Acceleration Stage Research Articles

Quasi-in-situ characterization of microstructure evolution in friction stir welding of aluminum alloy

The in-situ investigation of microstructure evolution during friction stir welding (FSW) can provide very important theoretical guidance to control the microstructure and mechanical properties of the FSW joint. In this study, a quasi-in-situ investigation method of the microstructure evolution in friction stir welding of AA1050 aluminum alloy was developed. The microstructure along the material flow path was characterized and analyzed by taking the strain, strain rate, and temperature into account simultaneously. The results show that the microstructure evolution during the FSW of aluminum alloy can be divided into four stages according to the material flow state and thermal history. Firstly, grain coarsening by static recovery and static recrystallization occurs at the static preparatory stage (or called the preheating stage). Secondly, grain refining by continuous dynamic recrystallization occurs at the acceleration stage, where the temperature gradually increases to nearly a constant. The grain size is mainly controlled by the accumulative total strain. The strain rate only affects the rate of dislocation generation and the type of β-fiber simple shear texture components. Thirdly, at the high-velocity flow stage, a dynamic equilibrium between plastic deformation and dynamic recrystallization is maintained, and the grain size only fluctuates within a small range. Finally, a second grain-coarsening process occurs through normal grain growth due to thermal activation at the deceleration stage. This process is inevitable because it occurs under the cover of the tool shoulder. The grain coarsening during the normal cooling stage was avoided in this study due to the rapid cooling used, which has been widely reported by published documents.

Analysis of the aerodynamic characteristics of the entire operation process of an ultra-high-speed elevator under the influence of high blockage ratio, hoistway, and car height parameters

Ultra-high-speed elevators are affected by various factors during operation, resulting in complex airflow disturbances and significant piston effects. To explore the aerodynamic characteristics and ventilation effects of the car at different stages of operation under multiple parameters, this paper first establishes a multi-parameter numerical model for the elevator system and verifies the numerical model through elevator experiments, and then analyzed the general variation characteristics of the pneumatic load during the car's acceleration, constant speed, and deceleration phases. On this basis, the influence of blockage ratio, hoistway and car height, and operating acceleration on multiple types of aerodynamic loads and hoistway ventilation was studied, with a special analysis of the viscous drag and pressure drag of the car. The results show that increasing the blockage ratio significantly increases the ventilation of the hoistway, with an increase in 1 and 0.7 factors in the acceleration and constant velocity stages, respectively. In the deceleration stage, the drag changes the most, with an increase in 3.1 factors, which hinders the ventilation of the hoistway. Meanwhile, the average lateral lift increased by 0.6 factors and the fluctuation increased, exacerbating the lateral vibration of the car. Viscous drag and pressure drag exhibit similar trends at each stage, but pressure drag is much higher than viscous drag. The height of the hoistway has a significant impact on the total drag of the car by increasing the pressure drag. In contrast, car height has the most significant effect on lateral lift and viscous drag.

Durability and damage model of polyacrylonitrile fiber reinforced concrete under freeze–thaw and erosion

In an alpine saline soil area, the combined effect of freeze–thaw and erosion ions causes the imbalance of concrete durability. In studying the macro–meso deterioration law and failure mechanism of polyacrylonitrile fiber-reinforced concrete (PANFC) under this action, PANFC specimens formed by open-air curing were prepared, and a composite salt solution containing 5% MgSO4, 5% Na2SO4, and 3.5% NaCl was used as the freeze–thaw medium for salt-freezing test. Results demonstrate that the degradation of PANFC under salt-frost conditions can be divided into the micro-damage stage and damage acceleration stage, with 50 cycles as the limit. When the content of PAN fiber is 1.5–1.8 kg/m3, the salt frost resistance of concrete is advantageous. The macro-scale results show that the relative dynamic elastic modulus and ultrasonic wave velocity of PANFC decrease with the increase of salt-freezing cycles, whereas the weight of PANFC increases before 25 salt-freezing cycles. The meso-scale results show that after 50 cycles, the evolution of micro-pores to macro-pores and micro-cracks in PANFC is accelerated. The pore size ratio of micro-pores (0–0.1 μm) decreases with the increase of cycles, and the pore size ratio of micro-cracks (greater than10 μm) increases with the increase of cycles. Failure mechanism analysis shows that the failure of PANFC results from the combined effect of surface damage and internal damage. Finally, the salt-frost damage model of PANFC was established on the basis of the damage mechanics and classical Aas-Jakobsen fatigue theory, and the damage determination value Dn was between 0.2527 and 0.2781. Using Dn, the failure criteria of concrete damaged under salt-frost conditions can be re-evaluated.

