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In the archive of the Ground Wide Angle Camera (GWAC), we found 43 white light flares from 43 stars, among which, three are sympathetic or homologous flares, and one of them also has a quasi-periodic pulsation with a period of $13.0\pm1.5$ minutes. Among these 43 flare stars, there are 19 new active stars and 41 stars that have available TESS and/or K2 light curves, from which we found 931 stellar flares. We also obtained rotational or orbital periods of 34 GWAC flare stars, of which 33 are less than 5.4 days, and ephemerides of three eclipsing binaries from these light curves. Combining with low resolution spectra from LAMOST and the Xinglong 2.16m telescope, we found that $L_{\rm H\alpha}/L_{\rm bol}$ are in the saturation region in the rotation-activity diagram. From the LAMOST medium-resolution spectrum, we found that Star \#3 (HAT 178-02667) has double H$\alpha$ emissions which imply it is a binary, and two components are both active stars. Thirteen stars have flare frequency distributions (FFDs) from TESS and/or K2 light curves. These FFDs show that the flares detected by GWAC can occur at a frequency of 0.5 to 9.5 yr$^{-1}$. The impact of flares on habitable planets was also studied based on these FFDs, and flares from some GWAC flare stars may produce enough energetic flares to destroy ozone layers, but none can trigger prebiotic chemistry on their habitable planets., Comment: 20 pages, 9 figures, 3 tables

When a wind turbine blade exposure to some degree of rainfall, water droplets in the atmosphere impact the blade at high velocity will causes erosion damages of the leading edge. The damages have significant influence to the aerodynamic performance of the blade, and also the cost of power generation. In this paper, a high velocity impact dynamics model of water droplet impact on wind turbine blade is develops based on SPH-FEM coupling method, where SPH model is used to model the large deformation region of the fluid domain, and FEM method is used to model the small deformation region of the structure domain. Together with properties of gelcoat material on the blade surface, effects of varying impact velocities and angles on the impact response of the gelcoat material are analysed through numerical simulation. The results show that during a high velocity impact event of water droplet, the contact force history appears two peaks. Also contact forces and strains on the blade material decreases with decreasing droplet impact velocity and impact angle, the total contact duration of the droplet during the impact decreases with increasing droplet impact velocity and angle. The present study is expected to provide theoretical guidance for enhancing the erosive capacity of wind turbine blade gelcoat material.

In this paper, the orthogonal cutting experiment and simulation analysis of Cu/PTFE composite materials are carried out with cemented carbide tools. The equivalent homogeneous model is adopted to realize the three-dimensional cutting simulation process. Compared with the experimental results, the predicted cutting force is in good agreement with that of the experimental results, and the deviation does not exceed 20%. The relationship between processing parameters and surface roughness under different cutting conditions is discussed in detail. The results show that the feed rate has a significant effect on the surface roughness, and the feed rate should be controlled during the machining process to obtain high surface quality. Through the observation of the turning surface, there are phenomena such as particle pulled off, cut off, and pressed in the processed surface morphology.

Particle swarm collaboration has many applications on the Internet. It is necessary to cluster a large number of algebraic matrices to obtain enough data. The current research focuses on the correlation between particle swarm coordination and matrix, and does not fully consider the difference between geometries. There is a large overlap, which leads to the same results for different matrices, leading to double counting problems. Therefore, based on the analysis of computer technology, this paper proposes a particle swarm optimization algorithm based on partial differential exact solutions. The selected geometric matrix has higher correlation and lower overlap. Experimental results show that this method can significantly improve the accuracy and efficiency of particle swarm coordination.

