Outer Position Research Articles

Inductive Effect of Lewis Acidic Dopants on the Band Levels of Perovskite for a Photocatalytic Reaction.

Band-edge modulation of halide perovskites as photoabsorbers plays significant roles in the application of photovoltaic and photochemical systems. Here, Lewis acidity of dopants (M) as the new descriptor of engineering the band-edge position of the perovskite is investigated in the gradiently doped perovskite along the core-to-surface (CsPbBr3-CsPb1-xMxBr3). Reducing M-bromide bond strength with an increase in hardness of acidic M increases the electron ability of basic Br, thus strengthening the Pb-Br orbital coupling in M-Pb-Br, noted as the inductive effect of dopants. Especially, the highly hard Lewis acidic Mg localized in the outer position of the perovskite induces the increase of work function and then shifts band edge upward along the core-to-surface of the perovskite. Thus, charge separation driven by the dopant-induced internal electric field induces the slow annihilation of the excited holes, improving the slow aromatic Csp3-H dissociation in the photocatalytic oxidation process by ∼211% (491.39 μmol g-1 h-1) enhancements, compared with undoped nanocrystals.

Precise Control of Selenium Functionalization in Non‐Fullerene Acceptors Enabling High‐Efficiency Organic Solar Cells

AbstractCentral π‐core engineering of non‐fullerene small molecule acceptors (NF‐SMAs) is effective in boosting the performance of organic solar cells (OSCs). Especially, selenium (Se) functionalization of NF‐SMAs is considered a promising strategy but the structure‐performance relationship remains unclear. Here, we synthesize two isomeric alkylphenyl‐substituted selenopheno[3,2‐b]thiophene‐based NF‐SMAs named mPh4F‐TS and mPh4F‐ST with different substitution positions, and contrast them with the thieno[3,2‐b]thiophene‐based analogue, mPh4F‐TT. When placing Se atoms at the outer positions of the π‐core, mPh4F‐TS shows the most red‐shifted absorption and compact molecular stacking. The PM6 : mPh4F‐TS devices exhibit excellent absorption, high charge carrier mobility, and reduced energy loss. Consequently, PM6 : mPh4F‐TS achieves more balanced photovoltaic parameters and yields an efficiency of 18.05 %, which highlights that precisely manipulating selenium functionalization is a practicable way toward high‐efficiency OSCs.

Precise Control of Selenium Functionalization in Non-Fullerene Acceptors Enabling High-Efficiency Organic Solar Cells.

Central π-core engineering of non-fullerene small molecule acceptors (NF-SMAs) is effective in boosting the performance of organic solar cells (OSCs). Especially, selenium (Se) functionalization of NF-SMAs is considered a promising strategy but the structure-performance relationship remains unclear. Here, we synthesize two isomeric alkylphenyl-substituted selenopheno[3,2-b]thiophene-based NF-SMAs named mPh4F-TS and mPh4F-ST with different substitution positions, and contrast them with the thieno[3,2-b]thiophene-based analogue, mPh4F-TT. When placing Se atoms at the outer positions of the π-core, mPh4F-TS shows the most red-shifted absorption and compact molecular stacking. The PM6 : mPh4F-TS devices exhibit excellent absorption, high charge carrier mobility, and reduced energy loss. Consequently, PM6 : mPh4F-TS achieves more balanced photovoltaic parameters and yields an efficiency of 18.05 %, which highlights that precisely manipulating selenium functionalization is a practicable way toward high-efficiency OSCs.

Comparative and mechanistic analysis of the ethanol gas sensing properties of ZnO@In2O3 and In2O3@ZnO spherical heterostructures

The space charge region formed in the spherical heterostructure materials through the electron transfer at the heterointerface is very beneficial for enhanced gas sensing performance. In particular, the inner and outer positions of the two materials that make up the spherical structure have a great influence on its performance. Herein, the spherical heterostructure ZnO@In2O3 and In2O3@ZnO were synthesized, respectively, by two-step chemical precipitation methods to investigate the effects of electron transfer direction on their gas sensing properties. The spherical heterostructures are composed of a solid sphere with a diameter of ∼300 nm and a porous structure with a thickness of ∼40 nm. Gas sensing test results showed similar gas sensing properties. However, spherical heterostructure ZnO@In2O3 displayed better gas sensing performances to ethanol, including higher sensitivity (96.6–100 ppm ethanol at 240 ℃, 3 times higher than that of In2O3@ZnO), a faster recovery rate, and higher selectivity. By comparison, the difference in electron transfer direction of these two heterostructure materials leads to different resistance modulation processes, thereby influencing their gas sensing response. These intrinsic electronic differences of ZnO and In2O3 also play an important role in the modulation of electron transfer. It is suggested that the structural design of heterostructure material is significant for the development of highly sensitive gas sensors.

