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Flexible pressure sensor is widely used in fields such as healthcare, intelligent prosthetics, and patient rehabilitation. However, how to ensure high sensitivity of the sensor while having a wide detection range remains a challenge. In order to address this challenge, a flexible pressure sensor with a wide detection range based on capacitive‐piezoresistive dual mode conversion is proposed. By manufacturing circular through‐holes on the dielectric layer of the sensor, the microstructure of the upper and lower electrode layers can achieve non‐contact and contact switching under different pressures through the through holes. This means that the sensor remains in capacitive mode at low pressure and then in piezoresistive mode at high pressure. By cleverly combining the two modes, the measurement range can reach 2 000 kPa and high sensitivity can be maintained during mode switching. In addition, its production process is simple, the cost is low, and it has a fast response time (120 ms) and good repeatability stability. The experimental results indicate that the sensor can achieve ideal performance in proximity detection, human behavior monitoring, and ultra high‐pressure detection, and has broad application prospects in providing a more powerful human‐computer interaction interface and expanding more comprehensive health monitoring. [ABSTRACT FROM AUTHOR]

To study the far-field aerodynamic noise of the leading-edge slat of a high-lift airfoil configuration, an experimental investigation of the BANC-II/30P30N airfoil model was carried out in the D5 areo-acoustic wind tunnel at Beihang University. A novel Kevlar-walled closed test section design was applied, as a way of upgrading the capabilities of a conventional aerodynamic wind tunnel to include far-field acoustic measurements for larger models at real Reynolds numbers. After the flap was retracted and the slat was deployed to isolate slat noise from other possible sources, the surface pressure distribution and the far-field sound pressure signals under different operating conditions were obtained by varying flow speed and angle of attack. The slat noise spectrum characteristics and the dependence of far-field noise on free stream velocity and airfoil incidence angle were acquired by the fast Fourier transform. The joint time-frequency analysis methods (short-time Fourier transform and continuous Morlet wavelet transform) were employed to process the far-field unsteady acoustic signal to identify the inherent physical mechanisms involved in the generation of multiple low-frequency tonal peaks emerging from the broadband component of the slat noise spectra. Results of the short-time Fourier transform (STFT) and wavelet analysis clearly showed that the dominant acoustic energy of these tonal noise was shared between the primary modes through rapid switching in time. Furthermore, the analysis results also indicated that an amplitude-modulation phenomenon exists in the dominant modes. The joint probability density function method was introduced to quantify the mode-switching phenomenon, and the results provided strong evidence that mode-switching occurs between the dominant modes of these low-frequency tones. [ABSTRACT FROM AUTHOR]

In this study, a coordinated control problem of power sources and actuators of a series-parallel hybrid electric vehicle on mode switching condition is addressed. There exist numerous nonlinear factors in the hybrid driveline system which induce system disturbance and will deteriorate the control performance on mode switching condition. However, coupled system nonlinearity is not taken into consideration for controller design on mode switching condition, which can lead to severe driveline oscillation and thus vehicle longitudinal jerk. For this reason, a disturbance observer and compensation method is introduced to resolve the control problem on mode switching condition. First, an analytic model of driveline torsional vibration considering disturbance brought by system nonlinearity is established and simplified for controller design. Based on the simplified model, a disturbance observer-sliding mode control strategy is proposed to suppress mode switching vibration. Numerical simulation is carried out to validate control performance of the DOB-SMC strategy. Simulation results demonstrate that DOB-SMC strategy has better ability to cancel the unwanted effects of disturbance brought by system nonlinearity compared with sliding mode control method, which can be regarded as an effective approach to attenuate vehicle longitudinal jerk and thus improve ride comfort on mode switching condition. [ABSTRACT FROM AUTHOR]

In this paper, the least squares method is used to determine the vertical height of the road space domain. Based on the road estimation method, the active suspension control mode switching model is constructed, and the dynamic characteristics of the vehicle in comfort, safety, and integrated modes are analyzed. The vibration signal is collected by the sensor, and the parameters such as vehicle driving conditions are solved for in reverse. A control strategy for multiple mode switching under different road surfaces and speeds is constructed. At the same time, the particle swarm optimization algorithm (PSO) is used to optimize the weight coefficients of LQR control under different modes, and the dynamic performance of vehicle driving is comprehensively analyzed. The test and simulation results show that the road estimation results under different speeds in the same road section are very close to the results obtained by the detection ruler method, and the overall error is less than 2%. Compared with the active suspension controlled by passive and traditional LQR, the multi-mode switching strategy can achieve a better balance between driving comfort and handling safety and stability, and also improve the driving experience more intelligently and comprehensively. [ABSTRACT FROM AUTHOR]

Aiming at the cruising range of electric vehicles, this paper proposes a control strategy for electric vehicle electromechanical composite braking mode switching based on motor braking force correction. The braking force of the motor is adjusted by factors such as braking intensity to improve the braking energy recovery, and the braking force distribution curve is designed considering the braking energy and braking safety and stability. The research results show the braking time, braking torque, and battery charge. The peak value of discharge current has been improved, and the braking energy recovery efficiency has increased by 9.17% and 3.32% respectively under different working conditions. Under different braking modes with an initial speed of 30 km h−1, the braking energy recovered by the battery has increased by 16.04 , 3.89, 9.63 kJ, the braking time and braking distance are also shorter, which highlights the superiority of this control strategy. [ABSTRACT FROM AUTHOR]

• A multifunctional direct expansion solar-air source heat pump system is proposed. • Comparison of performance to the system's own air source heat pump to establish switching logic. • The impact of the working temperature on the system performance in different season was studied. Solar energy is the most important renewable energy source for achieving carbon neutrality. The problem of steady and efficient operation must be promptly addressed due to the inconsistent and variable nature of solar energy. This research proposes a multifunctional heat pump using the R417A refrigerant, which combines a direct expansion solar heat pump (DXSHP) with an air source heat pump (ASHP), resulting in a direct expansion sola-air source heat pump (DX-S/AS-HP). The system could operate in three modes: combined cooling and heating, domestic water heating, and space heating. The performance of solar heat pump and air source heat pump in different modes was compared, and the switching logic of different modes was developed accordingly, and the performance of the system at different working temperatures was analyzed. The results demonstrate that in combined cooling and heating mode, the system's average comprehension coefficient of performance (COP) could approach 6.0. In DX-SHP mode, the average COP for domestic water heating and space heating is 3.94 and 4.25, respectively, which is greater than the air source heat pump in similar working conditions. Switching from DX-SHP to ASHP for domestic water heating is only necessary when solar irradiation is less than 300 W m −2, while switching to ASHP for space heating is only necessary when solar irradiation is absent. The greater the working temperature, the lower the COP. While the working temperature has little effect on thermal collecting efficiency. [ABSTRACT FROM AUTHOR]

