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Transverse galloping is a type of flow-induced vibration (FIV) that leads to critical design considerations for engineering structures. A purely nonlinear energy sink (NES) composed of a ball free to rotate in a circular track experimentally mitigated the galloping of a square in a previous study. The current study introduces a model for simulating the dynamics of the square prism coupled with a ball-in-track (BIT) NES and predicting the system behaviour at high flow speeds beyond the limits of the previously presented experiments. Numerical simulations employ the fitting of experimental data as inputs to define parameters. Wind tunnel static experiments provide the galloping force coefficient [[EQUATION]] relative to the prism angle of attack. Additionally, free rotation tests allow evaluating the ball damping coefficient [[EQUATION]] as a function of its mass and the NES track radius. The result of the rotation tests provides a critical angular speed beyond which the ball damping increases non-linearly. We point out the damping variation as an advantage of the BIT-NES; less damping at low angular velocities helps the ball start its rotation, while relatively large damping at higher speeds dissipates more energy from the vibrating system. Numerical results exhibit four response modes for the NES; oscillatory at low flow speeds, intermittent within a small range of higher flow speeds, rotational at higher flow speeds, and ineffective regime at flow speeds out of the NES effective range. Modelling the primary mass as a parametric excitation source for the NES provides an analytical estimation of the boundary between the oscillatory and intermittent regimes. Furthermore, we advance an analytical analysis of the power flow across the integrated prism-NES system to explain the NES behaviour and predict the limit of its effective range.

Various working conditions and bearing structures make remaining useful life (RUL) prediction more challenging. This paper presents a new intermediate domain support vector machine (SVM)-based transfer model for rolling bearing RUL prediction. This transfer model aims to solve the problem when the source degradation indexes are too poor to be applied by introducing the new intermediate domain. At first, high-quality feature degradation indexes are selected using the joint evaluation index and the principal component analysis (PCA) algorithm. Then, a maximum correlated kurtosis de-convolution (MCKD) algorithm is carried out to obtain the demarcation point between healthy and degradation stages. After selecting high quality domain, the objective function of intermediate domain SVM is designed, based on classical domain independent SVM, to optimize source to intermediate and intermediate to target transfer processes simultaneously. Finally, experiments using both ball and conical bearing datasets indicate that the proposed method has higher RUL prediction performance than existing models, which proves the advantage of multi-optimization transfer learning.

Ball-end milling cutters are one of the most widely used cutters in the automotive, aerospace, die and machine parts industries. In addition, milling chatter will reduce the surface quality and production efficiency, resulting in noise. It is particularly important to model the cutting force and analyze the flutter stability of ball-end milling cutters. In this paper, a simplified milling force model of ball-end milling cutter with three degrees of freedom was established based on Merchant bevel cutting theory. The model simplified the milling force coefficient. The expressions of instantaneous milling area considering the vibration displacements in X, Y and Z directions were derived. The nonlinear dynamic cutting force model of ball-end milling cutter with three degrees of freedom was established. The nonlinear chatter vibration mechanical model of ball-end milling cutter with three degrees of freedom was established by introducing the time delay term, the stability analysis is carried out by time domain simulation. The proposed models were experimentally verified.

Surface texture is critical to the functionality of the industrial parts. This work aims at effectively controlling the surface texture by applying the phase difference angle between adjacent passes using 5-axis ball-end milling. Because the texture pattern is complicated and formed by the combination of feed-interval and step-interval scallops, we proposed a level-contour-based fast simulation method to effectively generate the surface texture by inputting the phase difference angle with tilt and lead angles of the cutter. After clarifying the influence of these three parameters on the texture pattern, controlling on desired texture is conducted by modifying the tool path according to the simulated phase difference angle. As result, milled surface texture received a good correspondence with the simulation. Details of the cutting features are efficiently and comprehensively simulated. The mechanism underlying the sudden change of texture ridge direction is clarified as the major-minor ridge transition when phase difference angle increases to a certain level, wherein the surface roughness can be decreased because the rearrangement of the cutting region reduced the scallop height. Proposed fast simulation method is also put into the optimization process with case study to show the benefits it can bring to the surface texture design and control.

