Search

The working conditions of heavy-duty trucks are very complicated as the diesel shaking and resonance problems, which causes weld tears, separators to fall off, and other failures occur. Through experiments and finite element simulation, the natural frequency and vibration mode of a given 400 L diesel tank were calculated to study the influences of structural parameters such as the fill ratio (0.1-0.9), the number of baffle plates (0, 1, 2), the spacing of the plates (240 mm, 400 mm, 560 mm) and the aperture (38 mm, 78 mm, 118 mm) on the modal parameters with the wet mode method. The results of the hammering mode test and the simulation modal analysis agree well with the maximum error is 4.8%; the natural frequency of the diesel tank will increase with fill ratio decrease; the increase of the baffle plate number (0, 1, 2) can effectively increase the first-order natural frequency of the diesel tank, but the change of the natural frequency is not obvious on the higher order; the higher plates spacing has a smaller natural frequency; increasing the aperture will highly increase the natural frequency, 188 mm has better vibration safety.

Abstract The century-long development of surface sciences has witnessed the discoveries of a variety of quantum states. In the recently proposed “obstructed atomic insulators”, symmetric charges are pinned at virtual sites where no real atoms reside. The cleavage through these sites could lead to a set of obstructed surface states with partial electronic occupation. Here, utilizing scanning tunneling microscopy, angle-resolved photoemission spectroscopy and first-principles calculations, we observe spectroscopic signature of obstructed surface states in SrIn2P2. We find that a pair of surface states that are originated from the pristine obstructed surface states split in energy by a unique surface reconstruction. The upper branch is marked with a striking differential conductance peak followed by negative differential conductance, signaling its localized nature, while the lower branch is found to be highly dispersive. This pair of surface states is in consistency with our calculational results. Our finding not only demonstrates a surface quantum state induced by a new type of bulk-boundary correspondence, but also provides a platform for exploring efficient catalysts and related surface engineering.

For over 50 years, various ion beam facilities have been utilized to simulate the irradiation effect of neutrons on relevant nuclear materials. However, due to the limitation of single ion beam irradiation, the injection of H2+ and He+ into the sample coaxially is necessary to observe the synergy of hydrogen and helium displacement damage. This study presents a beam line design that is capable of separating ions with different charge mass ratios, screening out unwanted particles, and finally combining the separated beams again. Through this design, H+, H2+, and He+ beams can be completely separated with an axis deviation of less than 0.5 mm after beam combination. Furthermore, the proportion of H2+ and He+ can be adjusted by regulating the inlet air of the ion source, down to the accuracy of a single ion. An accelerating tube is employed to adjust the energy of implanted ions within 10–50 keV. This device also has the capability to efficiently transmit a single type of ion while filtering out extraneous ions (such as O+ beam). The fine-beam optical design not only makes it easy to adjust beam parameters but also eliminates the need for a high-precision power supply. The goal of this work is to have an analytical tool to understand the effect of each electromagnetic component on the ion trajectories.

To systematically study the influence of a propensity for a particular driving style on car-following risk, a safety potential field risk-quantification method that considers driving style is proposed. First, we classify driving behaviors and construct a field-based safety potential car-following model via analogy with intermolecular interactions; second, we establish a risk-quantification model by considering driving style, risk exposure, and risk severity and classify the consequent risk into four levels, high risk, medium risk, low risk, and safe, using the fuzzy C-means algorithm. Finally, we predict the car-following risk using the LightGBM algorithm in real time. The experimental results show that the LightGBM algorithm can recognize up to 86% of medium–high risk levels compared to the Decision Tree and Random Forest Algorithms. It can achieve effective prediction of car-following risk, which provides sufficient warning information to drivers and helps improve the overall safety of vehicle operation.