High-lift airfoil slat and passive control noise were studied experimentally. A serrated slat with different parameters was installed on the trailing edge. Far-field noise was measured in an aeroacoustic wind tunnel using a microphone array. The results showed that the generation mechanism of discrete noise in slat noise was closely related to the feedback loop in the slat cove. As the Mach number increased, the pure tone frequency moved to the right, and the peak value gradually increased, whereas the pure tone frequency was not affected by the angle of attack. Serrated slats with different sawtooth angles had different effects on the aerodynamic noise of the slat, and the frequency of discrete noise also changed. The serrated slat needed to reach a certain value in the sawtooth angle to have the effect of noise reduction. When the sawtooth angle was large, the effect of noise increase also occurred, and there was a phenomenon of mode switching. The selection of the dominant mode was also determined by the time of modal occurrence. The smaller the sawtooth angle, the more obvious the effect of slat noise. When the sawtooth angle reached a certain angle, the discrete noise disappeared, and the noise reduction effect was basically the same. The serrated slat had little effect on the lift coefficient at a low angle of attack. [ABSTRACT FROM AUTHOR]

Although smart home has received wide attention in recent years, numerous scholars focus more on energy optimization strategy than energy dispatch hardware device (named energy router). Meanwhile, this energy router should have several features, i.e., high renewable energy utilization, energy multi-port and low volume. Thus, this paper designs a nine-port energy router regarding smart home and proposes a multimode hierarchical management strategy for this energy router. First, for the multi-port demand of wind, solar, storage and utilization, this paper presents a nine-port energy router to improve the renewable energy consumption and power supply flexibility. In addition, to reduce the volume of the energy router, a non-isolated AC/DC hybrid topology is constructed through embedding the integrated power electronic converters, which achieves the miniaturization of the energy router. In order to improve the renewable energy utilization rate, the decentralized module control is proposed for the components of energy router to provide the voltage and frequency support for system, and realizes the power sharing of distributed generations (DGs). Furthermore, the power exchange control with three-mode switching is proposed to guarantee the global energy flow balance under complex conditions. Eventually, the feasibility of the energy router is verified by the simulation and experiments. [ABSTRACT FROM AUTHOR]

This paper proposes a smooth mode-switching method based on state trajectory control to suppress overshoot and to shorten switching time during the mode switching of LLC-C resonant converters. First, the resonant tank trajectories of the LLC and LCCL are analyzed. Second, through a transformation of the resonant tank trajectory, the optimal trajectory of the resonant tank switching is drawn. Then the switching optimization cycle time is calculated by a diagram of the optimal trajectory. Thus, the PWM conversion to the optimization cycle is controlled directly when the switching signal comes. By this control method, a smooth transition of the resonant tank voltage and current between the two modes is achieved. At last, a prototype with a rated power of 500 W is built to check the feasibility and effectiveness of the proposed switching method. Experiment results show that the current surge of the resonant tank is reduced from 12.3 to 8.6 A when the state trajectory control is applied. The voltage surge of the second resonant capacitor in parallel is reduced from 906 to 712 V. Meanwhile, the switching time is shortened by 0.21 ms, which speeds up the switching process. [ABSTRACT FROM AUTHOR]

The gas purging states affect electricity output and energy storage capacity of unitized regenerative fuel cells. In this study, a model of unitized regenerative fuel cell is established. Cell voltages and operating temperatures influences on the dynamic distribution of thermal fluid during purging process and the discharge of residual liquid water in electrolytic cell mode are investigated. The motivation of the present study is better understanding the gas purging characteristics and its effect on reaction behaviors of unitized regenerative fuel cells. Simulation results reveal a significant influence of purging gas temperature on the water flooding and a great effect of operating voltage on the water diffusion. The operating temperature of electrolytic cell model almost has little effect on purging results at different cell temperature and the same purging gas temperature. When the purging gas temperature is changed, higher temperatures of cell and purging gas facilitate liquid water discharging out from the cell regions. In cell water flooding situation, when having large liquid content, the purging gas has little effects on the water expelling process. • EC temperature exhibits obscure effect on water transportation under same purging temperature. • Higher cell temperature and purging temperature facilitate expelling water from the cell. • Purging temperature hardly affects water expelling during the cell flooding processes. • Liquid water remaining in CLs is less under higher cell voltage conditions. [ABSTRACT FROM AUTHOR]

This paper describes a novel rate and rate-integrating mode-switchable axisymmetric gyroscope. A precession angle tracking algorithm is developed to enable the gyro to switch automatically between rate and rate-integrating modes at preset rate points through a digital control system within the gyro. We also propose a vibrating amplitude control method for the rate-integrating mode that directly extracts the angular rate output to ensure switching stability. In rate mode, the bias instability and angle random walk of the gyro reach 0.106°/h and 0.011°/√h, respectively. Additionally, an input range of over ±5000°/s is measured in rate-integrating mode. The scale factor nonlinearity reaches approximately 116 ppm over the full-scale range. The control system implements effective steering control of the gyroscope, with a switching delay of 10 ms from rate mode to rate-integrating mode and 100 ms from rate-integrating to rate mode. The proposed system actualizes a new type of gyroscope with high accuracy and a wide input range, which combines the benefits of rate and rate-integrating modes. [ABSTRACT FROM AUTHOR]

Large-stroke rapid motion is required in many industrial servo systems (e.g. pick-and-place applications), on which constraints of control input and motion speed are usually imposed. This paper presents a hybrid control scheme for large-stroke rapid motion in such systems. The controller resorts to the time-optimal control (TOC) for maximum acceleration initially and then switches into a linear control law to achieve smooth settling. A speed regulation stage is inserted in the tracking process to prevent violating the speed constraint. To tackle the unmeasured speed and unknown disturbance, an extended state observer (ESO) can be included in the controller. The controller is applied to a permanent magnet synchronous motor (PMSM) servo system for large-stroke position regulation. Digital simulation via MATLAB is conducted first, followed by an experimental verification using a TMS320F28335 board. The results confirm that the proposed controller can track a wide range of target references with desirable performance under speed constraint and load disturbance and has a competitive advantage over the popular active disturbance-rejection control (ADRC) scheme. [ABSTRACT FROM AUTHOR]

Oxygen side flow channel structures have significant influence on the dynamic response of relevant parameters in operation mode switching procedures of a unitized regenerative fuel cell. In this paper, an unsteady, non-isothermal, two-phase, two-dimensional unitized regenerative fuel cell model is established to study the dynamic response of two-phase species concentration distributions, current density distributions etc. when the cell mode swiches from the fuel cell mode to the electrolyzer when using orientational flow channel at the oxygen side. The influence of eight oxygen-side channels on the mode switching process is compared. Results show that the required time for each parameter reaching the stable state in the fuel cell mode is longer than the dynamic response time after switching to electrolytic cell mode when using orientational flow channels. In addition, different flow channel structures at the oxygen-side affect the time requirement for stabilizing each parameter during mode switching, while they do not change the characteristics of the stable state mode. • An un-steady state model of URFCs with orientational channels is developed. • Dynamic response of operation parameters vary under channel structure effects. • Decreasing channel depth percentage enhances cell performance. • Orientational channels facilitate stabilizing operation parameters of URFCs. [ABSTRACT FROM AUTHOR]

