Composite adaptive control of belt polishing force for aero-engine blade

NASA Astrophysics Data System (ADS)

Zhsao, Pengbing; Shi, Yaoyao

2013-09-01

The existing methods for blade polishing mainly focus on robot polishing and manual grinding. Due to the difficulty in high-precision control of the polishing force, the blade surface precision is very low in robot polishing, in particular, quality of the inlet and exhaust edges can not satisfy the processing requirements. Manual grinding has low efficiency, high labor intensity and unstable processing quality, moreover, the polished surface is vulnerable to burn, and the surface precision and integrity are difficult to ensure. In order to further improve the profile accuracy and surface quality, a pneumatic flexible polishing force-exerting mechanism is designed and a dual-mode switching composite adaptive control(DSCAC) strategy is proposed, which combines Bang-Bang control and model reference adaptive control based on fuzzy neural network(MRACFNN) together. By the mode decision-making mechanism, Bang-Bang control is used to track the control command signal quickly when the actual polishing force is far away from the target value, and MRACFNN is utilized in smaller error ranges to improve the system robustness and control precision. Based on the mathematical model of the force-exerting mechanism, simulation analysis is implemented on DSCAC. Simulation results show that the output polishing force can better track the given signal. Finally, the blade polishing experiments are carried out on the designed polishing equipment. Experimental results show that DSCAC can effectively mitigate the influence of gas compressibility, valve dead-time effect, valve nonlinear flow, cylinder friction, measurement noise and other interference on the control precision of polishing force, which has high control precision, strong robustness, strong anti-interference ability and other advantages compared with MRACFNN. The proposed research achieves high-precision control of the polishing force, effectively improves the blade machining precision and surface consistency, and significantly reduces the surface roughness.

A prospective study of carpal tunnel syndrome: workplace and individual risk factors

PubMed Central

Burt, Susan; Deddens, James A; Crombie, Ken; Jin, Yan; Wurzelbacher, Steve; Ramsey, Jessica

2015-01-01

Objectives To quantify the risk for carpal tunnel syndrome (CTS) from workplace physical factors, particularly hand activity level and forceful exertion, while taking into account individual factors including age, gender, body mass index (BMI), and pre-existing medical conditions. Methods Three healthcare and manufacturing workplaces were selected for inclusion on the basis of range of exposure to hand activity level and forceful exertion represented by their jobs. Each study participants job tasks were observed and evaluated ’ onsite and videotaped for further analysis, including frequency and duration of exertion and postural deviation. Individual health assessment entailed electrodiagnostic testing of median and ulnar nerves, physical examination and questionnaires at baseline with annual follow-up for 2 years. Results The incidence of dominant hand CTS during the study was 5.11 per 100 person-years (29 cases). Adjusted HRs for dominant hand CTS were as follows: working with forceful exertion ≥20% but <60% of the time: 2.83 (1.18, 6.79) and ≥60% of the time vs <20%: 19.57 (5.96, 64.24), BMI ≥30 kg/m2 (obesity): 3.19 (1.28, 7.98). The American Conference for Governmental Industrial Hygienists (ACGIH) Threshold Limit Value (TLV) for hand activity level also predicted CTS, HR=1.40 (1.11, 1.78) for each unit increase in the TLV ratio, controlling for obesity and job strain. Conclusions Workplace and individual risk factors both contribute to the risk for CTS. Time spent in forceful exertion can be a greater risk for CTS than obesity if the job exposure is high. Preventive workplace efforts should target forceful exertions. PMID:23788614

Development of force sensing circuit to determine the optimal force required for effective dynamic tripod grip/writing

NASA Astrophysics Data System (ADS)

Suraj S., S.; Kulkarni, Palash; Bokadia, Pratik; Ramanathan, Prabhu; Nageswaran, Sharmila

2018-04-01

Handwriting is a combination of fine motor perceptions and cognitive skills to produce words on paper. For writing, the most commonly used and recommended grip is the dynamic tripod grip. A child's handwriting starts developing during the times of pre-schooling and improves over time. While writing, children apply excessive force on the writing instrument. This force is exerted by their fingers and as per the law of reaction, the writing instruments tend to exert an equal and opposite force, that could damage the delicate soft tissue structures in their fingers and initiate cramps and pains. This condition is also prevalent in adults who tend to write for long hours under pressure. An example would be adolescence student during the exams. Clinically this condition is termed as `Writer's Cramp', which is usually characterized by muscle fatigue and pain in the fingers. By understanding and fixing the threshold of the force that should be exerted by the fingers while gripping the instrument, the pain can be controlled or avoided. This research aims in designing an electronic module which can help in understanding the threshold of pressure which is optimum enough to establish a better contact between the fingers and the instrument and should be capable of controlling or avoiding the pain. The design of FSR based electronic system is explained with its circuitry and results of initial testing is presented in this paper.

Results of telerobotic hand controller study using force information and rate control

NASA Technical Reports Server (NTRS)

Willshire, Kelli F.; Harrison, F. W.; Hogge, Edward F.; Williams, Robert L.; Soloway, Donald

1992-01-01

To increase quantified information about the effectiveness and subjective workload of force information relayed through manipulator input control devices, a space related task was performed by eight subjects with kinesthetic force feedback and/or local force accommodation through three different input control devices (i.e., hand controllers) operating in rate control mode. Task completion time, manipulator work, and subjective responses were measured. Results indicated a difference among the hand controllers. For the Honeywell six degree-of-freedom hand controller, the overall task completion times were shortest, the amount of work exerted was the least, and was the most preferred by test subjects. Neither force accommodation with or without reflection resulted in shorter task completion times or reduced work although those conditions were better than no force information for some aspects. Comparisons of results from previous studies are discussed.

A convex optimization method for self-organization in dynamic (FSO/RF) wireless networks

NASA Astrophysics Data System (ADS)

Llorca, Jaime; Davis, Christopher C.; Milner, Stuart D.

2008-08-01

Next generation communication networks are becoming increasingly complex systems. Previously, we presented a novel physics-based approach to model dynamic wireless networks as physical systems which react to local forces exerted on network nodes. We showed that under clear atmospheric conditions the network communication energy can be modeled as the potential energy of an analogous spring system and presented a distributed mobility control algorithm where nodes react to local forces driving the network to energy minimizing configurations. This paper extends our previous work by including the effects of atmospheric attenuation and transmitted power constraints in the optimization problem. We show how our new formulation still results in a convex energy minimization problem. Accordingly, an updated force-driven mobility control algorithm is presented. Forces on mobile backbone nodes are computed as the negative gradient of the new energy function. Results show how in the presence of atmospheric obscuration stronger forces are exerted on network nodes that make them move closer to each other, avoiding loss of connectivity. We show results in terms of network coverage and backbone connectivity and compare the developed algorithms for different scenarios.

Influence of permittivity on gradient force exerted on Mie spheres.

PubMed

Chen, Jun; Li, Kaikai; Li, Xiao

2018-04-01

In optical trapping, whether a particle could be stably trapped into the focus region greatly depends on the strength of the gradient force. Individual theoretical study on gradient force exerted on a Mie particle is rare because the mathematical separation of the gradient force and the scattering force in the Mie regime is difficult. Based on the recent forces separation work by Du et al. [Sci. Rep.7, 18042 (2017)SRCEC32045-232210.1038/s41598-017-17874-1], we investigate the influence of permittivity (an important macroscopic physical quantity) on the gradient force exerted on a Mie particle by cooperating numerical calculation using fast Fourier transform and analytical analysis using multipole expansion. It is revealed that gradient forces exerted on small spheres are mainly determined by the electric dipole moment except for certain permittivity with which the real part of polarizability of the electric dipole approaches zero, and gradient forces exerted on larger spheres are complex because of the superposition of the multipole moments. The classification of permittivity corresponding to different varying tendencies of gradient forces exerted on small spheres or larger Mie particles are illustrated. Absorption of particles favors the trapping of small spheres by gradient force, while it is bad for the trapping of larger particles. Moreover, the absolute values of the maximal gradient forces exerted on larger Mie particles decline greatly versus the varied imaginary part of permittivity. This work provides elaborate investigation on the different varying tendencies of gradient forces versus permittivity, which favors more accurate and free optical trapping.

Determination of the Maximum Control Forces and Attainable Quickness in the Operation of Airplane Controls

NASA Technical Reports Server (NTRS)

Hertel, Heinrich

1930-01-01

This report is intended to furnish bases for load assumptions in the designing of airplane controls. The maximum control forces and quickness of operation are determined. The maximum forces for a strong pilot with normal arrangement of the controls is taken as 1.25 times the mean value obtained from tests with twelve persons. Tests with a number of persons were expected to show the maximum forces that a man of average strength can exert on the control stick in operating the elevator and ailerons and also on the rudder bar. The effect of fatigue, of duration and of the nature (static or dynamic) of the force, as also the condition of the test subject (with or without belt) were also considered.

Force-endurance capabilities of extravehicular activity (EVA) gloves at different pressure levels

NASA Technical Reports Server (NTRS)

Bishu, Ram R.; Klute, Glenn K.

1993-01-01

The human hand is a very useful multipurpose tool in all environments. However, performance capabilities are compromised considerably when gloves are donned. This is especially true to extravehicular activity (EVA) gloves. The primary intent was to answer the question of how long a person can perform tasks requiring certain levels of exertion. The objective was to develop grip force-endurance relations. Six subjects participated in a factorial experiment involving three hand conditions, three pressure differentials, and four levels of force exertion. The results indicate that, while the force that could be exerted depended on the glove, pressure differential, and the level of exertion, the endurance time at any exertion level depended just on the level of exertion expressed as a percentage of maximum exertion possible at that condition. The impact of these findings for practitioners as well as theoreticians is discussed.

Ready steady push--a study of the role of arm posture in manual exertions.

PubMed

Okunribido, Olanrewaju O; Haslegrave, Christine M

2008-02-01

This study investigated arm posture and hand forces during bi-manual pushing. Nine male and eight female participants performed isometric exertions at two reach distances (0 and elbow-grip) and six different positions of the hand interface (handle), defined by the plane (longitudinal, lateral, horizontal) and orientation (0 degrees and 45 degrees). Electrogoniometer instruments were used to measure the displacements/postures of the wrist and elbow joints and the forearm, and force measuring strain gauges were used to measure the exerted hand forces (x-, y- and z-components). The results showed that ability to vary arm posture, particularly the forearm, is important during build up of force and that people tend to seek for a balance in the forces applied at the hands by exerting more in the vertical direction. Also, lateral plane handle positions permitted exertion of greater forces than longitudinal and horizontal plane positions.

14 CFR 25.145 - Longitudinal control.

Code of Federal Regulations, 2011 CFR

2011-01-01

... 14 Aeronautics and Space 1 2011-01-01 2011-01-01 false Longitudinal control. 25.145 Section 25.145... control. (a) It must be possible, at any point between the trim speed prescribed in § 25.103(b)(6) and..., no change in trim control, or exertion of more than 50 pounds control force (representative of the...

14 CFR 25.145 - Longitudinal control.

Code of Federal Regulations, 2012 CFR

2012-01-01

... 14 Aeronautics and Space 1 2012-01-01 2012-01-01 false Longitudinal control. 25.145 Section 25.145... control. (a) It must be possible, at any point between the trim speed prescribed in § 25.103(b)(6) and..., no change in trim control, or exertion of more than 50 pounds control force (representative of the...

Fluctuation spectra and force generation in nonequilibrium systems.

PubMed

Lee, Alpha A; Vella, Dominic; Wettlaufer, John S

2017-08-29

Many biological systems are appropriately viewed as passive inclusions immersed in an active bath: from proteins on active membranes to microscopic swimmers confined by boundaries. The nonequilibrium forces exerted by the active bath on the inclusions or boundaries often regulate function, and such forces may also be exploited in artificial active materials. Nonetheless, the general phenomenology of these active forces remains elusive. We show that the fluctuation spectrum of the active medium, the partitioning of energy as a function of wavenumber, controls the phenomenology of force generation. We find that, for a narrow, unimodal spectrum, the force exerted by a nonequilibrium system on two embedded walls depends on the width and the position of the peak in the fluctuation spectrum, and oscillates between repulsion and attraction as a function of wall separation. We examine two apparently disparate examples: the Maritime Casimir effect and recent simulations of active Brownian particles. A key implication of our work is that important nonequilibrium interactions are encoded within the fluctuation spectrum. In this sense, the noise becomes the signal.

Contact position sensor using constant contact force control system

NASA Technical Reports Server (NTRS)

Sturdevant, Jay (Inventor)

1995-01-01

A force control system (50) and method are provided for controlling a position contact sensor (10) so as to produce a constant controlled contact force therewith. The system (50) includes a contact position sensor (10) which has a contact probe (12) for contacting the surface of a target to be measured and an output signal (V.sub.o) for providing a position indication thereof. An actuator (30) is provided for controllably driving the contact position sensor (10) in response to an actuation control signal (I). A controller (52) receives the position indication signal (V.sub.o) and generates in response thereto the actuation control signal (I) so as to provide a substantially constant selective force (F) exerted by the contact probe (12). The actuation drive signal (I) is generated further in response to substantially linear approximation curves based on predetermined force and position data attained from the sensor (10) and the actuator (30).

Comparison of the force exerted by hippocampal and DRG growth cones.

PubMed

Amin, Ladan; Ercolini, Erika; Ban, Jelena; Torre, Vincent

2013-01-01

Mechanical properties such as force generation are fundamental for neuronal motility, development and regeneration. We used optical tweezers to compare the force exerted by growth cones (GCs) of neurons from the Peripheral Nervous System (PNS), such as Dorsal Root Ganglia (DRG) neurons, and from the Central Nervous System (CNS) such as hippocampal neurons. Developing GCs from dissociated DRG and hippocampal neurons were obtained from P1-P2 and P10-P12 rats. Comparing their morphology, we observed that the area of GCs of hippocampal neurons was 8-10 µm(2) and did not vary between P1-P2 and P10-P12 rats, but GCs of DRG neurons were larger and their area increased from P1-P2 to P10-P12 by 2-4 times. The force exerted by DRG filopodia was in the order of 1-2 pN and never exceeded 5 pN, while hippocampal filopodia exerted a larger force, often in the order of 5 pN. Hippocampal and DRG lamellipodia exerted lateral forces up to 20 pN, but lamellipodia of DRG neurons could exert a vertical force larger than that of hippocampal neurons. Force-velocity relationships (Fv) in both types of neurons had the same qualitative behaviour, consistent with a common autocatalytic model of force generation. These results indicate that molecular mechanisms of force generation of GC from CNS and PNS neurons are similar but the amplitude of generated force is influenced by their cytoskeletal properties.

Comparison of the Force Exerted by Hippocampal and DRG Growth Cones

PubMed Central

Amin, Ladan; Ercolini, Erika; Ban, Jelena; Torre, Vincent

2013-01-01

Mechanical properties such as force generation are fundamental for neuronal motility, development and regeneration. We used optical tweezers to compare the force exerted by growth cones (GCs) of neurons from the Peripheral Nervous System (PNS), such as Dorsal Root Ganglia (DRG) neurons, and from the Central Nervous System (CNS) such as hippocampal neurons. Developing GCs from dissociated DRG and hippocampal neurons were obtained from P1-P2 and P10-P12 rats. Comparing their morphology, we observed that the area of GCs of hippocampal neurons was 8-10 µm2 and did not vary between P1-P2 and P10-P12 rats, but GCs of DRG neurons were larger and their area increased from P1-P2 to P10-P12 by 2-4 times. The force exerted by DRG filopodia was in the order of 1-2 pN and never exceeded 5 pN, while hippocampal filopodia exerted a larger force, often in the order of 5 pN. Hippocampal and DRG lamellipodia exerted lateral forces up to 20 pN, but lamellipodia of DRG neurons could exert a vertical force larger than that of hippocampal neurons. Force-velocity relationships (Fv) in both types of neurons had the same qualitative behaviour, consistent with a common autocatalytic model of force generation. These results indicate that molecular mechanisms of force generation of GC from CNS and PNS neurons are similar but the amplitude of generated force is influenced by their cytoskeletal properties. PMID:23991169

Subpiconewton intermolecular force microscopy.

PubMed

Tokunaga, M; Aoki, T; Hiroshima, M; Kitamura, K; Yanagida, T

1997-02-24

We refined scanning probe force microscopy to improve the sensitivity of force detection and control of probe position. Force sensitivity was increased by incorporating a cantilever with very low stiffness, 0.1 pN/ nm, which is over 1000-fold more flexible than is typically used in conventional atomic force microscopy. Thermal bending motions of the cantilever were reduced to less than 1 nm by exerting feed-back positioning with laser radiation pressure. The system was tested by measuring electrostatic repulsive forces or hydrophobic attractive forces in aqueous solutions. Subpiconewton intermolecular forces were resolved at controlled gaps in the nanometer range between the probe and a material surface. These levels of force and position sensitivity meet the requirements needed for future investigations of intermolecular forces between biological macromolecules such as proteins, lipids and DNA.

Forces and moments generated by the human arm: Variability and control

PubMed Central

Xu, Y; Terekhov, AV; Latash, ML; Zatsiorsky, VM

2012-01-01

This is an exploratory study of the accurate endpoint force vector production by the human arm in isometric conditions. We formulated three common-sense hypotheses and falsified them in the experiment. The subjects (n=10) exerted static forces on the handle in eight directions in a horizontal plane for 25 seconds. The forces were of 4 magnitude levels (10 %, 20%, 30% and 40% of individual MVC). The torsion moment on the handle (grasp moment) was not specified in the instruction. The two force components and the grasp moment were recorded, and the shoulder, elbow, and wrist joint torques were computed. The following main facts were observed: (a) While the grasp moment was not prescribed by the instruction, it was always produced. The moment magnitude and direction depended on the instructed force magnitude and direction. (b) The within-trial angular variability of the exerted force vector (angular precision) did not depend on the target force magnitude (a small negative correlation was observed). (c) Across the target force directions, the variability of the exerted force magnitude and directional variability exhibited opposite trends: In the directions where the variability of force magnitude was maximal, the directional variability was minimal and vice versa. (d) The time profiles of joint torques in the trials were always positively correlated, even for the force directions where flexion torque was produced at one joint and extension torque was produced at the other joint. (e) The correlations between the grasp moment and the wrist torque were negative across the tasks and positive within the individual trials. (f) In static serial kinematic chains, the pattern of the joint torques distribution could not be explained by an optimization cost function additive with respect to the torques. Plans for several future experiments have been suggested. PMID:23080084

Two-Pendulum Model of Propellant Slosh in Europa Clipper PMD Tank

NASA Technical Reports Server (NTRS)

Ng, Wanyi; Benson, David

2017-01-01

Model propellant slosh for Europa Clipper using two pendulums such that controls engineers can predict slosh behavior during the mission. Importance of predicting propellant slosh; (1) Sloshing changes CM (center of mass) of spacecraft and exerts forces and torques on spacecraft. (2) Avoid natural frequencies of structures. (3) Size ACS (Attitude Control Systems) thrusters to counteract forces and torques. Can model sloshing fluid as two pendulums with specific parameters (mass, length, damping),

Hybrid position/force control of multi-arm cooperating robots

NASA Technical Reports Server (NTRS)

Hayati, Samad

1986-01-01

This paper extends the theory of hybrid position/force control to the case of multi-arm cooperating robots. Cooperation between n robot arms is achieved by controlling each arm such that the burden of actuation is shared between the arms in a nonconflicting way as they control the position of and force on a designated point on an object. The object, which may or may not be in contact with a rigid environment, is assumed to be held rigidly by n robot end-effectors. Natural and artificial position and force constraints are defined for a point on the object and two selection matrices are obtained to control the arms. The position control loops are designed based on each manipulator's Cartesian space dynamic equations. In the position control subspace, a feature is provided which allows the robot arms to exert additional forces/torques to achieve compression, tension, or torsion in the object without affecting the execution of the motion trajectories. In the force control subspace, a method is introduced to minimize the total force/torque magnitude square while realizing the net desired force/torque on the environment.

Sensing And Force-Reflecting Exoskeleton

NASA Technical Reports Server (NTRS)

Eberman, Brian; Fontana, Richard; Marcus, Beth

1993-01-01

Sensing and force-reflecting exoskeleton (SAFiRE) provides control signals to robot hand and force feedback from robot hand to human operator. Operator makes robot hand touch objects gently and manipulates them finely without exerting excessive forces. Device attaches to operator's hand; comfortable and lightweight. Includes finger exoskeleton, cable mechanical transmission, two dc servomotors, partial thumb exoskeleton, harness, amplifier box, two computer circuit boards, and software. Transduces motion of index finger and thumb. Video monitor of associated computer displays image corresponding to motion.

Investigation of force, contact area, and dwell time in finger-tapping tasks on membrane touch interface.

PubMed

Liu, Na; Yu, Ruifeng

2018-06-01

This study aimed to determine the touch characteristics during tapping tasks on membrane touch interface and investigate the effects of posture and gender on touch characteristics variables. One hundred participants tapped digits displayed on a membrane touch interface on sitting and standing positions using all fingers of the dominant hand. Touch characteristics measures included average force, contact area, and dwell time. Across fingers and postures, males exerted larger force and contact area than females, but similar dwell time. Across genders and postures, thumb exerted the largest force and the force of the other four fingers showed no significant difference. The contact area of the thumb was the largest, whereas that of the little finger was the smallest; the dwell time of the thumb was the longest, whereas that of the middle finger was the shortest. Relationships among finger sizes, gender, posture and touch characteristics were proposed. The findings helped direct membrane touch interface design for digital and numerical control products from hardware and software perspectives. Practitioner Summary: This study measured force, contact area, and dwell time in tapping tasks on membrane touch interface and examined effects of gender and posture on force, contact area, and dwell time. The findings will direct membrane touch interface design for digital and numerical control products from hardware and software perspectives.

The effect of bracing availability on one-hand isometric force exertion capability.

PubMed

Jones, Monica L H; Reed, Matthew P; Chaffin, Don B

2013-01-01

Environmental obstructions that workers encounter can kinematically limit the postures that they can achieve. However, such obstructions can also provide an opportunity for additional support by bracing with the hand, thigh or other body part. The reaction forces on bracing surfaces, which are in addition to those acting at the feet and task hand, are hypothesised to improve force exertion capability, and become required inputs to biomechanical analysis of tasks with bracing. The effects of kinematic constraints and associated bracing opportunities on isometric hand force were quantified in a laboratory study of 22 men and women. Analyses of one-hand maximal push, pull and lift tasks demonstrated that bracing surfaces available at the thighs and non-task hand enabled participants to exert an average of 43% more force at the task hand. Task hand force direction deviated significantly from the nominal direction for exertions performed with bracing at both medium and low task hand locations. This study quantifies the effect of bracing on kinematically constrained force exertions. Knowledge that appropriate bracing surfaces can substantially increase hand force is critical to the evaluation of task-oriented strength capability. Force estimates may also involve large off-axis components, which have clear implications for ergonomic analyses of manual tasks.

The force exerted by a fireball

DOE Office of Scientific and Technical Information (OSTI.GOV)

Makrinich, G.; Fruchtman, A.

The force exerted by a fireball was deduced both from the change of the equilibrium position of a pendulum and from the change in the pendulum oscillation period. That measured force was found to be several times larger than the force exerted by the ions accelerated across the double layer that is assumed to surround the fireball. The force enhancement that is expected by ion-neutral collisions in the fireball is evaluated to be too small to explain the measured enhanced force. Gas pressure increase, due to gas heating through electron-neutral collisions, as recently suggested [Stenzel et al., J. Appl. Phys.more » 109, 113305 (2011)], is examined as the source for the force enhancement.« less

The control of mono-articular muscles in multijoint leg extensions in man.

PubMed Central

van Ingen Schenau, G J; Dorssers, W M; Welter, T G; Beelen, A; de Groot, G; Jacobs, R

1995-01-01

1. Movements often require control of direction and a magnitude of force exerted externally on the environment. Bi-articular upper leg muscles appear to play a unique role in the regulation of the net torques about the hip and knee joints, necessary for the control of this external force. 2. The aim of this study was to test the hypothesis that the mono-articular muscles act as work generators in powerful dynamic leg extensions, which means that they should be activated primarily in the phases during which they can contribute to work, irrespective of the net joint torques required to control the external force. 3. Cycling movements of six trained subjects were analysed by means of inverse dynamics, yielding net joint torques as well as activity patterns and shortening velocities of four mono- and four bi-articular leg muscles. 4. The results show that the mono-articular muscles exert force only in the phase in which these muscles shorten, whereas this appears not to be the case for the bi-articular muscles. 5. Reciprocal patterns of activation of the rectus femoris and hamstring muscles appear to tune the distribution of net joint torques about the hip and knee joints, necessary to control the (changing) direction of the force on the pedal. 6. An analysis of running in man and additional related literature based on animal studies appears to provide further support for the hypothesis that mono- and bi-articular muscles have essentially different roles in these powerful multijoint leg extension tasks. PMID:7602524

Algorithm Optimally Allocates Actuation of a Spacecraft

NASA Technical Reports Server (NTRS)

Motaghedi, Shi

2007-01-01

A report presents an algorithm that solves the following problem: Allocate the force and/or torque to be exerted by each thruster and reaction-wheel assembly on a spacecraft for best performance, defined as minimizing the error between (1) the total force and torque commanded by the spacecraft control system and (2) the total of forces and torques actually exerted by all the thrusters and reaction wheels. The algorithm incorporates the matrix vector relationship between (1) the total applied force and torque and (2) the individual actuator force and torque values. It takes account of such constraints as lower and upper limits on the force or torque that can be applied by a given actuator. The algorithm divides the aforementioned problem into two optimization problems that it solves sequentially. These problems are of a type, known in the art as semi-definite programming problems, that involve linear matrix inequalities. The algorithm incorporates, as sub-algorithms, prior algorithms that solve such optimization problems very efficiently. The algorithm affords the additional advantage that the solution requires the minimum rate of consumption of fuel for the given best performance.

Quantification of Staphylococcus aureus adhesion forces on various dental restorative materials using atomic force microscopy

NASA Astrophysics Data System (ADS)

Merghni, Abderrahmen; Kammoun, Dorra; Hentati, Hajer; Janel, Sébastien; Popoff, Michka; Lafont, Frank; Aouni, Mahjoub; Mastouri, Maha

2016-08-01

In the oral cavity dental restorative biomaterials can act as a reservoir for infection with opportunistic Staphylococcus aureus pathogen, which can lead to the occurrence of secondary caries and treatment failures. Our aim was to evaluate the adhesion forces by S. aureus on four dental restorative biomaterials and to correlate this finding to differences in specific surface characteristics. Additionally, the influence of salivary conditioning films in exerted adhesion forces was investigated. The substrate hydrophobicity was measured by goniometer and the surface free energy was calculated using the equilibrium advancing contact angle values of water, formamide, and diiodomethane on the tested surfaces. The surface roughness was determined using atomic force microscope (AFM). Additionally, cell force spectroscopy was achieved to quantify the forces that drive cell-substrate interactions. S. aureus bacterium exerted a considerable adhesion forces on various dental restorative materials, which decreased in the presence of saliva conditioning film. The influence of the surface roughness and free energy in initial adhesion appears to be more important than the effect of hydrophobicity, either in presence or absence of saliva coating. Hence, control of surface properties of dental restorative biomaterials is of crucial importance in preventing the attachment and subsequent the biofilm formation.

Grip force control during virtual object interaction: effect of force feedback,accuracy demands, and training.

PubMed

Gibo, Tricia L; Bastian, Amy J; Okamura, Allison M

2014-03-01

When grasping and manipulating objects, people are able to efficiently modulate their grip force according to the experienced load force. Effective grip force control involves providing enough grip force to prevent the object from slipping, while avoiding excessive force to avoid damage and fatigue. During indirect object manipulation via teleoperation systems or in virtual environments, users often receive limited somatosensory feedback about objects with which they interact. This study examines the effects of force feedback, accuracy demands, and training on grip force control during object interaction in a virtual environment. The task required subjects to grasp and move a virtual object while tracking a target. When force feedback was not provided, subjects failed to couple grip and load force, a capability fundamental to direct object interaction. Subjects also exerted larger grip force without force feedback and when accuracy demands of the tracking task were high. In addition, the presence or absence of force feedback during training affected subsequent performance, even when the feedback condition was switched. Subjects' grip force control remained reminiscent of their employed grip during the initial training. These results motivate the use of force feedback during telemanipulation and highlight the effect of force feedback during training.

Comparative evaluation of cemental abrasion caused by soft and medium bristle hardness toothbrushes at three predetermined toothbrushing forces: An in vitro study

PubMed Central

Joshi, Chaitanya Pradeep; Patil, Agraja Ganpat; Karde, Prerna Ashok; Mahale, Swapna Arunkumar; Dani, Nitin Hemchandra

2017-01-01

Background: Plaque control has been shown to have a pivotal role in maintaining optimal periodontal health. Toothbrushing as a mechanical plaque control tool is the most popular and effective option for self-performed oral health maintenance. However, the detrimental effects of bristle hardness and force exerted by toothbrushes on the tooth surface are the areas of concern. Objective: The aim of this in vitro study was to evaluate the abrasive effect of two different manual toothbrushes exerting predetermined forces on cemental surfaces of the teeth. Materials and Methods: Sixty extracted first molars were selected. Totally six experimental groups were formed based on the three predetermined forces 1.5, 3, and 4.5 Newton (N) and two types of manual toothbrushes, i.e., soft and medium bristle hardness. Buccal and lingual surfaces were independently brushed for 5000 cycles using specially designed toothbrushing machine. Throughout the experiment, type and quantity of toothpaste were kept constant. Post 5000 cycles of toothbrushing, change in surface roughness was measured using profilometer in microns and change in weight indicating loss of substance was measured in milligrams. Results: Abrasion of cementum is force dependent. Data revealed that both soft and medium bristle hardness toothbrushes cause significant cemental abrasion at 3 and 4.5 N forces. Conclusions: Higher is the force, more is the cemental surface abrasion. Soft bristled toothbrush causes more cemental abrasion than medium bristled toothbrush at 3 and 4.5 N forces. PMID:29386794

Stunted PFC activity during neuromuscular control under stress with obesity.

PubMed

Mehta, Ranjana K

2016-02-01

Obesity is an established risk factor for impaired cognition, which is primarily regulated by the prefrontal cortex (PFC). However, very little is known about the neural pathways that underlie obesity-related declines in neuromuscular control, particularly under stress. The purpose of this study was to determine the role of the PFC on neuromuscular control during handgrip exertions under stress with obesity. Twenty non-obese and obese young adults performed submaximal handgrip exertions in the absence and presence of a concurrent stressful task. Primary dependent measures included oxygenated hemoglobin (HbO2: a measure of PFC activity) and force fluctuations (an indicator of neuromuscular control). Higher HbO2 levels in the PFC were observed in the non-obese compared to the obese group (P = 0.009). In addition, higher HbO2 levels were observed in the stress compared to the control condition in the non-obese group; however, this trend was reversed in the obese group (P = 0.043). In general, force fluctuations increased by 26% in the stress when compared to the control condition (P = 0.001) and obesity was associated with 39% greater force fluctuation (P = 0.024). Finally, while not significant, obesity-related decrements in force fluctuations were magnified under stress (P = 0.063). The current study provides the first evidence that neuromuscular decrements with obesity were associated with impaired PFC activity and this relationship was augmented in stress conditions. These findings are important because they provide new information on obesity-specific changes in brain function associated with neuromuscular control since the knowledge previously focused largely on obesity-specific changes in peripheral muscle capacity.

49 CFR 236.341 - Latch shoes, rocker links, and quadrants.

Code of Federal Regulations, 2010 CFR

2010-10-01

..., INSPECTION, MAINTENANCE, AND REPAIR OF SIGNAL AND TRAIN CONTROL SYSTEMS, DEVICES, AND APPLIANCES Interlocking... downward force not exceeding a man's weight is exerted on the rocker while the lever is in the mid-stroke...

Excessive motor overflow reveals abnormal inter-hemispheric connectivity in Friedreich ataxia.

PubMed

Low, Sze-Cheen; Corben, Louise A; Delatycki, Martin B; Ternes, Anne-Marie; Addamo, Patricia K; Georgiou-Karistianis, Nellie

2013-07-01

This study sought to characterise force variability and motor overflow in 12 individuals with Friedreich ataxia (FRDA) and 12 age- and gender-matched controls. Participants performed a finger-pressing task by exerting 30 and 70 % of their maximum finger force using the index finger of the right and left hand. Control of force production was measured as force variability, while any involuntary movements occurring on the finger of the other, passive hand, was measured as motor overflow. Significantly greater force variability in individuals with FRDA compared with controls is indicative of cortico-cerebellar disruption affecting motor control. Meanwhile, significantly greater motor overflow in this group provides the first evidence of possible abnormal inter-hemispheric activity that may be attributable to asymmetrical neuronal loss in the dentate nucleus. Overall, this study demonstrated a differential engagement in the underlying default processes of the motor system in FRDA.

Forces exerted during microneurosurgery: a cadaver study

PubMed Central

Marcus, Hani J; Zareinia, Kourosh; Gan, Liu Shi; Yang, Fang Wei; Lama, Sanju; Yang, Guang-Zhong; Sutherland, Garnette R

2014-01-01

Background A prerequisite for the successful design and use of robots in neurosurgery is knowledge of the forces exerted by surgeons during neurosurgical procedures. The aim of the present cadaver study was to measure the surgical instrument forces exerted during microneurosurgery. Methods An experimental apparatus was set up consisting of a platform for human cadaver brains, a Leica microscope to provide illumination and magnification, and a Quanser 6 Degrees-Of-Freedom Telepresence System for tissue manipulation and force measurements. Results The measured forces varied significantly depending on the region of the brain (P = 0.016) and the maneuver performed (P < 0.0001). Moreover, blunt arachnoid dissection was associated with greater force exertion than sharp dissection (0.22 N vs. 0.03 N; P = 0.001). Conclusions The forces necessary to manipulate brain tissue were surprisingly low and varied depending on the anatomical structure being manipulated, and the maneuver performed. Knowledge of such forces could well increase the safety of microsurgery. © 2014 The Authors. The International Journal of Medical Robotics and Computer Assisted Surgery published by John Wiley & Sons, Ltd. PMID:24431265

Variation in Rising Limb of Colorado River Snowmelt Runoff Hydrograph Controlled by Dust Radiative Forcing in Snow

NASA Astrophysics Data System (ADS)

Painter, Thomas H.; Skiles, S. McKenzie; Deems, Jeffrey S.; Brandt, W. Tyler; Dozier, Jeff

2018-01-01

Common practice and conventional wisdom hold that fluctuations in air temperature control interannual variability in snowmelt and subsequent river runoff. However, recent observations in the Upper Colorado River Basin confirm that net solar radiation and by extension radiative forcing by dust deposited on snow cover exerts the primary forcing on snowmelt. We show that the variation in the shape of the rising limb of the annual hydrograph is controlled by variability in dust radiative forcing and surprisingly is independent of variations in winter and spring air temperatures. These observations suggest that hydroclimatic modeling must be improved to account for aerosol forcings of the water cycle. Anthropogenic climate change will likely reduce total snow accumulations and cause snowmelt runoff to occur earlier. However, dust radiative forcing of snowmelt is likely consuming important adaptive capacity that would allow human and natural systems to be more resilient to changing hydroclimatic conditions.

Control of robotic assistance using poststroke residual voluntary effort.

PubMed

Makowski, Nathaniel S; Knutson, Jayme S; Chae, John; Crago, Patrick E

2015-03-01

Poststroke hemiparesis limits the ability to reach, in part due to involuntary muscle co-activation (synergies). Robotic approaches are being developed for both therapeutic benefit and continuous assistance during activities of daily living. Robotic assistance may enable participants to exert less effort, thereby reducing expression of the abnormal co-activation patterns, which could allow participants to reach further. This study evaluated how well participants could perform a reaching task with robotic assistance that was either provided independent of effort in the vertical direction or in the sagittal plane in proportion to voluntary effort estimated from electromyograms (EMG) on the affected side. Participants who could not reach targets without assistance were enabled to reach further with assistance. Constant anti-gravity force assistance that was independent of voluntary effort did not reduce the quality of reach and enabled participants to exert less effort while maintaining different target locations. Force assistance that was proportional to voluntary effort on the affected side enabled participants to exert less effort and could be controlled to successfully reach targets, but participants had increased difficulty maintaining a stable position. These results suggest that residual effort on the affected side can produce an effective command signal for poststroke assistive devices.

Cyclic control stick

DOEpatents

Whitaker, Charles N.; Zimmermann, Richard E.

1989-01-01

A cyclic control stick of the type used in helicopters for reducing the safety hazards associated with such a mechanism in the event of a crewman being thrown violently into contact with the cyclic control stick resulting from a crash or the like. The cyclic control stick is configured to break away upon the exertion of an impact force which exceeds a predetermined value and/or is exerted for more than a momentary time duration. The cyclic control stick is also configured to be adjustable so as to locate the grip thereof as far away from the crewman as possible for safety reasons without comprising the comfort of the crewman or the use of the control stick, and a crushable pad is provided on the top of the grip for impact energy absorbing purposes.

The design and development of a triaxial wear-testing joint simulator.

PubMed

Green, A S; O'Connell, M K; Lyons, A S; James, S P

1999-01-01

Most of the existing wear testers created to wear test total hip replacements, specifically the acetabular component, are designed to exert only an axial force and provide rotation in a close approximation of the actual femoral movement. The Rocky Mountain Joint Simulator was designed to exert three orthogonal forces and provide rotations about the X-, Y- and Z-axes to more closely simulate the physiological forces and motions found in the human gait cycle. The RMJS was also designed with adaptability for other joints, such as knees or canine hips, through the use of hydraulics and a computer-programmable control system. Such adaptability and functionality allows the researcher to more closely model a gait cycle, thereby obtaining wear patterns that resemble those found in retrieved implants more closely than existing simulators. Research is ongoing into the tuning and evaluation of the machine and preliminary acetabular component wear test results will be presented at the conference.

Force Exertion Capacity Measurements in Haptic Virtual Environments

ERIC Educational Resources Information Center

Munih, Marko; Bardorfer, Ales; Ceru, Bojan; Bajd, Tadej; Zupan, Anton

2010-01-01

An objective test for evaluating functional status of the upper limbs (ULs) in patients with muscular distrophy (MD) is presented. The method allows for quantitative assessment of the UL functional state with an emphasis on force exertion capacity. The experimental measurement setup and the methodology for the assessment of maximal exertable force…

Soviet Dissent and the American National Interest.

DTIC Science & Technology

1986-06-01

upon the leaders to employ violence and terror against dissidents, which is in fact what is done. The police control mechanisms, which are exerted...form of nonjudicial action against dissidents. As a means of intimidation and reprisal, police forces and parapolice forces employ a variety of...individuals * ... and groups, seeking a variety of goals and objectives. Nevertheless, the phenomenon can be described relative to three basic

The Precarious Role of Education in Identity and Value Formation Processes: The Shift from State to Market Forces

ERIC Educational Resources Information Center

Desjardins, Richard

2015-01-01

This article briefly reviews the evolving role of major institutions thought to form, reproduce and transform individual as well as collective identities and values, with an emphasis on the impact of state vs market forces via educational systems. This is accompanied by a discussion of various pressures against the state to exert social control on…

Towards an on-chip platform for the controlled application of forces via magnetic particles: A novel device for mechanobiology

NASA Astrophysics Data System (ADS)

Monticelli, M.; Albisetti, E.; Petti, D.; Conca, D. V.; Falcone, M.; Sharma, P. P.; Bertacco, R.

2015-05-01

In-vitro tests and analyses are of fundamental importance for investigating biological mechanisms in cells and bio-molecules. The controlled application of forces to activate specific bio-pathways and investigate their effects, mimicking the role of the cellular environment, is becoming a prominent approach in this field. In this work, we present a non-invasive magnetic on-chip platform which allows for the manipulation of magnetic particles, through micrometric magnetic conduits of Permalloy patterned on-chip. We show, from simulations and experiments, that this technology permits to exert a finely controlled force on magnetic beads along the chip surface. This force can be tuned from few to hundreds pN by applying a variable external magnetic field.

THE EFFECTS OF DIFFERENT TRUNK INCLINATIONS ON BILATERAL TRUNK MUSCULAR ACTIVITIES, CENTRE OF PRESSURE AND FORCE EXERTIONS IN STATIC PUSHING POSTURES.

PubMed

Sanjaya, Kadek Heri; Lee, Soomin; Sriwarno, Andar Bagus; Shimomura, Yoshihito; Katsuura, Tetsuo

2014-06-01

In order to reconcile contradictory results from previous studies on manual pushing, a study was conducted to examine the effect of trunk inclination on muscular activities, centre of pressure (COP) and force exertion during static pushing. Ten subjects pushed at 0 degrees, 15 degrees, 30 degrees, and 45 degrees body inclinations in parallel and staggered feet stances. Wall and ground force plates measured pushing force, wall COP, vertical ground reaction force (GRF) and ground COP. Electromyogram data were recorded at 10 trunk muscle sites. Pushing force was found to increase with body inclination. GRF peaked at 15 degrees and reached its lowest level at the 45 degrees inclination. The lowest wall force plate standard deviation of COP displacement was found at the 30 degrees inclination. The lowest low back muscular activity was found at the 15 degrees and 30 degrees inclinations. Based on force exertion, muscular load, and stability, the 30 degrees body inclination was found to be the best posture for static pushing. This study also showed asymmetry in muscular activity and force exertion which has been received less attention in manual pushing studies. These findings will require further study.

Botulinum toxin type-A affects mechanics of non-injected antagonistic rat muscles.

PubMed

Ateş, Filiz; Yucesoy, Can A

2018-08-01

Botulinum toxin type A (BTX-A) effects on the mechanics of non-injected antagonistic muscles are unknown. The aim was to test the following hypotheses in a rat model: BTX-A injected into gastrocnemius medialis (GM) and lateralis (GL) (1) decreases forces of the antagonistic tibialis anterior (TA) and extensor digitorum longus (EDL), (2) reduces length range of force exertion and (3) increases passive forces of the TA, and (4) changes inter-antagonistic and inter-synergistic epimuscular myofascial force transmission (EMFT). Two groups of Wistar rats were tested: BTX (0.1 units of BTX-A were injected to the GM and GL, each) and Control (saline injected). Five-days post, TA, EDL, GM-GL, and soleus distal and EDL proximal isometric forces were measured after TA lengthening. BTX-A exposure caused forces of all muscles to decrease significantly. TA and EDL active force drops (maximally by 37.3%) show inter-compartmental spread. Length range of force exertion of the TA did not change, but its passive force increased significantly (by 25%). The percentages of intramuscular connective tissue content of the TA and EDL was higher (BTX: 20.0 ± 4.9% and 19.3 ± 4.1% vs. control: 13.1 ± 5.4% and 14.5 ± 4.0%, respectively). Calf muscles' forces were not affected by TA length changes for both groups indicating lacking inter-antagonistic EMFT. However, BTX-A altered EDL proximo-distal force differences hence, inter-synergistic EMFT. A major novel finding is that BTX-A affects mechanics of non-injected antagonistic muscles in test conditions involving only limited EMFT. The effects indicating a stiffer muscle with no length range increase contradict some treatment aims, which require clinical testing. Copyright © 2018 Elsevier Ltd. All rights reserved.

Synthetic oligorotaxanes exert high forces when folding under mechanical load

NASA Astrophysics Data System (ADS)

Sluysmans, Damien; Hubert, Sandrine; Bruns, Carson J.; Zhu, Zhixue; Stoddart, J. Fraser; Duwez, Anne-Sophie

2018-01-01

Folding is a ubiquitous process that nature uses to control the conformations of its molecular machines, allowing them to perform chemical and mechanical tasks. Over the years, chemists have synthesized foldamers that adopt well-defined and stable folded architectures, mimicking the control expressed by natural systems1,2. Mechanically interlocked molecules, such as rotaxanes and catenanes, are prototypical molecular machines that enable the controlled movement and positioning of their component parts3-5. Recently, combining the exquisite complexity of these two classes of molecules, donor-acceptor oligorotaxane foldamers have been synthesized, in which interactions between the mechanically interlocked component parts dictate the single-molecule assembly into a folded secondary structure6-8. Here we report on the mechanochemical properties of these molecules. We use atomic force microscopy-based single-molecule force spectroscopy to mechanically unfold oligorotaxanes, made of oligomeric dumbbells incorporating 1,5-dioxynaphthalene units encircled by cyclobis(paraquat-p-phenylene) rings. Real-time capture of fluctuations between unfolded and folded states reveals that the molecules exert forces of up to 50 pN against a mechanical load of up to 150 pN, and displays transition times of less than 10 μs. While the folding is at least as fast as that observed in proteins, it is remarkably more robust, thanks to the mechanically interlocked structure. Our results show that synthetic oligorotaxanes have the potential to exceed the performance of natural folding proteins.

Forces exerted by a correlated fluid on embedded inclusions.

PubMed

Bitbol, Anne-Florence; Fournier, Jean-Baptiste

2011-06-01

We investigate the forces exerted on embedded inclusions by a fluid medium with long-range correlations, described by an effective scalar field theory. Such forces are the basis for the medium-mediated Casimir-like force. To study these forces beyond thermal average, it is necessary to define them in each microstate of the medium. Two different definitions of these forces are currently used in the literature. We study the assumptions underlying them. We show that only the definition that uses the stress tensor of the medium gives the sought-after force exerted by the medium on an embedded inclusion. If a second inclusion is embedded in the medium, the thermal average of this force gives the usual Casimir-like force between the two inclusions. The other definition can be used in the different physical case of an object that interacts with the medium without being embedded in it. We show in a simple example that the two definitions yield different results for the variance of the Casimir-like force.

Usability of prostaglandin monotherapy eye droppers.

PubMed

Drew, Tom; Wolffsohn, James S

2015-09-01

To determine the force needed to extract a drop from a range of current prostaglandin monotherapy eye droppers and how this related to the comfortable and maximum pressure subjects could exert. The comfortable and maximum pressure subjects could apply to an eye dropper constructed around a set of cantilevered pressure sensors and mounted above their eye was assessed in 102 subjects (mean 51.2±18.7 years), repeated three times. A load cell amplifier, mounted on a stepper motor controlled linear slide, was constructed and calibrated to test the force required to extract the first three drops from 13 multidose or unidose latanoprost medication eye droppers. The pressure that could be exerted on a dropper comfortably (25.9±17.7 Newtons, range 1.2-87.4) could be exceeded with effort (to 64.8±27.1 Newtons, range 19.9-157.8; F=19.045, p<0.001), and did not differ between repeats (F=0.609, p=0.545). Comfortable and maximum pressures exerted were correlated (r=0.618, p<0.001), neither were influenced strongly by age (r=0.138, p=0.168; r=-0.118, p=0237, respectively), but were lower in women than in men (F=12.757, p=0.001). The force required to expel a drop differed between dropper designs (F=22.528, p<0.001), ranging from 6.4 Newtons to 23.4 Newtons. The force needed to exert successive drops increased (F=36.373, p<0.001) and storing droppers in the fridge further increased the force required (F=7.987, p=0.009). Prostaglandin monotherapy droppers for glaucoma treatment vary in their resistance to extract a drop and with some a drop could not be comfortably achieved by half the population, which may affect compliance and efficacy. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.

Another Look at Rocket Thrust

ERIC Educational Resources Information Center

Hester, Brooke; Burris, Jennifer

2012-01-01

Rocket propulsion is often introduced as an example of Newton's third law. The rocket exerts a force on the exhaust gas being ejected; the gas exerts an equal and opposite force--the thrust--on the rocket. Equivalently, in the absence of a net external force, the total momentum of the system, rocket plus ejected gas, remains constant. The law of…

Assessment of flow forces on large wood in rivers

USDA-ARS?s Scientific Manuscript database

Large wood (LW) exerts an important influence on the geomorphology and ecology of streams and rivers. LW management activities are diverse, including placement in streams for restoring habitats or controlling bank erosion and mitigation of LW-related hazards to bridges and other structures. Flow f...

Filopodial retraction force is generated by cortical actin dynamics and controlled by reversible tethering at the tip

PubMed Central

Bornschlögl, Thomas; Romero, Stéphane; Vestergaard, Christian L.; Joanny, Jean-François; Van Nhieu, Guy Tran; Bassereau, Patricia

2013-01-01

Filopodia are dynamic, finger-like plasma membrane protrusions that sense the mechanical and chemical surroundings of the cell. Here, we show in epithelial cells that the dynamics of filopodial extension and retraction are determined by the difference between the actin polymerization rate at the tip and the retrograde flow at the base of the filopodium. Adhesion of a bead to the filopodial tip locally reduces actin polymerization and leads to retraction via retrograde flow, reminiscent of a process used by pathogens to invade cells. Using optical tweezers, we show that filopodial retraction occurs at a constant speed against counteracting forces up to 50 pN. Our measurements point toward retrograde flow in the cortex together with frictional coupling between the filopodial and cortical actin networks as the main retraction-force generator for filopodia. The force exerted by filopodial retraction, however, is limited by the connection between filopodial actin filaments and the membrane at the tip. Upon mechanical rupture of the tip connection, filopodia exert a passive retraction force of 15 pN via their plasma membrane. Transient reconnection at the tip allows filopodia to continuously probe their surroundings in a load-and-fail manner within a well-defined force range. PMID:24198333

Ways of increasing muscular activity by means of isometric muscular exertion

NASA Technical Reports Server (NTRS)

Kovalik, A. V.

1980-01-01

The effect of isometric muscular exertion on the human body was investigated by having subjects perform basic movements in a sitting position in the conventional manner with additional muscle tension at 50% maximum force and at maximum force. The pulse, arterial pressure, skin temperature, respiratory rate, minute respiratory volume and electrical activity of the muscles involved were all measured. Performance of the exercises with maximum muscular exertion for 20 sec and without movement resulted in the greatest shifts in these indices; in the conventional manner substantial changes did not occur; and with isometric muscular exertion with 50% maximum force with and without movement, optimal functional shifts resulted. The latter is recommended for use in industrial exercises for the prevention of hypodynamia. Ten exercises are suggested.

Virtue and Vice: Morality Police and Social Control in Islamic Regimes

DTIC Science & Technology

2017-12-01

religious, and militant groups since its emergence in 1994. Because of this, the forces of the MPVPV were employed to exert control over the behavior of...wounds.393 Men were also subject to a strict dress and appearance code. Once the Taliban seized control of Kabul, the group mandated that every man...aggressive campaign to establish control over hostile populations. In the United States’ ongoing conflict with militant groups such as the Taliban

The effect of aircraft control forces on pilot performance during instrument landings in a flight simulator.

PubMed

Hewson, D J; McNair, P J; Marshall, R N

2001-07-01

Pilots may have difficulty controlling aircraft at both high and low force levels due to larger variability in force production at these force levels. The aim of this study was to measure the force variability and landing performance of pilots during an instrument landing in a flight simulator. There were 12 pilots who were tested while performing 5 instrument landings in a flight simulator, each of which required different control force inputs. Pilots can produce the least force when pushing the control column to the right, therefore the force levels for the landings were set relative to each pilot's maximum aileron-right force. The force levels for the landings were 90%, 60%, and 30% of maximal aileron-right force, normal force, and 25% of normal force. Variables recorded included electromyographic activity (EMG), aircraft control forces, aircraft attitude, perceived exertion and deviation from glide slope and heading. Multivariate analysis of variance was used to test for differences between landings. Pilots were least accurate in landing performance during the landing at 90% of maximal force (p < 0.05). There was also a trend toward decreased landing performance during the landing at 25% of normal force. Pilots were more variable in force production during the landings at 60% and 90% of maximal force (p < 0.05). Pilots are less accurate at performing instrument landings when control forces are high due to the increased variability of force production. The increase in variability at high force levels is most likely associated with motor unit recruitment, rather than rate coding. Aircraft designers need to consider the reduction in pilot performance at high force levels, as well as pilot strength limits when specifying new standards.

Optical Pulling and Pushing Forces in Bilayer P T -Symmetric Structures

NASA Astrophysics Data System (ADS)

Alaee, Rasoul; Christensen, Johan; Kadic, Muamer

2018-01-01

We investigate the optical force exerted on a parity-time-symmetric bilayer made of balanced gain and loss. We show that an asymmetric optical pulling or pushing force can be exerted on this system depending on the direction of impinging light. The optical pulling or pushing force has a direct physical link to the optical characteristics embedded in the non-Hermitian bilayer. Furthermore, we suggest taking advantage of the optically generated asymmetric force to launch vibrations of an arbitrary shape, which is useful for the contactless probing of mechanical deformations.

The effect of firefighter protective garments, self-contained breathing apparatus and exertion in the heat on postural sway.

PubMed

White, Scott C; Hostler, David

2017-08-01

Fire suppression wearing thermal protective clothing (TPC) and self-contained breathing apparatus (SCBA) challenges a firefighter's balance and may explain firefighter falls. Postural control based on force plate centre of pressure (COP) was compared for healthy subjects wearing TPC and SCBA before and after 20 min of heavy physical exertion in hot conditions. Baseline measures with and without TPC and SCBA (two different SCBA cylinder masses) were compared before and after exertion that included elements of fire suppression activities in an environmental chamber. COP excursion and variability increased with exertion for TPC and SCBA conditions compared to non-stressed conditions. The two different cylinder masses had no significant effect. Wearing TPC and SCBA when physically stressed in a hot environment increases postural sway and exacerbates postural control. Subjects compensated for the extra mass and adjusted to control postural sway with the addition of TPC and SCBA, but the stress protocol amplified these adjustments. Practitioner Summary: Firefighters wear thermal protective clothing (TPC) and self-contained breathing apparatus (SCBA) when heat-stressed and fatigued. Wearing TPC and SCBA was found to negatively impact balance when stressed, but not for non-stressed or two different sized SCBA tanks. Simulating fire-ground conditions wearing TPC and SCBA should be considered for improving balance.

Biomechanical risk factors for carpal tunnel syndrome: a pooled study of 2474 workers

PubMed Central

Harris-Adamson, Carisa; Eisen, Ellen A; Kapellusch, Jay; Garg, Arun; Hegmann, Kurt T; Thiese, Matthew S; Dale, Ann Marie; Evanoff, Bradley; Burt, Susan; Bao, Stephen; Silverstein, Barbara; Merlino, Linda; Gerr, Fred; Rempel, David

2015-01-01

Background Between 2001 and 2010, five research groups conducted coordinated prospective studies of carpal tunnel syndrome (CTS) incidence among US workers from various industries and collected detailed subject-level exposure information with follow-up of symptoms, electrophysiological measures and job changes. Objective This analysis examined the associations between workplace biomechanical factors and incidence of dominant-hand CTS, adjusting for personal risk factors. Methods 2474 participants, without CTS or possible polyneuropathy at enrolment, were followed up to 6.5 years (5102 person-years). Individual workplace exposure measures of the dominant hand were collected for each task and included force, repetition, duty cycle and posture. Task exposures were combined across the workweek using time-weighted averaging to estimate job-level exposures. CTS case-criteria were based on symptoms and results of electrophysiological testing. HRs were estimated using Cox proportional hazard models. Results After adjustment for covariates, analyst (HR=2.17; 95% CI 1.38 to 3.43) and worker (HR=2.08; 95% CI 1.31 to 3.39) estimated peak hand force, forceful repetition rate (HR=1.84; 95% CI 1.19 to 2.86) and per cent time spent (eg, duty cycle) in forceful hand exertions (HR=2.05; 95% CI 1.34 to 3.15) were associated with increased risk of incident CTS. Associations were not observed between total hand repetition rate, per cent duration of all hand exertions, or wrist posture and incident CTS. Conclusions In this prospective multicentre study of production and service workers, measures of exposure to forceful hand exertion were associated with incident CTS after controlling for important covariates. These findings may influence the design of workplace safety programmes for preventing work-related CTS. PMID:25324489

Relationship between grasping force and features of single-channel intramuscular EMG signals.

PubMed

Kamavuako, Ernest Nlandu; Farina, Dario; Yoshida, Ken; Jensen, Winnie

2009-12-15

The surface electromyographic (sEMG) signal can be used for force prediction and control in prosthetic devices. Because of technological advances on implantable sensors, the use of intramuscular EMG (iEMG) is becoming a potential alternative to sEMG for the control of multiple degrees-of-freedom (DOF). An invasive system is not affected by crosstalk, typical of sEMG, and provides more stable and independent control sites. However, intramuscular recordings provide more local information because of their high selectivity, and may thus be less representative of the global muscle activity with respect to sEMG. This study investigates the capacity of selective single-channel iEMG recordings to represent the grasping force with respect to the use of sEMG with the aim of assessing if iEMG can be an effective method for proportional myoelectric control. sEMG and iEMG were recorded concurrently from 10 subjects who exerted six grasping force profiles from 0 to 25/50N. The linear correlation coefficient between features extracted from iEMG and force was approximately 0.9 and was not significantly different from the degree of correlation between sEMG and force. This result indicates that a selective iEMG recording is representative of the applied grasping force and can be used for proportional control.

Effects of laparoscopic instrument and finger on force perception: a first step towards laparoscopic force-skills training.

PubMed

Raghu Prasad, M S; Manivannan, M; Chandramohan, S M

2015-07-01

In laparoscopic surgery, no external feedback on the magnitude of the force exerted is available. Hence, surgeons and residents tend to exert excessive force, which leads to tissue trauma. Ability of surgeons and residents to perceive their own force output without external feedback is a critical factor in laparoscopic force-skills training. Additionally, existing methods of laparoscopic training do not effectively train residents and novices on force-skills. Hence, there is growing need for the development of force-based training curriculum. As a first step towards force-based laparoscopic skills training, this study analysed force perception difference between laparoscopic instrument and finger in contralateral bimanual passive probing task. The study compared the isometric force matching performance of novices, residents and surgeons with finger and laparoscopic instrument. Contralateral force matching paradigm was employed to analyse the force perception capability in terms of relative (accuracy), and constant errors in force matching. Force perception of experts was found to be better than novices and residents. Interestingly, laparoscopic instrument was more accurate in discriminating the forces than finger. The dominant hand attempted to match the forces accurately, whereas non-dominant hand (NH) overestimated the forces. Further, the NH of experts was found to be most accurate. Furthermore, excessive forces were applied at lower force levels and at very high force levels. Due to misperception of force, novices and residents applied excessive forces. However, experts had good control over force with both dominant and NHs. These findings suggest that force-based training curricula should not only have proprioception tasks, but should also include bimanual force-skills training exercises in order to improve force perception ability and hand skills of novices and residents. The results can be used as a performance metric in both box and virtual reality based force-skills training.

Quantification of cellular penetrative forces using lab-on-a-chip technology and finite element modeling

PubMed Central

Sanati Nezhad, Amir; Naghavi, Mahsa; Packirisamy, Muthukumaran; Bhat, Rama; Geitmann, Anja

2013-01-01

Tip-growing cells have the unique property of invading living tissues and abiotic growth matrices. To do so, they exert significant penetrative forces. In plant and fungal cells, these forces are generated by the hydrostatic turgor pressure. Using the TipChip, a microfluidic lab-on-a-chip device developed for tip-growing cells, we tested the ability to exert penetrative forces generated in pollen tubes, the fastest-growing plant cells. The tubes were guided to grow through microscopic gaps made of elastic polydimethylsiloxane material. Based on the deformation of the gaps, the force exerted by the elongating tubes to permit passage was determined using finite element methods. The data revealed that increasing mechanical impedance was met by the pollen tubes through modulation of the cell wall compliance and, thus, a change in the force acting on the obstacle. Tubes that successfully passed a narrow gap frequently burst, raising questions about the sperm discharge mechanism in the flowering plants. PMID:23630253

Measurement of plasma momentum exerted on target by a small helicon plasma thruster and comparison with direct thrust measurement.

PubMed

Takahashi, Kazunori; Komuro, Atsushi; Ando, Akira

2015-02-01

Momentum, i.e., force, exerted from a small helicon plasma thruster to a target plate is measured simultaneously with a direct thrust measurement using a thrust balance. The calibration coefficient relating a target displacement to a steady-state force is obtained by supplying a dc to a calibration coil mounted on the target, where a force acting to a small permanent magnet located near the coil is directly measured by using a load cell. As the force exerted by the plasma flow to the target plate is in good agreement with the directly measured thrust, the validity of the target technique is demonstrated under the present operating conditions, where the thruster is operated in steady-state. Furthermore, a calibration coefficient relating a swing amplitude of the target to an impulse bit is also obtained by pulsing the calibration coil current. The force exerted by the pulsed plasma, which is estimated from the measured impulse bit and the pulse width, is also in good agreement with that obtained for the steady-state operation; hence, the thrust assessment of the helicon plasma thruster by the target is validated for both the steady-state and pulsed operations.

Design of a Low-Cost Air Levitation System for Teaching Control Engineering.

PubMed

Chacon, Jesus; Saenz, Jacobo; Torre, Luis de la; Diaz, Jose Manuel; Esquembre, Francisco

2017-10-12

Air levitation is the process by which an object is lifted without mechanical support in a stable position, by providing an upward force that counteracts the gravitational force exerted on the object. This work presents a low-cost lab implementation of an air levitation system, based on open solutions. The rapid dynamics makes it especially suitable for a control remote lab. Due to the system's nature, the design can be optimized and, with some precision trade-off, kept affordable both in cost and construction effort. It was designed to be easily adopted to be used as both a remote lab and as a hands-on lab.

Climate forcing by anthropogenic aerosols

NASA Technical Reports Server (NTRS)

Charlson, R. J.; Schwartz, S. E.; Hales, J. M.; Cess, R. D.; Coakley, J. A., Jr.; Hansen, J. E.; Hofmann, D. J.

1992-01-01

Although long considered to be of marginal importance to global climate change, tropospheric aerosol contributes substantially to radiative forcing, and anthropogenic sulfate aerosol, in particular, has imposed a major perturbation to this forcing. Both the direct scattering of short-wavelength solar radiation and the modification of the shortwave reflective properties of clouds by sulfate aerosol particles increase planetary albedo, thereby exerting a cooling influence on the planet. Current climate forcing due to anthropogenic sulfate is estimated to be -1 to -2 watts per square meter, globally averaged. This perturbation is comparable in magnitude to current anthropogenic greenhouse gas forcing but opposite in sign. Thus, the aerosol forcing has likely offset global greenhouse warming to a substantial degree. However, differences in geographical and seasonal distributions of these forcings preclude any simple compensation. Aerosol effects must be taken into account in evaluating anthropogenic influences on past, current, and projected future climate and in formulating policy regarding controls on emission of greenhouse gases and sulfur dioxide. Resolution of such policy issues requires integrated research on the magnitude and geographical distribution of aerosol climate forcing and on the controlling chemical and physical processes.

Climate forcing by anthropogenic aerosols.

PubMed

Charlson, R J; Schwartz, S E; Hales, J M; Cess, R D; Coakley, J A; Hansen, J E; Hofmann, D J

1992-01-24

Although long considered to be of marginal importance to global climate change, tropospheric aerosol contributes substantially to radiative forcing, and anthropogenic sulfate aerosol in particular has imposed a major perturbation to this forcing. Both the direct scattering of shortwavelength solar radiation and the modification of the shortwave reflective properties of clouds by sulfate aerosol particles increase planetary albedo, thereby exerting a cooling influence on the planet. Current climate forcing due to anthropogenic sulfate is estimated to be -1 to -2 watts per square meter, globally averaged. This perturbation is comparable in magnitude to current anthropogenic greenhouse gas forcing but opposite in sign. Thus, the aerosol forcing has likely offset global greenhouse warming to a substantial degree. However, differences in geographical and seasonal distributions of these forcings preclude any simple compensation. Aerosol effects must be taken into account in evaluating anthropogenic influences on past, current, and projected future climate and in formulating policy regarding controls on emission of greenhouse gases and sulfur dioxide. Resolution of such policy issues requires integrated research on the magnitude and geographical distribution of aerosol climate forcing and on the controlling chemical and physical processes.

Method and apparatus for adaptive force and position control of manipulators

NASA Technical Reports Server (NTRS)

Seraji, Homayoun (Inventor)

1995-01-01

The described and improved multi-arm invention of this application presents three strategies for adaptive control of cooperative multi-arm robots which coordinate control over a common load. In the position-position control strategy, the adaptive controllers ensure that the end-effector positions of both arms track desired trajectories in Cartesian space despite unknown time-varying interaction forces exerted through a load. In the position-hybrid control strategy, the adaptive controller of one arm controls end-effector motions in the free directions and applied forces in the constraint directions; while the adaptive controller of the other arm ensures that the end-effector tracks desired position trajectories. In the hybrid-hybrid control strategy, the adaptive controllers ensure that both end-effectors track reference position trajectories while simultaneously applying desired forces on the load. In all three control strategies, the cross-coupling effects between the arms are treated as disturbances which are compensated for by the adaptive controllers while following desired commands in a common frame of reference. The adaptive controllers do not require the complex mathematical model of the arm dynamics or any knowledge of the arm dynamic parameters or the load parameters such as mass and stiffness. Circuits in the adaptive feedback and feedforward controllers are varied by novel adaptation laws.

Determination of the myosin step size from mechanical and kinetic data.

PubMed Central

Pate, E; White, H; Cooke, R

1993-01-01

During muscle contraction, work is generated when a myosin cross-bridge attaches to an actin filament and exerts a force on it through some power-stroke distance, h. At the end of this power stroke, attached myosin heads are carried into regions where they exert a negative force on the actin filament (the drag stroke) and where they are released rapidly from actin by ATP binding. Although the length of the power stroke remains controversial, average distance traversed in the drag-stroke region can be determined when one knows both rate of cross-bridge dissociation and filament-sliding velocity. At maximum contraction velocity, the average force exerted in the drag stroke must balance that exerted in the power stroke. We discuss here a simple model of cross-bridge interaction that allows one to calculate the force exerted in the drag stroke and to relate this to the power-stroke distance h traversed by cross-bridges in the positive-force region. Both the rate at which myosin can be dissociated from actin and the velocity at which an actin filament can be translated have been measured for a series of myosin isozymes and for different substrates, producing a wide range of values for each. Nonetheless, we show here that the rate of myosin dissociation from actin correlates well with the velocity of filament sliding, providing support for the simple model presented and suggesting that the power stroke is approximately 10 nm in length. PMID:8460156

Issues in impedance selection and input devices for multijoint powered orthotics.

PubMed

Lemay, M A; Hogan, N; van Dorsten, J W

1998-03-01

We investigated the applicability of impedance controllers to robotic orthoses for arm movements. We had tetraplegics turn a crank using their paralyzed arm propelled by a planar robot manipulandum. The robot was under impedance control, and chin motion served as command source. Stiffness varied between 50, 100, or 200 N/m and damping varied between 5 or 15 N/m/s. Results indicated that a low stiffness and high viscosity provided better directional control of the tangential force exerted on the crank.

Axial force and efficiency tests of fixed center variable speed belt drive

NASA Technical Reports Server (NTRS)

Bents, D. J.

1981-01-01

An investigation of how the axial force varies with the centerline force at different speed ratios, speeds, and loads, and how the drive's transmission efficiency is affected by these related forces is described. The tests, intended to provide a preliminary performance and controls characterization for a variable speed belt drive continuously variable transmission (CVT), consisted of the design and construction of an experimental test rig geometrically similar to the CVT, and operation of that rig at selected speed ratios and power levels. Data are presented which show: how axial forces exerted on the driver and driven sheaves vary with the centerline force at constant values of speed ratio, speed, and output power; how the transmission efficiency varies with centerline force and how it is also a function of the V belt coefficient; and the axial forces on both sheaves as normalized functions of the traction coefficient.

Determination of the forces imposed by micro and nanopipettes during DOPC: DOPS liposome manipulation.

