Valley-Related Multipiezo Effect and Noncollinear Spin Current in an Altermagnet Fe2Se2O Monolayer.

An altermagnet exhibits many novel physical phenomena because of its intrinsic antiferromagnetic coupling and natural band spin splitting, which are expected to give rise to new types of magnetic electronic components. In this study, an Fe2Se2O monolayer is proven to be an altermagnet with out-of-plane magnetic anisotropy, and its Néel temperature is determined to be 319 K. The spin splitting of the Fe2Se2O monolayer reaches 860 meV. Moreover, an Fe2Se2O monolayer presents a pair of energy valleys, which can be polarized and reversed by applying uniaxial strains along different directions, resulting in a piezovalley effect. Under the strain, the net magnetization can be induced in the Fe2Se2O monolayer by doping with holes, thereby realizing a piezomagnetic property. Interestingly, noncollinear spin current can be generated by applying an in-plane electric field on an unstrained Fe2Se2O monolayer doped with 0.2 hole/formula unit. These excellent physical properties make the Fe2Se2O monolayer a promising candidate for multifunctional spintronic and valleytronic devices.

Marsdenia tenacissima genome reveals calcium adaptation and tenacissoside biosynthesis.

Marsdenia tenacissima is a medicinal plant widely distributed in the calcium-rich karst regions of southwest China. However, the lack of a reference genome has hampered the implementation of molecular techniques in its breeding, pharmacology and domestication. We generated the chromosome-level genome assembly in Apocynaceae using combined SMRT sequencing and Hi-C. The genome length was 381.76 Mb, with 98.9% of it found on 11 chromosomes. The genome contained 222.63 Mb of repetitive sequences and 21 899 predicted gene models, with a contig N50 of 6.57 Mb. Phylogenetic analysis revealed that M. tenacissima diverged from Calotropis gigantea at least 13.43 million years ago. Comparative genomics showed that M. tenacissima underwent ancient shared whole-genome duplication. This event, together with tandem duplication, contributed to 70.71% of gene-family expansion. Both pseudogene analysis and selective pressure calculations suggested calcium-related adaptive evolution in the M. tenacissima genome. Calcium-induced differentially expressed genes (DEGs) were mainly enriched in cell-wall-related processes. Domains (e.g. Fasciclin and Amb_all) and cis-elements (e.g. MYB and MYC) frequently occurred in the coding and promoter regions of cell-wall DEGs, respectively, and the expression levels of these genes correlated significantly with those of calcium-signal-related transcription factors. Moreover, calcium addition increased tenacissoside I, G and H contents. The availability of this high-quality genome provides valuable genomic information for genetic breeding and molecular design, and lends insights into the calcium adaptation of M. tenacissima in karst areas.

Influence of electronic correlation on the valley and topological properties of VSiGeP4 monolayer.

Valley is used as a new degree of freedom for information encoding and storage. In this work, the valley and topological properties of the VSiGeP4 monolayer were studied by adjusting the U value based on first-principles calculations. The VSiGeP4 monolayer remains in a ferromagnetic ground state regardless of the change in the U value. The magnetic anisotropy of the VSiGeP4 monolayer is initially in-plane, and then turns out-of-plane with the increase in the U value. Moreover, a topological phase transition is observed in the present VSiGeP4 monolayer with the increase in U value from 0 to 3 eV, i.e., the VSiGeP4 monolayer behaves as a bipolar magnetic semiconductor, a ferrovalley semiconductor, a half-valley metal characteristic, and a quantum anomalous Hall state. The mechanism of the topological phase transition behavior of the VSiGeP4 monolayer was analyzed. It was found that the variation in U values would change the strength of the electronic correlation effect, resulting in the valley and topological properties. In addition, carrier doping was studied to design a valleytronic device using this VSiGeP4 monolayer. By doping 0.05 electrons per f.u., the VSiGeP4 monolayer with a U value of 3 eV exhibits 100% spin polarization. This study indicates that the VSiGeP4 monolayer has potential applications in spintronic, valleytronic, and topological electronic nanodevices.

Multi-level chiral edge states in Janus M2XS2Se2 (M = V, Ti; X = W, Mo) monolayers with high Curie temperature and sizable nontrivial topological gaps.