Summary: Energy is the cornerstone of the existence and development of modern society. The energy consumption continues to increase, and the ensuing environmental pollution and increasing lack of traditional energy sources have also become the world's most concerned issues. The emergence of new energy has eased the current unfavorable situation. Among them, distributed photovoltaic (PV) power generation has been favored because of its abundant resources and no geographical restrictions. However, due to the scattered construction of solar PV power stations, it is not easy to manage. Therefore, research and development of PV remote monitoring systems for unified monitoring and management of PV power stations. In addition, the problem of solar cell output efficiency is also an important reason that restricts the utilization of solar energy. Improving the output efficiency of the battery based on the existing solar cell conversion efficiency is also a focus of current research. Based on the above background, the research content of this article is the network communication monitoring system for distributed PV power generation systems. This article first conducts the overall design of the PV remote monitoring system, constructs the system's distributed design structure, and divides the underlying hardware part of the system into control modules and transmission. According to the application requirements, the STM32 series single‐chip microcomputer is selected as the controller of the system control module and the transmission module. The hardware circuit design and software process implementation of the system are studied to realize the data collection, MPPT control, and remote data transmission of the photovoltaic system. Features: Finally, through experimental simulation, it was verified that the light intensity increased from 600 to 800 W/m2, and the output current of the inverter increased accordingly. The output current of the distributed PV power generation system was directly proportional to the change of the light intensity. The designed system is feasible. [ABSTRACT FROM AUTHOR]

In this article, a new compound consequent-pole double-rotor electric machine (CCPDRM) is proposed for hybrid propulsion system application. First, the operating principle and harmonic components in CCPDRMs are elucidated. The winding factor theory for conventional permanent magnet (PM) electric machines is further extended and applied in CCPDRMs. Then, this improved theory is adopted to investigate the structure and winding scheme requirement of the proposed CCPDRMs. In addition, the control strategy for the proposed CCPDRM is established. By utilizing a parameter sweep method, the variation trends of CCPDRMs’ torque density with respect to various geometrical parameters are revealed. Based on this, the structure of CCPDRMs is optimized to acquire a better electromagnetic performance. Next, the proposed CCPDRM is compared with a conventional compound bipolar double-rotor electric machine (CBDRM). It is found that the improved topology has a similar torque density but a much higher PM utilization factor and a lower PM demagnetization risk when compared with the CBDRM. Finally, a prototype is manufactured and tested in different operating modes. Furthermore, various mode-switching processes are performed to emulate the practical driving cycle of hybrid transportation. Both steady-state and dynamic mode-switching experimental results prove the effectiveness of CCPDRMs. [ABSTRACT FROM AUTHOR]

A reversible solid oxide cell can work as a fuel cell (FC) or an electrolyzer cell (EC) with superior efficiency in a single device, which has the potential to become the core of energy conversion and storage. Since the redox reaction occurs at the three phase boundary in the porous electrode, the microstructure of which has a significant effect on the dynamic performance of the cell. Current research on porous electrodes mainly focuses on parametric and steady-state analysis but lacks studies on dynamic performance. In this study, we investigate the mass transfer process and dynamic performance of rSOC fuel electrodes by 3D reconstruction and artificial generation combined with a two-dimensional lattice Boltzmann method. The results show that the effective diffusion coefficients and cell performance of the XCT cross-sectional and random sphere method are much higher than those of the Gaussian filter and fiber rod structure. The change in H 2 concentration is larger for switching from FC to EC compared to switching from EC to FC, but the transient steady-state difference and relaxation time of the voltage is smaller. These results can be used as a reference for the design and optimization of the porous electrodes in reversible solid oxide cells. [ABSTRACT FROM AUTHOR]

• A mathematical model on rotating tapered anisotropic thin-walled biconvex beam is formulated for CAS layup. • The effect of bending-torsion coupling on the first few natural frequencies under rotation is presented. • Transverse shear, primary and secondary warping is considered in the model. • Stability of the modes are studied under high rotation speeds using modal assurance criteria. • Effects of centrifugal acceleration, warping and inertial warping on the dynamic behaviour are studied. Accurate modelling and prediction of dynamic characteristics for rotating thin-walled blades have drawn attention as it is an essential part of structural health monitoring for various engineering and civil applications such as wind turbine, helicopter and aeroplane blades. With the advent of structural tailoring techniques, various non-classical effects and couplings implicitly affecting the behaviour of such structures are yet not fully explored. In this regard, the present work proposes a numerical model for finding the free vibration characteristics of anisotropic tapered biconvex closed cross-section beam under rotating conditions. The model is derived based on energy method following the Ritz approximation. Circumferentially asymmetric stiffness (CAS) ply configuration is considered in order to study the impact of flexural torsional coupling on the vibration characteristics. Transverse shear effects, primary and secondary warping were also included in the current model. Mode switching phenomenon is dissected elaborately for the first few frequencies under rotating and nonrotating conditions. The impact of rotational effects like centrifugal acceleration, centrifugal warping, inertial warping on the first few frequencies is also demonstrated. An iterative technique is adapted to solve the equations having these rotational effects. Modal Assurance Criterion (MAC) is done in order to judge the consistency of the modes at different rotating speeds. [ABSTRACT FROM AUTHOR]

With excellent air-ground multi-mode movements, the vertical take-off and landing (VTOL) air-ground integrated vehicle can easily traverse complex terrains and maintain high energy efficiency. During movement, path planning plays an important role in achieving the autonomous operation of the vehicle, which faces the following difficulty. A short air-ground multi-mode path requires efficient planning, with proper judgment of the timing and position for mode switching. To address this difficulty, we propose a new path planning algorithm, named Dynamically Directed Graph Algorithm (DDGA). It can realize short path search in limited search nodes via dynamically extracting key search nodes in maps and forming a dynamically directed graph. To be specific, adjacent nodes of the first obstacle traversed by the connection line from the current search node to the destination are defined as key search nodes. As the current node changes, key search nodes are dynamically updated. The above key search nodes and the directed paths between them form a dynamically directed graph. Considering the air-ground movement capability, obstacle areas below maximum flight altitudes in maps are defined as pending flight areas. The directed paths traversing these areas are considered in the above graph. Besides the two-dimensional distance cost, flight altitude cost is added to the cost values of different directed paths. This cost contributes to judging the proper switching timing and position. Compared to other algorithms, DDGA can find short paths with fewer search nodes in multiple obstacle maps. It efficiently plans a short air-ground multi-mode path for the VTOL air-ground integrated vehicle. [ABSTRACT FROM AUTHOR]

