Three-dimensional Mode Research Articles

Three-dimensional inversion of controlled-source electromagnetic data for surveying the Jiutianshan high-speed railway Tunnel, China

Controlled-source electromagnetic surveying was conducted to identify underground faults and potential water hazards that could affect the construction of the Jiutianshan High-speed Railway Tunnel in the Qinling Mountains, western China. The transmitter length was 978 m, and the receivers were positioned along five profiles that were located about 9.5 km from the transmitter. The observation parameter, the electric-field amplitude |Ex|, was inverted using a finite-memory quasi-Newton method in three-dimensional mode. The resultant model is divided into horizontal blocks and vertical layers. The vertical cross-section along the tunnel shows a pattern of alternating high- and low-resistivity layers. The electrical resistivity pattern is divided into two vertical layers, with a clear boundary between the high- and low-resistivity zones. Combined with the results from previous exploration, geological survey, and drilling data, the inversion results identify the strata and faults along the planned route, and four risk areas are delineated. Our results highlight the power of employing geophysical investigations for risk assessments along tunnels.

Design and Construction of a Snake-Like Robot Implementing Rectilinear and Sidewinding Gait Motions

Bio-inspired robots offer locomotion versatility in a wide variety of terrains that conventional robots cannot access. One such bio-inspired platform is snake-like robots, which are mechanisms designed to move like biological snakes. The aim of this paper was to implement and validate, through comparison in real and simulation tests on flat terrain, the design of a snake robot that allows movements in two perpendicular planes, by the application of three-dimensional locomotion modes. The prototype robot had a modular and sequential architecture composed of eight 3D printed segments. The necessary torques for each motor are found by means of a simulation in Matlab – Simulink and the SimScape tool. The Webots mobile robotics simulator was used to create a parameterized virtual model of the robot, where two types of gaits were programmed: sidewinding and rectilinear. Results showed that the robot undertakes lower than 1 second in execution time to reach the total distance in each of the proposed marches when comparted to the simulation. In addition, mean differences of 6 cm for the distances during the sidewinding mode experiment and 1.2 cm in the deviation in the rectilinear mode on flat terrain were obtained. In conclusion, there is a great similarity between the simulation tests and those performed with the actual robot, and it was also possible to verify that the behavior of the prototype robot is satisfactory over short distances.

Multiple Constraints-Based Adaptive Three-Dimensional Back-Stepping Sliding Mode Guidance Law against a Maneuvering Target

This paper addresses the issue of a complex three-dimension (3-D) terminal guidance process that is used against maneuvering targets while considering both the terminal impact angle (TIA) and field-of-view (FOV) angle constraints. According to the highly coupled and nonlinear 3-D terminal guidance model, an adaptive back-stepping sliding-mode guidance law algorithm is proposed in order to guarantee the stability and robustness of the guidance system. Considering the explicit expression of the line-of-sight (LOS) angle in the kinematics and dynamics of the terminal guidance process, the TIA constraint is transformed into an LOS constraint based on their well-known relationship. In view of the challenges in obtaining the motion information of maneuvering targets, an adaptive law design is introduced in order to estimate and compensate for external disturbances caused by the maneuvering of the target and modeling uncertainty. In addition, because the FOV angle represented by the overall leading angle is not a state variable in the sliding-mode guidance system, it is decoupled into two partial leading angles based on a specific transformation relation, so the 3-D terminal guidance control problem is converted into separate tracking system control issues in the pitch and yaw planes. Then, the Lyapunov stability theory is utilized to substantiate the stability of the guidance system, where the Lyapunov functions in both of the subsystems consist of the LOS and partial FOV state error terms. Finally, a series of simulations of various motion states of maneuvering targets under different terminal cases were carried out. It was proved that the terminal guidance design based on the strategies presented above was able to obtain the desired LOS constraints with satisfying the FOV limitation, and the simulation results verified the effectiveness, universality, and significance for practical applications of the proposed guidance design method.

