Final Speed Research Articles

Could Physics Teachers Also Have Misconceptions on Basic Kinematics?

The role of a physics teacher in learning is to facilitate student activities to construct correct conceptual understanding as that of a scientist. As the primary source of knowledge for students, a physics teacher is required to have the right concept, but this demand is not necessarily fully fulfilled. This study aims to determine the profile of physics teachers’ understanding of concepts on kinematics material detected by a four-tier misconception test. Participants in this study were 20 high school physics teachers in Surabaya. Based on the results of data analysis, it was found that the dominant misconceptions included: (1) Two objects that make the same displacement at the same time interval will have the same velocity, regardless of the type of movement of the two objects (2) Objects that move vertically straight up or down will always have the acceleration of motion equal to the acceleration of gravity which is directed downwards. (3) As long as the object’s position is at positive coordinates, it means the object is moving in the forward direction. (4) The graph of velocity against time, which has a positive gradient, means that the object always moves forward (5) In parabolic motion, the length of time an object is in the air only depends on the length of its path, the longest path will require the longest time. (6) In parabolic motion, the final speed of an object when it lands on the ground depends not only on its initial speed but also on its elevation angle. The findings of several misconceptions above show that even a physics teacher cannot escape misconceptions. Therefore, it is crucial for a teacher to be able to remedy the misconceptions he suffers so that these misconceptions are not transmitted to the students he teaches. This finding is the first step for researchers to detect misconceptions, followed by the application of certain learning methods to remedy misconceptions in future research.

Germination Characteristics and Seedling Growth of <italic>Pseudolysimachion nakaianum</italic> (Ohwi) T. Yamaz. Seeds According to Light Quality Type

Background and objective: This study was conducted to understand the effect of different quality of light-emitting diodes (LED) on the germination characteristics and growth of <i>Pseudolysimachion nakaianum</i>.Methods: The LED light irradiation was divided into white, red, blue, and red:blue (1:1). To investigate the germination characteristics, 30 seeds were placed in a Petri dish in three replicates for 8 days. Average germination rate, germination speed, germination uniformity, and average germination time were measured. To investigate the growth of seedlings, plant height, plant width, leaf length, leaf width, leaf number, fresh weight, dry weight and T/R ratio were examined 6 weeks after sowing, and chlorophyll fluorescence (maximum quantum yield, electron transport rate) was measured.Results: The final germination rate and germination speed were highest at red:blue (1:1) LED irradiation. Regarding growth and chlorophyll fluorescence measurements, red:blue LED showed the best growth results, with no significant difference in Fv/Fm between different types of light quality, and the electron transport rate was the highest under red:blue LED irradiation. Also, total fresh/dry weight and T/R ratio were highest for red:blue LED, it is presumed to promote the biomass of entire plant.Conclusion: The results proved that <i>Pseudolysimachion nakaianum</i> showed red LED conditions promoted germination, but cultivation under red:blue LED conditions is judged to be suitable for seedling growth and photosynthesis.

On the Formation of Coronal Mass Ejection with Low Final Speed

The two limb CMEs considered in this paper differ from the cases of type 1 and type 2 CMEs studied earlier in [1]. At the same time, they noticeably differ from each other in the nature of their formation, which remains not completely clear. It is unusual in the formation of the April 29, 2014 CME that its appearance is associated with the eruption of only a larger part of the magnetic rope. A specific feature of the February 11, 2014 CME is the fact that it already has a very high velocity of motion near the surface of the Sun - about 1300 km/s, which rapidly decreases as it moves away from the Sun. But they are united by the fact that they both have an extremely low final speed of the CME - no more than 350 km / s. The answer to the question of what determines the formation of these slow CMEs (ICMEs for short) is important for further studies of the dynamics and nature of CMEs.

