Impaired control of mediolateral body motion during walking is an important health concern. Developing treatments to improve mediolateral control is challenging, partly because the mechanisms by which muscles modulate mediolateral ground reaction force (and thereby modulate mediolateral acceleration of the body mass center) during unimpaired walking are poorly understood. To investigate this, we examined mediolateral ground reaction forces in eight unimpaired subjects walking at four speeds and determined the contributions of muscles, gravity, and velocity-related forces to the mediolateral ground reaction force by analyzing muscle-driven simulations of these subjects. During early stance (0–6% gait cycle), peak ground reaction force on the leading foot was directed laterally and i...

Why is maximal running speed reduced on curved paths? The leading explanation proposes that an increase in lateral ground reaction force necessitates a decrease in peak vertical ground reaction force, assuming that maximum leg extension force is the limiting factor. Yet, no studies have directly measured these forces or tested this critical assumption. We measured maximum sprint velocities and ground reaction forces for five male humans sprinting along a straight track and compared them to sprints along circular tracks of 1, 2, 3, 4 and 6 m radii. Circular track sprint trials were performed either with or without a tether that applied centripetal force to the center of mass. Sprinters generated significantly smaller peak resultant ground reaction forces during normal curve sprinting compared to straight sprinting. This provides direct evidence against the idea that maximum leg extension force is always achieved and is the limiting factor. Use of the tether increased sprint speed, but not to expected values. During curve sprinting, the inside leg consistently generated smaller peak forces compared to the outside leg. Several competing biomechanical constraints placed on the stance leg during curve sprinting likely make the inside leg particularly ineffective at generating the ground reaction forces necessary to attain maximum velocities comparable to straight path sprinting. The ability of quadrupeds to redistribute function across multiple stance legs and decouple these multiple constraints may provide a distinct advantage for turning performance. PMID:17337710

Change, constancy, and measurement. · Evidence .... ground. As each cannonball was fired, it was acted upon by two forces. 5. One force .... most famous yo-yo tricks (walking the dog, ... bers master the jumping activity, they can add ... that the end ball makes vertical circles around .... ing out of the cup (action- reaction).

In this research kinematics parameters derived from ground reaction forces were evaluated to limit differential diagnoses and measure the degree of disabilities during walking among neuropathic subjects. 25 neuropathic subjects affected by drop foot and 20 normal subjects were enrolled in the study. Each subject was tested in average 10+-2 times for calculating kinetics parameters derived from ground reaction forces. The results revealed that the center of pressure displacement pattern in sole of foot can be a good index for differential diagnoses and measuring the degree of disabilities. This research can extend the clinical applications of ground reaction force plate and introduce suitable criteria to measure the degree of disability among neuropathic patients.

The biomechanics of running in small animals have remained poorly characterized because of the difficulty of recording three-dimensional ground reaction forces. Available techniques limit investigations to animals with a body mass above 1 g. Here we present, for the first time, single-leg ground reaction forces of ants (body mass 10 mg), measured with a custom-built miniature force plate. We investigated forces and high-speed kinematics for straight level runs (average speed: 8.4 cm s(-1)) of Formica polyctena workers. The major finding was that the time course of ground reaction forces strongly differed from previous observations of larger insects. Maximum vertical force was reached during the first third of the tripod contact phase. During this period the body was decelerated predominantly by the front legs. Subsequently, the front legs pulled and accelerated the body. This 'climbing' type of stride may be useful on the bumpy and unstable substrates that the animals face in their natural habitats, and may therefore also occur on level ground. Propulsive forces were generated predominantly by the front and hind legs. Dragging of the gaster on the substrate resulted in a breaking momentum, which was compensated by the legs. Future investigations will reveal, whether the identified pattern is due to specialization. PMID:19617436

measurement were employed. In a few .... holes inthe ground even before lift-off. .... launch of a satellite carrying a dog named Laika on board. .... The rider jumps off the ... isaction and reaction at work (third law). The force acting on the cannon and the ball is the same. What happens ..... vertical rod that acts as a pivot point.

Background Achilles tendinopathies are characterised by pain and reduced function, and heavy-load exercises have been shown to be effective in the treatment of painful chronic Achilles tendinopathies. However, basic information is needed on how the biomechanics and neuromuscular control of the exercise are affected by Achilles tendon pain. Objective The authors aimed to determine the effects of experimental Achilles tendon pain on motor function during one-legged weight bearing ankle plantar and dorsal flexion exercises. Methods In a crossover study, with 16 healthy subjects tested on two different days separated by 1 week, three-dimensional ground reaction forces, ankle joint kinematics and surface electromyography (EMG) of the lower leg muscles were recorded during one-legged full weight-bearing ankle plantar (concentric) and dorsal (eccentric) flexion exercises. Measurements were done before, during and after either experimental Achilles tendon pain or a non-painful control condition. Pain was induced by intratendinous injections of hypertonic saline with isotonic saline injections as control. Joint kinematics, ground reaction force frequency contents and average EMG amplitudes were calculated. Results Compared with the control condition experimental Achilles tendon pain reduced the EMG activity in agonistic, synergistic and antagonistic muscles, and increased the ground reaction force frequency content around 10 Hz, during both eccentric and concentric movement phases. Conclusions These data show that experimental Achilles tendon pain causes widespread and reduced motor responses with functional effects on the ground reaction force.

The aim of this study was to identify differences in knee range of motion (ROM), movement speed, ground reaction forces (GRF) profile, neuromuscular activity, and muscle coactivation during the transition between stair descent and level walking in meniscectomized patients at high risk of knee osteoarthritis (OA) compared with the nonoperated leg and with healthy controls.

Objective: To (1) report ground reaction forces for healthy Rottweilers at a trot and (2) compare force platform data with values obtained for healthy Labradors. Study Design: Prospective, clinical study. Animals: Adult Rottweilers (n=9) and Labrador Retrievers (12) without orthopedic abnormalities. Methods: Dogs were trotted over a force platform at controlled speed and acceleration. Peak vertical and craniocaudal forces, associated impulses, stance time, rising, and falling slopes were analyzed and forces, impulses, and slopes were expressed as percentages of body weight. The effects of weight and anatomic measurements on force platform values were re-evaluated with analysis of covariance (ANCOVA). Results: In Rottweilers, peak vertical forces in thoracic limbs were significantly lower a...

Properties of ground surfaces condition locomotion, and quality of track surfaces is believed to be involved in the pathogenesis of many musculoskeletal injuries in the horse. Measuring ground reaction forces (GRF) is an interesting approach to assess those interactions. Forceplates are the most commonly used but they are not well suited to compare different ground surfaces at fast gaits. Embarked equipment, fixed under the horses hoof, would allow force measurement on any track. The objective of this work was (1) to design a device which enables the measurement of 3-D GRF on any ground, at any gait, for a given subject, (2) to determine its accuracy, and (3) to evaluate its performance and usefulness under physiological conditions. The resulting dynamometric horseshoe was composed of 4 pi...

Nonprimate terrestrial mammals may use digitigrade postures to help moderate distal limb joint moments and metapodial stresses that may arise during high-speed locomotion with high-ground reaction forces (GRF). This study evaluates the relationships between speed, GRFs, and distal forelimb kinematics in order to evaluate if primates also adopt digitigrade hand postures during terrestrial locomotion for these same reasons. Three cercopithecine monkey species (Papio anubis, Macaca mulatta, Erythrocebus patas) were videotaped moving unrestrained along a horizontal runway instrumented with a force platform. Three-dimensional forelimb kinematics and GRFs were measured when the vertical force component reached its peak. Hand posture was measured as the angle between the metacarpal segment and th...

This study compared differences between ballistic jump squat (B) and nonballistic back squat (NB) force, velocity, power, and relative acceleration duration, and the effect that the method used to identify the positive lifting phase had on these parameters. Ground reaction force and barbell kinematics were recorded from 30 resistance trained men during B and NB performance with 45% 1RM. Force, velocity, and power was averaged over positive lifting phases identified using the traditional peak barbell displacement (PD) and positive impulse method. No significant differences were found between B and NB mean force, and mean power, but B mean velocity was 14% greater than the NB equivalent. Positive impulse mean force was 24% greater than PD mean force, and B relative acceleration duration was 8.6% greater than the NB equivalent when PD was used to identify the end of the positive lifting phase. These results challenge common perceptions of B superiority for power development. PMID:22085898

The efficacy of 3 shock-absorbing materials was compared by determining impact characteristics with a drop test method and also by testing the effect of each material when used as a shoe insert in 16 asymptomatic subjects. Peak vertical ground reaction force (F1, F2, F3) and temporal force factors (T1, T2, T3) were obtained with a force plate at a high-frequency sampling rate. Impact force, impact time, impact slope, and impact energy were determined. A standard weight was dropped from 3 heights on each material covering the force plate while reduction of peak force was compared. Impact force was attenuated most effectively by Insert 3 (polymeric foam rubber) and averaged 11% less than that in shoes without inserts. Impact time was increased for all 3 inserts. Impact slope and impact energy were reduced significantly in Insert 3. There was a significant difference in peak vertical force F1 for all 3 inserts, in vertical force F2 for Insert 2 (viscoelastic polymeric material), and in vertical force F3 for Insert 2. Drop-test studies showed that at all ball heights, the highest mean peak force was observed consistently in Insert 2. PMID:7641428

Most bio-inspired robots have been based on animals with jointed, stiff skeletons. There is now an increasing interest in mimicking the robust performance of animals in natural environments by incorporating compliant materials into the locomotory system. However, the mechanics of moving, highly conformable structures are particularly difficult to predict. This paper proposes a planar, extensible-link model for the soft-bodied tobacco hornworm caterpillar, Manduca sexta, to provide insight for biologists and engineers studying locomotion by highly deformable animals and caterpillar-like robots. Using inverse dynamics to process experimentally acquired point-tracking data, ground reaction forces and internal forces were determined for a crawling caterpillar. Computed ground reaction forces were compared to experimental data to validate the model. The results show that a system of linked extendable joints can faithfully describe the general form and magnitude of the contact forces produced by a crawling caterpillar. Furthermore, the model can be used to compute internal forces that cannot be measured experimentally. It is predicted that between different body segments in stance phase the body is mostly kept in tension and that compression only occurs during the swing phase when the prolegs release their grip. This finding supports a recently proposed mechanism for locomotion by soft animals in which the substrate transfers compressive forces from one part of the body to another (the environmental skeleton) thereby minimizing the need for hydrostatic stiffening. The model also provides a new means to characterize and test control strategies used in caterpillar crawling and soft robot locomotion.

The goal of this study was to examine the hypothesis that the relationships between passive ankle stiffness and leg stiffness would be different between males and females. 10 males and 10 females performed hopping in place on two legs at three frequencies of 2.0, 2.5, and 3.0Hz. Based on a spring-mass model, leg stiffness, which is defined as the ratio of maximum ground reaction force to maximum center of mass displacement at the middle of the stance phase, was calculated using the vertical ground reaction force. Further, passive ankle stiffness was calculated as the slope of the passive ankle torque-angle relationship, which results from controlled passive ankle dorsiflexion. There was no significant difference in the leg stiffness between males and females at three hopping frequencies; h...

This study examined the foot biomechanics that are utilized when foot is in contact with the ground during a stance phase. The purpose of the study was to investigate the normalized ground reaction forces that impacted certain sections and points on the footprint, and to identify patterns in the degrees to which these forces occurred. Foot was modeled in such a manner that a vertex represented a bone and an edge represented a joint, and a graph that depicted the foot was created. Twelve nodes were marked on the footprint and these were linked together to create a gait path. By fusing the graph and the gait path and by manipulating the mathematical models, a profile for an ideal bipedal walking locomotion was developed. A male subject performed bipedal walking through a force plate system i...

We investigated postural sway in young subjects who were asked to rotate the head in the direction of visual targets. Thirteen subjects wore a helmet and stood on a force plate. They were asked to look at the targets quickly by directing the laser spot attached to the helmet on the target. Every subject showed consistent changes in the ground reaction force (Fx, Fy, Fz) and in the center of pressure (COP) associated with head movements. In 31% of all trials, force changes in Fx, Fy and Fz preceded head movements. During downward head movements, the anterior-posterior component of COP (COPx) exhibited the largest changes and the shortest latency. Ground reaction force in the anterior-posterior direction (Fx) also showed changes before the onset of downward head movements in 85% of the subjects (mean latency=-20 ms). However, the mean latency in other movements lagged behind the head movement onset. Electromyographic activities (EMGs) of the biceps femoris preceded the initiation of downward head movements by 22-54 ms in 2 subjects. These results indicate that goal-directed rotational head movements elicit COP changes. In addition, the COP changes preceding downward head movement suggest preparatory reactions related to anticipatory postural adjustments (APAs).   

Using a validated finite element model of the intact knee joint we aim to compute muscle forces and joint response in the stance phase of gait. The model is driven by reported in vivo kinematics–kinetics data and ground reaction forces in asymptomatic subjects. Cartilage layers and menisci are simulated as depth-dependent tissues with collagen fibril networks. A simplified model with less refined mesh and isotropic depth-independent cartilage is also considered to investigate the effect of model accuracy on results. Muscle forces and joint detailed response are computed following an iterative procedure yielding results that satisfy kinematics/kinetics constraints while accounting at deformed configurations for muscle forces and passive properties. Predictions confirm that muscle fo...

This study describes a novel calibration method for six-degrees-of-freedom force/torque sensors (FTsensors) using a pre-calibrated force plate (FP) as a reference measuring device. In this calibration method, the FTsensor is rigidly connected to a FP and force/torque data are synchronously recorded while a dynamic functional loading procedure is applied by the researcher. Based on these data an accurate calibration matrix for the FTsensor can easily be obtained via least-squares optimization. Using this calibration method, this study further investigated what loading methods are appropriate for the calibration of FTsensors intended for ambulatory measurement of ground reaction forces (GRFs). Seven different loading methods were compared (e.g., walking, pushing while standing on the FTsenso...

Using a validated finite element model of the intact knee joint we aim to compute muscle forces and joint response in the stance phase of gait. The model is driven by reported in vivo kinematics-kinetics data and ground reaction forces in asymptomatic subjects. Cartilage layers and menisci are simulated as depth-dependent tissues with collagen fibril networks. A simplified model with less refined mesh and isotropic depth-independent cartilage is also considered to investigate the effect of model accuracy on results. Muscle forces and joint detailed response are computed following an iterative procedure yielding results that satisfy kinematics/kinetics constraints while accounting at deformed configurations for muscle forces and passive properties. Predictions confirm that muscle forces and joint response alter substantially during the stance phase and that a simplified joint model may accurately be used to estimate muscle forces but not necessarily contact forces/areas, tissue stresses/strains, and ligament forces. Predictions are in general agreement with results of earlier studies. Performing the analyses at 6 periods from beginning to the end (0%, 5%, 25%, 50%, 75% and 100%), hamstrings forces peaked at 5%, quadriceps forces at 25% whereas gastrocnemius forces at 75%. ACL Force reached its maximum of 343 N at 25% and decreased thereafter. Contact forces reached maximum at 5%, 25% and 75% periods with the medial compartment carrying a major portion of load and experiencing larger relative movements and cartilage strains. Much smaller contact stresses were computed at the patellofemoral joint. This novel iterative kinematics-driven model is promising for the joint analysis in altered conditions. PMID:22721726

A model for prediction of damage to tankers during grounding is presented. The model takes into account the coupling between the external ship dynamics and the local damage process of the hull girder. The model for the local damage is based on a least upper bound solution with kinematic compatibility between all structural members. Friction is taken into account and it is shown how friction contributes to the horizontal resistance force and the vertical reaction force. The resistance of the structural members is expressed in closed forms thus requiring very small modeling time. The model was validated by small scale tests and a large scale test. Application of the theory is illustrated by a study of the grounding damage of a single hull VLCC.

The present study sought to establish links between hyperventilation and postural stability. Eight university students were asked to stand upright under two hyperventilation conditions applied randomly: (1) a metabolic hyperventilation induced by 5 min of hypercapnic-hyperoxic rebreathing (CO(2)-R); and, (2) a voluntary hyperventilation (VH) of 3 min imposed by a metronome set at 25 cycles per min. Recordings were obtained with eyes open, with the subjects standing on a force plate over 20-s periods. Ventilatory response, displacements in the centre of pressure in both the frontal and sagittal planes and fluctuations in the three planes of the ground reaction force were monitored in the time and frequency domains. Postural changes related to respiratory variations were quantified by coherence analysis. Myoelectric activities of the calf muscles were recorded using surface electromyography. Force plate measurements revealed a reduction in postural stability during both CO(2)-R and VH conditions, mainly in the sagittal plane. Coherence analysis provided evidence of a ventilatory origin in the vertical ground reaction force fluctuations during VH. Electromyographic analyses showed different leg muscles strategies, assuming the existence of links between the control of respiration and the control of posture. Our results suggest that the greater disturbing effects caused by voluntary hyperventilation on body balance are more compensated when respiration is under automatic control. These findings may have implications for understanding the organisation of postural and respiratory activities and suggest that stability of the body may be compromised in situations in which respiratory demand increases and requires voluntary control. PMID:21505845

Recent research suggests the importance of controlling rotational dynamics of a humanoid robot in balance maintenance and gait. In this paper, we present a novel balance strategy that controls both linear and angular momentum of the robot. The controller?s objective is defined in terms of the desired momenta, allowing intuitive control of the balancing behavior of the robot. By directly determining the ground reaction force (GRF) and the center of pressure (CoP) at each support foot to realize the desired momenta, this strategy can deal with non-level and non-stationary grounds, as well as different frictional properties at each foot-ground contact. When the robot cannot realize the desired values of linear and angular momenta simultaneously, the controller attributes higher priority to li...

