• Korean Journal of Applied Biomechanics
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• v.12 no.1
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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.

• Journal of the Korean Data and Information Science Society
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• v.22 no.3
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• pp.505-513
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• 2011

In this paper, we obtain the derivations of moments of discrete probability distributions by using the backward difference operators. Also, we presents such derivations for several well-known distributions; they are the binomial, Poisson, geometric, hypergeometric and negative hypergeometric distributions.

• Smart Structures and Systems
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• v.14 no.6
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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.

• Physical Therapy Korea
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• v.27 no.3
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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.

• Korean Journal of Applied Biomechanics
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• v.18 no.1
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• pp.129-135
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• 2008

This research was examined the effect of Backward Walk on ground reaction force and we achieved it by using ground reaction force machine during the Backward Walk activity with Latin and Rumba dance. We find that it was significant difference of vertical(Fz) ground reaction force of right foot in touchdown and toe-off and vertical(Fz), horizontal(Fx), front-rear(Fy) ground reaction force of left foot. There was not significant differences in vertical ground reaction force between superior athlete and unskilled athlete, but there was a significant difference in left foot. Through this, we know that the sports capability of left foot which has been developed through the training is better in superior athlete group. Therefore understanding of difference in ground reaction force and repeated training can help the unskilled athlete and beginner to accomplish the accurate movement.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.3
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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.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.8
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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.

• The Journal of Korean Physical Therapy
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• v.31 no.5
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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.

• The Journal of Korean Academy of Orthopedic Manual Physical Therapy
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• v.15 no.2
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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.

• Korean Journal of Applied Biomechanics
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• v.12 no.1
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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.