On the control of the final speed for a class of finite-dimensional linear systems: controllability and regulation

On the control of the final speed for a class of finite-dimensional linear systems: controllability and regulation

Predictor–Corrector Guidance for a Hypersonic Morphing Vehicle

In an effort to address the problem of hypersonic morphing vehicles reaching the target while avoiding no-fly zones, an improved predictor–corrector guidance method is proposed. Firstly, the aircraft motion model and the constraint model are established. Then, the basic algorithm is given. The Q-learning method is used to design the attack angle and sweep angle scheme to ensure that the aircraft can fly over low-altitude zones. The B-spline curve is used to determine the locations of flight path points, and the bank angle scheme is designed using the predictor–corrector method, so that the aircraft can avoid high-altitude zones. Next, the Monte Carlo reinforcement learning (MCRL) method is used to improve the predictor–corrector method and a Deep Neural Network (DNN) is used to fit the reward function. The planning method in this paper realizes the use of a variable sweep angle, while the improved method further improves the performance of the trajectory, including the attainment of greater final speed and a smaller turning angle. The simulation results verify the effectiveness of the proposed algorithm.

Faster variational quantum algorithms with quantum kernel-based surrogate models

Abstract We present a new optimization strategy for small-to-intermediate scale variational quantum algorithms (VQAs) on noisy near-term quantum processors which uses a Gaussian process surrogate model equipped with a classically-evaluated quantum kernel. VQAs are typically optimized using gradient-based approaches however these are difficult to implement on current noisy devices, requiring large numbers of objective function evaluations. Our approach shifts this computational burden onto the classical optimizer component of these hybrid algorithms, greatly reducing the number of quantum circuit evaluations required from the quantum processor. We focus on the variational quantum eigensolver (VQE) algorithm and demonstrate numerically that these surrogate models are particularly well suited to the algorithm’s objective function. Next, we apply these models to both noiseless and noisy VQE simulations and show that they exhibit better performance than widely-used classical kernels in terms of final accuracy and convergence speed. Compared to the typically-used stochastic gradient-descent approach to VQAs, our quantum kernel-based approach is found to consistently achieve significantly higher accuracy while requiring less than an order of magnitude fewer quantum circuit executions. We analyze the performance of the quantum kernel-based models in terms of the kernels’ induced feature spaces and explicitly construct their feature maps. Finally, we describe a scheme for approximating the best-performing quantum kernel using a classically-efficient tensor network representation of its input state and so provide a pathway for scaling this strategy to larger systems.

A speed-maximization trajectory optimization model on a reservation-based intersection control system

Cooperative CAV crossing a reservation-based intersection is an integrated control problem that consists of the trajectory modeling and scheduling optimization. In order to achieve the best system performance in the intersection, a final speed is traditionally modeled as large as possible when reaching the intersection in the trajectory modeling level, coupled with a delay-minimization problem. However, the delay optimization problem may not find the best solution in terms of the system efficiency. This paper aims to theoretically justify the best objective function and propose an optimal integrated control model. A speed-maximization trajectory optimization model is proposed based on the queue theory. The optimization model is formulated as a discrete-time mixed integer programming model based on the trajectory analysis. Through extensive numerical simulations with platooning and turning movements, the optimization model achieves better system performance than state-of-the-art methods. The results validate the advantages of maximizing the average speed using the discrete-time trajectory modeling method.

A compound framework incorporating improved outlier detection and correction, VMD, weight-based stacked generalization with enhanced DESMA for multi-step short-term wind speed forecasting

