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Ground reaction forces during treadmill running in microgravity.  

Science.gov (United States)

Astronauts perform treadmill exercise during long-duration space missions to counter the harmful effects of microgravity exposure upon bone, muscle, and cardiopulmonary health. When exercising in microgravity, astronauts wear a harness and bungee system that provides forces that maintain attachment to the treadmill. Typical applied forces are less than body weight. The decreased gravity-replacement force could result in differences in ground-reaction force at a given running speed when compared to those achieved in normal gravity, which could influence the adaptive response to the performed exercise. Seven astronauts (6 m/1 f) who completed approximately 6-month missions on the International Space Station (ISS) completed a preflight (1G) and multiple in-flight (0G) data collection sessions. Ground-reaction forces were measured during running at speeds of 8.0 kph and greater on an instrumented treadmill in the lab and on the ISS. Ground-reaction forces in 0G were less than in 1G for a given speed depending upon the gravity-replacement force, but did increase with increased speed and gravity-replacement force. Ground-reaction forces attained in 1G during slower running could be attained by increasing running speed and/or increasing gravity-replacement forces in 0G. Loading rates in 1G, however, could not be replicated in 0G. While current gravity-replacement force devices are limited in load delivery magnitude, we recommend increasing running speeds to increase the mechanical loads applied to the musculoskeletal system during 0G treadmill exercise, and to potentially increase exercise session efficiency. PMID:24835563

De Witt, John K; Ploutz-Snyder, Lori L

2014-07-18

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Crouched posture maximizes ground reaction forces generated by muscles.  

Science.gov (United States)

Crouch gait decreases walking efficiency due to the increased knee and hip flexion during the stance phase of gait. Crouch gait is generally considered to be disadvantageous for children with cerebral palsy; however, a crouched posture may allow biomechanical advantages that lead some children to adopt a crouch gait. To investigate one possible advantage of crouch gait, a musculoskeletal model created in OpenSim was placed in 15 different postures from upright to severe crouch during initial, middle, and final stance of the gait cycle for a total of 45 different postures. A series of optimizations was performed for each posture to maximize transverse plane ground reaction forces in the eight compass directions by modifying muscle forces acting on the model. We compared the force profile areas across all postures. Larger force profile areas were allowed by postures from mild crouch (for initial stance) to crouch (for final stance). The overall ability to generate larger ground reaction force profiles represents a mechanical advantage of a crouched posture. This increase in muscle capacity while in a crouched posture may allow a patient to generate new movements to compensate for impairments associated with cerebral palsy, such as motor control deficits. PMID:22542242

Hoang, Hoa X; Reinbolt, Jeffrey A

2012-07-01

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Ground Reaction Forces During Locomotion in Simulated Microgravity  

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Significant losses in bone density and mineral, primarily in the lower extremities have been reported following exposure to weightlessness. Recent investigations suggest that mechanical influences such as bone deformation and strain rate may be critically important in stimulating new bone formation. It was hypothesized that velocity, cadence and harness design would significantly affect lower limb impact forces during treadmill exercise in simulated zero gravity (0G). A ground-based hypogravity simulator was used to investigate which factors affect limb loading during tethered treadmill exercise. A fractional factorial design was used and 12 subjects were studied. The results showed that running on active and passive treadmills in the simulator with a tethering force close to the maximum comfortable level produced similar magnitudes for the peak ground reaction force. It was also found that these maximum forces were significantly lower than those obtained during overground trials, even when the speeds of locomotion in the simulator were 66 % greater than those in 1 G. Cadence had no effect on any of the response variables. The maximum rate of force application (DFDT-Max) was similar for overground running and exercise in simulated 0G, provided that the "weightless subjects ran on a motorized treadmill. These findings have implications for the use of treadmill exercise as a countermeasure for hypokinetic osteoporosis. As the relationship between mechanical factors and osteogenesis becomes better understood, results from human experiments in 0G simulators will help to design in-flight exercise programs that are more closely targeted to generate appropriate mechanical stimuli.

Davis, B. L.; Cavanagh, Peter R.; Sommer, H. J., III; Wu, G.

1996-01-01

4

Ground reaction force adaptations to tripedal locomotion in dogs.  

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To gain insight into the adaptive mechanisms to tripedal locomotion and increase understanding of the biomechanical consequences of limb amputation, this study investigated kinetic and temporal gait parameters in dogs before and after the loss of a hindlimb was simulated. Nine clinically sound Beagle dogs trotted on an instrumented treadmill and the ground reaction forces as well as the footfall patterns were compared between quadrupedal and tripedal locomotion. Stride and stance durations decreased significantly in all limbs when the dogs ambulated tripedally, while relative stance duration increased. Both vertical and craniocaudal forces were significantly different in the remaining hindlimb. In the forelimbs, propulsive force increased in the contralateral and decreased in the ipsilateral limb, while the vertical forces were unchanged (except for mean force in the contralateral limb). Bodyweight was shifted to the contralateral and cranial body side so that each limb bore ~33% of the dog's bodyweight. The observed changes in the craniocaudal forces and the vertical impulse ratio between the fore- and hindlimbs suggest that a nose-up pitching moment occurs during the affected limb pair's functional step. To regain pitch balance for a given stride cycle, a nose-down pitching moment is exerted when the intact limb pair supports the body. These kinetic changes indicate a compensatory mechanism in which the unaffected diagonal limb pair is involved. Therefore, the intact support pair of limbs should be monitored closely in canine hindlimb amputees. PMID:24881509

Fuchs, A; Goldner, B; Nolte, I; Schilling, N

2014-09-01

5

Ground reaction force characteristics of Tai Chi push hand.  

Science.gov (United States)

Abstract Push Hand is an advanced training technique for the Yang-style old frame 108 forms Tai Chi Chuan. It is performed by two practitioners. To clarify how people use forces during Push Hand training, it is important to review the ground reaction force (GRF). Here, we quantify the characteristics of the GRF during Push Hand training. Kinematic data and GRF data from 10 Tai Chi Chuan practitioners (29.9 ± 7.87 years) were synchronously recorded using a three-dimensional motion analysis system (200 frames · s(-1)) and three-dimensional force plates (1000 Hz). The resultant GRF for both feet for the 0%, 50% and 100% phases of attack and defence were compared to body weight using a paired-samples t-test. The differences in the resultant GRF between the 0%, 50% and 100% phases of attack and defence were tested by one-way repeated-measures ANOVA. The significance level was set to 0.05. The total resultant GRF was almost equal to the participant's body weight in push hand. This result was consistent throughout the entire push hand process. Our results revealed that the GRF was comparable to the body weight, implying that practitioners do not push or resist their opponents during the push hand process. PMID:24820103

Chang, Yao-Ting; Chang, Jia-Hao; Huang, Chen-Fu

2014-10-01

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Contributions of muscles to mediolateral ground reaction force over a range of walking speeds  

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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 increased significantly (p < 0.05) with walking speed. During early single support (14-30% gait cycle), peak ground reaction force on the stance foot was directed medially and increased significantly (p < 0.01) with speed. Muscles accounted for more than 92% of the mediolateral ground reaction force over all walking speeds, whereas gravity and velocity-related forces made relatively small contributions. Muscles coordinate mediolateral acceleration via an interplay between the medial ground reaction force contributed by the abductors and the lateral ground reaction forces contributed by the knee extensors, plantarflexors, and adductors. Our findings show how muscles that contribute to forward progression and body-weight support also modulate mediolateral acceleration of the body mass center while weight is transferred from one leg to another during double support. PMID:22884038

John, Chand T.; Seth, Ajay; Schwartz, Michael H.; Delp, Scott L.

2012-01-01

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The Effect of Increasing Inertia upon Vertical Ground Reaction Forces during Locomotion  

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The addition of inertia to exercising astronauts could increase ground reaction forces and potentially provide a greater health benefit. However, conflicting results have been reported regarding the adaptations to additional mass (inertia) without additional net weight (gravitational force) during locomotion. We examined the effect of increasing inertia while maintaining net gravitational force on vertical ground reaction forces and kinematics during walking and running. Vertical ground reaction force was measured for ten healthy adults (5 male/5 female) during walking (1.34 m/s) and running (3.13 m/s) using a force-measuring treadmill. Subjects completed locomotion at normal weight and mass, and at 10, 20, 30, and 40% of added inertial force. The added gravitational force was relieved with overhead suspension, so that the net force between the subject and treadmill at rest remained equal to 100% body weight. Peak vertical impact forces and loading rates increased with increased inertia during walking, and decreased during running. As inertia increased, peak vertical propulsive forces decreased during walking and did not change during running. Stride time increased during walking and running, and contact time increased during running. Vertical ground reaction force production and adaptations in gait kinematics were different between walking and running. The increased inertial forces were utilized independently from gravitational forces by the motor control system when determining coordination strategies.

DeWitt, John K.; Hagan, R. Donald; Cromwell, Ronita L.

2007-01-01

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Ground reaction forces in ballet dancers landing in flat shoes versus pointe shoes.  

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Reports in the literature suggest an abundance of lower extremity injuries in ballet dancers; however, few studies have identified the underlying causes of these injuries. Excessive ground reaction forces and shoe type are two potential contributing factors. Eighteen collegiate female ballet majors volunteered for this study. Each participant performed 12 trials of a basic ballet jump, six trials in flat shoes and 6 trials in pointe shoes, landing on a force plate. Ground reaction force (Newtons) and jump height (centimeters) were assessed for each trial. The mean ground reaction force and jump height for each shoe condition was used for statistical analysis. Two dependent t-tests were conducted to determine differences between the shoe types, one for ground reaction force and one for jump height. Alpha level was set at p < .05. We found that the ground reaction force was significantly higher when landing in flat shoes than in pointe shoes (p = .003). There was no significant difference in jump height between the two shoe conditions. This leads us to believe that the increase in ground reaction force was produced primarily by the shoe type. PMID:21703094

Walter, Heather L; Docherty, Carrie L; Schrader, John

2011-06-01

9

Comparison of vertical ground reaction forces during overground and treadmill running. A validation study  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract Background One major drawback in measuring ground-reaction forces during running is that it is time consuming to get representative ground-reaction force (GRF values with a traditional force platform. An instrumented force measuring treadmill can overcome the shortcomings inherent to overground testing. The purpose of the current study was to determine the validity of an instrumented force measuring treadmill for measuring vertical ground-reaction force parameters during running. Methods Vertical ground-reaction forces of experienced runners (12 male, 12 female were obtained during overground and treadmill running at slow, preferred and fast self-selected running speeds. For each runner, 7 mean vertical ground-reaction force parameters of the right leg were calculated based on five successful overground steps and 30 seconds of treadmill running data. Intraclass correlations (ICC(3,1 and ratio limits of agreement (RLOA were used for further analysis. Results Qualitatively, the overground and treadmill ground-reaction force curves for heelstrike runners and non-heelstrike runners were very similar. Quantitatively, the time-related parameters and active peak showed excellent agreement (ICCs between 0.76 and 0.95, RLOA between 5.7% and 15.5%. Impact peak showed modest agreement (ICCs between 0.71 and 0.76, RLOA between 19.9% and 28.8%. The maximal and average loading-rate showed modest to excellent ICCs (between 0.70 and 0.89, but RLOA were higher (between 34.3% and 45.4%. Conclusions The results of this study demonstrated that the treadmill is a moderate to highly valid tool for the assessment of vertical ground-reaction forces during running for runners who showed a consistent landing strategy during overground and treadmill running. The high stride-to-stride variance during both overground and treadmill running demonstrates the importance of measuring sufficient steps for representative ground-reaction force values. Therefore, an instrumented treadmill seems to be suitable for measuring representative vertical ground-reaction forces during running.

Kluitenberg Bas

2012-11-01

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Analysis of ground reaction force and electromyographic activity of the gastrocnemius muscle during double support.  

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Mechanisms associated with energy expenditure during gait have been extensively researched and studied. According to the double-inverted pendulum model energy expenditure is higher during double support, as lower limbs need to work to redirect the centre of mass velocity. This study looks into how the ground reaction force of one limb affects the muscle activity required by the medial gastrocnemius of the contralateral limb during step-to-step transition. Thirty-five subjects were monitored as to the medial gastrocnemius electromyographic activity of one limb and the ground reaction force of the contralateral limb during double support. After determination of the Pearson correlation coefficient (r), a moderate correlation was observed between the medial gastrocnemius electromyographic activity of the dominant leg and the vertical (Fz) and anteroposterior (Fy) components of ground reaction force of the non-dominant leg (r = 0.797, p < 0.000 1; r = -0.807, p < 0.000 1). A weak and moderate correlation was observed between the medial gastrocnemius electromyographic activity of the non-dominant leg and the Fz and Fy of the dominant leg, respectively (r = 0.442, p = 0.018; r = -0.684 p < 0.000 1). The results obtained suggest that during double support, ground reaction force is associated with the electromyographic activity of the contralateral medial gastrocnemius and that there is an increased dependence between the ground reaction force of the non-dominant leg and the electromyographic activity of the dominant medial gastrocnemius. PMID:22720393

Sousa, Andreia S P; Santos, Rubim; Oliveira, Francisco P M; Carvalho, Paulo; Tavares, João Manuel R S

2012-05-01

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A method for continuous monitoring of the Ground Reaction Force during daily activity  

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Theoretical models and experimental studies of bone remodeling have identified peak cyclic force levels (or cyclic tissue strain energy density), number of daily loading cycles, and load (strain) rate as possible contributors to bone modeling and remodeling stimulus. To test our theoretical model and further investigate the influence of mechanical forces on bone density, we have focused on the calcaneus as a model site loaded by calcaneal surface tractions which are predominantly determined by the magnitude of the external ground reaction force (GRF).

Whalen, Robert; Quintana, Jason; Emery, Jeff

1993-01-01

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RELATIONSHIPS AMONG SPRINT VELOCITIES, HORIZONTAL GROUND REACTION FORCE, AND ISOKINETIC TRUNK STRENGTH VARIABLES  

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Full Text Available The purpose of this study was to investigate the relationships among sprint velocities, horizontal ground reaction force, and isokinetic trunk strength variables. Voluntary 19 athletes were participated to the study [age (year= 20.9±2.3, training age (month= 91.3±48.2, body height (cm= 173.1±6.5, body weight (kg= 64.7±8.4] from different sports including in explosive strength. Sprints (10m, 20m, 30m, and 40m were tested on a non-motorized treadmill. Velocities (V10m, V20m, V30m, and V40m and horizontal ground reaction forces (HGRF-10m, HGRF-20m, HGRF-30m, and HGRF-40m of the sprints were calculated. Isokinetic trunk strength criteria (flexion-extension peak torques at 3 different angular velocities (30o.s-1, 90o.s-1, and 120o.s-1 were tested. Pearson Correlation Coefficient was used for statistical analysis. Probability level was p?0.05. All sprint velocities was correlated with all horizontal ground reaction forces (except the correlation between V10m and HGRF-20m and all isokinetic trunk flexion-extension peak torques (except the correlation between V10m and isokinetic trunk flexion peak torque at 120o.s-1. Statistically highest significant correlations have been found between V40m and all horizontal ground reaction forces and also between V40m and isokinetic trunk flexion-extension peak torques (30o.s-1, 90o.s-1, and 120o.s-1. There were significant relationships of horizontal ground reaction forces with isokinetic trunk extension-flexion peak torques at 30o.s-1, 90o.s-1, and 120o.s-1. In conclusion, isokinetic trunk flexion and extension strength values are crucial for improving sprint acceleration and horizontal component of ground reaction force.

Kale Mehmet

2013-12-01

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BILATERAL GROUND REACTION FORCES AND JOINT MOMENTS FOR LATERAL SIDESTEPPING AND CROSSOVER STEPPING TASKS  

Directory of Open Access Journals (Sweden)

Full Text Available Racquet sports have high levels of joint injuries suggesting the joint loads during play may be excessive. Sports such as badminton employ lateral sidestepping (SS and crossover stepping (XS movements which so far have not been described in terms of biomechanics. This study examined bilateral ground reaction forces and three dimensional joint kinetics for both these gaits in order to determine the demands of the movements on the leading and trailing limb and predict the contribution of these movements to the occurrence of overuse injury of the lower limbs. A force platform and motion-analysis system were used to record ground reaction forces and track marker trajectories of 9 experienced male badminton players performing lateral SS, XS and forward running tasks at a controlled speed of 3 m·s-1 using their normal technique. Ground reaction force and kinetic data for the hip, knee and ankle were analyzed, averaged across the group and the biomechanical variables compared. In all cases the ground reaction forces and joint moments were less than those experienced during moderate running suggesting that in normal play SS and XS gaits do not lead to high forces that could contribute to increased injury risk. Ground reaction forces during SS and XS do not appear to contribute to the development of overuse injury. The distinct roles of the leading and trailing limb, acting as a generator of vertical force and shock absorber respectively, during the SS and XS may however contribute to the development of muscular imbalances which may ultimately contribute to the development of overuse injury. However it is still possible that faulty use of these gaits might lead to high loads and this should be the subject of future work

William I. Sellers

2009-03-01

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Forelimb and hindlimb ground reaction forces of walking cats: Assessment and comparison with walking dogs.  

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The primary aim of this study was to assess the potential of force plate analysis for describing the stride cycle of the cat. The secondary aim was to define differences in feline and canine locomotion based on force plate characteristics. Ground reaction forces of 24 healthy cats were measured and compared with ground reaction forces of 24 healthy dogs. Force-time waveforms in cats generated by force plate analysis were consistent, as reflected by intra-class correlation coefficients for peak vertical force, peak propulsive force and peak braking force (0.94-0.95, 0.85-0.89 and 0.89-0.90, respectively). Compared with dogs, cats had a higher peak vertical force during the propulsion phase (cat, 3.89?±?0.19?N/kg; dog, 3.03?±?0.16?N/kg), and a higher hindlimb propulsive force (cat, -1.08?±?0.13?N/kg; dog, (-0.87?±?0.13?N/kg) and hindlimb impulse (cat, -0.18?±?0.03?N/kg; dog, -0.14?±?0.02?N/kg). Force plate analysis is a valuable tool for the assessment of locomotion in cats, because it can be applied in the clinical setting and provides a non-invasive and objective measurement of locomotion characteristics with high repeatability in cats, as well as information about kinetic characteristics. Differences in force-time waveforms between cats and dogs can be explained by the more crouched position of cats during stance and their more compliant gait compared with dogs. Feline waveforms of the medio-lateral ground reaction forces also differ between cats and dogs and this can be explained by differences in paw supination-pronation. PMID:25155217

Corbee, R J; Maas, H; Doornenbal, A; Hazewinkel, H A W

2014-10-01

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Effects of weighted sled towing on ground reaction force during the acceleration phase of sprint running.  

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Athletes use weighted sled towing to improve sprint ability, but little is known about its biomechanics. The purpose of this study was to investigate the effect of weighted sled towing with two different loads on ground reaction force. Ten physically active men (mean ± SD: age 27.9 ± 1.9 years; stature 1.76 ± 0.06 m; body mass 80.2 ± 9.6 kg) performed 5 m sprints under three conditions; (a) unresisted, (b) towing a sled weighing 10% of body mass (10% condition) and (c) towing a sled weighing 30% of body mass (30% condition). Ground reaction force data during the second ground contact after the start were recorded and compared across the three conditions. No significant differences between the unresisted and 10% conditions were evident, whereas the 30% condition resulted in significantly greater values for the net horizontal and propulsive impulses (P < 0.05) compared with the unresisted condition due to longer contact time and more horizontal direction of force application to the ground. It is concluded that towing a sled weighing 30% of body mass requires more horizontal force application and increases the demand for horizontal impulse production. In contrast, the use of 10% body mass has minimal impact on ground reaction force. PMID:24576071

Kawamori, Naoki; Newton, Robert; Nosaka, Ken

2014-01-01

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In-Shoe Plantar Pressures and Ground Reaction Forces during Overweight Adults' Overground Walking  

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Purpose: Because walking is highly recommended for prevention and treatment of obesity and some of its biomechanical aspects are not clearly understood for overweight people, we compared the absolute and normalized ground reaction forces (GRF), plantar pressures, and temporal parameters of normal-weight and overweight participants during…

de Castro, Marcelo P.; Abreu, Sofia C.; Sousa, Helena; Machado, Leandro; Santos, Rubim; Vilas-Boas, João Paulo

2014-01-01

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Ground reaction force comparison of controlled resistance methods to isoinertial loading of the squat exercise - biomed 2010.  

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The ground reaction force during the concentric (raising) portion of the squat exercise was compared to that of isoinertial loading (free weights) for three pneumatically controlled resistance methods: constant resistance, cam force profile, and proportional force control based on velocity. Constant force control showed lower ground reaction forces than isoinertial loading throughout the range of motion (ROM). The cam force profile exhibited slightly greater ground reaction forces than isoinertial loading at 10 and 40% ROM with fifty-percent greater loading at 70% ROM. The proportional force control consistently elicited greater ground reaction force than isoinertial loading, which progressively ranged from twenty to forty percent increase over isoinertial loading except for being approximately equal at 85% ROM. Based on these preliminary results, the proportional control shows the most promise for providing loading that is comparable in magnitude to isoinertial loading. This technology could optimize resistance exercise for sport-specific training or as a countermeasure to atrophy during spaceflight. PMID:20467098

Paulus, David C; Reynolds, Michael C; Schilling, Brian K

2010-01-01

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Analysis of kinematic data and determination of ground reaction force of foot in slow squat  

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In the present paper, the ground reaction force (GRF) acting on foot in slow squat was determined through a force measuring system, and at the same time, the kinematic data of human squat were obtained by analyzing the photographed image sequences. According to the height and body weight, six healthy volunteers were selected, three men in one group and the other three women in another group, and the fundamental parameters of subjects were recorded, including body weight, height and age, etc. Based on the anatomy characteristics, some markers were placed on the right side of joints. While the subject squatted at slow speed on the force platform, the ground reaction forces on the forefoot and heel for each foot were obtained through calibrated force platform. The analysis results show that the reaction force on heel is greater than that on forefoot, and double feet have nearly constant force. Moreover, from processing and analyzing the synchronously photographed image sequences in squat, the kinematic data of human squat were acquired, including mainly the curves of angle, angular velocity and angular acceleration varied with time for knee, hip and ankle joints in a sagittal plane. The obtained results can offer instructive reference for photographing and analyzing the movements of human bodies, diagnosing some diseases, and establishing in the future appropriate mathematical models for the human motion.

Zhang, Xu-Shu; Guo, Yuan; An, Mei-Wen; Chen, Wei-Yi

2013-02-01

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BILATERAL GROUND REACTION FORCES AND JOINT MOMENTS FOR LATERAL SIDESTEPPING AND CROSSOVER STEPPING TASKS  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Racquet sports have high levels of joint injuries suggesting the joint loads during play may be excessive. Sports such as badminton employ lateral sidestepping (SS) and crossover stepping (XS) movements which so far have not been described in terms of biomechanics. This study examined bilateral ground reaction forces and three dimensional joint kinetics for both these gaits in order to determine the demands of the movements on the leading and trailing limb and predict the contribution of thes...

Sellers, William I.; Gregor Kuntze; Mansfield, Neil J.

2009-01-01

20

Estimating Youth Locomotion Ground Reaction Forces Using an Accelerometer-Based Activity Monitor  

Digital Repository Infrastructure Vision for European Research (DRIVER)

To address a variety of questions pertaining to the interactions between physical activity, musculoskeletal loading and musculoskeletal health/injury/adaptation, simple methods are needed to quantify, outside a laboratory setting, the forces acting on the human body during daily activities. The purpose of this study was to develop a statistically based model to estimate peak vertical ground reaction force (pVGRF) during youth gait. 20 girls (10.9±0.9 years) and 15 boys (12.5±0.6 years) wore...

Neugebauer, Jennifer M.; Hawkins, David A.; Beckett, Laurel

2012-01-01

 
 
 
 
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The effect of ankle taping on the ground reaction force in vertical jump performance.  

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The purpose of this study was to investigate the effects of closed basket weave (CBW) ankle taping on the vertical ground reaction force during the contact phase before the take-off in vertical jump performance. We hypothesized that ankle taping would limit the capability for explosive force generation during the contact phase before the take-off in jump performance. Twelve healthy young men (age, 20.2 ± 1.3 years; height, 1.76 ± 0.05 m; body mass, 66.1 ± 6.1 kg; mean ± SD) performed a vertical jump performance on a force plate without (CON) or with ankle taping (CBW technique) of the right ankle joint. Vertical jump ability was assessed using 2 styles of vertical jump with no arm swing: a countermovement jump (CMJ) and squat jump (SJ). From the vertical ground reaction force (GRF), maximum jump height, vertical impulse (VI), rate of force development, maximum GRF (GRFmax), and time-series GRF (GRFts) during the contact phase before the take-off in jump performance were determined. Jump height was significantly lower for CBW (36.6 ± 6.6 cm) than CON (38.1 ± 6.7 cm) in CMJ, but not in SJ. Rate of force development and GRFts at 35, 40, 45, 50, 55, 60, and 65% of total time of the contact phase in jumping performance were also significantly smaller for CBW than CON in CMJ, but not in SJ. Conversely, VI and GRFmax were not significantly different between the groups in either jump condition. These results suggest that ankle taping impairs CMJ performance, because of a decreased ability to develop large force rapidly on the ground before the take-off. PMID:24126899

Koyama, Keiji; Kato, Tomoo; Yamauchi, Junichiro

2014-05-01

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Ability of sagittal kinematic variables to estimate ground reaction forces and joint kinetics in running.  

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Study Design Controlled laboratory study, cross-sectional design. Objective To determine if sagittal kinematic variables can be used to estimate select running kinetics. Background Excessive loading during running has been implicated in a variety of injuries, yet this information is typically not assessed during a standard clinical examination. Developing a clinically feasible strategy to estimate ground reaction forces and joint kinetics may improve the ability to identify those at an increased risk of injury. Methods Three-dimensional kinematics and ground reaction forces of 45 participants were recorded during treadmill running at self-selected speed. Kinematic variables used to estimate specific kinetic metrics included vertical excursion of the center of mass, foot inclination angle at initial contact, horizontal distance between the center of mass and heel at initial contact, knee flexion angle at initial contact, and peak knee flexion angle during stance. Linear mixed-effects models were fitted to explore the association between the kinetic and kinematic measures, including step rate and sex, with final models created using backward variable selection. Results Models were developed to estimate peak knee extensor moment (R(2) = 0.43), energy absorbed at the knee during loading response (R(2) = 0.58), peak patellofemoral joint reaction force (R(2) = 0.55), peak vertical ground reaction force (R(2) = 0.48), braking impulse (R(2) = 0.50), and average vertical loading rate (R(2) = 0.04). Conclusion Our findings suggest that insights into important running kinetics can be obtained from a subset of sagittal plane kinematics common to a clinical running analysis. Of note, the limb posture at initial contact influenced subsequent loading patterns in stance. J Orthop Sports Phys Ther 2014;44(10):825-830. Epub 25 August 2014. doi:10.2519/jospt.2014.5367. PMID:25156183

Wille, Christa M; Lenhart, Rachel L; Wang, Sijian; Thelen, Darryl G; Heiderscheit, Bryan C

2014-10-01

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Ambulatory assessment of 3D ground reaction force using plantar pressure distribution.  

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This study aimed to use the plantar pressure insole for estimating the three-dimensional ground reaction force (GRF) as well as the frictional torque (T(F)) during walking. Eleven subjects, six healthy and five patients with ankle disease participated in the study while wearing pressure insoles during several walking trials on a force-plate. The plantar pressure distribution was analyzed and 10 principal components of 24 regional pressure values with the stance time percentage (STP) were considered for GRF and T(F) estimation. Both linear and non-linear approximators were used for estimating the GRF and T(F) based on two learning strategies using intra-subject and inter-subjects data. The RMS error and the correlation coefficient between the approximators and the actual patterns obtained from force-plate were calculated. Our results showed better performance for non-linear approximation especially when the STP was considered as input. The least errors were observed for vertical force (4%) and anterior-posterior force (7.3%), while the medial-lateral force (11.3%) and frictional torque (14.7%) had higher errors. The result obtained for the patients showed higher error; nevertheless, when the data of the same patient were used for learning, the results were improved and in general slight differences with healthy subjects were observed. In conclusion, this study showed that ambulatory pressure insole with data normalization, an optimal choice of inputs and a well-trained nonlinear mapping function can estimate efficiently the three-dimensional ground reaction force and frictional torque in consecutive gait cycle without requiring a force-plate. PMID:20576436

Rouhani, H; Favre, J; Crevoisier, X; Aminian, K

2010-07-01

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Ground reaction forces and loading rates associated with parkour and traditional drop landing techniques.  

Science.gov (United States)

Due to the relative infancy of Parkour there is currently a lack of empirical evidence on which to base specific technique instruction upon. The purpose of this study was to compare the ground reaction forces and loading rates involved in two Parkour landing techniques encouraged by local Parkour instructors and a traditional landing technique recommended in the literature. Ten male participants performed three different drop landing techniques (Parkour precision, Parkour roll, and traditional) onto a force plate. Compared to the traditional technique the Parkour precision technique demonstrated significantly less maximal vertical landing force (38%, p Parkour roll technique compared to the traditional technique. It is unclear whether or not the Parkour precision technique produced lower landing forces and loading rates than the Parkour roll technique as no significant differences were found. The landing techniques encouraged by local Parkour instructors such as the precision and roll appear to be more appropriate for Parkour practitioners to perform than a traditional landing technique due to the lower landing forces and loading rates experienced. Key pointsParkour precision and Parkour roll landings were found to be safer than a traditional landing technique, resulting in lower maximal vertical forces, slower times to maximal vertical force and ultimately lesser loading rates.Parkour roll may be more appropriate (safer) to utilize than the Parkour precision during Parkour landing scenarios.The Parkour landing techniques investigated n this study may be beneficial for landing by non-Parkour practitioners in everyday life. PMID:24149735

Puddle, Damien L; Maulder, Peter S

2013-01-01

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Isokinetic analysis of ankle and ground reaction forces in runners and triathletes  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english OBJECTIVE: To analyze and compare the vertical component of ground reaction forces and isokinetic muscle parameters for plantar flexion and dorsiflexion of the ankle between long-distance runners, triathletes, and nonathletes. METHODS: Seventy-five males with a mean age of 30.26 (±6.5) years were di [...] vided into three groups: a triathlete group (n=26), a long-distance runner group (n = 23), and a non-athlete control group. The kinetic parameters were measured during running using a force platform, and the isokinetic parameters were measured using an isokinetic dynamometer. RESULTS: The non-athlete control group and the triathlete group exhibited smaller vertical forces, a greater ground contact time, and a greater application of force during maximum vertical acceleration than the long-distance runner group. The total work (180º/s) was greater in eccentric dorsiflexion and concentric plantar flexion for the non-athlete control group and the triathlete group than the long-distance runner group. The peak torque (60º/s) was greater in eccentric plantar flexion and concentric dorsiflexion for the control group than the athlete groups. CONCLUSIONS: The athlete groups exhibited less muscle strength and resistance than the control group, and the triathletes exhibited less impact and better endurance performance than the runners.

Natália Mariana Silva, Luna; Angelica Castilho, Alonso; Guilherme Carlos, Brech; Luis, Mochizuki; Eduardo Yoshio, Nakano; Júlia Maria D' Andrea, Greve.

1023-10-01

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External Load Affects Ground Reaction Force Parameters Non-uniformly during Running in Weightlessness  

Science.gov (United States)

Long-term exposure to microgravity induces detrimefits to the musculcskdetal system (Schneider et al., 1995; LeBlanc et al., 2000). Treadmill exercise is used onboard the International Space Station as an exercise countermeasure to musculoskeletal deconditioning due to spaceflight. During locomotive exercise in weightlessness (0G), crewmembers wear a harness attached to an external loading mechanism (EL). The EL pulls the crewmember toward the treadmill, and provides resistive load during the impact and propulsive phases of gait. The resulting forces may be important in stimulating bone maintenance (Turner, 1998). The EL can be applied via a bungee and carabineer clip configuration attached to the harness and can be manipulated to create varying amounts of load levels during exercise. Ground-based research performed using a vertically mounted treadmill found that peak ground reaction forces (GRF) during running at an EL of less than one body weight (BW) are less than those that occur during running in normal gravity (1G) (Davis et al., 1996). However, it is not known how the GRF are affected by the EL in a true OG environment. Locomotion while suspended may result in biomechanics that differ from free running. The purpose of this investigation was to determine how EL affects peak impact force, peak propulsive force, loading rate, and impulse of the GRF during running in 0G. It was hypothesized that increasing EL would result in increases in each GRF parameter.

DeWitt, John; Schaffner, Grant; Laughlin, Mitzi; Loehr, James; Hagan, R. Donald

2004-01-01

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Isokinetic analysis of ankle and ground reaction forces in runners and triathletes  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english OBJECTIVE: To analyze and compare the vertical component of ground reaction forces and isokinetic muscle parameters for plantar flexion and dorsiflexion of the ankle between long-distance runners, triathletes, and nonathletes. METHODS: Seventy-five males with a mean age of 30.26 (±6.5) years were di [...] vided into three groups: a triathlete group (n=26), a long-distance runner group (n = 23), and a non-athlete control group. The kinetic parameters were measured during running using a force platform, and the isokinetic parameters were measured using an isokinetic dynamometer. RESULTS: The non-athlete control group and the triathlete group exhibited smaller vertical forces, a greater ground contact time, and a greater application of force during maximum vertical acceleration than the long-distance runner group. The total work (180º/s) was greater in eccentric dorsiflexion and concentric plantar flexion for the non-athlete control group and the triathlete group than the long-distance runner group. The peak torque (60º/s) was greater in eccentric plantar flexion and concentric dorsiflexion for the control group than the athlete groups. CONCLUSIONS: The athlete groups exhibited less muscle strength and resistance than the control group, and the triathletes exhibited less impact and better endurance performance than the runners.

Natália Mariana Silva, Luna; Angelica Castilho, Alonso; Guilherme Carlos, Brech; Luis, Mochizuki; Eduardo Yoshio, Nakano; Júlia Maria D' Andrea, Greve.

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Isokinetic analysis of ankle and ground reaction forces in runners and triathletes  

Directory of Open Access Journals (Sweden)

Full Text Available OBJECTIVE: To analyze and compare the vertical component of ground reaction forces and isokinetic muscle parameters for plantar flexion and dorsiflexion of the ankle between long-distance runners, triathletes, and nonathletes. METHODS: Seventy-five males with a mean age of 30.26 (±6.5 years were divided into three groups: a triathlete group (n=26, a long-distance runner group (n = 23, and a non-athlete control group. The kinetic parameters were measured during running using a force platform, and the isokinetic parameters were measured using an isokinetic dynamometer. RESULTS: The non-athlete control group and the triathlete group exhibited smaller vertical forces, a greater ground contact time, and a greater application of force during maximum vertical acceleration than the long-distance runner group. The total work (180º/s was greater in eccentric dorsiflexion and concentric plantar flexion for the non-athlete control group and the triathlete group than the long-distance runner group. The peak torque (60º/s was greater in eccentric plantar flexion and concentric dorsiflexion for the control group than the athlete groups. CONCLUSIONS: The athlete groups exhibited less muscle strength and resistance than the control group, and the triathletes exhibited less impact and better endurance performance than the runners.

Natália Mariana Silva Luna

2012-09-01

29

GROUND REACTION FORCES AND LOADING RATES ASSOCIATED WITH PARKOUR AND TRADITIONAL DROP LANDING TECHNIQUES  

Directory of Open Access Journals (Sweden)

Full Text Available Due to the relative infancy of Parkour there is currently a lack of empirical evidence on which to base specific technique instruction upon. The purpose of this study was to compare the ground reaction forces and loading rates involved in two Parkour landing techniques encouraged by local Parkour instructors and a traditional landing technique recommended in the literature. Ten male participants performed three different drop landing techniques (Parkour precision, Parkour roll, and traditional onto a force plate. Compared to the traditional technique the Parkour precision technique demonstrated significantly less maximal vertical landing force (38%, p < 0.01, ES = 1.76 and landing loading rate (54%, p < 0.01, ES = 1.22. Similarly, less maximal vertical landing force (43%, p < 0.01, ES = 2.04 and landing loading rate (63%, p < 0.01, ES = 1.54 were observed in the Parkour roll technique compared to the traditional technique. It is unclear whether or not the Parkour precision technique produced lower landing forces and loading rates than the Parkour roll technique as no significant differences were found. The landing techniques encouraged by local Parkour instructors such as the precision and roll appear to be more appropriate for Parkour practitioners to perform than a traditional landing technique due to the lower landing forces and loading rates experienced

Damien L. Puddle

2013-03-01

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Analysis of ground reaction forces in step exercise depending on step pattern and stepping rate.  

Science.gov (United States)

The analysis of ground reaction forces (GRFs) helps one understand the magnitude and pattern of loading experienced by the body while in contact with the ground in locomotor actions. The GRFs reflect a general indicator of mechanical loading on the musculoskeletal system, establishing the "whole-body biomechanical intensity" of physical activity and allowing the comparison between different activities. Our purposes were to analyze the GRFs produced by step exercise particularly-the force profile, average GRF, peak GRF, impulse, and loading rate-on the ascending and descending movements in 18 skilled women, investigating the differences that exist between 4 stepping-rate conditions and between 4 step patterns. Two force platforms were used. These differences were studied using analyses of variance with repeated measures. Our results show that experienced subjects were able to deal with the increase of movement cadence in terms of external load, maintaining the GRF values at the same levels as the ones obtained for quick walking and moderate step running, activities that are considered safe. The results indicate that lower-extremity external loading can be effectively controlled by varying the stepping rate during step classes. With the correct use of this mechanical control, this activity could be included in exercise and rehabilitation programs. The knowledge about the magnitude of loading helps in selecting proper stepping rates and proper movements for inclusion in classes. PMID:19050651

Santos-Rocha, Rita; Veloso, António; Machado, Maria Lourdes

2009-01-01

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Assessment of changes in gait parameters and vertical ground reaction forces after total hip arthroplasty  

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Full Text Available The principal objectives of arthroplasty are relief of pain and enhancement of range of motion. Currently, postoperative pain and functional capacity are assessed largely on the basis of subjective evaluation scores. Because of the lack of control inherent in this method it is often difficult to interpret data presented by different observers in the critical evaluation of surgical method, new components and modes of rehabilitation. Gait analysis is a rapid, simple and reliable method to assess functional outcome. This study was undertaken in an effort to evaluate the gait characteristics of patients who underwent arthroplasty, using an Ultraflex gait analyzer. Materials and Methods: The study was based on the assessment of gait and weight-bearing pattern of both hips in patients who underwent total hip replacement and its comparison with an age and sex-matched control group. Twenty subjects of total arthroplasty group having unilateral involvement, operated by posterior approach at our institution with a minimum six-month postoperative period were selected. Control group was age and sex-matched, randomly selected from the general population. Gait analysis was done using Ultraflex gait analyzer. Gait parameters and vertical ground reaction forces assessment was done by measuring the gait cycle properties, step time parameters and VGRF variables. Data of affected limb was compared with unaffected limb as well as control group to assess the weight-bearing pattern. Statistical analysis was done by?t? test. Results: Frequency is reduced and gait cycle duration increased in total arthroplasty group as compared with control. Step time parameters including Step time, Stance time and Single support time are significantly reduced ( P value < .05 while Double support time and Single swing time are significantly increased ( P value < .05 in the THR group. Forces over each sensor are increased more on the unaffected limb of the THR group as compared to the control group. Vertical ground reaction force variables are also altered. Conclusion: Significant changes ( P value < .05 in gait parameters and vertical ground reaction forces show that gait pattern is not normalized after THR and weight-bearing is not equally shared by both hips. Patient walks with residual antalgic gait even after surgery, which results in abnormal loading around hip joints and the integrity of the prosthesis fixation could be compromised.

Bhargava P

2007-01-01

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A wearable force plate system for the continuous measurement of triaxial ground reaction force in biomechanical applications  

International Nuclear Information System (INIS)

The ambulatory measurement of ground reaction force (GRF) and human motion under free-living conditions is convenient, inexpensive and never restricted to gait analysis in a laboratory environment and is therefore much desired by researchers and clinical doctors in biomedical applications. A wearable force plate system was developed by integrating small triaxial force sensors and three-dimensional (3D) inertial sensors for estimating dynamic triaxial GRF in biomechanical applications. The system, in comparison to existent systems, is characterized by being lightweight, thin and easy-to-wear. A six-axial force sensor (Nitta Co., Japan) was used as a verification measurement device to validate the static accuracy of the developed force plate. To evaluate the precision during dynamic gait measurements, we compared the measurements of the triaxial GRF and the center of pressure (CoP) by using the developed system with the reference measurements made using a stationary force plate and an optical motion analysis system. The root mean square (RMS) differences of the two transverse components (x- and y-axes) and the vertical component (z-axis) of the GRF were 4.3 ± 0.9 N, 6.0 ± 1.3 N and 12.1 ± 1.1 N, respectively, corresponding to 5.1 ± 1.1% and 6.5 ± 1% of the maximum of each transverse component and 1.3 ± 0.2% of the maximum vertical component of GRF. The RMS distance between the two systems' CoP traces was 3.2 ± 0.8 mm, corresponding to 1.2 ± 0.3% of the length of the shoe. Moreover, based on the results of the assessment of the influence of the system on natural gait, we found that gait was almost never affected. Therefore, the wearable system as an alternative device can be a potential solution for measuring CoP and triaxial GRF in non-laboratory environments

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Functional data analysis on ground reaction force of military load carriage increment  

Science.gov (United States)

Analysis of ground reaction force on military load carriage is done through functional data analysis (FDA) statistical technique. The main objective of the research is to investigate the effect of 10% load increment and to find the maximum suitable load for the Malaysian military. Ten military soldiers age 31 ± 6.2 years, weigh 71.6 ± 10.4 kg and height of 166.3 ± 5.9 cm carrying different military load range from 0% body weight (BW) up to 40% BW participated in an experiment to gather the GRF and kinematic data using Vicon Motion Analysis System, Kirstler force plates and thirty nine body markers. The analysis is conducted in sagittal, medial lateral and anterior posterior planes. The results show that 10% BW load increment has an effect when heel strike and toe-off for all the three planes analyzed with P-value less than 0.001 at 0.05 significant levels. FDA proves to be one of the best statistical techniques in analyzing the functional data. It has the ability to handle filtering, smoothing and curve aligning according to curve features and points of interest.

Din, Wan Rozita Wan; Rambely, Azmin Sham

2014-06-01

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Metabolic Rate and Ground Reaction Force During Motorized and Non-Motorized Treadmill Exercise  

Science.gov (United States)

PURPOSE: To measure vertical ground reaction force (vGRF) and oxygen consumption (VO2) at several velocities during exercise using a ground-based version of the ISS treadmill in the M and NM modes. METHODS: Subjects (n = 20) walked or ran at 0.89, 1.34, 1.79, 2.24, 2.68, and 3.12 m/s while VO2 and vGRF data were collected. VO2 was measured using open-circuit spirometry (TrueOne 2400, Parvo-Medics). Data were averaged over the last 2 min of each 5-min stage. vGRF was measured in separate 15-s bouts at 125 Hz using custom-fitted pressure-sensing insoles (F-Scan Sport Sensors, Tekscan, Inc). A repeated-measures ANOVA was used to test for differences in VO2 and vGRF between M and NM and across speeds. Significance was set at P exercise for 5 min at treadmill speeds above 1.79 m/s in the NM mode; however, vGRF data were obtained for all subjects at each speed in both modes. VO2 was approx.40% higher during NM than M exercise across treadmill speeds. vGRF increased with treadmill speed but was not different between modes. CONCLUSION: Higher VO2 with no change in vGRF suggests that the additional metabolic cost associated with NM treadmill exercise is accounted for in the horizontal forces required to move the treadmill belt. Although this may limit the exercise duration at faster speeds, high-intensity NM exercise activates the hamstrings and plantarflexors, which are not specifically targeted or well protected by other in-flight countermeasures.

Everett, Meghan E.; Loehr, James A.; DeWitt, John K.; Laughlin, Mitzi; Lee, Stuart M. C.

2010-01-01

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Effects of slip-induced changes in ankle movement on muscle activity and ground reaction forces during running acceleration  

DEFF Research Database (Denmark)

Ground contact in running is always linked to a minimum amount of slipping, e.g., during the early contact phase when horizontal forces are high compared to vertical forces. Studies have shown altered muscular activation when expecting slips [2-4]. It is not known what the mechanical effect of such slip episodes are on joint loading or performance. The aim of the present study was to examine the effect of changes in ankle movement on ankle joint loading, muscle activity, and ground reaction forces during linear acceleration.

Ketabi, Shahin; Kersting, Uwe G.

2013-01-01

36

Landing ground reaction forces in figure skaters and non-skaters.  

Science.gov (United States)

Researchers and clinicians have suggested that overuse injuries to the lower back and lower extremities of figure skaters may be associated with the repeated high impact forces sustained during jump landings. Our primary aim was to compare the vertical ground reaction forces (GRFs) in freestyle figure skaters (n = 26) and non-skaters (n = 18) for the same barefoot single leg landing on a force plate from a 20 cm platform. Compared with non-skaters, skaters exhibited a significantly greater normalised peak GRF (3.50 ± 0.47 × body weight for skaters vs. 3.13 ± 0.45 × body weight for non-skaters), significantly shorter time to peak GRF (81.21 ± 14.01 ms for skaters vs. 93.81 ± 16.49 ms for non-skaters), and significantly longer time to stabilisation (TTS) of the GRF (2.38 ± 0.07 s for skaters vs. 2.22 ± 0.07 s for non-skaters). Skaters also confined their centre of pressure (CoP) to a significantly smaller mediolateral (M-L) (25%) and anterior-posterior (A-P) (40%) range during the landing phase, with the position of the CoP located in the mid to forefoot region. The narrower and more forward position of the CoP in skaters may at least partially explain the greater peak GRF, shorter time to peak, and longer TTS. Training and/or equipment modification serve as potential targets to decrease peak GRF by distributing it over a longer time period. More comprehensive studies including electromyography and motion capture are needed to fully characterise the unique figure skater landing strategy. PMID:24479611

Saunders, Nathan W; Hanson, Nicholas; Koutakis, Panos; Chaudhari, Ajit M; Devor, Steven T

2014-01-01

37

A Comparison of Accelerometers for Predicting Energy Expenditure and Vertical Ground Reaction Force in School-Age Children  

Science.gov (United States)

In this pilot study of 16 children, we evaluated the reliability and validity of three accelerometers (Mini-Motionlogger [MML], Computer Science Applications, Inc. Actigraph [CSA], and BioTrainer) as indicators of energy expenditure and vertical ground reaction force. The children wore 2 of each type of monitor while they walked, ran, and…

Garcia, Anne W.; Langenthal, Carla R.; Angulo-Barroso, Rosa M.; Gross, M. Melissa

2004-01-01

38

Running on a lower-body positive pressure treadmill : VO2max, respiratory response, and vertical ground reaction force  

DEFF Research Database (Denmark)

This study investigated maximal oxygen consumption (VO2max) and time to exhaustion while running on a lower-body positive pressure treadmill (LBPPT) at normal body weight (BW) as well as how BW support affects respiratory responses, ground reaction forces, and stride characteristics.

Raffalt, Peter C; Hovgaard-Hansen, Line

2013-01-01

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Ground Reaction Force Patterns in Stroke Patients with Various Degrees of Motor Recovery Determined by Plantar Dynamic Analysis  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Background: To study ground reaction force (GRF) patterns in stroke patients with variousdegrees of motor recovery, using plantar dynamic analysis.Methods: Forty-three people with hemiplegic stroke and 20 healthy subjects wereenrolled in the study. Motor impairment (motor recovery and muscle tone)and plantar dynamic data (GRF patterns, peak pressure, and walking speeds)were analyzed. GRF patterns were categorized into four patterns based onthe force magnitude (spatial features) through time (...

Chung-Yao Chen; Paul Wei-Hsien Hong; Chia-Ling Chen; Shih Wei Chou; Ching-Yi Wu; Pao-Tsai Cheng; Fuk-Tan Tang; Hsieh-Ching Chen

2007-01-01

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Effect of plantar flexion and eversion on mediolateral ground reaction force in subjects with functional ankle instability  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract   Background and Aim: The common mechanism for lateral ankle sprain is inversion, plantar flexion, or the combination of both, if untreated successfully can lead to chronic ankle instability. It seems that the foot position, while touching the ground, has an effective role to cause ankle sprain. Thus it is possible to prevent ankle sprain through limiting foot position. Therefore the aim of this research is to study the effect of plantar flexion and eversion on mediolateral ground reaction force while landing in individuals who suffering from functional ankle instability.    Materials and Methods: In this case-control research study 32 subjects (17 subjects with unilateral functional ankle instability (FAI and 15 control subjects, aged from 18 to 35 years, were tested. All subjects in instability group were selected by the orthopedic physician, then the anterior drawer and talar tilt tests were  performed for diagnosis of functional ankle instability and other physical examinations. Control group were matched with instability group by age, weight, height, gender and body mass index. The subjects standing with single leg on a 40 cm high platform in 25 cm front of a force-plate while the test leg relaxed and non-weight bearing. The subject landed on the test leg on the center of the force-plate. The subjects landed according to four types of position: A: neutral position of ankle and lateral foot wedge, B: neutral position of ankle, C: positive heel and lateral foot wedge and D: positive heel.   Results: Among control group, medial ground reaction force increased in the "C" position relative to "B" position (p=0.007 and "C" position relative to "D" position (p=0.018. In FAI group, lateral ground reaction force increased in "C" position relative to "B" position (p=0.001 and "C" position relative to "A" position (p=0.002. Also in FAI group medial ground reaction force decreased in "D" position relative to "A" position (p=0.014.   Conclusion: According to the findings, applying lateral foot wedge, while the ankle is in plantar flexion, increases the mediolateral ground reaction forces. Based on the results, position of plantar flexion is more possibly effective than inversion in ankle sprain. According to the study, the lateral foot wedge in ankle plantar flexion position may be more effective than in neutral one to change mediolateral ground reaction forces.   Key words: Functional ankle instability, Position of foot, Landing, Lateral foot wedge  

Ali Ashraf Jamshidi

2012-10-01

 
 
 
 
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Effects of backpack weight on posture, gait patterns and ground reaction forces of male children with obesity during stair descent.  