An Experimental Study on Outer Frame Position Control of Hydraulic Flight Motion Simulator With Model Compensation

The hydraulic flight motion simulator (HFMS) is the key equipment for the hardware-in-the-loop simulation in the field of aerospace and has been widely used on occasions requiring high maneuverability and large power. However, three mismatched uncertainties, including nonlinear friction torque, unbalanced gravity torque, and unknown inertia, bring some certain difficulties for receiving the high-precision outer frame position control of the HFMS. In this article, first, by means of an ingenious experimental design, the coupled friction torque and gravity torque were identified separately. Subsequently, through combining the established mathematical model and identification results, an adaptive robust controller with model compensation was investigated in which adaptive controller is not only used to estimate unknown system parameters but also able to online correct identified parameters, and the robust controller is able to guarantee the stability of the whole system. Additionally, the zero bias of the servo valve was also introduced to assist controller implementation. Finally, experimental results show that by using the method of torque identification to improve the model accuracy, the burden of parameter adaptation and robust items can be effectively alleviated, and the high-precision outer frame position control of HFMS can be realized.

Dark Off-limb Gap: Manifestation of a Temperature Minimum and the Dynamic Nature of the Chromosphere

We study off-limb emission of the lower solar atmosphere using high-resolution imaging spectroscopy in the Hβ and Ca ii 8542 Å lines obtained with the CHROMospheric Imaging Spectrometer (CHROMIS) and the CRisp Imaging SpectroPolarimeter (CRISP) on the Swedish 1 m Solar Telescope. The Hβ line-wing images show the dark intensity gap between the photospheric limb and chromosphere, which is absent in the Ca ii images. We calculate synthetic spectra of the off-limb emissions with the RH code in one-dimensional spherical geometry and find good agreement with the observations. The analysis of synthetic line profiles shows that the gap in the Hβ line-wing images maps the temperature minimum region between the photosphere and chromosphere due to the well-known opacity and emissivity gap of Balmer lines in this layer. However, the observed gap is detected farther from the line core in the outer line-wing positions than in the synthetic profiles. We found that an increased microturbulence in the model chromosphere is needed to reproduce the dark gap in the outer line wing, suggesting that the observed Hβ gap is the manifestation of the temperature minimum and the dynamic nature of the solar chromosphere. The temperature minimum produces a small enhancement in synthetic Ca ii line-wing intensities. Observed off-limb Ca ii line-wing emissions show similar enhancement below the temperature minimum layer near the edge of the photospheric limb.

Multi-harmonic electron cyclotron heating and current drive scenarios for non-inductive start-up and ramp-up in high field ST-40 spherical tokamak

Non-inductive start-up and ramp-up is an important topic for spherical tokamak reactor design as the central solenoid implementation is highly restrictive particularly for the low-aspect-ratio tokamak configuration. In the high field spherical tokamak (ST), ST-40 with B T0 ⩽ 3 T, a preparation is underway for high power ECH and ECCD current start-up/ramp-up experiments utilizing two MW-class 140/105 GHz gyrotrons. Here, we explored various ECH/ECCD scenarios for a low-field-side (LFS) launch-angle steerable waveguide launcher placed near the mid-plane region. Due to the large toroidal field variation of ST configuration, multiple cyclotron harmonic resonance layers could exist within the plasma. In this start-up and ramp-up regime, both fundamental and second harmonic ECH resonances must be considered. We find that even with the presence of X-II resonance layer in the plasma, an efficient X-I ECH and ECCD regime can be accessed for the low electron temperature T e0 as low as 200 eV which is a typical starting temperature of ECH heated plasmas in an open-field-line configuration. The presence of X-II resonance could become significant at higher T e0 as X-II absorption increases with T e0 which could reduce the current ramp-up efficiency as the power reaching X-I is reduced. Finally for the pure X-I regime where the 2Ωe resonance is moved outside the plasma with B T0 ∼ 3.4 T, we find that it is possible to reach the full current of I p ∼ 1 MA fully non-inductively with the ECH power of ∼1 MW at n e0 ∼ 1.0 × 1019 m−3 using 105 GHz frequency gyrotron. By reducing the outer limiter position R L ∼ 78 cm to 70 cm, the pure X-I regime is recovered at the rated ST-40 magnetic field of B T0 ∼ 3.0 T. This X-I regime is accessible with a relatively broad range of launched n II or the launching angles. A survey of X-mode X-II ECH and ECCD at higher density regimes is also shown for completeness.

