Acceleration Stage Research Articles

Surgery of Medial Epicondylitis (Golfer's Elbow), an Overview

Golfer's elbow, also known as medial epicondylitis, is a common disease. When doing activities that include wrist flexion and forearm pronation, repetitive forced wrist extension and forearm supination can lead to flexor-pronator tendon degeneration. An ongoing pathologic process in the tendon can lead to structural failure, irreversible fibrosis, or calcification. The most common complaint from patients is chronic, medial-sided elbow pain that gets worse with everyday activity. During the late cocking or early acceleration stages of the throwing action, athletes may have symptoms that are particularly severe. Injections of corticosteroids, activity modification, and NSAIDs are all examples of nonsurgical supportive therapy. After the acute symptoms have subsided, attention is directed toward injury prevention and flexor-pronator mass rehabilitation. Patients with severe symptoms are often the only ones who receive open surgical procedures. Hence the study aimed to summarize and explain the evidences regarding surgical management of medial epicondylitis (golfer’s elbow).

The Autonomic Imbalance of Myocardial Ischemia during Exercise Stress Testing: Insight from Short-Term Heart Rate Variability Analysis.

Exercise stress testing (EST) has limited power in diagnosing obstructive coronary artery disease (CAD). The heart rate variability (HRV) analysis might increase the sensitivity of CAD detection. This study aimed to evaluate the correlation between short-term HRV and myocardial ischemia during EST, including the acceleration, maximum, and recovery stages of heart rate (HR). The HRV during EST from 19 healthy (RHC) subjects and 35 patients with CAD (25 patients with insignificant CAD (iCAD), and 10 patients with significant CAD (sCAD)) were compared. As a result, all HRV indices decreased at the maximum stage and no significant differences between iCAD and sCAD were found. The low-frequency power of heart rate signal (LF) of the RHC group recovered relatively quickly from the third to the sixth minutes after maximum HR, compared with that of the sCAD group. The relative changes of most HRV indices between maximum HR and recovery stage were lower in the sCAD group than in the RHC group, especially in LF, the standard deviation of all normal to normal intervals (SDNN), and the standard deviation in the long axis direction of the Poincaré plot analysis (SD2) indices (p < 0.05). The recovery slope of LF was significantly smaller in the sCAD group than in the RHC group (p = 0.02). The result suggests that monitoring short-term HRV during EST provides helpful insight into the cardiovascular autonomic imbalance in patients with significant CAD. The relative change of autonomic tone, especially the delayed sympathetic recovery, could be an additional marker for diagnosing myocardial ischemia.

Comprehensive investigation of rock fracture behaviour in clay-rich rocks under the effect of temperature: Experimental study under three loading modes (I, I/II, II)

Rock fracture behaviour is a crucial aspect in many geological and engineering projects and can be affected by different environmental factors such as temperature, especially in projects where the rocks are exposed to a change in temperature such as geothermal energy, oil and gas exploitation, nuclear waste areas, etc. Therefore, this research aims to investigate the effect of temperature on rock fracture behaviour under four loading modes; pure mode I, pure mode II, and two mixed-mode loadings I/II in SCB specimens of clay-rich rocks (mudstone). Thirty-six SCB specimens were prepared and tested under three temperatures (Ambient temperature (AT), 250 and 500 °C), and some important parameters such as fracture toughness, fracture envelope, crack propagation speed, and crack acceleration were measured and discussed as a function of temperature. The main results concluded that due to the gradual loss of water from the structure of high clay content in the mudstone during thermal treatment, the behavior of mudstone gradually changed from ductile to brittle behaviour, and as a result, fracture toughness and crack propagation speed increased significantly. In addition, our results showed that the area under the fracture envelope which represents fracture resistance to growth under mixed-mode loading increased by 1.86 and 2.68 orders in magnitude after thermal treatment at temperatures of 250 and 500 °C, respectively. Under the four loading mode mixities, fracture grows through three main stages, high acceleration (0–5 mm), high deceleration (5–10 mm), and low deceleration (10–15 mm) stages. Crack propagation speed and crack acceleration depend strongly on the mode mixity ratio (KII/KI) and it increased by changing the loading mode from pure mode I to mixed mode loading I/II and pure mode II.