Both of NATM and shield tunnelling method can be applied to Diluvial and Neogene deposit, on which mega cities are located in Japan. Since the lining design method for both tunnelling methods are much different, the unified concept for tunnel lining design is expected. Therefore, in this research, a frame structure analysis model for tunnel lining design using the ground reaction curve was developed, which can take into account the earth pressure due to excavated surface displacement to active side including the effect of ground self-stabilization, and the excavated surface displacement before lining installation. Based on the developed model, a parameter study was carried out taking coefficient of subgrade reaction and grouting rate as a parameter, and the measured earth pressure acting on the lining at the site was compared with the calculated one by the developed model and the conventional model. As a result, it was confirmed that the developed model can represent earth pressure acting on the lining, lining displacement, and lining sectional force at ground ranging from soft ground to stiff ground.

A randomized, placebo-controlled, four-period cross-over laboratory study involving eight dogs was conducted to confirm the effective analgesic dose of firocoxib, a selective COX-2 inhibitor, in a synovitis model of arthritis. Firocoxib was compared to vedaprofen and carprofen, and the effect, defined as a change in weight bearing measured via peak ground reaction, was evaluated at treatment dose levels. A lameness score on a five point scale was also assigned to the affected limb. Peak vertical ground reaction force was considered to be the most relevant measurement in this study. The firocoxib treatment group performed significantly better than placebo at the 3h post-treatment time point and significantly better than placebo and carprofen at the 7h post-treatment time point. Improvement ...

The authors investigated into the fundamental characteristics of the external forces on foundation piles from flowing liquefied soil by experiments under a centrifuge condition. The followings were obtained as conclusions; the viscous force resulting from the ground flow velocity of liquefied soil was dominant when model ground was completely liquefied. On the contrary, the external force resulting from ground displacements was governing the pile deformation when the model ground was not liquefied, or partially liquefied. Furthermore, when the liquefied soil was overlaid with a non-liquefied soil, external forces resulting from ground displacements of the non-liquefied soil was dominant.   

Purpose: To evaluate the relative and absolute test-re-test reliability of a new step-execution test, "Step-Ex", for clinical use in elderly with and without balance problems. Method: Test-re-test design to assess intrarater reliability. Thirty-four healthy community-dwelling elderly (65-87 years), 16 with balance problems, were tested twice two weeks apart. Step-Ex consists of two portable force platforms that register vertical ground reaction forces connected to a computer for easy detection of temporal events and phases (reaction-, preparation-, stepping- and step execution phase). Standing with one foot on each platform, the subjects were given a tactile stimulus on the heel to initiate rapid steps forward. Results: Test-re-test agreement was good to very good: ICC2.6 0.83-0.87 (withou...

Human foot is a complex musculoskeletal system. As it is inconvenient to directly measure tension forces of muscles attaching on limbs, a new quantitative method for dynamics analysis of muscle forces of ankle joint was presented based on a developed wearable motion, ground reaction force (GRF) sensor system and AnyBody Modeling System. In the AnyBody Modeling System, which professionally concerns on musculoskeletal kinematic modeling and analysis, quantitative results of muscle forces can be calculated through an inverse dynamics method. In this study, a musculoskeletal model composed of the shank and multiple-units foot was established in the AnyBody Modeling System, and an experiment was implemented with the wearable sensor system on eight volunteers during their normal gait. Tension forces of muscles of ankle joint were calculated through the inverse dynamics analysis, and the results matched the muscle activation level tendency of electromyography (EMG) method, which was implemented in the experiment as a contradistinction. The method for estimating muscle forces of ankle joint in the study appears to be a practical means to determine muscle forces in musculoskeletal analysis of human limb, and the system may be used as a convenient instrument for on-the-spot medical applications.   

Sprint mechanics and field 100-m performances were tested in 13 subjects including 9 non-specialists, 3 French national-level sprinters and a world-class sprinter, to further study the mechanical factors associated with sprint performance. 6-s sprints performed on an instrumented treadmill allowed continuous recording of step kinematics, ground reaction forces (GRF), and belt velocity and computation of mechanical power output and linear force???velocity relationships. An index of the force application technique was computed as the slope of the linear relationship between the decrease in the ratio of horizontal-to-resultant GRF and the increase in velocity. Mechanical power output was positively correlated to mean 100-m speed (P P r s > 0.683; P P = 0.16). Step frequency, contact an...

Analyses of joint moments are important in the study of human motion, and are crucial for our understanding of e.g. how and why ACL injuries occur. Such analyses may be affected by artifacts due to inconsistencies in the equations of motion when force and movement data are filtered with different cut-off frequencies. The purpose of this study was to quantify the effect of these artifacts, and compare joint moments calculated with the same or different cut-off frequency for the filtering of force and movement data. 123 elite handball players performed sidestep cutting while the movement was recorded by eight 240 Hz cameras and the ground reaction forces were recorded by a 960 Hz force plate. Knee and hip joint moments were calculated through inverse dynamics, with four different combinations of cut-off frequencies for signal filtering: movement 10 Hz, force 10 Hz, (10-10); movement 15 Hz, force 15 Hz; movement 10 Hz, force 50 Hz (10-50); movement 15 Hz, force 50 Hz. The results revealed significant differences, especially between conditions with different filtering of force and movement. Mean (SD) peak knee abduction moment for the 10-10 and 10-50 condition were 1.27 (0.53) and 1.64 (0.68) Nm/kg, respectively. Ranking of players based on knee abduction moments were affected by filtering condition. Out of 20 players with peak knee abduction moment higher than mean+1S D with the 10-50 condition, only 11 were still above mean+1 SD when the 10-10 condition was applied. Hip moments were very sensitive to filtering cut-off. Mean (SD) peak hip flexion moment was 3.64 (0.75) and 5.92 (1.80) under the 10-10 and 10-50 conditions, respectively. Based on these findings, force and movement data should be processed with the same filter. Conclusions from previous inverse dynamics studies, where this was not the case, should be treated with caution. PMID:22227316

We study the modification by the presence of a plane wall of energy level shifts of two-level atoms which are in multipolar coupling with quantized electromagnetic fields in a thermal bath in a formalism which separates the contributions of thermal fluctuations and radiation reaction and allows a distinct treatment to atoms in the ground and excited states. The position dependent energy shifts give rise to an induced force acting on the atoms. We are able to identify three different regimes where the force shows distinct features and examine, in all regimes, the behaviors of this force in both the low temperature limit and the high temperature limit for both the ground state and excited state atoms, thus providing some physical insights into the atom-wall interaction at finite temperature. In particular, we show that both the magnitude and the direction of the force acting on an atom may have a clear dependence on atomic the polarization directions. In certain cases, a change of relative ratio of polarization...

Coaches have identified the batter's weight shift as a critical component for promoting proper timing and balance in a baseball swing. Analysing the weight shift through maximum horizontal (Fx) and vertical (Fz) ground reaction forces (GRFs) of professional batters (N = 29; height = 185 ± 6 cm; mass = 92 ± 9 kg), the purpose of this study was to compare GRFs among swings against fastballs and changeups. General linear models were used to compare three conditions of interest: successful results against fastballs, successful results against changeups, and unsuccessful results against changeups. Batters had a similar loading mechanism and initial weight transfer from back foot to front foot regardless of pitch type, but pea...

A system to synthesize in real-time the sound of footsteps on different materials is presented. The system is based on microphones which allow the user to interact with his own footwear. This solution distinguishes our system from previous efforts that require specific shoes enhanced with sensors. The microphones detect real footsteps sounds from users, from which the ground reaction force (GRF) is estimated. Such GRF is used to control a sound synthesis engine based on physical models. Evaluations of the system in terms of sound validity and fidelity of interaction are described.

Proximal muscle weakness is a common association of muscular dystrophies. Knees and hip extensor weakness limit the patients' ability to counteract flexor knee joints' moments. Therefore, patients try to toe walk to move the ground reaction force (GRF) anteriorly to help to stabilise the knee. We report a case of a patient with Becker's muscular dystrophy who lost his ability to walk completely following a bilateral Achilles tendons operation. The patient's ability to heel-strike moved his GRF posteriorly resulting in creation of excessive knees flexion moments. Three years following the operation and following a lengthy rehabilitation programme, the patient managed to mobilise using an orthosis. PMID:20871148

The aim of the current study was to investigate potential age-related differences in neural regulation strategies during maximal and sub-maximal hopping. Thirty-two boys from three different age groups (9-, 12- and 15-years), completed trials of both maximal and sub maximal hopping, and based on contact and flight times, measures of reactive strength index (RSI=jump height/contact time) and leg stiffness (peak ground reaction force/peak displacement of centre of mass) were collected respectively. During all trials, surface electromyograms (EMG) were recorded from four different muscle sites of the dominant lower limb, during 100ms pre-ground contact, and then four subsequent stretch reflex phases: background muscle activity (0-30ms), short-latency stretch reflex (31-60ms), intermediate15 l...

At the Yamanashi maglev test line, two types of ground coils are used. One is for propulsion and the other for levitation and guidance. To confirm the characteristics of electromagnetic force of the ground coil for levitation and guidance, we measured the electromagnetic force directly with a measurement coil. The measurements of electromagnetic force, magnetic spring and current corresponded with the computed values to prove that the characteristics of electromagnetic force satisfy the design requirements.   

Humans use equal push-off and heel strike work during the double support phase to minimize the mechanical work done on the center of mass (CoM) during the gait. Recently, a step-to-step transition was reported to occur over a period of time greater than that of the double support phase, which brings into question whether the energetic optimality is sensitive to the definition of the step-to-step transition. To answer this question, the ground reaction forces (GRFs) of seven normal human subjects walking at four different speeds (1.1–2.4m/s) were measured, and the push-off and heel strike work for three differently defined step-to-step transitions were computed based on the force, work, and velocity. To examine the optimality of the work and the impulse data, a hybrid theoretical-em...

The aim of this study was examining the effect of human factors such as plantar friction, contact period time, and impulse on shoe-sole trituration of drop foot patients. Twenty-five patients with drop foot and twenty normal subjects were recruited in the study. The force plate and its related software's recorded human factor (coefficient of friction, ground reaction force, time of stance phase) as time dependent parameters. Dynamic coefficient of friction patterns were categorized based on their magnitude versus time when the longitudinal axis of the sole was plotted as the Y-axis and the transverse axis of the sole as X-axis during stance phase. The result of this research indicated that the average coefficient of friction among drop foot patients is 77.53 % (p value drop foot patients is 7.56 % (p value drop foot. PMID:22689288

The purpose of this study was to assess the effects of jumping distance on the landing mechanics after a volleyball spike, to help in injury prevention and training for safer landing. Ground reaction forces and three-dimensional kinematic data were collected from six male university right-handed volleyball players under “Normal” and “Long” jumping distance conditions of landing after a spike. The results revealed that the landings under the Long jumping distance condition produced significantly greater centre of gravity velocities and larger mean loading rates. Although data were collected for bilateral landings with the two feet contacting the force platform at the same time, landing motion was asymmetric and the left leg was considered to play a more critical ...

Purpose Concerns have been raised regarding the effects of schoolbag carriage on adolescent schoolchildren and particularly those with a pre-existing spinal deformity. The purpose of this study was to determine the effect of school backpack loads in scoliotic and healthy school-age children during walking, in terms of peak vertical ground reaction forces and loading rates. We hypothesized that walking with a loaded backpack would have a greater effect on gait kinetics of scoliotic compared to healthy. Methods Eight children with idiopathic scoliosis and eight healthy children were assessed. Kinetic data were collected using two AMTI OR6-7 force-plates, while the subjects walked freely along a 6-m walkway under three walking conditions: (1) without a schoolbag, (2) carrying a schoolbag bila...

Handball is one of the top four athletic games with highest injury risks. The jump shot is the most accomplished goal shot technique and the lower extremities are mostly injured. As a basis for ankle sprain simulation, the aim of this study was to extend the ankle region of an existing musculoskeletal full-body model through incorporation of three prominent lateral ankle ligaments: ligamentum fibulotalare anterius (LFTA), ligamentum fibulotalare posterius (LFTP), ligamentum fibulocalcaneare (LFC). The specific objective was to calculate and visualise ligament force scenarios during the jumping and landing phases of controlled jump shots. Recorded kinematic data of performed jump shots and the corresponding ground reaction forces were used to perform inverse dynamics. The calculated peak fo...

Turning at high speed along acute curves is crucial for athletic performance. One determinant of curved sprinting speed is the ground reaction force that can be created by the supporting limb; the moment generated at the ankle joint may influence such force generation. Body lean associated with curved sprints positions the ankle joints in extreme in-/eversion, and may hinder the ankle moment generation. To examine the influence of ankle moment generation on curved sprinting performance, 17 male subjects performed maximum-effort curved sprints in footwear with and without a wedge. The wedged footwear was constructed with the intention to align the ankle joints closer to their neutral frontal-plane configuration during counter-clockwise curved sprints so greater joint moments might be genera...

Application of quantum principles to living cells requires a new approximation of the full quantum mechanical description of intracellular dynamics. We discuss what principal elements any such good approximation should contain. As one such element, the notion of "Catalytic force" Cf is introduced. Cf is the effect of the molecular target of catalysis on the catalytic microenvironment that adjusts the microenvironment towards a state that facilitates the catalytic act. This phenomenon is experimentally testable and has an intriguing implication for biological organization and evolution, as it amounts to "optimization without natural selection of replicators". Unlike the statistical-mechanical approaches to self-organization, the Cf principle does not encounter the problem of "tradeoff between stability and complexity" at the level of individual cell. Physically, the Cf is considered as a harmonic-like force of reaction, which keeps the state of the cell close to the ground state, defined here as a state where ...

The biological central pattern generator (CPG) integrates open and closed loop control to produce over-ground walking. The goal of this study was to develop a physiologically based algorithm capable of mimicking the biological system to control multiple joints in the lower extremities for producing over-ground walking. The algorithm used state-based models of the step cycle each of which produced different stimulation patterns. Two configurations were implemented to restore over-ground walking in five adult anaesthetized cats using intramuscular stimulation (IMS) of the main hip, knee and ankle flexor and extensor muscles in the hind limbs. An open loop controller relied only on intrinsic timing while a hybrid-CPG controller added sensory feedback from force plates (representing limb loading), and accelerometers and gyroscopes (representing limb position). Stimulation applied to hind limb muscles caused extension or flexion in the hips, knees and ankles. A total of 113 walking trials were obtained across all experiments. Of these, 74 were successful in which the cats traversed 75% of the 3.5 m over-ground walkway. In these trials, the average peak step length decreased from 24.9 ± 8.4 to 21.8 ± 7.5 (normalized units) and the median number of steps per trial increased from 7 (Q1 = 6, Q3 = 9) to 9 (8, 11) with the hybrid-CPG controller. Moreover, within these trials, the hybrid-CPG controller produced more successful steps (step length ? 20 cm ground reaction force ? 12.5% body weight) than the open loop controller: 372 of 544 steps (68%) versus 65 of 134 steps (49%), respectively. This supports our previous preliminary findings, and affirms that physiologically based hybrid-CPG approaches produce more successful stepping than open loop controllers. The algorithm provides the foundation for a neural prosthetic controller and a framework to implement more detailed control of locomotion in the future.

[Purpose] In this study, the effects of muscle fatigue involving only the quadriceps femoris on low back load during lifting were dynamically and mechanically investigated in relation to the degree of muscle fatigue and distance from a heavy object. [Methods] We measured the joint angle, electromyography and ground reaction force of 18 healthy male students during lifting at 3 fatigue levels of loads placed at 3 distances from the toes. [Results] At 25% fatigue of the quadriceps femoris, at the intermediate point of lifting, the knees were mostly extended and the body trunk was leaning forward, thus altering the mode of lifting. Myoelectrical activity of the quadriceps femoris was also decreased, and myoelectrical activity of the lumbar muscle decreased during the phase from the start of muscle activity to when the object was lifted off the floor. At 50% fatigue of the quadriceps femoris, no change in joint angles was seen during lifting, and as myoelectrical activity of the quadriceps femoris decreased, myoelectrical activity of the lumbar muscle increased during the phase from the start of muscle activity to when the object was lifted off the floor. In terms of ground reaction force, greater distance was associated with greater anterior load. [Conclusion] These results suggest that when the level of quadriceps femoris fatigue is relatively low, altering the mode of lifting somewhat lessens low back load, but when the level of quadriceps femoris fatigue is relatively high, compensatory changes cannot be made and an increase in low back load can increase the risk of lumbar injury.   

BACKGROUND: Joint moments computed using inverse dynamic techniques are important estimators of net joint loads. Joints moments computed from marker position and ground reaction force data filtered using different cut-off frequencies may capture changes in moment magnitudes at a single joint that exceed normal physiological response. Peak external knee abduction moment (KAM) generated during landing (ie, the drop vertical jump, DVJ) predicts anterior cruciate ligament injury risk using marker and force data filtered at different cut-off frequencies. The purpose of the current investigation was to determine the effects of using the same low cut-off frequencies versus different cut-off frequencies on joint moment magnitudes to evaluate if artificial smoothing attenuates actual resultant joint loads related to injury risk. METHODS: Twenty-two female, high school volleyball players performed three maximum DVJs in a laboratory setting. The average peak KAM was computed for each knee using marker and force data filtered with the same low cut-off frequencies and different cut-off frequencies. RESULTS: Peak KAMs were significantly larger using different cut-off frequencies. The order of athletes ranked based on the magnitude of their peak KAMs did not significantly change across all filtering cut-off frequencies. CONCLUSIONS: The magnitude of peak KAM may differ when the same low or different higher cut-off frequencies are used to filter marker and ground reaction forces (GRF) data collected using standard motion capture equipment. It is not clear to what extent the decrease in peak KAM reported when the same low cut-off frequencies were used was solely due to attenuation of the GRF signal. PMID:22893510

As new equipment is designed and analyzed to be installed in the double-shell waste storage tanks at the Hanford Site near Richland, Washington, the equipment and the tank integrity must be evaluated. These evaluations must consider the seismically induced loads, combined with other loadings. This paper addresses the hydrodynamic behavior and response of structural components submerged in the fluid waste. The hydrodynamic effects induced by the horizontal component of ground shaking is expressed as the sum of the impulsive and convective (sloshing) components. The impulsive component represents the effects of the fluid that may be considered to move in synchronism with the tank wall as a rigidly attached mass. The convective component represents the action of the fluid near the surface that experiences sloshing or rocking motion. The added-mass concept deals with the vibration of the structural component in a viscous fluid. The presence of the fluid gives rise to a fluid reaction force that can be interpreted as an added-mass effect and a damping contribution to the dynamic response of the submerged components. The distribution of the hydrodynamic forces on the internal components is not linear. To obtain the reactions and the stresses at the critical points, the force distribution is integrated along the length of the equipment submerged in the fluid.

