Search

A novel magnetic coupler (MC) with cross-coupling mode is proposed in this article, which has merits of fit-to-surface and lightweight in receiver, and supports stable and efficient charging for autonomous underwater vehicles (AUVs). The proposed magnetic structure employing an arc bipolar transmitter and a compact dipole-coil-based receiver utilizes horizontal flux to establish strong and stable coupling against three-dimensional misalignment; the MC structure is constructed and optimized according to the magnetic field distribution characteristics. The influence of geometric parameters on the MC's performance is obtained based on ANSYS Maxwell simulation, with which the parameters of MC are optimized. In order to fully verify the performance of the designed MC, an AUV wireless charging system circuit is also developed. A wireless charging system prototype is built and tested with a 600 g receiver, and it can deliver 1 kW at a dc-to-dc efficiency of 95.1%. The experimental results under various operating conditions indicate that the proposed MC is viable and can be used for charging the AUVs.

In building a predictive credit scoring model, feature selection is an essential pre-processing step that can improve the predictive accuracy and comprehensibility of models. In this study, we sele...

This letter develops a wireless charging system based on a novel orthogonal magnetic structure and primary-side power control to simplify the structure and reduce the weight of on-board pick-up for recharging the unmanned aerial vehicles (UAVs). The novel magnetic structure has a polarized transmitter with a flat U-type core and a perpendicular air-cored receiving coil, guaranteeing the magnetic flux operation space away from a UAV body by coil structure itself and also reducing the weight of a magnetic receiver. The power flow to the battery is controlled by the primary side based on charging current and voltage feedback by pick-up. Simulations based on ANSYS Maxwell and experiments are carried out to validate the proposal. The weight of a magnetic receiver is 130 g. And the system can deliver 500 W with a dc-to-battery efficiency of 90.8%, meanwhile 10 A constant current/50 V constant voltage charging for 12S lithium-ion battery is achieved by the closed-loop system.

Given the unique properties of sewage sludge-derived carbonaceous materials (SC) and the correlation of SC with recycling sewage sludge in an efficiently safe way, there is significant attraction f...

Composite tubes, which combine the advantageous properties of each layer, are in increasing demand in industry. The spin-bonding process shows great potential in producing composite tubes of dissimilar metals. In this study, the deformation synchronism index is proposed to describe the deformation uniformity between internal and external tube, which is defined as the ratio of difference in thickness reduction between external and internal tube to total thickness reduction. The process experiment and FE simulation are carried out to investigate the effect of heat treatment, initial thickness ratio and thickness reduction on bonding strength and deformation synchronism in spin-bonding of 3A21/5A03 composite tube. The results show that the deformation synchronism index decreased as the thickness ratio and yield stress ratio of internal tube to external tube reduced. The distribution of plastic strain was discontinuous across the interface of composite tube due to gradiently decreased stress field under the roller and different yield stresses between external and internal tube. The bonding strength increased at relatively smaller yield stress and greater thickness of internal tube. However, the maximum thickness reduction the composite tube could undertake before fracture was reduced when the external tube was thinner. This study is helpful for the design and optimization of the spin bonding process of composite tubes.

Based on the analysis of the experimental data for cylindrical lithium-ion battery under mechanical abuse, an equivalent mechanical model of spring-damping parallel unit connects a damping unit in series is proposed in this paper. By combining the equivalent mechanical model with the Crushable-Foam material model, the experiments and simulations on the flat plate tests, rigid rod tests and hemispherical punch tests are performed, the prediction error of the simulation model to the failure displacement is less than 11%. After that, the equivalent mechanical model is analyzed, a soft short-circuit failure prediction model is proposed. A failure warning system is designed according to the prediction model, and the warning system can prompt the soft short-circuit failure of the battery in time and has a certain safety margin.

The Golden Shield Project, aka the Great Firewall of China, is one of the most popular and vital information security and censorship technology project that is being used very strictly and extensively in the country since 2008. The Great Firewall has been preventing Internet users in China from visiting many foreign websites for one reason or the other and blocking them completely. This particular firewall implements information access control through some stringent security policies and takes the responsibility of controlling and censoring the flow of data. The Great Firewall makes China one of the strictest countries in the world when it comes to the internet freedom of the netizens residing in the mainland. In this paper, we will focus on the development of the Great Firewall that includes the timeline of its development, the censorship policy used for its implementation, its effects and the principles behind the technology used for its application. We will discuss where it stands after a decade of its implementation. We will also present a study of techniques like using a VPN to circumvent the heavily monitored firewall. These circumvention techniques have become very popular in the mainland because of severe information censorship. With this research, we aim to offer a clear understanding of the Great Firewall to the people from across the world.

