In active magnetic bearing-rotor systems, unbalance compensation is used to force the rotor to spin around its geometric axis for better rotary precision. A method, which produces the control signal ...according to the real-time position of the rotor's unbalance mass, is proposed to actualize the unbalance compensation. Unlike the unbalance force, the unbalance mass' magnitude and position are the inherent property of the rotor and independent of the rotor speed. While the rotor speed is varying, the unbalance mass position needs not to be recalculated continuously and frequently. It will significantly reduce the computational cost. Additionally, the seeking step size in the proposed method is a constant in order to avoid the signal disturbance, so that the control can achieve the further steady-going convergence. The control performance in the condition with different unbalance phases, different seeking step sizes and different noise levels are analyzed in simulations. The experiments indicate that the proposed method achieves the good effectiveness to suppress the rotor vibration. Furthermore, it is of benefit to reducing the computational cost and suitable for application in the varying-speed operation.
This paper presents a unique morphological evolution of metal‐organic inverse opals (Pb(NO3)2‐poly(St‐MMA‐AA)) subjected to an electrowetting process. The morphology of the building blocks changes ...from interconnected pores to separated hollow spheres during the electrowetting process, accompanied by an unusual blue‐shift of the stopband position and the decreased wettability of the film. This morphology evolution is attributed to the simultaneous collapse/reconstruction of the metal‐organic frame owing to the partial dissolution of the metal salt and the interfacial assembly of the metal‐organic coordination around the skeleton. The adjustable morphology can be developed as a novel and simple water‐lithography approach for the creation of the photonic crystal pattern.
A unique morphological evolution is demonstrated for metal‐organic inverse opals during an electrowetting process. The building blocks of inverse opals change from the interconnected pore to the separated hollow sphere with respect to electrowetting time, accompanied by a blue‐shift in the reflection bands and the decreased wettability of the film, which provides a facile strategy for the water‐lithography technique.
With the rapid development of technologies such as wireless communications and the Internet of Things (IoT), the proliferation of IoT devices will intensify the competition for spectrum resources. ...The introduction of cognitive radio technology in IoT can minimize the shortage of spectrum resources. However, the open environment of cognitive IoT may involve free-riding problems. Due to the selfishness of the participants, there are usually a large number of free-riders in the system who opportunistically gain more rewards by stealing the spectrum sensing results from other participants and accessing the spectrum without spectrum sensing. However, this behavior seriously affects the fault tolerance of the system and the motivation of the participants, resulting in degrading the system's performance. Based on the energy-harvesting cognitive IoT model, this paper considers the free-riding problem of Secondary Users (SUs). Since free-riders can harvest more energy in spectrum sensing time slots, the application of energy harvesting technology will exacerbate the free-riding behavior of selfish SUs in Cooperative Spectrum Sensing (CSS). In order to prevent the low detection performance of the system due to the free-riding behavior of too many SUs, a penalty mechanism is established to stimulate SUs to sense the spectrum normally during the sensing process. In the system model with multiple primary users (PUs) and multiple SUs, each SU considers whether to free-ride and which PU's spectrum to sense and access in order to maximize its own interests. To address this issue, a two-layer game-based cooperative spectrum sensing and access method is proposed to improve spectrum utilization. Simulation results show that compared with traditional methods, the average throughput of the proposed TL-CSAG algorithm increased by 26.3% and the proposed method makes the SUs allocation more fair.
Poly(3,4-ethylenedioxythiophene) (PEDOT) is an excellent hole-conducting polymer able to replace the liquid I-/I3 - redox electrolyte in dye-sensitized solar cells (DSCs). In this work we applied the ...in situ photoelectropolymerization technique to synthesize PEDOT and carried out a careful analysis of the effect of different doping anions on overall solar cell performance. The anions analyzed in this work are ClO4 -, CF3SO3 -, BF4 -, and TFSI−. The best solar cell performance was observed when the TFSI- anion was used. Photoelectrochemical and impedance studies reveal that the doped anions in the PEDOT hole conductor system have great influences on I − V curves, conductivity, and impedance. The optimization of these parameters allowed us to obtain an iodine-free solid-state DSC with a maximum J sc of 5.3 mA/cm2, V oc of 750 mV, and a conversion efficiency of 2.85% which is the highest efficiency obtained so far for an iodine-free solid-state DSC using PEDOT as hole-transport material.
Aiming at the current problems of low detection accuracy of high-voltage cabinet switches and large models that are difficult to deploy, a high-voltage cabinet switch detection method based on the ...improved EfficientNet-YOLOv5s model is proposed. Firstly, offline data expansion and online Mosaic data enhancement are performed based on the high-voltage switchgear images obtained by video frame extraction to alleviate the problems of unbalanced sample categories and the small number of samples. Secondly, the backbone network of the YOLOv5s model is replaced with a lightweight EfficientNet-B0 network, and the original convolution layer is replaced by depthwise separable convolution, and the original Squeeze-and-Excitation Networks were replaced with Efficient Channel Attention to optimize the efficiency and accuracy of the network model. To enhance the positioning information of small objects without bringing too much computational burden, the proposed improved multi-scale feature fusion Neck network uses the Bi-directional Concatenation(BiC) module to aggregate the feature maps of three adjacent layers. Finally, the H-Swish function is used to replace the Swish function in the MBConv structure, avoiding the exponential operation of the sigmoid function, and further improving the calculation efficiency of the model.
