Zonal activation of molecular carbon dioxide and hydrogen over dual sites Ni-Co-MgO catalyst for CO_(2) methanation:Synergistic catalysis of Ni and Co species

An in-depth mechanism in zonal activation of CO_(2)and H2molecular over dual-active sites has not been revealed yet.Here,Ni-Co-MgO was rationally constructed to elucidate the CO_(2)methanation mechanism.The abundant surface nickel and cobalt components as active sites led to strong Ni-Co interaction with charge transfer from nickel to cobalt.Notably,electron-enriched Coδ-species participated in efficient chemisorption and activation of CO_(2)to generate monodentate carbonate.Simultaneously,plentiful available Ni0sites facilitated H2dissociation,thus CO_(2)and H2were smoothly activated at zones of Coδ-species and Ni0,respectively.Detailed in situ DRIFTS,quasi situ XPS,TPSR,and DFT calculations substantiated a new formate evolution mechanism via monodentate carbonate instead of traditional bidentate carbonate based on synergistic catalysis of Coδ-species and Ni0.The zonal activation of CO_(2)and H2by tuning electron behaviors of double-center catalysts can boost heterogeneous catalytic hydrogenation performance.

Effects of active layer thickness on performance and stability of dual-active-layer amorphous InGaZnO thin-film transistors

Dual-active-layer(DAL)amorphous InGaZnO(IGZO)thin-film transistors(TFTs)are fabricated at low temperature without post-annealing.A bottom low-resistance(low-R)IGZO layer and a top high-resistance(high-R)IGZO layer constitute the DAL homojunction with smooth and high-quality interface by in situ modulation of oxygen composition.The performance of the DAL TFT is significantly improved when compared to that of a single-active-layer TFT.A detailed investigation was carried out regarding the effects of the thickness of both layers on the electrical properties and gate bias stress stabilities.It is found that the low-R layer improves the mobility,ON/OFF ratio,threshold voltage and hysteresis voltage by passivating the defects and providing a smooth interface.The high-R IGZO layer has a great impact on the hysteresis,which changes from clockwise to counterclockwise.The best TFT shows a mobility of 5.41 cm^2/V·s,a subthreshold swing of 95.0 mV/dec,an ON/OFF ratio of 6.70×10^7,a threshold voltage of 0.24 V,and a hysteresis voltage of 0.13 V.The value of threshold voltage shifts under positive gate bias stress decreases when increasing the thickness of both layers.

Impedance Modeling and Stability Analysis of Dual Active Bridge Converter with LC Input Filter

The dual active bridge(DAB)converter is gaining more and more attention in various applications such as energy storage systems,electric vehicles and smart grids.To improve the quality of the input current,a LC filter is often cascaded at the input side of the DAB converter.However,there are instable problems of this cascaded system due to the impedance interactions of the DAB converter and the LC filter,although the DAB converter is stable at the individual operation mode.To assess the stability of the cascaded system of the DAB converter and the LC filter,the impedance model of the DAB converter is firstly developed based on generalized state-space averaging method.The developed impedance model can be used to accurately predict the stability of the DAB converter with its LC input filter.Based on the stability analysis,the optimum filter parameter design guideline is determined.The impedance model and stability analysis are validated by the simulation and experimental results.

Analysis of Light Load Efficiency Characteristics of a Dual Active Bridge Converter Using Wide Band-Gap Devices

In this paper, the zero voltage switching (ZVS) region of a dual active bridge (DAB) converter with wide band-gap (WBG) power semiconductor device is analyzed. The ZVS region of a DAB converter varies depending on output power and voltage ratio. The DAB converters operate with hard switching at light loads, it is difficult to achieve high efficiency. Fortunately, WBG power semiconductor devices have excellent hard switching characteristics and can increase efficiency compared to silicon (Si) devices. In particular, WBG devices can achieve ZVS at low load currents due to their low parasitic output capacitance (Co,tr) characteristics. Therefore, in this paper, the ZVS operating resion is analyzed based on the characteristics of Si, silicon carbide (SiC) and gallium nitride (GaN). Power semiconductor devices. WBG devices with low Co,tr operate at ZVS at lower load currents compared to Si devices. To verify this, experiments are conducted and the results are analyzed using a 3 kW DAB converter. For Si devices, ZVS is achieved above 1.4 kW. For WBG devices, ZVS is achieved at 700 W. Due to the ZVS conditions depending on the switching device, the DAB converter using Si devices achieves a power conversion efficiency of 91% at 1.1 kW output. On the other hand, in the case of WBG devices, power conversion efficiency of more than 98% is achieved under 11 kW conditions. In conclusion, it is confirmed that the WBG device operates in ZVS at a lower load compared to the Si device, which is advantageous in increasing light load efficiency.