Objective: To analyze the volatile constituents in the leaves of Trifolium pratense L. and to explore the effects of different factors on the extraction efficiency. Methods: The volatile components were extracted by the headspace solid phase microextraction (HS-SPME) method and analyzed by gas chromatography-mass spectrometry (GC-MS), and the relative content of the components was calculated by the area normalization method. Results: The best headspace solid phase microextraction conditions of the volatile components of the leaves of Trifolium pratense L. were as follows: 50 μm DVB/CAR/PDMS extraction head was used, the extraction temperature was 70 °C, and extraction time was 40min. 82 compounds were identified from Trifolium pratense L. leaves by GC-MS, accounting for 93.02% of the total volatile components, and the total peak area of volatile components was 2.31x109. The compounds with higher content and active activity were beta.-Caryophyllene (6.48%) and Naphthalene, decahydro-4a-methyl-1-methylene-7-(1-methylethenyl) (4.11%). Conclusion: The type of extraction head, the extraction temperature and the extraction time have great influence on the extraction effect. The HS-SPME-GC-MS method is suitable for the rapid extraction, separation and analysis of the volatile components of the leaves of Trifolium pratense L.

Based on the pulse generation principle of Q-switching and cavity-dumping technologies, this paper designs a power supply with high voltage and narrow pulse for switching avalanche transistor with rising edge of ns level. In the power supply, an avalanche transistor and VOMS transistor are matched to design a driving circuit, which outputs 4.6ns narrow pulse signal. The circuit replaces the traditional cable transmission signal drive mode, reduces the whole signal transmission distance, and improves the signal transmission stability. It makes the two ends of the laser Q-switched crystal KD*P be pushed off instantaneously, which shortened the output laser pulse width from 18ns to 5.6ns. The power supply with high voltage and narrow pulse can be well used in many laser fields including communication, medical treatment, ocean exploration, etc.

The split bearing bores of diesel engine are generally bored after tightening bolts to install crankcase and cylinder block. Machining accuracy significantly affects the contact state during sliding bearing operation, thereby reducing the service life of bearing. For effectively suppressing misalignment of interface caused by deformation of bearing bore, this paper presents finite element model and experimental measurement. The theoretical analysis and numerical calculation of interface are carried out in this paper. The finite element models of bearing bore and interface between crankcase and cylinder block are established to quantitatively analyze the deformation characteristic and contact state. The results indicate that the contact pressure of interface increases gradually with increase of the pre-tightening torque. The sliding distance of interface is positively correlated with the contact pressure of interface. Furthermore, the direction and value of the principal stress are calculated by measuring the strain of nodes around the bearing bore. Differential forces on both sides of bearing bore lead to joint surface sliding. Finite element simulation results are compared with experimental results to verify the finite element model.

The grid planning is a crucial and basic work in the power system, but there are various uncertain factors in the power system, which cause dramatic influences to the size of the grid power investment, as well as the power system security and stability for next few years. Traditional planning methods are gradually hard to adapt the grid planning under situations especially with large amounts of uncertainties. To reduce the impact of uncertain factors of the power system, it is necessary to consider increasingly significant uncertainties in system planning. However, if all extreme scenarios all taken into account, generally, the optimization results will be really conservative. Therefore, to prevent a relatively conservative optimization scheme, this paper proposes a grid-based expansion planning model based on chance constraints which take fully considerations of system uncertain factors using genetic algorithm. Compared with other planning schemes, this method comprehensively considers the investment cost and the level of load loss. Finally, a test system with six nodes is used to verify the effectiveness of the proposed method. The economics of the optimization scheme using the proposed approaches are observed using the test system.

The available transmission capacity of the network has a great impact on the safety and reliability of the whole system. After the reform of electricity market, the grid is required to have the highest available transmission capacity (ATC) based on the existing load due to the uncertain factors. Therefore, it is necessary to consider the growing demand for available transmission capacity from the grid planning stage. Meanwhile, considering the uncertain factors have a great influence on the available transmission capacity (ATC), this paper first models the three uncertain factors and introduces the solving method of probabilistic available transfer capability, then proposes a grid expansion planning model considering the probabilistic available transmission capacity under the influence of uncertainties, which is applied to the six-node test system. Finally, the genetic algorithm is used to solve the final planning scheme. Compared with other planning schemes, this method can consider the comprehensive investment cost and the probability available transmission capacity. The case study shows that the method is effective and can achieve good results.