PubMed

Allen, Kathleen B; Layton, Bradley E

2009-11-01

Using micropipette-based probing methods and an image processing algorithm for measuring deformation, the bending energies of aspirated DOPC:DOPS liposomes were estimated both before and during manipulation with an injection pipette. We found that unlike cells, which are penetrable with pipettes as large as 2mum in diameter and at speeds as slow as 4mum/s, liposomes, without a cytoskeleton to resist deformation, are impenetrable with pipettes as small as 25nm in diameter and at speeds as great as 4000mum/s. Using energy calculations and the previously published mechanical properties of DOPC:DOPS liposomes, the forces that injection pipettes of various sizes can exert onto liposomes during probing were estimated. Forces ranged from approximately 1pN to 6pN, and the forces exerted onto these liposomes increased as pipette size diminished. The quantification of the amount of force exerted on liposomes or cells during manipulation can assist in minimizing the damage during single-liposome, single-cell, or single-organelle injections and surgeries.

Antagonistic actuation and stiffness control in soft inflatable robots

NASA Astrophysics Data System (ADS)

Althoefer, Kaspar

2018-06-01

Soft robots promise solutions for a wide range of applications that cannot be achieved with traditional, rigid-component robots. A key challenge is the creation of robotic structures that can vary their stiffness at will, for example, by using antagonistic actuators, to optimize their interaction with the environment and be able to exert high forces.

Forcings and feedbacks by land ecosystem changes on climate change

NASA Astrophysics Data System (ADS)

Betts, R. A.

2006-12-01

Vegetation change is involved in climate change through both forcing and feedback processes. Emissions of CO{2} from past net deforestation are estimated to have contributed approximately 0.22 0.51 Wm - 2 to the overall 1.46 Wm - 2 radiative forcing by anthropogenic increases in CO{2} up to the year 2000. Deforestation-induced increases in global mean surface albedo are estimated to exert a radiative forcing of 0 to -0.2 Wm - 2, and dust emissions from land use may exert a radiative forcing of between approximately +0.1 and -0.2 Wm - 2. Changes in the fluxes of latent and sensible heat due to tropical deforestation are simulated to have exerted other local warming effects which cannot be quantified in terms of a Wm - 2 radiative forcing, with the potential for remote effects through changes in atmospheric circulation. With tropical deforestation continuing rapidly, radiative forcing by surface albedo change may become less useful as a measure of the forcing of climate change by changes in the physical properties of the land surface. Although net global deforestation is continuing, future scenarios used for climate change prediction suggest that fossil fuel emissions of CO{2} may continue to increase at a greater rate than land use emissions and therefore continue to increase in dominance as the main radiative forcing. The CO{2} rise may be accelerated by up to 66% by feedbacks arising from global soil carbon loss and forest dieback in Amazonia as a consequence of climate change, and Amazon forest dieback may also exert feedbacks through changes in the local water cycle and increases in dust emissions.

Update: Exertional rhabdomyolysis, active component, U.S. Army, Navy, Air Force, and Marine Corps, 2011-2015.

PubMed

Armed Forces Health Surveillance Branch

2016-03-01

Among active component members of the U.S. Army, Navy, Air Force, and Marine Corps in 2015, there were 456 incident episodes of rhabdomyolysis likely due to physical exertion or heat stress ("exertional rhabdomyolysis"). Annual rates of incident diagnoses of exertional rhabdomyolysis increased 17% between 2014 and 2015. In 2015, the highest incidence rates occurred in service members who were male; younger than 20 years of age; black, non-Hispanic; members of the Marine Corps and Army; recruit trainees; and in combat-specific occupations. Most cases of exertional rhabdomyolysis were diagnosed at installations that support basic combat/recruit training or major ground combat units of the Army or Marine Corps. Medical care providers should consider exertional rhabdomyolysis in the differential diagnosis when service members (particularly recruits) present with muscular pain and swelling, limited range of motion, or the excretion of dark urine (e.g., myoglobinuria) after strenuous physical activity, particularly in hot, humid weather.

New weight factor for Brownian force exerted on micro/nano-particles in air flow

NASA Astrophysics Data System (ADS)

Zhang, Peijie; Lin, Jianzhong; Ku, Xiaoke

2018-05-01

In order to effectively describe the effect of Brownian force exerted on the micro/nano-particles in air flow, a new weight factor, which is defined as the ratio of the characteristic velocity of the Brownian motion to the macroscopic velocity, is proposed and applied to the particle settlement under gravity. Results show that the weight factor can quantitatively evaluate the effect of Brownian force on the particle motion. Moreover, the value of the weight factor can also be used to judge the particle motion pattern and determine whether the Brownian force should be taken into account.

Acoustic radiation force control: Pulsating spherical carriers.

PubMed

Rajabi, Majid; Mojahed, Alireza

2018-02-01

The interaction between harmonic plane progressive acoustic beams and a pulsating spherical radiator is studied. The acoustic radiation force function exerted on the spherical body is derived as a function of the incident wave pressure and the monopole vibration characteristics (i.e., amplitude and phase) of the body. Two distinct strategies are presented in order to alter the radiation force effects (i.e., pushing and pulling states) by changing its magnitude and direction. In the first strategy, an incident wave field with known amplitude and phase is considered. It is analytically shown that the zero- radiation force state (i.e., radiation force function cancellation) is achievable for specific pulsation characteristics belong to a frequency-dependent straight line equation in the plane of real-imaginary components (i.e., Nyquist Plane) of prescribed surface displacement. It is illustrated that these characteristic lines divide the mentioned displacement plane into two regions of positive (i.e., pushing) and negative (i.e., pulling) radiation forces. In the second strategy, the zero, negative and positive states of radiation force are obtained through adjusting the incident wave field characteristics (i.e., amplitude and phase) which insonifies the radiator with prescribed pulsation characteristics. It is proved that zero radiation force state occurs for incident wave pressure characteristics belong to specific frequency-dependent circles in Nyquist plane of incident wave pressure. These characteristic circles divide the Nyquist plane into two distinct regions corresponding to positive (out of circles) and negative (in the circles) values of radiation force function. It is analytically shown that the maximum amplitude of negative radiation force is exactly equal to the amplitude of the (positive) radiation force exerted upon the sphere in the passive state, by the same incident field. The developed concepts are much more deepened by considering the required power supply for distinct cases of zero, negative and positive radiation force states along with the frequency dependent asymmetry index. In addition, considering the effect of phase difference between the incident wave field and the pulsating object, and its possible variation with respect to spatial position of object, some practical points about the spatial average of generated radiation force, the optimal state of operation, the stability of zero radiation force states and the possibly of precise motion control are discussed. This work would extend the novel concept of smart carriers to and may be helpful for robust single-beam acoustic handling techniques. Furthermore, the shown capability of precise motion control may be considered as a new way toward smart acoustic driven micro-mechanisms and micro-machines. Copyright © 2017 Elsevier B.V. All rights reserved.

Adaptive control of dual-arm robots

NASA Technical Reports Server (NTRS)

Seraji, H.

1987-01-01

Three strategies for adaptive control of cooperative dual-arm robots are described. In the position-position control strategy, the adaptive controllers ensure that the end-effector positions of both arms track desired trajectories in Cartesian space despite unknown time-varying interaction forces exerted through the load. In the position-hybrid control strategy, the adaptive controller of one arm controls end-effector motions in the free directions and applied forces in the constraint directions, while the adaptive controller of the other arm ensures that the end-effector tracks desired position trajectories. In the hybrid-hybrid control strategy, the adaptive controllers ensure that both end-effectors track reference position trajectories while simultaneously applying desired forces on the load. In all three control strategies, the cross-coupling effects between the arms are treated as disturbances which are rejected by the adaptive controllers while following desired commands in a common frame of reference. The adaptive controllers do not require the complex mathematical model of the arm dynamics or any knowledge of the arm dynamic parameters or the load parameters such as mass and stiffness. The controllers have simple structures and are computationally fast for on-line implementation with high sampling rates.

Determinants and magnitudes of manual force strengths and joint moments during two-handed standing maximal horizontal pushing and pulling.

PubMed

Chow, Amy Y; Dickerson, Clark R

2016-04-01

Pushing and pulling are common occupational exertions that are increasingly associated with musculoskeletal complaints. This study focuses on the sensitivity of shoulder capacity to gender, handle height, exertion type (push or pull) and handle orientation for these tasks. All factors except for handle orientation influenced unilateral and total manual force strength (p < 0.01), with exertion type being the most influential. Interaction effects also existed between handle height and exertion type. Additionally, joint moments at the shoulders and low back were influenced by all factors studied (p < 0.01), with exertion type again being most influential. Knowledge of the relative influence of multiple factors on shoulder capacity can provide guidance regarding these factors when designing or evaluating occupational pushing and pulling tasks for a diverse population. Practitioner Summary: pushing and pulling comprise nearly half of all manual materials handling tasks. Practitioners often assess, design or modify these tasks while incorporating constraints, including manual force direction and handle interface. This study provides guidance to aid design of pushing and pulling tasks in the context of shoulder physical capacity.

Biomechanical analysis of loading/unloading a ladder on a truck.

PubMed

Moriguchi, Cristiane Shinohara; Carnaz, Leticia; de Miranda, Luiz Carlos; Marklin, Richard William; Coury, Helenice Jane Cote Gil

2012-01-01

Loading/unloading a ladder on vehicles are frequent tasks and involve overhead handling that may expose workers to risk factors of shoulder musculoskeletal disorders. The objective of the present study was to evaluate posture, forces required and perceived exertion when loading and unloading the ladder on a utility truck. Thirteen male overhead line workers from an electric utility in Brazil participated in this study. Shoulder elevation angle was measured using inclinometers. The required force to load/unload the ladder was measured by dynamometer. Subjective assessment of the perceived exertion was recorded to compare the exertion reported during the test conditions to the field conditions. The task of loading/unloading the ladder presented risks of shoulder musculoskeletal disorders (MSDs) to workers because it requires high levels of force (approximately 60% of the maximal force) combined with overhead posture of the shoulders (more than 100° from the neutral posture). Age and height presented to interfere in biomechanical risks presented in load/unload task. There was no significant difference between the subjective exertion during the test conditions and handling the ladder in the field. Ergonomic intervention is recommended to reduce these risks for shoulder MSDs.

Design of a Low-Cost Air Levitation System for Teaching Control Engineering

PubMed Central

Chacon, Jesus; Saenz, Jacobo; de la Torre, Luis; Diaz, Jose Manuel; Esquembre, Francisco

2017-01-01

Air levitation is the process by which an object is lifted without mechanical support in a stable position, by providing an upward force that counteracts the gravitational force exerted on the object. This work presents a low-cost lab implementation of an air levitation system, based on open solutions. The rapid dynamics makes it especially suitable for a control remote lab. Due to the system’s nature, the design can be optimized and, with some precision trade-off, kept affordable both in cost and construction effort. It was designed to be easily adopted to be used as both a remote lab and as a hands-on lab. PMID:29023381

Children with Heavy Prenatal Alcohol Exposure Experience Reduced Control of Isotonic Force

PubMed Central

Nguyen, Tanya T.; Levy, Susan S.; Riley, Edward P.; Thomas, Jennifer D.; Simmons, Roger W.

2013-01-01

Background Heavy prenatal alcohol exposure can result in diverse and extensive damage to the central nervous system, including the cerebellum, basal ganglia, and cerebral cortex. Given that these brain regions are involved in the generation and maintenance of motor force, we predicted that prenatal alcohol exposure would adversely affect this parameter of motor control. We previously reported that children with gestational alcohol exposure experience significant deficits in regulating isometric (i.e., constant) force. The purpose of the present study was to determine if these children exhibit similar deficits when producing isotonic (i.e., graded) force. Methods Children with heavy prenatal alcohol exposure and typically developing children completed a series of isotonic force contractions by exerting force on a load cell to match a criterion target force displayed on a computer monitor. Two levels of target force (5% or 20% of maximum voluntary force) were investigated in combination with varying levels of visual feedback. Results Compared to controls, children with heavy prenatal alcohol exposure generated isotonic force signals that were less accurate, more variable, and less complex in the time domain compared to control children. Specifically, interactions were found between group and visual feedback for response accuracy and signal complexity, suggesting that these children have greater difficulty altering their motor output when visual feedback is low. Conclusions These data suggest that prenatal alcohol exposure produces deficits in regulating isotonic force, which presumably result from alcohol-related damage to developing brain regions involved in motor control. These children will most likely experience difficulty performing basic motor skills and daily functional skills that require coordination of finely graded force. Therapeutic strategies designed to increase feedback and, consequently, facilitate visual-motor integration could improve isotonic force production in these children. PMID:22834891

Dual towline spin-recovery device

NASA Technical Reports Server (NTRS)

White, W. L. (Inventor)

1985-01-01

A device which corrects aerodynamic spin is described wherein a parachute exerts antispin forces on an aircraft to effect spin recovery. The dual parachute towlines and are each attached to the parachute and are attached to the rear fuselage equidistant to and on opposite sides of the aircraft centerline. As the parachute is deployed during spin, the parachute force acts through only the towing and exerts its force outboard of center on the aircraft. As a result, the parachute exerts not only an antispin torque, but additionally causes the aircraft to roll, creating a gyroscopic antispin rolling moment. The additional antispin rolling moment facilitates spin recovery by permitting a relatively smaller parachute to accomplish spin recovery equivalent to that of a larger parachute attached to the center of the rear fuselage.

CONTROL ROD DRIVE

DOEpatents

Chapellier, R.A.

1960-05-24

BS>A drive mechanism was invented for the control rod of a nuclear reactor. Power is provided by an electric motor and an outside source of fluid pressure is utilized in conjunction with the fluid pressure within the reactor to balance the loadings on the motor. The force exerted on the drive mechanism in the direction of scramming the rod is derived from the reactor fluid pressure so that failure of the outside pressure source will cause prompt scramming of the rod.

Covert Action: A Systems Approach

DTIC Science & Technology

2014-12-01

consider a covert action to support rebels within the Colombian province of Panama. The objective was relatively simple: support the creation of an...prevented Colombian reinforcements from either landing ashore or transiting from Colon to Panama City. The junta declared...154 He also exerted a significant level of control over the event by immediately deploying gunboats to the port which ensured that Colombian forces

Surface EMG in advanced hand prosthetics.

PubMed

Castellini, Claudio; van der Smagt, Patrick

2009-01-01

One of the major problems when dealing with highly dexterous, active hand prostheses is their control by the patient wearing them. With the advances in mechatronics, building prosthetic hands with multiple active degrees of freedom is realisable, but actively controlling the position and especially the exerted force of each finger cannot yet be done naturally. This paper deals with advanced robotic hand control via surface electromyography. Building upon recent results, we show that machine learning, together with a simple downsampling algorithm, can be effectively used to control on-line, in real time, finger position as well as finger force of a highly dexterous robotic hand. The system determines the type of grasp a human subject is willing to use, and the required amount of force involved, with a high degree of accuracy. This represents a remarkable improvement with respect to the state-of-the-art of feed-forward control of dexterous mechanical hands, and opens up a scenario in which amputees will be able to control hand prostheses in a much finer way than it has so far been possible.

Bottom-up vs. top-down effects on terrestrial insect herbivores: a meta-analysis.

PubMed

Vidal, Mayra C; Murphy, Shannon M

2018-01-01

Primary consumers are under strong selection from resource ('bottom-up') and consumer ('top-down') controls, but the relative importance of these selective forces is unknown. We performed a meta-analysis to compare the strength of top-down and bottom-up forces on consumer fitness, considering multiple predictors that can modulate these effects: diet breadth, feeding guild, habitat/environment, type of bottom-up effects, type of top-down effects and how consumer fitness effects are measured. We focused our analyses on the most diverse group of primary consumers, herbivorous insects, and found that in general top-down forces were stronger than bottom-up forces. Notably, chewing, sucking and gall-making herbivores were more affected by top-down than bottom-up forces, top-down forces were stronger than bottom-up in both natural and controlled (cultivated) environments, and parasitoids and predators had equally strong top-down effects on insect herbivores. Future studies should broaden the scope of focal consumers, particularly in understudied terrestrial systems, guilds, taxonomic groups and top-down controls (e.g. pathogens), and test for more complex indirect community interactions. Our results demonstrate the surprising strength of forces exerted by natural enemies on herbivorous insects, and thus the necessity of using a tri-trophic approach when studying insect-plant interactions. © 2017 John Wiley & Sons Ltd/CNRS.

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

PubMed Central

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

2012-01-01

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

Workplace and individual risk factors for carpal tunnel syndrome.

PubMed

Burt, Susan; Crombie, Ken; Jin, Yan; Wurzelbacher, Steve; Ramsey, Jessica; Deddens, James

2011-12-01

To quantify the relationship between workplace physical factors, particularly hand activity level (HAL) and forceful exertion and carpal tunnel syndrome (CTS), while taking into account individual factors. To compare quantitative exposure assessment measures with more practical ratings-based measures. In a group of healthcare and manufacturing workers, each study participant's job tasks were evaluated for HAL, forceful exertion and other physical stressors and videotaped for further analysis, including frequency and duration of exertion and postural deviation. Electrodiagnostic testing of median and ulnar nerves and questionnaires were administered to all participants. A CTS case required median mononeuropathy and symptoms on hand diagrams in fingers 1-3. Multiple logistic regression models were used to analyse associations between job and individual factors and CTS. Of 477 workers studied, 57 (11.9%) were dominant hand CTS cases. Peak force ≥70% maximum voluntary contraction versus <20% maximum voluntary contraction resulted in an OR of 2.74 (1.32-5.68) for CTS. Among those with a body mass index ≥30, the OR for ≥15 exertions per minute was 3.35 (1.14-9.87). Peak worker ratings of perceived exertion increased the odds for CTS by 1.14 (1.01-1.29) for each unit increase on the 10-point scale. The odds for CTS increased by 1.38 (1.05-1.81) for each unit increase on the HAL 10-point scale among men, but not women. Combined force and HAL values above the ACGIH TLV for HAL resulted in an OR of 2.96 (1.51-5.80) for CTS. Quantitative and ratings-based job exposure measures were each associated with CTS. Obesity increased the association between frequency of exertion and CTS.

Hydrophilic-coated catheters for intermittent catheterisation reduce urethral micro trauma: a prospective, randomised, participant-blinded, crossover study of three different types of catheters.

PubMed

Stensballe, J; Looms, D; Nielsen, P N; Tvede, M

2005-12-01

To compare two hydrophilic-coated (SpeediCath and LoFric and one uncoated gel-lubricated catheter (InCare Advance Plus) concerning withdrawal friction force and urethral micro trauma. 49 healthy male volunteers participated in this prospective, randomised, blinded, crossover study of three different bladder catheters. The withdrawal friction force was measured, and urine analysis of blood, nitrite and leucocytes, microbiological analysis of urine cultures and subjective evaluation of the catheters were performed. 40 participants completed the study and were included in the analysis. SpeediCath exerted a significantly lower mean withdrawal friction force and work than the gel-lubricated uncoated catheter, whereas LoFric exerted a significantly higher mean friction force than both of the other catheters. The hydrophilic catheters caused less microscopic haematuria and less pain than the gel-lubricated uncoated catheter. Furthermore, 93% of the participants preferred the hydrophilic catheters. Hydrophilic-coated catheters perform better than uncoated catheters with regard to haematuria and preference. SpeediCath, but not LoFric, exerts less withdrawal friction force than InCare Advance Plus.

A technique for studying cardiac myosin dynamics using optical tweezers

NASA Astrophysics Data System (ADS)

Paolino, Michael; Migirditch, Sam; Nesmelov, Yuri; Hester, Brooke; Appalachian State Biophysics; Optical Sciences Facility Team

A primary protein involved in human muscle contraction is myosin, which exists in α- and β- isoforms. Myosin exerts forces on actin filaments when ATP is present, driving muscle contraction. A significant decrease in the population of cardiac α-myosin has been linked to heart failure. It is proposed that slow β-myosin in a failing heart could, through introduction of a drug, be made to mimic the action of α-myosin, thereby improving cardiac muscle performance. In working towards testing this hypothesis, the focus of this work is to develop a technique to measure forces exerted by myosin on actin using optical tweezers. An actin-myosin arrangement is constructed between two optically trapped polystyrene microspheres. The displacement of a microsphere is monitored when ATP is introduced, and the force responsible is measured. With this achieved, we can then modify the actin-myosin arrangement, for example with varying amounts of α- and β- myosin and test the effects on forces exerted. In this work, assemblies of actin and myosin molecules and preliminary force measurements are discussed. North Carolina Space Grant.

Lightweight Seat Lever Operation Characteristics

NASA Technical Reports Server (NTRS)

Rajulu, Sudhakar

1999-01-01

In 1999, a Shuttle crew member was unable to operate the backrest lever for the lightweight seat in microgravity. It is essential that crew members can adjust this backrest lever, which is titled forward during launch and then moved backward upon reaching orbit. This adjustment is needed to cushion the crew members during an inadvertent crash landing situation. JSCs Anthropometry and Biomechanics Facility (ABF) performed an evaluation of the seat controls and provided recommendations on whether the seat lever positions and operations should be modified. The original Shuttle seats were replaced with new lightweight seats whose controls were moved, with one control at the front and the other at the back. The ABF designed a 12-person experiment to investigate the amount of pull force exerted by suited subjects, when controls were placed in the front and back of the lightweight seat. Each subject was asked to perform the pull test at least three times for each combination of lever position and suit pressure conditions. The results showed that, in general, the subjects were able to pull on the lever at the back position with only about half the amount of force that they were able to exert on the lever at the front position. In addition, the results also showed that subjects wearing the pressurized suit were unable to reach the seat lever when it was located at the back. The pull forces on the front lever diminished about 50% when subjects wore pressurized suits. Based on these results from this study, it was recommended that the levers should not be located in the back position. Further investigation is needed to determine whether the levers at the front of the seat could be modified or adjusted to increase the leverage for crew members wearing pressurized launch/escape suits.

Regulation of the position of statoliths in Chara rhizoids.

PubMed

Hejnowicz, Z; Sievers, A

1981-01-01

The behavior of statoliths in rhizoids differently oriented with respect to the gravity vector indicates that there are cytoskeleton elements which exert forces on the statoliths, mostly in the longitudinal directions. Compared to the sum of the forces acting on a statolith, the gravitational force is a relatively small component, i.e., less than 1/5 of the cytoskeleton force. The balance is disturbed by displacing the rhizoid from the normal vertical orientation. It is also reversibly disturbed by cytochalasin B such that some statoliths move against the gravity force. Phalloidin stabilizes the position of the statoliths against cytochalasin B. We infer that microfilaments are involved in controlling the position of statoliths, and that there is a considerable tension on these microfilaments. The vibration frequency of the microfilaments corresponding to this tension is in the ultrasonic range.

Dynamics of glide avalanches and snow gliding

NASA Astrophysics Data System (ADS)

Ancey, Christophe; Bain, Vincent

2015-09-01

In recent years, due to warmer snow cover, there has been a significant increase in the number of cases of damage caused by gliding snowpacks and glide avalanches. On most occasions, these have been full-depth, wet-snow avalanches, and this led some people to express their surprise: how could low-speed masses of wet snow exert sufficiently high levels of pressure to severely damage engineered structures designed to carry heavy loads? This paper reviews the current state of knowledge about the formation of glide avalanches and the forces exerted on simple structures by a gliding mass of snow. One particular difficulty in reviewing the existing literature on gliding snow and on force calculations is that much of the theoretical and phenomenological analyses were presented in technical reports that date back to the earliest developments of avalanche science in the 1930s. Returning to these primary sources and attempting to put them into a contemporary perspective are vital. A detailed, modern analysis of them shows that the order of magnitude of the forces exerted by gliding snow can indeed be estimated correctly. The precise physical mechanisms remain elusive, however. We comment on the existing approaches in light of the most recent findings about related topics, including the physics of granular and plastic flows, and from field surveys of snow and avalanches (as well as glaciers and debris flows). Methods of calculating the forces exerted by glide avalanches are compared quantitatively on the basis of two case studies. This paper shows that if snow depth and density are known, then certain approaches can indeed predict the forces exerted on simple obstacles in the event of glide avalanches or gliding snow cover.

Low-Back Biomechanics and Static Stability During Isometric Pushing

PubMed Central

Granata, Kevin P.; Bennett, Bradford C.

2006-01-01

Pushing and pulling tasks are increasingly prevalent in industrial workplaces. Few studies have investigated low-back biomechanical risk factors associated with pushing, and we are aware of none that has quantified spinal stability during pushing exertions. Data recorded from 11 healthy participants performing isometric pushing exertions demonstrated that trunk posture, vector force direction of the applied load, and trunk moment were influenced (p < .01) by exertion level, elevation of the handle for the pushing task, and foot position. A biomechanical model was used to analyze the posture and hand force data gathered from the pushing exertions. Model results indicate that pushing exertions provide significantly (p < .01) less stability than lifting when antagonistic cocontraction is ignored. However, stability can be augmented by recruitment of muscle cocontraction. Results suggest that cocontraction may be recruited to compensate for the fact that equilibrium mechanics provide little intrinsic trunk stiffness and stability during pushing exertions. If one maintains stability by means of cocontraction, additional spinal load is thereby created, increasing the risk of overload injury. Thus it is important to consider muscle cocontraction when evaluating the biomechanics of pushing exertions. Potential applications of this research include improved assessment of biomechanical risk factors for the design of industrial pushing tasks. PMID:16435695

Update: Exertional rhabdomyolysis, active component, U.S. Armed Forces, 2012-2016.

PubMed

2017-03-01

Among active component service members in 2016, there were 525 incident diagnoses of rhabdomyolysis likely due to physical exertion and/or heat stress ("exertional rhabdomyolysis"). The crude incidence rate in 2016 was 40.7 cases per 100,000 person-years. Annual rates of incident diagnoses of exertional rhabdomyolysis increased 46.2% between 2013 and 2016, with the greatest percentage change occurring between 2014 and 2015. In 2016, relative to their respective counterparts, the highest incidence rates of exertional rhabdomyolysis affected service members who were male; younger than 20 years of age; and black, non-Hispanic. During the surveillance period, annual incidence rates were highest among service members of the Marine Corps, intermediate among those in the Army, and lowest among those in the Air Force and Navy. Most cases of exertional rhabdomyolysis were diagnosed at installations that support basic combat/recruit training or major ground combat units of the Army or the Marine Corps. Medical care providers should consider exertional rhabdomyolysis in the differential diagnosis when service members (particularly recruits) present with muscular pain or swelling, limited range of motion, or the excretion of dark urine (possibly due to myoglobinuria) after strenuous physical activity, particularly in hot, humid weather.

Radiative Forcing Due to Major Aerosol Emitting Sectors in China and India

NASA Technical Reports Server (NTRS)

Streets, David G.; Shindell, Drew Todd; Lu, Zifeng; Faluvegi, Greg

2013-01-01

Understanding the radiative forcing caused by anthropogenic aerosol sources is essential for making effective emission control decisions to mitigate climate change. We examined the net direct plus indirect radiative forcing caused by carbonaceous aerosol and sulfur emissions in key sectors of China and India using the GISS-E2 chemistry-climate model. Diesel trucks and buses (67 mW/ sq. m) and residential biofuel combustion (52 mW/ sq. m) in India have the largest global mean, annual average forcings due mainly to the direct and indirect effects of BC. Emissions from these two sectors in China have near-zero net global forcings. Coal-fired power plants in both countries exert a negative forcing of about -30 mW/ sq. m from production of sulfate. Aerosol forcings are largest locally, with direct forcings due to residential biofuel combustion of 580 mW/ sq. m over India and 416 mW/ sq. m over China, but they extend as far as North America, Europe, and the Arctic

The Effect of Temporal Perception on Weight Perception

PubMed Central

Kambara, Hiroyuki; Shin, Duk; Kawase, Toshihiro; Yoshimura, Natsue; Akahane, Katsuhito; Sato, Makoto; Koike, Yasuharu

2013-01-01

A successful catch of a falling ball requires an accurate estimation of the timing for when the ball hits the hand. In a previous experiment in which participants performed ball-catching task in virtual reality environment, we accidentally found that the weight of a falling ball was perceived differently when the timing of ball load force to the hand was shifted from the timing expected from visual information. Although it is well known that spatial information of an object, such as size, can easily deceive our perception of its heaviness, the relationship between temporal information and perceived heaviness is still not clear. In this study, we investigated the effect of temporal factors on weight perception. We conducted ball-catching experiments in a virtual environment where the timing of load force exertion was shifted away from the visual contact timing (i.e., time when the ball hit the hand in the display). We found that the ball was perceived heavier when force was applied earlier than visual contact and lighter when force was applied after visual contact. We also conducted additional experiments in which participants were conditioned to one of two constant time offsets prior to testing weight perception. After performing ball-catching trials with 60 ms advanced or delayed load force exertion, participants’ subjective judgment on the simultaneity of visual contact and force exertion changed, reflecting a shift in perception of time offset. In addition, timing of catching motion initiation relative to visual contact changed, reflecting a shift in estimation of force timing. We also found that participants began to perceive the ball as lighter after conditioning to 60 ms advanced offset and heavier after the 60 ms delayed offset. These results suggest that perceived heaviness depends not on the actual time offset between force exertion and visual contact but on the subjectively perceived time offset between them and/or estimation error in force timing. PMID:23450805

Generation of synthetic surface electromyography signals under fatigue conditions for varying force inputs using feedback control algorithm.

PubMed

Venugopal, G; Deepak, P; Ghosh, Diptasree M; Ramakrishnan, S

2017-11-01

Surface electromyography is a non-invasive technique used for recording the electrical activity of neuromuscular systems. These signals are random, complex and multi-component. There are several techniques to extract information about the force exerted by muscles during any activity. This work attempts to generate surface electromyography signals for various magnitudes of force under isometric non-fatigue and fatigue conditions using a feedback model. The model is based on existing current distribution, volume conductor relations, the feedback control algorithm for rate coding and generation of firing pattern. The result shows that synthetic surface electromyography signals are highly complex in both non-fatigue and fatigue conditions. Furthermore, surface electromyography signals have higher amplitude and lower frequency under fatigue condition. This model can be used to study the influence of various signal parameters under fatigue and non-fatigue conditions.

Dual-arm manipulators with adaptive control

NASA Technical Reports Server (NTRS)

Seraji, Homayoun (Inventor)

1991-01-01

The described and improved multi-arm invention of this application presents three strategies for adaptive control of cooperative multi-arm robots which coordinate control over a common load. In the position-position control strategy, the adaptive controllers ensure that the end-effector positions of both arms track desired trajectories in Cartesian space despite unknown time-varying interaction forces exerted through a load. In the position-hybrid control strategy, the adaptive controller of one arm controls end-effector motions in the free directions and applied forces in the constraint directions; while the adaptive controller of the other arm ensures that the end-effector tracks desired position trajectories. In the hybrid-hybrid control strategy, the adaptive controllers ensure that both end-effectors track reference position trajectories while simultaneously applying desired forces on the load. In all three control strategies, the cross-coupling effects between the arms are treated as disturbances which are compensated for by the adaptive controllers while following desired commands in a common frame of reference. The adaptive controllers do not require the complex mathematical model of the arm dynamics or any knowledge of the arm dynamic parameters or the load parameters such as mass and stiffness. Circuits in the adaptive feedback and feedforward controllers are varied by novel adaptation laws.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hart, F.L.

A method is described for exerting forces on a subterranean formation for fracturing and increasing the width of a fracture wherein polymerizable materials capable of forming popcorn polymer are placed in the formation and polymerized in situ. Popcorn polymer is a hard, porous opaque material that is not soluble in ordinary solvents. The occurrence of popcorn polymer is well-known in chemical plants, such as for example a synthetic rubber plant. The forces that are exerted by the forming popcorn polymer have been known to split extra heavy steel pipe, snap a number of bolts, and force bubble traps upward throughmore » towers and, in general, exhibit forces greatly in excess of that needed to fracture and separate subterranean formations. (8 claims)« less

Gender power control, sexual experiences, safer sex practices, and potential HIV risk behaviors among young Asian-American women.

PubMed

Hahm, Hyeouk Chris; Lee, Jieha; Rough, Kathryn; Strathdee, Steffanie A

2012-01-01

We examined the prevalence of three domains of sexual behaviors among young Asian-American women: sexual experiences, safer sex practices, and potential HIV risk behaviors. We also investigated the impact of gender power control on these domains. Among sexually experienced women, 51% reported using condoms during their most recent sex act, 63% reported inconsistent condom use, and 18% reported ever having forced sex. Multiple logistic regression analyses revealed that women's perceived lower relationship power control was not associated with vaginal sex or safer sex practices, but it was powerfully associated with forced sex and all three potential HIV risk behaviors. This study demonstrates that control within young Asian-American women's intimate relationships exerts different associations depending on the type of sexual behavior. The application of the Theory of Gender and Power should be employed with prudence when designing HIV interventions for this population.

Gender Power Control, Sexual Experiences, Safer Sex Practices, and Potential HIV Risk Behaviors Among Young Asian-American Women

PubMed Central

Lee, Jieha; Rough, Kathryn; Strathdee, Steffanie A.

2012-01-01

We examined the prevalence of three domains of sexual behaviors among young Asian-American women: sexual experiences, safer sex practices, and potential HIV risk behaviors. We also investigated the impact of gender power control on these domains. Among sexually experienced women, 51% reported using condoms during their most recent sex act, 63% reported inconsistent condom use, and 18% reported ever having forced sex. Multiple logistic regression analyses revealed that women’s perceived lower relationship power control was not associated with vaginal sex or safer sex practices, but it was powerfully associated with forced sex and all three potential HIV risk behaviors. This study demonstrates that control within young Asian-American women’s intimate relationships exerts different associations depending on the type of sexual behavior. The application of the Theory of Gender and Power should be employed with prudence when designing HIV interventions for this population. PMID:21259042

System for Controlling the Stirring Pin of a Friction Stir Welding Apparatus

NASA Technical Reports Server (NTRS)

Ding, R. Jeffrey (Inventor); Romine, Peter L. (Inventor); Oelgoetz, Peter A. (Inventor)

2002-01-01

A control is provided for a friction stir welding apparatus comprising a pin tool which includes a shoulder and a rotating pin extending outwardly from the shoulder of the pin tool and which, in use, is plunged into a workpiece formed contacting workpiece members to stir weld the members together. The control system controls the penetration of the pin tool into the workpiece members which are mounted on a support anvil. The control system includes a pin length controller for controlling pin length relative to the shoulder and for producing a corresponding pin length signal. A pin force sensor senses the force being exerted on the pin during welding and produces a corresponding actual pin force signal. A probe controller controls a probe extending outwardly from the pin, senses a parameter related to the distance between the probe and the supporting anvil and produces a corresponding probe signal. A workpiece standoff sensor senses the standoff distance between the workpiece and the standoff sensor and produces a corresponding standoff signal. A control unit receives the various signals, together with a weld schedule, and, based on these signals and the weld schedule, controls the pin length controller so as to control pin penetration into the workpiece.

Action and Traction: Cytoskeletal Control of Receptor Triggering at the Immunological Synapse

PubMed Central

Comrie, William A.; Burkhardt, Janis K.

2016-01-01

It is well known that F-actin dynamics drive the micron-scale cell shape changes required for migration and immunological synapse (IS) formation. In addition, recent evidence points to a more intimate role for the actin cytoskeleton in promoting T cell activation. Mechanotransduction, the conversion of mechanical input into intracellular biochemical changes, is thought to play a critical role in several aspects of immunoreceptor triggering and downstream signal transduction. Multiple molecules associated with signaling events at the IS have been shown to respond to physical force, including the TCR, costimulatory molecules, adhesion molecules, and several downstream adapters. In at least some cases, it is clear that the relevant forces are exerted by dynamics of the T cell actomyosin cytoskeleton. Interestingly, there is evidence that the cytoskeleton of the antigen-presenting cell also plays an active role in T cell activation, by countering the molecular forces exerted by the T cell at the IS. Since actin polymerization is itself driven by TCR and costimulatory signaling pathways, a complex relationship exists between actin dynamics and receptor activation. This review will focus on recent advances in our understanding of the mechanosensitive aspects of T cell activation, paying specific attention to how F-actin-directed forces applied from both sides of the IS fit into current models of receptor triggering and activation. PMID:27014258

Electrophoretic and Electrolytic Deposition of Ceramic Particles on Porous Substrates

DTIC Science & Technology

1990-08-30

hydrodynamic drag force exerted on the particle due to the electroosmotic flow of the solvent inside the pore, the electrophoretic force exerted on the...8217 - electrophoretic velocity UN - electroosmotic velocity b - pore mean radius D - diffusion coefficient k - local deposition rate Large Peclet numbers and small...experimentally as the charge is acquired spontaneously on mixing the particles with the solvent and it may be reversed upon addition ot ionic compounds. The

Neuromuscular control of the head in an isometric force reproduction task: comparison of whiplash subjects and healthy controls.

PubMed

Descarreaux, Martin; Mayrand, Nancy; Raymond, Jean

2007-01-01

A number of recent scientific publications suggest that patients suffering from whiplash-associated disorders (WADs) exhibit sensorimotor deficits in the control of head and neck movements. The main objective of the present study was to evaluate if subjects with WADs can produce isometric neck extension and flexion forces with precision, variability, and a mode of control similar to the values of healthy subjects. A control group study with repeated measures. Neck force production parameters and neuromuscular control were measured in 17 whiplash and 14 control subjects. The experimental group included subjects who had a history of persistent neck pain or disability after a motor vehicle accident. Pain levels were assessed on a standard 100-mm visual analog pain scale at the beginning and end of the experiment. Each whiplash subject completed the neck disability index and the short-form 36 health survey (SF-36) questionnaire before the experiment. All subjects were asked to exert flexion and extension forces against a fixed head harness. Kinetic variables included time to peak force, time to peak force variability, peak force variability, and absolute error in peak force. Surface electrodes were applied bilaterally over the sternocleidomastoideus and paraspinal muscles. Electromyography (EMG)-dependent variables included EMG burst duration and amplitude using numerical integrated techniques. The average time to peak force was significantly longer for whiplash subjects than for the healthy controls. A significant increase in peak force variability was also observed in the whiplash group, and no group differences were noted for absolute error. Heightened muscular activity was seen in both paraspinal muscles, even though it only reached statistical significance for the left paraspinal muscle. Our results show that the whiplash subjects involved in the study were able to produce isometric forces with spatial precision similar to healthy controls using a motor strategy in which the time to peak force is increased. This trade-off between spatial precision and time to peak force probably reflects an adaptation aimed at limiting pain and further injuries.

Recording forces exerted on the bowel wall during colonoscopy: in vitro evaluation.

PubMed

Dogramadzi, S; Virk, G S; Bell, G D; Rowland, R S; Hancock, J

2005-12-01

A novel system for distributed force measurement between the bowel wall and the shaft of a colonoscope is presented. The system, based on the piezoresistive method, involves the integration of soft miniature transducers to a colonoscope to enable a wide range of forces to be sensed. The attached sensing sheath does not restrict the propulsion of the colonoscope nor notably alter its flexibility. The addition of the sensor sheath increases the colonoscope diameter by 15-20% depending on the type of the colonoscope (adult or paediatric). The transducer's accuracy is +/-20 grammes if it is not subjected to extensive static forces. Under large static force conditions the errors may increase to +/-50 grammes. The tactile force measuring sensors have provided preliminary results from experiments on a model of the large bowel. The force measurements confirm the predictions on the location and magnitude of the forces and that most of the forces are exerted whilst the instrument is looping. Copyright 2005 John Wiley & Sons, Ltd.

Effect of stance width on multidirectional postural responses

NASA Technical Reports Server (NTRS)

Henry, S. M.; Fung, J.; Horak, F. B.; Peterson, B. W. (Principal Investigator)

2001-01-01

The effect of stance width on postural responses to 12 different directions of surface translations was examined. Postural responses were characterized by recording 11 lower limb and trunk muscles, body kinematics, and forces exerted under each foot of 7 healthy subjects while they were subjected to horizontal surface translations in 12 different, randomly presented directions. A quasi-static approach of force analysis was done, examining force integrals in three different epochs (background, passive, and active periods). The latency and amplitude of muscle responses were quantified for each direction, and muscle tuning curves were used to determine the spatial activation patterns for each muscle. The results demonstrate that the horizontal force constraint exerted at the ground was lessened in the wide, compared with narrow, stance for humans, a similar finding to that reported by Macpherson for cats. Despite more trunk displacement in narrow stance, there were no significant changes in body center of mass (CoM) displacement due to large changes in center of pressure (CoP), especially in response to lateral translations. Electromyographic (EMG) magnitude decreased for all directions in wide stance, particularly for the more proximal muscles, whereas latencies remained the same from narrow to wide stance. Equilibrium control in narrow stance was more of an active postural strategy that included regulating the loading/unloading of the limbs and the direction of horizontal force vectors. In wide stance, equilibrium control relied more on an increase in passive stiffness resulting from changes in limb geometry. The selective latency modulation of the proximal muscles with translation direction suggests that the trunk was being actively controlled in all directions. The similar EMG latencies for both narrow and wide stance, with modulation of only the muscle activation magnitude as stance width changed, suggest that the same postural synergy was only slightly modified for a change in stance width. Nevertheless, the magnitude of the trunk displacement, as well as of CoP displacement, was modified based on the degree of passive stiffness in the musculoskeletal system, which increased with stance width. The change from a more passive to an active horizontal force constraint, to larger EMG magnitudes especially in the trunk muscles and larger trunk and CoP excursions in narrow stance are consistent with a more effortful response for equilibrium control in narrow stance to perturbations in all directions.

The Effect of Volumetric Porosity on Roughness Element Drag

NASA Astrophysics Data System (ADS)

Gillies, John; Nickling, William; Nikolich, George; Etyemezian, Vicken

2016-04-01

Much attention has been given to understanding how the porosity of two dimensional structures affects the drag force exerted by boundary-layer flow on these flow obstructions. Porous structures such as wind breaks and fences are typically used to control the sedimentation of sand and snow particles or create micro-habitats in their lee. Vegetation in drylands also exerts control on sediment transport by wind due to aerodynamic effects and interaction with particles in transport. Recent research has also demonstrated that large spatial arrays of solid three dimensional roughness elements can be used to reduce sand transport to specified targets for control of wind erosion through the effect of drag partitioning and interaction of the moving sand with the large (>0.3 m high) roughness elements, but porous elements may improve the effectiveness of this approach. A thorough understanding of the role porosity plays in affecting the drag force on three-dimensional forms is lacking. To provide basic understanding of the relationship between the porosity of roughness elements and the force of drag exerted on them by fluid flow, we undertook a wind tunnel study that systematically altered the porosity of roughness elements of defined geometry (cubes, rectangular cylinders, and round cylinders) and measured the associated change in the drag force on the elements under similar Reynolds number conditions. The elements tested were of four basic forms: 1) same sized cubes with tubes of known diameter milled through them creating three volumetric porosity values and increasing connectivity between the tubes, 2) cubes and rectangular cylinders constructed of brass screen that nested within each other, and 3) round cylinders constructed of brass screen that nested within each other. The two-dimensional porosity, defined as the ratio of total surface area of the empty space to the solid surface area of the side of the element presented to the fluid flow was conserved at 0.519 for the cubes and 0.525 for the mesh forms. Results from the study indicate that as volumetric porosity increases, the force of drag on an element increases although the 2-dimensional porosity remains unchanged for the case of the cube forms. The mesh forms show a similar result that with increasing number of internal forms present, drag increases, but the drag curves are different, suggesting the kind of porosity has an effect on drag. An important scaling parameter that controls drag on the cubes is the permeability (K) of the element, which is a function of the diameter of the tubes and the porosity. K seems to be of lesser importance for controlling drag on the mesh forms. We hypothesize that the drag force data do not universally collapse as a function of permeability due to Reynolds number dependency on flow conditions within the elements that can be laminar, transitional, or turbulent even though flow exterior to the forms is fully turbulent. For the mesh forms, the greatest effect on drag occurs with the addition of the first internal form with subsequent additions showing very little additional effect.

Multi-finger Prehension: An overview

PubMed Central

Zatsiorsky, Vladimir M.; Latash, Mark L.

2009-01-01

This paper reviews the available experimental evidence on what people do when they grasp an object with several digits and then manipulate it. In addition to the Introduction, the paper includes three parts each addressing a specific aspect of multi-finger prehension. Part II discusses manipulation forces, i.e. the resultant force and moment of force exerted on the object, and the digits contribution to such force production. Part III deals with internal forces defined as forces that cancel each other and do not disturb object equilibrium. The role of the internal forces in maintaining the object stability is discussed with respect to such issues as slip prevention, tilt prevention and resistance to perturbations. Part IV is devoted to the motor control of prehension. It covers such topics as prehension synergies, chain effects, the principle of superposition, inter-finger connection matrices and reconstruction of neural commands, mechanical advantage of the fingers, and the simultaneous digit adjustment to several mutually reinforcing or conflicting demands. PMID:18782719

Quantitative modeling and optimization of magnetic tweezers.

PubMed

Lipfert, Jan; Hao, Xiaomin; Dekker, Nynke H

2009-06-17

Magnetic tweezers are a powerful tool to manipulate single DNA or RNA molecules and to study nucleic acid-protein interactions in real time. Here, we have modeled the magnetic fields of permanent magnets in magnetic tweezers and computed the forces exerted on superparamagnetic beads from first principles. For simple, symmetric geometries the magnetic fields can be calculated semianalytically using the Biot-Savart law. For complicated geometries and in the presence of an iron yoke, we employ a finite-element three-dimensional PDE solver to numerically solve the magnetostatic problem. The theoretical predictions are in quantitative agreement with direct Hall-probe measurements of the magnetic field and with measurements of the force exerted on DNA-tethered beads. Using these predictive theories, we systematically explore the effects of magnet alignment, magnet spacing, magnet size, and of adding an iron yoke to the magnets on the forces that can be exerted on tethered particles. We find that the optimal configuration for maximal stretching forces is a vertically aligned pair of magnets, with a minimal gap between the magnets and minimal flow cell thickness. Following these principles, we present a configuration that allows one to apply > or = 40 pN stretching forces on approximately 1-microm tethered beads.

Quantitative Modeling and Optimization of Magnetic Tweezers

PubMed Central

Lipfert, Jan; Hao, Xiaomin; Dekker, Nynke H.

2009-01-01

Abstract Magnetic tweezers are a powerful tool to manipulate single DNA or RNA molecules and to study nucleic acid-protein interactions in real time. Here, we have modeled the magnetic fields of permanent magnets in magnetic tweezers and computed the forces exerted on superparamagnetic beads from first principles. For simple, symmetric geometries the magnetic fields can be calculated semianalytically using the Biot-Savart law. For complicated geometries and in the presence of an iron yoke, we employ a finite-element three-dimensional PDE solver to numerically solve the magnetostatic problem. The theoretical predictions are in quantitative agreement with direct Hall-probe measurements of the magnetic field and with measurements of the force exerted on DNA-tethered beads. Using these predictive theories, we systematically explore the effects of magnet alignment, magnet spacing, magnet size, and of adding an iron yoke to the magnets on the forces that can be exerted on tethered particles. We find that the optimal configuration for maximal stretching forces is a vertically aligned pair of magnets, with a minimal gap between the magnets and minimal flow cell thickness. Following these principles, we present a configuration that allows one to apply ≥40 pN stretching forces on ≈1-μm tethered beads. PMID:19527664

Calculation of a fluctuating entropic force by phase space sampling.

PubMed

Waters, James T; Kim, Harold D

2015-07-01

A polymer chain pinned in space exerts a fluctuating force on the pin point in thermal equilibrium. The average of such fluctuating force is well understood from statistical mechanics as an entropic force, but little is known about the underlying force distribution. Here, we introduce two phase space sampling methods that can produce the equilibrium distribution of instantaneous forces exerted by a terminally pinned polymer. In these methods, both the positions and momenta of mass points representing a freely jointed chain are perturbed in accordance with the spatial constraints and the Boltzmann distribution of total energy. The constraint force for each conformation and momentum is calculated using Lagrangian dynamics. Using terminally pinned chains in space and on a surface, we show that the force distribution is highly asymmetric with both tensile and compressive forces. Most importantly, the mean of the distribution, which is equal to the entropic force, is not the most probable force even for long chains. Our work provides insights into the mechanistic origin of entropic forces, and an efficient computational tool for unbiased sampling of the phase space of a constrained system.

Independence of reaction time and response force control during isometric leg extension.

PubMed

Fukushi, Tamami; Ohtsuki, Tatsuyuki

2004-04-01

In this study, we examined the relative control of reaction time and force in responses of the lower limb. Fourteen female participants (age 21.2 +/- 1.0 years, height 1.62 +/- 0.05 m, body mass 54.1 +/- 6.1 kg; mean +/- s) were instructed to exert their maximal isometric one-leg extension force as quickly as possible in response to an auditory stimulus presented after one of 13 foreperiod durations, ranging from 0.5 to 10.0 s. In the 'irregular condition' each foreperiod was presented in random order, while in the 'regular condition' each foreperiod was repeated consecutively. A significant interactive effect of foreperiod duration and regularity on reaction time was observed (P < 0.001 in two-way ANOVA with repeated measures). In the irregular condition the shorter foreperiod induced a longer reaction time, while in the regular condition the shorter foreperiod induced a shorter reaction time. Peak amplitude of isometric force was affected only by the regularity of foreperiod and there was a significant variation of changes in peak force across participants; nine participants were shown to significantly increase peak force for the regular condition (P < 0.001), three to decrease it (P < 0.05) and two showed no difference. These results indicate the independence of reaction time and response force control in the lower limb motor system. Variation of changes in peak force across participants may be due to the different attention to the bipolar nature of the task requirements such as maximal force and maximal speed.

Relationships between ground reaction force parameters during a sit-to-stand movement and physical activity and falling risk of the elderly and a comparison of the movement characteristics between the young and the elderly.

PubMed

Yamada, Takayoshi; Demura, Shin-ichi

2009-01-01

This study aimed to examine the relationships between ground reaction force during a sit-to-stand (STS) movement and physical activity and falling risk of the elderly and the difference of the movement characteristics between the young and the elderly. Sixty elderly females who can achieve a STS movement by themselves and 30 healthy young females were measured for ground reaction force during STS movement from a chair, adjusted for lower leg length height. The elderly's physical activity and falling risk were also assessed. Physical activity and falling risk significantly correlated with parameters on force exertion during hip lift-off and knee-hip joint extension phases (|r|=0.26-0.41). Significant differences were found in ground reaction force parameters of all phases between the young and the elderly and STS movement of the elderly was suggested to result in poor force exertion and slowing down. The above tendency was noticeable in the hip lift-off and knee-hip joint extension phases. In conclusion, force exertion in hip lift-off and knee-hip joint extension phases of STS movement is related to physical activity and falling risk in the elderly. These phases may be useful to evaluate the elderly's physical activity and falling risk.

Ergonomic Evaluation of Space Shuttle Light-Weight Seat Lever Position and Operation

NASA Technical Reports Server (NTRS)

Maida, J.; Rajulu, Sudhakar L.; Bond, Robert L. (Technical Monitor)

2000-01-01

During a Shuttle flight in the early part of 1999, one of the crewmembers was unable to operate the backrest lever for the light-weight seat in microgravity. It is essential that the crewmembers are able to adjust this back-rest lever, which is titled forward 2 degrees from vertical during launch and then moved backwards to 10 degrees aft of vertical upon reaching orbit. This adjustment is needed to cushion the crewmembers during an inadvertent crash landing situation. The original Shuttle seats, which had seat controls located on the front left and right sides of the seat, were replaced recently with the new light-weight seats. The controls for these new, seats were moved to the night side with one control at the front and the other at the back. While it was uncertain whether the problem encountered was unique to that crewmember or not it was clear to the personnel responsible for maintaining the Shuttle seats that not knowing the cause of the problem posed a safety concern for NASA. Hence the Anthropometry and Biomechanics Facility (ABF) of the Johnson Space Center was requested to perform an evaluation of the seat controls and provide NASA with appropriate recommendations on whether the seat lever positions and operations should be modified. The ABF designed an experiment to investigate the amount of pull force exerted by subjects, wearing an unpressurized or pressurized crew launch escape suit, when controls were placed in the front and back (on the right side) of the light-weight seat. Single-axis load cells were attached to the seat levers, which measured the maximum static pull forces that were exerted by the subjects. Twelve subjects, six male and six female, participated in this study. Each subject was asked to perform the pull test at least three times for each combination of lever position and suit pressure conditions. The results from this study showed that as a whole (or in general), the subjects were able to pull on the lever at the back position with only about half the amount of force that they were able to exert on the lever at the front position. In addition, the results also showed that subjects wearing the pressurized suit were unable to reach the seat lever when it was located at the back. Furthermore, the pull forces on the front lever diminished about 50 % when subjects wore the pressurized suits. Based on these results from this study, it was recommended to NASA that the levers should not be located in the back position. In addition, further investigation is needed on whether the levers at the front of the seat could be modified or adjusted to increase the leverage for crew members wearing pressurized launch/escape suits.

Functional sensibility assessment. Part II: Effects of sensory improvement on precise pinch force modulation after transverse carpal tunnel release.

PubMed

Hsu, Hsiu-Yun; Kuo, Li-Chieh; Chiu, Haw-Yen; Jou, I-Ming; Su, Fong-Chin

2009-11-01

Patients with median nerve compression at the carpal tunnel often have poor sensory afferents. Without adequate sensory modulation control, these patients frequently exhibit clumsy performance and excessive force output in the affected hand. We analyzed precision grip function after the sensory recovery of patients with carpal tunnel syndrome (CTS) who underwent carpal tunnel release (CTR). Thirteen CTS patients were evaluated using a custom-designed pinch device and conventional sensory tools before and after CTR to measure sensibility, maximum pinch strength, and anticipated pinch force adjustments to movement-induced load fluctuations in a pinch-holding-up activity. Based on these tests, five force-related parameters and sensory measurements were used to determine improvements in pinch performance after sensory recovery. The force ratio between the exerted pinch force and maximum load force of the lifting object was used to determine pinch force coordination and to prove that CTR enabled precision motor output. The magnitude of peak pinch force indicated an economic force output during manipulations following CTR. The peak pinch force, force ratio, and percentage of maximum pinch force also demonstrated a moderate correlation with the Semmes-Weinstein test. Analysis of these tests revealed that improved sensory function helped restore patients' performance in precise pinch force control evaluations. These results suggest that sensory information plays an important role in adjusting balanced force output in dexterous manipulation. (c) 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.

The effects of blocking N/OFQ receptors on orofacial pain following experimental tooth movement in rats.

PubMed

Shan, Di; He, Yuwei; Long, Hu; Zhou, Yang; Liu, He; Xu, Rui; Huang, Renhuan; Lai, Wenli

2016-11-01

The aim of this study was to determine the effects of nociceptin/orphanin FQ peptide receptor (N/OFQ receptor) antagonist on orofacial pain induced by experimental tooth movement in rats. A total of 36 male Sprague-Dawley rats weighing 200-300 g were divided into six groups: a control group, force group, force+saline intraperitoneal group, force+saline periodontal group, force+UFP-101 ([Nphe¹,Arg¹⁴,Lys¹⁵]N/OFQ-NH ₂ antagonist for N/OFQ receptor) intraperitoneal group, and force+UFP-1 01 periodontal group. Closed coil springs were ligated between the upper incisors and first molar to exert an orthodontic force (40 g) between the teeth. Injectable administration dosages were 30 μl saline or 30 μl saline containing 0.03 mg/kg UFP-1 01. Following the injections, orofacial pain levels were assessed through directed face grooming (mouth wiping). Statistical analyses were performed in SPSS 17.0 (Statistical Package for the Social Sciences) and p values less than 0.05 were considered as statistically significant. Orofacial pain levels were significantly higher in the force group than in the control group. Orofacial pain levels differed significantly between the force)group, force+saline periodontal group and force+UFP-101 periodontal group, but were similar between the control group, force+UFP-101 intraperitoneal group and force+saline intraperitoneal group. Moreover, orofacial pain levels did not differ between the force group, force+saline intraperitoneal group and force+UFP-1 01 intraperitoneal group. Periodontal, but not intraperitoneal, administration of UFP-101 could alleviate orofacial pain induced by experimental tooth movement in rats, suggesting that periodontal N/OFQ receptors participate in orofacial pain induced by experimental tooth movement.

Pressure effects on the nose by an in-flight oxygen mask during simulated flight conditions.

PubMed

Schreinemakers, J Rieneke C; Boer, C; van Amerongen, P C G M; Kon, M

2016-12-01

Dutch F-16 fighter pilots experience oxygen mask inflicted nasal trauma, including discomfort, pain, skin abrasions, bruises and bone remodelling. Pressure and shear forces on the nose might contribute to causing these adverse effects. In this study, it was evaluated how flight conditions affected the exerted pressure, and whether shear forces were present. The pressure exerted by the oxygen mask was measured in 20 volunteers by placing pressure sensors on the nose and chin underneath the mask. In the human centrifuge, the effects on the exerted pressure during different flight conditions were evaluated (+3G z , +6G z , +9G z , protocolised head movements, mounted visor or night vision goggles, NVG). The runs were recorded to evaluate if the mask's position changed during the run, which would confirm the presence of shear forces. Head movements increased the median pressure on the nose by 50 mm Hg and on the chin by 37 mm Hg. NVG, a visor and accelerative forces also increased the median pressure on the nose. Pressure drops on the nose were also observed, during mounted NVG (-63 mm Hg). The recordings showed the mask slid downwards, especially during the acceleration phase of the centrifuge run, signifying the presence of shear forces. The exerted pressure by the oxygen mask changes during different flight conditions. Exposure to changing pressures and to shear forces probably contributes to mask-inflicted nasal trauma. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/.

Enhancement of axial momentum lost to the radial wall by the upstream magnetic field in a helicon source

NASA Astrophysics Data System (ADS)

Takahashi, Kazunori; Ando, Akira

2017-05-01

Individual measurements of forces exerted to an upstream back wall, a radial source wall, and a magnetic field of a helicon plasma thruster, which has two solenoids upstream and downstream of a radiofrequency antenna, are precisely measured. Two different structures of magnetic field lines in the source are tested, where the solenoid current is supplied to either only the downstream solenoid or to both the solenoids. It is observed that the high density plasma exists upstream of the rf antenna when both the solenoids are powered, while the maximum density exists near the rf antenna when only the downstream solenoid is powered. Although the force exerted to the back wall is increased for the two solenoids case, the axial momentum lost to the radial wall is simultaneously enhanced; then the total force exerted to the whole structure of the thruster is found to be very similar for the two magnetic field configurations. It is shown that the individual force measurement provides useful information on the plasma momentum interacting with the physical boundaries and the magnetic fields.

A quantitative examination of the role of cargo-exerted forces in axonal transport

PubMed Central

Mitchell, Cassie S.; Lee, Robert H.

2009-01-01

Axonal transport, via molecular motors kinesin and dynein, is a critical process in supplying the necessary constituents to maintain normal neuronal function. In this study, we predict the role of cooperativity by motors of the same polarity across the entire spectrum of physiological axonal transport. That is, we examined how the number of motors, either kinesin or dynein, working together to move a cargo, results in the experimentally determined velocity profiles seen in fast and slow anterograde and retrograde transport. We quantified the physiological forces exerted on a motor by a cargo as a function of cargo size, transport velocity, and transport type. Our results show that the force exerted by our base case neurofilament (DNF=10nm, LNF=1.6μm) is ~1.25pN at 600nm/s; additionally, the force exerted by our base case organelle (DOrg=1μm) at 1,000nm/s is ~5.7pN. Our results indicate that while a single motor can independently carry an average cargo, cooperativity is required to produce the experimental velocity profiles for fast transport. However, no cooperativity is required to produce the slow transport velocity profiles; thus, a single dynein or kinesin can carry the average neurofilament retrogradely or anterogradely, respectively. The potential role cooperativity may play in the hypothesized mechanisms of motoneuron transport diseases such as Amyotrophic Lateral Sclerosis (ALS) is discussed. PMID:19150364

An in vitro force measurement assay to study the early mechanical interaction between corneal fibroblasts and collagen matrix.

PubMed

Roy, P; Petroll, W M; Cavanagh, H D; Chuong, C J; Jester, J V

1997-04-10

An in vitro force measurement assay has been developed to quantify the forces exerted by single corneal fibroblasts during the early interaction with a collagen matrix. Corneal fibroblasts were sparsely seeded on top of collagen matrices whose stiffness was predetermined by micromanipulation with calibrated fine glass microneedles. The forces exerted by individual cells were calculated from time-lapse videomicroscopic recordings of the 2-D elastic distortion of the matrix. In additional experiments, the degree of permanent reorganization of the collagen matrices was assessed by lysing the cells with 1% Triton X-100 solution at the end of a 2-hour incubation and recording the subsequent relaxation. The data suggest that a cell can exert comparable centripetal force during either extension of a cell process or partial retraction of an extended pseudopodia. The rates of force associated with pseudopodial extension and partial retraction were 0.180 +/- 0.091 (x 10(-8)) N/min (n = 8 experiments) and 0.213 +/- 0.063 (x 10(-8)) N/min (n = 8 experiments), respectively. Rupture of pseudopodial adhesion associated with cell locomotion causes a release of force on the matrix and a complete recoil of the pseudopodia concerned; a simultaneous release of force on the matrix was also observed at the opposite end of the cell. Lysis of cells resulted in 84 +/- 18% relaxation of the matrix, suggesting that little permanent remodeling of matrix is produced by the actions of isolated migrating cells.

Microgravity Fluid Separation Physics: Experimental and Analytical Results

NASA Technical Reports Server (NTRS)

Shoemaker, J. Michael; Schrage, Dean S.

1997-01-01

Effective, low power, two-phase separation systems are vital for the cost-effective study and utilization of two-phase flow systems and flow physics of two-phase flows. The study of microgravity flows have the potential to reveal significant insight into the controlling mechanisms for the behavior of flows in both normal and reduced gravity environments. The microgravity environment results in a reduction in gravity induced buoyancy forces acting on the discrete phases. Thus, surface tension, viscous, and inertial forces exert an increased influence on the behavior of the flow as demonstrated by the axisymmetric flow patterns. Several space technology and operations groups have studied the flow behavior in reduced gravity since gas-liquid flows are encountered in several systems such as cabin humidity control, wastewater treatment, thermal management, and Rankine power systems.

Automatic locking knee brace joint

NASA Technical Reports Server (NTRS)

Weddendorf, Bruce (Inventor)

1995-01-01

This invention is an apparatus for controlling the pivotal movement of a knee brace comprising a tang-and-clevis joint that has been uniquely modified. Both the tang and the clevis have a set of teeth that, when engaged, can lock the tang and the clevis together. In addition, the tang is biased away from the clevis. Consequently, when there is no axial force (i.e., body weight) on the tang, the tang is free to pivot within the clevis. However, when an axial force is exerted on the tang, the tang is pushed into the clevis, both sets of teeth engage, and the tang and the clevis lock together.

Wire electric-discharge machining and other fabrication techniques

NASA Technical Reports Server (NTRS)

Morgan, W. H.

1983-01-01

Wire electric discharge machining and extrude honing were used to fabricate a two dimensional wing for cryogenic wind tunnel testing. Electric-discharge cutting is done with a moving wire electrode. The cut track is controlled by means of a punched-tape program and the cutting feed is regulated according to the progress of the work. Electric-discharge machining involves no contact with the work piece, and no mechanical force is exerted. Extrude hone is a process for honing finish-machined surfaces by the extrusion of an abrasive material (silly putty), which is forced through a restrictive fixture. The fabrication steps are described and production times are given.

Force balancing in mammographic compression

DOE Office of Scientific and Technical Information (OSTI.GOV)

Branderhorst, W., E-mail: w.branderhorst@amc.nl; Groot, J. E. de; Lier, M. G. J. T. B. van

Purpose: In mammography, the height of the image receptor is adjusted to the patient before compressing the breast. An inadequate height setting can result in an imbalance between the forces applied by the image receptor and the paddle, causing the clamped breast to be pushed up or down relative to the body during compression. This leads to unnecessary stretching of the skin and other tissues around the breast, which can make the imaging procedure more painful for the patient. The goal of this study was to implement a method to measure and minimize the force imbalance, and to assess itsmore » feasibility as an objective and reproducible method of setting the image receptor height. Methods: A trial was conducted consisting of 13 craniocaudal mammographic compressions on a silicone breast phantom, each with the image receptor positioned at a different height. The image receptor height was varied over a range of 12 cm. In each compression, the force exerted by the compression paddle was increased up to 140 N in steps of 10 N. In addition to the paddle force, the authors measured the force exerted by the image receptor and the reaction force exerted on the patient body by the ground. The trial was repeated 8 times, with the phantom remounted at a slightly different orientation and position between the trials. Results: For a given paddle force, the obtained results showed that there is always exactly one image receptor height that leads to a balance of the forces on the breast. For the breast phantom, deviating from this specific height increased the force imbalance by 9.4 ± 1.9 N/cm (6.7%) for 140 N paddle force, and by 7.1 ± 1.6 N/cm (17.8%) for 40 N paddle force. The results also show that in situations where the force exerted by the image receptor is not measured, the craniocaudal force imbalance can still be determined by positioning the patient on a weighing scale and observing the changes in displayed weight during the procedure. Conclusions: In mammographic breast compression, even small changes in the image receptor height can lead to a severe imbalance of the applied forces. This may make the procedure more painful than necessary and, in case the image receptor is set too low, may lead to image quality issues and increased radiation dose due to undercompression. In practice, these effects can be reduced by monitoring the force imbalance and actively adjusting the position of the image receptor throughout the compression.« less

Backed Bending Actuator

NASA Technical Reports Server (NTRS)

Costen, Robert C.; Su, Ji

2004-01-01

Bending actuators of a proposed type would partly resemble ordinary bending actuators, but would include simple additional components that would render them capable of exerting large forces at small displacements. Like an ordinary bending actuator, an actuator according to the proposal would include a thin rectangular strip that would comprise two bonded layers (possibly made of electroactive polymers with surface electrodes) and would be clamped at one end in the manner of a cantilever beam. Unlike an ordinary bending actuator, the proposed device would include a rigid flat backplate that would support part of the bending strip against backward displacement; because of this feature, the proposed device is called a backed bending actuator. When an ordinary bending actuator is inactive, the strip typically lies flat, the tip displacement is zero, and the force exerted by the tip is zero. During activation, the tip exerts a transverse force and undergoes a bending displacement that results from the expansion or contraction of one or more of the bonded layers. The tip force of an ordinary bending actuator is inversely proportional to its length; hence, a long actuator tends to be weak. The figure depicts an ordinary bending actuator and the corresponding backed bending actuator. The bending, the tip displacement (d(sub t)), and the tip force (F) exerted by the ordinary bending actuator are well approximated by the conventional equations for the loading and deflection of a cantilever beam subject to a bending moment which, in this case, is applied by the differential expansion or contraction of the bonded layers. The bending, displacement, and tip force of the backed bending actuator are calculated similarly, except that it is necessary to account for the fact that the force F(sub b) that resists the displacement of the tip could be sufficient to push part of the strip against the backplate; in such a condition, the cantilever beam would be effectively shortened (length L*) and thereby stiffened and, hence, made capable of exerting a greater tip force for a given degree of differential expansion or contraction of the bonded layers. Taking all of these effects into account, the cantilever-beam equations show that F(sub b) would be approximately inversely proportional to d(sup 1/2) for d less than a calculable amount, denoted the transition displacement (dt). For d less than d(sub t), part of the strip would be pressed against the backplate. Therefore, the force F(sub b) would be very large for d at or near zero and would decrease as d increases toward d(sub t). At d greater than d(sub t), none of the strip would be pressed against the backplate and F(sub b) would equal the tip force F of the corresponding ordinary bending actuator. The advantage of the proposal is that a backed bending actuator could be made long to obtain large displacement when it encountered little resistance but it could also exert a large zero-displacement force, so that it could more easily start the movement of a large mass, throw a mechanical switch, or release a stuck mechanism.

Biological effects of compressive forces exerted on particulate bone grafts during socket preservation: animal study.

