The aim of this study was to determine the movement factors that cause differences in throwing records in javelin throwers who had similar running velocities. The movements of 81 female javelin ...throwers who participated in competitions were recorded using two cameras, and the coordinate values were obtained using the three-dimensional motion analysis technique. The preparatory phase was defined as the period from the last rear foot contact (RFC) to the fore foot contact (FFC), whereas the throwing phase was defined as the period from the FFC to javelin release. Among them, 14 athletes with approach velocity of 4.0-4.3 m/s at FFC were divided into a high (57.59 ± 3.60 m) and a low group (35.14 ± 8.23 m) for throwing records, and the kinematic data were compared. The high group had a significantly higher release velocity, showed larger maximum external rotation of the shoulder joint, and larger right shoulder velocity than the low group. Immediately during the throwing phase, the high group had a larger horizontal rotation of the upper trunk towards the throwing direction than the low group. Furthermore, the high group was characterized by greater height and segment length than the low group. These results indicate that the high group achieves larger terminal velocities owing to the faster rotation of the larger body. Thus, the results clearly show that high-performance athletes transfer greater kinetic energy to the javelin throw with a more rational throwing motion, even if they have a similar approach velocity.
The aim of this study was to determine the movement factors that cause differences in throwing records in javelin throwers who had similar running velocities. The movements of 81 female javelin ...throwers who participated in competitions were recorded using two cameras, and the coordinate values were obtained using the three-dimensional motion analysis technique. The preparatory phase was defined as the period from the last rear foot contact (RFC) to the fore foot contact (FFC), whereas the throwing phase was defined as the period from the FFC to javelin release. Among them, 14 athletes with approach velocity of 4.0-4.3 m/s at FFC were divided into a high (57.59 ± 3.60 m) and a low group (35.14 ± 8.23 m) for throwing records, and the kinematic data were compared. The high group had a significantly higher release velocity, showed larger maximum external rotation of the shoulder joint, and larger right shoulder velocity than the low group. Immediately during the throwing phase, the high group had a larger horizontal rotation of the upper trunk towards the throwing direction than the low group. Furthermore, the high group was characterized by greater height and segment length than the low group. These results indicate that the high group achieves larger terminal velocities owing to the faster rotation of the larger body. Thus, the results clearly show that high-performance athletes transfer greater kinetic energy to the javelin throw with a more rational throwing motion, even if they have a similar approach velocity.
This study aimed to estimate the factors that cause differences in competition level based on the competition performance structure among university student decathletes in Japan. The results of ...factor analysis using the maximum likelihood method (Oblimin rotation), assuming a five-factor structure estimated from parallel analysis and the information criterion, revealed the following competitive performance structures: "running speed and body projection," "running endurance," "rotational throwing power," "translational throwing power," and "vertical leaping power." Some of these were similar to the competitive performance structures of the world's top athletes, but they were found to have a unique structure: two throwing powers. The analysis results using latent rank theory allowed us to evaluate them on a seven-point scale. The calculated item reference profile, difficulty index, and discrimination index for each rank indicated that shot put and 100 and 400 m performance formed the basis of decathlon performance. In addition, high jump and pole vault, which fall under the category of "vertical leaping power," retained high difficulty and discrimination and were revealed to affect the stage of achievement of overall performance in the decathlon.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
•No-till farming is being increasingly used worldwide for more efficient crops.•In crop rotation, the straw of a crop can be used for the next cycle.•We developed a planter that performs even crushed ...straw coverage.•The coverage and planter performance are verified in simulations and implementation.•We provide the optimal parameters for even coverage and meeting operation standards.