To study the mechanical response of H96 brass, the quasi-static and dynamic compression experiments were performed by the universal-testing machine and the split Hopkinson pressure bar system. The selected temperature range was 293 K ∼ 873 K, the selected strain-rate range was 0.001/s ∼ 6000/s and the strains were up to 0.6. It was shown that, this alloy has remarkable strain hardening character, and this alloy is sensitive to strain-rate and temperature. In addition, the Dynamic Strain Aging phenomenon of this alloy occurs under the condition of 473 K and 0.001/s. According to the testing results and the thermal-activation dislocation mechanism, a plastic flow constitutive model was brought forth. This constitutive model can predict and describe the plastic flow behavior of H96 brass alloy in a wide range of temperature and strain rate.

High-precision machining technology has attracted increasing attention with the rapid development of modern industry. Jet electrochemical machining is a promising method for forming complex 3D shape surface by controlling the path and dwelling time of electrode nozzle moving over workpiece surface. The machining accuracy mainly relies on the stability of the material removal rate and the smoothness of the machined surface. In this paper, a new jet electrochemical machining method, which is based on a newly developed acid electrolyte, is proposed to improve its machining performance. The effects of voltage, interelectrode gap, electrolyte temperature and flow rate are discussed in this work. Stable machining can be achieved by selecting the optimum process parameters, and the surface roughness (Ra) can be reduced to 14.8 nm. Moreover, the obtained material removal rate distribution agrees well with the Gaussian function, which is recognized to have high capability to form complex 3D surface through controlling the movement of the tools.

New blade was designed by combining the advantage of sweepback and characteristic of flight trajectory. Mass and rotational inertia of turbine were calculated before using UDF and SDOF to build up the condition of fluid-driven simulation and observing the behavior of VAWT with airfoil NACA0012-800, LJY-800 and NACA23012-800. Results showed the potential of new designed airfoil and blade with better aerodynamic stability. Fluid-driven simulation gave out further suggestion that VAWT with high lift-drag ratio coefficient and power coefficient should be validated for its feasibility by fluid-driven simulation.

The composition and content of glucosinolates were investigated in ‘Nainaiqingcai’ mustard to reveal the diversity of the glucosinolates among the individual edible parts (leaves, petioles, and bolting stems). The results showed the significant differences of the composition and content of glucosinolates were found in the different edible parts of ‘Nainaiqingcai’ mustard. Eleven glucosinolates were detected in leaves of ‘Nainaiqingcai’ mustard, including six aliphatic glucosinolates, four indole glucosinolates and one aromatic glucosinolate. Only ten of the eleven glucosinolates were detected in petioles and bolting stems of ‘Nainaiqingcai’ mustard. The highest contents of glucosinolates in ‘Nainaiqingcai’ mustard was found in leaves. Aliphatic glucosinolates were predominant in the ‘Nainaiqingcai’ mustard, followed by indole and aromatic glucosinolates. Sinigrin was the predominant glucosinolate in the ‘Nainaiqingcai’ mustard. In summary, these findings provide a theoretical reference for the scientific consumption and a foundation for the further study of ‘Nainaiqingcai’ mustard in the future.

Interview technique, field investigation and quadrat sampling method were used to study the sleeping sites selection by Macaque Mulatta in Lu Mountain, Sichuan Province. 5 sleeping sites selection were recorded in the investigation. 12 quadrates (10m*10m) and 15 habitat factors were measured and calculated with principal component analysis. The results showed that the characteristics of the sleeping sites were the area of 1600m-1700m, the middle slope position of slope land with slope of 20°- 40°, certain macrophanerophytes density, the average DBH of the sleeping tree were less than 15 cm, the sleeping height were less than 6 m, the theropencedrymion with medium concealment, less disturbed human activities. The principal component analysis showed that the first 6 factors contributed 82.242% of the total variance reflecting the characters of the sleeping sites. It was indicated that the main ecological factors affecting the sleeping sites of the Macaca mulatta in Lu Mountain were terrain, sleeping height, feeding point distance, road distance, human interference distance, concealment, slope direction, etc.

