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In Hong Kong, a postcolonial city, history writing has been under pressure from British colonial and Chinese nationalist discourses. In the past decades, Hong Kong cinema has used nostalgia to faci...

Due to the extensive applications of power electronic devices in power grids, many insulation components will be stressed by high voltage PWM, multilevel or even more complex waveforms. In this paper, a high voltage generator able to produce various waveforms is developed. The generator is based on cascade connected multilevel modular converter (MMC) topology, including 20 half bridge MMC cells with the capability of 21 output voltage levels. Half of the series-connected MMC cells are charged positively, while the other half are charged negatively. Each positive and negative half bridge MMC cell is connected alternately to optimize the insulation design. The power supply of the driving circuit for each MMC cell is provided by an individual fly-back converter fed by the cell capacitor to realize a compact design. On the basis of simulations, a multilevel arbitrary waveform generator prototype was constructed, with the maximum peak-to-peak voltage of ∼ 28 kV. A capacitor switching strategy is utilized to solve the voltage-imbalance problem resulted from the difference of the element parameters and other reasons. Finally, it was tested on a typical insulation with a simulated defect.

PMMW imaging system can create interpretable imagery on the objects concealed under clothing, which gives the great advantage to the security check system. Paper addresses wavelet fusion to detect concealed objects using passive millimeter wave (PMMW) sequence images. According to PMMW real-time imager acquired image characteristics and storage methods，firstly, using the sum of squared difference (SSD) as the image-related parameters to screen the sequence images. Secondly, the selected images are optimized using wavelet fusion algorithm. Finally, the concealed objects are detected by mean filter, threshold segmentation and edge detection. The experimental results show that this method improves the detection effect of concealed objects by selecting the most relevant images from PMMW sequence images and using wavelet fusion to enhance the information of the concealed objects. The method can be effectively applied to human body concealed object detection in millimeter wave video.

Muti-baseLine SAR tomography can be used on 3D reconstruction of urban building based on SAR images acquired. In the near future, it is expected to become an important technical tool for urban multi-dimensional precision monitoring. For the moment，There is no effective method to verify the accuracy of tomographic SAR 3D point cloud of urban buildings. In this paper, a new method based on terrestrial Lidar 3D point cloud data to verify the accuracy of the tomographic SAR 3D point cloud data is proposed, 3D point cloud of two can be segmented into different facadeds. Then facet boundary extraction is carried out one by one, to evaluate the accuracy of tomographic SAR 3D point cloud of urban buildings. The experience select data of Pangu Plaza to analyze and compare, the result of experience show that the proposed method that evaluating the accuracy of tomographic SAR 3D point clou of urban building based on lidar 3D point cloud is validity and applicability

Under the changing and complex urban environment, gas pipeline leakage disasters are becoming increasingly complicated. In order to make a quantitative analysis of the coupling degree among each factor at different grades, this study adopts the comprehensive indexes of gas pipeline leakage disaster system based on AHP (Analytic Hierarchy Process) and Entropy method. The calculation model of coupling degree is then established in accordance with the coupling degree theory in physics. This study takes a region in Beijing as an example and calculates the coupling degree of urban gas pipeline leakage disaster system. The result shows the coupling degree of disaster system is 0.303, which indicates that the whole disaster system is in a status of moderately unbalanced development (acceptable interval). The occurrence of disaster is subject to disaster-inducing environment and disaster-bearing body, and the disaster-inducing environment is slightly more obstructive to occurrence of disaster. On the other side, controlling the disaster-inducing factors can reduce the coupling degree of disaster system. The model is helpful to evaluate the development state of the disaster system, and point out the direction of disaster control.

