Coupling of Penetrant and Polymer Motions During Small-Molecule Diffusion In a Glassy Polymer

Abstract

Multidimensional transition-state theory was used to simulate methane jump motions in glassy atactic polypropylene at 233 K in the limit of small methane concentrations. Transition states were found with respect to both penetrant and polymer degrees of freedom, using all generalized coordinates associated with atoms interacting with the methane penetrant. Animations followed the multidimensional reaction coordinate for three different jumps.

The jump mechanism involved polymer atoms retracting to form a channel, followed by penetrant motion through the channel. Methyl groups within 4 Å of the penetrant transition state location were displaced by 0.9 Å on average, while carbon atoms and methyl groups further than 9 Å from the penetrant transition state location were displaced by less than 0.2 Å.

The energy profiles along the diffusion path differed considerably among all jumps simulated, and the jump rate did not correlate simply with changes in particular types of degrees of freedom. Jumps for which the penetrant transition state location was within 5 Å of a chain start or end had average rates of order 60 μs^?1, while jumps further from a chain start or end were an order of magnitude slower.     

Dynamics,control, and simulation of the jump of a quadruped

Gross body motion of a six-link quadruped model is considered in the sagittal plane. The model includes eight representative muscles of fore- and hind limbs as force generators. The kinematics of the quadruped's long jump are studied, and the translational and the rotational components of the jump are decoupled. Stability of the model is achieved by state feedback. The motion of this model during starting, flight, and landing phases of motion is studied by digital computer simulation. It is shown that in the starting phase feedback is essential for the control of the takeoff velocity, while the jump itself can be carried out without feedback as a ballistic movement.     

Glycerolipids: common features of molecular motion in bilayers

In the present study, analysis of 2H NMR line-shape and spin-lattice relaxation behavior has been used to investigate the dynamics of several glycolipid and phospholipid bilayers. The gel-phase spectra of these lipids labeled at the C3 position of the glycerol backbone are broad (approximately 90 kHz) and characteristic of fast-limit axially asymmetric motion. Moreover, anisotropic spin-lattice relaxation is observed in all of these systems. The line-shape and relaxation features of the lipids in the gel phase were best simulated by using a fast-limit three-site jump model, with relative site populations of 0.46, 0.34, and 0.20. This motion is associated with an internal jump about the C2-C3 bond of the glycerol backbone. A second motion, rotation about the long axis of the molecule, is needed to account for the observed temperature dependence of the quadrupolar echo amplitude and the spectral line shape above and below the gel to liquid-crystalline phase transition temperature. On the other hand, the gel-phase spectra of phospholipids labeled at the C2 position of the glycerol backbone are also characterized by a fast internal motion, which is simulated by a two-site librational jump. The results indicate that the glycerol backbone dynamics of the glycolipid and phospholipid systems investigated in this study can be described in terms of common fast internal motions and a slower whole molecule axial motion. These results are compared with previous dynamic studies of similar systems.     

Validity of two alternative systems for measuring vertical jump height

Vertical jump height is frequently used by coaches, health care professionals, and strength and conditioning professionals to objectively measure function. The purpose of this study is to determine the concurrent validity of the jump and reach method (Vertec) and the contact mat method (Just Jump) in assessing vertical jump height when compared with the criterion reference 3-camera motion analysis system. Thirty-nine college students, 25 females and 14 males between the ages of 18 and 25 (mean age 20.65 years), were instructed to perform the countermovement jump. Reflective markers were placed at the base of the individual's sacrum for the 3-camera motion analysis system to measure vertical jump height. The subject was then instructed to stand on the Just Jump mat beneath the Vertec and perform the jump. Measurements were recorded from each of the 3 systems simultaneously for each jump. The Pearson r statistic between the video and the jump and reach (Vertec) was 0.906. The Pearson r between the video and contact mat (Just Jump) was 0.967. Both correlations were significant at the 0.01 level. Analysis of variance showed a significant difference among the 3 means F(2,235) = 5.51, p < 0.05. The post hoc analysis showed a significant difference between the criterion reference (M = 0.4369 m) and the Vertec (M = 0.3937 m, p = 0.005) but not between the criterion reference and the Just Jump system (M = 0.4420 m, p = 0.972). The Just Jump method of measuring vertical jump height is a valid measure when compared with the 3-camera system. The Vertec was found to have a high correlation with the criterion reference, but the mean differed significantly. This study indicates that a higher degree of confidence is warranted when comparing Just Jump results with a 3-camera system study.     

