Large Acceleration Research Articles

Optimization of conveyance of quantum particles by moving potential well

Quantum mechanical control of the position of a particle by using a trapping potential well is an important problem for the manipulation of a quantum particle. We study the probability of successful conveyance of the particle trapped in a potential well for a given length within a given fixed time, i.e., survival probability after the motion. For the actual motion of conveyance, we need to accelerate the particle to move and then decelerate it to stop at the destination. Acceleration and deceleration cause a dropoff of a particle from the trapping potential well. The relaxation of the survival probability in a process with a constant acceleration rate is studied in detail. First, the process is studied as the relaxation of the survival probability of the trapped particle by direct numerical calculations. The survival probability obeys an exponential decay in a long time, which is analyzed from a viewpoint of eigenvalue problem. The value of survival probability is also estimated by the Wentzel-Kramers-Brillouin method with connection formulas using the Airy function and the Weber function. The value is further estimated by a method of the resonance states. We emphasize the fact that an important source of dropoff comes from a nonanalytic change of velocity at the starting point. When the rested particle begins to move, the ground state of the rest frame is redistributed to eigenstates of the moving frame, and then each eigenstate of the moving frame evolves in time. The dephasing of wave functions of the distributed populations reduces the probability of successful conveyance. In general, a smooth start gives a small initial disturbance but it requires a large acceleration during the process to reach the destination in the fixed time which causes a larger dropoff in the process. Considering these conflicting facts, we study the survival probability in concrete conveyance schemes, i.e., protocols with (1) a sudden change of velocity to a constant velocity, (2) a sudden change of acceleration rate to a constant acceleration, and (3) a smooth change of acceleration by studying the real-time change of populations of the adiabatic (instantaneous) eigenstates. We observe the time evolution of the trapped probability and the population distribution during the conveyance process. In cases that the potential well has several bound states, we propose a method to select the particle trapped at the ground state by making use of the difference of survival probabilities of bound states. Published by the American Physical Society 2024

Detecting flying objects in synthetic aperture radar images using Moving Target Indicator methods

AbstractThe growing proliferation of synthetic aperture radar (SAR) sensors brings the tantalising prospect of extending their utility into ‘novel’ applications. One potential extension is the detection of fast moving and accelerating flying objects in SAR imagery. However, since SAR image formation typically assumes the scene to be static over the coherent processing interval, moving objects give rise to blurred point spread functions, significant range migration and even potential aliasing of target signatures. The result is reduced target to clutter ratio (TCR) and poor detection performance. Successful detection of airborne targets thus requires compensation for potentially large target acceleration and velocity values observed over the comparatively long dwell times typical of practical SAR collection paradigms. This paper considers this problem and presents two main ideas to achieve this goal: a carefully constructed Moving Target Indicator (MTI) detection method implemented using real‐world Ingara SAR data, and a theoretical ground clutter suppression method. The MTI detection method combines several well‐known techniques for the flying target detection problem: interferometric processing, clutter suppression, and autofocus, and provides an extended acceleration phase compensation technique for highly accelerating targets such as planes. This proposed processing pipeline has been applied to experimental data of a plane during take off (a challenging Doppler unambiguous moving target), with the goal of continued detecting and tracking of this target. A generalised SAR signal model is presented that parameterises a flying moving target signature in terms of range and azimuthal target velocities and accelerations. Data driven approaches for estimating these motion parameters are examined and applied to experimental data acquired with the Ingara SAR sensor. The detection method was found to improve TCR by around 6 dB, along with superior detection and tracking performance. Following this, a theoretical study into suppressing ground clutter via multi‐channel cross‐track interferometry is investigated. Three separate ground clutter suppression methods, coherent subtraction, conventional beamforming, and minimum variance distortionless response (MVDR) beamformer, are presented then analysed using stochastic simulations. The MVDR adaptive beamformer method was found to provide the best performance for the scenario simulated.

Regioselective Dimerization of Methylcyclopentadiene inside Cucurbit[7]uril.