Science.gov (United States)

This study investigates the effects of backpack weight on posture, gait pattern, and ground reaction forces for children with obesity in an attempt to define a safe backpack weight limit for them. A total of 16 obese (11.19 ± 0.66 years of age) and 21 normal body weight (11.13 ± 0.69 years of age) schoolboys were recruited. Two force plates and two video cameras were used. Multivariate analysis of variance with repeated measures was employed. Obese children showed increased trunk and head forward inclination angle, gait cycle duration and stance phase, decreased swing phase, and increased ground reaction force in the medial-lateral and anterior-posterior directions when compared with male children with a normal body weight. The changes were observed even with an empty backpack in comparison with normal body weight children and a 15% increase in backpack weight led to further instability and damage on their already strained bodies. PMID:24650337

Song, Qipeng; Yu, Bing; Zhang, Cui; Sun, Wei; Mao, Dewei

2014-01-01

42

A COMPARISON OF GOLF SHOE DESIGNS HIGHLIGHTS GREATER GROUND REACTION FORCES WITH SHORTER IRONS  

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Full Text Available In an effort to reduce golf turf damage the traditional metal spike golf shoe has been redesigned, but shoe-ground biomechanical evaluations have utilised artificial grass surfaces. Twenty-four golfers wore three different golf shoe traction designs (traditional metal spikes, alternative spikes, and a flat-soled shoe with no additional traction when performing shots with a driver, 3 iron and 7 iron. Ground action forces were measured beneath the feet by two natural grass covered force platforms. The maximum vertical force recorded at the back foot with the 3 iron and 7 iron was 0.82 BW (body weight and at the front foot 1.1 BW approximately in both the metal spike and alternative spike golf shoe designs. When using the driver these maximal vertical values were 0.49 BW at the back foot and 0.84 BW at the front foot. Furthermore, as performance of the backswing and then downswing necessitates a change in movement direction the range of force generated during the complete swing was calculated. In the metal spike shoe the vertical force generated at the back foot with both irons was 0.67 BW and at the front foot 0.96 BW with the 3 iron and 0.92 BW with the 7 iron. The back foot vertical force generated with the driver was 0.33 BW and at the front foot 0.83 BW wearing the metal spike shoe. Results indicated the greater force generation with the irons. When using the driver the more horizontal swing plane associated with the longer club reduced vertical forces at the back and front foot. However, the mediolateral force generated across each foot in the metal and alternative spike shoes when using the driver was greater than when the irons were used. The coefficient of friction was 0. 62 at the back and front foot whichever shoe was worn or club used

Paul Worsfold

2007-12-01

43

Three-dimensional kinematics and ground reaction forces during the instep and outstep soccer kicks in pubertal players.  

Science.gov (United States)

The purpose of the present study was to compare the three-dimensional kinematics of the lower extremities and ground reaction forces between the instep kick and the kick with the outside area of the foot (outstep kick) in pubertal soccer players. Ten pubertal soccer players performed consecutive kicking trials in random order after a two-step angled approach with the instep and the outstep portion of the foot. Three-dimensional data and ground reaction forces were measured during kicking. Paired t-tests indicated significantly higher (P kick compared with the outstep kick. Non-significant differences in angular and linear sagittal plane kinematic parameters, temporal characteristics, and ground reaction forces between the instep and outstep soccer kicks were observed (P > 0.05). In contrast, analysis of variance indicated that the outstep kick displayed higher hip internal rotation and abduction, knee internal rotation, and ankle inversion than the instep kick (P kick is more powerful than the outstep kick and that different types of kick require different types of skill training. PMID:20845213

Katis, Athanasios; Kellis, Eleftherios

2010-09-01

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An investigation into the vertical ground reaction force status in the coper and non-coper ACL-deficient knee subjects during walking on level ground  

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Full Text Available Background and Aim: An immaculate review of the literature reveals some changes on the vertical ground reaction force (VGRF in ACL deficient knee subjects. However, the details are not clear yet. The current study aimed to study these changes in the ACL-deficient and apparently healthy knees of the coper and non-coper ACL-deficient knee subjects in comparison with the normal knees. Materials and Methods: Sixteen unilateral ACL-torn subjects included 8 copers and 8 non-copers were recruited in this quasi-experimental study and were compared with 16 normal knee subjects (8 subjects matched to each coper and non-coper groups. All subjects walked barefoot and with their preferred speed in a 6-meter walkway and placed their wanted foot on the platform of a Zebris pedobarograph tool. The patients were asked to place their injured and healthy feet separately on the platform. The control group placed their foot matched to the ACL-deficient legs on the platform. The testes were repeated so much to have five acceptable trials. The outcome measures included the peak F1Z, F2Z, F3Z of the vertical ground reaction force values and the times to reach these peak values as well as total stance time of the tested feet. Results: The results showed only a significant lower F1Z value in the non-coper ACL-deficient knee subjects (p=0.008. No significant changes were shown in the F2Z, F3Z or the times reach to F1Z, F2Z and F3Z values (p>0.05. The stance time of the coper ACL-deficient knee subjects increased significantly in the non-coper ACL-deficeint knee subjects when compared to the coper and healthy knees (p=0.005. Conclusion: The reduced F1Z of the vertical ground reaction force at initial contact as well as increased total stance time seen only in non-coper ACL-deficient knee subjects reveals inadequate compensatory mechanism in these patients as a counter force stress at initial contact and weight bearing. However, the coper ACL-deficient knee subjects compensated these forces with good strategies and walked very similar to the control group. Keywords: Vercial ground reaction force (VGRF, Time to peak vertical ground reaction force components, Coper & non-coper ACL-deficient knee subjects, Pedobarography.

Narjes Soltani

2014-10-01

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Lower Extremity Strength and Hopping and Jumping Ground Reaction forces in Children with Neurofibromatosis Type 1  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The purpose of this study was to 1) extend the research findings of decreased muscular force production in grip strength to the lower extremity strength of children with NF1 and 2) to determine if there was a relationship between isometric strength and functional activities in children with NF1. Force production was assessed using a hand held dynamometer (HHD) and a functional task (hopping and jumping) on a force plate. Data from twenty-six children with NF1 were compared to data from 48 typ...

Johnson, Barbara; Macwilliams, Bruce; Carey, John C.; Viskochil, David H.; D’astous, Jacques L.; Stevenson, David A.

2012-01-01

46

Effects of muscle fatigue on the ground reaction force and soft-tissue vibrations during running: a model study.  

Science.gov (United States)

A modeling approach is used in this paper to study the effects of fatigue on the ground reaction force (GRF) and the vibrations of the lower extremity soft tissues. A recently developed multiple degrees-of-freedom mass-spring-damper model of the human body during running is used for this purpose. The model is capable of taking the muscle activity into account by using a nonlinear controller that tunes the mechanical properties of the soft-tissue package based on two physiological hypotheses, namely, "constant force" and "constant vibration." In this study, muscle fatigue is implemented in the model as the gradual reduction of the ability of the controller to tune the mechanical properties of the lower body soft-tissue package. Simulations are carried out for various types of footwear in both pre- and postfatigue conditions. The simulation results show that the vibration amplitude of the lower body soft-tissue package may considerably increase (up to 20%) with muscle fatigue, while the effects of fatigue on the GRF are negligible. The results of this modeling study are in line with the experimental studies that found muscle fatigue does not significantly change the GRF peaks, but may increase the level of soft-tissue vibrations (particularly for hard shoes). A major contribution of the current study is the formulation of a hypothesis about how the central nervous system tunes the muscle properties after fatigue. PMID:22180505

Nikooyan, Ali Asadi; Zadpoor, Amir Abbas

2012-03-01

47

Ground Reaction Force Patterns in Stroke Patients with Various Degrees of Motor Recovery Determined by Plantar Dynamic Analysis  

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Full Text Available Background: To study ground reaction force (GRF patterns in stroke patients with variousdegrees of motor recovery, using plantar dynamic analysis.Methods: Forty-three people with hemiplegic stroke and 20 healthy subjects wereenrolled in the study. Motor impairment (motor recovery and muscle toneand plantar dynamic data (GRF patterns, peak pressure, and walking speedswere analyzed. GRF patterns were categorized into four patterns based onthe force magnitude (spatial features through time (temporal features of thevertical GRF. Then stroke patients were classified into good (patterns III andIV and poor groups (patterns I and II.Results: Patients with hemiplegic stroke showed characteristic GRF patterns whichcould be categorized from bimodal (pattern IV to pathological shapes (I-III.The peak pressures on the paretic side in the metatarsal and toe areas werereduced in stroke patients compared with those in healthy subjects. Walkingspeeds were higher in the good group than in the poor group (p 0.4, p < 0.01, but not with hip and ankle movement or muscletone in the lower limb.Conclusions: GRF patterns, correlated with walking speeds, indicate underlying motorcontrol of hemiplegic or hemiparetic gait. Knee motor control may be themost important factor in determining walking performance. Plantar dynamicanalysis could allow clinicians an alternative assessment in detecting gaitchanges and planning therapeutic strategies in stroke patients.

Chung-Yao Chen

2007-02-01

48

Timing differences in the generation of ground reaction forces between the initial and secondary landing phases of the drop vertical jump ?  

Science.gov (United States)

Background Rapid impulse loads imparted on the lower extremity from ground contact when landing from a jump may contribute to ACL injury prevalence in female athletes. The drop jump and drop landing tasks enacted in the first and second landings of drop vertical jumps, respectively, have been shown to elicit separate neuromechanical responses. We examined the first and second landings of a drop vertical jump for differences in landing phase duration, time to peak force, and rate of force development. Methods 239 adolescent female basketball players completed drop vertical jumps from an initial height of 31 cm. In-ground force platforms and a three dimensional motion capture system recorded force and positional data for each trial. Findings Between the first and second landing, rate of force development experienced no change (P > 0.62), landing phase duration decreased (P = 0.01), and time to peak ground reaction force increased (P 0.12). Interpretation The current results have important implications for the future assessment of ACL injury risk behaviors. Rate of force development remained unchanged between first and second landings from equivalent fall height, while time to peak reaction force increased during the second landing. Neither factor was dependent on the total time duration of landing phase, which decreased during the second landing. Shorter time to peak force may increase ligament strain and better represent the abrupt joint loading that is associated with ACL injury risk. PMID:23899938

Bates, Nathaniel A.; Ford, Kevin R.; Myer, Gregory D.; Hewett, Timothy E.

2014-01-01

49

Ground reaction forces and throwing performance in elite and novice players in two types of handball shot.  

Science.gov (United States)

The purpose of this study was to examine the differences in the ground reaction force (GRF) patterns between elite and novice players during two types of handball shots, as well as the relationships between throwing performance and the GRF variables. Ball velocity and throwing accuracy were measured during jump shots and 3-step shots performed by 15 elite and 15 novice players. The GRF pattern was recorded for the vertical and the anterior-posterior GRF components (Kistler forceplate type-9281, 750Hz). One-way ANOVA was used for the group differences and the Pearson coefficient for the correlation between throwing performance and GRF variables (SPSS 21.0, p ? 0.05). The elite players performed better in both types of shot. Both groups developed consistent and similar GRF patterns, except for the novices' inconsistent Fz pattern in the 3-step shot. The GRF variables differed significantly between groups in the 3-step shot (p ? 0.05). Significant correlations were found only for ball velocity and predominantly for the novice players during the 3-step shot (p ? 0.05). The results possibly highlight a shortage in the novice ability to effectively reduce their forward momentum so as to provide a stable base of support for the momentum transfer up the kinetic chain, a situation that may predispose athletes to injury. PMID:25031672

Rousanoglou, Elissavet; Noutsos, Konstantinos; Bayios, Ioannis; Boudolos, Konstantinos

2014-03-27

50

NUMBER OF SUCCESSIVE CYCLES NECESSARY TO ACHIEVE STABILITY OF SELECTED GROUND REACTION FORCE VARIABLES DURING CONTINUOUS JUMPING  

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Full Text Available Because of inherent variability in all human cyclical movements, such as walking, running and jumping, data collected across a single cycle might be atypical and potentially unable to represent an individual's generalized performance. The study described here was designed to determine the number of successive cycles due to continuous, repetitive countermovement jumping which a test subject should perform in a single experimental session to achieve stability of the mean of the corresponding continuously measured ground reaction force (GRF variables. Seven vertical GRF variables (period of jumping cycle, duration of contact phase, peak force amplitude and its timing, average rate of force development, average rate of force relaxation and impulse were extracted on the cycle-by-cycle basis from vertical jumping force time histories generated by twelve participants who were jumping in response to regular electronic metronome beats in the range 2-2.8 Hz. Stability of the selected GRF variables across successive jumping cycles was examined for three jumping rates (2, 2.4 and 2.8 Hz using two statistical methods: intra-class correlation (ICC analysis and segmental averaging technique (SAT. Results of the ICC analysis indicated that an average of four successive cycles (mean 4.5 ± 2.7 for 2 Hz; 3.9 ± 2.6 for 2.4 Hz; 3.3 ± 2.7 for 2.8 Hz were necessary to achieve maximum ICC values. Except for jumping period, maximum ICC values took values from 0.592 to 0.991 and all were significantly (p < 0.05 different from zero. Results of the SAT revealed that an average of ten successive cycles (mean 10.5 ± 3.5 for 2 Hz; 9.2 ± 3.8 for 2.4 Hz; 9.0 ± 3.9 for 2.8 Hz were necessary to achieve stability of the selected parameters using criteria previously reported in the literature. Using 10 reference trials, the SAT required standard deviation criterion values of 0.49, 0.41 and 0.55 for 2 Hz, 2.4 Hz and 2.8 Hz jumping rates, respectively, in order to approximate the ICC results. The results of the study suggest that the ICC might be a less conservative but more objective method to evaluate stability of the data. Based on these considerations, it can be recommended that a force time history due to continuous, repetitive countermovement jumping should include minimum of four (the average from the ICC analysis and possibly as many as nine successive jumping cycles (the upper limit of the ICC analysis to establish stable mean values of the selected GRF data. This information is important for both experimental measurements and analytical studies of GRF signals due to continuous, repetitive countermovement jumping

Jasmes M.W. Brownjohn

2009-12-01

51

Predição da força de reação do solo durante a corrida na água Prediction of ground reaction force during water immersion running  

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Full Text Available Este estudo visou desenvolver um modelo para a predição da força de reação do solo na corrida subaquática. Participaram 20 sujeitos (9 homens e 11 mulheres, que realizaram corrida subaquática em dois níveis de imersão e três velocidades. Para cada sujeito foram coletadas seis passagens válidas em cada condição, com a utilização de uma plataforma subaquática de força. O modelo para predição da força foi construído por regressão linear múltipla. Foram consideradas variáveis dependentes a componente vertical e a componente ântero-posterior da força de reação do solo. As variáveis imersão, sexo, velocidade, massa corporal, densidade corporal e percentual de gordura foram consideradas independentes. Permaneceu no modelo final de regressão para a componente vertical a velocidade (pThis study aimed at developing a model to predict ground reaction force during deep-water running. A total of 20 subjects ((9 men, 11 women ran in water at two immersion levels and three different speeds. Each subject performed six valid trials in each condition, data being captured by an underwater force plate. The force prediction model was build by multiple linear regression. Dependent variables were the vertical and anteroposterior components of the ground reaction force; independent variables were runners' immersion, sex, speed, body mass, body density, and percentage of fat. At the final regression model for the vertical component, only speed remained (p<0.001, while for the anteroposterior component, speed, immersion, and body mass were maintained (all at p<0.001. The obtained model for the anteroposterior component of ground reaction force may be found satisfactory, as adjusted determination coefficient was 0.79. However, the prediction model for the vertical component cannot be recommended for prediction during deep-water running, since that coefficient was 0.18. It must be noted that the proposed prediction model applies to subjects provided that they have similar characteristics to those who took part in this study.

Alessandro Haupenthal

2010-09-01

52

Predição da força de reação do solo durante a corrida na água / Prediction of ground reaction force during water immersion running  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: Portuguese Abstract in portuguese Este estudo visou desenvolver um modelo para a predição da força de reação do solo na corrida subaquática. Participaram 20 sujeitos (9 homens e 11 mulheres), que realizaram corrida subaquática em dois níveis de imersão e três velocidades. Para cada sujeito foram coletadas seis passagens válidas em c [...] ada condição, com a utilização de uma plataforma subaquática de força. O modelo para predição da força foi construído por regressão linear múltipla. Foram consideradas variáveis dependentes a componente vertical e a componente ântero-posterior da força de reação do solo. As variáveis imersão, sexo, velocidade, massa corporal, densidade corporal e percentual de gordura foram consideradas independentes. Permaneceu no modelo final de regressão para a componente vertical a velocidade (p Abstract in english This study aimed at developing a model to predict ground reaction force during deep-water running. A total of 20 subjects ((9 men, 11 women) ran in water at two immersion levels and three different speeds. Each subject performed six valid trials in each condition, data being captured by an underwate [...] r force plate. The force prediction model was build by multiple linear regression. Dependent variables were the vertical and anteroposterior components of the ground reaction force; independent variables were runners' immersion, sex, speed, body mass, body density, and percentage of fat. At the final regression model for the vertical component, only speed remained (p

Alessandro, Haupenthal; Heiliane de Brito, Fontana; Caroline, Ruschel; Helio, Roesler; Adriano Ferreti, Borgatto.

2010-09-01

53

Reproducibility of the spatio-temporal variables and the ground reaction forces walking with fire fighting boots REPRODUCIBILIDAD DE LAS VARIABLES ESPACIO-TEMPORALES Y DE LAS COMPONENTES DE LA FUERZA DE REACCIÓN DEL SUELO EN LA MARCHA CON BOTAS DE BOMBERO [Reproducibility of the spatio-temporal variables and the ground reaction forces walking with fire fighting boo  

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AbstractThe aim of this study is to analyze the reproducibility of the spatio-temporal variables and the ground reaction forces (GRF) when walking with fire fighting boots in comparison to walking with low calf shoes. Spatio-temporal parameters and the variables related to the three components of the GRF of 39 people were recorded under two different walking conditions. A T-test to contrast the difference between the coefficients of variation (CV) in both conditions w...

Begoña Gavilanes; Raúl Martínez de Santos; Jesús Cámara Tobalina

2010-01-01

54

ANALYSIS OF THE VERTICAL GROUND REACTION FORCES AND TEMPORAL FACTORS IN THE LANDING PHASE OF A COUNTERMOVEMENT JUMP  

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Full Text Available In most common bilateral landings of vertical jumps, there are two peak forces (F1 and F2 in the force-time curve. The combination of these peak forces and the high frequency of jumps during sports produce a large amount of stress in the joints of the lower limbs which can be determinant of injury. The aim of this study was to find possible relationships between the jump height and F1 and F2, between F1 and F2 themselves, and between F1, F2, the time they appear (T1 and T2, respectively and the length of the impact absorption phase (T. Thirty semi-professional football players made five countermovement jumps and the highest jump of each player was analyzed. They were instructed to perform the jumps with maximum effort and to land first with the balls of their feet and then with their heels. All the data were collected using a Kistler Quattro Jump force plate with a sample rate of 500 Hz. Quattro Jump Software, v.1.0.9.0., was used. There was neither significant correlation between T1 and F1 nor between T1 and F2. There was a significant positive correlation between flight height (FH and F1 (r = 0.584, p = 0.01 but no significant correlation between FH and F2. A significant positive correlation between F1 and T2 (r = 0.418, p < 0.05 and a significant negative correlation between F2 and T2 (r = -0.406, p < 0.05 were also found. There is a significant negative correlation between T2 and T (r = -0. 443, p < 0.05. T1 has a little effect in the impact absorption process. F1 increases with increasing T2 but F2 decreases with increasing T2. Besides, increasing T2, with the objective of decreasing F2, makes the whole impact absorption shorter and the jump landing faster.

Daniel Rojano Ortega

2010-06-01

55

Força de reação do solo como subsídio para prescrição de exercícios aquáticos: estudo de caso / Ground reaction force as a subsidy for prescribing aquatic exercises: case study  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: Portuguese Abstract in portuguese OBJETIVO: Comparar a componente vertical da força de reação do solo nos exercícios de caminhada, corrida com deslocamento, corrida estacionária e salto vertical, realizados em ambiente aquático em diferentes níveis de imersão. MÉTODO: Participou deste estudo de caso um sujeito do sexo masculino (27 [...] anos, 1,80 m e 84,3 kg). Utilizou-se para a coleta de dados uma plataforma subaquática de força posicionada no fundo de uma piscina térmica. O sujeito realizou 30 tentativas válidas de cada exercício, imerso nos níveis do processo xifoide e do quadril. Os dados foram analisados com a utilização da estatística descritiva, teste "t" de Student para amostras pareadas e ANOVA, para medidas repetidas (p Abstract in english OBJECTIVE: To compare the vertical component of the ground reaction force in the exercises of walking, running, stationary running and vertical jump in the water, performed in different levels of immersion. METHODS: This case study was conducted with one subject (male, 27 years, 1,80 m and 84,3 kg). [...] An underwater force plate was used for data collection, placed at the bottom of a thermal swimming pool. The subject performed 30 valid passages for each exercise in two immersion levels: xiphoid process and hip. Data were analyzed through descriptive statistics, Student's "t" test for paired samples and ANOVA for repeated measures (p

Alessandro, Haupenthal; Caroline, Ruschel; Marcel, Hubert; Heiliane de Brito, Fontana; Helio, Roesler.

56

Força de reação do solo como subsídio para prescrição de exercícios aquáticos: estudo de caso / Ground reaction force as a subsidy for prescribing aquatic exercises: case study  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: Portuguese Abstract in portuguese OBJETIVO: Comparar a componente vertical da força de reação do solo nos exercícios de caminhada, corrida com deslocamento, corrida estacionária e salto vertical, realizados em ambiente aquático em diferentes níveis de imersão. MÉTODO: Participou deste estudo de caso um sujeito do sexo masculino (27 [...] anos, 1,80 m e 84,3 kg). Utilizou-se para a coleta de dados uma plataforma subaquática de força posicionada no fundo de uma piscina térmica. O sujeito realizou 30 tentativas válidas de cada exercício, imerso nos níveis do processo xifoide e do quadril. Os dados foram analisados com a utilização da estatística descritiva, teste "t" de Student para amostras pareadas e ANOVA, para medidas repetidas (p Abstract in english OBJECTIVE: To compare the vertical component of the ground reaction force in the exercises of walking, running, stationary running and vertical jump in the water, performed in different levels of immersion. METHODS: This case study was conducted with one subject (male, 27 years, 1,80 m and 84,3 kg). [...] An underwater force plate was used for data collection, placed at the bottom of a thermal swimming pool. The subject performed 30 valid passages for each exercise in two immersion levels: xiphoid process and hip. Data were analyzed through descriptive statistics, Student's "t" test for paired samples and ANOVA for repeated measures (p

Alessandro, Haupenthal; Caroline, Ruschel; Marcel, Hubert; Heiliane de Brito, Fontana; Helio, Roesler.

2010-06-01

57

Filtering ground reaction force data affects the calculation and interpretation of joint kinetics and energetics during drop landings.  

Science.gov (United States)

An inverse dynamic analysis and subsequent calculation of joint kinetic and energetic measures is widely used to study the mechanics of the lower extremity. Filtering the kinematic and kinetic data input to the inverse dynamics equations affects the calculated joint moment of force (JMF). Our purpose was to compare selected integral values of sagittal plane ankle, knee, and hip joint kinetics and energetics when filtered and unfiltered GRF data are input to inverse dynamics calculations. Six healthy, active, injury-free university student (5 female, 1 male) volunteers performed 10 two-legged landings. JMFs were calculated after two methods of data filtering. Unfiltered: marker data were filtered at 10 Hz, GRF data unfiltered. Filtered: both GRF and marker data filtered at 10 Hz. The filtering of the GRF data affected the shape of the knee and hip joint moment-time curves, and the ankle, knee and hip joint mechanical power-time curves. We concluded that although the contributions of individual joints to the support moment and to total energy absorption were not affected, the attenuation of high-frequency oscillations in both JMF and JMP time curves will influence interpretation of CNS strategies during landing. PMID:23434732

McCaw, Steven T; Gardner, Jacob K; Stafford, Lindsay N; Torry, Michael R

2013-12-01

58

Leg dominance may not be a predictor of asymmetry in peak joint moments and ground reaction forces during sit-to-stand movements.  

Science.gov (United States)

Sit-to-stand transfer is a common prerequisite for many daily tasks. Literature often assumes symmetric behavior across the left and right side. Although this assumption of bilateral symmetry is prominent, few studies have validated this supposition. This pilot study uniquely quantifies peak joint moments and ground reaction forces (GRFs), using a Euclidian norm approach, to evaluate bilateral symmetry and its relation to lower limb motor-dominance during sit to stand in ten healthy males. Peak joint moments and GRFs were determined using a motion capture system and inverse dynamics. This analysis included joint moment contributions from all three body planes (sagittal, coronal, and axial) as well as vertical and shearing GRFs. A paired, one-tailed t test was used, suggesting asymmetrical joint moment development in all three lower extremity joints as well as GRFs (P < .05). Furthermore, using an unpaired two-tailed t test, asymmetry developed during these movements does not appear to be predictable by participants' lower limb motor-dominance (P < .025). Consequently, when evaluating sit-to-stand it is suggested the effects of asymmetry be considered in the interpretation of data. The absence of a relationship between dominance and asymmetry prevents the suggestion that one side can be tested to infer behavior of the contralateral. PMID:24676526

Schofield, Jonathon S; Parent, Eric; Lewicke, Justin; Carey, Jason P; El-Rich, Marwan; Adeeb, Samer

2014-02-01

59

Reproducibility of the spatio-temporal variables and the ground reaction forces walking with fire fighting boots REPRODUCIBILIDAD DE LAS VARIABLES ESPACIO-TEMPORALES Y DE LAS COMPONENTES DE LA FUERZA DE REACCIÓN DEL SUELO EN LA MARCHA CON BOTAS DE BOMBERO [Reproducibility of the spatio-temporal variables and the ground reaction forces walking with fire fighting boo  

Directory of Open Access Journals (Sweden)

Full Text Available AbstractThe aim of this study is to analyze the reproducibility of the spatio-temporal variables and the ground reaction forces (GRF when walking with fire fighting boots in comparison to walking with low calf shoes. Spatio-temporal parameters and the variables related to the three components of the GRF of 39 people were recorded under two different walking conditions. A T-test to contrast the difference between the coefficients of variation (CV in both conditions was used. The CV of the spatio-temporal variables (i.e velocity (V, condition I = 2.01%; condition II = 1.81%, of the vertical (i.e. contact force (FZA of the left foot, condition I = 2.54%; condition II = 2.73% and of the antero-posterior GRF (i.e. maximum force (FXMAX of the left foot, condition I = 4.47%; condition II = 4.59% was lower than 12.5%, suggesting that these variables could be used to analyze the influence of fire fighting boots on the gait. However, the low reproducibility showed by medium-lateral parameters does not allow to use them. Apart from the bipodal phase no differences were found between the two walking conditions. Key words: biomechanics, footwear, variability.ResumenEl objetivo del presente trabajo es analizar la reproducibilidad de las variables espacio-temporales y de la fuerza de reacción del suelo (FRS durante la marcha con botas de bombero y compararla con la mostrada durante la marcha con calzado de cuero sin caña. Se registraron las variables espacio-temporales de 39 personas así como las variables que definen las tres componentes de la FRS con dos tipos de calzado diferente. Se utilizó la prueba T para contrastar la hipótesis referida a la diferencia del coeficiente de variación (CV entre los dos tipos de calzado. El CV de las variables espacio-temporales (p. ej. velocidad (V, condición I = 2,01%; condición II = 1,81%, así como de las que definen la componente vertical (p. ej. fuerza de apoyo (FZA del pie izquierdo, condición I = 2,54%; condición II = 2,73% y antero-posterior (p. ej. fuerza máxima (FXMAX del pie izquierdo, condición I = 4,47%; condición II = 4,59% de la FRS fue inferior a 12,5%, sugiriendo que estas variables pueden ser utilizadas para analizar la influencia de las botas de bombero sobre la marcha. La baja reproducibilidad mostrada por las variables que definen la componente medio-lateral desaconseja la utilización de las mismas para evaluar el efecto de las botas de bombero sobre la marcha. A excepción del tiempo de apoyo bipodal, el resto de variables durante la marcha con botas de bombero no mostró una variabilidad diferente a la obtenida durante la marcha con calzado de cuero sin caña.Palabras clave: biomecánica, calzado, variabilidad. AbstractThe aim of this study is to analyze the reproducibility of the spatio-temporal variables and the ground reaction forces (GRF when walking with fire fighting boots in comparison to walking with low calf shoes. Spatio-temporal parameters and the variables related to the three components of the GRF of 39 people were recorded under two different walking conditions. A T-test to contrast the difference between the coefficients of variation (CV in both conditions was used. The CV of the spatio-temporal variables (i.e velocity (V, condition I = 2.01%; condition II = 1.81%, of the vertical (i.e. contact force (FZA of the left foot, condition I = 2.54%; condition II = 2.73% and of the antero-posterior GRF (i.e. maximum force (FXMAX of the left foot, condition I = 4.47%; condition II = 4.59% was lower than 12.5%, suggesting that these variables could be used to analyze the influence of fire fighting boots on the gait. However, the low reproducibility showed by medium-lateral parameters does not allow to use them. Apart from the bipodal phase no differences were found between the two walking conditions.Key words: biomechanics, footwear, variability.

Begoña Gavilanes

2010-11-01

60

Estudo da variabilidade das forças de reação do solo na aquisição do andar independente em bebês / A study of ground reaction forces variability during acquisition of independent gait in toddlers  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: Portuguese Abstract in portuguese Este estudo avaliou o comportamento das forças de reação do solo (FRS) nos primeiros meses do andar independente, a fim de identificar mudanças na capacidade infantil de propulsionar e equilibrar o corpo em condição dinâmica. Foram avaliadas no período de três meses dez crianças com idade de 13 mese [...] s na primeira avaliação. As crianças caminharam em uma passarela de cinco metros de comprimento com duas plataformas de força embutidas. Foram estudadas magnitudes máximas e mínimas das FRS e as respectivas variabilidades. As avaliações foram comparadas através do teste não-paramétrico ANOVA de Friedman (p Abstract in english This study aimed to describe ground reaction forces' profiles during toddler's gait at the first months of the acquisition phase of independent walking, in order to identify whether there are changes in the ability to propel and balance the body in this dynamic condition. Ten thirteen-month old todd [...] lers volunteered to the study and were evaluated three times in a three-month interval. The toddlers walked over a 5 m long walkway with two force plates fixed at ground level. Vertical and horizontal peak reaction forces and variability coefficients were selected for analysis. To compare the results of the three evaluations ANOVA Friedman's tests were used at 5% level of significance. The walking experience achieved by the toddlers month after month was not sufficient to significantly change the biomechanical selected variables and statistically significant differences were not found for the selected variables along three months. However, a reduction in the variability coefficient for the vertical reaction forces suggests development towards an increasingly mature gait pattern.

Giovana, Levada; Paula Hentschel Lobo da, Costa.

2012-06-01

 
 
 
 
61

Estudo da variabilidade das forças de reação do solo na aquisição do andar independente em bebês / A study of ground reaction forces variability during acquisition of independent gait in toddlers  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: Portuguese Abstract in portuguese Este estudo avaliou o comportamento das forças de reação do solo (FRS) nos primeiros meses do andar independente, a fim de identificar mudanças na capacidade infantil de propulsionar e equilibrar o corpo em condição dinâmica. Foram avaliadas no período de três meses dez crianças com idade de 13 mese [...] s na primeira avaliação. As crianças caminharam em uma passarela de cinco metros de comprimento com duas plataformas de força embutidas. Foram estudadas magnitudes máximas e mínimas das FRS e as respectivas variabilidades. As avaliações foram comparadas através do teste não-paramétrico ANOVA de Friedman (p Abstract in english This study aimed to describe ground reaction forces' profiles during toddler's gait at the first months of the acquisition phase of independent walking, in order to identify whether there are changes in the ability to propel and balance the body in this dynamic condition. Ten thirteen-month old todd [...] lers volunteered to the study and were evaluated three times in a three-month interval. The toddlers walked over a 5 m long walkway with two force plates fixed at ground level. Vertical and horizontal peak reaction forces and variability coefficients were selected for analysis. To compare the results of the three evaluations ANOVA Friedman's tests were used at 5% level of significance. The walking experience achieved by the toddlers month after month was not sufficient to significantly change the biomechanical selected variables and statistically significant differences were not found for the selected variables along three months. However, a reduction in the variability coefficient for the vertical reaction forces suggests development towards an increasingly mature gait pattern.

Giovana, Levada; Paula Hentschel Lobo da, Costa.

62

The Origin of the Radiation Reaction Force  

CERN Document Server

The emission of radiation from an accelerated charge is analyzed. It is found that at zero velocity, the radiation emitted from the charge imparts no counter momentum to the emitting charge, and no radiation reaction force is created by the radiation. A reaction force is created by the stress force that exists in the curved electric field of the charge, and the work done in overcoming this force is the source of the energy carried by the radiation.

Harpaz, A

2000-01-01

63

A influência do uso acumulado de calçados de corrida sobre a força de reação do solo e as respostas de pressão plantar The influence of running shoes cumulative usage on the ground reaction forces and plantar pressure responses  

Directory of Open Access Journals (Sweden)

Full Text Available 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 registrar 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 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 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 < 0.01 and the loading rate showed a significant decrease at 200km in relation to the New condition (p < 0.01. Total area increased significantly from New to 100km (p < 0.01 of use and maintained a similar value when compared with the other conditions. There was a continuous and significant decrease (p < 0.01 on forefoot peak pressure as the mileage increased from New to 300km. The hallux peak pressure values were significantly smaller (p < 0.01 at 300km when compared with the New condition. Considering that the first peak, loading rate and plantar peak pressure values did not increase and that the plantar total contact area increased, it can be concluded that the running shoe did not suffer consistent alterations in ground reaction force and in plantar pressure after 300km of use.

Roberto Bianco

2011-12-01

64

Relação entre a mobilidade do tornozelo e pé e a magnitude da força vertical de reação do solo Relationship between ankle and foot mobility and the magnitude of the vertical ground reaction force  

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Full Text Available 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 sistema 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.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 have 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.

DL Vianna

2006-09-01

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Relação entre a mobilidade do tornozelo e pé e a magnitude da força vertical de reação do solo / Relationship between ankle and foot mobility and the magnitude of the vertical ground reaction force  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: Portuguese 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 sistema 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 have 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.

DL, Vianna; JMD, Greve.

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A influência do uso acumulado de calçados de corrida sobre a força de reação do solo e as respostas de pressão plantar / The influence of running shoes cumulative usage on the ground reaction forces and plantar pressure responses  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: Portuguese 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 registrar 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 plant [...] ar 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 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

Roberto, Bianco; Ana Paula da Silva, Azevedo; Carina Helena Wasem, Fraga; Fernanda Michelone, Acquesta; Luis, Mochizuki; Alberto Carlos, Amadio; Júlio Cerca, Serrão.

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Ground reaction force and electromyographic activity of transfemoral amputee gait: a case series / Força de Reação do Solo e atividade eletromiográfica da marcha de amputados transfemorais: uma série de casos  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in portuguese O comportamento da Força de Reação do Solo (FRS) e a atividade eletromiográfica formam uma parte dos dados que caracterizam a biomecânica da marcha. O estudo destes parâmetros é importante para a recuperação da locomoção e para compreensão do impacto da amputação e dos componentes protéticos nos mov [...] imentos desenvolvidos no andar. Portanto, esta série de casos tem como objetivo descrever a atividade eletromiográfica e a FRS de amputados transfemorais. Para mensurar a FRS, foi utilizada uma plataforma de força e um sistema de eletromiografia monitorou os músculos vasto lateral, bíceps femoral, tibial anterior e gastrocnêmio lateral da perna não-amputada. As médias das componentes vertical e ânteroposterior da FRS, a atividade eletromiográfica e variáveis descritivas foram analisadas. Foi observado uma diminuição da magnitude da FRS vertical e ânteroposterior e das variáveis descritivas da componente ânteroposterior da FRS durante a fase de propulsão na perna amputada. Houve aumento na atividade fásica muscular e co-ativação na perna não-amputada. Pode-se concluir que os amputados transfemorais unilaterais analisados nesta série de casos desenvolveram menor FRS na perna amputada e longos períodos de atividade eletromiográfica na perna não amputada durante a marcha. Abstract in english Ground reaction forces (GRF) and electromyographic activity form a part of the descriptive data that characterise the biomechanics of gait. The research of these parameters is important in establishing gait training and understanding the impact of amputation and prosthetic components on movement dur [...] ing the act of walking. Therefore, this case series describes the GRF and electromyographic activity in the gait of transfemoral amputees. A force plate was used to measure GRF, and an electromyographic system monitored the vastus lateralis, biceps femoris, tibialis anterior, and gastrocnemius lateralis muscles of the non-amputated leg. The average vertical and anteroposterior GRF time-curves, average electromyographic activity, and descriptor variables were then analysed. We observed decreases in vertical and anteroposterior GRF magnitudes as well as in anteroposterior GRF descriptor variables during the propulsive phase in the amputated leg. There were increases in phasic muscle activity and co-activation in the non-amputated leg. We concluded that, during walking, the unilateral transfemoral amputees (who were analysed in this case series) developed lower GRF in the amputated limb and a longer period of electromyographic activity in the non-amputated limb.

Alex Sandra Oliveira de, Cerqueira; Edward Yuji, Yamaguti; Luis, Mochizuki; Alberto Carlos, Amadio; Júlio Cerca, Serrão.

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Ground reaction force and electromyographic activity of transfemoral amputee gait: a case series / Força de Reação do Solo e atividade eletromiográfica da marcha de amputados transfemorais: uma série de casos  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in portuguese O comportamento da Força de Reação do Solo (FRS) e a atividade eletromiográfica formam uma parte dos dados que caracterizam a biomecânica da marcha. O estudo destes parâmetros é importante para a recuperação da locomoção e para compreensão do impacto da amputação e dos componentes protéticos nos mov [...] imentos desenvolvidos no andar. Portanto, esta série de casos tem como objetivo descrever a atividade eletromiográfica e a FRS de amputados transfemorais. Para mensurar a FRS, foi utilizada uma plataforma de força e um sistema de eletromiografia monitorou os músculos vasto lateral, bíceps femoral, tibial anterior e gastrocnêmio lateral da perna não-amputada. As médias das componentes vertical e ânteroposterior da FRS, a atividade eletromiográfica e variáveis descritivas foram analisadas. Foi observado uma diminuição da magnitude da FRS vertical e ânteroposterior e das variáveis descritivas da componente ânteroposterior da FRS durante a fase de propulsão na perna amputada. Houve aumento na atividade fásica muscular e co-ativação na perna não-amputada. Pode-se concluir que os amputados transfemorais unilaterais analisados nesta série de casos desenvolveram menor FRS na perna amputada e longos períodos de atividade eletromiográfica na perna não amputada durante a marcha. Abstract in english Ground reaction forces (GRF) and electromyographic activity form a part of the descriptive data that characterise the biomechanics of gait. The research of these parameters is important in establishing gait training and understanding the impact of amputation and prosthetic components on movement dur [...] ing the act of walking. Therefore, this case series describes the GRF and electromyographic activity in the gait of transfemoral amputees. A force plate was used to measure GRF, and an electromyographic system monitored the vastus lateralis, biceps femoris, tibialis anterior, and gastrocnemius lateralis muscles of the non-amputated leg. The average vertical and anteroposterior GRF time-curves, average electromyographic activity, and descriptor variables were then analysed. We observed decreases in vertical and anteroposterior GRF magnitudes as well as in anteroposterior GRF descriptor variables during the propulsive phase in the amputated leg. There were increases in phasic muscle activity and co-activation in the non-amputated leg. We concluded that, during walking, the unilateral transfemoral amputees (who were analysed in this case series) developed lower GRF in the amputated limb and a longer period of electromyographic activity in the non-amputated limb.

Alex Sandra Oliveira de, Cerqueira; Edward Yuji, Yamaguti; Luis, Mochizuki; Alberto Carlos, Amadio; Júlio Cerca, Serrão.

2013-02-01

69

Ground reaction force in basketball cutting maneuvers with and without ankle bracing and taping / Análise da força de reação do solo durante o cutting no basquetebol com e sem o uso de implementos no tornozelo  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in portuguese CONTEXTO E OBJETIVO: A lesão mais comum no basquetebol é a entorse de tornozelo. Assim, os atletas freqüentemente utilizam suportes externos como medidas profiláticas. O objetivo deste estudo é avaliar as respostas da força de reação do solo (FRS) durante a execução do movimento de cutting do basque [...] tebol com e sem acessórios de tornozelo. TIPO DE ESTUDO E LOCAL: Estudo comparativo. Delineamento experimental de grupo único com medidas repetidas; Divisão de Medicina de Reabilitação, Hospital das Clínicas, Faculdade de Medicina da Universidade de São Paulo, Brasil. MÉTODOS: Foram colhidas as forças vertical (Fy) e médio-lateral (Fz) em três condições (bandagem, Aircast e calçado esportivo) e analisados os picos de força e de propulsão no contato com o solo (Fymax1, Fzmax1, Fymax2 e Fzmax2), o gradiente de crescimento (pico/tempo) (GC Fymax1, GC Fzmax1, GC Fymax2 e GC Fzmax2) e o impulso após o contato. RESULTADOS: Os acessórios reduziram significativamente Fymax2 e GC Fymax2. GC FZmax1 foi maior na situação com tênis quando comparado com bandagem. No momento do impacto, a bandagem aumentou a Fy em relação ao calçado, mas em um intervalo de tempo maior, não aumentando a carga articular. Fz atingiu um pico em menor tempo, podendo gerar maior carga eversora/inversora. O Aircast exerceu um melhor efeito de absorção de impacto, pois gera menor Fy em um maior intervalo de tempo. CONCLUSÕES: Apesar do uso freqüente deste tipo de recurso pelos atletas, seu mecanismo de ação ainda é confuso. Mais estudos são necessários para esclarecer seus efeitos nas atividades esportivas a longo prazo. Abstract in english CONTEXT AND OBJECTIVE: In basketball, the most common injuries are ankle sprains. For this reason, players frequently use external ankle devices or taping as prophylactic and rehabilitation measures. The purpose of this study was to evaluate ground reaction force (GRF) responses in basketball player [...] s while performing typical cutting maneuvers with and without ankle bracing and ankle taping. DESIGN AND SETTING: Comparative study with experimental design of single-group repeated measurements, at Medical Rehabilitation Division, Hospital das Clínicas, Faculdade de Medicina, Universidade de São Paulo. METHODS: Vertical (Fy) and medial-lateral (Fz) GRF measurements were made under three conditions (taping, Aircast-type orthosis and basketball shoes alone), with analysis of peak forces at foot contact (Fymax1, Fzmax1, Fymax2 and Fzmax2), growth gradient (peak/time) (GG Fymax1, GG Fzmax1, GG Fymax2 and GG Fzmax2) and impulse after foot contact. RESULTS: Bracing significantly reduced Fymax2 and GG Fymax2. GG Fzmax1 was significantly higher for the sport shoe condition than for the taping condition. Taping increased Fy in relation to the sport shoe at foot contact, but over a longer time interval, without increasing excessive ankle loading. Fz reached a peak in less time, which might generate greater inversion/eversion loading on a player's foot. The Aircast exerted better shock-absorbing effect than did the other two conditions, since it generated less vertical force over longer time intervals and smaller medial-lateral forces in relation to taping. CONCLUSIONS: Ankle bracing and ankle taping action mechanisms are still unclear and therefore should be carefully prescribed. More studies are needed to clarify taping and bracing effects on sporting activities.

Isabel de Camargo Neves, Sacco; Henrique Yuji, Takahasi; Eneida Yuri, Suda; Linamara Rizzo, Battistella; Cristianne Akie, Kavamoto; José Augusto Fernandes, Lopes; Jeane Cintra Peixoto de, Vasconcelos.

70

Grounding-Induced Sectional Forces and Residual Strength of Grounded Ship Hulls  

DEFF Research Database (Denmark)

The aim of the present study is to determine the sectional forces induced by ship grounding and also to assess the residual strength of groundedship hulls. An analytical approach is used to estimate the grounding-induced sectional forces of ships. The extent and location of structural damage due to grounding is defined based on the ABS Safe Hull guide. The residual strength of damaged hulls is calculated by using a simple analytical formula. The method is applied to residual strength assessment of a damaged double hull tanker of 38,400 dwt due to grounding.

Pedersen, Preben Terndrup

1996-01-01

71

A COMPARISON OF UPPER-EXTREMITY REACTION FORCES BETWEEN THE YURCHENKO VAULT AND FLOOR EXERCISE  

Directory of Open Access Journals (Sweden)

Full Text Available The purpose of this study was to examine reaction forces transmitted to the upper extremities of high-level gymnasts during the round-off phase of the Yurchenko vault. A secondary purpose of this study was to compare reaction forces during the Yurchenko vault to reaction forces observed in a tumbling pass during the floor exercise. Ten high-level, female gymnasts volunteered to participate. Conditions of the independent variable were the Yurchenko vault and floor exercise; dependent variables were peak vertical and peak anterior-posterior reaction forces. Each participant performed three trials of both conditions with the trail hand contacting a force platform. Vertical and anterior-posterior reaction forces, normalized to body weight, were greater (p < 0.05 during the round-off phase of the Yurchenko vault (2.38 than during the floor exercise round-off (2.15. Vertical reaction forces during the round-off phase of the Yurchenko vault and floor exercise round-off are similar to reaction forces transmitted to upper extremities during other gymnastic skills and ground reaction forces transmitted to lower extremities while running and walking at various speeds. Results of this study reveal a need for further research considering methods aimed at reducing reaction forces transmitted to the upper extremities during the Yurchenko vault and floor exercise.

Matthew Kirk Seeley

2005-06-01

72

Tensor Forces and the Ground-State Structure of Nuclei  

International Nuclear Information System (INIS)

Two-nucleon momentum distributions are calculated for the ground states of nuclei with mass number A (le) 8, using accurate variational Monte Carlo wave functions derived from a realistic Hamiltonian with two- and three-nucleon potentials. The momentum distribution of 'np' pairs is found to be much larger than that of 'pp' pairs for values of the relative momentum in the range (300--600) MeV/c and vanishing total momentum. This large difference, more than an order of magnitude, is seen in all nuclei considered, and has a universal character originating from the tensor components present in any realistic nucleon-nucleon potential. The correlations induced by the tensor force strongly influence the structure of 'np' pairs, which are known to be predominantly in deuteron-like states, while they are ineffective for 'pp' pairs, which are mostly in 1S0 states. These features should be easily observable in two-nucleon knock-out processes, for example in A(e,e(prime) np) and A(e,e(prime) pp) reactions

73

Proceedings of the CEATI grounding and lightning task force workshop  

Energy Technology Data Exchange (ETDEWEB)

This workshop focused on recent advancements in power transmission grounding and lightning protection. The workshop was held by the members of CEATI's collaborative research program and task force as a means of improving the safety and reliability of power transmission lines, towers and substations. Presentations were given by leading experts in the electric power industry. New grounding and impedance measuring methods were presented. Lightning mitigation techniques were discussed. New innovations in ground resistance and ground impedance testing were presented, and methods of protecting telephone cables in substations were outlined. Recent advancements in simulation and diagnostic testing were also presented. The workshop featured 11 presentations, of which 6 have been catalogued separately for inclusion in this database. tabs., figs.

NONE

2009-07-01

74

Soot Reaction Properties (Ground-Based Study)  

Science.gov (United States)

Three major soot reaction processes are needed to predict soot properties in flame environments: soot growth, or the formation of soot on soot nuclei and soot particles; soot oxidation, or the reaction of soot with oxidizing species to yield the combustion products of soot oxidation; and soot nucleation, or the formation of soot nuclei from soot precursors having large molecular weights (generally thought to be large and particularly stable PAH molecules in flame environments, called stabilomers). These processes are addressed in the following, considering soot growth, oxidation and nucleation, in turn, by exploiting the soot and flame structure results for premixed and diffusion flames already discussed in Section 2.

Dai, Z.; El-Leathy, A. M.; Lin, K.-C.; Sunderland, P. B.; Xu, F.; Faeth, G. M.; Urban, D. L. (Technical Monitor); Yuan, Z.-G. (Technical Monitor)

2000-01-01

75

Regulation of reaction forces during the golf swing.  