Mangrove forests play a vital role in maintaining ecological balance in coastal regions. Accurately assessing changes in the ecosystem service value (ESV) of these mangrove forests requires more precise distribution data and an appropriate set of evaluation methods. In this study, we accurately mapped the spatial distribution data and patterns of mangrove forests in Guangxi province in 2016 and 2020, using 10 m spatial resolution Sentinel-2 imagery, and conducted a comprehensive evaluation of ESV provided by mangrove forests. The results showed that (1) from 2016 to 2020, mangrove forests in Guangxi demonstrated a positive development trend and were undergoing a process of recovery. The area of mangrove forests in Guangxi increased from 6245.15 ha in 2016 to 6750.01 ha in 2020, with a net increase of 504.81 ha, which was mainly concentrated in Lianzhou Bay, Tieshan Harbour, and Dandou Bay; (2) the ESV of mangrove forests was USD 363.78 million in 2016 and USD 390.74 million in 2020; (3) the value of fishery, soil conservation, wave absorption, and pollution purification comprises the largest proportions of the ESV of mangrove forests. This study provides valuable insights and information to enhance our understanding of the relationship between the spatial pattern of mangrove forests and their ecosystem service value.

With the rapid development of laser plasma accelerator, multiple functional beamlines have been designed to transport such pulsed particle beam with large energy spread and divergence angle. Accordingly, the demand for optimal design and online feedback of laser beamlines has also been put forward. We have developed a graphics processing unit–accelerated multiparticle beam transport simulation algorithm based on the open source project “HPSim” to meet the above need. The algorithm implements a series of functions such as the simulation of solenoids, the simulation of exponentially decreasing energy spectrum beams, and cross-programming and cross-language calls. In terms of computational efficiency, the algorithm is approximately 20 times more efficient than multiparticle simulation program tracewin, meeting the simulation time-consumption requirement of a hundred milliseconds for virtual accelerator software. The algorithm’s monoenergetic and exponentially decreasing energy spectrum beam simulation capabilities are verified in the beamline design for CLAPA-I and CLAPA-II at Peking University. The algorithm can be applied not only to virtual accelerator for real-time beam transport simulations but also to fast and efficient beamline magnets optimization design.

A new two-stage alignment on a moving base is proposed for a low-cost inertial navigation system with the aid of a Global Positioning System (GPS) receiver in the Earth-centered, Earth-fixed (ECEF) frame under large initial attitude errors. Both the state and measurement equations are derived using the additive quaternion error model in the ECEF frame for alignment without the need for level adjustment. The nonlinear velocity error equations in both the coarse and the fine stages are linearized further. An improved strong tracking filter is proposed for the coarse stage to converge quickly with large initial attitude errors. After the attitude errors converge to smaller values in the coarse stage, a standard Kalman filter is implemented for the fine stage. Experiments demonstrate that attitude error can converge quickly with the proposed adaptive alignment method.

Based on the zero-curvature equation and Lenard recursion equations, we propose a vector super long-wave-short-wave hierarchy associated with an (n+2)×(n+2)matrix spectral problem. A typical member in the hierarchy is the vector super Newell long-wave-short-wave equation. An infinite set of conservation laws for the vector super Newell long-wave-short-wave equation is constructed by using Liouville’s formula and the resulting super Riccati equation.

The navigation by the stellar refraction is important for a LEO (Low-Earth-Orbit) satellite, especially in a GNSS (Global Navigation Satellite System)-denied environment, since it is totally autonomous. However, the biggest barrier to the accurate navigation by the stellar refraction lies in the accurate stratospheric density. Therefore, the retrieval of the stratospheric density by the star occultation is proposed in this paper to acquire the stratospheric density globally with the high accuracy. Compared with the retrieval of the stratospheric density by the GPS (Global Positioning System) radio occultation, the retrieval by the star occultation can achieve a high vertical resolution. The retrieval of the stratospheric density by the star occultation is first derived in principle. Then, the performance of the retrieval, including the spatial resolution, the atmospheric attenuation, and the accuracy, was investigated in detail. The performance of the retrieval was also comprehensively verified by simulations. The simulation results prove that the retrieval of the stratospheric density by the star occultation can achieve a similar accuracy to that by the GPS radio occultation, but it has a higher vertical resolution than that by the GPS radio occultation, which is good for improving the accuracy of the navigation by the stellar refraction.