The preparation of a novel Nb2O5 blocking layer deposited between fluorine-doped tin oxide (FTO) and nanocrystalline TiO2 layer and its application for dye-sensitized ionic liquid solar cell have ...been studied. The Nb2O5 blocking layer prepared by the sputtering method on FTO has been characterized by scanning electron microscopy (SEM), cyclic voltammetry (CV), and X-ray photoelectron spectroscopy. Thin Nb2O5 films work as a potential blocking layer between FTO and TiO2 nanocrystalline film in ionic liquid electrolyte cells, improving V oc and finally giving a better conversion efficiency of dye-sensitized TiO2 solar cells. The remarkable improvements of V oc and the fill factor for the dye-sensitized solar cells suggest that such a thin Nb2O5 layer is an effective blocking layer at FTO and TiO2 interface, contributing to the suppression of recombination processes between unidirectional transporting electron and redox electrolytes in the process of TiO2 photoelectron conversion systems. SEM and CV reveal that the Nb2O5 blocking layer is electronic blocking rather than morphological blocking at the FTO/nanoTiO2 interface, which may give another direction on the suppression of charge recombination during photoelectron conversion process.
A method for multi-frequency periodic vibration suppressing in active magnetic bearing (AMB)-rotor systems is proposed, which is based on an adaptive finite-duration impulse response (FIR) filter in ...time domain. Firstly, the theoretic feasibility of the method is proved. However, two problems would be unavoidable, if the conventional adaptive FIR filter is adopted in practical application. One is that the convergence rate of the different frequency components may be highly disparate in multi-frequency vibration control. The other is that the computational complexity is significantly increased because the long memory FIR filter is required to match the transient response time of the AMB-rotor system. To overcome the problems above, the Fast Block Least Mean Square (FBLMS) algorithm is adopted to efficiently implement the computation in frequency domain at a computational cost far less than that of the conventional FIR filter. By the FBLMS algorithm, regardless of the number of the considered frequency components in vibration disturbance, the computational complexity would be invariable. Moreover, filter’s weights in the FBLMS algorithm have the intuitional relation with signal’s frequency. As a result, the convergence rate of each frequency component can be adjusted by assigning the individual step size parameter for each weight.
Experiments with the reciprocating simulating disturbance test and the rotating harmonic vibration test were carried out on an AMB-rigid rotor test rig with a vertical shaft. The experiment results indicate that the proposed method with the FBLMS algorithm can achieve the good effectiveness for suppressing the multi-frequency vibration. The convergence property of each frequency component can be adjusted conveniently. Each harmonic component of the vibration can be addressed, respectively, by reconfiguring the frequency components of the reference input signal.
In dye-sensitized TiO2 solar cells, charge recombination processes at interfaces between fluorine-doped tin oxide (FTO), TiO2, dye, and electrolyte play an important role in limiting the ...photon-to-electron conversion efficiency. From this point of view, a high work function material such as titanium deposited by sputtering on FTO has been investigated as an effective blocking layer for preventing electron leakage from FTO without influencing electron injection. X-ray photoelectron spectroscopy analysis indicates that different species of Ti (Ti4+, Ti3+, Ti2+, and a small amount of Ti0) exist on FTO. Electrochemical and photoelectrochemical measurements reveal that thin films of titanium species, expressed as TiOx, work as a compact blocking layer between FTO and TiO2 nanocrystaline film, improving Voc and the fill factor, finally giving a better conversion efficiency for dye-sensitized TiO2 solar cells with ionic liquid electrolytes.
A novel class of organic D-π-A dyes employing macrocyclic triphenylamine dimer as electron donor was designed and synthesized for dye-sensitized solar cells. The prepared compounds showed high ...chemical and elelctrochemical stabilities as well as good long-wave absorption. Photovoltaic devices based on these dyes showed high open circuit voltage (higher than that of N3) and achieved a solar energy to electricity conversion efficiency of 6.31%. All the performances indicate the dyes containing macrocyclic triphenylamine dimer is a good candidate for dyes sensitized solar cells.
Display omitted
Novel dyes comprising a triphenylamine donor, thiophene conjugated bridge and different numbers of anchor groups (cyanoacrylic acid acceptor) were synthesized and employed as photosensitizers in ...dye-sensitized solar cells. The absorbance of the dyes in solution was red shifted and the first oxidation potential decreased with increasing butoxy group:anchor group ratio. Solar cells based on the dyes exhibited energy conversion efficiencies of 6.7–7.4% at 100 mW cm
−2. Increasing butoxy group:anchor group ratio resulted in higher open-circuit voltage and higher efficiency.
