Acceleration Stage Research Articles

Improved value iteration for nonlinear tracking control with accelerated learning

AbstractIn this article, an adaptive critic scheme with a novel performance index function is developed to solve the tracking control problem, which eliminates the tracking error and possesses the adjustable convergence rate in the offline learning process. Under some conditions, the convergence and monotonicity of the accelerated value function sequence can be guaranteed. Combining the advantages of the adjustable and general value iteration schemes, an integrated algorithm is proposed with a fast guaranteed convergence, which involves two stages, namely the acceleration stage and the convergence stage. Moreover, an effective approach is given to adaptively determine the acceleration interval. With this operation, the fast convergence of the new value iteration scheme can be fully utilized. Finally, compared with the general value iteration, the numerical results are presented to verify the fast convergence and the tracking performance of the developed adaptive critic design.

The importance of Righi–Leduc heat flux to the ablative Rayleigh–Taylor instability during a laser irradiating targets

Abstract The Righi–Leduc heat flux generated by the self-generated magnetic field in the ablative Rayleigh–Taylor instability driven by a laser irradiating thin targets is studied through two-dimensional extended-magnetohydrodynamic simulations. The perturbation structure gets into a low magnetization state though the peak strength of the self-generated magnetic field could reach hundreds of teslas. The Righi–Leduc effect plays an essential impact both in the linear and nonlinear stages, and it deflects the total heat flux towards the spike base. Compared to the case without the self-generated magnetic field included, less heat flux is concentrated at the spike tip, finally mitigating the ablative stabilization and leading to an increase in the velocity of the spike tip. It is shown that the linear growth rate is increased by about 10% and the amplitude during the nonlinear stage is increased by even more than 10% due to the feedback of the magnetic field, respectively. Our results reveal the importance of Righi–Leduc heat flux to the growth of the instability and promote deep understanding of the instability evolution together with the self-generated magnetic field, especially during the acceleration stage in inertial confinement fusion.

Two typical phases of failure acceleration in rocks under uniaxial compression

The critical power-law acceleration of response quantities has been widely accepted and validated as an effective way to predict the failure time. However, in practical applications, only the data in the vicinity of the failure time exhibit critical power-law behaviour, which cannot describe the entire acceleration stage. In this study, it is shown that by using experimental results from the catastrophic failure of rocks under uniaxial compression, the acceleration of the mean strain presents two typical phases, and the final data in close proximity to the catastrophic time conform to the critical power-law trend. The early part of the acceleration stage is dominated by an exponential relationship with time to failure. Thus, the entire acceleration stage can be described using a combination of exponential and power-law functions. A prediction method based on a combined description of the entire acceleration failure process is proposed to forecast the failure time and is validated by experimental results. This combined description allows for an earlier warning of catastrophic failure than the power-law alone.

A Scalable, High-Efficiency, Low-Energy-Spread Laser Wakefield Accelerator Using a Tri-Plateau Plasma Channel.

The emergence of multi-petawatt laser facilities is expected to push forward the maximum energy gain that can be achieved in a single stage of a laser wakefield acceleration (LWFA) to tens of giga-electron volts, which begs the question-is it likely to impact particle physics by providing a truly compact particle collider? Colliders have very stringent requirements on beam energy, acceleration efficiency, and beam quality. In this article, we propose an LWFA scheme that can for the first time simultaneously achieve hitherto unrealized acceleration efficiency from the laser to the electron beam of >20% and a sub-1% energy spread using a stepwise plasma structure and a nonlinearly chirped laser pulse. Three-dimensional high-fidelity simulations show that the nonlinear chirp can effectively mitigate the laser waveform distortion and lengthen the acceleration distance. This, combined with an interstage rephasing process in the stepwise plasma, can triple the beam energy gain compared to that in a uniform plasma for a fixed laser energy, thereby dramatically increasing the efficiency. A dynamic beam loading effect can almost perfectly cancel the energy chirp that arises during the acceleration, leading to the sub-percent energy spread. This scheme is highly scalable and can be applied to petawatt LWFA scenarios. Scaling laws are obtained, which suggest that electron beams with parameters relevant for a Higgs factory could be reached with the proposed high-efficiency, low-energy-spread scheme.