Science.gov (United States)

During the golf swing, the reaction forces applied at the feet control translation and rotation of the body-club system. In this study, we hypothesized that skilled players using a 6-iron would regulate shot distance by scaling the magnitude of the resultant horizontal reaction force applied to the each foot with minimal modifications in force direction. Skilled players (n = 12) hit golf balls using a 6-iron. Shot distance was varied by hitting the ball as they would normally and when reducing shot distance using the same club. During each swing, reaction forces were measured using dual force plates (1200 Hz) and three-dimensional kinematics were simultaneously captured (110 Hz). The results indicate that, on average, the peak resultant horizontal reaction forces of the target leg were significantly less than normal (5%, p < 0.05) when reducing shot distance. No significant differences in the orientation of the peak resultant horizontal reaction forces were observed. Resultant horizontal reaction force-angle relationships within leg and temporal relationships between target and rear legs during the swing were consistent within player across shot conditions. Regulation of force magnitude with minimal modification in force direction is expected to provide advantages from muscle activation, coordination, and performance points of view. PMID:23898685

McNitt-Gray, J L; Munaretto, J; Zaferiou, A; Requejo, P S; Flashner, H

2013-06-01

76

Acute fatigue effects on ground reaction force of lower limbs during countermovement jumps / Estudio del efecto de la fatiga aguda en la fuerza del miembros inferiores durante saltos con contramovimiento / Estudo do efeito agudo da fadiga na força de membros inferiores durante saltos com contramovimento  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in portuguese Parâmetros associados com o desempenho do salto contramovimento foram identificados a partir de registros da força vertical em condições de fadiga e não fadiga. Quatorze variáveis foram definidas dividindo a força de reação vertical do solo em valores negativos e positivos de trabalho externo e o te [...] mpo em que os valores de força vertical foi menor e maior do que o peso corporal do indivíduo. As variações dos parâmetros foram avaliadas considerando a relação entre conjunto de elementos contráteis e elásticos nos membros inferiores. Determinou-se que o desempenho é baseado na otimização do impulso e não em um valor instantâneo da força; o tempo em que a força de reação do solo foi menor do que o peso corporal e o tempo de trabalho externo negativo são mais baixos sob fadiga. Os resultados sugerem que durante a fadiga há uma menor contribuição da energia elástica e do estado ativo de forma global, mas a participação de elementos contráteis poderia compensar parcialmente a queda de desempenho. Abstract in spanish Se identificaron parámetros asociados con el desempeño de saltos con contramovimiento a partir de registros de fuerza vertical en condiciones de fatiga y no fatiga. Catorce variables fueron definidas dividiendo la componente vertical de la curva de fuerza de reacción del suelo en valores negativos y [...] positivos de trabajo externo y tiempo en que los valores de fuerza resultaron menores o mayores que el valor del peso del individuo. Las variaciones de los parámetros fueron evaluadas considerando la relación entre el conjunto de elementos contráctiles y elásticos en los miembros inferiores. Se determinó que el desempeño está basado en la optimización del impulso y no en un valor instantáneo de fuerza; el tiempo en que la fuerza de reacción del suelo fue menor que el peso corporal y el tiempo de trabajo externo negativo resultaron más bajos en fatiga. Los resultados sugieren que durante la fatiga hay una menor contribución de la energía elástica y del estado activo de forma global, pero la participación de elementos contráctiles podría compensar parcialmente la caída en el desempeño. Abstract in english Parameters associated with the performance of countermovement jumps were identified from vertical ground reaction force recordings during fatigue and resting conditions. Fourteen variables were defined, dividing the vertical ground reaction force into negative and positive external working times and [...] times in which the vertical ground reaction force values were lower and higher than the participant's body weight. We attempted to explain parameter variations by considering the relationship between the set of contractile and elastic components of the lower limbs. We determined that jumping performance is based on impulsion optimization and not on instantaneous ground reaction force value: the time in which the ground reaction force was lower than the body weight, and negative external work time was lower under fatigue. The results suggest that, during fatigue, there is less contribution from elastic energy and from overall active state. However, the participation of contractile elements could partially compensate for the worsening of jumping performance.

Carlos Gabriel, Fábrica; Paula V., González; Jefferson Fagundes, Loss.

77

Acute fatigue effects on ground reaction force of lower limbs during countermovement jumps / Estudio del efecto de la fatiga aguda en la fuerza del miembros inferiores durante saltos con contramovimiento / Estudo do efeito agudo da fadiga na força de membros inferiores durante saltos com contramovimento  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in portuguese Parâmetros associados com o desempenho do salto contramovimento foram identificados a partir de registros da força vertical em condições de fadiga e não fadiga. Quatorze variáveis foram definidas dividindo a força de reação vertical do solo em valores negativos e positivos de trabalho externo e o te [...] mpo em que os valores de força vertical foi menor e maior do que o peso corporal do indivíduo. As variações dos parâmetros foram avaliadas considerando a relação entre conjunto de elementos contráteis e elásticos nos membros inferiores. Determinou-se que o desempenho é baseado na otimização do impulso e não em um valor instantâneo da força; o tempo em que a força de reação do solo foi menor do que o peso corporal e o tempo de trabalho externo negativo são mais baixos sob fadiga. Os resultados sugerem que durante a fadiga há uma menor contribuição da energia elástica e do estado ativo de forma global, mas a participação de elementos contráteis poderia compensar parcialmente a queda de desempenho. Abstract in spanish Se identificaron parámetros asociados con el desempeño de saltos con contramovimiento a partir de registros de fuerza vertical en condiciones de fatiga y no fatiga. Catorce variables fueron definidas dividiendo la componente vertical de la curva de fuerza de reacción del suelo en valores negativos y [...] positivos de trabajo externo y tiempo en que los valores de fuerza resultaron menores o mayores que el valor del peso del individuo. Las variaciones de los parámetros fueron evaluadas considerando la relación entre el conjunto de elementos contráctiles y elásticos en los miembros inferiores. Se determinó que el desempeño está basado en la optimización del impulso y no en un valor instantáneo de fuerza; el tiempo en que la fuerza de reacción del suelo fue menor que el peso corporal y el tiempo de trabajo externo negativo resultaron más bajos en fatiga. Los resultados sugieren que durante la fatiga hay una menor contribución de la energía elástica y del estado activo de forma global, pero la participación de elementos contráctiles podría compensar parcialmente la caída en el desempeño. Abstract in english Parameters associated with the performance of countermovement jumps were identified from vertical ground reaction force recordings during fatigue and resting conditions. Fourteen variables were defined, dividing the vertical ground reaction force into negative and positive external working times and [...] times in which the vertical ground reaction force values were lower and higher than the participant's body weight. We attempted to explain parameter variations by considering the relationship between the set of contractile and elastic components of the lower limbs. We determined that jumping performance is based on impulsion optimization and not on instantaneous ground reaction force value: the time in which the ground reaction force was lower than the body weight, and negative external work time was lower under fatigue. The results suggest that, during fatigue, there is less contribution from elastic energy and from overall active state. However, the participation of contractile elements could partially compensate for the worsening of jumping performance.

Carlos Gabriel, Fábrica; Paula V., González; Jefferson Fagundes, Loss.

2013-12-01

78

Force-activated reactivity switch in a bimolecular chemical reaction at the single molecule level  

Science.gov (United States)

Mechanical force can deform the reacting molecules along a well-defined direction of the reaction coordinate. However, the effect of mechanical force on the free-energy surface that governs a chemical reaction is still largely unknown. The combination of protein engineering with single-molecule AFM force-clamp spectroscopy allows us to study the influence of mechanical force on the rate at which a protein disulfide bond is reduced by some reducing agents in a bimolecular substitution reaction (so-called SN2). We found that cleavage of a protein disulfide bond by hydroxide anions exhibits an abrupt reactivity ``switch'' at 500 pN, after which the accelerating effect of force on the rate of an SN2 chemical reaction greatly diminishes. We propose that an abrupt force-induced conformational change of the protein disulfide bond shifts its ground state, drastically changing its reactivity in SN2 chemical reactions. Our experiments directly demonstrate the action of a force-activated switch in the chemical reactivity of a single molecule. References: Sergi Garcia-Manyes, Jian Liang, Robert Szoszkiewicz, Tzu-Ling Kuo and Julio M. Fernandez, Nature Chemistry, 1, 236-242, 2009.

Szoszkiewicz, Robert; Garcia-Manyes, Sergi; Liang, Jian; Kuo, Tzu-Ling; Fernandez, Julio M.

2010-03-01

79

Government Applications Task Force ground truth study of WAG 4  

International Nuclear Information System (INIS)

This report documents the Government Applications Task Force (GATF) Buried Waste Project. The project was initiated as a field investigation and verification of the 1994 Strategic Environmental Research and Development Program's (SERDP) Buried Waste Identification Project results. The GATF project team included staff from three US Department of Energy (DOE) Laboratories [Oak Ridge National Laboratory (ORNL), Los Alamos National Laboratory (LANL), and the Savannah River Technology Center (SRTC)] and from the National Exploitation Laboratory. Similar studies were conducted at each of the three DOE laboratories to demonstrate the effective use of remote sensing technologies. The three locations were selected to assess differences in buried waste signatures under various environmental conditions (i.e., climate, terrain, precipitation, geology, etc.). After a brief background discussion of the SERDP Project, this report documents the field investigation (ground truth) results from the 1994--1995 GATF Buried Waste Study at ORNL's Waste Area Grouping (WAG) 4. Figures for this report are located in Appendix A

80

Feedback Control of Floor Reaction Force Based on Force-Reflecting-Type Multilateral Control  

Science.gov (United States)

Real-world haptics is being studied not only for improving feedback on real-world haptic information in teleoperation but also for developing key technologies for future human support. For the remote operating of systems at distant places, haptic information is required in addition to visual information. The haptic information around a work environment can be the floor reaction force, which can be obtained using a movement-type haptic device. The floor reaction force from the environment that the mobile haptic device touches is fed back accurately to the operator. First, this paper proposes a general force-reflecting-type multilateral control. Second, this paper extends the control to feedback control of the floor reaction force by using force-reflecting-type multilateral control and a novel haptic device employing a biped robot with a slave system. The position response of a master system is transformed to a leg tip position command for the biped-type haptic device. In addition, the floor reaction force determined by the biped-type haptic device is fed back to the master system. The proposed method can determine the force feedback to the sole of the foot, which is not possible with a conventional stationary system. As a result, the floor reaction force from a large area can be obtained, and the operability of the control system is improved by using the proposed system.

Nagase, Kazuki; Katsura, Seiichiro

 
 
 
 
81

Radiation reaction force and unification of electromagnetic and gravitational fields  

International Nuclear Information System (INIS)

A unified theory of electromagnetic and gravitational fields should modify classical electrodynamics such that the radiation reaction force is accounted for. The analysis leads to a five-dimensional unified theory of five variables. The theory is supported by showing that, for the case of a charged particle moving in a constant magnetic field, the radiation reaction force is indeed included. Moreover, this example shows explicitly that physical changes are associated with the fifth variable. Thus, the notion of a physical five-dimensional space should be seriously taken into consideration

82

Deployment Control of Space Inflatable Structures Considering Reaction Forces  

Science.gov (United States)

In the process of deployment of an inflatable structure, when the stiffness of the structure increases rapidly, especially at the final moment of deployment, a large reaction force is generated around supporting points with the main body of a spacecraft. It is important to minimize the reaction force when deploying in order to decrease the influence on the satellite attitude and strength of supporting points as much as possible. The purpose of this study is to attain a method of optimal deployment control that minimizes the reaction force generated around supporting part. In order to achieve the goal, feedback control experiments using an electromagnetic valve to adjust the inner pressure was done during deployment of inflatable tube. In addition, the effectiveness of the proposed method was also examined when applying it to the structure of the different size. As a result, it is found that the suppression of the reaction force is attained by about 80% compared with the case where this control is not applied, and the effectiveness of the proposed feedback control method of inner pressure was confirmed. Moreover, considering the volume, it is able to apply this control method even with different scale structures.

Nakajima, Akira; Watanabe, Kazuki; Tsunoda, Hiroaki; Yamakawa, Hiroshi

83

Force as a Useful Variable in Reactions: Unfolding RNA  

Science.gov (United States)

The effect of force on the thermodynamics and kinetics of reactions is described. The key parameters are the difference in end-to-end distance between reactant and product for thermodynamics, and the distance to the transition state for kinetics. I focus the review on experimental results on force unfolding of RNA. Methods to measure Gibbs free energies and kinetics for reversible and irreversible reactions are described. The use of the worm-like-chain model to calculate the effects of force on thermodynamics and kinetics is illustrated with simple models. The main purpose of the review is to describe the simple experiments that have been done so far, and to encourage more people to enter a field that is new and full of opportunities. PMID:15139818

Tinoco, Ignacio

2014-01-01

84

A thermodynamic force generated by chemical gradient and adsorption reaction  

CERN Document Server

Biological units such as macromolecules, organelles, and cells are directed to a proper location under gradients of relevant chemicals. By considering a macroscopic element that has binding sites for a chemical adsorption reaction to occur on its surface, we show the existence of a thermodynamic force that is generated by the gradient and exerted on the element. By assuming local equilibrium and adopting the grand potential from thermodynamics, we derive a formula for such a thermodynamic force, which depends on the chemical potential gradient and Langmuir isotherm. The conditions under which the formula can be applied are demonstrated to hold in intracellular reactions. The role of the force in the partitioning of bacterial chromosome/plasmid during cell division is discussed.

Sugawara, Takeshi

2009-01-01

85

["Forced mouth opening reaction" associated with corticobasal degeneration].  

Science.gov (United States)

Corticobasal degeneration (CBD) is a slowly progressive disorder characterized by an asymmetrical akinetic-rigid syndrome, supranuclear ophthalmoplegia, dystonia, often accompanied by involuntary movements, particularly myoclonus, and associated with lateralized cortical signs such as alien limb behavior and apraxia. Computerized tomography demonstrates asymmetrical frontoparietal cortical atrophy in the later stages of the illness. Neuropathological examination reveals neuronal loss, gliosis and swollen achromatic neurons within the frontal and temporal cortices, and the substantia nigra. We discuss here a unique phenomenon not described so far in three patients with clinical features of CBD, one with subsequent autopsy observations. When awake, they all showed a common behavior, their mouth opened constantly and immediately, when a tongue-depresser was approached in front of it by the examiner. In two of them, their mouth also opened when its corner was stroked by a tongue-depressor. They could not control these phenomena at all, even they were asked not to open their mouth. We would like to call these phenomena "forced mouth opening reactions" because they were uncontrollable voluntarily. They may be divided into two groups, i.e. visual and tactile "forced mouth opening reactions". In all the patients the neurological, neuro-imaging and neuropathological data showed that the frontal lobes were damaged. Additionally, they had some frontal lobe release signs such as forced grasping, forced groping, or alien limb sign. We would like to apply the mechanism for these release signs to the "forced mouth opening reactions". Thus, we speculate that the frontal lobe contains a higher motor control mechanism for normal mouth opening movement, and the "forced mouth opening reactions" result from impairment of this control. PMID:9248334

Ohkawa, S; Yamasaki, H; Yoshida, T; Ohsumi, Y; Tabuchi, M

1997-04-01

86

Buoyant plumes with inertial and chemical reaction-driven forcing  

Science.gov (United States)

Plumes are formed when a continuous buoyant forcing is supplied at a localized source. Buoyancy can be created by either a heat flux, a compositional difference between the fluid coming from the source and its surroundings, or a combination of both. In this thesis, two types of laminar plumes with different forcing mechanisms were investigated: forced plumes and autocatalytic plumes. The forced plumes were compositionally buoyant and were injected with inertial forcing into a fluid filled tank. The autocatalytic plumes were produced without mechanical forcing by buoyancy that was entirely the consequence of a nonlinear chemical reaction -- the iodate-arsenous acid (IAA) reaction. This reaction propagates as a reacting front and produces buoyancy by its exothermicity, and by the compositional difference between the reactant and product. Both the forced and autocatalytic plumes were examined in starting and steady states. The starting, or transient, state of the plume occurs when it initially rises through a fluid and develops a plume head on top of a trailing conduit. The steady state emerges after the plume head has risen to the top of a fluid filled tank leaving only a persistent conduit. Plume behaviour was studied through experimentation, simulation, and by using simple theoretical analysis. We performed the first ever study of plumes as they crossed over the transition between buoyancy-driven to momentum-driven flow. Regardless of the driving mechanism, forced plumes were found to exhibit a single power law relationship that explains their ascent velocity. However, the morphology of the plume heads was found to depend on the dominating driving mechanism. Confined heads were produced by buoyancy-driven plumes, and dispersed heads by momentum-driven plumes. Autocatalytic plumes were found to have rich dynamics that are a consequence of the interplay between fluid flow and chemical reaction. These plumes produced accelerating heads that detached from the conduit, forming free vortex rings. A second-generation head would then develop at the point of detachment. The detachment process for plumes was sensitively dependent on small fluctuations in their initial formation. In some cases, head detachment could occur multiple times for a single experimental run, thereby producing several generations of autocatalytic vortex rings. Head detachment was reproduced and studied using autocatalytic plume simulations. Autocatalytic flame balls, a phenomenon closely related to autocatalytic plumes, were also simulated. Flame balls were found to have three dynamical regimes. Below a critical radius, the smallest flame balls experienced front death. Above this radius, they formed elongating, reacting tails. The largest flame balls formed filamentary tails unable to sustain a reaction.

Rogers, Michael C.

87

Quantum Vacuum and Inertial Reaction Force in Nonrelativistic QED  

CERN Document Server

The possible connection between the electromagnetic zero-point field (ZPF) and the inertia reaction force was first pointed out by Haisch, Rueda, and Puthoff (Phys. Rev. A, 49, 678, 1994), and then by Rueda and Haisch following a totally different and more satisfactory approach (Found. Phys., 28, 1057, 1998; Phys. Letters A, 240, 115, 1998; Annalen der Physik, 10 (5), 393, 2001). In the present paper, the approach taken by Rueda and Haisch will be followed, but the analysis will be done within a formulation that uses nonrelativistic quantum electrodynamics with the creation and annihilation operators rather than the approach of Rueda and Haisch using stochastic electrodynamics. We analyze the interaction between the zero-point field and an object under hyperbolic motion (constant proper acceleration), and find that there arises a reaction force which is proportional in magnitude, and opposite in direction, to the acceleration. This is suggestive of what we know as inertia. We also point out that the equivalen...

Sunahata, Hiroki; Haisch, Bernard

2013-01-01

88

The intersection of interfacial forces and electrochemical reactions.  

Science.gov (United States)

We review recent developments in experimental techniques that simultaneously combine measurements of the interaction forces or energies between two extended surfaces immersed in electrolyte solutions-primarily aqueous-with simultaneous monitoring of their (electro)chemical reactions and controlling the electrochemical surface potential of at least one of the surfaces. Combination of these complementary techniques allows for simultaneous real time monitoring of angstrom level changes in surface thickness and roughness, surface-surface interaction energies, and charge and mass transferred via electrochemical reactions, dissolution, and adsorption, and/or charging of electric double layers. These techniques employ the surface forces apparatus (SFA) combined with various "electrochemical attachments" for in situ measurements of various physical and (electro)chemical properties (e.g., cyclic voltammetry), optical imaging, and electric potentials and currents generated naturally during an interaction, as well as when electric fields (potential differences) are applied between the surfaces and/or solution-in some cases allowing for the chemical reaction equation to be unambiguously determined. We discuss how the physical interactions between two different surfaces when brought close to each other (<10 nm) can affect their chemistry, and suggest further extensions of these techniques to biological systems and simultaneous in situ spectroscopic measurements for chemical analysis. PMID:24229092

Israelachvili, Jacob N; Kristiansen, Kai; Gebbie, Matthew A; Lee, Dong Woog; Donaldson, Stephen H; Das, Saurabh; Rapp, Michael V; Banquy, Xavier; Valtiner, Markus; Yu, Jing

2013-12-27

89

(Environmental investigation of ground water contamination at Wright-Patterson Air Force Base, Ohio)  

Energy Technology Data Exchange (ETDEWEB)

This report presents information related to the sampling of ground water at the Wright-Patterson Air Force Base. It is part of an investigation into possible ground water contamination. Information concerns well drilling/construction; x-ray diffraction and sampling; soil boring logs; and chain-of-custody records.

1992-03-01

90

Forced thermal cycling of catalytic reactions: experiments and modelling  

DEFF Research Database (Denmark)

Recent studies of catalytic reactions subjected to fast forced temperature oscillations have revealed a rate enhancement increasing with temperature oscillation frequency. We present detailed studies of the rate enhancement up to frequencies of 2.5 Hz. A maximum in the rate enhancement is observed at about 1 Hz. A model for the rate enhancement that includes the surface kinetics and the dynamic partial pressure variations in the reactor is introduced. The model predicts a levelling off of the rate enhancement with frequency at about 1 Hz. The experimentally observed decrease above 1 Hz is explained by dynamic thermal limitations of the reactor. (c) 2007 Elsevier B.V. All rights reserved.

Jensen, SØren; Olsen, Jakob Lind

2007-01-01

91

Fore-Aft Ground Force Adaptations to Induced Forelimb Lameness in Walking and Trotting Dogs  

Science.gov (United States)

Animals alter their locomotor mechanics to adapt to a loss of limb function. To better understand their compensatory mechanisms, this study evaluated the changes in the fore-aft ground forces to forelimb lameness and tested the hypothesis that dogs unload the affected limb by producing a nose-up pitching moment via the exertion of a net-propulsive force when the lame limb is on the ground. Seven healthy Beagles walked and trotted at steady speed on an instrumented treadmill while horizontal force data were collected before and after a moderate lameness was induced. Peak, mean and summed braking and propulsive forces as well as the duration each force was exerted and the time to reach maximum force were evaluated for both the sound and the lame condition. Compared with the sound condition, a net-propulsive force was produced by the lame diagonal limbs due to a reduced braking force in the affected forelimb and an increased propulsive force in the contralateral hindlimb when the dogs walked and trotted. To regain pitch stability and ensure steady speed for a given locomotor cycle, the dogs produced a net-braking force when the sound diagonal limbs were on the ground by exerting greater braking forces in both limbs during walking and additionally reducing the propulsive force in the hindlimb during trotting. Consistent with the proposed mechanism, dogs maximize their double support phases when walking. Likely associated with the fore-aft force adaptations to lameness are changes in muscle recruitment that potentially result in short- and long-term effects on the limb and trunk muscles. PMID:23300614

Abdelhadi, Jalal; Wefstaedt, Patrick; Nolte, Ingo; Schilling, Nadja

2012-01-01

92

The ( overlinep, n?) ground state reaction in a relativistic framework  

Science.gov (United States)

A DWBA calculation for the 16O( overlinep, n? +) 16O( g.s.) reaction is presented. The calculation is done using the Dirac equation for the proton and neutron distortions. The LLEE effect on the production vertex is considered. Observables are predicted to be measurable with the present generation of machines. Information on the NN? vertex and reaction mechanism should be cleanly obtained.

Cooper, E. D.; Hicks, K. H.; Jennings, B. K.

1987-08-01

93

Decrease of reaction force of metal gaskets just after initial tightening  

International Nuclear Information System (INIS)

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

94

Understanding chemical binding using the Berlin function and the reaction force  

Science.gov (United States)

We use the derivative of the electron density with respect to the reaction coordinate, interpreted through the Berlin binding function, to identify portions of the reaction path where chemical bonds are breaking and forming. The results agree with the conventional description for SN2 reactions, but they are much more general and can be used to elucidate other types of reactions also. Our analysis offers support for, and detailed information about, the use of the reaction force profile to separate the reaction coordinates into intervals, each with characteristic extents of geometry change and electronic rearrangement.

Chakraborty, Debajit; Cárdenas, Carlos; Echegaray, Eleonora; Toro-Labbe, Alejandro; Ayers, Paul W.

2012-06-01

95

(Environmental investigation of ground water contamination at Wright-Patterson Air Force Base, Ohio)  

Energy Technology Data Exchange (ETDEWEB)

This Removal Action System Design has been prepared as a Phase I Volume for the implementation of the Phase II removal action at Wright-Patterson Air Force Base (WPAFB) near Dayton, Ohio. The objective of the removal action is to prevent, to the extent practicable, the migration of ground water contaminated with chlorinated volatile organic compounds (VOCS) across the southwest boundary of Area C. The Phase 1, Volume 9 Removal Action System Design compiles the design documents prepared for the Phase II Removal Action. These documents, which are presented in Appendices to Volume 9, include: Process Design, which presents the 30 percent design for the ground water treatment system (GWTS); Design Packages 1 and 2 for Earthwork and Road Construction, and the Discharge Pipeline, respectively; no drawings are included in the appendix; Design Package 3 for installation of the Ground Water Extraction Well(s); Design Package 4 for installation of the Monitoring Well Instrumentation; and Design Package 5 for installation of the Ground Water Treatment System; this Design Package is incorporated by reference because of its size.

1992-04-01

96

[Environmental investigation of ground water contamination at Wright-Patterson Air Force Base, Ohio  

International Nuclear Information System (INIS)

The Phase I, Task 5, Focused Feasibility Study (FFS) has been prepared as part of the Environmental Investigation of Ground Water Contamination Project being conducted by Wright-Patterson Air Force Base (WPAFB). The primary objective of this FFS was to select a cost-effective method of preventing migration of contaminated ground water across the southwestern boundary of Area C of the Base. The FFS presented in this document is a portion of a much larger effort being conducted at WPAFB. The detailed analysis of alternatives for the extraction, treatment, and discharge of contaminated ground water migrating across the southwest boundary of Area C at WPAFB led to the selection of a preferred removal action alternative. Specifically, this alternative is that ground water be extracted utilizing a three well array pumping at a total of 400 to 800 gpm, removed water be treated via air stripping to achieve appropriate effluent concentrations, and treated water be discharged to the Mad River in accordance with a National Pollution Discharge Elimination System (NPDES) permit and other relevant permits

97

Resonance tongues and patterns in periodically forced reaction-diffusion systems  

CERN Document Server

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.

Lin, A L; Meron, E; Swinney, H L; Lin, Anna L.; Hagberg, Aric; Meron, Ehud; Swinney, Harry L.

2004-01-01

98

(Environmental investigation of ground water contamination at Wright- Patterson Air Force Base, Ohio)  

Energy Technology Data Exchange (ETDEWEB)

This Health and Safety Plan (HSP) was developed for the Environmental Investigation of Ground-water Contamination Investigation at Wright-Patterson Air Force Base near Dayton, Ohio, based on the projected scope of work for the Phase 1, Task 4 Field Investigation. The HSP describes hazards that may be encountered during the investigation, assesses the hazards, and indicates what type of personal protective equipment is to be used for each task performed. The HSP also addresses the medical monitoring program, decontamination procedures, air monitoring, training, site control, accident prevention, and emergency response.

1991-10-01

99

Theoretical study of cytosine deamination from the perspective of the reaction force analysis.  

Science.gov (United States)

A theoretical study of two different mechanisms for the spontaneous deamination of cytosine is presented. In the first mechanism, a tetrahedral intermediate results in a two-step mechanism whereas in the second one, it is the result of a concerted step. In this work a link is made between the two pathways through the study of the evolution along the reaction coordinates of chemical concepts such as chemical potential, hardness and electronic populations within the framework of the reaction force analysis. The reaction force profile suggests that the concerted mechanism is composed of two asynchronous events. The observation of the reaction force profile appears as an easy way to identify asynchronous concerted steps and as a privileged tool to study the more or less asynchronous character of chemical reactions. PMID:18928267

Labet, Vanessa; Morell, Christophe; Grand, André; Toro-Labbé, Alejandro

2008-11-13

100

Forcing factors of cloud-to-ground lightning over Iberia: regional-scale assessments  

Directory of Open Access Journals (Sweden)

Full Text Available Cloud-to-ground lightning in a sector covering the Iberian Peninsula, the Balearic Islands and nearby seas (36–44° N, 10° W–5° E is analysed in the period from 2003 to 2009 (7 yr. Two Iberian lightning detection networks, composed of 18 sensors over Portugal and Spain, are combined for the first time in the present study. The selected characteristics are cloud-to-ground flashes (CGFs, first stroke peak current, polarity and multiplicity (number of strokes in a given flash. This study examines the temporal (on hourly, monthly and seasonal timescales and spatial variability of CGFs. The influence of five forcing factors on lightning (elevation, lifted index, convective available potential energy and daily minimum and maximum near-surface air temperatures over the Iberian sector is also assessed. For regional-scale assessments, six subsectors with different climatic conditions were analysed separately. Despite important regional differences, the strongest lightning activity occurs from late spring to early autumn, and mostly in the afternoon. Furthermore, CGFs are mainly located over high-elevation areas in late spring to summer, while they tend to occur over the sea in autumn. The results suggest that (1 orographically forced thunderstorms over mountainous areas, mostly from May to September, (2 tropospheric buoyancy forcing over western-central and northern regions in summer and over the Mediterranean regions in autumn, and (3 near-surface thermal contrasts from October to February largely control the location of lightning in Iberia. There is no evidence of different forcings by polarity. A clear correspondence between summertime precipitation patterns and CGFs is also found.

J. A. Santos

2013-07-01

 
 
 
 
101

Finite range effect in deuteron stripping reaction using realistic forces  

International Nuclear Information System (INIS)

An attempt is made to calculate the finite range effect in the DWBA theory for the A(d,p)B reaction using a realistic potential for the deuteron. Both S and D states are taken into consideration and a method is used to treat the hard core in the N-N interaction. The effect is shown to be energy and angle dependent and a comparison is made with previous results. (auth.)

102

The (p, n) reaction and the nucleon-nucleon force  

International Nuclear Information System (INIS)

The (p, n) charge exchange reaction is a powerful tool of nuclear structure physics, with spectroscopic characteristics that are closely related to the free interaction between nucleons. At proton energies in the range of 150-500 MeV, the interaction probes the spin dynamics in the charge exchange process and is particularly sensitive to nuclear pionic fields. At low energies, say less than 50 MeV bombarding energy, the reaction also probes the isovector density. An outstanding success of the reaction as a structural probe is the elucidation of the Gamow-Teller strength function in the nuclear excitation spectrum. However, the total strength found falls short of sum rule predictions by about 40%. Explanations of this quenching have been advanced along two lines, based on subnuclear degrees of freedom or on configuration mixing into high continuum states. Detailed theoretical arguments support the importance of configuration mixing. The subnuclear degrees of freedom may be comparable, but a decisive test is lacking. (author)

103

Probing the 8He ground state via the 8He(p,t)6He reaction  

International Nuclear Information System (INIS)

The weakly-bound 8He nucleus exhibits a neutron halo or thick neutron skin and is generally considered to have an ?+4n structure in its ground state, with the four valence neutrons each occupying 1p3/2 states outside the ? core. The 8He(p,t)6He reaction is a sensitive probe of the ground state structure of 8He, and we present a consistent analysis of new and existing data for this reaction at incident energies of 15.7 and 61.3A MeV, respectively. Our results are incompatible with the usual assumption of a pure (1p3/2)4 structure and suggest that other configurations such as (1p3/2)2(1p1/2)2 may be present with significant probability in the ground state wave function of 8He

104

Deterministic reaction models with power-law forces  

Energy Technology Data Exchange (ETDEWEB)

We study a one-dimensional particles system, in the overdamped limit, where nearest particles attract with a force inversely proportional to a power {alpha} of their distance and coalesce upon encounter. The detailed shape of the distribution function for the gap between neighbouring particles serves to discriminate between different laws of attraction. We develop an exact Fokker-Planck approach for the infinite hierarchy of distribution functions for multiple adjacent gaps and solve it exactly, at the mean-field level, where correlations are ignored. The crucial role of correlations and their effect on the gap distribution function is explored both numerically and analytically. Finally, we analyse a random input of particles, which results in a stationary state where the effect of correlations is largely diminished.

Ben-Avraham, Daniel; Gromenko, Oleksandr [Physics Department, Clarkson University, Potsdam, NY 13699-5820 (United States); Politi, Paolo [Istituto dei Sistemi Complessi, Consiglio Nazionale delle Ricerche, Via Madonna del Piano 10, 50019 Sesto Fiorentino (Italy)], E-mail: benavraham@clarkson.edu, E-mail: gromenko@clarkson.edu, E-mail: paolo.politi@isc.cnr.it

2009-12-11

105

Influence of Muscle-Tendon Wrapping on Calculations of Joint Reaction Forces in the Equine Distal Forelimb  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The equine distal forelimb is a common location of injuries related to mechanical overload. In this study, a two-dimensional model of the musculoskeletal system of the region was developed and applied to kinematic and kinetic data from walking and trotting horses. The forces in major tendons and joint reaction forces were calculated. The components of the joint reaction forces caused by wrapping of tendons around sesamoid bones were found to be of similar magnitude to the reaction forces betw...

Pandy, Marcus G.; Colin Burvill; Davies, Helen M. S.; Merritt, Jonathan S.

2008-01-01

106

LightForce: Orbital collision avoidance using ground-based laser induced photon pressure  

Science.gov (United States)

We propose to employ small orbit perturbations, induced by photon pressure from ground-based laser illumination, for collision avoidance in space. Possible applications would be a) protecting space assets from impacts with debris and b) stabilizing the orbital debris environment. In comparison to schemes aimed at de-orbiting debris using laser ablation, collision avoidance requires much less force and hence needs less sophisticated laser/telescope systems. In earlier research we concluded that a system consisting of a 10kW class laser, directed by a 1.5m telescope with adaptive optics, could avoid a significant fraction of collisions in low earth orbit. This paper describes our recent efforts which include refining our original analysis, employing higher fidelity simulations and presenting our planned experimental approach.

Stupl, Jan; Mason, James; Marshall, William; Levit, Creon; Smith, Craig; Olivier, Scot; Pertica, Alex; De Vries, Wim

2012-07-01

107

Influence of minimally invasive total hip replacement on hip reaction forces and their orientations.  

Science.gov (United States)

Minimally invasive surgery (MIS) is becoming increasingly popular. Supporters claim that the main advantages of MIS total hip replacement (THR) are less pain and a faster rehabilitation and recovery. Critics claim that safety and efficacy of MIS are yet to be determined. We focused on a biomechanical comparison between surgical standard and MIS approaches for THR during the early recovery of patients. A validated, parameterized musculoskeletal model was set to perform a squat of a 50th percentile healthy European male. A bilateral motion was chosen to investigate effects on the contralateral side. Surgical approaches were simulated by excluding the incised muscles from the computations. Resulting hip reaction forces and their symmetry and orientation were analyzed. MIS THR seemed less influential on the symmetry index of hip reaction forces between the operated and nonoperated leg when compared to the standard lateral approach. Hip reaction forces at peak loads of the standard transgluteal approach were 24% higher on the contralateral side when compared to MIS approaches. Our results suggest that MIS THR contributes to a greater symmetry of hip reaction forces in absolute value as well as force-orientation following THR. © 2014 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:1680-1687, 2014. PMID:25125147

Weber, Tim; Al-Munajjed, Amir A; Verkerke, Gijsbertus J; Dendorfer, Sebastian; Renkawitz, Tobias

2014-12-01

108

An Analysis of the Pressures, Forces and Moments Induced by the Ground Vortex Generated by a Single Impinging Jet  

Science.gov (United States)

When a jet STOVL aircraft is in STOL operation the jets impinge on the ground and generate wall jets flowing radially outward from the points at which the jets impinge. When the forward flowing part of a wall jet meets the free stream flow it is rolled back on itself forming a parabolic shaped ground vortex. Positive pressures are induced on the lower surface of the configuration ahead of the ground vortex and suction pressures are induced over the ground vortex itself. In addition, the suction pressures induced aft of the jet out of ground effect are reduced and lifting pressures are induced on the upper surface. This study analyzes available pressure and force data and develops a method for estimating the forces and moments induced in ground effect. The method includes the effects of configuration variables, height and operating conditions, as well as the effects of the location, deflection and shape of the jet. However, it is limited to single jets at subcritical nozzle pressure ratios. An analysis of the effects of moving over the ground vs. tests over a fixed ground plane is included.

Kuhn, Richard E.

1997-01-01

109

Calculations of three-nucleon reactions with N3LO chiral forces: achievements and challenges  

Science.gov (United States)

We discuss the application of the chiral N3LO forces to three-nucleon reactions and point to the challenges which will have to be addressed. Present approaches to solve three-nucleon Faddeev equations are based on a partial-wave decomposition. A rapid increase of the number of terms contributing to the chiral three-nucleon force when increasing the order of the chiral expansion from N2LO to N3LO forced us to develop a fast and effective method of automatized partial-wave decomposition. At low energies of the incoming nucleon below ?20 MeV, where only a limited number of partial waves is required, this method allowed us to perform calculations of reactions in the three-nucleon continuum using N3LO two- and three-nucleon forces. It turns out that inclusion of consistent chiral interactions, with relativistic 1/m corrections and short-range 2?-contact term omitted in the N3LO three-nucleon force, does not explain the long standing low energy Ay-puzzle. We discuss problems arising when chiral forces are applied at higher energies, where large three-nucleon force effects are expected. It seems plausible that at higher energies, due to a rapid increase of a number of partial waves required to reach convergent results, a three-dimensional formulation of the Faddeev equations which avoids partial-wave decomposition is desirable.

Wita?a, H.; Golak, J.; Skibi?ski, R.; Topolnicki, K.

2014-09-01

110

Using the reaction force and the reaction electronic flux on the proton transfer of formamide derived systems.  

Science.gov (United States)

In this work, we present a theoretical study of the mechanism of double proton transfer in formamide, formamide-thioformamide and thioformamide dimers. The reaction mechanisms were analyzed in terms of the energy profile and novel concepts such as the reaction force profile and reaction electronic flux, along with local electronic properties such as NBO analysis. All systems were characterized computationally using DFT/B3LYP 6-311G** on Gaussian09. These results show that the electronic processes take place mostly in the transition state for all the systems; in the formamide and thioformamide dimers, electron transfer has a synchronic nature, while the electron transfer is asynchronic in the formamide-thioformamide dimer. PMID:24618654

Inostroza-Rivera, Ricardo; Herrera, Bárbara; Toro-Labbé, Alejandro

2014-07-28

111

Complementarity of reaction force and electron localization function analyses of asynchronicity in bond formation in Diels-Alder reactions.  

Science.gov (United States)

We have computationally compared three Diels-Alder cycloadditions involving cyclopentadiene and substituted ethylenes; one of the reactions is synchronous, while the others are slightly or highly asynchronous. Synchronicity and weak asynchronicity are characterized by the reaction force constant ?(?) having just a single minimum in the transition region along the intrinsic reaction coordinate ?, while for high asynchronicity ?(?) has a negative maximum with minima on both sides. The electron localization function (ELF) shows that the features of ?(?) can be directly related to the formation of the new C-C bonds between the diene and the dienophile. There is thus a striking complementarity between ?(?) and ELF; ?(?) identifies the key points along ? and ELF describes what is happening at those points. PMID:24589878

Yepes, Diana; Murray, Jane S; Pérez, Patricia; Domingo, Luis R; Politzer, Peter; Jaque, Pablo

2014-04-14

112

Calculations of three-nucleon reactions with N3LO chiral forces: achievements and challenges  

CERN Document Server

We discuss the application of the chiral N3LO forces to three-nucleon reactions and point to the challenges which will have to be addressed. Present approaches to solve three-nucleon Faddeev equations are based on a partial-wave decomposition. A rapid increase of the number of terms contributing to the chiral three-nucleon force when increasing the order of the chiral expansion from N2LO to N3LO forced us to develop a fast and effective method of automatized partial wave decomposition. At low energies of the incoming nucleon below about 20MeV, where only a limited number of partial waves is required, this method allowed us to perform calculations of reactions in the three-nucleon continuum using N3LO two- and three-nucleon forces. It turns out that inclusion of consistent chiral interactions, with relativistic 1/m corrections and short-range 2pi-contact term omitted in the N3LO three-nucleon force, does not explain the long standing low energy Ay-puzzle. We discuss problems arising when chiral forces are appl...

Witala, Henryk; Skibinski, Roman; Topolnicki, Kacper

2013-01-01

113

The mechanism of chemisorption of hydrogen atom on graphene: Insights from the reaction force and reaction electronic flux  

Science.gov (United States)

At the PBE-D3/cc-pVDZ level of theory, the hydrogen chemisorption on graphene was analyzed using the reaction force and reaction electronic flux (REF) theories in combination with electron population analysis. It was found that chemisorption energy barrier is mainly dominated by structural work (˜73%) associated to the substrate reconstruction whereas the electronic work is the greatest contribution of the reverse energy barrier (˜67%) in the desorption process. Moreover, REF shows that hydrogen chemisorption is driven by charge transfer processes through four electronic events taking place as H approaches the adsorbent surface: (a) intramolecular charge transfer in the adsorbent surface; (b) surface reconstruction; (c) substrate magnetization and adsorbent carbon atom develops a sp3 hybridization to form the ?C-H bond; and (d) spontaneous intermolecular charge transfer to reach the final chemisorbed state.

Cortés-Arriagada, Diego; Gutiérrez-Oliva, Soledad; Herrera, Bárbara; Soto, Karla; Toro-Labbé, Alejandro

2014-10-01

114

The mechanism of chemisorption of hydrogen atom on graphene: Insights from the reaction force and reaction electronic flux.  

Science.gov (United States)

At the PBE-D3/cc-pVDZ level of theory, the hydrogen chemisorption on graphene was analyzed using the reaction force and reaction electronic flux (REF) theories in combination with electron population analysis. It was found that chemisorption energy barrier is mainly dominated by structural work (?73%) associated to the substrate reconstruction whereas the electronic work is the greatest contribution of the reverse energy barrier (?67%) in the desorption process. Moreover, REF shows that hydrogen chemisorption is driven by charge transfer processes through four electronic events taking place as H approaches the adsorbent surface: (a) intramolecular charge transfer in the adsorbent surface; (b) surface reconstruction; (c) substrate magnetization and adsorbent carbon atom develops a sp(3) hybridization to form the ?C-H bond; and (d) spontaneous intermolecular charge transfer to reach the final chemisorbed state. PMID:25296822

Cortés-Arriagada, Diego; Gutiérrez-Oliva, Soledad; Herrera, Bárbara; Soto, Karla; Toro-Labbé, Alejandro

2014-10-01

115

Assessment of ground-water contamination at Wurtsmith Air Force Base, Michigan, 1982-85  

Science.gov (United States)

Study of ground-water contamination at Wurtsmith Air Force Base, Michigan, defined the movement and distribution of volatile organic compounds in the glacial sand and gravel aquifer at known sites of contamination, and has defined new plumes at two other sites. The Arrow Street purge system, installed in 1982 to remove contaminants from the Building 43 plume, has lowered concentrations of trichloroethylene (TCE) in groundwater in the central part of the most contaminated area from a range of 1,000 to 2,000 microg/L to about 200 microg/L. TCE is not escaping off-Base from this area. In the southern part of the Base a plume containing principally TCE and dichloroethylene (DCE) has been delineated along Mission Drive. Maximum concentrations observed were 3,290 microg/L of TCE and 1,480 microg/L of DCE. Hydrologically suitable sites for purge wells were identified in the southern part of the plume using a new ground-water flow model of the Base. A benzene plume near the bulk-fuel storage area has shifted to a more northerly direction under influence of the Arrow Street purge system. Sites initially identified for purging the benzene plume have been repositioned because of the change in contaminant movement. JP-4 fuel was found to be accumulating in wells near the bulk-fuel storage area, largely in response to seasonal fluctuations in the water-table. It is thought to originate from a spill that occurred several years ago. In general, concentrations found in water do not differ greatly from those observed in 1981. Since 1981, concentrations of TCE have decreased significantly in the Alert Apron plume. Near the origin of the plume, the concentration of TCE has decreased from 1,000 microg/L in 1980 to 50 microg/L in 1984. Water from Van Etten Lake near the termination of the plume had only a trace of TCE at one site. Benzene detected in water from well AF2 seems to originate near the former site of buried fuel tanks west of the operational apron. During periods of normal purge pumping along Arrow Street, contaminants are drawn toward water-supply wells AF2, AF4, and AF5. (Author 's abstract)

Cummings, T.R.; Twenter, F.R.

1986-01-01

116

Calculated photon reactions on the ground and isomeric states of 236,237Np  

International Nuclear Information System (INIS)

We calculated photon-induced reactions on the 1.1 x 105-y ground state (gs) and 22.5-h isomer of 236Np and on the 2.1 x 106-y gas and 68-ns isomer of 237Np. We investigated the production of the short-lived isomer of 236Np, leading eventually to the high-energy gamma-ray emitter, 208Pb, via the (n,2n) as well as the (gamma,n) reactions on 237Np. Our results show that irradiation of the gs tends to produce primarily the isomer whereas photons hardly destroy the isomer at all. The use of photoexcitation and destruction of nuclear isomers in the field of nuclear waste disposal will be discussed

117

Influence of Muscle-Tendon Wrapping on Calculations of Joint Reaction Forces in the Equine Distal Forelimb  

Directory of Open Access Journals (Sweden)

Full Text Available The equine distal forelimb is a common location of injuries related to mechanical overload. In this study, a two-dimensional model of the musculoskeletal system of the region was developed and applied to kinematic and kinetic data from walking and trotting horses. The forces in major tendons and joint reaction forces were calculated. The components of the joint reaction forces caused by wrapping of tendons around sesamoid bones were found to be of similar magnitude to the reaction forces between the long bones at each joint. This finding highlighted the importance of taking into account muscle-tendon wrapping when evaluating joint loading in the equine distal forelimb.

Marcus G. Pandy

2008-05-01

118

Time-dependent quantum wave packet dynamics of S + OH reaction on its electronic ground state.  

Science.gov (United States)

Initial state-selected dynamics of the S((3)P) + OH (X(2)?) ? SO (X(3)?(-)) + H ((2)S) reaction on its electronic ground potential energy surface (X?(2)A") is investigated here by a time-dependent wave packet propagation (TDWP) approach. Total reaction probabilities for the three-body rotational angular momentum up to J = 138 are calculated to obtain converged integral reaction cross sections and state-specific rate constants employing the centrifugal sudden (CS) approximation. The convergence of the latter quantities is checked by varying all parameters used in the numerical calculations. The cross section and rate constant results are compared with those available in the literature, calculated with the aid of the quasi-classical trajectory method on the same potential energy surface. Reaction probabilities obtained with the TDWP approach exhibit dense oscillatory structures, implying formation of a metastable quasi-bound complex during the collision process. The effect of rotational and vibrational excitations of reagent OH on the dynamical attributes is also examined. While the rotational excitation of reagent OH decreases the reactivity, its vibrational excitation enhances the same. PMID:25010948

Goswami, Sugata; Rao, T Rajagopala; Mahapatra, S; Bussery-Honvault, B; Honvault, P

2014-08-01

119

Effects of brain polarization on reaction times and pinch force in chronic stroke  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract Background Previous studies showed that anodal transcranial DC stimulation (tDCS applied to the primary motor cortex of the affected hemisphere (M1affected hemisphere after subcortical stroke transiently improves performance of complex tasks that mimic activities of daily living (ADL. It is not known if relatively simpler motor tasks are similarly affected. Here we tested the effects of tDCS on pinch force (PF and simple reaction time (RT tasks in patients with chronic stroke in a double-blind cross-over Sham-controlled experimental design. Results Anodal tDCS shortened reaction times and improved pinch force in the paretic hand relative to Sham stimulation, an effect present in patients with higher impairment. Conclusion tDCS of M1affected hemisphere can modulate performance of motor tasks simpler than those previously studied, a finding that could potentially benefit patients with relatively higher impairment levels.

Giraux Pascal

2006-11-01

120

33 CFR 334.710 - The Narrows and Gulf of Mexico adjacent to Santa Rosa Island, Air Force Proving Ground Command...  

Science.gov (United States)

...2010-07-01 2010-07-01 false The Narrows and Gulf of Mexico adjacent to Santa Rosa Island, Air Force Proving Ground Command, Eglin...REGULATIONS § 334.710 The Narrows and Gulf of Mexico adjacent to Santa Rosa Island, Air Force Proving Ground Command,...

2010-07-01

 
 
 
 
121

Force Limiting Vibration Tests Evaluated from both Ground Acoustic Tests and FEM Simulations of a Flight Like Vehicle System Assembly  

Science.gov (United States)

Marshall Space Flight Center has conducted a series of ground acoustic tests with the dual goals of informing analytical judgment, and validating analytical methods when estimating vibroacoustic responses of launch vehicle subsystems. The process of repeatedly correlating finite element-simulated responses with test-measured responses has assisted in the development of best practices for modeling and post-processing. In recent work, force transducers were integrated to measure interface forces at the base of avionics box equipment. Other force data was indirectly measured using strain gauges. The combination of these direct and indirect force measurements has been used to support and illustrate the advantages of implementing the Force Limiting approach for equipment qualification tests. The comparison of force response from integrated system level tests to measurements at the same locations during component level vibration tests provides an excellent illustration. A second comparison of the measured response cases from the system level acoustic tests to finite element simulations has also produced some principles for assessing the suitability of Finite Element Models (FEMs) for making vibroacoustics estimates. The results indicate that when FEM models are employed to guide force limiting choices, they should include sufficient detail to represent the apparent mass of the system in the frequency range of interest.

Smith, Andrew; LaVerde, Bruce; Waldon, James; Hunt, Ron

2014-01-01

122

Analysis of balance, rapidity, force and reaction times of soccer players at different levels of competition.  

Science.gov (United States)

In the present study we analyzed 12 physical parameters, namely force, static and dynamic balance (both quantified by means of 4 parameters each), rapidity, visual reaction times and acoustic reaction times, over 185 subjects. 170 of them played soccer in teams enrolled in all the ten different Italian soccer leagues. Results show that 6 parameters (out of the 12 analyzed) permit to identify and discriminate top-level players, among those showing the same training frequency. The other parameters are strictly related to training frequency or do not discriminate among players or control subjects (non-athletes), such as visual and acoustic reaction times. Principal component analysis permits to identify 4 clusters of subjects with similar performances, thus representing a useful instrument to characterize the overall ability of players in terms of athletic characteristics, on the basis of their location on the principal component parameters plane. PMID:24130870

Ricotti, Leonardo; Rigosa, Jacopo; Niosi, Alberto; Menciassi, Arianna

2013-01-01

123

Hydrogeology and simulation of ground-water flow at Arnold Air Force Base, Coffee and Franklin counties, Tennessee  

Science.gov (United States)

The U.S. Air Force at Arnold Air Force Base (AAFB), in Coffee and Franklin Counties, Tennessee, is investigating ground-water contamination in selected areas of the base. This report documents the results of a comprehensive investigation of the regional hydrogeology of the AAFB area. Three aquifers within the Highland Rim aquifer system, the shallow aquifer, the Manchester aquifer, and the Fort Payne aquifer, have been identified in the study area. Of these, the Manchester aquifer is the primary source of water for domestic use. Drilling and water- quality data indicate that the Chattanooga Shale is an effective confining unit, isolating the Highland Rim aquifer system from the deeper, upper Central Basin aquifer system. A regional ground-water divide, approximately coinciding with the Duck River-Elk River drainage divide, underlies AAFB and runs from southwest to northeast. The general direction of most ground-water flow is to the north- west or to the northwest or to the southeast from the divide towards tributary streams that drain the area. Recharge estimates range from 4 to 11 inches per year. Digital computer modeling was used to simulate and provide a better understanding of the ground-water flow system. The model indicates that most of the ground-water flow occurs in the shallow and Manchester aquifers. The model was most sensitive to increases in hydraulic conductivity and changes in recharge rates. Particle-tracking analysis from selected sites of ground-water contamination indicates a potential for contami- nants to be transported beyond the boundary of AAFB.

