National University of Defense Technology
Recent publications
Block synchronization is an essential component of blockchain systems. Traditionally, blockchain systems tend to send all the transactions from one node to another for synchronization. However, such a method may lead to an extremely high network bandwidth overhead and significant transmission latency. It is crucial to speed up such a block synchronization process and save bandwidth consumption. A feasible solution is to reduce the amount of data transmission in the block synchronization process between any pair of peers. However, existing methods based on the Bloom filter or its variants still suffer from multiple roundtrips of communications and significant synchronization delay. In this paper, we propose a novel protocol named Gauze for fast block synchronization. It utilizes the Cuckoo filter (CF) to discern the transactions in the receiver’s mempool and the block to verify, providing an efficient solution to the problem of set reconciliation in the P2P (Peer-to-Peer Network) network. By up to two rounds of exchanging and querying the CFs, the sending node can acknowledge whether the transactions in a block are contained by the receiver’s mempool or not. Based on this message, the sender only needs to transfer the missed transactions to the receiver, which speeds up the block synchronization and saves precious bandwidth resources. The evaluation results show that Gauze outperforms existing methods in terms of the average processing latency (about 10× lower than Graphene) and the total synchronization space cost (about 10× lower than Compact Blocks) in different scenarios.
Condition monitoring and fault diagnosis on electromechanical actuators (EMAs) have gradually become a research hotspot in the field of aviation, but few studies have examined the failure mechanism of an EMA by establishing a dynamic model. As such, this paper establishes the two-degree-of-freedom radial dynamic models of ball screw pairs under normal and faulty conditions to analyze the dynamic characteristics that may occur in the vibration responses of normal and faulty ball screw pairs. After analyzing the simulation results of the established models, in this study, it is determined that after a spalling fault occurs in the inner raceway of a ball nut, the amplitude at the third harmonic of the ball passage frequency will increase significantly compared with the first and second harmonics of that frequency in the acceleration spectrum of the nut. This phenomenon can be regarded as a characteristic expression of the nut spalling fault in the acceleration spectrum, and it is verified by experiments on an EMA test rig. The experimental results show that this fault characteristic can also be observed even when the screw shaft rotating speed varies from 60 rpm to 420 rpm. However, under high-speed conditions, additional signal processing and noise reduction methods are required to solve the problem of background noise interference.
Light-weight and high-stiffness honeycomb sandwich plates are widely used in high- speed vehicles. Suppressing their low-frequency and broadband vibration is significant for improving safety and reducing noise, but remains challenging with limited mass cost. Bandgaps and chaotic band in nonlinear acoustic metamaterials (NAMs) offer an effective way for vibration reduction. This paper conceives a NAM sandwich plate and studies its vibration reduction properties based on numerical and experimental methods. We establish its nonlinear finite element model based on the equivalent homogeneous model and experiments. The influences of the resonator distribution, nonlinear stiffness, resonant frequencies, mass, amplitude and structural plate parameters on its vibration are thoroughly analyzed to achieve the best performance. Then, we manufacture an optimized NAM plate and experimentally demonstrate that all resonances of the high-stiffness NAM plate below 800 Hz are greatly reduced with only 17.7 % attached mass; particularly, the first low-frequency resonance at 93 Hz is reduced by 20 dB. This shows that the NAM strategy can robustly and effectively suppress the low-frequency and broadband vibration of the light-weight and high-stiffness plates with small mass cost, a synthetical performance desired for broad potential applications. The models, regularities, designs and experiments can also enlighten more studies on relate topics.
Accurate control and rapid regulation of the liquid nitrogen supplying pressure are the basis for the total temperature operation of the cryogenic wind tunnel. The pressure evolution during the discharging process and external pressurization in an accumulator are measured experimentally. The thermal boundary conditions of the tank during the test are mathematically obtained with the consideration of frosting and convective heat transfer. A numerical framework of two-phase flow based on the volume of fluid (VOF) and the heat and mass transfer model is carried out. The computed results with the accommodation coefficient of β = 10⁻⁶ in the Lee model are closer to the measured values than using the original value of 0.1, and the laminar model is more suitable for the numerical study of the gas-liquid transfer in the tank than the turbulent model. The growing dynamic process of gas-liquid interface and temperature distribution during the entire test is achieved. Thermal stratification is formed though the coming liquid nitrogen is highly subcooled. The liquid level has not been stable immediately but grows slowly when the pressure reaches the set value. The simulated temperature evolution, distribution, and the final volume fraction of gaseous nitrogen are satisfactorily consistent with the experiments. The results show that the numerical model can simulate the complex heat and mass transfer characteristics inside the cryogenic accumulator and provide theoretical guidance for injection pressure control.