A two harmonics circuit for the powering of the very fast RCS (Rapid Cycling Synchrotron) of the muon collider accelerator

This paper analyses the application of a two harmonics circuit with additional active filter for the powering of the four RCS stages of the muon acceleration to the ultimate 10 TeV energy level.

Detailed investigation and analysis of the dynamic evolutionary process of rainstorm debris flows in mountain settlements: a case study of Xiangbizui Gully

Short-term heavy rainfall often causes large-scale rainstorm debris flows in mountainous areas of Southwest China. Aiming to investigate the accumulation and movement of potential source material for the formation of debris flow hazards under extreme short-term heavy rainfall, this paper takes the Xiangbizui debris flow gully, Southwest China, as a case study. A detailed field engineering and geological investigation was carried out on the valley characteristics, formation conditions, provenance types, distribution range, loose solid material reserves that can be transformed into debris flows, and characteristics showing the variation in the grain size of the accumulated solids along the gully to further explore the characteristics of rainstorm-induced debris flow movement. The dynamic processes of debris flow movement and accumulation are numerically simulated to analyze the maximum velocity, accumulation height, range of influence, and evolutionary process based on the theory of continuous media of the approximate Voellmy solution and a high-precision three-dimensional model. The results indicated that rainstorms and steep terrain are the main factors stimulating debris flows. The amount of loose solid material in the channel is approximately 1550.61 × 104 m3, and the dynamic material reserves are approximately 396.41 × 104 m3. The maximum flow depth and velocity are approximately 3.5 m/s and 13 m/s, respectively, which mainly occur in the upper and middle reaches of the channel and in the accumulation fan at the outlet of the channel. The evolutionary process of the debris flow includes four stages: a 0–1,500 m initial acceleration stage, a 1,500–2,200 m fast forward movement stage, a 2,200–3,400 m acceleration stage in the middle and lower reaches, and a 3,400–4,300 m deceleration and end of accumulation stage. The research findings can provide a scientific basis and strong support for risk assessment and avoidance, as well as prevention and control of debris flows in mountainous areas with severe climate change.

Global scale identification of catchments phosphorus source shifts with urbanization: A phosphate oxygen isotope and Bayesian mixing model approach

Different scenarios of urban expansion can influence the dynamic characteristics of catchments in terms of phosphorus (P). It is important to identify the changes in P sources that occur during the process of urbanization to develop targeted policies for managing P in catchments. However, there is a knowledge gap in quantifying the variations of potential P sources associated with urbanization. By combining phosphate oxygen isotopes from global catchments with a Bayesian model and the urbanization process, we demonstrate that the characteristics of potential P sources (such as fertilizers, urban wastewater, faeces, and bedrock) change as urban areas expand. Our results indicate that using phosphate oxygen isotopes in conjunction with a Bayesian model provides direct evidence of the proportions of potential P sources. We classify catchment P loadings into three stages based on shifts in potential P sources during urban expansion. During the initial stage of urbanization (urban areas < 1.5 %), urban domestic and industrial wastewater are the main contributors to P loadings in catchments. In the mid-term acceleration stage (1.5 % ≤ urban areas < 3.5 %), efforts to improve wastewater treatment significantly reduce wastewater P input, but the increase in fertilizer P input offsets this reduction in sewage-derived P. In the high-level urbanization stage (urban areas ≥ 3.5 %), the proportions of the four potential P sources tend to stabilize. Remote areas bear the burden of excessive P loadings to meet the growing food demand and improved diets resulting from the increasing urban population. Our findings support the development of strategies for water quality management that better consider the driving forces of urbanization on catchment P loadings.

Growth assessment among northern Nigerian children using the middle phalanx of the third finger and its correlation with mandibular canine calcification.