Recently, more and more attention has been drawn to nanosecond pulsed surface dielectric barrier discharge (NPSDBD) due to its potential applications in flow control. A study of the interaction between high-speed airflows and NPSDBD generated by different nanosecond waveforms is presented in this paper. The effects of airflows on the discharge characteristics, such as plasma morphology, discharge current, the inception voltage of discharge, are investigated at different pulse rise times and flow velocities. The results show that the NPSDBD sustained by pulses with a fast rise time ( $\sim 20$ ns) is quasi-uniform, and relatively stable in the airflows. While the NPSDBD driven by pulses with a rise time more than 50 ns, it seems easier to be influenced by a flowing air of 60 m/s, with a filamentary pattern and a typical discharge current, which has two or more current peaks in the pulse front. In the case of pulses with slow rise time, the inception voltage of discharge increases with the flow velocity, but it almost remains constant in the case of fast rise time. In addition, the deposited energy of discharge generated by the pulses with slow rise time increases slightly with the influence of flowing air. The emission spectrum of NPSDBD is also examined. The variation of the emission spectrum with pulse waveforms is basically consistent with the different discharge behaviors driven by different pulse waveforms.

During the Two Sessions of 2018, Ruan Chengfa, the governor of Yunnan Province, proposed for the first time in the “Government Work Report” that the future development of Yunnan Province should rely on carrying out the “three green cards” strategic plan, in which the development of clean energy has obvious advantages in Yunnan Province. This paper aims to present the challenges and opportunities encountered in the development of major clean energy projects in our province, and to analyze the main impact of various forms of green capital injection on the clean energy sector by statistical analysis with reference to the index data in the “Statistical Yearbook of Yunnan Province” from the different investment perspectives of policy finance and commercial finance under “Green Finance”. In view of the current situation of clean energy development in our province, this paper puts forward relevant recommendations to provide a reference for government sectors, financial sectors, enterprises and other relevant subjects in Yunnan Province at the initial stage of formulating policy routes, so as to make timely adjustments to the problems in the development process to promote the development of “Green Finance” and “three green cards” strategic plan in Yunnan Province.

The paint removal and recoating are the very important process in airplane maintenance. The traditional technology is to use the chemical way corroding the paint with paint remover. For changing the defects, corrosion & pollution & manual working, of the traditional technology, the physical process which removes the paint of airplane with 250MPa/250kW ultra-high pressure rotary water jetting though the surface cleaner installed on the six axes robot is studied. The paint layer of airplane is very thin and close. The contradiction of water jetting paint removal is to remove the paint layer wholly and not damage the surface of airplane. In order to solve the contradiction, the best working condition must be reached through tests. The paint removal efficiency with ultra-high pressure and move speed of not damaged to the surface. The move speed of this test is about 2m/min, and the paint removal efficiency is about 30~40m 2 /h, and the paint removal active area is 85-90%. No-repeat and no-omit are the base requests of the robot program. The physical paint removal technology will be applied in airplane maintenance, and will face the safety detection of application permission.

Compressive sensing theory can recover the original signal from little observation data, by means of the non-adaptive measurement far below Nyquist sampling and the optimization method. Due to the number of track is limited and the uneven distribution of tracks, the traditional method is difficult to image effectively in the practical application, while the compressive sensing theory by tomoSAR three-dimensional imaging (MUSIC, APES, etc.) can solve the problem easily, and it can realize high resolution imaging of SAR in the height direction. This paper applied the Generalized Orthogonal Matching Pursuit (GOMP) algorithm to the SAR tomography imaging, which can accurately reconstruct the signal in the height direction. Meanwhile, in this paper, 14 images of ascend track from which is “TerraSAR-X” HH polarization mode in Beijing during the period of 2011–2014 were taken as the test data, and Beijing pangu7 star hotel is taken as the research target. Finally, the result indicates that our algorithm is better than typical Orthogonal Matching Pursuit (OMP) algorithm.