Precise wind speed forecasting contributes to wind power consumption and power grid schedule as well as promotes the implementation of global carbon neutrality policy. However, in existing research, the negative impact of outliers on forecasting models is ignored and the inherent shortcomings of the single predictors have not been taken seriously. Moreover, the intrinsic parameters of predictors are set by manual and empirical methods in some research, leading to difficulties in achieving optimal forecasting performance. To solve the shortcomings of existing research, a multi-step short-term wind speed forecasting framework is proposed by incorporating boxplot-medcouple (MC), variational mode decomposition (VMD), phase space reconstruction (PSR), weight-based stacked generalization with enhanced differential evolution slime mold algorithm (DESMA). Firstly, boxplot-MC is employed to achieve outlier detection and correction for preprocessing original wind speed data by analyzing values and trends. Then, the modified data is further adaptively decomposed into multiple subsequences by VMD, after which each subsequence is constructed into feature matrices through PSR. Subsequently, weight-based multi-model fusion strategy in layer-1 of stacked generalization is proposed to integrate the predicting values acquired by three primary learners, of which the weight coefficients are calculated with the error between actual values and predicting values. After that, kernel extreme learning machine (KELM) in layer-2 of stacked generalization is applied to predict the fusion result to obtain forecasting value corresponding to each subsequence. Meanwhile, an enhanced DESMA based on slime mold algorithm (SMA) and differential evolution (DE) is proposed to calibrate the parameters of KELM. Eventually, the final wind speed forecasting results are attained by summing the prediction values of all subsequences. Furthermore, comparative experiments from different aspects are undertaken on real datasets to ascertain the availability of the proposed framework. The experimental results are clarified as follows: (1) outlier detection and correction employing boxplot-MC is dedicated to analyzing values and trends effectively, with which the negative impact of outliers can be weakened while retaining valid data significantly; (2) VMD can prominently reduce the non-smoothness and volatility of wind speed data; (3) weight-based stacked generalization is conducive to exploiting the advantages of individual primary learners, contributing to compensating for instability; (4) DESMA enhances prediction accuracy by optimizing the parameters of KELM. Additionally, the code has been made available at https://github.com/fyc233/a-multi-step-short-term-wind-speed-forecasting-framework.git.

Study the behaviour of transient elastohydrodynamic lubrication contact at motion start-up in the presence of surface roughness

PurposeThis study aims to present a numerical solution for the analysis of the influence of surface roughness as presented by a sinusoidal ripple of different amplitude and wavelength on the performance of transient elastohydrodynamic lubrication at motion start-up under different operational parameters of entraining speed and load as well as different acceleration rates.Design/methodology/approachA statistical asperity micro-contact model represented by a sinusoidal ripple expressed by two parameters (wavelength and undeformed amplitude) is considered. The ball equation of motion is used to calculate the force on the ball as it starts to move. The time-dependent Reynolds equation is solved together with surface deformation and statistical asperity models using the Newton–Raphson technique with the Gauss–Seidel iteration method.FindingsThe behaviour of the film thickness was found to be strongly influenced by the acceleration rate for different ripple amplitude and wavelength parameters. The effect of increasing the final entraining speed will eventually lead to rapid film thickness build-up and increase the film thickness jump at the moment of motion start-up. The effect of increasing applied load is to reduce the deviation of the minimum film thickness jump at the start-up of motion, making its value approximately equal to the steady-state value over the entire run-time period.Originality/valueInfluence of surface roughness for various wavelength and undeformed amplitude on the performance of transient elastohydrodynamic lubrication at motion start-up is presented at different acceleration rates as well as for different operating parameters of entraining speed and load. Ball equation of motion is used to calculate the force on the ball as it starts to move.

Multi-Step-Ahead Wind Speed Forecast Method Based on Outlier Correction, Optimized Decomposition, and DLinear Model

Precise and dependable wind speed forecasting (WSF) enables operators of wind turbines to make informed decisions and maximize the use of available wind energy. This study proposes a hybrid WSF model based on outlier correction, heuristic algorithms, signal decomposition methods, and DLinear. Specifically, the hybrid model (HI-IVMD-DLinear) comprises the Hampel identifier (HI), the improved variational mode decomposition (IVMD) optimized by grey wolf optimization (GWO), and DLinear. Firstly, outliers in the wind speed sequence are detected and replaced with the HI to mitigate their impact on prediction accuracy. Next, the HI-processed sequence is decomposed into multiple sub-sequences with the IVMD to mitigate the non-stationarity and fluctuations. Finally, each sub-sequence is predicted by the novel DLinear algorithm individually. The predictions are reconstructed to obtain the final wind speed forecast. The HI-IVMD-DLinear is utilized to predict the real historical wind speed sequences from three regions so as to assess its performance. The experimental results reveal the following findings: (a) HI could enhance prediction accuracy and mitigate the adverse effects of outliers; (b) IVMD demonstrates superior decomposition performance; (c) DLinear has great prediction performance and is suited to WSF; and (d) overall, the HI-IVMD-DLinear exhibits superior precision and stability in one-to-four-step-ahead forecasting, highlighting its vast potential for application.