Haugh, C. J.; Mahoney, E. N.

1994-01-01

124

Surface/subsurface observation and removal mechanisms of ground reaction bonded silicon carbide  

Science.gov (United States)

Reaction Bonded Silicon Carbide (RBSiC) has long been recognized as a promising material for optical applications because of its unique combination of favorable properties and low-cost fabrication. Grinding of silicon carbide is difficult because of its high hardness and brittleness. Grinding often induces surface and subsurface damage, residual stress and other types of damage, which have great influence on the ceramic components for optical application. In this paper, surface integrity, subsurface damage and material removal mechanisms of RBSiC ground using diamond grinding wheel on creep-feed surface grinding machine are investigated. The surface and subsurface are studied with scanning electron microscopy (SEM) and optical microscopy. The effects of grinding conditions on surface and subsurface damage are discussed. This research links the surface roughness, surface and subsurface cracks to grinding parameters and provides valuable insights into the material removal mechanism and the dependence of grind induced damage on grinding conditions.

Yao, Wang; Zhang, Yu-Min; Han, Jie-cai; Zhang, Yun-long; Zhang, Jian-han; Zhou, Yu-feng; Han, Yuan-yuan

2006-01-01

125

Low-energy neutron-deuteron reactions with N3LO chiral forces  

CERN Document Server

We solve three-nucleon Faddeev equations with nucleon-nucleon and three-nucleon forces derived consistently in the framework of chiral perturbation theory at next-to-next-to-next-to-leading order in the chiral expansion. In this first investigation we include only matrix elements of the three-nucleon force for partial waves with the total two-nucleon (three-nucleon) angular momenta up to 3 (5/2). Low-energy neutron-deuteron elastic scattering and deuteron breakup reaction are studied. Emphasis is put on Ay puzzle in elastic scattering and cross sections in symmetric-space-star and neutron-neutron quasi-free-scattering breakup configurations, for which large discrepancies between data and theory have been reported.

Golak, J; Topolnicki, K; Witala, H; Epelbaum, E; Krebs, H; Kamada, H; Meissner, Ulf-G; Bernard, V; Maris, P; Vary, J; Binder, S; Calci, A; Hebeler, K; Langhammer, J; Roth, R; Nogga, A; Liebig, S; Minossi, D

2014-01-01

126

Comparison of three-dimensional patellofemoral joint reaction forces in persons with and without patellofemoral pain.  

Science.gov (United States)

The purpose of this study was to determine if persons with patellofemoral pain (PFP) exhibit differences in patellofemoral joint reaction forces (PFJRFs) during functional activities. Forty females (20 PFP, 20 controls) underwent two phases of data collection: (1) magnetic resonance imaging (MRI) and (2) biomechanical analysis during walking, running, stair ascent, and stair descent. A previously described three-dimensional model was used to estimate PFJRFs. Resultant PFJRFs and the orthogonal components were reported. The PFP group demonstrated lower peak resultant PFJRFs and posterior component and superior component of the PFJRFs compared with the control group across all conditions. However, the PFP group had a higher peak lateral component of the PFJRF in three out of the four conditions evaluated. The lower resultant PFJRFs suggested that individuals with PFP may employ strategies to minimize patellofemoral joint loading, but it did not result in diminished lateral forces acting on the patella. PMID:24603612

Chen, Yu-Jen; Powers, Christopher M

2014-08-01

127

Fluctuation-induced self-force and violation of action-reaction in a nonequilibrium steady state fluid  

Energy Technology Data Exchange (ETDEWEB)

We show that the fluctuations of a fluid driven out of equilibrium can induce a net force on a single asymmetric object immersed in it. The force originates in the restriction of the fluid's fluctuations at the object's boundaries, as in the Casimir effect. In contrast to the equilibrium situation, its emergence on a single obstacle is not ruled out by the second law of thermodynamics since the fluid is in a nonequilibrium state. We explicitly calculate this self-force on a deformed circle embedded in a fluid whose density fluctuations obey a stochastic reaction-diffusion equation. When two objects are considered, the presence of self-forces can violate the action-reaction principle. We illustrate this by calculating the internal Casimir-type forces between a circle and a plate. Their sum, instead of vanishing, provides the self-force exerting on the circle-plate assembly.

Buenzli, Pascal R, E-mail: pbuenzli@dfi.uchile.c [Departamento de Fisica, FCFM, Universidad de Chile, Santiago (Chile)

2009-04-01

128

Fluctuation-induced self-force and violation of action-reaction in a nonequilibrium steady state fluid  

Science.gov (United States)

We show that the fluctuations of a fluid driven out of equilibrium can induce a net force on a single asymmetric object immersed in it. The force originates in the restriction of the fluid's fluctuations at the object's boundaries, as in the Casimir effect. In contrast to the equilibrium situation, its emergence on a single obstacle is not ruled out by the second law of thermodynamics since the fluid is in a nonequilibrium state. We explicitly calculate this self-force on a deformed circle embedded in a fluid whose density fluctuations obey a stochastic reaction-diffusion equation. When two objects are considered, the presence of self-forces can violate the action-reaction principle. We illustrate this by calculating the internal Casimir-type forces between a circle and a plate. Their sum, instead of vanishing, provides the self-force exerting on the circle-plate assembly.

Buenzli, Pascal R.

2009-04-01

129

Fluctuation-induced self-force and violation of action-reaction in a nonequilibrium steady state fluid  

International Nuclear Information System (INIS)

We show that the fluctuations of a fluid driven out of equilibrium can induce a net force on a single asymmetric object immersed in it. The force originates in the restriction of the fluid's fluctuations at the object's boundaries, as in the Casimir effect. In contrast to the equilibrium situation, its emergence on a single obstacle is not ruled out by the second law of thermodynamics since the fluid is in a nonequilibrium state. We explicitly calculate this self-force on a deformed circle embedded in a fluid whose density fluctuations obey a stochastic reaction-diffusion equation. When two objects are considered, the presence of self-forces can violate the action-reaction principle. We illustrate this by calculating the internal Casimir-type forces between a circle and a plate. Their sum, instead of vanishing, provides the self-force exerting on the circle-plate assembly.

130

[Environmental investigation of ground water contamination at Wright-Patterson Air Force Base, Ohio]. Volume 9, Removal action system design  

Energy Technology Data Exchange (ETDEWEB)

This Removal Action System Design has been prepared as a Phase I Volume for the implementation of the Phase II removal action at Wright-Patterson Air Force Base (WPAFB) near Dayton, Ohio. The objective of the removal action is to prevent, to the extent practicable, the migration of ground water contaminated with chlorinated volatile organic compounds (VOCS) across the southwest boundary of Area C. The Phase 1, Volume 9 Removal Action System Design compiles the design documents prepared for the Phase II Removal Action. These documents, which are presented in Appendices to Volume 9, include: Process Design, which presents the 30 percent design for the ground water treatment system (GWTS); Design Packages 1 and 2 for Earthwork and Road Construction, and the Discharge Pipeline, respectively; no drawings are included in the appendix; Design Package 3 for installation of the Ground Water Extraction Well(s); Design Package 4 for installation of the Monitoring Well Instrumentation; and Design Package 5 for installation of the Ground Water Treatment System; this Design Package is incorporated by reference because of its size.

1992-04-01

131

Extraction of ground reaction forces for real-time synthesis of walking sounds  

DEFF Research Database (Denmark)

A shoe-independent system to synthesize real-time footstep sounds on different materials has been developed. A footstep sound is considered as the result of an interaction between an exciter (the shoe) and a resonator (the floor). To achieve our goal, we propose two different solutions. The first solution is based on contact microphones attached on the exterior part of each shoe, which capture the sound of a footstep. The second approach consists on using microphones placed on the floor. In both situations, the captured sound is analysed and used to control a sound synthesis engine. We discuss advantages and disadvantages of the two approaches.

Serafin, Stefania; Turchet, Luca

2009-01-01

132

Study of the ground-state wave function of 6He via the 6He(p, t)? transfer reaction  

International Nuclear Information System (INIS)

We have measured the 6He(p,t)? transfer reaction in inverse kinematics at 25 MeV/nucleon. The data were compared to DWBA calculations in order to extract the spectroscopic amplitudes for ?+2n and t+t configurations in the ground state of 6He. (orig.)

133

[Environmental investigation of ground water contamination at Wright-Patterson Air Force Base, Ohio]. Volume 5, Appendix A, Part 1, Field Investigation report  

Energy Technology Data Exchange (ETDEWEB)

This report presents information related to the sampling of ground water at the Wright-Patterson Air Force Base. It is part of an investigation into possible ground water contamination. Information concerns well drilling/construction; x-ray diffraction and sampling; soil boring logs; and chain-of-custody records.

1992-03-01

134

Novel and Unique Expression for the Radiation Reaction Force, Relevance of Newton's Third Law and Tunneling  

CERN Document Server

We derive the radiation reaction by taking into account that the acceleration of the charge is caused by the interaction with some heavy source particle. In the non relativistic case this leads, in contrast to the usual approach, immediately to a result which is Galilei invariant. Simple examples show that there can be small regions of extremely low velocity where the energy requirements cannot be fulfilled, and which the charged particle can only cross by quantum mechanical tunneling. The relativistic generalization is rather straight forward and leads to a unique result. The force is a four-vector, but only if the presence of the source is taken into account as well. It contains no third derivatives of the position as the Lorentz-Abraham-Dirac equation, and consequently no run away solutions. All examples considered so far give reasonable results.

Gromes, Dieter

2014-01-01

135

EMMI Rapid Reaction Task Force on "Thermalization in Non-abelian Plasmas"  

CERN Document Server

Recently, different proposals have been put forward on how thermalization proceeds in heavy-ion collisions in the idealized limit of very large nuclei at sufficiently high energy. Important aspects of the parametric estimates at weak coupling may be tested using well-established classical-statistical lattice simulations of the far-from-equilibrium gluon dynamics. This has to be confronted with strong coupling scenarios in related theories based on gauge-string dualities. Furthermore, closely related questions about far-from-equilibrium dynamics arise in early-universe cosmology and in non-relativistic systems of ultracold atoms. These were central topics of the EMMI Rapid Reaction Task Force meeting held on December 12-14, 2011, at the University of Heidelberg, which we report on.

Berges, Juergen; Gelis, Francois

2012-01-01

136

EMMI rapid reaction task force on ‘Thermalization in non-Abelian plasmas’  

Science.gov (United States)

Recently, different proposals have been put forward on how thermalization proceeds in heavy-ion collisions in the idealized limit of very large nuclei at sufficiently high energy. Important aspects of the parametric estimates at weak coupling may be tested using well-established classical-statistical lattice simulations of the far-from-equilibrium gluon dynamics. This has to be confronted with strong coupling scenarios in related theories based on gauge-string dualities. Furthermore, closely related questions about far-from-equilibrium dynamics arise in early-universe cosmology and in non-relativistic systems of ultracold atoms. These were central topics of the EMMI Rapid Reaction Task Force meeting held on 12-14 December 2011, at the University of Heidelberg, which we report on. Communicated by Professor Achim Schwenk

Berges, Jürgen; Blaizot, Jean-Paul; Gelis, François

2012-08-01

137

Sudden drop in ground support produces force-related unload response in human overground walking  

DEFF Research Database (Denmark)

Humans maneuver easily over uneven terrain. To maintain smooth and efficient gait the motor system needs to adapt the locomotor output to the walking environment. In the present study we investigate the role of sensory feedback in adjusting the soleus muscle activity during overground walking in 19 healthy volunteers. Subjects walked unrestrained over a hydraulically actuated platform. On random trials the platform was accelerated downward at 0.8 g, unloading the plantar flexor muscles in midstance or late stance. The drop of the platform resulted in a significant depression of the soleus muscle activity of -17.9% (SD 2) and -21.4% (SD 2), with an onset latency of 49 ms (SD 1) and 45 ms (SD 1) in midstance and late stance, respectively. Input to the vestibular apparatus (i.e., the head acceleration) occurred at a latency 10.0 ms (SD 2.4) following the drop and ankle dorsiflexion velocity was decreased starting 22 ms (SD 15) after the drop. To investigate the role of length- and velocity-sensitive afferents onthe depression in soleus muscle activity, the ankle rotation was arrested by using an ankle foot orthotic as the platform was dropped. Preventing the ankle movement did not significantly change the soleus depression in late stance [-18.2% (SD 15)], whereas the depression in midstance was removed [+4.9% (SD 13)]. It is concluded that force feedback from ankle extensors increases the locomotor output through positive feedback in late stance. In midstance the effect of force feedback was not observed, suggesting that spindle afferents may have a more significant effect on the output during this phase of the step cycle.

Af Klint, Richard; Nielsen, Jens Bo

2009-01-01

138

Radiation reaction force induced nonlinear mixing of Raman sidebands of an ultra-intense laser pulse in a plasma  

CERN Document Server

Stimulated Raman scattering of an ultra-intense laser pulse in plasmas is studied by perturbatively including the leading order term of the Landau-Lifshitz radiation reaction force in the equation of motion for plasma electrons. In this approximation, radiation reaction force causes phase shift in nonlinear current densities that drive the two Raman sidebands (anti-Stokes and Stokes waves), manifesting itself into the nonlinear mixing of two sidebands. This mixing results in a strong enhancement in the growth of the forward Raman scattering instability.

Kumar, Naveen; Keitel, Christoph H

2013-01-01

139

Ground-state and isomeric-state cross sections for the 165Ho(n,2n) 164Ho reaction from reaction threshold to 20 MeV  

Science.gov (United States)

By using the activation technique, the cross section for the reaction 165Ho(n,2n) 164Ho was measured at two neutron energies of 13.5 and 14.8 MeV to resolve inconsistencies in the existing database. The 94- and 91.39-keV ? rays from the decay of the 164Hom isomeric state and 164Hog ground state, respectively, were recorded with a high-resolution high-purity germanium detector. The monoenergetic neutron beam was produced via the 3H(d,n) 4He reaction. The cross sections also were estimated with the talys-1.4 nuclear model code that uses different level-density options at neutron energies that vary from the reaction threshold to 20 MeV. Results are also discussed and are compared with some corresponding values found in the literature.

Luo, Junhua; Jiang, Li

2014-01-01

140

Ground-water hydrology and water quality of the southern high plains aquifer, Melrose Air Force Range, Cannon Air Force Base, Curry and Roosevelt Counties, New Mexico, 2002-03  

Science.gov (United States)

In cooperation with the U.S. Air Force, the U.S. Geological Survey characterized the ground-water hydrology and water quality at Melrose Air Force Range in east-central New Mexico. The purpose of the study was to provide baseline data to Cannon Air Force Base resource managers to make informed decisions concerning actions that may affect the ground-water system. Five periods of water-level measurements and four periods of water-quality sample collection were completed at Melrose Air Force Range during 2002 and 2003. The water-level measurements and water-quality samples were collected from a 29-well monitoring network that included wells in the Impact Area and leased lands of Melrose Air Force Range managed by Cannon Air Force Base personnel. The purpose of this report is to provide a broad overview of ground-water flow and ground-water quality in the Southern High Plains aquifer in the Ogallala Formation at Melrose Air Force Range. Results of the ground-water characterization of the Southern High Plains aquifer indicated a local flow system in the unconfined aquifer flowing northeastward from a topographic high, the Mesa (located in the southwestern part of the Range), toward a regional flow system in the unconfined aquifer that flows southeastward through the Portales Valley. Ground water was less than 55 years old across the Range; ground water was younger (less than 25 years) near the Mesa and ephemeral channels and older (25 years to 55 years) in the Portales Valley. Results of water-quality analysis indicated three areas of different water types: near the Mesa and ephemeral channels, in the Impact Area of the Range, and in the Portales Valley. Within the Southern High Plains aquifer, a sodium/chloride-dominated ground water was found in the center of the Impact Area of the Range with water-quality characteristics similar to ground water from the underlying Chinle Formation. This sodium/chloride-dominated ground water of the unconfined aquifer in the Impact Area indicates a likely connection with the deeper water-producing zone. No pesticides, explosives, volatile organic compounds, semivolatile organic compounds, organic halogens, or perchlorate were found in water samples from the Southern High Plains aquifer at the Range.

Langman, Jeff B.; Gebhardt, Fredrick E.; Falk, Sarah E.

2004-01-01

 
 
 
 
141

Barrier modification in sub-barrier fusion reactions using Wong formula with Skyrme forces in semiclassical formalism  

CERN Document Server

We obtain the nuclear proximity potential by using semiclassical extended Thomas Fermi (ETF) approach in Skyrme energy density formalism (SEDF), and use it in the extended $\\ell$-summed Wong formula under frozen density approximation. This method has the advantage of allowing the use of different Skyrme forces, giving different barriers. Thus, for a given reaction, we could choose a Skyrme force with proper barrier characteristics, not-requiring extra ``barrier lowering" or ``barrier narrowing" for a best fit to data. For the $^{64}$Ni+$^{100}$Mo reaction, the $\\ell$-summed Wong formula, with effects of deformations and orientations of nuclei included, fits the fusion-evaporation cross section data exactly for the force GSkI, requiring additional barrier modifications for forces SIII and SV. However, the same for other similar reactions, like $^{58,64}$Ni+$^{58,64}$Ni, fits the data best for SIII force. Hence, the barrier modification effects in $\\ell$-summed Wong expression depends on the choice of Skyrme fo...

Kumar, Raj

2010-01-01

142

Atomic force microscopic detection enabling multiplexed low-cycle-number quantitative polymerase chain reaction for biomarker assays.  

Science.gov (United States)

Quantitative polymerase chain reaction is the current "golden standard" for quantification of nucleic acids; however, its utility is constrained by an inability to easily and reliably detect multiple targets in a single reaction. We have successfully overcome this problem with a novel combination of two widely used approaches: target-specific multiplex amplification with 15 cycles of polymerase chain reaction (PCR), followed by single-molecule detection of amplicons with atomic force microscopy (AFM). In test experiments comparing the relative expression of ten transcripts in two different human total RNA samples, we find good agreement between our single reaction, multiplexed PCR/AFM data, and data from 20 individual singleplex quantitative PCR reactions. This technique can be applied to virtually any analytical problem requiring sensitive measurement concentrations of multiple nucleic acid targets. PMID:24918650

Mikheikin, Andrey; Olsen, Anita; Leslie, Kevin; Mishra, Bud; Gimzewski, James K; Reed, Jason

2014-07-01

143

Reaction Force/Torque Sensing in a Master-Slave Robot System without Mechanical Sensors  

Directory of Open Access Journals (Sweden)

Full Text Available In human-robot cooperative control systems, force feedback is often necessary in order to achieve high precision and high stability. Usually, traditional robot assistant systems implement force feedback using force/torque sensors. However, it is difficult to directly mount a mechanical force sensor on some working terminals, such as in applications of minimally invasive robotic surgery, micromanipulation, or in working environments exposed to radiation or high temperature. We propose a novel force sensing mechanism for implementing force feedback in a master-slave robot system with no mechanical sensors. The system consists of two identical electro-motors with the master motor powering the slave motor to interact with the environment. A bimanual coordinated training platform using the new force sensing mechanism was developed and the system was verified in experiments. Results confirm that the proposed mechanism is capable of achieving bilateral force sensing and mirror-image movements of two terminals in two reverse control directions.

Kyoko Shibata

2010-07-01

144

Assessment of concentrations of trace elements in ground water and soil at the Small-Arms Firing Range, Shaw Air Force Base, South Carolina  

Science.gov (United States)

Ground-water samples were collected from four shallow water-table aquifer observation wells beneath the Small-Arms Firing Range study area at Shaw Air Force Base. Water-chemistry analyses indicated that total lead concentrations in shallow ground water beneath the study area do not exceed the U.S. Environmental Protection Agency maximum contaminant level established for lead in drinking water (0.05 milligrams per liter). All other trace element total concentrations in ground water beneath the study area were at or below the detection limit of the analytical methodology.

Landmeyer, J. E.

1994-01-01

145

Probing the {sup 8}He ground state via the {sup 8}He(p,t){sup 6}He reaction  

Energy Technology Data Exchange (ETDEWEB)

The weakly-bound {sup 8}He nucleus exhibits a neutron halo or thick neutron skin and is generally considered to have an {alpha}+4n structure in its ground state, with the four valence neutrons each occupying 1p{sub 3/2} states outside the {alpha} core. The {sup 8}He(p,t){sup 6}He reaction is a sensitive probe of the ground state structure of {sup 8}He, and we present a consistent analysis of new and existing data for this reaction at incident energies of 15.7 and 61.3A MeV, respectively. Our results are incompatible with the usual assumption of a pure (1p{sub 3/2}){sup 4} structure and suggest that other configurations such as (1p{sub 3/2}){sup 2}(1p{sub 1/2}){sup 2} may be present with significant probability in the ground state wave function of {sup 8}He.

Keeley, N. [CEA-Saclay DSM/DAPNIA/SPhN, F-91191 Gif-sur-Yvette (France)]. E-mail: nkeeley@cea.fr; Skaza, F. [CEA-Saclay DSM/DAPNIA/SPhN, F-91191 Gif-sur-Yvette (France); Lapoux, V. [CEA-Saclay DSM/DAPNIA/SPhN, F-91191 Gif-sur-Yvette (France); Alamanos, N. [CEA-Saclay DSM/DAPNIA/SPhN, F-91191 Gif-sur-Yvette (France); Auger, F. [CEA-Saclay DSM/DAPNIA/SPhN, F-91191 Gif-sur-Yvette (France); Beaumel, D. [Institut de Physique Nucleaire, IN2P3-CNRS, F-91406 Orsay (France); Becheva, E. [Institut de Physique Nucleaire, IN2P3-CNRS, F-91406 Orsay (France); Blumenfeld, Y. [Institut de Physique Nucleaire, IN2P3-CNRS, F-91406 Orsay (France); Delaunay, F. [Institut de Physique Nucleaire, IN2P3-CNRS, F-91406 Orsay (France); Drouart, A. [CEA-Saclay DSM/DAPNIA/SPhN, F-91191 Gif-sur-Yvette (France); Gillibert, A. [CEA-Saclay DSM/DAPNIA/SPhN, F-91191 Gif-sur-Yvette (France); Giot, L. [GANIL, Bld. Henri Becquerel, BP 5027, F-14021 Caen Cedex (France); Kemper, K.W. [Dept. of Physics, Florida State Univ., Tallahassee, FL 32306-4350 (United States); Nalpas, L. [CEA-Saclay DSM/DAPNIA/SPhN, F-91191 Gif-sur-Yvette (France); Pakou, A. [Dept. of Physics, Univ. of Ioannina, 45110 Ioannina (Greece); Pollacco, E.C.; Raabe, R. [CEA-Saclay DSM/DAPNIA/SPhN, F-91191 Gif-sur-Yvette (France); Roussel-Chomaz, P. [GANIL, Bld. Henri Becquerel, BP 5027, F-14021 Caen Cedex (France); Rusek, K. [Dept. of Nuclear Reactions, The Andrzej Soltan Institute for Nuclear Studies, ul. Hoza 69, PL-00681 Warsaw (Poland); Scarpaci, J.-A. [Institut de Physique Nucleaire, IN2P3-CNRS, F-91406 Orsay (France); Sida, J.-L. [CEA-Saclay DSM/DAPNIA/SPhN, F-91191 Gif-sur-Yvette (France); Stepantsov, S. [Flerov Lab. of Nuclear Reactions, JINR, Dubna, RU-141980 (Russian Federation); Wolski, R. [Flerov Lab. of Nuclear Reactions, JINR, Dubna, RU-141980 (Russian Federation)]|[Henryk Niewodniczanski Inst. of Nuclear Physics, PL-31342 Krakow (Poland)

2007-03-22

146

Charge transfer reactions of ground state O+ ions with H2 molecules  

International Nuclear Information System (INIS)

Cross sections for charge transfer between ground state (4S) O+ ions in H2 have been measured within the energy range 0.1-1.0 keV. A novel photoionization source which eliminates problems associated with metastable ions was used and the results resolve the large discrepancies between previous experiments. (author)

147

Collisional and photoinitiated reaction dynamics in the ground electronic state of Ca-HCl  

International Nuclear Information System (INIS)

Ca+HCl(?,j) reactive collisions were studied for different rovibrational states of the HCl reactant using wave-packet calculations in reactant Jacobi coordinates. A recently proposed potential-energy surface was used with a barrier of ?0.4 eV followed by a deep well. The possibility of an insertion mechanism due to this last well has been analyzed and it was found that once the wave packet passes over the barrier most of it goes directly to CaCl+H products, which shows that the reaction dynamics is essentially direct. It was also found that there is no significant change in the reaction efficiency as a function of the initial HCl rovibrational state, because CaHCl at the barrier has an only little elongated HCl bond. Near the threshold for reaction with HCl(?=0), however, the reaction shows significant steric effects for j>0. In a complementary study, the infrared excitation from the Ca-HCl van der Waals well was simulated. The spectrum thus obtained shows several series of resonances which correspond to quasibound states correlating to excited HCl(?) vibrations. The Ca-HCl binding energies of these quasibound states increase dramatically with ?, from 75 to 650 cm-1, because the wave function spreads increasingly over larger HCl bond lengths. Thus it explores the region of the barrier saddle point and the deep insertion well. Although also the charge-transfer contribution increases with ?, the reaction probability for resonances of the ?=2 manifold, which are well above the reaction threshold, is still negligible. This explains the relatively long lifetimes of these ?=2 resonances. The reaction probability becomes significant at ?=3. Our simulations have shown that an experimental study of this type will allow a gradual spectroscopic probing of the barrier for the reaction

148

The reaction force constant as an indicator of synchronicity/nonsynchronicity in [4+2] cycloaddition processes.  

Science.gov (United States)

A variety of experimental and computational analyses support the concept that a chemical reaction has a transition region, in which the system changes from distorted states of the reactants to distorted states of the products. The boundaries of this region along the intrinsic reaction coordinate ?, which includes the traditional transition state, are defined unambiguously by the minimum and maximum of the reaction force F(?), which is the negative gradient of the potential energy V(?). The transition region is characterized by the reaction force constant ?(?), the second derivative of V(?), being negative throughout. It has recently been demonstrated that the profile of ?(?) in the transition region is a sensitive indicator of the degree of synchronicity of a concerted reaction: a single ?(?) minimum is associated with full or nearly full synchronicity, while a ?(?) maximum (negative) between two minima is a sign of considerable nonsynchronicity, i.e. a two-stage concerted process. We have now applied reaction force analysis to the Diels-Alder cycloadditions of the various cyanoethylenes to cyclopentadiene. We examine the relative energy requirements of the structurally- and electronically-intensive phases of the activation processes. We demonstrate that the variation of ?(?) in the transition region is again indicative of the level of synchronicity. The fully synchronous cycloadditions are those in which the cyanoethylenes are symmetrically substituted. Unsymmetrical substitution leads to minor nonsynchronicity for monocyanoethylene but much more - i.e. two stages - for 1,1-dicyano- and 1,1,2-tricyanoethylene. We also show that the ?(?) tend to become less negative as the activation energies decrease. PMID:23575799

Yepes, Diana; Donoso-Tauda, Oscar; Pérez, Patricia; Murray, Jane S; Politzer, Peter; Jaque, Pablo

2013-05-21

149

Role of electronic-vibrational mixing in enhancing vibrational coherences in the ground electronic states of photosynthetic bacterial reaction center.  

Science.gov (United States)

We describe polarization controlled two-color coherence photon echo studies of the reaction center complex from a purple bacterium Rhodobacter sphaeroides. Long-lived oscillatory signals that persist up to 2 ps are observed in neutral, oxidized, and mutant (lacking the special pair) reaction centers, for both (0°,0°,0°,0°) and (45°,-45°,90°,0°) polarization sequences. We show that the long-lived signals arise via vibronic coupling of the bacteriopheophytin (H) and accessory bacteriochlorophyll (B) pigments that leads to vibrational wavepackets in the B ground electronic state. Fourier analysis of the data suggests that the 685 cm(-1) mode of B may play a key role in the H to B energy transfer. PMID:24433029

Ryu, Ian Seungwan; Dong, Hui; Fleming, Graham R

2014-02-01

150

3D FEM Numerical Simulation of Seismic Pile-supported Bridge Structure Reaction in Liquefying Ground  

Directory of Open Access Journals (Sweden)

Full Text Available This study examines the establishment of liquefied ground pile-soil-bridge seismic interaction analysis of three-dimensional finite element analysis method for the simulation of liquefied ground shaking table test of pile-soil seismic interaction analysis, undertake OpenSees finite element based numerical simulation platform, for the shaking table test based on two-phase saturated porous media, Comparative numerical and experimental results, detailed test pile dynamic response of bridge structure and dynamic properties, especially liquefaction pore pressure, liquefaction of pile foundation and the dynamic response of the free field. Finite element method can reasonably predict the site of pore pressure, dynamic response; despite the conventional beam element simulation of pile, pile dynamic response can still accurately simulated.

Ling XianZhang, Tang Liang and Xu Pengju

2011-04-01

151

Ground state transition of (p,t) reactions on Ni isotopes  

International Nuclear Information System (INIS)

Angular distributions of 58,60,62,64 Ni(p,t) ground state transitions at Ep = 25 MeV have been measured and compared with distorted wave Born approximation predictions. Relative enhancement factors for four Ni isotopes have been extracted. Comparison between the enhancement factors and the predictions of interacting boson approximation model has been made. It is found that a value of ?v = 6 is needed to describe the experimental result in SU(5) calculation

152

Pullback attractors for reaction-diffusion delay equations on unbounded domains with non-autonomous deterministic and stochastic forcing terms  

Science.gov (United States)

The existence of a pullback attractor in a space of higher regularity is established for the non-autonomous non-compact dynamical system associated with the reaction-diffusion delay equation with both non-autonomous deterministic and stochastic forcing terms defined on all n-dimensional space. The asymptotical compactness of the solutions is demonstrated by using the uniform estimates for far-field values of solutions and a new method.

Wang, Jingyu; Wang, Yejuan

2013-08-01

153

Some neutron and photon reactions on the ground and isomeric states of sup 236,237 Np  

Energy Technology Data Exchange (ETDEWEB)

We present results of calculated neutron- and photon-induced reactions on the 1.1 {times} 10{sup 5}{minus}y ground state and 22.5-h isomer of {sup 236}Np and on the 2.1 {times} 10{sup 6}{minus}y ground state and 68-ns isomer of {sup 237}Np. Of primary concern are the isomeric ratios produced although some photon absorption and photoneutron results are given. We discuss the production of the short-lived isomer of {sup 236}Np, via the (n,2n) and ({gamma},n) reactions on {sup 237}Np, leading eventually to the high-energy {gamma}-ray emitter, {sup 208}Pb; the photoproduction and destruction of the 60-keV, 68-ns isomer of {sup 237}Np, a possible gamma-ray laser candidate; and the use of photoexcitation and destruction of nuclear isomers in the field of nuclear waste disposal. The effect of the choice of the physics parameters on the calculated results is also illustrated. 14 figs., 2 tabs.

Gardner, D.G.; Gardner, M.A.

1989-09-11

154

Russian Military and Security Forces: A Postulated Reaction to a Nuclear Detonation  

Energy Technology Data Exchange (ETDEWEB)

In this paper, we will examine how Russia's military and security forces might react to the detonation of a 10-kiloton nuclear weapon placed next to the walls surrounding the Kremlin. At the time of this 'big bang,' Putin is situated outside Moscow and survives the explosion. No one claims responsibility for the detonation. No other information is known. Numerous variables will determine how events ultimately unfold and how the military and security forces will respond. Prior to examining these variables in greater detail, it is imperative to elucidate first what we mean by Russia's military and security forces.

Ball, D

2005-04-29

155

Exciplexes versus Loose Ion Pairs: How Does the Driving Force Impact the Initial Product Ratio of Photoinduced Charge Separation Reactions?  

Science.gov (United States)

Many donor–acceptor systems can undergo a photoinduced charge separation reaction, yielding loose ion pairs (LIPs). LIPs can be formed either directly via (distant) electron transfer (ET) or indirectly via the dissociation of an initially formed exciplex or tight ion pair. Establishing the prevalence of one of the reaction pathways is challenging because differentiating initially formed exciplexes from LIPs is difficult due to similar spectroscopic footprints. Hence, no comprehensive reaction model has been established for moderately polar solvents. Here, we employ an approach based on the time-resolved magnetic field effect (MFE) of the delayed exciplex luminescence to distinguish the two reaction channels. We focus on the effects of the driving force of ET and the solvent permittivity. We show that, surprisingly, the exciplex channel is significant even for an exergonic ET system with a free energy of ET of ?0.58 eV and for the most polar solutions studied (butyronitrile). Our findings demonstrate that exciplexes play a crucial role even in polar solvents and at moderate driving forces, contrary to what is usually assumed. PMID:25243054

2014-01-01

156

Reaction force analysis of the effect of Mg(II) on the 1,3 intramolecular hydrogen transfer in thymine.  

Science.gov (United States)

The 1,3 intramolecular hydrogen transfer reaction in free thymine and in Mg(II)-thymine have been studied at the density functional theory level. The mechanism of intramolecular proton transfer in these systems emerges from the analysis of the reaction force profile along the reaction path; it is rationalized in terms of structural and electronic reorganizations that take place during the chemical transformation. Results show that the presence of Mg(II) monocoordinated to thymine activates the hydrogenic motion by inducing structural and electronic changes in the molecular backbone. In the metallic complex, it is found that the hydrogen transfer is followed by a relaxation process that facilitates the metal cation migration to form a bicoordinated complex. PMID:16869699

Rincón, Elizabeth; Jaque, Pablo; Toro-Labbé, Alejandro

2006-08-01

157

Fission and cluster decay of the {sup 76}Sr nucleus in the ground state and formed in heavy-ion reactions  

Energy Technology Data Exchange (ETDEWEB)

Calculations for fission and cluster decay of {sup 76}Sr are presented for this nucleus to be in its ground state or formed as an excited compound system in heavy-ion reactions. The predicted mass distribution, for the dynamical collective mass transfer process assumed for fission of {sup 76}Sr, is clearly asymmetric, favoring {alpha} nuclei. Cluster decay is studied within a preformed cluster model, both for ground-state to ground-state decays and from excited compound system to the ground state(s) or excited states(s) of the fragments. {copyright} {ital 1997} {ital The American Physical Society}

Gupta, Raj K.; Sharma, Manoj K.; Singh, Sarbjit [Physics Department, Panjab University, Chandigarh-160014 (India); Nouicer, Rachid; Beck, Christian [Institut de Recherches Subatomiques, IN2P3/Universite Louis Pasteur, F-67037 Strasbourg (France)

1997-12-01

158

Measurement of the rates of reaction of the ground and metastable excited states of 02+, N0+ and 0+ with atmospheric gases at thermal energy  

International Nuclear Information System (INIS)

Thermal-energy reaction rate coefficients and product ion distributions have been measured for reactions of both the ground state and metastable electronic states of 02+, N0+ and 0+ with several neutral species, using a selected-ion flow tube. In general the excited-ion reaction rates are fast, frequently approaching the Langevin limit. Collisional quenching occurs for the reactions of N0+sup(star) with N2,02 and H2 and the quenching rates have been determined. The ion source also provided a substantial yield of doubly charged 02 permitting some measurements of reaction rates of 022+. (author)

159

Probing three-nucleon force using nucleon-deuteron breakup reactions  

International Nuclear Information System (INIS)

Possible evidence for the influence of three-nucleon forces (3NF) dates back to the observation that most realistic two-nucleon force models underpredict the triton binding energy by about 1 MeV. Though calculations which included 3NFs demonstrated that the triton binding energy problem could be remedied, they did not provide firm evidence of 3NFs, since the three-nucleon potentials used did not have rigid connections to realistic nucleon-nucleon (N-N) force models. To make the situation even more nebulous, the triton binding energy has been shown to be strongly sensitive to the strength of the N-N tensor force. In an effort to find three-nucleon (3N) observables that are insensitive to details of the N-N force and which might exhibit some sensitivity to 3NF effects, attention is now being focused on 3N continuum observables. In this paper the authors present their results for kinematically complete cross-section measurements of the space-star, coplanar-star and collinear configurations in neutron-deuteron (n-d) breakup at 13.0 MeV. These data are a subset of the results obtained in a recent experiment in which cross sections for 46 configurations were measured simultaneously. The experimental techniques will be described. These new data will be compared to previous n-d data, to proton-deuteron data and to rigorous n-d calculations

160

In situ measurement of structural mass, stiffness, and damping using a reaction force actuator and a laser Doppler vibrometer  

International Nuclear Information System (INIS)

The problem of structural parameter measurements needs a total solution bridging theory and experiments. In this paper, a practical methodology for in situ measurements of structural mass, stiffness, and damping is presented for built-up structures. As for the experimental uniqueness of the methodology, a reaction force actuator and non-contact optical device are utilized respectively as an input force generator and output displacement measurer, providing a fundamental data set of the proposed numerical algorithm for data-driven structural parameter estimation. The algorithm autonomously estimates the diagonalized mass, symmetric stiffness, optimal non-proportional damping, and suboptimal proportional damping matrices for multi-degrees-of-freedom structures. Structural parameter measurements of two built-up structures followed by a comparison with conventional measurements are used as examples for verification of the accuracy of the proposed methodology. (paper)

 
 
 
 
161

Effect of baffle on slosh reaction forces in rotating liquid helium subjected to a lateral impulse in microgravity  

Science.gov (United States)

Sloshing dynamics within a partially filled rotating Dewar of superfluid He II are investigated in response to a lateral impulse. The study investigates several factors, including how the rotating bubble of superfluid He II reacts to the impulse in microgravity, how the amplitudes of slosh reaction forces act on the Dewar with various rotating speeds, how the frequencies of the sloshing modes excited differ in terms of differences in rotating speeds, and how the sloshing dynamics differ with and without a baffle. The numerical computation of sloshing dynamics is based on the noninertial frame spacecraft-bound coordinates. Results of the simulations are illustrated.

Hung, R. J.; Long, Y. T.

1995-01-01

162

Quantum radiation reaction force on a one-dimensional cavity with two relativistic moving mirrors  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We consider a real massless scalar field inside a cavity with two moving mirrors in a two-dimensional spacetime, satisfying Dirichlet boundary condition at the instantaneous position of the boundaries, for arbitrary and relativistic laws of motion. Considering vacuum as the initial field state, we obtain formulas for the exact value of the energy density of the field and the quantum force acting on the boundaries, which extend results found in previous papers. For the partic...

Alves, Danilo T.; Granhen, Edney R.; Pires, Wagner P.

2009-01-01

163

Ultra-miniature force plate for measuring triaxial forces in the micronewton range.  

Science.gov (United States)

Measuring the ground reaction forces of a single leg is indispensable to understanding the dynamics of legged locomotion. Because of the technical state of the art, investigations are limited to animals with a body mass above 1 g. Here we present the design, fabrication, calibration and performance of a novel ultra-miniature force platform at the micronewton level. The sensor was built using the stereolithography technology and is equipped with semiconductor strain gauges. We found a highly linear signal response in the calibrated force range to ±1300 ?N. Individual tests revealed that our force plate still shows a linear response at forces as great as 4 mN, confirming a large measuring range and particular robustness. The sensitivity was above 50 V N(-1) in all directions, which makes it possible to resolve forces of 10 ?N. We demonstrated the suitability of the device on the basis of a typical ground reaction force measurement of an ant, Formica polyctena. PMID:24265430

Reinhardt, Lars; Blickhan, Reinhard

2014-03-01

164

A Q-GERT analysis of the space shuttle ground turnaround system at Vandenberg Air Force Base  

Science.gov (United States)

The efficient ground turnaround of the Space Shuttle is critical to the execution of national policies. Research identified four major subsystems within the Vandenberg Ground Turnaround System; the Orbiter Maintenance Subsystem, External Tank Subsystem, Solid Rocket Booster Subsystem, and Launch Pad Subsystem. A Q-GERT simulation of the ground Turnaround System was conducted to investigate the system and observe the interactions between the major subsystems. The Q-GERT model simulated the integration of Space Shuttle components to determine the subsystem most sensitive to change. The results indicate the Launch Pad Subsystem is the most critical in the Vandenberg Ground Turnaround System. However, further research is recommended in areas of logistics support, spares availability, and transportation of components.

Graham, S.; Jones, T. W.

1982-09-01

165

Novel and Unique Expression for the Radiation Reaction Force, Relevance of Newton's Third Law and Tunneling  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We derive the radiation reaction by taking into account that the acceleration of the charge is caused by the interaction with some heavy source particle. In the non relativistic case this leads, in contrast to the usual approach, immediately to a result which is Galilei invariant. Simple examples show that there can be small regions of extremely low velocity where the energy requirements cannot be fulfilled, and which the charged particle can only cross by quantum mechanical...

Gromes, Dieter; Thommes, Eduard

2014-01-01

166

EMMI Rapid Reaction Task Force Meeting on 'Quark Matter in Compact Star'  

CERN Document Server

The recent measurement of two solar mass pulsars has initiated an intense discussion on its impact on our understanding of the high-density matter in the cores of neutron stars. A task force meeting was held from October 7-10, 2013 at the Frankfurt Institute for Advanced Studies to address the presence of quark matter in these massive stars. During this meeting, the recent oservational astrophysical data and heavy-ion data was reviewed. The possibility of pure quark stars, hybrid stars and the nature of the QCD phase transition were discussed and their observational signals delineated.

Buballa, Michael; Drago, Alessandro; Fraga, Eduardo; Haensel, Pawel; Mishustin, Igor; Pagliara, Giuseppe; Schaffner-Bielich, Jurgen; Schramm, Stefan; Sedrakian, Armen; Weber, Fridolin

2014-01-01

167

Finite size corrections to the radiation reaction force in classical electrodynamics.  

Science.gov (United States)

We introduce an effective field theory approach that describes the motion of finite size objects under the influence of electromagnetic fields. We prove that leading order effects due to the finite radius R of a spherically symmetric charge is order R2 rather than order R in any physical model, as widely claimed in the literature. This scaling arises as a consequence of Poincaré and gauge symmetries, which can be shown to exclude linear corrections. We use the formalism to calculate the leading order finite size correction to the Abraham-Lorentz-Dirac force. PMID:20868166

Galley, Chad R; Leibovich, Adam K; Rothstein, Ira Z

2010-08-27

168

Kinesiological Study of Push-up Motion Using a Three-Dimensional Floor Reaction on a Force Plate  

Directory of Open Access Journals (Sweden)

Full Text Available To find an effective way to handle wheelchairs, 3-dimensional floor reactions of the hand and angular deviation of the elbow and wrist joints during push-up motion were studied in 10 healthy men. The push-up was carried out using 3 hand positions (fist, finger and palm and a push-up device. In all hand positions, anteroposterior force (Fx and the mediolateral force (Fy appeared after the vertical force (Fz. The end point of Fx and Fy was observed before that of Fz. Among the 4 different hand positions, Fx and Fy appeared first in the palm, followed by the finger and fist positions, and lastly in the push-up devices. The results indicate that the more unstable pushing-up the body is, the earlier and longer Fx and Fy are. Thus, Fx and Fy are considered to be good indicators of body balance during the push-up motion. The elbow joint showed a hyperextended position only when using the palm position in the maintenance phase. The wrist joint showed palmar flexion only when using the fist position.

Ikawa,Harutomo

1995-06-01

169

Ground-Water Hydrology and Water Quality of the Southern High Plains Aquifer, Cannon Air Force Base, Curry County, New Mexico, 1994-2005  

Science.gov (United States)

In cooperation with the U.S. Air Force, the U.S. Geological Survey has collected hydrologic data about the Southern High Plains aquifer at Cannon Air Force Base in east-central New Mexico since 1994. Under the guidance of the State of New Mexico, ground-water quality of the aquifer has been analyzed as part of annual monitoring at regulated sites at the base. This report provides a summary and interpretation of all available hydrologic data collected by the U.S. Geological Survey for Cannon Air Force Base environmental managers for the regulated sites of Landfill 5 and the Sewage Lagoons between 1994 and 2005. Cannon Air Force Base is in the Southern High Plains physiographic region, and saturated deposits of the Ogallala Formation underlying the base are within the western boundary of the Southern High Plains aquifer. The general direction of ground-water flow in the Southern High Plains aquifer at Cannon Air Force Base is from northwest to southeast. In 1962, ground water predominantly flowed northwest to southeast with minimal change in direction. Ground-water altitudes declined from 1962 to 1997, and a pronounced water-level recession (area of receding water level) developed northwest of the base, altering flow direction in this area. The recession northwest of the base and the subsequent change in direction of ground-water flow are indicative of local ground-water withdrawals upgradient from Cannon Air Force Base. Historical water levels in wells within a 3-mile radius of Cannon Air Force Base declined in 52 of 56 wells for various periods of record between 1962 and 2004. Forty-three of the wells indicated strong linear decreases with time, and the largest decline was 91.80 feet, an average annual decline of about 2.13 feet per year. Water levels in monitoring wells at Cannon Air Force Base reflected the regional decline; water levels declined for all wells with periods of record greater than 1 year, and the decreases were strongly linear. From 1994 to 2005, rates of declining water levels at the base ranged from 1.45 to 1.64 feet per year near the Sewage Lagoons and from 2.24 to 4.01 feet per year near Landfill 5. The largest variation in water levels at Cannon Air Force Base was observed in wells C, D, and S, which are located adjacent to Landfill 5 near the southern boundary of the base and near an irrigation well immediately south of the base boundary. Water levels in these wells indicated a pattern of summer water-level decline followed by partial winter water-level recovery, which was likely a result of drawdown and recovery during the irrigation and nonirrigation seasons. Ground-water sampling by the U.S. Geological Survey from 1994 to 2004 at monitoring wells associated with Landfill 5 and the Sewage Lagoons indicated temporal and spatial differences in water quality. At least one anthropogenic compound was detected in each monitoring well, but all concentrations detected were small and less than U.S. Environmental Protection Agency drinking-water standards. Anthropogenic compounds detected were either pesticide or industrial compounds. Perchlorate was detected in at least one sample from every well for which perchlorate was analyzed, and the source of perchlorate is likely natural and a result of atmospheric deposition. Trace-element concentrations in raw (pretreatment) ground water at Cannon Air Force Base were generally less than drinking-water standards (applicable to posttreatment samples), but maximum concentrations of aluminum, iron, and manganese exceeded secondary drinking-water standards, and maximum chromium concentrations exceeded the primary drinking-water standard. Spatial and temporal differences of nitrate, major ions, and specific conductance indicated anthropogenic and natural influences on the Southern High Plains aquifer at Cannon Air Force Base. Larger nitrate concentrations decreased in ground water near the Sewage Lagoons during and following decommissioning of the lagoons, and c

Langman, Jeff B.; Falk, Sarah E.; Gebhardt, Fredrick E.; Blanchard, Paul J.

2006-01-01

170

Uprooting force balance for pioneer woody plants: A quantification of the relative contribution of above- and below-ground plant architecture to uprooting susceptibility  

Science.gov (United States)

Cottonwood (Populus), willow (Salix), and tamarisk (Tamarix) populate riparian areas in many dryland regions, and their recruitment depends heavily on hydrogeomorphic conditions. The survival of pioneer woody seedlings depends in part on the establishment of root systems capable of anchoring plants in subsequent floods, and this root system development in turn influences the cohesion that plants provide to bars. The factors influencing the anchoring ability and resistance to scour of woody seedlings include plant frontal area and flexibility, root structure, and water table elevation. This study aims to quantify the factors comprising the force balance to uproot woody seedlings and saplings in two field sites characterized by different hydrologic conditions. The Bill Williams River (AZ) is an impounded river with elevated water table elevations produced by dam-released base flows. The Bitterroot River (MT) is an unimpounded river with a snowmelt hydrograph and seasonal fluctuations in river and water table elevation. We simulate uprooting from flooding events by saturating substrates and applying force near the base of the plant in a lateral, downstream direction until uprooting occurs, for a range of plant sizes but with a focus on small (willow. In contrast, root length and stem diameter are only weakly correlated with pull-out force. By combining pull test results with measurements of geomorphic and groundwater conditions, this study provides insights into the relative contribution of a plant's above-ground and below-ground architecture to uprooting potential and into the feedbacks between vegetation and morphodynamics on river bars.

Bywater-Reyes, S.; Wilcox, A. C.; Lightbody, A.; Skorko, K.; Stella, J. C.

2012-12-01

171

OPPORTUNITIES TO CONSTRAIN ASTROPHYSICAL REACTION RATES FOR THE s-PROCESS VIA DETERMINATION OF THE GROUND-STATE CROSS-SECTIONS  

International Nuclear Information System (INIS)

Modern models of s-process nucleosynthesis in stars require stellar reaction rates of high precision. Most neutron-capture cross-sections in the s-process have been measured, and for an increasing number of reactions the required precision is achieved. This does not necessarily mean, however, that the stellar rates are constrained equally well, because only the capture of the ground state of a target is measured in the laboratory. Captures of excited states can contribute considerably to stellar rates that are already at typical s-process temperatures. We show that the ground-state contribution X to a stellar rate is the relevant measure to identify reactions that are or could be well constrained by experiments and apply it to (n,?) reactions in the s-process. We further show that the maximum possible reduction in uncertainty of a rate via determination of the ground-state cross-section is given directly by X. An error analysis of X is presented, and it is found that X is a robust measure with mostly small uncertainties. Several specific examples (neutron capture of 79Se, 95Zr, 121Sn, 187Os, and 193Pt) are discussed in detail. The ground-state contributions for a set of 412 neutron-capture reactions around the s-process path are presented in a table. This allows identification of reactions that may be better constrained by experiments and that cannot be constrained solely by measuring ground-state cross-sections (and thus require supplementary studies). General trends and implications are discussed.