Optimized-Based Fault-Tolerant Control of an Electro-Hydraulic System with Disturbance Rejection

In this article, the design and implementation of a fault-tolerant controller are proposed for an electro-hydraulic actuator (EHA) in the presence of disturbances and actuator faults. The existence of nonlinearities, uncertainties, and a bias fault (i.e., internal leakage fault) in the system dynamics significantly decreases the desired performance. The nonlinear disturbance observers (NDO) are constructed to handle the adverse influences caused by the above disadvantages. The whole fault-tolerant control (FTC) scheme consists of two design loops: an inner force control loop and an outer position control loop. The inner loop is based on an optimized backstepping framework to achieve the optimal performance, whilst the problem of uncertainties and disturbances is dealt with using a terminal sliding mode directly designed from the position tracking error. It is shown by theoretical analysis that system stability is ensured under faulty conditions. Finally, simulation results and comparison studies are conducted to further verify the effectiveness of the proposed approach.

Current sensorless position-tracking control with angular acceleration error observers for hybrid-type stepping motors

This paper exhibits an advanced observer-based position-tracking controller for hybrid-type stepping motors with consideration of parameter and load uncertainties. As the main contribution, a current sensorless observer-based pole-zero cancellation speed controller is devised for the outer loop position-tracking controller including the convergence rate boosting mechanism. The features of this study are summarized as follows; first, the pole-zero cancellation angular acceleration error observer for the inner loop speed controller, second, the pole-zero cancellation speed control forcing the order of the controlled speed error dynamics to be 1, and, third, the outer loop position control incorporating the first-order target tracking system with its convergence rate booster. The resultant effectiveness is verified on a 10-W stepping motor control system.

Sliding mode disturbance observer and sliding mode controller for quadrotor UAV

The dynamics of quadrotor UAV is described considering internal uncertainty and external disturbance. The control system of quadrotor UAV is divided into inner loop attitude control system and outer loop position control system, In order to solve the problem of underactuated character. Three virtual control variables are introduced to decouple the position dynamics. Three sliding mode disturbance observers (SMDOs) are designed to estimate the total disturbances in the position dynamics. Then three sliding mode controllers (SMCs) are designed to drive the trajectory tracking errors to zero asymptotically. The simulation example is carried out to test the effectiveness of SMDOs and SMCs. Simulation results validate that the designed SMDOs and SMCs provide both fast exact tracking capability and strong disturbance rejection capability for the quadrotor UAV.

Distributed Output-Feedback Formation Tracking Control for Clustered Quadrotors

In this article, we study the cooperative formation tracking problem of clustered quadrotors without velocity and angular velocity measurements. In particular, the clustered quadrotors are required to track a reference trajectory while preserving a well-defined formation shape. However, the information interaction among the quadrotors is local and the reference trajectory information is only known to partial quadrotors. To overcome the aforementioned dilemmas caused by measurement incompleteness and interaction restriction, a distributed output-feedback control algorithm is proposed based on the cascaded framework. To be specific, by introducing two auxiliary dynamics with saturation constraints on their states, a distributed command force with a saturation attribute is first developed in the outer position loop. Next, in terms of a self-contained selection criterion of the control parameters, a bounded applied thrust and a nonsingular command attitude are extracted from the developed command force. Whereafter, an applied torque resorting to another auxiliary dynamics is developed in the inner attitude loop for the purpose of tracking the command attitude. It is shown that, despite the absence of the velocity and angular velocity information of clustered quadrotors, the concerned cooperative formation tracking objective is fulfilled by the proposed distributed control algorithm. Finally, simulations are performed to validate the built theoretical results.