The aim of this study is to analyse the corner kicks taken in the matches played in the FIFA 2018 World Cup. A total of 606 corner kicks that were used in 64 matches in the competitions were analysed. The data were analysed in terms of the parameters of the direction in which the corner kick is taken (right, left), the time interval in which the corner kick is taken (1-15, 16-30, 31-45, 46-60, 61-75, 76-90), the region where the ball falls in the penalty area (1 st , 2 nd , 3 rd , 4 th , 5 th , 6 th .), the player whom the ball meets in the penalty area (goalkeeper, defender, striker), the body part which contacts the ball (head, foot, hand), attack result (goal, out, corner kick, clearing the ball, goalkeeping) and the body part with which the goals are scored (head, foot). The results indicated that in FIFA 2018 World Cup competitions, the right and left corner kicks were almost evenly distributed, but unlike previous matches, the corner kicks were taken from the left between the 16 th and the 30 th minutes, and from the right between the 61 st and the 75 th minutes. Contrary to the previous World Cups, it was found that fewer corner kicks were taken by spreading the game to both wings, the time interval changed in the search for goals from corner kicks, the target area was used predominantly, and the attacking players stood out compared to the defence players, and an equal number of goals were scored with the head and foot.

In the past, most of the Population Balance Model-based ball mill scale-up studies were carried out using a mono-size ball charge and a single size fraction of the particulate material as the starting feed. It was reported that the breakage distribution parameters were independent of the mill diameter, specific breakage rate parameters varied with mill diameter as Dγ, and the mill diameter exponent γ was independent of particle size. However, in the industrial grinding operations, we have significantly broad size distributions for both the grinding media and the particulate contents of the mill. Therefore, experimental data generated under these conditions were taken from the literature and analyzed. These data pertain to the dry and wet batch grinding of limestone, quartz, and ores of vanadium and pyrochlore. Our analysis of the data showed that in contrast to the findings of the earlier researchers, the breakage distribution parameters were not independent of the mill diameter, and the value of γ for the specific breakage rate parameters varied with particle size in the case of multicomponent ores. Because of these complications, a single parameter, the specific rate of production of material that is finer than a specified size, was used as the basis for scale-up. It was found that the value of the mill diameter scale-up factor varied quite significantly with the breakage properties of the material, the size distribution of the particulate contents of the mill, the size of the desired product, and the mode of grinding (dry/wet). Therefore, ball mill scale-up models presently available need to be modified in light of these new findings.

A pilot-scale grinding technology of ceramic medium stirred mill was proposed in this study. Based on the specific productivity and grinding efficiency, the appropriate grinding parameters were ascertained as follows: material ball ratio of 0.7, ceramic ball medium size ratio (10 mm: 15 mm: 20 mm = 3:2:5), stirring speed of 110 rpm, grinding concentration of 50%, and medium filling rate of 90%. The stable running experiment was operated for 36 h at the optimum grinding parameters, and the iron concentrate grade 65.01% and iron recovery 89.29% were obtained after two stages magnetic separations when the content of −0.043 mm was 81.50%. Mineral liberation analyser (MLA) suggested that the liberation of iron from gangue was through grinding in the ceramic-medium stirred mill. Four NEUM-850 ceramic-medium stirred mills superseded the ball mills of second and third stage in the Aoshan concentrator, and the grinding unit consumption decreased by 48.38%.

In this paper, we propose a Wasserstein metric- based random path planning algorithm. Wasserstein Safe RRT (W-Safe RRT) provides finite-sample probabilistic guarantees on the safety of a returned path in an uncertain obstacle environment. Vehicle and obstacle states are modeled as distributions based upon state and model observations. We define limits on distributional sampling error so the Wasserstein distance between a vehicle state distribution and obstacle distributions can be bounded. This enables the algorithm to return safe paths with a confidence bound through combining finite sampling error bounds with calculations of the Wasserstein distance between discrete distributions. W-Safe RRT is compared against a baseline minimum encompassing ball algorithm, which ensures balls that minimally encompass discrete state and obstacle distributions do not overlap. The improved performance is verified in a 3D environment using single, multi, and rotating non-convex obstacle cases, with and without forced obstacle error in adversarial directions, showing that W-Safe RRT can handle poorly modeled complex environments.

The performance of ball screws degrades with two-stage features due to the deteriorating inner mechanism and environmental stress, which lowers the positioning accuracy of the ball screws. It thus affects the accuracy of computer numerical control machine tools. However, no research has been carried out on the degradation reliability for ball screws and current studies usually treat the performance degradation of ball screws as a deterministic, single-stage degradation process, ignoring the randomness and two-stage features in the degradation progress. To this end, we firstly formulated a framework of degradation reliability for ball screws, and then established a two-stage performance degradation model with eight unknown parameters. To estimate the unknown parameters, we proposed a two-phase, expectation-maximization estimation method. Finally, we established a degradation reliability model based on the degradation test data and validated the model through experimental data, which shows the model can capture the real-degradation behavior of ball screws.