Quantum anomalous Hall (QAH) insulators with dissipation-less chiral edge channels provide ideal platforms for the exploration of topological materials and low-power spintronic devices. However, the ultralow operation temperature and small nontrivial gaps are the bottlenecks for QAH insulators towards future applications. Here, a new family of QAH insulators, that is, Janus M2XS2Se2 (M = V, Ti; X = W, Mo) monolayers, are proposed to be ferromagnets with large perpendicular magnetic anisotropy (PMA) and high Curie temperature above room temperature. Moreover, the present M2XS2Se2 monolayers hold sizable nontrivial topological gaps, resulting in the 1st chiral edge state with Chern number C = -1. Unexpectedly, there also exists an occupied 2nd chiral edge state below the Fermi level. Although all M2XS2Se2 monolayers retain their PMA characteristics on application of biaxial strain, various topological phase transitions are present. The V2WS2Se2 monolayer preserves the QAH state regardless of strain, while the V2MoS2Se2 and Ti2WS2Se2 monolayers transform from QAH states to metallic states under tensile strains. The present M2XS2Se2 monolayers show competitive advantages among the reported materials for the development of topological electronic devices.

Coexisting Ferroelectric and Ferrovalley Polarizations in Bilayer Stacked Magnetic Semiconductors.

It has long been expected that the coexistence of ferroelectric and ferrovalley polarizations in one magnetic semiconductor could offer the possibility to revolutionize electronic devices. In this study, monolayer and bilayer YI2 are studied. Monolayer YI2 is a ferromagnetic semiconductor and exhibits a valley polarization up to 105 meV. All of the present bilayer YI2 regardless of stacking orders show antiferromagnetic states. Interestingly, the bilayer YI2 with 3R-type stackings shows not only valley polarization but also unexpected ferroelectric polarization, proving the concurrent ferrovalley and multiferroics behaviors. Moreover, the valley polarization of 3R-type bilayer YI2 can be reversed by controlling the direction of ferroelectric polarization through an electric field or manipulating the magnetization direction using an external magnetic field. The amazing phenomenon is also demonstrated in 2D van der Waals LaI2 and GdBr2 bilayers. A design idea of multifunctional devices is proposed based on the concurrent ferrovalley and multiferroics characteristics.

Diaphragms simulation, fabrication, and testing of a high temperature fiber optic F-P accelerometer based on MEMS.

High-sensitivity detection of vibrations under high temperatures is a topic of great interest in modern engineering such as thermal engine deep-sea aquaculture factory ship, aerospace, high temperature casting, energy, etc. As traditional accelerometers and some fiber optic F-P accelerometers have shown their sensing limits at about 400 °C and 650 °C, respectively, a high temperature fiber optic F-P accelerometer based on MEMS technology is proposed. To obtain a high-performance chip for the sensor, an examination of the theoretical performance of an L and Г-shaped cantilever beam diaphragm shows a sensitivity of 15.05 nm/g and 53.7 nm/g, respectively, and a wide working frequency range. Thanks to the designed sensor's various protections, frequency measurements with a high-temperature performance of 850 °C are recorded. The L-shaped cantilever beams diaphragm allows the sensor measurements at 850 °C with a repeatability of 5.46%, a working frequency range of 100-1000 Hz, an experimental sensitivity of 389 mV/g, an overall stability of 8 jumps at its adjacent frequency resolution range over 150 measurements, a linearity of 0.9856 and a maximum relative error maintained below 1.72%. In the field of application, it also exhibits a good relative error of measurement respecting the technical specification of 5 Hz.

A New Prediction Method of Displacement Errors Caused by Low Stiffness for Industrial Robot.

This paper presents a new method, a fast prediction method based on the Cartesian stiffness model and equivalent spring stiffness (FPM-CSES), to calculate displacement errors of deformation caused by low stiffness for industrial robot. First, the Cartesian stiffness model based on the Jacobian matrix was established for a robot, and then the displacement error model of deformations caused by external force was established based on Cartesian stiffness. Second, the transmission system of the robot's joint was analyzed, and an equivalent method for joint stiffness was presented based on a series spring system. Meanwhile, the stiffness of the key components including the servo motor, harmonic reducer, and timing belt was deduced in detail. Finally, a compared simulation and a measurement experiment were conducted on a 6-joint series robot. It was found that the FPM-CSES could calculate any configuration among the robot's workspace. Compared with the finite element analysis (FEA) method, the presented method is feasible and more efficient. The experimental results showed that the prediction accuracy of the FPM-CSES is rather high, with an average rate of more than 83.72%. Hence, the prediction method presented in this study is simple, fast, and reliable, and could be used to predict and analyze the displacement errors caused by the cutting force, and provide the basis for trajectory planning and error compensation, enhancing the robot's machining performance.