Plantar flexor series elasticity can be used to dissociate muscle-fascicle and muscle-tendon behavior and thus afferent feedback during human walking. We used electromyography (EMG) and high-speed ultrasonography concomitantly to monitor muscle activity and muscle fascicle behavior in 19 healthy volunteers as they walked across a platform. On random trials, the platform was dropped (8 cm, 0.9 g acceleration) or held at a small inclination (up to +/-3 degrees in the parasagittal plane) with respect to level ground. Dropping the platform in the mid and late phases of stance produced a depression in the soleus muscle activity with an onset latency of about 50 ms. The reduction in ground reaction force also unloaded the plantar flexor muscles. The soleus muscle fascicles shortened with a minimum delay of 14 ms. Small variations in platform inclination produced significant changes in triceps surae muscle activity; EMG increased when stepping on an inclined surface and decreased when stepping on a declined surface. This sensory modulation of the locomotor output was concomitant with changes in triceps surae muscle fascicle and gastrocnemius tendon length. Assuming that afferent activity correlates to these mechanical changes, our results indicate that within-step sensory feedback from the plantar flexor muscles automatically adjusts muscle activity to compensate for small ground irregularities. The delayed onset of muscle fascicle movement after dropping the platform indicates that at least the initial part of the soleus depression is more likely mediated by a decrease in force feedback than length-sensitive feedback, indicating that force feedback contributes to the locomotor activity in human walking. PMID:20032239

[Purpose] The purpose of this study was to clarify the difference in sit-to-walk (STW) motion between young adults (YG) and an elderly persons (EG). [Subjects and Methods] Twenty-seven subjects (9 in YG and 18 in EG) were instructed to perform STW and to walk 3 m at a comfortable speed and at maximal speed. Data were obtained using a 3D motion capture system for kinematic data, and two force plates for kinetic data. [Results] The time required for STW was similar for both groups at both comfortable and maximal speeds, but the forward velocity of the center of gravity of the whole body (COG-WB) was higher for YG, and upward COG-WB at the time of the first heel contact was faster for YG. Ground reaction force analyses showed many differences between the groups. For YG, COG-WB moved forward and the first swing side was longer than for EG. [Conclusion] Forward and lateral COG-WB movements before the toe-off generate a progressive force. We suggest that YG subjects may have sufficient muscle power in their lower extremity to bear the progressive force, or that EG subjects may have learned anticipatory postural control which has shorter forward movement due to aging and declining physical function.   

Sprint mechanics and field 100-m performances were tested in 13 subjects including 9 non-specialists, 3 French national-level sprinters and a world-class sprinter, to further study the mechanical factors associated with sprint performance. 6-s sprints performed on an instrumented treadmill allowed continuous recording of step kinematics, ground reaction forces (GRF), and belt velocity and computation of mechanical power output and linear force-velocity relationships. An index of the force application technique was computed as the slope of the linear relationship between the decrease in the ratio of horizontal-to-resultant GRF and the increase in velocity. Mechanical power output was positively correlated to mean 100-m speed (P acceleration was positively correlated to 100-m performance (r (s) > 0.683; P acceleration and 100-m performance (positively for the former, negatively for the two latter, all P  0.21). Last, anthropometric data of body mass index and lower-limb-to-height ratio showed no significant correlation with 100-m performance. We concluded that the main mechanical determinants of 100-m performance were (1) a "velocity-oriented" force-velocity profile, likely explained by (2) a higher ability to apply the resultant GRF vector with a forward orientation over the acceleration, and (3) a higher step frequency resulting from a shorter contact time. PMID:22422028

In this paper (Paper II), the isokinetic dynamics scheme described in Paper I is combined with the plane-wave based Car-Parrinello (CP) ab initio molecular dynamics (MD) method [R. Car and M. Parrinello, Phys. Rev. Lett. 55, 2471 (1985)] to enable the efficient study of chemical reactions and metallic systems. The Car-Parrinello approach employs ``on the fly'' electronic structure calculations as a means of generating accurate internuclear forces for use in a molecular dynamics simulation. This is accomplished by the introduction of an extended Lagrangian that contains the electronic orbitals as fictitious dynamical variables (often expressed directly in terms of the expansion coefficients of the orbitals in a particular basis set). Thus, rather than quench the expansion coefficients to obtain the ground state energy and nuclear forces at every time step, the orbitals are ``propagated'' under conditions that allow them to fluctuate rapidly around their global minimum and, hence, generate an accurate approximation to the nuclear forces as the simulation proceeds. Indeed, the CP technique requires the dynamics of the orbitals to be both fast compared to the nuclear degrees of freedom while keeping the fictitious kinetic energy that allows them to be propagated dynamically as small as possible. While these conditions can be easy to achieve in many types of systems, in metals and highly exothermic chemical reactions difficulties arise. (Note, the CP dynamics of metals is incorrect because the nuclear motion does not occur on the ground state electronic surface but it can, nonetheless, provide useful information.) In order to alleviate these difficulties the isokinetic methods of Paper I are applied to derive isokinetic CP equations of motion. The efficacy of the new isokinetic CPMD method is demonstrated on model and realistic systems. The latter include, metallic systems, liquid aluminum, a small silicon sample, the 2×1 reconstruction of the silicon 100 surface, and the Diels-Alder addition of 1,3-butadiene to the reconstructed silicon 100 surface.

Abstract in portuguese OBJETIVO: Analisar a amplitude de movimento do tornozelo e as forças de reação vertical do solo envolvidas na marcha de pacientes portadores de diabetes com e sem neuropatia periférica. CASUÍSTICA E MÉTODO: 36 indivíduos divididos em três grupos: Controle - GC: 10 indivíduos sem diabetes, Diabetes - GD: 10 indivíduos portadores de diabetes sem neuropatia periférica e Neuropatia - GDN: 16 indivíduos portadores de diabetes e neuropatia diabética periférica. Fo (more) i realizada análise da marcha - AMTI® OR6/6, e da amplitude de movimento articular tíbio-társica - Sistema Vicom 640® - de todos os participantes. RESULTADOS: O primeiro e segundo pico de força vertical de reação do solo são maiores no grupo Neuropatia e a amplitude de movimento articular do tornozelo é menor nos grupos Diabetes e Neuropatia. CONCLUSÃO: A amplitude de movimento da articulação tíbio-társica está diminuida nos diabetéticos, independente da presença ou ausência de neuropatia periférica, e os diabéticos com neuropatia periférica, apresentaram aumento no primeiro e no segundo pico da força de reação vertical do solo durante a marcha. Abstract in english OBJECTIVE: The purpose of this study was to analyze the range of movement of the ankle and the vertical ground reaction force involved in gait among diabetic patients with and without peripheral neuropathy. SAMPLE AND METHOD: 36 individuals were divided into three groups: Control group - CG: 10 individuals without diabetes, Diabetic group - DG: 10 individuals with diabetes without peripheral neuropathy and Neuropathy, and Diabetic neuropathic group - DNG: 16 individuals w (more) ith diabetes and peripheral diabetic neuropathy. Gait - AMTI® OR6/6m and range of tibiotarsal joint movement - System Vicom 640® was carried out in all the participants. RESULTS: The first and second vertical ground reaction force peaks were statistically higher in the neuropathy group, and the range of ankle motion was lower in the Diabetes and Neuropathy groups. CONCLUSION: The range of movement of the tibiotarsal joint is lower in diabetics, regardless of the presence or absence of peripheral neuropathy, and diabetics with peripheral neuropathy show an increase in the first and second vertical ground reaction force peaks during walking.

The focus of this paper is the problem of foot rotation in biped robots during the single-support phase. Foot rotation is an indication of postural instability, which should be carefully treated in a dynamically stable walk and avoided altogether in a statically stable walk. The author introduces the foot-rotation indicator (FRI) point, which is a point on the foot/ground-contact surface where the net ground-reaction force would have to act to keep the foot stationary. To ensure no foot rotation, the FRI point must remain within the convex hull of the foot-support area. In contrast with the ground projection of the center of mass (GCoM), which is a static criterion, the FRI point incorporates robot dynamics. As opposed to the center of pressure (CoP) -- better known as the zero-moment point (ZMP) in the robotics literature -- which may not leave the support area, the FRI point may leave the area. In fact, the position of the FRI point outside the footprint indicates the direction of the impending rotation and the magnitude of rotational moment acting on the foot. Owing to these important properties, the FRI point helps not only to monitor the state of postural stability of a biped robot during the entire gait cycle, but indicates the severity of instability of the gait as well. In response to a recent need, the paper also resolves the misconceptions surrounding the CoP/ZMP equivalence.

Abstract in portuguese OBJETIVO: Verificar a relação entre a mobilidade do tornozelo e do pé, e o pico da força vertical de reação do solo, considerada como porcentagem do peso corporal, gerada durante a fase de apoio da marcha. MÉTODOS: foram estudados pés normais do lado direito e esquerdo de 15 homens com 22,1±2,7 anos (19-28) e 15 mulheres 24,20±5,24 anos (19-34). Os parâmetros de exclusão foram: deformidades nos pés, doenças ou traumas, que pudessem acometer o sis (more) tema musculoesquelético e a marcha. A mobilidade do tornozelo e dos pés foi obtida através da goniometria da flexão plantar, dorsiflexão, extensão do hálux e extensão dos dedos, o pico da força vertical de reação do solo FRS, foi obtido pela baropodometria computadorizada do sistema FSCAN R. A correlação entre ambas foi feita pelo teste estatístico de Spearman. RESULTADOS: os indivíduos do grupo masculino apresentaram menores valores de mobilidade, e maiores valores do pico da força vertical de reação do solo, quando comparados com o grupo feminino. Não houve diferença entre os pés direito e esquerdo. No sexo feminino foi encontrada correlação negativa estatisticamente significante entre os valores da flexão plantar e a força vertical, e entre os valores da extensão dos dedos e a foça vertical. No sexo masculino, houve correlação negativa estatisticamente significante entre os valores da dorsiflexão e a força vertical. Entre os demais valores não foi encontrada correlação significante. CONCLUSÃO: Há relação entre a mobilidade e a força vertical gerada durante a marcha. Abstract in english OBJECTIVE: To investigate the relationship between ankle and foot mobility and the peak of the vertical ground reaction force, as a percentage of body weight, generated during the gait stance phase. METHOD: Fifteen men with mean age of 22.1 ± 2.7 years (range: 19-28) and fifteen women with mean age of 24.20 ± 5.24 years (range: 19-34) with normal feet were studied. The exclusion criteria were foot deformities or a history of trauma or diseases that might hav (more) e harmed both the musculoskeletal system and gait pattern. The ankle and foot mobility was obtained by means of goniometry on the plantar flexion, dorsiflexion, hallux extension and toe extension. The peak of the vertical ground reaction force was obtained by baropodometry using the FSCAN TM system. The Spearman statistical test was used to identify correlations. RESULTS: Males presented lower mobility values and higher peak values for the vertical ground reaction force, in comparison with females. There was no difference between the right and left foot. For females, there were statistically significant negative correlations between the values for plantar flexion and vertical force, and between the values for toe extension and vertical force. For males, there were statistically significant negative correlations between the values for dorsiflexion and vertical force. Among the remaining values, no significant correlation was found. CONCLUSION: There was a relationship between mobility and the vertical force generated during gait.

To better understand the structure of the low lying O/sup +/ states of even-even nuclides in the deformed rare-earth region, we have carried out calculations to generate the wavefunctions, energies and pair transfer rates from/to these states within a framework of exact diagonalization of the residual pairing and n-p forces. First we carried out exact diagonalization for the neutron and proton systems separately, using as a basis space the 126 vector space of four/five pairs within nine appropriate deformed Nilsson orbitals. For the pairing force we included both monopole and quadrupole terms. Next, we used the lowest eight eigenfunctions from both the neutron and the proton systems to generate a new basis space composed of the 64 possible neutron-proton product vectors. The n-p force was approximated by a quadrupole-quadrupole force term which was then diagonalized within the new basis space. The resulting wave functions were used to calculate the neutron pair transfer strength from and to the various low O/sup +/ states below 3 MeV in the even-even Gd, Dy and Er isotopes. Furthermore, for the case where the deformation parameters do not change appreciably between the pair of nuclides involved in the pair transfer reaction, reasonable global agreement was obtained for the measured (t,p) and (p,t) pair transfer reaction strengths both to the ground and excited states O/sup +/ states accessible in these isotopes. The observed enhancement of (t,p) pair transfer strength to excited states in some of these isotopes was reproduced by the calculation. The enhancement is due to subshell gap and large relative pair transfer amplitude for an orbital near the Fermi surface. 24 refs., 7 figs.

A closed form solution to the problem of steady state wedge cutting through a ductile metal plate is presented. The considered problem is an idealization of a ship bottom raking process, i.e. a continuous cutting damage of a ship bottom by a hard knife-like rock in a grounding event. A new kinematic model is proposed for the strain and displacement fields and it is demonstrated that the analysis is greatly simplified if the strain field is assumed to be dominated by plastic shear strains and moving hinge lines. Also, it is shown that the present shear model offers the basis for a convenient extension of the presented plate model to include more structural members as for example the stiffeners attached to a ship bottom plating. The fracture process is discussed and the model is formulated partly on the basis of the material fracture toughness. The effect offriction and the reaction force perpendicular to the direction of motion is derived theoretically in a new consistent manner. The perpendicular reaction force is of paramount importance for predicting the structural damage of a ship hull because it governs the vertical ship motion and rock penetration which is strongly coupled with the horizontal resistance and thus with the damaged length. The derived expressions are discussed and compared to previously published experimental results and formulas.

The goal of this study was to approach ankle instability by measuring the electromechanical delay of the peroneal muscles (foot pronators). For that purpose, supramaximal electrical stimulation of common peroneal nerve was applied when the subject was standing on a force plate in bipedal stance or monopedal stance, postures requiring greater ankle stabilization. The electromechanical delay (EMD) was defined as the time interval between the onset of the peroneus longus (PL) electromyogram detected by surface electrodes and the onset of the lateral ground reaction force (Fy) measured on a force plate. Ten healthy subjects (control group, C-G) and ten subjects with functional ankle instability ("FAI" group, FAI-G) performed the tests. In C-G, the mean EMD values decreased significantly ( PEMDs are sensitive to musculo-tendinous stiffness. They validate the choice of a PL EMD measurement as an indirect index of musculo-tendinous stiffness at the ankle. In both bipedal and monopedal stance conditions, EMD values were significantly higher in FAI subjects. They ranged from 12.64 (1.14) ms in the bipedal stance to 10.85 (1.07) ms in the monopedal stance. This suggests a lower musculo-tendinous stiffness at the ankle, which may contribute to the ankle instability. PMID:12560955

Objective-To document the caregiver placebo effect in owners and veterinarians of dogs with lameness from osteoarthritis. Design-Prospective, randomized, double-blinded, placebo-controlled, multicenter clinical trial. Animals-58 dogs with lameness secondary to osteoarthritis. Procedures-Dogs enrolled in the placebo arm of an FDA-approved study were evaluated to determine the relationship between subjective (caregiver responses) and objective (force platform gait analysis) patient outcome measures. Results-A caregiver placebo effect for owners evaluating their dog's lameness occurred 39.7% of the time. A caregiver placebo effect occurred 44.8% of the time when veterinarians examined dogs for lameness at a walk, 44.8% of the time when veterinarians examined dogs for lameness at a trot, and 43.1% of the time when veterinarians evaluated dogs for signs of pain on palpation of the joint. This effect was significantly enhanced with time. Mean ground reaction forces (GRFs) remained unchanged for dogs during treatment with the placebo. Individually, of 58 dogs, 5 had GRFs that worsened by ? 5% over 42 days, 7 had GRFs that improved by ? 5% over 42 days, and 46 had GRFs that remained unchanged. Conclusions and Clinical Relevance-A caregiver placebo effect was common in the evaluation of patient response to treatment for osteoarthritis by both pet owners and veterinarians. Force platform gait analysis was an unbiased outcome measure for dogs with lameness from osteoarthritis. A caregiver placebo effect should be considered when interpreting owner and veterinary reports of patient response to treatment. PMID:23113523

We describe a method to evaluate electronic forces by Path Integral Monte Carlo (PIMC). Electronic correlations, as well as thermal effects, are included naturally in this method. For fermions, a restricted approach is used to avoid the ``sign'' problem. The PIMC force estimator is local and has a finite variance. We applied this method to determine the bond length of H$_2$ and the chemical reaction barrier of H+H$_2\\longrightarrow $H$_2$+H. At low temperature, good agreement is obtained with ground state calculations. We studied the proton-proton interaction in an electron gas as a simple model for hydrogen impurities in metals. We calculated the force between the two protons at two electronic densities corresponding to Na ($r_s=3.93$) and Al ($r_s=2.07$) using a supercell with 38 electrons. The result is compared to previous calculations. We also studied the effect of temperature on the proton-proton interaction. At very high temperature, our result agrees with the Debye screening of electrons. As temperatu...