Urban building outline is not only a very important land cover type, but also the key of studying urban building. It is significance on urban construction planning and natural disasters monitoring. This paper discussed the method for building information extracting according to high-resolution SAR coherence image. Through theoretical analysis and test verifying, it had obtained a better effect for extracting the buildings’ profiles or top figures from the coherence image, which often expressed as ‘L’-style top structures from SAR SLC image. This method has been proved the further potential in extracting urban buildings’ structure and profile information, and has some extent of reference means.

Gas explosion is likely to become a new type of attack aimed at underground spaces by terrorists. In this paper, as an example for methane-air gaseous mixture, distribution characteristics of shock wave, flame, temperature field and toxic gaseous products generated from gas explosion in a long straight laneway were analyzed. Along the increasing axial distance, shock wave overpressure increases in original flammable gas area but decreases beyond the original gas area. Range of flame exceeds the original gas area. Flame accelerates continually in the original gas area but decelerates beyond the original gas area. The temperature attenuates slowly along the increasing distance in the flame area by virtue of flame front, but attenuates quickly along the increasing distance beyond the flame region. High temperature hazard involves farther area beyond the original gas area.

The underwater electrical explosion of an aluminum wire is influenced by many factors, such as wire parameters, pulsed power energy, etc. In this paper, underwater electrical explosion of an aluminum wire was investigated with pulsed voltage in the time scale of a few microseconds. A self-integrated Rogowski coil and a voltage divider were used for the measurements of current and voltage at the wire load, respectively. The deposited energy before breakdown was calculated based on experimental waveforms of current and voltage by mathematical method. Effects of the applied voltage, circuit inductance and parameters of Al wire on the electrical explosion and energy deposition were analyzed by means of experiments and calculation. The results show that the current rise rate has an important influence on explosion process, such as the energy deposition before breakdown, the electrical power as well as the various explosion stages. A higher current rise rate can be achieved by increasing applied voltage and decreasing circuit inductance. The inhomogeneity of the energy deposition will result in prematured breakdown as well as lowered energy deposition, making the explosion process of wire more complicated.

A high power C-band monolithic voltage controlled oscillator (VCO) based on AlGaN/GaN HEMT is presented. The oscillator design utilizes a common-gate negative resistance structure, and a HEMT device acted as a varactor is used to control the VCO's oscillation frequency. The VCO operating at 20V drain bias and −3V gate bias exhibits an output power of 26 dBm at the center frequency of 5.96 GHz with dc-to-RF efficiency of 30%. Phase noise is estimated to be −96 dBc/Hz at 500 KHz offset. With the varactor's voltage from −1.5 V to −16 V, the frequency tuning range is from 5.61 GHz to 6.38 GHz. The measured results show high output power, good power flatness and good tuning linearity over the tuning band. This work demonstrates the potential for AlGaN/GaN HEMT technology to be used in high power microwave oscillator applications in very compact transceiver systems.

Nanosecond pulsed plasma has an enormous potential in many applications. In this paper, the characteristics of barrier free nanosecond pulsed surface discharge are investigated by the use of an actuator with a strip-strip film electrode configuration, including the effect of electrode width and the gap distance on the plasma morphology and electrical characteristics at atmospheric pressure. It was found that it is relative easier to generate a quasi uniform discharge with a thinner electrode width and a smaller gap distance. The underlying physical mechanism was also discussed. Besides that, the influence of airflow on repetitive pulsed surface discharge was examined. By comparing to the discharge produced by two different pulse waveforms in airflows, we found that the discharge driven by a faster pulse behaves more stable. Finally, a model was developed to analyze the interaction of the airflow and the discharge channels.

Noise performance of AlGaN/GaN HEMT has received more and more worldwide attention in recent years. In this paper, a MMIC process in AlGaN/GaN technology has been developed. A LNA design is based on a AlGaN/GaN HEMT noise model and a complete model library of passive elements under the optimum bias for LNA design. The paper describes modeling, bias dependence of small-signal and noise parameters, circuit design of the LNA using noise model without transistor noise measurement, and demonstrates a NF of 2 dB at 8GHz.