The molecular confinement within rigid macrocyclic receptors can trigger catalytic activity and steer the selectivity of organic reactions. In this work, the dimerization of methylcyclopentadiene (MCPD) isomers in the presence of cucurbit[7]uril (CB7) was found to display, besides a large rate acceleration, a striking regioselectivity in aqueous solution at pH 3, different from the thermodynamic products predominating in the absence of the supramolecular catalyst. Among the different possible regioisomers and diastereomers, the endo-3,7-dimethyl-3a,4,7,7a-tetrahydro-1H-4,7-methanoindene adduct was selectively formed, which is otherwise found only as a minor product in the dimerization of neat MCPD or in commercial dimeric mixtures. This product originates from the reaction of the heteroternary complex of 1-MCPD and 2-MCPD within CB7, in which the methyl groups are positioned in an "anti-diaxial" arrangement and point towards the open portals of the macrocycle, resulting in a preferred packing of the reacting cyclopentadiene rings. The selectivity of the dimerization of MCPD in the absence and presence of CB7 is supported by quantum-chemical calculations. Insert abstract text here.

Strong Nongravitational Accelerations and the Potential for Misidentification of Near-Earth Objects

Nongravitational accelerations in the absence of observed activity have recently been identified on near-Earth objects (NEOs), opening the question of the prevalence of anisotropic mass loss in the near-Earth environment. Motivated by the necessity of nongravitational accelerations to identify 2010 VL65 and 2021 UA12 as a single object, we investigate the problem of linking separate apparitions in the presence of nongravitational perturbations. We find that nongravitational accelerations on the order of 1 × 10–9 au day−2 can lead to a change in plane-of-sky positions of ∼1 × 103 arcsec between apparitions. Moreover, we inject synthetic tracklets of hypothetical nongravitationally accelerating NEOs into the Minor Planet Center orbit identification algorithms. We find that at large nongravitational accelerations (∣A i ∣ ≥ 1 × 10−8 au day−2) these algorithms fail to link a significant fraction of these tracklets. We further show that if orbits can be determined for both apparitions, the tracklets will be linked regardless of nongravitational accelerations, although they may be linked to multiple objects. In order to aid in the identification and linkage of nongravitationally accelerating objects, we propose and test a new methodology to search for unlinked pairs. When applied to the current census of NEOs, we recover the previously identified case but identify no new linkages. We conclude that current linking algorithms are generally robust to nongravitational accelerations, but objects with large nongravitational accelerations may potentially be missed. While current algorithms are well-positioned for the anticipated increase in the census population from future survey missions, it may be possible to find objects with large nongravitational accelerations hidden in isolated tracklet pairs.

Prediction of huge earthquake-induced deformation of in-service embankments using crushed mudstone as a soil material with slaking and proposal of countermeasures

Evaluating the seismic resistance of embankments using crushed mudstone as a geomaterial is an urgent and crucial requirement. In this study, a ground investigation was conducted on the actual embankment. Based on the results, the seismic response of the embankment, simulating progressed slaking, was conducted by elastoplastic finite deformation analysis using two major types of earthquake motion: epicentral and subduction zone earthquakes. Based on the results of the geotechnical investigation, the embankment could be divided into three layers owing to differences in physical properties, and slaking progressed below the groundwater level in the embankment. The embankment did not exhibit large deformation during the epicentral earthquake owing to the short duration. For the subduction zone earthquake, the developed shear strain was from the two large acceleration groups and the subsequent smaller accelerations, resulting in large deformation. Seismic loading caused the gradual loss of the overconsolidation and decay of the structure which reduced the embankment strength. This analysis revealed that shear strain developed at the slope toe and the lower part of the embankment. Furthermore, the analysis after the earthquake was also conducted to examine whether or not countermeasure method is feasible for emergency restoration. The seismic resistance was greatly improved when a combination of ground improvement and replacement/counterweight fill methods were used to reinforce these areas, which is not only during but also after the earthquake. This study can contribute to the understanding of the seismic behavior of soil structures using materials undergoing internal deterioration and to the development of countermeasure methods for such structures.