172

Probing the three-nucleon force using nucleon-deuteron breakup reactions  

International Nuclear Information System (INIS)

Results of our recent kinematically complete cross-section measurements of the space-star and coplanar-star configurations in n-d breakup at 13.0 MeV are reported. The experimental setup and details of the analysis are described. The new data for the space-star configuration are in good agreement with previous n-d data but differ significantly from both ''exact'' n-d calculations and p-d data. In contrast, the new coplanar-star data are in fair agreement with the calculations but are in gross disagreement with previous n-d data. The implications of these data for three-nucleon forces are discussed. (orig.)

173

Theoretical study on reaction mechanism of ground-state cyano radical with 1,3-butadiene: prospect of pyridine formation.  

Science.gov (United States)

The reaction of ground-state cyano radicals, CN(X(2)?(+)), with the simplest polyene, 1,3-butadiene (C4H6(X(1)Ag)), is investigated to explore probable routes and feasibility to form pyridine at ultralow temperatures. The isomerization and dissociation channels for each of the seven initial collision complexes are characterized by utilizing the unrestricted B3LYP/cc-pVTZ and the CCSD(T)/cc-pVTZ calculations. With facilitation of RRKM rate constants, through ab initio paths composed of 7 collision complexes, 331 intermediates, 62 hydrogen atom, 71 hydrogen molecule, and 3 hydrogen cyanide dissociated products, the most probable paths at collision energies up to 10 kcal/mol, and thus the reaction mechanism, are determined. Subsequently, the corresponding rate equations are solved that the concentration evolutions of collision complexes, intermediates, and products versus time are obtained. As a result, the final products and yields are determined. The low-energy routes for the formation of most thermodynamically stable product, pyridine, are identified. This study, however, predicts that seven collision complexes would produce predominately 1-cyano-1,3-butadiene, CH2CHCHCHCN (p2) plus atomic hydrogen via the collision complex c1(CH2CHCHCH2CN) and intermediate i2(CH2CHCH2CHCN), with a very minor amount of pyridine. Our scheme also effectively excludes the presence of 2-cyano-1,3-butadiene, which has energy near-degenerate to 1-cyano-1,3-butadiene, as supported by experimental findings. PMID:25116460

Sun, B J; Huang, C H; Chen, S Y; Chen, S H; Kaiser, R I; Chang, A H H

2014-09-11

174

Study of the ground-state wave function of {sup 6}He via the {sup 6}He(p, t){alpha} transfer reaction  

Energy Technology Data Exchange (ETDEWEB)

We have measured the {sup 6}He(p,t){alpha} transfer reaction in inverse kinematics at 25 MeV/nucleon. The data were compared to DWBA calculations in order to extract the spectroscopic amplitudes for {alpha}+2n and t+t configurations in the ground state of {sup 6}He. (orig.)

Giot, L.; Roussel-Chomaz, P.; Demonchy, Ch.E.; Mittig, W.; Pita, S.; Savajols, H. [GANIL (DSM/CEA, IN2P3/CNRS), B.P. 5027, Caen Cedex 5 (France); Alamanos, N.; Auger, F.; Gillibert, A.; Jouanne, C.; Lapoux, V.; Nalpas, L.; Pollacco, E.C.; Sida, J.L.; Skaza, F. [Saclay, CEA/DSM/DAPNIA/SPhN, Gif-sur-Yvette Cedex (France); Cortina-Gil, M.-D.; Fernandez, J. [Universidad Santiago de Compostela, Departamento de Fisica de Particulas, Santiago de Compostela (Spain); Mackintosh, R.S. [The Open University, Department of Physics and Astronomy, Milton Keynes (United Kingdom); Pakou, A. [The University of Ioannina, Department of Physics, Ioannina (Greece); Rodin, A.; Stepantsov, S.; Ter-Akopian, G. [Dubna, FLNR, JINR, P.O. Box 79, Moscow (Russian Federation); Rusek, K. [The Andrzej Soltan Institute for Nuclear Studies, Hoza 69, Department of Nuclear Reactions, Warsaw (Poland); Thompson, I. [University of Surrey, Department of Physics, Guildford (United Kingdom)

2005-09-01

175

[Environmental investigation of ground water contamination at Wright-Patterson Air Force Base, Ohio]. Volume 3, Appendix A, Draft standard operating procedures and elements: Sampling and Analysis Plan (SAP): Phase 1, Task 4, Field Investigation, Draft  

Energy Technology Data Exchange (ETDEWEB)

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.

1991-10-01

176

Role of spin-orbit interaction and Skyrme forces in Ni-induced reactions  

International Nuclear Information System (INIS)

In the present work, the Skyrme nucleus-nucleus interaction in the semiclassical extended Thomas Fermi (ETF) approach, under frozen density approximation is used. The nuclear potential is obtained as a sum of the spin-orbit density-dependent VJ part and spin-orbit density-independent VP part of the Skyrme Hamiltonian density. Within the ETF approach, it is of interest to study the variation of spin-orbit part with increase in N/Z ratio of the compound systems. In the following, this study of the role of spin-orbit density part of interaction potential on nine even-mass compound nuclei (CN) 156-172Yb* formed in 56-72Ni+100Mo reactions where both spherical and deformed nuclei are involved

177

Progress on Light-Ion Fusion Reactions with Three-Nucleon Forces  

Science.gov (United States)

The description of structural and dynamical properties of nuclei starting from the fundamental interaction between nucleons has been a long-standing goal in nuclear physics. The ab initio No-Core Shell Model combined with the Resonating-Group Method (NCSM/RGM) is capable of addressing both structural and reaction properties of light-nuclei. While promising results have already been achieved starting from a two-body Hamiltonian, a truly realistic prediction of nuclear observables requires the treatment of the three-nucleon interaction. Using similarity-renormalization-group evolved two- and three-nucleon interactions, we will present recent applications to n-4He scattering process when accounting for the chiral two- plus three-nucleon interaction versus the chiral two-nucleon interaction. We compare our results to phase shifts obtained from R-matrix analysis of data up to 16 MeV neutron energy, below the d-3H threshold.

Hupin, G.; Quaglioni, S.; Langhammer, J.; Navrátil, P.; Calci, A.; Roth, R.

2014-08-01

178

Progress on Light-Ion Fusion Reactions with Three-Nucleon Forces  

CERN Document Server

The description of structural and dynamical properties of nuclei starting from the fundamental interaction between nucleons has been a long-standing goal in nuclear physics. The ab initio No-Core Shell Model combined with the Resonating-Group Method (NCSM/RGM) is capable of addressing both structural and reaction properties of light-nuclei. While promising results have already been achieved starting from a two-body Hamiltonian, a truly realistic prediction of nuclear observables requires the treatment of the three-nucleon interaction. Using similarity-renormalization-group evolved two- and three-nucleon interactions, we will present recent applications to n-4He scattering process when accounting for the chiral two- plus three-nucleon interaction versus the chiral two-nucleon interaction. We compare our results to phase shifts obtained from R-matrix analysis of data up to 16 MeV neutron energy, below the d-3H threshold.

Hupin, Guillaume; Langhammer, Joachim; Navrátil, Petr; Calci, Angelo; Roth, Robert

2014-01-01

179

State-to-state quantum dynamics of the F + HCl (vi = 0, ji = 0) ? HF(vf, jf) + Cl reaction on the ground state potential energy surface.  

Science.gov (United States)

The state-to-state reaction dynamics of the title reaction is investigated on the ground electronic state potential energy surface using two quantum dynamical methods. The results obtained using the Chebyshev real wave packet method are in excellent agreement with those obtained using the time-independent method, except at low translational energies. It is shown that this exothermic hydrogen abstraction reaction is direct, resulting in a strong back-scattered bias in the product angular distribution. The HF product is highly excited internally. Agreement with available experimental data is only qualitative. We discuss several possible causes of disagreement with experiment. PMID:23928838

Li, Anyang; Guo, Hua; Sun, Zhigang; K?os, Jacek; Alexander, Millard H

2013-10-01

180

[Environmental investigation of ground water contamination at Wright- Patterson Air Force Base, Ohio]. Volume 4, Health and Safety Plan (HSP); Phase 1, Task 4 Field Investigation report: Draft  

Energy Technology Data Exchange (ETDEWEB)

This Health and Safety Plan (HSP) was developed for the Environmental Investigation of Ground-water Contamination Investigation at Wright-Patterson Air Force Base near Dayton, Ohio, based on the projected scope of work for the Phase 1, Task 4 Field Investigation. The HSP describes hazards that may be encountered during the investigation, assesses the hazards, and indicates what type of personal protective equipment is to be used for each task performed. The HSP also addresses the medical monitoring program, decontamination procedures, air monitoring, training, site control, accident prevention, and emergency response.

1991-10-01

 
 
 
 
181

Quantum radiation reaction force on a one-dimensional cavity with two relativistic moving mirrors  

Science.gov (United States)

We consider a real massless scalar field inside a cavity with two moving mirrors in a two-dimensional spacetime, satisfying the Dirichlet boundary condition at the instantaneous position of the boundaries, for arbitrary and relativistic laws of motion. Considering vacuum as the initial field state, we obtain formulas for the exact value of the energy density of the field and the quantum force acting on the boundaries, which extend results found in previous papers [D. T. Alves, E. R. Granhen, H. O. Silva, and M. G. Lima, Phys. Rev. DPRVDAQ1550-7998 81, 025016 (2010); 10.1103/PhysRevD.81.025016L. Li and B.-Z. Li, Phys. Lett. APYLAAG0375-9601 300, 27 (2002); 10.1016/S0375-9601(02)00674-6L. Li and B.-Z. Li, Chin. Phys. Lett.CPLEEU0256-307X 19, 1061 (2002); 10.1088/0256-307X/19/8/310L. Li and B.-Z. Li, Acta Phys. Sin.WLHPAR1000-3290 52, 2762 (2003); C. K. Cole and W. C. Schieve, Phys. Rev. A 64, 023813 (2001)PLRAAN1050-294710.1103/PhysRevA.64.023813]. For the particular cases of a cavity with just one moving boundary, nonrelativistic velocities, or in the limit of infinity length of the cavity (a single mirror), our results coincide with those found in the literature.

Alves, Danilo T.; Granhen, Edney R.; Pires, Wagner P.

2010-08-01

182

Quantum radiation reaction force on a one-dimensional cavity with two relativistic moving mirrors  

International Nuclear Information System (INIS)

We consider a real massless scalar field inside a cavity with two moving mirrors in a two-dimensional spacetime, satisfying the Dirichlet boundary condition at the instantaneous position of the boundaries, for arbitrary and relativistic laws of motion. Considering vacuum as the initial field state, we obtain formulas for the exact value of the energy density of the field and the quantum force acting on the boundaries, which extend results found in previous papers [D. T. Alves, E. R. Granhen, H. O. Silva, and M. G. Lima, Phys. Rev. D 81, 025016 (2010); L. Li and B.-Z. Li, Phys. Lett. A 300, 27 (2002); L. Li and B.-Z. Li, Chin. Phys. Lett. 19, 1061 (2002); L. Li and B.-Z. Li, Acta Phys. Sin. 52, 2762 (2003); C. K. Cole and W. C. Schieve, Phys. Rev. A 64, 023813 (2001)]. For the particular cases of a cavity with just one moving boundary, nonrelativistic velocities, or in the limit of infinity length of the cavity (a single mirror), our results coincide with those found in the literature.

183

Comparative Finite Element Analysis of the Effects of Tillage Tool Geometry on Soil Disturbance and Reaction Forces  

Directory of Open Access Journals (Sweden)

Full Text Available In this study a comparative finite element analysis was conducted to investigate the effects of tillage tool geometry on soil disturbance and reaction forces. A nonlinear three dimensional finite element model, using ANSYS software, was developed to study the soil cutting process by trapezoidal (T1 and rectangular (T2 flat tools that inclined to the horizontal at three rake angles (R1 = 30°, R2 = 60° and R3 = 90°, therefore a total of six treatments were considered in this analysis. The soil media was assumed as elastic-perfectly plastic material with Drucker-Prager’s model. Results of this study revealed that the maximum vertical soil displaced by T1 is greater than that of T2; hence T1 disturbed the soil better than T2 . Results also showed that a significant reduction in draft force was noticed when cutting the soil with T1 in comparison to T2 . Designing the tool in the form of T1 significantly reduces the surface area of the tool; thus conserving the engineering material.

Mohamed Ahmed Elbashir

2014-04-01

184

A Comparison of the vertical ground reaction force during forward and backward walking In athletes with ankle sprain  

Directory of Open Access Journals (Sweden)

Full Text Available Background and Aim: Diabetes has world wide prevalence and it is estimated that up to ten years later, more than 300 million people would suffer from it. The disease has serious secondary complications. Physical activity can decrease the complications by altering the blood profiles. Patients with diabetes are unwilling to do physical exercise. Whole Body Vibration (WBV might be a proper substitution for exercise. The effects of WBV on patients with diabetes have not been studied enough, so the aim of this study was to evaluate the effects of WBV on the blood profiles in patients with diabetes type 2. Materials and Methods: Twenty patients with diabetes were assigned using matched assignment either into control (n=10 or intervention (n=10 group. Intervention group received the WBV with frequency of 30 Hz and amplitude of 2.5 mm for six weeks twice a week. The control group did not receive any intervention during this period. Blood profiles were measured in both groups at the baseline and the end of the study. Results: FBS and HbA1C decreased in intervention group in comparison with the control group but the differences were not statistically significant (P=0.44.  There were not significant statistical differences in Cholesterol, HDL, LDL and TG before and after the treatment between the two groups.Conclusion: The application of WBV with the above parameters might reduce FBS and HbA1C in patients with diabetes type 2. Increase in the amount of Glucose Transporter protein 4 (GLUT-4 is one of the contributing factors that these changes can be ascribed to.

H Sadeghi

2013-05-01

185

The effect of basketball footwear on the vertical ground reaction force during the landing phase of drop jumps  

Directory of Open Access Journals (Sweden)

Full Text Available Aunque la etiología de las lesiones por sobreuso es multifactorial, los impactos repetidos y la amortiguación insuficiente, han sido propuestos como dos de las principales causas de lesión. Los impactos son caracterizados por la fuerza de reacción vertical del suelo en dos picos. El primero de ellos, se corresponde con el aterrizaje de la parte delantera del pie (F1 y el segundo (F2, esta mas asociado a la producción de lesiones. El calzado de baloncesto, debido a su diseño y materiales, también podría ayudar a amortiguar el impacto del pie con la tierra. Sin embargo, no ha sido averiguado aún, si este calzado reduce dicho impacto. Objetivo. El objetivo de este estudio, fue determinar que el efecto del calzado de baloncesto sobre la fuerza de reacción de la tierra en la componente vertical durante el aterrizaje. Treinta estudiantes de la Universidad del País Vasco (Edad = 21.54 ± 1.12 años; masa corporal = 71.83 ± 8.15 kg; Altura = 177 ± 7 cm tomaron parte en este estudio. Todos ellos, realizaron 3 aterrizajes, después de ejecutar un salto drop (DL desde 30 cm (DL30 y desde 60 cm (DL60 de altura, en 2 condiciones diferentes: con calzado de baloncesto o con calzado de running. El periodo de descanso entre saltos fue de entre 60 a 90 sg. Se presentan datos desde 30 cm de altura, 2.27 ± 1.07, v (m. s–1 con calzado de baloncesto y de 2.49 ± 1.23 v (m • s–1 con calzado de running. Respecto a F2, el análisis concluyó que en ambas alturas desde 30 cm y desde 60 cm, se presentaron diferencias entre las botas de baloncesto y el calzado de running (6.20 ± 1.93 vs. 5.72 ± 1.79 Bw; 9.34 ± 2.16 vs. 8.27 ± 2.07 Bw. Los valores de F2 registrados con calzado de running fueron más bajos que los registrados con los de baloncesto (DL30: 11.13% DL60: 11.46%. Los impactos de la parte delantera y de reverso, son más altos cuando se ejecutan los saltos desde 60 cm con ambos calzados. El parámetro F2, fue el único estadísticamente distinto entre ambos calzados, desde ambas alturas de salto, con valores más bajos para el calzado de running.

Jes\\u00FAs C\\u00E1mara Tobalina

2013-01-01

186

Impingement effect of service module reaction control system engine plumes. Results of service module reaction control system plume model force field application to an inflight Skylab mission proximity operation situation with the inflight Skylab response  

Science.gov (United States)

Plume impingement effects of the service module reaction control system thruster firings were studied to determine if previous flight experience would support the current plume impingement model for the orbiter reaction control system engines. The orbiter reaction control system is used for rotational and translational maneuvers such as those required during rendezvous, braking, docking, and station keeping. Therefore, an understanding of the characteristics and effects of the plume force fields generated by the reaction control system thruster firings were examined to develop the procedures for orbiter/payload proximity operations.

Lobb, J. D., Jr.

1978-01-01

187

Simulated water-level declines caused by ground-water withdrawals near Holloman Air Force Base, Otero County, New Mexico  

Science.gov (United States)

The U.S. Geological Survey, in cooperation with the U.S. Air Force, Holloman Air Force Base, studied the potential change in water levels that could occur as a result of increased groundwater withdrawals from the middle-Tertiary to Holocene age basin-fill and alluvial deposits in the vicinity of the Air Force base in Otero County, New Mexico. Water level changes of 25 ft to as much as 60 ft below their 1982 levels are projected in the well field areas by the year 2001, based on an increased groundwater withdrawal of 10%. The 400-sq-mi area of unconsolidated material is relatively flat except for the alluvial fans adjacent to the mountain front. Perennial streams are not present in the study area. The aquifer has a saturated thickness that ranges from 0 to 3 ft. Intermittent streamflow from the nearby mountains infiltrates the alluvial fans and recharges the aquifer system. Groundwater is discharged from the area by underflow, evapotranspiration, and pumpage withdrawals from wells. (USGS)

Burns, A.W.; Hart, D.L., Jr.

1988-01-01

188

Study of the Reactions Controlling the Mobility of Uranium in Ground and Surface Water Systems in Contact with Apatite  

International Nuclear Information System (INIS)

The objective of this project was to define the mechanisms, equilibria, kinetics, and extent of sorption of aqueous uranium onto hydroxyapatite (Ca5(PO4)3(OH)) for a range of pH, ionic strength, aqueous uranium concentration, dissolved carbon/air CO2, and mineral surface area. We conducted chemical modeling, batch and flow-through experiments, chemical analysis, x-ray absorption and diffraction measurement, and electron microscopy. Our motivation was the need to immobilize U in water and soil to prevent it's entry into water supplies and ultimately, biological systems. Applying hydroxyapatite to in-situ treatment of uranium-bearing ground water could be an effective, low cost technology. We found that hydroxyapatite quickly, effectively, and reversibly sorbed uranium at a high capacity by inner-sphere complexation over a wide range of conditions. Our results indicate that at aqueous uranium concentrations below 10-20 ppb: (1) equilibrium sorption of uranium to hydroxyapatite occurs in hours, regardless of pH; (2) in ambient and CO2-free atmospheres, over 98% of initial uranium is sorbed to hydroxyapatite, (3) in waters in equilibrium with higher air CO2 concentrations, sorption removed over 97% of aqueous uranium, except above pH 9, where aqueous uranium concentrations were reduced by less than 40%, and (4) at near-neutral pH, bicarbonate alkalinities in excess of 500 slightly retarded sorption of uranium to hydroxyapatite, relative to lower alkalinities. Uranium sorption and precipitation are reversible and are not appreciably affected by ionic strength. The reversibility of these reactions requires that in situ treatment be carefully monitored to avoid breakthrough and de-sorption of uranium unto ground water. At typical surface conditions, sorption is the only mode of uranium sequestration below 20-50 ppb U - above this range, precipitation of uranium phosphate minerals begins to dominate sequestration processes. We verified that one m2 of hydroxyapatite can sorb over 7.53 X 10-6 moles or 1.8 mg of uranium in agreement with calculations based on phosphate and calcium oxide sites on the unit cell. Our work is significant because small masses of hydroxyapatite can sorb appreciable masses of uranium quickly over a wide range of chemistries. Preliminary work with ground water containing 260 ppb of uranium and cow bone char indicates that its sorptive capacity is appreciable less than pure hydroxyapatite. Pure crystalline hydroxyapatite sequestered 2.9 mg of uranium per m2 as opposed to 0.083 mg of uranium sequestered per m2 of cow bone char, or 27% versus 3.5% by surface area, respectively. Extended x-ray adsorption fine structure (EXAFS) spectroscopy defined mono- and bidentate sorption of uranium to phosphate and calcium oxide groups on the hydroxyapatite surface. The EXAFS data indicate that up to several thousand parts U per million parts hydroxyapatite, surface complexation, and not precipitation, is the predominant process. Above this uranium: hydroxyapatite mass ratio, precipitation of meta-autunite (H2(UO2)2(PO4)2 x 10H20) dominates the sequestration process

189

The physics of nuclear reactions  

International Nuclear Information System (INIS)

This new edition of the author's 'Nuclear Reactions' gives a general account of the interactions between nuclei and is intended for use by students in the second or third year of honours course. The chapters are headed; introduction, particle accelerators, kinematics, reactions of light nuclei, wave-mechanical theory of scattering, resonant scattering and reactions, reaction mechanisms, nuclear reactors, thermonuclear reactions, nuclear forces, and nuclear spin. A number of problems are set on each section and answers given. In an appendix the main properties of known types of nuclei in their ground states are summarized. (UK)

190

A Radial Basis Function (RBF)-Finite Difference Method for the Simulation of Reaction-Diffusion Equations on Stationary Platelets within the Augmented Forcing Method  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We present a computational method for solving the coupled problem of chemical transport in a fluid (blood) with binding/unbinding of the chemical to/from cellular (platelet) surfaces in contact with the fluid, and with transport of the chemical on the cellular surfaces. The overall framework is the Augmented Forcing Point Method (AFM) (\\emph{L. Yao and A.L. Fogelson, Simulations of chemical transport and reaction in a suspension of cells I: An augmented forcing point method ...

Shankar, Varun; Wright, Grady B.; Fogelson, Aaron L.; Kirby, Robert M.

2013-01-01

191

An experimental study on advancement of damping performance of foundations in soft ground. Pt.1: Forced vibration tests of a foundation block constructed on improved soil medium  

International Nuclear Information System (INIS)

Purpose of this study is to enhance attenuation performance of structures that will be constructed in the soft ground area. We conducted material tests to obtain basic properties of the soil cement column. The forced vibration tests then were carried out to acquire dynamic feature of the reinforced concrete block constructed on improved soil mediums. Additional forced vibration tests for various conditions of trenches dug along the block were conducted to obtain fundamental features of damping effect of the side surfaces of the test block. According to results of the material testing, densities of the soil cement columns were 1.45-1.52 g/cm3 and the unconfined compressive strengths were 2.4-4.2 times as large as the specified design strength (1 MPa). In comparison of resonance curves by experiments and simulation analysis, simulation analysis results estimated by the hybrid approach were in good agreement with experiment ones for both the X and Y-directions. From the results of the forced vibration test focusing on various condition of the trenches dug along the test block, it was indicated that response of tamping by the rammer decreased compared with that of treading. (authors)

192

Effects of the tensor force on the ground and first $2^{+}$ states of the magic $^{54}$Ca nucleus  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The magic nature of the $^{54}$Ca nucleus is investigated in the light of the recent experimental results. We employ both HFB and HF+BCS methods using Skyrme-type SLy5, SLy5+T and T44 interactions. The evolution of the single-particle spectra is studied for the N=34 isotones: $^{60}$Fe, $^{58}$Cr, $^{56}$Ti and $^{54}$Ca. An increase is obtained in the neutron spin-orbit splittings of $p$ and $f$ states due to the effect of the tensor force which also makes $^{54}$Ca a magic...

Yu?ksel, E.; Giai, N.; Khan, E.; Bozkurt, K.

2014-01-01

193

Effects of the tensor force on the ground state and first 2+ states of the magic Ca54 nucleus  

Science.gov (United States)

The magic nature of the Ca54 nucleus is investigated in light of recent experimental results. We employ both Hartree-Fock-Bogoliubov and Hartree-Fock (HF)+BCS methods using Skyrme-type SLy5, SLy5+T, and T44 interactions. The evolution of the single-particle spectra is studied for the N =34 isotones: Fe60, Cr58, Ti56, and Ca54. An increase is obtained in the neutron spin-orbit splittings of p and f states due to the effect of the tensor force which also makes Ca54 a magic nucleus candidate. Quasiparticle random-phase approximation calculations on top of HF+BCS are performed to investigate the first J?=2+ states of the calcium isotopic chain. A good agreement for excitation energies is obtained when we include the tensor force in the mean-field part of the calculations. The first 2+ states indicate a subshell closure for both Ca52 and Ca54 nuclei. We confirm that the tensor part of the interaction is quite essential in explaining the neutron subshell closure in Ca52 and Ca54 nuclei.

Yüksel, E.; Van Giai, N.; Khan, E.; Bozkurt, K.

2014-06-01

194

Effects of the tensor force on the ground and first $2^{+}$ states of the magic $^{54}$Ca nucleus  

CERN Document Server

The magic nature of the $^{54}$Ca nucleus is investigated in the light of the recent experimental results. We employ both HFB and HF+BCS methods using Skyrme-type SLy5, SLy5+T and T44 interactions. The evolution of the single-particle spectra is studied for the N=34 isotones: $^{60}$Fe, $^{58}$Cr, $^{56}$Ti and $^{54}$Ca. An increase is obtained in the neutron spin-orbit splittings of $p$ and $f$ states due to the effect of the tensor force which also makes $^{54}$Ca a magic nucleus candidate. QRPA calculations on top of HF+BCS are performed to investigate the first $J^{\\pi}$=$2^{+}$ states of the calcium isotopic chain. A good agreement for excitation energies is obtained when we include the tensor force in the mean-field part of the calculations. The first $2^{+}$ states indicate a subshell closure for both $^{52}$Ca and $^{54}$Ca nuclei. We confirm that the tensor part of the interaction is quite essential in explaining the neutron subshell closure in $^{52}$Ca and $^{54}$Ca nuclei.

Yüksel, E; Khan, E; Bozkurt, K

2014-01-01

195

Low-energy 2H(d,?)4He reaction and the D-state admixture in the 4He ground state  

International Nuclear Information System (INIS)

We have studied the low-energy 2H(d,?) 4He reaction based on a microscopic description of the nuclear wave functions. Our study reproduces the experimental reaction cross sections at E?3 MeV; it allows for an extrapolation of the data to energies relevant for big-bang nucleosynthesis resulting in a cross section about 35 times higher than given in present compilations. Our results indicate a D-state admixture in the 4He ground state of ?5--7 %

196

Influence of Coulomb and nuclear forces on the pattern of the double differential cross section d2sigma/d theta dE for deep inelastic reactions  

International Nuclear Information System (INIS)

The tremendous change in the pattern of the Wilczynski curves for deep inelastic reactions with the product Z1Z2 is interpreted within a model including both dissipation and statistical fluctuations. The competition between Coulomb and nuclear forces seems to account for this effect

197

Assessment of natural attenuation of ground-water contamination at sites FT03, LF13, and WP14/LF15, Dover Air Force Base, Delaware  

Science.gov (United States)

Water-quality, aquifer-sediment, and hydro-logic data were used to assess the effectiveness of natural attenuation of ground-water contamination at Fire Training Area Three, the Rubble Area Landfill, the Liquid Waste Disposal Landfill, and the Receiver Station Landfill in the East Management Unit of Dover Air Force Base, Delaware. These sites, which are contaminated with chlorinated solvents and fuel hydrocarbons, are under-going long-term monitoring to determine if natural attenuation continues to sufficiently reduce contaminant concentrations to meet regulatory requirements. This report is the first assessment of the effectiveness of natural attenuation at these sites since long-term monitoring began in 1999, and follows a preliminary investigation done in 1995?96. This assessment was done by the U.S. Geological Survey in cooperation with the U.S. Air Force.Since 1995?96, additional information has been collected and used in the current assessment. The conclusions in this report are based primarily on ground-water samples collected from January through March 2000. Previous analytical results from selected wells, available geologic and geo-physical well logs, and newly acquired information such as sediment organic-carbon measurements, hydraulic-conductivity measurements determined from slug tests on wells in the natural attenuation study area, and water-level measurements from surficial-aquifer wells also were used in this assessment. This information was used to: (1) calculate retardation factors and estimate contaminant migration velocities, (2) improve estimates of ground-water flow directions and inferred contaminant migration pathways, (3) better define the areal extent of contamination and the proximity of contaminants to discharge areas and the Base boundary, (4) develop a better under-standing of the vertical variability of contaminant concentrations and redox conditions, (5) evaluate the effects of temporal changes on concentrations in the plumes and source areas, and (6) determine whether intrinsic biodegradation is occurring at these sites.The water-quality data indicate that intrinsic biodegradation is occurring at all three sites. The strongest indication of intrinsic biodegradation is the detection of tetrachloroethene and trichloroethene breakdown products within and down-gradient of the source areas. The patterns of electron acceptors and metabolic by-products indicate that contaminant biodegradation has changed the prevailing geochemistry of the surficial aquifer, creating the strongly reducing conditions necessary for chlorinated solvent bio-degradation. Geochemical changes include depleted dissolved oxygen and elevated ferrous iron and methane levels relative to concentrations in uncontaminated zones of the surficial aquifer. At Fire Training Area Three and the Rubble Area Landfill sites, natural attenuation appears to be adequate for controlling the migration of the contaminant plumes. At the third site, the Liquid Waste Disposal and Receiver Station Landfills, the plume is larger and the uncertainty about the effectiveness of natural attenuation in reducing contaminant concentrations and controlling plume migration is greater. Ground-water data indicate, however, that U.S. Environmental Protection Agency maximum contaminant levels were not exceeded in any point-of-compliance wells located along the Base boundary.The information presented in this report led to the development of improved conceptual models for these sites, and to the recognition of four issues that are currently unclear and may need further study. These issues include delineating the areal and vertical extent of the contaminant plumes in greater detail, determining the extent of intrinsic biodegradation downgradient of the Liquid Waste Disposal and Receiver Station Landfills, deter-mining the fate of contaminants in the ground-water discharge areas, and determining the effect of temporal variability in source concentrations and ground-water

Barbaro, Jeffrey R.

2002-01-01

198

A comparison of ground-based and space flight data: Atomic oxygen reactions with boron nitride and silicon nitride  

Science.gov (United States)

The effects of atomic oxygen on boron nitride (BN) and silicon nitride (Si3N4) have been studied in low Earth orbit (LEO) flight experiments and in a ground-based simulation facility at Los Alamos National Laboratory. Both the in-flight and ground-based experiments employed the materials coated over thin (approx 250 Angstrom) silver films whose electrical resistance was measured in situ to detect penetration of atomic oxygen through the BN and Si3N4 materials. In the presence of atomic oxygen, silver oxidizes to form silver oxide, which has a much higher electrical resistance than pure silver. Permeation of atomic oxygen through BN, as indicated by an increase in the electrical resistance of the silver underneath, was observed in both the in-flight and ground-based experiments. In contrast, no permeation of atomic oxygen through Si3N4 was observed in either the in-flight or ground-based experiments. The ground-based results show good qualitative correlation with the LEO flight results, thus validating the simulation fidelity of the ground-based facility in terms of reproducing LEO flight results.

Cross, J. B.; Lan, E. H.; Smith, C. A.; Whatley, W. J.; Koontz, S. L.

1990-01-01

199

Accurate quantum wave packet calculations for the F + HCl ? Cl + HF reaction on the ground 1(2)A' potential energy surface.  

Science.gov (United States)

We present converged exact quantum wave packet calculations of reaction probabilities, integral cross sections, and thermal rate coefficients for the title reaction. Calculations have been carried out on the ground 1(2)A' global adiabatic potential energy surface of Deskevich et al. [J. Chem. Phys. 124, 224303 (2006)]. Converged wave packet reaction probabilities at selected values of the total angular momentum up to a partial wave of J = 140 with the HCl reagent initially selected in the v = 0, j = 0-16 rovibrational states have been obtained for the collision energy range from threshold up to 0.8 eV. The present calculations confirm an important enhancement of reactivity with rotational excitation of the HCl molecule. First, accurate integral cross sections and rate constants have been calculated and compared with the available experimental data. PMID:22423835

Bulut, Niyazi; K?os, Jacek; Alexander, Millard H

2012-03-14

200

2H(p, pp) n reaction as a probe of the short-range nuclear force  

International Nuclear Information System (INIS)

We examine the feasibility of using the 2H(p, pp) n reaction as a means of extracting information about the short-range behavior of the nuclear force not obtainable from N-N scattering experiments. To do this we use several separable potentials and examine the predicted cross section in various regions of phase space and for beam energies between 14 and 65 MeV. The questions that we address are likely to be insensitive to Coulomb effects. Both the form factor and the energy dependence of the potentials have been modified from the usual Yamaguchi form. The form of the energy dependence is chosen to obtain phase-shift equivalence for two different form factors while guaranteeing a unitary two-body scattering amplitude. The sensitivity of breakup results to the on-shell and off-shell aspects of the nuclear force is examined and discussed. Significant on-shell sensitivity occurs for breakup amplitudes in all states and for cross sections over all regions of phase space. Off-shell sensitivity appears only in the S = 1/2, L = 0 breakup amplitudes, with all S = 3/2 and all L > 0 amplitudes exhibiting negligible off-shell dependence. This result leads to only a very small (< or = 5%) off-shell sensitivity for quasifree scattering. However, cross sections far from quasifree scattering, and in particular cross sections in the final-state interaction region of phase space, exhibit as much as a 50% variation for phase-shift-equivalent potentials. This sensitivity is smivalent potentials. This sensitivity is small at low beam energy and increases with increasing energy. The energy dependence at negative energies of one potential is also altered to adjust the triton binding energy. This enables us to compare phase-shift-equivalent potentials differing off shell but predicting the same triton binding energy. The energy dependence of this potential is somewhat unconventional. Fixing of the triton binding energy reduces the off-shell sensitivity appreciably only for E approximately-less-than 20 MeV

 
 
 
 
201

Solar energy assessment in the Alpine area: satellite data and ground instruments integration for studying the radiative forcing of aerosols.  

Science.gov (United States)

The primary objective of this work is to purpose an approach for estimating the effect of aerosols on surface incoming shortwave radiation (SIS) in the Alpine region, which is based on the integration of different instruments: we develop a GIS model, whose output is corrected by monthly atmospheric coefficients, and then we progressively add details by daily updated atmospheric information. The assessment of solar energy availability at the earth's surface over a specific geographic area is crucial for planning photovoltaic panels installation. When modeling SIS with GIS instruments or retrieving it from satellites measurements, we have to account for terrain shadowing and atmospheric extinction, both of which are difficult to describe in the Alpine area, because of the topographic complexity and the local atmospheric circulation influence on the atmospheric composition. While advanced methods were developed to carefully describe the effect of topography, the atmospheric attenuation was considered so far only through monthly turbidity values, and the question remains whether it be possible to develop a time-effective routine to model the atmospheric effect on SIS at daily scale. As a first step we produced a WebGIS for the town of Bressanone, Italy, showing a classification of the roofs of the buildings according to the yearly amount of global irradiance. Furthermore we provide the annual electricity production based on the efficiency of the most common PV technologies. At this stage clear sky irradiance was computed with a GIS based model, and afterwards monthly correction coefficients were applied to add real sky conditions to the merely geometrical computations, which were obtained from 20 years of measurement collected by the pyranometer in the closest meteorological station. As a second step we investigate the influence of aerosol optical properties on SIS by running the radiative transfer model libRadtran by using as input the aerosol model defined for the measurement site of Bolzano, where we installed an AERONET sun-photometer for measuring aerosol optical properties and column water-vapor amount. The impact of aerosols on the surface irradiance was already demonstrated, in fact the literature shows that the daily aerosol direct forcing on the surface radiation in the Italian Po valley amounts on average to -12.2 Wm-2, with extremes values beyond -70 Wm-2. In particular here we examine the role in the radiation budget of the Alpine valleys of aerosol microphysical characteristics, such as size distribution, and optical properties, such as phase function, derived from the inversion of spectrally resolved sky radiances. After provided evidence of the radiative impact of atmospheric aerosols on solar energy availability in the Alpine area, the final step will be the enhancement of the most advanced existent algorithm for retrieving SIS in the Alpine area from satellite data, developed by MeteoSwiss in the framework of CM-SAF, which thoroughly considers the effect of topography and clouds, while can still be improved in terms of atmospheric input data.

Castelli, M.; Petitta, M.; Emili, E.

2012-04-01

202

Large-eddy simulation of pollutant dispersion from a ground-level area source over urban street canyons with irreversible chemical reactions  

Science.gov (United States)

In this study, the dispersion of chemically reactive pollutants is calculated by large-eddy simulation (LES) in a neutrally stratified urban canopy layer (UCL) over urban areas. As a pilot attempt, idealized street canyons of unity building-height-to-street-width (aspect) ratio are used. Nitric oxide (NO) is emitted from the ground surface of the first street canyon into the domain doped with ozone (O3). In the absence of ultraviolet radiation, this irreversible chemistry produces nitrogen dioxide (NO2), developing a reactive plume over the rough urban surface. A range of timescales of turbulence and chemistry are utilized to examine the mechanism of turbulent mixing and chemical reactions in the UCL. The Damköhler number (Da) and the reaction rate (r) are analyzed along the vertical direction on the plane normal to the prevailing flow at 10 m after the source. The maximum reaction rate peaks at an elevation where Damköhler number Da is equal or close to unity. Hence, comparable timescales of turbulence and reaction could enhance the chemical reactions in the plume.

Du, T. Z.; Liu, C.-H.; Zhao, Y. B.

2014-10-01

203

Rotational, steric, and coriolis effects on the F + HCl --> HF + Cl reaction on the 1(2)A' ground-state surface.  

Science.gov (United States)

We present a quantum study of the reaction F((2)P) + HCl(X(1)Sigma(+)) --> HF(X(1)Sigma(+)) + Cl((2)P) on a recently computed 1(2)A' ground-state surface, considering HCl in the ground vibrational state, with up to 16 rotational quanta j(0). We employ the real wavepacket (WP) and flux methods for calculating coupled-channel (CC) and centrifugal-sudden (CS) initial-state probabilities up to J = 80 and 140, respectively. We also report CC and CS ground-state cross sections and CS excited-state cross sections and discuss the dynamics analyzing WP time evolutions. The HCl rotation highly enhances reaction probabilities and cross sections, as it was previously found for probabilities at J reaction stereodynamics and energetics. Steric effects favor indeed the overcoming of the potential barrier and a linearly dominated mechanism. Attractive Coriolis couplings favor instead the energy flow from the HCl rotation to the F-H---Cl reactive vibration. WP snapshots confirm and explain the HCl rotational effects, because the density into the nearly collinear F-H---Cl product channel increases remarkably with j(0). Finally, our CS rate constant is underestimated with respect to the experiment, pointing out the need of more accurate multisurface and CC calculations. PMID:19371113

Defazio, Paolo; Petrongolo, Carlo

2009-04-23

204

Tensor Force Manifestations in ab Initio Study of the 2H(d, ?)4He, 2H(d, p)3H, and 2H(d, n)3He Reactions  

International Nuclear Information System (INIS)

The 2H(d, ?)4He capture reaction and the 2H(d, p)3H and 2H(d, n)3He transfer reactions at very low energies are studied in an extended microscopic cluster model with a realistic nucleon–nucleon force. Our results show that the tensor force in realistic interactions plays an essential and indispensable role to reproduce the very low-energy astrophysical S factor of these reactions. (author)

205

Ground states of molecules. XLIX. MINDO/3 study of the retro-diels-alder reaction of cyclohexene  

International Nuclear Information System (INIS)

The retro-Diels-Alder reaction of cyclohexene to form ethylene and butadiene has been studied, using MINDO/3. The transition state is predicted to be very unsymmetric, corresponding to weakening of one of the two breaking CC bonds. The calculated entropy of activation agrees well with experiment and the calculated secondary isotope effects for 4,4-dideuteriocyclohexene and 4,4,5,5-tetradeuteriocyclohexene are similar to those measured for an analogous reaction by Taagepera and Thornton. Discrepancies between the conclusions reached here and those from recent ab-initio calculations are discussed. 4 tables, 3 figures, 53 references

206

Procedures for addressing uncertainty and variability in exposure to characterize potential health risk from trichloroethylene contaminated ground water at Beale Air Force Base in California; TOPICAL  

International Nuclear Information System (INIS)

Conservative deterministic, screening-level calculations of exposure and risk commonly are used in quantitative assessments of potential human-health consequences from contaminants in environmental media. However, these calculations generally are based on multiple upper-bound point estimates of input parameters, particularly for exposure attributes, and can therefore produce results for decision makers that actually overstate the need for costly remediation. Alternatively, a more informative and quantitative characterization of health risk can be obtained by quantifying uncertainty and variability in exposure. This process is illustrated in this report for a hypothetical population at a specific site at Beale Air Force Base in California, where there is trichloroethylene (TCE) contaminated ground water and a potential for future residential use. When uncertainty and variability in exposure were addressed jointly for this case, the 95th-percentile upper-bound value of individual excess lifetime cancer risk was a factor approaching 10 lower than the most conservative deterministic estimate. Additionally, the probability of more than zero additional cases of cancer can be estimated, and in this case it is less than 0.5 for a hypothetical future residential population of up to 26,900 individuals present for any 7.6-y interval of a 70-y time period. Clearly, the results from application of this probabilistic approach can provide reasonable and equitable risk-acceptability asonable and equitable risk-acceptability criteria for a contaminated site

207

Procedures for addressing uncertainty and variability in exposure to characterize potential health risk from trichloroethylene contaminated ground water at Beale Air Force Base in California  

Energy Technology Data Exchange (ETDEWEB)

Conservative deterministic, screening-level calculations of exposure and risk commonly are used in quantitative assessments of potential human-health consequences from contaminants in environmental media. However, these calculations generally are based on multiple upper-bound point estimates of input parameters, particularly for exposure attributes, and can therefore produce results for decision makers that actually overstate the need for costly remediation. Alternatively, a more informative and quantitative characterization of health risk can be obtained by quantifying uncertainty and variability in exposure. This process is illustrated in this report for a hypothetical population at a specific site at Beale Air Force Base in California, where there is trichloroethylene (TCE) contaminated ground water and a potential for future residential use. When uncertainty and variability in exposure were addressed jointly for this case, the 95th-percentile upper-bound value of individual excess lifetime cancer risk was a factor approaching 10 lower than the most conservative deterministic estimate. Additionally, the probability of more than zero additional cases of cancer can be estimated, and in this case it is less than 0.5 for a hypothetical future residential population of up to 26,900 individuals present for any 7.6-y interval of a 70-y time period. Clearly, the results from application of this probabilistic approach can provide reasonable and equitable risk-acceptability criteria for a contaminated site.

Daniels, J I; Bogen, K T; Hall, L C

1999-10-05

208

The HNO3 forming branch of the HO2 + NO reaction: pre-industrial-to-present trends in atmospheric species and radiative forcings  

Directory of Open Access Journals (Sweden)

Full Text Available Recent laboratory measurements have shown the existence of a HNO3 forming branch of the HO2 + NO reaction. This reaction is the main source of tropospheric O3, through the subsequent photolysis of NO2, as well as being a major source of OH. The branching of the reaction to HNO3 reduces the formation of these species significantly, affecting O3 abundances, radiative forcing and the oxidation capacity of the troposphere. The Oslo CTM2, a three-dimensional chemistry transport model, is used to calculate atmospheric composition and trends with and without the new reaction branch. Results for the present day atmosphere, when both temperature and pressure effects on the branching ratio are accounted for, show an 11 % reduction in the calculated tropospheric burden of O3, with the main contribution from the tropics. An increase of the global, annual mean methane lifetime by 10.9 %, resulting from a 14.1 % reduction in the global, annual mean OH concentration is also found. Comparisons with measurements show that including the new branch improves the modelled O3 in the Oslo CTM2, but that it is not possible to conclude whether the NOy distribution improves. We model an approximately 11 % reduction in the tropical tropospheric O3 increase since pre-industrial times, and a 4 % reduction of the increase in total tropospheric burden. Also, an 8 % decrease in the trend of OH concentrations is calculated, when the new branch is accounted for. The radiative forcing due to changes in O3 over the industrial era was calculated as 0.33 W m?2, reducing to 0.26 W m?2 with the new reaction branch. These results are significant, and it is important that this reaction branching is confirmed by other laboratory groups.

I. S. A. Isaksen

2011-09-01

209

Ground-state correlations in 12C and the mechanism of the (e,e'p) reaction  

International Nuclear Information System (INIS)

In this thesis the results of an investigation into two aspects of the mechanism of the quasi-elastic (e,e'p) reaction: the interaction between the incident electron and the bound proton and the residual nucleus (final-state interaction (FSI)), are presented and used in the extraction of nuclear-structure information from (e,e'p) measurements on 12C. The experiments were carried out at NIKHEF-K with a high-resolution spectrometer. Two kinds of experiments have been performed on 12C. The first was aimed at obtaining accurate momentum distributions for various final states in 11B. Some special measurements were carried out in order to vary the parameters influencing the FSI. The role of coupled-channels effects in the 12C(e,e'p)11Be reaction is discussed. It is discussed whether some of the weak transitions observed in this reaction, can be associated with knockout from normally unoccupied shell-model orbitals. The second experiment on 12C was devoted to the e-p coupling. These measurements were supplemented with data taken on 6Li. The latter measurement allowed for measuring simultaneously knockout from the relatively dense 4He core and the relatively dilute deuteron. In this way the density dependence of the e-p coupling in the nucleus could be studied. The results of these experiments have been compared to various models that take into account the effect of the nuclear medium upon the e-p coupling. The possible role of charge-exchange and meson-exchange currents in the interpretation of these experiments is also considered. A brief survey of the formalism of the quasi-elastic (e,e'p) reaction is also presented. (author). 196 refs.; 53 figs.; 21 tabs

210

Objective Lightning Forecasting at Kennedy Space Center/Cape Canaveral Air Force Station using Cloud-to-Ground Lightning Surveillance System Data  

Science.gov (United States)

The 45th Weather Squadron (45 WS) forecasters at Cape Canaveral Air Force Station (CCAFS) in Florida include a probability of thunderstorm occurrence in their daily morning briefings. This information is used by personnel involved in determining the possibility of violating Launch Commit Criteria, evaluating Flight Rules for the Space Shuttle, and daily planning for ground operation activities on Kennedy Space Center (KSC)/CCAFS. Much of the current lightning probability forecast is based on a subjective analysis of model and observational data. The forecasters requested that a lightning probability forecast tool based on statistical analysis of historical warm-season (May - September) data be developed in order to increase the objectivity of the daily thunderstorm probability forecast. The tool is a set of statistical lightning forecast equations that provide a lightning occurrence probability for the day by 1100 UTC (0700 EDT) during the warm season. This study used 15 years (1989-2003) of warm season data to develop the objective forecast equations. The local CCAFS 1000 UTC sounding was used to calculate stability parameters for equation predictors. The Cloud-to-Ground Lightning Surveillance System (CGLSS) data were used to determine lightning occurrence for each day. The CGLSS data have been found to be more reliable indicators of lightning in the area than surface observations through local informal analyses. This work was based on the results from two earlier research projects. Everitt (1999) used surface observations and rawinsonde data to develop logistic regression equations that forecast the daily thunderstorm probability at CCAFS. The Everitt (1999) equations showed an improvement in skill over the Neumann-Pfeffer thunderstorm index (Neumann 1971), which uses multiple linear regression, and also persistence and climatology forecasts. Lericos et al. (2002) developed lightning distributions over the Florida peninsula based on specific flow regimes. The flow regimes were inferred from the average wind direction in the 1000-700 mb layer at Miami (MIA), Tampa (TBW), and Jacksonville (JAX), Florida, and the lightning data were from the National Lightning Detection Network. The results suggested that the daily flow regime may be an important predictor of lightning occurrence on KSC/CCAFS.

Lambert, Winifred; Wheeler, Mark

2004-01-01

211

Momentum-space 3N Faddeev calculations of hadronic and electromagnetic reactions with proton-proton Coulomb and three-nucleon forces included  

CERN Document Server

We extend our approach to incorporate the proton-proton (pp) Coulomb force into the three-nucleon (3N) momentum-space Faddeev calculations of elastic proton-deuteron (pd) scattering and breakup to the case when also a three-nucleon force (3NF) is acting. In addition we formulate that approach in the application to electron- and gamma-induced reactions on 3He. The main new ingredient is a 3-dimensional screened pp Coulomb t-matrix obtained by a numerical solution of a 3-dimensional Lippmann-Schwinger equation (LSE). The resulting equations have the same structure as the Faddeev equations which describe pd scattering without 3NF acting. That shows the practical feasibility of both presented formulations.

Witala, H; Golak, J; Gloeckle, W

2010-01-01

212

Reinterpretation of curved Hammett plots in reaction of nucleophiles with aryl benzoates: change in rate-determining step or mechanism versus ground-state stabilization.  

