• 제목/요약/키워드: backward difference

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포지션별 정구 플랫서비스의 운동학적분석 (Kinematic Analysis of Service Movement In Each Position of Soft Tennis)

  • 김헌수
    • 한국운동역학회지
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    • 제12권1호
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    • pp.221-231
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    • 2002
  • The purpose of this study was to clarify the differences in service patterns of a forward and backward soft tennis players using 3D motion analyzer. Subjects were 4 forward players of $24.0\pm5.23$yrs and 4 backward players of $23.5\pm1.73$yrs. The results were as following: 1. There was no difference among each positions on swinging-time. The longest racket swinging-time was in the phase of takeback, the second one was in follow-through. The shortest one was in the phase of forward-swing so called force production phase, which had an influence on ball's velocity. 2. The racket speed on impact was 16.3m/s in forward subject and 19.53m/s in backward subject, when each velocity of balls was 44.6m/s, 52.9m/s. Although there was no significant difference along by positions, backward subject showed faster result. 3. The maximum speed of each performance was reached before the impact, and the speed at impact along by positions did not show any significant difference. The summation of velocity was measured in good order as following; hip, shoulder, elbow, wrist, top of racket. 4. In the angular velocity of all examine except one, the angular velocity of forearm was bigger than the one of racket top although there was no statistically significant difference between forward and backward subject. 5. The service grip of the forward players was shorter than that of backward players.

후진 미분 연산자를 이용한 이산확률분포의 적률 유도 (Derivations of moments for discrete probability distributions using backward difference operators)

  • 조길호
    • Journal of the Korean Data and Information Science Society
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    • 제22권3호
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    • pp.505-513
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    • 2011
  • 본 논문의 목적은 후진 미분 연산자를 이용하여 이산확률분포에 대한 원점으로부터의 r차 적률을 구하는 공식을 유도한다. 이 공식을 이용함으로써 r차 적률은 0에서 계산된 $x^r$의 r번째 후진 미분 연산자까지의 일차결합으로써 계산됨을 알 수 있다.

Feedforward actuator controller development using the backward-difference method for real-time hybrid simulation

  • Phillips, Brian M.;Takada, Shuta;Spencer, B.F. Jr.;Fujino, Yozo
    • Smart Structures and Systems
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    • 제14권6호
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    • pp.1081-1103
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    • 2014
  • Real-time hybrid simulation (RTHS) has emerged as an important tool for testing large and complex structures with a focus on rate-dependent specimen behavior. Due to the real-time constraints, accurate dynamic control of servo-hydraulic actuators is required. These actuators are necessary to realize the desired displacements of the specimen, however they introduce unwanted dynamics into the RTHS loop. Model-based actuator control strategies are based on linearized models of the servo-hydraulic system, where the controller is taken as the model inverse to effectively cancel out the servo-hydraulic dynamics (i.e., model-based feedforward control). An accurate model of a servo-hydraulic system generally contains more poles than zeros, leading to an improper inverse (i.e., more zeros than poles). Rather than introduce additional poles to create a proper inverse controller, the higher order derivatives necessary for implementing the improper inverse can be calculated from available information. The backward-difference method is proposed as an alternative to discretize an improper continuous time model for use as a feedforward controller in RTHS. This method is flexible in that derivatives of any order can be explicitly calculated such that controllers can be developed for models of any order. Using model-based feedforward control with the backward-difference method, accurate actuator control and stable RTHS are demonstrated using a nine-story steel building model implemented with an MR damper.

뒤로 걷기 운동과 언어 지시가 20대 대학생들의 앞쪽 머리 자세에 미치는 즉각적인 효과 (The Immediate Effect of the Backward Walking Exercise and Verbal Command on the Forward Head Posture of College Students in their 20s)

  • 박한규;김태호;김동우
    • 한국전문물리치료학회지
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    • 제27권3호
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    • pp.185-190
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    • 2020
  • Background: Backward walking exercise may offer some unique and potentially beneficial differences compared with forward walking exercise. There is still a lack of research on backward walking exercises and forward head posture. Objects: The purpose of this study was to determine the effect of backward walking exercise on college students forward head posture in their 20s. Methods: Twenty-one subjects participated in the experiment. The subjects were those with a craniovertebral angle (CVA) of 55 degrees or less who understood the purpose and method of this study and voluntarily agreed. A camera capable of taking pictures of the lateral plane was installed at a distance of 1.5 meters before exercising. Pictures were taken before walking backward, and after walking for 15 minutes on the treadmill, the images were taken in the same way. The composition of the backward walking exercise was walking at a rate of 1.0 for 5 minutes, and the remaining 10 minutes were walking at a rate of 1.5. Wilcoxon signed rank test was used to compare CVA and craniorotational angle (CRA) before and after exercise. Results: As a result of this study, there was a significant difference in CVA before and after exercise (p < 0.05). There was a significant difference in CRA before and after exercise (p < 0.05). Conclusion: The backward walking exercise and verbal command seems to have positively influenced the changes in CVA and CRA among college students in their 20s. It seems that studies to confirm balance or muscle activity as well as changes in forward head posture through the long-term intervention of the backward walking exercise should be conducted.