In this paper, we study the long-time asymptotic behavior of the solution of the Cauchy problem for the generalized Sasa-Satsuma equation. Starting with the 3 × 3 Lax pair related to the generalized Sasa-Satsuma equation, we construct a Rieman-Hilbert problem, by which the solution of the generalized Sasa-Satsuma equation is converted into the solution of the corresponding RiemanHilbert problem. Using the nonlinear steepest decent method for the Riemann-Hilbert problem, we obtain the leading-order asymptotics of the solution of the Cauchy problem for the generalized SasaSatsuma equation through several transformations of the Riemann-Hilbert problem and with the aid of the parabolic cylinder function.

Laser plasma acceleration has made remarkable progress in the last few decades, but it also faces many challenges. Although the high gradient is a great potential advantage, the beam quality of the laser accelerator has a certain gap, or it is different from that of traditional accelerators. Therefore, it is important to explore and utilize its own features. In this article, some recent research progress on laser proton acceleration and its irradiation application, which was carried out on the compact laser plasma accelerator (CLAPA) platform at Peking University, have been introduced. By combining a TW laser accelerator and a monoenergetic beamline, proton beams with energies of less than 10 MeV, an energy spread of less than 1%, and with several to tens of pC charge, have been stably produced and transported in CLAPA. The beamline is an object–image point analyzing system, which ensures the transmission efficiency and the energy selection accuracy for proton beams with large initial divergence angle and energy spread. A spread-out Bragg peak (SOBP) is produced with high precision beam control, which preliminarily proved the feasibility of the laser accelerator for radiotherapy. Some application experiments based on laser-accelerated proton beams have also been carried out, such as proton radiograph, preparation of graphene on SiC, ultra-high dose FLASH radiation of cancer cells, and ion-beam trace probes for plasma diagnosis. The above applications take advantage of the unique characteristics of laser-driven protons, such as a micron scale point source, an ultra-short pulse duration, a wide energy spectrum, etc. A new laser-driven proton therapy facility (CLAPA II) is being designed and is under construction at Peking University. The 100 MeV proton beams will be produced via laser–plasma interaction by using a 2-PW laser, which may promote the real-world applications of laser accelerators in malignant tumor treatment soon.

Collection of particles from a laser-driven accelerator into a conventional beamline requires careful manipulation of the beam to handle the wide energy spread, large angular divergence and short pulse lengths characteristic of laser-driven acceleration. Accurate simulation of the first few millimetres is crucial in order to optimise the collecting elements such as solenoids or quadrupole magnets. Experiments and simulations both show significant emittance growth in this collection region. We have developed a multi-particle beam dynamics model using impact-t that includes the characteristic exponentially-decaying laser-driven energy spectrum and accurately models the emittance growth due to the large energy spread. In this paper we present theoretical relationships between energy spread and emittance growth, and compare these with the simulated emittance growth. Results show excellent correspondence between theory and simulation. The effect is negligible for low-energy proton accelerators, but is important for electron accelerators and for proposed high-energy laser-driven proton accelerators.

Fluid discrimination is an extremely important part of seismic data interpretation. It plays an important role in the refined description of hydrocarbon-bearing reservoirs. The conventional AVO inversion based on Zoeppritz’s equation shows potential in lithology prediction and fluid discrimination; however, the dispersion and attenuation induced by pore fluid are not fully considered. The relationship between dispersion terms in different frequency-dependent AVO equations has not yet been discussed. Following the arguments of Chapman, the influence of pore fluid on elastic parameters is analyzed in detail. We find that the dispersion and attenuation of Russell fluid factor, Lamé parameter, and bulk modulus are more pronounced than those of P-wave modulus. The Russell fluid factor is most prominent among them. Based on frequency-dependent AVO inversion, the uniform expression of different dispersion terms of these parameters is derived. Then, incorporating the P-wave difference with the dispersion terms, we obtain new P-wave difference dispersion factors which can identify the gas-bearing reservoir location better compared with the dispersion terms. Field data application also shows that the dispersion term of Russell fluid factor is optimal in identifying fluid. However, the dispersion term of Russell fluid factor could be unsatisfactory, if the value of the weighting parameter associated with dry rock is improper. Then, this parameter is studied to propose a reasonable setting range. The results given by this paper are helpful for the fluid discrimination in hydrocarbon-bearing rocks.