A simple strategy for jumping straight up

Jumping from a stationary standing position into the air is a transition from a constrained motion in contact with the ground to an unconstrained system not in contact with the ground. A simple case of the jump, as it applies to humans, robots and humanoids, is studied in this paper. The dynamics of the constrained rigid body are expanded to define a larger system that accommodates the jump. The formulation is applied to a four-link, three-dimensional system in order to articulate the ballistic motion involved. The activity of the muscular system and the role of the major sagittal muscle groups are demonstrated. The control strategy, involving state feedback and central feed forward signals, is formulated and computer simulations are presented to assess the feasibility of the formulations, the strategy and the jump.     

Gender and foot orthotic device effect on frontal plane hip motion during landing from a vertical jump

Excessive hip motion has been linked to lower extremity pathology. Foot orthoses are commonly used to control motion within lower extremity joints when lower extremity pathology and dysfunction are present. Few studies have investigated the effect of foot orthoses on hip angular kinematics during functional activities. Eighteen females and 18 males performed a vertical jump with and without a prefabricated foot orthoses to determine the biomechanical effect of foot orthoses on hip kinematics when landing from a jump. Data collection included three-dimensional motion analysis of the lower extremity. Paired t tests were performed to determine if differences existed within genders with and without foot orthoses. At the hip joint, there was significantly less hip adduction motion in the foot orthoses condition as compared with the no foot orthoses condition in females (p < .05). There were no differences between foot orthoses conditions in males. Females appear to have a different proximal response to foot orthoses when landing from a forward jump than males.     

Molecular motions and dynamics of a diunsaturated acyl chain in a lipid bilayer: implications for the role of polyunsaturation in biological membranes.

The nature and dynamics of the motions of a diunsaturated fatty acyl chain in a lipid bilayer were examined using a comprehensive simulation program for 2H NMR line shapes developed by Wittebort et al. [Wittebort, R. J., Olejniczak, E. T., & Griffin, R. G. (1987) J. Chem. Phys. 36, 5411-5420]. A motional model in which the isolinoleoyl chain (18:2 delta 6,9) adopts two conformations consistent with the low energy structures proposed for 1,4-pentadiene [Applegate, K. R., & Glomset, J. A. (1986) J. Lipid Res. 27, 658-680], but undergoes a rapid jump between these states, is sufficient to account for the experimentally observed quadrupolar couplings, the 2H-2H and 1H-2H dipolar couplings, the longitudinal relaxation times, and the changes in the average conformation of the chain that occur with a variation in temperature. The jump motion originates via rotations about the C7-C8 and the C8-C9 carbon bonds and leads to the low order parameters assigned to the C8 methylene segment (0.18) and the C9-C10 double bond (0.11). In contrast, the C6-C7 double bond, which is not involved in the two-site jump, characterized by a relatively large order parameter (0.56). Fatty acyl chains containing three or more double bonds likely cannot undergo the same jump motion and consequently will be highly ordered structures. Correlation times for diffusion of the molecular long axis of the diunsaturated acyl chain about the bilayer normal (approximately 10(-10) s) and for the local jump motion (approximately 10(-10) s) were calculated.(ABSTRACT TRUNCATED AT 250 WORDS)     

The influence of aerodynamic and biomechanical factors on long jump performance

A new analysis, based on the equations of motion, is made of the influence of aerodynamic drag on the trajectory and aerial range achieved by a long jumper. The general result is applied to a particular case, namely the world long jump record obtained by Bob Beamon at the Mexico Olympics in 1968. Calculations are also made of the influence of body height and jumping technique on overall long-jump performance. A comparison is made between the relative importance of aerodynamic and anthropometric aspects of long jump performance.     

Neuromechanical strategies employed to increase jump height during the initiation of the squat jump.

The maximal height attained in a vertical jump is heavily influenced by the execution of a large countermovement prior to the upward motion. When a jump must be executed without a countermovement, as in a squat jump, the maximal jump height is reduced. During such conditions, the human body may use other strategies in order to increase performance. The purpose of this research was to investigate the effects of two strategies employed during the initiation of the squat jump: the premovement silent period (PSP), and the small amplitude countermovement (SACM). Fifteen elite male volleyball players (20.6 +/- 1.6 years) and 13 untrained males (20.2 +/- 1.7 years) performed 10 maximal effort squat jumps from identical starting positions. The electromyographic activity of the vastus lateralis and biceps femoris was measured in conjunction with the vertical ground reaction force and vertical displacement. It was found that the presence of a PSP or a SACM of 1-3 cm did not increase maximal squat jump height significantly (p > 0.05), in neither the highly trained athletes nor the untrained individuals. These results suggest that these strategies do not play a major role in the determination of jump height. Researchers have assumed that a squat jump is purely concentric, and that there are no facilitating mechanisms present that may influence the performance of the jump. This study provides evidence to support this assumption.     

Drift compensation and its sensory basis in waterstriders (Gerris paludum F.)

