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Proton-conducting solid oxide fuel cells (P–SOFCs) are promising energy conversion devices that convert chemical energy directly to electrical energy. P–SOFCs have attracted significant attention in the past few years because of their superiority over the oxygen-ion-conducting solid oxide fuel cells (O–SOFCs) in terms of better feasibility of efficient operation at lower temperatures, non-dilution of fuel at the anode, and higher theoretical efficiency. This review focuses on the scientometric analysis of 1008 quality articles retrieved from the Scopus database. The historical trends and progress in P–SOFCs are presented starting from the inception of the demonstration of the concept of proton conductivity in solid oxide fuel cells from 1986 to 2021. Furthermore, the notable achievements in the material development of various components of P–SOFC are expounded. The scientometric analysis reveals that only 28% of the countries in the world are involved in P–SOFC research and the National Natural Science Foundation of China is the top featured funding sponsor for many research studies related to P–SOFC development. This article can serve as an easy guide for P–SOFC research enthusiasts to navigate through the overview of this research area and identify potential collaborators, funding sponsors, most impactful researchers, countries, and articles.

Solid oxide fuel cells (SOFCs) have the potential to replace conventional thermal power plants due to their high efficiency and low emission. As the activation loss of the cathode usually limits the SOFC performance, the development of high-performance and durable cathode materials has received extensive attention in the past few decades. It is therefore essential to keep track of the research progress to identify significant research gaps and future directions. In this study, we retrieved the bibliometric data of 1101 cutting-edge research articles focused on cathode development for SOFCs and conducted a scientometric review. Even though significant research in cathode development for intermediate to low temperature SOFCs started in the 1990s, significant growth in the research output appeared in the year 2000 and remarkably continued till 2010 before exhibiting a sinusoidal pattern. Overall, there is a record of average decadal progress in this research area. We found that only a small percentage of countries in the world (i.e., about 29%) are involved in the research for the development of intermediate to low temperature SOFC cathodes. A highlight of core assessment criteria for cathode developments is presented with a summary of the most recent articles (i.e., including those in 2021). This paper can help early-stage researchers, journal outlets, governments, funding authorities, and investors understand the current progress in this area and how close researchers are to a breakthrough that could lead to the commercialization of this emerging technology.

We conduct a systematic search for quasars with periodic variations from the archival photometric data of the Zwicky Transient Facility (ZTF) by cross matching with the quasar catalogues of the Sloan Digital Sky Survey and Véron-Cetty & Véron. We first select out primitive periodic candidates using the methods of the generalized Lomb-Scargle periodogram and auto-correlation function, and then estimate the false-alarm probability of the periodicity and calculate the Bayesian information criterion to compare between periodic and purely stochastic models. As such, we finally identify a sample of 127 candidates with the most significant periodic variations out of 143,700 quasars. This is the largest periodic quasar sample so far, thus providing a useful guiding sample for studying origins of quasar periodicity considering the moderate sampling rate and high-quality photometry of the ZTF data. We summarize the basic properties of the sample and briefly discuss the implications., submitted to MNRAS. Comments welcome

Energy consumption is an important comprehensive index of the hydraulic hexapod robot (HHR). In this paper, the kinematics model and the hydraulic system energy consumption model of HHR are established. In order to reduce the energy consumption, a centroid fluctuation gait that adds the movement of the centroid in the vertical direction is proposed. Then the gait parameters such as step length, gait cycle, average centroid height, centroid fluctuation height, and phase that influence the energy consumption are studied which could provide a theoretical basis for parameter optimization. In the same gait parameters, compared with using constant height gait, the energy consumption of HHR using centroid fluctuation gait is generally reduced, and the maximum energy saving can be more than 10%. Finally, a virtual prototype is used to verify the effectiveness of the proposed methods.

In this third paper of the series reporting on the reverberation mapping (RM) campaign of active galactic nuclei with asymmetric H$β$ emission-line profiles, we present results for 15 Palomar-Green (PG) quasars using spectra obtained between the end of 2016 to May 2021. This campaign combines long time spans with relatively high cadence. For 8 objects, both the time lags obtained from the entire light curves and the measurements from individual observing seasons are provided. Reverberation mapping of 9 of our targets has been attempted for the first time, while the results for 6 others can be compared with previous campaigns. We measure the H$β$ time lags over periods of years and estimate their black hole masses. The long duration of the campaign enables us to investigate their broad line region (BLR) geometry and kinematics for different years by using velocity-resolved lags, which demonstrate signatures of diverse BLR geometry and kinematics. The BLR geometry and kinematics of individual objects are discussed. In this sample, the BLR kinematics of Keplerian/virialized motion and inflow is more common than outflow., 35 pages, 18 figures, 8 tables, accepted for publication in The Astrophysical Journal Supplement

