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Aiming at the requirements of short-range, high-precision, and high-speed measurement of coaxial helicopter wingtip distance measurement, a millimeter-wave radar wingtip distance measurement scheme is proposed, and the ranging accuracy of frequency-modulated continuous wave millimeter-wave radar is improved by optimizing the frequency estimation method and the beat-frequency signal processing process. The multi-antenna data coherent superposition method and the correlation search for the estimated frequency are used to shorten the measurement period, and at the same time, the ranging accuracy of the millimeter-wave radar can be improved, and the single measurement time can be guaranteed. Based on frequency refinement, frequency offset method, phase method, amplitude method and fitted approximation method, the frequency estimation of millimeter wave radar differential frequency signal is combined with the influence of bandwidth, measured target shape and material on ranging to improve millimeter wave radar ranging performance comprehensively. Through simulations and experiments, the accuracy, stability, time consuming and application conditions of the optimized algorithm are comprehensively evaluated, and the feasibility of millimeter wave radar wingtip ranging is verified.

Get the influence of shooting on the ballistic elements and correction elements of grenade under the condition of extra-large elevation difference between artillery and target in plateau area through simulation, and drawn the comparison chart of different altitude and elevation difference between artillery and target by using the simulation data. Calculate the variation characteristics of the hit range of laser terminal guided projectile under the condition of the elevation difference of extra-large elevation difference between artillery and target at different altitudes, and the influence of altitude and extra-large elevation difference between artillery and target on the hit range of laser terminal guided projectile is analyzed and summarized. It has a certain reference value for improving the shooting accuracy under the condition of high altitude and extra-large elevation difference between artillery and target.

Due to the excellent physiochemical properties of graphene oxide (GO), the fabrication of superamphiphobic coatings based on GO can explore the application fields of GO. Herein, superamphiphobic GO coatings are fabricated by simple dip coating GO and organosilane polymer (GO-FAS) dispersion on the cotton fabric, with GO acting as solid lubricant originating from its low friction coefficient. Through compound with PS/PTFE and PVDF-HFP/FAS, the PVDF-HFP/FAS/GO-FAS coating exhibit enhanced anti-abrasion property and can withstand 200 cycles of sandpaper abrasion. This study provides an opportunity for the applications of graphene oxide as superamphiphobic materials.

Considering only the self-mixing interference taking place, the modulation effect of optical feedback in a single polarization a-cut Nd:YVO4 laser is presented. The output intensity of the laser with anisotropic gain medium is modulated with a wave plate (WP) in the external cavity. The rotation orientation and phase retardation of the WP regularly determinate the amplitude and phase of laser intensity fringe, because the feedback light component at the same polarization direction as the output laser can interact with the light field in the cavity. The corresponding theoretical model is established and the windowed Fourier transform method is utilized to quantitatively explain this phenomenon. By introducing the amplitude and phase modulation coefficients, comparisons of experimental results with simulation analysis show good consistency.

Accidents such as overvoltage, personal injury and motor damage caused by singlephase disconnection faults occur frequently in active distribution networks. In response to this problem, firstly, the negative-sequence differential impedance is defined and a protection method based on negative-sequence differential impedance is proposed, the method uses the amplitude of negative-sequence differential impedance as an action quantity and uses its phase to construct an adaptive braking threshold. Secondly, in case of protection failure under overload, the zero-sequence voltage amplitude difference is proposed as an auxiliary criterion, and the influence of different types of distributed generators on the zero-sequence voltage difference on both sides of the fault fracture is analyzed. Finally, it is verified by simulation that the method can be positioned reliably and is not affected by the neutral point grounding method, transition resistance, load and distributed generators.

With the help of the gas-filled recoil spectrometer SHANS and a digital data acquisition system, the fine structure of the decay for Pa was studied. The nuclides were produced through the 1p3n evaporation channel via the heavy-ion induced fusion evaporation reaction Ar + W. Based on the ER- - - and - correlation measurement, three new decays were observed in addition to the three branches known previously. The one with the largest decay energy was regarded as the ground state to ground state transition. The newly measured decay properties of Pa were examined in a framework of reduced width.

With the improvement of computer ability and the rapid development of computer vision technology, UAV has been widely used in other industries from the initial military field. At present, the most widely used UAV navigation is the global positioning system (GPS) of the United States, which can be easily interfered by human beings, resulting in certain errors. At present, there are four landing methods for manned aircraft, but no matter which one is, its concealment is poor. At the same time, compared with manned aircraft, UAV is generally smaller in size, so it is unable to follow the domestic microwave radar equipment in China. Through literature review, the origin and development of UAV and computational vision technology are comprehensively reviewed. The application of computer vision technology in agriculture, power, transportation, environmental protection, rescue, entertainment and other fields in recent years is summarized. The relevant survey data are analyzed and presented in the form of chart. Through the data, we can clearly find that the combination of computer vision and UAV still has a lot of room for improvement in the future.