We present an S-band high-power microwave (HPM) oscillator based on crossed-elliptical metamaterial (MTM) rings in a circular waveguide and powered by a high-power electron beam. Particle-in-cell (PIC) simulations demonstrate that when an output horn antenna of radius of 200 mm is used, an output power of 443 MW of a backward wave TE41 mode below its cutoff frequency at 2.80 GHz can be generated using a pulsed electron beam with a voltage of 990 kV and a current of 1.736 kA in a 1.8-T solenoidal magnetic field, corresponding to an electronic efficiency up to 26%. Meanwhile, another degenerate frequency of 2.80 GHz of a forward wave in the TM01 mode with an output power of 9 MW is also observed. When an output horn antenna of radius 150 mm is used, this crossed-elliptical MTM oscillator operates mainly in a forward TM01 mode at 2.80 GHz with an output power of 325 MW at an electronic efficiency of 19%, and at the same time, a backward wave TE41 mode below its cutoff frequency of 2.80 GHz with an output power of 8 MW can be observed. Simulations indicate that this slow-wave structure (SWS) consisting of a periodically crossed-elliptical MTM loaded circular waveguide can support degenerate mode operation. This result suggests that this configuration is favorable for mode switching and this work seeks to design a compact HPM source. [ABSTRACT FROM AUTHOR]

Transfer efficiency of a wireless power transfer (WPT) system is tightly related to the load, which varies greatly in a wide range during the charging process. Generally speaking, dual-sided control strategies are commonly applied to overcome the load variation and improve system efficiency. However, the system may suffer from hard switching, high control complexity, and auxiliary dc/dc converters. In this article, a dual-sided control strategy based on mode switching is proposed to approach an optimal load impedance, zero-voltage switching of all mosfets in WPT system, and a required output. In this control strategy, the output voltage of the inverter is adjusted in a wide range by switching the operation mode of the inverter to approach the optimal load impedance. The output current/voltage is regulated by the active rectifier control. Besides, a novel phase-locked method is proposed for the semi-bridgeless active rectifier control, which is simpler compared with the traditional phase-locked method. Finally, a 500-W prototype is built to verify the theoretical analysis, and the peak system efficiency of 93.9% is gained with k = 0.23. [ABSTRACT FROM AUTHOR]

To improve the mode switching quality of the power-split hybrid electric vehicle (PS-HEV), a compound torque coordinated control strategy is proposed. Aiming at the problem of engine dynamic response lag, the engine real-time torque estimator is designed, and then the torque ripple at the output end of the power coupling mechanism is reduced through the basic motor torque compensation. On this basis, considering the existence of non-ideal communication networks in actual vehicle control systems, the tremendous impact of communication network time delay and interruption on the mode switching stability and vehicle fuel consumption has been deeply revealed. Then the compound coordinated control strategy including the BP-smith predictive controller, motor torque change rate limiting module, network transmission mechanism with fixed communication priority and fault-tolerant torque coordinated control module is put forward and verified by simulation and hardware-in-the-loop test. The results show that the compound coordinated control strategy could still guarantee the system stability, mode switching smoothness and vehicle fuel economy under the interference of stochastic communication delay and interruption. [ABSTRACT FROM AUTHOR]

• The three-dimensional two-phase model for UR-PEMFC is established. • The accuracy of the model is validated through performance experiments. • The water–gas transport behavior of PEM-URFC during mode-switching is investigated. • Quantitative analysis of the FC mode startup dynamic response is conducted. • An optimized purging strategy benefiting FC startup and energy usage is proposed. The water–gas transport behavior of unitized regenerative proton exchange membrane fuel cell (UR-PEMFC) plays a key role in the rapid and stable mode-switching requirement. In this work, a UR-PEMFC is assembled and experimentally evaluated for its two modes performance. An experimentally validated three-dimensional two-phase model for UR-PEMFC is established, which considers transformed boundary conditions and multiphysics field governing equations, to investigate the water–gas two-phase transport behavior during mode-switching. The purge time, purge gas relative humidity (RH), and startup current density are used to quantify the dynamic response characteristics of the FC mode startup. The result shows that, compared with 0 % RH gas, after the 30 s purging, the average dissolved water content of catalyst-coated membrane (CCM) at 50 % RH and 100 % RH increased by 263.8 % and 365.9 %, respectively. Water saturation in the oxygen catalytic layer decreased by 4.14 % and 5.12 %, respectively. The FC startup exhibited the best response characteristics when purged for 28 s at 100 % RH and started with 0.1 A/cm2, the minimum voltage undershoot is 16 mV and the startup time is 37.8 s. Compared to the 0.2 A/cm2 and 0.3 A/cm2 startup, voltage undershoot decreased by 68.38 % and 134.9 %, and the startup time decreased by 8.21 % and 9.62 %, respectively. Moreover, with the purge gas RH between 52 % and 83 %, and the purge time between 16 s and 20 s, it is conducive to rapid and stable mode switching and efficient energy utilization. [ABSTRACT FROM AUTHOR]

This study proposes a unique multimodal underwater observation platform, called all-attitude multimode underwater vehicle (AMUV). AMUV integrates the movement capabilities of Argo buoy, Glider motion modes, and autonomous underwater vehicles (AUVs), enabling comprehensive underwater navigation. To explore the operational rules of individual modes and the changes in actuator and attitude during mode transitions, firstly, a dynamics model of AMUV is established, conforming the operating principles of the Argo buoy, Glider, and AUVs. Secondly, through open-loop simulations of different modes, the feasibility of the dynamic model is verified. Thirdly, through simulation experiments involving three typical mode switching processes, the mechanism of AMUV multi-mode switching is demonstrated. Finally, to examine the ability of the AMUV for multidimensional data acquisition, a simulation task focused on gathering multidimensional data of marine elements is designed. The simulation results indicate that the proposed AMUV has considerable potential for application in monitoring activities requiring the acquisition of multidimensional oceanographic data. • A novel multimode underwater vehicle capable of all-attitude motion was proposed. • A dynamic model suitable for AMUV was proposed and verified. • The variation law of the actuators and motion attitude in the process of mode switching was studied. • A multi-dimensional data acquisition task simulation experiment was conducted. [ABSTRACT FROM AUTHOR]

This study considers to asymptotically stabilise a switched linear system which transmits its feedback signals through a digital communication network. Such network can only provide a finite bit rate to represent feedback signals. In the concerned switched linear system, the mode mismatch may occur between the sensor and the controller due to the unknown switching time instants. It assumes that the mode switching is slow enough in the sense of combined dwell time and average dwell time, each individual mode is stabilisable and the available feedback bit rate is high enough, but still finite. In order to save network bandwidth resources, novel event‐triggering strategies are implemented, i.e. only when pre‐defined events are triggered, the system samples and transmits feedback signals. Then under the proposed event‐triggering strategies, a stabilising bit rate condition for the concerned switched linear system is derived. Moreover, this study proves that the obtained stabilising bit rate under the proposed event‐triggering strategies can be strictly lower than the stabilising bit rate required by the earlier work based on periodic sampling. Simulations are done to illustrate the bit rate superiority of the proposed event‐triggering strategies. [ABSTRACT FROM AUTHOR]