PubMed

Delgado-Ruiz, Rafael; Romanos, Georgios E; Alexandre Gerhke, Sergio; Gomez-Moreno, Gerardo; Maté-Sánchez de Val, José Eduardo; Calvo-Guirado, José Luis

2016-08-02

To compare different compressive forces exerted on a particulate graft material during socket preservation and their effects on bone regeneration. Six male dogs were used. The second, third, and fourth premolars, and the first molar were extracted bilaterally at the lower jaws. A particulate synthetic biphasic grafting material (60% HA and 40% β-tricalcium phosphate) was used. Three different standardized compressive forces were applied randomly during the socket preservation. The sample was divided into four experimental groups Test A (10 g), Test B (50 g), Test C (200 g), and Control (empty sockets). Collagen membranes were placed, and primary closure was obtained. Two months after the surgery the animals were sacrificed, and histomorphometric analysis of non-decalcified samples was performed at the coronal, middle, and apical thirds. Grafted sockets resulted in higher bony contour (3 ± 0.43 mm 2 ; P < 0.05). The particles penetrated up to the apical third in the group C but not in the other test groups and controls (P < 0.05). The percentage of new bone were higher at the coronal and apical thirds for Controls and group C compared to A and B groups (P < 0.05). The residual graft was higher for group C (53 ± 1.4%), followed by group B (45 ± 3.1%) and group A (35 ± 1.9%; P < 0.05). The percentages of connective tissue were higher at the middle third without differences between groups (P > 0.05). Within the limitations of this experimental animal study, it might be concluded that grafted sockets compressed with 200 g force will have higher bony contours; higher compressive forces facilitate the penetration of the particulate graft material into the apical area of the socket and results in more bone formation at the coronal, middle, and apical thirds. © 2016 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Traction force dynamics predict gap formation in activated endothelium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Valent, Erik T.; Nieuw Amerongen, Geerten P. van; Hinsbergh, Victor W.M. van

In many pathological conditions the endothelium becomes activated and dysfunctional, resulting in hyperpermeability and plasma leakage. No specific therapies are available yet to control endothelial barrier function, which is regulated by inter-endothelial junctions and the generation of acto-myosin-based contractile forces in the context of cell-cell and cell-matrix interactions. However, the spatiotemporal distribution and stimulus-induced reorganization of these integral forces remain largely unknown. Traction force microscopy of human endothelial monolayers was used to visualize contractile forces in resting cells and during thrombin-induced hyperpermeability. Simultaneously, information about endothelial monolayer integrity, adherens junctions and cytoskeletal proteins (F-actin) were captured. This revealed a heterogeneousmore » distribution of traction forces, with nuclear areas showing lower and cell-cell junctions higher traction forces than the whole-monolayer average. Moreover, junctional forces were asymmetrically distributed among neighboring cells. Force vector orientation analysis showed a good correlation with the alignment of F-actin and revealed contractile forces in newly formed filopodia and lamellipodia-like protrusions within the monolayer. Finally, unstable areas, showing high force fluctuations within the monolayer were prone to form inter-endothelial gaps upon stimulation with thrombin. To conclude, contractile traction forces are heterogeneously distributed within endothelial monolayers and force instability, rather than force magnitude, predicts the stimulus-induced formation of intercellular gaps. - Highlights: • Endothelial monolayers exert dynamic- and heterogeneous traction forces. • High traction forces correlate with junctional areas and the F-actin cytoskeleton. • Newly formed inter-endothelial gaps are characterized by opposing traction forces. • Force stability is a key feature controlling endothelial permeability.« less

Force Generation in Single Conventional Actomyosin Complexes under High Dynamic Load

PubMed Central

Takagi, Yasuharu; Homsher, Earl E.; Goldman, Yale E.; Shuman, Henry

2006-01-01

The mechanical load borne by a molecular motor affects its force, sliding distance, and its rate of energy transduction. The control of ATPase activity by the mechanical load on a muscle tunes its efficiency to the immediate task, increasing ATP hydrolysis as the power output increases at forces less than isometric (the Fenn effect) and suppressing ATP hydrolysis when the force is greater than isometric. In this work, we used a novel ‘isometric’ optical clamp to study the mechanics of myosin II molecules to detect the reaction steps that depend on the dynamic properties of the load. An actin filament suspended between two beads and held in separate optical traps is brought close to a surface that is sparsely coated with motor proteins on pedestals of silica beads. A feedback system increases the effective stiffness of the actin by clamping the force on one of the beads and moving the other bead electrooptically. Forces measured during actomyosin interactions are increased at higher effective stiffness. The results indicate that single myosin molecules transduce energy nearly as efficiently as whole muscle and that the mechanical control of the ATP hydrolysis rate is in part exerted by reversal of the force-generating actomyosin transition under high load without net utilization of ATP. PMID:16326899

Coordination of intrinsic and extrinsic hand muscle activity as a function of wrist joint angle during two-digit grasping.

PubMed

Johnston, Jamie A; Bobich, Lisa R; Santello, Marco

2010-04-26

Fingertip forces result from the activation of muscles that cross the wrist and muscles whose origins and insertions reside within the hand (extrinsic and intrinsic hand muscles, respectively). Thus, tasks that involve changes in wrist angle affect the moment arm and length, hence the force-producing capabilities, of extrinsic muscles only. If a grasping task requires the exertion of constant fingertip forces, the Central Nervous System (CNS) may respond to changes in wrist angle by modulating the neural drive to extrinsic or intrinsic muscles only or by co-activating both sets of muscles. To distinguish between these scenarios, we recorded electromyographic (EMG) activity of intrinsic and extrinsic muscles of the thumb and index finger as a function of wrist angle during a two-digit object hold task. We hypothesized that changes in wrist angle would elicit EMG amplitude modulation of the extrinsic and intrinsic hand muscles. In one experimental condition we asked subjects to exert the same digit forces at each wrist angle, whereas in a second condition subjects could choose digit forces for holding the object. EMG activity was significantly modulated in both extrinsic and intrinsic muscles as a function of wrist angle (both p<0.05) but only for the constant force condition. Furthermore, EMG modulation resulted from uniform scaling of EMG amplitude across all muscles. We conclude that the CNS controlled both extrinsic and intrinsic muscles as a muscle synergy. These findings are discussed within the theoretical frameworks of synergies and common neural input across motor nuclei of hand muscles. Copyright 2010 Elsevier Ireland Ltd. All rights reserved.

Motivational incentives lead to a strong increase in lateral prefrontal activity after self-control exertion

PubMed Central

Luethi, Matthias S.; Binder, Julia; Boesiger, Peter; Luechinger, Roger; Rasch, Björn

2016-01-01

Self-control is key to success in life. Initial acts of self-control temporarily impair subsequent self-control performance. Why such self-control failures occur is unclear, with prominent models postulating a loss of a limited resource vs a loss of motivation, respectively. Here, we used functional magnetic resonance imaging to identify the neural correlates of motivation-induced benefits on self-control. Participants initially exerted or did not exert self-control. In a subsequent Stroop task, participants performed worse after exerting self-control, but not if they were motivated to perform well by monetary incentives. On the neural level, having exerted self-control resulted in decreased activation in the left inferior frontal gyrus. Increasing motivation resulted in a particularly strong activation of this area specifically after exerting self-control. Thus, after self-control exertion participants showed more prefrontal neural activity without improving performance beyond baseline level. These findings suggest that impaired performance after self-control exertion may not exclusively be due to a loss of motivation. PMID:27217108

Work and power outputs determined from pedalling and flywheel friction forces during brief maximal exertion on a cycle ergometer.

PubMed

Hibi, N; Fujinaga, H; Ishii, K

1996-01-01

Work and power outputs during short-term, maximal exertion on a friction loaded cycle ergometer are usually calculated from the friction force applied to the flywheel. The inertia of the flywheel is sometimes taken into consideration, but the effects of internal resistances and other factors have been ignored. The purpose of this study was to estimate their effects by comparing work or power output determined from the force exerted on the pedals (pedalling force) with work or power output determined from the friction force and the moment of inertia of the rotational parts. A group of 22 male college students accelerated a cycle ergometer as rapidly as possible for 3 s. The total work output determined from the pedalling force (TWp) was significantly greater than that calculated from the friction force and the moment of inertia (TWf). Power output determined from the pedalling force during each pedal stroke (SPp) was also significantly greater than that calculated from the friction force and the moment of inertia. Percentage difference (% diff), defined by % diff = ¿(TWp - TWf)/TWf¿ x 100, ranged from 16.8% to 49.3% with a mean value of 30.8 (SD 9.1)%. It was observed that % diff values were higher in subjects with greater TWp or greater maximal SPp. These results would indicate that internal resistances and other factors, such as the deformation of the chain and the vibrations of the entire system, may have significant effects on the measurements of work and power outputs. The effects appear to depend on the magnitudes of pedalling force and pedal velocity.

Physical principles demonstrate that the biceps femoris muscle relative to the other hamstring muscles exerts the most force: implications for hamstring muscle strain injuries

PubMed Central

Dolman, Bronwyn; Verrall, Geoffrey; Reid, Iain

2014-01-01

Summary Of the hamstring muscle group the biceps femoris muscle is the most commonly injured muscle in sports requiring interval sprinting. The reason for this observation is unknown. The objective of this study was to calculate the forces of all three hamstring muscles, relative to each other, during a lengthening contraction to assess for any differences that may help explain the biceps femoris predilection for injury during interval sprinting. To calculate the displacement of each individual hamstring muscle previously performed studies on cadaveric anatomical data and hamstring kinematics during sprinting were used. From these displacement calculations for each individual hamstring muscle physical principles were then used to deduce the proportion of force exerted by each individual hamstring muscle during a lengthening muscle contraction. These deductions demonstrate that the biceps femoris muscle is required to exert proportionally more force in a lengthening muscle contraction relative to the semimembranosus and semitendinosus muscles primarily as a consequence of having to lengthen over a greater distance within the same time frame. It is hypothesized that this property maybe a factor in the known observation of the increased susceptibility of the biceps femoris muscle to injury during repeated sprints where recurrent higher force is required. PMID:25506583

Physical principles demonstrate that the biceps femoris muscle relative to the other hamstring muscles exerts the most force: implications for hamstring muscle strain injuries.

PubMed

Dolman, Bronwyn; Verrall, Geoffrey; Reid, Iain

2014-07-01

Of the hamstring muscle group the biceps femoris muscle is the most commonly injured muscle in sports requiring interval sprinting. The reason for this observation is unknown. The objective of this study was to calculate the forces of all three hamstring muscles, relative to each other, during a lengthening contraction to assess for any differences that may help explain the biceps femoris predilection for injury during interval sprinting. To calculate the displacement of each individual hamstring muscle previously performed studies on cadaveric anatomical data and hamstring kinematics during sprinting were used. From these displacement calculations for each individual hamstring muscle physical principles were then used to deduce the proportion of force exerted by each individual hamstring muscle during a lengthening muscle contraction. These deductions demonstrate that the biceps femoris muscle is required to exert proportionally more force in a lengthening muscle contraction relative to the semimembranosus and semitendinosus muscles primarily as a consequence of having to lengthen over a greater distance within the same time frame. It is hypothesized that this property maybe a factor in the known observation of the increased susceptibility of the biceps femoris muscle to injury during repeated sprints where recurrent higher force is required.

Procedure for utilizing the lift and thrust forces of ornithopters

NASA Technical Reports Server (NTRS)

Bezard, C.

1985-01-01

This procedure is distinguished by two beating wings which together describe, in space, a succession of interlaced triangles. On these wings, whose incidence varies automatically, identical forces are exerted: simultaneous lift and thrust when they make their descent, which is inclined toward the front of the craft, and lift alone when they make their ascent, which is inclined toward the rear of the craft and follows a slide horizontal movement. A mechanical device makes these movements possible. It includes: two wings with hollow profiles, connected by a framework located above a rigid frame and attached to it by bars with joints. These bars are moved with control rods which gear down the drive force. A mechanism with elastic bands or springs automatically varies the incidence of the wings.

Effect of the use of carprofen in dogs undergoing intense rehabilitation after lateral fabellar suture stabilization.

PubMed

Gordon-Evans, Wanda J; Dunning, Diane; Johnson, Ann L; Knap, Kim E

2011-07-01

To determine whether carprofen, a commercially available NSAID, would decrease perceived exertion and signs of pain in dogs and therefore increase muscle mass and hind limb function without decreasing range of motion after lateral fabellar suture stabilization. Randomized, blinded, controlled clinical trial. 35 dogs with cranial cruciate ligament rupture and lateral fabellar suture stabilization followed by rehabilitation. All dogs underwent surgical stabilization of cranial cruciate ligament rupture by placement of a lateral fabellar suture. Dogs received carprofen (2.2 mg/kg [1 mg/lb], PO, q 12 h) for the first 7 days after surgery and underwent concentrated rehabilitation exercises during weeks 3, 5, and 7 after surgery. Eighteen dogs also received carprofen (2.2 mg/kg, PO, q 12 h) during the weeks of concentrated rehabilitation. Outcomes were measured by a single investigator, who was blinded to group assignments, using pressure platform gait analysis, goniometry, thigh circumference, and mean workout speed at a consistent level of exertion. There were no differences between the 2 groups in ground reaction forces, thigh circumference, or exertion (mean workout speed) over time or at any individual time point. However, both groups improved significantly over time for all outcome measures. Providing carprofen to dogs during concentrated rehabilitation after lateral fabellar suture stabilization did not improve hind limb function, range of motion, or thigh circumference, nor did it decrease perceived exertion, compared with control dogs. Carprofen was not a compulsory component of a physical therapy regimen after lateral fabellar suture stabilization.

Investigation of the Forces Acting on Gliders in Automobile-pulley-winch and Airplane Towed Flight

NASA Technical Reports Server (NTRS)

Klemperer, W B

1942-01-01

The magnitude, the direction, and the fluctuation of towing forces exerted upon gliders by towing them aloft behind an automobile, by means of a winch, and by airplane were measured under a variety of conditions covering a range from gentle to severe types of operation. For these tests the towing forces did not exceed 92 percent of the gross weight of the glider. The results indicate that in pulley and winch towing the towing forces are of about the same magnitude as in automobile towing. Speed increases in the accelerated phases of the towing jerks encountered in airplane towing can readily become critical as speeds in excess of placard speeds can be attained. Passage through the slipstream of the towing airplane can be equivalent to a severe gust that, at high speed, may impose high wing loads and require large control moments.

Force Triggers YAP Nuclear Entry by Regulating Transport across Nuclear Pores.

PubMed

Elosegui-Artola, Alberto; Andreu, Ion; Beedle, Amy E M; Lezamiz, Ainhoa; Uroz, Marina; Kosmalska, Anita J; Oria, Roger; Kechagia, Jenny Z; Rico-Lastres, Palma; Le Roux, Anabel-Lise; Shanahan, Catherine M; Trepat, Xavier; Navajas, Daniel; Garcia-Manyes, Sergi; Roca-Cusachs, Pere

2017-11-30

YAP is a mechanosensitive transcriptional activator with a critical role in cancer, regeneration, and organ size control. Here, we show that force applied to the nucleus directly drives YAP nuclear translocation by decreasing the mechanical restriction of nuclear pores to molecular transport. Exposure to a stiff environment leads cells to establish a mechanical connection between the nucleus and the cytoskeleton, allowing forces exerted through focal adhesions to reach the nucleus. Force transmission then leads to nuclear flattening, which stretches nuclear pores, reduces their mechanical resistance to molecular transport, and increases YAP nuclear import. The restriction to transport is further regulated by the mechanical stability of the transported protein, which determines both active nuclear transport of YAP and passive transport of small proteins. Our results unveil a mechanosensing mechanism mediated directly by nuclear pores, demonstrated for YAP but with potential general applicability in transcriptional regulation. Copyright © 2017 Elsevier Inc. All rights reserved.

Aircraft control forces and EMG activity in a C-130 Hercules during strength-critical maneuvers.

PubMed

Hewson, D J; McNair, P J; Marshall, R N

2001-03-01

The force levels required to operate aircraft controls should be readily generated by pilots, without undue fatigue or exertion. However, maximum pilot applied forces, as specified in aircraft design standards, were empirically derived from the subjective comments of test pilots, and may not be applicable for the majority of pilots. Further, experienced RNZAF Hercules flying instructors have indicated that endurance and fatigue are problems for Hercules pilots. The aim of this study was to quantify aircraft control forces during emergency maneuvers in a Hercules aircraft and compare these forces with design standards. In addition, EMG data were recorded as an indicator of muscle fatigue during flight. Six subjects were tested in a C-130 Hercules aircraft. The maneuvers performed were low-level dynamic flight, one engine-off straight-and-level flight, and a two-engines-off simulated approach. The variables recorded were pilot-applied forces and EMG activity. Left rudder pedal force and vastus lateralis activity were both significantly greater during engine-off maneuvers than during low-level dynamic flight (p < 0.05). Maximum aircraft control forces for all controls were within 10% of the design standards. The mean EMG activity across all muscles and maneuvers was 26% MVC, with a peak of 61% MVC in vastus lateralis during the two-engine-off approach. The median frequency of the vastus lateralis EMG signal decreased 13.0% and 16.0% for the one engine-off and two-engine-off maneuvers, respectively. The forces required to fly a Hercules aircraft during emergency maneuvers are similar to the aircraft design standards. However, the levels of vastus lateralis muscle activation observed during the engine-off maneuvers can be sustained for approximately 1 min only. Thus, if two engines fail more than 1 min before landing, pilots may have to alternate control of the aircraft to share the workload and enable the aircraft to land safely.

Manipulating Neutral Atoms in Chip-Based Magnetic Traps

NASA Technical Reports Server (NTRS)

Aveline, David; Thompson, Robert; Lundblad, Nathan; Maleki, Lute; Yu, Nan; Kohel, James

2009-01-01

Several techniques for manipulating neutral atoms (more precisely, ultracold clouds of neutral atoms) in chip-based magnetic traps and atomic waveguides have been demonstrated. Such traps and waveguides are promising components of future quantum sensors that would offer sensitivities much greater than those of conventional sensors. Potential applications include gyroscopy and basic research in physical phenomena that involve gravitational and/or electromagnetic fields. The developed techniques make it possible to control atoms with greater versatility and dexterity than were previously possible and, hence, can be expected to contribute to the value of chip-based magnetic traps and atomic waveguides. The basic principle of these techniques is to control gradient magnetic fields with suitable timing so as to alter a trap to exert position-, velocity-, and/or time-dependent forces on atoms in the trap to obtain desired effects. The trap magnetic fields are generated by controlled electric currents flowing in both macroscopic off-chip electromagnet coils and microscopic wires on the surface of the chip. The methods are best explained in terms of examples. Rather than simply allowing atoms to expand freely into an atomic waveguide, one can give them a controllable push by switching on an externally generated or a chip-based gradient magnetic field. This push can increase the speed of the atoms, typically from about 5 to about 20 cm/s. Applying a non-linear magnetic-field gradient exerts different forces on atoms in different positions a phenomenon that one can exploit by introducing a delay between releasing atoms into the waveguide and turning on the magnetic field.

Optomechanical Control of Quantum Yield in Trans-Cis Ultrafast Photoisomerization of a Retinal Chromophore Model.

PubMed

Valentini, Alessio; Rivero, Daniel; Zapata, Felipe; García-Iriepa, Cristina; Marazzi, Marco; Palmeiro, Raúl; Fdez Galván, Ignacio; Sampedro, Diego; Olivucci, Massimo; Frutos, Luis Manuel

2017-03-27

The quantum yield of a photochemical reaction is one of the most fundamental quantities in photochemistry, as it measures the efficiency of the transduction of light energy into chemical energy. Nature has evolved photoreceptors in which the reactivity of a chromophore is enhanced by its molecular environment to achieve high quantum yields. The retinal chromophore sterically constrained inside rhodopsin proteins represents an outstanding example of such a control. In a more general framework, mechanical forces acting on a molecular system can strongly modify its reactivity. Herein, we show that the exertion of tensile forces on a simplified retinal chromophore model provokes a substantial and regular increase in the trans-to-cis photoisomerization quantum yield in a counterintuitive way, as these extension forces facilitate the formation of the more compressed cis photoisomer. A rationale for the mechanochemical effect on this photoisomerization mechanism is also proposed. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Contact inhibition of locomotion determines cell-cell and cell-substrate forces in tissues.

PubMed

Zimmermann, Juliane; Camley, Brian A; Rappel, Wouter-Jan; Levine, Herbert

2016-03-08

Cells organized in tissues exert forces on their neighbors and their environment. Those cellular forces determine tissue homeostasis as well as reorganization during embryonic development and wound healing. To understand how cellular forces are generated and how they can influence the tissue state, we develop a particle-based simulation model for adhesive cell clusters and monolayers. Cells are contractile, exert forces on their substrate and on each other, and interact through contact inhibition of locomotion (CIL), meaning that cell-cell contacts suppress force transduction to the substrate and propulsion forces align away from neighbors. Our model captures the traction force patterns of small clusters of nonmotile cells and larger sheets of motile Madin-Darby canine kidney (MDCK) cells. In agreement with observations in a spreading MDCK colony, the cell density in the center increases as cells divide and the tissue grows. A feedback between cell density, CIL, and cell-cell adhesion gives rise to a linear relationship between cell density and intercellular tensile stress and forces the tissue into a nonmotile state characterized by a broad distribution of traction forces. Our model also captures the experimentally observed tissue flow around circular obstacles, and CIL accounts for traction forces at the edge.

Magnetic tweezers optimized to exert high forces over extended distances from the magnet in multicellular systems

NASA Astrophysics Data System (ADS)

Selvaggi, L.; Pasakarnis, L.; Brunner, D.; Aegerter, C. M.

2018-04-01

Magnetic tweezers are mainly divided into two classes depending on the ability of applying torque or forces to the magnetic probe. We focused on the second category and designed a device composed by a single electromagnet equipped with a core having a special asymmetric profile to exert forces as large as 230 pN-2.8 μm Dynabeads at distances in excess of 100 μm from the magnetic tip. Compared to existing solutions our magnetic tweezers overcome important limitations, opening new experimental paths for the study of a wide range of materials in a variety of biophysical research settings. We discuss the benefits and drawbacks of different magnet core characteristics, which led us to design the current core profile. To demonstrate the usefulness of our magnetic tweezers, we determined the microrheological properties inside embryos of Drosophila melanogaster during the syncytial stage. Measurements in different locations along the dorsal-ventral axis of the embryos showed little variation, with a slight increase in cytoplasm viscosity at the periphery of the embryos. The mean cytoplasm viscosity we obtain by active force exertion inside the embryos is comparable to that determined passively using high-speed video microrheology.

The Role of Musculoskeletal Dynamics and Neuromuscular Control in Stress Development in Bone

NASA Technical Reports Server (NTRS)

DeWoody, Yssa

1996-01-01

The role of forces produced by the musculotendon units in the stress development of the long bones during gait has not been fully analyzed. It is well known that the musculotendons act as actuators producing the joint torques which drive the body. Although the joint torques required to perform certain motor tasks can be recovered through a kinematic analysis, it remains a difficult problem to determine the actual forces produced by each muscle that resulted in these torques. As a consequence, few studies have focused on the role of individual muscles in the development of stress in the bone. This study takes a control theoretic approach to the problem. A seven-link, eight degrees of freedom model of the body is controlled by various muscle groups on each leg to simulate gait. The simulations incorporate Hill-type models of muscles with activation and contraction dynamics controlled through neural inputs. This direct approach allows one to know the exact muscle forces exerted by each musculotendon throughout the gait cycle as well the joint torques and reaction forces at the ankle and knee. Stress and strain computed by finite element analysis on skeletal members will be related to these derived loading conditions. Thus the role of musculoskeletal dynamics and neuromuscular control in the stress development of the tibia during gait can be analyzed.

Strength capability while kneeling.

PubMed

Haslegrave, C M; Tracy, M F; Corlett, E N

1997-12-01

Work sometimes has to be carried out kneeling, particularly where jobs are performed in confined spaces as is common for miners, aircraft baggage handlers and maintenance workers. In order to assess the risks in performing forceful tasks under such conditions, data is needed on strength capabilities of kneeling subjects. A study was undertaken to measure isometric strength in single-handed exertions for male subjects and to investigate the effects on this of task layout factors (direction of force exertion, reach distance, height of the workpiece and orientation relative to the subject's sagittal plane). The data has been tabulated to show the degree to which strength may be reduced in different situations and analysis of the task factors showed their influence to be complex with direction of exertion and reach distance having the greatest effect. The results also suggest that exertions are weaker when subjects are kneeling on two knees than when kneeling on one knee, although this needs to be confirmed by direct experimental comparison.

Independently evolved upper jaw protrusion mechanisms show convergent hydrodynamic function in teleost fishes.

PubMed

Staab, Katie Lynn; Holzman, Roi; Hernandez, L Patricia; Wainwright, Peter C

2012-05-01

A protrusible upper jaw has independently evolved multiple times within teleosts and has been implicated in the success of two groups in particular: Acanthomorpha and Cypriniformes. We use digital particle image velocimetry (DPIV) to compare suction feeding flow dynamics in a representative of each of these clades: goldfish and bluegill. Using DPIV, we contrast the spatial pattern of flow, the temporal relationship between flow and head kinematics, and the contribution of jaw protrusion to the forces exerted on prey. As expected, the spatial patterns of flow were similar in the two species. However, goldfish were slower to reach maximal kinematic excursions, and were more flexible in the relative timing of jaw protrusion, other jaw movements and suction flows. Goldfish were also able to sustain flow speeds for a prolonged period of time as compared with bluegill, in part because goldfish generate lower peak flow speeds. In both species, jaw protrusion increased the force exerted on the prey. However, slower jaw protrusion in goldfish resulted in less augmentation of suction forces. This difference in force exerted on prey corresponds with differences in trophic niches and feeding behavior of the two species. The bluegill uses powerful suction to capture insect larvae whereas the goldfish uses winnowing to sort through detritus and sediment. The kinethmoid of goldfish may permit jaw protrusion that is independent of lower jaw movement, which could explain the ability of goldfish to decouple suction flows (due to buccal expansion) from upper jaw protrusion. Nevertheless, our results show that jaw protrusion allows both species to augment the force exerted on prey, suggesting that this is a fundamental benefit of jaw protrusion to suction feeders.

The force exerted by the membrane potential during protein import into the mitochondrial matrix

NASA Technical Reports Server (NTRS)

Shariff, Karim; Ghosal, Sandip; Matouschek, Andreas

2004-01-01

The force exerted on a targeting sequence by the electrical potential across the inner mitochondrial membrane is calculated on the basis of continuum electrostatics. The force is found to vary from 3.0 pN to 2.2 pN (per unit elementary charge) as the radius of the inner membrane pore (assumed aqueous) is varied from 6.5 to 12 A, its measured range. In the present model, the decrease in force with increasing pore width arises from the shielding effect of water. Since the pore is not very much wider than the distance between water molecules, the full shielding effect of water may not be present; the extreme case of a purely membranous pore without water gives a force of 3.2 pN per unit charge, which should represent an upper limit. When applied to mitochondrial import experiments on the protein barnase, these results imply that forces between 11 +/- 2 pN and 13.5 +/- 2.5 pN catalyze the unfolding of barnase in those experiments. A comparison of these results with unfolding forces measured using atomic force microscopy is made.

Automatic gain control of neural coupling during cooperative hand movements.

PubMed

Thomas, F A; Dietz, V; Schrafl-Altermatt, M

2018-04-13

Cooperative hand movements (e.g. opening a bottle) are controlled by a task-specific neural coupling, reflected in EMG reflex responses contralateral to the stimulation site. In this study the contralateral reflex responses in forearm extensor muscles to ipsilateral ulnar nerve stimulation was analyzed at various resistance and velocities of cooperative hand movements. The size of contralateral reflex responses was closely related to the level of forearm muscle activation required to accomplish the various cooperative hand movement tasks. This indicates an automatic gain control of neural coupling that allows a rapid matching of corrective forces exerted at both sides of an object with the goal 'two hands one action'.

Singularity and steering logic for control moment gyros on flexible space structures

NASA Astrophysics Data System (ADS)

Hu, Quan; Guo, Chuandong; Zhang, Jun

2017-08-01

Control moment gyros (CMGs) are a widely used device for generating control torques for spacecraft attitude control without expending propellant. Because of its effectiveness and cleanness, it has been considered to be mounted on a space structure for active vibration suppression. The resultant system is the so-called gyroelastic body. Since CMGs could exert both torque and modal force to the structure, it can also be used to simultaneously achieve attitude maneuver and vibration reduction of a flexible spacecraft. In this paper, we consider the singularity problem in such application of CMGs. The dynamics of an unconstrained gyroelastic body is established, from which the output equations of the CMGs are extracted. Then, torque singular state and modal force singular state are defined and visualized to demonstrate the singularity. Numerical examples of several typical CMGs configurations on a gyroelastic body are given. Finally, a steering law allowing output error is designed and applied to the vibration suppression of a plate with distributed CMGs.

Firing rate modulation of human motor units in different muscles during isometric contraction with various forces.

PubMed

Seki, K; Narusawa, M

1996-05-06

To examine the factors affecting the control of human motor units, rate coding strategies of the motor units were investigated in upper limb and intrinsic hand muscles during voluntary isometric contraction of steady force levels up to 80% of maximal voluntary contraction. Numerous spike trains from single motor units were recorded from the m. first dorsal interosseous (FDI) and the m. biceps brachii (BB) of eight human subjects by means of tungsten micro-electrodes, and the mean firing rate (MFR) was calculated for each subject and inter-individual comparisons made. The MFRs of the FDI were larger than that of the BB at the higher force level, and substantial differences were not found between these muscles at the lower force level. The slope of the linear regression line of MFRs vs. exerted forces for the FDI was more than twice that for the BB. Therefore, isometric force control of the FDI depends more on the rate coding strategy. The difference in rate coding between the FDI and BB motor units may be determined by factors other than muscle fiber composition, because both muscles are known to possess a similar composition of fiber types. Possible mechanisms underlying these characteristics of rate coding strategy are considered in this report.

Virtual exertions: evoking the sense of exerting forces in virtual reality using gestures and muscle activity.

PubMed

Chen, Karen B; Ponto, Kevin; Tredinnick, Ross D; Radwin, Robert G

2015-06-01

This study was a proof of concept for virtual exertions, a novel method that involves the use of body tracking and electromyography for grasping and moving projections of objects in virtual reality (VR). The user views objects in his or her hands during rehearsed co-contractions of the same agonist-antagonist muscles normally used for the desired activities to suggest exerting forces. Unlike physical objects, virtual objects are images and lack mass. There is currently no practical physically demanding way to interact with virtual objects to simulate strenuous activities. Eleven participants grasped and lifted similar physical and virtual objects of various weights in an immersive 3-D Cave Automatic Virtual Environment. Muscle activity, localized muscle fatigue, ratings of perceived exertions, and NASA Task Load Index were measured. Additionally, the relationship between levels of immersion (2-D vs. 3-D) was studied. Although the overall magnitude of biceps activity and workload were greater in VR, muscle activity trends and fatigue patterns for varying weights within VR and physical conditions were the same. Perceived exertions for varying weights were not significantly different between VR and physical conditions. Perceived exertion levels and muscle activity patterns corresponded to the assigned virtual loads, which supported the hypothesis that the method evoked the perception of physical exertions and showed that the method was promising. Ultimately this approach may offer opportunities for research and training individuals to perform strenuous activities under potentially safer conditions that mimic situations while seeing their own body and hands relative to the scene. © 2014, Human Factors and Ergonomics Society.

Capillary forces exerted by liquid drops caught between crossed cylinders. A 3-D meniscus problem with free contact line

NASA Technical Reports Server (NTRS)

Patzek, T. W.; Scriven, L. E.

1982-01-01

The Young-Laplace equation is solved for three-dimensional menisci between crossed cylinders, with either the contact line fixed or the contact angle prescribed, by means of the Galerkin/finite element method. Shapes are computed, and with them the practically important quantities: drop volume, wetted area, capillary pressure force, surface tension force, and the total force exerted by the drop on each cylinder. The results show that total capillary force between cylinders increases with decreasing contact angle, i.e. with better wetting. Capillary force is also increases with decreasing drop volume, approaching an asymptotic limit. However, the wetted area on each cylinder decreases with decreasing drop volume, which raises the question of the optimum drop volume to strive for, when permanent bonding is sought from solidified liquid. For then the strength of the bond is likely to depend upon the area of contact, which is the wetted area when the bonding agent was introduced in liquid form.

Acoustic Interaction Forces and Torques Acting on Suspended Spheres in an Ideal Fluid.

PubMed

Lopes, J Henrique; Azarpeyvand, Mahdi; Silva, Glauber T

2016-01-01

In this paper, the acoustic interaction forces and torques exerted by an arbitrary time-harmonic wave on a set of N objects suspended in an inviscid fluid are theoretically analyzed. We utilize the partial-wave expansion method with translational addition theorem and re-expansion of multipole series to solve the related multiple scattering problem. We show that the acoustic interaction force and torque can be obtained using the farfield radiation force and torque formulas. To exemplify the method, we calculate the interaction forces exerted by an external traveling and standing plane wave on an arrangement of two and three olive-oil droplets in water. The droplets' radii are comparable to the wavelength (i.e., Mie scattering regime). The results show that the acoustic interaction forces present an oscillatory spatial distribution which follows the pattern formed by interference between the external and rescattered waves. In addition, acoustic interaction torques arise on the absorbing droplets whenever a nonsymmetric wavefront is formed by the external and rescattered waves' interference.

The Force Exerted by the Membrane Potential During Protein Import into the Mitochondrial Matrix

NASA Technical Reports Server (NTRS)

Shariff, Karim; Ghosal, Sandip; Matouschek, Andreas

2002-01-01

The electrostatic force exerted on a targeting sequence by the electrical potential across the inner mitochondrial membrane is calculated and found to vary from 1.4 pN to 2.2 pN (per unit elementary charge) as the radius of the inner membrane pore (assumed aqueous) is varied from 12 to 6.5 Angstroms, its measured range. Since the pore is not very much wider than the distance between water molecules, the full shielding effect of water may not be present; the extreme case of a nonaqueous pore gives a force of 3.1 pN per unit charge, which represents an upper limit. When applied to mitochondrial import experiments on the protein harness, these results imply that a force of 11 plus or minus 4 pN is sufficient to catalyze the unfolding of harness during import. Comparison of these results with unfolding forces measured using atomic force microscopy suggests that the two are not inconsistent.

The force synergy of human digits in static and dynamic cylindrical grasps.

PubMed

Kuo, Li-Chieh; Chen, Shih-Wei; Lin, Chien-Ju; Lin, Wei-Jr; Lin, Sheng-Che; Su, Fong-Chin

2013-01-01

This study explores the force synergy of human digits in both static and dynamic cylindrical grasping conditions. The patterns of digit force distribution, error compensation, and the relationships among digit forces are examined to quantify the synergetic patterns and coordination of multi-finger movements. This study recruited 24 healthy participants to perform cylindrical grasps using a glass simulator under normal grasping and one-finger restricted conditions. Parameters such as the grasping force, patterns of digit force distribution, and the force coefficient of variation are determined. Correlation coefficients and principal component analysis (PCA) are used to estimate the synergy strength under the dynamic grasping condition. Specific distribution patterns of digit forces are identified for various conditions. The compensation of adjacent fingers for the force in the normal direction of an absent finger agrees with the principle of error compensation. For digit forces in anti-gravity directions, the distribution patterns vary significantly by participant. The forces exerted by the thumb are closely related to those exerted by other fingers under all conditions. The index-middle and middle-ring finger pairs demonstrate a significant relationship. The PCA results show that the normal forces of digits are highly coordinated. This study reveals that normal force synergy exists under both static and dynamic cylindrical grasping conditions.

The Force Synergy of Human Digits in Static and Dynamic Cylindrical Grasps

PubMed Central

Kuo, Li-Chieh; Chen, Shih-Wei; Lin, Chien-Ju; Lin, Wei-Jr; Lin, Sheng-Che; Su, Fong-Chin

2013-01-01

This study explores the force synergy of human digits in both static and dynamic cylindrical grasping conditions. The patterns of digit force distribution, error compensation, and the relationships among digit forces are examined to quantify the synergetic patterns and coordination of multi-finger movements. This study recruited 24 healthy participants to perform cylindrical grasps using a glass simulator under normal grasping and one-finger restricted conditions. Parameters such as the grasping force, patterns of digit force distribution, and the force coefficient of variation are determined. Correlation coefficients and principal component analysis (PCA) are used to estimate the synergy strength under the dynamic grasping condition. Specific distribution patterns of digit forces are identified for various conditions. The compensation of adjacent fingers for the force in the normal direction of an absent finger agrees with the principle of error compensation. For digit forces in anti-gravity directions, the distribution patterns vary significantly by participant. The forces exerted by the thumb are closely related to those exerted by other fingers under all conditions. The index-middle and middle-ring finger pairs demonstrate a significant relationship. The PCA results show that the normal forces of digits are highly coordinated. This study reveals that normal force synergy exists under both static and dynamic cylindrical grasping conditions. PMID:23544151

Gallium phosphide nanowires as a substrate for cultured neurons.

PubMed

Hällström, Waldemar; Mårtensson, Thomas; Prinz, Christelle; Gustavsson, Per; Montelius, Lars; Samuelson, Lars; Kanje, Martin

2007-10-01

Dissociated sensory neurons were cultured on epitaxial gallium phosphide (GaP) nanowires grown vertically from a gallium phosphide surface. Substrates covered by 2.5 microm long, 50 nm wide nanowires supported cell adhesion and axonal outgrowth. Cell survival was better on nanowire substrates than on planar control substrates. The cells interacted closely with the nanostructures, and cells penetrated by hundreds of wires were observed as well as wire bending due to forces exerted by the cells.

A Compact Forearm Crutch Based on Force Sensors for Aided Gait: Reliability and Validity.

PubMed

Chamorro-Moriana, Gema; Sevillano, José Luis; Ridao-Fernández, Carmen

2016-06-21

Frequently, patients who suffer injuries in some lower member require forearm crutches in order to partially unload weight-bearing. These lesions cause pain in lower limb unloading and their progression should be controlled objectively to avoid significant errors in accuracy and, consequently, complications and after effects in lesions. The design of a new and feasible tool that allows us to control and improve the accuracy of loads exerted on crutches during aided gait is necessary, so as to unburden the lower limbs. In this paper, we describe such a system based on a force sensor, which we have named the GCH System 2.0. Furthermore, we determine the validity and reliability of measurements obtained using this tool via a comparison with the validated AMTI (Advanced Mechanical Technology, Inc., Watertown, MA, USA) OR6-7-2000 Platform. An intra-class correlation coefficient demonstrated excellent agreement between the AMTI Platform and the GCH System. A regression line to determine the predictive ability of the GCH system towards the AMTI Platform was found, which obtained a precision of 99.3%. A detailed statistical analysis is presented for all the measurements and also segregated for several requested loads on the crutches (10%, 25% and 50% of body weight). Our results show that our system, designed for assessing loads exerted by patients on forearm crutches during assisted gait, provides valid and reliable measurements of loads.

A Compact Forearm Crutch Based on Force Sensors for Aided Gait: Reliability and Validity

PubMed Central

Chamorro-Moriana, Gema; Sevillano, José Luis; Ridao-Fernández, Carmen

2016-01-01

Frequently, patients who suffer injuries in some lower member require forearm crutches in order to partially unload weight-bearing. These lesions cause pain in lower limb unloading and their progression should be controlled objectively to avoid significant errors in accuracy and, consequently, complications and after effects in lesions. The design of a new and feasible tool that allows us to control and improve the accuracy of loads exerted on crutches during aided gait is necessary, so as to unburden the lower limbs. In this paper, we describe such a system based on a force sensor, which we have named the GCH System 2.0. Furthermore, we determine the validity and reliability of measurements obtained using this tool via a comparison with the validated AMTI (Advanced Mechanical Technology, Inc., Watertown, MA, USA) OR6-7-2000 Platform. An intra-class correlation coefficient demonstrated excellent agreement between the AMTI Platform and the GCH System. A regression line to determine the predictive ability of the GCH system towards the AMTI Platform was found, which obtained a precision of 99.3%. A detailed statistical analysis is presented for all the measurements and also segregated for several requested loads on the crutches (10%, 25% and 50% of body weight). Our results show that our system, designed for assessing loads exerted by patients on forearm crutches during assisted gait, provides valid and reliable measurements of loads. PMID:27338396

Small drill-hole, gas mini-permeameter probe

DOEpatents

Molz, III, Fred J.; Murdoch, Lawrence C.; Dinwiddie, Cynthia L.; Castle, James W.

2002-12-03

The distal end of a basic tube element including a stopper device with an expandable plug is positioned in a pre-drilled hole in a rock face. Rotating a force control wheel threaded on the tube element exerts force on a sleeve that in turn causes the plug component of the stopper means to expand and seal the distal end of the tube in the hole. Gas under known pressure is introduced through the tube element. A thin capillary tube positioned in the tube element connects the distal end of the tube element to means to detect and display pressure changes and data that allow the permeability of the rock to be determined.

Small drill-hole, gas mini-permeameter probe

DOEpatents

Molz, III, Fred J.; Murdoch, Lawrence C.; Dinwiddie, Cynthia L.; Castle, James W.

2002-01-01

The distal end of a basic tube element including a stopper device with an expandable plug is positioned in a pre-drilled hole in a rock face. Rotating a force control wheel threaded on the tube element exerts force on a sleeve that in turn causes the plug component of the stopper means to expand and seal the distal end of the tube in the hole. Gas under known pressure is introduced through the tube element. A thin capillary tube positioned in the tube element connects the distal end of the tube element to means to detect and display pressure changes and data that allow the permeability of the rock to be determined.

Boundaries steer the contraction of active gels

NASA Astrophysics Data System (ADS)

Schuppler, Matthias; Keber, Felix C.; Kröger, Martin; Bausch, Andreas R.

2016-10-01

Cells set up contractile actin arrays to drive various shape changes and to exert forces to their environment. To understand their assembly process, we present here a reconstituted contractile system, comprising F-actin and myosin II filaments, where we can control the local activation of myosin by light. By stimulating different symmetries, we show that the force balancing at the boundaries determine the shape changes as well as the dynamics of the global contraction. Spatially anisotropic attachment of initially isotropic networks leads to a self-organization of highly aligned contractile fibres, being reminiscent of the order formation in muscles or stress fibres. The observed shape changes and dynamics are fully recovered by a minimal physical model.

Relative Contribution of Arms and Legs in 30 s Fully Tethered Front Crawl Swimming

PubMed Central

Morouço, Pedro G.; Marinho, Daniel A.; Izquierdo, Mikel; Neiva, Henrique; Marques, Mário C.

2015-01-01

The relative contribution of arm stroke and leg kicking to maximal fully tethered front crawl swimming performance remains to be solved. Twenty-three national level young swimmers (12 male and 11 female) randomly performed 3 bouts of 30 s fully tethered swimming (using the whole body, only the arm stroke, and only the leg kicking). A load-cell system permitted the continuous measurement of the exerted forces, and swimming velocity was calculated from the time taken to complete a 50 m front crawl swim. As expected, with no restrictions swimmers were able to exert higher forces than that using only their arm stroke or leg kicking. Estimated relative contributions of arm stroke and leg kicking were 70.3% versus 29.7% for males and 66.6% versus 33.4% for females, with 15.6% and 13.1% force deficits, respectively. To obtain higher velocities, male swimmers are highly dependent on the maximum forces they can exert with the arm stroke (r = 0.77, P < 0.01), whereas female swimmers swimming velocity is more related to whole-body mean forces (r = 0.81, P < 0.01). The obtained results point that leg kicking plays an important role over short duration high intensity bouts and that the used methodology may be useful to identify strength and/or coordination flaws. PMID:26539511

Investigation of the Differential Contributions of Superficial and Deep Muscles on Cervical Spinal Loads with Changing Head Postures

PubMed Central

Cheng, Chih-Hsiu; Chien, Andy; Hsu, Wei-Li; Chen, Carl Pai-Chu; Cheng, Hsin-Yi Kathy

2016-01-01

Cervical spinal loads are predominately influenced by activities of cervical muscles. However, the coordination between deep and superficial muscles and their influence on the spinal loads is not well understood. This study aims to document the changes of cervical spinal loads and the differential contributions of superficial and deep muscles with varying head postures. Electromyography (EMG) of cervical muscles from seventeen healthy adults were measured during maximal isometric exertions for lateral flexion (at 10°, 20° and terminal position) as well as flexion/extension (at 10°, 20°, 30°, and terminal position) neck postures. An EMG-assisted optimization approach was used to estimate the muscle forces and subsequent spinal loads. The results showed that compressive and anterior-posterior shear loads increased significantly with neck flexion. In particular, deep muscle forces increased significantly with increasing flexion. It was also determined that in all different static head postures, the deep muscle forces were greater than those of the superficial muscle forces, however, such pattern was reversed during peak efforts where greater superficial muscle forces were identified with increasing angle of inclination. In summary, the identification of significantly increased spinal loads associated with increased deep muscle activation during flexion postures, implies higher risks in predisposing the neck to occupationally related disorders. The results also explicitly supported that deep muscles play a greater role in maintaining stable head postures where superficial muscles are responsible for peak exertions and reinforcing the spinal stability at terminal head postures. This study provided quantitative data of normal cervical spinal loads and revealed motor control strategies in coordinating the superficial and deep muscles during physical tasks. PMID:26938773

Investigation of the Differential Contributions of Superficial and Deep Muscles on Cervical Spinal Loads with Changing Head Postures.

PubMed

Cheng, Chih-Hsiu; Chien, Andy; Hsu, Wei-Li; Chen, Carl Pai-Chu; Cheng, Hsin-Yi Kathy

2016-01-01

Cervical spinal loads are predominately influenced by activities of cervical muscles. However, the coordination between deep and superficial muscles and their influence on the spinal loads is not well understood. This study aims to document the changes of cervical spinal loads and the differential contributions of superficial and deep muscles with varying head postures. Electromyography (EMG) of cervical muscles from seventeen healthy adults were measured during maximal isometric exertions for lateral flexion (at 10°, 20° and terminal position) as well as flexion/extension (at 10°, 20°, 30°, and terminal position) neck postures. An EMG-assisted optimization approach was used to estimate the muscle forces and subsequent spinal loads. The results showed that compressive and anterior-posterior shear loads increased significantly with neck flexion. In particular, deep muscle forces increased significantly with increasing flexion. It was also determined that in all different static head postures, the deep muscle forces were greater than those of the superficial muscle forces, however, such pattern was reversed during peak efforts where greater superficial muscle forces were identified with increasing angle of inclination. In summary, the identification of significantly increased spinal loads associated with increased deep muscle activation during flexion postures, implies higher risks in predisposing the neck to occupationally related disorders. The results also explicitly supported that deep muscles play a greater role in maintaining stable head postures where superficial muscles are responsible for peak exertions and reinforcing the spinal stability at terminal head postures. This study provided quantitative data of normal cervical spinal loads and revealed motor control strategies in coordinating the superficial and deep muscles during physical tasks.

The impact of rotator cuff tendinopathy on proprioception, measuring force sensation.

PubMed

Maenhout, Annelies G; Palmans, Tanneke; De Muynck, Martine; De Wilde, Lieven F; Cools, Ann M

2012-08-01

The impact of rotator cuff tendinopathy and related impingement on proprioception is not well understood. Numerous quantitative and qualitative changes in shoulder muscles have been shown in patients with rotator cuff tendinopathy. These findings suggest that control of force might be affected. This investigation wants to evaluate force sensation, a submodality of proprioception, in patients with rotator cuff tendinopathy. Thirty-six patients with rotator cuff tendinopathy and 30 matched healthy subjects performed force reproduction tests to isometric external and internal rotation to investigate how accurately they could reproduce a fixed target (50% MVC). Relative error, constant error, and force steadiness were calculated to evaluate respectively magnitude of error made during the test, direction of this error (overshoot or undershoot), and fluctuations of produced forces. Patients significantly overshoot the target (mean, 6.04% of target) while healthy subjects underestimate the target (mean, -5.76% of target). Relative error and force steadiness are similar in patients with rotator cuff tendinopathy and healthy subjects. Force reproduction tests, as executed in this study, were found to be highly reliable (ICC 0.849 and 0.909). Errors were significantly larger during external rotation tests, compared to internal rotation. Patients overestimate the target during force reproduction tests. This should be taken into account in the rehabilitation of patients with rotator cuff tendinopathy; however, precision of force sensation and steadiness of force exertion remains unaltered. This might indicate that control of muscle force is preserved. Copyright © 2012 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Mosby, Inc. All rights reserved.

Lateral forces exerted through ball or bar attachments in relation to the inclination of mini-implant underneath overdentures: in vitro study.

PubMed

Takagaki, Kyozo; Gonda, Tomoya; Maeda, Yoshinobu

2015-09-01

Lateral force to mini-implants should be avoided because mini-implants are weak mechanically because of its small diameter. Overdentures retained by mini-implants are usually formed using ball attachments. However, bar attachments can offer the advantage of splinting the mini-implants. This study examined the effect of attachments in withstanding these lateral forces in tilted mini-implants of overdentures. Strain gauges were attached to the mini-implants (2.5 × 18 mm) embedded in an acrylic resin block. Two mini-implants were inserted vertically (Control) or with one mini-implant inclined at 10° or 20° (10-inclined and 20-inclined, respectively). The female portions of the attachments were secured to the denture base. A prefabricated ball attachment and CAD/CAM-fabricated bar attachment were compared. A vertical load of 49 N was applied to the occlusal surface at a distance 10 mm away from the center of two mini-implants. The lateral force borne by the mini-implants was measured via the attached strain gauge. Mann-Whitney U-test and an analysis of Bonferroni correction were used to compare differences between the two attachments and among the three models (P < 0.05). The lateral force exerted to the inclined mini-implant was significantly greater than that borne by a vertical mini-implant for both attachment types. The lateral force on the 20° inclined mini-implants with bar attachments was smaller than that on mini-implants with ball attachments. Inclined mini-implants are subjected to greater stresses than vertical ones, and a bar attachment can reduce the lateral forces borne by the mini-implant when one mini-implant inclined at 20°. © 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

A Comparison of a Maximum Exertion Method and a Model-Based, Sub-Maximum Exertion Method for Normalizing Trunk EMG

PubMed Central

Cholewicki, Jacek; van Dieën, Jaap; Lee, Angela S.; Reeves, N. Peter

2011-01-01

The problem with normalizing EMG data from patients with painful symptoms (e.g. low back pain) is that such patients may be unwilling or unable to perform maximum exertions. Furthermore, the normalization to a reference signal, obtained from a maximal or sub-maximal task, tends to mask differences that might exist as a result of pathology. Therefore, we presented a novel method (GAIN method) for normalizing trunk EMG data that overcomes both problems. The GAIN method does not require maximal exertions (MVC) and tends to preserve distinct features in the muscle recruitment patterns for various tasks. Ten healthy subjects performed various isometric trunk exertions, while EMG data from 10 muscles were recorded and later normalized using the GAIN and MVC methods. The MVC method resulted in smaller variation between subjects when tasks were executed at the three relative force levels (10%, 20%, and 30% MVC), while the GAIN method resulted in smaller variation between subjects when the tasks were executed at the three absolute force levels (50 N, 100 N, and 145 N). This outcome implies that the MVC method provides a relative measure of muscle effort, while the GAIN-normalized EMG data gives an estimate of the absolute muscle force. Therefore, the GAIN-normalized EMG data tends to preserve the EMG differences between subjects in the way they recruit their muscles to execute various tasks, while the MVC-normalized data will tend to suppress such differences. The appropriate choice of the EMG normalization method will depend on the specific question that an experimenter is attempting to answer. PMID:21665489

Radiation Forces and Torques without Stress (Tensors)

ERIC Educational Resources Information Center

Bohren, Craig F.

2011-01-01

To understand radiation forces and torques or to calculate them does not require invoking photon or electromagnetic field momentum transfer or stress tensors. According to continuum electromagnetic theory, forces and torques exerted by radiation are a consequence of electric and magnetic fields acting on charges and currents that the fields induce…

Individual muscle control using an exoskeleton robot for muscle function testing.

PubMed

Ueda, Jun; Ming, Ding; Krishnamoorthy, Vijaya; Shinohara, Minoru; Ogasawara, Tsukasa

2010-08-01

Healthy individuals modulate muscle activation patterns according to their intended movement and external environment. Persons with neurological disorders (e.g., stroke and spinal cord injury), however, have problems in movement control due primarily to their inability to modulate their muscle activation pattern in an appropriate manner. A functionality test at the level of individual muscles that investigates the activity of a muscle of interest on various motor tasks may enable muscle-level force grading. To date there is no extant work that focuses on the application of exoskeleton robots to induce specific muscle activation in a systematic manner. This paper proposes a new method, named "individual muscle-force control" using a wearable robot (an exoskeleton robot, or a power-assisting device) to obtain a wider variety of muscle activity data than standard motor tasks, e.g., pushing a handle by hand. A computational algorithm systematically computes control commands to a wearable robot so that a desired muscle activation pattern for target muscle forces is induced. It also computes an adequate amount and direction of a force that a subject needs to exert against a handle by his/her hand. This individual muscle control method enables users (e.g., therapists) to efficiently conduct neuromuscular function tests on target muscles by arbitrarily inducing muscle activation patterns. This paper presents a basic concept, mathematical formulation, and solution of the individual muscle-force control and its implementation to a muscle control system with an exoskeleton-type robot for upper extremity. Simulation and experimental results in healthy individuals justify the use of an exoskeleton robot for future muscle function testing in terms of the variety of muscle activity data.

Contact inhibition of locomotion determines cell–cell and cell–substrate forces in tissues

PubMed Central

Zimmermann, Juliane; Camley, Brian A.; Rappel, Wouter-Jan; Levine, Herbert

2016-01-01

Cells organized in tissues exert forces on their neighbors and their environment. Those cellular forces determine tissue homeostasis as well as reorganization during embryonic development and wound healing. To understand how cellular forces are generated and how they can influence the tissue state, we develop a particle-based simulation model for adhesive cell clusters and monolayers. Cells are contractile, exert forces on their substrate and on each other, and interact through contact inhibition of locomotion (CIL), meaning that cell–cell contacts suppress force transduction to the substrate and propulsion forces align away from neighbors. Our model captures the traction force patterns of small clusters of nonmotile cells and larger sheets of motile Madin–Darby canine kidney (MDCK) cells. In agreement with observations in a spreading MDCK colony, the cell density in the center increases as cells divide and the tissue grows. A feedback between cell density, CIL, and cell–cell adhesion gives rise to a linear relationship between cell density and intercellular tensile stress and forces the tissue into a nonmotile state characterized by a broad distribution of traction forces. Our model also captures the experimentally observed tissue flow around circular obstacles, and CIL accounts for traction forces at the edge. PMID:26903658

The biomechanical effects of variation in the maximum forces exerted by trunk muscles on the joint forces and moments in the lumbar spine: a finite element analysis.

PubMed

Kim, K; Lee, S K; Kim, Y H

2010-10-01

The weakening of trunk muscles is known to be related to a reduction of the stabilization function provided by the muscles to the lumbar spine; therefore, strengthening deep muscles might reduce the possibility of injury and pain in the lumbar spine. In this study, the effect of variation in maximum forces of trunk muscles on the joint forces and moments in the lumbar spine was investigated. Accordingly, a three-dimensional finite element model of the lumbar spine that included the trunk muscles was used in this study. The variation in maximum forces of specific muscle groups was then modelled, and joint compressive and shear forces, as well as resultant joint moments, which were presumed to be related to spinal stabilization from a mechanical viewpoint, were analysed. The increase in resultant joint moments occurred owing to decrease in maximum forces of the multifidus, interspinales, intertransversarii, rotatores, iliocostalis, longissimus, psoas, and quadratus lumborum. In addition, joint shear forces and resultant joint moments were reduced as the maximum forces of deep muscles were increased. These results from finite element analysis indicate that the variation in maximum forces exerted by trunk muscles could affect the joint forces and joint moments in the lumbar spine.

Force per cross-sectional area from molecules to muscles: a general property of biological motors

PubMed Central

Meyer-Vernet, Nicole

2016-01-01

We propose to formally extend the notion of specific tension, i.e. force per cross-sectional area—classically used for muscles, to quantify forces in molecular motors exerting various biological functions. In doing so, we review and compare the maximum tensions exerted by about 265 biological motors operated by about 150 species of different taxonomic groups. The motors considered range from single molecules and motile appendages of microorganisms to whole muscles of large animals. We show that specific tensions exerted by molecular and non-molecular motors follow similar statistical distributions, with in particular, similar medians and (logarithmic) means. Over the 1019 mass (M) range of the cell or body from which the motors are extracted, their specific tensions vary as Mα with α not significantly different from zero. The typical specific tension found in most motors is about 200 kPa, which generalizes to individual molecular motors and microorganisms a classical property of macroscopic muscles. We propose a basic order-of-magnitude interpretation of this result. PMID:27493785

Flexible structure control laboratory development and technology demonstration

NASA Technical Reports Server (NTRS)

Vivian, H. C.; Blaire, P. E.; Eldred, D. B.; Fleischer, G. E.; Ih, C.-H. C.; Nerheim, N. M.; Scheid, R. E.; Wen, J. T.

1987-01-01

An experimental structure is described which was constructed to demonstrate and validate recent emerging technologies in the active control and identification of large flexible space structures. The configuration consists of a large, 20 foot diameter antenna-like flexible structure in the horizontal plane with a gimballed central hub, a flexible feed-boom assembly hanging from the hub, and 12 flexible ribs radiating outward. Fourteen electrodynamic force actuators mounted to the hub and to the individual ribs provide the means to excite the structure and exert control forces. Thirty permanently mounted sensors, including optical encoders and analog induction devices provide measurements of structural response at widely distributed points. An experimental remote optical sensor provides sixteen additional sensing channels. A computer samples the sensors, computes the control updates and sends commands to the actuators in real time, while simultaneously displaying selected outputs on a graphics terminal and saving them in memory. Several control experiments were conducted thus far and are documented. These include implementation of distributed parameter system control, model reference adaptive control, and static shape control. These experiments have demonstrated the successful implementation of state-of-the-art control approaches using actual hardware.

Forces exerted during exercises by patients with adolescent idiopathic scoliosis wearing fiberglass braces

PubMed Central

Romano, Michele; Carabalona, Roberta; Petrilli, Silvia; Sibilla, Paolo; Negrini, Stefano

2006-01-01

Objective To quantify and compare the forces exerted by scoliosis patients in fiberglass braces during exercises usually prescribed in departments where casts are made. The exercises are intended to increase corrective forces, activate muscles, stimulate ventilation and help the patient psychologically. Setting Outpatient care. Patients 17 consecutive adolescent patients wearing fiberglass brace for idiopathic scoliosis. Interventions Exercises (kyphotization, rotation, "escape from the pad") in different positions (sitting, supine, on all fours). Main outcome measure Pressure detected by the F-Socket System between the rib hump and the pad of the brace. Results In static and dynamic conditions, the position adopted did not alter the total pressure exerted by the brace, although the part of the sensor stimulated did vary. Kyphotization and rotation exercises produced a significant increase of pressure (+ 58.9% and +29.8%, respectively); however, the "escape from the pad" exercise, despite its name, did not produce any significant variation of pressure. Conclusion Exercises in the brace allow adjunctive forces to be applied on soft tissues and through them, presumably on the spine. Different exercises can be chosen to obtain different actions. Physical exercises and sporting activities are useful in mechanical terms, although other important actions should not be overlooked. PMID:16859544

Nearshore hydrodynamics at pocket beaches with contrasting wave exposure in southern Portugal

NASA Astrophysics Data System (ADS)

Horta, João; Oliveira, Sónia; Moura, Delminda; Ferreira, Óscar

2018-05-01

Pocket beaches on rocky coasts with headlands that control hydro-sedimentary processes are considered to be constrained sedimentary systems, generally with limited sediment inputs. Pocket beaches face severe changes over time. Under worst-case scenarios, these changes can result in the loss of the beach, causing waves to directly attack adjacent cliffs. Studies of nearshore hydrodynamics can help to understand such changes and optimise sediment nourishment procedures. The present work contributes to the knowledge of hydrodynamic forcing mechanisms at pocket beaches by providing a comprehensive description of the nearshore circulation at two beaches with contrasting wave exposures. Two pocket beaches in southern Portugal were studied by combining field measurements of waves and currents with numerical models (STWAVE and BOUSS-2D). The aim of this analysis was to evaluate nearshore hydrodynamics under different wave exposure forcing conditions (e.g. variable wave heights/directions and different tidal levels). The results show that the beach circulation can rapidly shift from longshore-to rip-dominated depending on changes in both the offshore wave direction and tidal levels. Waves with higher obliquity (for both low and moderate wave energy conditions) tend to generate longshore circulation in all considered tidal stages, while waves with lower obliquity tend to produce rip flow with higher-velocity rip currents during low to intermediate tidal stages. The results indicate that the location and intensity of rip currents strongly depend on geomorphological constraints, that is, the control exerted by shore platforms. A larger morphological control is observed at mean sea level because most platforms are submerged/exposed during high/low tide and therefore exert less control on nearshore circulation.

Effects of ladder parameters on asymmetric patterns of force exertion during below-knee amputees climbing ladders.

PubMed

Li, Weidong; Li, Shiqi; Fu, Yan; Chen, Jacon

2017-03-01

Different from walking, ladder climbing requires four-limb coordination and more energy exertion for below-knee amputees (BKAs). We hypothesized that functional deficiency of a disabled limb shall be compensated by the other three intact limbs, showing an asymmetry pattern among limbs. Hand and foot forces of six below-knee amputees and six able-bodied people were collected. Hand, foot and hand/foot sum force variances between groups (non-BKA, intact side and prosthetic side) were carefully examined. Our hypothesis was validated that there is asymmetry between prosthetic and intact side. Results further showed that the ipsilateral hand of the prosthetic leg is stronger than the hand on the intact side, compensating weakness of the prosthetic leg. Effects of ladder rung separations and ladder slant on asymmetric force distribution of BKAs were evaluated, indicating that rung separation has a more significant interactive effect on hand/foot force of BKAs than ladder slant.

The descent of ant: field-measured performance of gliding ants.

PubMed

Munk, Yonatan; Yanoviak, Stephen P; Koehl, M A R; Dudley, Robert

2015-05-01

Gliding ants avoid predatory attacks and potentially mortal consequences of dislodgement from rainforest canopy substrates by directing their aerial descent towards nearby tree trunks. The ecologically relevant measure of performance for gliding ants is the ratio of net horizontal to vertical distance traveled over the course of a gliding trajectory, or glide index. To study variation in glide index, we measured three-dimensional trajectories of Cephalotes atratus ants gliding in natural rainforest habitats. We determined that righting phase duration, glide angle, and path directness all significantly influence variation in glide index. Unsuccessful landing attempts result in the ant bouncing off its target and being forced to make a second landing attempt. Our results indicate that ants are not passive gliders and that they exert active control over the aerodynamic forces they experience during their descent, despite their apparent lack of specialized control surfaces. © 2015. Published by The Company of Biologists Ltd.

Multiple myxoid cysts secondary to occupation.

PubMed

Connolly, M; de Berker, D A R

2006-05-01

We report the case of a 50-year-old woman who presented with eight digital myxoid cysts (DMCs) involving the fingers of both hands. They developed within 12 months of the patient starting a job that involved pushing a garment into an embroidery mould, thus exerting a downward force on the fingertips. The pressure exerted from this force could have potentially damaged the joint synovial capsule, leading to rupture and loss of synovial gel, thus inducing myxoid cysts. This case suggests that DMCs may be related to occupation, and to our knowledge, this is only the second reported case of occupationally induced DMCs.

On the heating mechanism of magnetic flux loops in the solar atmosphere

NASA Technical Reports Server (NTRS)

Song, M. T.; Wu, S. T.

1984-01-01

An investigation is conducted of physical heating mechanisms due to the ponderomotive forces exerted by turbulent waves along the solar atmosphere's curved magnetic flux loops. Results indicate that the temperature difference between the inside and outside of the flux loop can be classified into three parts, two of which represent the cooling or heating effect exerted by the ponderomotive force, while the third is the heating effect due to turbulent energy conversion from the localized plasma. This heating mechanism is used to illustrate solar atmospheric heating by means of an example that leads to the formulation of plages.

Constrained handgrip force decreases upper extremity muscle activation and arm strength.

PubMed

Smets, Martin P H; Potvin, James R; Keir, Peter J

2009-09-01

Many industrial tasks require repetitive shoulder exertions to be performed with concurrent physical and mental demands. The highly mobile nature of the shoulder predisposes it to injury. The purpose of this study was to determine the effects of simultaneous gripping, at a specified magnitude, on muscle activity and maximal arm force in various directions. Ten female subjects performed maximal arm exertions at two different heights and five directions using both specified (30% maximum voluntary grip) and preferred (self-selected) grip forces. Electromyography was recorded from eight muscles of the right upper extremity. The preferred grip condition produced grip forces that were dependent on the combination of arm height and force direction and were significantly greater (arm force down), lower (to left, up and push forward), or similar to the specified grip condition. Regardless of the magnitude of the preferred grip force, specifying the grip resulted in decreased maximal arm strength (by 18-25%) and muscle activity (by 15-30%) in all conditions, indicating an interfering effect when the grip force was specified by visual target force-matching. Task constraints, such as specific gripping demands, may decrease peak force levels attainable and alter muscle activity. Depending on the nature of task, the amount of relative demand may differ, which should be considered when determining safety thresholds.

Surface-Controlled Properties of Myosin Studied by Electric Field Modulation.

PubMed

van Zalinge, Harm; Ramsey, Laurence C; Aveyard, Jenny; Persson, Malin; Mansson, Alf; Nicolau, Dan V

2015-08-04

The efficiency of dynamic nanodevices using surface-immobilized protein molecular motors, which have been proposed for diagnostics, drug discovery, and biocomputation, critically depends on the ability to precisely control the motion of motor-propelled, individual cytoskeletal filaments transporting cargo to designated locations. The efficiency of these devices also critically depends on the proper function of the propelling motors, which is controlled by their interaction with the surfaces they are immobilized on. Here we use a microfluidic device to study how the motion of the motile elements, i.e., actin filaments propelled by heavy mero-myosin (HMM) motor fragments immobilized on various surfaces, is altered by the application of electrical loads generated by an external electric field with strengths ranging from 0 to 8 kVm(-1). Because the motility is intimately linked to the function of surface-immobilized motors, the study also showed how the adsorption properties of HMM on various surfaces, such as nitrocellulose (NC), trimethylclorosilane (TMCS), poly(methyl methacrylate) (PMMA), poly(tert-butyl methacrylate) (PtBMA), and poly(butyl methacrylate) (PBMA), can be characterized using an external field. It was found that at an electric field of 5 kVm(-1) the force exerted on the filaments is sufficient to overcome the frictionlike resistive force of the inactive motors. It was also found that the effect of assisting electric fields on the relative increase in the sliding velocity was markedly higher for the TMCS-derivatized surface than for all other polymer-based surfaces. An explanation of this behavior, based on the molecular rigidity of the TMCS-on-glass surfaces as opposed to the flexibility of the polymer-based ones, is considered. To this end, the proposed microfluidic device could be used to select appropriate surfaces for future lab-on-a-chip applications as illustrated here for the almost ideal TMCS surface. Furthermore, the proposed methodology can be used to gain fundamental insights into the functioning of protein molecular motors, such as the force exerted by the motors under different operational conditions.

Structured box training improves stability of retraction while multitasking in colorectal surgery simulation.

PubMed

Kobiela, Jarek; Spychalski, Piotr; Łaski, Dariusz; Błażyńska-Spychalska, Agata; Łachiński, Andrzej J; Śledziński, Zbigniew; Hull, Tracy

2018-09-01

Laparoscopic colorectal surgery has an established role. The ability to multitask (use a retraction tool with one hand and navigate a laparoscopic camera with the other) is desired for efficient laparoscopic surgery. Surgical trainees must learn this skill to perform advanced laparoscopic tasks. The aim was to determine whether a box-training protocol improves the stability of retraction while multitasking in colorectal surgery simulation. Fifty-eight medical students were recruited to attend a basic laparoscopic box-training course. Ability to perform steady retraction with and without multitasking was measured initially and at the conclusion of the course. Before training, students demonstrated a decrease in performance while multitasking with a greater maximal exerted force, a greater range of force, and a greater standard deviation for traction and minimal exerted force, range of force and a greater standard deviation for countertraction. Statistically significant improvement (lower maximal exerted force and lower range of force) was observed for traction while multitasking after training. After the training, no statistically significant differences were found when the student performed a single task versus multitasking, both for traction and countertraction. A structured box-training curriculum improved the stability of retraction while multitasking in this colorectal surgery simulation. Although it did not improve stability of retraction as a single task, it did improve stability of retraction while multitasking. After training, this enables the trainee to retract as efficiently while operating the camera as they retract when only focusing on retraction as a single task. Copyright © 2018 Elsevier Inc. All rights reserved.