Research and application of forward three-dimensional design method of substation

During the operation of digital substations, they are vulnerable to the influence of different fault feature extraction, resulting in weak anti-interference in the detection process. To solve this problem, the singular value decomposition method is combined detection method to establish a prediction model. Firstly, the three-dimensional control mode model is established based on mathematical method to process the current signal with anti-interference; Secondly, the singular value method is used to optimize the current transmission process and denoise the fault signal feature extraction; Finally, the method of singular value decomposition is used to realize fault detection in substation operation.

Role of nitrogen source flow on the growth of 2D GaN crystals

As a class of non-layered compounds, ultrathin III-V semiconductors possess excellent physical and chemical properties, are promising candidates for optoelectronic and thermoelectric applications. Due to the strong chemical bonds both in plane and out of plane, the controllable growth of two-dimensional (2D) III-V semiconductors is quite challenging. In this study, we report the successful synthesis of 2D GaN crystals by chemical vapor deposition (CVD) on liquid Ga. The nitrogen source flow is found to be a key factor that governs the transformation of GaN growth from 2D layered mode to three-dimensional (3D) island mode. This study provides further understanding on the growth of non-layered 2D III-nitride materials.

Sympathetic electromagnetically induced transparency ground state cooling of a 40Ca+–27Al+ pair in an 27Al+ clock

We report on electromagnetically induced transparency cooling of 40Ca+ to sympathetically cool the three-dimensional secular modes of motion in a 40Ca+–27Al+ two-ion pair near the ground state. We observe simultaneous ground state cooling across all radial modes and axial modes of a 40Ca+–27Al+ ion pair, occupying a broader cooling range in frequency space over 3 MHz. The cooling time is observed to be less than 1 ms. The mean phonon number and heating rates of all motional modes are measured. This study is not only an important step for reducing the secular motion time-dilation shift uncertainty and uptime ratio of 27Al+ optical clock, but also essential for high-fidelity quantum simulations and quantum information processors using trapped ions.

Research on the Teaching Reform Path of Innovation and Entrepreneurship Education Courses in Local Undergraduate Universities

Taking the teaching reform of local undergraduate institutions as an example, this paper combines the cultivation of innovation and entrepreneurship with professional education, and proposes a three-dimensional practical teaching mode according to the idea of "combining theory and practice, systemic and phased". It is designed from classroom innovation and entrepreneurship theory education, practical case discussion, innovation and entrepreneurship project design, innovation and entrepreneurship competition and other dimensions, and built from three modules, such as target system, knowledge system and practice system, which can well solve the problem of innovation and entrepreneurship of college students.

A novel mode-division (de)multiplexer with degenerate modes output for MIMO-FREE applications

In this study, we propose a novel three-dimensional architecture mode (de)multiplexer with degenerate modes output using a pure silica FMF ring core transmission channel, which solves the problem caused by random mode rotation and can be used in multiple-input multiple-output free (MIMO-FREE) applications such as data center application in the future. By using the pure silica FMF ring core transmission channel and larger effective refractive index difference, the performance with low loss, high extinction ratio (ER) and low crosstalk is achieved. The main channel with a few-mode fiber (FMF) ring-core structure supports the modes LP01, LP11, and LP21, and the large effective refractive index difference between each mode in the core ensures low crosstalk characteristics between the modes. Using the pure silica core channel can effectively reduce propagation attenuation and fusion loss. Our proposed MUX/DEMUX with degenerate modes output is achieved when the degenerate modes LP11a/LP11b and LP21a/LP21b are transmitted as two independent mode signals, which can be used in MIMO-FREE applications. The extinction ratios (ERs) of the degenerate modes LP11 and LP21 are kept above 31.66 dB and 24.43 dB, respectively, and the ER of mode LP01 is kept above 38.72 dB in the C band. The coupling efficiency of mode LP01 is approximately 0 dB, which is almost unchanged with the increase of the wavelength. The coupling efficiency of LP11 is higher than −3.49 dB and that of LP21 is higher than −7.24 dB in the whole C-band. At 1550 nm, the coupling efficiencies of modes LP01, LP11, and LP21 are −0.002 dB, −0.052 dB, and −0.178 dB, respectively. The coupling efficiency and ER of LP01 mode are the best, and those of the degenerate mode LP11 are always better than those of mode LP21. Our proposed MUX/DEMUX achieves low crosstalk and high ER performance and solves the problem caused by the degenerate modes rotations during transmission.