Full inverse Compton Scattering: Total transfer of energy and momentum from electrons to photons

In this article we discuss a peculiar regime of Compton Scattering that assures the maximum transfer of energy and momentum from free electrons propagating in vacuum to the scattered photons. We name this regime Full Inverse Compton Scattering (FICS) because it is characterized by the maximum and full energy loss of the electrons in collision with photons: up to 100% of the electron kinetic energy is indeed transferred to the photon. In the case of relativistic electrons, characterized by a large Lorentz factor (γ≫1), FICS regime corresponds to an incident photon energy equal to mec22, i.e. approximately 255.5 keV. We interpret such an astonishing result as FICS being the time reversal of direct Compton Scattering of very energetic photons (of energy much greater than mec2) onto atomic electrons. Although the cross section of Compton scattering is decreasing with the energy of the incident photon, making the process less probable with respect to other reactions (pair production, nuclear reactions, etc.) when high energetic photons are bombarding a target, the kinematics straightforwardly implies that the back-scattered photons would have an energy reaching asymptotically mec22. FICS is instead the unique suitable working point in Compton scattering for achieving the total transfer of (kinetic) energy exactly from the electron to the photon. Experiencing transitions from the initial momentum to zero in the laboratory system, in FICS the electron is also subject to very large negative acceleration; this fact can lead to possible experiments of sensing the Unruh temperature and related photon bath. On the other side of the energy dynamic range, low relativistic electrons can be completely stopped by moderate energy photons (tens of keV), leading to full exchange of temperature between electron clouds and photon baths. Cosmic gamma ray sources can be affected in their evolution by this peculiar FICS regime of Compton scattering.

Flow Evolution and Vertical Accelerations in Wave‐Swash Interactions

AbstractWe report on a laboratory study of wave‐swash interactions, which occur in the very nearshore environment of a beach when the shallow swash flow of a breaking wave interacts with a subsequent wave. Wave‐swash interactions have been observed in the field, hypothesized to be important for nearshore transport processes, and categorized into different qualitative types, but quantitative descriptions of their dynamics have remained elusive. Using consecutive solitary waves with different wave heights and separations, we generate a wide variety of wave‐swash interactions with large flow velocities and vertical accelerations. We find that wave‐swash interactions can be quantitatively characterized in terms of two dimensionless parameters. The first of them corresponds to the wave height ratio for consecutive waves, and the second is a dimensionless measure of the time separation between consecutive wave crests. Using measurements of bed pressure and free‐surface displacement, we estimate the total vertical accelerations and focus on the peak upward‐directed acceleration. We find that wave‐swash interactions can generate vertical accelerations that can easily exceed gravity, despite occurring in very shallow water depths. The large vertical accelerations are upward‐directed and are quickly followed by onshore‐directed horizontal velocities. Together, our findings suggest that wave‐swash interactions are capable of inducing large material suspension events of sediment or solutes in sediment pores, and transporting them onshore. While the data are from a single location making it difficult to generalize the findings across the swash zone, the results clearly demonstrate the importance of large vertical accelerations in wave‐swash interactions.

Self-Healing and Shear-Stiffening Electrodes for Wearable Biopotential Sensing and Gesture Recognition.

The achievement of flexible skin electrodes for dynamic monitoring of biopotential is one of the challenging issues in flexible electronics due to the interference of large acceleration and heavy sweat that influence the stability of skin-electrode interfaces. This work presents materials and techniques to achieve self-healing and shear-stiffening electrodes and an associated flexible system that can be used for multichannel biopotential measurement on the skin. The electrode that is based on a composite of silver (Ag) flakes, Ag nanowires, and polyborosiloxane offers an electrical conductivity of 9.71 × 104 S/m and a rheological characteristic that ensures stable and fully conformal contact with skin and easy removal under different shear rates. The electrode can maintain its conductivity even after being stretched by more than 60% and becomes self-healed after mechanical damage. The combination of the electrodes with a screen-printed multichannel flexible sensor allows stable monitoring of both static and dynamic electromyography signals, leading to the acquisition of high-quality multilead biopotential signals that can be readily extracted to yield gesture recognition results with over 97.42% accuracy. The conductive self-healing materials and flexible sensors may be utilized in various daily biopotential sensing applications, allowing highly stable dynamic measurement to facilitate artificial intelligence-enabled health condition diagnosis and human-computer interface.