The stable behavior of low thermal conductivity in 1T-sandwich structure with different components

Designing materials with low thermal conductivity (κ) is of demand for thermal protection, heat insulation, thermoelectricity, etc. In this paper, based on the state-of-the-art first-principles calculations, we propose a framework of a 1T-sandwich structure for designing materials with low κ. The 1T-sandwich structure is the same as the well-known transition metal dichalcogenide but with light carbon atoms in the middle plane. Using different atoms to fill the outer positions, a few novel two-dimensional materials are constructed as study cases, i.e., Mg2C, Janus MgBeC, Be2C, and Mo2C. With a systematic and comparative study, the κ are calculated to be 3.74, 8.26, 14.80, and 5.13 W/mK, respectively. The consistent values indicate the stable behavior of low κ in the 1T-sandwich structure, being insensitive to the component. Our study would help design advanced functional materials with reliable heat transfer performance for practical applications, which reduces the influence of unavoidable impurities.

Observation of domain‐selective defect effects from a CVD‐grown graphene monolayer sandwiched at individual nanoparticle‐on‐mirror plasmonic junctions

AbstractThe author examines the different defect effects of chemical vapor deposition graphene monolayer (CVD‐GM) relying on domain position at an individual nanoparticle‐on‐mirror (NPoM) plasmonic junction. The NPoM, composed of Au nanoparticle (NP)/CVD‐GM/Au thin film (TF), could previously show the mode‐selective Raman enhancement, in which the center domain exhibited the highest Raman enhancement of both radial breathing like mode (RBLM) and D mode considering the local z‐directional electromagnetic (EM) field enhancement effect in the NPoM. Meanwhile, the outer domain of the NPoM also displays the near‐two symmetrical deep pits via atomic force microscope (AFM) with the accompanying lower I[D]/I[D*], higher FWHM[RBLM], I[RBLM], and relatively red‐shifted (tensile strained) Max [RBLM] from surface‐enhanced Raman scattering (SERS) information than the central case. With these observations, the physical loading of Au NP on CVD‐GM/Au TF may induce the threading effect on the most outer position of CVD‐GM at the NPoM, leading to sp2 defect‐rich domains. In contrast, the central domains, where the sp3 defects are rich, exhibit the opposite SERS spectral phenomena, indicating that the near‐flat surface shape of Au NP bottom has a higher probability to exert a strong charge transfer along the z‐direction, resulting in higher I[RBLM] and I[D]/I[D*] than the most outer domain. As such, the author anticipates various chemical sensing using subtle changes in CVD‐GM morphology at both the most outer and center positions in the NPoM with the comparison of each SERS spectral signature.

Cascade active disturbance rejection control of single‐rod electrohydrostatic actuator

AbstractElectrohydrostatic actuators (EHAs) are used to replace traditional centralized hydraulic systems to reduce weight and improve efficiency and maintainability. This paper proposes a cascade active disturbance rejection control (C‐ADRC) method for single‐rod EHAs with parametric uncertainties and severe external disturbances. The studied EHA can be transformed into a cascade connection of a first‐order pressure system and a second‐order position system. Two linear active disturbance rejection controllers are designed for the inner pressure system and the outer position system to estimate and compensate for various uncertainties in the two loops, respectively. The uniqueness of the C‐ADRC is that the two linear active disturbance rejection controllers are designed by making full use of the measurable states and known model information of the EHA system. It is theoretically proved that the closed‐loop system is semi‐globally uniformly ultimately bounded. Moreover, the proposed controller can theoretically ensure position tracking with desired accuracy as the bandwidth of extended state observers (ESOs) becomes sufficiently high. Simulation and experimental results verify the effectiveness of the proposed method.

The relationship between boll retention and defoliation of cotton at the fruiting site level

AbstractDefoliation is used to ease mechanical harvest and reduce lint staining of cotton (Gossypium hirsutum L.). Crop conditions are important determinants of its efficiency, but their effects have not been fully examined. We performed a multiple‐site field study during 2018–2020 (under 17 environmental conditions, covering three cotton regions in China) to explore the relationship between boll retention and defoliation at the fruiting site level. The hormonal defoliant, thidiazuron and boll opener, ethephon, were tank‐mixed or their combination product was used in this study. There was a positive Spearman ranking correlation between boll retention and defoliation in most experimental sites, with correlation coefficients (r) ranging from .275 to .725 at 7 d after application of harvest aids, suggesting that the leaves at fruiting sites bearing bolls dropped more easily than those at fruiting sites where abscission occurred. The positive correlation declined with the fruiting sites up the plant and away the mainstem. The differences in defoliation between fruiting sites with or without bolls were high (around 60–70%) at lower and/or inner positions, but low or negligible at upper and/or outer positions. It appears that the higher light intensity at upper and outer portions of plant may enhance leaf drop and thus reduce the dependence of defoliation on boll retention. In conclusion, a high boll retention would accelerate leaf removal, and may enhance leaf abscission on cloudy days or within more closed canopy.