The morphology evolution of copper powder was studied under various ball-milling experimental conditions, such as low and high rotation speeds and a ball diameter of 1 mm and 10 mm. A scanning electron microscope and X-ray diffractometer were used to analyze the copper powder particle size, morphology, structure, and crystallite size. The effect of ball size on copper powder particle morphology in dry-type milling was studied using a planetary ball mill. Spherical copper powders were obtained by ball milling at a high rotation speed and with a ball diameter of 1 mm. The experimental results suggest that the particle size and morphology can be controlled by changing the milling conditions during the ball milling. Ball motion was simulated by using a three-dimensional discrete-element model to obtain the force, energy, and power of the ball motion in the ball mill for two different ball sizes and low and high rotation speeds.

We investigated gaze behavior of expert goalkeepers during the prediction of penalty kicks in different spatiotemporal constraints: penalties taken from 11 and 6 m. From 11 m, goalkeepers were more successful in predicting ball direction, with longer movement time initiation and a visual strategy with more fixations and greater saccade rates than penalties from 6 m, where they exhibited fewer fixations with higher microsaccade rates. As long as the opponent’s distance is large and time pressure low, gaze can be frequently shifted between the kicker’s body and the ball, due to the low cost of saccades. Conversely, when the objects are close, there is increased reliance on foveal and parafoveal information. In conclusion, when the spatiotemporal constraint is less severe, goalkeepers adopt a visual strategy with more fixations and small saccades. When the spatiotemporal constraint is more severe, they rely on peripheral vision to monitor kickers’ movements through the use of microsaccades.

Scholars have highlighted executive attention as a vital organizational resource. However, as prior studies have examined different facets of attention, a theoretical tension has emerged as to whet...

Fe-Si/MnO-SiO2 soft magnetic composites (SMCs) are prepared by sintering ball milled Fe-Si/MnO2 core–shell structured composites. The correlation between the coating uniformity and electromagnetic properties have been investigated via adjusting ball milling parameters in detail. The results indicate that uniform MnO2 coating can be transformed into MnO-SiO2 composite coatings with high insulation due to the high temperature reaction between MnO2 and Si. Agate ball is more effective than stainless steel ball to improve the uniformity of MnO2 coating as well as the electromagnetic properties such as significantly higher resistivity, lower core loss and better frequency stability of permeability. Moreover, increasing the ball milling time from 4 h to 24 h can obviously improve the coating uniformity and thus result in the remarkable increase of the resistivity from 2.4 mΩ·cm to 356.9 mΩ·cm. And the core loss and dynamic loss decrease rapidly while the Ms shows a slight decline. When the ball milling time reaches 24 h, the Fe-Si SMCs exhibits superior magnetic properties such as high Ms (181.0 emu/g), very low core loss (361.5 kW/m3 at 100 kHz) and good frequency stability of permeability (65) from 50 Hz to 1000 kHz.

We consider functionals given by the sum of the perimeter and the double integral of some kernel g : ℝ N × ℝ N → ℝ + {g:\mathbb{R}^{N}\times\mathbb{R}^{N}\to\mathbb{R}^{+}} , multiplied by a “mass parameter” ε. We show that, whenever g is admissible, radial and decreasing, the unique minimizer of this functional among sets of given volume is the ball as soon as ε ≪ 1 {\varepsilon\ll 1} .

Milling is widely used as a versatile, highly automated manufacturing process. The selection of tool and its machining conditions is an ever-present challenge inherent in the process. To provide some findings contributable for the process planning, this study focuses on ball and filleted end milling. After the path interval determinations were explained briefly, the characteristics of each procedure were revealed with experimental verifications. The results of computational procedures showed good agreement with the experimental ones. Then, predominant frictional distance and cutting speed were proposed for effective selection of machining conditions. The discussion was given based on the results obtained from the demonstrations. Moreover, the relationships to path interval were elucidated through the discussion. In conclusion, several outcomes were organized from the experimental and numerical evidences.