Motion measurement system of compliant mechanisms using computer micro-vision.

Position sensing is essential to testify the validity of the mechanical design and verify the performance in micromanipulation. A practical system for non-contact micro-motion measurement of compliant nanopositioning stages and micromanipulators is proposed using computer micro-vision. The micro-motion measurement method integrates optical microscopy and an optical flow-based technique, in which the motions of complaint mechanisms are precisely detected and measured. Simulations are carried out to validate the robustness of the proposed method, while the micro-vision system and a laser interferometer measurement system are also built up for a series of experiments. The experimental results demonstrate that the proposed measurement system possesses high stability, extensibility, and precision with 0.06 µm absolute accuracy and 0.05 µm standard deviation.

Photonic generation of terahertz dual-chirp waveforms ranging from 364 to 392†GHz.

In this paper, we propose and experimentally demonstrate a photonic scheme based on frequency doubling and photo-mixing to generate dual-chirp signals in the terahertz (THz) band. A broadband dual-chirp THz signal with 28 GHz bandwidth, ranging from 364 GHz to 392 GHz, is successfully generated in the proof-of-concept experiment, resulting in a chirp rate of 0.028 GHz/ns for both up chirp and down chirp signals. THz dual-chirp signals featuring a large bandwidth are beneficial to enable high resolution and high accuracy by mitigating the range measurement error induced by the range-Doppler coupling effect. Therefore, the proposed system is expected to have a great potential for future THz radar applications.

Enhanced resistive switching performance in yttrium-doped CH3NH3PbI3 perovskite devices.

In this study, yttrium-doped CH3NH3PbI3 (Y-MAPbI3) and pure CH3NH3PbI3 (MAPbI3) perovskite films have been fabricated using a one-step solution spin coating method in a glove box. X-ray diffractometry and field-emission scanning electron microscopy were used to characterize the crystal structures and morphologies of perovskite films, respectively. It was found that the orientation of the crystal changed and the grains became more uniform in Y-MAPbI3 film, compared with the pure MAPbI3 perovskite film. The films were used to prepare the resistive switching memory devices with the device structure of Al/Y-MAPbI3 (MAPbI3)/ITO-glass. The memory performance of both devices was studied and showed a bipolar resistive switching behavior. The Al/MAPbI3/ITO device had an endurance of about 328 cycles. In contrast, the Al/Y-MAPbI3/ITO device exhibited an enhanced performance with a long endurance up to 3000 cycles. Moreover, the Al/Y-MAPbI3/ITO device also showed a higher ON/OFF ratio of over 103, long retention time (≥104 s), lower operation voltage (±0.5 V) and outstanding reproducibility. Additionally, the conduction mechanism of the high resistance state transformed from space-charge limited current for a Y free device to the Schottky emission after Y doping. The present results indicate that the Al/Y-MAPbI3/ITO device has a great potential to be used in high-performance memory devices.

Robust block-matching algorithm for motion estimation using an anti-interference similarity criterion and the bilateral optimization scheme.

As an essential component in applications such as video coding, autonomous navigation, and surveillance cameras, efficient and robust motion estimation is always required. This paper proposes a robust block-matching algorithm consisting of a rough matching step and a fine matching step for motion estimation. In the coarse matching step, an improved adaptive rood pattern search strategy combined with an anti-interference similarity criterion is developed to improve the computational efficiency and robustness. In the fine matching step, after performing a subpixel estimation procedure, a bilateral verification scheme is demonstrated to decrease the motion estimation errors caused by environmental disturbances. Experiments are carried out over popular video and image sequences, and several measurement indexes are used to quantify the performance of the proposed method and other motion estimation methods. Comparative analysis and quantitative evaluation demonstrate that the proposed method exhibits strong robustness and can achieve a good balance between computational efficiency and complexity.

Sub-Nyquist computational ghost imaging with deep learning.