Climate impact of anthropogenic aerosols on cirrus clouds

NASA Astrophysics Data System (ADS)

Penner, J.; Zhou, C.

2017-12-01

Cirrus clouds have a net warming effect on the atmosphere and cover about 30% of the Earth's area. Aerosol particles initiate ice formation in the upper troposphere through modes of action that include homogeneous freezing of solution droplets, heterogeneous nucleation on solid particles immersed in a solution, and deposition nucleation of vapor onto solid particles. However, the efficacy with which particles act to form cirrus particles in a model depends on the representation of updrafts. Here, we use a representation of updrafts based on observations of gravity waves, and follow ice formation/evaporation during both updrafts and downdrafts. We examine the possible change in ice number concentration from anthropogenic soot originating from surface sources of fossil fuel and biomass burning and from aircraft particles that have previously formed ice in contrails. Results show that fossil fuel and biomass burning soot aerosols with this version exert a radiative forcing of -0.15±0.02 Wm-2 while aircraft aerosols that have been pre-activated within contrails exert a forcing of -0.20±0.06 Wm-2, but it is possible to decrease these estimates of forcing if a larger fraction of dust particles act as heterogeneous ice nuclei. In addition aircraft aerosols may warm the climate if a large fraction of these particles act as ice nuclei. The magnitude of the forcing in cirrus clouds can be comparable to the forcing exerted by anthropogenic aerosols on warm clouds. This assessment could therefore support climate models with high sensitivity to greenhouse gas forcing, while still allowing the models to fit the overall historical temperature change.

Judgments about Forces in Described Interactions between Objects

ERIC Educational Resources Information Center

White, Peter A.

2011-01-01

In 4 experiments, participants made judgments about forces exerted and resistances put up by objects involved in described interactions. Two competing hypotheses were tested: (1) that judgments are derived from the same knowledge base that is thought to be the source of perceptual impressions of forces that occur with visual stimuli, and (2) that…

The Origins of Force--Misconceptions and Classroom Controversy.

ERIC Educational Resources Information Center

Steinberg, Melvin S.

Misconceptions associated with the origins of force and the effectiveness of a bridging strategy for developing correct conceptual models in mechanics are identified for high school physics teachers in this paper. The situation investigated was whether a table exerts an upward force on a book. Student misconceptions related to this phenomenon as…

Hand forces exerted by long-term care staff when pushing wheelchairs on compliant and non-compliant flooring.

PubMed

Lachance, Chantelle C; Korall, Alexandra M B; Russell, Colin M; Feldman, Fabio; Robinovitch, Stephen N; Mackey, Dawn C

2018-09-01

Purpose-designed compliant flooring and carpeting have been promoted as a means for reducing fall-related injuries in high-risk environments, such as long-term care. However, it is not known whether these surfaces influence the forces that long-term care staff exert when pushing residents in wheelchairs. We studied 14 direct-care staff who pushed a loaded wheelchair instrumented with a triaxial load cell to test the effects on hand force of flooring overlay (vinyl versus carpet) and flooring subfloor (concrete versus compliant rubber [brand: SmartCells]). During straight-line pushing, carpet overlay increased initial and sustained hand forces compared to vinyl overlay by 22-49% over a concrete subfloor and by 8-20% over a compliant subfloor. Compliant subflooring increased initial and sustained hand forces compared to concrete subflooring by 18-31% when under a vinyl overlay. In contrast, compliant flooring caused no change in initial or sustained hand forces compared to concrete subflooring when under a carpet overlay. Copyright © 2018 Elsevier Ltd. All rights reserved.

Astronaut-Induced Disturbances to the Microgravity Environment of the Mir Space Station

NASA Technical Reports Server (NTRS)

Newman, Dava J.; Amir, Amir R.; Beck, Sherwin M.

2001-01-01

In preparation for the International Space Station, the Enhanced Dynamic Load Sensors Space Flight Experiment measured the forces and moments astronauts exerted on the Mir Space Station during their daily on-orbit activities to quantify the astronaut-induced disturbances to the microgravity environment during a long-duration space mission. An examination of video recordings of the astronauts moving in the modules and using the instrumented crew restraint and mobility load sensors led to the identification of several typical astronaut motions and the quantification or the associated forces and moments exerted on the spacecraft. For 2806 disturbances recorded by the foot restraints and hand-hold sensor, the highest force magnitude was 137 N. For about 96% of the time, the maximum force magnitude was below 60 N, and for about 99% of the time the maximum force magnitude was below 90 N. For 95% of the astronaut motions, the rms force level was below 9.0 N. It can be concluded that expected astronaut-induced loads from usual intravehicular activity are considerably less than previously thought and will not significantly disturb the microgravity environment.

Superconducting rebalance acceleration and rate sensor

NASA Technical Reports Server (NTRS)

Torti, R.; Gerver, M.; Gondhalekar, V.; Maxwell, B.

1994-01-01

The goal of this program is the development of a high precision multisensor based on a high T(sub c) superconducting proof mass. The design of a prototype is currently underway. Key technical issues appear resolvable. High temperature superconductors have complicated, hysteretic flux dynamics but the forces on them can be linearly controlled for small displacements. Current data suggests that the forces on the superconductors decay over a short time frame and then stabilize, though very long term data is not available. The hysteretic force characteristics are substantial for large scale excursions, but do not appear to be an issue for the very small displacements required in this device. Sufficient forces can be exerted for non-contact suspension of a centimeter sized proof mass in a vacuum sealed nitrogen jacket cryostat. High frequency capacitive sensing using stripline technology will yield adequate position resolution for 0.1 micro-g measurements at 100 Hz. Overall, a reasonable cost, but very high accuracy, system is feasible with this technology.

Superconducting rebalance acceleration and rate sensor

NASA Astrophysics Data System (ADS)

Torti, R.; Gerver, M.; Gondhalekar, V.; Maxwell, B.

1994-05-01

The goal of this program is the development of a high precision multisensor based on a high T(sub c) superconducting proof mass. The design of a prototype is currently underway. Key technical issues appear resolvable. High temperature superconductors have complicated, hysteretic flux dynamics but the forces on them can be linearly controlled for small displacements. Current data suggests that the forces on the superconductors decay over a short time frame and then stabilize, though very long term data is not available. The hysteretic force characteristics are substantial for large scale excursions, but do not appear to be an issue for the very small displacements required in this device. Sufficient forces can be exerted for non-contact suspension of a centimeter sized proof mass in a vacuum sealed nitrogen jacket cryostat. High frequency capacitive sensing using stripline technology will yield adequate position resolution for 0.1 micro-g measurements at 100 Hz. Overall, a reasonable cost, but very high accuracy, system is feasible with this technology.

Optofluidics incorporating actively controlled micro- and nano-particles

PubMed Central

Kayani, Aminuddin A.; Khoshmanesh, Khashayar; Ward, Stephanie A.; Mitchell, Arnan; Kalantar-zadeh, Kourosh

2012-01-01

The advent of optofluidic systems incorporating suspended particles has resulted in the emergence of novel applications. Such systems operate based on the fact that suspended particles can be manipulated using well-appointed active forces, and their motions, locations and local concentrations can be controlled. These forces can be exerted on both individual and clusters of particles. Having the capability to manipulate suspended particles gives users the ability for tuning the physical and, to some extent, the chemical properties of the suspension media, which addresses the needs of various advanced optofluidic systems. Additionally, the incorporation of particles results in the realization of novel optofluidic solutions used for creating optical components and sensing platforms. In this review, we present different types of active forces that are used for particle manipulations and the resulting optofluidic systems incorporating them. These systems include optical components, optofluidic detection and analysis platforms, plasmonics and Raman systems, thermal and energy related systems, and platforms specifically incorporating biological particles. We conclude the review with a discussion of future perspectives, which are expected to further advance this rapidly growing field. PMID:23864925

Closed Loop Control of a Tethered Magnetic Capsule Endoscope

PubMed Central

Taddese, Addisu Z.; Slawinski, Piotr R.; Obstein, Keith L.; Valdastri, Pietro

2017-01-01

Magnetic field gradients have repeatedly been shown to be the most feasible mechanism for gastrointestinal capsule endoscope actuation. An inverse quartic magnetic force variation with distance results in large force gradients induced by small movements of a driving magnet; this necessitates robotic actuation of magnets to implement stable control of the device. A typical system consists of a serial robot with a permanent magnet at its end effector that actuates a capsule with an embedded permanent magnet. We present a tethered capsule system where a capsule with an embedded magnet is closed loop controlled in 2 degree-of-freedom in position and 2 degree-of-freedom in orientation. Capitalizing on the magnetic field of the external driving permanent magnet, the capsule is localized in 6-D allowing for both position and orientation feedback to be used in a control scheme. We developed a relationship between the serial robot's joint parameters and the magnetic force and torque that is exerted onto the capsule. Our methodology was validated both in a dynamic simulation environment where a custom plug-in for magnetic interaction was written, as well as on an experimental platform. The tethered capsule was demonstrated to follow desired trajectories in both position and orientation with accuracy that is acceptable for colonoscopy. PMID:28286886

Closed Loop Control of a Tethered Magnetic Capsule Endoscope.

PubMed

Taddese, Addisu Z; Slawinski, Piotr R; Obstein, Keith L; Valdastri, Pietro

2016-06-01

Magnetic field gradients have repeatedly been shown to be the most feasible mechanism for gastrointestinal capsule endoscope actuation. An inverse quartic magnetic force variation with distance results in large force gradients induced by small movements of a driving magnet; this necessitates robotic actuation of magnets to implement stable control of the device. A typical system consists of a serial robot with a permanent magnet at its end effector that actuates a capsule with an embedded permanent magnet. We present a tethered capsule system where a capsule with an embedded magnet is closed loop controlled in 2 degree-of-freedom in position and 2 degree-of-freedom in orientation. Capitalizing on the magnetic field of the external driving permanent magnet, the capsule is localized in 6-D allowing for both position and orientation feedback to be used in a control scheme. We developed a relationship between the serial robot's joint parameters and the magnetic force and torque that is exerted onto the capsule. Our methodology was validated both in a dynamic simulation environment where a custom plug-in for magnetic interaction was written, as well as on an experimental platform. The tethered capsule was demonstrated to follow desired trajectories in both position and orientation with accuracy that is acceptable for colonoscopy.

Hydroperiod regime controls the organization of plant species in wetlands

PubMed Central

Foti, Romano; del Jesus, Manuel; Rinaldo, Andrea; Rodriguez-Iturbe, Ignacio

2012-01-01

With urban, agricultural, and industrial needs growing throughout the past decades, wetland ecosystems have experienced profound changes. Most critically, the biodiversity of wetlands is intimately linked to its hydrologic dynamics, which in turn are being drastically altered by ongoing climate changes. Hydroperiod regimes, e.g., percentage of time a site is inundated, exert critical control in the creation of niches for different plant species in wetlands. However, the spatial signatures of the organization of plant species in wetlands and how the different drivers interact to yield such signatures are unknown. Focusing on Everglades National Park (ENP) in Florida, we show here that cluster sizes of each species follow a power law probability distribution and that such clusters have well-defined fractal characteristics. Moreover, we individuate and model those signatures via the interplay between global forcings arising from the hydroperiod regime and local controls exerted by neighboring vegetation. With power law clustering often associated with systems near critical transitions, our findings are highly relevant for the management of wetland ecosystems. In addition, our results show that changes in climate and land management have a quantifiable predictable impact on the type of vegetation and its spatial organization in wetlands. PMID:23150589

Force feedback vessel ligation simulator in knot-tying proficiency training.

PubMed

Hsu, Justin L; Korndorffer, James R; Brown, Kimberly M

2016-02-01

Tying gentle secure knots is an important skill. We have developed a force feedback simulator that measures force exerted during knot tying. This pilot study examines the benefits of this simulator in a deliberate practice curriculum. The simulator consists of silastic tubing with a force sensor. Knot quality was assessed using digital caliper measurement. Participants performed 10 vessel ligations as a pretest, then were shown force readings and tied knots until reaching proficiency targets. Average peak forces precurriculum and postcurriculum were compared using Student t test. Participants exerted significantly less force after completing the curriculum (.61 N ± .22 vs 1.42 N ± .53, P < .001), and had fewer air knots (10% vs 27%). The curriculum was completed in an average of 19.4 ± 6.27 minutes and required an average of 11.7 ± 4.03 knots to reach proficiency. This study demonstrates the feasibility of real-time feedback in learning to tie delicate knots. The curriculum can be completed in a reasonable amount of time, and may also work as a warm-up exercise before a surgical case. Copyright © 2016 Elsevier Inc. All rights reserved.

Rail commuter vehicle curving performance

DOT National Transportation Integrated Search

2002-04-01

This report presents results of a program to design and install a wayside wheel-rail force measurement system. The test site is capable of developing a set of measurements of lateral and vertical forces exerted between the wheel and the rail at caref...

Impact of distal median neuropathy on handwriting performance for patients with carpal tunnel syndrome in office and administrative support occupations.

PubMed

Kuo, Li-Chieh; Hsu, Hsiao-Man; Wu, Po-Ting; Lin, Sheng-Che; Hsu, Hsiu-Yun; Jou, I-Ming

2014-06-01

This study investigates the handwriting performance of patients with carpal tunnel syndrome (CTS) and healthy controls in office and administrative support occupations, adopting both biomechanical and functional perspectives. This work also explores how surgical intervention altered the performance of the CTS patients. Fourteen CTS patients and 14 control subjects were recruited to complete a self-reported survey and participate in sensory tests, hand strength, dexterity and handwriting tasks using a custom force acquisition pen along with motion capture technology. Based on the results of these, the sensory measurements, along with functional and biomechanical parameters, were used to determine the differences between the groups and also reveal any improvements that occurred in the CTS group after surgical intervention. The CTS patients showed significantly poorer hand sensibility and dexterity than the controls, as well as excessive force exertion of the digits and pen tip, and less efficient force adjustment ability during handwriting. After surgery and sensory recovery, the hand dexterity and pen tip force of the CTS patients improved significantly. The force adjustment abilities of the digits also increased, but these changes were not statistically significant. This study provides the objective measurements and novel apparatus that can be used to determine impairments in the handwriting abilities of office or administrative workers with CTS. The results can also help clinicians or patients to better understand the sensory-related deficits in sensorimotor control of the hand related to CTS, and thus develop and implement more suitable training or adaptive protocols.

Exercise-induced stress resistance is independent of exercise controllability and the medial prefrontal cortex

PubMed Central

Greenwood, Benjamin N.; Spence, Katie G.; Crevling, Danielle M.; Clark, Peter J.; Craig, Wendy C.; Fleshner, Monika

2014-01-01

Exercise increases resistance against stress-related disorders such as anxiety and depression. Similarly, the perception of control is a powerful predictor of neurochemical and behavioral responses to stress, but whether the experience of choosing to exercise, and exerting control over that exercise, is a critical factor in producing exercise-induced stress resistance is unknown. The current studies investigated whether the protective effects of exercise against the anxiety- and depression-like consequences of stress are dependent on exercise controllability and a brain region implicated in the protective effects of controllable experiences, the medial prefrontal cortex. Adult male Fischer 344 rats remained sedentary, were forced to run on treadmills or motorised running wheels, or had voluntary access to wheels for 6 weeks. Three weeks after exercise onset, rats received sham surgery or excitotoxic lesions of the medial prefrontal cortex. Rats were exposed to home cage or uncontrollable tail shock treatment three weeks later. Shock-elicited fear conditioning and shuttle box escape testing occurred the next day. Both forced and voluntary wheel running, but not treadmill training, prevented the exaggerated fear conditioning and interference with escape learning produced by uncontrollable stress. Lesions of the medial prefrontal cortex failed to eliminate the protective effects of forced or voluntary wheel running. These data suggest that exercise controllability and the medial prefrontal cortex are not critical factors in conferring the protective effects of exercise against the affective consequences of stressor exposure, and imply that exercise perceived as forced may still benefit affect and mental health. PMID:23121339

A Novel Method Of Gradient Forming and Fluid Manipulation in Reduced Gravity Environments

NASA Technical Reports Server (NTRS)

Ramachandran N.; Leslie, F.

1999-01-01

The use of magnetic fields to control the motion and position of non-conducting liquids has received growing interest in recent times. The possibility of using the forces exerted by a nonuniform magnetic field on a ferrofluid to not only achieve fluid manipulation but also to actively control fluid motion makes it an attractive candidate for applications such as heat transfer in space systems. Terrestrial heat transfer equipment often relies on the normal gravitational force to hold liquid in a desired position or to provide a buoyant force to enhance the heat transfer rate. The residual gravitational force present in a space environment may no longer serve these useful functions and other forces, such as surface tension, can play a significant role in determining heat transfer rates. Although typically overwhelmed by gravitational forces in terrestrial applications, the body force induced in a ferrofluid by a nonuniform magnetic field can help to achieve these objectives in a microgravity environment. This paper will address the fluid manipulation aspect and will comprise of results from model fluid experiments and numerical modeling of the problem. Results from a novel method of forming concentration gradients that are applicable to low gravity applications will be presented. The ground based experiments are specifically tailored to demonstrate the magnetic manipulation capability of a ferrofluid and show that gravitational effects can be countered in carefully designed systems. The development of governing equations for the system will be presented along with a sampling of numerical results.

From static to animated: Measuring mechanical forces in tissues

PubMed Central

2017-01-01

Cells are physical objects that exert mechanical forces on their surroundings as they migrate and take their places within tissues. New techniques are now poised to enable the measurement of cell-generated mechanical forces in intact tissues in vivo, which will illuminate the secret dynamic lives of cells and change our current perception of cell biology. PMID:28003332

Method and Apparatus for Characterizing Pressure Sensors using Modulated Light Beam Pressure

NASA Technical Reports Server (NTRS)

Youngquist, Robert C. (Inventor)

2003-01-01

Embodiments of apparatuses and methods are provided that use light sources instead of sound sources for characterizing and calibrating sensors for measuring small pressures to mitigate many of the problems with using sound sources. In one embodiment an apparatus has a light source for directing a beam of light on a sensing surface of a pressure sensor for exerting a force on the sensing surface. The pressure sensor generates an electrical signal indicative of the force exerted on the sensing surface. A modulator modulates the beam of light. A signal processor is electrically coupled to the pressure sensor for receiving the electrical signal.

Activity-driven changes in the mechanical properties of fire ant aggregations

NASA Astrophysics Data System (ADS)

Tennenbaum, Michael; Fernandez-Nieves, Alberto

2017-11-01

Fire ant aggregations are active materials composed of individual constituents that are able to transform internal energy into work. We find using rheology and direct visualization that the aggregation undergoes activity cycles that affect the mechanical properties of the system. When the activity is high, the aggregation approximately equally stores and dissipates energy, it is more homogeneous, and exerts a high outward force. When the activity is low, the aggregation is predominantly elastic, it is more heterogeneous, and it exerts a small outward force. We rationalize our results using a simple kinetic model where the number of active ants within the aggregation is the essential quantity.

Parametric Investigation of the Effect of Hub Pitching Moment on Blade Vortex Interaction (BVI) Noise of an Isolated Rotor

NASA Technical Reports Server (NTRS)

Malpica, Carlos; Greenwood, Eric; Sim, Ben

2016-01-01

At the most fundamental level, main rotor loading noise is caused by the harmonically-varying aerodynamic loads (acoustic pressures) exerted by the rotating blades on the air. Rotorcraft main rotor noise is therefore, in principle, a function of rotor control inputs, and thus the forces and moments required to achieve steady, or "trim", flight equilibrium. In certain flight conditions, the ensuing aerodynamic loading on the rotor(s) can result in highly obtrusive harmonic noise. The effect of the propulsive force, or X-force, on Blade-Vortex Interaction (BVI) noise is well documented. This paper presents an acoustics parametric sensitivity analysis of the effect of varying rotor aerodynamic pitch hub trim moments on BVI noise radiated by an S-70 helicopter main rotor. Results show that changing the hub pitching moment for an isolated rotor, trimmed in nominal 80 knot, 6 and 12 deg descent, flight conditions, alters the miss distance between the blades and the vortex in ways that have varied and noticeable effects on the BVI radiated-noise directionality. Peak BVI noise level is however not significantly altered. The application of hub pitching moment allows the attitude of the fuselage to be controlled; for example, to compensate for the uncomfortable change in fuselage pitch attitude introduced by a fuselage-mounted X-force controller.

Double-layer rotor magnetic shield performance analysis in high temperature superconducting synchronous generators under short circuit fault conditions

NASA Astrophysics Data System (ADS)

Hekmati, Arsalan; Aliahmadi, Mehdi

2016-12-01

High temperature superconducting, HTS, synchronous machines benefit from a rotor magnetic shield in order to protect superconducting coils against asynchronous magnetic fields. This magnetic shield, however, suffers from exerted Lorentz forces generated in light of induced eddy currents during transient conditions, e.g. stator windings short-circuit fault. In addition, to the exerted electromagnetic forces, eddy current losses and the associated effects on the cryogenic system are the other consequences of shielding HTS coils. This study aims at investigating the Rotor Magnetic Shield, RMS, performance in HTS synchronous generators under stator winding short-circuit fault conditions. The induced eddy currents in different circumferential positions of the rotor magnetic shield along with associated Joule heating losses would be studied using 2-D time-stepping Finite Element Analysis, FEA. The investigation of Lorentz forces exerted on the magnetic shield during transient conditions has also been performed in this paper. The obtained results show that double line-to-ground fault is of the most importance among different types of short-circuit faults. It was revealed that when it comes to the design of the rotor magnetic shields, in addition to the eddy current distribution and the associated ohmic losses, two phase-to-ground fault should be taken into account since the produced electromagnetic forces in the time of fault conditions are more severe during double line-to-ground fault.

Finite Element Modeling of Intermuscular Interactions and Myofascial Force Transmission

DTIC Science & Technology

2001-10-25

obtained explain force differences at the distal and proximal tendons of muscles that have mechanical interaction. This is in agreement with experimental...consequence is that active force generated within one muscle may be exerted at the tendon of another muscle. Keywords- Finite element method...7]. Therefore, in vivo there is an additional route for force transmission out off the muscle, which completely bypasses the tendon of the muscle

Biomechanically determined hand force limits protecting the low back during occupational pushing and pulling tasks.

PubMed

Weston, Eric B; Aurand, Alexander; Dufour, Jonathan S; Knapik, Gregory G; Marras, William S

2018-06-01

Though biomechanically determined guidelines exist for lifting, existing recommendations for pushing and pulling were developed using a psychophysical approach. The current study aimed to establish objective hand force limits based on the results of a biomechanical assessment of the forces on the lumbar spine during occupational pushing and pulling activities. Sixty-two subjects performed pushing and pulling tasks in a laboratory setting. An electromyography-assisted biomechanical model estimated spinal loads, while hand force and turning torque were measured via hand transducers. Mixed modelling techniques correlated spinal load with hand force or torque throughout a wide range of exposures in order to develop biomechanically determined hand force and torque limits. Exertion type, exertion direction, handle height and their interactions significantly influenced dependent measures of spinal load, hand force and turning torque. The biomechanically determined guidelines presented herein are up to 30% lower than comparable psychophysically derived limits and particularly more protective for straight pushing. Practitioner Summary: This study utilises a biomechanical model to develop objective biomechanically determined push/pull risk limits assessed via hand forces and turning torque. These limits can be up to 30% lower than existing psychophysically determined pushing and pulling recommendations. Practitioners should consider implementing these guidelines in both risk assessment and workplace design moving forward.

Using surface integrals for checking Archimedes' law of buoyancy

NASA Astrophysics Data System (ADS)

Lima, F. M. S.

2012-01-01

A mathematical derivation of the force exerted by an inhomogeneous (i.e. compressible) fluid on the surface of an arbitrarily shaped body immersed in it is not found in the literature, which may be attributed to our trust in Archimedes' law of buoyancy. However, this law, also known as Archimedes' principle (AP), does not yield the force observed when the body is in contact with the container walls, as is more evident in the case of a block immersed in a liquid and in contact with the bottom, in which a downward force that increases with depth is observed. In this work, by taking into account the surface integral of the pressure force exerted by a fluid over the surface of a body, the general validity of AP is checked. For a body fully surrounded by a fluid, homogeneous or not, a gradient version of the divergence theorem applies, yielding a volume integral that simplifies to an upward force which agrees with the force predicted by AP, as long as the fluid density is a continuous function of depth. For the bottom case, this approach yields a downward force that increases with depth, which contrasts to AP but is in agreement with experiments. It also yields a formula for this force which shows that it increases with the area of contact.

Calibration of EMG to force for knee muscles is applicable with submaximal voluntary contractions.

PubMed

Doorenbosch, Caroline A M; Joosten, Annemiek; Harlaar, Jaap

2005-08-01

In this study, the influence of using submaximal isokinetic contractions about the knee compared to maximal voluntary contractions as input to obtain the calibration of an EMG-force model for knee muscles is investigated. Isokinetic knee flexion and extension contractions were performed by healthy subjects at five different velocities and at three contraction levels (100%, 75% and 50% of MVC). Joint angle, angular velocity, joint moment and surface EMG of five knee muscles were recorded. Individual calibration values were calculated according to [C.A.M. Doorenbosch, J. Harlaar, A clinically applicable EMG-force model to quantify active stabilization of the knee after a lesion of the anterior cruciate ligament, Clinical Biomechanics 18 (2003) 142-149] for each contraction level. First, the output of the model, calibrated with the 100% MVC was compared to the actually exerted net knee moment at the dynamometer. Normalized root mean square errors were calculated [A.L. Hof, C.A.N. Pronk, J.A. van Best, Comparison between EMG to force processing and kinetic analysis for the calf muscle moment in walking and stepping, Journal of Biomechanics 20 (1987) 167-187] to compare the estimated moments with the actually exerted moments. Mean RMSD errors ranged from 0.06 to 0.21 for extension and from 0.12 to 0.29 for flexion at the 100% trials. Subsequently, the calibration results of the 50% and 75% MVC calibration procedures were used. A standard signal, representing a random EMG level was used as input in the EMG force model, to compare the three models. Paired samples t-tests between the 100% MVC and the 75% MVC and 50% MVC, respectively, showed no significant differences (p>0.05). The application of submaximal contractions of larger than 50% MVC is suitable to calibrate a simple EMG to force model for knee extension and flexion. This means that in clinical practice, the EMG to force model can be applied by patients who cannot exert maximal force.

Paramagnetic Beads and Magnetically Mediated Strain Enhance Cardiomyogenesis in Mouse Embryoid Bodies

PubMed Central

Geuss, Laura R.; Wu, Douglas C.; Ramamoorthy, Divya; Alford, Corinne D.; Suggs, Laura J.

2014-01-01

Mechanical forces play an important role in proper embryologic development, and similarly such forces can directly impact pluripotency and differentiation of mouse embryonic stem cells (mESC) in vitro. In addition, manipulation of the embryoid body (EB) microenvironment, such as by incorporation of microspheres or microparticles, can similarly influence fate determination. In this study, we developed a mechanical stimulation regimen using permanent neodymium magnets to magnetically attract cells within an EB. Arginine-Glycine-Aspartic Acid (RGD)-conjugated paramagnetic beads were incorporated into the interior of the EBs during aggregation, allowing us to exert force on individual cells using short-term magnetization. EBs were stimulated for one hour at different magnetic field strengths, subsequently exerting a range of force intensity on the cells at different stages of early EB development. Our results demonstrated that following exposure to a 0.2 Tesla magnetic field, ESCs respond to magnetically mediated strain by activating Protein Kinase A (PKA) and increasing phosphorylated extracellular signal-regulated kinase 1/2 (pERK1/2) expression. The timing of stimulation can also be tailored to guide ESC differentiation: the combination of bone morphogenetic protein 4 (BMP4) supplementation with one hour of magnetic attraction on Day 3 enhances cardiomyogenesis by increasing contractile activity and the percentage of sarcomeric α-actin-expressing cells compared to control samples with BMP4 alone. Interestingly, we also observed that the beads alone had some impact on differentiation by increasingly slightly, albeit not significantly, the percentage of cardiomyocytes. Together these results suggest that magnetically mediated strain can be used to enhance the percentage of mouse ESC-derived cardiomyocytes over current differentiation protocols. PMID:25501004

How mantle slabs drive plate tectonics.

PubMed

Conrad, Clinton P; Lithgow-Bertelloni, Carolina

2002-10-04

The gravitational pull of subducted slabs is thought to drive the motions of Earth's tectonic plates, but the coupling between slabs and plates is not well established. If a slab is mechanically attached to a subducting plate, it can exert a direct pull on the plate. Alternatively, a detached slab may drive a plate by exciting flow in the mantle that exerts a shear traction on the base of the plate. From the geologic history of subduction, we estimated the relative importance of "pull" versus "suction" for the present-day plates. Observed plate motions are best predicted if slabs in the upper mantle are attached to plates and generate slab pull forces that account for about half of the total driving force on plates. Slabs in the lower mantle are supported by viscous mantle forces and drive plates through slab suction.

Muscles advance the teeth in sand dollars and other sea urchins

PubMed Central

Ellers, O.; Telford, M.

1997-01-01

We demonstrate the action of the dental promoter muscles in advancing the continuously growing teeth of sand dollars and sea urchins. Teeth wear at the occlusal end, while new calcite is added to the opposite end. Dental ligaments rigidly hold teeth during chewing, but soften and reform during advancement. The source of forces that advance the teeth was unknown until our discovery of the dental promoter muscles. The muscles, which underly the tooth, attach centrally to the stereom of the pyramid of the Aristotle's lantern (jaw) and peripherally to a membrane that covers the distal end of the tooth. The muscles shorten along an axis nearly parallel to the long axis of the tooth. We stimulated contraction by addition of acetylcholine, with increasing concentrations of acetylcholine generating higher forces. Forces exerted by this muscle are appropriate for its size and are 1000 times lower than forces exerted by interpyramidal muscles that generate chewing forces. In sand dollars, a single muscle contraction of the dental promoter muscle can account for half the mean daily advancement of the teeth.

Acoustic Attraction

NASA Astrophysics Data System (ADS)

Oviatt, Eric; Patsiaouris, Konstantinos; Denardo, Bruce

2009-11-01

A sound source of finite size produces a diverging traveling wave in an unbounded fluid. A rigid body that is small compared to the wavelength experiences an attractive radiation force (toward the source). An attractive force is also exerted on the fluid itself. The effect can be demonstrated with a styrofoam ball suspended near a loudspeaker that is producing sound of high amplitude and low frequency (for example, 100 Hz). The behavior can be understood and roughly calculated as a time-averaged Bernoulli effect. A rigorous scattering calculation yields a radiation force that is within a factor of two of the Bernoulli result. For a spherical wave, the force decreases as the inverse fifth power of the distance from the source. Applications of the phenomenon include ultrasonic filtration of liquids and the growth of supermassive black holes that emit sound waves in a surrounding plasma. An experiment is being conducted in an anechoic chamber with a 1-inch diameter aluminum ball that is suspended from an analytical balance. Directly below the ball is a baffled loudspeaker that exerts an attractive force that is measured by the balance.

40 CFR 1066.210 - Dynamometers.

Code of Federal Regulations, 2014 CFR

2014-07-01

... to recreate the mechanical inertia and frictional forces that a vehicle exerts on road surfaces... drive axles may share a single drive roll. Use good engineering judgment to ensure that the dynamometer... engineering judgment. (3) The load applied by the dynamometer simulates forces acting on the vehicle during...

Snowboard Jumping, Newton's Second Law and the Force on Landing

ERIC Educational Resources Information Center

O'Shea, Michael J.

2004-01-01

An application of Newton's second law to a snowboarder dropping off a vertical ledge shows that the average normal force during landing (force exerted by the ground on the snowboarder) is determined by four factors. It is shown that the flexing of the legs, the softness of the snow, the angle of the landing surface and the forward motion of the…

Displaying Force and Torque of A Manipulator

NASA Technical Reports Server (NTRS)

Bejczy, A. K.; Dotson, R. S.; Primus, H. C.

1984-01-01

Display combines bar charts, vector diagrams, and numerical values to inform operator of forces and torques exerted by end effector of manipulator. On voice or keyboard command, eight-channel strip-chart recorder traces force and torque components and claw position of raw measurements from eight strain gage sensors in end effector. Especially helpful when operator's view of end effector is obscured.

Macroscopic kinematics of the Hall electric field under influence of carrier magnetic moments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sakai, Masamichi, E-mail: sakai@fms.saitama-u.ac.jp

2016-06-15

The relativistic effect on electromagnetic forces yields two types of forces which depend on the velocity of the relevant particles: (i) the usual Lorentz force exerted on a moving charged particle and (ii) the apparent Lorentz force exerted on a moving magnetic moment. In sharp contrast with type (i), the type (ii) force originates due to the transverse field induced by the Hall effect (HE). This study incorporates both forces into a Drude-type equation with a fully spin-polarized condition to investigate the effects of self-consistency of the source and the resultant fields on the HE. We also examine the self-consistencymore » of the carrier kinematics and electromagnetic dynamics by simultaneously considering the Drude type equation and Maxwell equations at low frequencies. Thus, our approach can predict both the dc and ac characteristics of the HE, demonstrating that the dc current condition solely yields the ordinary HE, while the ac current condition yields generation of both fundamental and second harmonic modes of the HE field. When the magnetostatic field is absent, the simultaneous presence of dc and ac longitudinal currents generates the ac HE that has both fundamental frequency and second harmonic.« less

Dietary nitrate increases tetanic [Ca2+]i and contractile force in mouse fast-twitch muscle

PubMed Central

Hernández, Andrés; Schiffer, Tomas A; Ivarsson, Niklas; Cheng, Arthur J; Bruton, Joseph D; Lundberg, Jon O; Weitzberg, Eddie; Westerblad, Håkan

2012-01-01

Dietary inorganic nitrate has profound effects on health and physiological responses to exercise. Here, we examined if nitrate, in doses readily achievable via a normal diet, could improve Ca2+ handling and contractile function using fast- and slow-twitch skeletal muscles from C57bl/6 male mice given 1 mm sodium nitrate in water for 7 days. Age matched controls were provided water without added nitrate. In fast-twitch muscle fibres dissected from nitrate treated mice, myoplasmic free [Ca2+] was significantly greater than in Control fibres at stimulation frequencies from 20 to 150 Hz, which resulted in a major increase in contractile force at ≤50 Hz. At 100 Hz stimulation, the rate of force development was ∼35% faster in the nitrate group. These changes in nitrate treated mice were accompanied by increased expression of the Ca2+ handling proteins calsequestrin 1 and the dihydropyridine receptor. No changes in force or calsequestrin 1 and dihydropyridine receptor expression were measured in slow-twitch muscles. In conclusion, these results show a striking effect of nitrate supplementation on intracellular Ca2+ handling in fast-twitch muscle resulting in increased force production. A new mechanism is revealed by which nitrate can exert effects on muscle function with applications to performance and a potential therapeutic role in conditions with muscle weakness. PMID:22687611

Dietary nitrate increases tetanic [Ca2+]i and contractile force in mouse fast-twitch muscle.

PubMed

Hernández, Andrés; Schiffer, Tomas A; Ivarsson, Niklas; Cheng, Arthur J; Bruton, Joseph D; Lundberg, Jon O; Weitzberg, Eddie; Westerblad, Håkan

2012-08-01

Dietary inorganic nitrate has profound effects on health and physiological responses to exercise. Here, we examined if nitrate, in doses readily achievable via a normal diet, could improve Ca(2+) handling and contractile function using fast- and slow-twitch skeletal muscles from C57bl/6 male mice given 1 mm sodium nitrate in water for 7 days. Age matched controls were provided water without added nitrate. In fast-twitch muscle fibres dissected from nitrate treated mice, myoplasmic free [Ca(2+)] was significantly greater than in Control fibres at stimulation frequencies from 20 to 150 Hz, which resulted in a major increase in contractile force at ≤ 50 Hz. At 100 Hz stimulation, the rate of force development was ∼35% faster in the nitrate group. These changes in nitrate treated mice were accompanied by increased expression of the Ca(2+) handling proteins calsequestrin 1 and the dihydropyridine receptor. No changes in force or calsequestrin 1 and dihydropyridine receptor expression were measured in slow-twitch muscles. In conclusion, these results show a striking effect of nitrate supplementation on intracellular Ca(2+) handling in fast-twitch muscle resulting in increased force production. A new mechanism is revealed by which nitrate can exert effects on muscle function with applications to performance and a potential therapeutic role in conditions with muscle weakness.

Selective Growth of Low Stored Energy Grains During δ Sub-solvus Annealing in the Inconel 718 Nickel-Based Superalloy

NASA Astrophysics Data System (ADS)

Agnoli, Andrea; Bernacki, Marc; Logé, Roland; Franchet, Jean-Michel; Laigo, Johanne; Bozzolo, Nathalie

2015-09-01

The microstructure stability during δ sub-solvus annealing in Inconel 718 was investigated, focusing on the conditions that may lead to the development of very large grains (about 100 μm) in a recrystallized fine grained matrix (4 to 5 μm) despite the presence of second-phase particles. Microstructure evolution was analyzed by EBSD (grain size, intragranular misorientation) and SEM ( δ phase particles). Results confirm that, in the absence of stored energy, the grain structure is controlled by the δ phase particles, as predicted by the Smith-Zener equation. If the initial microstructure is strained ( ɛ < 0.1) before annealing, then low stored energy grains grow to a large extent, despite the Zener pinning forces exerted by the second-phase particles on the grain boundaries. Those selectively growing grains could be those of the initial microstructure that were the least deformed, or they could result from a nucleation process. The balance of three forces acting on boundary migration controls the growth process: if the sum of capillarity and stored energy driving forces exceeds the Zener pinning force, then selective grain growth occurs. Such phenomenon could be simulated, using a level set approach in a finite element context, by taking into account the three forces acting on boundary migration and by considering a realistic strain energy distribution (estimated from EBSD measurements).

The effect of bandwidth on telerobot system performance

NASA Technical Reports Server (NTRS)

Uebel, Mark; Ali, Michael S.; Minis, Ioannis

1991-01-01

The purpose of the experiment was to determine the effect that various slave-joint bandwidths have on telerobot system performance. The telerobot system consisted of a slave arm controlled by a master. The slave incorporated an impedance loop to provide local compliance in addition to the compliance provided by the operator via force feedback. Three joint bandwidths, 0.5, 1.0, and 2.0 Hz, were used. The performance measures were the task completion time and the sums of the squared forces and moments exerted on the environment. The task consisted of peg-in-hole insertion and removal. The results of the experiment indicate a significant performance decrease at 0.5-Hz bandwidth relative to the 1- and 2-Hz bandwidths. There was no significant change in performance between the 1- and 2-Hz bandwidths.

Aerodynamic Leidenfrost effect

NASA Astrophysics Data System (ADS)

Gauthier, Anaïs; Bird, James C.; Clanet, Christophe; Quéré, David

2016-12-01

When deposited on a plate moving quickly enough, any liquid can levitate as it does when it is volatile on a very hot solid (Leidenfrost effect). In the aerodynamic Leidenfrost situation, air gets inserted between the liquid and the moving solid, a situation that we analyze. We observe two types of entrainment. (i) The thickness of the air gap is found to increase with the plate speed, which is interpreted in the Landau-Levich-Derjaguin frame: Air is dynamically dragged along the surface and its thickness results from a balance between capillary and viscous effects. (ii) Air set in motion by the plate exerts a force on the levitating liquid. We discuss the magnitude of this aerodynamic force and show that it can be exploited to control the liquid and even to drive it against gravity.

Modulation of monocytic leukemia cell function and survival by high gradient magnetic fields and mathematical modeling studies.

PubMed

Zablotskii, Vitalii; Syrovets, Tatiana; Schmidt, Zoe W; Dejneka, Alexandr; Simmet, Thomas

2014-03-01

The influence of spatially modulated high gradient magnetic fields on cellular functions of human THP-1 leukemia cells is studied. We demonstrate that arrays of high-gradient micrometer-sized magnets induce i) cell swelling, ii) prolonged increased ROS production, and iii) inhibit cell proliferation, and iv) elicit apoptosis of THP-1 monocytic leukemia cells in the absence of chemical or biological agents. Mathematical modeling indicates that mechanical stress exerted on the cells by high magnetic gradient forces is responsible for triggering cell swelling and formation of reactive oxygen species followed by apoptosis. We discuss physical aspects of controlling cell functions by focused magnetic gradient forces, i.e. by a noninvasive and nondestructive physical approach. Copyright © 2014 Elsevier Ltd. All rights reserved.

Optical force rectifiers based on PT-symmetric metasurfaces

NASA Astrophysics Data System (ADS)

Alaee, Rasoul; Gurlek, Burak; Christensen, Johan; Kadic, Muamer

2018-05-01

We introduce here the concept of optical force rectifier based on parity-time symmetric metasurfaces. Directly linked to the properties of non-Hermitian systems engineered by balanced loss and gain constituents, we show that light can exert asymmetric pulling or pushing forces on metasurfaces depending on the direction of the impinging light. This generates a complete force rectification in the vicinity of the exceptional point. Our findings have the potential to spark the design of applications in optical manipulation where the forces, strictly speaking, act unidirectionally.

Contradictory Evidence on Wave Forcing of Tropical Upwelling in the Brewer-Dobson Circulation - A Suggested Resolution

NASA Technical Reports Server (NTRS)

Zhou, Tiehan; Geller, Marvin A.; Lin, Wuyin

2011-01-01

ERA-40 data are analyzed to demonstrate that wave forcing at lower latitudes plays a crucial role in driving the tropical upwelling portion of the Brewer-Dobson circulation. It is shown that subtropical wave forcing is correlated with tropical upwelling on both intraseasonal and interannual time scales when transient waves are taken into account, and that tropical wave forcing exerts its influence on tropical upwelling via its body force on the zonal mean flow.

Decentralized control of large flexible structures by joint decoupling

NASA Technical Reports Server (NTRS)

Su, Tzu-Jeng; Juang, Jer-Nan

1994-01-01

This paper presents a novel method to design decentralized controllers for large complex flexible structures by using the idea of joint decoupling. Decoupling of joint degrees of freedom from the interior degrees of freedom is achieved by setting the joint actuator commands to cancel the internal forces exerting on the joint degrees of freedom. By doing so, the interactions between substructures are eliminated. The global structure control design problem is then decomposed into several substructure control design problems. Control commands for interior actuators are set to be localized state feedback using decentralized observers for state estimation. The proposed decentralized controllers can operate successfully at the individual substructure level as well as at the global structure level. Not only control design but also control implementation is decentralized. A two-component mass-spring-damper system is used as an example to demonstrate the proposed method.

The drag force on a subsonic projectile in a fluid complex plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ivlev, A. V.; Zhukhovitskii, D. I.

2012-09-15

The incompressible Navier-Stokes equation is employed to describe a subsonic particle flow induced in complex plasmas by a moving projectile. Drag forces acting on the projectile in different flow regimes are calculated. It is shown that, along with the regular neutral gas drag, there is an additional force exerted on the projectile due to dissipation in the surrounding particle fluid. This additional force provides significant contribution to the total drag.

Electro-hydrodynamic force field and flow patterns generated by a DC corona discharge in the air

NASA Astrophysics Data System (ADS)

Monrolin, Nicolas; Plouraboue, Franck; Praud, Olivier

2016-11-01

Ionic wind refers to the electro-convection of ionised air between high voltage electrodes. Microscopic ion-neutral collisions are responsible for momentum transfer from accelerated ions, subjected to the electric field, to the neutral gas molecules resulting in a macroscopic airflow acceleration. In the past decades it has been investigated for various purposes from food drying through aerodynamic flow control and eventually laptop cooling. One consequence of air acceleration between the electrodes is thrust generation, often referred to as the Biefeld-Brown effect or electro-hydrodynamic thrust. In this experimental study, the ionic wind velocity field is measured with the PIV method. From computing the acceleration of the air we work out the electrostatic force field for various electrodes configurations. This enables an original direct evaluation of the force distribution as well as the influence of electrodes shape and position. Thrust computation based on the flow acceleration are compared with digital scale measurements. Complex flow features are highlighted such as vortex shedding, indicating that aerodynamic effects may play a significant role. Furthermore, the aerodynamic drag force exerted on the electrodes is quantified by choosing an appropriate control volume. Authors thank Region Midi-Pyrenee and CNES Launcher Directorate for financial support.

Controlled Wake of a Moving Axisymmetric Bluff Body

NASA Astrophysics Data System (ADS)

Lee, E.; Vukasinovic, B.; Glezer, A.

2017-11-01

The aerodynamic loads exerted on a wire-mounted axisymmetric bluff body in prescribed rigid motion are controlled by fluidic manipulation of its near wake. The body is supported by a six-degree of freedom eight-wire traverse and its motion is controlled using a dedicated servo actuator and inline load cell for each wire. The instantaneous aerodynamic forces and moments on the moving body are manipulated by controlled interactions of an azimuthal array of integrated synthetic jet actuators with the cross flow to induce localized flow attachment over the body's aft end and thereby alter the symmetry of the wake. The coupled interactions between the wake structure and the effected aerodynamic loads during prescribed time-periodic and transitory (gust like) motions are investigated with emphasis on enhancing or diminishing the loads for maneuver control, and decoupling the body's motion from its far wake.

Cell Extrusion: A Stress-Responsive Force for Good or Evil in Epithelial Homeostasis.

PubMed

Ohsawa, Shizue; Vaughen, John; Igaki, Tatsushi

2018-02-05

Epithelial tissues robustly respond to internal and external stressors via dynamic cellular rearrangements. Cell extrusion acts as a key regulator of epithelial homeostasis by removing apoptotic cells, orchestrating morphogenesis, and mediating competitive cellular battles during tumorigenesis. Here, we delineate the diverse functions of cell extrusion during development and disease. We emphasize the expanding role for apoptotic cell extrusion in exerting morphogenetic forces, as well as the strong intersection of cell extrusion with cell competition, a homeostatic mechanism that eliminates aberrant or unfit cells. While cell competition and extrusion can exert potent, tumor-suppressive effects, dysregulation of either critical homeostatic program can fuel cancer progression. Copyright © 2018 Elsevier Inc. All rights reserved.

Forced and voluntary exercise differentially affect brain and behavior.

PubMed

Leasure, J L; Jones, M

2008-10-15

The potential of physical exercise to decrease body weight, alleviate depression, combat aging and enhance cognition has been well-supported by research studies. However, exercise regimens vary widely across experiments, raising the question of whether there is an optimal form, intensity and duration of exertion that would produce maximal benefits. In particular, a comparison of forced and voluntary exercise is needed, since the results of several prior studies suggest that they may differentially affect brain and behavior. In the present study, we employed a novel 8-week exercise paradigm that standardized the distance, pattern, equipment and housing condition of forced and voluntary exercisers. Exercising rats were then compared with sedentary controls on measures previously shown to be influenced by physical activity. Our results indicate that although the distance covered by both exercise groups was the same, voluntary exercisers ran at higher speed and for less total time than forced exercisers. When compared with sedentary controls, forced but not voluntary exercise was found to increase anxiety-like behaviors in the open field. Both forms of exercise increased the number of surviving bromodeoxyuridine (BrdU)+ cells in the dentate gyrus after 8 weeks of exercise, although forced exercisers had significantly more than voluntary exercisers. Phenotypic analysis of BrdU+ cells showed no difference between groups in the percentage of newborn cells that became neurons, however, because forced exercise maximally increased the number of BrdU+ cells, it ultimately produced more neurons than voluntary exercise. Our results indicate that forced and voluntary exercise are inherently different: voluntary wheel running is characterized by rapid pace and short duration, whereas forced exercise involves a slower, more consistent pace for longer periods of time. This basic difference between the two forms of exercise is likely responsible for their differential effects on brain and behavior.

Three-dimensional cellular deformation analysis with a two-photon magnetic manipulator workstation.

PubMed

Huang, Hayden; Dong, Chen Y; Kwon, Hyuk-Sang; Sutin, Jason D; Kamm, Roger D; So, Peter T C

2002-04-01

The ability to apply quantifiable mechanical stresses at the microscopic scale is critical for studying cellular responses to mechanical forces. This necessitates the use of force transducers that can apply precisely controlled forces to cells while monitoring the responses noninvasively. This paper describes the development of a micromanipulation workstation integrating two-photon, three-dimensional imaging with a high-force, uniform-gradient magnetic manipulator. The uniform-gradient magnetic field applies nearly uniform forces to a large cell population, permitting statistical quantification of select molecular responses to mechanical stresses. The magnetic transducer design is capable of exerting over 200 pN of force on 4.5-microm-diameter paramagnetic particles and over 800 pN on 5.0-microm ferromagnetic particles. These forces vary within +/-10% over an area 500 x 500 microm2. The compatibility with the use of high numerical aperture (approximately 1.0) objectives is an integral part of the workstation design allowing submicron-resolution, three-dimensional, two-photon imaging. Three-dimensional analyses of cellular deformation under localized mechanical strain are reported. These measurements indicate that the response of cells to large focal stresses may contain three-dimensional global deformations and show the suitability of this workstation to further studying cellular response to mechanical stresses.

Musical agency reduces perceived exertion during strenuous physical performance

PubMed Central

Fritz, Thomas Hans; Hardikar, Samyogita; Demoucron, Matthias; Niessen, Margot; Demey, Michiel; Giot, Olivier; Li, Yongming; Haynes, John-Dylan; Villringer, Arno; Leman, Marc

2013-01-01

Music is known to be capable of reducing perceived exertion during strenuous physical activity. The current interpretation of this modulating effect of music is that music may be perceived as a diversion from unpleasant proprioceptive sensations that go along with exhaustion. Here we investigated the effects of music on perceived exertion during a physically strenuous task, varying musical agency, a task that relies on the experience of body proprioception, rather than simply diverting from it. For this we measured psychologically indicated exertion during physical workout with and without musical agency while simultaneously acquiring metabolic values with spirometry. Results showed that musical agency significantly decreased perceived exertion during workout, indicating that musical agency may actually facilitate physically strenuous activities. This indicates that the positive effect of music on perceived exertion cannot always be explained by an effect of diversion from proprioceptive feedback. Furthermore, this finding suggests that the down-modulating effect of musical agency on perceived exertion may be a previously unacknowledged driving force for the development of music in humans: making music makes strenuous physical activities less exhausting. PMID:24127588

Musical agency reduces perceived exertion during strenuous physical performance.

PubMed

Fritz, Thomas Hans; Hardikar, Samyogita; Demoucron, Matthias; Niessen, Margot; Demey, Michiel; Giot, Olivier; Li, Yongming; Haynes, John-Dylan; Villringer, Arno; Leman, Marc

2013-10-29

Music is known to be capable of reducing perceived exertion during strenuous physical activity. The current interpretation of this modulating effect of music is that music may be perceived as a diversion from unpleasant proprioceptive sensations that go along with exhaustion. Here we investigated the effects of music on perceived exertion during a physically strenuous task, varying musical agency, a task that relies on the experience of body proprioception, rather than simply diverting from it. For this we measured psychologically indicated exertion during physical workout with and without musical agency while simultaneously acquiring metabolic values with spirometry. Results showed that musical agency significantly decreased perceived exertion during workout, indicating that musical agency may actually facilitate physically strenuous activities. This indicates that the positive effect of music on perceived exertion cannot always be explained by an effect of diversion from proprioceptive feedback. Furthermore, this finding suggests that the down-modulating effect of musical agency on perceived exertion may be a previously unacknowledged driving force for the development of music in humans: making music makes strenuous physical activities less exhausting.

Electrical Deflection of Polar Liquid Streams: A Misunderstood Demonstration

NASA Astrophysics Data System (ADS)

Ziaei-Moayyed, Maryam; Goodman, Edward; Williams, Peter

2000-11-01

The electrical deflection of polar liquid streams, commonly used as a textbook illustration of the behavior of polar molecules, is shown to be due to the formation of electrically charged droplets in the polar liquid stream, induced by a nearby charged object, rather than any force exerted on molecular dipoles. Streams of water and polar organic liquids could be deflected in a uniform electric field, which could not have exerted any force on dipolar species. Water and polar organic liquid streams formed within a grounded, electrically screened region could not be deflected after exiting the screened region, demonstrating that there is no electrical force on uncharged polar liquid droplets. Induced charging was observed also in insulating polar organic liquids and is suggested to be due to ionic impurities. A weak deflection of a stream of a nonpolar liquid (tetrachloroethylene) was also observed, indicating that such impurity effects are quite general, even in nonpolar liquids.

Geometrical Origins of Contractility in Disordered Actomyosin Networks

NASA Astrophysics Data System (ADS)

Lenz, Martin

2014-10-01

Movement within eukaryotic cells largely originates from localized forces exerted by myosin motors on scaffolds of actin filaments. Although individual motors locally exert both contractile and extensile forces, large actomyosin structures at the cellular scale are overwhelmingly contractile, suggesting that the scaffold serves to favor contraction over extension. While this mechanism is well understood in highly organized striated muscle, its origin in disordered networks such as the cell cortex is unknown. Here, we develop a mathematical model of the actin scaffold's local two- or three-dimensional mechanics and identify four competing contraction mechanisms. We predict that one mechanism dominates, whereby local deformations of the actin break the balance between contraction and extension. In this mechanism, contractile forces result mostly from motors plucking the filaments transversely rather than buckling them longitudinally. These findings shed light on recent in vitro experiments and provide a new geometrical understanding of contractility in the myriad of disordered actomyosin systems found in vivo.

Bone-breaking bite force of Basilosaurus isis (Mammalia, Cetacea) from the late Eocene of Egypt estimated by finite element analysis.

PubMed

Snively, Eric; Fahlke, Julia M; Welsh, Robert C

2015-01-01

Bite marks suggest that the late Eocence archaeocete whale Basilosaurus isis (Birket Qarun Formation, Egypt) fed upon juveniles of the contemporary basilosaurid Dorudon atrox. Finite element analysis (FEA) of a nearly complete adult cranium of B. isis enables estimates of its bite force and tests the animal's capabilities for crushing bone. Two loadcases reflect different biting scenarios: 1) an intitial closing phase, with all adductors active and a full condylar reaction force; and 2) a shearing phase, with the posterior temporalis active and minimized condylar force. The latter is considered probable when the jaws were nearly closed because the preserved jaws do not articulate as the molariform teeth come into occulusion. Reaction forces with all muscles active indicate that B. isis maintained relatively greater bite force anteriorly than seen in large crocodilians, and exerted a maximum bite force of at least 16,400 N at its upper P3. Under the shearing scenario with minimized condylar forces, tooth reaction forces could exceed 20,000 N despite lower magnitudes of muscle force. These bite forces at the teeth are consistent with bone indentations on Dorudon crania, reatract-and-shear hypotheses of Basilosaurus bite function, and seizure of prey by anterior teeth as proposed for other archaeocetes. The whale's bite forces match those estimated for pliosaurus when skull lengths are equalized, suggesting similar tradeoffs of bite function and hydrodynamics. Reaction forces in B. isis were lower than maxima estimated for large crocodylians and carnivorous dinosaurs. However, comparison of force estimates from FEA and regression data indicate that B. isis exerted the largest bite forces yet estimated for any mammal, and greater force than expected from its skull width. Cephalic feeding biomechanics of Basilosaurus isis are thus consistent with habitual predation.

Magnetothermal Convection in Nonconducting Diamagnetic and Paramagnetic Fluids

NASA Technical Reports Server (NTRS)

Edwards, Boyd F.; Gray, Donald D.; Huang, Jie

1996-01-01

Nonuniform magnetic fields exert a magnetic body force on electrically nonconducting classical fluids. These include paramagnetic fluids such as gaseous and liquid oxygen and diamagnetic fluids such as helium. Recent experiments show that this force can overwhelm the force of gravity even at the surface of the earth; it can levitate liquids and gases, quench candle flames, block gas flows, and suppress heat transport. Thermal gradients render the magnetic force nonuniform through the temperature-dependent magnetic susceptibility. These thermal gradients can therefore drive magnetic convection analogous to buoyancy-driven convection. This magnetothermal convection can overwhelm convection driven by gravitational buoyancy in terrestrial experiments. The objectives of the proposed ground-based theoretical study are (a) to supply the magnetothermohydrodynamic theory necessary to understand these recent experiments and (b) to explore the consequences of nonuniform magnetic fields in microgravity. Even the linear theory for the onset of magnetothermal convection is lacking in the literature. We intend to supply the linear and nonlinear theory based on the thermohydrodynamic equations supplemented by the magnetic body force. We intend to investigate the effect of magnetic fields on gas blockage and heat transport in microgravity. Since magnetic fields provide a means of creating arbitrary, controllable body force distributions, we intend to investigate the possibility of using magnetic fields to position and control fluids in microgravity. We also intend to investigate the possibility of creating stationary terrestrial microgravity environments by using the magnetic force to effectively cancel gravity. These investigations may aid in the design of space-based heat-transfer, combustion, and human-life-support equipment.

Crataegus special extract WS 1442 increases force of contraction in human myocardium cAMP-independently.

PubMed

Schwinger, R H; Pietsch, M; Frank, K; Brixius, K

2000-05-01

The mode of action of Crataegus extracts in the treatment of heart failure is still under examination. WS 1442, a standardized special extract from Crataegus leaves with flowers, exerts direct positive inotropic effects. This study was designed to investigate the mode of inotropic action of WS 1442 in human myocardium from patients with congestive heart failure (left ventricular myocardium from explanted hearts; NYHA IV, n = 8) as well as in nonfailing controls (right auricular trabeculae from patients with coronary heart disease, n = 8). WS 1442 effectively displaced specifically bound 3H-ouabain but did not influence the activity of adenylate cyclase [control, + Gpp(NH)p (10(-4) microM) 3,500 pmol cyclic adenosine monophosphate (cAMP)/20 min). In isolated left ventricular papillary muscle strips, WS 1442 significantly increased the force of contraction [basal, 1.8+/-0.2 mN; WS 1442 (50 microg/ml), 2.4+/-0.1 mN (130%)] and improved the frequency-dependent force generation (0.5 vs. 2.5 Hz: control, +0.1+/-0.01 mN; WS 1442, +0.9+/-0.3 mN) even in failing human myocardium. In fura-2-loaded muscle strips (right atrial trabeculae), WS 1442 increased both the Ca2+-transient and force generation. These effects also were observed in the lipophilic ethyl acetate-soluble fraction A, enriched in flavone derivatives. In conclusion, these findings suggest a pharmacologic mechanism of WS 1442 similar to the cAMP-independent positive inotropic action of cardiac glycosides. In addition, WS 1442 improves the force-frequency relation in failing human myocardium.

Tipepidine, a non-narcotic antitussive, exerts an antidepressant-like effect in the forced swimming test in adrenocorticotropic hormone-treated rats.

PubMed

Kawaura, Kazuaki; Ogata, Yukino; Honda, Sokichi; Soeda, Fumio; Shirasaki, Tetsuya; Takahama, Kazuo

2016-04-01

We investigated whether tipepidine exerts an antidepressant-like effect in the forced swimming test in adrenocorticotropic hormone (ACTH)-treated rats, which is known as a treatment-resistant depression model, and we studied the pharmacological mechanisms of the effects of tipepidine. Male Wistar rats (5-7 weeks old) were used in this study. Tipepidine (20 and 40 mg/kg, i.p.) decreased the immobility time in the forced swimming test in ACTH-treated rats. The anti-immobility effect of tipepidine was blocked by a catecholamine-depleting agent, alpha-methyl-p-tyrosine (300 mg/kg, s.c.), but not by a serotonin-depleting agent, p-chlorophenylalanine. The anti-immobility effect of tipepidine was also blocked by a dopamine D1 receptor antagonist, SCH23390 (0.02 mg/kg, s.c.) and an adrenaline α2 receptor antagonist, yohimbine (2 mg/kg, i.p.). In microdialysis technique, tipepidine (40 mg/kg, i.p.) increased the extracellular dopamine level of the nucleus accumbens (NAc) in ACTH-treated rats. These results suggest that tipepidine exerts an antidepressant-like effect in the forced swimming test in ACTH-treated rats, and that the effect of tipepidine is mediated by the stimulation of dopamine D1 receptors and adrenaline α2 receptors. The results also suggest that an increase in the extracellular dopamine level in the NAc may be involved in the antidepressant-like effect of tipepidine in ACTH-treated rats. Copyright © 2016. Published by Elsevier B.V.

Radiation Force Caused by Scattering, Absorption, and Emission of Light by Nonspherical Particles

NASA Technical Reports Server (NTRS)

Mishchenko, Michael I.; Hansen, James E. (Technical Monitor)

2001-01-01

General formulas for computing the radiation force exerted on arbitrarily oriented and arbitrarily shaped nonspherical particles due to scattering, absorption, and emission of electromagnetic radiation are derived. For randomly oriented particles with a plane of symmetry, the formula for the average radiation force caused by the particle response to external illumination reduces to the standard Debye formula derived from the Lorenz-Mie theory, whereas the average radiation force caused by emission vanishes.

Ectoderm exerts the driving force for gastrulation in the sand dollar Scaphechinus mirabilis.

PubMed

Takata, H; Kominami, T

2001-06-01

How the ectodermal layer relates to the invagination processes was examined in the sand dollar Scaphechinus mirabilis. When the turgor pressure of blastocoele was increased, invagination was completely blocked. In contrast, an increase in turgor pressure did not affect elongation of the gut rudiment in the regular echinoid Hemicentrotus pulcherrimus. Rhodamine-phalloidin staining showed that the distribution of actin filaments was different between two species of embryos. In S. mirabilis gastrulating embryos, abundant actin filaments were seen at the basal cortex of ectoderm in addition to archenteron cells, while the intense signal was restricted to the archenteron in H. pulcherrimus. To investigate whether actin filaments contained in the ectodermal layer exert the force of invagination, a small part of the ectodermal layer was aspirated with a micropipette. If S. mirabilis embryos were aspirated from the onset of gastrulation, invagination did not occur at all, irrespective of the suction site. Even after the archenteron had invaginated to one-half of its full length, further elongation of the archenteron was severely blocked by suction of the lateral ectoderm. In contrast, suction of the ectodermal layer did not affect the elongation processes in H. pulcherrimus. These results strongly suggest that the ectodermal layer, especially in the vegetal half, exerts the driving force of invagination in S. mirabilis.

Hydrodynamic modelling of aquatic suction performance and intra-oral pressures: limitations for comparative studies

PubMed Central

Van Wassenbergh, Sam; Aerts, Peter; Herrel, Anthony

2006-01-01

The magnitude of sub-ambient pressure inside the bucco-pharyngeal cavity of aquatic animals is generally considered a valuable metric of suction feeding performance. However, these pressures do not provide a direct indication of the effect of the suction act on the movement of the prey item. Especially when comparing suction performance of animals with differences in the shape of the expanding bucco-pharyngeal cavity, the link between speed of expansion, water velocity, force exerted on the prey and intra-oral pressure remains obscure. By using mathematical models of the heads of catfishes, a morphologically diverse group of aquatic suction feeders, these relationships were tested. The kinematics of these models were fine-tuned to transport a given prey towards the mouth in the same way. Next, the calculated pressures inside these models were compared. The results show that no simple relationship exists between the amount of generated sub-ambient pressure and the force exerted on the prey during suction feeding, unless animals of the same species are compared. Therefore, for evaluating suction performance in aquatic animals in future studies, the focus should be on the flow velocities in front of the mouth, for which a direct relationship exists with the hydrodynamic force exerted on prey. PMID:16849247

Exploring the free-energy landscape of a short peptide using an average force

NASA Astrophysics Data System (ADS)

Chipot, Christophe; Hénin, Jérôme

2005-12-01

The reversible folding of deca-alanine is chosen as a test case for characterizing a method that uses an adaptive biasing force (ABF) to escape from the minima and overcome the barriers of the free-energy landscape. This approach relies on the continuous estimation of a biasing force that yields a Hamiltonian in which no average force is exerted along the ordering parameter ξ. Optimizing the parameters that control how the ABF is applied, the method is shown to be extremely effective when a nonequivocal ordering parameter can be defined to explore the folding pathway of the peptide. Starting from a β-turn motif and restraining ξ to a region of the conformational space that extends from the α-helical state to an ensemble of extended structures, the ABF scheme is successful in folding the peptide chain into a compact α helix. Sampling of this conformation is, however, marginal when the range of ξ values embraces arrangements of greater compactness, hence demonstrating the inherent limitations of free-energy methods when ambiguous ordering parameters are utilized.

Shaping up synthetic cells

NASA Astrophysics Data System (ADS)

Mulla, Yuval; Aufderhorst-Roberts, Anders; Koenderink, Gijsje H.

2018-07-01

How do the cells in our body reconfigure their shape to achieve complex tasks like migration and mitosis, yet maintain their shape in response to forces exerted by, for instance, blood flow and muscle action? Cell shape control is defined by a delicate mechanical balance between active force generation and passive material properties of the plasma membrane and the cytoskeleton. The cytoskeleton forms a space-spanning fibrous network comprising three subsystems: actin, microtubules and intermediate filaments. Bottom-up reconstitution of minimal synthetic cells where these cytoskeletal subsystems are encapsulated inside a lipid vesicle provides a powerful avenue to dissect the force balance that governs cell shape control. Although encapsulation is technically demanding, a steady stream of advances in this technique has made the reconstitution of shape-changing minimal cells increasingly feasible. In this topical review we provide a route-map of the recent advances in cytoskeletal encapsulation techniques and outline recent reports that demonstrate shape change phenomena in simple biomimetic vesicle systems. We end with an outlook toward the next steps required to achieve more complex shape changes with the ultimate aim of building a fully functional synthetic cell with the capability to autonomously grow, divide and move.

Reserpine has a direct action as a calcium antagonist on mammalian smooth muscle cells.

PubMed Central

Casteels, R; Login, I S

1983-01-01

The effects of reserpine on excitation-contraction coupling and 45Ca exchange of smooth muscle cells of the rabbit ear artery and the guinea-pig taenia coli have been studied. Reserpine inhibited the spontaneous mechanical activity of the taenia coli and the force development induced by 59 mM-external K or 10(-5) M-carbachol. In the ear artery reserpine blocked the K-induced contraction but its effect on the contraction elicited by noradrenaline was smaller. At 0.2 mM-Ca, the inhibition of the tonic component of the noradrenaline-induced contraction was more pronounced than that of the phasic component. This reserpine action was fully reversible for the noradrenaline stimulus in the ear artery but less so for K-induced contractions. The inhibitory action on contractions induced in taenia coli by K-rich solution and by carbachol was even less reversible. The analysis of the effect of reserpine on the 45Ca exchange in the ear artery has revealed that it inhibits the increase of the fractional loss induced by K depolarization, but that it does not exert a significant effect on the increased fractional loss induced by 10(-5) M-noradrenaline. Reserpine slows down the filling with 45Ca of the agonist-sensitive store without affecting the steady-state amount of Ca taken up by the store. A study of the degree of filling of the store by measuring the force development and the 45Ca release elicited by noradrenaline in Ca-free medium, reveals that the force development after loading in a reserpine-containing medium remains less than the control, although the same amount of Ca is released from the store. It was shown by using tetrabenazine that the inhibitory action of reserpine on the Ca exchange and the force development is not due to an interaction of reserpine with the receptor molecules that are responsible for its depleting action on aminergic granules. These results strongly suggest that reserpine exerts a Ca antagonistic action on smooth muscle whereby it blocks the potential-dependent channels. However, reserpine also affects the receptor-operated channels to some extent and in addition at a high concentration it seems to exert an unspecific inhibitory action on the contractile system. PMID:6310099

Asymmetries in reactive and anticipatory balance control are of similar magnitude in Parkinson's disease patients.