Summary Watestriders (Gerris paludum F.), displaced by flowing water or wind, compensate for this by periodic jumps against the direction of drift so that they keep their average position — relative to the river bank, for instance — constant over long periods of time. To identify the cues used by the animals to compensate for drift, they were kept on an artificial stream with visual patterns along one or both sides. The velocity of the water flow and the pattern motion were varied. It is not possible to induce compensatory jumps in darkness by water or air current alone. Visual cues are indispensable for the reaction. The product of jump amplitude and jump frequency equals the drift velocity on average. The jump amplitudes are more or less independent of the flow velocity while the jump frequency is adjusted to it.     

Nanovid tracking: a new automatic method for the study of mobility in living cells based on colloidal gold and video microscopy.

We describe a new automatic technique for the study of intracellular mobility. It is based on the visualization of colloidal gold particles by video-enhanced contrast light microscopy (nanometer video microscopy) combined with modern tracking algorithms and image processing hardware. The approach can be used for determining the complete statistics of saltatory motility of a large number of individual moving markers. Complete distributions of jump time, jump velocity, stop time, and orientation can be generated. We also show that this method allows one to study the characteristics of random motion in the cytoplasm of living cells or on cell membranes. The concept is illustrated by two studies. First we present the motility of colloidal gold in an in vitro system of microtubules and a protein extract containing a kinesin-like factor. The algorithm is thoroughly tested by manual tracking of the videotapes. The second study involves the motion of gold particles microinjected in the cytoplasm of PTK-2 cells. Here the results are compared to a study using the spreading of colloidal gold particles after microinjection.     

Effect of arm motion on standing lateral jumps

The role of arm swing in jumping has been examined in numerous studies of standing jumps for height and forward distance, but no prior studies have explored its effect on lateral jumping. The purpose of the present study was to investigate the effect of arm motion on standing lateral jump performance and to examine the biomechanical mechanisms that may explain differences in jump distance. Six participants executed a series of jumps for maximum lateral distance from two in-ground force platforms for two jump cases (free and restricted arms) while an eight-camera, passive-reflector, motion capture system collected 3D position data throughout the movements. Inverse kinematics and dynamics analyses were performed for all jumps using three-dimensional (3D) link models to calculate segment angular velocities, joint moments, joint powers, and joint work. Free arm motion improved standing lateral jump performance by 29% on average. This improvement was due to increased takeoff velocity and improved lateral and vertical positions of the center of gravity (CG) at takeoff and touchdown. Improved velocity and position of the CG at takeoff resulted from a 33% increase in the work done by the body. This increase in work in free arm jumps compared to restricted arm jumps was found in both upper and lower body joints with the largest improvements (>30 J) occurring at the lower back, right hip, and right shoulder.     

Interactive computer graphics in the study of human body planar motion under free fall conditions

A computer program utilizing interactive graphics was developed in order to study the planar motion of a five-segment model of the human body. By providing instantaneous feedback and convenient graphical representation of the body, the program allows the user to quickly simulate and study body motions of interest. Consequently, the model is a useful tool for the researcher and may be readily employed for student instructional purposes.The configuration of the model, and the derivation and validation of the equations of motion, are included. Several options provided by the simulation are described.     

Test-retest reliability of knee biomechanics during stop jump landings

Studies that seek to determine the effects of an intervention on knee biomechanics during landing from a jump implicitly assume that the variables of interest are reliable both within and between data collection sessions. Currently, such reliability data are not available for a stop jump. Standard three-dimensional motion analysis was used to determine sagittal and frontal plane peak angles and moments and peak vertical ground reaction force within and between sessions for a stop jump. Twelve female recreational athletes participated in two data collection sessions spaced two weeks apart. Interclass correlation coefficients and coefficient of multiple correlation were used to determine within and between session reliability of peak knee flexion angle, peak internal knee extension moment, peak knee abduction angle, peak internal knee adduction moment and peak vertical ground reaction force. Overall reliability within a session (ICC (3,1) 0.631-0.881; CMC 0.672-0.958) and between sessions (ICC (3,k) 0.685-0.959; CMC 0.598-0.944) was good. Peak angles and moments were similar between sessions. The stop jump is less reliable within a session than a drop vertical jump reported previously in the literature. This is likely due to increased intrasubject variability between trials due to the less constrained nature of the task. Reliability of the stop jump is comparable to the drop vertical jump between sessions. Reliability of knee adduction moment is lower than reported for the drop vertical jump. The results of this study support the use of a stop jump task to evaluate knee biomechanics during landing in longitudinal studies with a repeated measures design.     