Contrasting the major characteristics of pinewood and Amazon hardwoods to provide high-quality cement-bonded particleboards

The combined effect of wood chemical composition, anatomical traits, and density on cement curing, matrix-reinforcement interface, and final performance of cement-bonded particleboards (CBPBs) needs deeper investigation. Besides, many uncharacterized Amazon hardwoods challenge softwoods' often-reported superiority for producing CBPBs. Certified Cordia goeldiana, Brosimum parinarioides, Parkia gigantocarpa, and Pinus oocarpa woods were characterized by histology, cell biometry, basic density, and chemical composition. The hydration kinetics of the Portland cement pastes was evaluated by isothermal heat conduction. The CBPBs production parameters were wood:cement ratio of 1:2.75, water:cement ratio of 1:2.5, 4% of CaCl2 additive (based on cement mass), and target density of 1.25 g cm−3. They were submitted to physical and mechanical tests, and the polished surfaces were analyzed by scanning electron microscopy. The cement kinetics showed that wood's higher contents of extractives and hemicelluloses harmed the initial dissolution stage of Portland cement curing but not the essential stages of acceleration and deacceleration. C. goeldiana wood showed the highest compatibility indexes with cement, and all hardwoods surpassed P. oocarpa. Thin-walled fibers, big-diameter fibers, and big-diameter pores favored cement impregnation. Debonding at wood-cement interfaces of CBPBs reinforced with higher-density woods was critical for crack propagation throughout the matrix. Less critical inter-particle cracks occurred in CBPBs reinforced with lower-density woods. The better interface and the highest volume of wood particles of the lowest-density P. gigantocarpa wood provided the CBPBs with the best physical and mechanical performance overcoming the chemical incompatibility relevant only in the initial dissolution stage of cement curing.

Recommendations for Effective Co-Management Model of Small-Scale Grouper (Serranidae) Fishery in South Sulawesi Province

Governance (policy) that regulates fisheries resources needs to involve industry in the supply chain (market) and small-scale grouper fishermen (community) within a co-management framework so that management is more effective while simultaneously supporting the Fisheries Improvement Project (FIP) which is driven by various parties globally (Conservation Alliance, 2021). This study aims to recommend a small-scale grouper fishery co-management model to be carried out in South Sulawesi Province. This study diagnoses the readiness (enabling condition) and willingness (motivation) of stakeholders so that they can be applied and implemented consistently (implementation). The results of this study indicate that the main approaches and strategies for the co-management model of small-scale grouper fisheries include (a) Optimizing the role of the market that promotes traceability and improving governance through a supply chain approach, (b) Synergy and synchronization of the role of government at all levels through an approach technocratic, (c) Strengthening fishermen and local institutions through a participatory approach, (d) Gathering multi-stakeholder support and collaboration through a collaborative approach. The recommended roadmap for small-scale grouper co-management in South Sulawesi Province includes three main stages, namely: (a) Initiation Stage: Commitment, Support, and Organizing, (b) Acceleration Stage: Joint Committee and Co-management Prototype, and (c) Stage Institutionalization: Scaling up and Organizing Fishermen's Forums.