Fuzzy Logic Controlled Dual Active Bridge Series Resonant Converter for DC Smart Grid Application

Over the last few years, smart grids have become a topic of intensive research, development and deployment across the world. This is due to the fact that, through the smart grid, stable and reliable power systems can be achieved. This paper presents a fuzzy logic control for dual active bridge series resonant converters for DC smart grid application. The DC smart grid consists of wind turbine and photovoltaic generators, controllable and DC loads, and power converters. The proposed control method has been applied to the controllable load＇s and the grid side＇s dual active bridge series resonant converters for attaining control of the power system. It has been used for management of controllable load＇s state of charge, DC feeder＇s voltage stability during the loads and power variations from wind energy and photovoltaic generation and power flow management between the grid side and the DC smart grid. The effectiveness of the proposed DC smart grid operation has been verified by simulation results obtained by using MATLAB and PLECS cards.

Improvement in the electrical performance and bias-stress stability of dual-active-layered silicon zinc oxide/zinc oxide thin-film transistor

Si-doped zinc oxide（SZO） thin films are deposited by using a co-sputtering method,and used as the channel active layers of ZnO-based TFTs with single and dual active layer structures.The effects of silicon content on the optical transmittance of the SZO thin film and electrical properties of the SZO TFT are investigated.Moreover,the electrical performances and bias-stress stabilities of the single- and dual-active-layer TFTs are investigated and compared to reveal the effects of the Si doping and dual-active-layer structure.The average transmittances of all the SZO films are about 90% in the visible light region of 400 nm-800 nm,and the optical band gap of the SZO film gradually increases with increasing Si content.The Si-doping can effectively suppress the grain growth of ZnO,revealed by atomic force microscope analysis.Compared with that of the undoped ZnO TFT,the off-state current of the SZO TFT is reduced by more than two orders of magnitude and it is 1.5 × 10^-12 A,and thus the on/off current ratio is increased by more than two orders of magnitude.In summary,the SZO/ZnO TFT with dual-active-layer structure exhibits a high on/off current ratio of 4.0 × 10^6 and superior stability under gate-bias and drain-bias stress.

Highly active and stable Co nanoparticles embedded in nitrogen-doped mesoporous carbon nanofibers for aqueous-phase levulinic acid hydrogenation

Developing a highly active and durable non-noble metal catalyst for aqueous-phase levulinic acid(LA)hydrogenation to g-valerolactone(GVL)is an appealing yet challenging task.Herein,we report well-dispersed Co nanoparticles(NPs)embedded in nitrogen-doped mesoporous carbon nanofibers as an efficient catalyst for aqueous-phase LA hydrogenation to GVL.The Co zeolitic imidazolate framework(ZIF-67)nanocrystals were anchored on the sodium dodecyl sulfate modified wipe fiber(WF-S),yielding one-dimensional(1-D)structured composite(ZIF-67/WF-S).Subsequently,Co NPs were uniformly embedded in nitrogen-doped mesoporous carbon nanofibers(Co^(R)NC/SMCNF)through a pyrolysis-reduction strategy using ZIF-67/WF-S as the precursor.Benefiting from introducing modified wipe fiber WF-S to enhance the dispersion of Co NPs,and Co^(0) with Co-N_xdual active sites,the resulting Co^(R)NC/SMCNF catalyst shows brilliant catalytic activity(206 h^(-1) turnover frequency).Additionally,the strong metal-support interactions greatly inhibited the Co NPs from aggregation and leaching from the mesoporous carbon nanofibers,and thus increasing the reusability of the Co^(R)NC/SMCNF catalyst(reusable nine times without notable activity loss).

