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The regular admittance controller cannot be easily transferred to the physical human–robot interaction scenario because of the dynamic stiffness of the human arm. The dynamic interaction of humans can cause high frequency and unsafe oscillation of the robot arm. Based on the adaptive control scheme, this paper presents an online sensory-based analytical approach to recognize and quantify the “stability index" named as a robust haptic observer. The observer performs the Fast Fourier Transform on the interaction force signal within a sliding window and quickly detects system oscillation through a simple mathematical transformation. Compared with the existing methods, it can calculate a normalized system stability index more accurately and faster. This quantified index is employed in a linearized adaptive law to tune the parameters of the admittance controller. Experimental validation of the proposed strategy is performed and compared with state-of-the-art work in a task of human-guided drawing. The results show that our proposed approach can effectively detect oscillation, and the drawing time is shortened by 15% with the same tracking accuracy. In addition, the energy consumption is 44.4% less on average. [ABSTRACT FROM AUTHOR]

Neural activity extraction and neural decoding from neural signals are an important part of critical components of brain-computer interface systems. With the development of brain-computer interface technology, the demand for precise external control and nervous activities in macaque monkey during unilateral hand grasp has increased the complexity of control and neural decoding, which puts forward higher requirements for the accuracy and stability of feature extraction and neural decoding. In this study, a micro Capsnet network architecture that consists of a few network layers, a vector feature structure, and optimization network parameters, is proposed to decrease the computing time and complexity, decrease artificial debugging, and improve the decoding accuracy. Compared with KNN, SVM, XGBOOST, CNN, SimpleRNN, and LSTM, the algorithm in this study improves the decoding accuracy by 98.03%, and achieves state-of-the-art accuracy and stronger robustness. Furthermore, the proposed algorithm can further enhance the control accuracy in the brain-computer interface. [ABSTRACT FROM AUTHOR]

Parametric interpolation has been widely used in robot control because of its advantages over traditional linear or circular interpolation. The NURBS interpolation based on S-shaped feedrate scheduling can realize the smooth continuous motion of robots, but it also faces two challenges. One challenge is that when the NURBS curve is split into multiple blocks, if one or more blocks are too short, the final feedrate profile is often discontinuous. The other challenge is that the NURBS curve cannot be obtained entirely due to calculation errors. In this paper, a high-precision NURBS interpolator based on S-shaped feedrate scheduling is proposed. In this interpolator, a bidirectional velocity scanning scheme is developed to effectively handle the too short split blocks of the NURBS curve. Meanwhile, an optimization algorithm is proposed to ensure the precision of NURBS curves. The feasibility and advantages of the proposed method are verified through case studies. [ABSTRACT FROM AUTHOR]

Qubit initialization is a critical task in quantum computation and communication. Extensive efforts have been made to achieve this with high speed, efficiency and scalability. However, previous approaches have either been measurement-based and required fast feedback, suffered from crosstalk or required sophisticated calibration. Here, we report a fast and high-fidelity reset scheme, avoiding the issues above without any additional chip architecture. By modulating the flux through a transmon qubit, we realize a swap between the qubit and its readout resonator that suppresses the excited state population to 0.08% ± 0.08% within 34 ns (284 ns if photon depletion of the resonator is required). Furthermore, our approach (i) can achieve effective second excited state depletion, (ii) has negligible effects on neighboring qubits, and (iii) offers a way to entangle the qubit with an itinerant single photon, useful in quantum communication applications. Reliable and fast active reset protocols are key to the functioning of quantum computing systems. Here, the authors use parametric driving to swap an excitation from a transmon qubit to its readout resonator within 34 ns, with negligible effects on neighboring qubits. [ABSTRACT FROM AUTHOR]

Active metasurfaces, whose optical properties can be modulated post-fabrication, have emerged as an intensively explored field in recent years. The efforts to date, however, still face major performance limitations in tuning range, optical quality, and efficiency, especially for non-mechanical actuation mechanisms. In this paper, we introduce an active metasurface platform combining phase tuning in the full 2π range and diffraction-limited performance using an all-dielectric, low-loss architecture based on optical phase change materials (O-PCMs). We present a generic design principle enabling binary switching of metasurfaces between arbitrary phase profiles and propose a new figure-of-merit (FOM) tailored for reconfigurable meta-optics. We implement the approach to realize a high-performance varifocal metalens operating at 5.2 μm wavelength. The reconfigurable metalens features a record large switching contrast ratio of 29.5 dB. We further validate aberration-free and multi-depth imaging using the metalens, which represents a key experimental demonstration of a non-mechanical tunable metalens with diffraction-limited performance. Here, the authors report an active all-dielectric metasurface platform based on phase change materials, combining phase tuning in the full 2π range, and demonstrate aberration-free and multi-depth imaging with a non-mechanical tunable metalens. [ABSTRACT FROM AUTHOR]