PubMed

Boonstra, Tjitske A; van Kordelaar, Joost; Engelhart, Denise; van Vugt, Jeroen P P; van der Kooij, Herman

2016-01-01

Many Parkinson's disease (PD) patients show asymmetries in balance control during quiet stance and in response to perturbations (i.e., reactive balance control) in the sagittal plane. In addition, PD patients show a reduced ability to anticipate to self-induced disturbances, but it is not clear whether these anticipatory responses can be asymmetric too. Furthermore, it is not known how reactive balance control and anticipatory balance control are related in PD patients. Therefore, we investigated whether reactive and anticipatory balance control are asymmetric to the same extent in PD patients. 14 PD patients and 10 controls participated. Reactive balance control (RBC) was investigated by applying external platform and force perturbations and relating the response of the left and right ankle torque to the body sway angle at the excited frequencies. Anticipatory postural adjustments (APAs) were investigated by determining the increase in the left and right ankle torque just before the subjects released a force exerted with the hands against a force sensor. The symmetry ratio between the contribution of the left and right ankle was used to express the asymmetry in reactive and anticipatory balance control; the correlation between the two ratio's was investigated with Spearman's rank correlation coefficients. PD patients were more asymmetric in anticipatory (p=0.026) and reactive balance control (p=0.004) compared to controls and the symmetry ratios were significantly related (ρ=0.74; p=0.003) in PD patients. These findings suggest that asymmetric reactive balance control during bipedal stance may share a common pathophysiology with asymmetries in the anticipation of voluntary perturbations during, for instance, gait initiation. Copyright © 2015 Elsevier B.V. All rights reserved.

Discrete control of linear distributed systems with application to the deformable primary mirror of a large orbiting telescope. Ph.D. Thesis - Rhode Island Univ.

NASA Technical Reports Server (NTRS)

Creedon, J. F.

1970-01-01

The results are presented of a detailed study of the discrete control of linear distributed systems with specific application to the design of a practical controller for a plant representative of a telescope primary mirror for an orbiting astronomical observatory. The problem of controlling the distributed plant is treated by employing modal techniques to represent variations in the optical figure. Distortion of the mirror surface, which arises primarily from thermal gradients, is countered by actuators working against a backing structure to apply a corrective force distribution to the controlled surface. Each displacement actuator is in series with a spring attached to the mirror by means of a pad intentionally introduced to restrict the excitation of high-order modes. Control is exerted over a finite number of the most significant modes.

Focal adhesion kinase is involved in mechanosensing during fibroblast migration

NASA Technical Reports Server (NTRS)

Wang, H. B.; Dembo, M.; Hanks, S. K.; Wang, Y.

2001-01-01

Focal adhesion kinase (FAK) is a non-receptor protein tyrosine kinase localized at focal adhesions and is believed to mediate adhesion-stimulated effects. Although ablation of FAK impairs cell movement, it is not clear whether FAK might be involved in the guidance of cell migration, a role consistent with its putative regulatory function. We have transfected FAK-null fibroblasts with FAK gene under the control of the tetracycline repression system. Cells were cultured on flexible polyacrylamide substrates for the detection of traction forces and the application of mechanical stimulation. Compared with control cells expressing wild-type FAK, FAK-null cells showed a decrease in migration speed and directional persistence. In addition, whereas FAK-expressing cells responded to exerted forces by reorienting their movements and forming prominent focal adhesions, FAK-null cells failed to show such responses. Furthermore, FAK-null cells showed impaired responses to decreases in substrate flexibility, which causes control cells to generate weaker traction forces and migrate away from soft substrates. Cells expressing Y397F FAK, which cannot be phosphorylated at a key tyrosine site, showed similar defects in migration pattern and force-induced reorientation as did FAK-null cells. However, other aspects of F397-FAK cells, including the responses to substrate flexibility and the amplification of focal adhesions upon mechanical stimulation, were similar to that of control cells. Our results suggest that FAK plays an important role in the response of migrating cells to mechanical input. In addition, phosphorylation at Tyr-397 is required for some, but not all, of the functions of FAK in cell migration.

Magnetic Control of Concentration Gradient in Microgravity

NASA Technical Reports Server (NTRS)

Leslie, Fred; Ramachandran, Narayanan

2005-01-01

A report describes a technique for rapidly establishing a fluid-concentration gradient that can serve as an initial condition for an experiment on solutal instabilities associated with crystal growth in microgravity. The technique involves exploitation of the slight attractive or repulsive forces exerted on most fluids by a magnetic-field gradient. Although small, these forces can dominate in microgravity and therefore can be used to hold fluids in position in preparation for an experiment. The magnetic field is applied to a test cell, while a fluid mixture containing a concentration gradient is prepared by introducing an undiluted solution into a diluting solution in a mixing chamber. The test cell is then filled with the fluid mixture. Given the magnetic susceptibilities of the undiluted and diluting solutions, the magnetic-field gradient must be large enough that the magnetic force exceeds both (1) forces associated with the flow of the fluid mixture during filling of the test cell and (2) forces imposed by any residual gravitation and fluctuations thereof. Once the test cell has been filled with the fluid mixture, the magnetic field is switched off so that the experiment can proceed, starting from the proper initial conditions.

Ascending aortic curvature as an independent risk factor for type A dissection, and ascending aortic aneurysm formation: a mathematical model.

PubMed

Poullis, Michael P; Warwick, Richard; Oo, Aung; Poole, Robert J

2008-06-01

To develop a mathematical model to demonstrate that ascending aortic curvature is an independent risk factor for type A dissections, in addition to hypertension, bicuspid aortic valve, aneurysm of ascending aorta, and intrinsic aortic tissue abnormalities, like Marfan's syndrome. A steady state one-dimensional flow analysis was performed, utilising Newton's third law of motion. Five different clinical scenarios were evaluated: (1) effect of aortic curvature; (2) effect of beta-blockers, (3) effect of patient size, (4) forces on a Marfan's aorta, and (5) site of entry flap in aortic dissection. Aortic curvature increases the forces exerted on the ascending aorta by a factor of over 10-fold. Aortic curvature can cause patients with a systolic blood pressure of 8 0mmHg to have greater forces exerted on their aorta despite smaller diameters and lower cardiac outputs, than patients with systolic blood pressures of 120 mmHg. In normal diameter aortas, beta-blockers have minimal effect compared with aortic curvature. Aortic curvature may help to explain why normal diameter aortas can dissect, and also that the point of the entry tear may be potentially predictable. Aortic curvature has major effects on the forces exerted on the aorta in patients with Marfan's syndrome. Aortic curvature is relatively more important that aortic diameter, blood pressure, cardiac output, beta-blocker use, and patient size with regard to the force acting on the aortic wall. This may explain why some patients with normal diameter ascending aortas with or without Marfan's syndrome develop type A dissections and aneurysms. Aortic curvature may also help to explain the site of entry tear in acute type A dissection. Further clinical study is needed to validate this study's finding.

Localized removal of layers of metal, polymer, or biomaterial by ultrasound cavitation bubbles

PubMed Central

Fernandez Rivas, David; Verhaagen, Bram; Seddon, James R. T.; Zijlstra, Aaldert G.; Jiang, Lei-Meng; van der Sluis, Luc W. M.; Versluis, Michel; Lohse, Detlef; Gardeniers, Han J. G. E.

2012-01-01

We present an ultrasonic device with the ability to locally remove deposited layers from a glass slide in a controlled and rapid manner. The cleaning takes place as the result of cavitating bubbles near the deposited layers and not due to acoustic streaming. The bubbles are ejected from air-filled cavities micromachined in a silicon surface, which, when vibrated ultrasonically at a frequency of 200 kHz, generate a stream of bubbles that travel to the layer deposited on an opposing glass slide. Depending on the pressure amplitude, the bubble clouds ejected from the micropits attain different shapes as a result of complex bubble interaction forces, leading to distinct shapes of the cleaned areas. We have determined the removal rates for several inorganic and organic materials and obtained an improved efficiency in cleaning when compared to conventional cleaning equipment. We also provide values of the force the bubbles are able to exert on an atomic force microscope tip. PMID:23964308

Mechanical properties of different airway stents.

PubMed

Ratnovsky, Anat; Regev, Noa; Wald, Shaily; Kramer, Mordechai; Naftali, Sara

2015-04-01

Airway stents improve pulmonary function and quality of life in patients suffering from airway obstruction. The aim of this study was to compare main types of stents (silicone, balloon-dilated metal, self-expanding metal, and covered self-expanding metal) in terms of their mechanical properties and the radial forces they exert on the trachea. Mechanical measurements were carried out using a force gauge and specially designed adaptors fabricated in our lab. Numerical simulations were performed for eight different stent geometries, inserted into trachea models. The results show a clear correlation between stent diameter (oversizing) and the levels of stress it exerts on the trachea. Compared with uncovered metal stents, metal stents that are covered with less stiff material exert significantly less stress on the trachea while still maintaining strong contact with it. The use of such stents may reduce formation of mucosa necrosis and fistulas while still preventing stent migration. Silicone stents produce the lowest levels of stress, which may be due to weak contact between the stent and the trachea and can explain their propensity for migration. Unexpectedly, stents made of the same materials exerted different stresses due to differences in their structure. Stenosis significantly increases stress levels in all stents. Copyright © 2015 IPEM. Published by Elsevier Ltd. All rights reserved.

Ontogenetic scaling of burrowing forces in the earthworm Lumbricus terrestris.

PubMed

Quillin, K J

2000-09-01

In hydrostatic skeletons, it is the internal fluid under pressure surrounded by a body wall in tension (rather than a rigid lever) that enables the stiffening of the organism, the antagonism of muscles and the transmission of force from the muscles to the environment. This study examined the ontogenetic effects of body size on force production by an organism supported with a hydrostatic skeleton. The earthworm Lumbricus terrestris burrows by forcefully enlarging crevices in the soil. I built a force-measuring apparatus that measured the radial forces as earthworms of different sizes crawled through and enlarged pre-formed soil burrows. I also built an apparatus that measured the radial and axial forces as earthworms of different sizes attempted to elongate a dead-end burrow. Earthworms ranging in body mass m(b) from hatchlings (0.012 g) to adults (8.9 g) exerted maximum forces (F, in N) during active radial expansion of their burrows (F=0.32 m(b)(0.43)) and comparable forces during axial elongation of the burrow (F=0.26 m(b)(0.47)). Both these forces were almost an order of magnitude greater than the radial anchoring forces during normal peristalsis within burrows (F=0.04 m(b)(0.45)). All radial and axial forces scaled as body mass raised to the 2/5 power rather than to the 2/3 power expected by geometric similarity, indicating that large worms exert greater forces than small worms on an absolute scale, but the difference was less than predicted by scaling considerations. When forces were normalized by body weight, hatchlings could push 500 times their own body weight, while large adults could push only 10 times their own body weight.

Revised model for the radiation force exerted by standing surface acoustic waves on a rigid cylinder

NASA Astrophysics Data System (ADS)

Liang, Shen; Chaohui, Wang

2018-03-01

In this paper, a model for the radiation force exerted by standing surface acoustic waves (SSAWs) on a rigid cylinder in inviscid fluids is extended to account for the dependence on the Rayleigh angle. The conventional model for the radiation force used in the SSAW-based applications is developed in plane standing waves, which fails to predict the movement of the cylinder in the SSAW. Our revised model reveals that, in the direction normal to the piezoelectric substrate on which the SSAW is generated, acoustic radiation force can be large enough to drive the cylinder even in the long-wavelength limit. Furthermore, the force in this direction can not only push the cylinder away, but also pull it back toward the substrate. In the direction parallel to the substrate, the equilibrium positions for particles can be actively tuned by changing Rayleigh angle. As an example considered in the paper, with the reduction of Rayleigh angle the equilibrium positions for steel cylinders in water change from pressure nodes to pressure antinodes. The model can thus be used in the design of SSAWs for particle manipulations.

Optical pulling and pushing forces exerted on silicon nanospheres with strong coherent interaction between electric and magnetic resonances.

PubMed

Liu, Hongfeng; Panmai, Mingcheng; Peng, Yuanyuan; Lan, Sheng

2017-05-29

We investigated theoretically and numerically the optical pulling and pushing forces acting on silicon (Si) nanospheres (NSs) with strong coherent interaction between electric and magnetic resonances. We examined the optical pulling and pushing forces exerted on Si NSs by two interfering waves and revealed the underlying physical mechanism from the viewpoint of electric- and magnetic-dipole manipulation. As compared with a polystyrene (PS) NS, it was found that the optical pulling force for a Si NS with the same size is enlarged by nearly two orders of magnitude. In addition to the optical pulling force appearing at the long-wavelength side of the magnetic dipole resonance, very large optical pushing force is observed at the magnetic quadrupole resonance. The correlation between the optical pulling/pushing force and the directional scattering characterized by the ratio of the forward to backward scattering was revealed. More interestingly, it was found that the high-order electric and magnetic resonances in large Si NSs play an important role in producing optical pulling force which can be generated by not only s-polarized wave but also p-polarized one. Our finding indicates that the strong coherent interaction between the electric and magnetic resonances existing in nanoparticles with large refractive indices can be exploited to manipulate the optical force acting on them and the correlation between the optical force and the directional scattering can be used as guidance. The engineering and manipulation of optical forces will find potential applications in the trapping, transport and sorting of nanoparticles.

A Biomechanical Assessment of Hand/Arm Force with Pneumatic Nail Gun Actuation Systems.

PubMed

Lowe, Brian D; Albers, James; Hudock, Stephen D

2014-09-01

A biomechanical model is presented, and combined with measurements of tip press force, to estimate total user hand force associated with two pneumatic nail gun trigger systems. The contact actuation trigger (CAT) can fire a nail when the user holds the trigger depressed first and then "bumps" the nail gun tip against the workpiece. With a full sequential actuation trigger (SAT) the user must press the tip against the workpiece prior to activating the trigger. The SAT is demonstrably safer in reducing traumatic injury risk, but increases the duration (and magnitude) of tip force exertion. Time integrated (cumulative) hand force was calculated for a single user from measurements of the tip contact force with the workpiece and transfer time between nails as inputs to a static model of the nail gun and workpiece in two nailing task orientations. The model shows the hand force dependence upon the orientation of the workpiece in addition to the trigger system. Based on standard time allowances from work measurement systems (i.e. Methods-Time Measurement - 1) it is proposed that efficient application of hand force with the SAT in maintaining tip contact can reduce force exertion attributable to the sequential actuation trigger to 2-8% (horizontal nailing) and 9-20% (vertical nailing) of the total hand/arm force. The present model is useful for considering differences in cumulative hand/arm force exposure between the SAT and CAT systems and may explain the appeal of the CAT trigger in reducing the user's perception of muscular effort.

A Biomechanical Assessment of Hand/Arm Force with Pneumatic Nail Gun Actuation Systems

PubMed Central

Lowe, Brian D.; Albers, James; Hudock, Stephen D.

2015-01-01

A biomechanical model is presented, and combined with measurements of tip press force, to estimate total user hand force associated with two pneumatic nail gun trigger systems. The contact actuation trigger (CAT) can fire a nail when the user holds the trigger depressed first and then “bumps” the nail gun tip against the workpiece. With a full sequential actuation trigger (SAT) the user must press the tip against the workpiece prior to activating the trigger. The SAT is demonstrably safer in reducing traumatic injury risk, but increases the duration (and magnitude) of tip force exertion. Time integrated (cumulative) hand force was calculated for a single user from measurements of the tip contact force with the workpiece and transfer time between nails as inputs to a static model of the nail gun and workpiece in two nailing task orientations. The model shows the hand force dependence upon the orientation of the workpiece in addition to the trigger system. Based on standard time allowances from work measurement systems (i.e. Methods-Time Measurement - 1) it is proposed that efficient application of hand force with the SAT in maintaining tip contact can reduce force exertion attributable to the sequential actuation trigger to 2–8% (horizontal nailing) and 9–20% (vertical nailing) of the total hand/arm force. The present model is useful for considering differences in cumulative hand/arm force exposure between the SAT and CAT systems and may explain the appeal of the CAT trigger in reducing the user’s perception of muscular effort. PMID:26321780

Building An Adaptive Cyber Strategy

DTIC Science & Technology

2016-06-01

forces. The primary mission of the military in any domain, including cyber , should be readiness to exert force if needed during crisis . AU/ACSC/SMITH...of crisis . The military must be able to AU/ACSC/SMITH, FI/AY16 manipulate the cyber environment, but should avoid direct use of force against...operations focus on maintaining a manageable threat level. Cyberspace is a continually evolving domain, and nations throughout the world can join in cyber

Preventive strength training improves working ergonomics during welding.

PubMed

Krüger, Karsten; Petermann, Carmen; Pilat, Christian; Schubert, Emil; Pons-Kühnemann, Jörn; Mooren, Frank C

2015-01-01

To investigate the effect of a preventive strength training program on cardiovascular, metabolic and muscular strains during welding. Welders are one of the occupation groups which typically have to work in extended forced postures which are known to be an important reason for musculoskeletal disorders. Subjects (exercise group) accomplished a 12-week strength training program, while another group served as controls (control group). Pre and post training examinations included the measurements of the one repetition maximum and an experimental welding test. Local muscle activities were analysed by surface electromyography. Furthermore, heart rate, blood pressure, lactate and rating of perceived exertion were examined. In the exercise group, strength training lead to a significant increase of one repetition maximum in all examined muscles (p<.05). During the experimental welding test muscle activities of trunk and shoulder muscles and arm muscles were significantly reduced in the exercise group after intervention (p<.05). While no changes of neither cardiovascular nor metabolic parameters were found, subjects of the exercise group rated a significantly decreased rate of perceived exertion welding (p<.05). Effects of strength training can be translated in an improved working ergonomics and tolerance against the exposure to high physical demands at work.

Centrosome centering and decentering by microtubule network rearrangement

PubMed Central

Letort, Gaëlle; Nedelec, Francois; Blanchoin, Laurent; Théry, Manuel

2016-01-01

The centrosome is positioned at the cell center by pushing and pulling forces transmitted by microtubules (MTs). Centrosome decentering is often considered to result from asymmetric, cortical pulling forces exerted in particular by molecular motors on MTs and controlled by external cues affecting the cell cortex locally. Here we used numerical simulations to investigate the possibility that it could equally result from the redistribution of pushing forces due to a reorientation of MTs. We first showed that MT gliding along cell edges and pivoting around the centrosome regulate MT rearrangement and thereby direct the spatial distribution of pushing forces, whereas the number, dynamics, and stiffness of MTs determine the magnitude of these forces. By modulating these parameters, we identified different regimes, involving both pushing and pulling forces, characterized by robust centrosome centering, robust off-centering, or “reactive” positioning. In the last-named conditions, weak asymmetric cues can induce a misbalance of pushing and pulling forces, resulting in an abrupt transition from a centered to an off-centered position. Taken together, these results point to the central role played by the configuration of the MTs on the distribution of pushing forces that position the centrosome. We suggest that asymmetric external cues should not be seen as direct driver of centrosome decentering and cell polarization but instead as inducers of an effective reorganization of the MT network, fostering centrosome motion to the cell periphery. PMID:27440925

Contraction-Only Exercise Machine

NASA Technical Reports Server (NTRS)

Doerr, Donald F.; Maples, Arthur B.; Campbell, Craig M.

1992-01-01

Standard knee-extension machine modified so subject experiences force only when lifting leg against stack of weights. Exerts little force on leg while being lowered. Hydraulic cylinder and reservoir mounted on frame of exercise machine. Fluid flows freely from cylinder to reservoir during contraction (lifting) but in constricted fashion from reservoir to cylinder during extension (lowering).

Textbook Presentations of Weight: Conceptual Difficulties and Language Ambiguities

ERIC Educational Resources Information Center

Taibu, Rex; Rudge, David; Schuster, David

2015-01-01

The term "weight" has multiple related meanings in both scientific and everyday usage. Even among experts and in textbooks, weight is ambiguously defined as either the gravitational force on an object or operationally as the magnitude of the force an object exerts on a measuring scale. This poses both conceptual and language difficulties…

Combined reduced forced expiratory volume in 1 second (FEV1) and peripheral artery disease in sedentary elders with functional limitations

USDA-ARS?s Scientific Manuscript database

Objectives: Because they are potentially modifiable and may coexist, we evaluated the combined occurrence of a reduced forced expiratory volume in 1-second (FEV1) and peripheral artery disease (PAD), including its association with exertional symptoms, physical inactivity, and impaired mobility, in s...

Project Physics Tests 2, Motion in the Heavens.

ERIC Educational Resources Information Center

Harvard Univ., Cambridge, MA. Harvard Project Physics.

Test items relating to Project Physics Unit 2 are presented in this booklet. Included are 70 multiple-choice and 22 problem-and-essay questions. Concepts of motion in the heavens are examined for planetary motions, heliocentric theory, forces exerted on the planets, Kepler's laws, gravitational force, Galileo's work, satellite orbits, Jupiter's…

Fundamentals of negative refractive index optical trapping: forces and radiation pressures exerted by focused Gaussian beams using the generalized Lorenz-Mie theory

PubMed Central

Ambrosio, Leonardo A.; Hernández-Figueroa, Hugo E.

2010-01-01

Based on the generalized Lorenz-Mie theory (GLMT), this paper reveals, for the first time in the literature, the principal characteristics of the optical forces and radiation pressure cross-sections exerted on homogeneous, linear, isotropic and spherical hypothetical negative refractive index (NRI) particles under the influence of focused Gaussian beams in the Mie regime. Starting with ray optics considerations, the analysis is then extended through calculating the Mie coefficients and the beam-shape coefficients for incident focused Gaussian beams. Results reveal new and interesting trapping properties which are not observed for commonly positive refractive index particles and, in this way, new potential applications in biomedical optics can be devised. PMID:21258549

Fundamentals of negative refractive index optical trapping: forces and radiation pressures exerted by focused Gaussian beams using the generalized Lorenz-Mie theory.

PubMed

Ambrosio, Leonardo A; Hernández-Figueroa, Hugo E

2010-11-04

Based on the generalized Lorenz-Mie theory (GLMT), this paper reveals, for the first time in the literature, the principal characteristics of the optical forces and radiation pressure cross-sections exerted on homogeneous, linear, isotropic and spherical hypothetical negative refractive index (NRI) particles under the influence of focused Gaussian beams in the Mie regime. Starting with ray optics considerations, the analysis is then extended through calculating the Mie coefficients and the beam-shape coefficients for incident focused Gaussian beams. Results reveal new and interesting trapping properties which are not observed for commonly positive refractive index particles and, in this way, new potential applications in biomedical optics can be devised.

An integrated control scheme for space robot after capturing non-cooperative target

NASA Astrophysics Data System (ADS)

Wang, Mingming; Luo, Jianjun; Yuan, Jianping; Walter, Ulrich

2018-06-01

How to identify the mass properties and eliminate the unknown angular momentum of space robotic system after capturing a non-cooperative target is of great challenge. This paper focuses on designing an integrated control framework which includes detumbling strategy, coordination control and parameter identification. Firstly, inverted and forward chain approaches are synthesized for space robot to obtain dynamic equation in operational space. Secondly, a detumbling strategy is introduced using elementary functions with normalized time, while the imposed end-effector constraints are considered. Next, a coordination control scheme for stabilizing both base and end-effector based on impedance control is implemented with the target's parameter uncertainty. With the measurements of the forces and torques exerted on the target, its mass properties are estimated during the detumbling process accordingly. Simulation results are presented using a 7 degree-of-freedom kinematically redundant space manipulator, which verifies the performance and effectiveness of the proposed method.

Fingertip touch improves postural stability in patients with peripheral neuropathy.

PubMed

Dickstein, R; Shupert, C L; Horak, F B

2001-12-01

The purpose of this work was to determine whether fingertip touch on a stable surface could improve postural stability during stance in subjects with somatosensory loss in the feet from diabetic peripheral neuropathy. The contribution of fingertip touch to postural stability was determined by comparing postural sway in three touch conditions (light, heavy and none) in eight patients and eight healthy control subjects who stood on two surfaces (firm or foam) with eyes open or closed. In the light touch condition, fingertip touch provided only somatosensory information because subjects exerted less than 1 N of force with their fingertip to a force plate, mounted on a vertical support. In the heavy touch condition, mechanical support was available because subjects transmitted as much force to the force plate as they wished. In the no touch condition, subjects held the right forefinger above the force plate. Antero-posterior (AP) and medio-lateral (ML) root mean square (RMS) of center of pressure (CoP) sway and trunk velocity were larger in subjects with somatosensory loss than in control subjects, especially when standing on the foam surface. The effects of light and heavy touch were similar in the somatosensory loss and control groups. Fingertip somatosensory input through light touch attenuated both AP and ML trunk velocity as much as heavy touch. Light touch also reduced CoP sway compared to no touch, although the decrease in CoP sway was less effective than with heavy touch, particularly on the foam surface. The forces that were applied to the touch plate during light touch preceded movements of the CoP, lending support to the suggestion of a feedforward mechanism in which fingertip inputs trigger the activation of postural muscles for controlling body sway. These results have clinical implications for understanding how patients with peripheral neuropathy may benefit from a cane for postural stability in stance.

Stopping power: Effect of the projectile deceleration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kompaneets, Roman, E-mail: kompaneets@mpe.mpg.de; Ivlev, Alexei V.; Morfill, Gregor E.

2014-11-15

The stopping force is the force exerted on the projectile by its wake. Since the wake does not instantly adjust to the projectile velocity, the stopping force should be affected by the projectile deceleration caused by the stopping force itself. We address this effect by deriving the corresponding correction to the stopping force in the cold plasma approximation. By using the derived expression, we estimate that if the projectile is an ion passing through an electron-proton plasma, the correction is small when the stopping force is due to the plasma electrons, but can be significant when the stopping force ismore » due to the protons.« less

Swing and Lift

ERIC Educational Resources Information Center

Barnes, Francis; Potter, Ann

1974-01-01

Presents theoretical fundamentals of sideways forces exerted on a cricket ball, an aerofoil, and a yacht, involving the properties of boundary layers and a description of velocity and circulation. (CC)

Compression force on the upper jaw during neonatal intubation: mannequin study.

PubMed

Doreswamy, Srinivasa Murthy; Almannaei, Khaled; Fusch, Chris; Shivananda, Sandesh

2015-03-01

Neonatal intubation is a technically challenging procedure, and pressure-related injuries to surrounding structures have been reported. The primary objective of this study was to determine the pressure exerted on the upper jaw during tracheal intubation using a neonatal mannequin. Multidisciplinary care providers working at a neonatal intensive care unit were requested to intubate a neonatal mannequin using the standard laryngoscope and 3.0-mm (internal diameter) endotracheal tube. Compression force exerted was measured by using pressure-sensitive film taped on the upper jaw before every intubation attempt. Pressure, area under pressure and time taken to intubate were compared between the different types of health-care professionals. Thirty care providers intubated the mannequin three times each. Pressure impressions were observed on the developer film after every intubation attempt (n = 90). The mean pressure exerted during intubation across all health-care providers was 568 kPa (SD 78). The mean area placed under pressure was 142 mm(2) (SD 45), and the mean time taken for intubation was 14.7 s (SD 4.3). There was no difference in pressure exerted on the upper jaw between frequent and less frequent intubators. It was found that pressure greater than 400 kPa was inadvertently applied on the upper jaw during neonatal intubation, far exceeding the 250 kPa shown to cause tissue injury in animal models. The upper jaw is exposed to a significant compression force during intubation. Although such exposure is brief, it has the potential to cause tissue injury. Contact of the laryngoscope blade with the upper jaw occurred in all intubation attempts with the currently used design of laryngoscope. © 2014 The Authors. Journal of Paediatrics and Child Health © 2014 Paediatrics and Child Health Division (Royal Australasian College of Physicians).

Escaping blood-fed malaria mosquitoes minimize tactile detection without compromising on take-off speed.

PubMed

Muijres, F T; Chang, S W; van Veen, W G; Spitzen, J; Biemans, B T; Koehl, M A R; Dudley, R

2017-10-15

To escape after taking a blood meal, a mosquito must exert forces sufficiently high to take off when carrying a load roughly equal to its body weight, while simultaneously avoiding detection by minimizing tactile signals exerted on the host's skin. We studied this trade-off between escape speed and stealth in the malaria mosquito Anopheles coluzzii using 3D motion analysis of high-speed stereoscopic videos of mosquito take-offs and aerodynamic modeling. We found that during the push-off phase, mosquitoes enhanced take-off speed using aerodynamic forces generated by the beating wings in addition to leg-based push-off forces, whereby wing forces contributed 61% of the total push-off force. Exchanging leg-derived push-off forces for wing-derived aerodynamic forces allows the animal to reduce peak force production on the host's skin. By slowly extending their long legs throughout the push-off, mosquitoes spread push-off forces over a longer time window than insects with short legs, thereby further reducing peak leg forces. Using this specialized take-off behavior, mosquitoes are capable of reaching take-off speeds comparable to those of similarly sized fruit flies, but with weight-normalized peak leg forces that were only 27% of those of the fruit flies. By limiting peak leg forces, mosquitoes possibly reduce the chance of being detected by the host. The resulting combination of high take-off speed and low tactile signals on the host might help increase the mosquito's success in escaping from blood-hosts, which consequently also increases the chance of transmitting vector-borne diseases, such as malaria, to future hosts. © 2017. Published by The Company of Biologists Ltd.

External Hand Forces Exerted by Long-Term Care Staff to Push Floor-Based Lifts: Effects of Flooring System and Resident Weight.

PubMed

Lachance, Chantelle C; Korall, Alexandra M B; Russell, Colin M; Feldman, Fabio; Robinovitch, Stephen N; Mackey, Dawn C

2016-09-01

The aim of this study was to investigate the effects of flooring type and resident weight on external hand forces required to push floor-based lifts in long-term care (LTC). Novel compliant flooring is designed to reduce fall-related injuries among LTC residents but may increase forces required for staff to perform pushing tasks. A motorized lift may offset the effect of flooring on push forces. Fourteen female LTC staff performed straight-line pushes with two floor-based lifts (conventional, motor driven) loaded with passengers of average and 90th-percentile resident weights over four flooring systems (concrete+vinyl, compliant+vinyl, concrete+carpet, compliant+carpet). Initial and sustained push forces were measured by a handlebar-mounted triaxial load cell and compared to participant-specific tolerance limits. Participants rated pushing difficulty. Novel compliant flooring increased initial and sustained push forces and subjective ratings compared to concrete flooring. Compared to the conventional lift, the motor-driven lift substantially reduced initial and sustained push forces and perceived difficulty of pushing for all four floors and both resident weights. Participants exerted forces above published tolerance limits only when using the conventional lift on the carpet conditions (concrete+carpet, compliant+carpet). With the motor-driven lift only, resident weight did not affect push forces. Novel compliant flooring increased linear push forces generated by LTC staff using floor-based lifts, but forces did not exceed tolerance limits when pushing over compliant+vinyl. The motor-driven lift substantially reduced push forces compared to the conventional lift. Results may help to address risk of work-related musculoskeletal injury, especially in locations with novel compliant flooring. © 2016, Human Factors and Ergonomics Society.

Design of anisotropic pneumatic artificial muscles and their applications to soft wearable devices for text neck symptoms.

PubMed

Hojoong Kim; Hyuntai Park; Jongwoo Kim; Kyu-Jin Cho; Yong-Lae Park

2017-07-01

Pneumatic artificial muscles (PAMs) are frequently used actuators in soft robotics due to their structural flexibility. They are generally characterized by the tensile force due to the axial contraction and the radial force with volume expansion. To date, most applications of P AMs have utilized axial contractions. In contrast, we propose a novel way to control radial expansions of particular P AMs using anisotropic behaviors. P AMs generally consist of a cylindrical rubber bladder that expands with injection of air and multiple flexible but inextensible strings or mesh that surround the bladder to generate axial contraction force. We propose methods of generating radial expansion force in two ways. One is to control the spatial density of the strings that hold the bladder, and the other is to give asymmetric patterns directly to the bladder for geometrical anisotropy. To evaluate the performance of the actuators, soft sensors made of a hyperelastic material and a liquid conductor were attached to the P AMs for measuring local strains and pressures of the PAMs. We also suggest use of the proposed PAMs to a wearable therapeutic device for treating text neck symptoms as an application. The P AMs were used to exert a pressure to the back of the neck to recover the original spinal alignment from the deformed shape.

A force sensor using nanowire arrays to understand biofilm formation (Conference Presentation)

NASA Astrophysics Data System (ADS)

Sahoo, Prasana K.; Cavalli, Alessandro; Pelegati, Vitor B.; Murillo, Duber M.; Souza, Alessandra A.; Cesar, Carlos L.; Bakkers, Erik P. A. M.; Cotta, Monica A.

2016-03-01

Understanding the cellular signaling and function at the nano-bio interface can pave the way towards developing next-generation smart diagnostic tools. From this perspective, limited reports detail so far the cellular and subcellular forces exerted by bacterial cells during the interaction with abiotic materials. Nanowire arrays with high aspect ratio have been used to detect such small forces. In this regard, live force measurements were performed ex-vivo during the interaction of Xylella fastidiosa bacterial cells with InP nanowire arrays. The influence of nanowire array topography and surface chemistry on the response and motion of bacterial cells was studied in detail. The nanowire arrays were also functionalized with different cell adhesive promoters, such as amines and XadA1, an afimbrial protein of X.fastidiosa. By employing the well-defined InP nanowire arrays platform, and single cell confocal imaging system, we were able to trace the bacterial growth pattern, and show that their initial attachment locations are strongly influenced by the surface chemistry and nanoscale surface topography. In addition, we measure the cellular forces down to few nanonewton range using these nanowire arrays. In case of nanowire functionalized with XadA1, the force exerted by vertically and horizontally attached single bacteria on the nanowire is in average 14% and 26% higher than for the pristine array, respectively. These results provide an excellent basis for live-cell force measurements as well as unravel the range of forces involved during the early stages of bacterial adhesion and biofilm formation.

The behaviour of the long-latency stretch reflex in patients with Parkinson's disease

PubMed Central

Rothwell, Jc; Obeso, Ja; Traub, Mm; Marsden, Cd

1983-01-01

The size of the long-latency stretch reflex was measured in a proximal (triceps) and distal (flexor pollicis longus) muscle in 47 patients with Parkinson's disease, and was compared with that seen in a group of 12 age-matched normal control subjects. The patients were classified clinically into four groups according to the degree of rigidity at the elbow or tremor. Stretch reflexes were evaluated while the subject was exerting a small force against a constant preload supplied by a torque motor, and the size of the reflex response was measured as fractional increase over basal levels of activity. When stretches were given at random intervals by increasing the force exerted by the motor by a factor of 2 or 3, there was a clear trend for the more severely affected patients to have larger long latency responses in the triceps muscle, although there was no change in the size of the short-latency, spinal component of the response. In contrast, there was no change in the size of the long-latency response of the flexor pollicis longus in any group of patients with Parkinson's disease. Despite any differences in reflex size, the inherent muscle stiffness of both muscles appeared to be normal in all groups of patients with Parkinson's disease, since the displacement trajectory of the limb following the force increase was the same as control values in the short (25 ms) period before reflex compensation could intervene. In 20 of the patients and in seven of the control subjects, servo-controlled, ramp positional disturbances were given to the thumb. Up to a velocity of 300°/s, the size of the long-latency stretch reflex was proportional to the log velocity of stretch. This technique revealed, in both moderately and severely rigid patients, increases in the reflex sensitivity of the flexor pollicis longus, which had not been clear using step torque stretches alone. However, whether using ramp or step displacements, long latency stretch reflex gain was not closely related to rigidity; reflex size was within the normal range in many patients with severe rigidity. Enhanced long latency stretch reflexes thus contribute to, but may not be solely responsible for, rigidity in Parkinson's disease. PMID:6842198

Interface Stability Influences Torso Muscle Recruitment and Spinal Load During Pushing Tasks

PubMed Central

LEE, P. J.; GRANATA, K. P.

2006-01-01

Handle or interface design can influence torso muscle recruitment and spinal load during pushing tasks. The objective of the study was to provide insight into the role of interface stability with regard to torso muscle recruitment and biomechanical loads on the spine. Fourteen subjects generated voluntary isometric trunk flexion force against a rigid interface and similar flexion exertions against an unstable interface, which simulated handle design in a cart pushing task. Normalized electromyographic (EMG) activity in the rectus abdominus, external oblique and internal oblique muscles increased with exertion effort. When using the unstable interface, EMG activity in the internal and external oblique muscle groups was greater than when using the rigid interface. Results agreed with trends from a biomechanical model implemented to predict the muscle activation necessary to generate isometric pushing forces and maintain spinal stability when using the two different interface designs. The co-contraction contributed to increased spinal load when using the unstable interface. It was concluded that handle or interface design and stability may influence spinal load and associated risk of musculoskeletal injury during manual materials tasks that involve pushing exertions. PMID:16540437

An integrated laser trap/flow control video microscope for the study of single biomolecules.

PubMed Central

Wuite, G J; Davenport, R J; Rappaport, A; Bustamante, C

2000-01-01

We have developed an integrated laser trap/flow control video microscope for mechanical manipulation of single biopolymers. The instrument is automated to maximize experimental throughput. A single-beam optical trap capable of trapping micron-scale polystyrene beads in the middle of a 200-microm-deep microchamber is used, making it possible to insert a micropipette inside this chamber to hold a second bead by suction. Together, these beads function as easily exchangeable surfaces between which macromolecules of interest can be attached. A computer-controlled flow system is used to exchange the liquid in the chamber and to establish a flow rate with high precision. The flow and the optical trap can be used to exert forces on the beads, the displacements of which can be measured either by video microscopy or by laser deflection. To test the performance of this instrument, individual biotinylated DNA molecules were assembled between two streptavidin beads, and the DNA elasticity was characterized using both laser trap and flow forces. DNA extension under varying forces was measured by video microscopy. The combination of the flow system and video microscopy is a versatile design that is particularly useful for the study of systems susceptible to laser-induced damage. This capability was demonstrated by following the translocation of transcribing RNA polymerase up to 650 s. PMID:10920045

POST‐SURGICAL REHABILITATION FOLLOWING FASCIOTOMIES FOR BILATERAL CHRONIC EXERTIONAL COMPARTMENT SYNDROME IN A SPECIAL FORCES SOLDIER: A CASE REPORT

PubMed Central

Miller, Joseph

2013-01-01

Background and Purpose: The etiology of Chronic Exertional Compartment Syndrome (CECS) is still unclear. The most commonly accepted theory suggests that it is a transient but debilitating process where there is an abnormally increased intracompartmental pressure during exercise/exertion due to non‐compliant expansion of the osteofascial tissues. This most commonly occurs in the lower leg. Surgical intervention is often performed for symptom relief. However, there has been limited scientifically‐based publication on post‐surgical rehabilitation, especially with regard to return to function in the military population. The purpose of this case report is to demonstrate the utilization of a recommended post‐operative protocol in a Special Forces Soldier. Case Description: The subject presented as a 25‐year‐old US Army Special Forces Soldier, who failed 8 weeks of conservative management for the diagnosis of CECS and subsequently underwent bilateral lower leg fasciotomies of the anterior and lateral compartments. Outcomes: Following recommended protocol guidelines he was progressed rapidly and within three months deployed without restriction or complications in a demanding combat zone. Discussion: This case report illustrates that following clearly defined, scientifically‐based rehabilitation guidelines helped in addressing all of the involved structures and musculoskeletal dysfunctions that presented following the surgical intervention for CECS in a unique subject. Level of Evidence: 5 PMID:24175149

Heat Control via Torque Control in Friction Stir Welding

NASA Technical Reports Server (NTRS)

Venable, Richard; Colligan, Kevin; Knapp, Alan

2004-01-01

In a proposed advance in friction stir welding, the torque exerted on the workpiece by the friction stir pin would be measured and controlled in an effort to measure and control the total heat input to the workpiece. The total heat input to the workpiece is an important parameter of any welding process (fusion or friction stir welding). In fusion welding, measurement and control of heat input is a difficult problem. However, in friction stir welding, the basic principle of operation affords the potential of a straightforward solution: Neglecting thermal losses through the pin and the spindle that supports it, the rate of heat input to the workpiece is the product of the torque and the speed of rotation of the friction stir weld pin and, hence, of the spindle. Therefore, if one acquires and suitably processes data on torque and rotation and controls the torque, the rotation, or both, one should be able to control the heat input into the workpiece. In conventional practice in friction stir welding, one uses feedback control of the spindle motor to maintain a constant speed of rotation. According to the proposal, one would not maintain a constant speed of rotation: Instead, one would use feedback control to maintain a constant torque and would measure the speed of rotation while allowing it to vary. The torque exerted on the workpiece would be estimated as the product of (1) the torque-multiplication ratio of the spindle belt and/or gear drive, (2) the force measured by a load cell mechanically coupled to the spindle motor, and (3) the moment arm of the load cell. Hence, the output of the load cell would be used as a feedback signal for controlling the torque (see figure).

Measurement and Analysis of Extreme Wave and Ice Actions in the Great Lakes for Offshore Wind Platform Design

DOE Office of Scientific and Technical Information (OSTI.GOV)

England, Tony; van Nieuwstadt, Lin; De Roo, Roger

This project, funded by the Department of Energy as DE-EE0005376, successfully measured wind-driven lake ice forces on an offshore structure in Lake Superior through one of the coldest winters in recent history. While offshore regions of the Great Lakes offer promising opportunities for harvesting wind energy, these massive bodies of freshwater also offer extreme and unique challenges. Among these challenges is the need to anticipate forces exerted on offshore structures by lake ice. The parameters of interest include the frequency, extent, and movement of lake ice, parameters that are routinely monitored via satellite, and ice thickness, a parameter that hasmore » been monitored at discrete locations over many years and is routinely modeled. Essential relationships for these data to be of use in the design of offshore structures and the primary objective of this project are measurements of maximum forces that lake ice of known thicknesses might exert on an offshore structure.« less

Modeling and estimation of tip contact force for steerable ablation catheters.

PubMed

Khoshnam, Mahta; Skanes, Allan C; Patel, Rajni V

2015-05-01

The efficacy of catheter-based cardiac ablation procedures can be significantly improved if real-time information is available concerning contact forces between the catheter tip and cardiac tissue. However, the widely used ablation catheters are not equipped for force sensing. This paper proposes a technique for estimating the contact forces without direct force measurements by studying the changes in the shape of the deflectable distal section of a conventional 7-Fr catheter (henceforth called the "deflectable distal shaft," the "deflectable shaft," or the "shaft" of the catheter) in different loading situations. First, the shaft curvature when the tip is moving in free space is studied and based on that, a kinematic model for the deflectable shaft in free space is proposed. In the next step, the shaft shape is analyzed in the case where the tip is in contact with the environment, and it is shown that the curvature of the deflectable shaft provides useful information about the loading status of the catheter and can be used to define an index for determining the range of contact forces exerted by the ablation tip. Experiments with two different steerable ablation catheters show that the defined index can detect the range of applied contact forces correctly in more than 80% of the cases. Based on the proposed technique, a framework for obtaining contact force information by using the shaft curvature at a limited number of points along the deflectable shaft is constructed. The proposed kinematic model and the force estimation technique can be implemented together to describe the catheter's behavior before contact, detect tip/tissue contact, and determine the range of contact forces. This study proves that the flexibility of the catheter's distal shaft provides a means of estimating the force exerted on tissue by the ablation tip.

Physical Fatigue, Fitness, and Muscle Function in Patients With Antineutrophil Cytoplasmic Antibody-Associated Vasculitis.

PubMed

McClean, Andrew; Morgan, Matthew D; Basu, Neil; Bosch, Jos A; Nightingale, Peter; Jones, David; Harper, Lorraine

2016-09-01

This study investigated differences in cardiorespiratory fitness, muscular function, perceived exertion, and anxiety/depression between patients and healthy controls (HCs) and assessed which of these variables may account for the fatigue experienced by patients. Fatigue was measured in 48 antineutrophil cytoplasmic antibody-associated vasculitis patients and 41 healthy controls using the Multidimensional Fatigue Inventory (MFI-20), focusing on the physical component. Quality of life, anxiety/depression, and sleep quality were assessed by validated questionnaires. Muscle mass was measured by dual-energy x-ray absorptiometry scan, strength as the maximal voluntary contraction (MVC) force, and endurance as sustained isometric contraction at 50% MVC of the quadriceps. Voluntary activation was assessed by superimposed electrical stimulation. Cardiorespiratory fitness ( ˙Vo2 max and oxygen pulse [O2 pulse]) and perceived exertion (Borg scale) were measured during progressive submaximal exercise. Patients reported elevated physical fatigue scores compared to HCs (patients MFI-20 physical 13 [interquartile range (IQR) 8-16], HCs MFI-20 physical 5.5 [IQR 4-8]; P < 0.001). Muscle mass was the same in both groups, but MVC and time to failure in the endurance test were lower due to reduced voluntary activation in patients. Estimated ˙Vo2 max and O2 pulse were the same in both groups. For the same relative workload, patients reported higher ratings of perceived exertion, which correlated with reports of MFI-20 physical fatigue (R(2)  = 0.2). Depression (R(2)  = 0.6), anxiety (R(2)  = 0.3), and sleep disturbance (R(2)  = 0.3) were all correlated with MFI-20 physical fatigue. These observations suggest that fatigue in patients is of a central rather than peripheral origin, supported by associations of fatigue with heightened perception of exertion, depression, anxiety, and sleep disturbance but normal muscle and cardiorespiratory function. © 2016, American College of Rheumatology.

Apparatus for Precise Indium-Bump Bonding of Microchips

NASA Technical Reports Server (NTRS)

Wild, Larry; Mulder, Jerry; Alvarado, Nicholas

2005-01-01

An improved apparatus has been designed and built for use in precise positioning and pressing of a microchip onto a substrate (which could, optionally, be another microchip) for the purpose of indium-bump bonding. The apparatus (see figure) includes the following: A stereomicroscope, A stage for precise positioning of the microchip in rotation angle (theta) about the nominally vertical pressing axis and in translation along two nominally horizontal coordinate axes (x and y), and An actuator system that causes a bonding tip to press the microchip against the substrate with a precisely controlled force. In operation, the microscope and the stage are used to position the microchip under the bonding tip and to align the indium bumps on the chip and the substrate, then the actuator system is used to apply a prescribed bonding force for a prescribed time. The improved apparatus supplants a partly similar prior apparatus that operated with less precision and repeatability, producing inconsistent and unreliable bonds. Results of the use of the prior apparatus included broken microchips, uneven bonds, and bonds characterized, variously, by overcompression or undercompression. In that apparatus, the bonding force was generated and controlled by use of a micrometer head positioned over the center of a spring-loaded scale, and the force was applied to the microchip via the scale, which was equipped for digital readout of the force. The inconsistency of results was attributed to the following causes: It was not possible to control the bonding force with sufficient precision or repeatability. Particularly troublesome was the inability to control the force at levels less than the weight of 150 g. Excessive compliance in the spring-loaded scale, combined with deviations from parallelarity of the substrate and bonding-tip surfaces, gave rise to nonuniformity in the pressure applied to the microchip, thereby generating excessive stresses and deformations in the microchip. In the improved apparatus, the bonding tip and the components that hold the substrate and the microchip are more rigid and precise than in the prior apparatus, so as to ensure less deviation from parallelarity of the bonding-tip and substrate surfaces, thereby ensuring more nearly uniform distribution of bonding force over the area of the microchip. The bonding force is now applied through, and measured by, a load cell that makes it possible to exert finer control over the force. The force can be set at any value between 0 and the weight of 800 g in increments of 0.2 g.

Vibration Control in Turbomachinery Using Active Magnetic Journal Bearings

NASA Technical Reports Server (NTRS)

Knight, Josiah D.

1996-01-01

The effective use of active magnetic bearings for vibration control in turbomachinery depends on an understanding of the forces available from a magnetic bearing actuator. The purpose of this project was to characterize the forces as functions shaft position. Both numerical and experimental studies were done to determine the characteristics of the forces exerted on a stationary shaft by a magnetic bearing actuator. The numerical studies were based on finite element computations and included both linear and nonlinear magnetization functions. Measurements of the force versus position of a nonrotating shaft were made using two separate measurement rigs, one based on strain gage measurement of forces, the other based on deflections of a calibrated beam. The general trends of the measured principal forces agree with the predictions of the theory while the magnitudes of forces are somewhat smaller than those predicted. Other aspects of theory are not confirmed by the measurements. The measured forces in the normal direction are larger than those predicted by theory when the rotor has a normal eccentricity. Over the ranges of position examined, the data indicate an approximately linear relationship between the normal eccentricity of the shaft and the ratio of normal to principal force. The constant of proportionality seems to be larger at lower currents, but for all cases examined its value is between 0.14 and 0.17. The nonlinear theory predicts the existence of normal forces, but has not predicted such a large constant of proportionality for the ratio. The type of coupling illustrated by these measurements would not tend to cause whirl, because the coupling coefficients have the same sign, unlike the case of a fluid film bearing, where the normal stiffness coefficients often have opposite signs. They might, however, tend to cause other self-excited behavior. This possibility must be considered when designing magnetic bearings for flexible rotor applications, such as gas turbines and other turbomachinery.

High-refractive index particles in counter-propagating optical tweezers - manipulation and forces

NASA Astrophysics Data System (ADS)

van der Horst, Astrid

2006-09-01

With a tightly focused single laser beam, also called optical tweezers, particles of a few nanometers up to several micrometers in size can be trapped and manipulated in 3D. The size, shape and refractive index of such colloidal particles are of influence on the optical forces exerted on them in the trap. A higher refractive-index difference between a particle and the surrounding medium will increase the forces. The destabilizing scattering force, however, pushing the particle in the direction of the beam, increases more than the gradient force, directed towards the focus. As a consequence, particles with a certain refractive index cannot be trapped in a single-beam gradient trap, and a limit is set to the force that can be exerted. We developed an experimental setup with two opposing high-numerical objectives. By splitting the laser beam, we created counter-propagating tweezers in which the scattering forces were canceled in the axial direction and high-refractive index and metallic particles could also be trapped. With the use of a separate laser beam combined with a quadrant photodiode, accurate position detection on a trapped particle in the counter-propagating tweezers is possible. We used this to determine trap stiffnesses, and show, with measurements and calculations, an enhancement in trap stiffness of at least 3 times for high-index 1.1-micrometer-diameter titania particles as compared to 1.4-micrometer-diameter silica particles under the same conditions. The ability to exert higher forces with lower laser power finds application in biophysical experiments, where laser damage and heating play a role. The manipulation of high-index and metallic particles also has applications in materials and colloid science, for example to incorporate high-index defects in colloidal photonic crystals. We demonstrate the patterning of high-index particles onto a glass substrate. The sample cell was mounted on a high-accuracy piezo stage combined with a long-range stage with motorized actuators. Because we used image analysis of the patterned structure to accurately find back the starting position and compensate for drift of the sample, we could move far away from the patterning region. This enabled us to select particles from a separate reservoir of a mixture of particles, and, one-by-one, position them at chosen locations. By time-sharing the laser beam using acousto-optic deflectors, we created multiple counter-propagating tweezers. We trapped an array of high-refractive index particles, and were able to move those particles individually. We used such a dynamic array of counter-propagating tweezers to create line-optical tweezers in which we trapped semi-conducting high-refractive index nanorods in three dimensions. We demonstrate full 3D translational and in-plane rotational control over the rods, which could not be held in single-beam line-tweezers. The configuration of two opposing objectives was also used for simultaneous trapping with one objective and confocal imaging of the fluorescently labeled particles using the other objective. By trapping particles with a refractive index contrast in a dispersion of index-matched particles, crystallization could be induced, which was imaged in three dimensions using confocal microscopy.

L-arginine supplementation prevents increases in intestinal permeability and bacterial translocation in male Swiss mice subjected to physical exercise under environmental heat stress.

PubMed

Costa, Kátia Anunciação; Soares, Anne Danieli Nascimento; Wanner, Samuel Penna; Santos, Rosana das Graças Carvalho dos; Fernandes, Simone Odília Antunes; Martins, Flaviano dos Santos; Nicoli, Jacques Robert; Coimbra, Cândido Celso; Cardoso, Valbert Nascimento

2014-02-01

Dietary supplementation with l-arginine has been shown to improve the intestinal barrier in many experimental models. This study investigated the effects of arginine supplementation on the intestinal permeability and bacterial translocation (BT) induced by prolonged physical exercise under heat stress. Under anesthesia, male Swiss mice (5-wk-old) were implanted with an abdominal sensor to record their core body temperature (T(core)). After recovering from surgery, the mice were divided into 3 groups: a non-supplemented group that was fed the standard diet formulated by the American Institute of Nutrition (AIN-93G; control), a non-supplemented group that was fed the AIN-93G diet and subjected to exertional hyperthermia (H-NS), and a group supplemented with l-arginine at 2% and subjected to exertional hyperthermia (H-Arg). After 7 d of treatment, the H-NS and H-Arg mice were forced to run on a treadmill (60 min, 8 m/min) in a warm environment (34°C). The control mice remained at 24°C. Thirty min before the exercise or control trials, the mice received a diethylenetriamine pentaacetic acid (DTPA) solution labeled with technetium-99m ((99m)Tc-DTPA) or (99m)Tc-Escherichia coli by gavage to assess intestinal permeability and BT, respectively. The H-NS mice terminated the exercise with T(core) values of ∼40°C, and, 4 h later, presented a 12-fold increase in the blood uptake of (99m)Tc-DTPA and higher bacterial contents in the blood and liver than the control mice. Although supplementation with arginine did not change the exercise-induced increase in T(core), it prevented the increases in intestinal permeability and BT caused by exertional hyperthermia. Our results indicate that dietary l-arginine supplementation preserves the integrity of the intestinal epithelium during exercise under heat stress, acting through mechanisms that are independent of T(core) regulation.

Short-Term Effects of Rolling Massage on Energy Cost of Running and Power of the Lower Limbs.

PubMed

Giovanelli, Nicola; Vaccari, Filippo; Floreani, Mirco; Rejc, Enrico; Copetti, Jasmine; Garra, Marco; Biasutti, Lea; Lazzer, Stefano

2018-05-10

Self-myofascial release (SMFR) is a type of self-massage that is becoming popular among athletes. However, SMFR effects on running performance have not been investigated yet. The aim of the present study was to evaluate the effects of SMFR on cost of running (Cr). In addition, we evaluated the effects of SMFR on lower limbs muscle power. The measurement of Cr and lower limb muscle power during squat jump (SJ) and counter movement jump (CMJ) were performed before (PRE), immediately after (POST) and 3hours after (POST 3h) a SMFR protocol (experimental condition). In the "control condition" testing session, the same measurements were performed without undergoing the SMFR protocol. Experimental and control conditions were tested in a randomized order. Cr at POST trended to increase as compared to PRE (+6.2±8.3%, p=0.052), while at POST 3h Cr was restored to PRE values (+0.28±9.5%, p=0.950). In the experimental condition, no significant "Time" effect was observed for maximal power exerted during SJ. On the other hand, maximal power exerted during CMJ at POST and POST 3h was significantly higher than that observed at PRE (+7.9±6.3%, p=0.002; and +10.0±8.7%, p=0.004, respectively). The rate of force development measured during CMJ also increased after SMFR, reaching statistical significance at 200 ms from force onset at POST 3h (+38.9%, p=0.024). an acute use of foam roller for SMFR performed immediately prior to running may negatively affect the endurance running performance, while its use should be added before explosive motor performances that include stretch-shortening cycles.

Nuclear reactor safety device

DOEpatents

Hutter, E.

1983-08-15

A safety device is described for use in a nuclear reactor for axially repositioning a control rod with respect to the reactor core in the event of a thermal excursion. It comprises a laminated strip helically configured to form a tube, said tube being in operative relation to said control rod. The laminated strip is formed of at least two materials having different thermal coefficients of expansion, and is helically configured such that the material forming the outer lamina of the tube has a greater thermal coefficient of expansion than the material forming the inner lamina of said tube. In the event of a thermal excursion the laminated strip will tend to curl inwardly so that said tube will increase in length, whereby as said tube increases in length it exerts a force on said control rod to axially reposition said control rod with respect to said core.

A Model for Predicting Integrated Man-Machine System Reliability: Model Logic and Description

DTIC Science & Technology

1974-11-01

3. Fatigue buildup curve. The common requirement of all tests on the Dynamic Strength factor is for the muscles involved to propel, support, or...move the body repeatedly or to support it continuously over time. The tests of our Static Strength factor emphasize the lifting power of the muscles ...or the pounds of pressure which the muscles can exert. ... In contrast to Dynamic Strength the force exerted is against external objects, rather

FDTD approach to optical forces of tightly focused vector beams on metal particles.

PubMed

Qin, Jian-Qi; Wang, Xi-Lin; Jia, Ding; Chen, Jing; Fan, Ya-Xian; Ding, Jianping; Wang, Hui-Tian

2009-05-11

We propose an improved FDTD method to calculate the optical forces of tightly focused beams on microscopic metal particles. Comparison study on different kinds of tightly focused beams indicates that trapping efficiency can be altered by adjusting the polarization of the incident field. The results also show the size-dependence of trapping forces exerted on metal particles. Transverse tapping forces produced by different illumination wavelengths are also evaluated. The numeric simulation demonstrates the possibility of trapping moderate-sized metal particles whose radii are comparable to wavelength.

Bone-Breaking Bite Force of Basilosaurus isis (Mammalia, Cetacea) from the Late Eocene of Egypt Estimated by Finite Element Analysis

PubMed Central

Snively, Eric; Fahlke, Julia M.; Welsh, Robert C.

2015-01-01

Bite marks suggest that the late Eocence archaeocete whale Basilosaurus isis (Birket Qarun Formation, Egypt) fed upon juveniles of the contemporary basilosaurid Dorudon atrox. Finite element analysis (FEA) of a nearly complete adult cranium of B. isis enables estimates of its bite force and tests the animal’s capabilities for crushing bone. Two loadcases reflect different biting scenarios: 1) an intitial closing phase, with all adductors active and a full condylar reaction force; and 2) a shearing phase, with the posterior temporalis active and minimized condylar force. The latter is considered probable when the jaws were nearly closed because the preserved jaws do not articulate as the molariform teeth come into occulusion. Reaction forces with all muscles active indicate that B. isis maintained relatively greater bite force anteriorly than seen in large crocodilians, and exerted a maximum bite force of at least 16,400 N at its upper P3. Under the shearing scenario with minimized condylar forces, tooth reaction forces could exceed 20,000 N despite lower magnitudes of muscle force. These bite forces at the teeth are consistent with bone indentations on Dorudon crania, reatract-and-shear hypotheses of Basilosaurus bite function, and seizure of prey by anterior teeth as proposed for other archaeocetes. The whale’s bite forces match those estimated for pliosaurus when skull lengths are equalized, suggesting similar tradeoffs of bite function and hydrodynamics. Reaction forces in B. isis were lower than maxima estimated for large crocodylians and carnivorous dinosaurs. However, comparison of force estimates from FEA and regression data indicate that B. isis exerted the largest bite forces yet estimated for any mammal, and greater force than expected from its skull width. Cephalic feeding biomechanics of Basilosaurus isis are thus consistent with habitual predation. PMID:25714832

Substrate stress relaxation regulates cell spreading

NASA Astrophysics Data System (ADS)

Chaudhuri, Ovijit; Gu, Luo; Darnell, Max; Klumpers, Darinka; Bencherif, Sidi A.; Weaver, James C.; Huebsch, Nathaniel; Mooney, David J.

2015-02-01

Studies of cellular mechanotransduction have converged upon the idea that cells sense extracellular matrix (ECM) elasticity by gauging resistance to the traction forces they exert on the ECM. However, these studies typically utilize purely elastic materials as substrates, whereas physiological ECMs are viscoelastic, and exhibit stress relaxation, so that cellular traction forces exerted by cells remodel the ECM. Here we investigate the influence of ECM stress relaxation on cell behaviour through computational modelling and cellular experiments. Surprisingly, both our computational model and experiments find that spreading for cells cultured on soft substrates that exhibit stress relaxation is greater than cells spreading on elastic substrates of the same modulus, but similar to that of cells spreading on stiffer elastic substrates. These findings challenge the current view of how cells sense and respond to the ECM.

Experimental verification of high energy laser-generated impulse for remote laser control of space debris.

PubMed

Lorbeer, Raoul-Amadeus; Zwilich, Michael; Zabic, Miroslav; Scharring, Stefan; Eisert, Lukas; Wilken, Jascha; Schumacher, Dennis; Roth, Markus; Eckel, Hans-Albert

2018-05-31

Walking along a beach one may notice debris being washed ashore from the vast oceans. Then, turning your head up at night you even might noticed a shooting star or a bright spot passing by. Chances are, that you witnessed space debris, endangering future space flight in lower earth orbit. If it was possible to turn cm-sized debris into shooting stars the problem might be averted. Unfortunately, these fragments counting in the 100 thousands are not controllable. To possibly regain control we demonstrate how to exert forces on a free falling debris object from a distance by ablating material with a high energy ns-laser-system. Thrust effects did scale as expected from simulations and led to speed gains above 0.3 m/s per laser pulse in an evacuated micro-gravity environment.

Frictionless segmented mechanics for controlled space closure

PubMed Central

Andrade, Ildeu

2017-01-01

ABSTRACT Extraction spaces may be needed to achieve specific orthodontic goals of positioning the dentition in harmony with the craniofacial complex. However, the fundamental reality that determines the occlusion final position is the control exerted by the orthodontist while closing the extraction spaces. A specific treatment objective may require the posterior teeth to remain in a constant position anteroposteriorly as well as vertically, while the anterior teeth occupy the entire extraction site. Another treatment objective may require the opposite, or any number of intentional alternatives of extraction site closure. The present case report describes a simple controlled segmented mechanic system that permitted definable and predictable force systems to be applied and allowed to predict the treatment outcome with confidence. This case was presented to the Brazilian Board of Orthodontics and Dentofacial Orthopedics (BBO) in partial fulfillment of the requirements for Diplomate certification. PMID:28444016

Optical force stamping lithography

PubMed Central

Nedev, Spas; Urban, Alexander S.; Lutich, Andrey A.; Feldmann, Jochen

2013-01-01

Here we introduce a new paradigm of far-field optical lithography, optical force stamping lithography. The approach employs optical forces exerted by a spatially modulated light field on colloidal nanoparticles to rapidly stamp large arbitrary patterns comprised of single nanoparticles onto a substrate with a single-nanoparticle positioning accuracy well beyond the diffraction limit. Because the process is all-optical, the stamping pattern can be changed almost instantly and there is no constraint on the type of nanoparticle or substrates used. PMID:21992538

Single-platelet nanomechanics measured by high-throughput cytometry

NASA Astrophysics Data System (ADS)

Myers, David R.; Qiu, Yongzhi; Fay, Meredith E.; Tennenbaum, Michael; Chester, Daniel; Cuadrado, Jonas; Sakurai, Yumiko; Baek, Jong; Tran, Reginald; Ciciliano, Jordan C.; Ahn, Byungwook; Mannino, Robert G.; Bunting, Silvia T.; Bennett, Carolyn; Briones, Michael; Fernandez-Nieves, Alberto; Smith, Michael L.; Brown, Ashley C.; Sulchek, Todd; Lam, Wilbur A.

2017-02-01

Haemostasis occurs at sites of vascular injury, where flowing blood forms a clot, a dynamic and heterogeneous fibrin-based biomaterial. Paramount in the clot's capability to stem haemorrhage are its changing mechanical properties, the major drivers of which are the contractile forces exerted by platelets against the fibrin scaffold. However, how platelets transduce microenvironmental cues to mediate contraction and alter clot mechanics is unknown. This is clinically relevant, as overly softened and stiffened clots are associated with bleeding and thrombotic disorders. Here, we report a high-throughput hydrogel-based platelet-contraction cytometer that quantifies single-platelet contraction forces in different clot microenvironments. We also show that platelets, via the Rho/ROCK pathway, synergistically couple mechanical and biochemical inputs to mediate contraction. Moreover, highly contractile platelet subpopulations present in healthy controls are conspicuously absent in a subset of patients with undiagnosed bleeding disorders, and therefore may function as a clinical diagnostic biophysical biomarker.

Currents in the DIII-D Tokamak

NASA Astrophysics Data System (ADS)

Azari, A.; Eidietis, N. W.

2012-10-01

Loss of vertical control of an elongated tokamak plasma results in a vertical displacement event (VDE) which can induce large currents on open field lines and exert high JxB forces on in-vessel components. An array of first-wall tile current monitors on DIII-D provides direct measurement of the poloidal halo currents. These measurements are analyzed to create a database of halo current magnitude and asymmetry, which are found to lie within the ranges seen by numerous other tokamaks in the ITPA Disruption Database. In addition, an analysis of halo asymmetry rotation is presented, as rotation at the resonance frequencies of in-vessel components could lead to significant amplification of the halo forces. Halo current rotation is found to be far more prevalent in old (1997-2002) DIII-D halo current data than recent data (2009), perhaps due to a change in divertor geometry over that time.

Understanding gas-surface interactions from direct force measurements using a specialized torsion balance

NASA Technical Reports Server (NTRS)

Cook, S. R.; Hoffbauer, M. A.

1996-01-01

The first comprehensive measurements of the magnitude and direction of the forces exerted on surfaces by molecular beams are discussed and used to obtain information about the microscopic properties of the gas-surface interactions. This unique approach is not based on microscopic measurements of the scattered molecules. The reduced force coefficients are introduced as a new set of parameters that completely describe the macroscopic average momentum transfer to a surface by an incident molecular beam. By using a specialized torsion balance and molecular beams of N2, CO, CO2, and H2, the reduced force coefficients are determined from direct measurements of the force components exerted on surface of a solar panel array material, Kapton, SiO2-coated Kapton, and Z-93 as a function of the angle of incidence ranging from 0 degrees to 85 degrees. The absolute flux densities of the molecular beams were measured using a different torsion balance with a beam-stop that nullified the force of the scattered molecules. Standard time-of-flight techniques were used to determine the flux-weighted average velocities of the various molecular beams ranging from 1600 m/s to 4600 m/s. The reduced force coefficients can be used to directly obtain macroscopic average properties of the scattered molecules, such as the flux-weighted average velocity and translational energy, that can then be used to determine microscopic details concerning gas-surface interactions without the complications associated with averaging microscopic measurements.

Transport Pathways—Proton Motive Force Interrelationship in Durum Wheat Mitochondria

PubMed Central

Trono, Daniela; Laus, Maura N.; Soccio, Mario; Pastore, Donato

2014-01-01

In durum wheat mitochondria (DWM) the ATP-inhibited plant mitochondrial potassium channel (PmitoKATP) and the plant uncoupling protein (PUCP) are able to strongly reduce the proton motive force (pmf) to control mitochondrial production of reactive oxygen species; under these conditions, mitochondrial carriers lack the driving force for transport and should be inactive. However, unexpectedly, DWM uncoupling by PmitoKATP neither impairs the exchange of ADP for ATP nor blocks the inward transport of Pi and succinate. This uptake may occur via the plant inner membrane anion channel (PIMAC), which is physiologically inhibited by membrane potential, but unlocks its activity in de-energized mitochondria. Probably, cooperation between PIMAC and carriers may accomplish metabolite movement across the inner membrane under both energized and de-energized conditions. PIMAC may also cooperate with PmitoKATP to transport ammonium salts in DWM. Interestingly, this finding may trouble classical interpretation of in vitro mitochondrial swelling; instead of free passage of ammonia through the inner membrane and proton symport with Pi, that trigger metabolite movements via carriers, transport of ammonium via PmitoKATP and that of the counteranion via PIMAC may occur. Here, we review properties, modulation and function of the above reported DWM channels and carriers to shed new light on the control that they exert on pmf and vice-versa. PMID:24821541

Stress focusing and collapse of a thin film under constant pressure

NASA Astrophysics Data System (ADS)

Hamm, Eugenio; Cabezas, Nicolas

2012-02-01

Thin elastic sheets and shells are prone to focus stress when forced, due to their near inextensibility. Singular structures such as ridges, vertices, and folds arising from wrinkles, are characteristic of the deformation of such systems. Usually the forcing is exerted at the boundaries or at specific points of the surface, in displacement controlled experiments. On the other hand, much of the phenomenology of stress focusing can be found at micro and nanoscales, in physics and biology, making it universal. We will consider the post-buckling regime of a thin elastic sheet that is subjected to a constant normal distributed force. Specifically, we will present experiments made on thin elastoplastic sheets that collapse under atmospheric pressure. For instance, in vacuum-sealing technology, when a flat plastic bag is forced to wrap a solid volume, a series of self-contacts and folds develop. The unfolded bag shows a pattern of scars whose structure is determined by the geometry of the volume and by the exact way it stuck to its surface, by friction. Inspired by this everyday example we study the geometry of folds that result from collapsing a hermetic bag on regular rigid bodies.