Beam shaping with limited amplitude weight values for satellite active phased array antenna

To gain the tradeoff between lower sidelobe and higher power amplifiers efficiency,a transmitting beam shaping scheme with limited amplitude weight values for satellite active phased array antenna is presented. The scheme is implemented by a dual coding genetic algorithm(GA). Phase and amplitude of array weight vectors for beam shaping are encoded by real coding and finite length binary coding,respectively,which,maintaining accuracy of results,reduces the amplitude dynamic range and improves the efficiency of power amplifiers. The presented algorithm,compared with complex-coded GA,increases the convergence rate due to the search space's decrease. In order to overcome the prematurity and obtain better global optimization or quasi-global optimization,a new dual coding GA based on "species diversity retention" strategy and adaptive crossover and mutation probability are presented.

A dual-period response of the Kuroshio Extension SST to Aleutian Low activity in the winter season

Based on our previous work, the winter sea surface temperature（SST） in the Kuroshio Extension（KE） region showed significant variability over the past century with periods of ~6 a between 1930 and 1950 and ~10 a between1980 and 2009. How the activity of the Aleutian Low（AL） induces this dual-period variability over the two different timespans is further investigated here. For the ~6 a periodicity during 1930–1950, negative wind stress curl（WSC）anomalies in the central subtropical Pacific associated with an intensified AL generate positive sea surface height（SSH） anomalies. When these wind-induced SSH anomalies propagate westwards to the east of Taiwan, China two years later, positive velocity anomalies appear around the Kuroshio to the east of Taiwan and then the mean advection via this current of velocity anomalies leads to a strengthened KE jet and thus an increase in the KE SST one year later. For the ~10 a periodicity during 1980–2009, a negative North Pacific Oscillation-like dipole takes2–3 a to develop into a significant positive North Pacific Oscillation-like dipole, and this process corresponds to the northward shift of the AL. Negative WSC anomalies associated with this AL activity in the central North Pacific are able to induce the positive SSH anomalies. These oceanic signals then propagate westward into the KE region after 2–3 a, favoring a northward shift of the KE jet, thus leading to the warming of the KE SST. The feedbacks of the KE SST anomaly on the AL forcing are both negative for these two periodicities. These results suggest that the dual-period KE SST variability can be generated by the two-way KE-SST-AL coupling.

One-step conversion of methane and formaldehyde to ethanol over SA-FLP dual-active-site catalysts: A DFT study

One-step conversion of methane and formaldehyde into ethanol is a 100% atom-efficient process for carbon resources utilization and environment protection but still faces eminent challenges due to the lacking of efficient catalysts. Therefore, developing active and stable catalysts is crucial for the co-conversion of methane and formaldehyde. Herein, twelve kinds of “Single-Atom”-“Frustrated Lewis Pair”(SA-FLP)dual-active-site catalysts are designed for the direct conversion of methane and formaldehyde to ethanol based on density functional theory(DFT) calculations and microkinetic simulations. The results show that the SA-FLP dual active sites can simultaneously activate methane at the SA site and activate formaldehyde at the FLP site. Among the twelve designed SA-FLP catalysts, Fe1-FLP shows the best performance in the co-conversion of methane and formaldehyde to ethanol with the rate-determining barrier of 1.15 e V.Ethanol is proved as the main product with the turnover frequency of 1.32 × 10^(-4)s^(-1)at 573 K and 3 bar.This work provides a universal strategy to design dual active sites on metal oxide materials and offers new insights into the effective conversion of methane and formaldehyde to desired C_(2) chemicals.

Photocatalytic uranium extraction boosted by dual effective active sites of porphyrin metal-organic frameworks

Porphyrinoid metal-organic frameworks(MOFs)with dual effective uranium uptake sites were synthesized through combined insitu and post-synthetic method.The MOF10@5 demonstrates the uptake amount of uranium reaches 1476 mg/g under visiblelight irradiation.The PN-MOF10@5 with dual uranyl uptake sites yields the amount of extracting uranyl of 1590 mg/g under visible-light irradiation.The density functional theory(DFT)calculations reveal strong interaction between uranyl and dual uranyl effective active sites.These MOFs demonstrate a powerful synthesis strategy for uranium extraction materials with dual effective active sites.

Current Loop Disturbance Suppression for Dual Three Phase Permanent Magnet Synchronous Generators Based on Modified Linear Active Disturbance Rejection Control

A modified four-dimensional linear active disturbance rejection control(LADRC)strategy is proposed for a dual three-phase permanent magnet synchronous generator(DTP-PMSG)system to reduce cross-coupling between the d and q axis currents in the d-q subspace and harmonic currents in the x-y subspace.In the d-q subspace,the proposed strategy uses a model-based LADRC to enhance the decoupling effect between the d and q axes and the disturbance rejection ability against parameter variation.In the x-y subspace,the 5th and 7th harmonic current suppression abilities are improved by using quasi-resonant units parallel to the extended state observer of the traditional LADRC.The proposed modified LADRC strategy improved both the steady-state performance and dynamic response of the DTP-PMSG system.The experimental results demonstrate that the proposed strategy is both feasible and effective.