Advanced Electric Propulsion Concepts for Fast Missions to the Outer Solar System and Beyond

Electric Propulsion (EP) comprises all types of space propulsion in which a certain amount of propellant is ionized and then accelerated by electric or magnetic fields, or both. This propulsion technology allows for much higher specific impulses (Isp > 2,000 s) than conventional chemical propulsion (Isp < 500 s), resulting in a major reduction of the propellant mass or a considerably higher final speed for a certain space mission. Hence, EP can enable very challenging space missions as DAWN has clearly shown. Furthermore, an EP system coupled with an advanced nuclear reactor could enable fast manned missions to Mars (one-way travel times less than 4 months). This propulsion technology can be scaled up to even higher specific impulses (Isp > 5,000s). However, the power needed for the same thrust is also increasing. An Oberth maneuver performed very close to the Sun could provide the additional power to a high-Isp Solar Electric Propulsion (SEP) system in order to reach the needed delta-v for challenging interstellar precursor missions. A breakthrough in power source specific mass is needed in order to enable missions with ultra-high specific impulses (> 10,000 s); this breakthrough could be realized having the power source not on board, as with Laser-powered Electric Propulsion (LEP), where the needed power is beamed to the spacecraft from an external laser source. In this case the on-board power source is limited to a light-weight photovoltaic receiver/converter. The development of ultra-high Isp ion thrusters powered by an external laser source could enable the most challenging interstellar precursor missions up to the Oort Cloud and beyond. This paper gives an update on the status of these advanced propulsion concepts, and provides some examples of interstellar precursor missions enabled by advanced EP systems which could be launched before 2040. Keywords: Interstellar, Electric Propulsion, Oberth, Laser

P102: Hemodynamic Ramp Studies in Continuous Flow Ventricular Assist Device in Fontan Patients: A Case Series

Purpose: There is limited experience in patients with single ventricle physiology using the Heartmate III (HM3). With a growing population of failing Fontan patients and long wait times for cardiac transplantation, the need for an appropriate strategy for durable mechanical support is increasing. Determination of the best strategies to optimize the HM3 device in Fontan circulation has not yet been elucidated. Methods: A retrospective case series of three patients with failing Fontan on VAD who underwent ramp studies by cardiac catheterization were reviewed with the intent of optimizing hemodynamics. Results: All patients had hypoplastic left heart syndrome, completed Fontan, and were on durable VAD. Patient 1 was a 19y male on a Heartware at 2640 rpm. Initial hemodynamics with a PCWP of 25 mmHg and Fontan pressure of 25 mmHg. Increase in RPM to 2900 bpm showed no change in Fontan pressure and decrease in PCWP to 20 mmHg. No change on adjustment back to 2700 RPM though improvement noted in tricuspid regurgitation in echocardiogram. Patient 2 was a 13y male on HM 3 at 5000 rpm with PCWP 15 mmHg and Fontan 19 mmHg. Tricuspid regurgitation on echocardiogram improved from moderate to mild and final VAD speed was 5200 RPM. Patient 3 was a 12y male on HM3 at 5100 rpm with PCWP of 15 mmHg and Fontan 18 mmHg. Increase up to 5500 RPM with no change in PCWP and Fontan at 17mmHg. Final speed at 5200 RPM with PCWP of 14mmHg and Fontan 17 mmHg. Conclusions: Significant hemodynamic changes on catheterization ramp study were not found. Increase in support from the VAD was made due to clinical indications and echocardiographic assessment of atrioventricular valve regurgitation. Hemodynamic data was useful in reassuring that changes made to the device were not detrimental to the patient. Further data on ramp studies and indications for changes in device speed will be useful in the care of these patients.

