Thanks to their many favorable advantages, polymer solar cells exhibit great potential for next-generation clean energy sources. Herein, we have successfully designed and synthesized a series of new ...fluorinated benzothiadiazole-based conjugated copolymers PBDTTEH-DTHBTff (P1), PBDTTEH-DTEHBTff (P2), and PBDTHDO-DTHBTff (P3). The power conversion efficiencies of 4.46, 6.20, and 8.30% were achieved for P1-, P2-, and P3-based devices within ∼100 nm thickness active layers under AM 1.5G illumination without any processing additives or post-treatments, respectively. The PCE of 8.30% for P3 is the highest value for the reported traditional single-junction polymer solar cells via a simple fabrication architecture without any additives or post-treatments. In addition, it is noteworthy that P3 also allows making high efficient polymer solar cells with high PCEs of 7.27 and 6.56% under the same condition for ∼200 and ∼300 nm thickness active layers, respectively. Excellent photoelectric properties and good solubility make polymer P3 become an alternative material for high-performance polymer solar cells.
Electromechanical oscillations of small magnitude and low frequency exist in the interconnected power system and often persist for long periods of time. Power system stabilizers (PSSs) are ...traditionally used to provide damping torque for the synchronous generators to suppress the oscillations by generating supplementary control signals for the generator excitation system. Numerous techniques have previously been proposed to design PSSs but many of them are synthesized based on a linearized model. This paper presents a nonlinear power system stabilizer based on synergetic control theory. Synergetic synthesis of the PSS is based fully on a simplified nonlinear model of the power system. The dynamic characteristics of the proposed PSS are studied in a typical single-machine infinite-bus power system and compared with the cases with a conventional PSS and without a PSS. Simulation results show the proposed PSS is robust for such nonlinear dynamic system and achieves better performance than the conventional PSS in damping oscillations.
A compact digitally controlled fuel cell/battery hybrid power source is presented in this paper. The hybrid power source composed of fuel cells and batteries provides a much higher peak power than ...each component alone while preserving high energy density, which is important and desirable for many modern electronic devices, through an appropriately controlled dc/dc power converter that handles the power flow shared by the fuel cell and the battery. Rather than being controlled to serve only as a voltage or current regulator, the power converter is regulated to balance the power flow to satisfy the load requirements while ensuring the various limitations of electrochemical components such as battery overcharge, fuel cell current limit (FCCL), etc. Digital technology is applied in the control of power electronics due to many advantages over analog technology such as programmability, less susceptibility to environmental variations, and low parts count. The user can set the FCCL, battery current limit, and battery voltage limit in the digital controller. A control algorithm that is suitable for regulating the multiple variables in the hybrid system is described by using a state-machine-based model; the issues about embedded control implementation are addressed; and the large-signal behavior of the hybrid system is analyzed on a voltage-current plane. The hybrid power source is then tested through simulation and validated on real hardware. This paper also discusses some important issues of the hybrid power source, such as operation under complex load profiles, power enhancement, and optimization of the hybrid system. The design presented here can not only be scaled to larger or smaller power capacities for a variety of applications but also be used for many other hybrid power sources
The excavation of deep mining roadways with traditional mining methods leads to various issues, such as the occurrence of large deformations, the waste of coal resources, complex conditions and the ...high cost of advanced support measures. In this study, we examined the roadway damage mechanism of the traditional gob-side entry driving method with coal pillars using the Suncun Coal Mine, the deepest mine in China, as an engineering case study. A method for the automatic formation of roadways in deep mining areas by roof cutting with high-strength bolt-grouting was proposed, and several quantitative evaluation indicators, namely, the roadway deformation control rate, anchor cable strength utilization ratio, and hydraulic prop strength utilization ratio, were established. The impacts of controlling the deformation of the surrounding rock were comparatively analysed in consideration of numerous factors, such as the mechanical parameters of the surrounding rock, roof cutting height, roof cutting angle, grouting anchor cable length, and hydraulic prop spacing. On this basis, the proposed method was applied in the field. The results showed that the automatically formed roadway cross-section exhibited decreased convergence deformation; moreover, the roof deformation was effectively controlled, and the passive hydraulic prop supports could be effectively replaced with the active support of grouting anchor cables, verifying the effect of the proposed method.