댄스스포츠 라틴댄스 룸바 Backward Walk 동작시 지면반력 변인 분석 (Analysis of the Ground Reaction Forces by the Dancesport Rumba Backward Walk Step)

  • 유혜숙;인희교;최인애
    • 한국운동역학회지
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    • 제18권1호
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    • pp.129-135
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    • 2008
  • 본 연구는 댄스스포츠 라틴댄스 룸바 Backward Walk 동작시 지면반력에 어떠한 영향을 미치는가를 규명하기 위해 지면반력기를 이용하여 결과를 도출하였다. 우수선수와 비우수선수간 t-test를 통해 비교하여 오른발의 동작시 수직(Fz)지면반력의 착지와 이지에서 유의한 차이를 보였고, 왼발에서는 수직(Fz), 좌우(Fx), 에서 착지와 수직(Fz), 좌우(Fx) 이지에서 유의차가 나타났다. 우수선수와 비우수선수간의 차이는 오른발에서 수직(Fz) 지면반력 이외 다른 방향에서는 유의차가 나타나지 않았으며, 왼발은 지면반력의 전후(Fy) 이지에서 유의한 차이가 없음이 밝혀졌다. 이는 일반적으로 왼발 운동능력이 트레이닝을 통하여 훈련된 우수선수 집단에서 더 발달되었음을 알 수 있다. 따라서 이러한 지면 반력의 차이를 이해하고, 비우수선수 및 초보자들의 경우 동작의 반복훈련 및 트레이닝을 통하여 양발을 균형 있게 발달시킴으로써 정확한 동작 수행이 도움을 줄 것으로 사료된다.

이중주파수 가진이 후향계단 유동에 미치는 영향 (Effect of Two-Frequency Forcing on Flow Behind a Backward-Facing Step)

  • 유정열;진송완;김성욱;최해천;김사량
    • 대한기계학회논문집B
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    • 제26권3호
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    • pp.423-431
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    • 2002
  • An experimental study is conducted to investigate the effect of two-frequency forcing on turbulent flow behind a backward-facing step at the Reynolds number of 27000 based on the step height. The forcing is provided from a thin slit located at the edge of the backward-facing step to increase mixing behind the backward-facing step and consequently to reduce the reattachment length. With single frequency forcing, the minimum reattachment length is obtained at the non-dimensional forcing frequency (F) of St$\_$h/ = 0.29. With two-frequency forcing, a subharmonic frequency (F/2) or biharmonic frequency (2F) is combined with the fundamental frequency (F), i.e. (F, F/2) or (F, 2F) forcing is applied. In the case of (F, F/2) forcing, the reattachment length is not much sensitive to the phase difference between F and F/2. However, the reattachment length significantly depends on the phase difference between F and 2F in the case of (F, 2F) forcing. At a certain range of the phase difference, the reattachment length becomes smaller than that of the single frequency forcing.

웨이블렛 변환을 이용한 HVDC 케이블 고장점 표정 알고리즘 (A Fault Location Algorithm Using Wavelet Transformation for HVDC Cables)

  • 권영진;강상희
    • 전기학회논문지
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    • 제57권8호
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    • pp.1311-1317
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    • 2008
  • In this paper, a fault location algorithm using wavelet transform is proposed for HVDC cable lines. The arriving instants of the first and second fault-induced backward travelling waves can be detected by using wavelet transform. The fault distance is estimated by using the time difference between the two instants of backward travelling waves and the velocity of the travelling wave. To distinguish between the backward wave from fault point and the backward wave from the remote end, polarities of backward waves are used. The proposed algorithm is verified varying with fault distances and fault resistances in underground cables of VSC(voltage source converter) HVDC system and CSC(Current Source Converter) HVDC respectively. Performance evaluations of the proposed algorithm shows that it has good ability for a fault location of HVDC cable faults.

