical absorption spectroscopic studies. Nonlinear optical studies done at 532 nm using 5 ns laser pulses show three photon absorption like behaviour. Both steady state and time resolved fluorescence studies reveal that the GO was functioning as a pathway for the decay of fluorescence from PVA. This is attributed to the energy level modifications of GO through hydroxyl groups with PVA. Raman spectroscopy also supports the interaction between GO and PVA ions through OH radicals.
Highly uniform parallel microfabrication using a large numerical aperture system
Authors: Zhang Zi-Yu , Zhang Chen-Chu , Hu Yan-Lei , Wang Chao-Wei , Li Jia-Wen , Su Ya-Hui , Chu Jia-Ru , Wu Dong
Published: July 2016

In this letter, we report an improved algorithm to produce accurate phase patterns for generating highly uniform diffraction-limited multifocal arrays in a large numerical aperture objective system. It is shown that based on the original diffraction integral, the uniformity of the diffraction-limited focal arrays can be improved from ∼75% to >97%, owing to the critical consideration of the aperture function and apodization effect associated with a large numerical aperture objective. The experimental results, e.g., 3 × 3 arrays of square and triangle, seven microlens arrays with high uniformity, further verify the advantage of the improved algorithm. This algorithm enables the laser parallel processing technology to realize uniform microstructures and functional devices in the microfabrication system with a large numerical aperture objective.
Demonstration of ultra-thin buried oxide germanium-on-insulator MOSFETs by direct wafer bonding and polishing techniques
Authors: Zheng Zejie , Yu Xiao , Xie Min , Cheng Ran , Zhang Rui , Zhao Yi
Published: July 2016

The ultra-thin body and ultra-thin buried-oxide (UTBB) Germanium-on-Insulator (GeOI) substrates have been fabricated by direct wafer bonding and polishing techniques. The Ge and BOX layer thicknesses are as thin as 9 and 13 nm, respectively. The UTBB GeOI substrates exhibit superior crystal quality (similar to the bulk single crystalline Ge) and sufficiently reduced surface roughness. As a result, the Hall hole mobility of UTBB GeOI reaches 1330 cm2/V s with a carrier concentration of 2 × 1016 cm−3. The inversion mode UTBB GeOI nMOSFETs have also been demonstrated with suppressed mobility degradation during Ge layer thinning, indicating the feasibility of this GeOI substrate formation technique in future CMOS technologies.
Characterisation of Al0.52In0.48P mesa p-i-n photodiodes for X-ray photon counting spectroscopy
Authors: Butera S. , Lioliou G. , Krysa A. B. , Barnett A. M.
Published: July 2016

Results characterising the performance of thin (2 μm i-layer) Al0.52In0.48P p+-i-n+ mesa photodiodes for X-ray photon counting spectroscopy are reported at room temperature. Two 200 μm diameter and two 400 μm diameter Al0.52In0.48P p+-i-n+ mesa photodiodes were studied. Dark current results as a function of applied reverse bias are shown; dark current densities <3 nA/cm2 were observed at 30 V (150 kV/cm) for all the devices analysed. Capacitance measurements as a function of applied reverse bias are also reported. X-ray spectra were collected using 10 μs shaping time, with the device illuminated by an 55Fe radioisotope X-ray source. Experimental results showed that the best energy resolution (FWHM) achieved at 5.9 keV was 930 eV for the 200 μm Al0.52In0.48P diameter devices, when reverse biased at 15 V. System noise analysis was also carried out, and the different noise contributions were computed.