Science.gov (United States)

A kinetic study is reported for the reaction of the anionic nucleophiles OH-, CN-, and N 3 - with aryl benzoates containing substituents on the benzoyl as well as the aryloxy moiety, in 80 mol % H2O - 20 mol % dimethyl sulfoxide at 25.0 degrees C. Hammett log k vs sigma plots for these systems are consistently nonlinear. However, a possible traditional explanation in terms of a mechanism involving a tetrahedral intermediate with curvature resulting from a change in rate-determining step is considered but rejected. The proposed explanation involves ground-state stabilization through resonance interaction between the benzoyl substituent and the electrophilic carbonyl center in the two-stage mechanism. Accordingly, the data are nicely accommodated on the basis of the Yukawa-Tsuno equation, which gives linear plots for all three nuceophiles. Literature reports of the mechanism of acyl transfer processes are reconsidered in this light. PMID:12444628

Um, Ik-Hwan; Han, Hyun-Joo; Ahn, Jung-Ae; Kang, Swan; Buncel, Erwin

2002-11-29

213

Electron-transfer reactions involving two harmonic potentials with a different force constant: The Zusman approach versus the spin-boson model  

International Nuclear Information System (INIS)

Two approaches: (a generalized spin-boson model with a nonlinear spin-boson coupling and the Zusman's stochastic Liouville formalism) are employed to analyze the electron-transfer reactions involving two harmonic potentials with a different force constant. An analytical rate formula, expressed as a convoluted integral of the individual rate kernel for each mode, is derived with full consideration of quantum tunneling effects. For a dominant solvent mode at low frequency, the formula can be reduced to the results of the Zusman's theory, showing asymmetry of the Marcus rate plot between the normal and the inverted regions

214

Investigation of nuclear forces in d + p elastic and p + d break-up reactions at intermediate energies  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In this thesis, the break-up and elastic channels of the reaction at a proton-beam energy of 190~MeV were studied using BINA. After accelerating the polarized-proton beam from POLIS with AGOR, reactions of protons with deuterons from a liquid-deuterium target took place at the center of BINA. The cross section and analyzing powers are measured as a function of the kinematical variable S for different combinations of the polar coordinates of the outgoing particles. As a conclusion and ...

Mardanpour-mollalar, Hossein

2008-01-01

215

The HNO3 forming branch of the HO2 + NO reaction: pre-industrial-to-present trends in atmospheric species and radiative forcings  

Directory of Open Access Journals (Sweden)

Full Text Available Recent laboratory measurements have shown the existence of a HNO3 forming branch of the HO2 + NO reaction. This reaction is the main source of atmospheric O3, through the subsequent photolysis of NO2, as well as being a major source of OH. The branching of the reaction to HNO3 reduces the formation of these species significantly, affecting O3 abundances, climate and the oxidation capacity of the troposphere. The Oslo CTM2, a three-dimensional chemistry transport model, is used to calculate atmospheric composition and trends with and without the new reaction branch. Results for the present day atmosphere, when both temperature and pressure effects on the branching ratio are accounted for, show an increase of the global, annual mean methane lifetime by 10.9 %, resulting from a 14.1 % reduction in the global, annual mean OH concentration. Comparisons with measurements show that including the new branch improves the modelled O3, but that it is not possible to conclude whether the NOy distribution improves. We model an approximately 11 % reduction in the tropical tropospheric O3 increase since pre-industrial times, as well as an 8 % decrease in the trend of OH concentration, when the new branch is accounted for. The radiative forcing due to changes in O3 over the industrial era was calculated as 0.33 W m?2, reducing to 0.26 W m?2 with the new reaction branch. These results are significant, and it is important that this reaction branching is confirmed by other laboratory groups.

I. S. A. Isaksen

2011-05-01

216

Self-Force with a Stochastic Component from Radiation Reaction of a Scalar Charge Moving in Curved Spacetime  

CERN Document Server

We give a quantum field theoretical derivation of the scalar Abraham-Lorentz-Dirac (ALD) equation and the self-force for a scalar charged particle interacting with a quantum scalar field in curved spacetime. We regularize the causal Green's function using a quasi-local expansion in the spirit of effective field theory and obtain a regular expression for the self-force. The scalar ALD equation obtained in this way for the classical motion of the particle checks with the equation obtained by Quinn earlier \\cite{Quinn}. We further derive a scalar ALD-Langevin equation with a classical stochastic force accounting for the effect of quantum fluctuations in the field, which causes small fluctuations on the particle trajectory. This equation will be useful for the study of stochastic motion of charges under the influence of both quantum or classical noise sources, derived either self-consistently (as done here) or put in by hand (with warnings). We show the possibility of secular effects from such stochastic influenc...

Galley, C R; Galley, Chad R.

2005-01-01

217

A global ab initio potential energy surface for the X?2A? ground state of the Si + OH ? SiO + H reaction  

International Nuclear Information System (INIS)

We report the first global potential energy surface (PES) for the X?2A? ground electronic state of the Si(3P) + OH(X2?) ? SiO(X1?g+) + H(2S) reaction. The PES is based on a large number of ab initio energies obtained from multireference configuration interaction calculations plus Davidson correction (MRCI+Q) using basis sets of quadruple zeta quality. Corrections were applied to the ab initio energies in the reactant channel allowing a proper description of long-range interactions between Si(3P) and OH(X2?). An analytical representation of the global PES has been developed by means of the reproducing kernel Hilbert space method. The reaction is found barrierless. Two minima, corresponding to the SiOH and HSiO isomers, and six saddle points, among which the isomerization transition state, have been characterized on the PES. The vibrational spectra of the SiOH/HSiO radicals have been computed from second-order perturbation theory and quantum dynamics methods. The structural, energetic, and spectroscopic properties of the two isomers are in good agreement with experimental data and previous high quality calculations

218

A global ab initio potential energy surface for the X{sup ?2}A{sup ?} ground state of the Si + OH ? SiO + H reaction  

Energy Technology Data Exchange (ETDEWEB)

We report the first global potential energy surface (PES) for the X{sup ?2}A{sup ?} ground electronic state of the Si({sup 3}P) + OH(X{sup 2}?) ? SiO(X{sup 1}?{sub g}{sup +}) + H({sup 2}S) reaction. The PES is based on a large number of ab initio energies obtained from multireference configuration interaction calculations plus Davidson correction (MRCI+Q) using basis sets of quadruple zeta quality. Corrections were applied to the ab initio energies in the reactant channel allowing a proper description of long-range interactions between Si({sup 3}P) and OH(X{sup 2}?). An analytical representation of the global PES has been developed by means of the reproducing kernel Hilbert space method. The reaction is found barrierless. Two minima, corresponding to the SiOH and HSiO isomers, and six saddle points, among which the isomerization transition state, have been characterized on the PES. The vibrational spectra of the SiOH/HSiO radicals have been computed from second-order perturbation theory and quantum dynamics methods. The structural, energetic, and spectroscopic properties of the two isomers are in good agreement with experimental data and previous high quality calculations.

Dayou, Fabrice, E-mail: fabrice.dayou@obspm.fr [Laboratoire d' Etude du Rayonnement et de la Matière en Astrophysique (UMR 8112 du CNRS), Observatoire de Paris-Meudon, Université Pierre et Marie Curie, 92195 Meudon Cedex (France); Duflot, Denis; Rivero-Santamaría, Alejandro; Monnerville, Maurice [Laboratoire de Physique des Lasers, Atomes et Molécules (UMR 8523 du CNRS), Université Lille I Sciences et Technologies, 59655 Villeneuve d' Ascq Cedex (France)

2013-11-28

219

Odd oxygen formation in the laser irradiation of O2 at 248 nm - Evidence for reactions of O2 in the Herzberg states with ground state O2  

Science.gov (United States)

Two O3 formation processes (initiation and autocatalytic) are studied in pure O2 and in O2+N2 and O2+Ar mixtures at pressures between 200 and 1600 torr and at temperatures between 298 and 370 K. Evidence is presented that the initiation process produces O3 through chemical reactions between ground state O2 and excited O2 in the Herzberg states, which are produced by the photoabsorption of O2 at 248 nm. For the autocatalytic process, the results are consistent with the proposal that the O3 formation is accelerated by photodissociating vibrationally excited O2(nu), produced in the photolysis of O3 following its initial formation. It is argued that the O2 Herzberg states and O2(nu) may play important roles in the odd oxygen chemistry in the middle atmosphere. It is estimated that the O2(A3Sigma-u(+))+O2 reaction may yield up to about 6 percent of the total odd oxygen production rate near 50 km.

Shi, Jichun; Barker, John R.

1992-01-01

220

Reaction of cyanoacetylene HCCCN(X 1Sigma+) with ground-state carbon atoms C(3P) in cold molecular clouds.  

Science.gov (United States)

The reaction of the simplest cyanopolyyne, cyanoacetylene [HCCCN(X (1)Sigma(+))], with ground-state atomic carbon C((3)P) is investigated theoretically to explore the probable routes for the depletion of the famed interstellar molecule HCCCN, and the formation of carbon-nitrogen-bearing species in extraterrestrial environments particularly of ultralow temperature. Six collision complexes (c1-c6) without entrance barrier as a result of the carbon atom addition to the pi systems of HCCCN are located. The optimized geometries and harmonic frequencies of the intermediates, transition states, and products along the isomerization and dissociation pathways of each collision complex are obtained by utilizing the unrestricted B3YLP6-311G(d,p) level of theory, and the corresponding CCSD(T)/cc-pVTZ energies are calculated. Subsequently, with the facilitation of Rice-Ramsperger-Kassel-Marcus (RRKM) and variational RRKM rate constants at collision energy of 0-10 kcal/mol, the most probable paths for the titled reaction are determined, and the product yields are estimated. Five collision complexes (c1-c3, c5, and c6) are predicted to give the same products, a chained CCCCN (p2)+H, via the linear and most stable intermediate, HCCCCN (i2), while collision complex c4 is likely to dissociate back to C+HCCCN. The study suggests that this class of reaction is an important route to the destruction of cyanoacetylene and cyanopolyynes in general, and to the synthesis of linear carbon-chained nitriles at the temperature as low as 10 K to be incorporated in future chemical models of interstellar clouds. PMID:16460162

Li, H Y; Cheng, W C; Liu, Y L; Sun, B J; Huang, C Y; Chen, K T; Tang, M S; Kaiser, R I; Chang, A H H

2006-01-28

 
 
 
 
221

How low-energy weak reactions can constrain three-nucleon forces and the neutron-neutron scattering length  

CERN Document Server

We show that chiral symmetry and gauge invariance enforce relations between the short-distance physics that occurs in a number of electroweak and pionic reactions on light nuclei. Within chiral perturbation theory this is manifested via the appearance of the same axial isovector two-body contact term in pi- d -> n n gamma, p-wave pion production in NN collisions, tritium beta decay, pp fusion, nu d scattering, and the hep reaction. Using a Gamow-Teller matrix element obtained from calculations of pp fusion as input we compute the neutron spectrum obtained in pi- d -> n n gamma. With the short-distance physics in this process controlled from p p -> d e+ nu_e the theoretical uncertainty in the nn scattering length extracted from pi- d -> n n gamma is reduced by a factor larger than three, to <~0.05 fm.

Gardestig, A

2006-01-01

222

Solvent effects and potential of mean force: a multilayered-representation quantum mechanical/molecular mechanics study of the CH3Br + CN- reaction in aqueous solution.  

Science.gov (United States)

The bimolecular nucleophilic substitution (SN2) reaction of CH3Br and CN(-) in aqueous solution was investigated using a multilayered-representation quantum mechanical and molecular mechanics methodology. The reactant complex, transition state, and product complex are identified and characterized in aqueous solution. The potentials of mean force are computed at both DFT and CCSD(T) levels of theory for the reaction region. The CCSD(T)/MM level of theory presents a free energy activation barrier height at 19.1 kcal mol(-1) which agrees very well with the experimental value of 20.7 kcal mol(-1), while the DFT/MM level of theory underestimated the barrier height at 16.5 kcal mol(-1). The results show that the aqueous environment has a significant contribution to the potential of mean force. Both the solvation effect and the polarization effect increase the activation barrier height by ?14.5 kcal mol(-1) and the solvation effect plays a major role by providing about 70% of the contribution. PMID:25159052

Xu, Yulong; Zhang, Jingxue; Wang, Dunyou

2014-10-01

223

The brute-force polarization of 23Na and the 23Na(n,?)24Na reaction  

International Nuclear Information System (INIS)

A Na target has been polarized by brute force to 22% and the ? radiation produced by polarized thermal neutron capture has been investigated. The 2+ channel spin contribution has been determined model independently and unambiguously for 22 primary transitions. The average 2+ channel contribution is 5.8(5)%. Spins of final levels are in agreement with previous assignments. For three levels spin restrictions have been made. The energies of positive parity levels are in agreement with a shell model calculation in the complete sd shell. (Auth.)

224

Well-construction, water-level, and water-quality data for ground-water monitoring wells for the J4 hydrogeologic study, Arnold Air Force Base, Tennessee  

Science.gov (United States)

Between December 1993 and March 1994, 27 wells were installed at 12 sites near the J4 test cell at Arnold Engineering Development Center in Coffee County, Tennessee. The wells ranged from 28 to 289 feet deep and were installed to provide information on subsurface lithology, aquifer characteristics, ground-water levels, and ground-water quality. This information will be used to help understand the effects of dewatering operations at the J4 test cell on the local ground-water-flow system. The J4 test cell, extending approximately 250 feet below land surface, is used in the testing of rocket motors. Ground water must be pumped continuously from around the test cell to keep it structurally intact. The amount of water discharged from the J4 test cell was monitored to estimate the average rate of ground-water withdrawal at the J4 test cell. Ground- water levels were monitored continuously at 14 wells for 12 months. Water-quality samples were collected from 26 of the new wells, 9 existing wells, and the ground-water discharge from the J4 test cell. All samples were analyzed for common inorganic ions, trace metals, and volatile organic compounds.

Haugh, C. J.

1996-01-01

225

Quantum mechanics/molecular mechanics minimum free-energy path for accurate reaction energetics in solution and enzymes: Sequential sampling and optimization on the potential of mean force surface  

Digital Repository Infrastructure Vision for European Research (DRIVER)

To accurately determine the reaction path and its energetics for enzymatic and solution-phase reactions, we present a sequential sampling and optimization approach that greatly enhances the efficiency of the ab initio quantum mechanics/molecular mechanics minimum free-energy path (QM/MM-MFEP) method. In the QM/MM-MFEP method, the thermodynamics of a complex reaction system is described by the potential of mean force (PMF) surface of the quantum mechanical (QM) subsystem with a small number of...

Hu, H.; Lu, Z.; Parks, Jm; Burger, Sk; Yang, W.

2008-01-01

226

Prediction of forces and moments for flight vehicle control effectors. Part 2: An analysis of delta wing aerodynamic control effectiveness in ground effect  

Science.gov (United States)

Many types of hypersonic aircraft configurations are currently being studied for feasibility of future development. Since the control of the hypersonic configurations throughout the speed range has a major impact on acceptable designs, it must be considered in the conceptual design stage. Here, an investigation of the aerodynamic control effectiveness of highly swept delta planforms operating in ground effect is presented. A vortex-lattice computer program incorporating a free wake is developed as a tool to calculate aerodynamic stability and control derivatives. Data generated using this program are compared to experimental data and to data from other vortex-lattice programs. Results show that an elevon deflection produces greater increments in C sub L and C sub M in ground effect than the same deflection produces out of ground effect and that the free wake is indeed necessary for good predictions near the ground.

Maughmer, Mark D.; Ozoroski, L.; Ozoroski, T.; Straussfogel, D.

1990-01-01

227

Forcing of Turing patterns in the chlorine dioxide-iodine-malonic acid reaction with strong visible light.  

Science.gov (United States)

We investigate the sensitivity of Turing patterns in the chlorine dioxide-iodine-malonic acid reaction to illumination by strong white light. Intense illumination results in an increase of [I(-)], in contrast to previous studies, which found only decreased [I(-)] for weak and intermediate intensities of illumination. We propose an expanded mechanism to explain the experimental observations. Both experimental and numerical results suggest that [ClO2] is the key parameter that determines whether the high iodide state is obtained under strong illumination. When strong illumination is applied through a spatially periodic mask with black and white stripes, a dark state with high [I(-)] is produced in the illuminated domain and a light state with low [I(-)] forms in the nonilluminated domain. Depending on the black:white ratio of the mask and its wavelength, Turing patterns can coexist with either the light or the dark state in the nonilluminated domain. PMID:23991763

Nagao, Raphael; Epstein, Irving R; Dolnik, Milos

2013-09-26

228

NRC Task Force report on review of the Federal/State program for regulation of commercial low-level radioactive waste burial grounds. Analysis of public comments  

International Nuclear Information System (INIS)

Correspondence after publication of NUREG-0217 in the Federal Register is listed by docket. A summary of the comments is given. Comments on the task force conclusions on federal/state roles, comprehensive regulator program, and need to study alternatives, provide adequate capacity, and avoid proliferation are analyzed. A breakdown of the comments of states, industry, and others on the task force conclusions and recommendations is tabulated

229

The role of reaction force and chemical potential in characterizing the mechanism of double proton transfer in the adenine-uracil complex.  

Science.gov (United States)

A theoretical study of the intermolecular double proton transfer in the adenine-uracil base pair has been performed to model the double proton transfer in the adenine-thymine dimer. The mechanism is analyzed in terms of the reaction force profile, which indicates that the activation of the transfer occurs via structural rearrangements to bring the interacting molecules close to each other to let the donor and acceptor atoms in the right position to achieve the transfer. It is found that only when the first proton transfer is partially completed does the second proton get activated, thus illustrating the asynchronous nature of the double proton-transfer process in base pair systems. PMID:17566987

Herrera, Bárbara; Toro-Labbé, Alejandro

2007-07-01

230

The CMS Experiment: on and under Ground Motions of Structures Due to the Magnetic Field Forces as Observed by the Link Alignment System  

Energy Technology Data Exchange (ETDEWEB)

This document describes results obtained from the Link Alignment System data recorded during the CMS Magnet Test (at SX5 on ground Hall) and the CRAFT08 and 09 periods data taking in the point P5 (UX5), 100 m underground. A brief description of the system is followed by the discussion of the detected relative displacements (from micrometres to centimetres) between detector elements and rotation of detector structures (from microradiants to milliradiants). Observed motions are studied as functions of the magnetic fi eld intensity. Comparisons between recorded data on and under ground are made. (Author) 23 refs.

Alberdi, J.; Arce, J.; Barcala, J. M.; Calvo, E.; Ferrando, A.; Josa, M. I.; Molinero, A.; Navarrete, J.; Oller, J. C.; Yuste, C.; Brochero, J.; Calderon, A.; Fernandez, M. G.; Gomez, G.; Gonzalez-Sanchez, F. J.; Martinez-Ribero, C.; Matorras, F.; Rodrigo, T.; Rui-Arbol, P.; Scodellaro, L.; Sobron, M.; Vila, I.; Virto, A. L.; Fernandez, J.

2010-05-01

231

Recalibration of a single-valued double many-body expansion potential energy surface for ground-state hydroperoxy and dynamics calculations for the oxygen atom + hydroxyl .fwdarw. oxygen + hydrogen atom reaction  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We report a new single-valued potential energy surface for the ground state of H02 from the double many-body expansion (DMBE) method. This new surface conforms with the three-body energy of recent ab initio CAS SCF/CCI calculations semiempirically corrected by the DMBE-SEC method and reproduces the most accurate estimates of the experimental dissociation energy, equilibrium geometry, and quadratic force constants for the hydroperoxyl radical. Using this new H02 (DMBE IV) potential...

Pastrana, M. R.; Quintales, L. A. M.; Branda?o, J.; Varandas, A. J. C.

1990-01-01

232

Dynamical response of the Galileo Galilei on the ground rotor to test the equivalence principle: Theory, simulation, and experiment. II. The rejection of common mode forces  

International Nuclear Information System (INIS)

'Galileo Galilei on the ground' (GGG) is a fast rotating differential accelerometer designed to test the equivalence principle (EP). Its sensitivity to differential effects, such as the effect of an EP violation, depends crucially on the capability of the accelerometer to reject all effects acting in common mode. By applying the theoretical and simulation methods reported in Part I of this work, and tested therein against experimental data, we predict the occurrence of an enhanced common mode rejection of the GGG accelerometer. We demonstrate that the best rejection of common mode disturbances can be tuned in a controlled way by varying the spin frequency of the GGG rotor

233

The separate reactions of the 2Psub(3/2) and 2Psub(1/2) ground states of Kr+ with a number of gases from 0.04 eV to several eV  

International Nuclear Information System (INIS)

The separate reactions of 2Psub(3/2) and 2Psup(1/2) ground states of Kr+ with O2, CO, N2O and OCS have been investigated over the mean relative kinetic energy range from 0.04 eV to several eV using a Flow-Drift-Tube (FDT) apparatus. The results have been interpreted in terms of transitions between states of the reaction intermediate that correlate adiabatically to either the reactants or charge transfer products. (Author)

234

NRC Task Force report on review of the federal/state program for regulation of commercial low-level radioactive waste burial grounds  

International Nuclear Information System (INIS)

The underlying issue explored in this report is that of Federal vs State regulation of commercial radioactive waste burial grounds. The need for research and development, a comprehensive set of standards and criteria, a national plan for low-level waste management, and perpetual care funding are closely related to the central issue and are also discussed. Five of the six commercial burial grounds are regulated by Agreement States; the sixth is regulated solely by the NRC (NRC also regulates Special Nuclear Material at the sites). The sites are operated commercially. The operators contribute to the perpetual care funds for the sites at varying rates. The States have commitments for the perpetual care of the decommissioned sites except for one site, located on Federally owned land. Three conclusions are reached. Federal control over the disposal of low-level waste should be increased by requiring joint Federal/State site approval, NRC licensing, Federal ownership of the land, and a Federally administered perpetual care program. The NRC should accelerate the development of its regulatory program for the disposal of low-level waste. The undisciplined proliferation of low-level burial sites must be avoided. NRC should evaluate alternative disposal methods, conduct necessary studies, and develop a comprehensive low-level waste regulatory program (i.e., accomplish the above recommendations) prior to the licensing of new disposal site

235

Electron acceleration and emission in a field of a plane and converging dipole wave of relativistic amplitudes with the radiation reaction force taken into account  

International Nuclear Information System (INIS)

A comparative analysis is performed of the electron emission characteristics as the electrons move in laser fields with ultra-relativistic intensity and different configurations corresponding to a plane or tightly focused wave. For a plane travelling wave, analytical expressions are derived for the emission characteristics, and it is shown that the angular distribution of the radiation intensity changes qualitatively even when the wave intensity is much less than that in the case of the radiation-dominated regime. An important conclusion is drawn that the electrons in a travelling wave tend to synchronised motion under the radiation reaction force. The characteristic features of the motion of electrons are found in a converging dipole wave, associated with the curvature of the phase front and nonuniformity of the field distribution. The values of the maximum achievable longitudinal momenta of electrons accelerated to the centre, as well as their distribution function are determined. The existence of quasi-periodic trajectories near the focal region of the dipole wave is shown, and the characteristics of the emission of both accelerated and oscillating electrons are analysed. (extreme light fields and their applications)

236

Experimental measurements of the ground cloud effluents and cloud growth for the May 20, 1975, Titan 3C launch at Air Force Eastern Test Range, Florida  

Science.gov (United States)

The experiment included surface level and airborne in situ cloud measurements of the exhaust effluents from the Titan IIIC solid rocket boosters. Simultaneous visible spectrum photographic pictures of the ground cloud as well as infrared imaging of the cloud were obtained to study the cloud rise, growth, and direction of travel within the earth's surface mixing layer. The NASA multilayer diffusion model predictions of cloud growth, direction of travel, and expected surface level effluent concentrations were made prior to launch and after launch using measured meteorological conditions. Prelaunch predictions were used to position the effluent monitoring instruments, and the postlaunch predictions were compared with the measured data. Measurement results showed that surface level effluent values were low, often below the detection limits of the instrumentation. The maximum surface level hydrogen chloride concentration measured 50 parts per billion at about 8 km from the launch pad. The maximum observed in-cloud (airborne measurement) hydrogen chloride concentration was 7 per million.

Gregory, G. L.; Storey, R. W., Jr.

1977-01-01

237

[Observation study on aerosol optical properties and radiative forcing using the ground-based and satellite remote sensing at background station during the regional pollution episodes].  

Science.gov (United States)

The significant effect of anthropogenic pollutants transportation on the physical and optical properties of regional background atmospheric aerosol was studied by using ground-based and satellite remote sensing data obtained at the atmospheric background station (Shangdianzi, Beijing) of North China during October 1 to 15 in 2011. The aerosol mass concentration and reactive gases concentration increased obviously during periods of October 4-5, October 7-9, and October 11-12. Comparing with the background period of October 1-3, volume concentration increased by a factor of 3-6 for reactive gases such as NO(x), and CO, and a factor of 10-20 for SO2. Mass concentration of PM2.5 was about 200 microg x m(-3) on October 9. During haze period, the AOD at 500 nm varied between 0.60 to 1.00. The single scattering albedo (SSA) was lower than 0.88. And the black carbon concentration increased 4-8 times, which suggested the aerosol absorption was very strong during this pollution episode. The absorption of aerosol particles could cause 100-400 W x m(-2) increase of atmospheric radiation. The surface radiation decreased by about 100-300 W x m(-2) due to the aerosol scattering and absorption. This could cause higher stability of atmosphere, which will significantly affect the cloud and precipitation, and thus the regional weather and climate. PMID:25247232

Zhang, Xiao-Ling; Xia, Xiang-Ao; Che, Hui-Zheng; Tang, Jie; Tang, Yi-Xi; Meng, Wei; Dong, Fan

2014-07-01

238

Light induced electron transfer reactions of metal complexes  

Energy Technology Data Exchange (ETDEWEB)

Properties of the excited states of tris(2,2'-bipyridine) and tris(1,10-phenanthroline) complexes of chromium(III), iron(II), ruthenium(II), osmium(II), rhodium(III), and iridium(III) are described. The electron transfer reactions of the ground and excited states are discussed and interpreted in terms of the driving force for the reaction and the distortions of the excited states relative to the corresponding ground states. General considerations relevant to the conversion of light into chemical energy are presented and progress in the use of polypyridine complexes to effect the light decomposition of water into hydrogen and oxygen is reviewed.

Sutin, N; Creutz, C

1980-01-01

239

Investigating the relationship between pressure force and acoustic waveform in footstep sounds  

DEFF Research Database (Denmark)

In this paper we present an inquiry into of the relationships between audio waveforms and ground reaction force in recorded footstep sounds. In an anechoic room, we recorded several footstep sounds produced while walking on creaking wood and gravel. The recordings were performed by using a pair of sandals embedded with six pressure sensors each. Investigations of the relationships between recorded force and footstep sounds is presented, together with several possible applications of the system.

Grani, Francesco; Serafin, Stefania

2013-01-01

240

Walking without impacts as a motion/force control problem  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The paper deals with the synthesis of control for impactless bipedal walking. In order of avoid impulses, both the specified motion of the biped and its ground reactions are controlled, yielding a combined motion and force control problem. A method for modeling and solving such problems is proposed. and then illustrated by the example of an impactless planar walk of a seven-link bipedal robot. Some numerical results of the motion simulation are reported.

Blajer, Wojciech; Schiehlen, Werner

1992-01-01

 
 
 
 
241

Análise da força articular resultante entre diferentes movimentos do ombro com e sem carga: estudo preliminar / Analysis of the joint reaction forces during different shoulder movements with and without external load: a preliminary study  

Scientific Electronic Library Online (English)

Full Text Available SciELO Portugal | Language: Portuguese Abstract in portuguese Os modelos de segmentos rígidos são extremamente úteis para auxiliar a compreensão do tipo de sobrecarga que as articulações estão expostas. O objetivo deste trabalho foi analisar a força articular resultante e momento proximal durante atividades sem e com carga externa, em um estudo preliminar. Um [...] indivíduo realizou flexão, extensão, abdução de ombro e flexão de cotovelo (sem e com carga). Dados cinemáticos foram obtidos por videogrametria (freqüência de amostragem de 50 campos/s). Um modelo de segmentos rígidos foi utilizado para obtenção dos dados cinéticos. O modelo é regido pelas equações de movimento de Newton-Euler. Os resultados encontrados evidenciaram aumentos não proporcionais na força e momento resultante. A força resultante longitudinal foi a única que apresentou aumento proporcional frente à carga externa. As componentes da força de cisalhamento e momento proximal apresentaram aumentos aleatórios. O aumento da carga externa promoveu aumentos da força e momento proximal, porém não de forma proporcional. As componentes de força e momento resultante sofrem influência da carga externa de maneira independente. Isto evidencia a necessidade de um controle rígido sobre os exercícios prescritos para diferentes disfunções do membro superior. Abstract in english Link segment models are extremely useful for increasing the comprehension of joint overload. The aim of the present study was to analyze proximal joint reaction forces and moments during different movements performed with and without external load. One subject performed shoulder flexion, extension a [...] nd abduction, and elbow flexion movements (with and without external load) Kinematic data were obtained by videogrammetry (frequency sample 50 fields/s). One link segment model was used to obtain kinetic data. The model is governed by Newton/Euler movement equations. The results suggested a not proportional increasing of proximal joint reaction forces and moments. The proximal joint reaction force longitudinal component was the only one that increased proportionally to the external load. Proximal joint reaction force shearing components and proximal moments presented increasing values of different magnitudes. The use of external load promoted increased magnitudes of proximal joint reaction force and moment, although it was not proportional. Proximal joint reaction force and moment are influenced in different ways by the external load. This suggests the need of a strict control of the prescribed exercises for different shoulder dysfunctions.

Daniel Cury, Ribeiro; Jefferson Fagundes, Loss; Joelly Mahnic de, Toledo; Marcelo Peduzzi de, Castro; Fábia Milman, Krumholz; Felipe de Osório, Marques.

242

Análisis cuantitativo de la evolución post-quirúrgica de la rotura de ligamento cruzado anterior mediante el uso de la plataforma de fuerza - Quantitative analysis of the evolution of post-surgical anterior cruciate ligament rupture using force platform  

Directory of Open Access Journals (Sweden)

Full Text Available ResumenEl analisis cinético mediante plataforma de fuerza es un método objetivo de cuantificar el apoyo de los miembros en los animales domésticos.SummaryKinetic análisis by jeans of force platforms is an objetive method to measure weight - bearing or ground reaction force (GRF.

Vilar, JM

2012-01-01

243

Transition from wing to leg forces during landing in birds.  

Science.gov (United States)

Transitions to and from the air are critical for aerial locomotion and likely shaped the evolution of flying animals. Research on take-off demonstrates that legs generate greater body accelerations compared with wings, and thereby contribute more to initial flight velocity. Here, we explored coordination between wings and legs in two species with different wingbeat styles, and quantified force production of these modules during the final phase of landing. We used the same birds that we had previously studied during take-off: zebra finch (Taeniopygia guttata, N=4) and diamond dove (Geopelia cuneata, N=3). We measured kinematics using high-speed video, aerodynamics using particle image velocimetry, and ground-reaction forces using a perch mounted on a force plate. In contrast with the first three wingbeats of take-off, the final four wingbeats during landing featured ~2 times greater force production. Thus, wings contribute proportionally more to changes in velocity during the last phase of landing compared with the initial phase of take-off. The two species touched down at the same velocity (~1 m s(-1)), but they exhibited significant differences in the timing of their final wingbeat relative to touchdown. The ratio of average wing force to peak leg force was greater in diamond doves than in zebra finches. Peak ground reaction forces during landing were ~50% of those during take-off, consistent with the birds being motivated to control landing. Likewise, estimations of mechanical energy flux for both species indicate that wings produce 3-10 times more mechanical work within the final wingbeats of flight compared with the kinetic energy of the body absorbed by legs during ground contact. PMID:24855670

Provini, Pauline; Tobalske, Bret W; Crandell, Kristen E; Abourachid, Anick

2014-08-01

244

Speciation of mineralized deep-level ground water in non-saline solid rock. Examination of interaction and reactions with wastes at sealed underground disposal sites  

International Nuclear Information System (INIS)

The report contains results of analysis and specification of ground waters in Germany and subsequent investigations into specific interaction mechanisms between selected waste types and relevant water samples. The activities reported are intended to enhance scientific knowledge of the processes involved and to yield data indicating suitability or non-suitability of wastes for ecologically safe underground disposal in non-saline rock. (orig./CB)

245

Comparison of natural and artificial forcing to study the dynamic behaviour of bell towers in low wind context by means of ground-based radar interferometry: the case of the Leaning Tower in Pisa  

Science.gov (United States)

The study of Cultural Heritage assets needs the application of non-destructive and non-invasive monitoring techniques. In particular, monuments and historical buildings which are open to the visitors and/or subject to important stress must be studied for their dynamic response. In the last 10?years the new ground-based radar interferometry technology has been developed allowing to monitor displacements from a point of sight far from the studied targets. It virtually provides a continuous mapping of displacements of the observed structures up to 10?µm with a range resolution of 0.75?m. In this paper, the application of ground-based interferometry on one very important historical building, the Leaning Tower of Pisa in Italy, is reported. The analysis of these kind of structures is important to catch their dynamic response to natural actions in general, and also to assess the effects due to pedestrian and users, and consequently to define functional capabilities and levels of acceptable dynamic stress. The studied structure was subject to artificial loading by synchronous movement of about 20 people. Artificial forcing led the structure to a resonance condition with the same frequency of the one due to the natural noise excitation, which was separately measured, and with an oscillation amplitude more than thirty times greater than the natural one (in conditions of weak wind). During the passive stages of the survey the recorded structural vibrations were very closed to the instrumental sensitivity, making difficult to distinguish vibration amplitudes amplifications of various segments at various heights. Through the spectral analysis of the acquired data it was possible to estimate the vibration frequencies of the first modal shapes of the structure along two orthogonal directions. The power spectra of the passive survey data have the same maximum frequency of the active but contain more noise at low frequency.

Marchisio, Mario; Piroddi, Luca; Ranieri, Gaetano; Calcina, Sergio V.; Farina, Paolo

2014-10-01

246

Grounding Bottom Damage and Ship Motion over a Rock  

DEFF Research Database (Denmark)

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.

Simonsen, Bo Cerup

1996-01-01

247

Design and Operation of a Borehole Straddle Packer for Ground-Water Sampling and Hydraulic Testing of Discrete Intervals at U.S. Air Force Plant 6, Marietta, Georgia  

Science.gov (United States)

A borehole straddle packer was developed and tested by the U.S. Geological Survey to characterize the vertical distribution of contaminants, head, and hydraulic properties in open-borehole wells as part of an ongoing investigation of ground-water contamination at U.S. Air Force Plant 6 (AFP6) in Marietta, Georgia. To better understand contaminant fate and transport in a crystalline bedrock setting and to support remedial activities at AFP6, numerous wells have been constructed that include long open-hole intervals in the crystalline bedrock. These wells can include several discontinuities that produce water, which may contain contaminants. Because of the complexity of ground-water flow and contaminant movement in the crystalline bedrock, it is important to characterize the hydraulic and water-quality characteristics of discrete intervals in these wells. The straddle packer facilitates ground-water sampling and hydraulic testing of discrete intervals, and delivery of fluids including tracer suites and remedial agents into these discontinuities. The straddle packer consists of two inflatable packers, a dual-pump system, a pressure-sensing system, and an aqueous injection system. Tests were conducted to assess the accuracy of the pressure-sensing systems, and water samples were collected for analysis of volatile organic compound (VOCs) concentrations. Pressure-transducer readings matched computed water-column height, with a coefficient of determination of greater than 0.99. The straddle packer incorporates both an air-driven piston pump and a variable-frequency, electronic, submersible pump. Only slight differences were observed between VOC concentrations in samples collected using the two different types of sampling pumps during two sampling events in July and August 2005. A test conducted to assess the effect of stagnation on VOC concentrations in water trapped in the system's pump-tubing reel showed that concentrations were not affected. A comparison was conducted to assess differences between three water-sampling methods - collecting samples from the well by pumping a packer-isolated zone using a submersible pump, by using a grab sampler, and by using a passive diffusion sampler. Concentrations of tetrachloroethylene, trichloroethylene and 1,2-dichloropropane were greatest for samples collected using the submersible pump in the packed-isolated interval, suggesting that the straddle packer yielded the least dilute sample.

Holloway, Owen G.; Waddell, Jonathan P.

2008-01-01

248

Testing nuclear forces by polarization transfer coefficients in d(\\vec p, \\vec p)d and d(\\vec p,\\vec d)p reactions at E^{lab}_p = 22.7 MeV  

CERN Document Server

The proton to proton polarization transfer coefficients K_x^{x'}, K_y^{y'}, K_z^{x'} and the proton to deuteron polarization transfer coefficients K_x^{x'}, K_y^{y'}, K_z^{x'}, K_x^{y'z'}, K_y^{z'z'}, K_z^{y'z'}, K_y^{x'z'} and K_y^{x'x'-y'y'} have been measured in d(\\vec p, \\vec p)d and d(\\vec p, \\vec d)p reactions at E^{lab}_p = 22.7 MeV, respectively. The data have been compared to predictions of modern nuclear forces obtained by solving the three-nucleon Faddeev equations in momentum space. Realistic (semi) phenomenological nucleon-nucleon potentials combined with model three-nucleon forces and modern chiral nuclear forces have been used. The AV18, CD Bonn, Nijm I and II nucleon-nucleon interactions have been applied alone or combined with the Tucson-Melbourne 99 three-nucleon force, adjusted separately for each potential to reproduce the triton binding energy. For the AV18 potential also the Urbana IX three-nucleon force have been used. In addition chiral NN potentials in the next-to-leading-order and ch...

Witala, H; Glöckle, W; Golak, J; Kamada, H; Kievsky, A; Nogga, A; Skibinski, R; Viviani, M

2006-01-01

249

Chiral nuclear forces and many-body applications  

Science.gov (United States)

Description of light nuclei and low-energy nuclear reactions can be given in a model-independent way by using chiral effective field theory of QCD. In this framework, nuclear forces are described by pion and nucleon rather than fundamental quark degrees of freedom in harmony with the symmetries of QCD. In this proceeding I discuss chiral nuclear forces derived within this framework and present our first results on the three-nucleon forces calculated up to next-to-nextto-next-to-leading order in chiral effective field theory. I will also discuss our recent lattice simulations of the 12C-spectrum where the next-to-next-to-leading order nuclear forces serve as an input. In addition to the ground state and excited spin-2 state, we find a resonance at -85(3) MeV with all of the properties of the Hoyle state and in agreement with the experimentally observed energy.

Krebs, Hermann

2012-09-01

250

Ground-Level Ozone  

Science.gov (United States)

Ground level or "bad" ozone is not emitted directly into the air, but is created by chemical reactions between oxides of nitrogen (NOx) and volatile ... the major sources of NOx and VOC. Breathing ozone can trigger a variety of health problems, particularly ...

251

Coaxial Atomic Force Microscope Tweezers  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 u...

Brown, Keith Andrew; Aguilar, J. A.; Westervelt, Robert M.

2010-01-01

252

Exact integral constraint requiring only the ground-state electron density as input on the exchange-correlation force - partial differential(V)(xc)(r)/partial differential(r) for spherical atoms.  

Science.gov (United States)

Following some studies of integral(n)(r)inverted DeltaV(r)dr by earlier workers for the density functional theory (DFT) one-body potential V(r) generating the exact ground-state density, we consider here the special case of spherical atoms. The starting point is the differential virial theorem, which is used, as well as the Hiller-Sucher-Feinberg [Phys. Rev. A 18, 2399 (1978)] identity to show that the scalar quantity paralleling the above vector integral, namely, integral(n)(r) partial differential(V)(r)/partial differential(r)dr, is determined solely by the electron density n(0) at the nucleus for the s-like atoms He and Be. The force - partial differential(V)/ partial differential(r) is then related to the derivative of the exchange-correlation potential V(xc)(r) by terms involving only the external potential in addition to n(r). The resulting integral constraint should allow some test of the quality of currently used forms of V(xc)(r). The article concludes with results from the differential virial theorem and the Hiller-Sucher-Feinberg identity for the exact many-electron theory of spherical atoms, as well as for the DFT for atoms such as Ne with a closed p shell. PMID:19026052

March, N H; Nagy, A

2008-11-21

253

A force platform for large human displacements.  

Science.gov (United States)

This paper provides details of a force platform assembly suitable for measuring the magnitude, position and direction of ground reaction forces for manual handling tasks involving several footsteps in any horizontal direction. An approach to increase the natural frequency with the use of a vibration absorber is used; this frequency was found to be 41+/-2 Hz. The results show a maximum error of 22 N (2% of the full scale output) when a person performs repetitive movements from a squat position to a full extension and back to the squat position. Static tests show the maximal errors to be, vertically, 1.5% of the full scale output (1818+/-33 N), and horizontally, 4.9% of the full scale output (1177+/-6 N). PMID:11413067

Desjardins, P; Gagnon, M

2001-03-01

254

Titanium(III) chemistry: electron-transfer reactions with ground-state poly(pyridine)osmium(III) complexes, quenching reactions with excited-state poly(pyridine)ruthenium(II) complexes, and formal reduction potentials  

International Nuclear Information System (INIS)

Potentiometric titrations of aquotitanium(III) with ferric ions have been performed in hydrochloric acid solution. The potentiometric data are described by E (V vs. NHE) = 0.03 - 0.059 log ([Ti(III)]/[Ti(IV)][H+]2) at 250C and 3.0 M ionic strength and are consistent with the interpretation that Ti3+(aq) and TiO2+ are the principal titanium(III) and titanium(IV) species, respectively, present at acid concentrations of 0.1 - 3.0 M. Rate constants for the oxidation of titanium(III) by a series of osmium(III) complexes, OsL33+, where L is a bipyridine or phenanthroline derivative, have been determined at 250C and 3.0 M ionic strength. The rates are interpreted in terms of the reactions of Ti3+(aq) and TiOH2+. The rate constants are correlated with the Marcus theory, and the exchange rate constants for the Ti4+ 3+(aq) and TiOH3+ 2+ couples are estimated. The rate constants for the reaction of titanium(III) with the excited states of the ruthenium(II) complexes RuL32+ are insensitive to the reduction potentials of the ruthenium(II) complexes. Arguments are presented to show that the quenching reactions proceed predominatly by energy-transfer mechanisms. The implications of these results for the production of Ti2+(aq) in quenching reactions are discussed. 6 figures, 5 tablesssed. 6 figures, 5 tables

255

A unified perspective on the hydrogen atom transfer and proton-coupled electron transfer mechanisms in terms of topographic features of the ground and excited potential energy surfaces as exemplified by the reaction between phenol and radicals.  

Science.gov (United States)

The relation between the hydrogen atom transfer (HAT) and proton-coupled electron transfer (PCET) mechanisms is discussed and is illustrated by multiconfigurational electronic structure calculations on the ArOH + R(*) --> ArO(*) + RH reactions. The key topographic features of the Born-Oppenheimer potential energy surfaces that determine the predominant reaction mechanism are the conical intersection seam of the two lowest states and reaction saddle points located on the shoulders of this seam. The saddle point corresponds to a crossing of two interacting valence bond states corresponding to the reactant and product bonding patterns, and the conical intersection corresponds to the noninteracting intersection of the same two diabatic states. The locations of mechanistically relevant conical intersection structures and relevant saddle point structures are presented for the reactions between phenol and the N- and O-centered radicals, (*)NH2 and (*)OOCH3. Points on the conical intersection of the ground doublet D0 and first excited doublet D1 states are found to be in close geometric and energetic proximity to the reaction saddle points. In such systems, either the HAT mechanism or both the HAT mechanism and the proton-coupled electron transfer (PCET) mechanism can take place, depending on the relative energetic accessibility of the reaction saddle points and the D0/D1 conical intersection seams. The discussion shows how the two mechanisms are related and how they blend into each other along intermediate reaction paths. The recognition that the saddle point governing the HAT mechanism is on the shoulder of the conical intersection governing the PCET mechanism is used to provide a unified view of the competition between the two mechanisms (and the blending of the two mechanisms) in terms of the prominent and connected features of the potential energy surface, namely the saddle point and the conical intersection. The character of the dual mechanism may be understood in terms of the dominant valence bond configurations of the intersecting states, which are zero-order approximations to the diabatic states. PMID:18465862

Tishchenko, Oksana; Truhlar, Donald G; Ceulemans, Arnout; Nguyen, Minh Tho

2008-06-01

256

Insect normal hovering flight in ground effect  

Science.gov (United States)

The ground effect on insect normal hovering is investigated using an immersed boundary-lattice Boltzmann method to solve the two-dimensional incompressible Navier-Stokes equations. A virtual model of an elliptic foil with oscillating translation and rotation near a body surface or ground is used. Computations have been carried out for some parameters including the distance between the foil and the surface, phase difference between the rotation and translation, and amplitude of oscillating rotation. The ground effect on the unsteady forces and vortical structures is analyzed. In particular, three typical regimes of force behavior due to the ground effect, i.e., force enhancement, force reduction, and force recovery regime, are identified and closely associated with the evolution of vortex structures. The results obtained in this study provide physical insight into the understanding of aerodynamics and flow structures for insect normal hovering flight with a ground effect and flying mechanisms relevant to insect perching on body.

Gao, Tong; Lu, Xi-Yun

2008-08-01

257

Mechanism of solid vertical bar liquid interfacial reactions. The reactive dissolution of p-chloranil in aqueous solution as studied by the channel flow cell with electrochemical detection and atomic force microscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A quantitative study of the hydrolytic dissolution of solid p-chloranil at alkaline pH using a combination of the channel flow cell and in situ atomic force microscopy measurements shows that the dissolution is driven by reaction of the substrate with hydroxide ions at, or very close to, the dissolving surface. The dissolution rate equation, deduced from the channel flow cell for single crystals of p-chloranil, is rate/mol cm-2 s-1 = 3.8 × 10-7[OH-]0 where [OH-]0/M is the hydroxide ion conce...

Booth, J.; Sanders, Ghw; Compton, Rg; Atherton, Jh; Brennan, Cm

1997-01-01

258

Abnormal {alpha} particles obtained in the {sup 28} Si + {sup 181} Ta reaction. Evidence for transitions from shape isomeric states to shape isomeric states and to the ground states of various nuclei  

Energy Technology Data Exchange (ETDEWEB)

The reaction {sup 28} Si + {sup 181} Ta has been studied at a bombarding energy of 125 MeV using C catcher foils. Long-lived coincidence events between 8.0 - 9.1 MeV {alpha} particles events fit with theoretical predictions for transitions from the second minima of the potential energy surfaces to the second minima of the daughter nuclei, and to the ground states of various nuclei. The data are interpreted in terms of production of long-lived isomeric states in the second well of the potential. The consequences of the results regarding the discovery of long-lived superheavy elements, are discussed. (author) 20 refs., 7 figs., 1 tab.

Marinov, A.; Gelberg, S. [Hebrew Univ., Jerusalem (Israel). Racah Inst. of Physics; Kolb, D. [Kassel Univ. (Gesamthochschule) (Germany). Fachbereich 18 -Physik

1997-12-31

259

Methods for Addressing Uncertainty and Variability to Characterize Potential Health Risk from Trichloroethylene-Contaminated Ground Water at Beale Air Force Base in California:Integration of Uncertainty and Variability in Pharmacokinetics and Dose-Response  

Energy Technology Data Exchange (ETDEWEB)

Traditional estimates of health risk are typically inflated, particularly if cancer is the dominant endpoint and there is fundamental uncertainty as to mechanism(s) of action. Risk is more realistically characterized if it accounts for joint uncertainty and interindividual variability within a systematic probabilistic framework to integrate the joint effects on risk of distributed parameters of all (linear as well as nonlinear) risk-extrapolation models involved. Such a framework was used to characterize risks to potential future residents posed by trichloroethylene (TCE) in ground water at an inactive landfill site on Beale Air Force Base in California. Variability and uncertainty were addressed in exposure-route-specific estimates of applied dose, in pharmacokinetically based estimates of route-specific metabolized fractions of absorbed TCE, and in corresponding biologically effective doses estimated under a genotoxic/linear (MA{sub G}) vs. a cytotoxic/nonlinear (MA{sub c}) mechanistic assumption for TCE-induced cancer. Increased risk conditional on effective dose was estimated under MA{sub G} based on seven rodent-bioassay data sets, and under MA{sub c} based on mouse hepatotoxicity data. Mean and upper-bound estimates of combined risk calculated by the unified approach were <10{sup -6} and 10{sup -4}, respectively, while corresponding estimates based on traditional deterministic methods were >10{sup -5} and 10{sup -4}, respectively. It was estimated that no TCE-related harm is likely to occur due to any plausible residential exposure scenario involving the site. The systematic probabilistic framework illustrated is particularly suited to characterizing risks that involve uncertain and/or diverse mechanisms of action.

Bogen, K T

2001-05-24

260

Methods for Addressing Uncertainty and Variability to Characterize Potential Health Risk From Trichloroethylene-Contaminated Ground Water Beale Air Force Base in California: Integration of Uncertainty and Variability in Pharmacokinetics and Dose-Response  

Energy Technology Data Exchange (ETDEWEB)

Traditional estimates of health risk are typically inflated, particularly if cancer is the dominant endpoint and there is fundamental uncertainty as to mechanism(s) of action. Risk is more realistically characterized if it accounts for joint uncertainty and interindividual variability after applying a unified probabilistic approach to the distributed parameters of all (linear as well as nonlinear) risk-extrapolation models involved. Such an approach was applied to characterize risks to potential future residents posed by trichloroethylene (TCE) in ground water at an inactive landfill site on Beale Air Force Base in California. Variability and uncertainty were addressed in exposure-route-specific estimates of applied dose, in pharmacokinetically based estimates of route-specific metabolized fractions of absorbed TCE, and in corresponding biologically effective doses estimated under a genotoxic/linear (MA{sub g}) vs. a cytotoxic/nonlinear (MA{sub c}) mechanistic assumption for TCE-induced cancer. Increased risk conditional on effective dose was estimated under MA{sub G} based on seven rodent-bioassay data sets, and under MA, based on mouse hepatotoxicity data. Mean and upper-bound estimates of combined risk calculated by the unified approach were <10{sup -6} and <10{sup -4}, respectively, while corresponding estimates based on traditional deterministic methods were >10{sup -5} and >10{sup -4}, respectively. It was estimated that no TCE-related harm is likely occur due any plausible residential exposure scenario involving the site. The unified approach illustrated is particularly suited to characterizing risks that involve uncertain and/or diverse mechanisms of action.

Bogen, K.T.