The rise in crude oil prices in 1973/74 and 1980/81 effected a drastic drop in mineral oil demands and a relocation of the petroleum industry's production facilities. Being forced to adapt to this development the petroleum industry succeeded in coping with the qualitative and quantitative changes in capacities more rapidly than other branches of the industry in comparable situations, and without governmental support. The rapid adaptation of the petroleum industry suggested a detailed analysis of the process of adaptation. Discussing the respective commercial grounds, this study describes the steps which were taken by the seven major German petroleum suppliers to adapt to the situation. Careful investigations provided complete accounts and reliable data and figures of the individual processes of adaptation. Typical reaction patterns were derived from the individual processes under alternative structural conditions. The statistics found in the annex are valuable sources for further studies. (orig.)

Background This study examined the effect of bilateral meniscectomy on ground reaction forces (GRFs) in sheep, and the therapeutic effect of two hyaluronan (HA) preparations. Methods Eighteen sheep were subjected to bilateral lateral meniscectomy and were treated from 16 to 20 weeks postoperatively with intraarticular Hyalgan (Fidia Farmaceutici), HYADD4-G (a novel amide derivative; Fidia Farmaceutici), or saline placebo (n = 6 per group). GRFs were assessed at baseline and 6, 12, 16, 22, and 26 weeks postoperatively. Rheological parameters and HA content of synovial fluid samples were assessed using micro-Fourier rheometry. Results Meniscectomy significantly reduced GRF and abolished the normal two-peak vector. GRF deficits were partially ameliorated by both HA preparations: Hyalgan incre...

Abstract The knee adduction moment (KAM) provides a major contribution to the elevated load in the medial compartment of the knee. An abnormally high KAM has been linked with the progression of knee osteoarthritis (OA). Footwear-generated biomechanical manipulations reduce the magnitude of this moment by conveying a more laterally shifted trajectory of the foot's center of pressure (COP), reducing the distance between the ground reaction force and the center of the knee joint, thus lowering the magnitude of the torque. We sought to examine the outcome of a COP shift in a cohort of female patients suffering from medial knee OA. Twenty-two female patients suffering from medial compartment knee OA underwent successive gait analysis testing and direct pedobarographic examination of the COP tra...

This paper presents a mechanical model of jumping robot based on the biological mechanism analysis of frog. By biological observation and kinematic analysis the frog jump is divided into take-off phase, aerial phase and landing phase. We find the similar trajectories of hindlimb joints during jump, the important effect of foot during take-off and the role of forelimb in supporting the body. Based on the observation, the frog jump is simplified and a mechanical model is put forward. The robot leg is represented by a 4-bar spring/linkage mechanism model, which has three Degrees of Freedom (DOF) at hip joint and one DOF (passive) at tarsometatarsal joint on the foot. The shoulder and elbow joints each has one DOF for the balancing function of arm. The ground reaction force of the model is ana...

Using gait analysis, we documented kinetic and temporospatial changes over a 7-year period in a single healthy individual with a transfemoral amputation walking with three different knees and matched foot components. The knee/foot pairs in chronological order were Four Bar Endolite knee/Endolite Dynamic Response foot; Ossur Total Knee 2000/Pathfinder I foot; and C-Leg knee/IC40 C-walk foot. The design of the suspension and socket were unchanged across the three prostheses. We found an increase in the braking component of A-P ground reaction force on the intact limb while using the C-Leg compared to the other two prosthetic fabrications. There was progressive change across the three component combinations, which included increased step length, increased walking velocity, and decreased doubl...

ObjectiveTo examine the relationship and differences between static and dynamic postural stability in healthy, physically active adults. DesignDescriptive laboratory study. SettingResearch laboratory. ParticipantsTen females (age: 21.6 +- 1.2 yrs, mass: 60.8 +- 7.6 kg, height: 165.0 +- 5.0 cm) and ten males (age: 25.1 +- 3.0 yrs, mass: 73.9 +- 8.7 kg, height: 173.5 +- 9.0 cm). Main outcome measuresStatic postural stability was measured during a single-leg standing task (standard deviation of the ground reaction forces). Dynamic postural stability was measured during a single-leg landing task using the Dynamic Postural Stability Index. Pearson’s r-coefficients were calculated to examine relationships between the two tests and a one-way ANOVA was calculated to examine potential differ...

Joint moment and power of the metatarsophalangeal (MP) joint in normal horizontal barefoot walking were determined in this study. The three-dimensional motion analysis with synchronous measurements of ground reaction forces and foot pressure distribution was performed with the two-segment foot model. Twenty-two adult subjects were selected for the study. Compared to the previous studies, results of this study showed reasonable joint moments from foot-flat to toe-off. The MP joint angles showed a very good agreement with the previous studies. The maximum MP joint moment was 0.13 ? 0.04 Nm/kg at pre-swing, approximately one-tenth of the ankle joint moment. A considerable energy absorption of approximately 6.56 %GC J/kg was found at the MP joint during 30~60% of the gait cycle. This study wou...

Abstract Denervation of selected ankle extensors in animals results in locomotor changes. These changes have been suggested to permit preservation of global kinematic characteristics of the hindlimb during stance. The peak ankle joint moment is also preserved immediately after denervation of several ankle extensors in the cat, suggesting that the animal's response to peripheral nerve injury may also be aimed at preserving ankle mechanical output. We tested this hypothesis by comparing joint moments and power patterns during walking before and after denervation of soleus and lateral gastrocnemius muscles. Hindlimb kinematics, ground reaction forces and electromyographic activity of selected muscles were recorded during level, downslope (-50%) and upslope (50%) walking before and 1-3 weeks a...

Aseptic loosening of acetabular components in total hip arthroplasty is the major cause of implant failure. Our hypothesis was that spraying autologous bone marrow?derived stromal cells (BMSCs) in fibrin glue onto the surface of hydroxyapatite-coated uncemented acetabular components would increase bone formation and contact in a caprine model. Ten million BMSCs were sprayed onto the acetabular cup at the time of surgery. Animals in the control group received fibrin glue only. Ground reaction force measurements were taken preoperatively and at 6 and 12 weeks postsurgery. After retrieval at 12 weeks new bone formation, bone?implant contact and fibrous tissue thickness adjacent to the cup were quantified. Viability and proliferation assays showed that the majority of the BMSCs survived sprayi...

This report presents a 27-year-old male professional soccer player who developed heterotopic ossification of his hip capsule and gluteus minimus tendon after an arthroscopic hip procedure. After removal of the heterotopic bone, the patient had a symptomatic deficiency of his hip capsule and gluteus minimus tendon. A series of orthobiologic treatments with platelet-rich plasma and bone marrow aspirate concentrate improved the patient's pain and strength as well as the morphologic appearance of the hip capsule and gluteus minimus tendon on magnetic resonance imaging. A series of motion analyses demonstrated significant improvement in his stance-leg ground reaction force and hip abduction, as well as linear foot velocity at ball strike and maximum hip flexion following ball strike in his kicking leg. Level of evidence IV. PMID:23052123

The coefficients at the lowest-order electrostatic, induction, and dispersion terms of the anisotropic long-range potential between the two KRb(1?+) molecules are evaluated through the static and dynamic molecular properties using the ab initio coupled cluster techniques. Adiabatic channel potentials for the ground-state molecules are obtained and used for the numerical quantum capture probability calculations in the spirit of the statistical adiabatic channel models. Capture rate coefficients for indistinguishable (polarized) and distinguishable (unpolarized) molecules at temperatures below 10 ?K agree well with those computed with the simple isotropic dispersion R-6 potential, but underestimate the measured ones [Ospelkaus et al., Science 327, 853 (2010)] up to a factor of 3. Preliminary assessment of the effects of higher-order long-range terms, retardation of dispersion forces, and magnetic dipole-dipole interaction does not offer any clear perspectives for drastic improvement of the capture approximation for the reactions studied.

Peripheral neuropathy is the most common long-term complication in diabetes and is involved in changes in diabetic gait and posture. The regression of nerve function leads to various deficits in the sensory and motor systems, impairing afferent and efferent pathways in the lower extremities. This study aimed to examine how reduced plantar-afferent feedback impacts the gait pattern. Cutaneous sensation in the soles of both feet was experimentally reduced by means of intradermal injections of an anaesthetic solution, without affecting foot proprioception or muscles. Ten subjects performed level walking at a controlled velocity before and after plantar anaesthesia. Muscle activity of five leg-muscles, co-contraction ratios for the knee and ankle joint, ground reaction forces (GRF), spatiotemp...

The two forces combined to bend the path of the cannonball into an arc ending ... the absence of gravity, very small (micro) gravitational forces are still detectable. ... Rockets are able to travel into space because of the action-reaction principle ...

Abstract in portuguese Acredita-se que a eficiência do calçado seja afetada pelo uso prolongado, mas as alterações biomecânicas ainda não estão bem compreendidas. O objetivo deste estudo é analisar a influência do uso de calçados de corrida na força de reação do solo e os parâmetros de pressão plantar. Três corredores do sexo masculino receberam quatro calçados de corrida para usarem em suas sessões de treinamento. O Sistema Gaitway e o Sistema de F-scan foram usados para regi (more) strar a força de reação do solo e parâmetros pressão plantar em diferentes regiões do pé. As coletas ocorreram em quatro momentos: novo e 100, 200 e 300 km de uso. O primeiro pico diminuiu da condição novo para os 300 km de uso (p Abstract in english The prolonged use of a running shoe is thought to affect the efficiency of its impact attenuation properties. However, its effect over biomechanical variables has yet not been well understood. The aim of this study was to examine the influence of running shoe usage on ground reaction force and plantar pressure parameters. Three male runners received four running shoes each to use at their training sessions. The Gaitway System was used to register the vertical component of (more) the ground reaction force, whereas the contact area and peak plantar pressure at different regions of the foot were assessed via the the F-scan System. Data collection occurred at baseline (when the shoes were new - New) and after 100, 200 and 300km of use. The first peak decreased significantly from New to 300km (p

This report presents information concerning field procedures employed during the monitoring, well construction, well purging, sampling, and well logging at the Wright-Patterson Air Force Base. Activities were conducted in an effort to evaluate ground water contamination.

ometer measurements with concomitant (nearly simultaneous) ground and airborne microphysical ... D) air motions within convective cloud systems, and to relate draft statistics to lower tropospheric ..... order to provide: a) Model forcing ...

Lightning strike location and peak current are monitored operationally in the Kennedy Space Center (KSC)/Cape Canaveral Air Force Station (CCAFS) area by the Cloud to Ground Lightning Surveillance System (CGLSS). The present study compiles ten years of CG...

We discuss a new torsion pendulum design for ground testing of prototype LISA (Laser Interferometer Space Antenna) displacement sensors. This new design is directly sensitive to net forces and therefore provides a more representative test of the noisy forces and parasitic stiffnesses acting on the test mass as compared to previous ground-based experiments. We also discuss a specific application to the measurement of thermal gradient effects.

Intermolecular Forces: this is a resource in the collection "Netorials". In this resource there is a review of Lewis structures, molecular geometry, electronegativity, or molecular polarity. After that, you can learn about the forces of attraction that exist between molecules. This module explores London forces and dipole-dipole forces (including hydrogen bonds). The Netorials cover selected topics in first-year chemistry including: Chemical Reactions, Stoichiometry, Thermodynamics, Intermolecular Forces, Acids & Bases, Biomolecules, and Electrochemistry.

A passive reactive barrier (Biowall) was installed at the OU-1 site at Altus Air Force Base, Oklahoma to treat TCE contamination in ground water from a landfill. Depth to ground water varies from 1.8 to 2.4 meters below land surface. To intercept and treat the plume of contamin...

We have investigated a general structure of the ground-state wave function for the Schr\\"odinger equation for $N$ identical interacting particles (bosons or fermions) confined in a harmonic anisotropic trap in the limit of large $N$. It is shown that the ground-state wave function can be written in a separable form. As an example of its applications, this form is used to obtain the ground-state wave function describing collective dynamics for $N$ trapped bosons interacting via contact forces.

auditory andmotor skill experiments. A numberof other ..... additional information has on the operator and how he uses it in learning. The consistency ...... serial reaction task and a forced paced discrete reaction task were used. Three levels ...

The aim of this study was to compare measures of power output applied to the center of mass of the barbell and body system (CM) obtained by multiplying ground reaction force (GRF) by (a) the velocity of the barbell; (b) the velocity of the CM derived from three-dimensional (3D) whole-body motion analysis, and (c) the velocity of the CM derived from GRF during lower-body resistance exercise. Ten resistance-trained men performed 3 maximal-effort single back squats with 60% 1 repetition maximum while GRF and whole-body motion were captured using synchronized Kistler force platforms and a Vicon Motus motion analysis system. Repeated measures analysis of variance of time-normalized kinematic and kinetic data obtained using the different methods showed that the barbell was displaced 13.4% (p < 0.05) more than the CM, the velocity of the barbell was 16.1% (p < 0.05) greater than the velocity of the CM, and power applied to the CM obtained by multiplying GRF by the velocity of the barbell was 18.7% (p < 0.05) greater than power applied to the CM obtained by multiplying the force applied to the CM by its resultant velocity. Further, the velocity of the barbell was significantly greater than the velocity of the trunk, upper leg, lower leg, and foot (p < 0.05), indicating that a failure to consider the kinematics of body segments during lower-body resistance exercise can lead to a significant overestimation of power applied to the CM. Strength and conditioning coaches and investigators are urged to obtain measures of power from the force applied to and the velocity of either the barbell (using inverse dynamics) or CM (GRF or 3D motion analysis). Failure to apply these suggestions could result in continued overestimation of CM power, compromising methodological integrity. PMID:22516904

An on-ground measurement of dust particle residual charges in the afterglow of a dusty plasma was performed in a rf discharge. An upward thermophoretic force was used to balance the gravitational force. It was found that positively-charged, negatively-charged and neutral dust particles coexisted for...

The basic conception on a vibration design is described for the representative system of the vibration isolation structure and vibration control structure. In the vibration isolation structure of a basal insulation system, a vibration isolation device consisting of the bearing (in which natural laminated rubber is used) that supports the structure load and the damper (in which steel products, lead, and oil are used) that suppresses the displacement is installed between the structures and foundation and isolated from the ground so as to reduce the earthquake input to structures. The representative vibration control device based on the installation system in a frame is an inter-layer damper that is installed via a wall with high rigidity. The damper consumes and absorbs the vibration energy intensively according to the displacement difference at the top and bottom of a frame. The damper is classified into a viscous damper and hysteresis damper. In the vibration control structure based on a top installation system, a 0.1 to 1% heavy object of the weight above the ground of structures is put on the roof or upper floor, and the movement of additional mass is controlled or adjusted to obtain dynamic reaction force. The vibration control system is classified into a passive type and active type. 19 refs., 24 figs., 1 tab.

Variations in ground thermal conditions in Svalbard were studied based on measurements and theoretical calculations. Ground temperature data was used to calibrate a transient heat flow model describing depth and time variations in temperatures. The model was subsequently forced with historical surface air temperature data records and downscaled global climate model runs to project ground temperatures. We discuss ground temperature development since the early 20th century, and the thermal responses in relation to ground characteristics and snow cover. The modelled ground temperatures show a gradually increase since the end of the Little Ice Age (mid 19th century on Svalbard), by about 1.5 °C to 2 °C at 20 m depth. The active layer thickness (ALT) is modelled to have increased slightly, with the rate of increase depending on water content of the near-surface layers. The used scenario runs predict a significant increase in ground temperatures and an increase of ALT depending on soil characteristics.

Experimental evidence is presented which indicates that the triplet excimer of naphthalene is L shaped. The preference for an L-shaped structure is interpreted as a compromise between the dispersion force which favors a coplanar structure and the electrostatic force which favors a P-shaped structure. The intermolecular attractive forces which are responsible for the formation of triplet excimers (of aromatic hydrocarbons) are therefore similar to those responsible for the formation of the ground state van der Waals dimers.

The decrease of reaction force of some metal gaskets inserted into the test flange at room temperature, 120 C(real cask temperature) and 200 C(accelerated condition) are measured. The reaction forces of metal gaskets in the room temperature have been almost not changed. The reaction force of 120 C and 200 C metal gaskets has decreased according to the temperature increase. After the temperature became stable, the decrease of the reaction force gradually proceeded, this decrease have been as same as previous studies. The bolts of transport and storage casks are usually tightened just after the loading of spent fuels, and then the temperature of metal gaskets at that time is almost the room temperature. The reaction forces of the metal gasket tightened at this condition would be decreased after the temperature increase due to the decay heat of spent fuels. It is confirmed that the loosening of the bolts might be happened if the tightening torque of bolts is not appropriate. It is easy to evaluate that the reaction forces of the metal gasket in storage condition according to Larson-Miller parameter or relaxation of the gasket material, but the decrease of the reaction forces of the metal gasket just after the loading is not able to evaluate by these method. It is necessary to evaluate the reaction forces according to plastic deformation property of the metal gaskets so as to fasten the gaskets safety.