Vessel Energy Requirement Prediction from Acceleration Stage Towing Tests on Scale Models

Abstract One of the most crucial tasks for naval architects is computing the energy required to meet the ship’s operational needs. When predicting a ship’s energy requirements, a series of hull resistance tests on a scale model vessel is carried out in constant speed stages, while the acceleration stage measurements are ignored. Another important factor in seakeeping analysis is the ship’s hydrodynamic added mass. The second law of dynamics states that all this valuable information, that is, the dependence of the hull resistance on the vessel’s speed and the added mass, is accessible from just one acceleration stage towing test done up to the maximum speed. Therefore, the acceleration stage, often overlooked in traditional towing experiments, can be a valuable source of information. For this reason, this work aims to generalise Froude’s scaling procedure to full-scale vessels for the accelerated stage towing tests.

Study on the three-stage method to calculation scattering parameters of prefabricated fragments along the axis based on energy conservation

To study the axial distribution rules of the initial velocity and direction angle of prefabricated fragments, first, the acceleration process of prefabricated fragments is divided into three stages:"detonation wave acceleration stage”,"metal medium interaction stage” and “detonation product acceleration stage”, to establish the three-stage detonation drive model based on energy conservation, the correction coefficients in the model were subsequently fitted using numerical simulations, finally, the test results are compared with the theoretical calculations of the model. The comparison results indicate: the axial distribution results of the prefabricated fragments initial velocity calculated by the three-stage detonation drive model fit well with the experimental results, and the error is within 100 m/s, and the axial distribution rules of the initial velocity showed a trend of the first increasing and then decreasing, the maximum value of the velocity all appeared at the ratio of the prefabricated fragment distance from the burst core to loading length was 0.7; the three-stage detonation drive model fit the results of axial distribution of the direction angle of prefabricated fragments accurately.

Experimental study on heat transfer and propagation speed of spill fire on porous media substrate with micro-inclination

During the transportation and usage of liquid fuel, leakage from container rupture can cause spill fires. When a spill fire occurs on porous media, the heat transfer mode will change. An experiment with the spill was carried out using a 15 × 150 cm porous media substrate to analyze the spill fire. The results showed that the propagation speed is inversely proportional to the square of the length of the transition zone in the uniform stage. Under horizontal conditions, the model calculation results had an error within 15% of the experimental values. When the substrate has an inclination angle, the speed model has a large error compared to the experimental results due to the influence of gravity. Additionally, the burning rate of spill fire was studied based on heat transfer analysis and experimental measurement. The burning rate of spill fire on porous media substrates was found to be significantly lower than that of a pool fire. In the acceleration and uniform stage, the burning rate increases with the increase in combustion equivalent diameter. In the deceleration stage, the burning rate decreases with the increase in equivalent diameter. The theoretical value of burning rate was consistent with the experimental value in the uniform stage.

Study on Axial Dispersion Characteristics of Double-Layer Prefabricated Fragments.

The axial distribution of initial velocity and direction angle of double-layer prefabricated fragments after an explosion were investigated via an explosion detonation test. A three-stage detonation driving model of double-layer prefabricated fragments was proposed. In the three-stage driving model, the acceleration process of double-layer prefabricated fragments is divided into three stages: "detonation wave acceleration stage", "metal-medium interaction stage" and "detonation products acceleration stage". The initial parameters of each layer of prefabricated fragments calculated by the three-stage detonation driving model of double-layer prefabricated fragments fit well with the test results. It was shown that the energy utilization rate of detonation products acting on the inner-layer and outer-layer fragments were 69% and 56%, respectively. The deceleration effect of sparse waves on the outer layer of fragments was weaker than that on the inner layer. The maximum initial velocity of fragments was located near the center of the warhead where the sparse waves intersected, located at around 0.66 times of the full length of warhead. This model can provide theoretical support and a design scheme for the initial parameter design of double-layer prefabricated fragment warheads.

Interferometric Mass Spectrometry.