With the progress and development of China’s reform and opening up and economic globalization, China has made great progress in science and technology, especially in computer vision technology. From the current development of our country, the progress and development of computer vision technology plays an important role in the development and utilization of UAV automatic navigation. With the continuous development of automatic navigation technology, artificial intelligence has been widely used in various fields, and computer vision technology as the main direction of this field has also been rapid development in recent years, which also makes the important branch of computer vision moving object tracking technology has more and more extensive application, such as intelligent security, intelligent transportation, safe driving And video analysis.

In this study, 218Ac and 221Th nuclides were produced via the heavy-ion induced fusion evaporation reaction 40Ar + 186W. Their decay properties were studied with the help of the gas-filled recoil spectrometer SHANS and a digital data acquisition system. The cross section ratio between 222Pa and 218Ac was extracted experimentally, with measured value 0.69(9). Two new possible α decay branches to 221Th are suggested. The valence neutron configurations for the daughter 217Ra are discussed in terms of the hindrance factors.

The water dimer demonstrates a completely different protype in water systems, it prefers not forming larger clusters instead existing in vapor phase stably, which contracts the viewpoint of the cooperative effect of hydrogen bond (O–H ··· O). It is well accepted that the cooperative effect is beneficial to forming more hydrogen bonds (O–H ··· O), leading to stronger H-bond (H ··· O) and increase in the O–H bond length with contraction of intermolecular distance. Herein, the high-precision ab initio methods of calculations applied on water dimer shows that the O–H bond length decreases and H-bond (H ··· O) becomes weaker with decreasing H-bond length and O ··· O distance, which can be considered as the uncooperative effect of hydrogen bond (O–H ··· O). It is ascribed to the exchange repulsion of electrons, which results in decrease of the O–H bond length and prevents the decrease in the O ··· O distance connected with the increasing scale of water clusters. Our findings highlight the uncooperative effect of hydrogen bond attributed to exchange repulsion of electrons as the mechanism for stabilizing water dimer in vapor phase, and open a new perspective for studies of hydrogen-bonded systems.

For traditional magnetorheological (MR) shock absorbers, the damping force is proportional to the square of the impact velocity. The instantaneous peak value of the damping force can easily cause damage to the load structure or human body, which will reduce the buffering efficiency. The viscous damping force is significantly affected by the size of the gap. Therefore, by changing the flow gap under different buffer strokes by presetting, the damping force can be maintained at a constant output in the full piston stroke, thereby improving the buffer efficiency. That is, a large gap is used at high speed and a small gap is used at low speed. The increase of the magnetic damping force at a small gap is applied to compensate for the decrease of the viscous force at low speed. Only constant current needs to be applied during buffering, which can greatly reduce costs. Based on this idea, a novel MR damper based on axial variable damping gap (MRD-VDG) is proposed. The MRD-VDG design method for the constant value output of the damping force in the full piston stroke is discussed and applied. According to the different requirements of the damping force under different piston displacements, the damping gap of different axial position are preset to realize the constant value output of the damping force during the stroke. The damping force under different damping gaps is analytically derived according to the Bingham-plastic nonlinear flow model with minor losses. Combining with the finite element analysis to obtain magnetic fields at different damping gaps between piston and cylinder. To validate the performance of the proposed design method, the prototype of MRD-VDG is fabricated. Damping characteristic test and impact test are performed to measure the damping characteristics of the MRD-VDG under different excited conditions. The results show that the piston displacement history of the damping force in the experiment is agreed well with the displacement history of the desired F-S curve under the assumed speed. The buffer efficiency of the prototype under designed conditions (the ratio of the corrected theoretical constant damping force to the actual peak damping force) exceeds 90%. This demonstrates the effectiveness of the MRD-VDG design. This design method has significant application prospects under impact condition without complex control (such as gun buffer, landing buffer, etc.)

Dynamic nature of hydrogen bond (H-bond) is central in molecular science of substance transportation, energy transfer, and phase transition in H-bonding networks diversely expressed as solution, crystal, and interfacial systems, thus attracting the state-of-the-art revealing of its phenomenological edges and sophisticated causes. However, the current understanding of the ground-state fluctuation from zero-point vibration (ZPV) lacks a firm quasi-classical base, concerning three basic dimensions as geometry, electronic structure, and interaction energy. Here, based on the ab initio molecular dynamics simulation of a ground-state water dimer, temporally separated fluctuation features in the elementary H-bond as the long-time weakening and the minor short-time strengthening are respectively assigned to two low-frequency intermolecular ZPV modes and two O–H stretching ones. Geometrically, the former modes instantaneously lengthen H-bond up to 0.2 Å whose time-averaged effect coverages to about 0.03 Å over 1-picosecond. Electronic-structure fluctuation crosses criteria’ borders, dividing into partially covalent and noncovalent H-bonding established for equilibrium models, with a 370% amplitude and the district trend in interaction energy fluctuation compared with conventional dragging models using frozen monomers. Extended physical picture within the normal-mode disclosure further approaches to the dynamic nature of H-bond and better supports the upper-building explorations towards ultrafast and mode-specific manipulation.