Solid-fuel rocket motors used by the United States Air Force (USAF) to launch missiles and spacecraft can produce ambient-air concentrations of hydrogen chloride (HCI) gas. The HCI gas is a reaction product exhausted from the rocket motor during normal launch or emitted as a result of a catastrophic abort destroying the launch vehicle. Depending on the concentration in ambient air, the HCI gas can be irritating or toxic to humans. The diagnostic and complex-terrain wind field and particle dispersion model used by the Lawrence Livermore National Laboratory`s (LLNL`s) Atmospheric Release Advisory Capability (ARAC) Program was applied to the launch of a Peacekeeper missile from Vandenberg Air Force Base (VAFB) in California. Results from this deterministic model revealed that under specific meteorological conditions, cloud passage from normal-launch and catastropic-abort situations can yield measureable ground-level air concentrations of HCI where the general public is located. To protect public health in the event of such cloud passage, scientifically defensible, emergency ambient-air concentration limits for HCI were developed and recommended to the USAF for use as launch-hold criteria. Such launch-hold criteria are used to postpone a launch unless the forecasted meteorological conditions favor the prediction of safe ground-level concentrations of HCl for the general public. The recommended concentration limits are a 2 ppM 1-h time-weighted average (TWA) concentration constrained by a 1-min 10-ppM average concentration. This recommended criteria is supported by human dose-response information, including data for sensitive humans (e.g., asthmatics), and the dose response exhibited experimentally by animal models with respiratory physiology or responses considered similar to humans.

Potential possibility of using centrifugal forces for production of noble ferroalloys was demonstrated for aluminothermic systems taken as an example. Combustibility limits in the field of centrifugal forces were associated with the onset of adiabatic conditions for combustion due to acceleration of combustion front by melted metal particles returned into the reaction zone by centrifugal forces.

Spiders use hemolymph pressure to extend their legs. This mechanism should be challenged when required to rapidly generate forces during jumping, particularly in large spiders. However, effective use of leg muscles could facilitate rapid jumping. To quantify the contributions of different legs and leg joints, we investigated jumping kinematics by high-speed video recording. We observed two different types of jumps following a disturbance: prepared and unprepared jumps. In unprepared jumps, the animals could jump in any direction away from the disturbance. The remarkable directional flexibility was achieved by flexing the legs on the leading side and extending them on the trailing side. This behaviour is only possible for approximately radial-symmetric leg postures, where each leg can fulfil similar functions. In prepared jumps, the spiders showed characteristic leg positioning and the jumps were directed anteriorly. Immediately after a preliminary countermovement in which the centre of mass was moved backwards and downwards, the jump was executed by extending first the fourth and then the second leg pair. This sequence provided effective acceleration to the centre of mass. At least in the fourth legs, the hydraulic and the muscular mechanism seem to interact to generate ground reaction forces. PMID:20405130

Objective. The aim of this randomized placebo-controlled trial was to evaluate the beneficial effect of a whole plant extract of Brachystemma calycinum D. Don (BCD) in naturally occurring osteoarthritis (OA) in dogs. Methods. Dogs had stifle/hip OA and poor limb loading based on the peak of the vertically oriented ground reaction force (PVF) measured using a force platform. At baseline, PVF and case-specific outcome measure of disability (CSOM) were recorded. Dogs (16 per group) were then assigned to receive BCD (200?mg/kg/day) or a placebo. The PVF was measured at week (W) 3 and W6. Locomotor activity was recorded throughout the study duration using collar-mounted accelerometer, and CSOM was assessed biweekly by the owner. Results. BCD-treated dogs had higher PVF at W3 and W6 when compared to Baseline (P BCD-treated dogs compared to baseline. No significant change was observed in either group for CSOM. Conclusions. Treatment with BCD improved the limb impairment and enhanced the locomotor activity in dogs afflicted by naturally-occurring OA. Those preclinical findings provide interesting and new information about the potential of BCD as an OA therapeutic. PMID:18095963

Lower-limb complications associated with diabetes include the development of plantar ulcers that can lead to infection and subsequent amputation. While we know from force-plate analyses that medial/lateral and anterior/posterior shear components of ground-reaction forces exist, little is known about the actual distribution of these stresses during daily activities or about the role that shear stresses play in causing plantar ulceration. Furthermore, one critical reason why these data have not been obtained previously is the lack of a validated, widely used, commercially available shear sensor, partly because of the various technical issues associated with measuring shear. In this study, we present a novel means of transducing plantar pressure and shear stress with a fiber-optic sensor. The pressure/shear sensor consists of an array of optical fibers lying in perpendicular rows and columns separated by elastomeric pads. We constructed a map of normal and shear stresses based on observed macrobending through the intensity attenuation from the physical deformation of two adjacent perpendicular fibers. Initial results show that this sensor exhibits low noise and responds to applied normal and shear loads with good repeatability. PMID:16187244

The biological mechanisms that maintain the position of teeth in their sockets establish a dynamic equilibrium between bone resorption and apposition. In order to reveal some of the dynamics involved in the tissue responses towards occlusal forces on periodontal ligament (PDL) and alveolar bone homeostasis, we developed the first mouse model of hyperocclusion. Swiss-Webster mice were kept in hyperocclusion for 0, 3, 6, and 9 d. Morphological and histological changes in the periodontium were assessed using micro-computed tomography (micro-CT) and ground sections with fluorescent detection of vital dye labels. Sections were stained for tartrate-resistant acid phosphatase, and the expression of receptor activator of nuclear factor-{kappa}B ligand (RANKL) and osteopontin (OPN) was analyzed by immunohistochemistry and real-time polymerase chain reaction (PCR). Traumatic occlusion resulted in enamel surface abrasion, inhibition of alveolar bone apposition, significant formation of osteoclasts at 3, 6 and 9 d, and upregulation of OPN and RANKL. Data from this study suggest that both OPN and RANKL contribute to the stimulation of bone resorption in the hyperocclusive state. In addition, we propose that the inhibition of alveolar bone apposition by occlusal forces is an important mechanism for the control of occlusal height that might work in synergy with RANKL-induced bone resorption to maintain normal occlusion.

During recovery from a stroke, body weight-bearing on a paretic leg is spontaneously avoided. In physiotherapy for hemiparetic gait, as long as the patients can use their non-paretic leg, adaptive and compensatory strategies are always used to support and move the body. We examined the effects of gait training using prosthetics to induce the use of a paretic leg during walking. The prosthesis was applied to the non-paretic leg of three right hemiparetic patients. Prosthetic gait training was performed until finishing 5 successive motor learning sessions involving walking over 200 m and the changes of asymmetric gait performances were analyzed. The ground reaction forces during the initial stance phase of the paretic leg were increased in all patients after prosthetic gait training. Simultaneously, the propulsive force produced by the paretic leg was increased in 2 patients. By contrast, another patient developed more use of his non-paretic leg for propulsion corresponding to acquiring stability on the paretic leg, resulting in an improvement in single-support-time asymmetry. Task-specific effects provided by prosthetic gait training may be able to reorganize the motor strategy for hemiparetic gait by inducing the use of the paretic leg to support and propell the body.   

We use the R-matrix theory to fit S-factor data on nuclear reactions involved in Big Bang nucleosynthesis. We derive the reaction rates with associated uncertainties, which are evaluated on statistical grounds. We provide S factors and reaction rates in tabular and graphical formats (available at ht...

Secondary atmospheric contamination with radioactive dust and chemical species deposited on the ground and resuspended by wind occur very widely. This process is particularly pronounced in case of extensive contamination of soil and under extreme weather conditions, for example, during dust storms. The mechanism of wind dust generation consists in the following. At low wind speed U=2-3 m/s, which is most common in midlatitude, small radioactive dust particles (diameter of hundredth of a micron to 10-20 microns) are lifted from soil surface due to turbulent vortexes. Under the gravitational force the particles of 1-2 micron diameter practically do not settle. Larger dust particles cannot remain in the air for a long time: they are lifted by turbulent vortexes and settle, their motion in the wind flow is jump-wise and the interaction of particles with the flow is called saltation /I/. Saltation is the main mechanism of dust generation up to the wind velocity at which wind erosion starts. The size of dust particles can be as large as 100 pm. When dropping they can be ricocheting from ground or pass the impulse to other particles which begin rolling over and jumping up. The process of dust transport by wind can be compared to a chain reaction. At the velocity of 10 m/s large particles of about 500 pm stop skipping and roll over only, while particles of more than 1 mm remain stationary. Thus, the fine fraction is blown out from the polydispersed soil particles. The intensity of wind resuspension of radioactive dust from the ground is characterized either by a resuspension factor or a resuspension rate.

The purpose of this study was to examine the effect of seat surface inclination on postural stability and forward reaching efficiency in 10 children with spastic cerebral palsy (CP) and 16 typically developing (TD) children. The children performed a static sitting and a forward reaching task while sitting on a height- and inclination-adjustable stool at flat, three anterior-inclined, and three posterior-inclined positions. Postural stability was expressed as normalized (with body weight) peak vertical ground reaction force, center of pressure displacement in the anterior/posterior directions (COP_AP), in the medial/lateral directions (COP_ML), and sway ratio (COP_AP/COP_ML). Reaching efficiency was expressed as reaction time and movement time of arm reaching forward to a target. The results showed that seat inclination affected children's postural stability and the effects were comparable for CP and TD children in all measures except for COP_ML. Children with CP presented much larger COP_ML than TD children at the posterior-inclined positions relative to the flat and the anterior-inclined positions. Seat inclination affected reaching efficiency for both groups of children equally. Efficiency was better at the anterior positions than the posterior positions. Anterior-inclined positions improved postural stability and reaching efficiency. Posterior positions posed greater postural challenge and the challenge was tougher for children with CP. (Contains 2 tables.)

Important chemical reactions for life often require multistep electron transfers (ET) and strong reducing forces. In these reactions, electron transfer proteins as ferredoxins (Fds) play a key role. For elucidation of the core electronic states in these electron transfer processes, an inorganic model compound [Fe2S2(S2-o-xyl)2] is used as our first study. It was experimentally characterized that the model compound is in a similar electronic state to the active site core in Fds. On the reduced form, the diiron core exists in a characteristic mixed-valence state that has mobile electron (spin). Hybrid density functional theory (HDFT) calculations are performed to investigate the chemical bond nature, electronic structures, and magnetic interactions. The spin states and energy levels are further discussed with spin Hamiltonians, which contain Heisenberg exchange term and double exchange term to describe the mixed-valence state. We have determined their effective exchange integrals (J) and resonance parameters (B) from (HDFT) calculations in several procedures. These magnetic interactions are in good agreement with experiments. To estimate B values, we propose a new procedure using molecular orbital energies. The B values are properly evaluated compared with other procedures, using total energies. The chemical bond natures and the ground electronic structures are elucidated in terms of chemical indices defined by the occupation number of natural orbitals. Finally, implications of the computational results are discussed in relation to rational design of biomolecular devices.

The electric induction force due to a time-varying current is used to account for the longitudinal recoil force exerted on the rails of railgun accelerators. As observed in the experiments, this induction force is longitudinal to the rails and can be the strongest at the heads of the rails. Besides, for the force due to a closed circuit, it is shown that the Riemann force law, which is based on a potential energy depending on a relative speed and is in accord with Newton's law of action and reaction, can reduce to the Lorentz force law.

A photoinduced Fe(II) spin crossover reaction in solution is studied with ultrafast x-ray absorption spectroscopy. The iron-nitrogen bond lengthens by 0.21+-0.03 Angstrom in the high-spin transient excited state relative to the ground state.

Two types of profiles of ski reaction forces during V2 skating have been reported by previous investigations. One of the differences between these two profiles is in the existence of the “flight phase,” i.e., the phase in between gliding and kicking off, in which the skis float above the snow while skiing. It has been suggested that the difference is caused by the skating velocity. The purpose of this study is to clarify whether or not there is a relationship between the occurrence of the flight phase and the increase in velocity during V2 skating. Seven elite male cross-country skiers performed two types of trials at different velocities (high and medium speeds). The high and medium speeds correspond to the competitive pace for a sprint race and a 10-km race, respectively. The kinematics was measured for each trial using two video cameras and a panning direct linear transformation technique. The flight phase was determined by the ski load data obtained from a sensor attached to the ski. No flight phase was confirmed during medium-speed skating, but a flight phase was confirmed during high-speed skating, indicating the existence of the flight phase is related to an increase in skating velocity. However, the hip- and knee-joint angles and the vertical displacement of the center of mass were not changed by an increase in skating velocity. These results suggested that the flight phase was a small change from the standpoint of kinematics, but it may cause changes in muscle activity since the leg muscle groups experience no ground reaction force.   

Variations in ground thermal conditions in Svalbard were studied based on measurements and modelling. Ground temperature data from boreholes were used to calibrate a transient heat flow model describing depth and time variations in temperatures. The model was subsequently forced with historical surface air temperature records and possible future temperatures downscaled from multiple global climate models. We discuss ground temperature development since the early 20th century, and the thermal responses in relation to ground characteristics and snow cover. The modelled ground temperatures show a gradual increase between 1912 and 2010, by about 1.5 °C to 2 °C at 20 m depth. The active layer thickness (ALT) is modelled to have increased slightly, with the rate of increase depending on water content of the near-surface layers. The used scenario runs predict a significant increase in ground temperatures and an increase of ALT depending on soil characteristics.

The presence of boundary surfaces in the vacuum alters the ground state of the quantized electromagnetic field and can lead to the appearance of vacuum forces. In the last decade, landmark measurements of the vacuum stress between conducting uncharged parallel plates (Casimir force) have been made. Recently the first micromachined MEMS (microelectromechanical system) device was fabricated that utilizes the Casimir force between parallel plates. The force dependence allows the device to serve as a highly sensitive position sensor. The are many other examples of quantum vacuum forces and effects besides the well known parallel plate Casimir force. Here we discuss potential roles of quantum vacuum forces and effects in MEMS systems and other systems. With the growing capability in nanofabrication, some of the roles may be actualized in the future. Because of the computational complexity, no theoretical results are yet available for a number of potentially interesting geometries and we can only speculate.

We demonstrate coaxial atomic force microscope (AFM) tweezers that can trap and place small objects using dielectrophoresis (DEP). An attractive force is generated at the tip of a coaxial AFM probe by applying a radio frequency voltage between the center conductor and a grounded shield; the origin of the force is found to be DEP by measuring the pull-off force vs. applied voltage. We show that the coaxial AFM tweezers (CAT) can perform three dimensional assembly by picking up a specified silica microsphere, imaging with the microsphere at the end of the tip, and placing it at a target destination.

Abstract in portuguese FUNDAMENTOS E OBJETIVO: O segmento mais freqüentemente lesado no basquetebol é o tornozelo, sendo a entorse por inversão a lesão mais comum. Para evitá-la, é comum o uso de implementos. O objetivo deste estudo foi avaliar a força reação do solo (FRS) em jogadores de basquete durante execução do salto em três situações: uso de tênis, bandagem e tênis, e tênis e órtese tipo Aircast. MÉTODOS: Oito atletas foram analisados durante o salto, através de uma p (more) lataforma de força, nas três situações citadas, para análise das componentes vertical e horizontal médio-lateral da FRS. RESULTADOS E CONCLUSÃO: Não houve diferença estatística significativa entre as três situações na componente vertical da FRS durante o salto, embora o uso de bandagem tenda a apresentar, na impulsão, maiores valores do pico de força vertical (3,10 ± 0,46PC; 3,01 ± 0,39PC; 3,03 ± 0,41PC) e do gradiente de crescimento (GC) (12,33 ± 12,21PC; 8,16 ± 3,89PC; 8,46 ± 3,85PC), e durante a aterrissagem, menores valores de pico de força vertical (5,18 ± 1,35PC; 5,56 ± 1,31PC; 5,49 ± 1,44PC) e do GC (88,83 ± 33,85PC; 95,63 ± 42,64PC; 94,53 ± 31,69PC). Durante a impulsão, a força medial do salto com Aircast foi significativamente menor que com tênis (p = 0,0249) e apresentou valor semelhante ao do uso da bandagem, enquanto a força lateral foi significativamente maior com a bandagem do que com tênis (p = 0,0485) e tendeu a ser maior do que o Aircast. Na aterrissagem o componente médio-lateral da FRS ficou inalterado nas três situações. Concluiu-se que a bandagem potencializou a força direcionada ao salto vertical durante a impulsão, porém não estabilizou tanto quanto o Aircast os movimentos de inversão e eversão do pé. Durante a aterrissagem, os implementos não foram efetivos para reduzir a força médio-lateral, mas com a bandagem, houve um tempo maior para absorção do impacto. Abstract in spanish FUNDAMENTOS Y OBJETIVO: EL segmento mas frecuentemente lesionado en el basquetbol es el tobillo, siendo la torsión por inversión interna la lesión mas común, para evitarla, es común el uso de ciertos implementos. El objetivo de este estudio fue el de evaluar la fuerza de reacción del suelo (frs) en jugadores de basquetbol durante la ejecución del salto en tres situaciones: uso de calzado deportivo, uso de vendaje y calzado deportivo, uso de calzado deportivo y orte (more) sis Aircast. MÉTODOS: Ocho atletas fueron analizados durante el salto, a través de la plataforma de fuerza en las tres situaciones citadas para el análisis de los componentes vertical y horizontal medio lateral de la FRS. RESULTADOS Y CONCLUSIÓN: No hubo diferencia estadística significativa entre las tres situaciones en la componente vertical de la FRS durante el salto, ahora el uso del vendaje tiende a presentar en la impulsión mayores valores del pico de fuerza vertical. (3,10 ± 0,46PC; 3,01 ± 0,39PC; 3,03 ± 0,41PC) y del gradiente de crecimiento (GC) (12,33 ± 12,21PC; 8,16 ± 3,89PC; 8,46 ± 3,85PC), y durante el aterrizaje, menores valores del pico de fuerza vertical (5,18 ± 1,35PC; 5,56 ± 1,31PC; 5,49 ± 1,44PC) e do GC (88,83 ± 33,85PC; 95,63 ± 42,64PC; 94,53 ± 31,69PC). Durante la impulsión, la fuerza medial del salto con Aircast fue significativamente menor que con el calzado deportivo (p = 0,0249), y presentó un valor semejante al uso del vendaje, en cuanto a la fuerza lateral fue significativamente mayor con el vendaje que con el calzado deportivo (p = 0,0485) y tendió a ser mayor que con el Aircast. En el aterrizaje el componente medio-lateral de la FRS quedó inalterado en las tres situaciones. Se concluye que el vendaje potencializó la fuerza direccionada al salto vertical durante la impulsión, porque no estabilizó tanto como con el Aircast los movimientos de inversión y eversión del pie. Durante el aterrizaje, los implementos no fueron efectivos para reducir la fuerza medio-lateral, más que con el vendaje, hubo un tiempo mayor para absorción del impacto. Abstract in english BASES AND OBJECTIVE: The segment most frequently injured in basketball is the ankle, being the inversion sprain the most common lesion. In order to avoid it, ankle devices are frequently used. The objective of this study was to evaluate the ground reaction force (GRF) in basketball players during jump performance in three situations: use of basketball sport shoes, sport shoes with bracing and sport shoes with Aircast-type orthosis. METHODS: Eight athletes were analyzed du (more) ring jump through a force platform in the three situations mentioned for the analysis of the medial-lateral vertical and horizontal components of the ground reaction force. RESULTS AND CONCLUSION: No significant statistical differences between the three situations were verified in the vertical ground reaction force during jump, although the use of bracing trends to present, during impulsion, higher peak values of the vertical force (3.10 ± 0.46PC; 3.01 ± 0.39PC; 3.03 ± 0.41PC) and the growth gradient (GC) (12.33 ± 12.21PC; 8.16 ± 3.89PC; 8.46 ± 3.85PC), and during landing, lower peak values of the vertical force (5.18 ± 1.35PC; 5.56 ± 1.31PC; 5.49 ± 1.44PC) and the GC (88.83 ± 33.85PC; 95.63 ± 42.64PC; 94.53 ± 31.69PC). During impulsion, the jump medial force with Aircast was significantly lower than with sport shoes (p = 0.0249) and presented values similar to values obtained with the use of bracing, while the lateral force was significantly higher with bracing than with the use of the sport shoes (p = 0.0485) and trended to be higher than with the use of the Aircast. In the landing, the medial-lateral component of the ground reaction force remained unchanged in the three situations. One concludes that the use of bracing has potentialized the force towards the vertical jump during impulsion, however, it did not stabilize the foot inversion and eversion movements as much as the Aircast. During landing, the devices were not effective to reduce the medial-lateral force, however, with the use of the bracing, a longer time for the impact absorption was verified.