Molecular origin of contact line stick-slip motion during droplet evaporation

PubMed Central

Wang, FengChao; Wu, HengAn

2015-01-01

Understanding and controlling the motion of the contact line is of critical importance for surface science studies as well as many industrial engineering applications. In this work, we elucidate the molecular origin of contact line stick-slip motion during the evaporation of liquid droplets on flexible nano-pillared surfaces using molecular dynamics simulations. We demonstrate that the evaporation-induced stick-slip motion of the contact line is a consequence of competition between pinning and depinning forces. Furthermore, the tangential force exerted by the pillared substrate on the contact line was observed to have a sawtooth-like oscillation. Our analysis also establishes that variations in the pinning force are accomplished through the self-adaptation of solid-liquid intermolecular distances, especially for liquid molecules sitting directly on top of the solid pillar. Consistent with our theoretical analysis, molecular dynamics simulations also show that the maximum pinning force is quantitatively related to both solid-liquid adhesion strength and liquid-vapor surface tension. These observations provide a fundamental understanding of contact line stick-slip motion on pillared substrates and also give insight into the microscopic interpretations of contact angle hysteresis, wetting transitions and dynamic spreading. PMID:26628084

A hemidesmosomal protein regulates actin dynamics and traction forces in motile keratinocytes

PubMed Central

Hiroyasu, Sho; Colburn, Zachary T.; Jones, Jonathan C. R.

2016-01-01

During wound healing of the skin, keratinocytes disassemble hemidesmosomes and reorganize their actin cytoskeletons in order to exert traction forces on and move directionally over the dermis. Nonetheless, the transmembrane hemidesmosome component collagen XVII (ColXVII) is found in actin-rich lamella, situated behind the lamellipodium. A set of actin bundles, along which ColXVII colocalizes with actinin4, is present at each lamella. Knockdown of either ColXVII or actinin4 not only inhibits directed migration of keratinocytes but also relieves constraints on actin bundle retrograde movement at the site of lamella, such that actin bundle movement is enhanced more than 5-fold. Moreover, whereas control keratinocytes move in a stepwise fashion over a substrate by generating alternating traction forces, of up to 1.4 kPa, at each flank of the lamellipodium, ColXVII knockdown keratinocytes fail to do so. In summary, our data indicate that ColXVII-actinin4 complexes at the lamella of a moving keratinocyte regulate actin dynamics, thereby determining the direction of cell movement.—Hiroyasu, S., Colburn, Z. T., Jones, J. C. R. A hemidesmosomal protein regulates actin dynamics and traction forces in motile keratinocytes. PMID:26936359

Electric force on plasma ions and the momentum of the ion-neutrals flow

NASA Astrophysics Data System (ADS)

Makrinich, G.; Fruchtman, A.; Zoler, D.; Boxman, R. L.

2018-05-01

The electric force on ions in plasma and the momentum flux carried by the mixed ion-neutral flow were measured and found to be equal. The experiment was performed in a direct-current gas discharge of cylindrical geometry with applied radial electric field and axial magnetic field. The unmagnetized plasma ions, neutralized by magnetized electrons, were accelerated radially outward transferring part of the gained momentum to neutrals. Measurements were taken for various argon gas flow rates between 13 and 100 Standard Cubic Centimeter per Minute, for a discharge current of 1.9 A and a magnetic field intensity of 136 G. The plasma density, electron temperature, and plasma potential were measured at various locations along the flow. These measurements were used to determine the local electric force on the ions. The total electric force on the plasma ions was then determined by integrating radially the local electric force. In parallel, the momentum flux of the mixed ion-neutral flow was determined by measuring the force exerted by the flow on a balance force meter (BFM). The maximal plasma density was between 6 × 1010 cm-3 and 5 × 1011 cm-3, the maximal electron temperature was between 8 eV and 25 eV, and the deduced maximal electric field was between 2200 V/m and 5800 V/m. The force exerted by the mixed ion-neutral flow on the BFM agreed with the total electric force on the plasma ions. This agreement showed that it is the electric force on the plasma ions that is the source of the momentum acquired by the mixed ion-neutral flow.

Predicting muscle forces during the propulsion phase of single leg triple hop test.

PubMed

Alvim, Felipe Costa; Lucareli, Paulo Roberto Garcia; Menegaldo, Luciano Luporini

2018-01-01

Functional biomechanical tests allow the assessment of musculoskeletal system impairments in a simple way. Muscle force synergies associated with movement can provide additional information for diagnosis. However, such forces cannot be directly measured noninvasively. This study aims to estimate muscle activations and forces exerted during the preparation phase of the single leg triple hop test. Two different approaches were tested: static optimization (SO) and computed muscle control (CMC). As an indirect validation, model-estimated muscle activations were compared with surface electromyography (EMG) of selected hip and thigh muscles. Ten physically healthy active women performed a series of jumps, and ground reaction forces, kinematics and EMG data were recorded. An existing OpenSim model with 92 musculotendon actuators was used to estimate muscle forces. Reflective markers data were processed using the OpenSim Inverse Kinematics tool. Residual Reduction Algorithm (RRA) was applied recursively before running the SO and CMC. For both, the same adjusted kinematics were used as inputs. Both approaches presented similar residuals amplitudes. SO showed a closer agreement between the estimated activations and the EMGs of some muscles. Due to inherent EMG methodological limitations, the superiority of SO in relation to CMC can be only hypothesized. It should be confirmed by conducting further studies comparing joint contact forces. The workflow presented in this study can be used to estimate muscle forces during the preparation phase of the single leg triple hop test and allows investigating muscle activation and coordination. Copyright © 2017 Elsevier B.V. All rights reserved.

Separation control with fluidic oscillators in water

NASA Astrophysics Data System (ADS)

Schmidt, H.-J.; Woszidlo, R.; Nayeri, C. N.; Paschereit, C. O.

2017-08-01

The present study assesses the applicability of fluidic oscillators for separation control in water. The first part of this work evaluates the properties of the fluidic oscillators including frequency, cavitation effects, and exerted thrust. Derived from the governing internal dynamics, the oscillation frequency is found to scale directly with the jet's exit velocity and the size of the fluidic oscillator independent of the working fluid. Frequency data from various experiments collapse onto a single curve. The occurrence of cavitation is examined by visual inspection and hydrophone measurements. The oscillation frequency is not affected by cavitation because it does not occur inside the oscillators. The spectral information obtained with the hydrophone provide a reliable indicator for the onset of cavitation at the exit. The performance of the fluidic oscillators for separation control on a bluff body does not seem to be affected by the presence of cavitation. The thrust exerted by an array of fluidic oscillators with water as the working fluid is measured to be even larger than theoretically estimated values. The second part of the presented work compares the performance of fluidic oscillators for separation control in water with previous results in air. The array of fluidic oscillators is installed into the rear end of a bluff body model. The drag improvements based on force balance measurements agree well with previous wind tunnel experiments on the same model. The flow field is examined by pressure measurements and with particle image velocimetry. Similar performance and flow field characteristics are observed in both water and air.

Flux control exerted by overt carnitine palmitoyltransferase over palmitoyl-CoA oxidation and ketogenesis is lower in suckling than in adult rats.

PubMed Central

Krauss, S; Lascelles, C V; Zammit, V A; Quant, P A

1996-01-01

We examined the potential of overt carnitine palmitoyltransferase (CPT I) to control the hepatic catabolism of palmitoyl-CoA in suckling and adult rats, using a conceptually simplified model of fatty acid oxidation and ketogenesis. By applying top-down control analysis, we quantified the control exerted by CPT I over total carbon flux from palmitoyl-CoA to ketone bodies and carbon dioxide. Our results show that in both suckling and adult rat, CPT I exerts very significant control over the pathways under investigation. However, under the sets of conditions we studied, less control is exerted by CPT I over total carbon flux in mitochondria isolated from suckling rats than in those isolated from adult rats. Furthermore the flux control coefficient of CPT I changes with malonyl-CoA concentration and ATP turnover rate. PMID:8912677

Effects of Rate of Movement on Effective Maximal Force Generated by Elbow Extensors.

ERIC Educational Resources Information Center

Updyke, Wynn F.; And Others

This study investigated the effects of the velocity of muscular contraction on the effective force (torque) exerted by forty 18- to 21-year-old males. The dynomemeter lever arm, the fulcrum of which was aligned with the axis of elbow rotation, allowed extension and flexion for the subjects. All subjects were tested at three velocities (.10, .20,…

Climbing, Slipping and Newton's Second Law

ERIC Educational Resources Information Center

O'Shea, Michael J.

2009-01-01

A point mass model of a climber ascending a rock slope is developed. Stability of the climber is defined via the maximum possible friction force exerted by the feet of the climber on rock and the maximum possible force that the hands of the climber can support in a handhold. This model is then generalized to a somewhat more realistic extended mass…

Fluid Flow, Newton's Second Law and River Rescue

ERIC Educational Resources Information Center

O'Shea, Michael J.

2006-01-01

We consider the situation of a boat pinned or wrapped against a rock by moving water in a river. The force exerted by moving water is calculated and the force required to extricate the boat is estimated. Rafts, canoes and kayaks are each considered. A rope system commonly employed by river runners to extricate a boat is analysed. This system…

Modeling the Sedimentation of Red Blood Cells in Flow under Strong External Magnetic Body Force using a Lattice Boltzmann Fictitious Domain Method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shi, Xing; Lin, Guang

To model the sedimentation of the red blood cell (RBC) in a square duct and a circular pipe, the recently developed technique derived from the lattice Boltzmann method and the distributed Lagrange multiplier/fictitious domain method (LBM-DLM/FD) is extended to employ the mesoscopic network model for simulations of the sedimentation of the RBC in flow. The flow is simulated by the lattice Boltzmann method with a strong magnetic body force, while the network model is used for modeling RBC deformation. The fluid-RBC interactions are enforced by the Lagrange multiplier. The sedimentation of the RBC in a square duct and a circularmore » pipe is simulated, revealing the capacity of the current method for modeling the sedimentation of RBC in various flows. Numerical results illustrate that that the terminal setting velocity increases with the increment of the exerted body force. The deformation of the RBC has significant effect on the terminal setting velocity due to the change of the frontal area. The larger the exerted force is, the smaller the frontal area and the larger deformation of the RBC are.« less

Apparatus measures swelling of membranes in electrochemical cells

NASA Technical Reports Server (NTRS)

Hennigan, T. J.

1965-01-01

Apparatus consisting of a pressure plate unit, four springs of known spring constant and a micrometer measures the swelling and force exerted by the polymer membranes of alkaline electrochemical cells.

Exercise-Induced Skeletal Muscle Damage.

ERIC Educational Resources Information Center

Evans, William J.

1987-01-01

Eccentric exercise, in which the muscles exert force by lengthening, is associated with delayed onset muscle soreness. How soreness occurs, how recovery proceeds, and what precautions athletes should take are described. (Author/MT)

Method for six-legged robot stepping on obstacles by indirect force estimation

NASA Astrophysics Data System (ADS)

Xu, Yilin; Gao, Feng; Pan, Yang; Chai, Xun

2016-07-01

Adaptive gaits for legged robots often requires force sensors installed on foot-tips, however impact, temperature or humidity can affect or even damage those sensors. Efforts have been made to realize indirect force estimation on the legged robots using leg structures based on planar mechanisms. Robot Octopus III is a six-legged robot using spatial parallel mechanism(UP-2UPS) legs. This paper proposed a novel method to realize indirect force estimation on walking robot based on a spatial parallel mechanism. The direct kinematics model and the inverse kinematics model are established. The force Jacobian matrix is derived based on the kinematics model. Thus, the indirect force estimation model is established. Then, the relation between the output torques of the three motors installed on one leg to the external force exerted on the foot tip is described. Furthermore, an adaptive tripod static gait is designed. The robot alters its leg trajectory to step on obstacles by using the proposed adaptive gait. Both the indirect force estimation model and the adaptive gait are implemented and optimized in a real time control system. An experiment is carried out to validate the indirect force estimation model. The adaptive gait is tested in another experiment. Experiment results show that the robot can successfully step on a 0.2 m-high obstacle. This paper proposes a novel method to overcome obstacles for the six-legged robot using spatial parallel mechanism legs and to avoid installing the electric force sensors in harsh environment of the robot's foot tips.

Dynamical friction on hot bodies in opaque, gaseous media

NASA Astrophysics Data System (ADS)

Masset, Frédéric S.; Velasco Romero, David A.

2017-03-01

We consider the gravitational force exerted on a point-like perturber of mass M travelling within a uniform gaseous, opaque medium at constant velocity V. The perturber irradiates the surrounding gas with luminosity L. The diffusion of the heat released is modelled with a uniform thermal diffusivity χ. Using linear perturbation theory, we show that the force exerted by the perturbed gas on the perturber differs from the force without radiation (or standard dynamical friction). Hot, underdense gas trails the mass, which gives rise to a new force component, the heating force, with direction +V, thus opposed to the standard dynamical friction. In the limit of low Mach numbers, the heating force has expression F_heat=γ (γ -1)GML/(2χ c_s^2), cs being the sound speed and γ the ratio of specific heats. In the limit of large Mach numbers, Fheat = (γ - 1)GML/(χV2)f(rminV/4χ), where f is a function that diverges logarithmically as rmin tends to zero. Remarkably, the force in the low Mach number limit does not depend on the velocity. The equilibrium speed, when it exists, is set by the cancellation of the standard dynamical friction and heating force. In the low Mach number limit, it scales with the luminosity-to-mass ratio of the perturber. Using the above results suggests that Mars- to Earth-sized planetary embryos heated by accretion in a gaseous protoplanetary disc should have eccentricities and inclinations that amount to a sizeable fraction of the disc's aspect ratio, for conditions thought to prevail at a few astronomical units.

Tethered swimming can be used to evaluate force contribution for short-distance swimming performance.

PubMed

Morouço, Pedro G; Marinho, Daniel A; Keskinen, Kari L; Badillo, Juan J; Marques, Mário C

2014-11-01

The purpose of this study was two-fold: (a) to compare stroke and the physiological responses between maximal tethered and free front crawl swimming and (b) to evaluate the contribution of force exertion for swimming performance over short distances. A total of 34 male swimmers, representing various levels of competitive performance, participated in this study. Each participant was tested in both a 30-second maximal tethered swimming test and a 50-m free swimming test. The tethered force parameters, the swimming speed, stroke (stroke rate [SR]), and the physiological responses (increase in blood lactate concentration [ΔBLa], heart rate, and rate of perceived exertion) were recorded and calculated. The results showed no differences in stroke and the physiological responses between tethered and free swimming, with a high level of agreement for the SR and ΔBLa. A strong correlation was obtained between the maximum impulse of force per stroke and the speed (r = 0.91; p < 0.001). Multiple regression analysis revealed that the maximum impulse and SR in the tethered condition explained 84% of the free swimming performance. The relationship between the swimming speed and maximum force tended to be nonlinear, whereas linear relationships were observed with the maximum impulse. This study demonstrates that tethered swimming does not significantly alter stroke and the physiological responses compared with free swimming, and that the maximum impulse per stroke should be used to evaluate the balance between force and the ability to effectively apply force during sprint swimming. Consequently, coaches can rely on tethered forces to identify strength deficits and improve swimming performance over short distances.

Compressive force generation by a bundle of living biofilaments

NASA Astrophysics Data System (ADS)

Ramachandran, Sanoop; Ryckaert, Jean-Paul

2013-08-01

To study the compressional forces exerted by a bundle of living stiff filaments pressing on a surface, akin to the case of an actin bundle in filopodia structures, we have performed particulate molecular dynamics simulations of a grafted bundle of parallel living (self-assembling) filaments, in chemical equilibrium with a solution of their constitutive monomers. Equilibrium is established as these filaments, grafted at one end to a wall of the simulation box, grow at their chemically active free end, and encounter the opposite confining wall of the simulation box. Further growth of filaments requires bending and thus energy, which automatically limit the populations of longer filaments. The resulting filament sizes distribution and the force exerted by the bundle on the obstacle are analyzed for different grafting densities and different sub- or supercritical conditions, these properties being compared with the predictions of the corresponding ideal confined bundle model. In this analysis, non-ideal effects due to interactions between filaments and confinement effects are singled out. For all state points considered at the same temperature and at the same gap width between the two surfaces, the force per filament exerted on the opposite wall appears to be a function of a rescaled free monomer density hat{ρ }_1^eff. This quantity can be estimated directly from the characteristic length of the exponential filament size distribution P observed in the size domain where these grafted filaments are not in direct contact with the wall. We also analyze the dynamics of the filament contour length fluctuations in terms of effective polymerization (U) and depolymerization (W) rates, where again it is possible to disentangle non-ideal and confinement effects.

Manipulator Performance Evaluation Using Fitts' Taping Task

DOE Office of Scientific and Technical Information (OSTI.GOV)

Draper, J.V.; Jared, B.C.; Noakes, M.W.

1999-04-25

Metaphorically, a teleoperator with master controllers projects the user's arms and hands into a re- mote area, Therefore, human users interact with teleoperators at a more fundamental level than they do with most human-machine systems. Instead of inputting decisions about how the system should func- tion, teleoperator users input the movements they might make if they were truly in the remote area and the remote machine must recreate their trajectories and impedance. This intense human-machine inter- action requires displays and controls more carefully attuned to human motor capabilities than is neces- sary with most systems. It is important for teleoperatedmore » manipulators to be able to recreate human trajectories and impedance in real time. One method for assessing manipulator performance is to observe how well a system be- haves while a human user completes human dexterity tasks with it. Fitts' tapping task has been, used many times in the past for this purpose. This report describes such a performance assessment. The International Submarine Engineering (ISE) Autonomous/Teleoperated Operations Manipulator (ATOM) servomanipulator system was evalu- ated using a generic positioning accuracy task. The task is a simple one but has the merits of (1) pro- ducing a performance function estimate rather than a point estimate and (2) being widely used in the past for human and servomanipulator dexterity tests. Results of testing using this task may, therefore, allow comparison with other manipulators, and is generically representative of a broad class of tasks. Results of the testing indicate that the ATOM manipulator is capable of performing the task. Force reflection had a negative impact on task efficiency in these data. This was most likely caused by the high resistance to movement the master controller exhibited with the force reflection engaged. Measurements of exerted forces were not made, so it is not possible to say whether the force reflection helped partici- pants control force during testing.« less

Force and time-dependent self-assembly, disruption and recovery of supramolecular peptide amphiphile nanofibers

NASA Astrophysics Data System (ADS)

Begum Dikecoglu, F.; Topal, Ahmet E.; Ozkan, Alper D.; Deniz Tekin, E.; Tekinay, Ayse B.; Guler, Mustafa O.; Dana, Aykutlu

2018-07-01

Biological feedback mechanisms exert precise control over the initiation and termination of molecular self-assembly in response to environmental stimuli, while minimizing the formation and propagation of defects through self-repair processes. Peptide amphiphile (PA) molecules can self-assemble at physiological conditions to form supramolecular nanostructures that structurally and functionally resemble the nanofibrous proteins of the extracellular matrix, and their ability to reconfigure themselves in response to external stimuli is crucial for the design of intelligent biomaterials systems. Here, we investigated real-time self-assembly, deformation, and recovery of PA nanofibers in aqueous solution by using a force-stabilizing double-pass scanning atomic force microscopy imaging method to disrupt the self-assembled peptide nanofibers in a force-dependent manner. We demonstrate that nanofiber damage occurs at tip-sample interaction forces exceeding 1 nN, and the damaged fibers subsequently recover when the tip pressure is reduced. Nanofiber ends occasionally fail to reconnect following breakage and continue to grow as two individual nanofibers. Energy minimization calculations of nanofibers with increasing cross-sectional ellipticity (corresponding to varying levels of tip-induced fiber deformation) support our observations, with high-ellipticity nanofibers exhibiting lower stability compared to their non-deformed counterparts. Consequently, tip-mediated mechanical forces can provide an effective means of altering nanofiber integrity and visualizing the self-recovery of PA assemblies.

Hydrodynamic Forces on Microbubbles under Ultrasound Excitation

NASA Astrophysics Data System (ADS)

Clark, Alicia; Aliseda, Alberto

2014-11-01

Ultrasound (US) pressure waves exert a force on microbubbles that can be used to steer them in a flow. To control the motion of microbubbles under ultrasonic excitation, the coupling between the volume oscillations induced by the ultrasound pressure and the hydrodynamic forces needs to be well understood. We present experimental results for the motion of small, coated microbubbles, with similar sizes and physico-chemical properties as clinically-available ultrasound contrast agents (UCAs). The size distribution for the bubbles, resulting from the in-house manufacturing process, was characterized by analysis of high magnification microscopic images and determined to be bimodal. More than 99% of the volume is contained in microbubbles less than 10 microns in diameter, the size of a red blood cell. The motion of the microbubbles in a pulsatile flow, at different Reynolds and Womersley numbers, is studied from tracking of high-speed shadowgraphy. The influence of ultrasound forcing, at or near the resonant frequency of the bubbles, on the hydrodynamic forces due to the pulsatile flow is determined from the experimental measurements of the trajectories. Previous evidence of a sign reversal in Saffman lift is the focus of particular attention, as this is frequently the only hydrodynamic force acting in the direction perpendicular to the flow pathlines. Application of the understanding of this physical phenomenon to targeted drug delivery is analyzed in terms of the transport of the microbubbles. NSF GRFP.

Force and time-dependent self-assembly, disruption and recovery of supramolecular peptide amphiphile nanofibers.

PubMed

Dikecoglu, F Begum; Topal, Ahmet E; Ozkan, Alper D; Tekin, E Deniz; Tekinay, Ayse B; Guler, Mustafa O; Dana, Aykutlu

2018-07-13

Biological feedback mechanisms exert precise control over the initiation and termination of molecular self-assembly in response to environmental stimuli, while minimizing the formation and propagation of defects through self-repair processes. Peptide amphiphile (PA) molecules can self-assemble at physiological conditions to form supramolecular nanostructures that structurally and functionally resemble the nanofibrous proteins of the extracellular matrix, and their ability to reconfigure themselves in response to external stimuli is crucial for the design of intelligent biomaterials systems. Here, we investigated real-time self-assembly, deformation, and recovery of PA nanofibers in aqueous solution by using a force-stabilizing double-pass scanning atomic force microscopy imaging method to disrupt the self-assembled peptide nanofibers in a force-dependent manner. We demonstrate that nanofiber damage occurs at tip-sample interaction forces exceeding 1 nN, and the damaged fibers subsequently recover when the tip pressure is reduced. Nanofiber ends occasionally fail to reconnect following breakage and continue to grow as two individual nanofibers. Energy minimization calculations of nanofibers with increasing cross-sectional ellipticity (corresponding to varying levels of tip-induced fiber deformation) support our observations, with high-ellipticity nanofibers exhibiting lower stability compared to their non-deformed counterparts. Consequently, tip-mediated mechanical forces can provide an effective means of altering nanofiber integrity and visualizing the self-recovery of PA assemblies.

Plasma sweeper to control the coupling of RF power to a magnetically confined plasma

DOEpatents

Motley, Robert W.; Glanz, James

1985-01-01

A device for coupling RF power (a plasma sweeper) from a phased waveguide array for introducing RF power to a plasma having a magnetic field associated therewith comprises at least one electrode positioned near the plasma and near the phased waveguide array; and a potential source coupled to the electrode for generating a static electric field at the electrode directed into the plasma and having a component substantially perpendicular to the plasma magnetic field such that a non-zero vector cross-product of the electric and magnetic fields exerts a force on the plasma causing the plasma to drift.

Cortical bone drilling: An experimental and numerical study.

PubMed

Alam, Khurshid; Bahadur, Issam M; Ahmed, Naseer

2014-12-16

Bone drilling is a common surgical procedure in orthopedics, dental and neurosurgeries. In conventional bone drilling process, the surgeon exerts a considerable amount of pressure to penetrate the drill into the bone tissue. Controlled penetration of drill in the bone is necessary for safe and efficient drilling. Development of a validated Finite Element (FE) model of cortical bone drilling. Drilling experiments were conducted on bovine cortical bone. The FE model of the bone drilling was based on mechanical properties obtained from literature data and additionally conducted microindentation tests on the cortical bone. The magnitude of stress in bone was found to decrease exponentially away from the lips of the drill in simulations. Feed rate was found to be the main influential factor affecting the force and torque in the numerical simulations and experiments. The drilling thrust force and torque were found to be unaffected by the drilling speed in numerical simulations. Simulated forces and torques were compared with experimental results for similar drilling conditions and were found in good agreement.CONCLUSIONS: FE schemes may be successfully applied to model complex kinematics of bone drilling process.

Charge-Induced Force Noise on Free-Falling Test Masses: Results from LISA Pathfinder

NASA Astrophysics Data System (ADS)

Armano, M.; Audley, H.; Auger, G.; Baird, J. T.; Binetruy, P.; Born, M.; Bortoluzzi, D.; Brandt, N.; Bursi, A.; Caleno, M.; Cavalleri, A.; Cesarini, A.; Cruise, M.; Danzmann, K.; de Deus Silva, M.; Diepholz, I.; Dolesi, R.; Dunbar, N.; Ferraioli, L.; Ferroni, V.; Fitzsimons, E. D.; Flatscher, R.; Freschi, M.; Gallegos, J.; García Marirrodriga, C.; Gerndt, R.; Gesa, L.; Gibert, F.; Giardini, D.; Giusteri, R.; Grimani, C.; Grzymisch, J.; Harrison, I.; Heinzel, G.; Hewitson, M.; Hollington, D.; Hueller, M.; Huesler, J.; Inchauspé, H.; Jennrich, O.; Jetzer, P.; Johlander, B.; Karnesis, N.; Kaune, B.; Killow, C. J.; Korsakova, N.; Lloro, I.; Liu, L.; López-Zaragoza, J. P.; Maarschalkerweerd, R.; Madden, S.; Mance, D.; Martín, V.; Martin-Polo, L.; Martino, J.; Martin-Porqueras, F.; Mateos, I.; McNamara, P. W.; Mendes, J.; Mendes, L.; Moroni, A.; Nofrarias, M.; Paczkowski, S.; Perreur-Lloyd, M.; Petiteau, A.; Pivato, P.; Plagnol, E.; Prat, P.; Ragnit, U.; Ramos-Castro, J.; Reiche, J.; Romera Perez, J. A.; Robertson, D. I.; Rozemeijer, H.; Rivas, F.; Russano, G.; Sarra, P.; Schleicher, A.; Slutsky, J.; Sopuerta, C.; Sumner, T. J.; Texier, D.; Thorpe, J. I.; Trenkel, C.; Vetrugno, D.; Vitale, S.; Wanner, G.; Ward, H.; Wass, P. J.; Wealthy, D.; Weber, W. J.; Wittchen, A.; Zanoni, C.; Ziegler, T.; Zweifel, P.; LISA Pathfinder Collaboration

2017-04-01

We report on electrostatic measurements made on board the European Space Agency mission LISA Pathfinder. Detailed measurements of the charge-induced electrostatic forces exerted on free-falling test masses (TMs) inside the capacitive gravitational reference sensor are the first made in a relevant environment for a space-based gravitational wave detector. Employing a combination of charge control and electric-field compensation, we show that the level of charge-induced acceleration noise on a single TM can be maintained at a level close to 1.0 fm s-2 Hz-1 /2 across the 0.1-100 mHz frequency band that is crucial to an observatory such as the Laser Interferometer Space Antenna (LISA). Using dedicated measurements that detect these effects in the differential acceleration between the two test masses, we resolve the stochastic nature of the TM charge buildup due to interplanetary cosmic rays and the TM charge-to-force coupling through stray electric fields in the sensor. All our measurements are in good agreement with predictions based on a relatively simple electrostatic model of the LISA Pathfinder instrument.

Microtechnologies for studying the role of mechanics in axon growth and guidance

PubMed Central

Kilinc, Devrim; Blasiak, Agata; Lee, Gil U.

2015-01-01

The guidance of axons to their proper targets is not only a crucial event in neurodevelopment, but also a potential therapeutic target for neural repair. Axon guidance is mediated by various chemo- and haptotactic cues, as well as the mechanical interactions between the cytoskeleton and the extracellular matrix (ECM). Axonal growth cones, dynamic ends of growing axons, convert external stimuli to biochemical signals, which, in turn, are translated into behavior, e.g., turning or retraction, via cytoskeleton–matrix linkages. Despite the inherent mechanical nature of the problem, the role of mechanics in axon guidance is poorly understood. Recent years has witnessed the application of a range of microtechnologies in neurobiology, from microfluidic circuits to single molecule force spectroscopy. In this mini-review, we describe microtechnologies geared towards dissecting the mechanical aspects of axon guidance, divided into three categories: controlling the growth cone microenvironment, stimulating growth cones with externally applied forces, and measuring forces exerted by the growth cones. A particular emphasis is given to those studies that combine multiple techniques, as dictated by the complexity of the problem. PMID:26283918

Microtechnologies for studying the role of mechanics in axon growth and guidance.

PubMed

Kilinc, Devrim; Blasiak, Agata; Lee, Gil U

2015-01-01

The guidance of axons to their proper targets is not only a crucial event in neurodevelopment, but also a potential therapeutic target for neural repair. Axon guidance is mediated by various chemo- and haptotactic cues, as well as the mechanical interactions between the cytoskeleton and the extracellular matrix (ECM). Axonal growth cones, dynamic ends of growing axons, convert external stimuli to biochemical signals, which, in turn, are translated into behavior, e.g., turning or retraction, via cytoskeleton-matrix linkages. Despite the inherent mechanical nature of the problem, the role of mechanics in axon guidance is poorly understood. Recent years has witnessed the application of a range of microtechnologies in neurobiology, from microfluidic circuits to single molecule force spectroscopy. In this mini-review, we describe microtechnologies geared towards dissecting the mechanical aspects of axon guidance, divided into three categories: controlling the growth cone microenvironment, stimulating growth cones with externally applied forces, and measuring forces exerted by the growth cones. A particular emphasis is given to those studies that combine multiple techniques, as dictated by the complexity of the problem.

Charge-Induced Force Noise on Free-Falling Test Masses: Results from LISA Pathfinder.

PubMed

Armano, M; Audley, H; Auger, G; Baird, J T; Binetruy, P; Born, M; Bortoluzzi, D; Brandt, N; Bursi, A; Caleno, M; Cavalleri, A; Cesarini, A; Cruise, M; Danzmann, K; de Deus Silva, M; Diepholz, I; Dolesi, R; Dunbar, N; Ferraioli, L; Ferroni, V; Fitzsimons, E D; Flatscher, R; Freschi, M; Gallegos, J; García Marirrodriga, C; Gerndt, R; Gesa, L; Gibert, F; Giardini, D; Giusteri, R; Grimani, C; Grzymisch, J; Harrison, I; Heinzel, G; Hewitson, M; Hollington, D; Hueller, M; Huesler, J; Inchauspé, H; Jennrich, O; Jetzer, P; Johlander, B; Karnesis, N; Kaune, B; Killow, C J; Korsakova, N; Lloro, I; Liu, L; López-Zaragoza, J P; Maarschalkerweerd, R; Madden, S; Mance, D; Martín, V; Martin-Polo, L; Martino, J; Martin-Porqueras, F; Mateos, I; McNamara, P W; Mendes, J; Mendes, L; Moroni, A; Nofrarias, M; Paczkowski, S; Perreur-Lloyd, M; Petiteau, A; Pivato, P; Plagnol, E; Prat, P; Ragnit, U; Ramos-Castro, J; Reiche, J; Romera Perez, J A; Robertson, D I; Rozemeijer, H; Rivas, F; Russano, G; Sarra, P; Schleicher, A; Slutsky, J; Sopuerta, C; Sumner, T J; Texier, D; Thorpe, J I; Trenkel, C; Vetrugno, D; Vitale, S; Wanner, G; Ward, H; Wass, P J; Wealthy, D; Weber, W J; Wittchen, A; Zanoni, C; Ziegler, T; Zweifel, P

2017-04-28

We report on electrostatic measurements made on board the European Space Agency mission LISA Pathfinder. Detailed measurements of the charge-induced electrostatic forces exerted on free-falling test masses (TMs) inside the capacitive gravitational reference sensor are the first made in a relevant environment for a space-based gravitational wave detector. Employing a combination of charge control and electric-field compensation, we show that the level of charge-induced acceleration noise on a single TM can be maintained at a level close to 1.0  fm s^{-2} Hz^{-1/2} across the 0.1-100 mHz frequency band that is crucial to an observatory such as the Laser Interferometer Space Antenna (LISA). Using dedicated measurements that detect these effects in the differential acceleration between the two test masses, we resolve the stochastic nature of the TM charge buildup due to interplanetary cosmic rays and the TM charge-to-force coupling through stray electric fields in the sensor. All our measurements are in good agreement with predictions based on a relatively simple electrostatic model of the LISA Pathfinder instrument.

Magnetic levitation-based Martian and Lunar gravity simulator

NASA Technical Reports Server (NTRS)

Valles, J. M. Jr; Maris, H. J.; Seidel, G. M.; Tang, J.; Yao, W.

2005-01-01

Missions to Mars will subject living specimens to a range of low gravity environments. Deleterious biological effects of prolonged exposure to Martian gravity (0.38 g), Lunar gravity (0.17 g), and microgravity are expected, but the mechanisms involved and potential for remedies are unknown. We are proposing the development of a facility that provides a simulated Martian and Lunar gravity environment for experiments on biological systems in a well controlled laboratory setting. The magnetic adjustable gravity simulator will employ intense, inhomogeneous magnetic fields to exert magnetic body forces on a specimen that oppose the body force of gravity. By adjusting the magnetic field, it is possible to continuously adjust the total body force acting on a specimen. The simulator system considered consists of a superconducting solenoid with a room temperature bore sufficiently large to accommodate small whole organisms, cell cultures, and gravity sensitive bio-molecular solutions. It will have good optical access so that the organisms can be viewed in situ. This facility will be valuable for experimental observations and public demonstrations of systems in simulated reduced gravity. c2005 Published by Elsevier Ltd on behalf of COSPAR.

Magnetic levitation-based Martian and Lunar gravity simulator.

PubMed

Valles, J M; Maris, H J; Seidel, G M; Tang, J; Yao, W

2005-01-01

Missions to Mars will subject living specimens to a range of low gravity environments. Deleterious biological effects of prolonged exposure to Martian gravity (0.38 g), Lunar gravity (0.17 g), and microgravity are expected, but the mechanisms involved and potential for remedies are unknown. We are proposing the development of a facility that provides a simulated Martian and Lunar gravity environment for experiments on biological systems in a well controlled laboratory setting. The magnetic adjustable gravity simulator will employ intense, inhomogeneous magnetic fields to exert magnetic body forces on a specimen that oppose the body force of gravity. By adjusting the magnetic field, it is possible to continuously adjust the total body force acting on a specimen. The simulator system considered consists of a superconducting solenoid with a room temperature bore sufficiently large to accommodate small whole organisms, cell cultures, and gravity sensitive bio-molecular solutions. It will have good optical access so that the organisms can be viewed in situ. This facility will be valuable for experimental observations and public demonstrations of systems in simulated reduced gravity. c2005 Published by Elsevier Ltd on behalf of COSPAR.

Dynein-mediated pulling forces drive rapid mitotic spindle elongation in Ustilago maydis

PubMed Central

Fink, Gero; Schuchardt, Isabel; Colombelli, Julien; Stelzer, Ernst; Steinberg, Gero

2006-01-01

Spindle elongation segregates chromosomes and occurs in anaphase, an essential step in mitosis. Dynein-mediated pulling forces position the spindle, but their role in anaphase is a matter of debate. Here, we demonstrate that dynein is responsible for rapid spindle elongation in the model fungus Ustilago maydis. We show that initial slow elongation is supported by kinesin-5, which is located in the spindle mid-zone. When the spindle reaches ∼2 μm in length, the elongation rate increases four-fold. This coincides with the appearance of long and less-dynamic microtubules (MTs) at each pole that accumulate dynein at their tips. Laser-mediated nanosurgery revealed that these MTs exert pulling forces in control cells, but not in dynein mutants. In addition, dynein mutants undergo initial slow anaphase, but fail to establish less-dynamic MTs and do not perform rapid spindle elongation, suggesting that dynein drives anaphase B. This is most likely mediated by cortical sliding of astral MTs along stationary dynein, which is off-loaded from the MT plus-end to the cortex. PMID:17024185

Development of Device to Evoke Stretch Reflexes by Use of Electromagnetic Force for the Rehabilitation of the Hemiplegic Upper Limb after Stroke

NASA Astrophysics Data System (ADS)

Hayashi, Ryota; Ishimine, Tomoyasu; Kawahira, Kazumi; Yu, Yong; Tsujio, Showzow

In this research, we focus on the method of rehabilitation with stretch reflexes for the hemiplegic upper limb in stroke patients. We propose a new device which utilizes electromagnetic force to evoke stretch reflexes. The device can exert an assisting force safely, because the electromagnetic force is non contact force. In this paper, we develop a support system applying the proposed device for the functional recovery training of the hemiplegic upper limb. The results obtained from several clinical tests with and without our support system are compared. Then we discuss the validity of our support system.

Resolving the Pinning Force of Nanobubbles with Optical Microscopy

NASA Astrophysics Data System (ADS)

Tan, Beng Hau; An, Hongjie; Ohl, Claus-Dieter

2017-02-01

Many of the remarkable properties of surface nanobubbles, such as unusually small contact angles and long lifetimes, are related to the force that pins them onto their substrates. This pinning force is yet to be quantified experimentally. Here, surface-attached nanobubbles are pulled with an atomic force microscope tip while their mechanical responses are observed with total internal reflection fluorescence microscopy. We estimate that a pinning force on the order of 0.1 μ N is required to unpin a nanobubble from its substrate. The maximum force that the tip can exert on the nanobubble is limited by the stability of the neck pulled from the bubble and is enhanced by the hydrophobicity of the tip.

Observation and Uses of Position-Space Bloch Oscillations in an Ultracold Gas.

PubMed

Geiger, Zachary A; Fujiwara, Kurt M; Singh, Kevin; Senaratne, Ruwan; Rajagopal, Shankari V; Lipatov, Mikhail; Shimasaki, Toshihiko; Driben, Rodislav; Konotop, Vladimir V; Meier, Torsten; Weld, David M

2018-05-25

We report the observation and characterization of position-space Bloch oscillations using cold atoms in a tilted optical lattice. While momentum-space Bloch oscillations are a common feature of optical lattice experiments, the real-space center-of-mass dynamics are typically unresolvable. In a regime of rapid tunneling and low force, we observe real-space Bloch oscillation amplitudes of hundreds of lattice sites, in both ground and excited bands. We demonstrate two unique capabilities enabled by tracking of Bloch dynamics in position space: measurement of the full position-momentum phase-space evolution during a Bloch cycle, and direct imaging of the lattice band structure. These techniques, along with the ability to exert long-distance coherent control of quantum gases without modulation, may open up new possibilities for quantum control and metrology.

Observation and Uses of Position-Space Bloch Oscillations in an Ultracold Gas

NASA Astrophysics Data System (ADS)

Geiger, Zachary A.; Fujiwara, Kurt M.; Singh, Kevin; Senaratne, Ruwan; Rajagopal, Shankari V.; Lipatov, Mikhail; Shimasaki, Toshihiko; Driben, Rodislav; Konotop, Vladimir V.; Meier, Torsten; Weld, David M.

2018-05-01

We report the observation and characterization of position-space Bloch oscillations using cold atoms in a tilted optical lattice. While momentum-space Bloch oscillations are a common feature of optical lattice experiments, the real-space center-of-mass dynamics are typically unresolvable. In a regime of rapid tunneling and low force, we observe real-space Bloch oscillation amplitudes of hundreds of lattice sites, in both ground and excited bands. We demonstrate two unique capabilities enabled by tracking of Bloch dynamics in position space: measurement of the full position-momentum phase-space evolution during a Bloch cycle, and direct imaging of the lattice band structure. These techniques, along with the ability to exert long-distance coherent control of quantum gases without modulation, may open up new possibilities for quantum control and metrology.

Effects of tiotropium on lung hyperinflation, dyspnoea and exercise tolerance in COPD.

PubMed

O'Donnell, D E; Flüge, T; Gerken, F; Hamilton, A; Webb, K; Aguilaniu, B; Make, B; Magnussen, H

2004-06-01

The aim of this study was to test the hypothesis that use of tiotropium, a new long-acting anticholinergic bronchodilator, would be associated with sustained reduction in lung hyperinflation and, thereby, would improve exertional dyspnoea and exercise performance in patients with chronic obstructive pulmonary disease. A randomised, double-blind, placebo-controlled, parallel-group study was conducted in 187 patients (forced expiratory volume in one second 44 +/- 13% pred): 96 patients received 18 microg tiotropium and 91 patients received placebo once daily for 42 days. Spirometry, plethysmographic lung volumes, cycle exercise endurance and exertional dyspnoea intensity at 75% of each patient's maximal work capacity were compared. On day 42, the use of tiotropium was associated with the following effects at pre-dose and post-dose measurements as compared to placebo: vital capacity and inspiratory capacity (IC) increased, with inverse decreases in residual volume and functional residual capacity. Tiotropium increased post-dose exercise endurance time by 105 +/- 40 s (21%) as compared to placebo on day 42. At a standardised time near end-exercise (isotime), IC, tidal volume and minute ventilation all increased, whilst dyspnoea decreased by 0.9 +/- 0.3 Borg scale units. In conclusion, the use of tiotropium was associated with sustained reductions of lung hyperinflation at rest and during exercise. Resultant increases in inspiratory capacity permitted greater expansion of tidal volume and contributed to improvements in both exertional dyspnoea and exercise endurance.

Too dog tired to avoid danger: self-control depletion in canines increases behavioral approach toward an aggressive threat.

PubMed

Miller, Holly C; DeWall, C Nathan; Pattison, Kristina; Molet, Mikaël; Zentall, Thomas R

2012-06-01

This study investigated whether initial self-control exertion by dogs would affect behavioral approach toward an aggressive threat. Dogs were initially required to exert self-control (sit still for 10 min) or not (caged for 10 min) before they were walked into a room in which a barking, growling dog was caged. Subject dogs spent 4 min in this room but were free to choose where in the room they spent their time. Approaching the unfamiliar conspecific was the predisposed response, but it was also the riskier choice (Lindsay, 2005). We found that following the exertion of self-control (in comparison with the control condition), dogs spent greater time in proximity to the aggressor. This pattern of behavior suggests that initial self-control exertion results in riskier and more impulsive decision making by dogs.

On the contribution of circumferential resonance modes in acoustic radiation force experienced by cylindrical shells

NASA Astrophysics Data System (ADS)

Rajabi, Majid; Behzad, Mehdi

2014-10-01

A body insonified by a constant (time-varying) intensity sound field is known to experience a steady (oscillatory) force that is called the steady-state (dynamic) acoustic radiation force. Using the classical resonance scattering theorem (RST) which suggests the scattered field as a superposition of a resonance field and a background (non-resonance) component, we show that the radiation force acting on a cylindrical shell may be synthesized as a composition of three components: background part, resonance part and their interaction. The background component reveals the pure geometrical reflection effects and illustrates a regular behavior with respect to frequency, while the others demonstrate a singular behavior near the resonance frequencies. The results illustrate that the resonance effects associated to partial waves can be isolated by the subtraction of the background component from the total (steady-state or dynamic) radiation force function (i.e., residue component). In the case of steady-state radiation force, the components are exerted on the body as static forces. For the case of oscillatory amplitude excitation, the components are exerted at the modulation frequency with frequency-dependant phase shifts. The results demonstrate the dominant contribution of the non-resonance component of dynamic radiation force at high frequencies with respect to the residue component, which offers the potential application of ultrasound stimulated vibro-acoustic spectroscopy technique in low frequency resonance spectroscopy purposes. Furthermore, the proposed formulation may be useful essentially due to its intrinsic value in physical acoustics. In addition, it may unveil the contribution of resonance modes in the dynamic radiation force experienced by the cylindrical objects and its underlying physics.

Mesoscale disturbances in the tropical stratosphere excited by convection - Observations and effects on the stratospheric momentum budget

NASA Technical Reports Server (NTRS)

Pfister, Leonhard; Scott, Stanley; Loewenstein, Max; Bowen, Stuart; Legg, Marion

1993-01-01

Aircraft temperature and pressure measurements as well as satellite imagery are used to establish the amplitudes and the space and time scale of potential temperature disturbances over convective systems. A conceptual model is proposed for the generation of mesoscale gravity waves by convection. The momentum forcing that a reasonable distribution of convection might exert on the tropical stratosphere through convectively excited mesoscale gravity waves of the observed amplitudes is estimated. Aircraft measurements show that presence of mesoscale disturbances in the lower stratospheric temperature, disturbances that appear to be associated with underlying convection. If the disturbances are convectively excited mesoscale gravity waves, their amplitude is sufficient that their breakdown in the upper stratosphere will exert a zonal force comparable to but probably smaller than the planetary-scale Kelvin waves.

Traction Stresses Exerted by Adherent Cells: From Angiogenesis to Metastasis

NASA Astrophysics Data System (ADS)

Reinhart-King, Cynthia

2010-03-01

Cells exert traction stresses against their substrate that mediate their ability to sense the mechanical properties of their microenvironment. These same forces mediate cell adhesion, migration and the formation of stable cell-cell contacts during tissue formation. In this talk, I will present our data on the traction stresses generated by endothelial cells and metastatic breast cancer cells focused on understanding the processes of angiogenesis and metastasis, respectively. In the context of capillary formation, our data indicate that the mechanics of the substrate play a critical role in establishing endothelial cell-cell contacts. On more compliant substrates, endothelial cell shape and traction stresses polarize and promote the formation of stable cell-cell contacts. On stiffer substrates, traction stresses are less polarized and cell connectivity is disrupted. These data indicate that the mechanical properties of the microenvironment may drive cell connectivity and the formation of stable cell-cell contacts through the reorientation of traction stresses. In our studies of metastatic cell migration, we have found that traction stresses increase with increasing metastatic potential. We investigated three lines of varying metastatic potential (MCF10A, MCF7 and MDAMB231). MDAMB231, which are the most invasive, exert the most significant forces as measured by Traction Force Microscopy. These data present the possibility that cellular traction stress generation aids in the ability of metastatic cells to migrate through the matrix-dense tumor microenvironment. Such measurements are integral to link the mechanical and chemical microenvironment with the resulting response of the cell in health and disease.

Drag and lift forces in granular media

NASA Astrophysics Data System (ADS)

Guillard, F.; Forterre, Y.; Pouliquen, O.

2013-09-01

Forces exerted on obstacles moving in granular media are studied. The experiment consists in a horizontal cylinder rotating around the vertical axis in a granular medium. Both drag forces and lift forces experienced by the cylinder are measured. The first striking result is obtained during the first half rotation, before the cylinder crosses its wake. Despite the symmetry of the object, a strong lift force is measured, about 20 times the buoyancy. The scaling of this force is studied experimentally. The second remarkable observation is made after several rotations. The drag force dramatically drops and becomes independent of depth, showing that it no longer scales with the hydrostatic pressure. The rotation of the cylinder induces a structure in the packing, which screens the weight of the grains above

Off-road machine controls: investigating the risk of carpal tunnel syndrome.

PubMed

Oliver, M; Rickards, J; Biden, E

2000-11-01

Occupationally induced hand and wrist repetitive strain injuries (RSI) such as carpal tunnel syndrome (CTS) are a growing problem in North America. The purpose of this investigation was to apply a modification of the wrist flexion/ extension models of Armstrong and Chaffin (1978, 1979) to determine if joystick controller use in off-road machines could contribute to the development of CTS. A construction equipment cab in the laboratory was instrumented to allow force, displacement and angle measurements from 10 operators while they completed an approximately 30-min joystick motion protocol. The investigation revealed that both the external fingertip and predicted internal wrist forces resulting from the use of these joysticks were very low, indicating that the CTS risk associated with this factor was slight. However, the results also indicated that, particularly for the 'forward' and 'left' right side motions and for all left side motions, force was exerted by other portions of the fingers and hand, thereby under-predicting the tendon tension and internal wrist forces. Wrist angles observed were highest for motions that moved the joysticks to the sides rather than front to back. Thus, the 'right' and 'left' motions for both hands posed a higher risk for CTS development. When the right hand moved into the 'right' position and the left hand moved into the 'left' position, the wrist went into extension in both cases. Results indicate that neither learning nor fatigue affected the results.

Traction in smooth muscle cells varies with cell spreading

NASA Technical Reports Server (NTRS)

Tolic-Norrelykke, Iva Marija; Wang, Ning

2005-01-01

Changes in cell shape regulate cell growth, differentiation, and apoptosis. It has been suggested that the regulation of cell function by the cell shape is a result of the tension in the cytoskeleton and the distortion of the cell. Here we explore the association between cell-generated mechanical forces and the cell morphology. We hypothesized that the cell contractile force is associated with the degree of cell spreading, in particular with the cell length. We measured traction fields of single human airway smooth muscle cells plated on a polyacrylamide gel, in which fluorescent microbeads were embedded to serve as markers of gel deformation. The traction exerted by the cells at the cell-substrate interface was determined from the measured deformation of the gel. The traction was measured before and after treatment with the contractile agonist histamine, or the relaxing agonist isoproterenol. The relative increase in traction induced by histamine was negatively correlated with the baseline traction. On the contrary, the relative decrease in traction due to isoproterenol was independent of the baseline traction, but it was associated with cell shape: traction decreased more in elongated than in round cells. Maximum cell width, mean cell width, and projected area of the cell were the parameters most tightly coupled to both baseline and histamine-induced traction in this study. Wide and well-spread cells exerted larger traction than slim cells. These results suggest that cell contractility is controlled by cell spreading.

Dynamics of Cell Area and Force during Spreading

PubMed Central

Brill-Karniely, Yifat; Nisenholz, Noam; Rajendran, Kavitha; Dang, Quynh; Krishnan, Ramaswamy; Zemel, Assaf

2014-01-01

Experiments on human pulmonary artery endothelial cells are presented to show that cell area and the force exerted on a substrate increase simultaneously, but with different rates during spreading; rapid-force increase systematically occurred several minutes past initial spreading. We examine this theoretically and present three complementary mechanisms that may accompany the development of lamellar stress during spreading and underlie the observed behavior. These include: 1), the dynamics of cytoskeleton assembly at the cell basis; 2), the strengthening of acto-myosin forces in response to the generated lamellar stresses; and 3), the passive strain-stiffening of the cytoskeleton. PMID:25517168

Changing Teachers, Changing Times. Teachers' Work and Culture in the Postmodern Age. Professional Development and Practice Series.

ERIC Educational Resources Information Center

Hargreaves, Andy

This book examines the personal, moral, cultural, and political dimensions of teaching in the context of rapid and far-reaching change within teachers' work and in the world beyond it. The chapters in Part One examine the powerful forces for change in society and how those forces are exerting pressure on existing institutions. Issues such as the…

Effects of High-Speed Power Training on Muscle Performance and Braking Speed in Older Adults

PubMed Central

Sayers, Stephen P.; Gibson, Kyle

2012-01-01

We examined whether high-speed power training (HSPT) improved muscle performance and braking speed using a driving simulator. 72 older adults (22 m, 50 f; age = 70.6 ± 7.3 yrs) were randomized to HSPT at 40% one-repetition maximum (1RM) (HSPT: n = 25; 3 sets of 12–14 repetitions), slow-speed strength training at 80%1RM (SSST: n = 25; 3 sets of 8–10 repetitions), or control (CON: n = 22; stretching) 3 times/week for 12 weeks. Leg press and knee extension peak power, peak power velocity, peak power force/torque, and braking speed were obtained at baseline and 12 weeks. HSPT increased peak power and peak power velocity across a range of external resistances (40–90% 1RM; P < 0.05) and improved braking speed (P < 0.05). Work was similar between groups, but perceived exertion was lower in HSPT (P < 0.05). Thus, the less strenuous HSPT exerted a broader training effect and improved braking speed compared to SSST. PMID:22500229

Determination and evaluation of acceptable force limits in single-digit tasks.

PubMed

Nussbaum, Maury A; Johnson, Hope

2002-01-01

Acceptable limits derived from psychophysical methodologies have been proposed, measured, and employed in a range of applications. There is little existing work, however, on such limits for single-digit exertions and relatively limited evidence on several fundamental issues related to data collection and processing of a sequence of self-regulated exertion levels. An experimental study was conducted using 14 male and 10 female participants (age range 18-31 years) from whom maximal voluntary exertions and maximal acceptable limits (MALs) were obtained using the index finger and thumb. Moderate to high levels of consistency were found for both measures between sessions separated by one day. Single MAL values, determined from a time series of exertions, were equivalent across three divergent processing methods and between values obtained from 5- and 25-min samples. A critical interpretation of these and earlier results supports continued use of acceptable limits but also suggests that they should be used with some caution and not equated with safe limits. This research can be applied toward future development of exertion limits based on perceived acceptability.

An Experimental Investigation on the Static Equilibria and Dynamics of Liquid Bridges. Degree Awarded by the University of Alabama, 1997

NASA Technical Reports Server (NTRS)

Resnick, Andrew Howard

1997-01-01

A liquid bridge is a volume of liquid held between two or more solid supports. In the case of small disk supports with a sharp edge, the contact line between the bridge and the support disk will be anchored along the edge of the disk. For these cases the solid presents a geometrical singularity and the contact angle is indeterminate within a given range. This dissertation presents research conducted on liquid bridges with anchored contact lines. The three major topics covered are: determining the role of support geometry on static equilibria, liquid bridge dynamical behavior, and forces exerted by a liquid bridge on a support structure. The work was primarily experimental and conducted in a "Plateau tank" that allowed for the simulation of equivalent low-gravity conditions. The main thrust of the experimental work involved the use of a high resolution optical measurement system for imaging the dynamic zone shape, measurement of the static and dynamic contact angles and non-invasive analysis of excited surface modes. The liquid bridge was manipulated by computer controlled linear actuators which allowed precise control over the physical characteristics of the bridge. Experiments have been carried out to locate a bifurcation point along the maximum volume axisymmetric stability margin. Below the critical slenderness the bifurcation from an axisymmetric to a stable nonaxisymmetric configuration is supercritical. However, above this critical slenderness, the bifurcation is subcritical. A series of experiments analyzed the effect on axisymmetric bridge stability by using support disks of different radii, The shape behavior as transition points were approached, as well as the limiting case of a vanishing support radius was investigated. Experiments were performed to determine the resonant frequencies of axisymmetric bridges subject to lateral vibrations. Anomolous results led to a series of experiments to characterize nonlinearities present in the dynamic bridge shape. Finally, an attempt was made to experimentally measure the force exerted by the bridge on the lower support disk. This was done through use of a force balance apparatus. Particular attention was paid to the behavior of the bridge as the minimum volume stability limit was approached.

Hydrostatic pressure and shear stress affect endothelin-1 and nitric oxide release by endothelial cells in bioreactors.

PubMed

Vozzi, Federico; Bianchi, Francesca; Ahluwalia, Arti; Domenici, Claudio

2014-01-01

Abundant experimental evidence demonstrates that endothelial cells are sensitive to flow; however, the effect of fluid pressure or pressure gradients that are used to drive viscous flow is not well understood. There are two principal physical forces exerted on the blood vessel wall by the passage of intra-luminal blood: pressure and shear. To analyze the effects of pressure and shear independently, these two stresses were applied to cultured cells in two different types of bioreactors: a pressure-controlled bioreactor and a laminar flow bioreactor, in which controlled levels of pressure or shear stress, respectively, can be generated. Using these bioreactor systems, endothelin-1 (ET-1) and nitric oxide (NO) release from human umbilical vein endothelial cells were measured under various shear stress and pressure conditions. Compared to the controls, a decrease of ET-1 production by the cells cultured in both bioreactors was observed, whereas NO synthesis was up-regulated in cells under shear stress, but was not modulated by hydrostatic pressure. These results show that the two hemodynamic forces acting on blood vessels affect endothelial cell function in different ways, and that both should be considered when planning in vitro experiments in the presence of flow. Understanding the individual and synergic effects of the two forces could provide important insights into physiological and pathological processes involved in vascular remodeling and adaptation. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Physical stress modifies top-down and bottom-up forcing on plant growth and reproduction in a coastal ecosystem.

PubMed

Daleo, Pedro; Alberti, Juan; Bruschetti, Carlos Martin; Pascual, Jesos; Iribarne, Oscar; Silliman, Brian R

2015-08-01

Bottom-up and top-down effects act together to exert strong control over plant growth and reproduction, but how physical stress modifies those interactive forces remains unclear. Even though empirical evidence is scarce, theory predicts that the importance of both top-down- and bottom-up forces may decrease as physical stress increases. Here, we experimentally evaluate in the field the separate and interactive effect of salinity, nutrient availability, and crab herbivory on plant above- and belowground biomass, as well as on sexual and clonal reproduction in the salt marsh plant Spartina densiflora. Results show that the outcome of the interaction between nutrient availability and herbivory is highly context dependent, not only varying with the abiotic context (i.e., with or without increased salinity stress), but also with the dependent variable considered. Contrary to theoretical predictions, our results show that, consistently across different measured variables, salinity stress did not cancel bottom-up (i.e., nutrients) or top-down (i.e., consumers) control, but has additive effects. Our results support emerging theory by highlighting that, under many conditions, physical stress can act additively with, or even stimulate, consumer control, especially in cases where the physical stress is only experienced by basal levels of the trophic chain. Abiotic stress, as well as bottom-up and top-down factors, can affect salt marsh structure and function not only by affecting biomass production but also by having other indirect effects, such as changing patterns in plant biomass allocation and reproduction.

A comparative CFD study of four inferior vena cava filters.

PubMed

López, Josep M; Fortuny, Gerard; Puigjaner, Dolors; Herrero, Joan; Marimon, Francesc

2018-03-30

Computational fluid dynamics was used to simulate the flow of blood within an inferior vena cava (IVC) geometry model that was reconstructed from computed tomography images obtained from a real patient. The main novelty of the present work is that we simulated the implantation of 4 different filter models in this realistic IVC geometry. We considered different blood flow rates in the range between V in =20 and V in =80 cm 3 /s, and all simulations were performed with both the Newtonian and a non-Newtonian model for the blood viscosity. We compared the hemodynamics performance of the different filter models, and we paid a special attention to the total drag force, F d , exerted by the blood flow on the filter surface. This force is the sum of 2 contributions: the viscous skin friction force, which was found to be roughly proportional to the filter surface area, and the pressure force, which depended on the particular filter geometry design. The F d force is relevant because it must be balanced by the total force exerted by the filter hooks/struts on the IVC wall at the attachment locations. For the highest V in value investigated, the variation in F d among filters was from 116 to 308 dyne. We also showed how the present results can be extrapolated to obtain good estimates of the drag forces if the blood viscosity levels change, ie, if the patient with a filter implanted is treated with anticoagulant therapy. Copyright © 2018 John Wiley & Sons, Ltd.

Cant deficiency, curving speeds and tilt

DOT National Transportation Integrated Search

2011-01-01

In the US, increasing passenger speeds to improve trip time usually involves increasing speeds through curves. Increasing speeds through curves will increase the lateral force exerted on track during curving, thus requiring more intensive track maint...

14 CFR 29.733 - Tires.

Code of Federal Regulations, 2013 CFR

2013-01-01

... static ground reaction corresponding to the critical center of gravity; and (3) A load on nose wheel... gravity and exerts a force of 1.0 g downward and 0.25 g forward, the reactions being distributed to the...

14 CFR 29.733 - Tires.

Code of Federal Regulations, 2012 CFR

2012-01-01

... static ground reaction corresponding to the critical center of gravity; and (3) A load on nose wheel... gravity and exerts a force of 1.0 g downward and 0.25 g forward, the reactions being distributed to the...

The Aerodynamic Forces and Moments Exerted on a Spinning Model of the NY-1 Airplane as Measured by the Spinning Balance

NASA Technical Reports Server (NTRS)

Bamber, M J; Zimmerm, N, C h

1934-01-01

A preliminary investigation of the effects of changes in the elevator and rudder settings and of small changes in attitude upon the aerodynamic forces and moments exerted upon a spinning airplane was undertaken with the spinning balance in the 5-foot vertical tunnel of the National Advisory Committee for Aeronautics. The tests were made on a 1/12-scale model of the ny-1 airplane. Data by which to fix the attitude, the radius of spin, and the rotational and air velocities were taken from recorded spins of the full-scale airplane. Two spinning conditions were investigated. All six components of the aerodynamic reaction were measured and are presented in coefficient form refereed to airplane axes. The results indicate that the change in yawing moment produced by the rudder with the elevator up was the only component of force or moment produced by the elevator and rudder that could not have been balanced in an actual spin by small changes in attitude and angular velocity.

Phosphate and acidosis act synergistically to depress peak power in rat muscle fibers.

PubMed

Nelson, Cassandra R; Debold, Edward P; Fitts, Robert H

2014-11-15

Skeletal muscle fatigue is characterized by the buildup of H(+) and inorganic phosphate (Pi), metabolites that are thought to cause fatigue by inhibiting muscle force, velocity, and power. While the individual effects of elevated H(+) or Pi have been well characterized, the effects of simultaneously elevating the ions, as occurs during fatigue in vivo, are still poorly understood. To address this, we exposed slow and fast rat skinned muscle fibers to fatiguing levels of H(+) (pH 6.2) and Pi (30 mM) and determined the effects on contractile properties. At 30°C, elevated Pi and low pH depressed maximal shortening velocity (Vmax) by 15% (4.23 to 3.58 fl/s) in slow and 31% (6.24 vs. 4.55 fl/s) in fast fibers, values similar to depressions from low pH alone. Maximal isometric force dropped by 36% in slow (148 to 94 kN/m(2)) and 46% in fast fibers (148 to 80 kN/m(2)), declines substantially larger than what either ion exerted individually. The strong effect on force combined with the significant effect on velocity caused peak power to decline by over 60% in both fiber types. Force-stiffness ratios significantly decreased with pH 6.2 + 30 mM Pi in both fiber types, suggesting these ions reduced force by decreasing the force per bridge and/or increasing the number of low-force bridges. The data indicate the collective effects of elevating H(+) and Pi on maximal isometric force and peak power are stronger than what either ion exerts individually and suggest the ions act synergistically to reduce muscle function during fatigue. Copyright © 2014 the American Physiological Society.

Beller Lectureship Talk: Active response of biological cells to mechanical stress

NASA Astrophysics Data System (ADS)

Safran, Samuel

2009-03-01

Forces exerted by and on adherent cells are important for many physiological processes such as wound healing and tissue formation. In addition, recent experiments have shown that stem cell differentiation is controlled, at least in part, by the elasticity of the surrounding matrix. We present a simple and generic theoretical model for the active response of biological cells to mechanical stress. The theory includes cell activity and mechanical forces as well as random forces as factors that determine the polarizability that relates cell orientation to stress. This allows us to explain the puzzling observation of parallel (or sometimes random) alignment of cells for static and quasi-static stresses and of nearly perpendicular alignment for dynamically varying stresses. In addition, we predict the response of the cellular orientation to a sinusoidally varying applied stress as a function of frequency and compare the theory with recent experiments. The dependence of the cell orientation angle on the Poisson ratio of the surrounding material distinguishes cells whose activity is controlled by stress from those controlled by strain. We have extended the theory to generalize the treatment of elastic inclusions in solids to ''living'' inclusions (cells) whose active polarizability, analogous to the polarizability of non-living matter, results in the feedback of cellular forces that develop in response to matrix stresses. We use this to explain recent observations of the non-monotonic dependence of stress-fiber polarization in stem cells on matrix rigidity. These findings provide a mechanical correlate for the existence of an optimal substrate elasticity for cell differentiation and function. [3pt] *In collaboration with R. De (Brown University), Y. Biton (Weizmann Institute), and A. Zemel (Hebrew University) and the experimental groups: Max Planck Institute, Stuttgart: S. Jungbauer, R. Kemkemer, J. Spatz; University of Pennsylvania: A. Brown, D. Discher, F. Rehfeldt.

The effect of the earth's rotation on ground water motion.

PubMed

Loáiciga, Hugo A

2007-01-01

The average pore velocity of ground water according to Darcy's law is a function of the fluid pressure gradient and the gravitational force (per unit volume of ground water) and of aquifer properties. There is also an acceleration exerted on ground water that arises from the Earth's rotation. The magnitude and direction of this rotation-induced force are determined in exact mathematical form in this article. It is calculated that the gravitational force is at least 300 times larger than the largest rotation-induced force anywhere on Earth, the latter force being maximal along the equator and approximately equal to 34 N/m(3) there. This compares with a gravitational force of approximately 10(4) N/m(3).

Method and apparatus for removal of gaseous, liquid and particulate contaminants from molten metals

DOEpatents

Hobson, D.O.; Alexeff, I.; Sikka, V.K.

1987-08-10

Method and apparatus for removal of nonelectrically-conducting gaseous, liquid, and particulate contaminants from molten metal compositions by applying a force thereto. The force (commonly referred to as the Lorentz Force) exerted by simultaneous application of an electric field and a magnetic field on a molten conductor causes an increase, in the same direction as the force, in the apparent specific gravity thereof, but does not affect the nonconducting materials. This difference in apparent densities cause the nonconducting materials to ''float'' in the opposite direction from the Lorentz Force at a rapid rate. Means are further provided for removal of the contaminants and prevention of stirring due to rotational forces generated by the applied fields. 6 figs.

Method and apparatus for removal of gaseous, liquid and particulate contaminants from molten metals

DOEpatents

Hobson, David O.; Alexeff, Igor; Sikka, Vinod K.

1988-01-01

Method and apparatus for removal of nonelectrically-conducting gaseous, liquid, and particulate contaminants from molten metal compositions by applying a force thereto. The force (commonly referred to as the Lorentz Force) exerted by simultaneous application of an electric field and a magnetic field on a molten conductor causes an increase, in the same direction as the force, in the apparent specific gravity thereof, but does not affect the nonconducting materials. This difference in apparent densities cause the nonconducting materials to "float" in the opposite direction from the Lorentz Force at a rapid rate. Means are further provided for removal of the contaminants and prevention of stirring due to rotational forces generated by the applied fields.

Theoretical and Experimental Investigation of Particle Trapping via Acoustic Bubbles

NASA Astrophysics Data System (ADS)

Chen, Yun; Fang, Zecong; Merritt, Brett; Saadat-Moghaddam, Darius; Strack, Dillon; Xu, Jie; Lee, Sungyon

2014-11-01

One important application of lab-on-a-chip devices is the trapping and sorting of micro-objects, with acoustic bubbles emerging as an effective, non-contact method. Acoustically actuated bubbles are known to exert a secondary radiation force on micro-particles and trap them, when this radiation force exceeds the drag force that acts to keep the particles in motion. In this study, we theoretically evaluate the magnitudes of these two forces for varying actuation frequencies and voltages. In particular, the secondary radiation force is calculated directly from bubble oscillation shapes that have been experimentally measured for varying acoustic parameters. Finally, based on the force estimates, we predict the threshold voltage and frequency for trapping and compare them to the experimental results.

