Search

Abstract A slow-wave structure improvement for enhancing the 2π-mode electronic efficiency is embodied in the validation of an extended interaction oscillator (EIO), which has an electronic efficiency of 6.52% at 0.22 THz from particle-in-cell (PIC) calculations. A 2π-mode bi-periodic slow-wave structure (BPSWS) with staggered long and short slots is utilized for optimizing the circuit performance. The proposed BPSWS has the capability of combining the respective advantages for both π and 2π-mode in terms of coupling performance and output performance, thus supporting a strongly-coupled 2π-mode with higher coupling capability. Compared with the typical mono-periodic SWS (MPSWS), the adopted strongly-coupled 2π-mode effectively improves the characteristic impedance M2R/Q by 103% to 66.79 Ω, the coupling coefficient by 66% to 0.497, and the normalized wave-amplitude by 22%. Accordingly, 503 W of average output power can be derived for the BPSWS-EIO with a 25.7 kV and 0.3 A sheet beam injected. Cold-test experiments were conducted, confirming that the 0.22 THz structure exhibits commendable fabrication precision and consistency and thus demonstrates the expected frequency response.

IntroductionService robot technology is increasingly gaining prominence in the field of artificial intelligence. However, persistent limitations continue to impede its widespread implementation. In this regard, human motion pose estimation emerges as a crucial challenge necessary for enhancing the perceptual and decision-making capacities of service robots.MethodThis paper introduces a groundbreaking model, YOLOv8-ApexNet, which integrates advanced technologies, including Bidirectional Routing Attention (BRA) and Generalized Feature Pyramid Network (GFPN). BRA facilitates the capture of inter-keypoint correlations within dynamic environments by introducing a bidirectional information propagation mechanism. Furthermore, GFPN adeptly extracts and integrates feature information across different scales, enabling the model to make more precise predictions for targets of various sizes and shapes.ResultsEmpirical research findings reveal significant performance enhancements of the YOLOv8-ApexNet model across the COCO and MPII datasets. Compared to existing methodologies, the model demonstrates pronounced advantages in keypoint localization accuracy and robustness.DiscussionThe significance of this research lies in providing an efficient and accurate solution tailored for the realm of service robotics, effectively mitigating the deficiencies inherent in current approaches. By bolstering the accuracy of perception and decision-making, our endeavors unequivocally endorse the widespread integration of service robots within practical applications.

Abstract In this paper, a piecewise sine waveguide (PWSWG) is proposed as the slow-wave structure (SWS) to develop high-power terahertz (THz) traveling wave tubes (TWTs). The PWSWG is an improvement over the rectangular waveguide wherein its two E-planes simultaneously oscillate up and down along the longitudinal direction. The oscillation curve in the H-plane is a piecewise sine curve formed by inserting line segments into the peaks and troughs of the sine curve. The simulation analysis and experimental verification show that the PWSWG offers the advantages of large interaction impedance and excellent electromagnetic transmission performance. Furthermore, the calculation results of beam–wave interaction show that the TWT based on PWSWG SWS can generate a radiated power of 253.1 W at the typical frequency of 220 GHz, corresponding to a gain of 37.04 dB and an interaction efficiency of 6.92%. Compared with the conventional SWG TWTs, the PWSWG TWT has higher interaction efficiency and shorter saturation tube length. In conclusion, the PWSWG proposed in this paper can be considered a suitable SWS for high-power THz radiation sources.

Microalgae are promising feedstock for oil production. The authors report that a transcription factor NobZIP77 can regulate oil synthesis by sensing the blue light, and explore these findings to greatly enhance oil productivity via genetic and process engineering in Nannochloropsis oceanica.

Based on the coupling mode theory and numerical simulation, intramode-group coupling in orbital angular momentum (OAM) fibers with elliptical deformation is analyzed in depth. The elliptical deformation not only introduces a time delay difference between even and odd modes of the same high-order vector mode but also destroys the structure of the high-order vector modes; the structural damage depends on the strength of the elliptical deformation. When the elliptical deformation is relatively small, the structural damage of high-order vector modes can be ignored and coupling can be thought as occurring only between two OAM modes composed of the same high-order vector mode. While the elliptical deformation becomes larger, the structural damage cannot be ignored, coupling appears among four OAM modes in the same OAM mode group, and the coupling between two OAM modes composed of the same high-order vector mode is more serious. The results will pave the way for the establishment of accurate propagation models and the optimization of the OAM fiber design.