The feedback system of seismic vibrators minimizes the difference between the theoretical sweep and the seismic signal radiated into the earth. This requires the determination of the correct source signature, that is, the characteristic of the baseplate motion that is a true representation of the downgoing wave. The prevalent systems use ground-force-based vibrator control, which assumes that the amplitudes of the seismic waves are proportional to the force applied to the ground. Mathematical solution of the pressure boundary-value problem of linear elasticity is the theoretical underpinning of this method. However, the ground force has a significant disadvantage of not being a directly measurable parameter. It has to be inferred, with significant uncertainty, as a ''weighted sum'' of the ...

To assess the effect of leg length on jumping ability in small insects, the jumping movements and performance of a sub-family of leafhopper insects (Hemiptera, Auchenorrhyncha, Cicadellidae, Ulopinae) with short hind legs were analysed and compared with other long-legged cicadellids (Hemiptera, Auchenorrhyncha, Cicadellidae). Two species with the same jumping characteristics but distinctively different body shapes were analysed: Ulopa, which had an average body length of 3 mm and was squat, and Cephalelus, which had an average body length of 13 mm with an elongated body and head. In both, the hind legs were only 1.4 times longer than the front legs compared with 1.9-2.3 times in other cicadellid leafhoppers. When the length of the hind legs was normalised relative to the cube root of their body mass, their hind legs had a value of 1-1.1 compared with 1.6-2.3 in other cicadellids. The hind legs of Cephalelus were only 20% of the body length. The propulsion for a jump was delivered by rapid and synchronous rotation of the hind legs about their coxo-trochanteral joints in a three-phase movement, as revealed by high-speed sequences of images captured at rates of 5000 s(-1). The hind tarsi were initially placed outside the lateral margins of the body and not apposed to each other beneath the body as in long-legged leafhoppers. The hind legs were accelerated in 1.5 ms (Ulopa) and 2 ms (Cephalelus) and thus more quickly than in the long-legged cicadellids. In their best jumps these movements propelled Ulopa to a take-off velocity of 2.3 m s(-1) and Cephalelus to 2 m s(-1), which matches that of the long-legged cicadellids. Both short-legged species had the same mean take-off angle of 56 degrees but Cephalelus adopted a lower angle of the body relative to the ground (mean 15 degrees) than Ulopa (mean 56 degrees). Once airborne, Cephalelus pitched slowly and rolled quickly about its long axis and Ulopa rotated quickly about both axes. To achieve their best performances Ulopa expended 7 microJ of energy, generated a power output of 7 mW, and exerted a force of 6 mN; Cephalelus expended 23 microJ of energy, generated a power output of 12 mW and exerted a force of 11 mN. There was no correlation between leg length and take-off velocity in the long- and short-legged species, but longer legged leafhoppers had longer take-off times and generated lower ground reaction forces than short-legged leafhoppers, possibly allowing the longer legged leafhoppers to jump from less stiff substrates. PMID:18375856

A composite type breakwater with back-filling was applied to improve the stability acting on wave forces. In this paper, 2-dimensional wave tank tests were carried out to reveal the effects of the interaction wave forces and back-filling reaction forces. The back-filling reaction forces acting on the breakwater were measured by 2-dimensional load cell. The composite type breakwater with back-filling is stability more than without back-filling structures. And it is confirmed that the existing design method is safety side evaluation more than the experimental results.   

We show that quantum-mechanical molecular-dynamics simulations in a finite-temperature local-density approximation based on the calculation of the electronic ground state and of the Hellmann-Feynman forces after each time step are feasible for liquid noble and transition metals. This is possible with the use of Vanderbilt-type ultrasoft'' pseudopotentials and efficient conjugate-gradient techniques for the determination of the electronic ground state. Results for liquid copper and vanadium are presented.

With clayey ground as the object, the previous paper proposed a new method to establish soil pressure on backside, equilibrium pressure on excavation side, passive pressure on the excavation side, and subgrade reaction coefficient for the excavation side. These factors are used in the elasto-plasticity method which is used in designing excavation earth retaining structures. This paper discusses extension of the subgrade reaction coefficient setting method proposed in the previous and present papers, so that effects of hard ground existing below the excavation bottom can be considered. This paper also shows the results of discussions on applicability of the soil pressures and subgrade reaction coefficient proposed in the previous and present papers. As a result, a new proposal is made on a rational and practical setting method for soil pressures and subgrade reaction coefficient as input items of the elasto-plasticity method used in designing ordinary excavation earth retaining structures in clayey ground. In contrast to the conventional method, the proposed method includes shear resistance in surface of an earth retaining wall, excavation width, thickness of the subject ground, depth from the ground surface, distance from the hard ground below the excavation bottom, and the Poission ratio of the ground. 10 refs., 18 figs., 12 tabs.

This paper focuses on the method of designing structures against liquefaction and a subsequent lateral flow. Shaking table tests and analyses were carried out to clarify the mechanism of pile stresses caused by the liquefaction-induced lateral flow. As a result, it is proved that the design of structure against liquefaction shall reflect changes in the natural frequency while considering the additional inertia force of liquefaction ground. It has also become possible to economically design structures by assuming that the liquefaction-induced lateral flow is a ground displacement force.   

Vibrationally adiabatic ground-state potential curves for the CH{sub 3} + H{sub 2} {yields} CH{sub 4} + H (I) and CD{sub 3} + H{sub 2} {yields} CD{sub 4}H + H (II) reactions were obtained by adding zero-point energies of harmonic vibrations orthogonal to intrinsic reaction coordinate (IRC) to bare potential curves along IRC. It was clarified that both the barrier height and barrier width of reaction II are smaller than those of reaction I. This computational result qualitatively explains the experimental observation of Momose et al. (J. Chem. Phys. 108 (1998) 7334) that reaction II occurs but reaction I does not occur in solid parahydrogen at 5 K. (author)

Exact solutions are found to the equations of a standard nuclear quark model exemplified by the Bonn model which is defined in terms of an effective pairing force. We show, by symmetry arguments, that, in general, the ground state of this model is not color neutral. In particular, color-neutral states have, in general, higher energy than the ground state. A novel BCS-type formalism, which is able to describe exactly color symmetrical BCS states, is used to show that the model admits, but only as excited states, color-neutral superconductivity. Therefore, such a model, with just a pairing force, is unrealistic as a model for the color-neutral confined phase which prevails at normal nuclear densities. Finally, the paper shows that there exists a color-neutral superconducting phase independently of whether the model is based on the pairing force or a more realistic three-body string force.

A unified approach to the calculation of dispersive forces on ground-state bodies and atoms is given. It is based on the ground-state Lorentz force density acting on the charge and current densities attributed to the polarization and magnetization in linearly, locally, and causally responding media. The theory is applied to dielectric macro- and micro-objects, including single atoms. Existing formulas valid for weakly polarizable matter are generalized to allow also for strongly polarizable matter. In particular when micro-objects can be regarded as single atoms, well-known formulas for the Casimir-Polder force on atoms and the van der Waals interaction between atoms are recovered. It is shown that the force acting on medium atoms--in contrast to isolated atoms--is in general screened by the other medium atoms.

Recently, to help mitigate global climate-change and energy problems, much effort has recently been devoted to developing methods for sequestering anthropogenic CO2 from coal-fired power plants. One of the most promising methods is geological CO2 sequestration (GS). Some prior studies of geological CO2 sequestration have mainly examined the physical processes that occur during the sequestration of CO2. However, most of the relevant studies are based on hydrological transport, using simulation models rather than studying actual interfacial chemical reactions in the ground. The mechanisms, kinetics, and environmental impact of interfacial reactions among CO2-H2O-mineral surfaces at the molecular scale have not been well understood. Changes in the porosity of the mineral phases at the geological formation sites, especially the dissolution of the mineral phase or precipitation of secondary minerals in the pores, will affect the fate and transport of CO2 and the integrity of seals and the matrix within the reservoirs. So far, little is known about the kinetics of the possible geochemical reactions of supercritical CO2 in brine and pre-existing mineral interfaces, or about the ultimate fate and transport of the injected CO2. We investigated the physico-chemical property changes of reference mineral samples (clay minerals) as well as field site samples (sandstone and caprock from the Illinois Basin) by chemical reactions at CO2-H2O-mineral interfaces. We investigated whether reactions between caprock and CO2 can change the integrity of caprock. Our experimental results with caprock samples (CONSOL coal mine sites, West Virginia) indicate that after 14 days in contact with 1 atm CO2 saturated saline water at 80°C, the concentrations of dissolved metals have increased from zero to as high as 47,000 ppm. In our experiments with caprocks and sandstones from GS sites of the Midwest Geological Sequestration Consortium, we found that the most significant extent of dissolution occurs within a day. This result implies that monitoring the earliest stage of reactions of sandstone with CO2 is crucial to understanding the CO2-water-rock interactions in deep saline aquifers. The second experiments investigated the effects of different reaction conditions on the reaction pathways and the extents of reaction. Freshly cleaved surfaces of phlogopite (KMg3(Si3Al)O10(F,OH)2) were prepared as thin layers. Using in situ high pressure (1000-1500 psi) and temperature (55-95oC) small angle x-ray scattering (SAXS) reactor, the real time reactions were monitored. After CO2 was injected into the microreactor, the scattering pattern changed due to surface morphology changes with time. This reaction occurs significantly, even within one hour. After each experiment, each sample was measured by atomic force microscope (AFM). By incorporating aqueous chemistry with in situ SAXS and AFM, we monitored real-time nanoscale reactions resulting from dissolution of pre-existing minerals and precipitation of new mineral phases at CO2-water-rock interfaces. Those morphological changes can be key information to understand the changes in porosity and permeability in GS sites.

We study the force-induced unfolding of random disordered RNA or single-stranded DNA polymers. The system undergoes a second order phase transition from a collapsed globular phase at low forces to an extensive necklace phase with a macroscopic end-to-end distance at high forces. At low temperatures, the sequence inhomogeneities modify the critical behaviour. We provide numerical evidence for the universality of the critical exponents which, by extrapolation of the scaling laws to zero force, contain useful information on the ground state (f=0) properties. This provides a good method for quantitative studies of scaling exponents characterizing the collapsed globule. We analyse the statistics of rearrangements, in particular below the critical force, and its implications for force-extension experiments on single molecules.

An approach to the problem of the Casimir force on magnetodielectric bodies is outlined, which is based on the calculation of the ground-state Lorentz force acting on the polarization and magnetization charges and currents that constitute the bodies within the framework of linear, macroscopic electrodynamics. As an application, planar structures are considered and a correct generalization of Casimir's original formula to the case where the two highly reflecting plates are embedded in a medium is given.

Polytetrafluoroethylene (PTFE) was ground with SrO using a planetary ball mill in air. The grinding stimulates the solid reaction between PTFE and SrO at room temperature. PTFE is decomposed by the solid reaction and fluorine in PTFE is transformed into strontium fluoride. The results show that it is possible to mineralize highly stable polymer PTFE by grinding with proper additive.   

A series of experiments were carried out at Argonne National Laboratory to search for examples of proton emission from ground and low­lying states in odd­Z nuclei at the proton drip­line. Recoils from fusion evaporation reactions were separated from other reaction products and dispersed according...

INTRODUCTION: Metal-on-Metal-Hip-Resurfacing-Arthroplasty (MoMHRA) cup malorientation has been associated with wear and pseudotumour risk. Cup orientation influences risk of edge loading, which increases wear and subsequent serum metal ion levels. However, not all malorientated cups have increased wear. The aim of this study was to identify whether patientspecific activity patterns influence the risk of edge loading of a given cup orientation. METHODS: Fourteen unilaterally resurfaced subjects were studied. Subjects were divided into three groups: Well-orientated cups-low metal ions(n=6), mal-orientated cups-high metal ions(n=4) and malorientated cups-low metal ions(n=4). Motion analysis data of each subject performing gait and sit-to-stand(STS) was captured. Ground reaction forces were recorded using 3 force plates. Following motion capture, markers on the pelvis and thighs were replaced and subjects underwent a CT scan. The data were used to build musculoskeletal models for each subject, using measured hip joint centre(HJC) locations. Subject-specific hip reaction forces(HRF) were computed. These were transformed into the local coordinate system of the cup and the distance the HRF vector made with the cup-edge during different activities was determined. RESULTS: The HRF of subjects with mal-positioned cups and high ion levels were closest to the edge of the acetabular component for both activities(p<0.001). The mean distance of the HRF from the cup-edge during stance phase for this group was 14.8mm(SD:3.5), in comparison to 16.4mm(SD:2.7) for the mal-orientated low ions groups and 18.5mm(SD:2.5) for the well-positioned low ions group. Similar differences in distance to edge were observed during the STS activities. CONCLUSION: Findings suggest that edge-loading is influenced by both cup orientation and intrinsic subject-specific activity patterns. Although subjects with mal-orientated cups are more likely to edge-load, intrinsic activity patterns of patients during functional activity may prevent edge-loading and explain why some subjects with mal-positioned components have low ion levels.

Various resonant and near-resonant patterns form in a light-sensitive Belousov-Zhabotinsky (BZ) reaction in response to a spatially-homogeneous time-periodic perturbation with light. The regions (tongues) in the forcing frequency and forcing amplitude parameter plane where resonant patterns form are identified through analysis of the temporal response of the patterns. Resonant and near-resonant responses are distinguished. The unforced BZ reaction shows both spatially-uniform oscillations and rotating spiral waves, while the forced system shows patterns such as standing-wave labyrinths and rotating spiral waves. The patterns depend on the amplitude and frequency of the perturbation, and also on whether the system responds to the forcing near the uniform oscillation frequency or the spiral wave frequency. Numerical simulations of a forced FitzHugh-Nagumo reaction-diffusion model show both resonant and near-resonant patterns similar to the BZ chemical system.

PURPOSE: Patellar tendon abnormality (PTA) on diagnostic imaging is part of the diagnostic criteria for patellar tendinopathy. A PTA in addition to altered landing strategies are primary risk factors that increase the likelihood of asymptomatic athletes developing patellar tendinopathy. Therefore, the aim of this study was to examine risk factors that are predictors of the presence and severity of a PTA in junior pre-elite athletes. METHODS: Ten junior pre-elite male basketball athletes with a PTA were matched with ten athletes with normal patellar tendons. Participants had patellar tendon morphology, Victorian Institute of Sport Assessment score (VISA), body composition, lower limb flexibility and maximum vertical jump height measured prior to performing five successful stop-jump tasks. During each stop-jump task, both two- and threedimensional kinematics and ground reaction forces were recorded. Multiple regression analyses were used to identify factors for estimating PTA presence and severity, and discriminate analysis used to classify PTA presence. RESULTS: Sixty-eight percent of variance for presence of a PTA was accounted for by hip joint range of motion (ROM), knee joint angle at initial foot-ground contact (IC) during stop-jump and quadriceps flexibility, whereas hip joint ROM and VISA accounted for 62% of variance for PTA severity. Prediction of the presence of a PTA was achieved with 95% accuracy and 95% cross-validation. CONCLUSIONS: An easily implemented, reliable and valid movement screening tool comprising of three criterion enables coaches and/or clinicians to predict for the presence and severity of a PTA in asymptomatic athletes. This enables identification of asymptomatic athletes at higher risk of developing patellar tendinopathy, which allows the development of effective preventative measures to aid in the reduction of patellar tendinopathy injury prevalence. PMID:23059860

We present and discuss the analytical r-mode solution to the linearized hydrodynamic equations of a slowly rotating, Newtonian, barotropic, non-magnetized, perfect-fluid star in which the gravitational radiation reaction force is present.