Novel optical properties in graded photonic super-crystals can be further explored if new types of graded photonic super-crystals are fabricated. In this paper, we report holographic fabrication of graded photonic super-crystal with eight graded lattice clusters surrounding the central non-gradient lattices through pixel-by-pixel phase engineering in a spatial light modulator. The prospect of applications of octagon graded photonic super-crystal in topological photonics is discussed through photonic band gap engineering and coupled ring resonators. [ABSTRACT FROM AUTHOR]

Aims: To investigate the relative contributions of pH, organic anions concentration, and phosphatase activity to rhizosphere soil phosphorus availability and crop phosphorus uptake in polycultures. Methods: A field experiment was conducted for three consecutive years in a split-plot design with main plots treated with two phosphorus levels and subplots treated with maize and alfalfa grown alone or intercropped. Results: Intercropped maize and alfalfa had 0.35 and 0.24 units lower rhizosphere pH, 28% and 30% higher total organic anions (TOA) concentration, and 21% and 41% greater acid phosphatase activity than those in monoculture. These changes in root exudates induced significant increases in rhizosphere phosphorus concentration of intercropped maize and alfalfa by 21% and 41%, and pH and TOA had greatest contributions, respectively. Rhizosphere phosphorus mobilization facilitated phosphorus uptake of intercropped maize, but this facilitation was offset by phosphorus uptake reduction due to decreased crown root surface area. Lateral root volume enhancement accounted for phosphorus uptake improvement of intercropped alfalfa by 86.6%, while rhizosphere phosphorus mobilization only had a 0.2% contribution. Conclusions: Rhizosphere pH and organic anions exhibit greater contributions than acid phosphatase activity in enhancing rhizosphere phosphorus availability. However, root surface area of maize and lateral root volume of alfalfa unveil greater influences on crop phosphorus uptake than rhizosphere pH and organic anions. [ABSTRACT FROM AUTHOR]

Aims: Cereal can stimulate legume N fixation through competition for soil mineral N. In addition, organic acids in the rhizosphere can mobilize external nutrients, which may help nodulation. However, how much NO3− and NH4+ competition and organic acids in the rhizosphere of intercropped crops contribute to N fixation remains unclear and requires study. Methods: Field and greenhouse experiments were conducted to quantify effects of N competition and organic acids on N fixation in a maize/alfalfa intercropping system. Results: Intercropping increased nitrogen derived from the atmosphere (%Ndfa), nodules number, and leghemoglobin content by 43.66%, 85.53%, 141.05%, respectively, leading to significantly improved total N uptake and yield, compared to monoculture. The improved %Ndfa was not only due to the depletion of NO3−, but also significantly correlated with the decrease of NO3−/NH4+ ratio and the increase of citric acid in rhizosphere of alfalfa, which could mobilize soluble resources for N fixation under no N addition. Overall, 15.4%–21.5% of N fixed by alfalfa was transferred to associated maize, and the improved N fixation enhanced N transfer. Conclusions: Our findings provide a mechanism for how root interactions facilitate N fixation, highlighting the importance of NO3−/NH4+ ratio and citric acid in nutrient mobilization for N fixation. [ABSTRACT FROM AUTHOR]

Reconfigurable beam steering components are indispensable to support optical and photonic network systems operating with high adaptability and with various functions. Currently, almost all such components are made of solid parts whose structures are rigid, and hence their functions are difficult to be reconfigured. Also, optical concentration beam steering is still a very challenging problem compared to radio frequency/microwave steering. Here we show a watermill-like beam steering system that can adaptively guide concentrating optical beam to targeted receivers. The system comprises a liquid droplet actuation mechanism based on electrowetting-on-dielectric, a superlattice-structured rotation hub, and an enhanced optical reflecting membrane. The specular reflector can be adaptively tuned within the lateral orientation of 360°, and the steering speed can reach ~353.5° s−1. This work demonstrates the feasibility of driving a macro-size solid structure with liquid microdroplets, opening a new avenue for developing reconfigurable components such as optical switches in next-generation sensor networks. Adaptive elements for optical beam steering are increasingly important to support nascent optical and photonic networks. This work presents a beam steering device based on a liquid droplet actuation method, capable of providing 360 degrees lateral steering with low energy consumption and a fast response time. [ABSTRACT FROM AUTHOR]