In traditional artillery shooting, meteorological information is provided by meteorological unit, but because of the inconsistency between meteorological observation sites and shooting sites, there are errors in meteorological data, which affects shooting accuracy. In order to reduce the influence of meteorological data errors on firing accuracy, it is proposed to acquire multi-meteorological data along the ballistic trajectory by using the dropsonde carried by the UAV, and calculate the meteorological data along the ballistic trajectory for artillery firing. Through simulation calculation, using meteorological data along the ballistic for artillery firing can effectively improve firing accuracy.

Aiming at the phenomenon of low firing accuracy and low hit probability of guided projectiles in Plateau area, based on the differential equation of kinematics of guided projectiles, the variation and regularity of hit range at different altitudes are simulated and calculated. The measures to improve hitting accuracy are proposed and simulated.

We demonstrate a very strong magnetic resonance in metamaterials for high-performance sensing. The metamaterials comprise a periodic array of a pair of closely spaced metal nanodisks that are placed on metal substrate. The strong magnetic resonance is essentially an antisymmetric resonant mode resulting from the near-field plasmon hybridization within the pair of metal nanodisks. Because the magnetic resonance has great electromagnetic field enhancement, ultra-narrow bandwidth and nearly perfect absorption, the metamaterials have very high sensitivity (S = 991 nm/RIU, S* = 47/RIU) and figure of merit (FOM = 124, FOM* = 17 702), which may find potential applications in label-free biosensing.

Since roaming was found as a new but common reaction path of isomerization, many of its properties, especially those of roaming transition state (TSR), have been studied recently on many systems. However, the mechanism of roaming is still not clear at the atomic level. In this work, we used first-principles calculations to illustrate the detailed structure of TSR in an internal isomerization process of nitrobenzene. The calculations distinctively show its nature of antiferromagnetic coupling between two roaming fragments. Moreover, the effect of dispersion is also revealed as an important issue for the stability of the TSR. Our work provides a new insight from the view of electronic structure towards the TSR and contributes to the basic understanding of the roaming systems., 7 pages, 2 figures

A new hybrid approach is presented to study the dynamic behaviour of a rotor- foundation system, in which a shaft coupled with various discontinuities are connected to a flexible foundation via discrete spring subunits. By modelling the rotor with the modified transfer matrix method and describing the flexible foundation through the appropriate modal model, the proposed technique facilitates a computationally efficient modelling approach where a mixture of theoretical, numerical or experimental models can be incorporated into one overall numerical model. Particularly, the present model enables one to conveniently consider both the free and forced vibrations as well as effects of various combinations of discontinuities encountered in the rotor. Some results are compared with available results in previous publications and those from the finite element method to validate the model. Parametric studies are also performed to demonstrate the accuracy and versatility of the developed method for substructure coupling analysis.

The resonant interaction between XUV ultra-short laser pulses and atomic hydrogen is systematically studied by numerically solving the time-dependent Schrodinger equation in this paper. Triple-peak structures are found to appear in the harmonics emitted provided that the incident laser is resonant with the 1 s-2p transition of the hydrogen atom. Moreover, the energy difference between neighboring peaks is the same and turns out to be proportional to the peak field strength E 0. Based on the theory of strong field approximation, and taking the interactions of the 1 s-2p bound energy levels into consideration, theoretical interpretations of the phenomena mentioned are successfully presented. This work provides a possible approach for generating XUV radiation with a tunable frequency via the interaction between atoms and XUV laser pulses.

The complete fusion reaction 40 Ca+ 175 Lu was studied at a beam energy of 5.1 MeV u �1 . Evaporation residues recoiled from the target were separated from the primary beam by the gas-filled recoil separator SHANS and then implanted into the focal plane detection system. Based on the energy-positiontime correlation measurement, neutron-deficient nuclei − 208 213 Ac, 212 Pa and 211 Th produced in this reaction were identified. Previously reported decay properties of the ground state in 212 Pa were confirmed and improved values of − + 5.1 1.7 ms and 8.250(20) MeV for the half-life and α-particle energy of 212 Pa were obtained. No correlated decay chain arising from 211 Pa was observed and an upper limit for the cross section of 211 Pa was estimated.

A gas-filled recoil separator was designed and built newly at Institute of Modern Physics (IMP) in Lanzhou. With the recent commissioning of the separator, the decay properties of 271Ds were studied via the 208Pb (64Ni, n) reaction at a beam energy of 313.3 MeV. One α-decay chain for 271Ds was established in total. The experimental result is consistent with the values reported in the literature.

With the recent commissioning of a gas-filled recoil separator at Institute of Modern Physics (IMP) in Lanzhou, the decay properties of (271)Ds (Z = 110) were studied via the Pb-208(Ni-64, n) reaction at a beam energy of 313.3MeV. Based on the separator coupled with a position sensitive silicon strip detector, we carried out the energy-position-time correlation measurements for the implanted nucleus and its subsequent decay alpha's. One alpha-decay chain for (271)Ds was established. The.. energy and decay time of the (271)Ds nucleus were measured to be 10.644 MeV and 96.8 ms, which are consistent with the values reported in the literature.