It is the purpose of this study to quantify the sea-bottom soil reaction effect on the dynamics of a Steel Catenary Riser by incorporating the soil reaction forces into the theoretical model of the dynamic equilibrium system. The calculations for the soil reaction forces have been performed quasi-statically, assuming specified embedment depths and trenching geometries. The plane stresses of the soil are determined with the aid of the commercial Geotechnical software, Phase2. Accordingly, the stresses are integrated around the arched riser-soil contact surface for the derivation of vertical soil reaction forces that resist to the penetration of the riser. These force-values are introduced in the nonlinear dynamic model as concentrated loads which are applied at the touchdown point (TDP). Se...

mems, for actuating force producing reaction means to. Accordingly, it is an object of .... and solenoid valve 19 to jet nozzzle 23, illustratively posi- tioned below the ..... discussed, hydraulic, mechanical, or pneumatic amplifica- tion and valve ...

We investigate pattern formation in self-oscillating systems forced by an external periodic perturbation. Experimental observations and numerical studies of reaction-diffusion systems and an analysis of an amplitude equation are presented. The oscillations in each of these systems entrain to rational multiples of the perturbation frequency for certain values of the forcing frequency and amplitude. We focus on the subharmonic resonant case where the system locks at one fourth the driving frequency, and four-phase rotating spiral patterns are observed at low forcing amplitudes. The spiral patterns are studied using an amplitude equation for periodically forced oscillating systems. The analysis predicts a bifurcation (with increasing forcing) from rotating four-phase spirals to standing two-phase patterns. This bifurcation is also found in periodically forced reaction-diffusion equations, the FitzHugh-Nagumo and Brusselator models, even far from the onset of oscillations where the amplitude equation analysis is ...

The kinetics analysis of ankle, knee and hip joints during gait is fundamental for rehabilitation and clinical diagnosis but data are commonly obtained by means of the laboratory-restricted equipment such as a force plate and optical camera system, which usually require complicated computing programs and professional operation. In this study, we have developed a wearable sensor system to facilitate joint kinetics analysis to assess body movement in daily activities. The sensor system is composed of a shoe-based force sensor which measures ground reaction force (GRF) and center of pressure (CoP), and a leg-attached motion sensor consisting of three uniaxial gyroscopes units which detect lower limbs movement. This paper presents a kinetics analysis of ankle, knee and hip joints in the sagittal plane by using the sensor system on human normal level walking during whole gait phases. In order to estimate the joint kinetics, an inverse kinetics method based on the sensing signals and gait characteristics was developed. In the validation experiments with 10 subjects, joint kinetics was calculated using data synchronously measured by the sensor system and a force plate & optical camera system. The root mean square (RMS) differences of the ankle, knee and hip joints moments between the two systems in a gait cycle were (2±0.34) (mean±standard deviation) Nm, (7.2±1.34) Nm and (11.2±1.3) Nm, being (5.4±0.7)%, (6±0.32)% and (6.1±0.25)% of the maximal magnitude of ankle, knee and hip joints moments respectively. The RMS differences of the ankle, knee and hip joints powers between the two systems in a gait cycle were (4.2±0.4) W, (5.7±2.1) W and (5.7±0.3) W, being (8.4±0.4)%, (4.1±0.5)% and (6.4±0.4)% of the maximal magnitude of joint powers respectively. The experimental results demonstrate the feasibility and effectiveness of the joint kinetics analysis using the wearable sensor system for a daily application in gait analysis.   

As station entered its third year of continuous operations, the scientific workload continued to occupy a significant amount of the Expedition crews time. The Expedition 6 crew worked unremittingly on the scientific mission in face of the changes wrought following the loss of Columbia, conducting experiments in bioastronautics research (BR), physical science (PS), space product development (SPD), space flight (SF), and fundamental space biology (FSB): A Study of Radiation Doses Experienced by Astronauts in EVA (BR), Chromosomal Aberrations in Blood Lymphocytes of Astronauts (BR), Effect of Prolonged Space Flight on Human Skeletal Muscle (BR), Effects of EVA and Long-term Exposure to Microgravity on Pulmonary Function (BR), Foot/Ground Reaction Forces During Space Flight (BR), Promoting Sensorimotor Response Generalizability (BR), Renal Stone Risk During Space Flight (BR), Space Flight-induced Reactivation of Latent Epstein-Barr Virus (BR), Subregional Assessment of Bone Loss in the Axial Skeleton in Long-term Space Flight (BR), Investigating the Structure of Paramagnetic Aggregates from Colloidal Emulsions (PS), Protein Crystal Growth-Single Locker Thermal Enclosure System (PS), Zeolite Crystal Growth (PS), Materials International Space Station Experiment (SPD), Microgravity Acceleration Measurement System (SPD), Space Acceleration Measurement System-II (SPD), Crew Earth Observations (SF), and Earth Knowledge Acquired by Middle-School Students (FSB).

[Purpose] The present study compared the ground reaction forces and temporospatial characteristics of the initial foot movement following anteroposterior platform perturbation between elderly fallers and non-fallers. [Subjects] Eighty-one elderly female subjects aged between 60 to 70 years were divided into faller (N=36) and non-faller (N=45) groups. [Methods] A motorized platform translation was applied as a perturbation. The response characteristics were recorded using a forceplate and a six-video camera 3D ViconTM motion analysis system. [Results] Both faller and non-faller groups showed a forward single step pattern greater than a backward single step pattern. The swing duration time of the non-faller group was significantly longer than that of the fallers, whereas step velocity of the fallers showed higher values than that of the non-fallers during forward single step. [Conclusion] The step ability in the faller group was decreased compared to the non-faller group during the forward single step. The findings suggest that the muscle performance of the primary muscles for balance recovery should be promoted in the elderly. Moreover, stability and ability to stand on one leg should be a measurement and training concern for the elderly to reduce the likelihood of falls.   

Excited states in 16C were populated via the 9Be(17N,16C+?)X one-proton knockout reaction. The lifetime of the 21+ state in 16C was measured using the recoil distance method. The extracted lifetime of ?21+=11.4?0.9+0.8(stat)±0.7(systB?)?1.5+0.0(systfeeding) ps yields a deduced B(E2;21+?01+)=4.21?0.26+0.34(stat)?0.24+0.28(systB?)?0.00+0.64(systfeeding)e2fm4 value in good agreement with a previous measurement. The one-proton knockout cross section is used to extract the proton amplitude of the 16C 21+ state, which confirms the neutron dominant character of this state. Gamma-ray branching ratios between the 22+ state and the 21+ and ground states were also determined. The results are compared with p-sd shell model and no-core shell model (with NN and NN+NNN) calculations. The inclusion of three-body forces are essential in order for the no-core shell model calculations to reproduce the experimental findings on the ?-ray branching ratios.

The purpose of the study was to develop and evaluate a new heel cushion in shoes for use with knee-ankle-foot orthoses having a medial single hip joint (Primewalk orthoses) in order to improve walking velocity and efficiency. Primewalk orthoses and shoes were made for a 24-year-old man having paraplegia with flaccid paresis (level T-7; grade A, ASIA impairment scale) of 2 years' duration. Walking exercises were assigned. Shoes were modified with the sole made of hard rubber and the addition of soft rubber heel cushions. The walking speed, centre of foot pressure during walking, and ground reaction force were evaluated. The patient also subjectively assessed the devices. The modifications to the shoes resulted in a 1.94-fold increase in walking speed (8.6 to 16.7 m/min), a 1.87-fold increase in step length (16.7 to 31.3 cm) and a 54.8% decrease in the physiological cost index (7.7 to 3.48 beats/min). The centre of foot pressure during walking was found to deviate towards the lateral margin of the foot. The horizontal rotation of the pelvis increased simultaneously. The patient reported increased amplitude of flail motion of the trunk and decreased burden to the upper limbs. It was concluded that the modified new heel cushion of the shoe provided freedom to the lower legs and thereby increased walking efficiency. PMID:16466159

Traditionally, golf biomechanics has focused upon achieving consistency in swing kinematics and kinetics, whilst variability was considered to be noise and dysfunctional. There has been a growing argument that variability is an intrinsic aspect of skilled motor performance and plays a functional role. Two types of variability are described: 'strategic shot selection' and 'movement variability'. In 'strategic shot selection', the outcome remains consistent, but the swing kinematics/kinetics (resulting in the desired ball flight) are free to vary; 'movement variability' is the changes in swing kinematics and kinetics from trial to trial when the golfer attempts to hit the same shot. These changes will emerge due to constraints of the golfer's body, the environment, and the task. Biomechanical research has focused upon aspects of technique such as elite versus non-elite kinematics, kinetics, kinematic sequencing, peak angular velocities of body segments, wrist function, ground reaction forces, and electromyography, mainly in the search for greater distance and clubhead velocity. To date very little is known about the impact of variability on this complex motor skill, and it has yet to be fully researched to determine where the trade-off between functional and detrimental variability lies when in pursuit of enhanced performance outcomes. PMID:22900407

The fatigue failure of thermoplastic ankle-foot orthoses (AFOs) was observed in clinics. However, there was no standard evaluation for the AFOs to enhance the understanding of how AFOs become more readily acceptable to patients. Therefore, this study aimed to develop an ankle-foot simulator (AFS) as a testing apparatus for AFOs, and performed a pilot test to investigate the failure mechanism of anterior ankle-foot orthosis (AAFO). The accuracy and repeatability of the AFS during cyclic walking, cyclic stepping and cyclic stepping with the AAFO in sagittal plane were measured. The root mean square errors (RMSEs) of cyclic walking of AFS compared to a target gait data were less than 80.52N and 2.55 degrees in the vertical ground reaction force and in the kinematics, respectively. The RMSE of ankle plantarflexion and dorsiflexion of AFS in the cyclic stepping tests were less than 1.25 degrees. The repeatability was assessed by standard deviation, which were less than 9.46N and 0.72 degrees in all testing conditions. A typical failure progression of five AAFOs was observed and graded for four phases under cyclic stepping test. Failure always initiated at the junction of anterior tarsal bar and lateral (or medial) bar of the AAFOs, from which the rest failures were extended. It is suggested that this junction must be reinforced or prevented the stress concentration to elongate the endurance of AAFO. PMID:20439163

Deep squatting places a burden on the lower limb muscles and influences postural balance. We attempted to determine the effects of postural changes on the rectus femoris, tibialis anterior, gastrocnemius, soleus, and extensor digitorum brevis muscles during squatting in 8 healthy male subjects. Three squatting conditions were involved: full squatting (FS), tiptoe squatting (TT), and tiptoe squatting on a 15° slope (TTS), performed randomly and recorded in a period of 4 min for each task. The influence of the squatting condition on electromyography and vertical ground reaction force parameters was examined in order to observe the effect of postural alteration on muscle activity and balance control. The results showed that the change of squatting posture from FS to TT decreased the activity of the rectus femoris and tibialis anterior muscles. FS has been suspected as a main cause of musculoskeletal complaint during prolonged squatting. In contrast, as the heel was lifted, the extensor digitorum brevis muscle increased to 39% of maximum activation. On the other hand, sway analysis at TT showed balance instability regarding the large area occupation of the center of pressure displacement. The presence of a 15° slope significantly reduced the muscular load. This simple study suggests that the inclusion of a sloping surface in daily activities that requires a squatting posture would be an effective means to reduce muscular load.   

Bimetallic rod-shaped nanomotors swim autonomously in hydrogen peroxide solutions. Here we present a scaling analysis, computational simulations, and experimental data that show that the nanomotor locomotion is driven by fluid slip around the nanomotor surface due to electrical body forces. The body forces are generated by a coupling of charge density and electric fields induced by electrochemical reactions occurring on the nanomotor surface. We describe the dependence of nanomotor motion on the nanomotor surface potential and reaction-driven flux.

Develop a model that simulates a human running in 0 G using the European Space Agency s (ESA) Subject Loading System (SLS). The model provides ground reaction forces (GRF) based on speed and pull-down forces (PDF). DESIGN The theoretical basis for the Running Model was based on a simple spring-mass model. The dynamic properties of the spring-mass model express theoretical vertical GRF (GRFv) and shear GRF in the posterior-anterior direction (GRFsh) during running gait. ADAMs VIEW software was used to build the model, which has a pelvis, thigh segment, shank segment, and a spring foot (see Figure 1).the model s movement simulates the joint kinematics of a human running at Earth gravity with the aim of generating GRF data. DEVELOPMENT & VERIFICATION ESA provided parabolic flight data of subjects running while using the SLS, for further characterization of the model s GRF. Peak GRF data were fit to a linear regression line dependent on PDF and speed. Interpolation and extrapolation of the regression equation provided a theoretical data matrix, which is used to drive the model s motion equations. Verification of the model was conducted by running the model at 4 different speeds, with each speed accounting for 3 different PDF. The model s GRF data fell within a 1-standard-deviation boundary derived from the empirical ESA data. CONCLUSION The Running Model aids in conducting various simulations (potential scenarios include a fatigued runner or a powerful runner generating high loads at a fast cadence) to determine limitations for the T2 vibration isolation system (VIS) aboard the International Space Station. This model can predict how running with the ESA SLS affects the T2 VIS and may be used for other exercise analyses in the future.

The compaction of DNA by the HU protein from Thermotoga maritima (TmHU) is analysed on a single-molecule level by the usage of an optical tweezers-assisted force clamp. The condensation reaction is investigated at forces between 2 and 40 pN applied to the ends of the DNA as well as in dependence on ...

An enhanced sampling method-biased Brownian dynamics-is developed for the calculation of diffusion-limited biomolecular association reaction rates with high energy or entropy barriers. Biased Brownian dynamics introduces a biasing force in addition to the electrostatic force between the reactants, a...

This paper presents a modeling analysis of the geochemical evolution of a contaminated sandy aquifer at a uranium mill tailings site in the western United States. The tailings pond contains fluids having a pH of 1.5 to 3.5 and high levels of As, Be, Cd, Cr, Pb, Mo, Ni, Se, 226Ra, 228Ra, 230Th, 238U, and 234U. Seepage of tailings fluids into the aquifer has formed a low-pH ground water plume. The reclamation plan is to install a low-permeability cover on the tailings pond to stop the seepage and allow the plume to be attenuated by reactions with the aquifer matrix and flushed by uncontaminated upgradient ground water. To evaluate this reclamation scenario, ground water and sediment core samples were analyzed along one flowpath. Speciation-solubility and mass-transfer modeling revealed two sets of chemical reactions for acid seepage and flushing, respectively. The current concentrations and distribution of ground water constituents can be interpreted as being controlled by stepwise pH-buffer reactions with calcite, amorphous aluminum hydroxide, and amorphous iron hydroxides. These buffer reactions divide the aquifer into zones of near-constant pH, separated by interface zones. For the flushing stage, it is predicted that reactions with surface-bound species will dominate the reaction paths, and more pore volumes are required to neutralize the plume than predicted by models that do not consider surface reactions. Direct mineralogical and surface analysis is needed to substantiate this assertion. PMID:11798046

One of the most important subjects in the superconducting Maglev system is a method for providing onboard service power. As a solution, a linear generator is being developed that can collect power without contact by utilizing the harmonic magnetic field around the ground coils and generate an electromagnetic force between them and the superconducting magnets by controlling the current in the generator coils. By using this controllable electromagnetic force, it becomes possible to add magnetic damping to the electrodynamic levitation system with a small damping force. This paper describes the results of the running tests of the linear generator using zero-phase current control, combined with the magnetic damping function.   

China's traditionally nuclear missile force has added a conventional force component with an inventory of over 1,000 short-range ballistic missiles and an emerging class of theater ballistic and ground-launched cruise missiles. This growing conventional missile force provides Beijing an operational-tactical and strategic capability in theater without the political and practical constraints associated with nuclear-armed missiles. China's emerging inventory of conventional antiship ballistic missiles (ASBMs) affords its military an extra employment option enhancing its layered defense posture against potential offshore threats beyond Taiwan. The military's conventional missiles, operational doctrine, and threat perceptions create conditions for China's escalation to conventional missile atta...

The U.S. Air Force has developed a novel remedial technology for treatment of ground water that is contaminated with chlorinated solvents. The contamination is treated in a reactive barrier constructed with plant mulch. The barrier is constructed by excavating a trench across t...

We show, in the context of quantum combinatorial optimization, or quantum annealing, how the nonlinear Schrödinger-Langevin-Kostin equation can dynamically drive the system toward its ground state. We illustrate, moreover, how a frictional force of Kostin type can prevent the appearance of genuinely...

We submit to the community of physicists and mathematical physicists the following problem: prove that the ground-state energy of a system of N particles without spin, without statistics, and interacting by central forces increases with angular momentum. For two particles, this is obvious. For more than two we give a number of arguments which support our conjecture.

This study was undertaken to assist the Air Force Technical Applications Center (AFTAC) in conducting a sulfur hexafluoride SF6 tracer test known as GAUNTLET at the Dugway Proving Ground, UT. Seven separate 4-hour long releases of SF6 were performed durin...

An electrostatic-control led torsion pendulum was constructed to test the in-flight performance of an electrostatic inertial sensor on ground. An electrostatic-controlled torque resolution of 6 × 10-13 N m Hz-1/2 and a force resolution of 3.6 × 10-11 N Hz-1/2 from 2 mHz to 0.1 Hz were achieved.