Downscaling wind speed based on coupled environmental factors and machine learning

AbstractWind speed changes impact society and have important implications for climate change studies. Thus, high‐resolution and high‐quality wind speed datasets are necessary for environmental monitoring and ecosystem research. However, there is no complete set of high spatial and temporal resolution wind speed datasets for China. Additionally, it is extremely challenging to produce wind speed data at high spatial and temporal resolution for large‐scale regions with diverse climate types and complex topographies, such as China. In this study, we used multisource remote sensing images, obtained data on various environmental factors through the Google Earth Engine and Evapotranspiration (ET) Watch Cloud platforms, and combined machine learning algorithms to downscale the ERA5 reanalysis wind speed data, and finally obtained the daily wind speed datasets with 1 km spatial resolution for China in 2015. To verify the accuracy of the model and data products, we selected several metrics to evaluate in conjunction with the actual site observed data. The results show that the multifactor combination model of artificial neural network combining land surface temperature, sunshine durations and roughness factors outperforms a single‐factor combination model, and the results were in good agreement with the original data (R2 of 0.95 and RMSE of 0.40 m·s−1). The final wind speed data products were also in good agreement with the observed meteorological data (R2 range of 0.86–0.95 and RMSE range of 0.33–0.44 m·s−1); moreover, the accuracy and precision were greatly improved over the original data. This study provided a dataset that has potential applications in future climate change and ecosystem studies.

Physiological quality of Capsicum chinense 'Adjuma' seeds during development

Once “bode” pepper plants (Capsicum) have continuous development and fructification, it is not possible to determine a specific season for seed physiologic maturation and harvest. This research aimed to evaluate physiological quality of “bode” pepper (Capsicum chinense 'Adjuma’) during fruit development and enzymes expression on seed germination. Manually extracted seeds were submitted to physiological tests being evaluated germination at first count (FC), final (G), and germination speed index (GSI), additionally, enzymatic analyses were carried. The lowest values for the physiological tests were observed for initial development stages. The greatest for FC, G and IVG were observed for seeds from fruits 70 days after anthesis (DAA). Superoxide dismutase enzyme has the highest values on seeds harvested at 49 DAA while malate dehydrogenase has more expression at 70 DAA. Catalase, alcohol dehydrogenase, and esterase have the higher expression at 63 DAA. The maturation stage influences bode pepper seed physiological quality, being seeds harvested at 70 DAA those with the better results on the evaluated parameters, thus, considered physiologically mature and the indicated time for harvest.

Knowledge Transfer Genetic Programming With Auxiliary Population for Solving Uncertain Capacitated Arc Routing Problem

The uncertain capacitated arc routing problem (UCARP) is an NP-hard combinatorial optimization problem with a wide range of applications in logistics domains. Genetic programming (GP) hyper-heuristic has been successfully applied to evolve routing policies to effectively handle the uncertain environment in this problem. The real world usually encounters different but related instances due to events, such as season change and vehicle breakdowns, and it is desirable to transfer knowledge gained from solving one instance to help solve another related one. However, the solutions found by the GP process can lack diversity, and the existing methods use the transferred knowledge mainly during initialization. Thus, they cannot sufficiently handle the change from the source to the target instance. To address this issue, we develop a novel knowledge transfer GP with an auxiliary population. In addition to the main population for the target instance, we initialize an auxiliary population using the transferred knowledge and evolve it alongside the main population. We develop a novel scheme to carefully exchange the knowledge between the two populations, and a surrogate model to evaluate the auxiliary population efficiently. The experimental results confirm that the proposed method performed significantly better than the state-of-the-art GP approaches for a wide range of uncertain arc routing instances, in terms of both final performance and convergence speed.