Blade crack is one of the most common blade failures of rotating machines which may lead to catastrophic accidents. Although many nonlinear vibrations of breathing crack have been investigated, there are few reports on the axial-bending coupling vibration caused by crack. With the aim of providing physical insight into the mechanisms of axis-bending coupling due to crack, a novel axial-bending coupled breathing crack model (ABCBCM) for the rotating blade is proposed in this study. The proposed ABCBCM is analytically formulated based on the Timoshenko beam theory and Castigliano’s principle, and validated by comparing the natural and dynamic characteristics with the finite element model (FEM) and experimental tests. In addition, the effects of boundary conditions (rotational speed), crack parameters (crack depth and crack location) and loading conditions (excitation load) on the vibration characteristics of the cracked blade are investigated. The results indicate that the blade axial response is more sensitive to the nonlinearity caused by the breathing crack than the bending response; the axial-bending coupling caused by the crack changes the equilibrium position of the axial and bending displacement; the phase portrait of axial response and the orbit of axial-bending displacement are effective methods to detect breathing crack; and the axial displacement amplitude ratio and the axial acceleration amplitude ratio also are valuable indicators to estimate the severity of the blade crack. The proposed model can provide valuable insights for fault diagnosis and safety monitoring of cracked blade.
In order to improve controller performance in the process of spacecraft rendezvous with collision-free, Adaptive Interfered Fluid Dynamical System Sliding Mode Control (AIFDS-SMC) is proposed, which is based on the theory of Interfered Fluid Dynamical System (IFDS), State Dependent Riccati Equation (SDRE) and Sliding Mode Control (SMC). This method uses an improved IFDS feedback control method. Combining the attraction potential function to ensure that different initial states can converge to any target state. Based on the IFDS-SMC, the parameters of approaching controller are adjusted by using the optimal control theory SDRE, and AIFDS-SMC with optimized fuel consumption is obtained. The above methods are applied to the problem of spacecraft rendezvous and obstacle avoidance, also comparisons of the simulation results are made. The results show that the AIFDS-SMC has better fuel economy and better control accuracy than the IFDS-SMC.
We report here a method to fabricate the (6 + 1) × 1 bi-directional pump/signal combiner with high pump coupling efficiency and negligible degradation for the M² value of signal light. The pump coupling efficiency for all the six pump fibers is more than 98 %. A CCD camera is firstly used in the alignment fusion process of the fiber bundle and the output fiber, which is precise and convenient. The degradation ratio of the M² value of the signal light is 2.2 % after fusion process, which is, to the best of our knowledge, the minimum reported value for the same type of combiner. In addition, the home-made combiner is applied in a counter-directional pumping amplifier, whose maximum output power is 4 kW with the slope efficiency of 81.3 %. The temperature rise coefficient of the home-made combiner is 12.1 °C/kW, indicating the great potential of the combiner in high-power laser applications.
Fibre lasers operating at the mid-IR have attracted enormous interest due to the plethora of applications in defence, security, medicine, and so on. However, no continuous-wave (CW) fibre lasers beyond 4 μm based on rare-earth-doped fibres have been demonstrated thus far. Here, we report efficient mid-IR laser emission from HBr-filled silica hollow-core fibres (HCFs) for the first time. By pumping with a self-developed thulium-doped fibre amplifier seeded by several diode lasers over the range of 1940–1983 nm, narrow linewidth mid-IR emission from 3810 to 4496 nm has been achieved with a maximum laser power of about 500 mW and a slope efficiency of approximately 18%. To the best of our knowledge, the wavelength of 4496 nm with strong absorption in silica-based fibres is the longest emission wavelength from a CW fibre laser, and the span of 686 nm is also the largest tuning range achieved to date for any CW fibre laser. By further reducing the HCF transmission loss, increasing the pump power, improving the coupling efficiency, and optimizing the fibre length together with the pressure, the laser efficiency and output power are expected to increase significantly. This work opens new opportunities for broadly tunable high-power mid-IR fibre lasers, especially beyond 4 μm.
Sparse Polynomial Chaos Expansion (PCE) is widely used in various engineering fields to quantitatively analyse the influence of uncertainty, while alleviating the problem of dimensionality curse. However, current sparse PCE techniques focus on choosing features with the largest coefficients, which may ignore uncertainties propagated with high order features. Hence, this paper proposes the idea of selecting polynomial chaos basis based on information entropy, which aims to retain the advantages of existing sparse techniques while considering entropy change as output uncertainty. A novel entropy-based optimization method is proposed to update the state-of-the-art sparse PCE models. This work further develops an entropy-based synthetic sparse model, which has higher computational efficiency. Two benchmark functions and a computational fluid dynamics (CFD) experiment are used to compare the accuracy and efficiency between the proposed method and classical methods. The results show that entropy-based methods can better capture the features of uncertainty propagation, improving accuracy and reducing sparsity while avoiding over-fitting problems.
Compact terahertz (THz) functional devices are greatly sought after for high-speed wireless communication, biochemical sensing, and non-destructive inspection. However, controlled THz generation, along with transport and detection, has remained a challenge especially for chip-scale devices due to low-coupling efficiency and unavoidable absorption losses. Here, based on the topological protection of electromagnetic waves, we demonstrate nonlinear generation and topologically tuned confinement of THz waves in an engineered lithium niobate chip forming a wedge-shaped Su–Schrieffer–Heeger lattice. Experimentally measured band structures provide direct visualization of the THz localization in the momentum space, while robustness of the confined mode against chiral perturbations is also analyzed and compared for both topologically trivial and nontrivial regimes. Such topological control of THz waves may bring about new possibilities in the realization of THz integrated circuits, promising for advanced photonic applications.
