Search

Shape memory alloys (SMA) are widely used in micro-electro-mechanical systems due to shape memory effect and hyperelasticity. The surface effects on mechanical properties cannot be ignored because of their small structure size. Based on Euler Bernoulli beam theory and Gurtin-Murdoch surface elasticity theory, the influence of tension-compression asymmetry factors on SMA beams is considered, and a phase transformation mechanical model of SMA nanobeams considering surface effects is established. The effects of surface effects on load, curvature and neutral axis displacement are investigated The study demonstrates that regardless of whether considering the surface effect, the neutral axis displacement initially increases and subsequently decreases with the growth of the dimensionless bending moment. The neutral axis displacement of nanobeams can be significantly affected by taking surface effects into account. When considering the surface effect, the difference in neutral axis displacement of the nanobeam increases as the nanobeam’s size diminishes. Neglecting surface effects will underestimate the bending stiffness of the microbeam.

In this design, a VTOL aircraft system is used as the controlled object. Aiming at the trajectory tracking problem of its position and attitude output, a trajectory tracking control method based on double closed-loop PD control is adopted to design. The trajectory tracking system of VTOL aircraft is decomposed into a track tracking subsystem and a roll tracking subsystem. At the same time, a double closed-loop PD control structure based on position outer loop and attitude inner loop is constructed, and a PD controller based on feedforward compensation is designed. The pole assignment method is used to set and select PD parameters. The stability of the double closed-loop system is ensured by the engineering method of making the reaction speed of the inner loop greater than that of the outer loop. Then, MATLAB software is used to simulate whether the control system can track the given trajectory. Simulation results show that this method simplifies the design process of the control system and makes certain that VTOL aircraft can track arbitrary trajectory outputs with three state outputs as soon as possible, thus meeting the needs of underactuated VTOL aircraft for arbitrary trajectory tracking.

Vanadyl Phosphate (VOPO4) is an attractive candidate for catalytic materials. Previous works by S. C. Lim, R. Gautier, N. Dupre, et al,have reported that VOPO4 co-exists in seven polymorphs including α Ι-, α Ι′-, α II-, β-, γ-, δ-, ε-, and ω-VOPO4. However, there is no systematic investigation on these seven polymorphs. Here, based on density functional theory (DFT) calculations, all these structures, stability and the differences of band structures are compared in detail. The results show that α Ι-, α Ι′-, α II-, β-, γ-, and ε-VOPO4 are indirect bandgap semiconductors, while δ-VOPO4 exhibits a direct band structure and ω-VOPO4 belongs to insulators. Our work can shed light on the perspective of the application of VOPO4.

Diffractive lenses (DLs) can realize high-resolution imaging with light weight and compact size. Conventional DLs suffer large chromatic and off-axis aberrations, which significantly limits their practical applications. Although many achromatic methods have been proposed, most of them are used for designing small aperture DLs, which have low diffraction efficiencies. In the designing of diffractive achromatic lenses, increasing the aperture and improving the diffraction efficiency have become two of the most important design issues. Here, a novel phase-coded diffractive lens (PCDL) for achromatic imaging with a large aperture and high efficiency is proposed and demonstrated experimentally, and it also possesses wide field-of-view (FOV) imaging at the same time. The phase distribution of the conventional phase-type diffractive lens (DL) is coded with a cubic function to expand both the working bandwidth and the FOV of conventional DL. The proposed phase-type DL is fabricated by using the laser direct writing of grey-scale patterns for a PCDL of a diameter of 10 mm, a focal length of 100 mm, and a cubic phase coding parameter of 30π. Experimental results show that the working bandwidth and the FOV of the PCDL respectively reach 50 nm and 16° with over 8% focusing efficiency, which are in significant contrast to the counterparts of conventional DL and in good agreement with the theoretical predictions. This work provides a novel way for implementing the achromatic, wide FOV, and high-efficiency imaging with large aperture DL.