When dealing with post-processing steps of additively manufactured parts, the issue of the surface finishing of freeform surfaces has to be addressed. The flexibility of ball end milling makes this machining operation particularly suitable to finish such parts. However, literature records dealing with this kind of cutting operation on additively manufactured alloys are very scarce. The microstructural anisotropy induced by the additive manufacturing process may influence the machinability of a metal alloy such produced, distinguishing it from the same alloy conventionally fabricated. At present, there is no thorough understanding of the influence of additively built component anisotropy on ball end milling operations, resulting in the unpredictability of the part behavior once machined. In this work, ball end milling was carried out on both additively and conventionally manufactured Ti6Al4V alloy workpieces characterized by an inclination angle of 15°, 45°, and 75°. For the first time, the impact of the peculiar microstructural features induced by additive manufacturing was studied in ball end milling operations with different tool paths orientations. The interpretation of the results was helped by the comparison with the wrought alloy. The machinability was assessed in terms of cutting forces, surface topography, surface defects, and chip morphology. The results demonstrated that the additively manufactured alloy allowed for better machinability than the wrought one only when the cutting edge was parallel to the α phase colonies within the prior β grains, thus favoring the material removal by locally decreasing the material resistance to cutting.

The paper presents the first attempt to compare two short stories – Anna in the Neck by Anton Chekhov and a well-known short story by the Greek author Emmanuel Roidis Psychology of a Husband from Syros. Both texts were published at the same time (in 1895) and are considered to be masterpieces. The initial motivation for such textual analysis became almost a complete coincidence between the plots of the two stories. A series of telling coincidences and contradictions observed between the analyzed stories require some kind of explanation which will allow us to view both texts from the different angle. The paper aims to determine the correlation between the writers’ biographies and the personality traits with the characteristics of the protagonists and the style of story telling.

Distribution power flow (DPF) and distribution generation (DG) placement are important problems in modern distribution systems (DSs). The DPF problem is modelled as an optimization problem of minimizing the node power mismatches, while considering the corrections of node voltages as solution variables. The node locations and DG ratings of DG placement (DGP) problem are considered as optimization parameters with an objective of minimizing the network loss (NL). The soccer game optimization (SGO) models the movements of soccer game players by "move-off" and "move-forward" phases, and has the drawback of performing simple arithmetic average for representing random stochastic movements of players during its "move-forward" phase. This paper endeavours to first remodel the move-forward phase by adapting Levy Flight mechanism to simulate the random jumping action of players to a long distance in getting the ball and scoring a goal, and then develop new modified SGO (MSGO) based methods for solving the formulated DPF and DGP problems. The simulation study exhibited that the proposed DPF method is 751 and 666 times faster than the NR PF technique and the DGP method is able to save the NL by 65% and 69% for 33 and 69 node systems respectively.

New results about the influence of a small iron borided layer (~ 36 µm) obtained by the powder-pack boriding process (PPBP) and diffusion annealing post-process (DAP) were evaluated. Dry sliding wear tests on PPBP, PPBP + DAP and untreated AISI 1018 steel were performed under the pin-on-disc configuration, and balls of Al2O3 and WC were used as a counterpart at different sliding distances. Also, the contact pressures of the layer/substrate system were evaluated using the finite element model with the aid of the ABAQUS software. The results showed that the Al2O3 ball presented the major coupling (ball-disc), and the PPBP + DAP reduces the specific wear rate around ~ 304 times related to the untreated AISI 1018 steel to 500 m under severe sliding conditions.

In this study, residual stresses of cold-forged ball studs were investigated by the contour method with using widely available wire-Electro-Discharging Machine (wire-EDM) and Coordinate Measuring Machine (CMM). After the wire-EDM cutting, one of the steps of the contour method, it was revealed that the surface contour data was affected from the cutting step. Therefore, to increase the accuracy of the measured residual stresses, one of the ball studs were heat-treated to normalize residual stresses due to cold forging. The contour data of the heat-treated sample was subtracted from the as-forged surface contour to eliminate any cutting-induced artefacts. The final residual stress profiles suggested that the subtracting procedure minimized the cutting errors. In addition, a new classification approach for the cutting-induced errors for the contour method was introduced. According to final stress maps obtained by the contour method, it was revealed that high compressive residual stresses were obtained at the socket regions of the ball studs, as expected. Balancing tensile residual stresses were observed at the inner regions.

Ball end magnetorheological finishing (BEMRF) is a process employed for precision finishing of flattened, intricate form complex 3D surfaces up to the nano level. Roughness of a surface determines ...

Ball-rolling dung beetles shape a portion of dung into a ball and roll it away from the dung pile for later burial and consumption. These beetles perform dances (rotations and pauses) atop their dung balls in order to choose an initial rolling direction and to correct their rolling direction (reorient). Previous mathematical modeling showed that dung beetles can use reorientation to move away from the dung pile more efficiently. In this work, we study if reorientation can help beetles avoid competition (i.e., avoid having their dung balls captured), and if so, under what circumstances? This is investigated by implementing a model with two different type of beetles, a roller with a dung ball and a searcher which seeks to capture that dung ball. We show that reorientation can help rollers avoid searchers in a wide range of conditions, but that there are some circumstances in which rolling without reorienting can be a beetle's optimal strategy. We also show that rollers can minimize the probability that their dung ball is captured without making precise measurements of the time interval between dances or the angular deviation for dances.