Velocity-Based Gait Planning for Underactuated Bipedal Robot on Uneven and Compliant Terrain

This article develops a gait planning method for underactuated bipedal robot on uneven and compliant terrain. First, we employ a linear spring-damper model to describe foot-ground compliant contact, and establish a decoupled robot–ground three-dimensional dynamic mode. Second, based on a velocity-based bipedal stability definition and human walking characteristics, we propose a gait planning method to realize underactuated bipedal walking on uneven and compliant terrain. We decouple bipedal gait planning into sagittal and lateral master-slave ones. By planning the motion state of Center-of-Mass (CoM) of a robot, we make the movement of lateral and sagittal coincident such that bipedal walking is realized. Finally, underactuated bipedal walking with an average walking speed of 0.216 m/s and a step length of 183.9 mm is realized on uneven terrain where the maximum height of unevenness is 32 mm. The experimental results show that underactuated bipedal walking can be realized on uneven and compliant terrain by using the proposed method to control robot CoM and track its desired velocity.

Role of polarization-photon coupling in ultrafast terahertz excitation of ferroelectrics

We investigate the role of polarization-photon coupling (specifically, the polarization-oscillation-induced radiation electric field) in the excitation of ferroelectric thin films by an ultrafast terahertz electric field pulse. Analytical formulas are developed to predict how the frequencies and relaxation time of three-dimensional soft mode phonons (intrinsic polarization oscillation) are modulated by the radiation electric field and epitaxial strain. Ultrafast terahertz-pulse-driven excitation of harmonic polarization oscillation in strained single-domain ferroelectric thin film is then simulated using a dynamical phase-field model that considers the coupled strain-polarization-photon dynamics. The frequencies and relaxation time extracted from such numerical simulations agree well with analytical predictions. In relatively thin films, it is predicted that the radiation electric field slightly reduces the frequencies but significantly shortens the relaxation time. These results demonstrate the necessity of considering polarization-photon coupling in understanding and predicting the response of ferroelectric materials to ultrafast pulses of terahertz and higher frequencies.

Experimental investigation of three-dimensional modes in the wake of a rotationally oscillating cylinder

Three-dimensionalities in the wake of flow past a circular cylinder executing sinusoidal rotary oscillations about its axis is studied experimentally. The results of water tunnel experiments on a rotationally oscillating cylinder for Reynolds number of 250 with varying amplitude and forcing frequency are discussed. Qualitative studies using hydrogen bubble and laser-induced fluorescence flow visualisation techniques are performed. Observation made for oscillating amplitude, $\theta _{0} = {\rm \pi}/4$ and $\theta _{0}=3{\rm \pi} /4$ , and a low normalised forcing frequency, $FR$ , of 0.75 and 0.5, respectively, confirmed a mode having a spanwise non-dimensional wavelength of $\sim$ 1.8 which is also observed for a rotating cylinder. On increasing forcing frequency this mode disappears and a new mode with a bean-shaped structure and a much smaller spanwise normalised wavelength of $\sim$ 0.8 appears at an $FR$ of 1 and an oscillation amplitude of ${\rm \pi} /2$ . This mode remains almost stable until a forcing frequency of $FR=1.4$ . At higher forcing frequency, $FR=2.75$ , and oscillation amplitude of $3{\rm \pi} /4$ , a mode with cellular structure and a normalised spanwise wavelength of $\sim$ 1.6 is identified. The cells in this mode flatten up with increasing downstream distance and are shed alternately with respect to the adjacent cell. Certain combinations of forcing parameters resulted in a forced two-dimensionality of the wake. Quantitative studies using hot-wire measurements and particle image velocimetry confirm the presence of these modes and wake characteristics. Wake mode map in the forcing frequency and amplitude plane is presented showing regions of newly discovered modes and wake lock-on boundaries.