The directionality of the response of gross primary productivity (GPP) to climate has been shown to vary across the globe. This effect has been hypothesized to be the result of the interaction between multiple bioclimatic factors, including environmental energy (i.e. temperature and radiation) and water availability. This is due to the tight coupling between water and carbon cycling in plants and the fact that temperature often drives plant water demand. Using GPP data extracted from 188 sites of FLUXNET2015 and observation-driven terrestrial biosphere models (TBMs), we disentangled the confounding effects of temperature, precipitation and carbon dioxide on GPP, and examined their long-term effects on productivity across the globe. Based on the FLUXNET2015 data, we observed a decline in the positive effect of temperature on GPP, while the positive effects of precipitation and CO2 were becoming stronger during 2000–2014. Using data derived from TBMs between 1980 and 2010 we found similar effects globally. The modeled data allowed us to investigate these effects more thoroughly over space and time. In arid regions, the modeled response to precipitation increased since 1950, approximately 30 years earlier than in humid regions. We further observed the negative effects of summer temperature on GPP in arid regions, suggesting greater aridity stress on productivity under global warming. Our results imply that aridity stress, triggered by rising temperatures, has reduced the positive influence of temperature on GPP, while increased precipitation and elevated CO2 may alleviate negative aridity impacts.

The metamaterial with negative Poison’s ratio is widely used due to its special mechanical and physical properties. Based on the theory of periodic solution and bifurcation of nonlinear dynamics, we mainly focus on the nonlinear vibration behaviors and parameter control of a simply supported concave hexagonal composite sandwich plate with negative Poisson’s ratio in auxetic honeycombs subjected to in-plane and transverse excitation. The Melnikov function is improved by introducing the curvilinear coordinate frame and Poincaré map to detect the existence and number of the periodic solutions. The effects of the forcing excitation coefficient on nonlinear dynamics as well as the parameter control conditions are presented. Numerical method is performed to obtain the phase portraits of the number and corresponding positions of multiple periodic orbits.

A material removal mechanism of a single-tip tool cutting/scratch is the foundation for the analysis and prediction of the grinding process. A novel method for conducting single-tip, relatively high speed, and force-measurable nano-cutting tests with controllable cutting length are proposed to investigate the elastic–plastic deformation. Nano-cutting tests of single-crystal silicon are implemented at the cutting speeds of 0.1 m s−1 and 1 m s−1 which are close to the real grinding speed and much higher than that of single-tip tool scratch tests reported. Remarkable elastic recovery rate over 50% is observed in both cutting speeds. A semi-empirical model describing the relationship between the elastic recovery rate and residual depth is proposed. The normal force is studied in the whole cutting range. The findings of the elastic–plastic deformation behavior under relatively high cutting speed are valuable for the further mechanisms and process analysis of the ultra-fine grinding of brittle materials.

Bijie City, Guizhou Province belongs to the alpine cold climate. In order to understand the nutritional values of ‘Nainaiqingcai’ mustard, the contents of main nutrients among different edible parts (leaves, petioles, and bolting stem) in ‘Nainaiqingcai’ mustard under the alpine cold climate were investigated. The results showed that significant differences were found among different edible parts. The levels of chlorophyll, carotenoids, ascorbic acid, soluble soilds, and soluble proteins were followed as the trends of leaves > petioles > bolting stem.Whereas the sugar components showed different distributions, and the lowest content of sugar was detected in leaves. Moreover, significant negatively correlation were found between sugar and the other nutrients. Most of the extremely significant positive correlations were found between sugar components, and the correlation coefficient is high (except for the correlation between fructose and sucrose). The highest correlation coefficient was between chlorophyll and carotenoids, up to 1.000. In summary, the information in this study provides a theoretical reference for the study of nutritional quality of ‘Nainaiqingcai’ mustard under the alpine cold climate.