Counterbalance of cutting force for advanced milling operations

NASA Astrophysics Data System (ADS)

Tsai, Nan-Chyuan; Shih, Li-Wen; Lee, Rong-Mao

2010-05-01

The goal of this work is to concurrently counterbalance the dynamic cutting force and regulate the spindle position deviation under various milling conditions by integrating active magnetic bearing (AMB) technique, fuzzy logic algorithm and an adaptive self-tuning feedback loop. Since the dynamics of milling system is highly determined by a few operation conditions, such as speed of spindle, cut depth and feedrate, therefore the dynamic model for cutting process is more appropriate to be constructed by experiments, instead of using theoretical approach. The experimental data, either for idle or cutting, are utilized to establish the database of milling dynamics so that the system parameters can be on-line estimated by employing the proposed fuzzy logic algorithm as the cutting mission is engaged. Based on the estimated milling system model and preset operation conditions, i.e., spindle speed, cut depth and feedrate, the current cutting force can be numerically estimated. Once the current cutting force can be real-time estimated, the corresponding compensation force can be exerted by the equipped AMB to counterbalance the cutting force, in addition to the spindle position regulation by feedback of spindle position. On the other hand, for the magnetic force is nonlinear with respect to the applied electric current and air gap, the characteristics of the employed AMB is investigated also by experiments and a nonlinear mathematic model, in terms of air gap between spindle and electromagnetic pole and coil current, is developed. At the end, the experimental simulations on realistic milling are presented to verify the efficacy of the fuzzy controller for spindle position regulation and the capability of the dynamic cutting force counterbalance.

Differences in radial expansion force among inferior vena cava filter models support documented perforation rates.

PubMed

Robins, J Eli; Ragai, Ihab; Yamaguchi, Dean J

2018-05-01

Inferior vena cava (IVC) filters are used in patients at risk for pulmonary embolism who cannot be anticoagulated. Unfortunately, these filters are not without risk, and complications include perforation, migration, and filter fracture. The most prevalent complication is filter perforation of the IVC, with incidence varying among filter models. To our knowledge, the mechanical properties of IVC filters have not been evaluated and are not readily available through the manufacturer. This study sought to determine whether differences in mechanical properties are similar to differences in documented perforation rates. The radial expansion forces of Greenfield (Boston Scientific, Marlborough, Mass), Cook Celect (Cook Medical, Bloomington, Ind), and Cook Platinum filters were analyzed with three replicates per group. The intrinsic force exerted by the filter on the measuring device was collected in real time during controlled expansion. Replicates were averaged and significance was determined by calculating analysis of covariance using SAS software (SAS Institute, Cary, NC). Each filter model generated a significantly different radial expansion force (P < .001), and force was distributed at significantly different rates (P < .001) during expansion. The largest radial expansion force at minimal caval diameter was seen in the Cook Platinum filter, followed by the Cook Celect and Greenfield filters. Radial force dispersion during expansion was greatest in the Cook Celect, followed by the Cook Platinum and Greenfield filters. Differences in radial expansion forces among IVC filter models are consistent with documented perforation rates. Cook Celect IVC filters have a higher incidence of perforation compared with Greenfield filters when they are left in place for >90 days. Evaluation of Cook Celect filters yielded a significantly higher radial expansion force at minimum caval diameter, with greater force dispersion during expansion. Copyright © 2018 Society for Vascular Surgery. Published by Elsevier Inc. All rights reserved.

Dynamic Analysis of Hammer Mechanism "Twin Hammer" of Impact Wrench

NASA Astrophysics Data System (ADS)

Konečný, M.; Slavík, J.

This paper describes function of the hammer mechanism "Twin hammer" the impact wrench, calculation of dynamic forces exerted on the mechanism and determining the contact pressures between the parts of the mechanism. The modelling of parts was performed in system Pro ENGINEER—standard. The simulation and finding dynamic forces was performed in advanced module Pro ENGINEER—mechanism design and finding contacts pressures in modul Pro ENGENEER—mechanica.

Hydrodynamic Forces on Spillway Torque-Tube Gates

DTIC Science & Technology

2010-10-01

damping coefficient associated with that of an equivalent viscous damper representing the energy dissipation mechanism from the structure itself plus the...in the figure the viscous damper with coef- ficient CD that exerts the drag force on the gate. The degree of freedom is defined as the rotation of...the following simplifying as- sumptions are postulated. Water is assumed an incompressible, inviscid, and homogeneous fluid , and its flow is taken as

Vacuum-actuated percutaneous insertion/implantation tool for flexible neural probes and interfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sheth, Heeral; Bennett, William J.; Pannu, Satinderpall S.

A flexible device insertion tool including an elongated stiffener with one or more suction ports, and a vacuum connector for interfacing the stiffener to a vacuum source, for attaching the flexible device such as a flexible neural probe to the stiffener during insertion by a suction force exerted through the suction ports to, and to release the flexible device by removing the suction force.

Physics of Artificial Gravity

NASA Technical Reports Server (NTRS)

Bukley, Angie; Paloski, William; Clement, Gilles

2006-01-01

This chapter discusses potential technologies for achieving artificial gravity in a space vehicle. We begin with a series of definitions and a general description of the rotational dynamics behind the forces ultimately exerted on the human body during centrifugation, such as gravity level, gravity gradient, and Coriolis force. Human factors considerations and comfort limits associated with a rotating environment are then discussed. Finally, engineering options for designing space vehicles with artificial gravity are presented.

Stochastic dynamics and mechanosensitivity of myosin II minifilaments

NASA Astrophysics Data System (ADS)

Albert, Philipp J.; Erdmann, Thorsten; Schwarz, Ulrich S.

2014-09-01

Tissue cells are in a state of permanent mechanical tension that is maintained mainly by myosin II minifilaments, which are bipolar assemblies of tens of myosin II molecular motors contracting actin networks and bundles. Here we introduce a stochastic model for myosin II minifilaments as two small myosin II motor ensembles engaging in a stochastic tug-of-war. Each of the two ensembles is described by the parallel cluster model that allows us to use exact stochastic simulations and at the same time to keep important molecular details of the myosin II cross-bridge cycle. Our simulation and analytical results reveal a strong dependence of myosin II minifilament dynamics on environmental stiffness that is reminiscent of the cellular response to substrate stiffness. For small stiffness, minifilaments form transient crosslinks exerting short spikes of force with negligible mean. For large stiffness, minifilaments form near permanent crosslinks exerting a mean force which hardly depends on environmental elasticity. This functional switch arises because dissociation after the power stroke is suppressed by force (catch bonding) and because ensembles can no longer perform the power stroke at large forces. Symmetric myosin II minifilaments perform a random walk with an effective diffusion constant which decreases with increasing ensemble size, as demonstrated for rigid substrates with an analytical treatment.

Zero-g simulation system for therapeutic application

NASA Technical Reports Server (NTRS)

Dane, D. H.

1971-01-01

System aids in therapeutic retraining of damaged muscles or functions as walking support during therapy. Articulated harness assembly contains patient, suspension system supports harness assembly in such a way as to counterbalance exertion of external forces on patient.

Switching skeletons: hydrostatic support in molting crabs

NASA Technical Reports Server (NTRS)

Taylor, Jennifer R A.; Kier, William M.; Walker, I. D. (Principal Investigator)

2003-01-01

Skeletal support systems are essential for support, movement, muscular antagonism, and locomotion. Crustaceans shed their rigid exoskeleton at each molt yet are still capable of forceful movement. We hypothesize that the soft water-inflated body of newly molted crabs may rely on a hydrostatic skeleton, similar to that of worms and polyps. We measured internal hydrostatic pressure and the force exerted during claw adduction and observed a strong correlation between force and hydrostatic pressure, consistent with hydrostatic skeletal support. This alternation between the two basic skeletal types may be widespread among arthropods.

Fast computation of radiation pressure force exerted by multiple laser beams on red blood cell-like particles

NASA Astrophysics Data System (ADS)

Gou, Ming-Jiang; Yang, Ming-Lin; Sheng, Xin-Qing

2016-10-01

Mature red blood cells (RBC) do not contain huge complex nuclei and organelles, makes them can be approximately regarded as homogeneous medium particles. To compute the radiation pressure force (RPF) exerted by multiple laser beams on this kind of arbitrary shaped homogenous nano-particles, a fast electromagnetic optics method is demonstrated. In general, based on the Maxwell's equations, the matrix equation formed by the method of moment (MOM) has many right hand sides (RHS's) corresponding to the different laser beams. In order to accelerate computing the matrix equation, the algorithm conducts low-rank decomposition on the excitation matrix consisting of all RHS's to figure out the so-called skeleton laser beams by interpolative decomposition (ID). After the solutions corresponding to the skeletons are obtained, the desired responses can be reconstructed efficiently. Some numerical results are performed to validate the developed method.

Advanced Active-Magnetic-Bearing Thrust-Measurement System

NASA Technical Reports Server (NTRS)

Imlach, Joseph; Kasarda, Mary; Blumber, Eric

2008-01-01

An advanced thrust-measurement system utilizes active magnetic bearings to both (1) levitate a floating frame in all six degrees of freedom and (2) measure the levitation forces between the floating frame and a grounded frame. This system was developed for original use in measuring the thrust exerted by a rocket engine mounted on the floating frame, but can just as well be used in other force-measurement applications. This system offers several advantages over prior thrust-measurement systems based on mechanical support by flexures and/or load cells: The system includes multiple active magnetic bearings for each degree of freedom, so that by selective use of one, some, or all of these bearings, it is possible to test a given article over a wide force range in the same fixture, eliminating the need to transfer the article to different test fixtures to obtain the benefit of full-scale accuracy of different force-measurement devices for different force ranges. Like other active magnetic bearings, the active magnetic bearings of this system include closed-loop control subsystems, through which the stiffness and damping characteristics of the magnetic bearings can be modified electronically. The design of the system minimizes or eliminates cross-axis force-measurement errors. The active magnetic bearings are configured to provide support against movement along all three orthogonal Cartesian axes, and such that the support along a given axis does not produce force along any other axis. Moreover, by eliminating the need for such mechanical connections as flexures used in prior thrust-measurement systems, magnetic levitation of the floating frame eliminates what would otherwise be major sources of cross-axis forces and the associated measurement errors. Overall, relative to prior mechanical-support thrust-measurement systems, this system offers greater versatility for adaptation to a variety of test conditions and requirements. The basic idea of most prior active-magnetic-bearing force-measurement systems is to calculate levitation forces on the basis of simple proportionalities between changes in those forces and changes in feedback-controlled currents applied to levitating electromagnetic coils. In the prior systems, the effects of gap lengths on fringing magnetic fields and the concomitant effects on magnetic forces were neglected. In the present system, the control subsystems of the active magnetic bearings are coupled with a computer-based automatic calibration system running special-purpose software wherein gap-length-dependent fringing factors are applied to current and magnetic-flux-based force equations and combined with a multipoint calibration method to obtain greater accuracy.

Ratings of perceived exertion by women with internal or external locus of control.

PubMed

Hassmén, P; Koivula, N

1996-10-01

Ratings of perceived exertion are frequently used to estimate the strain and effort experienced subjectively by individuals during various forms of physical activity. A number of factors, both physiological and psychological in origin, have been suggested to work as modifiers of the exertion perceived by the individual. It has been reported in nonsport-related research that individuals with an internal locus of control seem to pay more attention to relevant information and use the available information more adequately than individuals with an external locus of control. The reputed inferior information-processing abilities of externals compared with internals could possibly also influence the ratings of perceived exertion, with externals being less accurate in their ratings. Whether locus of control might be such a factor was investigated. Fifty women worked on an ergometer cycle at four different work loads. The results showed statistically significant differences in subjective ratings of perceived exertion between externals and internals, especially at heavier work loads. Such differences might be because of unequal information-processing abilities, as the observed discrepancies occurred at higher work intensities, when more cues are available for processing.

Development of a method to analyze single cell activity by using dielectrophoretic levitation.

PubMed

Hakoda, M; Hachisu, T; Wakizaka, Y; Mii, S; Kitajima, N

2005-01-01

In cell fusion and genetic recombination, although the activity of single cells is extremely important, there is no method to analyze single cell activity. Development of a quick analyzing method for single cell activity is desired in various fields. Dielectrophoresis (DEP) refers to the force exerted on the induced dipole moment of an uncharged dielectric and/or conductive particle by a nonuniform electric field. By applying DEP, we obtained experimentally a relationship between the cell activity and the dielectric property, Re[K(omega)], and examined how to evaluate the single cell activity by measuring Re[K(omega)] of a single cell. A cone and plate electrode geometry was adapted in order to achieve the feedback-controlled DEP levitation. The single cell is exposed to a nonuniform field induced by the cone and plate electrode, and a more polarizable cell is moved to the direction of the cone electrode by the DEP force. The cell settles in the position where the DEP force and gravity are balanced by controlling applied voltage. This settled position, measured on the center axis of the cone electrode, depended on the dielectric constant of the cell. From these results, the relationship between the specific growth rates in cell growth phase and the dielectric properties Re[K(omega)] was obtained. Furthermore, the effect on the cell activity of various stresses, such as concentration of carbon dioxide, temperature, etc., was examined.

Dynamics of cell area and force during spreading.

PubMed

Brill-Karniely, Yifat; Nisenholz, Noam; Rajendran, Kavitha; Dang, Quynh; Krishnan, Ramaswamy; Zemel, Assaf

2014-12-16

Experiments on human pulmonary artery endothelial cells are presented to show that cell area and the force exerted on a substrate increase simultaneously, but with different rates during spreading; rapid-force increase systematically occurred several minutes past initial spreading. We examine this theoretically and present three complementary mechanisms that may accompany the development of lamellar stress during spreading and underlie the observed behavior. These include: 1), the dynamics of cytoskeleton assembly at the cell basis; 2), the strengthening of acto-myosin forces in response to the generated lamellar stresses; and 3), the passive strain-stiffening of the cytoskeleton. Copyright © 2014 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Dopamine D2/D3 but not dopamine D1 receptors are involved in the rapid antidepressant-like effects of ketamine in the forced swim test.

PubMed

Li, Yan; Zhu, Zhuo R; Ou, Bao C; Wang, Ya Q; Tan, Zhou B; Deng, Chang M; Gao, Yi Y; Tang, Ming; So, Ji H; Mu, Yang L; Zhang, Lan Q

2015-02-15

Major depressive disorder is one of the most prevalent and life-threatening forms of mental illnesses. The traditional antidepressants often take several weeks, even months, to obtain clinical effects. However, recent clinical studies have shown that ketamine, an N-methyl-D-aspartate (NMDA) receptor antagonist, exerts rapid antidepressant effects within 2h and are long-lasting. The aim of the present study was to investigate whether dopaminergic system was involved in the rapid antidepressant effects of ketamine. The acute administration of ketamine (20 mg/kg) significantly reduced the immobility time in the forced swim test. MK-801 (0.1 mg/kg), the more selective NMDA antagonist, also exerted rapid antidepressant-like effects. In contrast, fluoxetine (10 mg/kg) did not significantly reduced the immobility time in the forced swim test after 30 min administration. Notably, pretreatment with haloperidol (0.15 mg/kg, a nonselective dopamine D2/D3 antagonist), but not SCH23390 (0.04 and 0.1 mg/kg, a selective dopamine D1 receptor antagonist), significantly prevented the effects of ketamine or MK-801. Moreover, the administration of sub-effective dose of ketamine (10 mg/kg) in combination with pramipexole (0.3 mg/kg, a dopamine D2/D3 receptor agonist) exerted antidepressant-like effects compared with each drug alone. In conclusion, our results indicated that the dopamine D2/D3 receptors, but not D1 receptors, are involved in the rapid antidepressant-like effects of ketamine. Copyright © 2014 Elsevier B.V. All rights reserved.

Method for Molding Structural Parts Utilizing Modified Silicone Rubber

NASA Technical Reports Server (NTRS)

Weiser, Erik S. (Inventor); Baucom, Robert M. (Inventor); Snoha, John J. (Inventor)

1998-01-01

This invention improves upon a method for molding structural parts from preform material. Preform material to be used for the part is provided. A silicone rubber composition containing entrained air voids is prepared. The silicone rubber and preform material assembly is situated within a rigid mold cavity used to shape the preform material to die desired shape. The entire assembly is heated in a standard heating device so that the thermal expansion of the silicone rubber exerts the pressure necessary to force the preform material into contact with the mold container. The introduction of discrete air voids into the silicone rubber allows for accurately controlled pressure application on the preform material at the cure temperature.

Challenges in realizing a self-contained hydraulically-driven contractile fiber actuator.

PubMed

Smela, Elisabeth

2017-07-01

The field of soft robots would benefit from electrically controlled contractile actuators in the form of fibers that achieve a strain of 20% in less than a second while exerting high force. This work explores possible designs for achieving this goal using self-contained electroosmotic fluid pumping within a tube-shaped structure. The most promising configuration is a combination of a bellows and a McKibben-type muscle, since pumping fluid from the former to the latter results in contraction of both portions. Realizing such a device entails challenges in fabrication and electrokinetic fluid pumping in closed systems. Further studies of electroosmotic flow in salt-free organic solvents are needed.

Controlling the Nanoscale Patterning of AuNPs on Silicon Surfaces

PubMed Central

Williams, Sophie E.; Davies, Philip R.; Bowen, Jenna L.; Allender, Chris J.

2013-01-01

This study evaluates the effectiveness of vapour-phase deposition for creating sub-monolayer coverage of aminopropyl triethoxysilane (APTES) on silicon in order to exert control over subsequent gold nanoparticle deposition. Surface coverage was evaluated indirectly by observing the extent to which gold nanoparticles (AuNPs) deposited onto the modified silicon surface. By varying the distance of the silicon wafer from the APTES source and concentration of APTES in the evaporating media, control over subsequent gold nanoparticle deposition was achievable to an extent. Fine control over AuNP deposition (AuNPs/μm2) however, was best achieved by adjusting the ionic concentration of the AuNP-depositing solution. Furthermore it was demonstrated that although APTES was fully removed from the silicon surface following four hours incubation in water, the gold nanoparticle-amino surface complex was stable under the same conditions. Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) were used to study these affects. PMID:28348330

Taxonomy based analysis of force exchanges during object grasping and manipulation

PubMed Central

Martin-Brevet, Sandra; Jarrassé, Nathanaël; Burdet, Etienne

2017-01-01

The flexibility of the human hand in object manipulation is essential for daily life activities, but remains relatively little explored with quantitative methods. On the one hand, recent taxonomies describe qualitatively the classes of hand postures for object grasping and manipulation. On the other hand, the quantitative analysis of hand function has been generally restricted to precision grip (with thumb and index opposition) during lifting tasks. The aim of the present study is to fill the gap between these two kinds of descriptions, by investigating quantitatively the forces exerted by the hand on an instrumented object in a set of representative manipulation tasks. The object was a parallelepiped object able to measure the force exerted on the six faces and its acceleration. The grasping force was estimated from the lateral force and the unloading force from the bottom force. The protocol included eleven tasks with complementary constraints inspired by recent taxonomies: four tasks corresponding to lifting and holding the object with different grasp configurations, and seven to manipulating the object (rotation around each of its axis and translation). The grasping and unloading forces and object rotations were measured during the five phases of the actions: unloading, lifting, holding or manipulation, preparation to deposit, and deposit. The results confirm the tight regulation between grasping and unloading forces during lifting, and extend this to the deposit phase. In addition, they provide a precise description of the regulation of force exchanges during various manipulation tasks spanning representative actions of daily life. The timing of manipulation showed both sequential and overlapping organization of the different sub-actions, and micro-errors could be detected. This phenomenological study confirms the feasibility of using an instrumented object to investigate complex manipulative behavior in humans. This protocol will be used in the future to investigate upper-limb dexterity in patients with sensory-motor impairments. PMID:28562617

Active control of flexural vibrations in beams

NASA Technical Reports Server (NTRS)

Gerhold, Carl H.

1987-01-01

The feasibility of using piezoelectric actuators to control the flexural oscillations of large structures in space is investigated. Flexural oscillations are excited by impulsive loads. The vibratory response can degrade the pointing accuracy of cameras and antennae, and can cause high stresses at structural node points. Piezoelectric actuators have the advantage of exerting localized bending moments. In this way, vibration is controlled without exciting rigid body modes. The actuators are used in collocated sensor/driver pairs to form a feedback control system. The sensor produces a voltage that is proportional to the dynamic stress at the sensor location, and the driver produces a force that is proportional to the voltage applied to it. The analog control system amplifies and phase shifts the sensor signal to produce the voltage signal that is applied to the driver. The feedback control is demonstrated to increase the first mode damping in a cantilever beam by up to 100 percent, depending on the amplifier gain. The damping efficiency of the control system when the piezoelectrics are not optimally positioned at points of high stress in the beam is evaluated.

Examination of vehicle performance at high speed and high cant deficiency

DOT National Transportation Integrated Search

2011-03-16

In the US, increasing passenger speeds to improve trip time : usually involves increasing speeds through curves. Increasing : speeds through curves will increase the lateral force exerted on : track during curving, thus requiring more intensive track...

77 FR 60169 - Safety Advisory 2012-04; Worn Rail Conditions

Federal Register 2010, 2011, 2012, 2013, 2014

2012-10-02

... located on the high side of a curve, due to the exertion of wheel flange forces. Vertical rail head wear... locations that exhibit excessive rail head wear and RCF. 3. Review its current engineering instructions to...

Trinity sure-II

NASA Astrophysics Data System (ADS)

Swartz, Clifford E.

1998-11-01

What could be simpler? Exert a force on a mass, and it accelerates. F=ma! You can work that formula into any number of problems about objects on inclined planes, or Atwood's machine, or blocks sliding along a surface with coefficient of friction, μ.

The Human Shoulder Suspension Apparatus: A Causal Explanation for Bilateral Asymmetry and a Fresh Look at the Evolution of Human Bipedality.

PubMed

Osborn, Michelle L; Homberger, Dominique G

2015-09-01

The combination of large mastoid processes and clavicles is unique to humans, but the biomechanical and evolutionary significance of their special configuration is poorly understood. As part of the newly conceptualized shoulder suspension apparatus, the mastoid processes and clavicles are shaped by forces exerted by the musculo-fascial components of the cleidomastoid and clavotrapezius muscles as they suspend the shoulders from the head. Because both skeletal elements develop during infancy in tandem with the attainment of an upright posture, increased manual dexterity, and the capacity for walking, we hypothesized that the same forces would have shaped them as the shoulder suspension apparatus evolved in ancestral humans in tandem with an upright posture, increased manual dexterity, and bipedality with swinging arms. Because the shoulder suspension apparatus is subjected to asymmetrical forces from handedness, we predicted that its skeletal features would grow asymmetrically. We used this prediction to test our hypothesis in a natural experiment to correlate the size of the skeletal features with the forces exerted on them. We (1) measured biomechanically relevant bony features within the shoulder suspension apparatus in 101 male human specimens (62 of known handedness); and (2) modeled and analyzed the forces within the shoulder suspension apparatus from X-ray CT data. We identified eight right-handed characters and demonstrated the causal relationship between these right-handed characters and the magnitude and direction of forces acting on them. Our data suggest that the presence of the shoulder suspension apparatus in humans was a necessary precondition for human bipedality. © 2015 Wiley Periodicals, Inc.

Extracting source characteristics and dynamics of the August 2010 Mount Meager landslide from broadband seismograms

NASA Astrophysics Data System (ADS)

Allstadt, Kate

2013-09-01

methods can substantially improve the characterization of the dynamics of large and rapid landslides. Such landslides often generate strong long-period seismic waves due to the large-scale acceleration of the entire landslide mass, which, according to theory, can be approximated as a single-force mechanism at long wavelengths. I apply this theory and invert the long-period seismic waves generated by the 48.5 Mm3 August 2010 Mount Meager rockslide-debris flow in British Columbia. Using data from five broadband seismic stations 70 to 276 km from the source, I obtain a time series of forces the landslide exerted on the Earth, with peak forces of 1.0 × 1011 N. The direction and amplitude of the forces can be used to determine the timing and occurrence of events and subevents. Using this result, in combination with other field and geospatial evidence, I calculate an average horizontal acceleration of the rockslide of 0.39 m/s2 and an average apparent coefficient of basal friction of 0.38 ± 0.02, which suggests elevated basal fluid pressures. The direction and timing of the strongest forces are consistent with the centripetal acceleration of the debris flow around corners in its path. I use this correlation to estimate speeds, which peak at 92 m/s. This study demonstrates that the time series recording of forces exerted by a large and rapid landslide derived remotely from seismic records can be used to tie post-slide evidence to what actually occurred during the event and can serve to validate numerical models and theoretical methods.

Mechanical Coordination of Single-Cell and Collective-Cell Amoeboid Migration

NASA Astrophysics Data System (ADS)

Del Alamo, Juan Carlos

Amoeboid migration consists of the sequential repetition of pseudopod extensions and retractions driven by actin polymerization and actomyosin contraction, and requires cells to apply mechanical forces on their surroundings. We measure the three-dimensional forces exerted by chemotaxing Dictyostelium cells, and examine wild-type cells as well as mutants with defects in contractility, F-actin polymerization, internal F-actin crosslinking, and cortical integrity. We find that cells pull on their substrate adhesions using two distinct, yet interconnected mechanisms: axial actomyosin contractility and cortical tension. The 3D pulling forces generated by both mechanisms are internally balanced by an increase in cytoplasmic pressure that allows cells to push on their substrate, and we show that these pushing forces are relevant for cell invasion and migration in three-dimensional environments. We observe that cells migrate mainly by forming two stationary adhesion sites at the front and back of the cell, over which the cell body moves forward in a step-wise fashion. During this process, the traction forces at each adhesion site are switched off and subsequently their direction is reversed. The cell migration speed is found to be proportional to the rate at which cells are able regulate these forces to produce the cell shape changes needed for locomotion, which is increased when axial contractility overcomes the stabilizing effect of cortical tension. This spatiotemporal coordination is conserved in streams of multiple migratory cells connected head to tail, which also migrate by exerting traction forces on stationary sites. Furthermore, we observe that trailing cells reuse the adhesion sites of the leading cells. Finally, we provide evidence that the above modes of migration may be conserved in a range of other amoeboid-type moving cells such as neutrophils.

The impact of working technique on physical loads - an exposure profile among newspaper editors.

PubMed

Lindegård, A; Wahlström, J; Hagberg, M; Hansson, G-A; Jonsson, P; Wigaeus Tornqvist, E

2003-05-15

The aim of this study was to investigate the possible associations between working technique, sex, symptoms and level of physical load in VDU-work. A study group of 32 employees in the editing department of a daily newspaper answered a questionnaire, about physical working conditions and symptoms from the neck and the upper extremities. Muscular load, wrist positions and computer mouse forces were measured. Working technique was assessed from an observation protocol for computer work. In addition ratings of perceived exertion and overall comfort were collected. The results showed that subjects classified as having a good working technique worked with less muscular load in the forearm (extensor carpi ulnaris p=0.03) and in the trapezius muscle on the mouse operating side (p=0.02) compared to subjects classified as having a poor working technique. Moreover there were no differences in gap frequency (number of episodes when muscle activity is below 2.5% of a reference contraction) or muscular rest (total duration of gaps) between the two working technique groups. Women in this study used more force (mean force p=0.006, peak force p=0.02) expressed as % MVC than the men when operating the computer mouse. No major differences were shown in muscular load, wrist postures, perceived exertion or perceived comfort between men and women or between cases and symptom free subjects. In conclusion a good working technique was associated with reduced muscular load in the forearm muscles and in the trapezius muscle on the mouse operating side. Moreover women used more force (mean force and peak force) than men when operating the click button (left button) of the computer mouse.

Changes in the flexor digitorum profundus tendon geometry in the carpal tunnel due to force production and posture of metacarpophalangeal joint of the index finger: an MRI study.

PubMed

Martin, Joel R; Paclet, Florent; Latash, Mark L; Zatsiorsky, Vladimir M

2013-02-01

Carpal tunnel syndrome is a disorder caused by increased pressure in the carpal tunnel associated with repetitive, stereotypical finger actions. Little is known about in vivo geometrical changes in the carpal tunnel caused by motion at the finger joints and exerting a fingertip force. The hands and forearms of five subjects were scanned using a 3.0 T magnetic resonance imaging scanner. The metacarpophalangeal joint of the index finger was placed in: flexion, neutral and extension. For each joint posture subjects either produced no active force (passive condition) or exerted a flexion force to resist a load (~4.0 N) at the fingertip (active condition). Changes in the radii of curvature, position and transverse plane area of the flexor digitorum profundus tendons at the carpal tunnel level were measured. The radius of curvature of the flexor digitorum profundus tendons, at the carpal tunnel level, was significantly affected by posture of the index finger metacarpophalangeal joint (P<0.05) and the radii was significantly different between fingers (P<0.05). Actively producing force caused a significant shift (P<0.05) in the flexor digitorum profundus tendons in the ventral (palmar) direction. No significant change in the area of an ellipse containing the flexor digitorum profundus tendons was observed between conditions. The results show that relatively small changes in the posture and force production of a single finger can lead to significant changes in the geometry of all the flexor digitorum profundus tendons in the carpal tunnel. Additionally, voluntary force production at the fingertip increases the moment arm of the FDP tendons about the wrist joint. Copyright © 2012 Elsevier Ltd. All rights reserved.

Combined reduced forced expiratory volume in 1 second (FEV1) and peripheral artery disease in sedentary elders with functional limitations.

PubMed

Vaz Fragoso, Carlos A; Hsu, Fang-Chi; Brinkley, Tina; Church, Timothy; Liu, Christine K; Manini, Todd; Newman, Anne B; Stafford, Randall S; McDermott, Mary M; Gill, Thomas M

2014-09-01

Because they are potentially modifiable and may coexist, we evaluated the combined occurrence of a reduced forced expiratory volume in 1 second (FEV1) and peripheral artery disease (PAD), including its association with exertional symptoms, physical inactivity, and impaired mobility, in sedentary elders with functional limitations. Cross sectional. Lifestyle Interventions and Independence in Elder (LIFE) Study. A total of 1307 sedentary community-dwelling persons, mean age 78.9, with functional limitations (Short Physical Performance Battery [SPPB] <10). A reduced FEV1 was defined by a z-score less than -1.64 (

Self-reported post-exertional fatigue in Gulf War veterans: roles of autonomic testing

PubMed Central

Li, Mian; Xu, Changqing; Yao, Wenguo; Mahan, Clare M.; Kang, Han K.; Sandbrink, Friedhelm; Zhai, Ping; Karasik, Pamela A.

2014-01-01

To determine if objective evidence of autonomic dysfunction exists from a group of Gulf War veterans with self-reported post-exertional fatigue, we evaluated 16 Gulf War ill veterans and 12 Gulf War controls. Participants of the ill group had self- reported, unexplained chronic post-exertional fatigue and the illness symptoms had persisted for years until the current clinical study. The controls had no self-reported post-exertional fatigue either at the time of initial survey nor at the time of the current study. We intended to identify clinical autonomic disorders using autonomic and neurophysiologic testing in the clinical context. We compared the autonomic measures between the 2 groups on cardiovascular function at both baseline and head-up tilt, and sudomotor function. We identified 1 participant with orthostatic hypotension, 1 posture orthostatic tachycardia syndrome, 2 distal small fiber neuropathy, and 1 length dependent distal neuropathy affecting both large and small fiber in the ill group; whereas none of above definable diagnoses was noted in the controls. The ill group had a significantly higher baseline heart rate compared to controls. Compound autonomic scoring scale showed a significant higher score (95% CI of mean: 1.72–2.67) among ill group compared to controls (0.58–1.59). We conclude that objective autonomic testing is necessary for the evaluation of self-reported, unexplained post-exertional fatigue among some Gulf War veterans with multi-symptom illnesses. Our observation that ill veterans with self-reported post-exertional fatigue had objective autonomic measures that were worse than controls warrants validation in a larger clinical series. PMID:24431987

Gravity Responsive NADH Oxidase of the Plasma Membrane

NASA Technical Reports Server (NTRS)

Morre, D. James (Inventor)

2002-01-01

A method and apparatus for sensing gravity using an NADH oxidase of the plasma membrane which has been found to respond to unit gravity and low centrifugal g forces. The oxidation rate of NADH supplied to the NADH oxidase is measured and translated to represent the relative gravitational force exerted on the protein. The NADH oxidase of the plasma membrane may be obtained from plant or animal sources or may be produced recombinantly.

Manipulation of domain-wall solitons in bi- and trilayer graphene

NASA Astrophysics Data System (ADS)

Jiang, Lili; Wang, Sheng; Shi, Zhiwen; Jin, Chenhao; Utama, M. Iqbal Bakti; Zhao, Sihan; Shen, Yuen-Ron; Gao, Hong-Jun; Zhang, Guangyu; Wang, Feng

2018-01-01

Topological dislocations and stacking faults greatly affect the performance of functional crystalline materials1-3. Layer-stacking domain walls (DWs) in graphene alter its electronic properties and give rise to fascinating new physics such as quantum valley Hall edge states4-10. Extensive efforts have been dedicated to the engineering of dislocations to obtain materials with advanced properties. However, the manipulation of individual dislocations to precisely control the local structure and local properties of bulk material remains an outstanding challenge. Here we report the manipulation of individual layer-stacking DWs in bi- and trilayer graphene by means of a local mechanical force exerted by an atomic force microscope tip. We demonstrate experimentally the capability to move, erase and split individual DWs as well as annihilate or create closed-loop DWs. We further show that the DW motion is highly anisotropic, offering a simple approach to create solitons with designed atomic structures. Most artificially created DW structures are found to be stable at room temperature.

Scalability of the muscular action in a parametric 3D model of the index finger.

PubMed

Sancho-Bru, Joaquín L; Vergara, Margarita; Rodríguez-Cervantes, Pablo-Jesús; Giurintano, David J; Pérez-González, Antonio

2008-01-01

A method for scaling the muscle action is proposed and used to achieve a 3D inverse dynamic model of the human finger with all its components scalable. This method is based on scaling the physiological cross-sectional area (PCSA) in a Hill muscle model. Different anthropometric parameters and maximal grip force data have been measured and their correlations have been analyzed and used for scaling the PCSA of each muscle. A linear relationship between the normalized PCSA and the product of the length and breadth of the hand has been finally used for scaling, with a slope of 0.01315 cm(-2), with the length and breadth of the hand expressed in centimeters. The parametric muscle model has been included in a parametric finger model previously developed by the authors, and it has been validated reproducing the results of an experiment in which subjects from different population groups exerted maximal voluntary forces with their index finger in a controlled posture.

A visualization study on two-phase gravity drainage in porous media by using magnetic resonance imaging.

PubMed

Teng, Ying; Liu, Yu; Jiang, Lanlan; Song, Yongchen; Zhao, Jiafei; Zhang, Yi; Wang, Dayong

2016-09-01

Gravity drainage characteristics are important to improve our understanding of gas-liquid or liquid-liquid two-phase flow in porous media. Stable or unstable displacement fronts that controlled by the capillary force, viscous force, gravitational force, etc., are relevant features of immiscible two-phase flow. In this paper, three dimensionless parameters, namely, the gravity number, the capillary number and the Bond number, were used to describe the effect of the above mentioned forces on two-phase drainage features, including the displacement front and final displacing-phase saturation. A series of experiments on the downward displacement of a viscous fluid by a less viscous fluid in a vertical vessel that is filled with quartz beads are performed by using magnetic resonance imaging (MRI). The experimental results indicate that the wetting properties at both high and low capillary numbers exert remarkable control on the fluid displacement. When the contact angle is lower than 90°, i.e., the displaced phase is the wetting phase, the average velocity Vf of the interface of the two phases (displacement front velocity) is observably lower than when the displaced phase is the non-wetting phase (contact angle higher than 90°). The results show that a fingering phenomenon occurs when the gravity number G is less than the critical gravity number G'=Δμ/μg. Moreover, the higher Bond number results in higher final displacing-phase saturation, whereas the capillary number has an opposite effect. Copyright © 2016 Elsevier Inc. All rights reserved.

Evidence of the no-slip boundary condition of water flow between hydrophilic surfaces using atomic force microscopy.

PubMed

Maali, Abdelhamid; Wang, Yuliang; Bhushan, Bharat

2009-10-20

In this study we present measurements of the hydrodynamic force exerted on a glass sphere glued to an atomic force microscopy (AFM) cantilever approaching a mica surface in water. A large sphere was used to reduce the impact of the cantilever beam on the measurement. An AFM cantilever with large stiffness was used to accurately determine the actual contact position between the sphere and the sample surface. The measured hydrodynamic force with different approach velocities is in good agreement with the Taylor force calculated in the lubrication theory with the no-slip boundary conditions, which verifies that there is no boundary slip on the glass and mica surfaces. Moreover, a detailed procedure of how to subtract the electrostatic double-layer force is presented.

Task- and time-dependent modulation of Ia presynaptic inhibition during fatiguing contractions performed by humans

PubMed Central

Maerz, Adam H.; Gould, Jeffrey R.; Enoka, Roger M.

2011-01-01

Presynaptic modulation of Ia afferents converging onto the motor neuron pool of the extensor carpi radialis (ECR) was compared during contractions (20% of maximal force) sustained to failure as subjects controlled either the angular position of the wrist while supporting an inertial load (position task) or exerted an equivalent force against a rigid restraint (force task). Test Hoffmann (H) reflexes were evoked in the ECR by stimulating the radial nerve above the elbow. Conditioned H reflexes were obtained by stimulating either the median nerve above the elbow or at the wrist (palmar branch) to assess presynaptic inhibition of homonymous (D1 inhibition) and heteronymous Ia afferents (heteronymous Ia facilitation), respectively. The position task was briefer than the force task (P = 0.001), although the maximal voluntary force and electromyograph for ECR declined similarly at failure for both tasks. Changes in the amplitude of the conditioned H reflex were positively correlated between the two conditioning methods (P = 0.02) and differed between the two tasks (P < 0.05). The amplitude of the conditioned H reflex during the position task first increased (129 ± 20.5% of the initial value, P < 0.001) before returning to its initial value (P = 0.22), whereas it increased progressively during the force task to reach 122 ± 17.4% of the initial value at failure (P < 0.001). Moreover, changes in conditioned H reflexes were associated with the time to task failure and force fluctuations. The results suggest a task- and time-dependent modulation of presynaptic inhibition of Ia afferents during fatiguing contractions. PMID:21543747

Present-day stress field of Southeast Asia

NASA Astrophysics Data System (ADS)

Tingay, Mark; Morley, Chris; King, Rosalind; Hillis, Richard; Coblentz, David; Hall, Robert

2010-02-01

It is now well established that ridge push forces provide a major control on the plate-scale stress field in most of the Earth's tectonic plates. However, the Sunda plate that comprises much of Southeast Asia is one of only two plates not bounded by a major spreading centre and thus provides an opportunity to evaluate other forces that control the intraplate stress field. The Cenozoic tectonic evolution of the Sunda plate is usually considered to be controlled by escape tectonics associated with India-Eurasia collision. However, the Sunda plate is bounded by a poorly understood and complex range of convergent and strike-slip zones and little is known about the effect of these other plate boundaries on the intraplate stress field in the region. We compile the first extensive stress dataset for Southeast Asia, containing 275 A-D quality (177 A-C) horizontal stress orientations, consisting of 72 stress indicators from earthquakes (located mostly on the periphery of the plate), 202 stress indicators from breakouts and drilling-induced fractures and one hydraulic fracture test within 14 provinces in the plate interior. This data reveals that a variable stress pattern exists throughout Southeast Asia that is largely inconsistent with the Sunda plate's approximately ESE absolute motion direction. The present-day maximum horizontal stress in Thailand, Vietnam and the Malay Basin is predominately north-south, consistent with the radiating stress patterns arising from the eastern Himalayan syntaxis. However, the present-day maximum horizontal stress is primarily oriented NW-SE in Borneo, a direction that may reflect plate-boundary forces or topographic stresses exerted by the central Borneo highlands. Furthermore, the South and Central Sumatra Basins exhibit a NE-SW maximum horizontal stress direction that is perpendicular to the Indo-Australian subduction front. Hence, the plate-scale stress field in Southeast Asia appears to be controlled by a combination of Himalayan orogeny-related deformation, forces related to subduction (primarily trench suction and collision) and intraplate sources of stress such as topography and basin geometry.

The Microbubble or the Microparticle?

EPA Science Inventory

Decompression sickness (DCS) has long been attributed to physical forces exerted by inert gas bubbles that may form in tissues, resulting in vascular occlusion and tissue disruption. Bubble formation occurs when a decrease in ambient pressure exceeds the rate at which soluble ine...

Directional mass transport in an atmospheric pressure surface barrier discharge.

PubMed

Dickenson, A; Morabit, Y; Hasan, M I; Walsh, J L

2017-10-25

In an atmospheric pressure surface barrier discharge the inherent physical separation between the plasma generation region and downstream point of application reduces the flux of reactive chemical species reaching the sample, potentially limiting application efficacy. This contribution explores the impact of manipulating the phase angle of the applied voltage to exert a level of control over the electrohydrodynamic forces generated by the plasma. As these forces produce a convective flow which is the primary mechanism of species transport, the technique facilitates the targeted delivery of reactive species to a downstream point without compromising the underpinning species generation mechanisms. Particle Imaging Velocimetry measurements are used to demonstrate that a phase shift between sinusoidal voltages applied to adjacent electrodes in a surface barrier discharge results in a significant deviation in the direction of the plasma induced gas flow. Using a two-dimensional numerical air plasma model, it is shown that the phase shift impacts the spatial distribution of the deposited charge on the dielectric surface between the adjacent electrodes. The modified surface charge distribution reduces the propagation length of the discharge ignited on the lagging electrode, causing an imbalance in the generated forces and consequently a variation in the direction of the resulting gas flow.

Insect flight on fluid interfaces: a chaotic interfacial oscillator

NASA Astrophysics Data System (ADS)

Mukundarajan, Haripriya; Prakash, Manu

2013-11-01

Flight is critical to the dominance of insect species on our planet, with about 98 percent of insect species having wings. How complex flight control systems developed in insects is unknown, and arboreal or aquatic origins have been hypothesized. We examine the biomechanics of aquatic origins of flight. We recently reported discovery of a novel mode of ``2D flight'' in Galerucella beetles, which skim along an air-water interface using flapping wing flight. This unique flight mode is characterized by a balance between capillary forces from the interface and biomechanical forces exerted by the flapping wings. Complex interactions on the fluid interface form capillary wave trains behind the insect, and produce vertical oscillations at the surface due to non-linear forces arising from deformation of the fluid meniscus. We present both experimental observations of 2D flight kinematics and a dynamic model explaining the observed phenomena. Careful examination of this interaction predicts the chaotic nature of interfacial flight and takeoff from the interface into airborne flight. The role of wingbeat frequency, stroke plane angle and body angle in determining transition between interfacial and fully airborne flight is highlighted, shedding light on the aquatic theory of flight evolution.

Lack of muscle contractile property changes at the time of perceived physical exhaustion suggests central mechanisms contributing to early motor task failure in patients with cancer-related fatigue.

PubMed

Kisiel-Sajewicz, Katarzyna; Davis, Mellar P; Siemionow, Vlodek; Seyidova-Khoshknabi, Dilara; Wyant, Alexandria; Walsh, Declan; Hou, Juliet; Yue, Guang H

2012-09-01

Fatigue is one of the most common symptoms reported by cancer survivors, and fatigue worsens when patients are engaged in muscle exertion, which results in early motor task failure. Central fatigue plays a significant role, more than muscle (peripheral) fatigue, in contributing to early task failure in cancer-related fatigue (CRF). The purpose of this study was to determine if muscle contractile property alterations (reflecting muscle fatigue) occurred at the end of a low-intensity muscle contraction to exhaustion and if these properties differed between those with CRF and healthy controls. Ten patients (aged 59.9±10.6 years, seven women) with advanced solid cancer and CRF and 12 age- and gender-matched healthy controls (aged 46.6±12.8 years, nine women) performed a sustained contraction of the right arm elbow flexion at 30% maximal level until exhaustion. Peak twitch force, time to peak twitch force, rate of peak twitch force development, and half relaxation time derived from electrical stimulation-evoked twitches were analyzed pre- and post-sustained contraction. CRF patients reported significantly greater fatigue as measured by the Brief Fatigue Inventory and failed the motor task earlier, 340±140 vs. 503±155 seconds in controls. All contractile property parameters did not change significantly in CRF but did change significantly in controls. CRF patients perceive physical exhaustion sooner during a motor fatigue task with minimal muscular fatigue. The observation supports that central fatigue is a more significant factor than peripheral fatigue in causing fatigue feelings and limits motor function in cancer survivors with fatigue symptoms. Copyright © 2012. Published by Elsevier Inc.

A Negative Allosteric Modulator for α5 Subunit-Containing GABA Receptors Exerts a Rapid and Persistent Antidepressant-Like Action without the Side Effects of the NMDA Receptor Antagonist Ketamine in Mice

PubMed Central

Nelson, Mackenzie E.; Krimmel, Samuel R.; Georgiou, Polymnia; Gould, Todd D.

2017-01-01

Abstract New antidepressant pharmacotherapies that provide rapid relief of depressive symptoms are needed. The NMDA receptor antagonist ketamine exerts rapid antidepressant actions in depressed patients but also side effects that complicate its clinical utility. Ketamine promotes excitatory synaptic strength, likely by producing high-frequency correlated activity in mood-relevant regions of the forebrain. Negative allosteric modulators of GABA-A receptors containing α5 subunits (α5 GABA-NAMs) should also promote high-frequency correlated electroencephalogram (EEG) activity and should therefore exert rapid antidepressant responses. Because α5 subunits display a restricted expression in the forebrain, we predicted that α5 GABA-NAMs would produce activation of principle neurons but exert fewer side effects than ketamine. We tested this hypothesis in male mice and observed that the α5 GABA-NAM MRK-016 exerted an antidepressant-like response in the forced swim test at 1 and 24 h after administration and an anti-anhedonic response after chronic stress in the female urine sniffing test (FUST). Like ketamine, MRK-016 produced a transient increase in EEG γ power, and both the increase in γ power and its antidepressant effects in the forced swim test were blocked by prior administration of the AMPA-type glutamate receptor antagonist 2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo[f]quinoxaline-7-sulfonamide (NBQX). Unlike ketamine, however, MRK-016 produced no impairment of rota-rod performance, no reduction of prepulse inhibition (PPI), no conditioned-place preference (CPP), and no change in locomotion. α5 GABA-NAMs, thus reproduce the rapid antidepressant-like actions of ketamine, perhaps via an AMPA receptor (AMPAR)-dependent increase in coherent neuronal activity, but display fewer potential negative side effects. These compounds thus demonstrate promise as clinically useful fast-acting antidepressants. PMID:28275719

A numerical analysis of forces exerted by laminar flow on spreading cells in a parallel plate flow chamber assay.

PubMed

Olivier, L A; Truskey, G A

1993-10-01

Exposure of spreading anchorage-dependent cells to laminar flow is a common technique to measure the strength of cell adhesion. Since cells protrude into the flow stream, the force exerted by the fluid on the cells is a function of cell shape. To assess the relationship between cell shape and the hydrodynamic force on adherent cells, we obtained numerical solutions of the velocity and stress fields around bovine aortic endothelial cells during various stages of spreading and calculated the force required to detach the cells. Morphometric parameters were obtained from light and scanning electron microscopy measurements. Cells were assumed to have a constant volume, but the surface area increased during spreading until the membrane was stretched taut. Two-dimensional models of steady flow were generated using the software packages ANSYS (mesh generation) and FIDAP (problem solution). The validity of the numerical results was tested by comparison with published results for a semicircle in contact with the surface. The drag force and torque were greatest for round cells making initial contact with the surface. During spreading, the drag force and torque declined by factors of 2 and 20, respectively. The calculated forces and moments were used in adhesion models to predict the wall shear stress at which the cells detached. Based upon published values for the bond force and receptor number, round cells should detach at shear stresses between 2.5 and 6 dyn/cm(2), whereas substantially higher stresses are needed to detach spreading and fully spread cells. Results from the simulations indicate that (1) the drag force varies little with cell shape whereas the torque is very sensitive to cell shape, and (2) the increase in the strength of adhesion during spreading is due to increased contact area and receptor densities within the contact area. (c) 1993 John Wiley & Sons, Inc.

How to Activate a Plant Gravireceptor. Early Mechanisms of Gravity Sensing Studied in Characean Rhizoids during Parabolic Flights1

PubMed Central

Limbach, Christoph; Hauslage, Jens; Schäfer, Claudia; Braun, Markus

2005-01-01

Early processes underlying plant gravity sensing were investigated in rhizoids of Chara globularis under microgravity conditions provided by parabolic flights of the A300-Zero-G aircraft and of sounding rockets. By applying centrifugal forces during the microgravity phases of sounding rocket flights, lateral accelerations of 0.14g, but not of 0.05g, resulted in a displacement of statoliths. Settling of statoliths onto the subapical plasma membrane initiated the gravitropic response. Since actin controls the positioning of statoliths and restricts sedimentation of statoliths in these cells, it can be calculated that lateral actomyosin forces in a range of 2 × 10−14 n act on statoliths to keep them in place. These forces represent the threshold value that has to be exceeded by any lateral acceleration stimulus for statolith sedimentation and gravisensing to occur. When rhizoids were gravistimulated during parabolic plane flights, the curvature angles of the flight samples, whose sedimented statoliths became weightless for 22 s during the 31 microgravity phases, were not different from those of in-flight 1g controls. However, in ground control experiments, curvature responses were drastically reduced when the contact of statoliths with the plasma membrane was intermittently interrupted by inverting gravistimulated cells for less than 10 s. Increasing the weight of sedimented statoliths by lateral centrifugation did not enhance the gravitropic response. These results provide evidence that graviperception in characean rhizoids requires contact of statoliths with membrane-bound receptor molecules rather than pressure or tension exerted by the weight of statoliths. PMID:16183834

How to activate a plant gravireceptor. Early mechanisms of gravity sensing studied in characean rhizoids during parabolic flights.

PubMed

Limbach, Christoph; Hauslage, Jens; Schäfer, Claudia; Braun, Markus

2005-10-01

Early processes underlying plant gravity sensing were investigated in rhizoids of Chara globularis under microgravity conditions provided by parabolic flights of the A300-Zero-G aircraft and of sounding rockets. By applying centrifugal forces during the microgravity phases of sounding rocket flights, lateral accelerations of 0.14 g, but not of 0.05 g, resulted in a displacement of statoliths. Settling of statoliths onto the subapical plasma membrane initiated the gravitropic response. Since actin controls the positioning of statoliths and restricts sedimentation of statoliths in these cells, it can be calculated that lateral actomyosin forces in a range of 2 x 10(-14) n act on statoliths to keep them in place. These forces represent the threshold value that has to be exceeded by any lateral acceleration stimulus for statolith sedimentation and gravisensing to occur. When rhizoids were gravistimulated during parabolic plane flights, the curvature angles of the flight samples, whose sedimented statoliths became weightless for 22 s during the 31 microgravity phases, were not different from those of in-flight 1g controls. However, in ground control experiments, curvature responses were drastically reduced when the contact of statoliths with the plasma membrane was intermittently interrupted by inverting gravistimulated cells for less than 10 s. Increasing the weight of sedimented statoliths by lateral centrifugation did not enhance the gravitropic response. These results provide evidence that graviperception in characean rhizoids requires contact of statoliths with membrane-bound receptor molecules rather than pressure or tension exerted by the weight of statoliths.

Evaluation of muscle activity, bite force and salivary cortisol in children with bruxism before and after low level laser applied to acupoints: study protocol for a randomised controlled trial.

PubMed

Salgueiro, Mônica da Consolação Canuto; Bortoletto, Carolina Carvalho; Horliana, Anna Carolina RattoTempestini; Mota, Ana Carolina Costa; Motta, Lara Jansiski; Motta, Pamella de Barros; MesquitaFerrari, Raquel Agnelli; Fernandes, Kristianne Porta Santos; Bussadori, Sandra Kalil

2017-08-08

Bruxism is a repetitive activity that causes tooth wear, audible sounds, and discomfort. Preventive measures have been studied for conditions that can exert a negative influence on physiological development in children. Low-level laser therapy administered over acupoints is an effective, painless, low-cost treatment option that has achieved good results. Thus, the aim of the proposed study is to evaluate changes in muscle activity, bite force and salivary cortisol in children with bruxism after the application of low-level laser to accupoints. The children will be randomly allocated to four groups of 19 individuals: G1 - low-level laser; G2 - occlusal splint; G3 - placebo laser; and G4 - control (without bruxism). The BTS TMJOINT electromyography will be used to determine muscle activity and a digital gnathodynamometer will be used to measure bite force. Salivary cortisol will be analysed at baseline as well as one and six months after treatment. Two-way ANOVA will be employed and complemented by Tukey's test. Bruxism is a repetitive activity of the masticatory muscles that can have negative consequences if not treated, such as tooth wear, noises, discomfort and anxiety. Thus, control and treatment measures should be taken. Although low-level laser therapy over acupoints has been indicated for children, the effects of this treatment modality have not yet been studied. NCT02757261 on 8 April 2016. This study protocol received a grant from the Brazilian fostering agency São Paulo Research Foundation (FAPESP: #2015/24731-0).

A model for neurite growth and neuronal morphogenesis.

PubMed

Li, G H; Qin, C D

1996-02-01

A model is presented for tensile regulation of neuritic growth. It is proposed that the neurite tension can be determined by Hooke's law and determines the growth rate of neurites. The growth of a neurite is defined as the change in its unstretched length. Neuritic growth rate is assumed to increase in proportion to tension magnitude over a certain threshold [Dennerll et al., J. Cell Biol. 107: 665-674 (1988)]. The movement of branch nodes also contributes to the neuronal morphogenesis. It is supposed that the rate of a branch-node displacement is in proportion to the resultant neuritic tension exerted on this node. To deal with the growth-cone movement, it is further supposed that the environment exerts a traction force on the growth cone and the rate of growth-cone displacement is determined by the vector sum of the neuritic tension and the traction force. A group of differential equations are used to describe the model. The key point of the model is that the traction force and the neuritic tension are in opposition to generate a temporal contrast-enhancing mechanism. Results of a simulation study suggest that the model can explain some phenomena related to neuronal morphogenesis.

The effectiveness of fish oil supplementation in asthmatic rats is limited by an inefficient action on ASM function.

PubMed

Miranda, D T S Z; Zanatta, A L; Dias, B C L; Fogaça, R T H; Maurer, J B B; Donatti, L; Calder, P C; Nishiyama, A

2013-09-01

Episodes of acute exacerbation are the major clinical feature of asthma and therefore represent an important focus for developing novel therapies for this disease. There are many reports that the n-3 fatty acids found in fish oil exert anti-inflammatory effects, but there are few studies of the action of fish oil on airway smooth muscle (ASM) function. In the present investigation, we evaluated the effect of fish oil supplementation on smooth muscle force of contraction in ovalbumin-induced asthmatic Wistar rats, and its consequences on static lung compliance, mucus production, leukocyte chemotaxis and production of proinflammatory cytokines. Fish oil supplementation suppressed the infiltration of inflammatory cells into the lung in asthmatic animals (2.04 ± 0.19 × 10(6) cells vs. 3.33 ± 0.43 × 10(6) cells in the control asthmatic group; P < 0.05). Static lung compliance increased with fish oil supplementation in asthmatic rats (0.640 ± 0.053 mL/cm H2O vs. 0.399 ± 0.043 mL/cm H2O; P < 0.05). However, fish oil did not prevent asthma-associated lung eosinophilia and did not affect the concentrations of tumor necrosis factor-α and interleukin-1β in lung tissue or the proportion of the airways obliterated with mucus. Fish oil had no effect on the force of contraction in asthmatic rats in response to acetylcholine (3.026 ± 0.274 mN vs. 2.813 ± 0.364 mN in the control asthmatic group). In conclusion, although fish oil exerts some benefits in this model of asthma, its effectiveness appears to be limited by an inefficient action on airway smooth muscle function.

Gravitational forces and moments on spacecraft

NASA Technical Reports Server (NTRS)

Kane, T. R.; Likins, P. W.

1975-01-01

The solution of problems of attitude dynamics of spacecraft and the influence of gravitational forces and moments is examined. Arguments are presented based on Newton's law of gravitation, and employing the methods of Newtonian (vectorial) mechanics, with minimal recourse to the classical concepts of potential theory. The necessary ideas were developed and relationships were established to permit the representation of gravitational forces and moments exerted on bodies in space by other bodies, both in terms involving the mass distribution properties of the bodies, and in terms of vector operations on those scalar functions classically described as gravitational potential functions.

Compartmentalized storage tank for electrochemical cell system

NASA Technical Reports Server (NTRS)

Piecuch, Benjamin Michael (Inventor); Dalton, Luke Thomas (Inventor)

2010-01-01

A compartmentalized storage tank is disclosed. The compartmentalized storage tank includes a housing, a first fluid storage section disposed within the housing, a second fluid storage section disposed within the housing, the first and second fluid storage sections being separated by a movable divider, and a constant force spring. The constant force spring is disposed between the housing and the movable divider to exert a constant force on the movable divider to cause a pressure P1 in the first fluid storage section to be greater than a pressure P2 in the second fluid storage section, thereby defining a pressure differential.

Measurement of the Forces Acting on Gliders in Towed Flight

NASA Technical Reports Server (NTRS)

Klenperer, W B

1940-01-01

The magnitude, the direction, and the fluctuations of tow forces exerted upon gliders by towing them aloft behind an automobile were measured under a variety of conditions covering a range from gentle to severe types of operation. For these tests, the glider towing force did not exceed 1.6 of the gross weight of the glider. V-G records obtained during the towed-flight period as well as during the subsequent return glide to earth showed accelerations in the range from 3 to -1 g. The results of preliminary airplane tow tests are also presented.

Implications of the Babinet Principle for Casimir interactions

NASA Astrophysics Data System (ADS)

Maghrebi, Mohammad F.; Jaffe, Robert L.; Abravanel, Ronen

2011-09-01

We formulate the Babinet Principle (BP) as a relation between scattering amplitudes and combine it with multiple scattering techniques to derive new properties of electromagnetic Casimir forces. We show that the Casimir force exerted by a planar conductor or dielectric on a self-complementary perforated planar mirror is approximately half that on a uniform mirror independent of the distance between them. Also, the BP suggests that Casimir edge effects are generically anomalously small. Furthermore, the BP can be used to relate any planar object to its complementary geometry, a relation we use to estimate Casimir forces between two screens with apertures.

Counterrotating-Shoulder Mechanism for Friction Stir Welding

NASA Technical Reports Server (NTRS)

Nunes, Arthur C., Jr.

2007-01-01

A counterrotating-shoulder mechanism has been proposed as an alternative to the mechanism and fixtures used in conventional friction stir welding. The mechanism would internally react most or all of the forces and torques exerted on the workpiece, making it unnecessary to react the forces and torques through massive external fixtures. In conventional friction stir welding, a rotating pin tool is inserted into, and moved along, a weld seam. As the pin tool moves, it stirs together material from the opposite sides of the seam to form the weld. A large axial plunge force must be exerted upon the workpiece through and by the pin tool and a shoulder attached above the pin tool in order to maintain the pressure necessary for the process. The workpiece is secured on top of an anvil, which supports the workpiece against the axial plunge force and against the torque exerted by the pin tool and shoulder. The anvil and associated fixtures must be made heavy (and, therefore, are expensive) to keep the workpiece stationary. In addition, workpiece geometries must be limited to those that can be accommodated by the fixtures. The predecessor of the proposed counterrotating-shoulder mechanism is a second-generation, self-reacting tool, resembling a bobbin, that makes it possible to dispense with the heavy anvil. This tool consists essentially of a rotating pin tool with opposing shoulders. Although the opposing shoulders maintain the necessary pressure without need to externally apply or react a large plunge force, the torque exerted on the workpiece remains unreacted in the absence of a substantial external fixture. Depending on the RPM and the thickness of the workpiece, the torque can be large. The proposed mechanism (see figure) would include a spindle attached to a pin tool with a lower shoulder. The spindle would be coupled via splines to the upper one of three bevel gears in a differential drive. The middle bevel gear would be the power-input gear and would be coupled to the upper and lower bevel gears. The lower bevel gear would be attached to the upper shoulder and would slide and rotate freely over the spindle. The spindle would be fastened by its threaded upper end to an external submechanism that would exert axial tension on the spindle to load the workpiece in compression between the shoulders. By reducing or eliminating (relative to the use of a self reacting tool) the torque that must be reacted externally, the use of the proposed tool would reduce the tendency toward distortion or slippage of the workpiece. To begin a weld, the spindle would be inserted through a hole in the workpiece or run-on tab at the beginning of the seam and fastened to the loading submechanism. Rotation and axial loading would be increased gradually from zero and, after a time to be determined by trial and error, translation along the weld seam would be increased gradually from zero to a steady weld speed. The weld would be ended by running the mechanism off the workpiece or, if the lower shoulder were detachable, by detaching the lower shoulder from the spindle and pulling the pin tool out.

Air Warfare and Air Base Defense 1914-1973

DTIC Science & Technology

1988-01-01

ground commanders diluted German efforts. Rommel described the prob- lem in organizational terms: " One thing that worked very seriously against us was...exerted severe pressure on the Marines. Japanese attempts at reinforcing their garri - son were constant and could be defeated only by air attacks on the...and in many cases pure chance that favors one side over the other. In response to a request by the Air Force Director of Plans, the Office of Air Force

Implicit theories about willpower predict the activation of a rest goal following self-control exertion.

PubMed

Job, Veronika; Bernecker, Katharina; Miketta, Stefanie; Friese, Malte

2015-10-01

Past research indicates that peoples' implicit theories about the nature of willpower moderate the ego-depletion effect. Only people who believe or were led to believe that willpower is a limited resource (limited-resource theory) showed lower self-control performance after an initial demanding task. As of yet, the underlying processes explaining this moderating effect by theories about willpower remain unknown. Here, we propose that the exertion of self-control activates the goal to preserve and replenish mental resources (rest goal) in people with a limited-resource theory. Five studies tested this hypothesis. In Study 1, individual differences in implicit theories about willpower predicted increased accessibility of a rest goal after self-control exertion. Furthermore, measured (Study 2) and manipulated (Study 3) willpower theories predicted an increased preference for rest-conducive objects. Finally, Studies 4 and 5 provide evidence that theories about willpower predict actual resting behavior: In Study 4, participants who held a limited-resource theory took a longer break following self-control exertion than participants with a nonlimited-resource theory. Longer resting time predicted decreased rest goal accessibility afterward. In Study 5, participants with an induced limited-resource theory sat longer on chairs in an ostensible product-testing task when they had engaged in a task requiring self-control beforehand. This research provides consistent support for a motivational shift toward rest after self-control exertion in people holding a limited-resource theory about willpower. (c) 2015 APA, all rights reserved).

The Composite Strain Index (COSI) and Cumulative Strain Index (CUSI): methodologies for quantifying biomechanical stressors for complex tasks and job rotation using the Revised Strain Index.

PubMed

Garg, Arun; Moore, J Steven; Kapellusch, Jay M

2017-08-01

The Composite Strain Index (COSI) quantifies biomechanical stressors for complex tasks consisting of exertions at different force levels and/or with different exertion times. The Cumulative Strain Index (CUSI) further integrates biomechanical stressors from different tasks to quantify exposure for the entire work shift. The paper provides methodologies to compute COSI and CUSI along with examples. Complex task simulation produced 169,214 distinct tasks. Use of average, time-weighted average (TWA) and peak force and COSI classified 66.9, 28.2, 100 and 38.9% of tasks as hazardous, respectively. For job rotation the simulation produced 10,920 distinct jobs. TWA COSI, peak task COSI and CUSI classified 36.5, 78.1 and 66.6% jobs as hazardous, respectively. The results suggest that the TWA approach systematically underestimates the biomechanical stressors and peak approach overestimates biomechanical stressors, both at the task and job level. It is believed that the COSI and CUSI partially address these underestimations and overestimations of biomechanical stressors. Practitioner Summary: COSI quantifies exposure when applied hand force and/or duration of that force changes during a task cycle. CUSI integrates physical exposures from job rotation. These should be valuable tools for designing and analysing tasks and job rotation to determine risk of musculoskeletal injuries.

Visual force feedback in laparoscopic training.

PubMed

Horeman, Tim; Rodrigues, Sharon P; van den Dobbelsteen, John J; Jansen, Frank-Willem; Dankelman, Jenny

2012-01-01

To improve endoscopic surgical skills, an increasing number of surgical residents practice on box or virtual reality (VR) trainers. Current training is focused mainly on hand-eye coordination. Training methods that focus on applying the right amount of force are not yet available. The aim of this project is to develop a low-cost training system that measures the interaction force between tissue and instruments and displays a visual representation of the applied forces inside the camera image. This visual representation continuously informs the subject about the magnitude and the direction of applied forces. To show the potential of the developed training system, a pilot study was conducted in which six novices performed a needle-driving task in a box trainer with visual feedback of the force, and six novices performed the same task without visual feedback of the force. All subjects performed the training task five times and were subsequently tested in a post-test without visual feedback. The subjects who received visual feedback during training exerted on average 1.3 N (STD 0.6 N) to drive the needle through the tissue during the post-test. This value was considerably higher for the group that received no feedback (2.6 N, STD 0.9 N). The maximum interaction force during the post-test was noticeably lower for the feedback group (4.1 N, STD 1.1 N) compared with that of the control group (8.0 N, STD 3.3 N). The force-sensing training system provides us with the unique possibility to objectively assess tissue-handling skills in a laboratory setting. The real-time visualization of applied forces during training may facilitate acquisition of tissue-handling skills in complex laparoscopic tasks and could stimulate proficiency gain curves of trainees. However, larger randomized trials that also include other tasks are necessary to determine whether training with visual feedback about forces reduces the interaction force during laparoscopic surgery.

Dynamics of levitated objects in acoustic vortex fields.

PubMed

Hong, Z Y; Yin, J F; Zhai, W; Yan, N; Wang, W L; Zhang, J; Drinkwater, Bruce W

2017-08-02

Acoustic levitation in gaseous media provides a tool to process solid and liquid materials without the presence of surfaces such as container walls and hence has been used widely in chemical analysis, high-temperature processing, drop dynamics and bioreactors. To date high-density objects can only be acoustically levitated in simple standing-wave fields. Here we demonstrate the ability of a small number of peripherally placed sources to generate acoustic vortex fields and stably levitate a wide range of liquid and solid objects. The forces exerted by these acoustic vortex fields on a levitated water droplet are observed to cause a controllable deformation of the droplet and/or oscillation along the vortex axis. Orbital angular momentum transfer is also shown to rotate a levitated object rapidly and the rate of rotation can be controlled by the source amplitude. We expect this research can increase the diversity of acoustic levitation and expand the application of acoustic vortices.

Selective attention to visual compound stimuli in squirrel monkeys (Saimiri sciureus).

PubMed

Ploog, Bertram O

2011-05-01

Five squirrel monkeys served under a simultaneous discrimination paradigm with visual compound stimuli that allowed measurement of excitatory and inhibitory control exerted by individual stimulus components (form and luminance/"color"), which could not be presented in isolation (i.e., form could not be presented without color). After performance exceeded a criterion of 75% correct during training, unreinforced test trials with stimuli comprising recombined training stimulus components were interspersed while the overall reinforcement rate remained constant for training and testing. The training-testing series was then repeated with reversed reinforcement contingencies. The findings were that color acquired greater excitatory control than form under the original condition, that no such difference was found for the reversal condition or for inhibitory control under either condition, and that overall inhibitory control was less pronounced than excitatory control. The remarkably accurate performance throughout suggested that a forced 4-s delay between the stimulus presentation and the opportunity to respond was effective in reducing "impulsive" responding, which has implications for suppressing impulsive responding in children with autism and with attention deficit disorder. Copyright © 2011 Elsevier B.V. All rights reserved.

The Role of Motivation, Glucose and Self-Control in the Antisaccade Task

PubMed Central

Kelly, Claire L.; Sünram-Lea, Sandra I.; Crawford, Trevor J.