Accelerator mass spectrometry (AMS) is a widely used technique with multiple applications, including geology, molecular biology, and archeology. In order to achieve a high dynamic range, AMS requires tandem accelerators and large magnets, which thus confines it to big laboratories. Here we propose interferometric mass spectrometry (Interf-MS), a novel method of mass separation which uses quantum interference. Interf-MS employs the wave-like properties of the samples and as such is complementary to AMS, in which samples are particle-like. This complementarity has two significant consequences: (i) in Interf-MS separation is performed according to the absolute mass m, and not to the mass-to-charge ratio m/q, as in AMS; (ii) in Interf-MS the samples are in the low-velocity regime, in contrast to the high-velocity regime used in AMS. Potential applications of Interf-MS are compact devices for mobile applications, sensitive molecules that break at the acceleration stage and neutral samples which are difficult to ionize.

Effect of geogrid on dry-shrinkage cracking of loess

In this paper, an experimental approach is employed to investigate the reinforcing impact of geogrids on the dry-shrinkage cracking of loess. At various evaporation temperatures and for varying specimen thicknesses, the evolution of the surface fissures induced in the loess samples with and without geogrids was monitored and analyzed. According to the findings, the evaporation rate of the samples increased when the evaporation temperature was increased, and the thickness of the samples was reduced under the same conditions. At higher temperatures, geogrids had a substantial impact on reducing the evaporation rate and suppressing the dry-shrinkage cracks. The occurrence and development of the dry-shrinkage cracks of loess are divided into three stages: the formation stage, the acceleration stage, and the stabilization stage. The maximum crack width was reduced by 20%–34% for different sample thicknesses. The ratio of the number of cracks to the number of fracture nodes in the reinforced soil was lower than that of the unreinforced soil. This reduction ratio changed further from 5.6% to 24.4% with the increased thickness. The geogrids can effectively reduce the evaporation rate of water and the development rate of the dry-shrinkage cracks in loess. Consequently, the crack distribution in the loess samples is uniform and prevents the formation of large and long cracks. Using a 3D discrete element model, it is feasible to simulate the loess before and after the geogrid reinforcement.

Tripartite Uncertainty, Quantum, and Classical Correlations Dynamics under Unruh Effect

AbstractHow the dynamics of classical and quantum correlations due to the Unruh effect are reflected in the properties of tripartite entropic uncertainty is investigated. It is found that, despite the quantum correlations disappearing at the limit of infinite acceleration, the uncertainty about the measurement outcome is at its minimum. This is due to the three‐qubit system still containing classic correlations at that stage of acceleration. Additionally, the decrease in the entropic uncertainty when the measured qubit interacts strongly with the scalar field can be attributed to the increase in classical correlations. Furthermore, it is found that the entropic uncertainty is fully anti‐correlated to classical correlations, and minimal uncertainty can be obtained even in the absence of quantum correlations. A tremendously tight constraint that effectively defined the properties of tripartite entropic uncertainty based on the difference between the total correlation and the Holevo quantities is achieved.

Study on the fatigue properties and constitutive model of siltstone under the coupled action of dry‒wet cycles and cyclic loads

To study the fatigue properties of siltstone under the coupled action of dry‒wet cycles and cyclic loads, uniaxial fatigue tests were conducted on rock samples. The results show that the fatigue stress‒strain curve of siltstone exhibits a "sparse-dense-sparse" characteristic. The trend of the variation in peak strain can be divided into three stages: the initial stage, the isokinetic stage, and the acceleration stage. With an increasing number of dry‒wet cycles, upper stress limit, or stress amplitude or with a decreasing loading frequency, a rock sample will have a more significant plastic deformation during the failure process, and its failure life will be shortened. Additionally, to construct a constitutive equation under the coupled action of dry‒wet cycles and cyclic loads, a fractional-order viscoelastoplastic fatigue model was established by introducing a Scott-Blair fractional-order element to replace the Newton damper in the Nishihara model. The cyclic loads were decomposed into static loads and cyclic loads with an average stress of zero. Based on the theory of viscoelastic mechanics, energy storage compliance and energy consumption compliance were introduced, and a compliance correction coefficient α was proposed. A constitutive equation under cyclic loads with zero average stress was established. To consider the impact of dry‒wet cycles, a dry‒wet correction coefficient Dn was also proposed. Finally, the constitutive equation of siltstone under the coupled action of dry‒wet cycles and cyclic loads was derived. The model can effectively describe the nonlinear characteristics of rock fatigue deformation and entire failure process. The experimental data verify the rationality of the model.