Assessment and Non-Destructive Evaluation of the Influence of Residual Solvent on a Two-Part Epoxy-Based Adhesive Using Ultrasonics

Polymers are increasingly being used in higher demanding applications due to their ability to tailor the properties of structures while allowing for a weight and cost reduction. Solvents play an important role in the manufacture of polymeric structures since they allow for a reduction in the polymer’s viscosity or assist with the dispersion of fillers into the polymer matrix. However, the incorrect removal of the solvent affects both the physical and chemical properties of polymeric materials. The presence of residual solvent can also negatively affect the curing kinetics and the final quality of polymers. Destructive testing is mainly performed to characterize the properties of these materials. However, this type of testing involves using lab-type equipment that cannot be taken in-field to perform in situ testing and requires a specific sample preparation. Here, a method is presented to non-destructively evaluate the curing process and final viscoelastic properties of polymeric materials using ultrasonics. In this study, changes in longitudinal sound speed were detected during the curing of an aerospace epoxy adhesive as a result of variations in polymer chemistry. To simulate the presence of residual solvent, samples containing different weight percentages of isopropyl alcohol were manufactured and tested using ultrasonics. Thermogravimetric analysis was used to show changes in the decomposition of the adhesive due to the presence of IPA within the polymer structure. Adding 2, 4, and 6 wt.% of IPA decreased the adhesive’s lap shear strength by 40, 58, and 71%, respectively. Ultrasonics were used to show how the solvent influenced the curing process and the final sound speed of the adhesive. Young’s modulus and Poisson’s ratio were determined using both the longitudinal and shear sound speeds of the adhesive. Using ultrasonics has the potential to non-invasively characterize the quality of polymers in both an in-field and manufacturing settings, ensuring their reliability during use in demanding applications.

Condition Indicator Developed for All-Metal Progressing Cavity Pumps

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 209763, “Development of an All-Metal Progressing-Cavity-Pump Condition Indicator,” by John W. Sheldon, SPE, C-FER Technologies; Justin MacDonald, SPE, Athabasca Oil; and Evan Noble, SPE, Technical Consultant, et al. The paper has not been peer reviewed. _ All-metal progressing cavity pumps (AMPCPs) are frequently used in oil and gas applications to produce high temperature fluids to surface but can exhibit accelerated wear during operation that results in decreasing volumetric efficiency over the pump’s life. In the complete paper, the authors present a proposed condition indicator that estimates the wear experienced by an AMPCP at any point in operation and takes into consideration the potential effects of downhole operating conditions. The proposed condition indicator also can be extrapolated into the future and used to estimate the potential remaining useful life (RUL) of an AMPCP. Introduction AMPCPs are composed of a metal stator and rotor, which enables them to operate in much higher temperature fluids compared with standard elastomeric PCPs. Because of metal-on-metal contact between the stator and rotor, AMPCPs typically experience more accelerated wear than elastomeric PCPs, resulting in reduced pump efficiency and shorter overall pump life. While decreasing pump efficiency can be a result of pump wear, it also can be caused by changes in operating conditions, such as increasing pump differential pressure or decreasing pump speed. For this reason, when estimating the state or condition of an AMPCP, pump efficiency alone may be a misleading or imperfect indicator. This paper expands on previous work in the literature by developing a condition indicator that can be used over the course of pump operation to diagnose pump-upset events or estimate the RUL of the AMPCP. Estimating Pump Wear Currently, no method exists of directly measuring the wear on the stator and rotor during operation. Earlier researchers proposed an indirect means of measuring stator and rotor wear based on the degradation of the pump-performance curve over time. The following calculation process is used to estimate the degradation in pump performance relative to a comparatively higher performing reference pump at any point in production. The estimate of pump performance is provided in the form of a pump-wear index (PWI). 1. A reference pump-performance curve is first selected and plotted. This pump-performance curve should correspond to a substantially more efficient pump and allow comparison of the performance of different actual operating pumps. The reference pump-performance curve selected by the authors in the complete paper reflects an operating speed of 200 rev/min. 2. The reference pump-performance curve then is shifted using an equation provided in the complete paper to be the performance curve for the reference pump running at the speed of the actual operating pump. The equation is derived using the assumption that pump slippage is independent of pump speed. The newly shifted reference pump-performance curve is calculated using a corresponding pump speed of 150 rev/min. 3. The volumetric efficiency of the actual operating pump is then plotted based on the pump’s actual operating differential pressure. 4. The degradation in pump performance, also referred to as the PWI, is then calculated as the ratio of the final reference pump speed to the actual operating pump speed. Thereafter, this procedure is then conducted for each production data point over the course of a pump’s time in operation.