Grid-connected converters are expected to provide ancillary service utilising their spare capacities during operation. This study proposes a novel control strategy for clustered micro-grids to compensate voltage-unbalance of the power grid at the point of common coupling. Every micro-grid are interfaced to the power grid through a micro-grid inverter (MGI). All MGIs are designed independently with positive-sequence (PS) and negative-sequence (NS) control loops. Every micro-grid autonomously performs grid synchronisation and mode switching. After grid-connecting, a dynamic capacity allocation method is proposed for the MGIs to optimise its PS and NS capacity according to the grid voltage unbalance factor. Furthermore, a V–I droop control of the NS control loops is developed, with which each MGI can regulate its NS current according to the NS voltage in a droop manner. With the proposed method, all micro-grids participate in grid voltage unbalance compensation according to their own potential capacities without communications. Finally, a micro-grid cluster model with three micro-grids is built on Matlab/Simulink to validate the proposed control strategy. [ABSTRACT FROM AUTHOR]

Grid‐connected converters are expected to provide ancillary service utilising their spare capacities during operation. This study proposes a novel control strategy for clustered micro‐grids to compensate voltage‐unbalance of the power grid at the point of common coupling. Every micro‐grid are interfaced to the power grid through a micro‐grid inverter (MGI). All MGIs are designed independently with positive‐sequence (PS) and negative‐sequence (NS) control loops. Every micro‐grid autonomously performs grid synchronisation and mode switching. After grid‐connecting, a dynamic capacity allocation method is proposed for the MGIs to optimise its PS and NS capacity according to the grid voltage unbalance factor. Furthermore, a V–I droop control of the NS control loops is developed, with which each MGI can regulate its NS current according to the NS voltage in a droop manner. With the proposed method, all micro‐grids participate in grid voltage unbalance compensation according to their own potential capacities without communications. Finally, a micro‐grid cluster model with three micro‐grids is built on Matlab/Simulink to validate the proposed control strategy. [ABSTRACT FROM AUTHOR]

The existence of operational dead zone during mode switching in noninverting buck–boost converter results in oscillation of the output voltage and instability of the system during high power operation. The mechanism and effect of the operational dead zone are analyzed, the conditions that need to be met when eliminating the operational dead zone are researched, and a multimode smooth switching control strategy which can completely eliminate the operational dead zone is proposed. The converter works with three operating modes, the method of theoretical analysis combined with experimental correction is used to set the mode switching parameters, to ensure that the actual voltage gains of the converter on both sides of the mode switching points are equal. A single-degree-of-freedom buck–boost mode is designed to replace the pass-through mode to maintain the converter's stable output. And the converter's operating power level and overall power transmission efficiency can be improved, when the control parameters are designed to reduce the interval length of the boost mode and the single-degree-of-freedom buck–boost mode. Finally, a 700-W experimental prototype is built to verify the effectiveness of the proposed solution. [ABSTRACT FROM AUTHOR]

Developing an intelligent robot platform that has multiple motion modes and can actively adjust the motion mode according to an operation situation is necessary in resolving the inability of single-mode robots to adapt completely to complex environments. In this study, we designed a robot that has multiple motion modes and can switch freely in these existing modes. The robot has the following modes: Four-legged walking, two-legged walking, pulse scrolling, and crawler movement. In the robot's design, these modes are not just simple mechanisms involving superposition and motion switching. These modes involve a degree of freedom in reuse, thereby reducing the number of drives and obtaining a compact structure while achieving a coherent transition of each action mode. For higher load ratios, motion continuity are increased. The robot platform can balance itself during movement by adjusting its own mechanism or providing additional force and change its shape and posture over some obstacles by adjusting its own mechanism. [ABSTRACT FROM AUTHOR]

To improve the real-time capability, adaptivity, and efficiency of the energy management strategy in the actual driving cycle, a real-time energy management strategy is investigated for commute hybrid electric vehicles, which integrates mode switching with variable threshold and adaptive equivalent consumption minimization strategy. The proposed strategy includes offline and online parts. In the offline part based on the historical traffic data on the route of the commute vehicle, particle swarm optimization is applied to optimize all the thresholds of mode switching, equivalence factor of the equivalent consumption minimization strategy, and the engine torque and speed at the engine-alone propelling mode so as to establish their mappings on the battery state of charge and power demand. In the online part, the established mappings are involved in the energy management supervisor to generate timely appropriate mode switching signals, and an adaptive equivalence factor for instantaneous optimization equivalent consumption minimization strategy and the optimal engine torque and speed at engine-alone propelling mode. To fully demonstrate the effectiveness of the proposed strategy, the simulation results and comparison with some other strategies and the benchmark dynamic programming strategy are presented by implementing the strategies on the GT-SUITE test platform. The comparison result indicates that the control effect of the proposed energy management strategy is much nearer to that of the benchmark dynamic programming than those of other strategies (the rule-based control, the conventional equivalent consumption minimization strategy, the adaptive equivalent consumption minimization strategy, the rule-based-equivalent consumption minimization strategy, and the stochastic dynamic programming strategy) with the respective improvement in fuel efficiency by 25.9%, 13.25%, 4.6%, 1.32%, and 1.13%. [ABSTRACT FROM AUTHOR]

In this communication, an orbital angular momentum (OAM) mode-reconfigurable antenna based on a uniform circular array (UCA) is presented. To realize multiple switchable operating states while maintaining a relatively simple structure, a simplified feeding scheme is developed. By introducing a set of optimal reference phases for different OAM modes, the tunable phase states for the entire array are degenerated, which leads to a reduction in the total number of required phase states. Then, the excitation phases are decomposed into two parts and generated by the reconfigurable radiators and reconfigurable feed network, respectively. In addition, p-i-n diodes are selected as switches to control the operating states of the radiators and feed network. Therefore, OAM-mode switching capability can be obtained by altering the direct current (dc) bias configurations of the diodes. The antenna design is validated by both simulation and measurement. Results indicate that the proposed eight-element array antenna produces six operating states corresponding to OAM modes l = ±1, ±2, and ±3. The measured overlapped band among the states with $\vert \text{S}_{\mathbf {11}}\vert < -15$ dB covers 2.33–2.73 GHz. Moreover, the proposed antenna also features the advantages of easy fabrication and low cost. [ABSTRACT FROM AUTHOR]

Unitized regenerative fuel cells operate in not only fuel cell but also water electrolyzer mode. Heat management is important for the stable operation of unitized regenerative fuel cells. In this work, temperature and heat flux on the surface of the gas diffusion layer at the hydrogen side of a unitized regenerative fuel cell are experimentally measured using thin film sensors. Four pairs of sensors with good linear relation coefficient are inserted in the unitized regenerative fuel cell. The variation of temperature and heat flux on the gas diffusion layer surface during mode switching is obtained. The effect of mode switching on temperature and heat flux in the unitized regenerative fuel cell is analyzed. Experimental results show that reactant switching significantly affects temperature and heat flux. Reactant switching also causes decreased temperature and variation in heat flux. Despite of the decrease of temperature caused by the low-temperature water, the temperature increases with the operation of the URFC. When the effect of reactant switching is ignored, temperature is further found to increase in fuel cell and water electrolyzer modes, and heat flux remains relatively stable. • Thin film sensors are inserted in a URFC to measure temperature and heat flux. • Reactants switching has significant effect on the temperature and heat flux. • Temperature increases and heat flux maintains steady in both FC and WE modes. [ABSTRACT FROM AUTHOR]