Virtual training system is important to improve the force operational capability. Due to urgent training needs for new type howitzer, the virtual training system was established based on analysis of a variety of training methods. From the system characteristic, the function modules were designed. Methods were specially expounded in realizing the ballistic function expression and setting up the troubles database. The process is shown to transform the trajectory coordinate system into the earth coordinate system. Meanwhile, it is suggested that troubleshooting training should be included into equipment training system. The system realizes the functions, such as threedimensional modeling, force generation, trajectory computation, troubles database establishment, evaluation, operation plan’s preparation and so on. The system is good at training effect through military trial. Keywords-Ballistic function; Howitzer; Troubleshooting; Virtual training

Activity recognition system based on MEMS sensors and wearable computer can produce updates on microblog automatically and frequently. Miniature sensors like the accelerometers made with MEMS technologies can measure body movements continuously while GPS constrains activity recognition within a small set of possible activities. Context information about a person's activities is made into short text messages shared among group members in order to keep social networking. The work for identifying daily activities from inertial sensor data with hidden Markov models (HMMs) is described.

In this paper, A12O3 ultrathin film used as the surface passivation layer for AlGaN/GaN high electron mobility transistor (HEMT) is deposited by thermal atomic layer deposition (ALD), thereby avoiding plasma-induced damage and erosion to the surface. A comparison is made between the surface passivation in this paper and the conventional plasma enhanced chemical vapor deposition (PECVD) SiN passivation. A remarkable reduction of the gate leakage current and a significant increase in small signal radio frequency (RF) performance are achieved after applying Al2O3+BCB passivation. For the Al2O3+BCB passivated device with a 0.7 μm gate, the value of fmax reaches up to 100 GHz, but it decreases to 40 GHz for SiN HEMT. The fmax/ft ratio (≥ 4) is also improved after Al2O3+BCB passivation. The capacitance–voltage (C–V) measurement demonstrates that Al2O3+BCB HEMT shows quite less density of trap states (on the order of magnitude of 1010 cm−2) than that obtained at commonly studied SiN HEMT.

An optimized modeling method of 8 × 100 μm AlGaN/GaN-based high electron mobility transistor (HEMT) for accurate continuous wave (CW) and pulsed power simulations is proposed. Since the self-heating effect can occur during the continuous operation, the power gain from the continuous operation significantly decreases when compared to a pulsed power operation. This paper extracts power performances of different device models from different quiescent biases of pulsed current–voltage (I–V) measurements and compared them in order to determine the most suitable device model for CW and pulse RF microwave power amplifier design. The simulated output power and gain results of the models at Vgs = −3.5 V, Vds = 30 V with a frequency of 9.6 GHz are presented.

In this paper, the off-state breakdown characteristics of two different AlGaN/GaN high electron mobility transistors (HEMTs), featuring a 50-nm and a 150-nm GaN thick channel layer, respectively, are compared. The HEMT with a thick channel exhibits a little larger pinch-off drain current but significantly enhanced off-state breakdown voltage (BVoff). Device simulation indicates that thickening the channel increases the drain-induced barrier lowering (DIBL) but reduces the lateral electric field in the channel and buffer underneath the gate. The increase of BVoff in the thick channel device is due to the reduction of the electric field. These results demonstrate that it is necessary to select an appropriate channel thickness to balance DIBL and BVoff in AlGaN/GaN HEMTs.

The author made some discussion and research on the related technical details of the vacuum interrupter computer aided design system. And then, the author developed the vacuum interrupter computer aided design system by using SolidWorks, Visual Basic and Microsoft office Access. The author used Visual Basic to make secondary developing to the SolidWorks, and used Microsoft office Access to manage the data and projects in the database. The system combined the computer aided choosing, parametric drawing, database management and so on to be a powerful tool. It is shown that by using it there is an infinite improvement to the quality, and efficiency in the design, as well as the automation situation. The paper described the structure and the achievement of the vacuum interrupter computer aided design system. Besides, the author also introduced some related key technologies in the developing and so on.