This experiment analyzed the bioactive compounds content and antioxidant capacities of different edible parts (the leaves, petioles and bolting stem) of ‘Nianaiqingcai’ mustard. The results showed that significant differences were found among different edible parts. The levels of chlorophylls (chlorophyll a, chlorophyll b, and total chlorophyll), carotenoids (neoxanthin, violaxanthin, lutein, β-carotene and total carotenoids), proanthocyanidins, flavonoids, total phenolic and antioxidant capacities were all followed as the trend of leaves > petioles > bolting stem, and the bioactive compound contents and antioxidant capacities of the leaves were far greater than other parts. Correlation analysis showed that there was a significant positive correlation between all indicators. The correlations between individuals of chlorophyll and carotenoids were extremely high, and the level even reached 1.000. Even the lowest correlation coefficient between ABTS and total phenolics was as high as 0.965. This study provides a theoretical basis and data reference for people’s daily diet

Surface electromyography (EMG) signal from trunk muscles is often contaminated by electrocardiography (ECG) artifacts. This study presents a novel method for muscle activity onset detection by processing surface EMG against ECG artifacts. The method does not require removal of ECG artifacts from raw surface EMG signals. Instead, it applies the sample entropy (SampEn) analysis to highlight EMG activity and suppress ECG artifacts in the signal complexity domain. A SampEn threshold can then be determined for detection of muscle activity. The performance of the proposed method was examined with different SampEn analysis window lengths, using a series of combinations of 'clean' experimental EMG and ECG recordings over a wide range of signal to noise ratios (SNRs) from -10 to 10 dB. For all the examined SNRs, the window length of 128 ms yielded the best performance among all the tested lengths. Compared with the conventional amplitude thresholding and integrated profile methods, the SampEn analysis based method achieved significantly better performance, demonstrated as the shortest average latency or error among the three methods (p < 0.001 for any of the examined SNRs except 10 dB).

We study the Auger effect in the presence of strong x-ray free-electron lasers (XFELs) propagating through resonant argon vapors by solving the Maxwell-Bloch equations numerically. The simulations ...

The reference source system is a key factor to ensure the successful location of the satellite interference source. Currently, the traditional system used a mechanical rotating antenna which leaded to the disadvantages of slow rotation and high failure-rate, which seriously restricted the system's positioning-timeliness and became its obvious weaknesses. In this paper, a multi-beam antenna scheme based on the horn array was proposed as a reference source for the satellite interference location, which was used as an alternative to the traditional reference source antenna. The new scheme has designed a small circularly polarized horn antenna as an element and proposed a multi-beamforming algorithm based on planar array. Moreover, the simulation analysis of horn antenna pattern, multi-beam forming algorithm and simulated satellite link cross-ambiguity calculation have been carried out respectively. Finally, cross-ambiguity calculation of the traditional reference source system has also been tested. The comparison between the results of computer simulation and the actual test results shows that the scheme is scientific and feasible, obviously superior to the traditional reference source system.

We present a general scheme for multiparty-controlled teleportation of an arbitrary m-qudit (d-dimensional quantum system) state by using non-maximally entangled states as the quantum channel. The sender performs m generalized Bell-state measurements on her 2m particles, the controllers take some single-particle measurements with the measuring basis Xd and the receiver only needs to introduce one auxiliary two-level particle to extract quantum information probabilistically with the fidelity unit if he cooperates with all the controllers. All the parties can use some decoy photons to set up their quantum channel securely, which will forbid a dishonest party to eavesdrop freely. This scheme is optimal as the probability that the receiver obtains the originally unknown m-qudit state equals the entanglement of the quantum channel.