Study on simulation of multifield coupled wear in reciprocating electrical contact

PurposeConventional wear models cannot satisfy the requirements of electrical contact wear simulation. Therefore, this study aims to establish a novel wear simulation model that considered the influence of thermal-stress-wear interaction to achieve high accuracy under various current conditions, especially high current.Design/methodology/approachThe proposed electrical contact wear model was established by combining oxidation theory and the modified Archard wear model. The wear subroutine was written in FORTRAN, and adaptive mesh technology was used to update the wear depth. The simulation results were compared with the experimental results and the typically used stress-wear model. The temperature of the contact surface, distribution of the wear depth and evolution of the wear rate were analyzed.FindingsWith the increase in the current flow, the linear relationship between the wear depth and time changed to the parabola. Electrical contact wear occurred in two stages, namely, acceleration and stability stages. In the acceleration stage, the wear rate increased continuously because of the influence of material hardness reduction and oxidation loss.Originality/valueIn previous wear simulation models, the influence of multiple physical fields in friction and wear has been typically ignored. In this study, the oxidation loss during electrical contact wear was considered, and the thermo-stress-wear complete coupling method was used to analyze the wear process.

Underdense relativistically thermal plasma produced by magnetically assisted direct laser acceleration

Successive stages of direct laser acceleration driven by two laser pulses in an applied magnetic field enable volumetric generation of bulk-relativistic, persistently hot plasma at gas-jet-accessible and optically diagnosable density. Theory and kinetic simulations demonstrate robustness to experimentally relevant parameters and indicate that this approach is capable of accessing a relativistically thermal plasma regime of significant interest for basic plasma physics, laser-plasma physics, and laboratory astrophysics.

High transformer ratio electron acceleration for CEPC plasma injector

The CEPC Plasma Injector is designed as the beam energy multiplier for avoiding the dipole magnet issue of the Circular Electron Positron Collider (CEPC) booster. Besides the final energy, other requirements including the energy stability, bunch charge and energy spread all make the injector design very challenging. With respect to the electron acceleration, a high transformer ratio plasma wakefield acceleration stage is necessary if we constrain the beam energy at the end of the linac and the plasma injector are 10[Formula: see text]GeV and 45.5[Formula: see text]GeV, respectively. In this work, we use the particle-in-cell code QuickPIC to design the electron acceleration stage. Based on the current conceptual design, a comprehensive analysis of single-parameter tolerance is performed. Through the tolerance studies, we obtain some useful guidance for the further optimization of the injector.

Time-dependent crack growth mechanism in Ni-based single crystal superalloys at high-temperature

The microscopic mechanism of time-dependent crack growth (TDCG) in single crystal (SC) Ni-based superalloys under a relatively high-temperature condition (900 °C) is critically investigated. Two alloy types are compared: alloy A containing 3% rhenium (Re) and alloy B containing no Re. With an initial stress intensity (K) value of 40 MPam1/2, both alloys show similar two step TDCG, i.e. a steady stage followed by an acceleration stage. The total life to failure (tf) of alloy B is, however, an order of magnitude shorter than alloy A. In addition to the conventional fractography, cross-sectional analyses (EBSD and EDS) are also conducted for an interrupted crack tip. Two distinct fracture modes are then identified in both alloys: {111}<112> twin-induced shear fracture and non-crystallographic fracture along dendrite boundaries. The twin systems observed are the secondary ones having a relatively smaller Schmid factor compared to the primary ones that remain inactive under the <100> tension. In the case of alloy A, the twin induces local phase transformation involving TCP precipitation, decomposition of γ (Ni)/γ’ (Ni3Al) structure and recrystallization, which eventually enhances local ductility and dominates the crack growth rate. In the case of alloy B, the macroscopic appearances of these fracture modes are much the same, but they are significantly facilitated by micro-voids formed exclusively in γ channel whose stability is much lower than that in alloy A. The apparently brittle TDCG nature of alloy B compared to alloy A can be interpreted as an enhanced localization of plasticity at the crack tip.