We propose a deep learning computational ghost imaging (CGI) scheme to achieve sub-Nyquist and high-quality image reconstruction. Unlike the second-order-correlation CGI and compressive-sensing CGI, which use lots of illumination patterns and a one-dimensional (1-D) light intensity sequence (LIS) for image reconstruction, a deep neural network (DAttNet) is proposed to restore the target image only using the 1-D LIS. The DAttNet is trained with simulation data and retrieves the target image from experimental data. The experimental results indicate that the proposed scheme can provide high-quality images with a sub-Nyquist sampling ratio and performs better than the conventional and compressive-sensing CGI methods in sub-Nyquist sampling ratio conditions (e.g., 5.45%). The proposed scheme has potential practical applications in underwater, real-time and dynamic CGI.

Nonlinearity-aware optoelectronic terahertz discrete multitone signal transmission with a zero-bias diode.

The terahertz band has been recognized as a promising candidate to support future rate-greedy applications such as 6G communications. Optoelectronic terahertz communications are beneficial for the realization of high-speed transmission. In this Letter, we propose and experimentally demonstrate an optoelectronic terahertz transmission system with intensity modulation and direct detection, where a discrete multitone (DMT) waveform with high-order quadrature amplitude modulation (QAM) is used. A zero-bias diode (ZBD) is used in the system as a simple, cost-effective direct detection terahertz receiver. A nonlinearity-aware digital signal reception routine is proposed to mitigate the nonlinear impairments induced by subcarrier-to-subcarrier beating interference from the ZBD. In this experiment, up to a 60 Gbit/s line rate 16QAM-DMT signal is successfully transmitted over a 3 m wireless link in the 310 GHz band, and the mean signal-to-noise ratio is improved by 3 dB with nonlinearity-aware signal processing routine. The advantageous features of such a scheme make it a promising solution for terahertz wireless communications.

Interface hybridization and spin filter effect in metal-free phthalocyanine spin valves.

Spin-orbit coupling (SOC) has long been regarded as the core interaction to determine the efficiency of spin conserved transport in semiconductor spintronics. In this report, a spin-valve device with a Co/metal-free phthalocyanine (H2Pc)/Co stacking structure is fabricated. The magnetoresistance effect was successfully obtained in the device. It is also found that the magnetoresistance response is relatively smaller than that of metallic phthalocyanines, clearly implying that SOC is not the key factor to affect the magnetoresistance in phthalocyanine spin-valves. The dominant mechanism that determines the spin transport efficiency in the present H2Pc devices was systemically explored by combining both experimental measurements and first-principles calculation analysis. It was noticed that both the crystalline structure and molecular orientation of the H2Pc layer could be modified by the contact under-layer materials, which changes the magnetization intensity of the ferromagnetic metallic electrode due to the strong interface hybridization of Co/H2Pc. Meanwhile, the theoretical calculations clearly demonstrated that the spin filter effect from the second H2Pc layer should be responsible for the decrease of the magnetoresistance response in the present spin-valves compared to those using metallic phthalocyanine layers. This investigation may trigger new insights into the role of SOC strength and interface hybridization in organic spintronics.

Method of fiber transfer delay measurement based on phase quantization and delay synthesis.

A novel method, to the best of our knowledge, of fiber transfer delay (FTD) measurement based on phase quantization and delay synthesis is proposed and demonstrated. By detecting the differential phase shifts of a set of frequency-multiplied RF signals transmission through the fiber link with and without the FTD under the test, the ${2}\pi $2π phase ambiguity problem can be solved. To avoid the phase quantization error near the digital quantization boundary, a self-check and error-correction method is proposed so as to greatly improve the reliability of measurement. In the experiment, the measurement repeatability around 0.018 ps within a period of 80 s is achieved for a back-to-back fiber link, and a test resolution of 0.03 ps is proved with a motorized tunable delay line. The system is available for measurement of a large FTD range up to 100 µs with no dead zone.

Unusual interfacial magnetic interactions for τ-MnAl with Fe(Co) atomic layers.