Polymeric carbon nitride (C3N4) with atomic thick layers has displayed ultrashort carrier transfer and ion/molecule migration path for enhancement of photocatalytic performance. However, rational modulation towards electron configurations of ultra-thin C3N4 nanosheets is still a challenge, because the existing exfoliation strategies suffer from uncontrollable atom-defects and edge functional groups, leading to poor solar-to-fuel conversion efficiency. Herein, a post-redox method is developed to form atomic thick C3N4 nanosheets with optimized electron configurations through liquid exfoliation and C-reduction. The as-prepared carbon-reduced atomic thick C3N4 (CRed-AT-C3N4) expose more active sites, greatly enhance charge carrier mobility and distinctly reduce the optical band gap, thus leading to a remarkably improved photocatalytic hydrogen evolution rate of 246.2 μmol h−1 under visible light irradiation (λ > 420 nm), which is 17-fold higher than that of the pristine counterpart. The apparent quantum efficiency reaches 18.52 % at 420 nm and surpasses most of existing C3N4-based photocatalysts.

Four novel materials containing isoindigo derivatives were synthesized via Stille coupling reaction. These polymers not only have excellent electrochromic properties (the highest electrochromic efficiency reaches 195 cm2 C−1), but also have low charge transfer resistance (Rct). The range of switching threshold is from −1.7 V to −4.0 V and the current ratio of the device beyond 10−5 for memory device. Moreover, the polymers can also be used as explosive detector. A sharp drop in the fluorescence intensity of the polymer appeared when trinitrotoluene (TNT) or 2, 4, 6-trinitrophenol (TNP) was added.

Walking is the most easily achievable way to reduce obesity and to keep fit. Step counting devices are helpful for users to develop regular walking habits, but they may mistake some abnormal situations (SHAKING, SWING, JITTER, PENDULUM, etc.) for walking and thus result in step counting errors. Such errors will inflate the number of steps, and lead to biased inter-user comparisons or competitions. To fix the problem, we developed an effective algorithm to detect abnormal step counting, which extract 13 non-directional features from acceleration data, and feed them into One-Class Support Vector Machine (OCSVM) to check wether it is abnormal. The detection algorithm has been tested on a dataset composed of 600 minutes real world data, which is captured by 10 users. It is shown that the proposed algorithm is capable of detecting most of the abnormal situations while not mistaking normal activity (walking/running) for abnormal. While the false alarm rate is 5.08%, the algorithm detects 90.72% of abnormal situations. The AUC (Area Under the Curve) of the proposed algorithm reaches 0.9252, which shows that the algorithm is very effective for abnormal situation detection.

This paper describes a methodology used for the implementation flow of a system on chip circuit containing a complex clock design. The clock generation module contained 2 clock sources and 11 generated clocks. Many of them have interactive relationship. and the 2 clock sources generate the internal clocks in various modes. It uses the combination of bottom-up strategy and top-down strategy to accomplish the clock generation module implementation first, and then finish the whole chip design. This methodology of the solution makes the whole structure of the design distinct, saves a lot of iterative time, and reduces chip power consumption.

Details of an electro-optic, hybrid current-sensing instrument, and its application to high-voltage power line current measurement, are presented. The current is first detected via a Rogowski coil, followed by conversion of the detected current into a frequency-modulated optical pulse signal in the high-voltage area. Subsequently, the optical pulse signal is transmitted to the ground through an optical fiber cable. Finally, the measured current is recovered from the optical pulse signal by a ground-located signal-processing module. Compared with conventional current transformers, widely used for high-voltage line current measurement, this instrument provides a significant reduction in size, weight, and cost, together with features of convenient installation, secure operation, and high accuracy. Furthermore, it can be configured to be compatible with conventional secondary meters widely used in today's power plants and substations. In 1996, a prototype of this instrument was demonstrated online at a power substation and has shown good accuracy, stability, and safety for more than two years.

A scheme of WDM+OCDMA system employing optical hard-limiter (OHL) is proposed, and its performance of normalized throughput is analyzed. The upper bound of the normalized throughput is obtained when all the simultaneous users are equally allocated to different wavelength channels. The lower bound of the normalized throughput is obtained when all the simultaneous users are firstly allocated to the same wavelength channels. Compared with the performance of WDM+OCDMA system without OHL, both the upper bound and lower bound of the normalized throughput in WDM+OCDMA system with OHL can be improved.