Summary: With the occurrence of reversible electrochemical reactions, mode switching considerably affects the electric performance of unitized regenerative fuel cells (URFCs) owing to the complicated mass and heat transfer. Although limited researches have been done, no such studies on mass and heat transfer through a three‐dimensional view are envisioned during mode switching. A three‐dimensional full‐cell model was developed and validated to study the dynamic characteristics of a proton exchange membrane‐based URFC during mode switching. Mode switching was performed by changing operation voltage from 0.60 to 1.65 V. Results showed that species and heat transfer affect the electric performance of the cell during mode switching, especially through the third dimensional. Local water starvation occurs on oxygen side catalyst layer and thus results in slight reduction on current density and hydrogen generation. Restricted to heat transfer capacity through ribs, heat transfer process adds total response time in URFCs. Heat flux and surface heat transfer coefficient are forecasted on the hydrogen and oxygen sides. A total time of 4 seconds is essential for URFC reaching a new relative balanced state. [ABSTRACT FROM AUTHOR]

Highlights • A 3D simulation is performed to study cell performance during mode switching. • Local water starvation causes reduction on current density and hydrogen generation. • High inlet velocity and low fuel cell voltage effectively improve cell performance. Abstract Mode switching is essential in a unitized regenerative fuel cell system. The switching of electricity, reactants, and reversible electrochemical reactions occurs, thereby affecting cell performance. During model switching, insufficient reactant supply may cause severe concentration, especially along the width of the catalyst layer which is not currently considered in a low-dimensional model. To fill this gap, a three-dimensional simulation in a proton exchange membrane unitized regenerative fuel cell is performed and validated to investigate the dynamic responses of current density and mass transfer. Results certify that reductions on current density and hydrogen generation are severe, as the cell is switched to a high electrolysis voltage. The analysis of species transfer along the width of the porous layers indicates that the deterioration is attributed to the occurrence of serious concentration polarization which is caused by the severe local water starvation on the catalyst layer, especially below the rib. A high inlet velocity for reactant and low fuel cell voltage are conducive for remitting local water starvation to improve cell performance effectively. However, a slight deterioration cannot be avoided completely before the water supply arrives, which is limited by the high rates of electrochemical reactions at a high electrolysis voltage. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The energy efficiency of hydraulic manipulator is low due to single mode operation. • A novel system is presented to extend multiple modes of cylinder, valve and pump. • Efficient mode configuration and multi-variable controller are both designed. • Inlet, outlet and potential energy losses are decreased with precise motion tracking. • Energy-saving ratios reach 25.8–35.3% with a three-joint manipulator in excavator. Abstract The conventional hydraulic drive system for a heavy-load mobile manipulator is usually operated under single mode, such that both inlet/outlet and potential energy losses are large to lower the energy efficiency. In this paper, a novel electro-hydraulic drive system is presented to improve energy efficiency. Extended control degrees of freedom are obtained utilizing the independent metering valve and electronic controlled pump. Then, multiple operating modes are carried out pertaining to the cylinder, valve, and pump. To achieve both optimal energy efficiency and precise motion tracking, both multi-mode switching and multi-variable controller are designed to accommodate with time-varying and uncertain load characteristics. As a consequence, the inlet, outlet, and potential energy losses can be decreased simultaneously. The experimental validation is conducted by using a three-joint manipulator in a 2 t excavator. A duty cycle of movement including all three actuators and covering full load quadrants is used to evaluate the efficiency improvement. Compared with the conventional load sensing system, the proposed multi-mode switching system using the pump pressure with valve meter-in control mode yields a 25.8% energy-saving ratio. Furthermore, the pump flow with valve mete-out control mode yields a 35.3% energy-saving ratio. Using this combined control mode, higher efficiency can be obtained due to the minimum inlet losses, but faster dynamic response together with higher overshoot will appear. It is proved that the energy efficiency is improved, while the motion tracking performance is not degraded by introducing the multi-mode switching. [ABSTRACT FROM AUTHOR]

Highlights • Gas purge on URFC voltage during mode switching from EC to FC mode is studied. • High purge gas flow rate is preferred than long purge time during gas purge. • Gas purging in hydrogen side is essential for mode switching from EC to FC mode. • FC mode startup current and EC mode operation current affect mode switching. Abstract In unitized regenerative fuel cells, residual water at the end of electrolysis cell mode greatly affects the cell voltage during mode switching from electrolysis cell to fuel cell mode. Therefore, the residual water removing is essential to realize the mode switching, which requires the knowledge on gas purge effect on cell voltage dynamic response. In this study, gas purge effect in oxygen and hydrogen sides on cell voltage dynamic response is investigated, respectively. In addition, the effects of fuel cell mode startup current density and electrolysis cell mode operating current density are analyzed. The results show that: the increases of gas purging time and purging gas flow rate promote the mode switching from electrolysis cell to fuel cell modes. High flow rate of purging gas is preferred than long gas purging time during mode switching when the same amount of purging gas is used. In addition, gas purging in hydrogen side is necessary. The influence of residual water in hydrogen side increases with the startup current density of FC mode, and long purging time is required for high startup current density of FC mode. Electrolysis cell mode operating current density increase leads fuel cell mode performance decrease under the same gas purge condition. [ABSTRACT FROM AUTHOR]

Abstract The process during mode switching from electrolysis cell mode to fuel cell mode is unclear. In this work, dynamic responses under different mode switching strategies from electrolysis cell mode to fuel cell mode are investigated using a unitized regenerative fuel cell with an oxygen side transparent window. Effects of time interval between reactant and current switching, gas flow rate, fuel cell mode startup current density, and gas purging time on the cell voltage are studied. The experimental results indicate that pre-reactant switching is an effective way to consume the residual water at the end of an electrolysis cell mode, and a sufficient time interval between reactant and current transition can promote the smooth mode switching under low current density. Oxygen flow rate increase can promote smooth startup of FC mode when the time interval between reactants and current transitions is not long enough, and hydrogen flow rate has little effect on the mode switching from EC mode to FC mode. In addition, the method, combining electrolysis reaction and gas purge, can efficiently eliminate the residual water and prevent water-starved condition when FC mode starts up. Highlights • Influence factors on mode switching from EC to FC modes are experimentally tested. • Pre-reactant switching is suitable for FC mode startup under low current density. • Oxygen flow rate increase promotes mode switching and hydrogen flow rate has no help. • Combine electrolysis reactions and gas purge is an efficient way for mode switching. [ABSTRACT FROM AUTHOR]