In agricultural fields with full straw retention, shredded straw tends to be thrown unevenly. To achieve uniform crushed straw throwing in dense fields of rice stubble, and high-quality straw mulching in dense fields, the conveying device of a no-till planter to perform uniform throwing of crushed straw stubble on fields and determine the device operation mechanism was analyzed. Using kinematics and dynamics analyses of particles of crushed rice straw during lifting and dispersion, a flexible-body model of rod-shaped and agglomerate-shaped crushed straw and a coupling model that included the mechanical structure of the device were developed. By integrating computational fluid dynamics and the discrete element method, the gas–solid coupling theory in numerical simulations and motion analysis of crushed straw particles was used to determine the flow field and motion characteristics under different parameters. The simulation focused on the conveying performance of different pipelines under four scenarios with varying throwing blade speed, conveying volume, pipeline diameter, and initial feeding velocity. The influence of these parameters on both the conveying device performance and their own variation was determined. Actual operations that are then compared with test results to achieve optimal operation were demonstrated. By adopting the Box-Behnken design, the throwing speed of crushed straw was set to the evaluation index a response surface test was performed on the throwing blade speed, conveying volume of crushed straw, and pipeline diameter. The optimization results showed that the predicted optimal parameters were 2300 rpm throwing blade speed, 1.4 kg/s conveying volume, and 220 mm pipeline diameter. The simulated planter achieved an optimized throwing speed of 14.6 m/s. Then, a field test verification was conducted, and the results were averaged. The planter achieved a throwing speed of 14.8 m/s with the same optimal parameters. The straw lifting and throwing device provides high conveying performance and satisfies requirements for real-time operation. This study provides a theoretical basis and supporting data for innovating seeding technologies and optimizing equipment to achieve uniform crushed straw-throwing in dense fields of rice stubble.
Abstract
As we all know, Dalton’s law of the partial pressure is equivalent to Dalton’s law of the partial volume. On the other hand, through experiments, it can be proved that Dalton’s law of the ...partial volume is correct, and Dalton’s law of the partial pressure can be derived from Dalton’s law of the partial volume, implying that both laws are equivalent to each other. Combined with the teaching of middle school physics and university basic physics, with different ideas and methods, this paper presents a variety of proof methods of Dalton’s law of the partial volume to be equivalent to Dalton’s law of the partial pressure. Different proof methods can improve the understanding and application of Dalton’s law of the partial pressure and law of the partial volume. It is proved that the relevant content of Dalton’s ideal gas partial pressure law is further supplemented and perfected, which plays a role throwing some light on this field.
A leveler containing quaternary ammonium cations, namely poly (1-vinyl imidazole co 1, 4-butanediol diglycidyl ether) (VIBDGE) was synthesized and studied in this work. Quantum chemical calculations ...and molecular dynamics simulation of VIBDGE were employed to get insight to the adsorption model by assessing the molecular configuration and electronic orbital parameters. The simulation results reveal that VIBDGE will spontaneously absorb on the copper surface because of its tiling way, the generated nitrogen ions and the large molecular volume of VIBDGE. Galvanostatic measurements (GMs) and cyclic voltammetry (CV) tests were performed to investigate the electrochemical behaviors of VIBDGE and its synergistic mechanism with other additives. The results of GMs demonstrate VIBDGE exhibits good inhibiting performance in copper deposition. However, the reactant, namely 1-vinyl imidazole and 1, 4-butanediol diglycidyl ether, have no inhibition effect. Additionally, GMs results show that adsorption competition between bis-(sodium sulfopropyl)-disulfide (SPS) and VIBDGE is kinetically controlled and a steady state can be achieved regardless of the injection order of additives. The steady potential at lower rpm is less polarized and thus very beneficial for achieving uniform plating of through-hole (TH). The CV testes show that VIBDGE is capable of inhibiting copper deposition in the absence of chloride ions and chloride ions have a synergistic effect with VIBDGE. In addition, VIBDGE and PEG have competitive adsorption in copper deposition process. Consistent with the results of the GMs, the CV results illustrate that in the VIBDGE-SPS-PEG-Cl- system, the amount of copper deposited in the center of TH is more than that of the surface. Through the results of electroplating, it is confirmed that VIBDGE-SPS-PEG-Cl- system significantly improves the throwing power which is in accordance with simulation and electrochemical experiments.
The deep squat test (DST) is a screening test to assess the function of the lower extremity and the flexibility of ankle dorsiflexion. Previous study reported that approximately 70% of players with ...disabled throwing shoulder and/or elbows were unable to perform DST. The aim of this study was to reveal the relationship between performance of DST and history of disabled throwing shoulder/elbow.