Dual active sites engineering of electrocatalysts for alkaline hydrogen evolution

Hydrogen evolution reaction(HER)in alkaline medium plays an important role in producing green hydrogen but suffers from sluggish reaction kinetics owing to additional water dissociation step.Extensive research interest has been placed on engineering dual active sites(i.e.,water-dissociation sites and hydrogen-adsorption/recombination sites)within a catalyst to enhance the HER activity.This article reviews recent progress in developing alkaline HER catalysts with high-efficiency dual active sites via strategies of heterogeneous interfaces constructing and heteroatoms doping or alloying.The latest advances in the component design,synthetic strategy,catalytic performance,and mechanistic understanding are discussed with selective examples of the hybrid between metal/alloy or metal phosphide/nitride/sulfide and transition metal hydroxides,oxyhydroxide or bicarbonates.Furthermore,remaining challenges and perspectives in the field of dualsite engineering are highlighted for future development of better alkaline HER electrocatalysts.

Intention and automaticity toward physical and sedentary screen-based leisure activities in adolescents:A profile perspective

Purpose： Physical activity （PA） and sedentary behavior （SB） are increasingly considered independent health behaviors. Additionally, current research suggests that both controlled and automatic determinants account for their adoption. The purpose of this article was to identify intention-automaticity profiles toward PA and screen-based SB and to examine how those profiles are associated with different behavioral patterns. Method： Two cross-sectional studies based on self-report questionnaires were conducted with French high school students （Study 1： n = 198; Study 2： n = 185）. Results： In all, 4 distinct motivational profiles appeared. The first 3 clusters emerged in both studies： ＂PA＂ （high levels of automaticity and intention for PA, low levels of automaticity and intention for screen-based SB）; ＂screen＂ （high levels of automaticity and intention for screen-based SB, low levels of automatieity and intention for PA）, and ＂mixed＂ （high levels of all variables）, whereas the fourth cluster was observed only in Study 2： ＂high control＂ （below-mean levels of automaticity, high levels of intention toward both PA and screen-based SB）. Adolescents with a screen profile displayed the least healthy behavioral pattern, whereas those in the PA profile demonstrated the most favorable behaviors. Conclusion： Future research is needed to extend these results to other populations using complementary assessment methods of automatic psychological processes and PA and SB behaviors.2018 Published by Elsevier B.V.on behalf of Shanghai University of Sport. This is an open access article under the CC BY-NC-ND license.（http：//creativecommons.org/licenses/by-nc-nd/4.0/）.

Novel dual-band antenna for multi-mode GNSS applications

A novel dual-band antenna is proposed for mitigating the multi-path interference in the global navigation satellite system（GNSS） applications. The radiation patches consist of a shortedannular-ring reduced-surface-wave（SAR-RSW） element and an inverted-shorted-annular-ring reduced-surface-wave（ISAR-RSW）element. One key feature of the design is the proximity-coupled probe feeds to increase impedance bandwidth. The other is the defected ground structure band rejection filters to suppress the interaction effect between the SAR-RSW and the ISAR-RSW elements. In addition, trans-directional couplers are used to obtain tight coupling. Measurement results indicate that the antenna has a larger than 10 d B return loss bandwidth and a less than 3 d B axial-ratio（AR） bandwidth in the range of（1.164 – 1.255） GHz and（1.552 – 1.610） GHz. The gain of the passive antenna in the whole operating band is more than 7 d Bi.