The recently discovered intrinsic magnetic topological insulator MnBi_{2}Te_{4} has been met with unusual success in hosting emergent phenomena such as the quantum anomalous Hall effect and the axion insulator states. However, the surface-bulk correspondence of the Mn-Bi-Te family, composed by the superlatticelike MnBi_{2}Te_{4}/(Bi_{2}Te_{3})_{n} (n=0,1,2,3…) layered structure, remains intriguing but elusive. Here, by using scanning tunneling microscopy and angle-resolved photoemission spectroscopy techniques, we unambiguously assign the two distinct surface states of MnBi_{4}Te_{7} (n=1) to the quintuple-layer (QL) Bi_{2}Te_{3} termination and the septuple-layer (SL) MnBi_{2}Te_{4} termination, respectively. A comparison of the experimental observations with theoretical calculations reveals diverging topological behaviors, especially the hybridization effect between the QL and SL, on the two terminations. We identify a gap on the QL termination, originating from the hybridization between the topological surface states of the QL and the bands of the SL beneath, and a gapless Dirac-cone band structure on the SL termination with time-reversal symmetry. The quasiparticle interference patterns further confirm the topological nature of the surface states for both terminations, continuing far above the Fermi energy. The QL termination carries a spin-helical Dirac state with hexagonal warping, while at the SL termination, a strongly canted helical state from the surface lies between a pair of Rashba-like splitting bands from its neighboring layer. Our work elucidates an unprecedented hybridization effect between the building blocks of the topological surface states and also reveals the termination-dependent time-reversal symmetry breaking in a magnetic topological insulator.

A combination of electron cooling and rf system is an effective method to compress the beam bunch length in storage rings. A simulation code based on multiparticle tracking was developed to calculate the bunched ion beam cooling process, in which the electron cooling, intrabeam scattering (IBS), ion beam space-charge field, transverse and synchrotron motion are considered. Meanwhile, bunched ion beam cooling experiments have been carried out in the main cooling storage ring (CSRm) of the Heavy Ion Research Facility in Lanzhou, to investigate the minimum bunch length obtained by the cooling method, and study the dependence of the minimum bunch length on beam and machine parameters. The experiments show comparable results to those from simulation. Based on these simulations and experiments, we established an analytical model to describe the limitation of the bunch length of the cooled ion beam. It is observed that the IBS effect is dominant for low intensity beams, and the space-charge effect is much more important for high intensity beams. Moreover, the particles will not be bunched for much higher intensity beam. The experimental results in CSRm show a good agreement with the analytical model in the IBS dominated regime. The simulation work offers us comparable results to those from the analytical model both in IBS dominated and space-charge dominated regimes.

Multiple Co atoms were assembled in the half unit cells (HUCs) of a Si(111)-(7 × 7) surface via vertical atom manipulation at room temperature. Combining scanning tunneling microscopy and first-principles calculations, we have determined the adsorption sites and spin-related properties of six Co atoms assembled in both faulted HUCs (FHUCs) and unfaulted HUCs (UHUCs). These multi-Co atoms do not form metal clusters, which usually have a definite adsorption configuration, because of the strong interaction between Si and Co atoms. Both the adsorption properties and magnetic moments of six Co atoms show strong HUC dependence. The six Co atoms in UHUC retain the adsorption sites of isolated single Co atoms, whereas the Co atoms in FHUC indirectly interact with each other via the mediation of Si atoms, leading to a deviation from the adsorption sites of single Co atoms. Around the suggested U _eff value, the six-Co-atom configuration in UHUC is calculated to have a large magnetic moment of 11.78 μ B, while the six-Co-atom configuration in FHUC only has a magnetic moment of 1.02 μ B because of the anti-ferromagnetic-like coupling between the Co spins.