Adaptive Fault-Tolerant Distributed Formation Control of Clustered Vertical Takeoff and Landing UAVs

This article investigates the formation control issue of clustered vertical takeoff and landing (VTOL) unmanned airborne vehicles (UAVs) subject to undesired perturbations composed by actuator faults, parametric uncertainties, and external disturbances. In particular, a cluster of VTOL UAVs fly together in a given velocity with a well-specified formation configuration. For this purpose, an adaptive fault-tolerant distributed control algorithm via local information interaction is proposed under a hierarchical framework. Specifically, a distributed command force resorting to projection-based adaptation is first synthesized in the outer position loop. Such a command force is of a saturation attribute in order that a boundeddesired thrust and a nonsingular command attitude can be extracted in terms of appropriate control parameters. Next, in the inner attitude loop, a desired torque also with the help of projection-based adaptation is synthesized. Given that the underlying undirected topology is connected, it is shown based on the Lyapunov theory that the proposed adaptive fault-tolerant distributed control algorithm ensures the accomplishment of the concerned formation control objective of the clustered VTOL UAVs in spite of the undesired perturbations. Simulations validate and further highlight the effectiveness of the proposed distributed control algorithm.

Eugene Rivers and the responsibility of intellectuals

Eugene Rivers and the responsibility of intellectuals

Mechanical, thermogravimetric, and dynamic mechanical analysis of basalt and flax fibers intertwined vinyl ester polymer composites

AbstractThe selection of fibers and their stacking sequence, which affect structural integrity and functional properties, are critical parts of polymer composite design. In this work, the influence of various stacking sequences made of basalt and flax fiber layers on the mechanical, thermal, and dynamic mechanical analyses of vinyl ester polymer composites was investigated. The stacking sequence designed by alternate basalt and flax layers showed higher tensile and flexural strengths, with basalt layers in the outer positions. The high‐strength basalt fiber retains considerable stress, particularly in the outer layer, reducing stress transfer to the remaining core layers. The basalt and flax fiber alternative layered sequence with outer basalt layers shows a slightly lower thermal degradation temperature (467°C) than the only basalt layered sequence composite (474°C). Because of the high thermal resistance of the outer basalt layers, heat flow to the next fiber layers is reduced. The dynamic mechanical analysis reveals that the polymer composite intertwined with only basalt fiber was found to have a higher storage modulus. On the other hand, the outer basalt layers intertwined with the core flax layers composite showed a 122% higher damping value than the stacking sequence made of only basalt fiber due to the porous structure of flax fibers dissipating more vibration energy.

Air-Stable Dy(III)-Macrocycle Enantiomers: From Chiral to Polar Space Group

Air-Stable Dy(III)-Macrocycle Enantiomers: From Chiral to Polar Space Group

High‐Performance All‐Small‐Molecule Organic Solar Cells Enabled by Regio‐Isomerization of Noncovalently Conformational Locks

AbstractThe power conversion efficiencies (PCEs) of organic solar cells (OSCs) have surpassed 19% thanks to the innovation of polymer donors and molecular acceptors. However, the batch‐to‐batch variations in polymer materials are detrimental to the reproducibility of the device performance. In comparison, small‐molecule donors (SMDs) possess some unique advantages, such as well‐defined molecular weights, easy purification, and excellent batch‐to‐batch repeatability. Herein, a pair of regioisomeric SMDs (BT‐O1 and BT‐O2) has been synthesized with alkoxy groups as S···O noncovalently conformational locks (NoCLs) at the inner and outer position, respectively. Theoretical and experimental results reveal that the regioisomeric effect has a significant influence on the light‐harvest ability, energy levels, molecular geometries, internal reorganization energy, and packing behaviors for the two SMDs. As a result, BT‐O2‐based binary device shows an impressive PCE of 13.99%, much higher than that of BT‐O1 based one (4.07%), due to the better‐aligned energy level, more balanced charge transport, less charge recombination, lower energy loss, and more favorable phase separation. Furthermore, the fullerene derivative PC71BM is introduced into BT‐O2:H3 as the third component to achieve a notable PCE of 15.34% (certified 14.6%). Overall, this work reveals that NoCLs is a promising strategy to achieve high‐performance SMDs for all‐small‐molecule OSCs.