Effects of Backward Walking Training with Task Orientation on the Functional Gait of Children with Spastic Hemiplegia

  • Choi, Ji Young;Son, Sung Min;Kim, Chang Ju
    • The Journal of Korean Physical Therapy
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    • 제31권5호
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    • pp.292-297
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    • 2019
  • Purpose: This study examined the effects of backward walking training with task orientation on the functional walking ability of children with cerebral palsy. Methods: This study was a single-blinded, randomized controlled trial with a crossover design conducted at a single rehabilitation facility with cross-over to the other intervention arm following a two-week break. For a total of 12 children with spastic hemiplegia cerebral palsy, the forward walking training group (n=6) underwent training three times a week for three weeks, 40 minutes a day, and the backward walking training group (n=6) was also trained under the same conditions. To identify the functional walking ability, variables, such as the walking speed, stride length, and step length, were measured using a walk analyzer (OptoGait, Microgate S.r.l, Italy). Results: Both groups showed significant increases in walking speed, stride length, and step length (p<0.01). The backward walking group showed more significant improvement in the walking speed from pre- to post-test (p<0.05). The gait characteristics were similar in the two groups (stride length and step length) but the walking speed in the backward walking group showed a mean difference between the positive effects higher than the forward walking group. Conclusion: Task-oriented backward walking training, which was conducted on the ground, may be a more effective treatment approach for improving the walking functions of spastic hemiplegia children than forward walk training.

트레드밀 전.후방 보행에서 경사도와 속도에 따른 넙다리네갈래근 테이핑 적용 시 근활성도 비교 (Comparison to muscle activity of quadriceps femoris when apply a taping according to slope and speed during forward and backward walking on treadmill)

  • 김병곤;임미선;서현규
    • 대한정형도수물리치료학회지
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    • 제15권2호
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    • pp.50-62
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    • 2009
  • Purpose: to analyze and compare mucsle activity of Quadriceps femoris depending on the existence of taping while normal people walk forward and backward on treadmill when the slope and speed changes on treadmill. Method: Among 40 people who participated in this study, 20 experimenter who apply a taping walk forward and backward to 0%, 5%, 10% gradient per 2km/h and 4km/h using treadmill to give arbitrary walking behavior, 20 experimenter who doesn't apply a taping also walk forward and backward to 0%, 5%, 10% gradient per 2km/h and 4km/h using treadmill. To analyze muscle activity, We use an electromyography and Kinesio tape of good elasticity for obtained suffient effects in the experiment. Result: During backward walking in 2km/h, Vastus medialis and Vastus lateralis showed significant differences(p<0.05) when apply a taping. During backward walking in 2km/h, Vastus medialis and Rectus femoris, and Vastus lateralis all showed significant differences(p<0.05). During backward walking in 2km/h, Vastus medialis and Vastus lateralis showed significant differences in 10% gradient(p<0.05). During backward walking in 4km/h, Vastus medialis and Rectus femoris, and Vastus lateralis all showed significant differences(p<0.05). During backward walking in 4km/h, By the difference in slope, Vastus medialis and Vastus lateralis showed significant differences between 0% and 10% gradient(p<0.05). Conclusion: In comparison to muscle activity of Quadriceps femoris when apply a taping according to slope and speed during forward and backward walking on treadmill, when apply a taping and walk backward and 10% gradient on treadmill in 4km/h, maximum of muscle activity is shown.

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탱고 backward walk 동작시 신발 굽 유형에 따른 하지의 근전도 분석 (EMG Analysis of Lower Extremity Muscles under different heel types of shoes when performing Tango Backward Walk)

  • 정미라;서국웅;강영택;염창홍
    • 한국운동역학회지
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    • 제12권1호
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    • pp.31-46
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    • 2002
  • The purpose of this research is to provide scientific training guides and the basis for preventing injuries in performing tango backward walk by comparing the effects the height and shape of a heel will have on leg muscles and determining the difference between skilled and unskilled dancers through EMG analysis according to different types of shoes Total eight female athletes were selected for this research. Four with six years of professional dancing experience and another four with one year of dance sports experience. Utilizing the EMG system, rectus femoris, biceps femoris, anterior tibialis, gastrocnemius were measured under different heights (0cm, 5cm, 7cm, 9cm) and shapes (flat, fine, wide) of a heel. Experiments were conducted calculating EMG peak value and muscle load ration under different types of shoes in order to analyze the EMG of leg muscles and Erector Spinae when performing tango backward walk. The result was as follows: 1. The EMG peak value of leg muscles showed significant difference under different heights of a heel in anterior tibialis(p<.001) and gastrocnemius(p.<01) in case of skilled dancers, and in biceps femoris(p.<01) in case of unskilled dancers. 2. The EMG peak value of leg muscles showed significant difference under different shapes of a heel in anterior tibialis(p<.001) and gastrocnemius(p<.001) in case of skilled dancers, and showed no significant difference in case of unskilled dancers. 3. The muscle load ration of leg muscles showed different degrees of muscle contribution between skilled and unskilled dancers. The muscle load ration was in the order of anterior tibialis, rectus femoris, biceps femoris, and gastrocnemius in case of skilled dancers and anterior tibialis, gastrocnemius, biceps femoris, and rectus femoris in case of unskilled dancers.