Summary: In this work, a proton exchange membrane unitized regenerative fuel cell with a 25 cm2 active area and a transparent window was designed to study the influence of mode switching from the fuel cell mode to the electrolysis cell mode on the cell voltage and the gas‐liquid two‐phase flow behaviors in the oxygen flow channels. Results indicate that: the growth rate of electrolysis cell voltage before the water pumped to the oxygen flow channels decreases with the increase of the fuel cell current density; while the growth rate of electrolysis cell voltage before the water pumped to the oxygen flow channels increases with the cell temperature; the voltage of electrolysis cell mode before the water pumped to the oxygen flow channels decreases with the increase of water flow rate; the different voltage reduction speeds are attributed to the different water flow rates. The water temperature has an obscure influence on the cell voltage of electrolysis cell mode before the water pumped to the oxygen flow channels. [ABSTRACT FROM AUTHOR]

Summary: Mode switching between fuel cell and water electrolyzer of a unitized regenerative fuel cell alters two‐phase flow dynamics in the channels. To fully understand the mode switching, the observation of two‐phase flow is necessary. In this work, experiments are conducted to investigate the two‐phase flow in the flow field of a unitized regenerative fuel cell during mode switching. A transparent window is assembled at the oxygen side to allow a direct view of the serpentine flow field. The two‐phase flow are captured by a high‐speed camera. Water has a significant effect on the mode switching. The switching from water electrolyzer to fuel cell is difficult because of the flooding problem. High temperature causes insufficient water in water electrolyzer mode without water supply and membrane dehydration in fuel cell mode. The voltage in fuel cell mode decreases more rapidly with fuel cell current density during mode switching. [ABSTRACT FROM AUTHOR]

We report an all-fiber ring laser that emits linearly polarized (LP) modes based on the intracavity all-fiber mode multiplexer/demultiplexer (MUX/DEMUX). Multiple LP modes in ring fiber laser are generated by taking advantage of mode MUX/DEMUX. The all-fiber mode MUX/DEMUX are composed of cascaded mode-selective couplers (MSCs). The output lasing mode of the ring fiber laser can be switched among the three lowest-order LP modes by employing combination of a mode MUX and a simple N × 1 optical switch. The slope efficiencies, optical spectra and mode profiles are measured. [ABSTRACT FROM AUTHOR]

In this paper, the problem of joint mode switching and power adaptation is studied for simultaneous wireless information and power transfer (SWIPT) over a fading channel. The receiver dynamically switches between information decoding (ID) and energy harvesting (EH) modes while the transmitter dynamically adapts the transmit power. Considering the nonlinearity of practical EH circuits, a realistic nonlinear EH model is adopted rather than the idealistic linear EH model. To characterize the ultimate performance tradeoff between ID and EH, an optimization problem is formulated to maximize the average harvested energy under the constraints on the average achievable rate and the average transmit power, which is a nonconvex and combinatorial problem. To solve this problem, first, the optimal power adaptation scheme for the nonlinear EH receiver that operates only in the EH mode is proposed. Using this scheme, the jointly optimal solution for the mode switching and power adaptation is then derived. By comparing the obtained results to the existing results, various useful and interesting insights into the optimized SWIPT system with nonlinear EH are presented. An important insight into the impact of nonlinear EH is that, to exploit the high energy conversion efficiency of the nonlinear circuit, the EH mode has to be selected only in the moderate range of channel gains. Also, in the EH mode, the power has to be adapted to the short-term power threshold only for the moderate channel gains. [ABSTRACT FROM AUTHOR]

Industrial combustion systems such as power generation gas turbines, rocket motors, furnaces and boilers often face the problem of large-amplitude self-excited pressure oscillations that occur due to the onset of thermoacoustic instability. To prevent the onset of such instability, understanding the effects of fuel–air equivalence ratio ϕ , and fuel flow rate V f on self-excited nonlinear thermoacoustic oscillations is of fundamental and practical importance. Experimental investigation of the roles of these parameters on triggering thermoacoustic instability in a swirl combustor has received very little attention. In this work, we design a swirling thermocoustic combustor and conduct a series of experimental tests. Autocorrelation and recurrence analysis of phase space trajectories reconstructed from the acoustic pressure time trace are performed. These experimental tests allow us to study the effect of the fuel–air equivalence ratio ϕ on the onset of thermoacoustic instability by varying the fuel volume flow rate V f . We demonstrate that the fuel volume flow rate and the equivalence ratio play different but critical roles on generating thermoacoustic instability at different frequencies and amplitudes. Maximum sound pressure level can be as high as 135 dB. In addition, mode switching, (i.e. frequency swap) is found to occur between approximately ω 3 ≈ 510 Hz and ω 1 ≈ 170 Hz, depending on the equivalence ratio ϕ. Furthermore, the dominant frequency corresponding to the maximum amplitude is shown to be shifted by approximately 20%, as the fuel flow rate V f is increased and the combustion condition is changed from lean to rich. These findings are quite useful for designing a feedback control strategy to stabilize an unstable combustor. The present work opens up an applicable means to design a stable swirling combustor. [ABSTRACT FROM AUTHOR]

This article presents a mode identification method for structural optimization with global mode constraints to overcome the mode switching problem. In engineering design, the natural frequencies of global vibrations for a complex structure, the orders of which would not be constant in optimization loops, are usually very difficult to constrain. In this case, an incorrect constraint may lead to an unreliable design. A mode identification technique based on modal effective mass fraction is implemented to track the global modes such that the constraints will be updated subsequently and the optimizer can run correctly. A study case with comparison to traditional modal assurance criterion approaches demonstrates the advantages of this technique. An optimization framework has been developed with thenewproposed mathematical model.Twonumerical optimization examples, of a space truss and a simplified satellite structure are presented to demonstrate the feasibility and applicability of this process. [ABSTRACT FROM AUTHOR]

Universal concerns about degradation in ambient environment, stringent emission legislations, depletion of petroleum reserves, security of fuel supply and global warming have motivated research and development of engines operating on alternative combustion concepts, which also have capability of using renewable as well as conventional fuels. Low temperature combustion (LTC) is an advanced combustion concept for internal combustion (IC) engines, which has attracted global attention in recent years. LTC concept is different from the conventional spark ignition (SI) combustion as well as compression ignition (CI) diffusion combustion concepts. LTC technology offers prominent benefits in terms of simultaneous reduction of both oxides of nitrogen (NO x ) and particulate matter (PM), in addition to reduction in specific fuel consumption (SFC). However, controlling ignition timing and combustion rate are primary challenges to be tackled before LTC technology can be implemented in automotive engines commercially. This review covers fundamental aspects of development of LTC engines and its evolution, historical background and origin of LTC concept, encompassing LTC principle, its advantages, challenges and prospects. Detailed insights into preparation of homogeneous charge by external and internal measures for mineral diesel and gasoline like fuels are covered. Fuel requirements and fuel induction system design aspect for LTC engines are also discussed. Combustion characteristics of LTC engines including combustion chemistry, heat release rate (HRR), combustion duration, knock characteristics, high load limit, fuel conversion efficiencies and combustion instability are summarized. Emission characteristics are reviewed along with insights into PM and NO x emissions from LTC engines. Finally, different strategies for controlling combustion rate and combustion timings for gasoline and mineral diesel like fuels are discussed, showing the way forward for this technology in future towards its commercialization. [ABSTRACT FROM AUTHOR]