RoboCup is one of the greatest human endeavors to operationalize research in the field of robotics and artificial intelligence. RoboCup soccer simulation 3D (RoboCup3D) competition provide a great opportunity to work with humanoid robots without the need for hardware. One of the most important goals of the teams participating in RoboCup3D league is the ability to increase the number of shoots. The reason for this importance is that superiority over the opponent requires a powerful and precise shoot. The methods introduced for shooting so far are mostly based on Inverse Kinematics (IK) and point analysis. The assumption of these methods is that the positions of the robot and the ball is fixed. However, this is not always the case for shooting. In this paper, a shooting strategy is presented for situations where the robot is walking. Here, a curved path is designed to movement the robot towards the ball so that the robot will eventually have an optimal position to shoot. In general, the vision preceptor in RoboCup3D has noise. Hence, robot movement parameters such as speed and angle are more precisely adjusted by the Q-learning algorithm. Finally, when the robot is in the optimal position relative to the ball and the goal, the IK module is applied to the shooting strategy. Simulations and experiments prove the superiority of the proposed algorithm compared to most teams in RoboCupSoccer and Iran’s Open RoboCup3D leagues.

Background: Stress ball is a new favourite gadget people like to use to fight stress, reduce tension. But there are not many scientific reports on the benefits of stress ball exercises. Objective: the present study aimed to investigate the level of stress among student population and the effectiveness of the use of stress ball exercises among student population. Methods: A cross sectional study was conducted through a convenience sampling method. The participants were administered with a self developed questionnaire consisting of 17 questions. The responses were collected using google forms. Descriptive statistics, frequency analysis and chi square test was used to analyze the data. Results: Males are more stressed than female in college environment and after stress ball exercise students feels reduced irritability and nervousness thus using stress ball exercise during stress management is more significant. Conclusion: The study concluded an innovative finding that Majority of the student population were stressed due to academic reasons and respondents feel that stress ball users showed a satisfactory recovery from their stress.

In order to improve the machining quality and efficiency and optimize NC machining programming, based on the existing cutting force models for ball-end, a cutting force prediction model of free-form surface for ball-end was established. By analyzing the force of the system during the cutting process, we obtained the expression equation of the instantaneous undeformed chip thickness during the milling process and then determined the rule of the influence of the lead angle and the tilt angle on the instantaneous undeformed chip thickness. It was judged whether the cutter edge microelement is involved in cutting, and the algorithm flow chart is given. After that, the cutting force prediction model of free-form surface for ball-end and pseudocodes for cutting force prediction were given. MATLAB was used to simulate the prediction force model. Finally, through the comparative analysis experiment of the measured cutting force and the simulated cutting force, the experimental results are basically consistent with the theoretical prediction results, which proves that the model established in this paper can accurately predict the change of the cutting force of the ball-end cutter in the process of milling free-form surface, and the error of the cutting force prediction model established in this paper is reduced by 15% compared with the traditional cutting force prediction model.

Augmented Human (AH) is a research field enhancing human physical abilities or supporting human activity using advanced technologies. As one of the AH approaches, previous studies have attached an actuator to a human body or tools used for an activity. The attached actuators are used to control their movements to support an activity. In this study, instead of attaching actuators, we propose to directly apply noncontact ultrasound force to a lightweight tool to manipulate it. The advantage of using noncontact force is that users do not need to wear a specific device and to process tools used for the activity. As a proof-of-concept system, we developed an ultrasound-based curveball system by which table tennis players can shoot a curveball regardless of their physical ability. In the system, a moving ping-pong ball (PPB) is a target tool for remote manipulation. The system curves the trajectory of a moving PPB by continuously focusing ultrasound on it. Users can control the curve timing and the curve direction (left or right) using a racket-shaped controller. In the user study, we conducted an actual table tennis match using the curveball system and qualitatively confirmed that the player using the system had the upper hand. Another user study using a ball dispenser quantitatively showed that the ultrasound-driven curveball increased the number of mistakes of the opponent player 2.95 times. These results indicate that the proposed concept is feasible.