Purpose Cholecystectomy (XGB) is widely recognized as a risk factor for colon cancer (CC). Continuous exposure of the colonic epithelium to deoxycholic acid (DCA) post-XGB may exert cytotoxic effects and be involved in the progression of CC. However, the functions of the XGB-induced DCA increase and the underlying mechanism remain unclear. Methods Colitis-associated CC (CAC) mouse models constructed by AOM-DSS inducement were used to confirm the effect of XGB on the CC progression. Hematoxylin & eosin staining was performed to assess the tumor morphology of CAC mouse models tissues. Various cell biological assays including EdU, live-cell imaging, wound-healing assays, and flow cytometry for cell cycle and apoptosis were used to evaluate the effect of DCA on CC progression. The correlation among XGB, DCA, and CC and their underlying mechanisms were detected with immunohistochemistry, mass spectrometry, transcriptome sequencing, qRT-PCR, and western blotting. Results Here we proved that XGB increased the plasma DCA level and promoted colon carcinogenesis in a colitis-associated CC mouse model. Additionally, we revealed that DCA promoted the proliferation and migration of CC cells. Further RNA sequencing showed that 120 mRNAs were upregulated, and 118 downregulated in DCA-treated CC cells versus control cells. The upregulated mRNAs were positively correlated with Wnt signaling and cell cycle-associated pathways. Moreover, DCA treatment could reduced the expression of the farnesoid X receptor (FXR) and subsequently increased the levels of β-Catenin and c-Myc in vitro and in vivo . Moreover, the FXR agonist GW4064 decreased the proliferation of CC cells by repressing the expression of β-catenin. Conclusion We concluded that XGB-induced DCA exposure could promote the progression of CC by inhibiting FXR expression and enhancing the Wnt-β-catenin pathway.
In recent years, machine learning, especially various deep neural networks, as an emerging technique for data analysis and processing, has brought novel insights into the development of fiber lasers, in particular complex, dynamical, or disturbance-sensitive fiber laser systems. This paper highlights recent attractive research that adopted machine learning in the fiber laser field, including design and manipulation for on-demand laser output, prediction and control of nonlinear effects, reconstruction and evaluation of laser properties, as well as robust control for lasers and laser systems. We also comment on the challenges and potential future development.
Physical field reconstruction is highly desirable for the measurement and control of engineering systems. The reconstruction of the temperature field from limited observation plays a crucial role in thermal management for electronic equipment. Deep learning has been employed in physical field reconstruction, whereas the accurate estimation for the regions with large gradients is still difficult. To solve the problem, we propose a novel deep learning method based on partition modeling to accurately reconstruct the temperature field of electronic equipment from limited observation. Firstly, the temperature field reconstruction (TFR) task of electronic equipment is modeled mathematically and transformed as an image-to-image regression problem. Then a partition modeling framework consisting of an adaptive UNet and a shallow multilayer perceptron (MLP) is developed to establish the mapping from the observation to the temperature field. The adaptive UNet is utilized to reconstruct the whole temperature field, while the MLP is designed to predict the patches with large temperature gradients. Numerical case studies employing finite element simulation data are conducted to demonstrate the accuracy of the proposed method. Furthermore, the generalization is evaluated by investigating cases under different heat source layouts, power intensities, and observation point locations. The maximum absolute errors of the reconstructed temperature field are less than 1 K under the partition modeling approach.
The meticulous design of semiconductor photocatalysts has been known as the key to achieve a highly efficient and selective photocatalytic reaction toward solving the current environmental pollution and energy crisis. Recently, the combination of two or more semiconductors to form step-scheme (S-scheme) heterojunction photocatalysts has emerged as a rising star in photocatalysis due to their capability for optimizing the photogenerated charge carrier utilization and maximizing the reduction-oxidation potential of the photocatalytic system. Herein, this review summarizes and highlights the recent development of the S-scheme heterojunction photocatalysts. We first concisely compile the working mechanism of S-scheme photocatalysts, followed by discussing their characterization techniques. Then, we discuss and overview the applications of the S-scheme photocatalysts in water splitting, CO2 conversion, wastewater purification, H2O2 production, N2 fixation and so on. Finally, we conclude this review with a brief discussion of significant challenges and future prospects in the development of S-scheme photocatalytic systems.
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3,274 members
Yaming Chen
  • College of Aerospace Science and Engineering
Chengkun Wu
  • College of Computer
Jiayu Dai
  • Department of Physics
Xinwang Liu
  • College of Computer
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Address
No.109 Deya Road, Kaifu District, 410073, Changsha, Hunan, China
Head of institution
LI Xiang
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www.nudt.edu.cn
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