1999-09-29

 
 
 
 
261

Methods for Addressing Uncertainty and Variability to Characterize Potential Health Risk From Trichloroethylene-Contaminated Ground Water Beale Air Force Base in California: Integration of Uncertainty and Variability in Pharmacokinetics and Dose-Response; TOPICAL  

International Nuclear Information System (INIS)

Traditional estimates of health risk are typically inflated, particularly if cancer is the dominant endpoint and there is fundamental uncertainty as to mechanism(s) of action. Risk is more realistically characterized if it accounts for joint uncertainty and interindividual variability after applying a unified probabilistic approach to the distributed parameters of all (linear as well as nonlinear) risk-extrapolation models involved. Such an approach was applied to characterize risks to potential future residents posed by trichloroethylene (TCE) in ground water at an inactive landfill site on Beale Air Force Base in California. Variability and uncertainty were addressed in exposure-route-specific estimates of applied dose, in pharmacokinetically based estimates of route-specific metabolized fractions of absorbed TCE, and in corresponding biologically effective doses estimated under a genotoxic/linear (MA(sub g)) vs. a cytotoxic/nonlinear (MA(sub c)) mechanistic assumption for TCE-induced cancer. Increased risk conditional on effective dose was estimated under MA(sub G) based on seven rodent-bioassay data sets, and under MA, based on mouse hepatotoxicity data. Mean and upper-bound estimates of combined risk calculated by the unified approach were and lt;10(sup -6) and and lt;10(sup -4), respectively, while corresponding estimates based on traditional deterministic methods were and gt;10(sup -5) and and gt;10(sup -4), respectively. It was estimated that no TCE-related hay. It was estimated that no TCE-related harm is likely occur due any plausible residential exposure scenario involving the site. The unified approach illustrated is particularly suited to characterizing risks that involve uncertain and/or diverse mechanisms of action

262

Photon-induced neutron polarization from the 2H(?,n-vector)1H reaction within the NN-force model with an intermediate dibaryon  

International Nuclear Information System (INIS)

A model for the NN force, which is induced by the formation of an intermediate dibaryon dressed with ?- and other meson fields, has been developed by the present authors in previous years. This model is applied to the deuteron photodisintegration processes with the main focus on the ?-induced polarization Py' of the neutron at energies below E? y' still remain. However, in combination with the previous results a consistent description can be achieved simultaneously for many observables

263

Mechanism of solid/liquid interfacial reactions. The maleic acid driven dissolution of calcite: An atomic force microscopy study under defined hydrodynamic conditions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The dissolution of calcite (CaCO3) in the presence of aqueous solutions containing maleic acid (cis-HOOC-CH=CH-COOH) in the pH range 4.3-8.2 has been studied by means of atomic force microscopy utilizing a flow cell of known hydrodynamics and modelable convection/diffusion. The latter permits the interpretation of dissolution rate data as measured by the z-piezo voltage in terms of a mechanism involving concentrations of solution species local to the dissolving crystal surface. In this way th...

Hong, Q.; Suarez, Mf; Coles, Ba; Compton, Rg

1997-01-01

264

A force plate based method for the calibration of force/torque sensors.  

Science.gov (United States)

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 FTsensor). Calibration matrices were calculated based on the raw data from the seven loading methods individually and all loading methods combined. Performance of these calibration matrices was subsequently compared in an in situ trial. During the in situ trial, five common work tasks (e.g., walking, manual lifting, pushing) were performed by an experimenter, while standing on the FP wearing a "ForceShoe" with two calibrated FTsensors attached to its sole. Root-mean-square differences (RMSDs) between the FTsensor and FP outcomes were calculated over all tasks. Using the calibration matrices based on all loading methods combined resulted in small RMSDs (GRF: matrices based on "pushing against manual resistance" resulted in similar RMSDs, proving it to be the best single loading method. PMID:22444348

Faber, Gert S; Chang, Chien-Chi; Kingma, Idsart; Schepers, H Martin; Herber, Sebastiaan; Veltink, Peter H; Dennerlein, Jack T

2012-04-30

265

Deuteration effect on the NH/ND stretch band of the jet-cooled 7-azaindole and its tautomeric dimers: Relation between the vibrational relaxation and the ground-state double proton-transfer reaction  

International Nuclear Information System (INIS)

Highlights: • Deuteration effect on IR spectra of 7-azaindole tautomeric dimers is investigated. • The NH/ND stretch levels are found to relax basically within the monomer unit. • Only the NH stretch of the tautomeric dimer exhibits a drastic deuteration effect. • The deuteration effect is related to the double proton-transfer reaction. - Abstract: Infrared spectra of NH and ND stretch bands of the 7-azaindole (7-AI) dimer and its tautomeric dimer are observed to investigate a deuteration effect on the spectra and also a ground-state double proton-transfer (DPT) reaction. We examined the three isotopic species for each dimers; undeuterated one (NH–NH) and one or two hydrogen atom(s) of the NH groups is deuterated ones (NH–ND and ND–ND, respectively). It is found that the ND stretch band profiles of the NH–ND and ND–ND tautomeric dimers are very similar with each other. This result is very distinct from the result of the comparison of the NH stretch band profiles of the NH–NH and NH–ND dimers in our previous paper. For a further discussion, we examined the deuteration effect in the case of the 7-AI dimer. It is found that band profiles of the NH stretch of the NH–NH and the NH–ND dimers and also the ND stretch of the NH–ND and the ND–ND dimers exhibit similar patterns, respectively. These facts indicates that the vibrational relaxation from the NH/ND stretch level of the dimer basically proceed within a monomer unit. The large deuteration effect of the NH stretch band profile observed previously is found to be characteristic of the tautomeric dimer. This behavior is related to a large anharmonicity of the potential energy surface originating from an existence of the double-proton transfer reaction barrier

266

Determination of external forces in alpine skiing using a differential global navigation satellite system.  

Science.gov (United States)

In alpine ski racing the relationships between skier kinetics and kinematics and their effect on performance and injury-related aspects are not well understood. There is currently no validated system to determine all external forces simultaneously acting on skiers, particularly under race conditions and throughout entire races. To address the problem, this study proposes and assesses a method for determining skier kinetics with a single lightweight differential global navigation satellite system (dGNSS). The dGNSS kinetic method was compared to a reference system for six skiers and two turns each. The pattern differences obtained between the measurement systems (offset ± SD) were -26 ± 152 N for the ground reaction force, 1 ± 96 N for ski friction and -6 ± 6 N for the air drag force. The differences between turn means were small. The error pattern within the dGNSS kinetic method was highly repeatable and precision was therefore good (SD within system: 63 N ground reaction force, 42 N friction force and 7 N air drag force) allowing instantaneous relative comparisons and identification of discriminative meaningful changes. The method is therefore highly valid in assessing relative differences between skiers in the same turn, as well as turn means between different turns. The system is suitable to measure large capture volumes under race conditions. PMID:23917257

Gilgien, Matthias; Spörri, Jörg; Chardonnens, Julien; Kröll, Josef; Müller, Erich

2013-01-01

267

Determination of External Forces in Alpine Skiing Using a Differential Global Navigation Satellite System  

Directory of Open Access Journals (Sweden)

Full Text Available In alpine ski racing the relationships between skier kinetics and kinematics and their effect on performance and injury-related aspects are not well understood. There is currently no validated system to determine all external forces simultaneously acting on skiers, particularly under race conditions and throughout entire races. To address the problem, this study proposes and assesses a method for determining skier kinetics with a single lightweight differential global navigation satellite system (dGNSS. The dGNSS kinetic method was compared to a reference system for six skiers and two turns each. The pattern differences obtained between the measurement systems (offset ± SD were ?26 ± 152 N for the ground reaction force, 1 ± 96 N for ski friction and ?6 ± 6 N for the air drag force. The differences between turn means were small. The error pattern within the dGNSS kinetic method was highly repeatable and precision was therefore good (SD within system: 63 N ground reaction force, 42 N friction force and 7 N air drag force allowing instantaneous relative comparisons and identification of discriminative meaningful changes. The method is therefore highly valid in assessing relative differences between skiers in the same turn, as well as turn means between different turns. The system is suitable to measure large capture volumes under race conditions.

Erich Müller

2013-08-01

268

Motion synthesis and force distribution analysis for a biped robot.  

Science.gov (United States)

In this paper, the method of generating biped robot motion using recorded human gait is presented. The recorded data were modified taking into account the velocity available for robot drives. Data includes only selected joint angles, therefore the missing values were obtained considering the dynamic postural stability of the robot, which means obtaining an adequate motion trajectory of the so-called Zero Moment Point (ZMT). Also, the method of determining the ground reaction forces' distribution during the biped robot's dynamic stable walk is described. The method was developed by the authors. Following the description of equations characterizing the dynamics of robot's motion, the values of the components of ground reaction forces were symbolically determined as well as the coordinates of the points of robot's feet contact with the ground. The theoretical considerations have been supported by computer simulation and animation of the robot's motion. This was done using Matlab/Simulink package and Simulink 3D Animation Toolbox, and it has proved the proposed method. PMID:21761810

Trojnacki, Maciej T; Zieli?ska, Teresa

2011-01-01

269

Accurate Hellman-Feynman force method for the study of the first and second derivatives of potential energy hypersurface  

International Nuclear Information System (INIS)

The authors review the method of calculating a reliable H-F-force, starting from the underlying theorem, and examine the accuracy of calculated H-F force. The authors then show some recent applications of the method to geometry optimizations of the molecules in ground and excited states and of the transition state of a chemical reaction. Further, when the H-F theorum is used, an analytic expression of the second derivative becomes much simpler than a straightforward second derivative of the energy. The authors report calculations of force constants by this method and explain the electronic origins of the second derivatives

270

Some applications of the virial theorem to molecular force fields: the zero virial reaction coordinate and diatomic potentials from the normalized kinetic field functions  

International Nuclear Information System (INIS)

For a fixed-angle potential energy surface (PES), W(Q), following the zero virial path (ZVP), on which ?/sub ?//sup N/Q/sub ?/ . del /sub ?/W(Q) = 0, provides an efficient way for locating the transition state and generating a good approximation to the minimum-energy reaction path; vector Q = (Q1, ..., Q/sub N/ stands for nuclear coordinates. An algorithm which employs the ZVP following is proposed for exploring PESs when starting from the reactant (or product) region. It seems that this approach allows one to avoid some discontinuities in the reaction coordinate, which often result from the bottom-following procedures. The implications of the integral forms of the virial theorem are examined and a new way of constructing potential energy functions W(R) for diatomic molecules is proposed. It starts with the normalization of the kinetic component T(R) of the potential: integral0/sup infinity/[T(R) - T(infinity)]dR = Z/sub A/Z/sub B/, where Z/sub A/ and Z/sub B/ are the nuclear charges and R is the internuclear distance. The modified potentials are derived for four different analytical representations of T(R), T/sub X(R)(X = M, R, RM, and HH) by the Morse, Rydberg, Rosen--Morse, and Hulbert--Hirschfelder functions, respectively. The three-parameter modified potentials (X = M, R, and RM) are tested against known spectroscopic data for H2+ and H2.The modified potentials require one less experimental constant to fie one less experimental constant to fit the potential parameters than do their original analogs. It follows that the Morse and Rydberg functions constitute satisfactory representations of the kinetic component T(R), and that enforcing its normalization improves predictions of spectroscopic constants and relations between them. 46 references

271

Ground water  

International Nuclear Information System (INIS)

There is growing evidence that the Nation's ground water is contaminated by a variety of sources. These include unprotected industrial, municipal, and radioactive disposal sites, petroleum exploration and mining activities, agricultural operations such as insecticide spraying, high de-icing salts and others. As of March 1980, more than 8000 chemical tests have been performed on well water, with chlorinated organic solvents found most frequently. Because 100 million Americans may be threatened by unfit drinking water, EPA has developed a new ground water strategy. It will enlist the help of State and local governments who already have programs under way and it will involve broad public debate and participation

272

Transonic and supersonic ground effect aerodynamics  

Science.gov (United States)

A review of recent and historical work in the field of transonic and supersonic ground effect aerodynamics has been conducted, focussing on applied research on wings and aircraft, present and future ground transportation, projectiles, rocket sleds and other related bodies which travel in close ground proximity in the compressible regime. Methods for ground testing are described and evaluated, noting that wind tunnel testing is best performed with a symmetry model in the absence of a moving ground; sled or rail testing is ultimately preferable, though considerably more expensive. Findings are reported on shock-related ground influence on aerodynamic forces and moments in and accelerating through the transonic regime - where force reversals and the early onset of local supersonic flow is prevalent - as well as more predictable behaviours in fully supersonic to hypersonic ground effect flows.

Doig, G.

2014-08-01

273

A theoretical study for the reaction of vinyl cyanide C2H3CN(X1A') with the ground state carbon atom C(3P) in cold molecular clouds.  

Science.gov (United States)

The reaction of the ground state atomic carbon, C(3P), with simple unsaturated nitrile, C2H3CN(X1A' (vinyl cyanide), is investigated theoretically to explore the probable routes for the formation of carbon-nitrogen-bearing species in extraterrestrial environments particularly of ultralow temperature. Five collision complexes without entrance barrier as a result of the carbon atom addition to the pi systems of C2H3CN are characterized. The B3YLP/6-311G(d,p) level of theory is utilized in obtaining the optimized geometries, harmonic frequencies, and energies of the intermediates, transition states, and products along the isomerization and dissociation pathways of each collision complex. Subsequently, with the facilitation of computed RRKM rate constants at collision energy of 0-10 kcal/mol, the most probable paths for each collision complexes are determined, of which the CCSD(T)/6-311G(d,p) energies are calculated. The major products predicted are exclusively due to the hydrogen atom dissociations, while the products of H2, CN, and CH2 decompositions are found negligible. Among many possible H-elimination products, cyano propargyl (p4) and 3-cyano propargyl (p5) are the most probable, in which p5 can be formed via two intermediates, cyano allene (i8) and cyano vinylmethylene (i6), while p4 is yielded from i8. The study suggests this class of reaction is an important route to the synthesis of unsaturated nitriles at the temperature as low as 10 K, and the results are valuable for future chemical models of interstellar clouds. PMID:15743245

Su, Hsiu-Fen; Kaiser, R I; Chang, A H H

2005-02-15

274

Dispersion Forces  

CERN Document Server

In this book, a modern unified theory of dispersion forces on atoms and bodies is presented which covers a broad range of advanced aspects and scenarios. Macroscopic quantum electrodynamics is shown to provide a powerful framework for dispersion forces which allows for discussing general properties like their non-additivity and the relation between microscopic and macroscopic interactions. It is demonstrated how the general results can be used to obtain dispersion forces on atoms in the presence of bodies of various shapes and materials. Starting with a brief recapitulation of volume I, this volume II deals especially with bodies of irregular shapes, universal scaling laws, dynamical forces on excited atoms, enhanced forces in cavity quantum electrodynamics, non-equilibrium forces in thermal environments and quantum friction. The book gives both the specialist and those new to the field a thorough overview over recent results in the field. It provides a toolbox for studying dispersion forces in various contex...

Buhmann, Stefan Yoshi

2012-01-01

275

Coaxial atomic force microscope tweezers  

Science.gov (United States)

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 versus applied voltage. We show that the coaxial AFM tweezers 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.

Brown, K. A.; Aguilar, J. A.; Westervelt, R. M.

2010-03-01

276

The human foot and heel-sole-toe walking strategy: a mechanism enabling an inverted pendular gait with low isometric muscle force?  

Science.gov (United States)

Mechanically, the most economical gait for slow bipedal locomotion requires walking as an 'inverted pendulum', with: I, an impulsive, energy-dissipating leg compression at the beginning of stance; II, a stiff-limbed vault; and III, an impulsive, powering push-off at the end of stance. The characteristic 'M'-shaped vertical ground reaction forces of walking in humans reflect this impulse-vault-impulse strategy. Humans achieve this gait by dissipating energy during the heel-to-sole transition in early stance, approximately stiff-limbed, flat-footed vaulting over midstance and ankle plantarflexion (powering the toes down) in late stance. Here, we show that the 'M'-shaped walking ground reaction force profile does not require the plantigrade human foot or heel-sole-toe stance; it is maintained in tip-toe and high-heel walking as well as in ostriches. However, the unusual, stiff, human foot structure--with ground-contacting heel behind ankle and toes in front--enables both mechanically economical inverted pendular walking and physiologically economical muscle loading, by producing extreme changes in mechanical advantage between muscles and ground reaction forces. With a human foot, and heel-sole-toe strategy during stance, the shin muscles that dissipate energy, or calf muscles that power the push-off, need not be loaded at all--largely avoiding the 'cost of muscle force'--during the passive vaulting phase. PMID:22572024

Usherwood, J R; Channon, A J; Myatt, J P; Rankin, J W; Hubel, T Y

2012-10-01

277

Ship Grounding on Rock - I. Theory  

DEFF Research Database (Denmark)

This paper presents a set of analytical expressions which can be used to calculate the reaction force on a ship bottom deformed by a conical rock with a rounded tip. Closed form solutions are given for the resistance of inner and outer bottom plating, longitudinal stiffeners, girders and bulkheads and transverse frames, floors and bulkheads. The expressions are derived by use of an energy method or a type of 'upper bound' method which rigorously takes into account the effects of large plastic deformations, friction and fracture. A high level of generality for the methodology has been obtained by postulating a global mode of deformation for the structure around the rock with one free parameter, the plate split angle, related to the shape of thedeformation mode. It is assumed that intersections between structural components stay intact during the entire deformation process so the resistance of the individual structural members are derived according to the global deformation mode. The resistance of the entire structure is found by minimizing the energy disspiation from all the deformed members with respect to the plate split angle. In a subsequent paper it is shown that the theoreticl model predicts the damage of four large scale tests and an accidental grounding with errors less than 10%. Moreover, it is illustrated by an example that the model evaluation of a grounding scenario is sufficientlty fast to be used in a probabilistic framework in a Formal safety Assessment.

Simonsen, Bo Cerup

1997-01-01

278

Deflection of electron beams by ground planes  

International Nuclear Information System (INIS)

Analytic methods are used to determine the effect of a nearby ground plane on the trajectory of a relativistic electron beam passing through dense gas. The beam is shown to respond to the ground plane in one of two distinct modes, determined by beam current and energy. Low-power beams deflect from the ground plane and tear longitudinally. High-power beams do not deflect or tear but tilt, i.e., the beam axis is no longer parallel to the direction of propagation. This conclusion is reached by computing the net beam force as a superposition of the ''bare'' ground-plane forces, the shielding forces from the beam-generated plasma, the body coupling forces induced by beam tilt, and the force that arises as the beam separates from the plasma. Effects from electromagnetic retardation and ground resistivity are shown to be negligible in typical cases of interest, and the interaction between ground planes and other external forces is discussed as well

279

Dam Forces  

Science.gov (United States)

Students learn how the force of water helps determine the size and shape of dams. They use clay to build models of four types of dams, and observe the force of the water against each type. They conclude by deciding which type of dam they, as Splash Engineering engineers, will design for Thirsty County.

Integrated Teaching And Learning Program And Laboratory

280

Different forces  

CERN Multimedia

The different forces, together with a pictorial analogy of how the exchange of particles works. The table lists the relative strength of the couplings, the quanta associated with the force fields and the bodies or phenomena in which they have a dominant role.

1982-01-01

 
 
 
 
281

Strong Force  

CERN Multimedia

Without the strong force, there could be no life. The carbon in living matter is synthesised in stars via the strong force. Lighter atomic nuclei become bound together in a process called nuclear fusion. A minor change in this interaction would make life impossible. As its name suggests, the strong force is the most powerful of the 4 forces, yet its sphere of influence is limited to within the atomic nucleus. Indeed it is the strong force that holds together the quarks inside the positively charged protons. Without this glue, the quarks would fly apart repulsed by electromagnetism. In fact, it is impossible to separate 2 quarks : so much energy is needed, that a second pair of quarks is produced. Text for the interactive: Can you pull apart the quarks inside a proton?

282

Modelo dinâmico de simulação e otimização da força normal de reação do solo para um mecanismo de corte basal / Dynamic model of simulation and optimization of the normal force of soil reaction for a mechanism of base cutter  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: Portuguese Abstract in portuguese O modelo físico foi baseado no método de Newton-Euler, sendo o mesmo desenvolvido utilizando o programa computacional científico Mathematica®. Realizaram-se várias simulações, nas quais se procurou obter a força normal de reação do solo variando velocidades de avanço (0,69; 1,12; 1,48; 1,82 e 2,12 m [...] s-1); perfis de solo (senoidal, rampa ascendente e descendente) e altura do camalhão (0,025 e 0,05 m). Após as simulações iniciais, o mecanismo foi otimizado utilizando o programa computacional científico Matlab®, tendo como critério (função-objetivo) a minimização da força normal de reação do perfil (F N) e como variáveis de projeto os comprimentos das barras (L1y, L2, l3 e L4), altura da operação (L7), o comprimento inicial da mola (Lmo) e a constante elástica da mola (k t). A falta de robustez do mecanismo em relação à variável altura de operação foi contornada por meio do uso de mola com baixa rigidez e grande comprimento. Os resultados demonstraram que o mecanismo otimizado obteve desempenho de flutuação muito bom, em relação ao mecanismo inicial. Abstract in english The physical model was based on the method of Newton-Euler. The model was developed by using the scientific computer program Mathematica®. Several simulations where tried varying the progress speeds (0.69; 1.12; 1.48; 1.82 and 2.12 m s-1); soil profiles (sinoidal, ascending and descending ramp) and [...] height of the profile (0.025 and 0.05 m) to obtain the normal force of soil reaction. After the initial simulations, the mechanism was optimized using the scientific computer program Matlab® having as criterion (function-objective) the minimization of the normal force of reaction of the profile (FN). The project variables were the lengths of the bars (L1y, L2, l3 and L4), height of the operation (L7), the initial length of the spring (Lmo) and the elastic constant of the spring (k t). The lack of robustness of the mechanism in relation to the variable height of the operation was outlined by using a spring with low rigidity and large length. The results demonstrated that the mechanism optimized showed better flotation performance in relation to the initial mechanism.

Carlos E. S., Volpato; Oscar A., Braunbeck; Carlos A. A. de, Oliveira.

283

Modelo dinâmico de simulação e otimização da força normal de reação do solo para um mecanismo de corte basal Dynamic model of simulation and optimization of the normal force of soil reaction for a mechanism of base cutter  

Directory of Open Access Journals (Sweden)

Full Text Available O modelo físico foi baseado no método de Newton-Euler, sendo o mesmo desenvolvido utilizando o programa computacional científico Mathematica®. Realizaram-se várias simulações, nas quais se procurou obter a força normal de reação do solo variando velocidades de avanço (0,69; 1,12; 1,48; 1,82 e 2,12 m s-1; perfis de solo (senoidal, rampa ascendente e descendente e altura do camalhão (0,025 e 0,05 m. Após as simulações iniciais, o mecanismo foi otimizado utilizando o programa computacional científico Matlab®, tendo como critério (função-objetivo a minimização da força normal de reação do perfil (F N e como variáveis de projeto os comprimentos das barras (L1y, L2, l3 e L4, altura da operação (L7, o comprimento inicial da mola (Lmo e a constante elástica da mola (k t. A falta de robustez do mecanismo em relação à variável altura de operação foi contornada por meio do uso de mola com baixa rigidez e grande comprimento. Os resultados demonstraram que o mecanismo otimizado obteve desempenho de flutuação muito bom, em relação ao mecanismo inicial.The physical model was based on the method of Newton-Euler. The model was developed by using the scientific computer program Mathematica®. Several simulations where tried varying the progress speeds (0.69; 1.12; 1.48; 1.82 and 2.12 m s-1; soil profiles (sinoidal, ascending and descending ramp and height of the profile (0.025 and 0.05 m to obtain the normal force of soil reaction. After the initial simulations, the mechanism was optimized using the scientific computer program Matlab® having as criterion (function-objective the minimization of the normal force of reaction of the profile (FN. The project variables were the lengths of the bars (L1y, L2, l3 and L4, height of the operation (L7, the initial length of the spring (Lmo and the elastic constant of the spring (k t. The lack of robustness of the mechanism in relation to the variable height of the operation was outlined by using a spring with low rigidity and large length. The results demonstrated that the mechanism optimized showed better flotation performance in relation to the initial mechanism.

Carlos E. S. Volpato

2005-08-01

284

Reaction Control Engine for Space Launch Initiative  

Science.gov (United States)

Engineers at the Marshall Space Flight Center (MSFC) have begun a series of engine tests on a new breed of space propulsion: a Reaction Control Engine developed for the Space Launch Initiative (SLI). The engine, developed by TRW Space and Electronics of Redondo Beach, California, is an auxiliary propulsion engine designed to maneuver vehicles in orbit. It is used for docking, reentry, attitude control, and fine-pointing while the vehicle is in orbit. The engine uses nontoxic chemicals as propellants, a feature that creates a safer environment for ground operators, lowers cost, and increases efficiency with less maintenance and quicker turnaround time between missions. Testing includes 30 hot-firings. This photograph shows the first engine test performed at MSFC that includes SLI technology. Another unique feature of the Reaction Control Engine is that it operates at dual thrust modes, combining two engine functions into one engine. The engine operates at both 25 and 1,000 pounds of force, reducing overall propulsion weight and allowing vehicles to easily maneuver in space. The low-level thrust of 25 pounds of force allows the vehicle to fine-point maneuver and dock while the high-level thrust of 1,000 pounds of force is used for reentry, orbit transfer, and coarse positioning. SLI is a NASA-wide research and development program, managed by the MSFC, designed to improve safety, reliability, and cost effectiveness of space travel for second generation reusable launch vehicles.

2002-01-01

285

Modelo 3D para quantificação das forças articulares e momentos proximais resultantes para o membro superior / 3D model for analysis of resultant proximal reaction forces and moments for the upper limb  

Scientific Electronic Library Online (English)

Full Text Available SciELO Portugal | Language: Portuguese Abstract in portuguese Objetivos: Este estudo teve como objetivo implementar um modelo biomecânico, de segmentos articulados, associado à dinâmica inversa que permita a análise em três dimensões das forças de reação proximais e momentos proximais resultantes para diferentes gestos do membro superior. Método: Os gestos ava [...] liados foram: flexão, extensão e abdução de ombro e flexão de cotovelo, os quais foram realizados por um indivíduo do sexo masculino. O modelo implementado é composto por cinco segmentos rígidos (mão, antebraço, braço, escápula e tronco) conectados. As equações de movimento de Newton-Euler foram utilizadas para quantificação das forças e momentos proximais resultantes. Para registro cinemático foram utilizadas cinco câmeras digitais, com freqüência de amostragem de 50 campos/seg. A precisão estimada do sistema de videogrametria foi, em média, de 1,7 mm. Foi monitorada a atividade eletromiográfica dos músculos deltóide (anterior, médio e posterior), bíceps braquial, tríceps braquial e peitoral maior. O modelo foi avaliado através da comparação qualitativa dos resultados de momento proximal resultante, com a atividade eletromiográfica. Resultados: Os resultados sugerem que o modelo apresenta resultados coerentes. O sinal eletromiográfico e o momento proximal apresentam sincronismo temporal. Conclusão: O modelo foi capaz de estimar as forças de reacção e momentos proximais resultantes nos diferentes gestos. Abstract in english Objectives: The aim of this study was to implement a biomechanical model, with linked segments associated with inverse dynamics, to analyze proximal net forces and moments during different upper limbs’ activities. Methods: one male subject performed flexion, extension and abduction of the shoulder a [...] nd flexion of the elbow. The model is composed of five connected rigid segments (hand, forearm, arm, scapula and trunk). The Newton-Euler motion equations were used to quantify proximal net reaction forces and moments. For kinematics recording, five cameras with a frequency sample of 50 fps were used. Videogrammetry accuracy was, on average, 1,7mm. The following muscles had their activities monitored: deltoid (anterior, medial, posterior), biceps brachialis, triceps brachialis, pectoralis major. The model was evaluated by qualitative comparison of proximal net moments with electromyographic signal of agonist muscles. Results: The results showed a temporal synchronism between the proximal net moments and agonist EMG activity. Conclusions: The model was able to estimate proximal net forces and moments during different upper limbs’ activities.

Daniel Cury, Ribeiro; Jefferson Fagundes, Loss.

286

EXTENDED HÜCKEL ORBITAL FORCES  

Directory of Open Access Journals (Sweden)

Full Text Available The forces acting on individual atoms in a molecule, arising from the distorting effect on the molecular framework of the electrons in the different populated molecular orbitals, are calculated within a simple Extended Hückel formalism. The method, which is strongly dependent on the properties of overlap integrals, is applied to the study of several processes and reactions of chemical interest, such as conformational stability of molecules, torsional stability for rotations around a single bond of some simple molecules and the connection between the forces acting upon atoms and the rules derived from conservation of orbital symmetry in concerted reaction. The results show good agreement with the experimental evidence and the known symmetry rules

Federico Eisner

2003-12-01

287

Common muscle synergies for control of center of mass and force in nonstepping and stepping postural behaviors  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We investigated muscle activity, ground reaction forces, and center of mass (CoM) acceleration in two different postural behaviors for standing balance control in humans to determine whether common neural mechanisms are used in different postural tasks. We compared nonstepping responses, where the base of support is stationary and balance is recovered by returning CoM back to its initial position, with stepping responses, where the base of support is enlarged and balance is recovered by pushi...

Chvatal, Stacie A.; Torres-oviedo, Gelsy; Safavynia, Seyed A.; Ting, Lena H.

2011-01-01

288

Centripetal Force  

Science.gov (United States)

In this animation a ball bounces off the sides of the circle, and the number of sides double, until the circle appears to exert force on a ball that is constant in size and always directed towards the center.

Wpsu

2010-04-09

289

Aberrant Assembly Complexes of the Reaction Center Light-harvesting 1 PufX (RC-LH1-PufX) Core Complex of Rhodobacter sphaeroides Imaged by Atomic Force Microscopy.  

Science.gov (United States)

In the purple phototrophic bacterium Rhodobacter sphaeroides, many protein complexes congregate within the membrane to form operational photosynthetic units consisting of arrays of light-harvesting LH2 complexes and monomeric and dimeric reaction center (RC)-light-harvesting 1 (LH1)-PufX "core" complexes. Each half of a dimer complex consists of a RC surrounded by 14 LH1 ?? subunits, with two bacteriochlorophylls (Bchls) sandwiched between each ?? pair of transmembrane helices. We used atomic force microscopy (AFM) to investigate the assembly of single molecules of the RC-LH1-PufX complex using membranes prepared from LH2-minus mutants. When the RC and PufX components were also absent, AFM revealed a series of LH1 variants where the repeating ?1?1(Bchl)2 units had formed rings of variable size, ellipses, and spirals and also arcs that could be assembly products. The spiral complexes occur when the LH1 ring has failed to close, and short arcs are suggestive of prematurely terminated LH1 complex assembly. In the absence of RCs, we occasionally observed captive proteins enclosed by the LH1 ring. When production of LH1 units was restricted by lowering the relative levels of the cognate pufBA transcript, we imaged a mixture of complete RC-LH1 core complexes, empty LH1 rings, and isolated RCs, leading us to conclude that once a RC associates with the first ?1?1(Bchl)2 subunit, cooperative associations between subsequent subunits and the RC tend to drive LH1 ring assembly to completion. PMID:25193660

Olsen, John D; Adams, Peter G; Jackson, Philip J; Dickman, Mark J; Qian, Pu; Hunter, C Neil

2014-10-24

290

Comparative analysis of the ground reaction forces, during the support phase, in a group of pregnant women on their 3rd trimester of pregnancy and in a group of not pregnant women  

Digital Repository Infrastructure Vision for European Research (DRIVER)

OBJETIVO: caracterizar e comparar as forças de reação do solo (FRS), durante a fase de apoio num ciclo de marcha da mulher grávida do 3º trimestre e na não grávida. MATERIAL E MÉTODOS: 20 mulheres, 10 grávidas e dez não grávidas, participaram voluntariamente neste estudo. Os valores relativos às forças de reação do solo (FRS) foram medidos (1000 Hz) usando uma plataforma de força (BERTEC 4060-15), ligada a um amplificador (BERTEC AM 6300) e a um conversor analógico-digita...

Santos, Rubim; Gil, Belandina; Marques, Alda; Vilas Boas, Joa?o; Silva, Jose?

2008-01-01

291

Level locomotion in wood ants: evidence for grounded running.  

Science.gov (United States)

In order to better understand the strategies of locomotion in small insects, we have studied continuous level locomotion of the wood ant species Formica polyctena. We determined the three-dimensional centre of mass kinematics during the gait cycle and recorded the ground reaction forces of single legs utilising a self-developed test site. Our findings show that the animals used the same gait dynamics across a wide speed range without dissolving the tripodal stride pattern. To achieve higher velocities, the ants proportionally increased stride length and stepping frequency. The centre of mass energetics indicated a bouncing gait, in which horizontal kinetic and gravitational potential energy fluctuated in close phase. We determined a high degree of compliance especially in the front legs, as the effective leg length was nearly halved during the contact phase. This leads to only small vertical oscillations of the body, which are important in maintaining ground contact. Bouncing gaits without aerial phases seem to be a common strategy in small runners and can be sufficiently described by the bipedal spring-loaded inverted pendulum model. Thus, with our results, we provide evidence that wood ants perform 'grounded running'. PMID:24744414

Reinhardt, Lars; Blickhan, Reinhard

2014-07-01

292

On contribution of three-body forces to Nd interaction at intermediate energies  

International Nuclear Information System (INIS)

Available data on large-angle nucleon-deuteron elastic scattering Nd ? dN below the pion threshold give a signal for three-body forces. There is a problem of separation of possible subtle aspects of these forces from off-shell effects in two-nucleon potentials. By considering the main mechanisms of the process Nd ? dN, we show qualitatively that in the quasi-binary reaction N + d ? (NN) + N with the final spin singlet NN-pair in the S-state the relative contribution of the 3N forces differs substantially from the elastic channel. It gives a new testing ground for the problem in question

293

Nuclear reactions  

International Nuclear Information System (INIS)

This chapter of the textbook overviews nuclear reactions discussing the reaction mechanisms and the types of nuclear reactions, e.g. those induced by neutrons, by protons, by alpha particles and gamma photons, and finally, deuteron and thermonuclear reactions

294

On Grounding of Fast Ships  

DEFF Research Database (Denmark)

The paper deals with analysis of grounding of high-speed crafts. It is the purpose to present a comprehensive mathematical model for calculation of the overall dynamic ship response during grounding. This procedure is applied to derive the motions, the time varying sectional forces and the local loads during grounding on plane, sloping, sandy bottoms for six different designs of fast monohull ships made from steel, aluminium or GRP sandwich materials. The results show that the effect of the hull flexibility is to reduce the overall dynamic sectional loads on the hull girder. The considered numerical examples also indicate that, even with impact speeds of 40 knots against a 1:10 sloping bottom, the global strength of the hull girder is not exceeded by the grounding induced loads.For the local deformation of high-speed ship hulls at the point of contact withthe ground, the paper presents experimental results from crushing tests of aluminium hull girder components with realistic full-scale scantlings. A comparison with existing simplified calculation procedures for ductile metallic structures show that these procedures cannot be used to predict the crushing behaviour of the fore body of high speed ships.

Simonsen, Bo Cerup; Pedersen, Preben Terndrup

1997-01-01

295

Transition States from Empirical Force Fields  

DEFF Research Database (Denmark)

This is an overview of the use of empirical force fields in the study of reaction mechanisms. EVB-type methods (including RFF and MCMM) produce full reaction surfaces by mixing, in the simplest case, known force fields describing reactants and products. The SEAM method instead locates approximate transition structures by energy minimization along the intersection of the component force fields. The TSFF approach (including Q2MM) designs a new force field mimicking the transition structure as an energy minimum. The scope and applicability of the various methods are compared.

Norrby, Per-Ola

2003-01-01

296

Measurement of 241Am Ground State Radiative Neutron Capture Cross Section with Cold Neutron Beam. Progress Report on Research Contract HUN14318 for the CRP on Minor Actinide Neutron Reaction Data (MANREAD)  

International Nuclear Information System (INIS)

The ground state cross section of 242Am has been measured with beams of cold neutrons at the Budapest Research Reactor using the X-ray emission of the decay product of 242Pu. This methodology avoids the uncertainty caused by resonance neutrons in the pile activations. The target was characterized with gamma and X-ray spectrometry. The obtained ground state cross section is 540 ± 32 b, which is at the low end of the most recent literature values, but agrees with most of them within their uncertainty. (author)

297

"Force," ontology, and language  

Science.gov (United States)

We introduce a linguistic framework through which one can interpret systematically studentsâ understanding of and reasoning about force and motion. Some researchers have suggested that students have robust misconceptions or alternative frameworks grounded in everyday experience. Others have pointed out the inconsistency of studentsâ responses and presented a phenomenological explanation for what is observed, namely, knowledge in pieces. We wish to present a view that builds on and unifies aspects of this prior research. Our argument is that many studentsâ difficulties with force and motion are primarily due to a combination of linguistic and ontological difficulties. It is possible that students are primarily engaged in trying to define and categorize the meaning of the term âforceâ as spoken about by physicists. We found that this process of negotiation of meaning is remarkably similar to that engaged in by physicists in history. In this paper we will describe a study of the historical record that reveals an analogous process of meaning negotiation, spanning multiple centuries. Using methods from cognitive linguistics and systemic functional grammar, we will present an analysis of the force and motion literature, focusing on prior studies with interview data. We will then discuss the implications of our findings for physics instruction.

Brookes, David T.; Etkina, Eugenia

2010-06-30

298

Seismic Analysis of Elevated Water Storage Tanks Subjected to Six Correlated Ground Motion Components  

Directory of Open Access Journals (Sweden)

Full Text Available In this work, rotational components of ground motion acceleration were defined according toimproved method from the corresponding available translational components based on transversely isotropicelastic wave propagation in the soil. With such improvement, it becomes possible to consider frequencydependent wave velocities on rotational components of ground motion. For this purpose, three translationalcomponents of El Centro earthquake (24 January 1951 were adopted to generate their relative rotationalcomponents based on SV and SH wave incidence by Fast Fourier transform with 4096 discrete frequencies.The translational and computed rotational motions were then applied to the concrete elevated water storagetanks with different structural characteristics and water elevations. The finite element method is used for thenonlinear analysis of water storage tanks considering the fluid-structure interaction using Lagrangian-Lagrangian approach and the concrete material nonlinearities have been taken into account through William-Warnke model. The nonlinear response of these structures considering the six components of ground motionshowed that the rotational components of ground motion can increase or decrease the maximum displacementand reaction force of the structure. These variations are depending on the frequency of structure andpredominant frequencies of translational and rotational components of ground motion.

L. Kalani Sarokolayi

2013-01-01

299

TARDEC's Intelligent Ground Systems overview  

Science.gov (United States)

The mission of the Intelligent Ground Systems (IGS) Area at the Tank Automotive Research, Development and Engineering Center (TARDEC) is to conduct technology maturation and integration to increase Soldier robot control/interface intuitiveness and robotic ground system robustness, functionality and overall system effectiveness for the Future Combat System Brigade Combat Team, Robotics Systems Joint Project Office and game changing capabilities to be fielded beyond the current force. This is accomplished through technology component development focused on increasing unmanned ground vehicle autonomy, optimizing crew interfaces and mission planners that capture commanders' intent, integrating payloads that provide 360 degree local situational awareness and expanding current UGV tactical behavior, learning and adaptation capabilities. The integration of these technology components into ground vehicle demonstrators permits engineering evaluation, User assessment and performance characterization in increasingly complex, dynamic and relevant environments to include high speed on road or cross country operations, all weather/visibility conditions and military operations in urban terrain (MOUT). Focused testing and experimentation is directed at reducing PM risk areas (safe operations, autonomous maneuver, manned-unmanned collaboration) and transitioning technology in the form of hardware, software algorithms, test and performance data, as well as User feedback and lessons learned.

Jaster, Jeffrey F.

2009-05-01

300

Analytical model for heterogeneous reactions in mixed porous media  

Energy Technology Data Exchange (ETDEWEB)

The funnel/gate system is a developing technology for passive ground-water plume management and treatment. This technology uses sheet pilings as a funnel to force polluted ground water through a highly permeable zone of reactive porous media (the gate) where contaminants are degraded by biotic or abiotic heterogeneous reactions. This paper presents a new analytical nonequilibrium model for solute transport in saturated, nonhomogeneous or mixed porous media that could assist efforts to design funnel/gate systems and predict their performance. The model incorporates convective/dispersion transport, dissolved constituent decay, surface-mediated degradation, and time-dependent mass transfer between phases. Simulation studies of equilibrium and nonequilibrium transport conditions reveal manifestations of rate-limited degradation when mass-transfer times are longer than system hydraulic residence times, or when surface-mediated reaction rates are faster than solute mass-transfer processes (i.e., sorption, film diffusion, or intraparticle diffusion). For example, steady-state contaminant concentrations will be higher under a nonequilibrium transport scenario than would otherwise be expected when assuming equilibrium conditions. Thus, a funnel/gate system may fail to achieve desired ground-water treatment if the possibility of mass-transfer-limited degradation is not considered.

Hatfield, K. [Univ. of Florida, Gainesville, FL (United States). Dept. of Civil Engineering; Burris, D.R. [Armstrong Lab., Tyndall AFB, FL (United States). Environmental Research Lab.; Wolfe, N.L. [EPA, Athens, GA (United States)

1996-08-01

 
 
 
 
301

Dynamic performance assessment of selected sport shoes on impact forces.  

Science.gov (United States)

Few investigators have evaluated the performance characteristics of non-running sport shoes. The purpose of this study was to assess the dynamic performance characteristics of four different shoe models during landings. Five male subjects performed 25 voluntary hanging drop landings (60 cm) onto a force platform (1000 Hz) for each of four shoe conditions (C1 and C2 = basketball shoe, C3 = running shoe, C4 = volleyball shoe). Ground reaction force data were evaluated for maximum forefoot (F1) and rearfoot (F2) impact forces as well as the respective times of occurrence of these events (T1, T2). Results of the group data analysis indicated a preferential performance rank order of C1, C3, C4, C2 although significant interaction effects were observed, indicating a need for single-subject analyses. Three techniques were incorporated to assess individual subject condition differences, all of which elicited unique rank orders for the shoes although each identified C1 as the "best" shoe condition. The results of the study support the necessity for within-subject analyses conducted with an adequate number of trials when attempting to detect subtle performance differences that may exist between various sport shoes. Whether the observed statistically significant differences are biomechanically meaningful remains an important unanswered question. PMID:1943627

Dufek, J S; Bates, B T; Davis, H P; Malone, L A

1991-09-01

302

Radiation Reaction at Extreme Intensity  

Directory of Open Access Journals (Sweden)

Full Text Available The radiation reaction force is examined for an idealized short pulse ofelectromagnetic radiation and for a plane wave. Exact solutions (without radiation reactionare discussed, the total radiated power is calculated. A new and simpler approach to theapproximate form of the equation of motion is presented that automatically removes the runawaysolutions. Finally, analytical solutions are presented for the equations of motion that includethe radiation reaction forces in the very high intensity regime. A classical scattering angle isde¯ned and it shows that the electron is scattered in a small cone in the forward direction. Theradiation reaction corrections to this angle are also considered.

Richard T. Hammond

2008-03-01

303

Feed forward and feedback control for over-ground locomotion in anaesthetized cats  

Science.gov (United States)

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.

Mazurek, K. A.; Holinski, B. J.; Everaert, D. G.; Stein, R. B.; Etienne-Cummings, R.; Mushahwar, V. K.

2012-04-01

304

An ergonomic modular foot platform for isometric force/torque measurements in poststroke functional assessment: A pilot study  

Directory of Open Access Journals (Sweden)

Full Text Available The main goal of this article is to present the design, technical development, and preliminary validation of an innovative mechatronic device for force/torque measurements taken from the human foot using pilot data. The device, formed by a mobile platform equipped with two six-axis force/torque sensors, was used to perform accurate quantitative measurements during isometric exercises, aimed at performing functional assessment tests in poststroke patients undergoing a rehabilitation treatment. Results from pilot data provide a validation of the device. A large clinical trial has been planned to test whether the platform can be used in the clinical practice. We suggest that measurements of ground reaction forces taken from the foot of poststroke patients during the initiation of activities of daily living tasks can provide information about their motor recovery and enlighten possible areas of application, ranging from isometric motor exercise in neurorehabilitation to foot-based human-machine interface.

Stefano Mazzoleni, PhD

2012-08-01

305

Electrical Subsurface Grounding Analysis  

Energy Technology Data Exchange (ETDEWEB)

The purpose and objective of this analysis is to determine the present grounding requirements of the Exploratory Studies Facility (ESF) subsurface electrical system and to verify that the actual grounding system and devices satisfy the requirements.

J.M. Calle

2000-11-01

306

Attractive Optical Forces from Blackbody Radiation  

Science.gov (United States)

Blackbody radiation around hot objects induces ac Stark shifts of the energy levels of nearby atoms and molecules. These shifts are roughly proportional to the fourth power of the temperature and induce a force decaying with the third power of the distance from the object. We explicitly calculate the resulting attractive blackbody optical dipole force for ground state hydrogen atoms. Surprisingly, this force can surpass the repulsive radiation pressure and actually pull the atoms against the radiation energy flow towards the surface with a force stronger than gravity. We exemplify the dominance of the “blackbody force” over gravity for hydrogen in a cloud of hot dust particles. This overlooked force appears relevant in various astrophysical scenarios, in particular, since analogous results hold for a wide class of other broadband radiation sources.

Sonnleitner, M.; Ritsch-Marte, M.; Ritsch, H.

2013-07-01

307

The ground based plan  

International Nuclear Information System (INIS)

The paper presents a report of ''The Ground Based Plan'' of the United Kingdom Science and Engineering Research Council. The ground based plan is a plan for research in astronomy and planetary science by ground based techniques. The contents of the report contains a description of:- the scientific objectives and technical requirements (the basis for the Plan), the present organisation and funding for the ground based programme, the Plan, the main scientific features and the further objectives of the Plan. (U.K.)

308

The (3He,?) reaction mechanism  

International Nuclear Information System (INIS)

The ?-rays emitted after the 163Dy(3He,?xn) reactions at E(3He)=45 MeV have been measured. The transferred angular momentum in the reaction is deduced from the side-feeding ?-intensities of the ground bands in the residual 162-xDy isotopes. With decreasing ?-energy the average spin transfer increases from ?5? to ?11?. The (3He,?) reaction at these energies is dominated by direct processes. Even at the highest spin transfer the contribution from the compound reaction channel is negligible. 12 refs., 5 figs., 2 tabs

309

Constructivist Grounded Theory?  

Directory of Open Access Journals (Sweden)

Full Text Available AbstractI refer to and use as scholarly inspiration Charmaz’s excellent article on constructivist grounded theory as a tool of getting to the fundamental issues on why grounded theory is not constructivist. I show that constructivist data, if it exists at all, is a very, very small part of the data that grounded theory uses.

Barney G. Glaser, PhD, Hon. PhD

2012-06-01

310

Grounds Maintenance Cost Report.  

Science.gov (United States)

A grounds maintenance study was accomplished over the period of March 1965 through February 1966 to--(1) determine current grounds maintenance cost distribution; (2) provide basis for future grounds maintenance budgeting, and (3) provide basic data by which future landscape project designs can be developed to project or reduce maintenance costs.…

Joice, Donald K.

311

Force transmissibility versus displacement transmissibility  

Science.gov (United States)

It is well-known that when a single-degree-of-freedom (sdof) system is excited by a continuous motion of the foundation, the force transmissibility, relating the force transmitted to the foundation to the applied force, equals the displacement transmissibility. Recent developments in the generalization of the transmissibility to multiple-degree-of-freedom (mdof) systems have shown that similar simple and direct relations between both types of transmissibility do not appear naturally from the definitions, as happens in the sdof case. In this paper, the authors present their studies on the conditions under which it is possible to establish a relation between force transmissibility and displacement transmissibility for mdof systems. As far as the authors are aware, such a relation is not currently found in the literature, which is justified by being based on recent developments in the transmissibility concept for mdof systems. Indeed, it does not appear naturally, but the authors observed that the needed link is present when the displacement transmissibility is obtained between the same coordinates where the applied and reaction forces are considered in the force transmissibility case; this implies that the boundary conditions are not exactly the same and instead follow some rules. This work presents a formal derivation of the explicit relation between the force and displacement transmissibilities for mdof systems, and discusses its potential and limitations. The authors show that it is possible to obtain the displacement transmissibility from measured forces, and the force transmissibility from measured displacements, opening new perspectives, for example, in the identification of applied or transmitted forces. With this novel relation, it becomes possible, for example, to estimate the force transmissibility matrix with the structure off its supports, in free boundary conditions, and without measuring the forces. As far as force identification is concerned, this novel approach significantly decreases the computational effort when compared to conventional approaches, as it requires only local information of the sets of coordinates involved. Numerical simulations and experimental examples are presented and discussed, to illustrate the proposed developments.

Lage, Y. E.; Neves, M. M.; Maia, N. M. M.; Tcherniak, D.

2014-10-01

312

Incomplete fusion reactions  

International Nuclear Information System (INIS)

A review of incomplete fusion reactions is given. The localization of the entrance chanel angular momentum window is discussed for incident energies lower than 10 MeV per nucleon and is found to depend on the target deformation. With deformed target 'peripheral' collisions are observed with l values in the vicinity of lsub(cr) for complete fusion, while for spherical targets, the l window is centered around values lower than 0.5 lsub(cr). These properties are discussed on the grounds of available theoretical models. All other properties of the reactions such as cross sections, angular distributions, shape of the energy spectra of light ejectiles are discussed to bring additional informations about the reaction mechanism. (orig.)

313

46 CFR 120.376 - Grounded distribution systems (Neutral grounded).  

Science.gov (United States)

...have the ground connection accessible for checking insulation resistance of the generator to ground before the generator is connected...grounded alternating current system must be grounded to the hull. On a nonmetallic vessel, the neutral must be connected...