Aims: Mycorrhizae and root exudates have been considered the two important pathways for nitrogen (N) transfer from legume to non-legume plants. The present study aimed to investigate contribution of the relative importance of arbuscular mycorrhizal fungi and root exudates in short-term N transfer. Methods: A field experiment was conducted to explore N transfer from alfalfa to maize under two different N application levels using 15N leaf labeling. Results: N transfer amount ranged from 7 to 10 mg N plant−1 from alfalfa to maize and significantly decreased (by 11%–22%) with N fertilizer application. Intercropping of 4 rows of maize and 6 rows of alfalfa with 30 cm intra-row spacing (IMA43) was the optimal intercropping mode, which increased N transfer, total N uptake and yield by 18%, 15% and 11%, respectively. The relative importance of arbuscular mycorrhizal fungi and root exudates on N transfer was dependent on soil N availability. Under no N addition, hyphal length density (HLD) of rhizosphere soil explained the largest significant amount (50%) of the variability in N transfer and crop yield. However, root exudates explained 77% of the variability in N transfer and crop yields with N fertilizer application. Conclusions: Our findings highlighted that N transfer is reliant more on arbuscular mycorrhizal fungi than root exudates in N-deficient soil, whereas root exudates play a more important role in N-fertilized soil. [ABSTRACT FROM AUTHOR]

Active manganese dioxide was prepared and applied in the synthesis of glucuronic acid by selective oxidation from methyl glucoside. The active manganese dioxide was characterized by XPS, XRD, SEM, TGA and N adsorption-desorption test. The selective oxidation of methyl glucoside to glucuronic acid is studied with active manganese dioxide under the microwave radiation circumstance in different reaction conditions. The results show that active manganese dioxide displays a good oxidizability and selectivity under the microwave radiation. When methyl glucoside and active manganese dioxide react in a ratio of one to four at 80 °C for 2 h, glucuronic acid reached the highest yield to be 79 %. [ABSTRACT FROM AUTHOR]

We present the numerical studies of a novel hybrid graphene-metal Fano metamaterial, which is composed of a graphene grating (graphene ribbon array) and a square closed ring resonator (SCRR) separated by a dielectric substrate. The destructive interference between the narrow and broad electrical dipolar surface plasmons induced respectively on the surface of the graphene ribbon and the SCRR leads to the classical analog of electromagnetically induced transparency (EIT). By decreasing the thickness of the substrate spacer (enhancing the coupling between the two components), a double EIT system could be achieved. More importantly, the transparency windows in the hybrid structures can be actively controlled by varying the applied gate voltage on the graphene ribbon. Large effective group index and small loss within the transparency windows suggest the promising slow-light applications. [ABSTRACT FROM AUTHOR]

In this paper, we proposed a novel dual-frequency cross polarization converter that can simultaneously work at two frequencies in the reflection mode, which is constructed of an L-shaped perforated graphene sheet printed on a dielectric material backed by a gold ground plane. For the normal incidence, the optical rotation at these two working frequencies originates from the simultaneous excitation of both eigenmodes that are characterized as the results of the localized surface plasmon resonances. Moreover, by merely varying the Fermi energy of the graphene, both working frequencies can be tuned within a large frequency range, which suggests numerous potential optical applications. [ABSTRACT FROM AUTHOR]

In this paper, we report novel designs of tunable THz plasmonic devices based on liquid metals. The designed devices will be able to dynamically control and change the spectrum responses of extraordinary THz wave transmissions. Different THz device configurations are investigated, and numerical simulations have been conducted to theoretically verify the performance of the proposed structures. Moreover, an equivalent circuit model has been developed to describe the operating principle of the proposed THz devices. Good agreement has been achieved between the theoretical models and the numerical results. These new THz devices are expected to be applied in various areas of sensing, communication, and imaging. [ABSTRACT FROM AUTHOR]

With excellent photo-electric and electro-optical effects, the photorefractive spatial light modulators can work as optically addressed modulators in optical information processing systems and parallel optical computing systems. The photo-induced current pulses of the photorefractive spatial light modulator observed in the experiments are analyzed to conclude the characteristics, and to find the relationship between the properties of the current pulse and the structural parameters. Furthermore, the origin of the photo-induced current pulse is analyzed, and the methods to improve the operation speed of the spatial light modulators are proposed. The research results will be significant for extending the applications of the photorefractive spatial light modulators, and pushing ahead the research of all-optical modulation materials and devices for optical supercomputing. [ABSTRACT FROM AUTHOR]

Due to the serious flow separations and centralized vortices, there are high secondary losses in highly loaded turbines. It is imperative to find measures to control the flow separation and vortices hence improve the turbine performance. This paper reports our recent progress on flow separation and vortices control in highly loaded turbine cascades by using bowed blades. Two sets of highly loaded turbine cascades with the turning angles of 113° and 160°, and each with 7 bowed blade angles 0° (straight), ±10°, ±20° and ±30° were experimentally investigated. Both internal flow field measurement and flow visualization on the blade surfaces were conducted, and the effects of blade bowing on the flow topology, distribution of vorticity and the flow energy loss were discussed. The results show that, for the cascade with the turning angle of 113°, the appropriately positive bow angle could reduce the flow energy loss; whereas for the cascade with the turning angle of 160°, the well selected negative bow angle can give the better aerodynamic performance. [ABSTRACT FROM AUTHOR]