On the definition of the deuterium-tritium ion beam parameters for the SORGENTINA-RF fusion neutron source

The SORGENTINA-RF project aims to develop a 14 MeV fusion neutron source to produce medical radioisotopes with special focus on ^{99}Mo. The facility is based on a positive ion source with an acceleration stage to produce a deuterium (D^{+}) and tritium (T^{+}) ion beam that, impacting on a titanium-coated rotating target, allows fusion reactions to take place. Maximizing the neutron production rate is one of the main issues to be addressed in the project and the optimization of some key parameters of the ion beam is of paramount importance in this regard. In this study, a methodology is discussed to reach a definition of the beam characteristics for an effective and sustainable operation of the plant. The most convenient layout that has been found out is based on a single ion source fed by a deuterium and tritium gas mixture. Eventually, a series of considerations about the operation of the ion source and fuel cycle have been drawn.

Flame front dynamics, shape and structure on acceleration and deflagration-to-detonation transition

Developing a new generation of rocket engines based on detonation principles needs methods which ensure stability of operation including the onset of detonation wave after mild ignition. This aspect is crucial for ensuring safety of such engines. In the present paper the transition processes associated with flame acceleration and the onset of a detonation mode are under investigation. High-speed flame front photography has been performed during the deflagration of a premixed gas mixture in a long smooth tube. The evolution of flame front structure and shape has been determined, starting from the moment of deflagration initiation and ending with the occurrence of a local explosion leading to the formation of a detonation wave. Four characteristic flame propagation stages have been identified: the initial flame acceleration stage, followed by the apparent velocity deceleration stage, followed by the nearly constant propagation velocity stage, and finally the second acceleration stage, during which detonation is formed. The changes in process dynamics with a change in the initial pressure have been demonstrated. The behavior of flame front at the early stage of acceleration has been identified. The experimental findings are compared with the theoretical models available in the literature. At the initial stage of the accelerated propagation of flame extended along the channel walls — until deceleration — the velocity of the leading tip of the front is effectively described by the exponential relationship proposed by C. Clanet and G. Searby (1996). The most interesting and poorly studied, in the authors' opinion, stage of the deflagration-to-detonation transition process, the intensive repeated acceleration stage, during which flame shape changes abruptly, has been described in detail. The laminar burning velocity of the stoichiometric acetylene–oxygen mixture diluted with either nitrogen or argon at a reduced initial pressure (8–21 kPa) has been identified.

Importance of the surface roughness of a steel fibre pulled out from cement paste by slowly increasing load cycles

Pull-out tests of fibres were conducted using slow cyclic tension to evaluate the behaviour of the bond between cement paste and steel fibres with different types of surface roughness. Even though the load amplitude increases in small steps between the cycles, the development of the residual slip increment proves the absence of a complete bond at the beginning of loading. During the load steps, the residual slip evolves in the deceleration, steady, and acceleration stages. The bond stiffness during the ascending and descending parts of the load-slip curve increases up to the last load cycles, indicating that loading compacts the matrix near the fibre surface. The growth of the roughness of the fibre surface increases the amount of cement paste adhered to the surface of fibres pulled out, explaining the changes in the behaviour of the bond and the increase in the pull-out capacity of these fibres.

Assessment of ride comfort of traction elevators using ISO 18738-1:2012 and ISO 2631-4: 2001 standards