Application of Multimedia Human-Computer Interaction Technology in Preschool Children Drama Education

With the continuous development of multimedia technology and children’s drama education as a very important part of preschool education, the combination of the two has attracted the attention of many scholars at home and abroad. Drama education for preschool children is the initial stage of children’s learning and the most important part of preschool education system. At the same time, preschool children drama education is the most basic stage of children’s intellectual development. The correct and reasonable preschool children drama education plays a great role in promoting their intelligence and development. The drama education for preschool children based on multimedia human-computer interaction technology not only expands new teaching methods for the traditional drama education model but also provides a good platform for teachers to choose teaching resources and injects new vitality into preschool children’s music education. This paper proposes the application of multimedia human-computer interaction technology in preschool children’s drama education. We analyze the current preschool children’s drama education curriculum reform that has limitations. The level of teachers’ drama education needs to be improved. Young children lack awareness of drama. Drama education for children lacks strong support from parents and other problems. In order to solve the above problems, we focus on voice interaction technology, image interaction technology, and somatosensory interaction technology in multimedia human-computer interaction technology, which establishes a set of teacher-multimedia-student three-dimensional crossover multidirection learning activity modes. In the multidirection learning mode, students can quickly develop their sense of rhythm. Teachers use image interaction technology to guide students to think about the relationship between content and form, so as to gradually form their own unique style of drama. At the same time, somatosensory interaction technology can cultivate teaching tasks seamlessly connected with the environment, so that students can follow the hologram through hands-on practice. Finally, this paper sets up a questionnaire on the experience of human-computer interaction mode in preschool children’s drama education, mainly to conduct a questionnaire survey on front-line drama teachers, aiming at preschool children’s drama learning activities and teachers’ teaching methods. In numerical experiments, we show teachers’ evaluation of the teaching effect of speech synthesis technology integrated into preschool children’s drama education and the classroom effect evaluation of speech synthesis technology integrated into preschool children’s drama education. The evaluation results show that the application effect of multimedia human-computer interaction technology in preschool children’s drama education is good, which can provide better services for preschool children’s drama education.

Three-Dimensional Analytical Solutions for Acoustic Transverse Modes in a Cylindrical Duct with Axial Temperature Gradient and Non-Zero Mach Number

Cylindrical ducts with axial mean temperature gradient and mean flows are typical elements in rocket engines, can combustors, and afterburners. Accurate analytical solutions for the acoustic waves of the longitudinal and transverse modes within these ducts can significantly improve the performance of low order acoustic network models for analyses of acoustic behaviours and combustion instabilities in these kinds of ducts. Here, we derive an acoustic wave equation as a function of pressure perturbation based on the linearised Euler equations (LEEs), and the modified WKB approximation method is applied to derive analytical solutions based on very few assumptions. The eigenvalue system is built based on the proposed solutions and applied to predict the resonant frequencies and growth rate for transverse modes. Validations of the proposed solutions are performed by comparing them to the numerical results directly calculated from the LEEs. Good agreements are found between analytical reconstruction and numerical results of three-dimensional transverse modes. The system with both mean temperature profile and mean flow presents a larger absolute value of the growth rate than the condition of either uniform mean temperature or no mean flow.