BACKGROUND: Assessment of growth especially skeletal maturation, is considered vital in the treatment planning of orthodontic patients that require jaw modification. Appropriate treatment timing for jaw growth modification will determine the outcome of such intervention especially when clinicians take advantage of the pubertal growth spurt. The need for a quick, reliable and cost effective method using the mandibular canine calcification stages will be of immerse help to the orthodontist. AIMS:To determine the level of association between mandibular canine calcification stages and skeletal maturation stages.MATERIALS AND METHODS: It was a prospective cross-sectional descriptive study comprising 74 participants (5-17 years). Skeletal maturation was evaluated using the middle phalanx of the third finger (MP3), and the Demirjian method was used to stage the mandibular canine calcification stages (MCCS). The chi-square test of association and Spearman Spearman’s correlation coefficient were used to test the association and correlation between MP3 and the MCCS, respectively. The level of statistical significance was set at p&lt;0.05.RESULTS: Overall, there was a statistically significant association between MP3-skeletal maturation and the MCCS (male r=0.836 p value&lt;0.001; female r=0.824 p value&lt;0.001). The stage of acceleration of pubertal growth spurt (MP3-FG) was more associated with MCCS-G for both males and females. The peak pubertal growth spurt (MP3-G) was more associated with MCCS-H for males and MCCS-G for females. CONCLUSION: There was gender variation between the association of the period of peak pubertal growth (MP3-G) and the mandibular canine calcification stage. However, There was a significant correlation between the MP3 developmental stages and MCCS.

Dynamic Analysis of a Long Run-Out Rockslide Considering Dynamic Fragmentation Behavior in Jichang Town: Insights from the Three-Dimensional Coupled Finite-Discrete Element Method

To clearly realize the dynamic process as well as the dynamic fragmentation behavior of a long run-out rockslide, a novel numerical method for landslide simulation of the coupled finite-discrete element method (FDEM) was applied and the Jichang rockslide was used as a case. The calibrated simulation result of the FDEM in a rockslide deposit corresponds well with the real rockslide deposit. The main run-out process of the rockslide lasts for 75 s and can be divided into acceleration and deceleration stages, which last for 33 s and 42 s, respectively. The maximum overall rockslide movement speed is 35 m/s while the partial sliding mass reaches 45 m/s. The fracturing, fragmentation, and disintegration processes of the sliding mass can be clearly observed from the dynamic scenarios. Fracture energy generated by rock fracturing constantly increases with time in a non-linear form. Of the total fracture energy, 54% is released in the initial 5 s because of fracturing, and 39% of the total fracture energy is released because of fragmentation and disintegration in the last 35 s. The accumulated friction energy increases in the whole run-out process, and its magnitude is much greater than the kinetic energy and fracture energy of the sliding mass.

Influence of horizontal resistance loads on spatiotemporal and ground reaction force variables during maximal sprint acceleration

This study aimed to elucidate the influence of horizontal resistance loads on the spatiotemporal and ground reaction force (GRF) variables during maximal sprint acceleration. Nine male sprinters (20.2 ± 1.2 years; 175.3 ± 4.5 cm, 69.7 ± 6.1 kg) performed sprint-running with six loading conditions of one unresisted and five resisted loads of 4, 6, 8, 10, and 12 kg using a resistance training device with intelligent drag technology. During the trials, the GRFs for all steps were determined using a 50-m force plate system. The spatiotemporal and GRF variables at running velocity of every 0.5 m/s were obtained and compared across the loading conditions. The maximal running velocity under 0, 4, 6, 8, 10, and 12 kg loading conditions were 9.84 ± 0.41, 8.55 ± 0.41, 8.09 ± 0.33, 7.62 ± 0.34, 7.11 ± 0.31, and 6.71 ± 0.29 m/s, respectively. ANOVA revealed significant main effects of load on the measured variables (η2 = 0.236–0.715, p &lt; 0.05), except for stance-averaged anteroposterior GRF and braking impulse. However, the observed differences between the loading conditions were small, with approximately 4% (1.3–7.5%) for the GRF variables and approximately 9% (1.2–22.3%) for the spatiotemporal variables. The present study indicates that horizontal resistance load in sprint acceleration has little impact on the spatiotemporal and GRF variables at a given running velocity. In contrast to a general recommendation, one should adopt a heavy load in resisted sprint aiming to improve performance in the earlier stage of maximal sprint acceleration.