PurposeRide comfort is one of the important factors affecting passenger health. Therefore, the elevator industry usually uses the International Organization for Standardization (ISO) 18738-1 standard to evaluate elevator ride quality and optimize elevator design. However, this method has certain limitations in its evaluation of comfort due to the problem of boundary division. The ISO 2631-4 standard is used as a general method of comfort evaluation in the current rail transit system, but it has not been applied in the elevator industry. In order to explore the difference and connection between the two standards, the author aims to conduct a detailed analysis on this.Design/methodology/approachBased on the elevator internet, a large amount of measured data of normal and abnormal vibration of elevator car were collected and analyzed and preprocessed; based on ISO 18738-1:2012 standard and ISO 2631-4:2001 standard, the differences of ride comfort assessment methods in the two standards were analyzed, and the ride comfort assessment study of elevator under normal and abnormal vibration conditions was carried out.FindingsThe experimental results show that the comfort assessment results of ISO 2631-4:2001 standard and ISO18738-1:2012 standard are consistent under two vibration conditions. At the same time, ISO 2631-4:2001 can not only provide a more accurate quantitative description of comfort, but also roughly determine the comfort interval of each vibration, which can provide theoretical reference for elevator vibration classification and car comfort design.Originality/valueThe authors designed an Internet of Things (IOT)-based elevator vibration signal acquisition method to address the shortcomings of the previous elevator ride comfort assessment methods, which can realize the dynamic assessment of elevator ride comfort; by comparing the assessment results of elevator ride comfort under normal vibration and abnormal vibration, the feasibility of ISO 2631-4:2001 for elevator ride comfort assessment was fully verified. In addition, the experimental results also give the influence of abnormal vibration on elevator riding comfort under the stages of start-stop, uniform speed, acceleration and deceleration, which can provide theoretical support for elevator vibration suppression and comfort transformation.

Three-dimensional structure of freely-propagating flame prior to deflagration-to-detonation transition

The paper analyzes numerically the development of the freely expanding flame before the transition to detonation in three-dimensional space. The risks related to the transition to detonation in unconfined space arise at launch places and near-Earth space during rocket engine accidents. Clear and adequate models for such scenarios are in demand for the elaboration of safety measures. Here it is shown that the process of transition to detonation involves multidimensional effects related to the generation of compression waves and their amplification when interacting with the developing flame. The necessary conditions for deflagration-to-detonation transition are flame acceleration up to near-sonic speed and generation of transversal compression waves (propagating along the flame front). So, while the subsonic stage of flame acceleration can be successfully described by the quasi one-dimensional model supplemented by a known self-similar law of the flame area growth (folding factor), the model for the pre-detonation stage should take into account considered multidimensional effects. The presented results imply that there is no unambiguous relation between the transition to detonation and the folding factor.

Electron beam energy slicing performance in laser wakefield acceleration

The first stage of electron acceleration, the plasma cathode, is a key part of LWFA. Output parameters of this stage such as beam charge, mean energy, energy spread, and emittance can be varied in a rather broad range depending on laser pulse and gas target conditions. These parameters are usually evaluated via particle-in-cell (PIC) simulations. However, if an essential improvement of the beam quality could be further performed with a conventional beamline, the selection of an acceleration regime, including laser pulse and gas target characteristics, should be done taking into account not only PIC simulations but also beam transport simulations. Here is shown that improvements of electron beam quality via energy slicing using magneto-optics (MO) may become an important step in developing full-optical electron accelerators and radiation devices. Since the typical energy of electrons presently achieves sub-GeV in a single acceleration stage, the elaboration of slicing techniques for quasi-mono-energetic, high density LWFA beams is of particular interest. Depending on the efficiency of beam slicing the reverse problem of initial beam energy distribution and, therefore, a proper acceleration regime can be solved. An efficient slicing may allow operation with broader beam energy spreads, higher charges, and getting better stability in contrast to narrower beam energy spreads requiring far more precise control over laser and gas target parameters. Even though this technique has been used in classical particle accelerators, its limitations have not been well studied in LWFA with their less stable beams. MO slicing is explored numerically with use of realistic LWFA electron beams obtained from 3D PIC simulations at various target parameters.

Acoustic viscous boundary layer beyond laminar regime: Particle Image Velocimetry measurements

The current study reports an experimental investigation of flow regimes for acoustically oscillating flows in the near-wall region of a resonator. Particle Image Velocimetry (PIV) is used to measure axial and transverse velocity components inside an empty square resonator over the acoustic cycle for a wide range of Reynolds numbers and at a high Womersley number. The measurements are compared with LDV measurements in a circular duct. A good agreement between the PIV and LDV measurements is observed. The measured transverse distribution of the axial velocity agrees well with the Stokes boundary layer expectations up to the Reynolds number (based on acoustic velocity and viscous boundary layer depth) of 240. At higher Reynolds numbers, the measured velocity distribution deviates from the theoretical expectations, suggesting a change of regime at a Reynolds number between 240 and 272. To assert the critical Reynolds number, the velocity fluctuations and Reynolds stress are estimated. At Reynolds number of 272, an increase in the value of the Reynolds stress is observed at the edge of the viscous penetration depth which is regarded as an indication of changing the flow regime. To better qualify the high amplitude acoustic flow, the spectrum of the turbulent kinetic energy and evolution of the integral length scale over the acoustic cycle are investigated. The decay of turbulent kinetic energy with the wavenumber complies with the universal slope (−5/3). The integral length scale increases during the deceleration stage and decreases at the beginning of the acceleration stage.