[Display omitted] • The electricity and mass transfer of URFC are analyzed by experiments combined with simulation methods. • T -type flow channels are proposed and the effects on performance are comparatively discussed. • Start-up performance of URFC is various when using channels having different cross-sections. • Two-phase mass transportation inside URFCs is various and related with performance changing. Different flow channel structures of unitized regenerative fuel cells have great effects on the flow process of reactive gas, liquid product and flowing purge gas inside channels and the transport process of them in the porous media layer. In this study, the unitized regenerative fuel cell with three different kinds of channel structures are designed and manufactured based on the numerical simulation. By utilizing the unitized regenerative fuel cell testing set-up, the output electricity performance test of the single cell in the fuel cell mode, electrolytic cell mode and mode switching process are realized, and effective verification data are provided for the two-phase model verification of unitized regenerative fuel cells. The results show that different channel configurations result in various performance behaviors during different procedures of the cell. Using the channel having 1 mm square cross-section structures can perform better start-up performance, compared to the T -wide and T -narrow section channels. When entering into electrolysis cell mode, compared to the cell with T -section channels, the output performance of the cell constructed with 1 mm square section channel is decreased obviously at the initial stage of start-up because of the residual water affecting. The present experiments combined with simulation works facilitate better understanding how the performance and two-phase species changing at the operating procedures of unitized regenerative fuel cells with different flow channels. [ABSTRACT FROM AUTHOR]

The bike-sharing system has advanced urban transportation by enabling more flexibility for short-distance travel. However, there has been a paucity of knowledge about the relationship between the bike-sharing system and the public transit system. In this paper, we solicit a one-year biking trip data consisting of approximately 17 million trips from Citi Bike, the largest dock-based bike-sharing system in New York City. Then, we analyze the bike usage patterns by applying the K-means clustering method based on three clustering variables: the start trips, end trips, and station empty status. Lastly, we identify three relationships between bike-sharing and public transit: competition, integration, and complementation. The results show that the bike-sharing system is well integrated with the public transit system to enhance urban ridership and solve the "last mile problem." The paper also portrays the unequal distribution landscape of the bike-sharing system, which is concentrated on transportation hubs but has relatively limited coverage in low- to medium-density residential areas. Thus, the study would help stakeholders to better understand the different roles that the bike-sharing system plays in the city. It can guide the development and expansion of the system to improve spatial equity in urban and transportation planning. [ABSTRACT FROM AUTHOR]

Integrated oscillators with octave frequency tuning range (FTR) are desirable for wireless transceivers supporting multiple frequency bands. In this paper, we describe a wide-FTR CMOS voltage-controlled oscillator (VCO) based on a novel area-efficient series resonator mode-switching scheme that preserves resonator quality factor $Q$ across the entire octave tuning range. This allows the CMOS VCO to simultaneously achieving wide FTR, area efficiency, and low phase noise, demonstrating state-of-the-art figure of merit (FoM) for > 10-GHz octave-tuning range VCOs. We also analyze the relationship between $Q$ and FTR across common resonator band-switching schemes, quantifying performance limits and highlighting the benefits of using mode-switching for wide-FTR VCOs. The proposed approach is demonstrated through a 6.4–14-GHz (74.6% FTR) VCO implemented in 65-nm CMOS that achieves 186–188-dB VCO FoM, demonstrating good FoM across the entire FTR. The scalability of this approach toward achieving even larger FTR is also demonstrated by a triple-mode 2.2–8.7-GHz (119% FTR) CMOS VCO. Area efficiency of the proposed mode-switching scheme is demonstrated by the state-of-the-art 197-dB FoM area achieved by the 14-GHz VCO. [ABSTRACT FROM AUTHOR]

We propose and experimentally demonstrate an all-fiber optical mode switching structure supporting independent switching, exchanging, adding, and dropping functionalities in which each mode can be switched individually. The mode switching structure consists of cascaded mode selective couplers (MSCs) capable of exciting and selecting specific higher order modes in few-mode fibers with high efficiency and one multiport optical switch routing the independent spatial modes to their destinations. The data carried on three different spatial modes can be switched, exchanged, added, and dropped through this all-fiber structure. For this experimental demonstration, optical on-off-keying (OOK) signals at 10-Gb/s carried on three spatial modes are successfully processed with open and clear eye diagrams. The mode switch exhibits power penalties of less than 3.1 dB after through operation, less than 2.7 dB after exchange operation, less than 2.8 dB after switching operation, and less than 1.6 dB after mode adding and dropping operations at the bit-error rate (BER) of 10-3, while all three channels carried on three spatial modes are simultaneously routed. The proposed structure, compatible with current optical switching networks based on single-mode fibers, can potentially be used to expand the switching scalability in advanced and flexible short-reach mode-division multiplexing-based networks. [ABSTRACT FROM AUTHOR]

Knowledge concerning the complicated changes of mass and heat transfer is desired to improve the performance and durability of unitized regenerative fuel cells (URFCs). In this study, a transient, non-isothermal, single-phase, and multi-physics mathematical model for a URFC based on the proton exchange membrane is generated to investigate transient responses in the process of operation mode switching from fuel cell (FC) to electrolysis cell (EC). Various heat generation mechanisms, including Joule heat, reaction heat, and the heat attributed to activation polarizations, have been considered in the transient model coupled with electrochemical reaction and mass transfer in porous electrodes. The polarization curves of the steady-state models are validated by experimental data in the literatures. Numerical results reveal that current density, gas mass fractions, and temperature suddenly change with the sudden change of operating voltage in the mode switching process. The response time of temperature is longer than that of current density and gas mass fractions. In both FC and EC modes, the cell temperature and gradient of gas mass fraction in the oxygen side are larger than that in the hydrogen side. The temperature difference of the entire cell is less than 1.5 K. The highest temperature appears at oxygen-side catalyst layer under the FC mode and at membrane under a more stable EC mode. The cell is exothermic all the time. These dynamic responses and phenomena have important implications for heat analysis and provide proven guidelines for the improvement of URFCs mode switching. [ABSTRACT FROM AUTHOR]

In this study, design and analysis of a mode-switching vertical take-off and landing (VTOL) unmanned aerial vehicle (UAV) with level flight capability is considered. The design of the platform includes both multirotor and fixed-wing (FW) conventional airplane structures; therefore named as VTOL-FW. The aircraft is modeled using aerodynamical principles including post-stall conditions. Trim conditions are obtained by solving constrained optimization problems. Linear analysis techniques are utilized for trim conditions in examining stability and controllability. The proposed method for control includes implementation of multirotor and airplane mode controllers and an algorithm to switch between them in achieving transitions between VTOL and FW flight modes. Thus, VTOL-FW UAV's flight characteristics are expected to be improved by enlarging operational flight envelope through enabling mode-switching, agile maneuvers, and increasing survivability. Simulations and flight tests showed that VTOL-FW UAV demonstrates multirotor and airplane flight characteristics with extra benefits. [ABSTRACT FROM AUTHOR]