Research on the Mechanics Principle of 100-Meter Running

Fascinated by “superpowers” all over time, people are increasingly attracted by speed, a form of superpowers, which can be seen from the “flash” in movies or “locomotive” in American TV series. Given such obsession with the pursuit of speed, this paper selects the 100-meter race that reflects the speed of human beings as the research topic. This research analyzes the most basic movement of humans, that is, running. Firstly, with humans regarded as particles, 100-meter running is divided into stages of start, acceleration, maintenance, and sprint in this paper. By analyzing the speed, acceleration, reaction time, stride length, stride frequency, and other indicators of top athletes represented by Bolt in different stages, MATLAB simulation is conducted for comparison and summary. Secondly, with humans regarded as non-particles for analysis, simulation research is implemented on the landing mode of feet, the force exertion mode of arms, and some leg muscles combined with torque. Finally, this paper carried out experiments to understand the laws of particle motion mechanics in 100-meter running as well as figure out how various stride frequencies and arm swings affect running speed, in addition to analyzing the influence of resistance on running posture. Theoretically and experimentally exploring the principles of running mechanics, this paper initiates a detailed discussion of the influencing factors and their improvement from an innovative perspective, so as to put forward suggestions for teenagers to optimize their running performance.

Functional Connectivity of Entorhinal Cortex Predicts Tau in the Elderly

AbstractBackgroundHuman neuroimaging efforts to understand the pathophysiology of Alzheimer’s disease (AD) have solely focused on the amyloid‐beta (Aβ) deposition and tau neurofibrillary tangle formation. Until recently, the idea of a connectivity‐based molecular functional framework for understanding AD pathophysiology was missing, which eluded researchers from connecting functional connectivity (FC) with Aβ/Tau deposition.MethodThe initial dataset includes 631 older (67.44 ± 6.48 years) adults (521 healthy controls and 110 mild cognitive impairment (MCI)) who have been imaged for Tau pathology as well as resting‐state functional magnetic resonance imaging (rsfMRI) and structural MRI scans. Using Schaefer’s 200 parcellation atlas and a regional cutoff (SUVR = 1.25), we identified four groups of tau staging based on the number of regions having higher than cutoff tau SUVR (no tau stage (N = 193), pre‐acceleration stage (N = 222), acceleration stage (N = 149), and post‐acceleration stage (N = 67)). Since the entorhinal cortex (EC) is widely regarded as the epi‐center for tau accumulation, the left and right EC time series were derived from rsfMRI data using the Desikan‐Killiany atlas and used as seed regions for our Pearson correlation coefficient based functional connectivity analysis with all 200 regions in the Schaefer atlas. Finally, linear regression models were run to predict the mean regional accumulation of tau based on the strength of mean FC between that region and EC.ResultAs shown in Fig. 1, left/right EC functional connectivity is strongly associated with the accumulation of tau in that region during the pre‐acceleration phase (left: t = 3.586, p &lt; 0.0004; right: t = 4.404, p &lt; 0.0001) and in the acceleration phase (left: t = 6.229, p &lt; 0.0001; right: t = 7.577, p &lt; 0.0001) (results not shown). The functional connectivity values from left/right EC for the pre‐acceleration phase are plotted on the surface of the brain, as shown in Fig. 2.ConclusionOur results provide evidence of the role of functional connectivity in tau spreading from EC to the rest of the brain and can help throw light on the dynamic patterns of tau spreading in MCI/AD subjects in different disease stages.

Insights Into Lightning K‐Leader Initiation and Development From Three Dimensional Broadband Interferometric Observations