Experimental and theoretical investigation of the heating characteristic of C3H6 catalytic combustion over Pt/Al2O3 catalyst

The purpose of this study is to investigate the effect of C3H6 catalytic combustion on the heating characteristic over DOC, tracking C3H6 conversion efficiency (XC3H6) and gas mixture temperature to optimize the control strategy during active DPF regeneration. The temperature programmed oxidation and constant temperature oxidation test were conducted on a fixed-bed quartz reactor with a uniformly coated Pt/Al2O3 catalyst. The comparative effects of temperature and C3H6 concentration on the DOC performance including the light-off activity, XC3H6 and heating characteristic were systematically discussed. Experimental results showed that XC3H6 was weakened with higher C3H6 concentration in low-temperature conditions, for C3H6 easily adhering to the active site surface of the catalyst and exhibiting a inhibitory effect on self-catalytic oxidation. In high-temperature conditions, XC3H6 did not decrease with the addition of C3H6 concentration, for the adsorption effect of C3H6 weakened. DOC outlet temperature rise response characteristics in constant temperature oxidation test could be divided into three stages: slow start stage/temperature rise delay stage, acceleration stage and stabilization stage. In the test under oxygen-enrich conditions, there was a nearly linear relationship between the DOC outlet temperature rising amplitude and C3H6 concentration, as the addition of C3H6 led to the more participation of C3H6 in the oxidation reaction to release heat. The order of temperature rising amplitude of C3H6/O2/H2O/N2 at 300, 400 and 500 °C was θ300 °C>θ400 °C>θ500 °C, respectively, which was closely related to C3H6 combustion in front of the DOC.

Experimental and theoretical studies on heavy fluid layers with reshock

The Richtmyer–Meshkov instability of a heavy fluid layer with reshock is investigated experimentally and theoretically, to reveal the mechanisms of the interfacial instabilities and motions of waves and interfaces under reshock conditions. Three kinds of heavy fluid layers with different thicknesses in unperturbed and perturbed cases are considered, highlighting the effects of initial layer thickness on the interface evolution. A general one-dimensional theory for describing the interaction between unperturbed interfaces and waves under reshock conditions is constructed, which supports the instability analysis and theoretical modeling in the perturbed cases. The perturbed fluid-layer results indicate that as the fluid-layer thickness decreases, the inhibition of squeezing effects on perturbation growth is gradually stronger than the promotion of rarefaction-wave effects on perturbation growth. The whole mixing width of fluid layers after reshock acceleration exhibits an approximately linear growth feature, and the reshocked mixing width growth rate is weakly dependent on the initial layer thickness, which is different from the finding before reshock. The linear amplitude growth of the right interface after reshock is promoted by the interface coupling effects but is still smaller than the prediction of the empirical linear model. When the squeezing effects are weak, the nonlinear model, which considers the modification of rarefaction-wave effects, can well predict the perturbation growth during and after the acceleration stage of rarefaction waves.

Influence of the transient airflow pattern on the temporal evolution of microparticle resuspension: Application to ventilated duct during fan acceleration

This study investigates experimentally the influence of the temporal airflow pattern properties to which microparticles are exposed on the dynamics of the resuspension phenomenon for transient airflow conditions representative of a fan start, i.e., involving a temporal acceleration period before reaching steady state. The extent to which the average steady state velocity and the average acceleration affect the characteristics of the curve depicting the temporal evolution of the fraction of particles remaining on the duct wall, i.e., the time at which resuspension starts and the curve shape, is investigated. These results are analyzed regarding the properties of the instantaneous velocity signal in the viscous sublayer. It is demonstrated that a threshold turbulent kinetic energy must be exceeded for resuspension to begin. The results are also presented in terms of resuspension rate, i.e., of instantaneous rate of particles removed from the duct surface, versus time. This enables to demonstrate that the highest resuspension rate values are recorded at the very beginning of the phenomenon, typically during the fan acceleration stage, and that high mean acceleration values are responsible for high resuspension rates.Copyright © 2022 American Association for Aerosol Research