Study on the Protective Effect of Viscous Buffering Device under Explosive Load

In recent years, with the complex and changeable international situation, local wars and conflicts abroad have occurred frequently, which seriously threaten the safety of human life and property. Against this background, high-precision and high-intensity strikes against key targets such as enemy command posts and ordnance reserves have become the norm in modern warfare. As the undercard of national security, the security and protection capabilities of underground military facilities are of great importance. Underground structures not only play the role of emergency evacuation of personnel to avoid air and missile attacks, but also the core of the combat command system, where key facilities such as military underground factories and warehouses are located. The security of these facilities has a direct bearing on the outcome of a war and even the fate of a country. In view of this, taking effective measures to improve the explosion resistance, durability and survivability of underground protective structures has become an important research topic in the field of military engineering in various countries. Under the action of the explosion of conventional weapons at a certain distance, the underground protective structures can be damaged due to insufficient resistance. The powerful shock wave generated by the explosion, with its huge kinetic energy and impact force, will cause a large vibration acceleration ring inside the structure, which is very easy to cause casualties and equipment damage within the structure, thus posing a serious threat to the safety of underground engineering. In order to improve the anti-explosion performance of the protective structure under the action of blast impact load, the underground protection engineering structure has been continuously upgraded and optimized, among which the layered protective structure has been widely used because of its relatively excellent protection effect. The layered protective structure realizes a relatively effective protection system through a well-designed camouflage layer, a bullet shielding layer, a dispersed layer and a main structure. However, although significant progress has been made in the optimization of three-layer materials, the defects such as the unstable state of the dispersed layer and the possibility of reducing the overall protection performance with time or external conditions are still an urgent problem to be solved. This system is designed to replace or partially replace the traditional dispersed layer, which is not only designed to effectively absorb and dissipate the blast wave energy transmitted by the bomb shielding layer, but also fundamentally solve the problem of the reduction of protection effect caused by the change of the state of the dispersed layer. In this study, the simulation technology will be used to deeply explore the structural dynamic response of the protective structure after the addition of buffer energy dissipation device under the blast impact load, and the key factors affecting the protection effect will be systematically analyzed, the simulation parameters will be accurately set, and the protection effect under different parameter combinations will be simulated, so as to find an optimal parameter configuration scheme. This study not only helps to deepen the understanding of the anti-explosion performance of underground protection structures, but also provides valuable theoretical basis and practical guidance for the design and construction of underground protection projects in the future.

Verifying Motion Sickness Induction in Automated Vehicles Using Motion-Based Driving Simulators

Motion sickness in passengers of automated vehicles could prevent users from taking advantage of the automation features, as well as lead to unsafe takeover conditions. To conduct motion sickness research, the first step requires motion sickness induction, and its verification. In the current study, twenty-nine participants experienced being a passenger in a fully self-driving vehicle on a motion-based driving simulator. A Control route designed to mimic typical driving conditions on a driving simulator, and a Treatment route that produced large lateral accelerations were tested. The Treatment route was also tested with a non-driving related task (NDRT). Results showed that exposure duration and increased lateral accelerations significantly increased motion sickness. Addition of the cognitively demanding NDRT led to a reduction in motion sickness, suggesting the possibility of a masking effect when engaged in an NDRT in an automated vehicle. Overall, the designed Treatment route was verified to successfully induce motion sickness.