Wind is one of the most destructive external loads of transmission lines, and typhoon-caused severe damage or even destruction of electric power facilities occurred frequently. In order to research the critical wind speed of instability failure of UHV transmission tower-line coupling system under typhoon, the UHV transmission line in Zhejiang is chosen as the research subject and a finite element model of the UHV tower-line coupling system is established. By using the improved generalized force calculation method, the dynamic response of the transmission tower is converted to the static response. Then the LRC method is used to calculate the equivalent static wind load of the tower and obtains the wind response of the UHV transmission tower-line coupling system. The results show that under the typhoon wind field, the component at the junction of the tower head and the body first reaches the supercritical state. Specifically, when the wind speed at 10-meters height reaches 31m/s, the profile component of the tower head will be damaged. With the increase of wind speed, the damaged area of the tower head also expends. When the wind speed at 10-meters height reaches 37m/s, the main load-bearing component of the tower head-body junction will lose its stability, which will directly threaten the safety of the transmission tower.

The vibrating screen has absolute advantages in the sorting equipment due to its simple structure, reliable operation and large processing capacity. Therefore, the vibrating screen is widely used in powder material sorting equipment. Because powder materials usually contain a certain amount of moisture, high-frequency vibration can effectively separate materials with different particle sizes, and together with the feeding and unloading of the belt conveyor, it forms a sorting device. This article mainly includes the calculation of the feeding conveyor mechanism, the calculation of the sieve plate size selection, the calculation of the entire vibration screening mechanism and the calculation of the unloading conveyor mechanism. In addition, the strength and fatigue strength of the key parts of the equipment are checked, and the installation and use of the equipment are explained in detail.

The wind-induced swing angle of insulator strings directly affects the electrical insulation performance and the construction cost of the UHV transmission project. However, due to not considering the fluctuating wind pressure, the calculation results of wind-induced swing tend to be conservative when adopting the recommended guidelines of standard especially in the face of severe weather. This paper simulates the transient wind field of strong winds based on time-space correlation characteristics and constructs the fluctuating wind load distribution model exerting on the UHV transmission line. Then a refined finite element model of the multi-span transmission line including the entire tensile section is established. And the swing angle of the insulator strings calculation formula is fitted based on the calculation results of the wind-induced swing response. The calculation result shows the swing angle decreases with the increase of ice thickness, and the magnified coefficient of the wind-induced swing angle at the target tower under the basic wind speed of 15m/s is 1.03.

Aiming at the characteristic of power data with multiple sources, wide distribution and complex association, this paper proposes a power data integration method based on Database-Table Metadata Semantic (DTMS), which can realize the integration of grid data at the metadata layer. Firstly, based on the structure of the database, the semantic expression is established between database and table; Secondly, this paper combines the Jaccard distance similarity method and the edit distance similarity method to achieve semantic matching between metadata and technical terms, which can solve the shortcomings of the single similarity method. Finally, according to the characteristics of power data assets, a power data integration scheme based on DTMS is proposed for multi-source power data integration. Through experiments, the accuracy of the algorithm in this paper has reached 95.8%.

To solve the problem of product quality control in multi-variety and small-batch production mode, a quality control chart recognition model of MC-GA optimized BP was established by using Monte Carlo method to simulate the product quality data characteristics of different varieties and combining the data processing capability of neural network and the adaptive global optimization search capability of genetic algorithm; then the MC(Monte Carlo method)-GA(Genetic Algorithm) optimized BP(Back Propagation Neuron Network) was compared with the traditional MC-BP is compared and analyzed in terms of accuracy, time and error in quality control graph pattern recognition, and it is concluded that the former is better in quality control graph pattern recognition. It can be seen that the MC-GA optimized BP model is more effective in identifying the quality status of products in the multi-variety and small-batch production mode, and can accurately predict the stability of the manufacturing process, so as to enhance the competitiveness of enterprises.

With the advancement of global informatization, cyber risk has become an important factor hindering the informatization process, and cyber security issues have become the focus of public attention. Computer network security incidents include viruses, Trojan horses, worms, network monitoring, hacker attacks, malware, phishing, botnets, etc. In order to help netizens to prevent network security incidents more effectively, in response to the characteristics of network risk prevention data management, network Research and design of risk prevention database and data warehouse. At present, the development of computer technology is very rapid, but there are still many problems in the security of computer networks. Therefore, in order to avoid these problems hindering the development of the computer, the author analyses and discusses the technology related to computer network security protection in the information age, hoping to solve the computer network security problems and make the computer network more secure.