The performance and durability of orthopedic implants are mainly determined by their surface integrity. Ball burnishing (BB) is a kind of finishing treatment which improves the surface dependant mechanical properties of metallic biomaterials. In this work, this process was applied on the flat surface of 316L stainless steel to enhance its microhardness and wear resistance. The mathematical modeling of microhardness Vickers was performed by the response surface method (RSM) based on Box–Behnken plans, and the optimum regime was applied under several passes to investigate the effect of number of passes (i) on the surface properties. The evolution of microhardness, nano-hardness and elastic modulus was then examined. Wear resistance, in terms of variation of Coefficient of friction and wear loss, was also investigated. Finally, XRD analysis was performed to evaluate any change in structure produced by BB. The results show that burnishing treatment permits to raise the microhardness by up to 38.3% and to reduce the wear loss by up to 65.2%. Nano-hardness and elastic modulus were also increased after application of the process. XRD patterns indicate that grain refinement was induced with no change in phases composition. The number of passes is proved effective in increasing the depth of the hardened layer, which influences subsequently on the frictional behavior of 316L stainless steel.

Background:: Angular contact ball bearings are the most popular bearing type used in the high speed spindle for machining centers, The performance of the bearing directly affects the machining efficiency of the machine tool, Obtaining a higher value is the direction of its research and development. Objective:: By analyzing the research achievements and patents of electric spindle angular contact bearings, summarizing the development trend provides a reference for the development of electric spindle bearings. Methods:: Through the analysis of the relevant technology of the electric spindle angular contact ball bearing, the advantages and disadvantages of the angular contact ball bearing are introduced, and the research results are combined with the patent analysis. Results:: With the rapid development of high-speed cutting and numerical control technology and the needs of practical applications, the spindle requires higher and higher speeds for bearings. In order to meet the requirements of use, it is necessary to improve the bearing performance by optimizing the structure size and improving the lubrication conditions. Meanwhile, reasonable processing and assembly methods will also have a beneficial effect on bearing performance. Conclusion:: With the continuous deepening of bearing technology research and the use of new structures and ceramic materials has made the bearing's limit speed repeatedly reach new highs. The future development trend of high-speed bearings for electric spindles is environmental protection, intelligence, high speed, high precision and long life.

Data-based methods are capable to monitor machine components. Approaches for semi-supervised anomaly detection are trained using sensor data that describe the normal state of machine components. Thus, such approaches are interesting for industrial practice, since sensor data do not have to be labeled in a time-consuming and costly way. In this work, an ensemble approach for semi-supervised anomaly detection is used to detect anomalies. It is shown that the ensemble approach is suitable for condition monitoring of ball screws. For the evaluation of the approach, a data set of a regular test cycle of a ball screw from automotive industry is used.

Quantum computers are at the forefront of computing; however, few people understand how they work and their capabilities. We present two versions of an interactive activity designed for high school students (ages 13 to 18) that introduce a core quantum concept—entanglement. The first version illustrates a simple connection between two particles, and the second explores different ways that two particles could be entangled. This activity works well for entry-level quantum computing learning and requires minimal materials.

A novel desulphurization technology has been put forward using a dispersed in-situ phases induced by an explosive reaction of a composite ball. A composite ball with this function has been designed...

My interest in the lubrication mechanisms of a ball bouncing and impacting an oily plate brought me into contact with Professor Duncan Dowson. Our very first meeting was at a conference where we presented almost identical results. After that, in 1995, I was invited to Leeds University for a one-semester visit. I was still a PhD student and the visit helped me a lot to develop as a person and as a scientist Duncan helped me in this development through his skilful guidance and by putting me in touch with other knowledgeable people in my field. The bouncing ball problem was about understanding elastohydrodynamic lubrication (EHL) under non-steady conditions. In fact, most EHL contacts operate under non-steady conditions since load, speed and curvature often varies rapidly during the operation of machine elements such as gears, rolling bearings and cam mechanisms. In this paper, I will tell you about the bouncing ball problem and how Duncan Dowson became an important person for me.

Ball-end cutters are widely used in industries of dies, molds, and aerospace, which have the problem of poor machined surface quality due to the low cutting speed near the tool-tip. With the increase in the complexity of parts, it will become more and more difficult to avoid the tool-tip participating in the cutting. In this paper, the velocity effect sensitivity of ball-end cutter is analyzed, and several key positions, including the intersection points of the CWE boundaries, are selected to describe the cutting speed in three dimensions. The relationships between the cutting speed of the critical points and important variables such as: machining inclination angle and the feed direction were investigated. The optimal range of feed direction is obtained when the tool-tip engages in the contact circle. The core aim of the feed direction selection is to make the tool engagement area in a high position by changing the feed direction, to avoid surface damage caused by ploughing and improve the quality of the machined surface. Finally, an experimental study was carried out, and the results corroborate the effectiveness of the selection method. In the experiment, it was also found that cutting-out from the cutter contact position can improve the surface quality in the directions of non-optimal range, and the milling force and chips shape will vary with the change of the feed direction.