Successful Large Cryogenic Pellets Production and Acceleration for Shattered Pellet Injection for ITER Disruption Mitigation System

Successful Large Cryogenic Pellets Production and Acceleration for Shattered Pellet Injection for ITER Disruption Mitigation System

Attitude estimation for an all-rotating monocopter through attitude decomposition and MARG Sensor fusion

A monocopter is a biology-inspired aircraft based on samara. Due to the constant high spin during flight, attitude estimation is highly challenging. The difficulty of attitude estimation is extracting the effective gravity acceleration information from the large centripetal acceleration interference. Based on the characteristics of monocopters, our study proposes a method to accomplish monocopter attitude estimation through onboard sensor fusion. Our method decomposes the body attitude angles into two-disc attitude angles and three relative attitude angles. Through five steps (a priori body attitude estimation, relative attitude calculation, gravity acceleration information extraction, body attitude estimation through data fusion, and disc attitude estimation), a low-cost attitude determination method relying only on magnetic, angular rate, and gravity sensors is achieved. Finally, the performance of our proposed attitude estimation method is demonstrated through tests on a rotational platform and three degrees of freedom virtual flight testing of a monocopter. The test results show that the attitude estimation method has high precision and the ability for practical applications.

Focal mechanics and disaster characteristics of the 2024 M 7.6 Noto Peninsula Earthquake, Japan

On January 1, 2024, a devastating M 7.6 earthquake struck the Noto Peninsula, Ishikawa Prefecture, Japan, resulting in significant casualties and property damage. Utilizing information from the first six days after the earthquake, this article analyzes the seismic source characteristics, disaster situation, and emergency response of this earthquake. The results show: 1) The earthquake rupture was of the thrust type, with aftershock distribution showing a north-east-oriented belt-like feature of 150 km. 2) Global Navigation Satellite System (GNSS) and Interferometric synthetic aperture radar (InSAR), observations detected significant westward to north-westward co-seismic displacement near the epicenter, with the maximum horizontal displacement reaching 1.2 m and the vertical uplift displacement reaching 4 m. A two-segment fault inversion model fits the observational data well. 3) Near the epicenter, large Peak Ground Velocity (PGV) and Peak Ground Acceleration (PGA) were observed, with the maxima reaching 145 cm/s and 2681 gal, respectively, and the intensity reached the highest level 7 on the Japanese (Japan Meteorological Agency, JMA) intensity standard, which is higher than level 10 of the United States Geological Survey (USGS) Modified Mercalli Intensity (MMI) standard. 4) The observation of the very rare multiple strong pulse-like ground motion (PLGM) waveform poses a topic worthy of research in the field of earthquake engineering. 5) As of January 7, the earthquake had left 128 deaths and 560 injuries in Ishikawa Prefecture, with 1305 buildings completely or partially destroyed, and had triggered a chain of disasters including tsunamis, fires, slope failures, and road damage. Finally, this paper summarizes the emergency rescue, information dissemination, and other disaster response and management measures taken in response to this earthquake. This work provides a reference case for carrying out effective responses, and offers lessons for handling similar events in the future.

Solvent and Temperature Dependencies of the Rates of Thermal Cis-to-Trans Isomerization of Tetra-(ortho)substituted 4-Aminoazobenzenes Containing 2,6-Dimethoxy Groups.

The kinetics of thermal cis-to-trans isomerization of two tetra-(ortho)substituted 4-aminoazobenzene derivatives containing 2,6-dimethoxy groups in the 4-aminobenzene ring and either 2',6'-dimethyl (1) or 2',6'-dichloro groups in another ring was studied in 16 and 9 solvents, respectively, at room temperature. In addition, the kinetics of isomerization of 1 was studied at variable temperatures in 6 solvents. The solvent effects were analyzed in terms of multiparameter correlations using the Kamlet-Taft, Catalan, and Laurence scales. The temperature dependencies were analyzed in terms of the isokinetic relationship by using Exner's method. The correlation analysis was also extended to several previously reported systems, including isomerization of unsubstituted 4-aminoazobenzene and push-pull 4-NR2-4'-NO2 azobenzenes. It was established that for all 4-aminoazobenzenes in contrast to push-pull azobenzenes, the increase in solvent dipolarity does not affect or even inhibit isomerization rates; however, the increase in solvent acidity induces large rate accelerations. The isokinetic relationship holds only in aprotic solvents, while in alcohols and water, the temperature dependencies do not pass through the common point at T = Tiso, indicating different mechanisms operating in protic and aprotic solvents. The acceleration effect by protic solvents does not represent a type of general acid catalysis as follows from the small solvent isotope effect kH/kD = 1.26 in water. It is suggested that protic solvents induce a change in the reaction mechanism supposedly from inversion to rotation by hydrogen bonding stabilization of the negative charge developed on the azo group in a resonance structure involving a 4-amino group.