AbstractWe report detailed observations of K‐leaders and the activity between them with the three‐dimensional Broadband Interferometric Mapping and Polarization system (BIMAP‐3D) at Los Alamos National Laboratory. It is found that K‐leaders have a general propagation trend of initial acceleration and then gradual deceleration, and the corresponding very high frequency (VHF) radiation power is exponentially correlated with the leader speed. Based on the 3D development and simultaneous electric field change measurement, some simple K‐leaders can be modeled with time‐evolving point charges at the propagating leader tip and at the stationary origin. We found that the charge magnitude increases during the initial acceleration stage and stays relatively constant for the rest of the development. K‐leaders are observed to interact with other branches; the branches affect the leader's propagation speed, and may affect the charge transfer. After the occurrence of a K‐leader, VHF emissions are quenched for several milliseconds. VHF sources then reappear in an impulsive and scattered manner as “twinkling,” and these sources are found not uniquely on the so‐called needles, but also on the main channel. These twinkling sources start near the apparent positive leader tip, and extend back toward the direction of the flash origin at about 105 m/s, while the apparent positive tip continues to extend forward at about 104 m/s. The twinkling extending toward the direction of flash origin appears to initiate the following K‐leader, although it may be interrupted by a K‐leader along a different branch, or simply die out without more K‐leader activity.

Speed of metal deformation of welded pipe sections in the process of natural tests

It is clear that testing on Menage Charpey samples and other materials, which may not match the durability of pipe walls, does not reflect the real picture of visco-plastic failures, which does not allow the development of a methodology or model for predicting the residual life (failure-free) gas pipelines have a three-year term of operation. At the same time, theoretical and laboratory studies do not always provide sufficient evidence for nutrition, directly related to the reliability and trouble-free operation of pipelines. It is likely that in the laboratory minds of enterprises and scientific foundations, it is important to create and identify all the factors that characterize the growing and widespread use of metal in gas pipelines to represent nature. and testing of cutting gas pipelines with a length of 150-250 m. However, due to the technical complexity of their implementation, in the field Our minds will never again be faced with the need to identify a new set of registration parameters. In addition, the testing of highly labor-intensive procedures, including ensuring the safety of their implementation, requires large material and hourly costs. Serial testing of enclosed pipes in the drains of a specially lined landfill and cutting on this basis is quite consistent with the results of field testing of gas pipelines. Field testing of pipes allows for consistently inexpensive research when testing new types of steel and pipe designs. Therefore, laboratory data need to be verified and necessarily clarified based on the results of pneumatic testing of long-life pipe sections, so that at the present time there is an urgent need to combine laboratory and field tests pipes of the gas pipeline. Such testing is not widespread, but as a result of their experimentation, important information is taken away from the behavior and power of metal in the minds of vantagement and exploitation, those closest to exploitation. Full-scale testing was carried out at a specially trained test site for cutting pipes intended for the construction of main gas pipelines, which made it possible to determine the kinematic and dynamic parameters of the alignment of the model gas pipeline under operating conditions. importance and in minds as close as possible to the operational ones. Analysis of the results of the field (natural) tests is to confirm that from the moment of initiation of the collapse in the central pipe, the fluidity of the main crack (on both sides of the initiator) increases and increases distance approximately 2-3 diameters from the cut, reaching a maximum. Changing the fluidity after tightening the central pipe can be either symmetrical or asymmetrical to the cut in the middle pipe. This is due to the technique of carrying out the experiment and the formation of cracks, including displacements of the cutting edge in the middle of the pipe and various influences on the metal of the pipes in the zone of local tearing. The underlying regularity is that the maximum fluidity is not evident at the crack acceleration stage. It is necessary to note that in order to carry out the experiment, so that the achieved high fluidity of the structure is preserved when the top of the crack enters the final plot. This is ensured by consistent selection of the viscosity of the metal of the central pipe.

Numerical Investigation of the Effects of Diffusion Time on the Mechanisms of Transition from a Turbulent Jet Flame to Detonation in a H2-Air Mixture

The current study primarily aimed to simulate detonation initiation via turbulent jet flame acceleration in partial-premixed H2-air mixtures. Different vertical concentration gradients were generated by varying the duration of hydrogen injection (diffusion time) within an enclosed channel filled with air. H2-air mixtures with average hydrogen concentrations of 22.5% (lean mixture) and 30% (near stoichiometric mixture) were investigated at diffusion times of 3, 5, and 60 s. Numerical results show that the vertical concentration gradient significantly influences the early stage of flame acceleration (FA). In the stratified lean mixture, detonation began at all the diffusion times, and comparing the flame-speed graphs showed that a decrease in the diffusion time and an increase in the mixture inhomogeneity speeded up the flame propagation and the jet flame-to-detonation transition occurrence in the channel. In the stratified H2-air mixture with an average hydrogen concentration of 30%, the transition from a turbulent jet flame to detonation occurred in all the cases, and the mixture inhomogeneity weakened the FA and delayed the detonation initiation.