Athletes alter ball flight trajectory in interceptive ball sports to change task constraints that their opponents must overcome to successfully meet the ball in flight. This systematic review identified how athletes change their techniques to alter the ball flight trajectory in high-performance interceptive sports where the ball is projected by the hand towards an opponent. Studies that reported the kinematics or ball flight characteristics of these movements were searched for using SportsDiscus, Scopus, MEDLINE and CINAHL Plus databases up to 27 April 2021. Forty-eight articles met the inclusion criteria, including 19 baseball, 12 cricket, five handball, four softball, three volleyball and five water polo studies. Extracted data were presented as ranges and descriptively analysed to report athlete sporting actions. Trajectory deviation can be caused by imparting an altered seam orientation or spin rate and axis of rotation on the ball. Athletes impart sidespin or manipulate seam orientation to cause lateral deviation while topspin and backspin are used to create vertical changes in the flight path. Adjusting the shoulder, forearm, wrist, hand and fingers of the throwing or striking arm can be used to impart an altered seam orientation or spin rate and axis of rotation on the ball. The findings of this review could assist coaches and athletes across a variety of sports to improve the ability to deviate the ball during flight.

This study examined whether profiles varying in actual and perceived locomotor and ball skill competencies would be identified and whether these profiles would differ in relation to children's characteristics. Participants were 127 (70 boys; 57 girls) French-speaking Canadian children (5-11 years). Actual and perceived motor competencies were, respectively, measured using the Test of Gross Motor Development - Third version and the pictorial scale of Perceived Movement Skill Competence. Latent profile analyses revealed four profiles: (1)

This experimental study deals with the effect of modifying an Si-rich LM6 cast alloy by ball milling with Si/Al powder particulates in which alloying was conducted via semi-solid liquid processing....

Purpose: The aim of this study was to investigate the frequency of change of directions (COD) and examine the influences of position, leg dominance and anthropometrics on COD in elite youth soccer match play.\ud Methods: Twenty-four elite male English Premier League (EPL) academy players (19.0 ± 1.9 years) were individually recorded during ten competitive U18s and U23s matches. Video footage of individual players was analysed using a manual notation system to record COD frequency, direction, estimated angle and recovery time. The influences of position, anthropometrics and leg dominance were accounted for.\ud Results: Elite youth soccer players performed on average 305 ± 50 CODs with on average 19.2 ± 3.9 seconds of recovery. The frequency of CODs was independent of position, leg dominance, anthropometry and occurred equally between left and right direction and forwards and backwards direction. CODs were mostly ≤90° (77%) and there were significantly less CODs in the 2nd half (−29, ES = 1.23, P< 0.001). The average and peak within match demands within 15 and 5-minute periods were 49 and 62 CODs, and 16 and 25 CODs, respectively.\ud Conclusion: This study is the first to illustrate COD frequencies of elite youth soccer match play, providing practitioners guidance to prepare soccer players for competitive match demands.

Rolling bearings are widely used in the products of aviation and space technology. To ensure their long-term trouble-free operation, it is necessary to have accurate and reliable information about the forces acting on the bearings. The required values of forces and, accordingly, the required durability of bearings are usually determined on the basis of the traditional design scheme of a double-support beam (smooth beam mounted on two hinged supports). The paper presents a new interpretation of the features of the operation of bearing units on ball radial single-row bearings installed according to the cross located arrangement. It is shown that under conditions of combined loading, including radial and axial forces, the generally accepted theoretical model of a doublesupport beam is not implemented. There is no single calculation model that adequately reflects the nature of the interaction of bearing parts over the entire range of external loads. In the most general case, this model can be represented by a sequence of five statically indeterminate calculation schemes, which are modified and transformed into one another. So, with an increase in the external radial force, the cantilevered beam with additional hinge support scheme is first implemented, which, then, is transformed into the double-sided jamming scheme, and that, later, is transformed into the two double hinge supports scheme. It is also possible to implement two intermediate transition schemes. A specific example shows that in the products of aviation and space technology, determining the durability of bearings based on the traditional model is not advisable, since it can give an overestimated value with an error of 28,37 to 26663,9 times.