A total of 1,439 youth baseball players (10.9 years; range 6–16 years), who participated in pre-season medical examination were included in the study. Players who experienced shoulder or elbow pain of the throwing side during or after playing baseball in the past were defined as players with a history of disabled throwing shoulder/elbow. The DST was evaluated by having the players perform a full squat with while having their arms crossed in front of their chest and their feet apart without lifting the heel off the floor or falling backwards. The relationship between a history of disabled throwing shoulder/elbow and the ability to perform DST was analyzed.
Among the study participants, 499 (34.7%) had a history of disabled throwing shoulder/elbow, and 532 players (37.0%) were unable to perform DST. Of the players with disabled throwing shoulder/elbow history, 227 players (45.5%) were unable to perform DST, as were 305 players out of 940 players (32.5%) without a disability; this difference was statistically significant (P < 0.001).
Inability to perform DST may be related to the previous incidence of disabled throwing shoulder/elbow.
This research aims at studying the effect of feedback on well-being (vitality, and positive and negative affect), competence valuation, perceived competence, motivation, and performance (throwing ...speed and accuracy) in a throwing task. Thirty nine expert women handball players, with experience in international handball competitions, participated in this study. They were indiscriminately ascribed to one of three different experimental conditions measuring feedback: (positive, negative, and none). Significant differences in well-being (positive affect) and throwing speed were found among the three feedback groups. More concretely, higher levels of positive affect and throwing speed were found in the negative feedback group in comparison with the other two groups (positive and no-feedback). These results have important implications for athletes' well-being and performance, and for coaches' training programs.
We consider Gedanken experiments to destroy an extremal or near-extremal Banados-Teitelboim-Zanelli (BTZ) black hole by throwing matter into the horizon. These black holes are vacuum solutions to ...(2+1)-dimensional gravity theories, and are asymptotically AdS3. Provided the null energy condition for the falling matter, we prove the following-(i) in a Mielke-Baekler model without ghost fields, when torsion is present, an extremal BTZ black hole can be overspun and becomes a naked conical singularity; (ii) in three-dimensional Einstein gravity and chiral gravity, which both live in the torsionless limits of the Mielke-Baekler model, an extremal BTZ black hole cannot be overspun; and (iii) in both Einstein gravity and chiral gravity, a near-extremal BTZ black hole cannot be overspun, leaving the weak cosmic censorship preserved. To obtain these results, we follow the analysis of Sorce and Wald on their Gedanken experiments to destroy a Kerr-Newman black hole, and calculate the second order variation of the black hole mechanics. Furthermore, Wald's type of Gedanken experiments provide an operational procedure of proving the third law of black hole dynamics. Through the AdS/CFT correspondence, our results on BTZ black holes also indicate that a third law of thermodynamics holds for the holographic conformal field theories dual to three-dimensional Einstein gravity and chiral gravity.
As overhead sports continue to grow in popularity, there has been increased interest in optimizing sports performance and injury prevention in these athletes. The hip, core, and kinetic chain have ...become a focus of research in recent decades, and their importance in upper extremity mechanics is now being recognized.
An extensive review was carried out to identify papers correlating the hip, core and/or kinetic chain in overhead athletic performance and injury.
Recent literature has shown that efficiency and synchrony of the hips and core during an overhead movement (such as in baseball, golf, tennis, or volleyball) is essential for a powerful and precise execution of the task. Impairments of the hip and core, particularly abnormal joint mobility or weakness, can limit efficient energy transfer through the kinetic chain and may negatively impact performance. Recent epidemiologic studies have found hip pain to be common in adolescent, collegiate, and adult athletes. Moreover, hip pain in overhead athletes specifically has also been found to occur at a high rate. Abnormalities in hip range of motion, hip morphology, and core strength can lead to abnormal mechanics upstream in the kinetic chain, which may place athletes at risk of injuries.
In this review, the complex and multifaceted relationship between the hip, core, and kinetic chain is highlighted with an emphasis on recent literature and relevant findings.
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