Application of Cross model for granular flow and impact analysis using three-dimensional B-spline material point method

Granular flow and impact, such as landslides and debris flows, are typical problems involving large deformations of non-Newtonian free surfaces, which are of great interest in geological engineering and also pose challenges for traditional mesh-based numerical methods. As an enhancement of the traditional Material Point Method (MPM), the B-Spline Material Point Method (BSMPM) can not only effectively reduce mesh-crossing and quadrature errors, but also facilitate the tracking and capturing of free surfaces and contact interfaces. In this paper, the non-Newtonian general Cross model, the rheological parameters of which are determined by the Bingham model and the Mohr-Coulomb yield criterion, is introduced into the three-dimensional BSMPM (3D BSMPM) for simulating granular flow and impact problems. Interparticle effects of granular materials are represented by artificial damping forces. Dynamic simulations are carried out on the collapse of sand column and glass beads, the flow of bentonite suspensions, and the impact between granular mass and elastic obstacles. The overall evolution of granular flow and impact behavior are presented and compared with existing experimental and/or original MPM results. It is found that the proposed method well reproduces the overall process of granular flow and impact behavior, including its various stages of formation, acceleration, deceleration, and deposition, as well as the impact pressure. The results show that the granular flow and impact behavior can be well represented by the proposed 3D BSMPM with the Cross rheological model, demonstrating the effectiveness of the proposed method in simulating complicated environmental fluid dynamics.

Synergistic effect of silica fume and ultra-fine glass microsphere on macro properties and hydration of coarse-aggregate UHPC

This study investigated the synergistic effect of silica fume (SF) and ultrafine glass microspheres (UGM) in coarse-aggregate ultra-high performance concrete (CA-UHPC). Comprehensive assessments were conducted on macro properties, encompassing fluidity, mechanical properties, dry shrinkage, and chloride penetration resistance, while the hydration process was analyzed through the hydration heat, hydration products, and microstructure. The findings reveal that the fluidity of CA-UHPC exhibits a diminishing trend with escalating SF content but significantly improves with the incorporation of UGM. CA-UHPC containing 8 % SF attains the highest 28-day compressive strength of 166.9 MPa, while further increasing in SF content leads to reduced compressive strength. The introduction of SF and UGM effectively enhances the flexural strength by fostering stronger bonding between fibers and the matrix. Both SF and UGM increase dry shrinkage but enhance chloride penetration resistance. Notably, the combined use of SF and UGM significantly reduces the DRCM by 66.7 %. SF reduces the heat release during the acceleration stage and consumes more Ca(OH)2 than generated by Portland cement hydration, while UGM exhibits higher reactivity than FA and contributes more to the binder hydration. The combination of SF and UGM further improves the hydration degree and reduces porosity, resulting in a finer pore structure. This study underscores the advantages of incorporating SF and UGM in CA-UHPC, providing valuable insights for future research and applications in the field of UHPC.

A sequentially coupled chemical-mechanical damage constitutive model for carbonate rocks