The circulation growth of non-impulsive starting jet

An analytical model that can be used to predict the circulation growth process for non-impulsive starting jets has been developed by extending the over-pressure correction model for impulsive starting jets. Only the jet velocity function U0(t) is needed to obtain the circulation growth process of non-impulsive starting jet. The non-impulsive starting jets generated by nozzle and orifice configurations are performed numerically with two acceleration schemes (represented by two kinds of velocity functions) and different acceleration stage stroke ratios LaD (modifying the acceleration time ta in each velocity function to obtain LaD=0.05:0.2:1.25) to verify the accuracy of the proposed analytical model. The influence of radial velocity distribution in the jet inflow boundary is ignored in the process of constructing this model, but this has been proven to be reasonable. The time-averaged relative error with the growth process of the total circulation predicted by this model is about 11% to 26%, which is smaller than the 44% to 88% obtained by the classical slug model. For the range of LaD from 0.05 to 1.25, the relative error with the prediction of the total circulation at the end of the acceleration stage is from 4% to 28%, as compared to the 39% to 96% for the slug model.

Particle Injection and Nonthermal Particle Acceleration in Relativistic Magnetic Reconnection* *Released January 10, 2023.

Magnetic reconnection in the relativistic regime has been proposed as an important process for the efficient production of nonthermal particles and high-energy emission. Using fully kinetic particle-in-cell simulations, we investigate how the guide-field strength and domain size affect the characteristic spectral features and acceleration processes. We study two stages of acceleration: energization up until the injection energy γ inj and further acceleration that generates a power-law spectrum. Stronger guide fields increase the power-law index and γ inj, which suppresses acceleration efficiency. These quantities seemingly converge with increasing domain size, suggesting that our findings can be extended to large-scale systems. We find that three distinct mechanisms contribute to acceleration during injection: particle streaming along the parallel electric field, Fermi reflection, and the pickup process. The Fermi and pickup processes, related to the electric field perpendicular to the magnetic field, govern the injection for weak guide fields and larger domains. Meanwhile, parallel electric fields are important for injection in the strong guide-field regime. In the post-injection stage, we find that perpendicular electric fields dominate particle acceleration in the weak guide-field regime, whereas parallel electric fields control acceleration for strong guide fields. These findings will help explain the nonthermal acceleration and emission in high-energy astrophysics, including black hole jets and pulsar wind nebulae.

Development and Rotation Characteristics Analysis of a Large-Scale Deployable Arm

In the spin-off acceleration stage during high-speed rotation in space, the deployable arm of the space gravity simulation device must withstand a large axial centrifugal force and a driving torque. In this paper, a large-scale high-speed rotating deployable arm is proposed, and the relevant characteristics during the rotation process are analyzed. A new driving mode of towed deployment is proposed that can lead to the rapid and efficient deployment of a large-scale deployable arm. First, an optimized configuration of a deployable arm is proposed. Second, the deployment driving process of the deployable arm under several different drag driving modes is simulated and analyzed, and a comparative analysis is performed to select a simple and reliable drag deployment driving scheme. Then, the effects of various disturbances on the posture of the deployable arm during the rotation process are explored, guiding the posture control of the deployable arm. Finally, a 10 m four-unit prototype is developed for the stiffness and rotation tests, which verify that the theoretical analysis in this paper is correct.