Modern electronic materials are characterized by a great variety of broken-symmetry ground states and excitations. Their control requires understanding and tuning underlying driving forces of spin-charge-lattice coupling, critical to macroscopic properties and applications. We report representative model calculations which demonstrate some of the richness of the phenomena and the challenges for successful microscopic modeling.

Two-phase flows are encountered in a wide range of applications both on-ground and in space. The dynamics of such flows in the absence of gravity is completely different from that in normal gravity due to the absence of buoyancy forces. A deeper understanding of the behavior of multiphase flows is e...

Studies of limb bone loading during terrestrial locomotion have focused primarily on birds and mammals. However, data from a broader functional and phylogenetic range of species are critical for understanding the evolution of limb bone function and design. Turtles are an interesting lineage in this context. Although their slow walking speeds and robust limb bones might lead to low locomotor forces and limb bone stresses similar to other non-avian reptiles, their highly sprawled posture could produce high bending loads, leading to high limb bone stresses similar to those of avian and mammalian species, as well as high torsion. To test between these possibilities, we evaluated stresses experienced by the femur of river cooter turtles (Pseudemys concinna) during terrestrial walking by synchronizing measurements of three-dimensional joint kinematics and ground reaction forces (GRFs) during isolated hindlimb footfalls. Further, we evaluated femoral safety factors for this species by comparing our locomotor stress calculations with the results of mechanical property tests. The net GRF magnitude at peak tensile bone stress averaged 0.35 BW (body weight) and was directed nearly vertically for the middle 40-65% of the contact interval, essentially orthogonal to the femur. Peak bending stresses experienced by the femur were low (tensile: 24.9+/-9.0 MPa; compressive: -31.1+/-9.1 MPa) and comparable to those in other reptiles, yet peak shear stresses were higher than those in other reptiles, averaging 13.7+/-4.2 MPa. Such high torsion is present despite cooters lacking a large tail, a feature that has been hypothesized to contribute to torsion in other reptiles in which the tail is dragged along the ground. Comparison of femoral stresses to measurements of limb bone mechanical properties in cooters indicates safety factors to yield of 13.9 in bending and 6.3 in torsion, considerably higher than values typical for birds and mammals, and closer to the elevated values calculated for other reptile species. Thus, not only do turtle limb bones seem considerably ;over-designed' for resisting the loads that they encounter, but comparisons of bone loading across tetrapod lineages are consistent with the hypothesis that low limb bone loads, elevated torsion and high safety factors may be primitive features of limb bone design. PMID:18375843

Background The goal of this study was to test the mechanical performance of a prototype knee-ankle-foot orthosis (KAFO) powered by artificial pneumatic muscles during human walking. We had previously built a powered ankle-foot orthosis (AFO) and used it effectively in studies on human motor adaptation, locomotion energetics, and gait rehabilitation. Extending the previous AFO to a KAFO presented additional challenges related to the force-length properties of the artificial pneumatic muscles and the presence of multiple antagonistic artificial pneumatic muscle pairs. Methods Three healthy males were fitted with custom KAFOs equipped with artificial pneumatic muscles to power ankle plantar flexion/dorsiflexion and knee extension/flexion. Subjects walked over ground at 1.25 m/s under four conditions without extensive practice: 1) without wearing the orthosis, 2) wearing the orthosis with artificial muscles turned off, 3) wearing the orthosis activated under direct proportional myoelectric control, and 4) wearing the orthosis activated under proportional myoelectric control with flexor inhibition produced by leg extensor muscle activation. We collected joint kinematics, ground reaction forces, electromyography, and orthosis kinetics. Results The KAFO produced ~22%–33% of the peak knee flexor moment, ~15%–33% of the peak extensor moment, ~42%–46% of the peak plantar flexor moment, and ~83%–129% of the peak dorsiflexor moment during normal walking. With flexor inhibition produced by leg extensor muscle activation, ankle (Pearson r-value = 0.74 ± 0.04) and knee ( r = 0.95 ± 0.04) joint kinematic profiles were more similar to the without orthosis condition compared to when there was no flexor inhibition (r = 0.49 ± 0.13 for ankle, p = 0.05, and r = 0.90 ± 0.03 for knee, p = 0.17). Conclusion The proportional myoelectric control with flexor inhibition allowed for a more normal gait than direct proportional myoelectric control. The current orthosis design provided knee torques smaller than the ankle torques due to the trade-off in torque and range of motion that occurs with artificial pneumatic muscles. Future KAFO designs could incorporate cams, gears, or different actuators to transmit greater torque to the knee. PMID:3455838

The pile foundation is heavily damaged at the boundary division of the ground types, liquefied ground and non-liquefied ground, during an earthquake and there is a possibility of the collapse of the piles. In this study, we conduct a shaking table test and effective stress analysis of the influence of soil liquefaction and the seismic inertial force exerted on the pile foundation. When the intermediate part of the pile, there is at the boundary division, is subjected to section force, this part increases in size as compared to the pile head in certain instances. Further, we develop a seismic resistance method for a pile foundation in liquefaction using seismic isolation rubber and it is shown the middle part seismic isolation system is very effective.

The photoinduced electron transfer (PET) reaction within a ternary copper complex [Cu(phen)(Htrp)]{sup +} (Htrp: L-tryptophanato; phen: 1,10-phenanthroline) (1) and in presence of DNA has been studied in homogeneous buffer medium and in reverse micelles. An intramolecular electron transfer occurs within the photoexcited complex (1) from tryptophan to phen. The copper complex can displace ethidium bromide from DNA backbone and on photoexcitation can oxidize DNA in a deoxygenated environment due to intermolecular electron transfer, although the intramolecular electron transfer is thermodynamically favorable. A prominent magnetic field effect (MFE) has been found even in homogeneous aqueous medium for the triplet born radicals both in case of intra and intermolecular electron transfer reactions. In case of intramolecular electron transfer the observation of MFE is similar to that of linked donor-acceptor system. However the observation of MFE for the intermolecular electron transfer between non-covalently bound complex-DNA systems is rather rare. Some non-covalent weak interaction, e.g. hydrophobic interaction between the phen ligand and DNA base pairs and electrostatic force of attraction between [Cu(phen)(Htrp)]{sup +} complex and DNA may lead to partial intercalation of the copper complex within DNA that is responsible for such a rare observation. - Research Highlights: On photoexcitation intra-molecular electron transfer occurs from tryptophan (Htrp) to phenanthroline (phen) within [Cu(phen)(Htrp)]ClO{sub 4}. In presence of CT DNA a ground state complex is formed between CT DNA and ternary copper compound. On photoexcitation of the complex an intermolecular electron transfer occurs from DNA base to phen instead of Htrp. Magnetic field effect has been used to detect the triplet born radical ions in solution and in reverse micelles.

The forces generated by the muscles with origin on the human femur play a major role in transtibial amputee gait, as they are the most effective of the means that the body can use for propulsion. By estimating the forces generated by the thigh muscles of transtibial amputees, and comparing them to the forces generated by the thigh muscles of normal subjects, it is possible to better estimate the energy output needed from prosthetic devices. The purpose of this paper is to obtain the forces generated by the thigh muscles of transtibial amputees and compare these with forces obtained from the same muscles in the case of normal subjects. Two transtibial amputees and four normal subjects similar in size to the amputees were investigated. Level ground walking was chosen as the movement to be st...

In this thesis, a very general quantization scheme for the macroscopic electromagnetic field in arbitrary linearly responding media is presented. It offers a unified approach to QED in such media. Applying the quantization scheme, a theory of the dispersion forces on the basis of the Lorentz force is developed. By regarding the dispersion force as the (ground-state or thermal-state) expectation value of the Lorentz force that acts on appropriately defined charge and current densities, Casimir, Casimir-Polder, and van der Waals forces are united in a very natural way that makes transparent their common physical basis. Application of the theory to planar structures yields generalizations of well-known Lifschitz and Casimir-type formulas. (orig.)

Times for indoor 200 m sprint races are notably worse than those for outdoor races. In addition, there is a considerable bias against competitors drawn in inside lanes (with smaller bend radii). Centripetal acceleration requirements increase average forces during sprinting around bends. These increased forces can be modulated by changes in duty factor (the proportion of stride the limb is in contact with the ground). If duty factor is increased to keep limb forces constant, and protraction time and distance travelled during stance are unchanging, bend-running speeds are reduced. Here, we use results from the 2004 Olympics and World Indoor Championships to show quantitatively that the decreased performances in indoor competition, and the bias by lane number, are consistent with this 'constant limb force' hypothesis. Even elite athletes appear constrained by limb forces. PMID:17148323

Utilizing the compound nuclear reaction [sup 58]Ni+[sup 50]Cr and a new low-energy proton detector ball, we have observed the ground-state proton decay of [sup 105]Sb. A proton energy of 478[plus minus]15 keV was measured along with an estimated ground-state proton branching ratio of [similar to]1%, compatible with emission from a [ital d][sub 5/2] level and a spectroscopic factor of order unity.

This paper presents a novel force controller to suppress torsional vibration of two-mass resonant system. The resonance ratio control is one of the effective control methods of two-mass resonant system. In this method, the ratio between the resonant frequency of motor and arm is determined arbitrary according to the feedback of estimated reaction torque. The reaction torque is estimated by using position sensitive detector (PSD). Since the estimation method does not need the parameter identification, the torsion information is obtained with accuracy.To attain the affinity and adaptability to environment, motion systems should control the reaction force from the environment. In the force control system, the force response is regarded as a disturbance of the arm portion. The arm disturbance is observed by the arm disturbance observer. The proposed force control system is based on both the conventional PD control and the resonance ratio control and the determination method of pole placement is discussed. The proposed force control system can realize both the suppression of the inner torsional reaction torque and the adaptation to outer force inputs. The numerical and experimental results show viability of the proposed method.   

The present invention is a variable thrust cartridge comprising a water-molten aluminum reaction chamber from which a slug is propelled. The cartridge comprises a firing system that initiates a controlled explosion from the reaction chamber. The explosive force provides a thrust to a slug, preferably contained within the cartridge.

Twenty four remitted schizophrenics and twenty four neurotic depressives were studied on three measures of visual information processing, viz., simple reaction time, choice reaction time, and a forced choice span of apprehension test. The groups were matched for age, sex, and educational status. The...

The aim of this study was to analyse the principal mechanics of circles. Seventeen university male gymnasts performed circles on an instrumented pommel horse model that enabled the pommel reaction forces to be recorded at 1000 Hz with two force plates. The circles were also videotaped using two digital video cameras operating at 60 frames per second. During circles, the vertical component of the reaction forces peaked in the double-hand support phases. Changes in the velocity of the centre of mass corresponded to the change in the tangential components of horizontal reaction forces. The velocity of the centre of mass had its peaks in the single-hand support phases and its local minimums in the double-hand support phases. The velocity of the ankles and that of the centre of mass of the...

An accurate, dynamic, functional model of the skull that can be used to predict muscle forces, bite forces, and joint reaction forces would have many uses across a broad range of disciplines. One major issue however with musculoskeletal analyses is that of muscle activation pattern indeterminacy. A very large number of possible muscle force combinations will satisfy a particular functional task. This makes predicting physiological muscle recruitment patterns difficult. Here we describe in detail the process of development of a complex multibody computer model of a primate skull (Macaca fascicularis), that aims to predict muscle recruitment patterns during biting. Using optimisation criteria based on minimisation of muscle stress we predict working to balancing side muscle force ratios, peak bite forces, and joint reaction forces during unilateral biting. Validation of such models is problematic; however we have shown comparable working to balancing muscle activity and TMJ reaction ratios during biting to those observed in vivo and that peak predicted bite forces compare well to published experimental data. To our knowledge the complexity of the musculoskeletal model is greater than any previously reported for a primate. This complexity, when compared to more simple representations provides more nuanced insights into the functioning of masticatory muscles. Thus, we have shown muscle activity to vary throughout individual muscle groups, which enables them to function optimally during specific masticatory tasks. This model will be utilised in future studies into the functioning of the masticatory apparatus. PMID:22721994

A mechanism is said to be force balanced if, for any arbitrary motion, it does not apply reaction forces on the base. Moreover, if it does not apply torques on the base, the mechanism is said to be moment balanced or dynamically balanced. In this paper, a new method to determine the complete set of force and moment balanced planar four-bar linkages is presented. Using complex variables to model the kinematics of the linkage, the force and moment balancing constraints are written as algebraic equations over complex variables and joint angular velocities. Using polynomial division, necessary and sufficient conditions for the balancing of planar four-bar linkages are derived.

The demonstration of the IGRS approach conducted at SWMU 143 on the White Sands Missile Range has provided information needed to complete a technical performance assessment and cost analysis of the technology. At least 70% of the Cr(VI) present in contaminated sediment at the site was reduced, thus verifying the effectiveness of the approach. Most of the treatment occurred in a zone located from {approximately}4 to 10 ft below ground surface, which appears to be a higher permeability interval. A deeper zone from {approximately}10 to 16 ft that contains lower levels of contamination was essentially unaffected. The deeper zone is somewhat finer grained and has a higher clay content and is, thus, less permeable. It appears that most of the treatment gas was channeled through the higher, more-permeable zone and the lower zone was bypassed. Treatment of the lower zone could probably be accomplished, however, if a second injection well were installed and screened across the zone so that treatment gas could be forced into this interval. The amount of H{sub 2}S consumed during the test exceeded the amount predicted by the laboratory treatability study. In addition, the levels of H{sub 2}S observed at the extraction wells were relatively low, even though a significant level of treatment was observed at the site. It is inferred that interfering reactions or slower reaction kinetics are the likely source of consumption of extra H{sub 2}S observed in the field. Future laboratory work will be undertaken to investigate the nature of these chemical reactions and the reaction rates associated with the gaseous reduction of Cr(VI) in soils. Elucidation of these effects may reveal methods for improving the effectiveness of the technology and reducing unit costs. A life-cycle cost model was developed for the technology based on demonstration information (Hogan 1998). This model suggests that the technology should compare favorably with excavation from a cost basis for larger sites, especially when depths exceed 15 or 20 ft. Site-specific information should be provided as input to the model to evaluate this, however, because costs vary significantly, depending on site characteristics. The IGRS approach is considered ready for application as a remediation tool based on the success of the field demonstration at the White Sands Missile Range. It is expected that a large-scale test or deployment will take place at a US Department of Energy CrO{sub 4}{sup 2{minus}} contaminated site within the next several years. In addition, further laboratory-testing activities are planned to identify other metal and radionuclide contaminants that can be immobilized through the gaseous reduction approach.

Biological molecular machines are proteins that operate under isothermal conditions hence are referred to as free energy transducers. They can be formally considered as enzymes that simultaneously catalyze two chemical reactions: the free energy-donating reaction and the free energy-accepting one. Most if not all biologically active proteins display a slow stochastic dynamics of transitions between a variety of conformational substates composing their native state. In the steady state, this dynamics is characterized by mean first-passage times between transition substates of the catalyzed reactions. On taking advantage of the assumption that each reaction proceeds through a single pair (the gate) of conformational transition substates of the enzyme-substrates complex, analytical formulas were derived for the flux-force dependence of the both reactions, the respective stalling forces and the degree of coupling between the free energy-accepting (output) reaction flux and the free energy-donating (input) one. Th...

Though it is well-known that 1+1 D hyperbolic motion in space and time is reaction-free, it is not widely acknowledged that a classical point charge can also execute a curved path through space, i.e. in 2+1 D, without incurring a reaction force. This note catalogs the full family of reaction-free trajectories, giving a geometrical interpretation by which means the curved path possibility is easily related to the better known case of hyperbolic motion in 1+1 D.

A detailed investigation was made of a landing pier of steel pipe piles damaged by the 1995 Hyogoken-Nambu earthquake; the external force which acted thereon and the mechanism of failure were inferred. The pier was of an open type supported by vertical and batter piles and was constructed in front of the sea wall caisson. The investigation covered the displacement and inclination of the sea wall and the pier, and the buckling and deformation of the steel pipe piles were examined after the piles were extracted. In the vicinity of the area near the investigated pier, a horizontal acceleration of 327 gal had been recorded, so a large inertial force may have acted on the sea wall caisson and the pier. In addition, the replacement sand below the caisson may have undergone liquefaction, causing the sand and the rubble to shift, and imposing a horizontal force directly upon the piles, thus causing their breakage. Hence, in the present analysis a total of eight cases were studied under various conditions including the presence/absence of horizontal force due to ground movement, the loading direction and the magnitude of the horizontal load, in addition to the inertial force of the structure generated by the earthquake. As a result, it was found that the case wherein the inertial force of the structure was in the direction opposite to that of the ground deformation load most correctly explained the condition of the damage which actually occurred.   

Ground motions at the frequencies (between 0.01 and 0.1 Hz) of ocean infragravity and swell waves were observed on a cross-shore transect extending landward from the edge of a southern California coastal cliff. Cliff top ground motions are coherent and in phase with water level fluctuations at the cliff base. Vertical ground motions at infragravity and single frequencies decay rapidly with inland distance from the cliff edge (e-folding scale is about 12 m), and at the edge decrease by several orders of magnitude between high tide when waves reach the cliff base, and low tide when the waterline is about 50 m from the cliff base. The observed cross-shore decay scales are qualitatively consistent with gravitational loading and attraction of water waves at tidally modulated distances from the cliff base. At approximately constant distance from the waterline, ground motions vary roughly linearly with nearshore swell wave energy. In contrast to these locally forced ground motions, double frequency band (0.1-0.2 Hz) cliff top vertical ground motions are remotely generated with spatially uniform magnitudes approximately equal to those observed 14 km inland. Near the cliff edge, ground tilt dominates the observed large (relative to vertical) cross-shore acceleration at infragravity frequencies, contributes significantly to cross-shore acceleration at swell frequencies, and is a small fraction of cross-shore acceleration at higher frequencies.