Study on the Microstructure Evolution and Strength Damage Mechanism of Dolomite under Dissolution Condition

Dolomite is a common type of natural soluble rock. The strength of rock decreases under the action of corrosion, which has a significant impact on the self-stability and long-term safety of the tunnel surrounding the rock. To reveal the microscopic structure evolution and strength-damage law of carbonate rock caused by chemical corrosion, a series of tests such as rock chemical corrosion test, rock uniaxial compression test and electron microscope scanning test are conducted at different pH values on the dolomite of the Doushantuo Formation. The rock dissolution at different pH values exhibits four typical stages: the initial dissolution stage, secondary dissolution acceleration stage, stable dissolution rate stage and dissolution attenuation stage. During the dissolution process, the initial dissolution rate is 25.91 times that of the stable stage, and the maximum strength attenuation is 76.2% after 21 days of dissolution. For macroscopic failure, the rock is developed from 1 to 2 external fractures to multiple internal and external fractures and penetrated, and the specimen transforms from brittle to flexible. For microstructure, the sample exhibits corrosion characteristics along the joint surface, intensified corrosion at the edge, etc. The porosity increase rate is 0.6%/d; however, the length–width ratio of the pores is maintained at 1.7–1.85, indicating that the development rate of pores in different directions is similar. The results of this study have enriched the study of the dolomite dissolution mechanism and, in addition, have important reference value for the stability evaluation of tunnel surrounding rock in karst environments.

Failure mechanisms of corroded/non-corroded RC cylinder under axial compressive loading evaluated by AE technique

This study applied the acoustic emission (AE) technique to investigate mechanical behaviors and failure processes of corroded and non-corroded reinforced concrete (RC) cylinders, subjected to compressive loading. RC cylinders with 150 mm diameter and 300 mm height were tested. A set of twelve specimens was arranged into four groups of three specimens. These were the specimens corroded at the initiation stage, at the acceleration stage, at the deterioration stage of rebars, and another group was prepared as non-corroded specimens. The other set of twelve specimen was corroded as the same as the one, but axial rebars were coated with epoxy resin. After performing electrical corrosion, by applying 200 mA current under salt water immersion of 3% chloride concentration, axial compression tests were conducted on all specimens up to failure, using the AE technique. The corrosion of rebars inside the cylinders trends to decrease the compressive load-carrying performance of the RC cylinders, with the occurrence of early damages during the axial compression test. The analysis of the measured AE parameters enabled the classification of the generated damages into shear-type and tensile-type damages, which provided a characteristic signature of the failure mechanism of the tested cylinders. Next, it provided a 3D visualization of the damage events location and evolution inside the cylinders. Then, it gave the means to correlate the damage process of the RC cylinders, with their specific condition related to their corrosion level, prior to the compression test.

Large eddy simulation investigation of flame acceleration and deflagration to detonation transition of methane‐air mixture in rectangular channel

Large eddy simulation is used to simulate flame acceleration and deflagration to detonation transition of methane-air mixtures in a small-scale 3D channel. The simulation results show the changing of the flame surface 3D structure in the stage of flame acceleration and deflagration to detonation transition. In the first stage, the flame velocity increases exponentially because of the expansion of combustion products and the wrinkle of flame surface. In the next stage, the interaction between flame and pressure wave makes flame accelerate continuously, and the acceleration rate of the flame velocity decreases first and then increases. As the pressure of the leading shock increases, the boundary layer is heated by the preheating area in front of the flame surface at the channel wall. Because the cross section of the channel is square, the ultrafast flame first appears in the boundary layer of the four inner edges between the channel wall, then it appears in the boundary layer on the channel wall. The ultrafast flame generates oblique shock waves continuously moving to the center of the channel and colliding with each other, which promote the occurrence of local explosion and the coupling of flame surface and leading shock wave.