Unsteady mechanisms in shock wave and boundary layer interactions over a forward-facing step

The flow over a forward-facing step (FFS) at $Ma_\infty =1.7$ and $Re_{\delta _0}=1.3718\times 10^{4}$ is investigated by well-resolved large-eddy simulation. To investigate effects of upstream flow structures and turbulence on the low-frequency dynamics of the shock wave/boundary layer interaction (SWBLI), two cases are considered: one with a laminar inflow and one with a turbulent inflow. The laminar inflow case shows signs of a rapid transition to turbulence upstream of the step, as inferred from the streamwise variation of $\langle C_f \rangle$ and the evolution of the coherent vortical structures. Nevertheless, the separation length is more than twice as large for the laminar inflow case, and the coalescence of compression waves into a separation shock is observed only for the fully turbulent inflow case. The dynamics at low and medium frequencies is characterized by a spectral analysis, where the lower frequency range is related to the unsteady separation region, and the intermediate one is associated with the shedding of shear layer vortices. For the turbulent inflow case, we furthermore use a three-dimensional dynamic mode decomposition to analyse the individual contributions of selected modes to the unsteadiness of the SWBLI. The separation shock and Görtler-like vortices, which are induced by the centrifugal forces in the separation region, are strongly correlated with the low-frequency unsteadiness in the current FFS case. Similarly as observed previously for the backward-facing steps, we observe a slightly higher non-dimensional frequency (based on the separation length) of the low-frequency mode than for SWBLI in flat plate and ramp configurations.

Towards the Growth of Hexagonal Boron Nitride on Ge(001)/Si Substrates by Chemical Vapor Deposition.

The growth of hexagonal boron nitride (hBN) on epitaxial Ge(001)/Si substrates via high-vacuum chemical vapor deposition from borazine is investigated for the first time in a systematic manner. The influences of the process pressure and growth temperature in the range of 10−7–10−3 mbar and 900–980 °C, respectively, are evaluated with respect to morphology, growth rate, and crystalline quality of the hBN films. At 900 °C, nanocrystalline hBN films with a lateral crystallite size of ~2–3 nm are obtained and confirmed by high-resolution transmission electron microscopy images. X-ray photoelectron spectroscopy confirms an atomic N:B ratio of 1 ± 0.1. A three-dimensional growth mode is observed by atomic force microscopy. Increasing the process pressure in the reactor mainly affects the growth rate, with only slight effects on crystalline quality and none on the principle growth mode. Growth of hBN at 980 °C increases the average crystallite size and leads to the formation of 3–10 well-oriented, vertically stacked layers of hBN on the Ge surface. Exploratory ab initio density functional theory simulations indicate that hBN edges are saturated by hydrogen, and it is proposed that partial de-saturation by H radicals produced on hot parts of the set-up is responsible for the growth.

Mode vortex and turbulence in ventilated cavitation over hydrofoils

In this paper, the complex interaction of gas-vortex-turbulence in ventilated cavitation over a NACA0015 hydrofoil is investigated by using large eddy simulation. The proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) are used for analyzing the three-dimensional fluctuation modes of gas-liquid interfaces induced by turbulent coherent structures in ventilated cavitation. The results show that among the first four dominant POD modes possessing 99.5% modal kinetic energy in the ventilated cavitating flow, and the turbulent POD mode 2 contains the multi-scale coherent structures and acts as a bridge for the energy scale transition from mode 1 to mode 3 through the gas-liquid interface oscillations. The DMD modal structures are reconstructed from the roller-shaped energetic structure captured by POD mode 2, which further reveal the process of breaking down near the hydrofoil leading edge, changing into the hairpin shape and finally stretching into the horseshoe shape above the hydrofoil trailing edge for the turbulent coherent structures on the cavity interfaces. Such low-frequency wake structures are energetic but sustained by means of the high-frequency turbulent fluctuations, with the interfacial oscillation amplitude changed through the formation and transition of the multi-scale coherent structures. Further, the modal turbulent kinetic energy transport theory is introduced to describe the ventilated coherent structures. It is worth noting that the large-scale energetic structures in POD mode 2 are mainly drawing energy from mean flows through the Reynolds stress, and the modal turbulent energy stored by shedding vortex and air cavities in the ventilated wake flow is redistributed and balanced due to the turbulent and pressure diffusion effects. Besides, the uneven spatial distribution of turbulent energy caused by the vortex structures of different modal scales is proved to promote the spatial oscillation level of the ventilated cavity interfaces. This study is helpful to understand the interaction mechanism between turbulence and gas-liquid interfacial fluctuations for the ventilated wake flow.