Phosphoric acid-doped polybenzimidazole (PA-PBI) used in high-temperature proton exchange membranes (HT-PEMs) frequently suffers from a serious loss of mechanical strength because of the ...“plasticizing effect” of the dopant acid. Conventional cross-linking approaches generally enhance membrane stability. However, acid doping levels (ADLs) and consequently proton conductivity inevitably decrease. This is due to the formation of more compact molecular structures and a reduced amount of functional imidazole units, caused by their consumption in introducing the cross-linker. To resolve the common problems of current PA-PBI-based HT-PEMs, herein, a highly acidophilic imidazole-rich cross-linked network with superior “antiplasticizing” ability is constructed based on a novel multifunctional cross-linker. This unique bischloro/bibenzimidazole (“A2B2-type”) molecular structure has extremely high reactivity, including “self-reaction” among the cross-linkers and “inter-reaction” between the cross-linker and PBI molecules. The resulting imidazole-rich cross-linked membranes exhibit the desired combination of high ADLs, high conductivity, outstanding dimensional–mechanical stability, and excellent fuel cell performance. In comparison to a corresponding linear PBI membrane, one membrane with a high content of the cross-linker of 30% has a 100 wt % increased acid uptake, a doubling in proton conductivity at 200 °C, and a maximum power density of 533 mW·cm–2 at 160 °C without humidification.
Automatically formed roadway (AFR) by roof cutting with bolt grouting (RCBG) is a new deep coal mining technology. By using this technology, the broken roadway roof is strengthened, and roof cutting ...is applied to cut off stress transfer between the roadway and gob to ensure the collapse of the overlying strata. The roadway is automatically formed owing to the broken expansion characteristics of the collapsed strata and mining pressure. Taking the Suncun Coal Mine as the engineering background, the control effect of this new technology on roadways was studied. To compare the law of stress evolution and the surrounding rock control mechanisms between AFR and traditional gob-side entry driving, a comparative study of geomechanical model tests on the above methods was carried out. The results showed that the new technology of AFR by RCBG effectively reduced the stress concentration of the roadway compared with gob-side entry driving. The side abutment pressure peak of the solid coal side was reduced by 24.3%, which showed an obvious pressure-releasing effect. Moreover, the position of the side abutment pressure peak was far from the solid coal side, making it more beneficial for roadway stability. The deformation of AFR surrounding rock was also smaller than the deformation of the gob-side entry driving by the overload test. The former was more beneficial for roadway stability than the latter under higher stress conditions. Field application tests showed that the new technology can effectively control roadway deformation. Moreover, the technology reduced roadway excavation and avoided resource waste caused by reserved coal pillars.
The design and fabrication of a robust nanoporous membrane in large scale is still a challenge and is of fundamental importance for practical applications. Here, a robust three/two-dimensional ...polymer/graphene oxide heterogeneous nanoporous membrane is constructed in large scale via the self-assembly approach by chemically designing a robust charge-density-tunable nanoporous ionomer with uniform pore size. To obtain a nanoporous polymer that maintains high mechanical strength and promotes multifunctionality, we designed a series of amphiphilic copolymers by introducing a positively charged pyridine moiety into the engineered polymer polyphenylsulfone. The multiphysical–chemical properties of the membrane enable it to work as a nanogate switch with synergy between wettability and surface charge change in response to pH. Then we systematically studied the transmembrane ionic transport properties of this two-/three-dimensional porous system. By adjusting the charge density of the copolymer via chemical copolymerization through a controlled design route, the rectifying ratio of this asymmetric membrane could be amplified 4 times. Furthermore, we equipped a concentration-gradient-driven energy harvesting device with this charge-density-tunable nanoporous membrane, and a maximum power of ≈0.76 W m–2 was obtained. We expect this methodology for construction of a charge-density-tunable heterogeneous membrane by chemical design will shed light on the material design, and this membrane may further be used in energy devices, biosensors, and smart gating nanofluidic devices.
Based on the data of the Chinese A-share listed firms in China Shanghai and Shenzhen Stock Exchange from 2014 to 2021, this article explores the relationship between common institutional investors ...and the quality of management earnings forecasts. The study used the multiple linear regression model and empirically found that common institutional investors positively impact the precision of earnings forecasts. This article also uses graph neural networks to predict the precision of earnings forecasts. Our findings have shown that common institutional investors form external supervision over restricting management to release a wide width of earnings forecasts, which helps to improve the risk warning function of earnings forecasts and promote the sustainable development of information disclosure from management in the Chinese capital market. One of the marginal contributions of this paper is that it enriches the literature related to the economic consequences of common institutional shareholding. Then, the neural network method used to predict the quality of management forecasts enhances the research method of institutional investors and the behavior of management earnings forecasts. Thirdly, this paper calls for strengthening information sharing and circulation among institutional investors to reduce information asymmetry between investors and management.
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