Horizontal well and large-scale hydraulic fracturing are the main technical means for tight gas development at present. However, tight gas reservoirs are characterized by strong heterogeneity, and different types of gas Wells have different production characteristics and pressure propagation laws. In view of the above problems, based on the physical characteristics and reservoir reconstruction evaluation of tight gas reservoir in GAS Reservoir A in Sichuan Basin, three types of reservoir hydraulic fracture models and numerical simulation models were generated by using numerical simulation method, and the production dynamic prediction and pressure wave propagation law were studied. The simulation results show that: (1) In the beginning of production, the deflated area is mainly hydraulic fracture reconstruction area, and the drainage radius of all kinds of gas Wells expands at similar speed; (2) When the drainage range is expanded in the untransformed area, the dimensionless drainage radius expansion speed of gas well is positively correlated with the reservoir physical property. The dimensionless drainage radius and drainage area of class I and II horizontal Wells are relatively faster, while that of Class III Wells is slightly slower.

This paper presents an embedded controller for the quadruped hydraulic robot WLBOT. First, we give an overview of a WLBOT system. Second, the hardware design and the software architecture of the embedded controller are introduced. The embedded controller takes charge of multi-sensor information processing and signal output of the servo valve, as well as receiving control command and sending processed information via Control Area Network (CAN) bus. What's more, the realization of the 2kHz high-speed control of the embedded controller is illustrated. Finally, the platform is constructed, in which the feasibility of the design and the validity of the control algorithm is verified. It shows that WLBOT can walk properly in a PID controller as expected.

In this paper, a hierarchical-distributed control system of WLBOT is proposed. The control system is divided into three layers, the decision-making layer, the coordination layer, and the executive layer. The decision-making layer realizes human-computer interactive display and motion control instructions sending. The coordination layer realizes data coordination and movement planning. The execution layer realizes joint angle control and data collection. The communication between layers is based on WIFI and CAN bus. The control system uses the model-based control method to plan the movement trajectory and control WLBOT moving. Finally, the hierarchical-distributed control system is tested on WLBOT. From the experimental results, the control system can control the WLBOT moving correctly, and each foot is following the corresponding planning trajectory.

The low operating voltage of 1.4 V limits the widespread application of flexible Zn-air batteries (ZABs) in wearable electronics. However, a high-voltage flexible ZAB has not been achieved yet, which results from the few choices of fitted flexible electrolytes. Now we propose a novel, universal, and simple strategy to design all-in-one and membrane-free acid-alkaline flexible electrolytes based on thermo-reversible Pluronic® F127 hydrogels. Benefiting from the unique sol–gel transition property of Pluronic® F127 hydrogel, the acid and alkaline can be decoupled but integrated simultaneously in one hydrogel. Surprisingly, the as-developed ZAB achieves an unprecedentedly high voltage of 2 V, surpassing all the existing flexible ZABs. Meanwhile, this battery exhibits remarkable high-voltage stability of 37 h and a large area capacity of 1.35 mAh cm−2 without the use of costly bipolar membranes. Our work presents a pioneering example for flexible high-voltage ZAB and may further inspire other designs of flexible high-voltage aqueous batteries and decoupled dual-electrolyte batteries.

Solid oxide fuel cells (SOFCs) are a kind of clean and efficient device to convert chemical energy in fuels into electricity. However, since anodes with high catalytic activity and carbon tolerance are still underdeveloped, the consequent serious performance degradation of the cells under operational conditions significantly confines their commercial applications. Here we propose a new strategy to remove carbon deposition by in-situ formation of alkali metal carbonate on the anode surface. A multi-phase composite anode, which is composed of an orthorhombic single perovskite main phase, a Ruddlesden-Popper (RP) layered perovskite second phase, and an in-situ exsolved FeNi alloy minor phase, is developed by one-step reduction of La0.65Li0.05Sr0.3Fe0.8Ni0.2O3-δ (LLSFN0.05) at a high temperature. The deficiencies of the RP phase and A-site caused by Li dopant would increase oxygen bulk diffusion, and FeNi nanoparticles would boost the catalytic activity. Moreover, when dealing with carbon fuel, lithium carbonate can be synthesized on the anode surface, serving as a good oxygen ion conductor and an efficient catalyst for coke removal by gasification. A single cell with our reduced LLSFN0.05 anode exhibited maximum power densities of 596, 467, and 424 mW cm−2 at 750 ℃ with H2, CO, and wet C2H6 as the fuel, respectively. In addition, the cells could have a long-term stable operation for over 80 h using CO as the fuel at 200 mA cm−2. This study provides a new material design strategy to develop a highly active and coke-resistant anode.