Three-dimensional quantum droplets in spin-orbit-coupled Bose-Einstein condensates

Quantum droplets (QDs) are a recently discovered new state of matter in ultracold atoms. We study three-dimensional (3D) self-trapped modes in spinor Bose-Einstein condensates with spin-orbit coupling (SOC), described by coupled Gross-Pitaevskii equations including beyond-mean-field Lee-Huang-Yang terms. The 3D QDs, semi-vortex and mixed-mode states, of a large size with an anisotropic density profile, exist with a wide large values of the norm as the Lee-Huang-Yang terms eliminate the collapse. The effect of the intra- and inter-component of the nonlinearity and SOC on characteristics of the QDs is systematically addressed. Using the linear-stability analysis and direct simulations, we have checked the stability of all the 3D QDs states, stressing they are stable against small perturbations in propagation in limited scales. The present analysis opens a new way for creating multidimensional solitary waves, and may be developed in other directions, including nonlinear optics, not only in conservative, but also in dissipative systems.

Effects of Cooling Rate on the Solidification Process of Pure Metal Al: Molecular Dynamics Simulations Based on the MFPT Method

Isothermal solidification process of pure metal Al was studied by molecular dynamics (MD) simulation using EAM potential. The effects of different cooling rates on the isothermal solidification process of metallic Al were studied. Al was first subjected to a rapid cooling process, and then it was annealing under isothermal conditions. The mean first-passage times (MFPT) method and Johnson-Mehl-Avrami (JMA) law were used to qualify the solidification kinetic processing, and the nucleation rate, critical nucleus size, Avrami exponent and growth exponent of grains were calculated. Results show that the nucleation rate and critical size decrease as the cooling rate increases. Also, an increase in the cooling rate leads to the increase of grain growth rate. At all investigated cooling rates, nucleation and growth processes are in the typical three-dimensional growth mode.

Electrochemical Study of the Electrodeposition of a Dense Nanocrystalline Fe Film from Fe(II) Ions Dissolved in an Ionic Liquid

The electrodeposition behavior of Fe was studied in phenyltrimethylammonium chloride-ethylene glycol eutectic-based ionic liquids (TMPAC-EG EILs) containing FeCl2 through electrochemical measurement and the deposit characterization. Some kinetic parameters (standard rate constants, transfer coefficients and activation energy for standard rate constants) as well as transport properties were obtained and discussed as function of temperature. The values of transfer coefficient (0.32–0.39) are significantly lower than conventional value (0.5). Electrodeposition of Fe follows three-dimensional progressive nucleation and growth mode, which is unaffected by temperature. Besides, it is found that deposition temperature plays a central role in controlling surface morphology and structure of the resultant Fe coatings. At low temperature (333–353 K), smooth and dense iron coating can be obtained. The phase structure changes from a nanocrystalline α-Fe to amorphous phase (metallic glass) as the deposition temperature increases from 333 K to 353 K.

Electromagnetic Penetration and Reflection Analysis in Fractal Structures Using Three-Dimensional Empirical Mode Decomposition

In this study, fuzz structures in tungsten surfaces are artificially generated using the midpoint displacement algorithm (MDA) based on the random fractal. The finite-difference time-domain (FDTD) method is employed to simulate electromagnetic wave propagation in the fuzz structures with different fractal dimension sizes. To analyze electromagnetic penetrations and reflections around the fuzz structures, we adopt the three-dimensional empirical mode decomposition (TEMD) to decompose simulation results by FDTD in the spatial frequency domain. The computation results showed that the distribution of electric field intensity is decomposed into 3-D intrinsic mode functions (IMFs), indicating resonances triggered by electromagnetic waves hitting the fuzz structures in the tungsten surface from high spatial frequency to low spatial frequency. These decomposed IMFs revealed the optical properties of fuzz structures regarding the relationship between fractal dimension sizes and the electromagnetic penetrations and reflections in the tungsten surface.