High performance laser-driven flyers based on a refractory metamaterial perfect absorber.

Laser-driven flyers (LDFs), which can drive metal particles to ultra-high speeds by feeding high-power laser, have been widely used in many fields, such as ignition, space debris simulation, and dynamic high-pressure physics. However, the low energy-utilization efficiency of the ablating layer hinders the development of LDF devices towards low power consumption and miniaturization. Herein, we design and experimentally demonstrate a high-performance LDF based on the refractory metamaterial perfect absorber (RMPA). The RMPA consists by a layer of TiN nano-triangular array, a dielectric layer and a layer of TiN thin film, and is realized by combing the vacuum electron beam deposition and colloid-sphere self-assembled techniques. RMPA can greatly improve the absorptivity of the ablating layer to about 95%, which is comparable to the metal absorbers, but obviously larger than that of the normal Al foil (∼10%). This high-performance RMPA brings a maximum electron temperature of ∼7500 K at ∼0.5 µs and a maximum electron density of ∼1.04 × 1016 cm-3 at ∼1 µs, which are higher than that the LDFs based on normal Al foil and metal absorbers due to the robust structure of RMPA under high-temperature. The final speed of the RMPA-improved LDFs reaches to about 1920 m/s measured by the photonic Doppler velocimetry system, which is about 1.32 times larger than the Ag and Au absorber-improved LDFs, and about 1.74times larger than the normal Al foil LDFs under the same condition. This highest speed unambiguously brings a deepest hole on the Teflon slab surface during the impact experiments. The electromagnetic properties of RMPA, transient speed and accelerated speed, transient electron temperature and density have been systematically investigated in this work.

In-Field Recording of Six Biaxial Angles and Plantar Pressures in Weightlifting through a Wearable System.

Monitoring and evaluation of the techniques used in weightlifting are based on the subjective observation of the coach, which can ignore important aspects of short duration. This study aimed to implement an embedded system to register the angular variation of the hip, knee, and ankle joints, and plantar pressure during training. Four professional and four amateur athletes performed five snatch lifts. To evaluate the angular measurement, the tests were simultaneously videotaped and the results were contrasted. The angular data presented a correlation coefficient of 0.92 and a delay of 495 ± 200 ms. The characterization of the sensors was implemented in a microcontroller with a mean absolute percentage error of 18.8% in the measurements. When comparing the average results between the elite and amateur groups, the amateur group performed a delayed descent in the first three phases of the lift and an accelerated descent in the fourth phase. A not uniform plantar pressure was registered in the same group, causing a reduction in the final speed of recovery with the barbell. The proposed system has been developed for biaxial angular registration of hip, knee, ankle, and plantar pressure during weightlifting snatch. The option to contrast between signals presented by the system met the requirements requested by the coaching staff and is seen as a promising quantitative analysis tool to support the coach and the athlete.

Research on Start-Stop Performance of Journal Bearing Based on an Isothermal and Mixed Lubrication Model With Different Acceleration and Deceleration Forms in Consideration

Abstract In order to explore the influence of different acceleration and deceleration forms on the bearing performance during acceleration and deceleration, an isothermal and mixed lubrication model for journal bearings was established. In this model, the fluid mechanics was solved by the Reynolds equation with mass conservation boundary condition, while the contact mechanics was predicted by Greenwood and Tripp (GT) contact model. By the developed model and using different functions of the shaft speed, the start-stop performances of the journal-bearing system under different acceleration scenarios were analyzed. The effects of working conditions, lubrication oil temperature, and bearing structure parameters on the start-stop performance of the journal-bearing system were studied. It was found that the larger starting acceleration can help the journal-bearing system enter the hydrodynamic lubrication faster in the acceleration phase. In the deceleration phase, slow deceleration helps the journal-bearing system maintain hydrodynamic lubrication for a longer time. The higher final speed, lower lubrication oil temperature, and lower bearing clearance can make the journal-bearing system have a better performance in the start-stop process.