Sliding mode control of time‐varying delay Markov jump with quantized output

This paper investigates the quantized sliding mode control of Markov jump systems with time‐varying delay. A dynamical adjustment law is explored to quantize the system output. By constructing an observer‐based integral sliding surface, a sliding mode controller is designed to take over the dynamical motion of state estimation and ensure the reachability of sliding surface. A new scaling manner is developed to build the bound between the system output and quantized error. With the help of separation strategies for controller synthesis and general transition probabilities and a lower bound theorem for nonlinear integral terms, a new synthesis method to ensure the required stability and meet the required performance is proposed in the form of linear matrix inequalities. The validity of the proposed control method is illustrated by a numerical example.     

The relationship between muscle kinetic parameters and kinematic variables in a complex movement

Summary Kinematic variables of the vertical jump (jumping height, jump phase durations and joint angles) were measured on 39 male physical education students. In addition, kinetic parameters of the hip and knee extensors, and of the plantar flexors (maxima voluntary force and its rate of development) were recorded on the same subjects, in isometric conditions. The results demonstrated significant positive correlations between kinetic parameters of the active muscle groups and jumping height (r=0.217−0.464). The dominant effect on these correlations was due to the knee extensors. Correlations between these parameters and the duration of the jump phases were much weaker. Correlation coefficients between kinetic parameters and limb angles in the lowest body position showed that fast force production in one muscle group was related to a significant decrease in the joint angles of distant body segments. Multiple correlation coefficients between leg extensor parameters and kinematic variables (ranging between 0.256 for the duration of the counter-movement phase and 0.616 for jump height) suggested that kinetic parameters could explain more than a quarter of the variability of this complex human movement. Therefore, the conclusion was drawn that an extended set of measurements of the relevant musculo-skeletal system parameters could predict a considerable amount of the variability of human movement. However, high correlation coefficients between the same kinetic parameters of different muscle groups suggest that not all active muscle groups have to be included in the measurements.     

Gender difference in the relationship of performance in the handgrip and standing long jump tests to lean limb volume in young adults

Summary Groups of young, adult males and females performed the handgrip and standing long jump tests. Their total forearm and leg volumes were calculated from a series of circumference and length measurements, and the lean volumes (bone + muscle) calculated by taking the skinfold thickness into consideration. In the handgrip, the mean female performance was 298 N compared with 496 N for the males. In the standing long jump, mean performance expressed as distance x body mass was 87.3 kg · m for females compared with 137.7 kg · m for males. These superior performances of males could simply reflect their greater muscle mass, as the mean lean volumes of female and male limbs respectively were 0.54 l and 0.89 l for forearms, and 11.82 l and 14.82 l for the two legs. However, when the performances of males and females were grouped by lean limb volume, it was found that while in both tests there were linear relationships, males and females did not share a common line. In both tests the male relationship was at a higher level than the female; therefore, for a given lean volume, the male performance was significantly superior to that of the female. The gender difference found in this study has not been seen in other studies in which the performance of skeletal muscle has been related to the cross-sectional area of the active muscles and the possible reasons for the differences are considered.     

Effects of combined whole body vibration and resistance training on lower quadrants electromyographic activity,muscle strength and power in athletes

BackgroundWhole body vibration (WBV) with resistance training is one of the increasing ways of gaining ankle and foot complex muscle strength and power for the rehabilitative and prophylactic purpose in athletes.ObjectiveThe purpose of the study was to compare the effects of combined WBV and resistance training (RVE) with strength training alone (RE) on alteration of gastrocnemius lateralis and vastus medialis obliquus muscle activity and strength, and power performance in athletes.MethodsThe study was performed on 23 university-level male athletes who were randomized into two groups as RVE (n = 12; age 22.2 ± 1.94 years) and RE (n = 11; age 21.60 ± 1.78 years). The training program was scheduled three times per week for six weeks (18 sessions). Gastrocnemius lateralis (GL) and vastus medialis obliquus (VMO) were measured for muscle activity and isometric strength with surface EMG device and handheld dynamometer respectively. Counter-movement jump (CMJ) was used for measuring power. All the participants were assessed for outcome measures at baseline and then after 6 weeks. Group (RVE vs. RE) by time (pre vs. post) effects were compared through a 2-way interaction utilizing mixed model repeated measure ANOVA.ResultsAfter training, VMO muscle activity (group effects) increased significantly in the RVE group (p < 0.05). However, both the groups showed statistically significant time and group × time interaction effects for muscle activity of VMO, isometric strength (VMO and GL), and CMJ (p < 0.05).ConclusionWBV might serve as an adjunct modality for enhancement of the neuromuscular activity of the VMO muscle. However, RVE had no additive effect when compared to RE alone on muscle strength and power in athletes. The long-term impacts of combined WBV and resistance training on other foot and ankles muscle should be investigated in future studies.     