Modelling the constitutive relations of chemically corroded carbonate rocks is important for the design and stability evaluation of engineering constructions in karst areas (e.g., mines, tunnels and dams, etc.) [1-4]. This paper presents a sequentially coupled chemical-mechanical (C-M) damage constitutive model for engineering rocks in karst areas. First, the chemical damage caused by carbonate dissolution and the mechanical damage caused by external loads are investigated based on experimental results. After that, the chemical damage is expressed by the degradation ratio of Young's modulus under the effect of the chemically induced secondary pores compaction. The chemically induced secondary pore is quantified by reactive transport behavior considering the geochemical procedure of free-face dissolution and precipitation under different H+ concentrations, temperature and corrosion periods [5]. The mechanical damage is formulated based on a statistical theory [6,7], which underlines the strength of the mesoscopic element and considers the damage initiation threshold. To capture the nonlinear strength responses of the mesoscopic element at various chemical damage and confining pressures, a modified Mohr-Coulomb (M-C) criterion is introduced, in which the instantaneous friction angle and cohesion are expressed as functions of the confining pressure and chemical damage. The proposed model is validated and shows good agreement with experimental data.&#x0D; Result of this research shows that: (1) the porosity increases with increasing corrosion period and the increase rate (i.e., the slope of the porosity curve) is steep initially and then decreases gradually (see Fig. 1 (a)). (2) As shown in Fig. 1 (b), Young's modulus decrease with porosity growth. (3) The C-M coupled damage evolution curve is S-shaped and consists of four stages (see Fig. 1(c)), i.e., a linear elastic stage, a stable damage stage, a damage acceleration stage and a post-peak stage. In damage stage 1, stress is lower than the mechanical damage initiation threshold and the stress-strain curve is in a linear elastic state. At this stage, mechanical damage doesn’t initiate (i.e., ). Therefore, the total damage (Dcm) evolution curve is horizontal and only contains chemical damage (Dc=0.165) caused by carbonate dissolution. Once the axial strain exceeds the mechanical damage initiation threshold, the damage enters stage 2. In this stage, total damage (Dcm) begins to slightly rise and steadily increases with the increasing load. In damage stage 3, the damage-strain curve rises concave upward. After the peak strength point, damage development comes to stage 4, i.e., the post-peak stage.&#x0D;

Kinetic characterization of gas mixture separation by hydrate method with 1,3-dioxolane and multi-walled carbon nanotubes complex synergistic system

In the transition to cleaner energy sources, low-carbon energy gases are expected to dominate fuel consumption. Hydrate-based gas separation technology is poised to play a key role in the decarbonization pathway for energy gases with high CO2 content. However, the current hydrate gas separation method faces challenges, including a long induction period, slow growth rate, and low separation efficiency. In light of these challenges, this paper investigates the kinetics of CH4/CO2 gas mixture hydrate formation and its separation efficiency in 1,3-dioxolane (DIOX) and multi-walled carbon nanotubes (MWCNTs). The experimental results showed that both DIOX and MWCNTs, when used in low concentrations, had a certain thermodynamic promotion effect, with DIOX showing a superior performance. DIOX outperforms MWCNTs in terms of gas consumption and induction time. whereas MWCNTs was superior to DIOX in terms of growth rate, and the purification rate at the same concentration could be increased by 32.66 %∼234.43 % compared with the DIOX system. Subsequently, this paper further investigated the effect of 300 ppm DIOX complexed with different concentrations of MWCNTs on hydrate formation and separation efficiency. DIOX was found to occupy the main promotional role in this complex system, retaining the growth acceleration stage in the DIOX system. When compounded with 200 ppm MWCNTs, the T90 time was shortened by 28.78 %∼59.29 %, and the purification rate could be increased by 86.4 % compared with a single 300 ppm DIOX system. This work provides guidance on the use and compounding of thermodynamic and kinetic promoters and aids hydrate technology where faster hydrate growth rates and more efficient gas mixture separation are required.

Beam current from downramp injection in electron-driven plasma wakefields

We study the stability of plasma wake wave and the properties of density-downramp injection in an electron-driven plasma accelerator. In this accelerator type, a short high-current electron bunch (generated by a conventional accelerator or a laser–wakefield acceleration stage) drives a strongly nonlinear plasma wake wave (blowout), and accelerated electrons are injected into it using a sharp density transition which leads to the elongation of the wake. The accelerating structure remains highly stable until the moment some electrons of the driver reach almost zero energy, which corresponds to the best interaction length for optimal driver-to-plasma energy transfer efficiency. For a particular driver, this efficiency can be optimised by choosing appropriate plasma density. Studying the dependence of the current of the injected bunch on driver and plasma parameters, we show that it does not depend on the density downramp length as long as the condition for trapping is satisfied. Most importantly, we find that the current of the injected bunch primarily depends on just one parameter which combines both the properties of the driver (its current and duration) and the plasma density.