In order to meet the requirement for the real-time of the hydraulic walking robot (WLBOT) and the stability of its movement, an embedded controller is proposed, which takes charge of multi-sensor information processing and signal output of the servo valve. The controller is capable of receiving control command and sending processed information while communicating with an embedded single board computer PCM-3365 via Control Area Network (CAN) bus at a 200 Hz frequency. In this paper, an appropriate interrupt cycle is selected and a 2 kHz high-speed control loop is run after we research the relationship between analog-to-digital converter direct memory access (ADC–DMA) interrupt cycle, data volume, and sampling rate. Significantly, the control strategy of WLBOT joint is introduced and a proportional-integral-derivative (PID) compound controller with velocity feedforward compensation (VFC) is realized. Meanwhile, the Chebyshev filtering algorithm is utilized to attenuate the vibration noise of joint signals. What’s more, an impedance controller is designed to gain better locomotion behavior and compliance in joint force control. Finally, the joint angle tracking and robot walking experiments are implemented, where the feasibility of the design and the validity of the control algorithm is verified. The results show that the PID velocity feedforward compensation controller can reduce the maximum tracking error by 39.13% and 71.31% in the knee and hip joint and the impedance control can reduce the standard deviation (SD) of the foot force by 36.06% and 72.79%.

The hybrid direct coal fuel cell (HDCFC) is a promising technology for the generation of power using coal, which is abundant and cheap. However, restricted contact between the solid carbon in the coal and the anode of the cell not only limits the electrochemical oxidation sites, but also adversely affects the transport of electrons and ions. Herein, we demonstrate a new strategy of using Cu-modified Ni foams as the three-dimensional outer anode for a high-performance HDCFC with 3D structure, that is rich in electrochemical reaction sites and beneficial for electron and ion transport when filled with molten carbonates and anthracite coal. Moreover, the CuNi alloy layer formed on the surface of Ni foam is of excellent coking-resistance and capable of preventing ash-clogging, therefore effectively promoting the durability of an electrolyte-supported HDCFC. An excellent maximum power density of 378 mW cm−2 at 750 °C is achieved using the prepared 3D anode with anthracite coal as fuel. Besides, the cell exhibited stable operation for more than 13 h at 100 mA cm−2, promising a new electrode design strategy for developing high-performance HDCFC anodes.

Hydraulic fracturing horizontal well is the key technology of tight gas development. After fracturing, the gas well shows the characteristics of great difference in production energy and many factors affecting production capacity. Therefore, taking 10 fractured horizontal wells in JQ gas field in Sichuan Basin as an example, comprehensively considering the influence of geological and engineering factors, and based on the statistical analysis of gas well productivity and the laws of various index parameters, 17 geological and engineering parameters were selected, and the main factors controlling productivity were studied by grey correlation method. The results show that the tight gas fracturing horizontal well can obtain high production, which is jointly determined by geological and engineering factors. The five main control factors affecting the productivity of tight gas fracturing horizontal well are as follows: proppant type, preflush, ϕ·h. Sand volume and reservoir volume.

A new type of bow appendage is proposed to reduce resistance of high-speed ship with a Froude Number of 0.4–0.5 in this paper. The ship bow appendage can restrain the bow waves of high-speed ships, thus enabling to decrease the principal wave-making resistance significantly. In this study, resistance experiments and numerical simulation calculations on a ship model were carried out. This new type of bow appendage was designed according to wave pattern of the ship model at the Froude Number of 0.45, aiming to restrain the peak of bow wave. Numerical calculation shows that the bow appendage can affect the wave-making state and reduce the resistance of ship model at high speed, and the effect of the bow appendage is sensitive to its installation position and the model speed. The ship model experiments were conducted to verify the effects of the bow appendage on reducing the resistance of ship model. Experiment results show that this bow appendage is able to restrain bow wave of the ship model and reduce the total resistance by more than 8% to the maximum extent. The water spray induced by the bow appendage can be improved by optimization of the shape.

Hybrid direct coal fuel cells (HDCFCs) have the potential to convert coal into electrical power in a clean and efficient manner. However, the related coal pretreatment method and the anode activity should both be improved, before the HDCFCs could match the performance of other direct coal fuel cells such as those based on solid oxide. In this study, we pyrolysed bituminous coal at 800 °C followed by modification with acetic acid, in order to remove organic volatiles and reintroduce surface functional groups, respectively. The result was a modified char that was highly pure and with high oxidation activity. Further, the Ni-(Y2O3)0.08(ZrO2)0.92 anode was infiltrated with Ag nanoparticles as an effective catalyst to promote the electro-oxidation of carbon. Under optimised conditions, the HDCFC with Ag-infiltrated anode and modified char as fuel demonstrated a maximum power density (403 mW cm−2 at 750 °C) that exceeds previous results for coal-based fuels. The cell also showed stable operation for 14 h, with a fuel conversion of 97.22% and Faradic efficiency of 61.06% using 0.4 g modified char.