The interfacial magnetic interaction and coupling mechanism for τ-MnAl with Fe(Co) atomic layers have been studied using first principles calculations. The stable surface and interface were firstly determined by the surface energy of τ-MnAl and interface energy of τ-MnAl/Fe(Co) films, respectively. Their magnetic coupling interactions were investigated by varying the Fe(Co) atomic layer numbers. It is noted that both Fe and Co exhibited ferromagnetic coupling with τ-MnAl. Interestingly, an unusual oscillation phenomenon of magnetic coupling for τ-MnAl with Fe(Co) atomic layers was observed depending on the layer thickness of Fe(Co). Moreover, Fe and Co showed different oscillation modes. The energy difference between antiferromagnetic and ferromagnetic states is larger for τ-MnAl/Fe and τ-MnAl/Co when the Fe(Co) layer numbers are even and odd, respectively. Their mechanisms were analyzed based on the band structures and the confinement of electrons in quantum wells. It is found that the magnetic coupling oscillation in τ-MnAl/Fe originated from both the spin up Δ1 band and spin down Δ5 band at the [capital Gamma, Greek, macron] points. Comparatively, the oscillation of τ-MnAl/Co is due to the spin up band at the X[combining macron] point. The present results could provide insight to further understand interfacial exchange interactions among magnetic layers.

Calibration method for hand-eye system with rotation and translation couplings.

This paper develops a novel hand-eye calibration method for hand-eye systems with rotation and translation coupling terms. First, a nonlinear camera model with distortion terms and a model of a hand-eye system with rotation and translation coupling terms are established. Based on a non-linear optimization method and a reverse projection method, a decoupling calibration method for a lower-degree-of-freedom hand-eye system is proposed. Then the path planning for the calibration process is carried out. Based on the analysis of coupling constraints and hand-eye system motion constraints, three types of hand-eye calibration paths with high efficiency and easy operation are developed. In addition, the influence of key parameters on hand-eye calibration accuracy is analyzed. Finally, calibration experiments and parametric influence experiments are carried out. The results demonstrate that the proposed method is effective and practical for calibrating the hand-eye system.

Development of a 3-PRR Precision Tracking System with Full Closed-Loop Measurement and Control.

A 3-PRR (three links with each link consisting of a prismatic pair and two rotating pairs) parallel platform was designed for application in a vacuum environment. To meet the requirement of high tracking accuracy of the 3-PRR parallel platform, a full closed-loop control precision tracking system with laser displacement sensors and linear grating encoders was analysed and implemented. Equally-spaced laser displacement sensors and linear grating encoders were adopted not only for measurement but also for feedback control. A feed-forward control method was applied for comparison before conducting the closed-loop feedback control experiments. The closed-loop control experiments were conducted by adopting the PI (proportion and integration) feedback control and RBF (radial basis function) neural network control algorithms. The experimental results demonstrate that the feed-forward control, PI feedback control, and RBF neural-network control algorithms all have a better control effect than that of semi-closed-loop control, which proves the validity of the designed full closed-loop control system based on the combination of laser displacement sensors and linear grating encoders.

Photonics-enabled compressive sensing with spectral encoding using an incoherent broadband source.

In this Letter, we propose an approach to achieving photonics-enabled compressive sensing of sparse wideband radio frequency signals in which an incoherent broadband source is applied, and the mixing and integration functions are realized in the optical domain. A spectrum shaper is employed to slice and encode the spectrum of the broadband light according to a predetermined random sequence. Because of the dispersion-induced group delay, the mixing between the incoming signal and the random bit sequence is achieved. At the output of the spectrum shaper, an array of photodetectors is employed to realize down-sampling, and the input sparse signal can be captured in a single-shot mode. Since no pulsed laser is employed, our scheme obviates the need for time-domain synchronization between the repetitive ultra-fast pulses and the random sequence. Experimental demonstrations and numerical results are presented to verify the feasibility and potential of the approach.

Multifocus image fusion method for image acquisition of 3D objects.

We propose a multifocus image fusion method for achieving all-in-focus images of three-dimensional objects based on the combination of transform domain and spatial domain techniques. First, the source images are decomposed into low-frequency and high-frequency components by the discrete wavelet transform technique. Next, a correlation coefficient is employed to obtain the maximum similarity among low-frequency components. Then, in order not to interrupt the correlations among decomposition layers, the comparison among high-frequency components is executed by transforming them to spatial domain. In addition, a sliding window is used to evaluate the local saliency of the pixels more accurately. Finally, the fused image is synthesized from source images and the saliency map. The variance, entropy, spatial frequency, mutual information, edge intensity, and similarity measure (QAB/F) are used as metrics to evaluate the sharpness of the fused image. Experimental results demonstrate that the fusion performance of the proposed method is enhanced compared with that of the other widely used techniques. In the application of three-dimensional surface optical detection, the proposed method is suitable for obtaining the complete image at varying distances in the same scene, so as to prepare for subsequent defect identification.