A quantum secure direct communication network scheme is proposed with quantum superdense coding and decoy photons. The servers on a passive optical network prepare and measure the quantum signal, i.e., a sequence of the $d$-dimensional Bell states. After confirming the security of the photons received from the receiver, the sender codes his secret message on them directly. For preventing a dishonest server from eavesdropping, some decoy photons prepared by measuring one photon in the Bell states are used to replace some original photons. One of the users on the network can communicate any other one. This scheme has the advantage of high capacity, and it is more convenient than others as only a sequence of photons is transmitted in quantum line., 6 pages, 2 figure

Objective. This study explored the feasibility of detecting hidden muscle activity in surface electromyogram (EMG) baseline. Approach. Power spectral density (PSD) analysis and multi-scale entropy (MSE) analysis were used. Both analyses were applied to computer simulations of surface EMG baseline with the presence (representing activity data) or absence (representing reference data) of hidden muscle activity, as well as surface electrode array EMG baseline recordings of healthy control and amyotrophic lateral sclerosis (ALS) subjects. Main results. Although the simulated reference data and the activity data yielded no distinguishable difference in the time domain, they demonstrated a significant difference in the frequency and signal complexity domains with the PSD and MSE analyses. For a comparison using pooled data, such a difference was also observed when the PSD and MSE analyses were applied to surface electrode array EMG baseline recordings of healthy control and ALS subjects, which demonstrated no distinguishable difference in the time domain. Compared with the PSD analysis, the MSE analysis appeared to be more sensitive for detecting the difference in surface EMG baselines between the two groups. Significance. The findings implied the presence of a hidden muscle activity in surface EMG baseline recordings from the ALS subjects. To promote the presented analysis as a useful diagnostic or investigatory tool, future studies are necessary to assess the pathophysiological nature or origins of the hidden muscle activity, as well as the baseline difference at the individual subject level.

This study investigates the effect of the involuntary motor activity of paretic-spastic muscles on the classification of surface electromyography (EMG) signals.Two data collection sessions were designed for 8 stroke subjects to voluntarily perform 11 functional movements using their affected forearm and hand at relatively slow and fast speeds. For each stroke subject, the degree of involuntary motor activity present in the voluntary surface EMG recordings was qualitatively described from such slow and fast experimental protocols. Myoelectric pattern recognition analysis was performed using different combinations of voluntary surface EMG data recorded from the slow and fast sessions.Across all tested stroke subjects, our results revealed that when involuntary surface EMG is absent or present in both the training and testing datasets, high accuracies (96%,98%, respectively, averaged over all the subjects) can be achieved in the classification of different movements using surface EMG signals from paretic muscles. When involuntary surface EMG was solely involved in either the training or testing datasets, the classification accuracies were dramatically reduced (89%,85%, respectively). However, if both the training and testing datasets contained EMG signals with the presence and absence of involuntary EMG interference, high accuracies were still achieved (97%).The findings of this study can be used to guide the appropriate design and implementation of myoelectric pattern recognition based systems or devices toward promoting robot-aided therapy for stroke rehabilitation.

Vortex structures in high-transition-temperature superconductors are studied by solving Bogoliubov–de Gennes equations based on a model Hamiltonian with competing antiferromagnetic (AF) and d-wave superconducting orderings in the presence of a long-range Coulomb interaction. We show that transition from a checkerboard pattern to stripe structure for spin density wave (SDW), charge density wave, and d-wave orderings may occur by enhancing the strength of the on-site repulsion U in the absence of the long-range Coulomb interaction. The long-range Coulomb interaction provides an intrinsic mechanism for electron depletion inside an AF-like vortex core, and the field-induced AF order was screened and confined onto the near core region. Consequently, two-dimensional modulations or the checkerboard patterns of vortex charge distribution and SDW order recovered for underdoped samples of large U when a reasonably large long-range Coulomb interaction Vc strength had been introduced into the model Hamiltonian.