Abstract Duckweed is one kind of promising bioenergy plant with prominent advantages such as fast growth rate and high starch content. However, almost all previous studies focused on the natural duckweed germplasms. In this study, heavy‐ion irradiation was used to establish a mutant library of Lemna aequinoctialis 6002, and one mutant named submarine‐1 (sub‐1) was screened, which could accumulate more starch but with smaller granules. Unexpectedly, under proper external growth conditions such as poor nutritional status and insufficient growth space, sub‐1 mutant would sink underwater due to formation of dense tissue structure and large amount of fine starch particles with the extension of cultivation time. The starch content in the sinking sub‐1 increased to over 45% (dry weight) and was 12% higher than the floating sub‐1, highlighting that submergence can be considered as a spontaneous and efficient indicator for screening of high‐starch duckweed. Additionally, the saccharification efficiency of starch and ethanol yield had increased in sub‐1 mutant compared to the wild type. Based on the unique characteristics of sub‐1 mutant, a cultivation model of submerged duckweed in a simulated aquaculture pond was designed to get more starch‐rich biomass, enabling effective production of renewable bioenergy.

Wood formation of trees is a complex and costly developmental process, whose regulatory network is involved in the protein-protein and protein-DNA interactions. To detect such interactions in wood development, we developed a high-throughput screening system with 517 Gal4-AD-wood-associated transcription factors (TFs) library from Populus alba × P. glandulosa cv “84K.” This system can be used for screening the upstream regulators and interacting proteins of targets by mating-based yeast-one hybrid (Y1H) and yeast-two-hybrid (Y2H) method, respectively. Multiple regulatory modules of lignin biosynthesis were identified based on this Populus system. Five TFs interacted with the 500-bp promoter fragment of PHENYLALANINE AMMONIA-LYASE 2 (PAL2), the first rate-limiting enzyme gene in the lignin biosynthesis pathway, and 10 TFs interacted with PaMYB4/LTF1, a key regulator of lignin biosynthesis. Some of these interactions were further validated by EMSA and BiFC assays. The TF-PaPAL2 promoter interaction and TF-PaMYB4 interaction revealed a complex mechanism governing the regulation of lignin synthesis in wood cells. Our high-throughput Y1H/Y2H screening system may be an efficient tool for studying regulatory network of wood formation in tree species.

We propose and verify a simple precoding-less scheme to generate quadrature phase shift keying (QPSK) modulated vector millimeter-wave signal based on a single phase modulator (PM). The electrical vector data is first up-converted to achieve a 12 GHz radio frequency (RF) vector signal, then the RF vector signal is added with the other unmodulated RF source at 18 GHz, of which the generations are enabled by a digital signal processing (DSP). Next, the coupled RF source drive a PM to generate multi-frequency optical sidebands. A wavelength selective switch is adopted to pick out two optical sidebands at different frequencies which will beat frequency in the photo-detector (PD). In this scheme, we set up a simulation platform to generate 48 GHz QPSK modulated vector millimeter-wave signals and analyzed the performance. The results show when the input power for the generated 1-Gbaud/s vector millimeter-wave into PD is not less than −18 dBm, the bit-error ratio can be below 3.8 × 10−3, which demonstrate that the generated vector millimeter-wave signal enabled by our proposed scheme can work well.

Brassinosteroid (BR) signaling has long been reported to have an effect on xylem development, but the detailed mechanism remains unclear, especially in tree species. In this study, we find PdC3H17, which was demonstrated to mediate xylem formation driven by auxin in our previous report, is also involved in BR-promoted xylem development. Y1H analysis, EMSA, and transcription activation assay confirmed that PdC3H17 was directly targeted by PdBES1, which is a key transcriptional regulator in BR signaling. Tissue specificity expression analysis and in situ assay revealed that PdC3H17 had an overlapping expression profile with PdBES1. Hormone treatment examinations verified that xylem phenotypes in PdC3H17 transgenic plants, which were readily apparent in normal condition, were attenuated by treatment with either brassinolide or the BR biosynthesis inhibitor propiconazole. The subsequent quantitative real-time polymerase chain reaction (qRT-PCR) analyses further revealed that BR converged with PdC3H17 to influence transcription of downstream xylem-related genes. Additionally, the enhancement of xylem differentiation by auxin in PdC3H17 overexpression plants was significantly attenuated compared with wild-type and dominant negative plants due to BR deficiency, which suggested that the BR- and auxin-responsive gene PdC3H17 acted as an mediation of these two hormones to facilitate xylem development. Taken together, our results demonstrate that BR signaling converges with auxin-mediated PdC3H17 to regulate xylem formation in Populus and thus provide insight into the regulation mechanism of BRs and the crosstalk with auxin signaling on xylem formation.