The outdoor intelligent transportation of a pharmaceutical factory requires the workshop to put forward task requirements according to the situation and provide multiple AGVs that can meet both man-machine control and networked scheduling. On the basis of existing AGV, an AGV control method based on human-computer interaction is proposed. First, design the overall architecture of the control system, use the touch screen to design and develop the AGV mobile client and task request client to form an industrial wireless network. The establishment of a network enables the AGV mobile client, task request client and vehicle management system to achieve cross-platform communication. Based on this, the client system sets and controls the AGV, which effectively solves the AGV’s man-machine control and networking scheduling problems. After functional testing and performance verification, the system works stably, with good flexibility and scalability.

Objective: It is hoped that the DNN-Hidden Markov Model (HMM) acoustic model and the long-short-term memory neural network-Hidden Markov (LSTM-HMM) acoustic model can be used to improve the accuracy rate of speech recognition in keyword detection. Method: First, the principles of speech recognition and related algorithms are introduced. Then, a DNN algorithm is applied to the speech recognition system, and a keyword detection system is established based on the DNN-HMM acoustic model. As for the experimental comparison, the proposed DNN model is used for acoustic modeling, and the effect of the DNN algorithm on the performance of the recognition system is analyzed experimentally. Results: The size of the training parameters of the proposed LSTM model is 436570, the size of the training parameters of the deep neural network (DNN) is 698100, and the size of the training parameters of the Gaussian mixture model (GMM) is 1226700. The accuracy of speech recognition based on the LSTM-HMM model and DNN-HMM model is 965% and 91.6%, respectively, which is significantly higher than 78.5% of the traditional speech recognition model (GMM-HMM). Conclusion: The speech recognition technology based on LSTM-HMM and DNN-HMM models has higher accuracy and is more suitable for speech keyword detection.

Precise positioning is one of the key steps in defect detection for printed circuit boards. This paper proposes a method to evaluate the roundness of printed circuit board image by least squares method and determine the position of the target circle by area sorting and screening method to realize the accurate extraction of the positioning parameters of the circular reference point (positioning circle). The CCD camera is used to capture images of the printed circuit board, and the median filtering is used for image preprocessing. The printed circuit board is separated from the image background by the gray projection segmentation technique, and the object in the image smaller than the positioning circle area is hidden. After comparing the circularity of the graphic in the printed circuit board image, two positioning circles are found according to the size of the graphic area to determine the coordinates of the center of the circle. The experimental results show that the positioning circle detection result of this method is accurate and requires less time than the traditional Hough transform detection circle.

In this work, a cerium doped CoP nanoparticles (NPs) embedded in carbon nanotubes (CNTs) for efficient and durable hydrogen evolution was developed. The detailed preparation process was described as the followings. First, cerium was introduced into ZIF-67 to form Ce-doped ZIF-67 by a joint nucleation method. Then, the Ce-doped Co-CNTs was synthesized by carbonization of Ce-doped ZIF-67. During the process, the Co2+ was reduced to form Co NPs and the elegant nanostructure of CNTs was formed by the catalytic effect of Co NPs. Finally, by using Ce-doped Co-CNTs as the precursor, the target catalyst (Ce0.05-doped CoP CNTs) was obtained through a chemical vapour deposition (CVD) process in the presence of NaH2PO2. Results of the transmission electron microscopy (TEM) and scanning electron microscopy (SEM) showed that the target catalyst maintained the original rhombic dodecahedron morphology of ZIF-67 and the CoP NPs were embedded in CNTs and distributed uniformly throughout the catalyst. In electrochemical measurements, the catalyst showed the best performance for HER in 0.5 M H2SO4 solution. The onset potential, Tafel slope, electron transfer resistance (R ct) and double-layer capacitance (C dl) of the target catalyst was 49 mV, 78 mV dec-1, 19.2 Ω and 10.5 mF cm-2, respectively. Meanwhile, the catalyst yielded a current density of 10 mA cm-2 merely at an overpotential of 146 mV. Furthermore, it maintained 90% of the original current density in a chronoamperometry measurement and showed no obvious decay even after 2000 cycles scans in a long-term durability test.