This paper describes work towards a mobile-robot following controller which has the ability to incorporate a leader's behavioral cues into its controller formulation. The paper presents the mathematical formulation of the controller, and presents robot experimental studies used to investigate the controller. The controller continuously estimates the future predicted position of the leader (robot or human) as he/she/it moves, and then directs the follower robot to this position. A Kalman filter is employed for estimation that uses vision-based measurements of leader position, a dynamics model of the leader, and a behavioral-cue model of the leader. Singer's model is used to propagate the leader's state. A behavioral-cue model serves to create pseudo-measurements to further help the Kalman filter estimate the leader's future position. The controller is implemented on an ER Scorpion robot. Experiments are conducted using several different controllers. Results demonstrate that compared to other controllers, the proposed controller can more consistently follow the leader around sharp corners where line-of-sight is lost, as can happen often in indoor environments. However, in cases of more gradual movement where line-of-sight is not lost, a simpler vision-only controller has advantages.

A new modified Angelov current—voltage characteristic model equation is proposed to improve the drain—source current (Ids) simulation of an AlGaN/GaN-based (gallium nitride) high electron mobility transistor (AlGaN/GaN-based HEMT) at high power operation. Since an accurate radio frequency (RF) current simulation is critical for a correct power simulation of the device, in this paper we propose a method of AlGaN/GaN high electron mobility transistor (HEMT) nonlinear large-signal model extraction with a supplemental modeling of RF drain—source current as a function of RF input power. The improved results of simulated output power, gain, and power added efficiency (PAE) at class-AB quiescent bias of Vgs = −3.5 V, Vds = 30 V with a frequency of 9.6 GHz are presented.

The impacts of varying layout geometries on the channel temperature of multi-finger AlGaN/GaN HEMTs are investigated by three-dimensional (3-D) thermal simulations. Micro-Raman thermography is selected to obtain a detailed and accurate temperature distribution of the sample for the verification of the 3-D thermal models. Thermal boundary resistance (TBR) plays an important role in the temperature distribution and is taken into account in the thermal model in order to improve the accuracy of the simulated results. The influence from the number of fingers, finger width and gate pitch on the gate temperature are systematically analysed using 3-D thermal simulations with validated model parameters. Furthermore, a robust method that could efficiently reduce the thermal crosstalk of multi-finger AlGaN/GaN HEMTs is proposed to optimize the thermal design of the device.

The effects of varying layout geometries and various thermal boundary resistances (TBRs) on the thermal resistance of multi-finger AlGaN/GaN HEMTs are thoroughly investigated using a combination of a two-dimensional electro-thermal model coupled with the three-dimensional thermal model. Temperature measurement using micro-Raman thermography is performed to verify and enhance the accuracy of the thermal model. Simulation results indicate that thermal resistance weakly depends on the layout design because of the high thermal conductivity of SiC. Meanwhile, the analysis reveals that optimizing the TBR of the device could efficiently reduce the thermal resistance since TBR takes a significant proportion of the total thermal resistance.

The current voltage (IV) characteristics are greatly influenced by the dispersion effects in AlGaN/GaN high electron mobility transistors. The direct current (DC) IV and pulsed IV measurements are performed to give a deep investigation into the dispersion effects, which are mainly related to the trap and self-heating mechanisms. The results show that traps play an important role in the kink effects, and high stress can introduce more traps and defects in the device. With the help of the pulsed IV measurements, the trapping effects and self-heating effects can be separated. The impact of time constants on the dispersion effects is also discussed. In order to achieve an accurate static DC IV measurement, the steady state of the bias points must be considered carefully to avoid the dispersion effects.