A Two-Dimensional Second Order Conservative Front-Tracking Method with an Original Marker Advection Approach Based on Jump Relations

A two-dimensional front-tracking method is developed for handling complex shape interfaces satisfying the volume conservation. In order to validate the proposed front-tracking method, a complete convergence study is carried out on several analytical test cases for which the interface is widely stretched and deformed. Comparisons to different existing approaches show that our front-tracking method is second order accurate in space with lower errors than existing interface tracking techniques of the literature.We also propose an original marker advection method which takes into account the jump relations valid at interface in order to deal with the contrast of physical properties encountered in two-phase flow simulations. The conservative front-tracking method computed in this work is shown to be able to describe interfaces with high accuracy even for poorly resolved Eulerian grids.     

Bayesian species delimitation using multilocus sequence data

In the absence of recent admixture between species, bipartitions of individuals in gene trees that are shared across loci can potentially be used to infer the presence of two or more species. This approach to species delimitation via molecular sequence data has been constrained by the fact that genealogies for individual loci are often poorly resolved and that ancestral lineage sorting, hybridization, and other population genetic processes can lead to discordant gene trees. Here we use a Bayesian modeling approach to generate the posterior probabilities of species assignments taking account of uncertainties due to unknown gene trees and the ancestral coalescent process. For tractability, we rely on a user-specified guide tree to avoid integrating over all possible species delimitations. The statistical performance of the method is examined using simulations, and the method is illustrated by analyzing sequence data from rotifers, fence lizards, and human populations.     

Neuromuscular control and hop performance in youth and adult male and female football players

ObjectivesTo compare neuromuscular control and hop performance between youth and adult male and female football players.DesignCross-sectional study.Participants119 youth players (13–16 years; 68 males) and 88 adult players (17–26 years; 44 males).Main outcome measuresNeuromuscular control assessed with drop vertical jump (DVJ) and tuck jump assessment (TJA). Hop performance assessed with single-leg hop for distance and side hop.ResultsAdult females had smaller normalized knee separation distances (NKSD) during DVJ at initial contact (77.9 ± 18.5 vs. 86.1 ± 11.0, p = 0.010) and at maximum knee flexion (59.7 ± 23.4 vs.74.1 ± 18.1, p = 0.001) compared to youth females. TJA revealed more technique errors in youths compared to adults (males 10 (8–11) vs. 8 (7–10); females 11 (9–12) vs. 9 (8–11), p < 0.05). Youths demonstrated inferior hop performance (males single-leg hop 142 ± 18 vs. 163 ± 17, side hop 41 ± 12 vs. 52 ± 12, p < 0.001; females side hop 32 ± 10 vs. 38 ± 14, p < 0.05).ConclusionsYouth players demonstrated reduced neuromuscular control during TJA and inferior hop performance compared to adult players. Adult female players demonstrated greater knee valgus during DVJ compared to youth female players.     

Anterior cruciate ligament injury about 20 years post‐treatment: A kinematic analysis of one‐leg hop

Reduced dynamic knee stability, often evaluated with one‐leg hops (OLHs), is reported after anterior cruciate ligament (ACL) injury. This may lead to long‐standing altered movement patterns, which are less investigated. 3D kinematics during OLH were explored in 70 persons 23 ± 2 years after ACL injury; 33 were treated with physiotherapy in combination with ACL reconstruction (ACL_R) and 37 with physiotherapy alone (ACL_PT). Comparisons were made to 33 matched controls. We analyzed (a) maximal knee joint angles and range of motion (flexion, abduction, rotation); (b) medio‐lateral position of the center of mass (COM) in relation to knee and ankle joint centers, during take‐off and landing phases. Unlike controls, ACL‐injured displayed leg asymmetries: less knee flexion and less internal rotation at take‐off and landing and more lateral COM related to knee and ankle joint of the injured leg at landing. Compared to controls, ACL_R had larger external rotation of the injured leg at landing. ACL_PT showed less knee flexion and larger external rotation at take‐off and landing, and larger knee abduction at Landing. COM was more medial in relation to the knee at take‐off and less laterally placed relative to the ankle at landing. ACL injury results in long‐term kinematic alterations during OLH, which are less evident for ACL_R.