Lunar Penetrating Radar (LPR) onboard the rover that is part of the Chang’e-3 (CE-3) mission was firstly utilized to obtain in situ measurements about geological structure on the lunar surface and the thickness of the lunar regolith, which are key elements for studying the evolutional history of lunar crust. Because penetration depth and resolution of LPR are related to the scientific objectives of this mission, a series of ground-based experiments using LPR was carried out, and results of the experimental data were obtained in a glacial area located in the northwest region of China. The results show that the penetration depth of the first channel antenna used for LPR is over 79 m with a resolution of 2.8 m, and that for the second channel antenna is over 50.8 m with a resolution of 17.1 cm.

Among different energy storage devices, the lithium-sulfur (Li-S) battery is the subject of recent attention. However, the capacity decay caused by polysulfide shuttle leading to sluggish kinetics of polysulfide redox reactions is the main hindrance for its practical application in Li-S batteries. Herein, molybdenum carbide nanoparticles anchored on carbon nanotubes (Mo2C/CNT) are reported to serve as an efficient cathode material to enhance the electrochemical kinetics of polysulfide conversion in Li-S batteries. Mo2C/CNT shows strong adsorption and activation of polar polysulfides and therefore accelerates the redox kinetics of polysulfides, reduces the energy barrier, effectively mitigates the polarization and polysulfide shuttle, thus improving the electrochemical performance. The S-Mo2C/CNT composite with 70 wt% sulfur loading exhibits high specific discharge capacity (1206 mA h g-1 at 0.5 C), excellent high-rate performance, long cycle life (900 cycles), and outstanding Coulombic efficiency (∼100%) at a high rate (2 C) corresponding to a capacity decay of only 0.05%. Remarkably, the S-Mo2C/CNT cathode with high areal sulfur loading of 2.5 mg cm-2 exhibits high-rate capacities and stable cycling performance over 100 cycles, offering the potential for use in high energy Li-S batteries.

Surface acoustic wave sensors with grapheme/PANI nanocomposite sensitive films for detecting nitric oxide (NO) were fabricated and experimentally studied. Morphological characterization and functionalization of the sensing material were explored using SEM and FTIR, respectively. The study of sensor response compared film sensitivity, response time, reversibility, and limit of detection for nanocomposite films, pure grapheme and pure PANI to the detection of NO. The response and recovery times were 40s and 20s when detecting 4ppm NO, respectively. The frequency response was discovered to be linear in the NO concentration range 1–50 ppm. The nanocomposite sensors had improved sensitivities compared to the polymer devices, and better response times.

Measurement results of some properties of the Miyun 50m radio telescope (MRT50) of the National Astronomical Observatories, such as pointing calibration, antenna beams, system noise temperature, gain and gain variations with elevation are introduced. By using a new de-convolution technique developed by our group, the broadening effect on measured beams caused by the width of an extended radio source has been removed so that we obtained higher accuracy on the measurements of MRT50 beams.

The method of Ti/TiO2 photoelectrode preparation using laser-assisted sol–gel is introduced. The prepared TiO2 film is investigated by x-ray diffraction (XRD), atomic force microscopy (AFM), electrochemical impedance spectroscopy (EIS) and amperometry, and it illustrates that the TiO2 film mainly consists of anatase TiO2 nanoparticles on its surface and exhibits a superior photocatalytic activity when compared with that calcined by oven. The proposed electrode is employed as a sensor for flow injection analysis (FIA) to determine chemical oxygen demand (COD). The measuring principle is based on the photocurrent responses on the electrode, which are proportional to the COD values. The linear range is 50–1000 mg l−1, and the detection limit is 15 mg l−1 (S/N = 3). This method is characterized by short analysis time, simplicity, low environmental impact and long lifetime of the sensor. Additionally, the COD values obtained from the proposed and the conventional method agree well as demonstrated by the significant correlation between the two sets of COD values (R = 0.9961, N = 20).