Cathodoluminescence emission and electron energy loss absorption from a 2D transition metal dichalcogenide in van der Waals heterostructures

Nanoscale variations of optical properties in transition metal dichalcogenide (TMD) monolayers can be explored with cathodoluminescence (CL) and electron energy loss spectroscopy (EELS) using electron microscopes. To increase the CL emission intensity from TMD monolayers, the MoSe2 flakes are encapsulated in hexagonal boron nitride (hBN), creating van der Waals (VdW) heterostructures. Until now, the studies have been exclusively focused on scanning transmission electron microscopy (STEM-CL) or scanning electron microscopy (SEM-CL), separately. Here, we present results, using both techniques on the same sample, thereby exploring a large acceleration voltage range. We correlate the CL measurements with STEM-EELS measurements acquired with different energy dispersions, to access both the low-loss region at ultra-high spectral resolution, and the core-loss region. This provides information about the weight of the various absorption phenomena including the direct TMD absorption, the hBN interband transitions, the hBN bulk plasmon, and the core losses of the atoms present in the heterostructure. The S(T)EM-CL measurements from the TMD monolayer only show emission from the A exciton. Combining the STEM-EELS and S(T)EM-CL measurements, we can reconstruct different decay pathways leading to the A exciton CL emission. The comparison with SEM-CL shows that this is also a good technique for TMD heterostructure characterization, where the reduced demands on sample preparation are appealing. To demonstrate the capabilities of SEM-CL imaging, we also measured on a SiO2/Si substrate, quintessential in the sample preparation of two-dimensional materials, which is electron-opaque and can only be measured in SEM-CL. The CL-emitting defects of SiO2 make this substrate challenging to use, but we demonstrate that this background can be suppressed by using lower electron energy.

Transformer-based modeling of abnormal driving events for freeway crash risk evaluation

A crash risk evaluation model aims to estimate crash occurrence possibility by establishing the relationships between traffic flow status and crash occurrence. Based upon which, Proactive Traffic Safety Management (PTSM) systems have been developed and implemented. The current crash risk evaluation models relied on high dense traffic detectors, which limited the applications of PTSM to infrastructures with enough sensing devices. To address such application limitation issue, this study employed the widespread abnormal driving event information that is generated by emerging driving monitoring and vehicle connection techniques to develop the crash risk evaluation model. Specifically, to characterize abnormal driving events, a six-tuple embedding method was proposed to store their space, time and kinetics features. Given their irregular and discrete distributions on roadways, a Transformer model with self-attention mechanism was proposed to extract the spatial distribution characteristics. In addition, a time-decay function was integrated to fit the temporal impacts of abnormal driving events on crash risk. Empirical data from a freeway in China were utilized for the analyses. The results showed that abnormal driving events with lower speed, larger acceleration and duration are more likely to cause crashes. The accumulation of multiple events in the time period of less than 3 min would lead to a sharp increase of crash risk. Besides, compared to the average metrics of the widely adopted Convolutional Neural Network (CNN), XGBoost, and logistic regression models, the proposed model achieved higher accuracy (0.841) and AUC (0.777), with average improvement of 2.5 % and 9.1 % respectively.