RED-DTB: A Dual Token Bucket Based Queue Management Algorithm

Improving the Quality of Service (QoS) of Internet traffic is widely recognized as a critical issue for the next-generation networks. In this paper, we present a new algorithm for the active queue management, namely RED-DTB. This buffer control technique is used to enforce approximate fairness among a large number of concurrent Internet flows. Like RED (Random Early Detection) algorithm, the RED-DTB mechanism can be deployed to actively respond to the gateway congestion, keep the gateway in a healthy state, and protect the fragile flows from being stolen bandwidth by greedy ones. The algorithm is based on the so-called Dual Token Bucket (DTB) pattern. That is, on the one hand, every flow is rate-limited by its own token bucket, to ensure that it can not consume more than its fair share of bandwidth; On the other hand, to make some compensations to less aggressive flows, such as connections with larger round trip time or smaller sending window, and to gain a relatively higher system utilization coefficient, all flows, depending on their individual behavior, may have a chance to fetch tokens from the public token bucket when they run out of their own share of tokens. The algorithm is analyzed and evaluated by simulations, and is proved to be effective in protecting the gateway buffer and controlling the fair allocation of bandwidth among flows.

Onsite-effects of dual-hemisphere versus conventional single-hemisphere transcranial direct current stimulation A functional MRI study

We performed functional MRI examinations in six right-handed healthy subjects.During functional MRI scanning,transcranial direct current stimulation was delivered with the anode over the right primary sensorimotor cortex and the cathode over the left primary sensorimotor cortex using dual-hemispheric transcranial direct current stimulation.This was compared to a cathode over the left supraorbital area using conventional single-hemispheric transcranial direct current stimulation. Voxel counts and blood oxygenation level-dependent signal intensities in the right primary sensorimotor cortex regions were estimated and compared between the two transcranial direct current stimulation conditions.Our results showed that dual-hemispheric transcranial direct current stimulation induced greater cortical activities than single-hemispheric transcranial direct current stimulation.These findings suggest that dual-hemispheric transcranial direct current stimulation may provide more effective cortical stimulation than single-hemispheric transcranial direct current stimulation.

基于回流功率优化的直流微网DC-DC变流器超螺旋滑模控制

针对直流微网系统中双有源桥直流变换器在系统发生扰动时动态特性差及在单移相调制下变换器效率不高等问题,该文在扩展移相调制下提出一种结合回流功率优化的超螺旋滑模控制策略。首先,分析双有源全桥(dual-active-bridge,DAB)变换器在扩展移相调制下两种模式的传输功率、回流功率数学模型及软开关特性,并以传输功率数学模型为基础建立DAB变换器的降阶模型。其次,以回流功率作为目标函数,以传输功率和软开关特性作为约束条件,通过Karush-Kuhn-Tucker(KKT)条件法寻找最优移相比组合;利用DAB变换器降阶模型设计超螺旋滑模控制中的等效部分,采用超螺旋算法作为切换部分,这两部分与内移相比D1共同作用生成外移相比D2,用于调节变换器的输出电压。最后进行了仿真及实验验证,实验结果表明:在负载投切、输入电压突变、参考电压改变时变换器具有良好的动态性能,同时能有效地减小回流功率。

Recognition of Group Activities Using Complex Wavelet Domain Based Cayley-Klein Metric Learning

A group activity recognition algorithm is proposed to improve the recognition accuracy in video surveillance by using complex wavelet domain based Cayley-Klein metric learning.Non-sampled dual-tree complex wavelet packet transform(NS-DTCWPT)is used to decompose the human images in videos into multi-scale and multi-resolution.An improved local binary pattern(ILBP)and an inner-distance shape context(IDSC)combined with bag-of-words model is adopted to extract the decomposed high and low frequency coefficient features.The extracted coefficient features of the training samples are used to optimize Cayley-Klein metric matrix by solving a nonlinear optimization problem.The group activities in videos are recognized by using the method of feature extraction and Cayley-Klein metric learning.Experimental results on behave video set,group activity video set,and self-built video set show that the proposed algorithm has higher recognition accuracy than the existing algorithms.

双有源桥变换器双移相控制动态特性优化方法

为了提高双移相控制的双有源桥DAB(dual active bridge)变换器负载切换的动态响应性能及减小电流应力,研究了1种改进型双移相NDPS(novel dual phase shift)控制方法,通过改变传统双移相TDPS(traditional dual phase shift)控制内移相角移动方向,重构了传输功率与移相比的关系,增大了移相比调节范围。研究了电流应力最小化条件下双移相控制最优移相比的求解方法,对比分析NDPS与TDPS控制方式负载切换时的动态响应特性。最后搭建了DAB变换器实验平台对理论分析进行实验验证,实验结果表明,轻载条件下,基于电流应力最小化方法得到的最优移相比组合可以有效减小电流应力,同时NDPS比TDPS控制方式有更好的动态响应特性。