The method of preparation of a Rh2O3/Ti electrode by using laser calcination and the characterization by x-ray diffractometer were proposed. The electrode, which could develop organic electrocatalytical oxidation, was employed as an amperometric sensor, together with a flow injection analysis, to measure chemical oxygen demand (COD) of waste water in a speedy way. The measuring principle was based on the current responses on the modified electrode which were proportional to the COD value. Under the optimized experimental condition, the linear range was 50–2000 mg l−1, and the detection limit was 20.0 mg l−1 (S/N = 3). This method was successfully applied to determine the COD in samples without pretreatment. It was characterized by short analysis time, simplicity, low environmental impact, limited reagent consumption, easy automation and long lifetime of the sensor. Additionally, the COD values obtained by using the proposed method were within ±5% of those given by the conventional COD method.

Research is carried out on the basis of the traditional two-end matched circuit of a capacitive voltage divider with a long measurement cable. Transmission progress in the circuit is analyzed theoretically. A match condition of the circuit is acquired, which requires that the circuit satisfies two conditions: (1) the measurement error should be small for a pulse with a duration of less than twice the delay time of the measurement cable; (2) the initial division ratio and the stable division ratio of the circuit are the same. Two matched methods of the circuit are acquired, including the first-order matched method and the second-order matched method. Numerical simulations are carried out. According to the simulation results, the relative errors of the circuits with a cable of 20 m are less than 1.5%, obtained by using both match methods for measurement of rectangular pulses with rise and fall times of 5 ns. An improved circuit is presented, which is suitable for any situation where the low-voltage capacitance of the capacitive divider is even smaller than the capaictance of the measurement cable. A verification experment is carried out, and the test result confirms the simulation result.

A polyvinylidene-fluoride (PVDF)-based magnetoelectric torque (MET) device is designed with elastic layer sand-wiched by PVDF layers, and low-frequency MET effect is carefully studied. It is found that elastic modulus and thickness of the elastic layer have great influences on magnetoelectric (ME) voltage coefficient (alpha(ME)) and working range of frequency in PVDF-based MET device. The decrease of the modulus and thickness can help increase the alpha(ME). However, it can also reduce the working range in the low frequency. By optimizing the parameters, the giant alpha(ME) of 320 V/cm.Oe (1 Oe = 79.5775 A.m(-1)) at low frequency (1 Hz) can be obtained. The present results may help design PVDF-based MET low-frequency magnetic sensor with improved magnetic sensitivity in a relative large frequency range.

A few factors effecting the reaction of plasma dehydrocoupling of methane have been investigated. The experiment shows that plasma power load, i.e. the ratio of methane flow to plasma power, is the most important factor effecting methane dehydrocoupling. The products of the reaction are mainly acetylene, ethylene, ethane and unreacted methane etc. If oxygen with a suitable molar ratio is introduced into plasma region at a reasonable position, the selectivity of C2 hydrocarbons can be increased greatly.

Marine gravity field information has a great significance for the resource, environment and military affairs. As a new way to get marine gravity data, the satellite altimetry technique makes up for what ship measuring means lack. The paper carries out the researches on how altimeter data applied for calculating marine gravity anomaly based on inverse Stokes formula. In the article, the editing of 14-track Jason-1 data over South China Sea for 7 years is for collinear processing and cross-point adjustment. The inverse Stokes formula and fast Flourier transform technique are applied to calculate marine gravity anomaly of the region (0°~23°N, 103°~120°E), and to draw gravity anomaly map. Compared with the gravity anomaly by ship observation, RMS is 12.6mGal, and single altimetry satellite has a good precision.