Verification of Astrometrically Accelerating Stars from Hipparcos and Gaia. I. Methodology and Application to HIP 44842

A large number of candidate binary stars with apparent acceleration on the sky has emerged from analysis of astrometric data collected by the Hipparcos, Tycho-2, and Gaia space missions. Although the apparent acceleration can serve as a relatively reliable indicator of binarity, it provides scarce information about the orbital and physical parameters of the components. With an emphasis on the search for stellar-mass black holes and neutron stars hidden in binary systems, we start a broader effort to characterize the most promising candidates using follow-up ground-based observations. Accurate quantification of orbital and physical parameters of systems with dim or invisible companions requires combination of Hipparcos, Gaia, and precision spectroscopic measurements. In this paper, we review the necessary steps in this implementation and describe the improved Hipparcos–Gaia sample of long-term astrometric accelerations, which includes correction of sky-correlated systematic errors using the vector spherical decomposition method. As an example, we study one Hipparcos star with a large acceleration, HIP 44842, where the companion is revealed to be a normal main-sequence star.

Adaptive‐saturation‐based transient stability enhancement for grid‐following inverters

AbstractThis paper proposes an adaptive saturation module to enhance the transient stability of grid‐following inverters after voltage‐dip inception and fault‐clearance moment. The equal‐area criterion reveals that a large acceleration area will be obtained due to the step change of current reference according to grid codes, which may lead to the loss of synchronism with the grid. It is found that the saturation module used with the phase‐locked loop can enhance the transient stability performance by reducing the acceleration area. To simultaneously adapt to the two cases (the inception and clearance of the voltage‐dip fault), an adaptive saturation module that can automatically adjust the clamping mode is proposed, which is the main contribution of the paper. The selection of the threshold value for the saturation module is also presented. A comprehensive comparison is made between the proposed solution and state‐of‐art solutions. Finally, the effectiveness of the proposed control strategy is confirmed by the experimental tests.

Investigation of the effect of loading pulses on the ballast resilient modulus with SmartRock in a large-scale triaxial test

Ballast resilient modulus is a key metric for assessing track resiliency and guiding railroad maintenance. Large-scale triaxial tests are used to determine the ballast resilient modulus and mechanical properties. Replicating complex train-induced loading pulses from field observations in a laboratory setting is challenging owing to technical limitations. Consequently, laboratory tests often employ simplified half-sine and haversine loading pulses with various rest intervals to simulate real-world conditions. However, the effects of different pulses on the obtained ballast resilient modulus remain unclear. In this study, large-scale triaxial tests were conducted using SmartRock sensors to investigate the effects of various cyclic loading pulses on the resilient modulus of the railroad ballast. A new index, called the cyclic loading duration ratio (CLDR), was introduced to categorize these pulses. The results revealed that the resilient modulus correlated with the CLDR, with its impact contingent upon the deviator stress. A CLDR value of 0.20 emerged as a critical threshold, yielding the lowest resilient modulus. Values below this threshold resulted in an increased resilient modulus owing to the consequential large axial acceleration. This study provides insights into the micromechanical resilience reactions of railroad ballast under diverse loading pulses and offers guidance for pulse selection in triaxial testing.

The Influence of Nonlinear High-Intensity Dynamic Processes on the Standing Wave Precession of a Non-Ideal Hemispherical Resonator.

The properties of small size, low noise, high performance and no wear-out have made the hemispherical resonator gyroscope a good choice for high-value space missions. To enhance the precision of the hemispherical resonator gyroscope for use in tasks with large angular velocities and angular accelerations, this paper investigates the standing wave precession of a non-ideal hemispherical resonator under nonlinear high-intensity dynamic conditions. Based on the thin shell theory of elasticity, a dynamic model of a hemispherical resonator is established by using Lagrange's second kind equation. Then, the dynamic model is equivalently transformed into a simple harmonic vibration model of a point mass in two-dimensional space, which is analyzed using a method of averaging that separates the slow variables from the fast variables. The results reveal that taking the nonlinear terms about the square of the angular velocity and the angular acceleration in the dynamic equation into account can weaken the influence of the 4th harmonic component of a mass defect on standing wave drift, and the extent of this weakening effect varies with the dimensions of the mass defects, which is very important for steering the development of the high-precision hemispherical resonator gyroscope.