The hydrolysis of aluminum (Al) is a relatively simple method for on-demand hydrogen generation for niche (low-power

Highly transparent leafhopper (Thaia rubiginosa) wings are self-decorated with embroidered ball-shaped proteinaceous brochosmoes as distinct anti-predator defenses. The non-sticky brochosomal coating serves as antireflective structures for camouflage in vegetated environments. Inspired by the leafhopper wings, this study reports a new type of reversible antireflection coating enabled by integrating self-assembly methodologies using a shape memory polymer. The resulting embroidered ball-like structure array establishes a refractive index transition on surface, and thereby behaves omnidirectional antireflective characteristics in a broadband visible light region. Interestingly, the highly transparent appearance can be instantly erased and recovered by submerging in common liquids, such as water and ethanol, or by applying contact pressures at ambient conditions. Furthermore, the reversibility and structure-shape effect on the antireflective characteristics are systematically evaluated in this study.

Underwater swimmers present unique opportunities for using bodily reconfiguration for self propulsion. Origami-inspired designs are low-cost, fast to fabricate, robust, and can be used to create compliant mechanisms useful in energy efficient underwater locomotion. In this paper, we demonstrate an origami-inspired robot that can change its body shape to ingest and expel water, creating a jet that propels it forward similarly to cephalopods. We use the magic ball origami pattern, which can transform between ellipsoidal (low volume) and spherical (high volume) shapes. A custom actuation mechanism contracts the robot to take in fluid, and the inherent mechanics of the magic ball returns the robot to its natural shape upon release. We describe the design and control of this robot and verify its locomotion in a water tank. The resulting robot is able to move forward at 6.7 cm/s (0.2 body lengths/s), with a cost of transport of 2.0.

Robot soccer is a classic research direction in the field of robotics. From the appearance of soccer robot, it is mainly divided into wheeled robot and humanoid robot. At present, humanoid robots and small group wheeled robots mainly compete on two-dimensional plane. Because of the small competitive dimension, the offensive and defensive tactics tend to be simple. In order to enhance the competitiveness and appreciation of humanoid. And complex motion devices based on human motion capture data (HMCD) are designed Human simulation has gradually become one of the effective means of robot design. In order to enhance the competitiveness and appreciation of humanoid, this paper innovatively designs a set of consistent kicking actions based on darwin-op2 robot, combined with HMCD method, realizes the effect of actively lobbing ball. Ideally, the robot can basically kick the ball above 35cm. Besides the robot can basically kick the ball above 30cm in practice, and the success rate is as high as 75%. It improves the competitiveness from two-dimensional to three-dimensional, which provides new ideas and schemes for attack and defense tactics and expands the dimension of competition. It also provides a new direction for the development of humanoid robot football in the future.

Ball milling is widely used in industry to mill particulate material. The primary purpose of this process is to attain an appropriate product size with the least possible energy consumption. The process is also extensively utilised in pharmaceuticals for the comminution of the excipients or drugs. Surprisingly, for ball mill, little is known concerning the mechanism of size reduction. Traditional prediction approaches are not deemed useful to provide significant insights into the operation or facilitate radical step changes in performance. Therefore, the discrete element method (DEM) as a computational modelling approach has been used in this paper. In previous research, DEM has been applied to simulate breaking behaviour through the impact energy of all ball collisions as the driving force for fracturing. However, the nature of pharmaceutical material fragmentation during ball milling is more complex. Suitable functional equations which link broken media and applied energy do not consider the collision of particulate media of different shapes or collisions of particulate media (such as granules) with balls and rotating mill drum. This could have a significant impact on fragmentation. Therefore, this paper aimed to investigate the fragmentation of bounded particles into DEM granules of different shape/size during the ball milling process. A systematic study was undertaken to explore the effect of milling speed on breakage behaviour. Also, in this study, a combination of a density-based clustering method and discrete element method was employed to numerically investigate the number and size of the fragments generated during the ball milling process over time. It was discovered that the collisions of the ball increased proportionally with rotation speed until reaching the critical rotation speed. Consequently, results illustrate that with an increase of rotation speed, the mill power increased correspondingly. The caratacting motion of mill material together with balls was identified as the most effective regime regarding the fragmentation, and fewer breakage events occurred for centrifugal motion. Higher quantities of the fines in each batch were produced with increased milling speed with less quantities of grain fragments. Moreover, the relationship between the number of produced fragment and milling speed at the end of the process exhibited a linear tendency.