2010-10-01

314

46 CFR 183.376 - Grounded distribution systems (neutral grounded).  

Science.gov (United States)

...have the ground connection accessible for checking insulation resistance of the generator to ground before the generator is connected...grounded alternating current system must be grounded to the hull. On a nonmetallic vessel, the neutral must be connected...

2010-10-01

315

Nuclear reactions  

International Nuclear Information System (INIS)

In reviewing work at Harwell over the past 25 years on nuclear reactions it is stated that a balance has to be struck in both experiment and theory between work on cross-sections of direct practical relevance to reactors and on those relevant to an overall understanding of reaction processes. The compound nucleus and direct process reactions are described. Having listed the contributions from AERE, Harwell to developments in nuclear reaction research in the period, work on the optical model, neutron capture theory, reactions at doorway states with fine structure, and sum-rules for spectroscopic factors are considered in more detail. (UK)

316

Observations on Recent Trends in Armored Forces.  

Science.gov (United States)

To provide initial insights about how several ground forces other than the U.S. Army are viewing the utility of armored fighting vehicles in irregular and hybrid warfare environments. A team from RAND Arroyo Center is in the early stages of research on a ...

D. E. Johnson, I. J. Gordon

2010-01-01

317

A 3D mathematical model to predict spinal joint and hip joint force for trans-tibial amputees with different SACH foot pylon adjustments.  

Science.gov (United States)

A solid-ankle cushioned heel (SACH) foot is a non-joint foot without natural ankle function. Trans-tibial amputees may occur toe scuffing in the late swing phase due to a lack of active dorsiflexion. To address this problem, clinical guidelines suggests shortening the pylon to produce a smooth gait. However, this causes a leg length discrepancy, induces asymmetry in the hip joint, and causes an overload of L5/S1 joint force. Therefore, this study aimed to investigate the influence of different prosthesis pylons on the hip joint and L5/S1 joint forces. Ten subjects were recruited using leg length for normalisation. Four different pylon reductions (0%, 1%, 2%, and 3%) were used for gait analysis. A Vicon system and force plates were used to collect kinematic data and ground reaction force, respectively. The software package MATLAB was used to create a mathematical model for evaluating the symmetry and force of the hip joint and the low back force of the L5/S1 joint. The model was validated by the correlation coefficient (CC=0.947) and root mean square (RMS=0.028 BW). The model estimated that the 1% group had a symmetrical hip joint force and a lower L5/S1 joint force in the vertical direction. This study indicates that a 1% pylon shortening on a SACH prosthesis is appropriate for a trans-tibial amputee. PMID:25042463

Yu, Chung-huang; Hung, Yu-Cheng; Lin, Yang-Hua; Chen, Guan-Xun; Wei, Shun-Hwa; Huang, Chang-Hung; Chen, Chen-Sheng

2014-09-01

318

STS-30 deorbit and reentry ground track  

Science.gov (United States)

Rockwell International (RI) supplied artist concept titled 'STS-30 Deorbit and Reentry Track' shows Atlantis, Orbiter Vehicle (OV) 104, deorbit and reentry ground track. Ground track and map portray OV-104's deorbit over Madagascar, atmospheric reentry maneuvers, approach to the California coast, and landing at Edwards Air Force Base (EAFB), California. the transport trailer of the Payload Environmental Transportation System (PETS). Magellan, destined for unprecedented studies of Venusian topographic features, will be deployed by the crew of NASA's STS-30 mission in April 1989. View provided by KSC with alternate number KSC-88PC-1086.

1989-01-01

319

Electroweak reactions with light nuclei  

Directory of Open Access Journals (Sweden)

Full Text Available The investigation of light nuclei with ab-initio methods provides an optimal setting to probe our knowledge on nuclear forces, because the few-nucleon problem can be solved accurately. Nucleons interact not only in pairs but also via many-body forces. Theoretical e?orts need to be taken towards the identi?cation of nuclear observables sensitive to the less known many-nucleon forces. Electromagnetic reactions can potentially provide useful information on this. We present results on photo-absorption and electron scattering o? light nuclei, emphasizing the role of three-body forces and the comparison with experimental data. On the other hand, reactions induced by weak probes, like neutrino interactions with nucleonic matter, are relevant to astrophysics and can be calculated with few-body techniques. In this case, since often no experiment is possible, ab-initio predictions provide valuable input for astrophysical simulations.

Bacca S.

2010-04-01

320

Energy shift and Casimir-Polder force for an atom out of thermal equilibrium near a dielectric substrate  

Science.gov (United States)

We study the energy shift and the Casimir-Polder force of an atom out of thermal equilibrium near the surface of a dielectric substrate. We first generalize, adopting the local source hypothesis, the formalism proposed by Dalibard, Dupont-Roc, and Cohen-Tannoudji [J. Phys. (Paris) 43, 1617 (1982), 10.1051/jphys:0198200430110161700; J. Phys. (Paris) 45, 637 (1984), 10.1051/jphys:01984004504063700], which separates the contributions of thermal fluctuations and radiation reaction to the energy shift and allows a distinct treatment of atoms in the ground and excited states, to the case out of thermal equilibrium, and then we use the generalized formalism to calculate the energy shift and the Casimir-Polder force of an isotropically polarizable neutral atom. We identify the effects of the thermal fluctuations that originate from the substrate and the environment and discuss in detail how the Casimir-Polder force out of thermal equilibrium behaves in three different distance regions in both the low-temperature limit and the high-temperature limit for both the ground-state and excited-state atoms, with special attention devoted to the distinctive features as opposed to thermal equilibrium. In particular, we recover the distinctive behavior of the atom-wall force out of thermal equilibrium at large distances in the low-temperature limit recently found in a different theoretical framework, and furthermore we give a concrete region where this behavior holds.

Zhou, Wenting; Yu, Hongwei

2014-09-01

 
 
 
 
321

Electronic transitions and intermolecular forces  

International Nuclear Information System (INIS)

This thesis describes two different subjects - electronic transitions and intermolecular forces - that are related mainly by the following observation: The wavenumber at which an electronic transition in an atom or molecule occurs, depends on the environment of that atom or molecule. This implies, for instance, that when a molecule becomes solvated its absorption spectrum may be shifted either to the blue or to the red side of the original gasphase spectrum. In part I attention is paid to the experimental aspects of VUV spectroscopy, both in the gasphase and in the condensed phase. In part II a series of papers are presented, dealing with the calculation of intermolecular forces (and some related topics) both for the ground state and for the excited state interactions, using different non-empirical methods. The calculations provide, among other results, a semiquantitative interpretation of the spectral blue shifts encountered in our experiments. (Auth.)

322

Significance of redistribution reactions defected by in situ atomic force microscopy during early stages of fast scan rate redox cycling experiments at a solid 7,7,8,8-tetracyanoquinodimethane-glassy carbon electrode-aqueous (electrolyte) interface  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The reduction of solid 7,7,8,8-tetracyanoquinodimethane (TCNQ) at an electrode-TCNQ-aqueous (electrolyte) is complex, irrespective of whether the solid on the electrode surface is attached by direct adherence or formed by electrochemical deposition. In order to understand the origin of reaction pathways that accompany the [TCNQ]0/- process, fast scan rate (0.1 Vs-1) redox cycling and potential step experiments on TCNQ mechanically attached to a glassy carbon electrode placed in aqueous soluti...

Suarez, Mf; Bond, Am; Compton, Rg

1999-01-01

323

The Grounded Theory Bookshelf  

Directory of Open Access Journals (Sweden)

Full Text Available Bookshelf will provide critical reviews and perspectives on books on theory and methodology of interest to grounded theory. This issue includes a review of Heaton’s Reworking Qualitative Data, of special interest for some of its references to grounded theory as a secondary analysis tool; and Goulding’s Grounded Theory: A practical guide for management, business, and market researchers, a book that attempts to explicate the method and presents a grounded theory study that falls a little short of the mark of a fully elaborated theory.Reworking Qualitative Data, Janet Heaton (Sage, 2004. Paperback, 176 pages, $29.95. Hardcover also available.

Vivian B. Martin, Ph.D.

2005-03-01

324

Applying the cost of generating force hypothesis to uphill running  

Directory of Open Access Journals (Sweden)

Full Text Available Historically, several different approaches have been applied to explain the metabolic cost of uphill human running. Most of these approaches result in unrealistically high values for the efficiency of performing vertical work during running uphill, or are only valid for running up steep inclines. The purpose of this study was to reexamine the metabolic cost of uphill running, based upon our understanding of level running energetics and ground reaction forces during uphill running. In contrast to the vertical efficiency approach, we propose that during incline running at a certain velocity, the forces (and hence metabolic energy required for braking and propelling the body mass parallel to the running surface are less than during level running. Based on this idea, we propose that the metabolic rate during uphill running can be predicted by a model, which posits that (1 the metabolic cost of perpendicular bouncing remains the same as during level running, (2 the metabolic cost of running parallel to the running surface decreases with incline, (3 the delta efficiency of producing mechanical power to lift the COM vertically is constant, independent of incline and running velocity, and (4 the costs of leg and arm swing do not change with incline. To test this approach, we collected ground reaction force (GRF data for eight runners who ran thirty 30-second trials (velocity: 2.0–3.0 m/s; incline: 0–9°. We also measured the metabolic rates of eight different runners for 17, 7-minute trials (velocity: 2.0–3.0 m/s; incline: 0–8°. During uphill running, parallel braking GRF approached zero for the 9° incline trials. Thus, we modeled the metabolic cost of parallel running as exponentially decreasing with incline. With that assumption, best-fit parameters for the metabolic rate data indicate that the efficiency of producing mechanical power to lift the center of mass vertically was independent of incline and running velocity, with a value of ?29%. The metabolic cost of uphill running is not simply equal to the sum of the cost of level running and the cost of performing work to lift the body mass against gravity. Rather, it reflects a constant cost of perpendicular bouncing, decreased costs of parallel braking and propulsion and of course the cost of lifting body mass against gravity.

Wouter Hoogkamer

2014-07-01

325

Applying the cost of generating force hypothesis to uphill running.  

Science.gov (United States)

Historically, several different approaches have been applied to explain the metabolic cost of uphill human running. Most of these approaches result in unrealistically high values for the efficiency of performing vertical work during running uphill, or are only valid for running up steep inclines. The purpose of this study was to reexamine the metabolic cost of uphill running, based upon our understanding of level running energetics and ground reaction forces during uphill running. In contrast to the vertical efficiency approach, we propose that during incline running at a certain velocity, the forces (and hence metabolic energy) required for braking and propelling the body mass parallel to the running surface are less than during level running. Based on this idea, we propose that the metabolic rate during uphill running can be predicted by a model, which posits that (1) the metabolic cost of perpendicular bouncing remains the same as during level running, (2) the metabolic cost of running parallel to the running surface decreases with incline, (3) the delta efficiency of producing mechanical power to lift the COM vertically is constant, independent of incline and running velocity, and (4) the costs of leg and arm swing do not change with incline. To test this approach, we collected ground reaction force (GRF) data for eight runners who ran thirty 30-second trials (velocity: 2.0-3.0 m/s; incline: 0-9°). We also measured the metabolic rates of eight different runners for 17, 7-minute trials (velocity: 2.0-3.0 m/s; incline: 0-8°). During uphill running, parallel braking GRF approached zero for the 9° incline trials. Thus, we modeled the metabolic cost of parallel running as exponentially decreasing with incline. With that assumption, best-fit parameters for the metabolic rate data indicate that the efficiency of producing mechanical power to lift the center of mass vertically was independent of incline and running velocity, with a value of ?29%. The metabolic cost of uphill running is not simply equal to the sum of the cost of level running and the cost of performing work to lift the body mass against gravity. Rather, it reflects a constant cost of perpendicular bouncing, decreased costs of parallel braking and propulsion and of course the cost of lifting body mass against gravity. PMID:25083347

Hoogkamer, Wouter; Taboga, Paolo; Kram, Rodger

2014-01-01

326

Fusion reactions at high energies  

International Nuclear Information System (INIS)

Experimental fusion excitation functions for heavy-ion induced reactions are compared to results calculated with a classical dynamical model employing different conservative and dissipative forces. The overall agreement between present experimental data and theory is good over the whole mass range. The theoretical fusion cross sections of the heavier systems are sensitive to the assumed forces at the higher energies. As the energy is increased, however, the onset of other reaction processes make it difficult to identify fusion and one-body dissipation is no longer valid

327

The Fifth Force, the Sixth Force and the Spring Force  

Directory of Open Access Journals (Sweden)

Full Text Available Upon  revisiting the famous Pound-Rebka-Snider experiments on the gravitational red-shift , the fifth and even the sixth force in nature are in fact the stretching and compression force of the spring , where the spring term is the cosmological constant in Einstein’s field equations.

Ling Man Tsang

2012-04-01

328

Nuclear Reactions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Nuclear reactions generate energy in nuclear reactors, in stars, and are responsible for the existence of all elements heavier than hydrogen in the universe. Nuclear reactions denote reactions between nuclei, and between nuclei and other fundamental particles, such as electrons and photons. A short description of the conservation laws and the definition of basic physical quantities is presented, followed by a more detailed account of specific cases: (a) formation and decay o...

???????, ???? ???????????; ???????, ???? ??????????; Diadechko, Alla Mykolaivna; Velytchenko, A.

2009-01-01

329

Design of Low Cost Force Sensor System for Human Machine Interaction – Force Feedback Joystick  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The paper describes a low cost force sensor system ready to be evaluated in force-feedback joystick designed for a medical haptics application. It is based on low-cost parts from home appliance scale with strain gauge technology, and of-theshelf IC instrumentation amplifier. The development process, electronic circuitry and designed software are presented. Experimental results give a good ground to believe that this approach can provide sufficient quality in further development of human-machi...

Miloš Petkovi?; ?or?evic?, Goran S.

2011-01-01

330

Simple Assessment of Post-Grounding Loads and Strength of Ships  

DEFF Research Database (Denmark)

The aim of the present study is to determine the sectional forces induced by the ship grounding and also to assess the residual strength of grounded ship hulls. An analytical approach is used to estimate the grounding- induced sectional forces of ships. The extent and location of structural damage due to grounding is defined based on the ABS Safe Hull guide. The residual strength of damaged hulls is calculated by using a simple analytical formula. The method is applied to the residual strength assessment of a double-hull tanker of 38.400 dwt damaged due to grounding.

Pedersen, Preben Terndrup

1997-01-01

331

Your School Grounds Handbook.  

Science.gov (United States)

This handbook discusses the process of planning school grounds. It presents ideas for creating good educational landscapes and provides step-by-step procedures to achieve this goal. The steps include ground surveying and analysis, establishing community and school needs and wants, planning changes and preparing the design process, publicizing and…

1997

332

Relational grounding facilitates development of scientifically useful multiscale models  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract We review grounding issues that influence the scientific usefulness of any biomedical multiscale model (MSM. Groundings are the collection of units, dimensions, and/or objects to which a variable or model constituent refers. To date, models that primarily use continuous mathematics rely heavily on absolute grounding, whereas those that primarily use discrete software paradigms (e.g., object-oriented, agent-based, actor typically employ relational grounding. We review grounding issues and identify strategies to address them. We maintain that grounding issues should be addressed at the start of any MSM project and should be reevaluated throughout the model development process. We make the following points. Grounding decisions influence model flexibility, adaptability, and thus reusability. Grounding choices should be influenced by measures, uncertainty, system information, and the nature of available validation data. Absolute grounding complicates the process of combining models to form larger models unless all are grounded absolutely. Relational grounding facilitates referent knowledge embodiment within computational mechanisms but requires separate model-to-referent mappings. Absolute grounding can simplify integration by forcing common units and, hence, a common integration target, but context change may require model reengineering. Relational grounding enables synthesis of large, composite (multi-module models that can be robust to context changes. Because biological components have varying degrees of autonomy, corresponding components in MSMs need to do the same. Relational grounding facilitates achieving such autonomy. Biomimetic analogues designed to facilitate translational research and development must have long lifecycles. Exploring mechanisms of normal-to-disease transition requires model components that are grounded relationally. Multi-paradigm modeling requires both hyperspatial and relational grounding.

Lam Tai

2011-09-01

333

Relational grounding facilitates development of scientifically useful multiscale models.  

Science.gov (United States)

We review grounding issues that influence the scientific usefulness of any biomedical multiscale model (MSM). Groundings are the collection of units, dimensions, and/or objects to which a variable or model constituent refers. To date, models that primarily use continuous mathematics rely heavily on absolute grounding, whereas those that primarily use discrete software paradigms (e.g., object-oriented, agent-based, actor) typically employ relational grounding. We review grounding issues and identify strategies to address them. We maintain that grounding issues should be addressed at the start of any MSM project and should be reevaluated throughout the model development process. We make the following points. Grounding decisions influence model flexibility, adaptability, and thus reusability. Grounding choices should be influenced by measures, uncertainty, system information, and the nature of available validation data. Absolute grounding complicates the process of combining models to form larger models unless all are grounded absolutely. Relational grounding facilitates referent knowledge embodiment within computational mechanisms but requires separate model-to-referent mappings. Absolute grounding can simplify integration by forcing common units and, hence, a common integration target, but context change may require model reengineering. Relational grounding enables synthesis of large, composite (multi-module) models that can be robust to context changes. Because biological components have varying degrees of autonomy, corresponding components in MSMs need to do the same. Relational grounding facilitates achieving such autonomy. Biomimetic analogues designed to facilitate translational research and development must have long lifecycles. Exploring mechanisms of normal-to-disease transition requires model components that are grounded relationally. Multi-paradigm modeling requires both hyperspatial and relational grounding. PMID:21951817

Hunt, C Anthony; Ropella, Glen E P; Lam, Tai ning; Gewitz, Andrew D

2011-01-01

334

Convection in drying and freezing ground  

Science.gov (United States)

In this paper, we analyse the drying of a soil composed of particles, water and solute impurities, and study the occurrence of convective instabilities during evaporation. We find that the main driving force for instability is the formation of a concentration gradient at the soil surface due to the evaporation of water. A similar phenomenon may occur during the thawing of frozen ground in Arctic regions.

Faizal, Mir; Peppin, Stephen

2014-08-01

335

Three-nucleon forces and the trinucleon bound states  

International Nuclear Information System (INIS)

A summary of the bound-state working group session of the ''International Symposium on the Three-Body Force in the Three-Nucleon System'' is presented. The experimental evidence for three-nucleon forces has centered on two ground state properties: the tritium binding energy and the trinucleon form factors. Both are discussed

336

The Grounded Theory Bookshelf  

Directory of Open Access Journals (Sweden)

Full Text Available The Grounded Theory Perspective III: Theoretical Coding, Barney G. Glaser (Sociology Press, 2005. Not intended for a beginner, this book further defi nes, describes, and explicates the classic grounded theory (GT method. Perspective III lays out various facets of theoretical coding as Glaser meticulously distinguishes classic GT from other subsequent methods. Developed many years after Glaser’s classic GT, these methods, particularly as described by Strauss and Corbin, adopt the grounded theory name and engender ongoing confusion about the very premises of grounded theory. Glaser distinguishes between classic GT and the adscititious methods in his writings, referring to remodeled grounded theory and its offshoots as Qualitative Data Analysis (QDA models.

Dr. Alvita Nathaniel, DSN, APRN, BC

2005-06-01

337

Ground Effect in Flight  

Science.gov (United States)

The present paper aims to analyze the propulsion of birds and fishes undergoing the ground effect as well as the lift of high-speed ground vehicle. Applying the analytical method which was developed for flutter of a soft plate placed at an arbitrary position in subsonic channel flows, calculations are carried out first for non-oscillatory case in compressible flow and then for oscillating cases of birds and fishes in incompressible flow. The results obtained show that the ground effect acts to increase not only the lift in steady flight but also the thrust and propulsive efficiency in oscillating modes. This method holds not only in the case of very close proximity to the ground but also in compressible flow case, so it would be applicable to the flutter analysis of high-speed ground vehicle with wings.

Tanida, Yoshimichi

338

Airport Ground Staff Scheduling  

DEFF Research Database (Denmark)

Modern airports are centers of transportation that service a large number of aircraft and passengers every day. To facilitate this large volume of transportation, airports are subject to many logistical and decision problems that must continuously be solved to make sure each flight and passenger travels safely and efficiently through the airport. When an aircraft lands, a significant number of tasks must be performed by different groups of ground crew, such as fueling, baggage handling and cleaning. These tasks must be complete before the aircraft is able to depart, as well as check-in and security services. These tasks are collectively known as ground handling, and are the major source of activity with airports. The business environments of modern airports are becoming increasingly competitive, as both airports themselves and their ground handling operations are changing to private ownership. As airports are in competition to attract airline routes, efficient and reliable ground handling operations are imperative for the viability and continued growth of both airports and airlines. The increasing liberalization of the ground handling market prompts ground handling operators to increase cost effectiveness and deliver fast and reliable service. This thesis presents models and algorithms for general optimization and decision problems arising within ground handling. The thesis contains an introductory part which provide an overview of the ground handling environment and reviews a series of optimization problems from the specific perspective of airport ground handling. In addition, the thesis contains five scientific papers, which consider specific optimization problems within ground handling in detail. The considered problems range from generalized approaches to workforce planning, to highly detailed scheduling problems arising in the highly dynamic environment of airports.

Clausen, Tommy

2010-01-01

339

Grounded running in quails: simulations indicate benefits of observed fixed aperture angle between legs before touch-down.  

Science.gov (United States)

Many birds use grounded running (running without aerial phases) in a wide range of speeds. Contrary to walking and running, numerical investigations of this gait based on the BSLIP (bipedal spring loaded inverted pendulum) template are rare. To obtain template related parameters of quails (e.g. leg stiffness) we used x-ray cinematography combined with ground reaction force measurements of quail grounded running. Interestingly, with speed the quails did not adjust the swing leg's angle of attack with respect to the ground but adapted the angle between legs (which we termed aperture angle), and fixed it about 30ms before touchdown. In simulations with the BSLIP we compared this swing leg alignment policy with the fixed angle of attack with respect to the ground typically used in the literature. We found symmetric periodic grounded running in a simply connected subset comprising one third of the investigated parameter space. The fixed aperture angle strategy revealed improved local stability and surprising tolerance with respect to large perturbations. Starting with the periodic solutions, after step-down step-up or step-up step-down perturbations of 10% leg rest length, in the vast majority of cases the bipedal SLIP could accomplish at least 50 steps to fall. The fixed angle of attack strategy was not feasible. We propose that, in small animals in particular, grounded running may be a common gait that allows highly compliant systems to exploit energy storage without the necessity of quick changes in the locomotor program when facing perturbations. PMID:23831138

Andrada, Emanuel; Rode, Christian; Blickhan, Reinhard

2013-10-21

340

Two-body forces and amplitudes in the three-body model for the 4He(d(pol), p?)n reaction with Ed = 12 and 17 MeV  

International Nuclear Information System (INIS)

The 4He(d(pol), p?)n cross section, vector and tensor analyzing-power data with 12 and 17 MeV deuterons at kinematic conditions including proton-alpha quasifree scattering, neutron-alpha and proton-alpha final-state interactions, as well as collinearity, are compared with the predictions of the three-body model using different nucleon-alpha and neutron-proton forces. In general, better two-body potentials give a better fit to the data, except for the vector analyzing-power data. The roles of the impulse and multiple-scattering amplitudes are studied to understand the sensitivity to two-body potentials and to understand the reason for the successes and the failures of the model. 16 refs.; 6 figs.; 1 table

 
 
 
 
341

Nuclear reactions  

International Nuclear Information System (INIS)

New prospects are envisaged for nuclear physics, for the theory and also the probes used. New reaction types and new concepts have been discovered, such as the viscosity and friction concepts especially important in the case of high-velocity heavy-ion reactions

342

Forces and gravity  

...Forces and gravity Forces and gravity This site uses cookies. By continuing to use this site you agree to our use of cookies....here Activities Public engagement Resources Physicists in Primary Schools Topics Forces and gravity Public engagement Resources Physicists in Primary Schools Topics Electricity Forces and ... gravity Experiments Apparatus Safety notes Forces and magnets Sound Solids Light Solids, liquids and gases Sunlight and space travel Forces and springs Earth ...and the Solar System Electricity generation: Part 1 Electricity generation: Part 2 Forces and gravity Is gravity real or does the Earth just suck? Supports ...

343

Rotational Ground Motions Radiated by Vibrating Structures  

Science.gov (United States)

Vibrating structures, founded on flexible ground, radiate energy into the soil. This happens regardless of how the structure has been excited, i.e. by motion of its base, or by some force applied above ground level. The mechanism through which this happens is referred to in engineering as soil-structure interaction. Through this mechanism, the building foundation moves, and, in general, there is coupling between the translational and rotational waves. In particular, for in-plane excitation, even in a 2D model, there is coupling between the horizontal and the rocking motions of the foundation. Hence, a structure excited by purely horizontal motion of its base, or by horizontal force applied above ground level will act as a source of rotational motions in the ground. To this end, a simple 2D soil-structure interaction model will be presented, and results for the rotation of the foundation as a source of rotational waves in the soil. The model consists of a building, modeled as a shear beam, founded on a circular foundation imbedded in a homogeneous, isotropic and elastic half-space, and excited by incident wave motion (plane P or SV waves, or Rayleigh waves), or by horizontal motion of its base. The wave function expansion method is used to represent the motion in the soil. The boundary condition along the contact surface between the soil and the foundation is perfect bond (i.e. welded contact).

Todorovska, M. I.

2006-12-01

344

Surface and Interfacial Forces  

CERN Document Server

This systematic introduction to the topic includes theoretical concepts to help readers understand and predict surface forces, while also integrating experimental techniques and practical applications with up-to-date examples plus motivating exercises. Starting with intermolecular forces, the authors discuss different surfaces forces, with a major part devoted to surface forces between solid surfaces in liquid media. In addition, they cover surface forces between liquid-vapor interfaces and between liquid-liquid interfaces.

Butt, Hans-Jurgen

2010-01-01

345

46 CFR 183.376 - Grounded distribution systems (neutral grounded).  

Science.gov (United States)

... 2010-10-01 2010-10-01 false Grounded distribution systems (neutral grounded). 183.376 Section 183.376 Shipping...Sources and Distribution Systems § 183.376 Grounded distribution systems (neutral...

2010-10-01

346

Force Control in Monopod Hopping Robot While Landing  

Directory of Open Access Journals (Sweden)

Full Text Available In this paper, the issue of control of impact forces generated during the interaction between the hopping ro-bot toe and the ground while landing has been considered. The force thus generated can damage the robot altogether. With the objective to control these impact forces, impedance control strategy has been applied to the hopping robot system. The dynamics pertaining to the impact between robot toe and ground has been modeled as in case of a ball bouncing on the ground. Bond Graph theory has been used for the modeling of the hopping robot system. Simulation results show that impact forces generated during the landing has been controlled to a specified limiting value. This model and the corresponding analysis can be further extended for understanding the dynamics involved in continuous hopping of robot with constant height and velocity control.

Satish Chandra Jain

2010-11-01

347

Comprehending illocutionary force.  

Science.gov (United States)

According to speech act theory (Searle, 1969), utterances have both a propositional content and an illocutionary force (the speech act performed with the utterance). Four experiments were conducted to examine whether utterance comprehension involves speech act recognition. Participants in all experiments first read remarks that could be characterized by a particular speech act (e.g., beg). A recognition probe reaction time procedure was used in Experiments 1 and 2; participants indicated whether a probe word had literally appeared in the last remark that they had read. Participants were significantly slower at making this judgment (and made significantly more errors) when the probe represented the speech act performed with the prior remark than when it did not. A lexical decision task was used in Experiments 3 and 4, and participants were significantly faster at verifying target words representing the speech act performed with a remark, relative to control words. Overall, the results suggest that speech act recognition may be an important component of the comprehension of conversational remarks. PMID:11277467

Holtgraves, T; Ashley, A

2001-01-01

348

Ground State Spin Logic  

Science.gov (United States)

Designing and optimizing cost functions and energy landscapes is a problem encountered in many fields of science and engineering. These landscapes and cost functions can be embedded and annealed in experimentally controllable spin Hamiltonians. Using an approach based on group theory and symmetries, we examine the embedding of Boolean logic gates into the ground-state subspace of such spin systems. We describe parameterized families of diagonal Hamiltonians and symmetry operations which preserve the ground-state subspace encoding the truth tables of Boolean formulas. The ground-state embeddings of adder circuits are used to illustrate how gates are combined and simplified using symmetry. Our work is relevant for experimental demonstrations of ground-state embeddings found in both classical optimization as well as adiabatic quantum optimization.

Whitfield, James; Faccin, Mauro; Biamonte, Jacob

2013-03-01

349

Ground State Spin Logic  

CERN Document Server

Designing and optimizing cost functions and energy landscapes is a problem encountered in many fields of science and engineering. These landscapes and cost functions can be embedded and annealed in experimentally controllable spin Hamiltonians. Using an approach based on group theory and symmetries, we examine the embedding of Boolean logic gates into the ground state subspace of such spin systems. We describe parameterized families of diagonal Hamiltonians and symmetry operations which preserve the ground state subspace encoding the truth tables of Boolean formulas. The ground state embeddings of adder circuits are used to illustrate how gates are combined and simplified using symmetry. Our work is relevant for experimental demonstrations of ground state embeddings found in both classical optimization as well as adiabatic quantum optimization.

Whitfield, J D; Biamonte, J D

2012-01-01

350

Neutrino nuclear response and photo nuclear reaction  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Photo nuclear reactions are shown to be used for studying neutrino/weak nuclear responses involved in astro-neutrino nuclear interactions and double beta decays. Charged current weak responses for ground and excited states are studied by using photo nuclear reactions through isobaric analog states of those states, while neutral current weak responses for excited states are studied by using photo nuclear reactions through the excited states. The weak interaction strengths are...

Ejiri, H.; Titov, A. I.; Boswell, M.; Young, A.

2013-01-01

351

Macroscopic QED in linearly responding media and a Lorentz-Force approach to dispersion forces  

Energy Technology Data Exchange (ETDEWEB)

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.)

Raabe, Christian

2008-07-08

352

Forces in general relativity  

International Nuclear Information System (INIS)

Many textbooks dealing with general relativity do not demonstrate the derivation of forces in enough detail. The analyses presented herein demonstrate straightforward methods for computing forces by way of general relativity. Covariant divergence of the stress-energy-momentum tensor is used to derive a general expression of the force experienced by an observer in general coordinates. The general force is then applied to the local co-moving coordinate system of a uniformly accelerating observer, leading to an expression of the inertial force experienced by the observer. Next, applying the general force in Schwarzschild coordinates is shown to lead to familiar expressions of the gravitational force. As a more complex demonstration, the general force is applied to an observer in Boyer-Lindquist coordinates near a rotating, Kerr black hole. It is then shown that when the angular momentum of the black hole goes to zero, the force on the observer reduces to the force on an observer held stationary in Schwarzschild coordinates. As a final consideration, the force on an observer moving in rotating coordinates is derived. Expressing the force in terms of Christoffel symbols in rotating coordinates leads to familiar expressions of the centrifugal and Coriolis forces on the observer. It is envisioned that the techniques presented herein will be most useful to graduate level students, as well as those undergraduate students having experience with general relativity and tensor anance with general relativity and tensor analysis.

353

The 'impact' of force filtering cut-off frequency on the peak knee abduction moment during landing: artefact or 'artifiction'?  

Science.gov (United States)

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

Roewer, Benjamin D; Ford, Kevin R; Myer, Gregory D; Hewett, Timothy E

2014-01-01

354

Force, work and power output of lower limb muscles during human maximal-effort countermovement jumping.  

Science.gov (United States)

The purpose of this study was to simulate human maximal-effort countermovement jumping with a three-dimensional neuromusculoskeletal model. The specific aim was to investigate muscle force, work and power output of major lower limb muscles during the motion. A neuromusculoskeletal model that has nine rigid body segments, 20 degrees of freedom, 32 Hill-type lower limb muscles was developed. The neural activation input signal was represented by a series of step functions with step duration of 0.05 s. The excitation-contraction dynamics of the contractile element, the tissues around the joints to limit the joint range of motion, as well as the foot-ground interaction were implemented. A simulation was started from a standing posture. Optimal pattern of the activation input signal was searched through numerical optimization with a goal of maximizing the height reached by the mass center of body after jumping up. As a result, feasible kinematics, ground reaction force profile and muscle excitation profile were generated. It was found that monoarticular muscles had major contributions of mechanical work and power output, whereas biarticular muscles had minor contributions. Hip adductors, abductors and external rotator muscles were vigorously activated, although their mechanical work and power output was minor because of their limited length change during the motion. Joint flexor muscles such as m. iliopsoas, m. biceps femoris short head and m. tibialis anterior were activated in the beginning of the motion with an effect of facilitating the generation of a countermovement. PMID:15811607

Nagano, Akinori; Komura, Taku; Fukashiro, Senshi; Himeno, Ryutaro

2005-08-01

355

Isospin dependence of nucleon correlations in ground-state nuclei  

Science.gov (United States)

The dispersive optical model (DOM) as presently implemented can investigate the isospin (nucleon asymmetry) dependence of the Hartree-Fock-like potential relevant for nucleons near the Fermi energy. Data constraints indicate that a Lane-type potential adequately describes its asymmetry dependence. Correlations beyond the mean field can also be described in this framework, but this requires an extension that treats the non-locality of the Hartree-Fock-like potential properly. The DOM has therefore been extended to properly describe ground-state properties of nuclei as a function of nucleon asymmetry in addition to standard ingredients like elastic nucleon scattering data and level structure. Predictions of nucleon correlations at larger nucleon asymmetries can then be made after data at smaller asymmetries constrain the potentials that represent the nucleon self-energy. A simple extrapolation for Sn isotopes generates predictions for increasing correlations of minority protons with increasing neutron number. Such predictions can be investigated by performing experiments with exotic beams. The predicted neutron properties for the double closed-shell 132Sn nucleus exhibit similar correlations as those in 208Pb . Future relevance of these studies for understanding the properties of all nucleons, including those with high momentum, and the role of three-body forces in nuclei are briefly discussed. Such an implementation will require a proper treatment of the non-locality of the imaginary part of the potentials and a description of high-momentum nucleons as experimentally constrained by the ( e, e' p) reactions performed at Jefferson Lab.

Charity, R. J.; Dickhoff, W. H.; Sobotka, L. G.; Waldecker, S. J.

2014-02-01

356

Three-Nucleon Forces  

CERN Document Server

The role of three-nucleon forces in ab initio calculations of nuclear systems is investigated. The difference between genuine and induced many-nucleon forces is emphasized. Induced forces arise in the process of solving the nuclear many-body problem as technical intermediaries towards calculationally converged results. Genuine forces make up the Hamiltonian; they represent the chosen underlying dynamics. The hierarchy of contributions arising from two-, three- and many-nucleon forces is discussed. Signals for the need of the inclusion of genuine three-nucleon forces are studied in nuclear systems, technically best under control, especially in three-nucleon and four-nucleon systems. Genuine three-nucleon forces are important for details in the decription of some observables. Their contributions to observables are small on the scale set by two-nucleon forces.

Sauer, Peter U

2014-01-01

357

The Centripetal Force Requirement  

Science.gov (United States)

This webpage discusses the role of centripetal acceleration and centripetal force. The site also provides an animation to show how circular motion requires an inward force. Links to related concepts are provided.

2007-07-27

358

A Simple Derivation of Lorentz Self Force  

CERN Document Server

We derive the Lorentz self force for an arbitrarily moving charged particle via averaging the retarded fields. The derivation is simple and at the same time pedagogically accessible. We obtain the radiation reaction for a charged particle moving in a conic. We pin down the underlying concept of mass renormalization.

Haque, Asrarul

2014-01-01

359

Solvation force simulations in atomic force microscopy  

Science.gov (United States)

Solvation force oscillation in octamethylcyclotetrasiloxane (OMCTS) versus the distance between an atomic force microscope (AFM) tip and mica substrate has been studied through molecular dynamics simulations. A driving spring model in a liquid-vapor molecular ensemble is used to explore the force oscillation mechanism. It has been found that OMCTS fluid in tip-substrate contact has a strong tendency to form a layered structure, starting from n = 8 layers. The force profile obtained from simulation is qualitatively similar to those in contact mode AFM experiments. However, the bulk-like diffusion and rotation of OMCTS molecules underneath the AFM tip suggest that, under the tip-substrate confinement geometry, the layered OMCTS film cannot form a solidified structure except under n = 2 extreme contact-layer confinement.

Xu, Rong-Guang; Leng, Yongsheng

2014-06-01

360

Seismic force for base isolated nuclear power plants  

International Nuclear Information System (INIS)

In this report, dynamic and static seismic forces for base isolation system of nuclear power plants are described. First, concept of seismic force in guidelines of base isolated FBR plants, which was edited by CRIEPI in 'Verification Tests of FBR Seismic Isolation Systems' consigned from MITI, are mentioned. Second, proposed seismic spectrum is applied to ground motions in Hyogoken Nanbu Earthquake (1995). Assuming amplification factor of soil is 3, proposed seismic spectra agree with these ground motions as a result. Furthermore, calculation methods of static seismic force in which characteristics of seismic isolation systems are taken into account, are presented and the static force for Class A of nuclear power plants is compared with seismic force used in general base isolated buildings. (author)

 
 
 
 
361

Forces in General Relativity  

Science.gov (United States)

Many textbooks dealing with general relativity do not demonstrate the derivation of forces in enough detail. The analyses presented herein demonstrate straightforward methods for computing forces by way of general relativity. Covariant divergence of the stress-energy-momentum tensor is used to derive a general expression of the force experienced…

Ridgely, Charles T.

2010-01-01

362

Crossflow force transducer. [LMFBR  

Energy Technology Data Exchange (ETDEWEB)

A force transducer for measuring lift and drag coefficients for a circular cylinder in turbulent water flow is presented. In addition to describing the actual design and construction of the strain-gauged force- ring based transducer, requirements for obtained valid fluid force test data are discussed, and pertinent flow test experience is related.

Mulcahy, T M

1982-05-01

363

Nuclear reactions  

International Nuclear Information System (INIS)

The nuclear reactions are transformation processes that experiment the nuclei when being bombarded with particles of electromagnetic radiation or other nuclei. This type of reactions allows obtaining a great quantity of radio nuclides are not present in the nature. In the nuclear reactions it is conserved the load and the mass - energy. When the projectile is a loaded particle, it should have high kinetic energy to be able to conquer the repulsion electrostatic of the nucleus. This is achieved by means of the accelerators of particles. The accelerators are devices that accelerate the particles for application of an electric field. They can be circular or lineal. The modern accelerators allow that the particles reach enormous energy, for the radionuclides production, neutron activation analysis, trace analysis and nuclear reactors. Most of the nuclides obtained in accelerators, decays for positrons emission. Some of them have applications in of nuclear medicine diagnose

364

Quantum control: May the electric force be with you  

Science.gov (United States)

Intense laser fields can apply strong forces to molecules, distorting molecular potentials. Now, these effects have been used to precisely control the branching ratios of a polyatomic photodissociation reaction.

Stolow, Albert

2014-09-01

365

Ground Water Contamination  

Science.gov (United States)

This detailed discussion explains that most ground water contamination is the result of human activity, and that several laws have been passed with an aim to minimize effects. The Clean Water Act and the Safe Drinking Water Act are explained along with the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA, or Superfund), the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), the Resource Conservation and Recovery Act (RCRA), and the Toxic Substances Control Act (TSCA). Other terms explained include zone of contribution, interaquifer leakage, and plume of contamination. Special tables included at this site are Typical Sources of Potential Ground Water Contamination by Land Use Category and Potential Harmful Components of Common Household Products. There is also a full page diagram showing some potential sources of ground water contamination.

366

Ground motion predictions  

International Nuclear Information System (INIS)

Nuclear generated ground motion is defined and then related to the physical parameters that cause it. Techniques employed for prediction of ground motion peak amplitude, frequency spectra and response spectra are explored, with initial emphasis on the analysis of data collected at the Nevada Test Site (NTS). NTS postshot measurements are compared with pre-shot predictions. Applicability of these techniques to new areas, for example, Plowshare sites, must be questioned. Fortunately, the Atomic Energy Commission is sponsoring complementary studies to improve prediction capabilities primarily in new locations outside the NTS region. Some of these are discussed in the light of anomalous seismic behavior, and comparisons are given showing theoretical versus experimental results. In conclusion, current ground motion prediction techniques are applied to events off the NTS. Predictions are compared with measurements for the event Faultless and for the Plowshare events, Gasbuggy, Cabriolet, and Buggy I. (author)

367

Ground Source Heat Pumps  

Directory of Open Access Journals (Sweden)

Full Text Available A heat pump is a device that is able to transfer heat from one fluid at a lower temperature to another at a higher temperature. Ground source heat pumps are generally classified by the type of ground loop. The coefficient of performance (COP is used to define the heating performance of heat pumps. Both the COP and EER values are valid only at the specific test conditions used in the rating. A ground source pump could reach 450%, compared with an efficient gas boiler of 90% obviously this is a big difference. The cost of equipment, material and installation can be expensive, depending on the type of heat pump installation planned.

Lale Valizade

2013-07-01

368

Centrifugal force: an appreciation  

Directory of Open Access Journals (Sweden)

Full Text Available The centrifugal force is used to increase the physical understanding of five examples taken from fluid dynamics, geophysics and the solar system, as well as four hypothetical orbital problems. Each example involves a balance of forces between the centrifugal force and one or two other forces, such as a pressure gradient and a component of the force of gravity. Among the examples chosen for examination are: the orbital motion of fluid particles in surface grav-ity waves, the boundary layer character of steady flow next to a curved rigid surface, the tornado, the rotating self-gravitating mass and the three-body problem.

Kern E. Kenyon

2011-07-01

369

The Role of Quantum Vacuum Forces in Microelectromechanical Systems  

CERN Document Server

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.

MacLay, G J

2006-01-01

370

Reaction mechanisms  

International Nuclear Information System (INIS)

The 1988 progress report of the Reaction Mechanisms laboratory (Polytechnic School, France), is presented. The research topics are: the valence bond methods, the radical chemistry, the modelling of the transition states by applying geometric constraints, the long range interactions (ion - molecule) in gaseous phase, the reaction sites in gaseous phase and the mass spectroscopy applications. The points of convergence between the investigations of the mass spectroscopy and the theoretical chemistry teams, as well as the purposes guiding the research programs, are discussed. The published papers, the conferences, the congress communications and the thesis, are also reported

371

Ground and air resonance of bearingless rotors in hover  

Science.gov (United States)

A finite element formulation is used to investigate ground and air resistence in hover for a bearingless rotor. Aerodynamic forces are studied using quasi-steady strip theory, and unsteady aerodynamic effects are introduced through an inflow dynamics model. Reasonable correlation was found between predicted ground and air resonance results and data obtained from measurements using a 1/8th Froude-scaled dynamic model. Systematic parametric studies of the effects of various design parameters were performed, and lag frequency was found to significantly influence ground resonance stability, whereas pitch-lag coupling, blade sweep and pitch link stiffness had powerful effects on air resonance stability.

Jang, Jinseok; Chopra, Inderjit

1987-01-01

372

Forces in molecules.  

Science.gov (United States)

Chemistry is determined by the electrostatic forces acting within a collection of nuclei and electrons. The attraction of the nuclei for the electrons is the only attractive force in a molecule and is the force responsible for the bonding between atoms. This is the attractive force acting on the electrons in the Ehrenfest force and on the nuclei in the Feynman force, one that is countered by the repulsion between the electrons in the former and by the repulsion between the nuclei in the latter. The virial theorem relates these forces to the energy changes resulting from interactions between atoms. All bonding, as signified by the presence of a bond path, has a common origin in terms of the mechanics determined by the Ehrenfest, Feynman and virial theorems. This paper is concerned in particular with the mechanics of interaction encountered in what are classically described as 'nonbonded interactions'--are atoms that 'touch' bonded or repelling one another? PMID:17328425

Hernández-Trujillo, Jesús; Cortés-Guzmán, Fernando; Fang, De-Chai; Bader, Richard F W

2007-01-01

373

Quantum fictitious forces  

International Nuclear Information System (INIS)

We present Heisenberg's equation of motion for the radial variable of a free non-relativistic particle in D dimensions. The resulting radial force consists of three contributions: (i) the quantum fictitious force which is either attractive or repulsive depending on the number of dimensions, (ii) a singular quantum force located at the origin, and (iii) the centrifugal force associated with non-vanishing angular momentum. Moreover, we use Heisenberg's uncertainty relation to introduce a lower bound for the kinetic energy of an ensemble of neutral particles. This bound is quadratic in the number of atoms and can be traced back to the repulsive quantum fictitious potential. All three forces arise for a free particle: ''Force without force''. (orig.)

374

Quantum fictitious forces  

DEFF Research Database (Denmark)

We present Heisenberg's equation of motion for the radial variable of a free non-relativistic particle in D dimensions. The resulting radial force consists of three contributions: (i) the quantum fictitious force which is either attractive or repulsive depending on the number of dimensions, (ii) a singular quantum force located at the origin, and (iii) the centrifugal force associated with non-vanishing angular momentum. Moreover, we use Heisenberg's uncertainty relation to introduce a lower bound for the kinetic energy of an ensemble of neutral particles. This bound is quadratic in the number of atoms and can be traced back to the repulsive quantum fictitious potential. All three forces arise for a free particle: "Force without force".

Dahl, Jens Peder

2002-01-01

375

On the entropy of radiation reaction  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The inexorable development of ever more powerful laser systems has re-ignited interest in electromagnetic radiation reaction and its significance for the collective behaviour of charged matter interacting with intense electromagnetic fields. The classical radiation reaction force on a point electron is non-conservative, and this has led some authors to question the validity of methods used to model ultra-intense laser-matter interactions including radiation reaction. We explain why such conce...

Burton, David; Noble, Adam

2014-01-01

376

On the entropy of radiation reaction  

CERN Document Server

The inexorable development of ever more powerful laser systems has re-ignited interest in electromagnetic radiation reaction and its significance for the collective behaviour of charged matter interacting with intense electromagnetic fields. The classical radiation reaction force on a point electron is non-conservative, and this has led some authors to question the validity of methods used to model ultra-intense laser-matter interactions including radiation reaction. We explain why such concern is unwarranted.

Burton, David A

2013-01-01

377

Nuclear halos: structure and reactions  

International Nuclear Information System (INIS)

This contribution reports recent results on reactions of 11Be and 11Li with light and heavy target nuclei. The angular distributions of fast neutrons in coincidence with selected nuclear fragments illustrate the interplay between halo structure and reaction mechanism. It is shown that the unbound nucleus 10Li has an l=0 ground state characterized by a large scattering length, of the order of -20fm. The neutron halo of 11Li can best be interpreted in terms of a strongly correlated state with appreciable (2s1/2)2 and (1p1/2)2 components. ((orig.))

378

Force Limited Vibration Testing  

Science.gov (United States)

This slide presentation reviews the concept and applications of Force Limited Vibration Testing. The goal of vibration testing of aerospace hardware is to identify problems that would result in flight failures. The commonly used aerospace vibration tests uses artificially high shaker forces and responses at the resonance frequencies of the test item. It has become common to limit the acceleration responses in the test to those predicted for the flight. This requires an analysis of the acceleration response, and requires placing accelerometers on the test item. With the advent of piezoelectric gages it has become possible to improve vibration testing. The basic equations have are reviewed. Force limits are analogous and complementary to the acceleration specifications used in conventional vibration testing. Just as the acceleration specification is the frequency spectrum envelope of the in-flight acceleration at the interface between the test item and flight mounting structure, the force limit is the envelope of the in-flight force at the interface . In force limited vibration tests, both the acceleration and force specifications are needed, and the force specification is generally based on and proportional to the acceleration specification. Therefore, force limiting does not compensate for errors in the development of the acceleration specification, e.g., too much conservatism or the lack thereof. These errors will carry over into the force specification. Since in-flight vibratory force data are scarce, force limits are often derived from coupled system analyses and impedance information obtained from measurements or finite element models (FEM). Fortunately, data on the interface forces between systems and components are now available from system acoustic and vibration tests of development test models and from a few flight experiments. Semi-empirical methods of predicting force limits are currently being developed on the basis of the limited flight and system test data. A simple two degree of freedom system is shown and the governing equations for basic force limiting results for this system are reviewed. The design and results of the shuttle vibration forces (SVF) experiments are reviewed. The Advanced Composition Explorer (ACE) also was used to validate force limiting. Test instrumentation and supporting equipment are reviewed including piezo-electric force transducers, signal processing and conditioning systems, test fixtures, and vibration controller systems. Several examples of force limited vibration testing are presented with some results.

Scharton, Terry; Chang, Kurng Y.

2005-01-01

379

Cross reaction and thermonuclear reaction rates forthe 58Ni(p,?)59Cu reaction  

International Nuclear Information System (INIS)

The yield from the 58Ni(p,?)59Cu reaction has been measured by detection of annihilation radiation in coincidence from the decay of 82 s 59Cu. Both thin (600?g cm-2) and thick (117 mg cm-2) targets have been used, the latter being thick enough to stop the proton beam at all incident energies. The cross section calculated from the thin target yield contains much structure and is in reasonably good agreement with previous studies. Thermonuclear reaction rates have been calculated from both thin and thick target yields for tempertures of interest in explosive nucleosynthesis. Both thin and thick target rates are in very good agreement with previous determinations but the thin rates are, on the average, 35% higher than thick target rates. The reaction rate for T99>=2 for both ground state and stellar reactions based on thin target measurements is recommended and analytic fits to the recommended rates are given. (auth)

380

Coding Issues in Grounded Theory  

Science.gov (United States)

This paper discusses grounded theory as one of the qualitative research designs. It describes how grounded theory generates from data. Three phases of grounded theory--open coding, axial coding, and selective coding--are discussed, along with some of the issues which are the source of debate among grounded theorists, especially between its…

Moghaddam, Alireza

2006-01-01