Optical encoders/decoders based on fiber gratings are designed and fabricated. Experiment on one interference user 2.5Gb/s symbol overlapping optical fast frequency-hopping CDMA (SO-FFH OCDMA) system is demonstrated. Multiaccess interference in SO-FFH OCDMA system is studied, and is compared with that of traditional FFH OCDMA system. Experiment result shows that multi-access interference will degrade the system performance. With one interference user, SO-FFH OCDMA can also decode data correctly at data bit rate 2.5Gb/s.

An analysis of the code parameters that are important to asynchronous coherent time-spreading OCDMA system is presented. Relationship between the mean intensity of aperiodic cross-correlation and multiple-access interference (MAI) and beat noise (BN) is deduced. Considering the mean system performance, MAI and BN can be calculated directly from aperiodic auto-correlation function, and the aperiodic cross-correlation function is not needed. Hence, a computational saving can be achieved For 511 length Gold sequence, coherent time-spreading OCDMA system can support 12 interfering users for the mean performance.

Estimating the number of simultaneous users on channel, optimum threshold value in multi-wavelength optical CDMA(MW OCDMA) is achieved according to maximum likelihood principle. When MW OCDMA system has large number of simultaneous users on channel, optimum threshold value will vary with the number of simultaneous users, and the receiver will adjust the optimum threshold accordingly. Theoretical analysis and analogy simulation show that BER of MW OCDMA system will degrade greatly when employing the proposed optimum threshold value by maximum likelihood principle.

A new one-dimensional optical orthogonal codes named extend modified hyperbolic congruence codes(EMHC), is first constructed, and its performance is analyzed. Using EMHC for time spreading and prime codes (PC) for wavelength hopping, a new two-dimensional optical orthogonal codes named EMHC/PC is constructed. Then, the performance of EMHC/PC is analyzed, and is also compared with EQC/PC. It is shown that EMHC/PC has the same code cardinality and code length, but has better cyclic cross-correlation performance. Therefore, EMHC/PC can support more simultaneous users in optical CDMA networks.

The performance of normalized throughput in WDM+OCDMA is compared with that of MW OCDMA system after considering the effect of chromatic dispersion. Normalized throughput in MW OCDMA system will be reduced after considering the effect of chromatic dispersion. Both WDM+OCDMA and MW OCDMA systems have comparable performance of normalized throughput when traffic load is light. However, WDM+OCDMA system has better performance when traffic load is heavy. Furthermore, the peaked normalized throughput of WDM+OCDMA system is larger than that of MW OCDMA system.

A scheme of WDM+OCDMA system employing optical hard-limiter(OHL) is proposed, and its performance of normalized throughput is analyzed. Upper bound of normalized throughput is obtained when all simultaneous users are equally allocated to different wavelength channels. Lower bound of normalized throughput is obtained when all simultaneous users are firstly allocated to same wavelength channels. Compared with the performance of WDM+OCDMA system without OHL, both upper bound and lower bound of normalized throughput in WDM+OCDMA system with OHL can be improved.

The performance of normalized throughput in a hybrid WDMA-OCDMA system is studied. Effect of optical beat noise and dispersion on the normalized throughput is analyzed. The scheme of BCH channel coding is proposed to improve the performance of a hybrid WDMA-OCDMA system. Analysis result shows that the normalized throughput can be improved greatly when traffic load is medium. Furthermore, the maximum normalized throughput will increase for the BCH-coded hybrid WDMA-OCDMA system

We report on the characterization of a room temperature terahertz detector based on a GaN/AlGaN high electron mobility transistor integrated with three patch antennas. Experimental results prove that both horizontal and perpendicular electric fields are induced in the electron channel. A photocurrent is generated when the electron channel is strongly modulated by the gate voltage. Despite the large channel length and gate-source/drain distance, significant horizontal and perpendicular fields are achieved. The device is well described by the self-mixing of terahertz fields in the electron channel. The noise-equivalent power and responsivity are estimated to be and 3 mA=W at 292 K, respectively. No decrease in responsivity is observed up to a modulation frequency of 5 kHz. The detector performance can be further improved by engineering the source-gate-drain geometry to enhance the nonlinearity.