The menopause transition: a critical stage for cardiovascular disease risk acceleration in women.

The menopause transition is a critical period for cardiovascular health. During this stage, women experience adverse changes in multiple components that are key for optimal cardiovascular health. Additionally, women struggle to maintain ideal health behaviors, which if adopted collectively, have been shown in observational studies to prevent more than 70% of coronary heart disease cases. Significant efforts should be directed toward increasing awareness among women and healthcare professionals about the menopause transition as a stage of cardiovascular disease risk acceleration that is amenable to reduction with positive lifestyle measures.

Creep mechanical tests and shear rheological model of the anchorage rock mass under water‒rock coupling.

The development of deep geotechnical engineering is restricted by the complex geological conditions of deep rock masses and the unknown creep mechanism of rock in water-rich environments. To study the shear creep deformation law of the anchoring rock mass under different water content conditions, marble was used as the bedrock to make anchoring specimens, and shear creep tests of the anchoring rock mass under different water contents were carried out. The influence of water content on rock rheological characteristics is explored by analysing the related mechanical properties of the anchorage rock mass. The coupling model of the anchorage rock mass can be obtained by connecting the nonlinear rheological element and the coupling model of the anchorage rock mass in series. Related studies show that (1) shear creep curves of anchorage rock masses under different water contents have typical creep characteristics, including decay, stability and acceleration stages. The creep deformation of the specimens can be improved with increasing moisture content. (2) The long-term strength of the anchorage rock mass shows an opposite change law with increasing water content. The creep rate of the curve increases gradually with increasing water content. The creep rate curve shows a U-shaped change under high stress. (3) The nonlinear rheological element can explain the creep deformation law of rock in the acceleration stage. By connecting the nonlinear rheological element with the coupled model of anchoring rock mass in series, the coupled model of water‒rock under water cut conditions can be obtained. The model can be used to study and analyse the whole process of shear creep of an anchored rock mass under different water contents. This study can provide theoretical support for the stability analysis of anchor support tunnel engineering under water cut conditions.

Smith–Purcell Radiation from Highly Mobile Carriers in 2D Quantum Materials

AbstractTerahertz (THz) radiation has broad applications ranging from medical imaging to spectroscopy. One viable source of high‐intensity THz radiation is the Smith–Purcell (SP) effect, which involves charge carriers moving over a periodic surface. Conventional SP emitters use electron beams to generate charge carriers, necessitating bulky electron acceleration stages. Here, a compact design for generating THz SP radiation using mobile charge carriers within 2D materials is proposed. This circumvents the beam alignment and beam divergence challenge, allowing for a reduction in the electron‐grating separation from tens of nm to 5 nm or less, leading to more efficient near‐field excitation and a potentially chip‐level THz source. In such a configuration, it is shown that the optimal electron velocity and the corresponding maximum radiation intensity can be predicted from the electron‐grating separation. The numerical demonstration shows that hot electrons can excite SP radiation in graphene on a silicon grating, and the radiation intensity can be increased by graphene surface plasmons. This study can be extended to a broad variety of charge carriers in 2D materials, thus allowing for compact, tunable, and low‐cost THz sources.

Aging characteristics and lifespan prediction for composite insulator silicone rubber in a mountainous region environment

In this study, the aging process of composite insulator silicone rubber in a mountainous region environment was studied and a lifespan prediction model was constructed. Silicone rubber samples with various exposure times were analyzed based on the microstructure, physical properties, functional groups, and chemical environment of silicon. All experimental results corresponded to three aging stages: platform stage, upturn stage, and acceleration stage. Based on linear regression method, the peak content of Si(-O)2 and shore hardness A were selected to establish the lifespan prediction model for silicone rubber. Verification of the model showed that the residual lifespan error is less than 1.5 years. This study is based on a systematic analysis of three stages of the aging process for silicone rubber in composite insulators and obtaining critical aging parameters. Furthermore, a lifespan prediction model is proposed and validated.