In nonlinear multisensor system, abrupt state changes and unknown variance of measurement noise are very common, which challenges the majority of the previously developed models for precisely known multisensor fusion techniques. In terms of this issue, an adaptive cubature information filter (CIF) is proposed by embedding strong tracking filter (STF) and variational Bayesian (VB) method, and it is extended to multi-sensor fusion under the decentralized fusion framework with feedback. Specifically, the new algorithms use an equivalent description of STF, which avoid the problem of solving Jacobian matrix during determining strong trace fading factor and solve the interdependent problem of combination of STF and VB. Meanwhile, A simple and efficient method for evaluating global fading factor is developed by introducing a parameter variable named fading vector. The analysis shows that compared with the traditional information filter, this filter can effectively reduce the data transmission from the local sensor to the fusion center and decrease the computational burden of the fusion center. Therefore, it can quickly return to the normal error range and has higher estimation accuracy in response to abrupt state changes. Finally, the performance of the developed algorithms is evaluated through a target tracking problem.

Reversed Cherenkov radiation has not been observed due to the absence of suitable all-metal left-handed materials for beam transport and suitable couplers for extracting the signal. Here, Duanet al. develop a metamaterial to observe reversed Cherenkov radiation using real charged particles.

Polarization division multiplexing (PDM) doubles the bitrate of flexible transponders, whereas the joint effects of fast state of polarization (SOP) rotations, first-order polarization mode dispersion (PMD), and second-order PMD (SOPMD) would severely degrade the system performance. In this paper, we propose and experimentally validate a novel dynamic polarization demultiplexing scheme using extended Kalman filter (EKF) in digital signal processing of flexible receivers. The idea comes from two-stage PMD compensator in optical domain to perform SOP tracking and equalization of first-order PMD and SOPMD. After parameters optimization of EKF, the scheme can track up SOP rotations more than 35 times and 50 times faster than that of constant modulus algorithm (CMA) and CMA/multiple modulus algorithm (MMA), respectively. More importantly, when SOP keeps a fast rotation of 1.00, 10.00, or 20.02 Mrad/s, the system tolerances of first-order PMD and SOPMD that the joint scheme achieves are 28.57 ps and 793 ps2 for 28 GBaud PDM-QPSK at optical signal-to-noise rate (OSNR) of 17 dB, and 50 ps and 4836 ps2 for 10 GBaud PDM-16 quadratic-amplitude modulation (QAM) at OSNR of 23 dB, respectively. In addition, the proposed scheme has a fast convergence speed of about 50 symbols (equal to 5 ns). The calculation complexities of each symbol that the proposed scheme consumes are just about 44% of CMA for PDM-QPSK, and 31% of CMA/MMA for PDM-16 QAM.

We propose and investigate a new scheme to realize optical logic gates using polarization addition with direct detection. Two polarizations of an optical signal are modulated, respectively, by independent binary inputs to represent four different states, while direct detection is used to map the four states to the corresponding binary output. Up to 25 logic gates, including all the basic logic gates, can be implemented by adjusting bias voltages of the two modulators, peak-peak voltages of the driving signals, and the rotation angle between the two polarizations. A modified Poincare sphere and a simplified 2-D description are developed to illustrate the principle of the proposed scheme. Experiments are successfully carried out to realize all of the six basic logic gates at 1 Gb/s. Influences on the performance of logic gates are also studied by considering some key factors, such as the extinction ratio of Mach-Zehnder modulator (MZM), input power, and rotation-angle deviation.

Dual-mode index modulation aided orthogonal frequency division multiplexing (DM-OFDM) is recently proposed, which modulates all subcarriers to eliminate the limits of spectrum efficiency (SE) in OFDM with index modulation (OFDM-IM). In DM-OFDM, the subcarriers within each subblock are divided into two groups, which are modulated by two distinguishable constellation alphabets drawn from the inner and the outer constellation points of a given M-ary QAM constellation. In this paper, a new DM-OFDM scheme, called DM-OFDM with constellation power allocation (DM-OFDM-CPA) is proposed, where the two groups of subcarriers within each subblock are set at different power levels and modulated by different M-ary PSK symbols, leading to the improvement of the system performance at low-order modulation. At the receiver, a low-complexity maximum likelihood (LC-ML) detector and two reduced search complexity detectors, based on energy detection and log-likelihood ratio (LLR) criterion, respectively, are employed for demodulation. Then, the bit error rate (BER) analyses based on pairwise error probability are provided for the proposed DM-OFDM-CPA, and the power ratio between the two groups is optimized to maximize achievable BER performance for a given signal to noise ratio. The simulation results confirm that at a given SE, the proposed DM-OFDM-CPA achieves a significantly better BER performance than the existing OFDM-IM. When the modulation order is lower than 16, it outperforms the classic DM-OFDM. The results also show that two reduced search complexity detectors, especially the LLR detector, provide similar performance to the LC-ML detector in the DM-OFDM-CPA.