The breakup reactions of weakly-bound nuclei at energies around the Coulomb barrier and the corresponding coupling effect on the other reaction channels are hot topics nowadays. To overcome the difficulty in identifying both heavier and lighter fragments simultaneously, a new kind of ionization-chamber based detector telescope has been designed and manufactured. It consists of a PCB ionization chamber and three different thickness silicon detectors installed inside the chamber, which form a multilayer ΔE-E R telescope. The working conditions were surveyed by using an α source. An in-beam test experiment shows that the detector has good particle identification for heavy particles like 17F and 16O as well as light particles like protons and alpha particles. The measured quasi-elastic scattering angular distribution and the related discussions for 17F+208Pb are presented.

Several factors affecting plasma oxidation of n-heptane in liquid phase have been investigated. The experimental results show that the temperature of n-heptane is the first major factor affecting formations of heptanol and heptanone, and then oxygen flow and plasma power etc. follow in proper order. Under a typical condition the selectivity of product formation is far superior to that of plasma oxidation in the gas phase.

In this paper, a new method to reduce noises within chaotic signals based on ICA (independent component analysis) and EMD (empirical mode decomposition) is proposed. The basic idea is decomposing chaotic signals and constructing multidimensional input vectors, firstly, on the base of EMD and its translation invariance. Secondly, it makes the independent component analysis on the input vectors, which means that a self adapting denoising is carried out for the intrinsic mode functions (IMFs) of chaotic signals. Finally, all IMFs compose the new denoised chaotic signal. Experiments on the Lorenz chaotic signal composed of different Gaussian noises and the monthly observed chaotic sequence on sunspots were put into practice. The results proved that the method proposed in this paper is effective in denoising of chaotic signals. Moreover, it can correct the center point in the phase space effectively, which makes it approach the real track of the chaotic attractor.

Recently, an indirect method has been proposed to study the optical model potential of exotic nuclear systems by fitting the transfer reaction angular distribution. The sensitivity test of this transfer method is performed with 208Pb(7Li,6He)209Bi as an example, by varying the potential parameters individually. The results indicate that, except for the ambiguity in the real potential depth V, other optical potential parameters of 6He+209 Bi as well as the structural information of the reactions can be extracted reliably. Moreover, the radius parameter of the bound state, rbound, is an extraordinarily sensitive parameter, which should be taken care of in the calculation procedure. The present work provides a theoretical reference for the application of the transfer method.

A compact high precision eight-axis automatism and two-axis manual soft-ray polarimeter with a multilayer has been designed, constructed, and installed in 3W1B at the Beijing Synchrotron Radiation Facility (BSRF). Four operational modes in the same device, which are double-reflection, double-transmission, front-reflection-behind-transmission and front-transmission-behind-reflection, have been realized. It can be used for the polarization analysis of synchrotron radiation. It also can be used to characterize the polarization properties of the optical elements in the soft X-ray energy range. Some experiments with Mo/Si and Cr/C multilayers have been performed by using this polarimeter with good results obtained.

Ca-based additives have been widely used as a sulfur adsorbent during coal pyrolysis and gasification. The Ca speciation and evolution during the pyrolysis of coal with Ca additives have attracted great attention. In this paper, Ca species in the coal chars prepared from the pyrolysis of Ca(OH)2 or ...

Although dilute magnetic semiconductors have promising potentials in spintronics applications, the mechanism of their ferromagnetism remains ambiguous. The extensive theoretical models and exotic experimental evidences provide self-consistent but usually contradictory explanations on its either intrinsic or extrinsic origins. We find room temperature ferromagnetism in a series of Zn1−xCoxO (0.03 ≤ x ≤ 0.10) thin films prepared using magnetron co-sputtering method and treated with post-annealing at temperatures 350°C and 500°C. The origin of the ferromagnetism is investigated in terms of electronic structure combining hard x-ray absorption spectroscopy (XAS) at Zn and Co K-edge, and soft x-ray XAS at O K-edge and Co L2,3-edge. The full multiple scattering theory is employed to reinforce the interpretation of the XAS spectra, which concludes that full substitution of zinc by cobalt is responsible for the room temperature ferromagnetism due to the d states of cobalt within the framework of bound magnetic polaron. Moreover, the evidence of cobalt nanoclusters is detected at highly doped and annealed samples. The first principles calculation confirms the electronic structural evidences via the formation energy.