A high power density monolithic power amplifier operated at Ku band is presented utilizing a 0.3 m AlGaN/GaN HEMT production process on a 2-inch diameter semi-insulating (SI) 4H-SiC substrate by MOCVD. Over the 12-14 GHz frequency range, the single chip amplifier demonstrates a maximum power of 38 dBm (6.3 W), a peak power added efficiency (PAE) of 24.2% and linear gain of 6.4 to 7.5 dB under a 10% duty pulse condition when operated at Vds D 25 V and Vgs D - 4 V. At these power levels, the amplifier exhibits a power density in excess of 5 W/mm.

The analysis of the frequency dispersion characteristics of the gate-drain capacitance of GaN HEMT indicates that the gate fringe capacitance is responsible for the dispersion difference between the gate-drain capacitance and circle Schottky diode. By fitting the relationship between the additional capacitance of trap and frequency, we discover that the additional capacitance of trap can meet single energy level model only under small gate bias, and meet both single and consecutive energy level model under strong reverse gate bias. The gate fringe capacitance dispersion appears after SiN passivation. It suggests that the trap observed by fringe capacitance is introduced by passivation, which lies in the surface of the ungated region between source and drain. Finally, the low frequency noise technology is used to validate the feasibility of abstracting trap parameter by the gate fringe capacitance. The time constant of single energy level trap obtained by low frequency noise technology is consistent with the result obtained by the gate fringe capacitance under strong reverse gate bias.

The method of multi-bias capacitance voltage measurement is presented. The physical meaning of gate—source and gate—drain capacitances in AlGaN/GaN HEMT and the variations in them with different bias conditions are discussed. A capacitance model is proposed to reflect the behaviors of the gate—source and gate—drain capacitances, which shows a good agreement with the measured capacitances, and the power performance obtains good results compared with the measured data from the capacitance model.

The accurate extraction of AlGaN/GaN HEMT small-signal models, which is an important step in large-signal modeling, can exactly reflect the microwave performance of the physical structure of the device. A new method of extracting the parasitic elements is presented, and an open dummy structure is introduced to obtain the parasitic capacitances. With a Schottky resistor in the gate, a new method is developed to extract Rg. In order to characterize the changes of the depletion region under various drain voltages, the drain delay factor is involved in the output conductance of the device. Compared to the traditional method, the fitting of S 11 and S 22 is improved, and fT and fmax can be better predicted. The validity of the proposed method is verified with excellent correlation between the measured and simulated S -parameters in the range of 0.1 to 26.1 GHz.

The advent of fully integrated GaN PA-LNA circuits makes it meaningful to investigate the noise performance under high drain bias. However, noise performance of AlGaN/GaN HEMTs under high bias has not received worldwide attention in theoretical studies due to its complicated mechanisms. The noise value is moderately higher and its rate of increase is fast with increasing high voltage. In this paper, several possible mechanisms are proposed to be responsible for it. Impact ionization under high electric field incurs great fluctuation of carrier density, which increases the drain diffusion noise. Besides, higher gate leakage current related shot noise and a more severe self-heating effect are also contributors to the noise increase at high bias. Analysis from macroscopic and microscopic perspectives can help us to design new device structures to improve noise performance of AlGaN/GaN HEMTs under high bias.

For a further improvement of the noise performance in AlGaN/GaN HEMTs, reducing the relatively high gate leakage current is a key issue. In this paper, an experiment was carried out to demonstrate that one method during the device fabrication process can lower the noise. Two samples were treated differently after gate recess etching: one sample was annealed before metal deposition and the other sample was left as it is. From a comparison of their Ig–Vg characteristics, a conclusion could be drawn that the annealing can effectively reduce the gate leakage current. The etching plasma-induced damage removal or reduction after annealing is considered to be the main factor responsible for it. Evidence is given to prove that annealing can increase the Schottky barrier height. A noise model was used to verify that the annealing of the gate recess before the metal deposition is really effective to improve the noise performance of AlGaN/GaN HEMTs.