2015-01-01

Research shows that self-control is resource limited and there is a gradual weakening in consecutive self-control task performance akin to muscle fatigue. A body of evidence suggests that the resource is glucose and consuming glucose reduces this effect. This study examined the effect of glucose on performance in the antisaccade task - which requires self-control through generating a voluntary eye movement away from a target - following self-control exertion in the Stroop task. The effects of motivation and individual differences in self-control were also explored. In a double-blind design, 67 young healthy adults received a 25g glucose or inert placebo drink. Glucose did not enhance antisaccade performance following self-control exertion in the Stroop task. Motivation however, predicted performance on the antisaccade task; more specifically high motivation ameliorated performance decrements observed after initial self-control exertion. In addition, individuals with high levels of self-control performed better on certain aspects of the antisaccade task after administration of a glucose drink. The results of this study suggest that the antisaccade task might be a powerful paradigm, which could be used as a more objective measure of self-control. Moreover, the results indicate that level of motivation and individual differences in self-control should be taken into account when investigating deficiencies in self-control following prior exertion. PMID:25826334

Depletion forces on circular and elliptical obstacles induced by active matter

NASA Astrophysics Data System (ADS)

Leite, L. R.; Lucena, D.; Potiguar, F. Q.; Ferreira, W. P.

2016-12-01

Depletion forces exerted by self-propelled particles on circular and elliptical passive objects are studied using numerical simulations. We show that a bath of active particles can induce repulsive and attractive forces which are sensitive to the shape and orientation of the passive objects (either horizontal or vertical ellipses). The resultant force on the passive objects due to the active particles is studied as a function of the shape and orientation of the passive objects, magnitude of the angular noise, and distance between the passive objects. By increasing the distance between obstacles the magnitude of the repulsive depletion force increases, as long as such a distance is less than one active particle diameter. For longer distances, the magnitude of the force always decreases with increasing distance. We also found that attractive forces may arise for vertical ellipses at high enough area fraction.

Precise measurements of droplet-droplet contact forces in quasi-2D emulsions

NASA Astrophysics Data System (ADS)

Lowensohn, Janna; Orellana, Carlos; Weeks, Eric

2015-03-01

We use microscopy to visualize a quasi-2D oil-in-water emulsion confined between two parallel slides. We then use the droplet shapes to infer the forces they exert on each other. To calibrate our force law, we set up an emulsion in a tilted sample chamber so that the droplets feel a known buoyant force. By correlating radius of the droplet and length of contacts with the buoyant forces, we validate our empirical force law. We improve upon prior work in our lab by using a high-resolution camera to image each droplet multiple times, thus providing sub-pixel resolution and reducing the noise. Our new technique identifies contact forces with only a 1% uncertainty, five times better than prior work. We demonstrate the utility of our technique by examining the normal modes of the droplet contact network in our samples.

Depletion forces on circular and elliptical obstacles induced by active matter.

PubMed

Leite, L R; Lucena, D; Potiguar, F Q; Ferreira, W P

2016-12-01

Depletion forces exerted by self-propelled particles on circular and elliptical passive objects are studied using numerical simulations. We show that a bath of active particles can induce repulsive and attractive forces which are sensitive to the shape and orientation of the passive objects (either horizontal or vertical ellipses). The resultant force on the passive objects due to the active particles is studied as a function of the shape and orientation of the passive objects, magnitude of the angular noise, and distance between the passive objects. By increasing the distance between obstacles the magnitude of the repulsive depletion force increases, as long as such a distance is less than one active particle diameter. For longer distances, the magnitude of the force always decreases with increasing distance. We also found that attractive forces may arise for vertical ellipses at high enough area fraction.

A semi-flexible model prediction for the polymerization force exerted by a living F-actin filament on a fixed wall

NASA Astrophysics Data System (ADS)

Pierleoni, Carlo; Ciccotti, Giovanni; Ryckaert, Jean-Paul

2015-10-01

We consider a single living semi-flexible filament with persistence length ℓp in chemical equilibrium with a solution of free monomers at fixed monomer chemical potential μ1 and fixed temperature T. While one end of the filament is chemically active with single monomer (de)polymerization steps, the other end is grafted normally to a rigid wall to mimic a rigid network from which the filament under consideration emerges. A second rigid wall, parallel to the grafting wall, is fixed at distance L < < ℓp from the filament seed. In supercritical conditions where monomer density ρ1 is higher than the critical density ρ1c, the filament tends to polymerize and impinges onto the second surface which, in suitable conditions (non-escaping filament regime), stops the filament growth. We first establish the grand-potential Ω(μ1, T, L) of this system treated as an ideal reactive mixture, and derive some general properties, in particular the filament size distribution and the force exerted by the living filament on the obstacle wall. We apply this formalism to the semi-flexible, living, discrete Wormlike chain model with step size d and persistence length ℓp, hitting a hard wall. Explicit properties require the computation of the mean force f ¯ i ( L ) exerted by the wall at L and associated potential f ¯ i ( L ) = - d W i ( L ) / d L on a filament of fixed size i. By original Monte-Carlo calculations for few filament lengths in a wide range of compression, we justify the use of the weak bending universal expressions of Gholami et al. [Phys. Rev. E 74, 041803 (2006)] over the whole non-escaping filament regime. For a filament of size i with contour length Lc = (i - 1) d, this universal form is rapidly growing from zero (non-compression state) to the buckling value f b ( L c , ℓ p ) = /π 2 k B T ℓ p 4 Lc 2 over a compression range much narrower than the size d of a monomer. Employing this universal form for living filaments, we find that the average force exerted by a living filament on a wall at distance L is in practice L independent and very close to the value of the stalling force Fs H = ( k B T / d ) ln ( ρ ˆ 1 ) predicted by Hill, this expression being strictly valid in the rigid filament limit. The average filament force results from the product of the cumulative size fraction x = x ( L , ℓ p , ρ ˆ 1 ) , where the filament is in contact with the wall, times the buckling force on a filament of size Lc ≈ L, namely, Fs H = x f b ( L ; ℓ p ) . The observed L independence of Fs H implies that x ∝ L-2 for given ( ℓ p , ρ ˆ 1 ) and x ∝ ln ρ ˆ 1 for given (ℓp, L). At fixed ( L , ρ ˆ 1 ), one also has x ∝ ℓp - 1 which indicates that the rigid filament limit ℓp → ∞ is a singular limit in which an infinite force has zero weight. Finally, we derive the physically relevant threshold for filament escaping in the case of actin filaments.

An Investigation of Land-Atmosphere Coupling from Local to Regional Scales

NASA Astrophysics Data System (ADS)

Brunsell, N. A.; Van Vleck, E.; Rahn, D. A.

2017-12-01

The exchanges of mass and energy between the surface and atmosphere have been shown to depend upon both local and regional climatic influences. However, the degree of control exerted by the land surface on the coupling metrics is not well understood. In particular, we lack an understanding of the relationship between the local microclimate of a site and the regional forces responsible for land-atmosphere coupling. To address this, we investigate a series of metrics calculated from eddy covariance data and ceilometer data, land surface modeling and remotely sensed observations in the central United States to diagnose these interactions and predict the change from one coupling regime (e.g. wet/dry coupling) to another state. The stability of the coupling is quantified using a Lyapunov exponent based methodology. Through the use of a wavelet information theoretic approach, we isolate the roles local energy partitioning, as well as the temperature and moisture gradients on controlling and changing the coupling regime. Taking a multi-scale observational approach, we first examine the relationship at the tower scale. Using land surface models, we quantify to what extent current models are capable of properly diagnosing the dynamics of the coupling regime. In particular, we focus on the role of the surface moisture and vegetation to initiate and maintain precipitation feedbacks. We extend this analysis to the regional scale by utilizing reanalysis and remotely sensed observations. Thus, we are able to quantify the changes in observed coupling patterns with linkages to local interactions to address the question of the local control that the surface exerts over the maintenance of land-atmosphere coupling.

A submerged membrane bioreactor with pendulum type oscillation (PTO) for oily wastewater treatment: membrane permeability and fouling control.

PubMed

Qin, Lei; Fan, Zheng; Xu, Lusheng; Zhang, Guoliang; Wang, Guanghui; Wu, Dexin; Long, Xuwei; Meng, Qin

2015-05-01

In this study, a novel submerged membrane bioreactor (SMBR) with pendulum type oscillation (PTO) hollow fiber membrane modules was developed to treat oily wastewater and control the problem of membrane fouling. To assess the potential of PTO membrane modules, the effect of oscillation orientation and frequency on membrane permeability was investigated in detail. The forces exerted on sludge flocs in the oscillating SMBR were analyzed to evaluate the impact of membrane oscillating on the cake layer resistance reduction. Results showed that the optimized PTO SMBR system exhibited 11 times higher membrane permeability and better fouling controllability than the conventional MBR system. By hydrodynamic analysis, it was found that the cooperative effect of bubble-induced turbulence and membrane oscillation in PTO SMBR system generated strong shear stress at liquid-membrane interface in vertical and horizontal direction and effectively hindered the particles from depositing on membrane surface. Copyright © 2015 Elsevier Ltd. All rights reserved.

On-demand Droplet Manipulation via Triboelectrification

NASA Astrophysics Data System (ADS)

Wang, Wei; Vahabi, Hamed; Cackovic, Matthew; Jiang, Rui; Kota, Arun

2017-11-01

Controlled manipulation of liquid droplets has attracted tremendous interest across different scientific fields over the past two decades. To date, a variety of external stimuli-mediated methods such as magnetic field, electric field, and light have been developed for manipulating droplets on surfaces. However, these methods usually have drawbacks such as complex fabrication of manipulation platform, low droplet motility, expensive actuation system and lack of precise control. In this work, we demonstrate the controlled manipulation of liquid droplet with both high (e.g., water) and low (e.g., n-hexadecane) dielectric strengths on a smooth, slippery surface via triboelectric effect. Our highly simple, facile and portable methodology enables on-demand, precise manipulation of droplets using solely the electrostatic attraction or repulsion force, which is exerted on the droplet by a simple charged actuator (e.g., Teflon film). We envision that our triboelectric effect enabled droplet manipulation methodology will open a new avenue for droplet based lab-on-a-chip systems, energy harvesting devices and biomedical applications.

Process Analytical Technology for High Shear Wet Granulation: Wet Mass Consistency Reported by In-Line Drag Flow Force Sensor Is Consistent With Powder Rheology Measured by At-Line FT4 Powder Rheometer.

PubMed

Narang, Ajit S; Sheverev, Valery; Freeman, Tim; Both, Douglas; Stepaniuk, Vadim; Delancy, Michael; Millington-Smith, Doug; Macias, Kevin; Subramanian, Ganeshkumar

2016-01-01

Drag flow force (DFF) sensor that measures the force exerted by wet mass in a granulator on a thin cylindrical probe was shown as a promising process analytical technology for real-time in-line high-resolution monitoring of wet mass consistency during high shear wet granulation. Our previous studies indicated that this process analytical technology tool could be correlated to granulation end point established independently through drug product critical quality attributes. In this study, the measurements of flow force by a DFF sensor, taken during wet granulation of 3 placebo formulations with different binder content, are compared with concurrent at line FT4 Powder Rheometer characterization of wet granules collected at different time points of the processing. The wet mass consistency measured by the DFF sensor correlated well with the granulation's resistance to flow and interparticulate interactions as measured by FT4 Powder Rheometer. This indicated that the force pulse magnitude measured by the DFF sensor was indicative of fundamental material properties (e.g., shear viscosity and granule size/density), as they were changing during the granulation process. These studies indicate that DFF sensor can be a valuable tool for wet granulation formulation and process development and scale up, as well as for routine monitoring and control during manufacturing. Copyright © 2016. Published by Elsevier Inc.

Instrument for spatially resolved simultaneous measurements of forces and currents in particle beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Spethmann, A., E-mail: spethmann@physik.uni-kiel.de; Trottenberg, T., E-mail: trottenberg@physik.uni-kiel.de; Kersten, H., E-mail: kersten@physik.uni-kiel.de

The article presents a device for spatially resolved and simultaneous measurements of forces and currents in particle beams, especially in beams composed of ions and neutral atoms. The forces are exerted by the impinging beam particles on a plane circular conductive target plate of 20 mm diameter mounted on a pendulum with electromagnetic force compensation. The force measurement in the micronewton range is achieved by electromagnetic compensation by means of static Helmholtz coils and permanent magnets attached to the pendulum. Exemplary measurements are performed in the 1.2 keV beam of a broad beam ion source. The simultaneous measurements of forcesmore » and currents onto the same target are compared with each other and with Faraday cup measurements.« less

Measuring the multi-scale integration of mechanical forces during morphogenesis.

PubMed

Blanchard, Guy B; Adams, Richard J

2011-10-01

The elaborate changes in morphology of an organism during development are the result of mechanical contributions that are a mixture of those generated locally and those that influence from a distance. We would like to know how chemical and mechanical information is transmitted and transduced, how work is done to achieve robust morphogenesis and why it sometimes fails. We introduce a scheme for separating the influence of two classes of forces. Active intrinsic forces integrate up levels of scale to shape tissues. Counter-currently, extrinsic forces exert influence from higher levels downwards and feed back directly and indirectly upon the intrinsic behaviours. We identify the measurable signatures of different kinds of forces and identify the frontiers where work is most needed. Copyright © 2011 Elsevier Ltd. All rights reserved.

Stirling engine power control and motion conversion mechanism

DOEpatents

Marks, David T.

1983-01-01

A motion conversion device for converting between the reciprocating motion of the pistons in a Stirling engine and the rotating motion of its output shaft, and for changing the stroke and phase of the pistons, includes a lever pivoted at one end and having a cam follower at the other end. The piston rod engages the lever intermediate its ends and the cam follower engages a cam keyed to the output shaft. The lever pivot can be moved to change the length of the moment arm defined between the cam follower and the piston rod the change the piston stroke and force exerted on the cam, and the levers can be moved in opposite directions to change the phase between pistons.

Nuclear reactor control apparatus

DOEpatents

Sridhar, Bettadapur N.

1983-10-25

Nuclear reactor safety rod release apparatus comprises a ring which carries detents normally positioned in an annular recess in outer side of the rod, the ring being held against the lower end of a drive shaft by magnetic force exerted by a solenoid carried by the drive shaft. When the solenoid is de-energized, the detent-carrying ring drops until the detents contact a cam surface associated with the lower end of the drive shaft, at which point the detents are cammed out of the recess in the safety rod to release the rod from the drive shaft. In preferred embodiments of the invention, an additional latch is provided to release a lower portion of a safety rod under conditions that may interfere with movement of the entire rod.

Pooling job physical exposure data from multiple independent studies in a consortium study of carpal tunnel syndrome

PubMed Central

Kapellusch, Jay M.; Garg, Arun; Bao, Stephen S.; Silverstein, Barbara A.; Burt, Susan E.; Dale, Ann Marie; Evanoff, Bradley A.; Gerr, Frederic E.; Harris-Adamson, Carisa; Hegmann, Kurt T.; Merlino, Linda A.; Rempel, David M.

2015-01-01

Pooling data from different epidemiological studies of musculoskeletal disorders (MSDs) is necessary to improve statistical power and to more precisely quantify exposure–response relationships for MSDs. The pooling process is difficult and time-consuming, and small methodological differences could lead to different exposure–response relationships. A subcommittee of a six-study research consortium studying carpal tunnel syndrome: (i) visited each study site, (ii) documented methods used to collect physical exposure data and (iii) determined compatibility of exposure variables across studies. Certain measures of force, frequency of exertion and duty cycle were collected by all studies and were largely compatible. A portion of studies had detailed data to investigate simultaneous combinations of force, frequency and duration of exertions. Limited compatibility was found for hand/wrist posture. Only two studies could calculate compatible Strain Index scores, but Threshold Limit Value for Hand Activity Level could be determined for all studies. Challenges of pooling data, resources required and recommendations for future researchers are discussed. PMID:23697792

Forced ethanol ingestion by Wistar rats from a juvenile age increased voluntary alcohol consumption in adulthood, with the involvement of orexin-A.

PubMed

Mendoza-Ruiz, Luis-Gabriel; Vázquez-León, Priscila; Martínez-Mota, Lucía; Juan, Eduardo Ramírez San; Miranda-Páez, Abraham

2018-08-01

Human adolescents who drink alcohol are more likely to become alcoholics in adulthood. Alcohol administration (intraperitoneally) or drinking (in a 2-bottle free choice paradigm) during the juvenile/adolescent age of rats promotes voluntary alcohol consumption in adulthood. On the other hand, there is growing evidence that the orexinergic system plays a role in several rewarded behaviors, including alcohol ingestion. Since it is unknown what effect is exerted in adulthood by forced oral ethanol intake and/or administration of orexin-A (OX-A) in juvenile rats, the present study aimed to evaluate this question. A group of male Wistar rats was forced to drink ethanol (10% v/v) as the only liquid in the diet from weaning (postnatal day 21) to postnatal day 67 (46 days), followed by a forced withdrawal period. An age-matched group was raised drinking tap water (control). OX-A or its vehicle was microinjected intracerebroventricularly (i.c.v.) (1 nmol/0.6 μL) to explore its effect as well. Locomotor activity and voluntary ethanol consumption were later assessed in all groups. The rats forced to consume ethanol early in life showed an elevated level of ambulation and alcohol ingestion in adulthood. A single injection of OX-A increased locomotor activity and acute ethanol intake in rats with or without prior exposure to alcohol at the juvenile stage. In conclusion, forced ethanol consumption in juvenile rats led to increased voluntary alcohol drinking behavior during adulthood, an effect likely facilitated by OX-A. Copyright © 2018 Elsevier Inc. All rights reserved.

Measuring collective transport by defined numbers of processive and nonprocessive kinesin motors.

PubMed

Furuta, Ken'ya; Furuta, Akane; Toyoshima, Yoko Y; Amino, Misako; Oiwa, Kazuhiro; Kojima, Hiroaki

2013-01-08

Intracellular transport is thought to be achieved by teams of motor proteins bound to a cargo. However, the coordination within a team remains poorly understood as a result of the experimental difficulty in controlling the number and composition of motors. Here, we developed an experimental system that links together defined numbers of motors with defined spacing on a DNA scaffold. By using this system, we linked multiple molecules of two different types of kinesin motors, processive kinesin-1 or nonprocessive Ncd (kinesin-14), in vitro. Both types of kinesins markedly increased their processivities with motor number. Remarkably, despite the poor processivity of individual Ncd motors, the coupling of two Ncd motors enables processive movement for more than 1 μm along microtubules (MTs). This improvement was further enhanced with decreasing spacing between motors. Force measurements revealed that the force generated by groups of Ncd is additive when two to four Ncd motors work together, which is much larger than that generated by single motors. By contrast, the force of multiple kinesin-1s depends only weakly on motor number. Numerical simulations and single-molecule unbinding measurements suggest that this additive nature of the force exerted by Ncd relies on fast MT binding kinetics and the large drag force of individual Ncd motors. These features would enable small groups of Ncd motors to crosslink MTs while rapidly modulating their force by forming clusters. Thus, our experimental system may provide a platform to study the collective behavior of motor proteins from the bottom up.

High-speed adaptive contact-mode atomic force microscopy imaging with near-minimum-force

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ren, Juan; Zou, Qingze, E-mail: qzzou@rci.rutgers.edu

In this paper, an adaptive contact-mode imaging approach is proposed to replace the traditional contact-mode imaging by addressing the major concerns in both the speed and the force exerted to the sample. The speed of the traditional contact-mode imaging is largely limited by the need to maintain precision tracking of the sample topography over the entire imaged sample surface, while large image distortion and excessive probe-sample interaction force occur during high-speed imaging. In this work, first, the image distortion caused by the topography tracking error is accounted for in the topography quantification. Second, the quantified sample topography is utilized inmore » a gradient-based optimization method to adjust the cantilever deflection set-point for each scanline closely around the minimal level needed for maintaining stable probe-sample contact, and a data-driven iterative feedforward control that utilizes a prediction of the next-line topography is integrated to the topography feeedback loop to enhance the sample topography tracking. The proposed approach is demonstrated and evaluated through imaging a calibration sample of square pitches at both high speeds (e.g., scan rate of 75 Hz and 130 Hz) and large sizes (e.g., scan size of 30 μm and 80 μm). The experimental results show that compared to the traditional constant-force contact-mode imaging, the imaging speed can be increased by over 30 folds (with the scanning speed at 13 mm/s), and the probe-sample interaction force can be reduced by more than 15% while maintaining the same image quality.« less

Distinct neural control of intrinsic and extrinsic muscles of the hand during single finger pressing.

PubMed

Dupan, Sigrid S G; Stegeman, Dick F; Maas, Huub

2018-06-01

Single finger force tasks lead to unintended activation of the non-instructed fingers, commonly referred to as enslaving. Both neural and mechanical factors have been associated with this absence of finger individuality. This study investigates the amplitude modulation of both intrinsic and extrinsic finger muscles during single finger isometric force tasks. Twelve participants performed single finger flexion presses at 20% of maximum voluntary contraction, while simultaneously the electromyographic activity of several intrinsic and extrinsic muscles associated with all four fingers was recorded using 8 electrode pairs in the hand and two 30-electrode grids on the lower arm. The forces exerted by each of the fingers, in both flexion and extension direction, were recorded with individual force sensors. This study shows distinct activation patterns in intrinsic and extrinsic hand muscles. Intrinsic muscles exhibited individuation, where the agonistic and antagonistic muscles associated with the instructed fingers showed the highest activation. This activation in both agonistic and antagonistic muscles appears to facilitate finger stabilisation during the isometric force task. Extrinsic muscles show an activation independent from instructed finger in both agonistic and antagonistic muscles, which appears to be associated with stabilisation of the wrist, with an additional finger-dependent modulation only present in the agonistic extrinsic muscles. These results indicate distinct muscle patterns in intrinsic and extrinsic hand muscles during single finger isometric force pressing. We conclude that the finger specific activation of intrinsic muscles is not sufficient to fully counteract enslaving caused by the broad activation of the extrinsic muscles. Copyright © 2018 Elsevier B.V. All rights reserved.

High-speed adaptive contact-mode atomic force microscopy imaging with near-minimum-force.

PubMed

Ren, Juan; Zou, Qingze

2014-07-01

In this paper, an adaptive contact-mode imaging approach is proposed to replace the traditional contact-mode imaging by addressing the major concerns in both the speed and the force exerted to the sample. The speed of the traditional contact-mode imaging is largely limited by the need to maintain precision tracking of the sample topography over the entire imaged sample surface, while large image distortion and excessive probe-sample interaction force occur during high-speed imaging. In this work, first, the image distortion caused by the topography tracking error is accounted for in the topography quantification. Second, the quantified sample topography is utilized in a gradient-based optimization method to adjust the cantilever deflection set-point for each scanline closely around the minimal level needed for maintaining stable probe-sample contact, and a data-driven iterative feedforward control that utilizes a prediction of the next-line topography is integrated to the topography feeedback loop to enhance the sample topography tracking. The proposed approach is demonstrated and evaluated through imaging a calibration sample of square pitches at both high speeds (e.g., scan rate of 75 Hz and 130 Hz) and large sizes (e.g., scan size of 30 μm and 80 μm). The experimental results show that compared to the traditional constant-force contact-mode imaging, the imaging speed can be increased by over 30 folds (with the scanning speed at 13 mm/s), and the probe-sample interaction force can be reduced by more than 15% while maintaining the same image quality.

Lactate and pH evaluation in exhausted humans with prolonged TASER X26 exposure or continued exertion.

PubMed

Ho, Jeffrey D; Dawes, Donald M; Cole, Jon B; Hottinger, Julie C; Overton, Kenneth G; Miner, James R

2009-09-10

Safety concerns about TASER Conducted Electrical Weapon (CEW) use and media reports of deaths after exposure have been expressed. CEWs are sometimes used on exhausted subjects to end resistance. The alternative is often a continued struggle. It is unclear if CEW use is metabolically different than allowing a continued struggle. We sought to determine if CEW exposure on exhausted humans caused worsening acidosis when compared with continued exertion. This was a prospective study of human volunteers recruited during a CEW training course. Volunteers were from several different occupations and represented a wide range of ages and body mass index characteristics. Medical histories, baseline pH and lactate values were obtained. Patients were assigned to one of four groups: 2 control groups consisting of Exertion only and CEW Exposure only, and the 2 experimental groups that were Exertion plus CEW Exposure and Exertion plus additional Exertion. Blood sampling occurred after Exertion and after any CEW exposure. This was repeated every 2-min until 20 min after protocol completion. Descriptive statistics were used to compare the four groups. The experimental groups and the control groups were compared individually at each time point using Wilcoxon rank sum tests. Lactate and pH association was assessed using multiple linear regression. Forty subjects were enrolled. There were no median pH or lactate differences between CEW Exposure groups at baseline, or between Exertion protocol groups immediately after completion. The CEW Exposure only group had higher pH and lower lactate values at all time points after exposure than the Exertion only group. After completing the Exertion protocol, there was no difference in the pH or lactate values between the continued Exertion group and the CEW Exposure group at any time points. Subjects who had CEW Exposure only had higher pH and lower lactate values than subjects who completed the Exertion protocol only. CEW exposure does not appear to worsen acidosis in exhausted subjects any differently than briefly continued exertion.

Simultaneous vibration control and energy harvesting using actor-critic based reinforcement learning

NASA Astrophysics Data System (ADS)

Loong, Cheng Ning; Chang, C. C.; Dimitrakopoulos, Elias G.

2018-03-01

Mitigating excessive vibration of civil engineering structures using various types of devices has been a conspicuous research topic in the past few decades. Some devices, such as electromagnetic transducers, which have a capability of exerting control forces while simultaneously harvesting energy, have been proposed recently. These devices make possible a self-regenerative system that can semi-actively mitigate structural vibration without the need of external energy. Integrating mechanical, electrical components, and control algorithms, these devices open up a new research domain that needs to be addressed. In this study, the feasibility of using an actor-critic based reinforcement learning control algorithm for simultaneous vibration control and energy harvesting for a civil engineering structure is investigated. The actor-critic based reinforcement learning control algorithm is a real-time, model-free adaptive technique that can adjust the controller parameters based on observations and reward signals without knowing the system characteristics. It is suitable for the control of a partially known nonlinear system with uncertain parameters. The feasibility of implementing this algorithm on a building structure equipped with an electromagnetic damper will be investigated in this study. Issues related to the modelling of learning algorithm, initialization and convergence will be presented and discussed.

Electromagnetic panel deployment and retraction using the geomagnetic field in LEO satellite missions

NASA Astrophysics Data System (ADS)

Inamori, Takaya; Sugawara, Yoshiki; Satou, Yasutaka

2015-12-01

Increasingly, spacecraft are installed with large-area structures that are extended and deployed post-launch. These extensible structures have been applied in several missions for power generation, thermal radiation, and solar propulsion. Here, we propose a deployment and retraction method using the electromagnetic force generated when the geomagnetic field interacts with electric current flowing on extensible panels. The panels are installed on a satellite in low Earth orbit. Specifically, electrical wires placed on the extensible panels generate magnetic moments, which interfere with the geomagnetic field. The resulting repulsive and retraction forces enable panel deployment and retraction. In the proposed method, a satellite realizes structural deployment using simple electrical wires. Furthermore, the satellite can achieve not only deployment but also retraction for avoiding damage from space debris and for agile attitude maneuvers. Moreover, because the proposed method realizes quasi-static deployment and the retraction of panels by electromagnetic forces, low impulsive force is exerted on fragile panels. The electrical wires can also be used to detect the panel deployment and retraction and generate a large magnetic moment for attitude control. The proposed method was assessed in numerical simulations based on multibody dynamics. Simulation results shows that a small cubic satellite with a wire current of 25 AT deployed 4 panels (20 cm × 20 cm) in 500 s and retracted 4 panels in 100 s.

Effect of epidural anaesthesia on clinician-applied force during vaginal delivery.

PubMed

Poggi, Sarah H; Allen, Robert H; Patel, Chirag; Deering, Shad H; Pezzullo, John C; Shin, Young; Spong, Catherine Y

2004-09-01

Epidural anesthesia (EA) is used in 80% of vaginal deliveries and is linked to neonatal and maternal trauma. Our objectives were to determine (1) whether EA affected clinician-applied force on the fetus and (2) whether this force influenced perineal trauma. After informed consent, multiparas with term, cephalic, singletons were delivered by 1 physician wearing a sensor-equipped glove to record force exerted on the fetal head. Those with EA were compared with those without for delivery force parameters. Regression analysis was used to identify predictors of vaginal laceration. The force required for delivery was greater in patients with EA (n = 27) than without (n = 5) (P < .01). Clinical parameters, including birth weight (P = .31) were similar between the groups. Clinician force was similar in those with no versus first- versus second-degree laceration (P = .5). Only birth weight was predictive of laceration (P = .02). Epidural use resulted in greater clinician force required for vaginal delivery of the fetus in multiparas, but this force was not associated with perineal trauma.

Use of piezoelectric multicomponent force measuring devices in fluid mechanics

NASA Technical Reports Server (NTRS)

Richter, A.; Stefan, K.

1979-01-01

The characterisitics of piezoelectric multicomponent transducers are discussed, giving attention to the advantages of quartz over other materials. The main advantage of piezoelectric devices in aerodynamic studies is their ability to indicate rapid changes in the values of physical parameters. Problems in the accuracy of measurments by piezoelectric devices can be overcome by suitable design approaches. A practical example is given of how such can be utilized to measure rapid fluctuations of fluid forces exerted on a circular cylinder mounted in a water channel.

Forces Exerted by Waves on a Pipeline at or Near the Ocean Bottom

DTIC Science & Technology

1977-10-01

horizontal anl . vertical range of the force data over the two wave cycles, and an envelope curve was drawn over these points. Examination of these plots as a...0. t.64 .396 14.30 .*If? 7.4% 7.94 7.94 31.29 * 6034 .043 -43.67 o0£a .260 0. 3.80 .986 1-4.8 .6192 1.2d. 9.26 IN 26 20.40 *4563 2.61 25057 3221 .250

The force applied to successfully turn a foetus during reattempts of external cephalic version is substantially reduced when performed under spinal analgesia.

PubMed

Suen, Stephen Sik Hung; Khaw, Kim S; Law, Lai Wa; Sahota, Daljit Singh; Lee, Shara Wee Yee; Lau, Tze Kin; Leung, Tak Yeung

2012-06-01

To compare the forces exerted during external cephalic version (ECV) on the maternal abdomen between ( 1 ) the primary attempts performed without spinal analgesia (SA), which failed and ( 2 ) the subsequent reattempts performed under SA. Patients with an uncomplicated singleton breech-presenting pregnancy suitable for ECV were recruited. During ECV, the operator wore a pair of gloves, which had thin piezo-resistive pressure sensors measuring the contact pressure between the operator's hands and maternal abdomen. For patients who had failed ECV, reattempts by the same operator was made with patients under SA, and the applied force was measured in the same manner. The profile of the exerted forces over time during each attempt was analyzed and denoted by pressure-time integral (PTI: mmHg sec). Pain score was also graded by patients using visual analogue scale. Both PTI and pain score before and after the use of SA were then compared. Overall, eight patients who had a failed ECV without SA underwent a reattempt with SA. All of them had successful version and the median PTI of the successful attempts under SA were lower than that of the previous failed attempts performed without SA (127 386 mmHg sec vs. 298,424 mmHg sec; p = 0.017). All of them also reported a 0 pain score, which was significantly lower than that of before (median 7.5; p = 0.016). SA improves the success rate of ECV as well as reduces the force required for successful version.

Effects of antagonistic and synergistic muscles' co-activation on mechanics of activated spastic semitendinosus in children with cerebral palsy.

PubMed

Ateş, Filiz; Temelli, Yener; Yucesoy, Can A

2018-02-01

Most activities involve co-activation of several muscles and epimuscular myofascial force transmission (EMFT) can affect their mechanics. This can be relevant for spastic muscles of cerebral palsy (CP) patients. Isometric spastic semitendinosus (ST) forces vs. knee angle (KA-F ST ) data were collected intra-operatively to test the following hypotheses: (i) Inter-antagonistic EMFT elevates F ST , (ii) changes the shape of KA-F ST characteristics, (iii) reduces the muscle's joint range of force exertion (Range-F ST ) and (iv) combined inter-antagonistic and synergistic EMFT further changes those effects. 11 limbs of 6 patients with CP (mean (SD) = 7.7 (4.7) years; GMFCS levels = II-IV) were tested in 3 conditions from 120° to full extension: ST activated (I) exclusively, (II) simultaneously with an antagonist, and (III) with added activation of synergists. Condition II increased F ST (e.g., peak force = 87.6 N (30.5 N)) significantly (by 33.6%), but condition III caused no further change. No condition changed the muscle's wide Range-F ST (100.7° (15.9°)) significantly. Therefore, only the first hypothesis was confirmed. Co-activating its antagonist elevates forces of activated spastic ST substantially, but does not change its joint range of force exertion. Added activation of its synergists causes no further effects. Therefore, EMFT effects in CP can be relevant and need to be tested in other knee flexors. Copyright © 2017 Elsevier B.V. All rights reserved.

Electromagnetic attachment mechanism

NASA Technical Reports Server (NTRS)

Monford, Leo G., Jr. (Inventor)

1992-01-01

An electromagnetic attachment mechanism is disclosed for use as an end effector of a remote manipulator system. A pair of electromagnets, each with a U-shaped magnetic core with a pull-in coil and two holding coils, are mounted by a spring suspension system on a base plate of the mechanism housing with end pole pieces adapted to move through openings in the base plate when the attractive force of the electromagnets is exerted on a strike plate of a grapple fixture affixed to a target object. The pole pieces are spaced by an air gap from the strike plate when the mechanism first contacts the grapple fixture. An individual control circuit and power source is provided for the pull-in coil and one holding coil of each electromagnet. A back-up control circuit connected to the two power sources and a third power source is provided for the remaining holding coils. When energized, the pull-in coils overcome the suspension system and air gap and are automatically de-energized when the pole pieces move to grapple and impose a preload force across the grapple interface. A battery backup is a redundant power source for each electromagnet in each individual control circuit and is automatically connected upon failure of the primary source. A centerline mounted camera and video monitor are used in cooperation with a target pattern on the reflective surface of the strike plate to effect targeting and alignment.

Fire-induced albedo change and surface radiative forcing in sub-Saharan Africa savanna ecosystems: Implications for the energy balance

NASA Astrophysics Data System (ADS)

Dintwe, Kebonye; Okin, Gregory S.; Xue, Yongkang

2017-06-01

Surface albedo is a critical parameter that controls surface energy balance. In dryland ecosystems, fires play a significant role in decreasing surface albedo, resulting in positive radiative forcing. Here we investigate the long-term effect of fire on surface albedo. We devised a method to calculate short-, medium-, and long-term effect of fire-induced radiative forcing and their relative effects on energy balance. We used Moderate Resolution Imaging Spectroradiometer (MODIS) data in our analysis, covering different vegetation classes in sub-Saharan Africa (SSA). Our analysis indicated that mean short-term fire-induced albedo change in SSA was -0.022, -0.035, and -0.041 for savannas, shrubland, and grasslands, respectively. At regional scale, mean fire-induced albedo change in savannas was -0.018 and -0.024 for northern sub-Saharan of Africa and the southern hemisphere Africa, respectively. The short-term mean fire-induced radiative forcing in burned areas in sub-Saharan Africa (SSA) was 5.41 W m-2, which contributed continental and global radiative forcings of 0.25 and 0.058 W m-2, respectively. The impact of fire in surface albedo has long-lasting effects that varies with vegetation type. The long-term energetic effects of fire-induced albedo change and associated radiative forcing were, on average, more than 19 times greater across SSA than the short-term effects, suggesting that fires exerted far more radiative forcing than previously thought. Taking into account the actual duration of fire's effect on surface albedo, we conclude that the contribution of SSA fires, globally and throughout the year, is 0.12 W m-2. These findings provide crucial information on possible impact of fire on regional climate variability.

Short Term Microgravity Effect on Isometric Hand Grip and Precision Pinch Force with Visual and Propioceptive Feedback

NASA Astrophysics Data System (ADS)

Pastacaldi, P.; Bracciaferri, F.; Neri, G.; Porciani, M.; Zolesi, V.

Experiments executed on the upper limb are assuming increasing significance in the frame of the Human Physiology in space, for at least two reasons: -the upper limb is the principal means of locomotion for the subject living in aspace station -fatigue can have a significant effect the hand, for the ordinary work on board,and in particular for the extra-vehicular activities. The degradation of the performances affecting the muscular-skeletal apparatus can be easily recognized on the upper limb, by exerting specific scientific protocols, to be repeated through the permanence of the subject in weightlessness conditions. Also, the effectiveness of adequate counter-measures aimed to the reduction of calcium and muscular mass need to be verified, by means of specific assessments on the upper limb. Another aspect relevant to the effect of microgravity on the upper limb is associated with the alteration of the motor control programs due to the different gravity factor, affecting not only the bio-mechanics of the subject, but in general all his/her psycho- physical conditions, induced by the totally different environment. Specific protocols on the upper limb can facilitate the studies on learning mechanisms for the motor control. The results of such experiments can be transferred to the Earth, useful for treatment of subjects with local traumas or diseases of the Central Nervous System.In the frame of the mission of the Italian astronaut Roberto Vittori on board the International Space Station (ISS), the Italian Space Agency (ASI) has promoted the program "Marco Polo", with a number of experiments devoted to the study of the effect of microgravity on the human body. The experiment CHIRO ("Crew's Health: Investigation on Reduced Operability) is a part of the program. Its purpose is the determination of the influence of the altered gravity on the control of the grip force exerted by the hand or by a group of fingers and the adaptive behavior of this control through the permanence of the subject in the reduced gravity. The instrumentation has been lifted on board the International Space Station (ISS) on 24 March 2002. The experiment will be exe cuted by the astronaut during his permanence on board the ISS, from the 25t h April 2002.

14 CFR 29.733 - Tires.

Code of Federal Regulations, 2014 CFR

2014-01-01

... 14 Aeronautics and Space 1 2014-01-01 2014-01-01 false Tires. 29.733 Section 29.733 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS... gravity and exerts a force of 1.0 g downward and 0.25 g forward, the reactions being distributed to the...

Computational Design Tool for Bridge Hydrodynamic Loading in Inundated Flows of Midwest Rivers

DOT National Transportation Integrated Search

2009-12-01

The hydraulic forces experienced by an inundated bridge deck have great importance in the design of bridges. The proper estimation of loading exerted by the flow on the structure is important for design plans and is pertinent for evaluating its vulne...

Proposed low-temperature solar engine

NASA Technical Reports Server (NTRS)

Peoples, J. A.; Kearns, G. B.

1976-01-01

Engine, proposed for conversion of Sun's heat to motion without need for heat pumps and associated equipment, uses expansion and contraction of aluminum rod to drive tow out-of-phase windlasses. Linear displacement of 0.076 cm in rod will exert sufficient force to drive pumps, generators, and compressors.

Muscular force transmission: a unified, dual or multiple system? A review and some explorative experimental results.

PubMed

Huijing, P

1999-10-01

Structures contributing to force transmission in muscle are reviewed combining some historical and relatively recently published experimental data. Also, effects of aponeurotomy and tenotomy are reviewed shortly as well as some new experimental results regarding these interventions that reinforce the concept of myofascial force transmission. The review is also illustrated by some new images of single muscle fibres from Xenopus Laevis indicative of such transmission and some data about locations of insertion of human gluteus maximus muscle. From this review and the new material, emerges a line of thought indicating that mechanical connections between muscle fibres and intramuscular connective tissue play an important role in force transmission. New experimental observations are presented for non-spanning muscle (i.c., rat biceps femoris muscle), regarding the great variety of types of intramuscular connections that exist i n addition to myo-tendinous junctions at the perimuscular ends of muscle fibres. Such connections are classified as (1) tapered end connections, (2) Myo-myonal junctions, (3) myo-epimysial junctions and (3) Myo-endomysial junctions. This line of thought is followed up by consideration of a possible role of connections of intra- and extramuscular connective tissue in force transmission out of the muscle. Experimental results of an explorative nature, regarding the interactions of extensor digitorum longus (EDL), tibialis anterior (TA) and hallucis longus (HAL) muscles within a relatively intact dorsal flexor compartment of the rat hind leg, indicate that: (1) length force properties of EDL are influenced by TA activity in a length dependent fashion. Depending on TA length, force exerted by EDL, kept at constant origin insertion distance, is variable and the effect is influenced by EDL length itself as well; (2) Force is transmitted from muscle to extramuscular connective tissue and vice versa. As a consequence force exerted at proximal and distal tendons of a muscle are not always equal. The difference being transmitted by extramuscular connective tissue and may appear at the tendons of other muscles or may be transmitted via connective tissue directly to bone. It is concluded that the system of force transmission from skeletal muscle should be considered as a multiple system.

Magnetic Control of Convection in Electrically Nonconducting Fluids

NASA Technical Reports Server (NTRS)

Huang, Jie; Gray, Donald D.; Edwards, Boyd F.

1999-01-01

Inhomogeneous magnetic fields exert a body force on electrically nonconducting, magnetically permeable fluids. This force can be used to compensate for gravity and to control convection. The effects of uniform and nonuniform magnetic fields on a laterally unbounded fluid layer heated from below or above are studied using a linear stability analysis of the Navier-Stokes equations supplemented by Maxwell's equations and the appropriate magnetic body force. For a uniform oblique field, the analysis shows that longitudinal rolls with axes parallel to the horizontal component of the field are the rolls most unstable to convection. The corresponding critical Rayleigh number and critical wavelength for the onset of such rolls are less than the well-known Rayleigh-Benard values in the absence of magnetic fields. Vertical fields maximize these deviations, which vanish for horizontal fields. Horizontal fields increase the critical Rayleigh number and the critical wavelength for all rolls except longitudinal rolls. For a nonuniform field, our analysis shows that the magnetic effect on convection is represented by a dimensionless vector parameter which measures the relative strength of the induced magnetic buoyancy force due to the applied field gradient. The vertical component of this parameter competes with the gravitational buoyancy effect, and a critical relationship between this component and the Rayleigh number is identified for the onset of convection. Therefore, Rayleigh-Benard convection in such fluids can be enhanced or suppressed by the field. It also shows that magnetothermal convection is possible in both paramagnetic and diamagnetic fluids. Our theoretical predictions for paramagnetic fluids agree with experiments. Magnetically driven convection in diamagnetic fluids should be observable even in pure water using current technology.

The acoustic radiation force on a heated (or cooled) rigid sphere - Theory

NASA Technical Reports Server (NTRS)

Lee, C. P.; Wang, T. G.

1984-01-01

A finite amplitude sound wave can exert a radiation force on an object due to second-order effect of the wave field. The radiation force on a rigid small sphere (i.e., in the long wavelength limit), which has a temperature different from that of the environment, is presently studied. This investigation assumes no thermally induced convection and is relevant to material processing in the absence of gravity. Both isotropic and nonisotropic temperature profiles are considered. In this calculation, the acoustic effect and heat transfer process are essentially decoupled because of the long wavelength limit. The heat transfer information required for determining the force is contained in the parameters, which are integrals over the temperature distribution.

Measuring axial pump thrust

DOEpatents

Suchoza, Bernard P.; Becse, Imre

1988-01-01

An apparatus for measuring the hydraulic axial thrust of a pump under operation conditions is disclosed. The axial thrust is determined by forcing the rotating impeller off of an associated thrust bearing by use of an elongate rod extending coaxially with the pump shaft. The elongate rod contacts an impeller retainer bolt where a bearing is provided. Suitable measuring devices measure when the rod moves to force the impeller off of the associated thrust bearing and the axial force exerted on the rod at that time. The elongate rod is preferably provided in a housing with a heat dissipation mechanism whereby the hot fluid does not affect the measuring devices.

Measuring axial pump thrust

DOEpatents

Suchoza, B.P.; Becse, I.

1988-11-08

An apparatus for measuring the hydraulic axial thrust of a pump under operation conditions is disclosed. The axial thrust is determined by forcing the rotating impeller off of an associated thrust bearing by use of an elongate rod extending coaxially with the pump shaft. The elongate rod contacts an impeller retainer bolt where a bearing is provided. Suitable measuring devices measure when the rod moves to force the impeller off of the associated thrust bearing and the axial force exerted on the rod at that time. The elongate rod is preferably provided in a housing with a heat dissipation mechanism whereby the hot fluid does not affect the measuring devices. 1 fig.

Modeling of the motion of the actin filament on the myosin motility assays

NASA Astrophysics Data System (ADS)

Young, Yuan; Shelley, Mike

2007-11-01

In motility assays, cytoskeletal actin filaments (actin filaments) glide over a surface coated with motor proteins, and the different modes of motion provide a simple measure of the force exerted by the motor proteins (Bourdieu, 1995). Motivated by these experiments, we consider the actin filament as a slender, elastic filament immersed in Stokesian flow, driven by a tangential forcing that mimics the force by the motor proteins. We find qualitative agreement on several points between our analysis and simulations and experimental observations. Furthermore, we study the correlation between filament transport and the characteristics of motion with the spatial pattern of motor protein density.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carbone, Ludovico; Ciani, Giacomo; Dolesi, Rita

We have measured surface-force noise on a hollow replica of a LISA proof mass surrounded by its capacitive motion sensor. Forces are detected through the torque exerted on the proof mass by means of a torsion pendulum in the 0.1-30 mHz range. The sensor and electronics have the same design as for the flight hardware, including 4 mm gaps around the proof mass. The measured upper limit for forces would allow detection of a number of galactic binaries signals with signal-to-noise ratio up to {approx_equal}40 for 1 yr integration. We also discuss how LISA Pathfinder will substantially improve this limit,more » approaching the LISA performance.« less

Antithrombotic Protective Effects of Arg-Pro-Gly-Pro Peptide during Emotional Stress Provoked by Forced Swimming Test in Rats.

PubMed

Grigor'eva, M E; Lyapina, L A

2017-01-01

Blood coagulation was enhanced and all factors (total, enzyme, and non-enzyme) of the fibrinolytic system were suppressed in rats in 60 min after forced swimming test. Argininecontaining tetrapeptide glyproline Arg-Pro-Gly-Pro administered prior to this test activated fibrinolysis and prevented hypercoagulation. Administration of this peptide in 5 min after swimming test also enhanced anticoagulant, fibrinolytic, and antithrombotic activity of the blood. Therefore, glyproline Arg-Pro-Gly-Pro exerted both preventive and curative effects on the hemostasis system and prevented enhancement of blood coagulation provoked by emotional stress modeled by forced swimming test.

Hindrances to precise recovery of cellular forces in fibrous biopolymer networks.

PubMed

Zhang, Yunsong; Feng, Jingchen; Heizler, Shay I; Levine, Herbert

2018-01-11

How cells move through the three-dimensional extracellular matrix (ECM) is of increasing interest in attempts to understand important biological processes such as cancer metastasis. Just as in motion on flat surfaces, it is expected that experimental measurements of cell-generated forces will provide valuable information for uncovering the mechanisms of cell migration. However, the recovery of forces in fibrous biopolymer networks may suffer from large errors. Here, within the framework of lattice-based models, we explore possible issues in force recovery by solving the inverse problem: how can one determine the forces cells exert to their surroundings from the deformation of the ECM? Our results indicate that irregular cell traction patterns, the uncertainty of local fiber stiffness, the non-affine nature of ECM deformations and inadequate knowledge of network topology will all prevent the precise force determination. At the end, we discuss possible ways of overcoming these difficulties.

Direct Cytoskeleton Forces Cause Membrane Softening in Red Blood Cells

PubMed Central

Rodríguez-García, Ruddi; López-Montero, Iván; Mell, Michael; Egea, Gustavo; Gov, Nir S.; Monroy, Francisco

2015-01-01

Erythrocytes are flexible cells specialized in the systemic transport of oxygen in vertebrates. This physiological function is connected to their outstanding ability to deform in passing through narrow capillaries. In recent years, there has been an influx of experimental evidence of enhanced cell-shape fluctuations related to metabolically driven activity of the erythroid membrane skeleton. However, no direct observation of the active cytoskeleton forces has yet been reported to our knowledge. Here, we show experimental evidence of the presence of temporally correlated forces superposed over the thermal fluctuations of the erythrocyte membrane. These forces are ATP-dependent and drive enhanced flickering motions in human erythrocytes. Theoretical analyses provide support for a direct force exerted on the membrane by the cytoskeleton nodes as pulses of well-defined average duration. In addition, such metabolically regulated active forces cause global membrane softening, a mechanical attribute related to the functional erythroid deformability. PMID:26083919

Hindrances to precise recovery of cellular forces in fibrous biopolymer networks

NASA Astrophysics Data System (ADS)

Zhang, Yunsong; Feng, Jingchen; Heizler, Shay I.; Levine, Herbert

2018-03-01

How cells move through the three-dimensional extracellular matrix (ECM) is of increasing interest in attempts to understand important biological processes such as cancer metastasis. Just as in motion on flat surfaces, it is expected that experimental measurements of cell-generated forces will provide valuable information for uncovering the mechanisms of cell migration. However, the recovery of forces in fibrous biopolymer networks may suffer from large errors. Here, within the framework of lattice-based models, we explore possible issues in force recovery by solving the inverse problem: how can one determine the forces cells exert to their surroundings from the deformation of the ECM? Our results indicate that irregular cell traction patterns, the uncertainty of local fiber stiffness, the non-affine nature of ECM deformations and inadequate knowledge of network topology will all prevent the precise force determination. At the end, we discuss possible ways of overcoming these difficulties.

Theory of nanobubble formation and induced force in nanochannels

NASA Astrophysics Data System (ADS)

Arai, Noriyoshi; Koishi, Takahiro; Ebisuzaki, Toshikazu

2017-10-01

This paper presents a fundamental theory of nanobubble formation and induced force in confined nanochannels. It is shown that nanobubble formation between hydrophobic plates can be predicted from their surface tension and geometry, with estimated values for the surface free energy and the force acting on the plates in good agreement with the results of molecular dynamics simulation and experimentation. When a bubble is formed between two plates, vertical attractive force and horizontal retract force due to the shifted plates are applied to the plates. The net force exerted on the plates is not dependent on the distance between them. The short-range force between hydrophobic surfaces due to hydrophobic interaction appears to correspond to the force estimated by our theory. We compared between experimental and theoretical values for the binding energy of a molecular motor system to validate our theory. The tendency that the binding energy increases as the size of the protein increases is consistent with the theory.

A quantitative method for measuring forces applied by nail braces.

PubMed

Erdogan, Fatma G

2011-01-01

Nail bracing is a conservative method used for ingrown nails; however, lack of objective measurements limits its use for various nails. Double-string nail braces with extra metal springs were applied to 12 patients with 21 chronic, thick, and overcurved ingrown nails. Force was measured with a force gauge meter. Treatment was stopped once patients stood on their tiptoes and walked in shoes pain free without braces. A force gauge meter was also used on a model nail to show the forces applied by various nail braces and to compare their pulling forces. After 6 to 10 months of treatment, all of the patients were pain free; 600 to 1,000 centi Newtons of force were applied to the nails. As the width of the nail increased, so did the force. Braces exert more force on larger nails, which may shorten treatment durations. By measuring forces, it may be possible to standardize force and duration of treatment according to variables such as nail thickness, nail width, angle of ingrown nail, and duration of symptoms.

Endovascular Crossing of Chronic Total Occlusions Using an Impulse: An Explorative Design Study.

PubMed

Sakes, Aimée; van der Wiel, Marleen; Dodou, Dimitra; Breedveld, Paul

2017-06-01

In this study we investigated whether exerting an impulse on a Chronic Total Occlusion (CTO) improves the success rate of CTO crossing as compared to the currently used method of statically pushing the guidewire against the CTO. A prototype (Ø2 mm) was developed that generates translational momentum using a spring-loaded indenter and converts it to an impulse during impact. Mechanical performance was evaluated by measuring the peak force and momentum for different spring compressions and strike distances in air and blood-mimicking fluid. Puncture performance, in terms of number of punctures, number of strikes to puncture, and energy transfer from the indenter to the CTO, was assessed for six tip shapes (stamp, wedge, spherical, pointed, hollow spherical, and ringed) on three CTO models with different weight percentages of gelatin and calcium. As a control, a Ø0.4 mm rigid rod was tested. A maximum indenter momentum of 1.3 mNs (velocity of 3.4 m/s), a peak force of 19.2 N (vs. 1.5 N reported in literature and 2.7 N for the control), and CTO displacement of 1.4 mm (vs. 2.7 mm for the control) were measured. The spherical and ringed tips were most effective, with on average 2.3 strikes to puncture the most calcified CTO model. The prototype generated sufficient peak forces to puncture highly calcified CTO models, which are considered most difficult to cross during PCI. Furthermore, CTO displacement was minimized, resulting in a more effective procedure. In future, a smaller, faster, and flexible clinical prototype will be developed.

Untangling Slab Dynamics Using 3-D Numerical and Analytical Models

NASA Astrophysics Data System (ADS)

Holt, A. F.; Royden, L.; Becker, T. W.

2016-12-01

Increasingly sophisticated numerical models have enabled us to make significant strides in identifying the key controls on how subducting slabs deform. For example, 3-D models have demonstrated that subducting plate width, and the related strength of toroidal flow around the plate edge, exerts a strong control on both the curvature and the rate of migration of the trench. However, the results of numerical subduction models can be difficult to interpret, and many first order dynamics issues remain at least partially unresolved. Such issues include the dominant controls on trench migration, the interdependence of asthenospheric pressure and slab dynamics, and how nearby slabs influence each other's dynamics. We augment 3-D, dynamically evolving finite element models with simple, analytical force-balance models to distill the physics associated with subduction into more manageable parts. We demonstrate that for single, isolated subducting slabs much of the complexity of our fully numerical models can be encapsulated by simple analytical expressions. Rates of subduction and slab dip correlate strongly with the asthenospheric pressure difference across the subducting slab. For double subduction, an additional slab gives rise to more complex mantle pressure and flow fields, and significantly extends the range of plate kinematics (e.g., convergence rate, trench migration rate) beyond those present in single slab models. Despite these additional complexities, we show that much of the dynamics of such multi-slab systems can be understood using the physics illuminated by our single slab study, and that a force-balance method can be used to relate intra-plate stress to viscous pressure in the asthenosphere and coupling forces at plate boundaries. This method has promise for rapid modeling of large systems of subduction zones on a global scale.

Compact, Controlled Resistance Exercise Device

NASA Technical Reports Server (NTRS)

Paulus, David C.; DeWitt, John K.; Reich, Alton J.; Shaw, James E.; Deaconu, Stelu S.

2011-01-01

Spaceflight leads to muscle and bone atrophy. Isoinertial (free-weight) exercises provide a sufficient stimulus to elicit increases in both muscle strength and bone mineral density in Earth-based studies. While exercise equipment is in use on the International Space Station for crewmember health maintenance, current devices are too large to place in a transport vehicle or small spacecraft. Therefore, a portable computer controlled resistance exercise device is being developed that is able to simulate the inertial loading experienced when lifting a mass on Earth. This portable device weighs less than 50 lb and can simulate the resistance of lifting and lowering up to 600 lb of free-weights. The objective is to allow crewmembers to perform resistance exercise with loads capable of maintaining muscle and bone health. The device is reconfigurable and allows for the performance of typical Earth-based free-weight exercises. Forces exerted, volume of work, range of motion, time-under-tension, and speed/ acceleration of movement are recorded and can be remotely monitored to track progress and modify individual protocols based on exercise session data. A performance evaluation will be completed and data will be presented that include ground-reaction force comparisons between the device and free-weight dead-lifts over a spectrum of resistance levels. Movement biomechanics will also be presented.

Myosin filament activation in the heart is tuned to the mechanical task

PubMed Central

Reconditi, Massimo; Caremani, Marco; Pinzauti, Francesca; Powers, Joseph D.; Narayanan, Theyencheri; Stienen, Ger J. M.; Linari, Marco; Lombardi, Vincenzo

2017-01-01

The mammalian heart pumps blood through the vessels, maintaining the dynamic equilibrium in a circulatory system driven by two pumps in series. This vital function is based on the fine-tuning of cardiac performance by the Frank–Starling mechanism that relates the pressure exerted by the contracting ventricle (end systolic pressure) to its volume (end systolic volume). At the level of the sarcomere, the structural unit of the cardiac myocytes, the Frank–Starling mechanism consists of the increase in active force with the increase of sarcomere length (length-dependent activation). We combine sarcomere mechanics and micrometer–nanometer-scale X-ray diffraction from synchrotron light in intact ventricular trabeculae from the rat to measure the axial movement of the myosin motors during the diastole–systole cycle under sarcomere length control. We find that the number of myosin motors leaving the off, ATP hydrolysis-unavailable state characteristic of the diastole is adjusted to the sarcomere length-dependent systolic force. This mechanosensing-based regulation of the thick filament makes the energetic cost of the systole rapidly tuned to the mechanical task, revealing a prime aspect of the Frank–Starling mechanism. The regulation is putatively impaired by cardiomyopathy-causing mutations that affect the intramolecular and intermolecular interactions controlling the off state of the motors. PMID:28265101

The asymmetric evolution of the Colombian Eastern Cordillera. Tectonic inheritance or climatic forcing? New evidence from thermochronology and sedimentology

NASA Astrophysics Data System (ADS)

Ramirez-Arias, Juan Carlos; Mora, Andrés; Rubiano, Jorge; Duddy, Ian; Parra, Mauricio; Moreno, Nestor; Stockli, Daniel; Casallas, Wilson

2012-11-01

New thermochronological data, facies, paleocurrents and provenance allow us to refine the chronology of deformation in the central segment of the Colombian Eastern Cordillera. Based on a new extensive AFT dataset, we document the spatial evolution of active deformation, from the axial zone of the Eastern Cordillera at about 50 Ma in to active growth of the frontal thin skinned structures in Late Miocene time. Paleocurrents allow us to push backwards into the Middle to Early Late-Miocene the emergence of the easternmost frontal thrust; whereas careful assessment of exposure gates tied to AFT data enable to refine the unroofing history for Eocene to Miocene times. Based on that, we produced a kinematically restored cross section with higher resolution than previous assessments. Using these datasets, we compare the evolution of the central segment of the Eastern Cordillera in this region with the evolution of adjacent areas in the context of climatic forcing of orogenic evolution. We find that in this region and, in the Eastern Cordillera in general, tectonic inheritance and transpression exert an initial dominant control on the initial orogen asymmetry, which is later enhanced due to an orographically-focused erosion. We therefore suggest that it is not climate alone the factor controlling orogenic asymmetry in the Eastern Cordillera of Colombia.

Effects provoked by chronic undernourishment on the fibre type composition and contractility of fast muscles in male and female developing rats.

PubMed

Pereyra-Venegas, J; Segura-Alegría, B; Guadarrama-Olmos, J C; Mariscal-Tovar, S; Quiróz-González, S; Jiménez-Estrada, I

2015-10-01

In this study, we compare the effects of pre- and post-natal food deprivation on the relative proportion of fibre types and contractile responses in the extensor digitorum longus (EDL) muscle of female and male rats at different post-natal ages. EDL muscles from undernourished male (UM) rats showed a higher proportion of Type IIB than IIA fibres and larger normalized twitch responses (with respect to muscle weight) than those of controls (CM). In contrast, EDL muscles from control (CF) and undernourished female rats (UF) showed no significant differences in their fibre type composition and normalized twitch forces at most of the ages analysed. Our data are indicative that the EDL muscles from undernourished males are more susceptible to the effects exerted by low food income than the EDL muscles from female rats. It is proposed that changes in the reactive oxygen species (ROS) concentration and hormonal factors, due to undernutrition, are involved in the alterations observed in the fibre type composition and force production of EDL muscles in undernourished male rats and that estrogens may have an antioxidant protective role on the undernourished EDL muscles in female rats. Journal of Animal Physiology and Animal Nutrition © 2014 Blackwell Verlag GmbH.

Impact of hand forces and start/stop frequency on physiological responses to three forms of pushing and pulling: a South African perspective.

PubMed

Ai, Todd

2012-01-01

There has been limited attention given to the physiological demands of pushing and pulling, especially in industrially developing countries such as South Africa. Two key factors affecting the physiological demands of these tasks are the hand forces exerted and the start/stop frequency. The purpose of the current study was therefore to investigate the physiological responses to pushing and pulling at various loads and start/stop frequencies. 36 male subjects participated in the study and were required to complete a total of 18 conditions (three techniques: pushing, two- and one-handed pulling; three loads: 200, 350 and 500 kg; and two frequencies: 2 and 4 stops per minute). During each condition the heart rate, oxygen uptake and energy expenditure were measured. Pushing was found to elicit significantly lower responses for all three dependent variables than either form of pulling. The start/stop frequency was also found to have a significant impact on subject responses. The findings of this study indicate that the technique adopted to maneuver loads is critical in determining the physical demands placed on the human operator. Furthermore increasing the frequency of start/stops plays an important role, thus the forces exerted during these two phases are important from a physiological perspective.

Biomechanical analysis of acromioclavicular joint dislocation treated with clavicle hook plates in different lengths.

PubMed

Shih, Cheng-Min; Huang, Kui-Chou; Pan, Chien-Chou; Lee, Cheng-Hung; Su, Kuo-Chih

2015-11-01

Clavicle hook plates are frequently used in clinical orthopaedics to treat acromioclavicular joint dislocation. However, patients often exhibit acromion osteolysis and per-implant fracture after undergoing hook plate fixation. With the intent of avoiding future complications or fixation failure after clavicle hook plate fixation, we used finite element analysis (FEA) to investigate the biomechanics of clavicle hook plates of different materials and sizes when used in treating acromioclavicular joint dislocation. Using finite element analysis, this study constructed a model comprising four parts: clavicle, acromion, clavicle hook plate and screws, and used the model to simulate implanting different types of clavicle hook plates in patients with acromioclavicular joint dislocation. Then, the biomechanics of stainless steel and titanium alloy clavicle hook plates containing either six or eight screw holes were investigated. The results indicated that using a longer clavicle hook plate decreased the stress value in the clavicle, and mitigated the force that clavicle hook plates exert on the acromion. Using a clavicle hook plate material characterized by a smaller Young's modulus caused a slight increase in the stress on the clavicle. However, the external force the material imposed on the acromion was less than the force exerted on the clavicle. The findings of this study can serve as a reference to help orthopaedic surgeons select clavicle hook plates.

14 CFR 23.445 - Outboard fins or winglets.

Code of Federal Regulations, 2014 CFR

2014-01-01

... 14 Aeronautics and Space 1 2014-01-01 2014-01-01 false Outboard fins or winglets. 23.445 Section 23.445 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT... with loads induced by the fins or winglets and moments or forces exerted on the horizontal surfaces or...

14 CFR 23.445 - Outboard fins or winglets.

Code of Federal Regulations, 2012 CFR

2012-01-01

... 14 Aeronautics and Space 1 2012-01-01 2012-01-01 false Outboard fins or winglets. 23.445 Section 23.445 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT... with loads induced by the fins or winglets and moments or forces exerted on the horizontal surfaces or...

Touch Sensor for Robots

NASA Technical Reports Server (NTRS)

Primus, H. C.

1986-01-01

Touch sensor for robot hands provides information about shape of grasped object and force exerted by gripper on object. Pins projecting from sensor create electrical signals when pressed. When grasped object depresses pin, it contacts electrode under it, connecting electrode to common electrode. Sensor indicates where, and how firmly, gripper has touched object.

Gas pressure in sealed electrochemical cells measured externally

NASA Technical Reports Server (NTRS)

Sherfey, J. M.

1967-01-01

Piezoresistive transducer measures gas pressure inside sealed secondary electrochemical cells without breaking the seal. This method is based on the observed fact that the force exerted by the cell faces on the clamp tightening them against the transducer is a function of the gas pressure inside the cell.

14 CFR 29.733 - Tires.

Code of Federal Regulations, 2011 CFR

2011-01-01

... static ground reaction corresponding to the critical center of gravity; and (3) A load on nose wheel tires (to be compared with the dynamic rating established for those tires) equal to the reaction... gravity and exerts a force of 1.0 g downward and 0.25 g forward, the reactions being distributed to the...

14 CFR 29.733 - Tires.

Code of Federal Regulations, 2010 CFR

2010-01-01

... static ground reaction corresponding to the critical center of gravity; and (3) A load on nose wheel tires (to be compared with the dynamic rating established for those tires) equal to the reaction... gravity and exerts a force of 1.0 g downward and 0.25 g forward, the reactions being distributed to the...

Interacting Compasses

ERIC Educational Resources Information Center

Riveros, Hector G.; Betancourt, Julian

2009-01-01

The use of multiple compasses to map and visualize magnetic fields is well-known. The magnetic field exerts a torque on the compasses aligning them along the lines of force. Some science museums show the field of a magnet using a table with many compasses in a closely packed arrangement. However, the very interesting interactions that occur…

Women in Multiculturalism: Everywhere You Look, There We Are!

ERIC Educational Resources Information Center

De Hon, Jacqueline

Multiculturalism takes on a broader definition in this intercultural communication paper. All groups which exert influence on an individual's way of thinking are classified as cultures. An overview of intergender communication offers insights into women's history and ways patriarchal forces have shaped gender roles. A discussion of General…

The lift force on a drop in unbounded plane Poiseuille flow

NASA Technical Reports Server (NTRS)

Wohl, P. R.

1976-01-01

The lift force on a deformable liquid sphere moving in steady, plane Poiseuille-Stokes flow and subjected to an external body force is calculated. The results are obtained by seeking a solution to Stokes' equations for the motion of the liquids inside and outside the slightly perturbed sphere surface, as expansions valid for small values of the ratio of the Weber number to the Reynolds number. When the ratio of the drop and external fluid viscosities is small, the lift exerted on a neutrally buoyant drop is found to be approximately one-tenth of the magnitude of the force reported by Wohl and Rubinow acting on the same drop in unbounded Poiseuille flow in a tube. The resultant trajectory of the drop is calculated and displayed as a function of the external body force.

Force-frequency and fatigue properties of motor units in muscles that control digits of the human hand.

PubMed

Fuglevand, A J; Macefield, V G; Bigland-Ritchie, B

1999-04-01

Modulation of motor unit activation rate is a fundamental process by which the mammalian nervous system encodes muscle force. To identify how rate coding of force may change as a consequence of fatigue, intraneural microstimulation of motor axons was used to elicit twitch and force-frequency responses before and after 2 min of intermittent stimulation (40-Hz train for 330 ms, 1 train/s) in single motor units of human long finger flexor muscles and intrinsic hand muscles. Before fatigue, two groups of units could be distinguished based on the stimulus frequency needed to elicit half-maximal force; group 1 (n = 8) required 9.1 +/- 0.5 Hz (means +/- SD), and group 2 (n = 5) required 15.5 +/- 1.1 Hz. Twitch contraction times were significantly different between these two groups (group 1 = 66. 5 ms; group 2 = 45.9 ms). Overall 18% of the units were fatigue resistant [fatigue index (FI) > 0.75], 64% had intermediate fatigue sensitivity (0.25

The effect of electrohydrodynamic force on the lift coefficient of a NACA 0015 airfoil

NASA Astrophysics Data System (ADS)

Yusof, Y.; Hossain, A.; Abdullah, A. H.; Nasir, Rizal M. E.; Hamid, A.; Muthmainnah, N.; N, M.

2017-11-01

Lift, the force component that is perpendicular to the line of flight, is generated when a small aircraft moves through the air. With the help of the sets of flaps and slats on its wing, the pilot controls his aircraft manoeuvring in the air. In this study, we preferred to cut the drawbacks of the flaps system by introducing the electrohydrodynamic actuator. Widely known as plasma actuator, it is able to improve the induced lift force as well as the efficiency of a small aircraft system. A dielectric-barrier-discharge actuator using a 6 kV AC power supply was developed and tested on a NACA 0015 airfoil using copper as the electrodes and kapton as its dielectric component. The experimental results showed that it was successful in presenting a positive effect of the plasma actuator on the lift coefficient of the airfoil at smaller angle of attack, where enhancements ranged between 0.7% and 1.8%. However, at a higher angle, the results were not as swayed as it was desired since the energy exerted by the plasma actuator on the lift performance of the airfoil was inadequate. Further tests are needed using higher rated voltage supply and other equipment to improve the capability of the actuator in refining the aerodynamic performance of the airfoil.