Targeting a surface cavity of alpha 1-antitrypsin to prevent conformational disease

Conformational diseases are caused by a structural rearrangement within a protein that results in aberrant intermolecular linkage and tissue deposition. This is typified by the polymers that form with the Z deficiency variant of alpha 1-antitrypsin (Glu-342 --> Lys). These polymers are retained within hepatocytes to form inclusions that are associated with hepatitis, cirrhosis, and hepatocellular carcinoma. We have assessed a surface hydrophobic cavity in alpha1-antitrypsin as a potential target for rational drug design in order to prevent polymer formation and the associated liver disease. The introduction of either Thr-114 --> Phe or Gly-117 --> Phe on strand 2 of beta-sheet A within this cavity significantly raised the melting temperature and retarded polymer formation. Conversely, Leu-100 --> Phe on helix D accelerated polymer formation, but this effect was abrogated by the addition of Thr-114 --> Phe. None of these mutations affected the inhibitory activity of alpha 1-antitrypsin. The importance of these observations was underscored by the finding that the Thr-114 --> Phe mutation reduced polymer formation and increased the secretion of Z alpha 1-antitrypsin from a Xenopus oocyte expression system. Moreover cysteine mutants within the hydrophobic pocket were able to bind a range of fluorophores illustrating the accessibility of the cavity to external agents. These results demonstrate the importance of this cavity as a site for drug design to ameliorate polymerization and prevent the associated conformational disease.     

Analytical and multibody modeling for the power analysis of standing jumps

Two methods for the power analysis of standing jumps are proposed and compared in this article. The first method is based on a simple analytical formulation which requires as input the coordinates of the center of gravity in three specified instants of the jump. The second method is based on a multibody model that simulates the jumps processing the data obtained by a three-dimensional (3D) motion capture system and the dynamometric measurements obtained by the force platforms. The multibody model is developed with OpenSim, an open-source software which provides tools for the kinematic and dynamic analyses of 3D human body models. The study is focused on two of the typical tests used to evaluate the muscular activity of lower limbs, which are the counter movement jump and the standing long jump. The comparison between the results obtained by the two methods confirms that the proposed analytical formulation is correct and represents a simple tool suitable for a preliminary analysis of total mechanical work and the mean power exerted in standing jumps.     

The maximal and submaximal vertical jump: implications for strength and conditioning

The vertical jump is a widely used activity to develop explosive strength, particularly in plyometric and maximal power training programs. It is a multijoint action that requires substantial muscular effort from primarily the ankle, knee, and hip joints. It is not known if submaximal performances of a vertical jump have a proportional or differential training effect on the major lower-limb muscles compared to maximal jump performance. Therefore, the purpose of this study was to investigate the contribution that each of the major lower-limb joints makes to vertical jump performance as jump height increases and to comment on the previously mentioned uncertainty. Adult males (N = 20) were asked to perform a series of submaximal (LOW and HIGH) and maximal (MAX) vertical jumps while using an arm swing. Force, motion, and electromyographical data were recorded during each performance and used to compute a range of kinematic and kinetic data, including ankle, knee, and hip joint torques, powers, and work done. It was found that the contribution to jump height made by the ankle and knee joints remains largely unchanged as jump height increases (work done at the ankle: LOW =1.80, HIGH = 1.97, MAX = 2.06 J.kg(-1), F = 3.596, p = 0.034; knee: LOW = 1.62, HIGH = 1.77, MAX = 1.94 J.kg(-1), F = 1.492, p = 0.234) and that superior performance in the vertical jump is achieved by a greater effort of the hip extensor muscles (work done at the hip: LOW = 1.03, HIGH = 1.84, MAX = 3.24 J.kg(-1), F = 110.143, p < 0.001). It was concluded that the role of submaximal and maximal jumps can be differentiated in terms of their effect on ankle, knee, and hip joint muscles and may be of some importance to training regimens in which these muscles need to be differentially trained.     

Optimal control simulations reveal mechanisms by which arm movement improves standing long jump performance

Optimal control simulations of the standing long jump were developed to gain insight into the mechanisms of enhanced performance due to arm motion. The activations that maximize standing long jump distance of a joint torque actuated model were determined for jumps with free and restricted arm movement. The simulated jump distance was 40 cm greater when arm movement was free (2.00 m) than when it was restricted (1.60 m). The majority of the performance improvement in the free arm jump was due to the 15% increase (3.30 vs. 2.86 m/s) in the take-off velocity of the center of gravity. Some of the performance improvement in the free arm jump was attributable to the ability of the jumper to swing the arms backwards during the flight phase to alleviate excessive forward rotation and position the body segments properly for landing. In restricted arm jumps, the excessive forward rotation was avoided by "holding back" during the propulsive phase and reducing the activation levels of the ankle, knee, and hip joint torque actuators. In addition, swinging the arm segments allowed the lower body joint torque actuators to perform 26 J more work in the free arm jump. However, the most significant contribution to developing greater take-off velocity came from the additional 80 J work done by the shoulder actuator in the jump with free arm movement.