We propose and investigate a new scheme to realize all-optical logic gates using a single I/Q modulator with direct detection. Both intensity and phase of the optical signal are utilized to represent the four different states of two binary inputs, whereas direct detection is used to map the four states to the corresponding binary output. This structure is very simple and has the potential to reach high speed. All of the basic logic gates can be implemented by adjusting the bias voltages of the two arms, peak-peak voltages of the driving signals, and the phase shift. Experiments are successfully carried out to realize all six basic logic gates at the data rate up to 10 Gb/s with eye diagrams clearly observed. Extinction ratios (ERs) of the output signals are increased for all these logic gates, compared with the original input signals. ER decreases when increasing the data rate from 1 to 10 Gb/s. Up to 24 logic gates can be implemented by using a single I/Q modulator.

In an optical fiber communication system, polarization-dependent loss (PDL), referring to polarization-dependent optical power attenuation, might be a main system performance limiting factor. PDL causes a difference in signal power and imbalance of optical signal-to-noise ratio (OSNR) between the two polarization branches. The OSNR asymmetry will eventually deteriorate the overall system performance. At present, most of the equalization methods of PDL in the literature can only accomplish power imbalance equalization and are, thus, not the true equalization of PDL. Besides, in some extreme environments, like lightning strikes, Kerr and Faraday effects would generate ultra-fast rotation of state of polarization (RSOP), as fast as mega-radian per second. The fast RSOP in combination with PDL makes the eigenmodes of the PDL randomly time-varying, which will put a heavy burden on the equalization module of the receiver. Faced with this dilemma, in this paper, we propose a scheme for the true equalization of PDL in the presence of fast RSOP through an approach based on the combination of the polarization-time code and Kalman filter. The proposed approach is proved to be very effective and provides significant performance. With a 1.2 dB OSNR penalty, it can jointly equalize large PDL (7 dB) and fast RSOP (up to 1 Mrad/s).

We propose and demonstrate a new data-aided in-band optical-signal-to-noise ratio (OSNR) monitoring method, which employs the periodic property of a specially designed short training sequence to differentiate the signal power from noise and is proved to be insensitive to the first-order polarization mode dispersion (PMD). This method is verified in a typical 112-Gb/s polarization multiplexed-quadrature phase shift keying and a 224-Gb/s polarization multiplexed-16 quadrature amplitude modulation coherent optical transmission system. The results show that the method is highly accurate, with the monitoring error less than 1 dB in the OSNR range of 7-30 dB under different linewidths and has good robustness to a large amount of residual accumulated CD and first-order PMD.

This paper is concerned with the filtering problem caused by the inaccuracy variance of measurement noise in real nonlinear systems. A novel weighted fusion estimation method of multiple different variance estimators is presented to estimate the variance of the measurement noise. On this basis, a hybrid adaptive cubature Kalman filtering structure is proposed. Furthermore, the information filter of the hybrid adaptive cubature Kalman filter is also studied, and the stability and filtering accuracy of the filter are theoretically discussed. The final simulation examples verify the validity and effectiveness of the hybrid adaptive cubature Kalman filtering methods proposed in this paper.

The LiNbO3-based polarization controller is widely used, but it needs to be calibrated in order to cancel the remaining birefringence. The calibration of the LiNbO3 polarization controller is untrivial because there are several stages, and for each stage, at least four parameters, including VA, Bias, VC, Bias, V 0, and V ¿ , need to be calibrated. A smart calibration approach is presented theoretically and experimentally. The particle swarm optimization (PSO) algorithm is used as an adaptive searching algorithm. The experiment results show that the PSO algorithm is powerful to optimize the operation of LiNbO3-based multistage polarization controllers. It takes only less than 1 min for all the stages of the polarization controller to be thoroughly calibrated.

The orbital angular momentum (OAM) of light can be another physical dimension that we exploit to make multiplexing in the spatial domain. The design of the OAM mode supporting fiber attracts many attentions in the field of the space division multiplexing (SDM) system. This paper reviews the recent progresses in photonic crystal fiber (PCF) supporting OAM modes, and summarizes why a PCF structure can be used to support stable OAM transmission modes. The emphasis is on the circular PCFs, which possess many excellent features of transmission performance, such as good-quality OAM modes, enough separation of the effective indices, low confinement loss, flat dispersion, a large effective area, and a low nonlinear coefficient. We also compare the transmission properties between the circular PCF and the ring core fiber, as well as the properties between the OAM EDFA based on circular PCF and the OAM EDFA based on the ring core fiber. At last, the challenges and prospects of OAM fibers based on the PCF structure are also discussed.